New constraints on the tectono-magmatic evolution of the central Gangdese belt from Late Cretaceous magmatic suite in southern Tibet

Journal Pre-proof New constraints on the tectono-magmatic evolution of the central Gangdese belt from Late Cretaceous magmatic suite in southern Tibet

Yuanku Meng, M. Santosh, Guangzhou Mao, Peijun Lin, Jinqing Liu, Peng Ren PII:

S1342-937X(19)30304-1

DOI:

https://doi.org/10.1016/j.gr.2019.10.014

Reference:

GR 2246

To appear in:

Gondwana Research

Received date:

27 June 2019

Revised date:

14 October 2019

Accepted date:

27 October 2019

Please cite this article as: Y. Meng, M. Santosh, G. Mao, et al., New constraints on the tectono-magmatic evolution of the central Gangdese belt from Late Cretaceous magmatic suite in southern Tibet, Gondwana Research(2019), https://doi.org/10.1016/ j.gr.2019.10.014

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2019 Published by Elsevier.

Journal Pre-proof

New constraints on the tectono-magmatic evolution of the central Gangdese belt from Late Cretaceous magmatic suite in southern Tibet Yuanku Menga,b*, M. Santoshc,d,e, Guangzhou Maoa*, Peijun Linf, Jinqing Liua,b, Peng Reng a

College of Earth Science and Engineering, Shandong University of Science and

of

Technology, Qingdao 266590, China b

ro

Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China

c

-p

School of Earth Sciences and Resources, China University of Geosciences (Beijing),

re

Beijing 100083, China d

Department of Earth Sciences, University of Adelaide, Adelaide SA 5005, Australia

e

lP

Yonsei Frontier Lab, Yonsei University, Seoul 03722, Republic of Korea

f

China g

na

Testing center of Shandong Bureau of China Metallurgical Geology Bureau, Jinan 250014,

Abstract

Jo ur

Chang’An University, Xi’an 710064, China

In the Gangdese magmatic belt of southern Tibet, widespread Late Mesozoic

magmatism

has

been

reported,

although

their

petrogenesis and tectonic evolution remain ambiguous. Here we present new zircon U-Pb and geochemical data on a gabbro-diorite suite near the Namling County in the central Gangdese belt, that provide insights into the geodynamic processes in this region. Zircon U-Pb data from LA-ICP-MS and SHRIMP II analyses

Journal Pre-proof

indicate that the granite crystallized at ca. 87 Ma, and the gabbro-diorite suite was emplaced at ca. 91-95 Ma, both suggesting an early Late Cretaceous magmatism in the central Gangdese belt. The gabbro-diorite suite displays wide ranges of SiO2 (57.21-44.25 wt. %) and MgO contents (9.04-3.18 wt. %), with

of

high Al2O3 (21.47-16.14 wt. %) and Na2O/K2O (1.10-5.84) values. Compared to these, the granite rocks show limited variations of

ro

SiO2 (76.97-76.40 wt. %), high Na2O+K2O (8.84-8.04 wt. %),

values

and

significant

re

(30.77-20.39)

-p

K2O/Na2O (2.33-1.30) and Sr/Y (48.99-80.36), with low Mg# Eu

anomalies

lP

(Eu/Eu*=1.20-0.24). The gabbro-diorite rocks are characterized by

na

typical arc-type features including enrichment of light rare earth elements (LREE) (LaN/YbN=11.52-5.06>1) and large ion lithophile

Jo ur

elements (LILE) (e.g. Cs, K and Rb), but are depleted in high strength field elements (HSFE) (e.g. Nb, Ta, Ti and P). The granitic rocks are also enriched in LREE (LaN/YbN=55.42-26.55>1) and LILE (e.g. Cs, Rb, K and Pb), but depleted in HSFE (e.g. Nb, Ta, Ti and P). The gabbro-diorite rocks show distinctly positive εNd(t) (+3.5 to +4.2)

and εHf(t) values (+8.5 to +15.6) values with a restricted

range, with relatively homogeneous and low (87Sr/86Sr)I ratios (0.704213-0.703820). The granitic rocks also show positive εNd(t) values

(+4.1

to

+4.4)

and

consistent

(87Sr/86Sr)I

ratios

Journal Pre-proof

(0.703977-0.703180). Our data suggest that the gabbro-diorite rocks were mostly sourced from partial melting of the depleted mantle that was metasomatized by fluids released from the subducted Neo-Tethys oceanic slab. The granite was probably produced by partial melting of the juvenile crust with no

of

participation of mantle material. We correlate the magmatism with tectonics associated with the roll-back of the Neo-Tethys oceanic

Gabbro-diorite

suite;

Granite

dike;

Zircon

re

Keywords:

-p

ro

slab during the early Late Cretaceous.

na

1. Introduction

lP

geochronology; Geochemistry; Gangdese magmatic belt.

Jo ur

The Cretaceous tectono-magmatic events in southern Tibet have been correlated to northward subduction of the Neo-Tethys oceanic slab beneath the Lhasa terrane (e.g. Yin and Harrison, 2000; Zhu et al., 2011; Zhang et al., 2014a; Meng et al., 2019). However, the petrogenesis and geodynamic setting of the early Late Cretaceous (100~80 Ma) magmatic suites in this region remain debated. Some studies suggest that the early Late Cretaceous magmatism was associated with the mid-oceanic ridge subduction of the Neo-Tethys Ocean (e.g. Guan et al., 2010; Meng et al., 2010; Zhang et al., 2010; Guo et al., 2013; Zhu et al., 2013;

Journal Pre-proof

Wu et al., 2018), whereas other workers invoke the rollback of the Neo-Tethys oceanic slab to explain the magmatic activities in the Gangdese belt (e.g. Ma et al., 2013a, b, 2015, 2017a; Xu et al., 2015; Meng et al., 2019). Alternate models include flat slab subduction (e.g. Wen et al., 2008a, b), normal-angle northward

of

subduction (Ji et al., 2009) and high-angle oblique subduction (Wang et al., 2013). Previous models on the petrogenesis of early

ro

Late Cretaceous adakite-like rocks in this region include: (1) partial

-p

melting of thickened juvenile crust (e.g. Wen et al., 2008b; Guan et

re

al., 2010; Ma et al., 2013b; Ji et al., 2014); (2) partial melting of

lP

subducted oceanic slab (Zhang et al., 2010; Jiang et al., 2014); and

na

(3) differentiation of mafic magmas (Wang et al., 2013; Xu et al., 2015; Meng et al., 2019).

Jo ur

Compared to the eastern Gangdese belt, the early Late Cretaceous gabbroic rocks in the central belt are poorly studied. Therefore, with a view to delineate the geodynamic setting of the mantle magmatism in the central Gangdese region, we investigate a suite of magmatic rocks in the Shanba area of the Namling County (study area), including gabbro, diorite and granite. We present petrologic, geochronological, whole-rock geochemical and Sr-Nd-Hf isotope dataset for the diorite-gabbro suite and the accompanying granitic rocks with a view to evaluate the magma

Journal Pre-proof

petrogenesis and tectonic setting. Our results provide new constraints on the early Late Cretaceous tectono-magmatic evolution in southern Tibet.

2. Geological background and sample description 2.1 Geological background

of

The Himalayan-Tibetan plateau is mainly composed of Himalaya, Lhasa, Qiangtang, Songpan-Ganzi and Qaidam-Kunlun

ro

terranes, which are separated by well-defined sutures (e.g. Yin and

-p

Harrison, 2000) (Fig.1a). The Lhasa terrane, located between the

re

Indus-Yarlung Tsangpo suture zone (IYSZ) and Bangong-Nujiang

lP

suture zone (BNSZ), was considered as a remnant drifted from

na

Gondwana continent during the Permian (e.g. Zhu et al., 2011; Pan et al., 2012). Based on the distribution of regional faults and

Jo ur

ultra-high pressure (UHP) rocks, as well as Hf isotope features, Zhu et al. (2011) and Hou et al. (2015) suggested that the Lhasa terrane can be divided into three segments, namely the northern Lhasa, the central and the southern Lhasa sub-terranes. However, Yang et al. (2009) and Zhang et al. (2014b) suggested that the Lhasa terrane can be divided into two segments rather than three, the southern and northern sub-terranes. In this study, we adopt the three-fold sub-division of the Lhasa terrane as suggested by Zhu et al. (2011). The southern Lhasa sub-terrane, which is located

Journal Pre-proof

between the IYSZ and Luobadui-Milashan fault (LMF) over 2000 km in length (Fig.1a), is known as the Gangdese magmatic belt that is mainly comprised of granitoids and intermediate-acidic volcanic sequences. Available geochronological data identify four distinct stages in the Gangdese belt during the periods of 230~152 Ma,

of

109~80 Ma, 65~40 Ma and 33-13 Ma, respectively (e.g. Ji et al., 2009; Meng et al., 2016a, b, 2018a, b; Wang et al., 2016). The

ro

230~152 Ma magmatic activities belong to the early evolutionary

-p

history of the Neo-Tethys oceanic northward subduction beneath

re

the Lhasa terrane (e.g. Meng et al., 2016a, b, 2018a; Wang et al.,

lP

2016; Ma et al., 2017b). However, some researchers argued that

na

the Neo-Tethys oceanic northward subduction began not earlier than the early stage of Early Cretaceous (~145 Ma), and suggested

Jo ur

that the 230~152 Ma magmatism is associated with the southward subduction of the Bangong-Nujiang oceanic crust (e.g. Zhu et al., 2011; Wang et al., 2014; Zhang et al., 2019). In an alternate model, Dong and Zhang (2013) suggested that the Late Triassic-Early Jurassic magmatism was induced by the breakoff or rollback of the Sumdo oceanic crust (Paleo-Tethys Ocean). The 109~80 Ma magmatism in the Gangdese belt is correlated to the northward subduction of the Neo-Tethys oceanic crust (e.g. Yin and Harrison, 2000; Chung et al., 2005, 2009; Ji et al., 2009; Zhu et al., 2011, and

Journal Pre-proof

references therein). However, the petrogenesis and tectonic history of the Early Late Cretaceous (100~80 Ma) magmatic event remains ambiguous (e.g. Wen et al., 2008a, b; Ji et al., 2009; Zhang et al., 2010; Ma et al., 2013a, b, 2015, 2017a; Gao et al., 2017). The 100~80 Ma magmatic suites mainly comprise granitoid rocks that

of

can be divided into two groups: normal arc-type and adakite-like rocks (Xu et al., 2015; Ma et al., 2017c; Meng et al., 2019). In

ro

addition, a few field outcrops of mafic rocks also were identified in

-p

the Gangdese belt. Integrated with published data, the Late

re

Mesozoic igneous rocks are characterized by high

176

Hf/177Hf ratios

lP

and significantly positive εHf(t) values as well as young model ages

na

reflecting depleted mantle compositions (Ji et al., 2009; Zhu et al., 2011; Hou et al., 2015). The 65~40 Ma magmatism in the

Jo ur

Gangdese belt is the most dominant, constituting the main body of the Gangdese composite batholiths (e.g. Ji et al., 2009; Mo et al., 2007, 2008, 2009; Zhu et al., 2011; Meng et al., 2018b). These rocks are mainly represented by granitoids and intermediate-acidic volcanic rocks. The granitoid rocks show wide ranges of geochemical and Hf isotope compositions (Ji et al., 2009; Xu et al., 2015; Zhou et al., 2018). Coeval with the granitoid rocks in the Gangdese belt, the Linzizong volcanic rocks define three different Formations, and also have wide variations of geochemical and Hf

Journal Pre-proof

isotope compositions. According to geochemical and isotopic signatures, Mo et al. (2007, 2009) proposed that the 65~40 Ma magmatism was related to syn-collisional and major-collisional processes. Ji et al. (2009) and Zhu et al. (2015) argued that the 65~40 Ma magmatism represents the complex geodynamic

of

processes, including continuous subduction, rollback and breakoff of the Neo-Tethys oceanic crust. The 33~13 Ma magmatism is the

ro

youngest in the Gangdese belt. This stage belongs to the typical

-p

post-collisional setting (Hou et al., 2004; Mo et al., 2007, 2008;

re

Meng et al., 2018c). The rock types mainly consist of granite

lP

porphyry and diorite porphyry as well as few mafic stocks. The

thickened

na

Miocene granitoid porphyries are products of partial melting of lithosphere,

and

were

emplaced

into

the

Jo ur

Paleocene-Eocene batholiths as small stocks, dike swarms and rock knobs. Geochemically, the 33-13 Ma granitoid porphyries show adakite-like features, and most of the porphyries have relatively enriched Hf isotopes representing incorporation of ancient crustal material (Hou et al., 2004; Ji et al., 2009; Chen et al., 2014). The nature of magmatism associated with the Oligocene-Miocene granitoid porphyries is still ambiguous, with some workers suggesting these to be products of partial melting of thickened Lhasa lower crust (Chung et al., 2003; Hou et al., 2004; Chen et al.,

