Source and petrogenesis of Paleoproterozoic meta-mafic rocks intruding into the North Liaohe Group: Implications for back-arc extension prior to the formation of the Jiao-Liao-Ji Belt, North China Craton

Accepted Manuscript Source and petrogenesis of Paleoproterozoic meta-mafic rocks intruding into the North Liaohe Group: Implications for back-arc extension prior to the formation of the Jiao-Liao-Ji Belt, North China Craton Wang Xu, Fulai Liu, Zhonghua Tian, Lishuang Liu, Lei Ji, Yongsheng Dong PII: DOI: Reference:

S0301-9268(17)30550-8 https://doi.org/10.1016/j.precamres.2018.01.011 PRECAM 5001

To appear in:

Precambrian Research

Received Date: Revised Date: Accepted Date:

30 September 2017 12 January 2018 21 January 2018

Please cite this article as: W. Xu, F. Liu, Z. Tian, L. Liu, L. Ji, Y. Dong, Source and petrogenesis of Paleoproterozoic meta-mafic rocks intruding into the North Liaohe Group: Implications for back-arc extension prior to the formation of the Jiao-Liao-Ji Belt, North China Craton, Precambrian Research (2018), doi: https://doi.org/10.1016/ j.precamres.2018.01.011

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

Source and petrogenesis of Paleoproterozoic meta-mafic rocks intruding into the North Liaohe Group: Implications for back-arc extension prior to the formation of the Jiao-Liao-Ji Belt, North China Craton Wang Xu a,*, Fulai Liu a,*, Zhonghua Tian a, Lishuang Liu a, Lei Ji a, Yongsheng Dong b a

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037,

China b

College of Earth Science, Jilin University, Changchun 130061, China

*Corresponding author. Email address: [email protected] (Wang Xu); [email protected] (Fulai Liu)

Abstract

Meta-mafic rocks as sills, dykes and veins are widely distributed within the North Liaohe Group, Liaodong Peninsula, which consist mainly of meta-diabase/gabbro and (garnet) amphibolite with minor felsic clastic rocks as enclaves. Although a long-standing debate existed about the petrogenesis for the meta-mafic rocks, it is a critical judgement for using geochemistry and geochronology of these rocks to reveal the complicated tectonic evolution of the Paleoproterozoic Jiao-Liao-Ji Belt (JLJB). 1

In this paper, a combined study of zircon U-Pb isotopic data, whole-rock geochemistry and Sm-Nd isotope analyses are reported for these rocks to investigate their sources, petrogenesis and tectonic settings. Abundant zircon U-Pb LA-ICP-MS age data reveal that the meta-mafic rocks have a magmatic emplacement age of ca. 2130 Ma with a metamorphic age of ca. 1878 Ma. These meta-mafic rocks have characteristic geochemical compositions with moderate SiO2 (46.68–53.90 wt.%), low TiO2 (0.56–2.33 wt.%) and variable total Fe2O3 (9.65–17.58 wt.%), MgO (2.77–11.49 wt.%), Cr (1.44–1580 ppm) and Ni (6.4–168 ppm) similar to evolved tholeiitic basalt. They exhibit enriched mid-ocean ridge basalt (E-MORB)-like geochemical features (e.g., trace element patterns) with highly variable εNd(t) values from -1.5 to +3.1, relative enrichment of light rare earth elements (LREEs) and depletion of high field strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf and Ti). The geochemical trends of major and trace elements and Nd isotopes suggest that the primary magma for these meta-mafic rocks were probably derived from partial melting of a depleted asthenospheric mantle in the spinel stability field, with extensive fractional crystallization of a three-phase assemblage of olivine, clinopyroxene and plagioclase, crustal assimilation (e.g., continental detritus), and limited metasomatism from subduction-related fluids and/or melts. In view of the widespread distribution of Paleoproterozoic magmatism, including the Liaoji granites, and the voluminous sedimentary rocks in the Liaodong Peninsula, a newly tectonic model has been proposed that a ca. 2.1 Ga oceanic plate subduction event induced a back-arc basin opening, which closed to form the JLJB in the period of ca. 1.9 Ga. 2

Keywords

Meta-mafic rock; geochemistry; back-arc basin; Paleoproterozoic Jiao-Liao-Ji Belt; North China Craton