Journal Pre-proof

2014), whereas others considering these to be derived from partial melting of mafic lower crust that was metasomatized by subducted fluids (Guo et al., 2007; Xu, 2010). 2.2 Summary of the gabbroic rocks in the central Gangdese In the central Gangdese belt, gabbroic rocks are exposed

of

sporadically, as small stocks and dikes (Fig.1b). Hou et al. (2001), Xiong et al. (2001) and Gao et al. (2003) regarded these stocks as

ro

the vestiges of the Yarlung Tsangpo ophiolites. However, others

-p

refuted this idea and argued that the gabbroic plutons are

re

components of the Gangdese composite batholiths, related to the

lP

northward subduction of the Neo-Tethys Ocean (e.g. Dong et al.,

na

2006, 2008; Qiu et al., 2015; Meng et al., 2016a). According to previous studies, the gabbroic rocks can be classified into three

Jo ur

stages: (i) Late Triassic to Early Jurassic; (ii) early Late Cretaceous; (iii) Late Paleocene to Early Eocene. These rocks comprise hornblende gabbro, gabbroic diorite, gabbro norite and gabbro diabase, as well as minor ultramafic rocks (e.g. hornblendite). Mo et al. (2005) and Dong et al. (2006, 2008) investigated the gabbroic rocks in the central Gangdese belt, and proposed that they were formed during the Early Eocene (53-40 Ma), as products of India-Asia collision. Subsequently, Qiu et al. (2015), Meng et al. (2016a) and Wang et al. (2017) identified the Late Triassic to Early

Journal Pre-proof

Jurassic gabbroic intrusions in the central belt, and argued that they were derived by partial melting of hydrous mantle related to northward subduction of the Neo-Tethys oceanic slab. Furthermore, Qiu et al. (2015) concluded that the central Gangdese belt preserves evidence for multiple underplating of mafic magmas

of

which induced magma mixing during >205 to 40 Ma. Therefore, the central Gangdese belt might contain multiple mafic magma events.

ro

Although some studies related to the gabbroic rocks were carried

-p

out in the central Gangdese belt, these mainly focused on the Late

re

Triassic to Early Jurassic intrusions (e.g. Qiu et al., 2015; Meng et

lP

al., 2016a; Wang et al., 2017). Figure 1b shows the few Late

na

Cretaceous mafic plutons reported in the central Gangdese belt (Schärer et al., 1984; Ye et al., 2015; Xu et al., 2015), although

Jo ur

systematic and integrated studies on these rocks are lacking. 2.3 Sample descriptions 2.3.1 Field observations

The study area is located in the southern part of the Namling County (Xigaze region), in a region with good infrastructure for geological survey and sampling (Fig.1c), and the gabbro-diorite suite is well-exposed (Fig.2a-d). Field studies show that this suite is dominantly composed of foliated gabbro, coarse-grained gabbro, gabbroic diorite and diorite. In addition to the gabbroic rocks, a

Journal Pre-proof

granitic dike, emplaced as a thick sheet-like intrusion trending NE within the gabbro-diorite suite, and was also identified (Fig.1c, Fig.2e). The granitic dike is approximately 5-15 m wide and over 1-km long (Fig.2e). The presence of verdigris on the surface of the granitic dike (Fig.2f) indicates that the dike is associated with

of

Cu-related mineralization. The samples from the gabbro-diorite composite suite can be

ro

divided into three groups. Groups I and II are normal diorite and

-p

gabbro whereas group III is represented by granitic rocks. Based

re

on field, petrological and mineralogical data, the group I and group

lP

II rocks can be divided into different sub-groups, such as

na

hornblende gabbro (lacking pyroxene), coarse-grained gabbro (containing pyroxene), fine-grained gabbro and diorite. The

Jo ur

petrology and microstructures of the representative gabbro-diorite sub-groups are described below. 2.3.2 Petrography and EPMA analyses Group I: the fine-grain diorite samples are characterized by amphibole (~45%) and plagioclase (~50%), as well as minor amounts of biotite and quartz (Supplementary Figure 1a). Electron probe microanalysis (EPMA) reveals that the plagioclase mainly belongs to andesine and labradorite, and the amphibole belongs to hornblende, but few are actinolite. In addition, another diorite

Journal Pre-proof

subgroup belongs to medium-coarse grain diorite (Supplementary Figure 1b) that comprises euhedral plagioclases (~55%) marked by typical polysynthetic twinning and biotite (~10%) and epidote (~30%). The epidote formed from the alteration of amphibole. Group

II:

gabbro

samples

include

three

subgroups

of

(Supplementary Figure 1c-e). Subgroup I: hornblende gabbro is composed of typical subhedral to euhedral amphibole crystals and

ro

euhedral plagioclase grains. The EPMA results reveal that the

-p

amphibole is hornblende (few crystals belonging to actinolite), and

re

the plagioclase ranges in composition from anorthite to bytownite.

lP

Although this group lacks pyroxene, the calcic plagioclase and Subgroup II:

na

hornblende indicate a gabbroic composition.

medium-coarse grained gabbro is comprised of pyroxene,

Jo ur

plagioclase and biotite. The EPMA data show that the pyroxene is diopside, and the plagioclase is andesine and labradorite. Subgroup III: medium-coarse gabbro is composed of plagioclase, hornblende, diopside and biotite. The hornblende crystals surrounding diopside indicate a reaction rim texture. Group III: the coarse-grained granitic dike mainly comprises K-feldspar, quartz and plagioclase, with only minor mafic minerals (Supplementary Figure 1f), corresponding to granite. The representative BSE images of thin sections of the

Journal Pre-proof

gabbro-diorite suite are shown in Supplementary Figure 2. The chemical compositions are given in Supplementary Table 1.

3. Results 3.1 Zircon U-Pb geochronology The

representative

zircon

CL

images

are

given

in

of

Supplementary Figure 3. The white and red circles represent zircon LA-ICP-MS U-Pb and SHRIMP II dating sites, respectively, and the

ro

yellow dotted circle represents sites where in situ Lu-Hf isotope

-p

analyses were performed. Zircon grains from the gabbro-diorite

re

suite are characterized by prismatic morphologies and high Th/U

lP

ratios (mean value=1.04) (>0.4), suggesting an igneous origin

several

grains

na

(Corfu et al., 2003; Hoskin and Schaltegger, 2003). In addition, show

tabular

zoning

indicative

of

an

Jo ur

intermediate-mafic magma origin (Hoskin and Schaltegger, 2003). The zircon from the granite shows prismatic shapes and clear oscillatory zoning as well as high Th/U ratios (mean value=0.80) (>0.4) that together indicate a felsic magmatic origin (Hoskin and Schaltegger, 2003). The zircon U-Pb data and Th/U ratio calculations are listed in Supplementary Table 2. Three samples from the gabbro-diorite suite yielded weighted mean

206

Pb/238U ages of 94.63 ± 0.72 Ma (sample NM112; N=19,

MSWD=1.8), 90.66 ± 0.88 Ma (sample NM113; N=18, MSWD=1.3)

Journal Pre-proof

and 91. 08 ± 0.65 Ma (sample NM114; N=18, MSWD=0.85), which are interpreted as the emplacement and crystallization ages of the gabbro-diorite suite. Another two samples collected from the granite rocks yielded weighted average

206

Pb/238U ages of 87.69 ±

0.58 Ma (sample MG111-1; N=33, MSWD=2.3) and 86.5 ± 1.6 Ma

of

(sample MG111-2; N=9, MSW=1.9) that constrain the crystallization ages of the granite belonging to Coniacian stage of Late

ro

Cretaceous. The 206Pb/238U versus 207Pb/235U plots shown in Figure

-p

3 demonstrate that the analytical spots fall along the Concordia,

re

with no indication of apparent common Pb loss. The analytical

lP

results are consistent with the field observations (Fig.2e) that the

na

granite is younger than the gabbro-diorite suite. 3.2 Zircon Lu-Hf isotope compositions

Jo ur

A total of 43 in situ zircon Lu-Hf isotope analyses were carried out on the gabbro-diorite suite. The Hf isotopic results are given in Supplementary Table 3. The results reveal that the 176Lu/177Hf ratios vary from 0.000193 to 0.001617 (mean value=0.000587), suggesting low

176

Lu/177Hf accumulations. The

176

Hf/177Hf values of

the analytical zircons from the gabbro-diorite suite range between 0.282970 and 0.283168, and the zircon εHf(t) values range from +8.5 to +15.6, suggesting a depleted mantle feature. The TDM1 ages range from 117 Ma to 393 Ma, with a mean value of 241 Ma.

Journal Pre-proof

The younger model ages suggest juvenile mantle compositions rather than ancient or enriched mantle. The Lu-Hf isotopic data are plotted in Supplementary Figure 4. 3.3 Whole-rock major and trace-elemental composition 3.3.1 Major-element compositions

of

The whole-rock major element compositions are given in Supplementary Table 4. The gabbro-diorite suite shows variable

ro

SiO2 contents ranging from 44.3 wt. % to 57.2 wt. %

-p

(Supplementary Table 4). On the TAS diagram, all the samples fall

re

into the gabbro-diorite and granite fields (Fig.4a), which are

lP

consistent with the field observations and petrologic data (Figure 2

na

and Supplementary Figure 1). All the samples plot in the sub-alkaline field (Fig.4a). Figure 4b defines calc-alkali features for

Jo ur

the gabbro-diorite samples, but the granite samples show a transitional affinity. According to the SiO2 versus K2O diagram (Fig.4c), the gabbro-diorite suite can be separated into two groups, high-K calc-alkaline for diorite samples (SiO2>50 wt. %) and medium-low K calc-alkaline fields (SiO2<50 wt. %). The granite samples show a high-K calc-alkaline feature. In the triangular plot (Fig.4d), the gabbro-diorite rocks display tholeiitic and calc-alkaline features, respectively, and the granite rocks show calc-alkaline nature. The rocks from the gabbro-diorite suite have different

Journal Pre-proof

geochemical affinities that might be related to later magma evolution and differentiation (Fig.5c, e, g). Furthermore, the granite rocks show weakly peraluminous nature in the molecular Al2O3/Na2O+K2O versus molecular Al2O3/CaO+Na2O+K2O diagram, suggesting a transitional affinity between S- and I-type granite

of

(Fig.4e). Additionally, they have low Mg# (Mg#=Mg/Mg+FeT) values consistent with typical crustal melts (Fig.4f).

ro

In the Harker diagrams (Fig.5), the gabbro-diorite samples

-p

have no obvious relations between SiO2 and other oxides (e.g.

re

Al2O3, BaO, TiO2, P2O5 and MnO). However, SiO2 shows better

lP

relations with CaO, Fe2O3T and MgO, indicating that fractionation of

na

pyroxene, amphibole and plagioclase played a key role in the evolution of the gabbro-diorite suite (Fig.5c, e, g). Fig.5i-j plots

Jo ur

suggest no significant magma mixing during the evolution of the gabbro-diorite suite as suggested by magma mixing models that were proposed by Langmuir et al. (1978). Moreover, the samples from the diorite-gabbro suite have low TiO2 (0.50-1.40 wt. %) and high Al2O3 (16.14-21.47 wt. %) contents, similar to high-alumina basalts (Fig.5a). 3.3.2 Trace-element compositions The ∑REE contents range from 37.4 to 161.76 ppm for the gabbro-diorite suite (mean value=89.18 ppm), whereas the granite

Journal Pre-proof

rocks have low REE contents varying from 26.13 to 47.90 ppm (mean value=35.25 ppm). In addition, the lower REE contents of the granite as compared to the mafic suite exclude the possibility that the granite was derived from partial melting of the gabbro-diorite suite. The chondrite-normalized REE patterns

of

presented in Figure 6 show that the gabbro-diorite samples are enriched in light REE (LREE) with LaN/YbN ratios varying from 5.06

ro

to 11.52, and diorite rocks show higher REE contents than the

-p

gabbroic rocks that indicate a fractionation process. No prominent

re

Eu anomalies (Eu/Eu*=0.75-1.33) are seen for the gabbro-diorite

lP

suite (Fig.6a), whereas the granite shows a significant Eu negative

na

anomaly (Fig.6c), which is associated with feldspar fractional crystallization or cumulates in the magma source. Additionally, the

Jo ur

gabbro-diorite suite shows different REE features, which are inconsistent with those of OIB, E-MORB and N-MORB as shown in Figure 6a. Therefore, we exclude the possibility that the mafic suite belongs to the nappe complex derived from the southern Yarlung Tsangpo ophiolites as suggested by Hou et al. (2001) and Gao et al. (2003). In the primitive-mantle normalized trace element variation spider diagrams, the gabbro-diorite suite and granite are both enriched in large ion lithophile elements (LILE) (e.g. Cs, Rb, K, U

Journal Pre-proof

and Pb), but depleted in high field strength elements (e.g. Nb, Ta, P and Ti) (Fig.6b and 6d). These geochemical features indicate a crustal characteristic or arc-related magma affinity (e.g. Kelemen, 1990). In addition, the gabbro-diorite and granite rocks show enrichment

in

Zr-Hf,

which

are

probably

related

to

of

subduction-released fluids or melts leading to incompatible element (e.g. Zr, Hf) concentration.

ro

3.4 Whole-rock Sr-Nd isotope compositions

-p

Seventeen representative samples from the diorite-gabbro and

re

granite were analyzed for whole-rock Sr-Nd isotopes. The

lP

analytical data are given in Supplementary Table 5. The results 87

Sr/86Sr

na

show slightly variable Sr-Nd compositions, with initial

varying from 0.703820 to 0.704213, with εNd(t) values from +4.2 to

Jo ur

+3.5. The second stage model ages (TDM2) (based on the depleted mantle) of the diorite-gabbro is in the range of 606-550 Ma (mean value= 575 Ma). The granite rocks also display initial 87