1. Introduction

The North China Craton (NCC) as the largest craton in China experienced a cratonization event in the Paleoproterozoic (~1.85 Ga; e.g., Zhao et al., 2002; Wu et al., 2014; Zhai, 2014). This key period of complicated tectonic history is directly recorded in three Paleoproterozoic orogenic belts, including the Khondalite Belt (KB), Trans-North China Orogen (TNCO) and Jiao-Liao-Ji Belt (JLJB) from west to east (Fig. 1a; e.g., Zhao et al., 2005; Zhao et al., 2012). Among these belts, the JLJB has the most complicated tectonic evolutionary history, as it underwent multiple metamorphic and magmatic events (e.g., Zhao et al., 2012; Liu et al., 2015, and references therein). Due to a lack of direct evidence of oceanic plate subduction, the tectonic setting and evolution history of the JLJB remain debated for a long time, and two primary models have been proposed: (1) closure of an intra-continental rift (e.g., Zhang and Yang, 1988; Li et al., 2001, 2005; Luo et al., 2004, 2008; Li and Zhao, 2007) and (2) collision between an arc and a continent (e.g., Bai, 1993; Faure et al., 2004). Furthermore, based on previous studies, Zhao et al. (2012) and Zhao and Zhai (2013) proposed that the JLJB is a Paleoproterozoic rift-and-collision belt, which underwent Paleoproterozoic (2.2–1.9 Ga) rifting to form an ocean basin, dividing the Eastern Block into the Longgang and Nangrim blocks, then closed through subduction 3

and collision at ca. 1.9 Ga. The reported ca. 2.1 Ga meta-mafic rocks intruding into the North Liaohe Group (Fig. 1b; LBGMR, 1975a, b; Dong et al., 2012; Meng et al., 2014; Yuan et al., 2015; Wang et al., 2016), which are widely distributed within the JLJB, provide key clues for understanding the tectonic evolution process of the JLJB, because (1) the original stratigraphic sequences in the JLJB have been completely destroyed by intensive multi-stage deformations (e.g., Liu et al., 2015), it is difficult to reconstruct the depositional environment for these voluminous meta-sedimentary rocks; (2) late Mesozoic lithospheric thinning and crustal extension across the whole NCC make it difficult to recognize the Paleoproterozoic deformation accurately in the JLJB (e.g., Li et al., 2005, 2013; Yang et al., 2007a; Liu et al., 2011); (3) the geochemical features of the granitic magmas within the JLJB mainly reflect the magmatic crystallization process and the compositions of their source rocks rather than their tectonic settings (e.g., Frost et al., 2001; Li et al., 2002); and (4) the composition of mafic-ultramafic rocks can reflect their sources and tectonic settings directly (e.g., Li et al., 2006; Yang et al., 2007b). Although the petrography, geochronology and geochemistry of these meta-mafic rocks have been reported in previous studies, the tectonic setting of these meta-mafic rocks is still controversial, and the following four tectonic settings have been proposed: (1) continental arc (Faure et al., 2004; Yuan et al., 2015); (2) ocean island arc (Ma et al., 2007); (3) back-arc basin (Wang et al., 2011; Meng et al., 2014) and (4) intra-continental rifting (Yu et al., 2007; Dong et al., 2012; Wang et al., 2016). In this regard, based on detailed geological mapping at a 1:50,000 Scale, we report 4

new zircon U-Pb data, whole-rock geochemistry, and Sm-Nd isotope analysis of the meta-mafic rocks in the North Liaohe Group, then use these data to trace their source and petrogenesis, and finally to constrain the tectonic setting in which they were evolved.

2. Geological setting

The Liaodong Peninsula is located in the northeastern segment of the Eastern Block, which is composed of the Longgang Block in the northwest, the JLJB in the center and the Nangrim Block in the southeast (Fig. 1a; Zhao et al., 2005). The Longgang Block is composed mainly of Archean tonalite-trondhjemite-granodiorite (TTG) suites, and minor amounts of ultramafic to mafic volcanic and sedimentary supracrustal rocks (i.e., Anshan Group), including banded iron formations (BIF) (Wu et al., 2005; Wan et al., 2005, 2013). In addition, ca. 3.8 Ga continental crust was identified in Eastern Hebei and Anshan (Liu et al., 1992). Traditionally, the Nangrim Block is thought to be composed of Archean to Paleoproterozoic supracrustal and granitoid rocks, with a single Archean basement in the North Korea area (Zhao et al., 2006, and references therein). However, detrital zircons from sands in rivers, which originate in and run through the Nangrim Block, show minor Archean material, implying that the Nangrim Block is a Paleoproterozoic unit similar to the JLJB (Wu et al., 2016, and references therein). The JLJB consists

mainly of sedimentary and volcanic

successions

metamorphosed from greenschist to amphibolite facies, with associated granitic and 5