Sr/86Sr ratios of 0.703977 to 0.703180, and homogeneous Nd

isotope compositions, with εNd(t) values ranging from +4.1 to +4.4. Similar to the gabbro-diorite suite, the granite rocks yield young model ages ranging from 534 Ma to 556 Ma. The whole-rock Sr-Nd analytical results suggest that the gabbro-diorite suite and granite both have depleted mantle compositions. In the (87Sr/86Sr)I versus

Journal Pre-proof

εNd(t) diagram (Fig.7), all the samples fall in the mantle evolution array and correspond with the Mesozoic magmatic rocks of the Gangdese belt. Furthermore, the gabbro-diorite rocks show similar Sr-Nd isotope compositions with the Yeba and Zhengga mafic rocks.

of

4. Discussion 4.1 The emplacement timing and significance of the granite

ro

The field relationship suggests that the granite was emplaced

-p

later than the gabbro-diorite complex (Fig.2e). The U-Pb data on

re

zircon grains from the granite dike indicate emplacement at

lP

87.69±0.5 Ma (MSWD=2.3), belonging to Late Cretaceous

na

(Coniacian stage) rather than Miocene as previously considered (Fig.3g-j). However, SHRIMP II dating results reveal a complex

Jo ur

geochronological feature, indicating a continuous crystallization process (Fig.3i-j). The zircon SHRIMP II results can be divided into two stages. Stage two is represented by three zircon grains, yielding a weighted mean age of 78.0±1.5 Ma (MSWD=0.061). Stage one comprises nine zircon crystals, giving a mean weighted age of 86.5±1.6 Ma. In addition, one zircon shows a weighted age of 80.0±1.3 Ma between stage one and stage two. All the grains analyzed using SHRIMP II fall along a Concordia diagram (Fig.3i). Combined with results of SHRIMP II, we argue that the granite

Journal Pre-proof

experienced a continuous crystallization process, with stage one representing an early crystallization process, and stage two suggesting a late crystallization phase. Most zircon grains from the granite dikes were formed during stage one, suggesting that stage one represents the main crystallization and emplacement time. The

of

ages reported in this study suggest that the granite dike crystallized at ca. 87 Ma, belonging to Late Cretaceous (Coniacian stage)

ro

rather than Miocene as previously considered.

-p

4.2 Crustal contamination and fractional crystallization of the

re

gabbro-diorite suite

lP

Figure 6 shows that the gabbro-diorite rocks are characterized

na

by enrichment of LREE and LILE (e.g. Cs, Ba, Th and U), but are depleted in HREE and HFSE (e.g. Nb, Ta, Ti and P). These

Jo ur

features suggest crustal magma affinity or arc-type magma source. Mafic magmas derived depleted mantle source usually undergo crustal contamination, and display typical arc-type or crustal magma geochemical features. Generally, crustal contamination is inevitable for mantle-derived melts during their ascent through a crustal magma chamber or crust (e.g. Castillo et al., 1999). It is recognized that crustal melts generally have significantly low MgO contents, low Mg# and εNd(t) values, as well as low Nb/La ratios, but have high (87Sr/86Sr)i and La/Nb ratios (Rudnick, 1992;

Journal Pre-proof

Rudnick and Fountain, 1995; Rudnick and Gao, 2003). Thus, any crustal melt participation and input will cause an increase of (87Sr/86Sr)I and decrease in εNd(t) values significantly for the mantle-derived melts (Rogers et al., 2000). In this study, the analyzed

samples

have

significant

positive

εNd(t)

values

of

(+4.16~+3.48) and low (87Sr/86Sr)I ratios (0.704213~0.703820) excluding the possibility of crustal material. In the discrimination

ro

diagrams (Fig.8a-f), all the gabbro-diorite samples demonstrate

-p

homogeneous Sr-Nd isotope compositions indicating that crustal

re

contamination played only a negligible or minor role in the magma

lP

evolution. In addition, if the mantle-derived melts undergo

na

significant crustal contamination, they will show negative or positive trends along the Nb/La versus MgO and La/Nb versus SiO2 plots.

Jo ur

The discrimination diagrams reveal that all the samples have relatively homogeneous ratios of Nb/La and La/Nb when the MgO and SiO2 contents decrease or increase, indicating that magma did not witness significant crustal contamination (Fig.8g-h). Coeval mafic rocks and felsic rocks are interpreted by magma mixing or assimilation fractional crystallization (AFC) in the Gangdese belt (e.g. Dong et al., 2006, 2008; Mo et al., 2005; 2009; Qiu et al., 2015; Meng et al., 2016b, 2019). As shown in Figures 6-7 and Supplementary Figure 4, the diorites (SiO2=54.3 to 57.21 wt. %)

Journal Pre-proof

have similar Sr-Nd-Hf isotope compositions and REE and trace elements patterns with the gabbros, suggesting a genetic link. Plots in Figure 8a-h indicates that the fractional crystallization played an important role in the formation of the diorite rocks rather than magma mixing

and AFC processes. Thus, the fractional

of

crystallization process can better explain the wide ranges of SiO2 and MgO contents. Furthermore, the diorites show higher REE

ro

contents than the gabbros, which also suggest a fractional

-p

crystallization process because incompatible REE are preferentially

re

concentrated in the magma. Fig.5i-j shows non-mixing modeling

lP

curves, suggesting a fractional crystallization process rather than

na

magma mixing (Langmuir et al., 1978). In addition to geochemical and isotope evidence, the field relations also agree with the

Jo ur

fractional crystallization (Fig.2b-d). 4.3 Petrogenesis

4.3.1 Granite rocks

In the Gangdese belt, the majority of granitoid rocks show I-type features with low A/CNK ratios (<1.1) and lack typical Al-rich minerals (e.g. muscovite, garnet and cordierite) (e.g. Tafti, 2011; Hou et al., 2015; Meng et al., 2018b, c). In addition, the granitoid rocks from this belt are characterized by depleted Sr-Nd-Hf isotopic compositions, and reflect juvenile crustal components (e.g. Ji et al.,

Journal Pre-proof

2009; Tafti, 2011; Zhu et al. 2011; Hou et al., 2015). In this study, the

granite

peraluminous

rocks

demonstrate

feature

metaluminous

(Fig.4e),

with

to

A/CNK

weakly [molar

Al2O3/(CaO+Na2O+K2O)] ratios varying from 1.01 to 1.10, suggesting an I-type granitic feature. The decrease in P2O5 with

of

increasing SiO2 (Fig.9g) indicates that the granite belongs to I-type granite because P2O5 decreases with fractional crystallization

ro

process in I-type granite and increases in S-type granite as

-p

suggested by Chappell and White (1992). In addition, the granite

re

rocks have significantly positive εNd(t) values (mantle array) that are

lP

inconsistent with S-type granite (Fig.7b) (e.g. Ma et al., 2017a).

na

Recently, Ma et al. (2017a) and Zhang et al. (2019) reported some granite rocks characterized by the absence of mafic minerals

Jo ur

in southern Tibet (Gangdese region and central-Lhasa), and pointed out that these rocks are highly evolved, and show A-type granite features. In general, A-type granites have a close affinity with extensional settings (e.g. Eby, 1992; Hao et al., 2019; Meng et al., 2018d). The Gangdese region experienced tectonic extension during the early Late Cretaceous (100~80 Ma) (Ma et al., 2015; Xu et al., 2015; Ye et al., 2015; Meng et al., 2019) and asthenosphere upwelling (mid-oceanic ridge subduction or rollback) (e.g. Zhang et al., 2010). Moreover, several studies on the more evolved S- and

Journal Pre-proof

I-type granites also suggest A-type granitic features (e.g. Meng et al., 2018d; Zhang et al., 2019), especially high-silica A-type granites (King et al., 1997; Wu et al., 2007). Although the granite rocks in this study show I-type granitic feature, the possibility of A-type affinity cannot be excluded. The

of

geochemical features suggest that the granites have relatively high alkaline contents (Na2O+K2O>8.0 wt. %) and alkali index

ro

(0.69-0.61), but low contents of P2O5 (<0.02 wt. %) and CaO (<1.1

-p

wt. %) (Fig.9d, 9g) that correspond with A-type granites as

re

proposed by Eby (1990).

lP

In the normalized REE patterns (Fig.6c), the granites have

with

na

high light REE contents and low heavy REE contents inconsistent highly-fractionated

granites

(HFG),

but

exclude

the

are

Jo ur

classification as A-type granites (Fig.10a-e). A-type granites usually formed

at

high-temperatures

(>800

℃,

mean

temperature=891 ℃, up to 944 ℃) (e.g. Hao et al., 2019), whereas I- or S-type granites are from at relatively low temperature (mean temperatures at 800 ℃ and 770 ℃). Whole-rock zircon saturation and zircon Ti thermometers suggest that the granite rocks were crystallized at a low temperature (<800℃) (Fig.10f) excluding their correlation as A-type. Although Fig.10d suggests fractionated granite nature, the REE patterns and other features do not support

Journal Pre-proof

of high degree of fractionation. Combined with petrologic, mineral chemical and geochemical features, we argue that the granite from the study area belongs to typical I-type granite (unfractionated granite). 4.3.2 Evaluation on the adakite rocks Geochemically, normal adakites have SiO2 content ≥ 56 wt. %, 15 wt. %, and Na2O/K2O>1 (Defant and

of

Al2O3 content ≥

ro

Drummond, 1990). Compared to normal arc-type rocks, they

-p

possess high Sr contents (>400 ppm), and enriched in Eu (Eu

re

positive anomaly), but are strongly depleted in Yb (≤1.9 ppm) and Y

lP

(≤18 ppm) (Defant and Drmmond, 1990; Richards and Kerrich,

na

2007). Plots in Figure 9 (c, e, and f) indicate that the granite rocks have geochemical features that are inconsistent with typical

Jo ur

adakites, following the definition by Defant and Drmmond (1990) and Richards and Kerrich (2007). The Y versus Sr/Y and YbN versus (La/Yb)N diagrams are regarded as effective tools in discriminating adakite and classic arc magma, where the granite shows adakite features. In the Gangdese belt, the early Late Cretaceous granitoid rocks can be divided into adakitic rocks and normal arc-type rocks (e.g. Xu et al., 2015; Meng et al., 2019). It is notable that adakitic rocks overlap with normal arc-type rocks in space and time, suggesting a complex setting in the Gangdese belt.

Journal Pre-proof

Competing models are also proposed related to the petrogenesis of adakitic rocks in the Gangdese belt (e.g. Ji et al., 2012; Xu et al., 2015; Ma et al., 2017c; Meng et al., 2019). Among these, Xu et al. (2015) and Meng et al. (2019) argued that the early Late Cretaceous adakitic rocks are marked by high Sr/Y and (La/Yb)N ratios which are related to amphibole fractionation rather than

in the Gangdese belt (Defant et al., 1992). He et al. (2011)

ro

slab

of

typical adakites that formed by partial melting of subducted oceanic

-p

argued that the high Sr/Y and (La/Yb)N ratios can result in multiple

re

settings. Combined with previous studies, we also propose that the

lP

high Sr/Y and (La/Yb)N ratios of intermediate-felsic rocks from the

na

Gangdese do not represent adakitic features that were produced due to subducted young oceanic crust or thickened crust. Adakites

Jo ur

or adakitic rocks can be formed in the following settings: (I) partial melting of subducted oceanic slab (Defant and Drummond, 1990); (II) partial melting of thickened or foundering crust (Atherton and Petford, 1993; Xu et al., 2002, 2007); (III) crystallization and differentiation (Macpherson et al., 2006; Richards and Kerrich, 2007; Xu et al., 2015; Meng et al., 2019); (IV) magma mixing (e.g. Chen et al., 2004; Guo et al., 2007); (V) partial melting of granulite rocks (Jiang et al., 2007) and (VI) high Sr/Y magma source (Kamei et al., 2009; Zhang et al. 2009; Moyen, 2009). However, adakitic

Journal Pre-proof

rocks, formed in the III to VI settings above belong to pseudo-adakites (e.g. He et al., 2011; Wang et al., 2013; Meng et al., 2019). He et al. (2011) proposed that Sr versus SiO2 and Sr versus CaO diagrams can better discriminate pseudo adakites. If adakitic rocks are products of partial melting of subducted oceanic slab or partial melting of thickened crust and foundering, they will

of

show high Sr and steep slope, which can exclude the possibilities

ro

of fractional crystallization and magma mixing. The granites have

-p

similar trends with normal granitoid rocks, suggesting a pseudo

re

adakitic feature (Fig.11a-b). Moreover, Figure 11c-d also suggests

lP

that the granite rocks belong to normal granitoids rather than typical

na

adakites. The diorites from the gabbro-diorite complex also suggest a pseudo adakitic feature. High Sr diorite rocks are products of

Jo ur

differentiation crystallization that has been proved in Figure 8. Therefore, the Y versus Sr/Y and YbN versus (La/Yb)N diagrams are not effective in discriminating pseudo adakites (Fig.9a-b). In conclusion, we argue that the granite and diorites of the complex cannot be ascribed to adakite rocks. Combined with published data and "adakitic rocks" distribution features, we conclude that the early Late Cretaceous granitoid rocks belong to typical arc-type rocks. 4.3.3 Magma source of the granite The Mesozoic granitoid rocks show positive Sr-Nd-Hf isotope

Journal Pre-proof

features, corresponding to deplete mantle feature (e.g. Ji et al., 2009; Zhu et al., 2011; Hou et al., 2015) (Fig. 7 and Supplementary Figure 4a). Their young Nd-Hf model ages and isotope features indicate that the majority of granitoid rocks were derived from partial melting (recycling) of juvenile crust (Ji et al., 2009; Ma et al.,

of

2019). In our study area, the granites have low Mg# (<40) values indicating a partial melting of pure crustal material (Fig.4f). However,

ro

it has been shown that mantle material injection played a key role in

-p

the formation of the Gangdese composite batholiths, indicating

re

multiple mafic magma underplating and magma mixing during the

lP

Mesozoic and Early Cenozoic (>40 Ma) (e.g. Dong et al., 2005; Qiu

na

et al., 2015; Ma et al., 2017d; Meng et al., 2019). The Mesozoic granitoid rocks from the Gangdese batholith demonstrate high Mg#

Jo ur

values (>40), indicating magma mixing (e.g. Meng et al., 2019). Coeval mafic enclaves and mafic rocks occur with the granitoid rocks in space and time (e.g. Qiu et al., 2015; Meng et al., 2019). However, the partial melting of pure crustal material forming granitic plutons is rare in the Gangdese belt. Although the granite sheet intruded into the gabbro-diorite suite (Fig.2e-f), the mafic magma contamination

played

a

negligible

role

as

suggested

by

homogeneous Sr-Nd isotope composition (Supplementary Table 5) and related plots (Fig.9h) (Langmuir et al., 1978). The granite rocks

Journal Pre-proof

have significantly positive εNd(t) values plotting into the mantle evolution array, and possess similar Sr-Nd isotope compositions with the Mesozoic magmatic rocks. Combined with petrological features and geochemical indicators, as well as Sr-Nd isotopes, we suggest that the granite rocks are products of partial melting

of

(recycling) of the juvenile crust, and mantle material played a negligible role in the formation of the granite.

ro

4.3.4 The gabbro-diorite suite

-p

Cumulate gabbroic rocks can be divided into two types,

Compared

the

sheeted

cumulate

rocks

cumulate

display

rocks,

the

coarse-medium-fine

na

annular-texture

to

lP

2015).

re

sheeted- and annular-texture cumulate rocks (e.g. Shao et al.,

grained texture from the core to the margin of the intrusion. Field

Jo ur

observations exclude the possibility that the gabbro-diorite complex belongs to group with annular texture (Fig.2a-d). It is known that the sheeted-texture

gabbro

rocks

with

cumulate

texture

are

characterized by the following characteristics: (i) horizontal rhythmic layering or "graded layer

";

(ii) oriented minerals; (iii)

mega-crystal texture; and (iv) poikilitic texture. Field evidence reveals that the gabbro-diorite complex lacks typical sheetedtexture, and mainly display massive texture (Fig.2a-d). Additionally, the rocks collected from the suite have no Eu positive anomaly that

Journal Pre-proof

is inconsistent with the effect of crystal cumulation.

Generally,

cumulate gabbro shows positive Eu anomalies due to plagioclase crystal accumulation in the magma chamber (e.g. Piccardo and Guarnieri, 2011; Parlak et al., 2019). Furthermore, mineral microstructures are inconsistent with typical cumulate gabbro, in

of

the absence of meta-crystals (e.g. hornblende) and mineral orientation. In this study, the rocks show high REE contents (Fig.6a)

ro

are also inconsistent with mafic cumulate rocks that are

-p

characterized by low REE contents (e.g. Zhou et al., 2005; Caroff et

re

al., 2011; Kristoffer et al., 2015). Based on the above features, we

lP

infer that the gabbro-diorite suite in our study does not belong to

na

the class.

The REE, trace element spider diagrams and homogeneous

gabbroic

Jo ur

Sr-Nd-Hf isotope reveal that the diorites are products of the magma

crystallization

differentiation.

Zircon

geochronology of these rocks reveals crystallization during 94.63 to 90.66 Ma. Gabbroic magmas are generally associated with the partial melting of mantle material. In our study area, the gabbro-diorite rocks show depleted Sr-Nd-Hf isotopes and young Hf-Nd model ages, suggesting that the gabbro-diorite rocks were sourced from partial melting of the depleted mantle (Fig.7 and Supplementary

Journal Pre-proof

Figure 4a-b). The La/Yb versus Sm/Yb diagram suggests that the gabbro-diorite suite was sourced from ca. 15-17% melting of garnet peridotite (Supplementary Figure 5). In the zircon U-Pb age versus εHf(t) diagram, the gabbro-diorite rocks fall in the same region with the Mesozoic granitoids from the Gangdese composite batholiths

of

(Supplementary Figure 4a). Previous studies suggest that the Mesozoic Gangdese batholiths formed through the northward

ro

subduction of the Neo-Tethys oceanic slab beneath the Lhasa

-p

terrane (e.g. Yin and Harrison, 2000; Ji et al., 2009; Tafti, 2011; Zhu

re

et al., 2011; Hou et al., 2015; Meng et al., 2016a, b, 2019). In the

lP

Sr-Nd diagram (Fig.7), the gabbro-diorite rocks plot into the mantle

na

array and demonstrate similar Sr-Nd isotopes with the Early Jurassic Yeba basalts and early Late Cretaceous Zhengga

Jo ur

gabbro-diorite suite (Fig.7). The Yeba basalts were derived from a common and heterogeneous mantle that was metasomatized by sediments/fluids released from the subducted Neo-Tethys oceanic crust (e.g. Zhu et al., 2008; Ma et al., 2017c; Wei et al., 2017; Ma et al., 2018). However, crustal contamination (enriched compositions) played a key role in the petrogenetic process of the Yeba Formation basalts (e.g. Zhu et al., 2008; Wei et al., 2017). In contrast, the enriched components (e.g. crustal material and sediments) had only a minor or negligible role during the evolution of the

Journal Pre-proof

gabbro-diorite suite in study area (Fig.5i-j and Fig.8). Therefore, the early Late Cretaceous gabbro-diorite rocks show more depleted Sr-Nd-Hf isotopes than the Early Jurassic Yeba Formation basalts. Furthermore,

the

coeval

Zhengga

gabbro-diorite

complex

(crystallization ca. 94 Ma) shows a complex magma source, with

of

group I formed by the fractional crystallization of clinopyroxene and accumulation of plagioclase without significant contamination,

ro

whereas group II was sourced from the fractional crystallization of

-p

plagioclase and clinopyroxene with the same magma source but

re

showing significant crustal contamination in the eastern Gangdese

lP

belt (Ma et al., 2013a). We thus infer a heterogeneous magma

na

source in the Gangdese belt. Recently, Wang et al. (2019) also reported that the Paleogene gabbroic rocks show geochemical and

Jo ur

isotope variations along the Gangdese arc. The mafic rocks from the west-east segments of the Gangdese belt have distinct geochemical and isotope compositions suggesting hybrid magma sources during the Neo-Tethys oceanic subduction. Fluids/sediments and melts from the down-going oceanic slab induce partial melting of the lithosphere mantle in such setting. In the (Ta/La)PM versus (Hf/Sm)PM diagram (Supplementary Figure 6a), the majority of samples plot into the hydrated mantle source. Supplementary Figure 6b-c further suggests that fluids derived from

Journal Pre-proof

slab dehydration are the dominant factor that induced partial melting of the depleted mantle. In combination with the Sr-Nd-Hf isotope features, we argue that the dehydration of the Neo-Tethys oceanic slab induced the partial melting of the depleted mantle forming the gabbro-diorite rocks (Fig.12). Petrographic studies

of

reveal that the gabbro-diorite rocks contain abundant hornblende and calcic plagioclase (Supplementary Figures 1a-e and 2), the

ro

latter (An>50) characterized by labradorite and bytownite crystals

-p

(Supplementary Table 1), suggesting high-pressure H2O-rich

re

setting (e.g. Sisson et al., 1993; Qiu et al., 2015; Meng et al.,

lP

2016a). During the later evolution and ascent, the gabbro-diorite

na

suite did not witness any significant crustal contamination. 4.4 Magma processes and fractional crystallization

Jo ur

In Figure 5, the linear relations with decreasing of Cao, Fe2O3T and MgO contents with increasing of SiO2, suggest crystallization of mafic minerals and plagioclase during magma evolution. This is also indicated by the plots in Cr versus V, Sr versus Rb/Sr and Ba versus Rb/Sr diagrams (Supplementary Figure 7a-c). The geochemical

discrimination

diagrams

further

demonstrate

pyroxene-, hornblende- and plagioclase-dominated evolution fractionation. The Cpx- and Opx-dominated fractionation probably suggests the presence of minor olivine during the early-stage

Journal Pre-proof

evolution. The granite rocks display fractionation of K-feldspar (Supplementary Figure 7a-c). Additionally, negative anomalies of Eu

and

significant

Ba

depletions

indicate

that

alkali

feldspar-dominated fractionation (K-plagioclase) (Fig.6c-d). 4.5 Genetic affiliation

of

Yin et al. (1994) identified two regional faults which are the Gangdese thrust (GT) and Great converse thrust (GCT). Due to

ro

strong tectonic activities of two faults during the Oligocene-Miocene,

-p

it is possible that the mafic rock assemblages from the ophiolites

re

were transported to the Gangdese belt forming new tectonic

lP

mélanges. Our study area is adjacent to the ophiolites of the IYSZ

na

(Fig.1b-c). According to the data from geophysical studies and regional faults as well as rock assemblages, the early workers

Jo ur

considered that the gabbro-diorite complexes of the middle segment of the Gangdese batholith (Fig.1b) belong to the ophiolites of the IYSZ rather than the Gangdese batholiths (Hou et al., 2001; Xiong et al., 2001; Gao et al., 2003). Later, some workers attributed the gabbro-diorite complexes to the Gangdese batholith, and proposed that these complexes are products of the northward subduction of the Neo-Tethys oceanic lithosphere and Indian-Asian collision (e.g. Dong et al., 2006, 2008; Qiu et al., 2015; Meng et al., 2016a; Wang et al., 2017). The data from field observations,

Journal Pre-proof

petrology, geochemistry, and isotopes in this study indicate arc-type features for the gabbro-diorite complex in the Shanba region (Fig.1c). Based on regional geology and published data, we conclude that the Shanba gabbro-diorite suite belongs to the Gangdese batholiths rather than being remnants of the ophiolites

of

from the IYSZ. 4.6 Tectonic implications

ro

Previous studies suggested that a juvenile island-arc terrane

-p

accreted to the southernmost Lhasa terrane during the Cretaceous

re

(e.g. Ji et al., 2009; Zhu et al., 2011; Ma et al., 2013a; Hou et al.,

lP

2015; Meng et al., 2019). However, the subduction style of the

na

Neo-Tethys oceanic crust has been debated, including mid-oceanic ridge subduction (e.g. Zhang et al., 2010; Guo et al., 2013; Wu et

Jo ur

al., 2018), rollback of the Neo-Tethys oceanic slab (e.g. Ma et al., 2013a; Xu et al., 2015; Meng et al., 2019) and high-angle oblique subduction (Wang et al., 2013). The REE, trace elements patterns and Sr-Nd-Hf features suggest an arc-related setting (Fig.6a-b). In the Nb/Yb versus Th/Yb diagram, the gabbro-diorite rocks plot into the continental arc (Supplementary Figure 8e). Other geochemical data also suggest that the gabbro-diorite complex was formed in an active continental margin setting (Supplementary Figure 8a-d). We therefore correlate

Journal Pre-proof

the early Late Cretaceous magmatism with the Neo-Tethys oceanic subduction beneath the Lhasa terrane (Fig.12). There is a striking flare-up of Early Late Cretaceous magmatic events in the Gangdese belt. Based on the discovery of charnockites in the eastern Gangdese, Zhang et al. (2010)

of

proposed a mid-oceanic subduction model to decipher the high-temperature garnet-bearing granulite. Moreover, Guo et al. also

attested

to

this

model

ro

(2013)

and

argued

that

-p

high-temperature metamorphism in the southeastern Lhasa terrane

re

was associated with the Neo-Tethys oceanic ridge subduction. The

lP

mid-oceanic ridge subduction setting is generally characterized by

na

H2O-poor, CO2-rich environment and high oxygen fugacity (fO2). The high-temperature metamorphism granulite and presence of

Jo ur

charnockite are restricted to the eastern Gangdese (Nyingchi region). If the Early Late Cretaceous magmatic rocks were products of the high-heat flux mid-oceanic ridge subduction in the whole Gangdese belt, the Gangdese arc should be in a dry and H2O-poor setting. However, the recent discoveries of H2O-rich hornblende gabbro-diorite

rocks

are

contradictory

with

the

model

of

mid-oceanic subduction (e.g. Meng et al., 2019). In addition, Dong and Xu (2016) concluded that the eastern Gangdese region (Nyingchi region) experienced rapid exhumation during the

Journal Pre-proof

Miocene leading to the lower crust of the Nyingchi region being exhumed and exposed on the surface. It is therefore possible that the high-temperature granulite and charnockite represent the lower crustal compositions (Rudnick and Presper, 1990; Rudnick, 1992; Gao et al., 2004) rather than the products of the Neo-Tethys

of

oceanic-ridge subduction. Additionally, several studies have established that the Gangdese belt is mainly composed of I-type Mid-oceanic ridge subduction will usually generate a

ro

granites.