mafic intrusions and medium- to high-pressure granulites. The sedimentary and volcanic successions include the Ji’an and Laoling groups in Jilin Province, the South and North Liaohe groups in Liaoning Province, the Fenzishan and Jingshan groups in Shandong Province, the Wuhe Group in Anhui Province, and the Macheonayeong Group in North Korea (Zhao et al., 2005, 2012; Liu et al., 2015). The granitoid plutons are composed of (1) ca. 2.17 Ga monzogranites, identified as A-type granites associated with an intra-continental rift (e.g., Lu et al., 2004a; Li and Zhao., 2007) and (2) ca. 1.87 Ga rapakivi granite, syenite, diorite and granite pegmatite, which indicate a post-collisional extensional setting (Hao et al., 2004; Yang et al., 2007c; Wang et al., 2011; Liu et al., 2017a). Medium- to high-pressure pelitic or mafic granulites with clockwise P-T-t paths, found in the Ji’an, South Liaohe, and Jingshan groups, suggest that the JLJB marks the collision zone between the Longgang and Nangrim Blocks 1.95–1.85 Ga (Zhao et al., 2005, 2012; Zhou et al., 2008; Tam et al., 2012; Liu et al., 2013, 2015). After the 1.90–1.85 Ga orogenic event, the Liaodong Peninsula was covered by Meso- to Neoproterozoic and Paleozoic sediments, and was widely intruded by Mesozoic intrusive rocks (Yang et al., 2007b). Large-scale meta-mafic intrusions as sills, dykes and veins are widely distributed in the Haicheng-Helan-Lianshanguan area, and intrude into the voluminous meta-sedimentary rocks of the North Liaohe Group (Fig. 1b). The North Liaohe Group contains a consistent sequence from a lower volcano-sedimentary succession through carbonate-dominated clastic rocks to an upper pelite-rich clastic sequence. The North Liaohe Group can be subdivided from the bottom upward into the 6

Langzishan, Lieryu, Gaojiayu, Dashiqiao and Gaixian formations (LBGMR, 1989; Li et al., 2005; Liu et al., 2015). As previous studies, the detrital zircons from the North Liaohe Group show characteristic U-Pb age peaks at ca. 2.1 Ga (intense) and ca. 2.5 Ga (weak), suggesting that the Paleoproterozoic Liaoji granitoids and Neoarchean basement rocks may be the major provenances of the North Liaohe Group (e.g., Luo et al., 2008; Liu et al., 2015).

3. Field occurrence and petrography

The meta-mafic rocks are widespread in the studied area and approximately E-W trending, with 180 km in length, and 5–40 km in width (Fig. 1b). They occur as veins, dykes and sills intruding into the meta-sedimentary and volcanic successions (e.g., marble and phyllitic slate) of the North Liaohe Group (Fig. 2a–c; Yuan et al., 2015; Wang et al., 2016). Some meta-mafic rock outcrops contain felsic clastic rocks (e.g., feldspathic quartz-sandstone) occurring as enclaves. These enclaves appear irregular in sections, featuring sharp contacts and a melting corrosion structure (Fig. 2d). The relationship between the host mafic magma and the felsic clastic rock enclaves provides powerful evidence of wall-rock contamination. According to their texture, mineral composition and variable degrees of alteration and metamorphism, the meta-mafic rocks can be subdivided into two types: meta-diabase/gabbro (Fig. 2e–f) and amphibolite (Fig. 2g–h). The meta-diabase/gabbro is exposed primarily in the central and north parts of the North Liaohe Group (Dong et al., 2012; Meng et al., 2014; Yuan et al., 2015; 7

Wang et al., 2016). The meta-diabase is dark grey in color and medium- to fine-grained, with blastophitic texture. It is mainly composed of plagioclase (euhedral-subhedral), chlorite, and actinolite with secondary minerals of quartz, biotite and relict clinopyroxene and accessory minerals (e.g., magnetite and titanite; Fig. 2e–f). Most plagioclases have undergone variable degrees of sericitization. Meta-gabbro has a coarse-grained blastogabbroic texture with a similar assemblage to the meta-diabase. The amphibolite is mainly distributed within the south margin of the North Liaohe Group (Yu et al., 2007; Meng et al., 2014). It is black to grey in color and medium- to fine-grained, with crystalloblastic texture and massive or gneissic structure. It consists mainly of plagioclase (~47%) and hornblende (~50%) with accessory minerals of magnetite and titanite (~3%) (Fig. 2g–h). In addition, a small amount of garnets have been found in some outcrops (e.g., Xu et al., 2017).