-p

wide variety of magmas, with chemical compositions ranging from

re

adakites-high-Mg andesites to alkaline and tholeiitic mafic volcanic

lP

rocks (e.g. Abratis and Worner, 2001; Tang et al., 2012). Therefore,

na

the lithology in our study area is inconsistent with the rocks that are produced by mid-oceanic subduction.

Gangdese

Jo ur

Compared to the Nyingchi region, the central-western region

experienced

low-rate

exhumation

and

denudation, so the middle-upper crustal components are preserved in the absence of exposed lower crust. It has been suggested that the northward subduction of the Neo-Tethys oceanic slab had an important effect on the southernmost part of the Eurasian continent for a distance of over >2000 km prior to India-Asia collision (Xiong et al., 2019). The mid-oceanic ridge subduction of the Neo-Tethys is likely to influence the whole of Gangdese belt, and multiple

Journal Pre-proof

high-temperature, Nb-rich and high-Mg mafic rocks might have been produced during the early Late Cretaceous. Furthermore, the duration of mid-oceanic ridge subduction can extend over 40 Ma from initiation to termination. Similar examples were reported in the Andes orogen (Kula-Farallon ridge subduction) and the western

of

Junggar area (e.g. Tang et al., 2012). In contrast, the flare-up of the Early Late Cretaceous magmatism had a short duration. In addition

ro

to these, the Early Late Cretaceous magmatic rock types and

-p

geochemical features are inconsistent with the typical rocks

re

generated by ridge subduction which are characterized by

lP

high-temperature and MORB-, OIB-like features. Also, the

na

high-angle oblique subduction model cannot explain the Early Late Cretaceous magmatic flare-up and mantle underplating (e.g. Ma et

Jo ur

al., 2015; Meng et al., 2019).

In combination with regional setting and published data, as well the results reported in this study, we propose that the gabbro-diorite suite formed in an active continental margin setting, and the rollback of the Neo-Tethys oceanic slab might be the major factor that contributed to the flare-up of the Early Late Cretaceous magmatism in the Gangdese belt.

5. Conclusions (1) The gabbro-diorite suite was emplaced at ca. 91-95 Ma,

Journal Pre-proof

and the granite crystallized at ca. 87 Ma. These rocks thus belong to the Early Late Cretaceous magmatic event. (2) The gabbro-diorite rocks are products of partial melting of the depleted mantle, and slab dehydration played a key role in causing the partial melting of the lithosphere mantle. However, the

of

granite rocks were derived from partial melting (recycling) of the juvenile crust.

ro

(3) There is no major crustal or sediment contamination in the

-p

formation of the gabbro-diorite suite during the magma evolution.

re

The diorite rocks of the suite are related to fractionation

lP

crystallization of the gabbroic magma.

na

(4) The granite belongs to typical I-type granite, and mantle material was not involved in the formation of the magma.

Jo ur

(5) The rollback of the Neo-Tethys oceanic slab might be responsible for the Early Late magmatism in southern Tibet.

Acknowledgements We thank Editor Prof. Zeming Zhang and three anonymous reviewers for their valuable comments that improved the manuscript greatly. We also thank Prof. Zhiqin Xu for her academic guidance and warm-hearted help in the geological survey of the southern Tibet. This study was co-supported by the Key Laboratory

Journal Pre-proof

of Deep-Earth Dynamics of Ministry of Natural Resources (Open foundation) (J1901-16), the Natural Foundation of Shandong province (No.ZR2019QD002, ZR2017BD033), National Natural Science Foundation of China (41902230) and special foundation of the central subordinate University (No. 300102278105). In addition,

of

first author Dr. Yuanku Meng thanks Boxian Meng for his guidance

ro

and help.

-p

Appendix A. Descriptions of analytical methods

re

A.1. Electron probe microanalyses

lP

The representative thin sections from the gabbro-diorite suite

na

were selected for electron probe microanalysis (EPMA). The EPMA analysis was carried out at the testing center of Shandong Bureau

Jo ur

of China Metallurgical Geology Bureau (Jinan). Mineral chemical compositions were determined using a JEOL JXA-8230 microprobe with a 15.0 kv excitation voltage, 20 nA beam current and 5 µm beam spot in diameter. A.2. Zircon U-Pb dating analyses Zircon grains were separated using magnetic and heavy liquid methods at the Institution of Geological Survey and Mapping of Hebei Province (Langfang), China. The selected zircons were mounted in epoxy and polished down to half-section for

Journal Pre-proof

Cathodo-luminescence (CL) images, to reveal the internal textures of studied zircons. Zircon LA-ICP-MS U-Pb dating was conducted at the Wuhan Sample Solution Analytical Technology Co., Ltd (China) using a Neptune ICP-MS attached to a New Wave 213 nm laser ablation system (Thermo Finnigan Element 2) with an

of

in-house sample cell. Fixed 35 µm diameter laser beam was adopted with a laser pulse frequency of 8~10 Hz. The ablated

ro

material was transported into the plasma torch by He-Ar mixed

Pb/206Pb age of 608.5±0.4 Ma, 206Pb/238U age of 600.3±0.3 Ma)

re

207

-p

gases. The standard zircon samples GJ-1 (internal standard,

206

lP

and 91500 (external standard,

Pb/238U age of 1064.4±4.8 Ma)

na

were used to correct the zircon U-Th-Pb isotopic fractionation. The analytical results were processed using ICPMSDataCal10.9

Jo ur

software (Liu et al., 2010). The Concordia plots and weighted average U-Pb ages were obtained by Isoplot 4.11 program (Ludwig, 2003). The common lead (Pb) correction was performed using Com Pb Corr# 3_15G program, following Andersen (2002). Detailed principles and procedures of zircon LA-ICP-MS dating technique followed those described by Chang et al. (2006). Zircon grains from the granite samples were analyzed using SHRIMP II technique at the Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, Beijing. A primary O2- ion beam

Journal Pre-proof

of 6 nA was used to bombard the zircon surface with a 20 µm diameter spot size. Standard zircons 91500 (U=91 mm), SL 13 (U=238 ppm) and M257 (U=840 ppm) were used for elemental abundance calibration (Williams, 1998). TEMORA is 206Pb/238U age of 417 Ma analyzed for calibration of

206

Pb/238U ratios after three

described by Williams (1998).

ro

A.3. Zircon Lu-Hf isotopic analyses

of

analyses. SHRIMP II analytical methods and conditions are

-p

In situ Zircon Hf isotopic analyses were carried out using a

re

New Wave U-Pb 213 laser ablation microprobe attached to a

lP

Neptune MC-ICP-MS technique at the State Key Laboratory for

na

Mineral Deposits Research, Nanjing University. Laser beam of analytical spot was 40 µm diameter and the pulse frequency of

Jo ur

laser beam was 8~10 Hz. Standard zircon 91500 was used for evaluating the accuracy of the analytical spots that yielded a weighted mean

176

Hf/177Hf ratio of 0.282296±8 (2σ, MSWD=0.58)

(Goolaerts et al., 2004). The measured

176

Lu/177Hf ratios and

176

Lu

decay constant of 1.867×10−11/annual were used for calculating the (176Hf/177Hf)initial values (Söderlund et al., 2004). The chondritic values of 176Hf/177Hf (0.282785 ± 11; 2σ) and 176Lu/177Hf (0.03361 ± 1; 2σ) were used for calculating epsilon Hf (εHf(t)) values (Bouvier et al., 2008). The model ages (TDM) ages were calculated by using a

Journal Pre-proof 176

Lu/177Hf value of 0.015 of the average continental crust (Vervoort

and Blichert-Toft, 1999; Griffin et al., 2000, 2002). A.4. Whole-rock major-trace analyses Whole-rock major and trace element analyses were performed at the Wuhan Sample Solution Analytical Technology Co., Ltd

of

(China). Major elements were analyzed using a XRF spectrometer, with an analytical precision of ± 5%. Trace and rare earth elements

ro

(REE) concentrations were analyzed using an Agilent 7500a

re

better ± 10% (some are ± 5%).

-p

ICP-MS technique, with the precision of the ICP-MS analyses being

lP

A.5. Whole-rock Sr-Nd isotopic analyses

na

Seventeen representative samples from the gabbro-diorite suite and the granite were selected for whole-rock Sr-Nd isotope

Jo ur

analyses. The samples were assayed on a VG 354 mass spectrometer with five collectors at the Center of Modern Analysis, Nanjing University, China. The whole procedural blanks are <300 pg for Sr, <30 pg for Sm, <100 pg for Rb and <100 pg for Nd. The Sr-Nd isotope ratios were normalized relative to =8.375209 and

86

Sr/88Sr

146

NBS-987 yielded

Nd/144Nd = 0.7219, respectively. Sr standard

87

Sr/86Sr = 0.710233 ± 0.000006 (2σ) and Nd

standard La Jolla gave

143

Nd/144Nd = 0.511863 ± 0.000006 (2σ).

The details on Sr and Nd isotope measurements are as those

Journal Pre-proof

described in Li et al (2011a, b).

References Abratis, M., Worner, G., 2001. Ridge collision, slab-window formation, and the flux of Pacific asthenosphere into the Caribbean realm. Geology 29, 127-130. Andersen, T., 2002. Correction of common lead in U-Pb analyses that do not

of

report 204Pb. Chem. Geol. 192 (1-2), 59-79.

ro

Atherton, M.P., and Petford, N., 1993. Generation of sodium rich magmas from newly underplated basaltic crust. Nature 362, 144-146.

-p

Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu-Hf and Sm-Nd isotopic

re

composition of Chur: constraints from unequilibrated chondrites and

Sci. Lett. 273, 48-57.

lP

implications for the bulk composition of terrestrial planets. Earth Planet.

na

Boynton, W.V., 1984. Cosmo chemistry of the rare earth elements: meteorite studies. In: Henderson, P. (Ed.), Rare Earth Elements Geochemistry.

Jo ur

Elsevier, Amsterdam, pp. 63-114. Castillo, P.R., Janney, P.E., Solidum, R.U., 1999. Petrology and geochemistry of Camiguin Island, southern Philippines: insights to the source of adakites and other lavas in a complex arc setting. Contributions to Mineralogy and Petrology 134(1), 33-51. Caroff, M., Coint, N., Hallot, E., Hamelin, C., Peucat, J.J., Charreteur, G., 2011. The mafic-silicic layered intrusions of Saint-Jean-du-Doigt (France) and North-Guernsey (Channel Islands), Armorican Massif: Gabbro-diorite layering and mafic cumulate-pegmatoid association. Lithos 125, 675-692. Chang, Z.S., Vervoort, J.D., McClelland, W.C., Knaack, C., 2006. U-Pb dating of zircon by LA-ICP-MS. Geochem. Geophys. Geosyst. 7 (5), 1-14. Chappell, B.W. & White, A. J. R. (1992). I- and S-type granites in the Lachlan Fold Belt. Transactions of the Royal Society of Edinburgh: Earth Sciences

Journal Pre-proof 83, 1-26. Chen, B., Jahn, B.M., Arakawa, Y., Zhai, M.G., 2004. Petrogenesis of the Mesozoic intrusive complexes from the southern Taihang Orogen, North China Craton: elemental and Sr-Nd-Pb isotopic constraints. Contrib. Mineral. Petrol. 148(4), 489-501. Chen, X.J., Xu, Z.Q., Meng, Y.K., He, Z.Y., 2014. Petrogenesis of Miocene Adakitic Diorite-Porphyrite in Middle Gangdese Batholith, SouthernTibet: Constraints

from

Geochemistry,

Geochronology

and

Sr-Nd-Hf

of

isotopes．Acta Petrologica Sinica 30(8), 2253-2268 (in Chinese with

ro

English abstract).

Chung, S.L., Chu, M.F., Ji, J.Q., O’Reilly, S.Y, Pearson, N.J, Liu, D.Y., Lee,

-p

T.Y., Lo, C.H., 2009, The nature and timing of crustal thickening in

re

southern Tibet: Tectonophysics 477, 36-48.

lP

Chung, S.L., Chu, M.F., Zhang, Y.Q., Xie, Y.W., Lo, C.H., Lee, T.Y., Lan, C.Y., Li, X.H., Zhang, Q., Wang, Y.Z., 2005. Tibetan tectonic evolution inferred

na

from spatial and temporal variations in post-collisional magmatism. Earth Sci. Rev. 68,173-196.

Jo ur

Chung, S.L., Liu, D., Ji, J., Chu, M.F., Lee, H.Y., Wen, D.J., Lo, C.H., Lee, T.Y., Qian, Q., Zhang, Q., 2003. Adakites from continental collision zones: Melting of thickened lower crust beneath southern Tibet: Geology 31, 1021-1024.

Corfu, F., Hanchar, J.M., Hoskin, P.W.O., and Kinny, P., 2003. Atlas of zircon textures, Rev. Mineral. Geochem., 53, 469–500, Doi:10.2113/0530469. Defant, M., Xu, J., Kepezhinskas, P., Wang, Q., Zhang, Q., Xiao, L., Defant, M., 2002. Adakites: some variations on a theme. Acta Petrol. Sin. 18, 129-142 in English. Defant, M.J., Drummond, M.S., 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere. Nature 347, 662-665. Defant, M.J., Jackson, T.E., Drmmond, M.S., De Boer J, Z., Bellon, H., Feigenson, M.D., Maury, R.C., Stewart, R.H., 1992. The geochemistry of

Journal Pre-proof young volcanism throughout western Panama and southeastern Costa Rica: An overview. Journal of the Geological Society 149 (4), 569-579. Dong, G.C., Mo, X.X., Zhao, Z.D., Guo, T.Y., Wang, L.L., Chen, T., 2005. Geochronologic constraints by SHRIMP II zircon U-Pb dating on magma underplating in the Gangdese belt following India-Eurasia collision. Acta Geologica Sinica (English Edition), 79(6): 784–794. Dong, G.C., Mo, X.X., Zhao, Z.D., Zhu, D.C., Song, Y.T., Wang, L., 2008. Gabbros from southern Gangdese: implication for mass exchange

of

between mantle and crust. Acta Petrologica Sinica 24, 203-210 (in

ro

Chinese with English Abstract).

Dong, G.C., Mo, X.X., Zhu, D.C., Wang, L.L., Chen, T., Li, B., 2006. Magma

-p

mixing in middle part of Gangdese magma belt: evidences from granitoid

re

complex. Acta Petrologica Sinica 22, 835-844 (in Chinese with English

lP

abstract).

Dong, H.W., Xu, Z.Q., 2016. Kinematics, fabrics and geochronology analysis in

108-123.

na

the Medog shear zone, Eastern Himalayan syntaxis. Tectonophysics 667,

Jo ur

Dong, X., Zhang, Z.M., 2013. Genesis and tectonic significance of the Early Jurassic magmatic rocks from the southern Lhasa terrane. Acta Petrol. Sinica 29 (6),1933-1948 (in Chinese with English abstract). Eby, G., 1992. Chemical subdivision of the A-type granitoids: Petrogenetic and tectonic implication: Geology 20, 641-644. Eby, G.N., 1990. The A-type granitoids: A review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26(1-2), 115-134. Gao, J.H., Zeng, L.S., Guo, C.L., Li, Q.L., Wang, Y.Y., 2017. Late Cretaceous tectonics and magmatism in Gangdese batholith, Southern Tibet: A record from the mafic-diorite swarms within the Baidui Complex, Lhasa. Acta Petrologica Sinica 33(8), 2412-2436 (in Chinese with English abstract). Gao, S., Rudnick, R.L., Yuan, H.L., Liu, X.M., Liu, Y.S., Xu, W.L., Ling, W.L.,

Journal Pre-proof Ayers, J., Wang, X.C., Wang, Q.H., 2004. Recycling lower continental crust in the North China Craton. Nature 432, 892-897. Gao, Y.F., Hou, Z.Q., Wei, R.H., Cai, J.H., Meng, X.J., Huang, W., 2003. Origin of a basic-ultrabasic belt on the northern bank of the Yarlung Zangbo River. Geological Bulletin of China 22(10), 789-797 (in Chinese with English abstract). Goolaerts, A., Mattielli, N., de Jong, J., Weis, D., Scoates, J.S., 2004. Hf and Lu isotopic reference values for the zircon standard 91500 by MC-ICP-MS.

of

Chem. Geol. 206, 1-9.

ro

Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., Achterbergh, E.V., O’Reilly, S.Y., 2000. The Hf isotope composition of Cratonic mantle:

-p

LA–MC–ICP–MS analysis of zircon megacrysts in kimberlites. Geochim.

re

Cosmochim. Acta 64 (1), 133–147.

lP

Griffin, W.L., Wang, X., Jackson, S.E., Pearson, N.J., O’Reilly, S.Y., Xu, X., Zhou, X., 2002. Zircon chemistry and magma mixing, SE China: in–situ

(3–4), 237–269.

na

analysis of Hf isotopes, Tonglu and Pingtan igneous complexes. Lithos 61

Mo, X,

Jo ur

Guan, Q., Zhu, D.C., Zhao, Z.D., Zhang, L.L., Liu, M., Li, X.W., Yu, F.,

X., 2010. Late Cretaceous adakites in the eastern segment of the Gangdese belt, southern Tibet: Products of Neo-Tethyan ridge subduction? Acta Petrologica Sinica 26 (7), 2165-2179. Guo, F., Nakamuru, E., Fan, W.M., Kobayoshi, K., Li, C.W., 2007. Generation of Palaeocene adakitic andesites by magma mixing; Yanji Area, NE China. J. Petrol. 48(4), 661–692. Guo, L., Zhang, H.F., Harris, N., Pan, F.B. and Xu, W.C., 2013. Late Cretaceous

(~81

Ma)

high-temperature

metamorphism

in

the

southeastern Lhasa terrane: implication for the Neo-Tethys ocean ridge subduction. Tectonophysics 608, 112-126. Guo, Z.F., Wilson, M., Liu, J.Q., 2007. Post-collisional adakites in south Tibet: Products of Partial melting of subduction-modified lower crust. Lithos

Journal Pre-proof 96(1-2), 205-224. Hao, L.L., Wang, Q., Wyman, D.A., Ma, L., Wang, J., Xia, X.P., Qu, Q., 2019. First

identification

of

postcollisional

A-type

magmatism

in

the

Himalayan-Tibetan orogen. Geology 47, 187-190. He, Y.S., Li, S.G., Hoefs, J., Huang, F., Liu, S.A., Hou, Z.H., 2011. Post-collisional granitoids from the Dabie orogen: New evidence for partial melting of thickened continental crust. Geochimica et Cosmochimica Acta 75, 3815-3838.

of

Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneous

ro

and metamorphic petrogenesis. Rev. Mineral. Geochem. 53, 27-62. Hou, Z.Q., Gao, Y. F., Qu, X. M., Rui, Z. Y., Mo, X. X., 2004. Origin of adakitic

-p

intrusives generated during mid-Miocene east-west extension in southern

re

Tibet. Earth and Planetary Science Letters 220, 139-155.

lP

Hou, Z.Q., Duan, L.F., Lu, Y.J., Zheng, Y.C., Zhu, D.C., Yang, Z.M., Yang, Z.S., Wang, B.D., Pei, Y.R., Zhao, Z.D.,

Mccuaig, T.C., 2015. Lithospheric

na

Architecture of the Lhasa Terrane and Its Control on Ore Depositsin the Himalayan-Tibetan Orogen. Economic Geology 110, 1541-1575.

Jo ur

Hou, Z.Q., Gao, Y.F., Huang, W., 2001. The discovery and geological significance of the ophiolite belt in the northern bank of the Yarlung Zangbo River. Geological Review 47(4), 344 (in Chinese). Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification of the common volcanic rocks. Can. J. Earth Sci. 8 (5), 523-548. Ji, W.Q., Wu, F.Y., Chung, S.L., Liu, C.Z., 2009. Geochronology and Petrogenesis of granitic rocks in the Gangdese batholith, southern Tibet. Sci. China (Ser. D) 52 (9), 1240-1261. Ji, W.Q., Wu, F.Y., Chung, S.L., Liu, C.Z., 2014. The gangdese magmatic constraints on a latest cretaceous lithospheric delamination of the Lhasa terrane, southern Tibet. Lithos 210-211, 168-180. Ji, W.Q., Wu, F.Y., Liu, C.Z., Chung, S.L., 2012. Early Eocene crustal thickening in southern Tibet: new age and geochemical constraints from

Journal Pre-proof the Gangdese batholith. J. Asian Earth Sci. 53, 82–95. Jiang, N., Liu, Y.S., Zhou, W.G., Yang, J.H., Zhang, S.Q., 2007. Derivation of Mesozoic adakitic magmas from ancient lower crust in the North China craton. Geochim. Cosmochim. Acta 71(10), 2591-2608. Jiang, Z.Q., Wang, Q., Wyman, D.A., Li, Z.X., Yang, J.H., Shi, X.B., Ma, L., Tang, G.J., Gou, G.N., Jia, X.H., Guo, H.F., 2014. Transition from oceanic to continental lithosphere subduction in southern Tibet: evidence from the Late Cretaceous-Early Oligocene (~91-30 Ma) intrusive rocks in the

of

Chanang-Zedong area, southern Gangdese. Lithos 196-197, 213-231.

ro

Kamei, A., Miyake, Y., Owada, M., Kimura, J.I., 2009. A pseudo adakite derived

Japan arc. Lithos 112, 615-625. P.B.,

Johnson,

element

Kinzler,

depletions

R.J., in

Irving,

arc

A.J.,

basalts

1990.

due

to

lP

High-field-strength

K.T.M.,

re

Kelemen,

-p

from partial melting of tonalitic to granodioritic crust, Kyushu, southwest

mantle-magma interaction. Nature 345 (6275), 521-524.

na

King, P.L., White, A.J.R., Chappell, B.W., Allen, C.M., 1997. Characterization and origin of aluminous A-type granites from the Lachlan Fold Belt,

Jo ur

southeastern Australia. Journal of Petrology 38(3), 371-391. Kristoffer, S., Kelemen, P.B., Rosing, M.T., 2015. The petrogenesis of ultramafic rocks in the >3.7 Ga Isua supracrustal belt, southern West Greenland: Geochemical evidence for two distinct magmatic cumulate trends. Gondwana Research 28, 565-580. Langmuir, C.H., Vocke, R.D., Hanson, G.N., Hart, S.R., 1978. A general mixing equation with applications to Icelandic basalts. Earth Planet. Sci. Lett. 37, 380-392. Li, C.F., Li, X.H., Li, Q.L., Guo, J.H., Li, X.H., 2011a. Directly determining 143Nd/144Nd isotope ratios using thermal ionization mass spectrometry for geological samples without separation of Sm-Nd. J. Anal. At. Spectrom. 26, 2012-2022. Li, C.F., Li, X.H., Li, Q.L., Guo, J.H., Li, X.H., Tao, L., 2011b. An evaluation of a

Journal Pre-proof single-step extraction chromatography separation method for Sm-Nd isotope analysis of micro samples of silicate rocks by high-sensitivity thermal ionization mass spectrometry. Anal. Chim. Acta 706, 297-304. Liu, Y.S., Hu, Z.C., Zong, K.Q., Gao, C.G., Gao, S., Xu, J., Chen, H.H., 2010. Reappraisement and refinement of zircon U-Pb isotope and trace element analyses by LA-ICP-MS. Chin. Sci. Bull. 55 (15), 1535–1546 (English Edition). Ludwig, K.R., 2003. Use's manual for Isoplot 3.00: a geochronological tool for

of

Microsoft Excel. Berkeley Geochronology Center Special Publications 4,

ro

1-70.

Ma, L., Wang, Q., Kerr, A.C., Yang, J.H., Xia, X.P., Ou, Q., Yang, Z.Y., Sun, P.,

-p

2017a. Paleocene (c.62 Ma) leucogranites in southern Lhasa, Tibet:

re

products of syn-collisional crustal anataxis during slab roll-back? Journal

lP

of Petrology 58(11), 2089-2114.

Ma, L., Wang, Q., Wyman, A.D., Jiang, Z.Q., Yang, J.H., Qiu, L.L., 2013a. Late

Petrological

na

Cretaceous crustal growth in the Gangdese area, southern Tibet: and

Sr-Nd-Hf-O

isotopic

evidence

from

Zhengga

Jo ur

diorite-gabbro. Chemical Geology 349-350, 54-70. Ma, L., Wang, Q., Wyman, D.A., Jiang, Z.Q., Wu, F.Y., Li, X.H., Yang, J.H., Gou, G.N., Guo, H.F., 2015. Late Cretaceous back-arc extension and arc system evolution in the Gangdese area, southern Tibet: geochronological, petrological, and Sr-Nd-Hf-O isotopic evidence from Dagze diabases. J. Geophys. Res. Solid Earth 120 (9), 6159-6181. Ma, L., Wang, Q., Wyman, D.A., Li, Z.X., Jiang, Z.Q., Yang, J.H., Gou, G.N., Guo, H.F., 2013b. Late Cretaceous (100–89 Ma) magnesian charnockites with adakitic affinities in the Milin area, eastern Gangdese: Partial melting of subducted oceanic crust and implications for crustal growth in southern Tibet. Lithos 175-176, 315-332. Ma, S.W., Meng, Y.K., Xu, Z.Q., Liu, X.J., 2017b. The discovery of late Triassic mylonitic granite and geologic significance in the middle Gangdese

Journal Pre-proof batholiths, southern Tibet. Journal of Geodynamics 104, 49-64. Ma, X.X., Xu, Z.Q., Meert, J.G., 2017c. Syn–convergence extension in the southern Lhasa terrane: evidence from Late Cretaceous adakitic granodiorite and coeval gabbroic-dioritic dykes. J. Geodyn. 110, 12-30. Ma, X.X., Meert, J., Xu, Z.Q., Zhao, Z.B., 2018. The Jurassic Yeba Formation in the Gangdese arc of S. Tibet: implications for upper plate extension in the

Lhasa

terrane.