4. Analytical methods

4.1. Zircon U-Pb dating and rare-earth element (REE) analysis

Seven meta-mafic rock samples (D1002, D1009-5, D1009-7, D2050-1, D3038-2, D5048-4 and P12-10-1b) from the Helan area were selected for zircon U-Pb dating. After crushing these fresh samples, the heavy mineral fraction, including zircon, was separated using standard techniques including heavy liquid and magnetic separation methods. Then, the zircons were extracted from each crushed-rock sample by hand-picking under a binocular microscope. The zircon grains were mounted in epoxy 8

resin

discs,

sectioned

and

polished

to

reveal

their

cross-sections.

Cathodoluminescence (CL) images of zircon grains were taken using a JSM6510 scanning electron microscope (SEM; JEOL, Tokyo, Japan) attached to a Gatan CL detector (Oxford, UK). Zircon U-Th-Pb analyses were performed using a New Wave Up 193 nm laser ablation system (American New Wave Research Inc., Fremont, CA, USA)

and

laser

ablation–inductively

coupled

plasma–mass

spectrometry

(LA-ICP-MS) (PlasmaQuant®; Analytik Jena AG, Jena, Germany) at Beijing Createch Testing Technology Co. Ltd. All analyses were conducted with a beam diameter of 32 μm, a 10-Hz repetition rate, and energy of 2.5 J/cm. Zircons 91500 and GJ-1, and glass NIST610, were used as reference standards. The ICPMSDataCal 8.4 program was used for fractionation correction and calculation of the dating results (Liu et al., 2010). Isotopic ratios (i.e., 208

207

Pb/206Pb,

206

Pb/238U,

207

U/235U and

Pb/232Th) were corrected using Harvard zircon 91500 as the external standard for

zircons, and REE concentrations were corrected using 29Si as an internal standard and NIST610 as an external standard. Common lead was corrected using the method of Anderson (2002). Uncertainties in the age analysis are given by 1σ, and errors in the weighted mean ages are given by 2σ (95% confidence level). Concordia diagrams, weighted average age calculation and probability density plotting were conducted using Isoplot/Ex 3.0 (Ludwig, 2003).

4.2. Major and trace elements

After petrographic examination, 16 fresh samples of meta-mafic rocks from the 9

studied area were selected, crushed and powdered in an agate mill for geochemical analysis. Elemental analyses were conducted at the National Research Center for Geoanalysis, the Chinese Academy of Geological Sciences (CAGS), China. Major elements were determined through X-ray fluorescence (XRF) (PW4400; PANalytical, Almelo, Holland), with uncertainty of less than 3% based on the Chinese national standard GB/T 14506.28-2010. Trace element concentrations were determined using inductively coupled plasma mass spectrometry (ICP–MS) (PE300D) with uncertainty of 5% based on the Chinese national standard GB/T 14506.30-2010. Loss-on-ignition (LOI) contents of the samples were measured after heating to 900 °C for 3 h in a Muffle furnace.

4.3. Sm-Nd isotopes

Eight samples were chosen for whole-rock Sm-Nd isotope analyses. Sm-Nd and REEs were isolated on quartz columns using Teflon coated with HDEHP, di (2-ethylhexyl) orthophosphoric acid and conventional cation exchange procedures, as described by Chen et al. (2000, 2007). Nd was loaded as phosphate on pre-conditioned Re filaments and measurements were performed in a Re double-filament configuration. Sm and Nd were measured using a Finnigan MAT-262 multi-collector mass spectrometer (Bremen, Germany) at the Laboratory for Radiogenic Isotope Geochemistry, University of Science and Technology of China (USTC). Procedural blanks were <50 pg for Sm and Nd. corrected for mass fractionation by normalization to 10

146

143

Nd/144Nd values were

Nd/144Nd = 0.7219. The La

Jolla standards for Nd were analyzed during the data acquisition period. Precision of 147

Sm/144Nd ratios was better than 0.5%, and precision of the measured Nd isotopic

ratios was better than 0.003%.