International

Geology

Review, https://doi.org/10.1080/00206814.2018.1434835.

of

Ma, X.X., Meert, J., Xu, Z.Q., Zhao, Z.B., 2017d. Evidence of magma mixing

ro

identified in the Early Eocene Caina pluton from the Gangdese Batholith, southern Tibet. Lithos 278-281, 126-139.

Thirlwall M.F., 2006. Adakites without

-p

Macpherson C.G., Dreher S.T.

re

slab melting: high pressure differentiation of island arc magma, Mindanao,

lP

the Philippines. Earth Planet. Sci. Lett. 243(3-4), 581-593. Mahoney, J.J., Frei, R., Tejada, M.L.G., Mo, X.X., Leat, P.T., Nägler, T.F., 1998.

na

Tracing the Indian Ocean mantle domain through time: isotopic results from old West Indian, East Tethyan, and South Pacific seafloor. Journal of

Jo ur

Petrology 39, 1285-1306.

Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geol. Soc. Am. Bull. 101 (5), 635-643. Meng, F.Y., Zhao, Z.D., Zhu, D.C., Zhang, L.L., Guan, Q., Liu, M., Yu, F., Mo, X.X., 2010. Petrogenesis of Late Cretaceous adakite-like rocks in Mamba from the eastern Gangdese, Tibet. Acta Petrologica Sinica 26(7), 2180-2192 (in Chinese with English abstract). Meng, Y.K., 2016. Tectonic evolution of the southern region in the middle Gangdese batholith, southern Tibet (Doctoral Dissertation). Beijing: Chinese Academy of Geological Sciences, 1-278 (in Chinese with English abstract). Meng, Y.K., Dong, H.W., Cong, Y., Xu, Z.Q., Cao, H., 2016b. The early-stage evolution of the Neo-Tethys Ocean: Evidence from granitoids in the middle

Journal Pre-proof Gangdese batholith, southern Tibet. Journal of Geodyanamics 94-95, 34-49. Meng, Y.K., Ma, S.W., Xu, Z.Q., Chen, X.J., Ma, X.X., 2018c. Geochronology, geochemistry and petrogenesis of the granitoid porphyries from Jiama ore deposit in Gangdese belt. Earth Science 43(4), 1142-1163 (in Chinese with English abstract). Meng, Y.K., Santosh, M., Li, R.H., Xu, Y., Hou, F.H., 2018d. Petrogenesis and tectonic implications of Early Cretaceous volcanic rocks from Lingshan

of

Island in the Sulu Orogenic Belt. Lithos 312-313, 244-257.

ro

Meng, Y.K., Xiong, F.H., Xu, Z.Q., Ma, X.X., 2019. Petrogenesis of Late Cretaceous mafic enclaves and their host granites in the Nyemo region of

-p

southern Tibet: Implications for the tectonic-magmatic evolution of the

re

Central Gangdese Belt. Journal of Asian Earth Sciences 176, 27-41.

lP

Meng, Y.K., Xu, Z.Q., Gao, S., Xu, Y., Li, R.H., 2018b. The identification of the Eocene magmatism and tectonic significance in the middle Gangdese belt,

na

southern Tibet. Acta petrologica Sinica 34(3), 513-546. Meng, Y.K., Xu, Z.Q., Santosh, M., Ma, X.X., Chen, X.J., Guo, G.L., Liu, F.,

Jo ur

2016a. Late Triassic crustal growth in southern Tibet: evidence from the Gangdese magmatic belt. Gondwana Res. 37, 449-464. Meng, Y.K., Xu, Z.Q., Xu, Y., Ma, S.W., 2018a. Late Triassic granites from the Quxu batholith shedding a new light on the evolution of the Gangdese belt in southern Tibet. Acta Geologica Sinica 92(2), 462-481(English edition). Middlemost, E.A.K., 1994. Naming materials in the magma/igneous rock system. Earth Sci. Rev. 37, 215-224. Mo, X.X., Dong, G.C., Zhao, Z.D., Guo, T.Y., Wang, L.L., Chen, T., 2005. Timing of magma mixing in the Gangdise magmatic belt during the India– Asia collision: zircons SHRIMP U–Pb dating. Acta Geologica Sinica 79, 66-76. Mo, X.X., Hou, Z.Q., Niu, Y.L., Dong, G.C., Qu, X.M., Zhao, Z.D., Yang, Z.M., 2007. Mantle contributions to crustal thickening during continental collision:

Journal Pre-proof evidence from Cenozoic igneous rocks in southern Tibet. Lithos 96 (1-2), 225-242. Mo, X.X., Niu, Y.L., Dong, G.C., Zhao, Z.D., Hou, Z.Q., Zhou, S., Ke, S., 2008. Contribution of syn-collisional felsic magmatism to continental crust growth: a case study of the Paleogene Linzizong volcanic succession in southern Tibet. Chem. Geol. 250, 49-67. Mo, X.X., Zhao, Z.D., Yu, X.H., Dong, G.C., Li, Y.G., Zhou, S., Liao, Z.L., Zhu, D.C., 2009. Cenozoic collisional-Postcollisional igneous rocks in the

of

Tibetan Plateau. Beijing: Geological Publishing House, 1-380 (in

ro

Chinese).

signature. Lithos 112, 556-574

-p

Moyen, J.F., 2009. High Sr/Y and La/Yb ratios: the meaning of the adakitic

re

Pan, G.T., Wang, L.Q., Li, R.H., Yuan, S.H., Ji, W.H., Yin, F.G., Zhang, W.P.,

lP

Wang, B.D., 2012. Tectonic evolution of the Qinghai-Tibet Plateau. Journal of Asian Earth Sciences 53 (7), 3-13.

na

Parlak, O., Bağcı, U., Rızaoğlu, T., Ionescu, C., Güzide Önal, Höck, V., Kozlu, H., 2019. Petrology of ultramafic to mafic cumulate rocks from the Göksun

Jo ur

(Kahramanmaraş) ophiolite, southeast Turkey. Geoscience Frontier. https://doi.org/10.1016/j.gsf.2018.11.004 Piccardo, G.N., Guarnieri, L.G., 2011. Gabbro-norite cumulates from strongly depleted MORB melts in the Alpine-Apennine ophiolites. Lithos 124(3-4), 200-214.

Peccerillo, A., Taylor, S.R., 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey. Contrib. Miner. Petrol. 58, 63-81. Petford, N., Atherton, M., 1996. Na–rich partial melts from newly underplated basaltic crust: the Cordillera Blanca Batholith, Peru. J. Petrol. 37, 1491-1521. Qiu, J.S., Wang, R.Q., Zhao, J.L., Yu, S.B., 2015. Petrogenesis of the Early

Journal Pre-proof Jurassicgabbro–granite complex in the middle segment of the Gangdese belt and its implications for tectonic evolution of Neo–Tethys: a case study of the Dongga pluton in Xigaze. Acta Petrol. Sin. 31 (12), 3569– 3580 (in Chinese with English abstract). Rapp, R.P., Watson, E.B., 1995. Dehydration melting of metabasalt at 8–32 kbar: implications for continental growth and crust-mantle recycling. J. Petrol. 36, 891-931. Richards, J.P., Kerrich, R., 2007. Adakie-like rocks: their diverse origins and

of

questionable role in metallogenesis. Econ. Geol. 102 (4), 537-576.

ro

Rogers, G., Macdonald, R., Fitton, J. G., George, R., Smith, M., Barreiro B., 2000. Two mantle plumes beneath the East African rift system: Sr, Nd,

re

Science Letters 176, 387–400.

-p

and Pb isotope evidence from Kenya Rift basalts: Earth and Planetary

lP

Rudnick, R., Gao, S., 2003. Composition of the continental crust. In: Rudnick R. The crust, treatise on geochemistry, Amsterdam: Elsevier 3, 1-64.

na

Rudnick, R.L., 1992. Xenoliths samples of the lower continental crust. In: Fountain, DM, Arculus K R. Continental lower crust. Elsevier, 269-316.

Jo ur

Rudnick, R.L., Fountain, D.M., 1995. Nature and composition of the continental crust: A lower crustal perspective: Reviews of geophysics-richmond Virginia then Washington 33, 267-309. Rudnick, R.L.,

Presper,

T.,

1990.

Geochemistry of

intermediate

to

high-pressure granulities. In: Vielzeuf D., Vidal P. Granulites and crustal evolution. Kluwer, 523-550. Shao, J.A., Tian, W., Zhang, J.H., 2015. Early Permian cumulates in northern margin of north China craton and their tectonic significances. Earth Science-Journal of China University of Geosciences 40(9), 1441-1457 (in Chinese with English abstract). Schärer, U., Xu, R.-H., Allègre, C.J. 1984. U–Pb geochronology of Gangdese (Transhimalaya) plutonism in the Lhasa–Xigaze region, Tibet. Earth and Planetary Science Letters, 69: 311-320.

Journal Pre-proof Sisson, T.W., Grove, T.L., 1993. Experimental investigations of the role of H2O in

calc-alkaline

differentiation

and

subduction

zone

magmatism.

Contributions to Mineralogy and Petrology 113(2), 143-166. Söderlund, U., Patchett, P.J., Vervoort, J.D., Isachsen, C.E., 2004. The 176Lu decay constant determined by Lu_Hf and U_Pb isotope systematics of Precambrian mafic intrusions. Earth Planet. Sci. Lett. 219, 311-324. Sun, S.S., McDonough,W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. Geol.

of

Soc. Lond., Spec. Publ. 42, 313-345.

ro

Sun, T., Zhou, X.M., Chen, P.R., Li, H.M., Zhou, H.Y., Wang, Z.C., Shen, W.Z., 2003. Strongly peraluminous granites of Mesozoic in Eastern Nanling

re

(Series D) 33(12), 1209-1218.

-p

Region, southern China and implications for tectonics. Science in China

lP

Tafti, R., 2011. Metallogeny, geochronology and tectonic setting of the Gangdese belt, southern Tibet, China. PhD Thesis, 1-477.

na

Tang, G.J., Wyman, D.A., Wang, Q., Li, J., Li, Z.X., Zhao, Z.H., Sun, W.D., 2012. Asthenosphere–lithosphere interaction triggered by a slab window

Jo ur

during ridge subduction: Trace element and Sr–Nd–Hf–Os isotopic evidence from Late Carboniferous tholeiites in the western Junggar area (NW China). Earth and Planetary Science Letters 329-330, 84-96. Vervoort, J.D., Blichert-Toft, J., 1999. Evolution of the depleted mantle: Hf isotope evidence from juvenile rocks through time. Geochim. Cosmochim. Acta 63, 533–556. Wang, C., Ding, L., Zhang, L.Y., Kapp, P., Pullen, A., Yue, Y.H., 2016. Petrogenesis of middle–Late Triassic volcanic rocks from the Gangdese belt, southern Lhasa terrane: implications for early subduction of Neo-Tethyan oceanic lithosphere. Lithos 262, 320-333. Wang, C., Wei, Q.R., Liu, X.N., Ding, P.F., Bo, T., Sun, Y., Zhang, X.Q., Wang, J.Y., 2014.Post-collision related late Indosinian granites of Gangdese terrane: evidence from zircon U-Pb geochronology and petrogeo

Journal Pre-proof chemistry. Earth Sci.-J. China Univ. Geosci. 39 (9), 1277–1230 (in Chinese with English abstract). Wang, L., Zeng, L.S., Gao, L.E., Chen, Z.Y., 2013. Early Cretaceous high Mg# and high Sr/Y clinopyroxene-bearing diorite in the southeast Gangdese batholith, southern Tibet. Acta Petrol. Sin. 29 (6), 1977-1994 (in Chinese with English abstract). Wang, R.Q., Qiu, J.S., Yu, S.B., Zhao, J.L., 2017. Crust–mantle interaction during Early Jurassic subduction of Neo-Tethyan oceanic slab: Evidence

ro

subterrane, Tibet. Lithos 292-293, 262-277.

of

from the Dongga gabbro–granite complex in the southern Lhasa

Wang, Y.F., Zeng, L.S., Gao, J.H., Zhao, L.H., Gao, L.E., Shang, Z., 2019.

-p

Along-arc variations in isotope and trace element compositions of

lP

Lithos 324-325, 877-892.

re

Paleogene gabbroic rocks in the Gangdese batholith, southern Tibet.

Watson, E.B., Wark, D.A., and Thomas, J.B., 2006. Crystallization

na

thermometers for zircon and rutile. Contrib. Mineral. Petrol 151, 413-433. Wei, Y.Q., Zhao, Z.D., Niu, Y.L., Zhu, D.C., Liu, D., Wang, Q., Hou, Z.Q., Mo,

Jo ur

X.X., Wei, J.C., 2017. Geochronology and geochemistry of the Early Jurassic Yeba Formation volcanic rocks in southern Tibet: Initiation of back-arc rifting and crustal accretion in the southern Lhasa terrane. Lithos 278-281, 477-490.