5. Results

5.1. Geochronology

Seven zircon samples from the southern margin of the North Liaohe Group (Fig. 1b) were chosen for zircon U-Pb dating. The CL images and REE patterns of representative zircons are shown in Fig. 3, and zircon U-Pb and REE data are presented in Supplementary Tables S1 and S2, respectively. The abnormally high light rare earth element (LREE) concentrations of some igneous zircons (data not shown) may be inherited from inclusions (e.g., apatite) in these zircons, or may suggest late disturbance (Wu and Zheng, 2004). Data with 1σ > 40 Ma in

207

Pb/206Pb ages are

omitted from calculations of weighted mean 207Pb/206Pb ages, and from plots of U-Pb concordia. It is noteworthy that different types of rocks contain different types of zircons. The meta-diabase mainly preserves igneous zircons, whereas the amphibolite contains primarily metamorphic zircons.

5.1.1. Zircon U-Pb dating and REE patterns for meta-diabase

Sample D1002-2 (N40°55′19″, E123°26′43″) According to CL images and Th and U contents, the zircons in sample D1002-2 can be subdivided into two groups. One group is gray in color and subhedral and 11

stubby in shape, which has low length/width ratios, with internal growth zonation in CL images. The dated zircon domains have relatively low Th (< 3650 ppm) and U (< 2350 ppm) contents with high Th/U ratios (mostly 0.87-2.30), indicating they are magmatic in origin (Hoskin and Black, 2000; Wu and Zheng, 2004). Seventeen analyses show variable lead loss, with 10 analyses on or near concordia and a weighted mean 207Pb/206Pb age of 2133 ± 14 Ma (MSWD = 1.6), which represents the emplacement age. The second group appears dark-luminescent in CL imaging and has high Th (> 4740 ppm) and U (> 2450 ppm) contents with Th/U ratios of 1.34-2.43. Five analyses show variable lead loss with

207

Pb/206Pb ages of ca. 1959–1869 Ma,

which are considered to represent the subsequent Paleoproterozoic metamorphic event (Fig. 3a). The igneous and metamorphic zircons exhibit the same REE patterns, consistent with alteration and/or low-grade metamorphism (Fig. 4a). Sample D1009-5 (N40°55′01″, E123°25′59″) CL and transmitted light images show two types of zircons in sample D1009-5. One type is gray-luminescent in CL imaging and has no internal structure. These zircons are euhedral, platy, almost transparent, and show striped absorption patterns in transmitted light images, which show high and steep HREE patterns in chondrite-normalized REE diagrams (Fig. 4b), indicating they are magmatic in origin. Twelve concordia analyses provide a weighted mean 207Pb/206Pb age of 2100 ± 12 Ma (MSWD = 0.89), representing the emplacement age. The second type is opaque, anhedral and granular in shape, and dark-luminescent in CL imaging. Twelve analyses show various levels of lead loss, and three of these on concordia yield a weighted 12

mean

207

Pb/206Pb age of 1957 ± 29 Ma (MSWD = 0.16) interpreted as the

metamorphic age (Fig. 3b). Sample D1009-7 (N40°54′48″, E123°25′44″) The zircons from sample D1009-7 have similar features to the first type of zircons of sample D1009-5, being transparent, euhedral and platy in shape, , and exhibiting striped absorption patterns (Fig. 3c). The dated zircon domains have high Th/U ratios (0.81–1.80) and high HREE contents, with fairly steep HREE patterns and positive Ce anomalies (Fig. 4c), indicating they are igneous zircons. Twenty-five analyses show variable lead loss, with ten analyses on concordia providing a weighted mean

207

Pb/206Pb age of 2110 ± 23 Ma (MSWD = 1.8), representing the magma

crystallization age (Fig. 3c). Sample D5048-4 (N40°58′22″, E123°21′28″) Zircon crystals from sample D5048-4 are lath-shaped, with gray color and striped absorption patterns in CL imaging (Fig. 3d). The dated zircon domains have high Th/U ratios (0.45-1.48), and show similar REE patterns to sample 1009-7 (Fig. 4d). Twenty-eight analyses on or near concordia yield a weighted mean

207

Pb/206Pb

age of 2164 ± 6 Ma (MSWD = 0.90); this age is interpreted as the crystallization age for the meta-diabase. In addition, one analysis with low LREE contents (Fig. 4d) yields a younger

207

Pb/206Pb age of ca. 1922 Ma, which is similar to the metamorphic

ages identified in other samples (e.g., D1009-5) (Fig. 3d).

13

5.1.2. Zircon U-Pb dating and REE patterns for amphibolite

Sample D2050-1 (N40°51′15″, E123°22′38″) Zircons separated from sample D2050-1 are anhedral-granular in shape, with homogeneous CL images (Fig. 3e), and have lower Th/U (generally 0.01–0.08). In chondrite-normalized REE diagrams, these zircons exhibit lower REE contents than those of the igneous zircons (Fig. 4e), indicating they are metamorphic in origin (Hoskin and Black, 2000; Geisler et al., 2003; Wu and Zheng, 2004). Twenty-eight analyses yield concordant

207

Pb/206Pb ages varying from 1933 to 1839 Ma with a

weighted mean age of 1886 ± 8 Ma (MSWD = 0.98; Fig. 3e), which can be well-interpreted as the amphibolites facies metamorphic age. Sample D3038-2 (N40°54′03″, E123°25′07″) Zircons from sample D3038-2 have simple morphologies (i.e., granular to rounded). They are light-gray luminescent in CL imaging with no internal structures (Fig. 3f). They are characterized by low Th/U ratios (generally 0.04–0.10), and low total REE contents (Fig. 4f). These features are similar to those of zircons from sample D2050-1, suggesting a metamorphic origin. Nineteen analyses on the similar zircon domains yield a metamorphic weighted mean 207Pb/206Pb age of 1850 ± 13 Ma (MSWD = 0.95). In addition, one analysis with a high Th/U ratio (9.70) records a 207

Pb/206Pb age of ca. 2067 Ma, being consistent with the emplacement ages noted in

other samples (e.g., D1009-5) (Fig. 3f). Sample P12-10-1b (N40°53′47″, E123°23′22″) Zircons from sample P12-10-1b are granular to rounded in shape, with 14

length-to-width ratios of 1:1. They are transparent and colorless in transmitted light images with homogeneous CL imaging (Fig. 3g). The dated zircon domains have very low Th/U ratios (~0.01) and low total REE contents (Fig. 4g). These features are similar to those of zircons of samples D2050-1 and D3038-2, suggesting they are metamorphic in origin. Twenty-two analyses, which are concordant or nearly concordant, yield a weighted mean 207Pb/206Pb age of 1880 ± 14 Ma (MSWD = 1.15). This age is considered to be the metamorphic age (Fig. 3g). In summary, all the zircons separated from meta-mafic rock samples in the southern part of the North Liaohe Group record two distinct age groups of ca. 2137–2116 Ma (n = 83) and ca. 1957–1839 Ma (n = 114), with major age peaks at ca. 2130 Ma and ca. 1878 Ma (Fig. 3h), which represent the emplacement age and metamorphic age for the meta-mafic rocks, respectively. In addition, some zircon grains in the studied samples give 207Pb/206Pb ages of ca. 2560–2320 Ma (Fig. 3a, c, e and g), which can be interpreted as inherited zircons from the source rocks or results from wall-rock contamination. 5.2. Geochemistry 5.2.1. Effects of metamorphism and alteration on chemical compositions

According to petrographic observations and variable LOI values (0.28–2.44%, Table 1), the meta-mafic rocks within the North Liaohe Group have undergone greenschist- to amphibolite-facies metamorphism and varying degrees of alteration. In this regard, it is necessary to evaluate the effects of metamorphism and alteration on 15

the chemical compositions of the meta-mafic rocks. A number of elements (K, Ba, Sr, Ti, V, Th, Ce, Nb and Y) with different geochemical behaviors are selected to plot against Zr (Fig. 5), because Zr in igneous rocks is generally considered the most immobile during low- to medium-grade metamorphism and alteration, except for the case of seafloor-hydrothermal alteration (e.g., Wood et al., 1979; Gibson et al., 1982). As shown in Fig. 5, the high-field-strength elements [HFSEs; e.g., REE (e.g., Ce), Nb, Y and Ti], Th and siderophile elements (e.g., V) have strong correlations with Zr, indicating these elements are essentially immobile and preserve the original signatures. On the contrary, most large-ion-lithophile elements (LILEs; e.g., K, Ba and Sr), except for Ca (not shown), are scattered for the meta-mafic rocks, suggesting varying degrees of mobility during metamorphism and alteration. The result is similar to those of Pearce and Cann (1973) and Staudigel et al. (1996). Thus, these immobile elements are used for rock classification and further discussions, whereas the mobile elements (LILE, e.g., Ba) are omitted from discussions of the tectonic setting and source of the meta-mafic rocks.