Wen, D.R., Chung, S.L., Song, B., Iizuka, Y., Yang, H.J., Ji, J.Q., Liu, D.Y., Gallet, S., 2008b. Late Cretaceous Gangdese intrusions of adakitic geochemical characteristics, SE Tibet: Petrogenesis and tectonic implications. Lithos 105, 1-11. Wen, D.R., Liu, D.Y., Chung, S.L., Chu, M.F., Ji, J.Q., Zhang, Q., Song, B., Lee, T.Y., Yeh, M.W., Lo, C.H., 2008a. Zircon SHRIMP U-Pb ages of the Gangdese batholith and implications for Neotethyan subduction in southern Tibet. Chem. Geol. 252 (3-4),191-201. Whalen, J., Currie, K., Chappell, B., 1987. A-type granites: Geochemical

Journal Pre-proof characteristics,

discrimination

and

petrogenesis:

Contributions

to

Mineralogy and Petrology 95, 407-419. Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe. In: McKibben, M.A., Shanks, W.C., Ridley, W.I. (Eds.), Applications of Microanalytical Techniques to Understanding Mineralizing Processes, Review of Economic Geology 7, 1-35. Wright, J.B., 1969. A simple alkalinity ratio and its application to questions of non-orogenic granite genesis. Geol. Mag. 106 (4), 370-384.

of

Wu, C.D., Zheng, Y.C., Xu, B., Hou, Z.Q., 2018. The genetic relationship

ro

between JTA-like magmas and typical adakites: An example from the Late Cretaceous Nuri complex, southern Tibet. Lithos 320-321, 265-279.

-p

Wu, F.Y., Li, X.H., Yang, J.H., Zheng, Y.F., 2007. Discussion on the

re

petrogenesis of granites. Acta Petrologica Sinica 23(6), 1217-1238.

lP

Xiong, F., Meng, Y.K., Yang, J.S., Liu, Z., Xu, X.Z., Eslami, A., Zhang, R., 2019. Geochronology and petrogenesis of the mafic dykes from the Purang

na

ophiolite: Implications for evolution of the western Yarlung-Tsangpo suture zone,

Tibet.

Geoscience

Frontiers.

doi:

Jo ur

http://doi.org/10.1016/j.gsf.2019.05.006. Xiong, Y.Q., Zhou, F.H., Yao, Z.X., 2001. The Aeromagnetic Anomaly Investigation in the Central-Western Segment of Tibetan Plateau. Beijing: Geological Publishing House, 72-88 (in Chinese). Xu, H.J., Ma, C.Q. Ye, K., 2007. Early cretaceous granitoids and their implications for the collapse of the Dabie orogen, eastern China: SHRIMP zircon U-Pb dating and geochemistry. Chem. Geol. 240(3-4), 238-259. Xu, J.F., Shinjo, R., Defant, M.J., Wang, Q. and Rapp, R.P., 2002. Origin of Mesozoic adakitic intrusive rocks in the Ningzhen area of east China: partial melting of delaminated lower continental crust? Geology 30(12), 1111-1114. Xu, W.C., 2010. Spatial Variation of Zircon U-Pb Ages and Hf Isotopic compositions of the Gangdese granitoids and its geologic Implications

Journal Pre-proof (Dissertation). China University of Geosciences, Wuhan (in Chinese with English abstract). Xu, W.C., Zhang, H.F., Luo, B.J., Guo, L., Yang, H., 2015. Adakite–like geochemical signature produced by amphibole–dominated fractionation of arc magmas: an example from the Late Cretaceous magmatism in Gangdese belt, southern Tibet. Lithos 232, 197-210. Yang, J.S., Xu, Z.Q., Li, Z.L., Xu, X.Z., Li, T.F., Ren, Y.F., Li, H.Q., Chen, S.Y., Robinson, P.T., 2009. Discovery of an eclogite belt in the Lhasa block,

of

Tibet: A new border for Paleo-Tethys? Journal of Asian Earth Sciences

ro

34(1), 76-89.

Ye, L.J., Zhao, Z.D., Liu, D., Zhu, D.C., Dong, G.C., Mo, X.X., Hu, Z.C., Liu,

-p

Y.S., 2015. Late Cretaceous diabase and granite dike in Namling, Tibet:

re

petrogenesis and implications for extension. Acta Petrol. Sin. 31 (5),

lP

1298-1312 (in Chinese with English abstract). Yin A, Harrison TM, Ryerson FJ, Chen, W., Kidd, W.S.F., Copeland, P., 1994.

na

Tertiary structural evolution of the Gangdese thrust system, southeastern Tibet. Journal of Geophysical Research, 99(9): 18175-18201.

Jo ur

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan Tibetan orogen. Annu. Rev. Earth Planet. Sci. Lett. 28, 211-280. Zhang, L.X., Wang, Q., Zhu, D.C., Li, S.M., Zhao, Z.D., Zhang, L.L., Chen, Y., Liu, S.A., Zheng, Y.C., Wang, R., Liao, Z.L., 2019. Generation of leucogranites via fractional crystallization: a case from the Late Triassic Luoza batholith in the Lhasa Terrane, southern Tibet. Gondwana Res. 66, 63-76. Zhang, S.B., Zheng, Y.F., Zhao, Z.F., Wu, Y.B., Yuan, H.L. Wu, F.Y., 2009. Origin of TTG-like rocks from anatexis of ancient lower crust: geochemical evidence from Neoproterozoic granitoids in South China. Lithos 113, 347-368. Zhang, S.Q., Mahoney, J.J., Mo, X.X., Ghazi, A.M., Milani, L., Crawford, A.J., Guo, T.Y., Zhao, Z.D., 2005. Evidence for a widespread Tethyan upper

Journal Pre-proof mantle with Indian-Oceantype isotopic characteristics. Journal of Petrology 46, 829-858. Zhang, Z.M., Zhao, G.C., Santosh, M., Wang, J.L., Dong, X., Shen, K., 2010. Late Cretaceous charnockite with adakitic affinities from the Gangdese batholith, southeastern Tibet: evidence for Neo-Tethyan mid-ocean ridge subduction? Gondwana Res. 17, 615-631. Zhang, Z.M., Dong, X., Xiang, H., He, Z.Y., and Liou, J.G., 2014a. Metagabbros of the Gangdese arc root, South Tibet: Implications for the

of

growth of continental crust. Geochimica et Cosmochimica Acta 143,

ro

268-284.

Zhang, Z.M., Dong, X., Santosh, M., and Zhao, G.C., 2014b. Metamorphism

-p

and tectonic evolution of the Lhasa terrane, Central Tibet. Gondwana

re

Research 25, 170-189.Zhou, L.M., Wang, R., Hou, Z.Q., Li, C., Zhao, H.,

lP

Li, X.W., Qu, W.J., 2018. Hot Paleocene-Eocene Gangdese arc: growth of continental crust in southern Tibet. Gondwana Res. 62, 178-197.

na

Zhou, C.Y., Wu, F.Y., Ge, W.C., Sun, D.Y., Abdel Rahman, A.A., Zhang, J.H., and Cheng, R.Y., 2005. Age, geochemistry and petrogenesis of the

Jo ur

cumulate gabbro in Tahe, northern Da Hinggan Mountain. Acta Petrologica Sinica 21(3), 763-775 (in Chinese with English abstract). Zhu, D.C., Pan, G.T., Chung, S.L., Liao, Z.L., Wang, L.Q., Li, G.M., 2008. SHRIMP zircon age and geochemical constraints on the origin of lower Jurassic volcanic rocks from the Yeba formation, southern Gangdese, South Tibet. International Geology Review 50(5), 442-471. Zhu, D.C., Wang, Q., Zhao, Z.D., Chung, S.L., Cawood, P.A., Niu, Y.L., Liu, S.A., Wu, F.Y., Mo, X.X., 2015. Magmatic record of India-Asia collision. Sci. Rep. 5, 14289. https:// doi.org/10.1038/srep14289. Zhu, D.C., Zhao, Z.D., Niu, Y.L., Mo, X.X., Chung, S.L., Hou, Z.Q., Wang, L.Q., Wu, F.Y., 2011. The Lhasa terrane: record of a microcontinent and its histories of drift and growth. Earth Planet. Sci. Lett. 301 (1-2), 241-255. Zhu, D.C., Zhao, Z.D., Niu, Y., Dilek, Y., Hou, Z.Q., Mo, X.X., 2013. The origin

Journal Pre-proof and pre-Cenozoic evolution of the Tibetan Plateau. Gondwana Research, 23: 1429-1454.

Figure Captions Figure 1 (a) Simplified tectonic framework of the Himalaya-Tibetan plateau (after Yin and Harrison, 2000; Zhu et al., 2011); (b) Geological simplified map

of

of the study and adjacent regions and previous studies related to gabbroic

ro

rocks (base maps are after 1:25, 0000 Lhasa and Xigaze regional geological maps (No. H46C003001 and H45C003004), PRC); (c) Geological sampling

-p

locations (after 1:25, 0000 geological map (map No. H46C003001) and

re

geological survey)

lP

Figure 2 (a-d) Field outcrops of the gabbro-diorite suite; (e-f) field pictures and

na

distributions of the granite rocks

granite (g-j)

Jo ur

Figure 3 Zircon U-Pb age Concordia plots for the gabbro-diorite suite (a-f) and

Figure 4 (a) TAS diagram (after Middlemost, 1994), dotted line for Irvine line (after Irvine and Baragar, 1971); (b) Alkalinity ratio (A.R.) versus SiO2 plot (after Wright, 1969); (c) SiO2 versus K2O plot (after Peccerillo and Taylor, 1976); (d) Fe2O3T-Na2O+K2O-MgO diagram (after Irvine and Baragar, 1971); (e)

A/CNK

(molar

Al2O3/(CaO+Na2O+K2O))

versus

A/NK

(molar

Al2O3/(Na2O+K2O)) plot (after Maniar and Piccoli, 1989); (f) SiO2 versus Mg# plot (Mg#=100×molar Mg/(Mg+Total Fe)) (after Rapp and Watson, 1995)

Figure 5 (a-h) Harker diagrams of the gabbro-diorite suite (SiO2 versus major oxides); (i-j) SiO2/Al2O3 versus Fe2O3/Al2O3 and SiO2/Al2O3 versus

Journal Pre-proof Al2O3/MgO (mixing curve after Langmuir et al., 1978)

Figure 6 Chondrite-normalized REE patterns (a for the gabbro-diorite suite, c for the granite); primitive mantle normalized multiple trace element diagram (b for the gabbro-diorite suite, d for the granite). The chondrite normalization values are from Boynton (1984), and primitive mantle normalization values are adopted from Sun and McDonough (1989); OIB, E-MORB and N-MORB patterns are after Sun and McDonough (1989); tetrad effect line is after Sun et

of

al. (2003); OIB=oceanic island basalt; E-MORB=enriched mid-oceanic ridge

ro

basalt; N-MORB=normal mid-oceanic ridge basalt

-p

Figure 7 (87Sr/86Sr)I versus εNd(t) diagram for the gabbro-diorite suite (the

re

Mesozoic magmatic rocks field is after Ji et al., 2009; Linzizong volcanic field is

lP

after Mo et al., 2007, 2008, 2009; Zhengga and Milin mafic rocks fields are after Ma et al., 2013a, b, 2015; the Neo-Tethys ophiolites field is after Mahoney

na

et al. (1998) and Zhang et al., 2005; the Yeba basaltic rocks field is after Zhu et

Jo ur

al., 2008; the Langxian adakites filed is after Wen et al., 2008a)

Figure 8 (a-h) Fractional crystallization (FC) and crustal contamination (or magma

mixing)

discrimination

diagrams

of

whole-rock

Sr-Nd

and

geochemistry for the gabbro-diorite suite

Figure 9 (a-b) Y versus Sr/Y and YbN versus (La/Yb)N diagrams (base maps are after Defant et al., 2002; Petford and Atherton, 1996); (c-h) Harker diagrams of SiO2 versus oxides (Al2O3, CaO, P2O5 and Na2O/K2O) and Sr of the granite rocks; (h) Na2O/Fe2O3T versus Al2O3/Fe2O3T (mixing curve is after Langmuir et al., 1978)

Figure 10 (a-e) Discrimination diagrams for A-type granitic rocks (a-d base

Journal Pre-proof maps are after Whalen et al., 1987; e base map is after Eby, 1990); (f) zircon Ti (Watson et al., 2006) and whole-rock zircon saturation geothermometers

Figure 11 Discrimination diagrams for normal adakites and pseudo-adakites (base maps are after He et al., 2011)

Figure 12 Geodynamic model for the southern Tibet during Early Late Cretaceous (ca. 100-85 Ma); LMF=Luobadui-Milashan Fault (after Zhu et al.,

Jo ur

na

lP

re

-p

ro

of

2011)

Journal Pre-proof

Highlights  The gabbro-diorite and granite crystallized at the Early Late Cretaceous.  The gabbro-diorite suite was products of partial melting of the depleted mantle, and slab dehydration played a key role.

of

 The granite was partial melting of pure crust with no injection of mantle material.

ro

 The rollback of the Neo-Tethys accounts for the magmatic

Jo ur

na

lP

re

-p

flare-up in the southern Tibet during the Early Late Cretaceous.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12