5.2.2. Major and trace element and Sm-Nd isotope compositions

Major and trace element data for 16 meta-mafic rock samples from the North Liaohe Group are presented in Table 1. Sm and Nd concentrations, 143

147

Sm/144Nd and

Nd/144Nd ratios, and TDM1 and TDM2 model ages for eight samples are listed in Table

2. The εNd(t) values have been calculated at 2130 Ma (protolith age) based on the

16

zircon U-Pb age data. The meta-mafic rocks are basic (SiO2 = 46.68–53.90 wt.%) with a relatively large range of major and trace element compositions. They have high abundances of total Fe2O3 (9.65–17.58 wt.%) and CaO (5.50–11.23 wt.%), low concentrations of TiO2 (0.56–2.33 wt.%) and Al2O3 (10.21–15.89 wt.%) (Table 1; Fig 7), and variable MgO contents (2.77–11.49 wt.%) and Mg# values [0.27–0.70; Mg# = Mg/(Mg+Fe2+)], plotting within the sub-alkaline basalt field in the Zr/TiO2 versus Nb/Y diagram (Fig. 6a, Winchester and Floyd, 1977). On the FeOT/MgO versus SiO2 diagram (Fig. 6b, Miyashiro，1974) most of them belong to the typical tholeiitic series, consistent with the positive correlation between FeOT/MgO and TiO2 (not shown). In spite of varying REE contents with LaN = 20–75, as a result of high degrees of fractionation, meta-mafic rock samples show uniform chondrite-normalized REE patterns with LREE enrichment (LaN/YbN = 1.6–4.0; LaN/SmN = 1.1–2.3) and relatively flat HREE patterns (DyN/YbN = 1.1–1.4) (Fig. 7a). Some samples have Eu anomalies (Eu/Eu* = 0.81–1.26) due to extensive crystallization differentiation or accumulation of plagioclase. In primitive mantle (PM)-normalized trace element patterns (Fig. 7a), the samples show strong negative anomalies in Nb, Ta, P and Ti (Fig. 7b; cf. Meng et al., 2014; Wang et al., 2016). The meta-mafic rocks have relatively variable 143

147

Sm/144Nd (0.1500-0.1737) and

Nd/144Nd (0.511838–0.512328). They display considerable variation in calculated

εNd(t) values ranging from −2.8 to +3.1 (Table 2). It is notable that the Nd model ages of the MNLH are considerably older than the formation ages (Table 2), 17

indicating a two-component mixing process (Wu et al., 2005).

6. Discussion

6.1. Formation age of the meta-mafic rocks and constraints on the depositional age of the North Liaohe Group

Previous studies of zircon U-Pb and baddeleyite Pb-Pb dating for the meta-mafic rocks are mainly focused on the western and northern parts of the North Liaohe Group. Their formation ages were inconsonant, including 2060 Ma (Yu et al., 2007), 2110 Ma (Dong et al., 2012), 2161–2144 Ma (Meng et al., 2014), 2125 Ma (Yuan et al., 2015) and 2115 Ma (Wang et al., 2016), and most of them are older than ca. 2.1 Ga. In the present study, however, four meta-diabase and three amphibolite samples were mainly collected from the southern region of the North Liaohe Group, with the aim of constraining precisely their formation ages at a large scale (Fig. 1b). All the igneous zircons from four meta-mafic rock samples yielded consistent

207

Pb/206Pb ages with a

weighted mean age of 2133 ± 14 Ma for sample D1002-2 (Fig. 3a), 2100 ± 12 Ma for sample D1009-5 (Fig. 3b), 2110 ± 23 Ma for sample D1009-7 (Fig. 3c) and 2164 ± 6 Ma for sample D5048-4 (Fig. 3d), with peak ages of 2116 Ma and 2137 Ma (n = 83) (Fig. 3h). Together with the results of previous studies, these analyses suggest ~2130 Ma as the formation age of the meta-mafic rocks. As previous studies, the depositional age of the North Liaohe Group is debatable for a long time. Lu et al. (2004b) suggested that the depositional age for the Liaohe Group ranged from 2.16 to 1.85 Ga. Subsequently, some researchers used 18

LA-ICP-MS methods dating on the detrital zircons from meta-sedimentary rocks in the North Liaohe Group, and regarded the minimum peak age of igneous zircons and the maximum peak age of metamorphic zircons as the maximum and minimum depositional ages for the North Liaohe Group, respectively; these studies indicate that the North Liaohe Group was deposited at 2.05–1.95 Ga (Luo et al., 2004b, 2008; Liu et al., 2015). In the present studies, detailed geological mapping at a 1:50,000 Scale has revealed that the abundant mafic rocks as sills, dykes and veins widely intruded into the meta-sedimentary rocks of the North Liaohe Group (Fig. 2a–c). Therefore, the depositional age for the North Liaohe Group is well-constrained before ca. 2.13 Ga, rather than at 2.05–1.85 Ga as previous studies.

6.2. Crystal fractionation

In general, primary magma can reflect the conditions of partial melting (e.g., pressure and temperature) and the composition of the source they were derived from (e.g., Klein and Langmuir, 1987; Niu et al., 2002; Niu and O’Hara, 2008). However, the primary magma composition can be modified by shallow level processes (e.g., fractional crystallization) during the magma intrusion and cooling process. Therefore, it is necessary to evaluate the effect of crystal fractionation on the abundances and ratios of elements before analyzing the source and petrogenesis. The meta-mafic rocks have variable SiO2, total Fe2O3, MgO, Cr and Ni contents (Table 1), indicating that all meta-mafic rock samples in the studied area represent evolved magmas, which experienced fractional crystallization rather than being 19

directly derived from mantle melting. In selected element versus Mg# diagrams, all meta-mafic rock samples display regular trends of decreasing CaO, CaO/Al2O3, Cr and

Ni

with

decreasing

Mg#

(Fig.

8e–h),

indicative

of

dominant

olivine/clinopyroxene fractionation. The increase in total Fe2O3 and TiO2 abundances with decreasing MgO concentration (Fig. 8c, d) is the result of Fe-Ti oxide accumulation, consistent with a mass of accessory magnetite and titanite existing in these samples (Fig. 2c, d). Furthermore, the positive correlation between Al2 O3 and Mg# is consistent with extensive plagioclase and olivine/clinopyroxene fractionation (Fig. 8b). In summary, all meta-mafic rock samples from the North Liaohe Group are derived from a common parental magma, which was subjected to crystal separation of a three-phase assemblage of olivine, clinopyroxene and plagioclase, and resulted in a lack of correlation between SiO2 and Mg# (Fig. 8a).

6.3. Magma source and petrogenesis

The source and petrogenesis of the meta-mafic rocks in the North Liaohe Group have been a long-standing issue of debate. The core problem is that the meta-mafic rocks are characterized by enrichment of most incompatible elements, except for negative anomalies of Nb-Ta-Ti (Fig. 7b), and considerable variation in Sm-Nd isotopic composition (Table 2). These features could be due to a subduction-related arc, inherited from the metasomatized continental lithospheric mantle (CLM), or reflected contamination of felsic rocks from the continental crust (CC). However, previous studies rejected that contamination from CC was existed during the magma 20

crystallization of the meta-mafic rocks (Meng et al., 2014; Yuan et al., 2015; Wang et al., 2016).

6.3.1. A single source?

Wang et al. (2011) and Meng et al. (2014) considered that the geochemical features of the meta-mafic rocks were similar to those of the typical island arc basalts; they possibly formed in a back-arc basin derived from a depleted mantle source that was metasomatized by subduction-related fluid. Stern et al. (1990) concluded that early back-arc basin basalts in the Mariana Trough have a strong arc component, which decreases in importance relative to mid-ocean ridge basalts (MORB) as the back-arc basin widens. The typical arc features can be identified in the early stages of modern back-arc basins; however, it is still difficult to interpret the strong arc component as material from a Paleoproterozoic back-arc basin undergoing collisional orogenesis. In addition, several lines of evidence exist against these typical island arc features. (1) The studied samples present characteristic incompatible trace element patterns and contents similar to those of enriched mid-ocean ridge basalts (E-MORB), and are distinguished from subduction-zone basalts (Fig. 9). (2) The studied samples have tholeiitic compositions (Fig. 6b), which differ from typical arc basalts with dominantly calc-alkaline nature. (3) On the Ti-Sm-V discrimination diagram (Fig. 10a; Vermeesch, 2006), which has been proved to be the best performing quadratic discriminant analysis method using incompatible elements for mafic rocks, most samples plot within the MORB field, rather than island arc basalts. (4) The studied 21

samples show an increasing trend from E-MORB to CC on a plot of Nb/Yb-Th/Yb (Fig. 10b; Pearce, 2008), and this tendency differs from the volcanic arc array. (5) Most samples show no obvious depletions of Zr and Hf relative to Nd and Sm, which are often-quoted “diagnostic” features for arc-related magmatic rocks (Fig. 7b; Kelemen et al., 2014; Meng et al., 2014; Wang et al., 2016). Therefore, the possibility of a single volcanic arc component for the meta-mafic rocks in the North Liaohe Group should be precluded. Some studies suggested a subcontinental lithospheric mantle (SCLM) source for the meta-mafic rocks (e.g., Yuan et al., 2015; Wang et al., 2016). In general, large-scale partial melting of the SCLM, which is the coldest part of the mantle, will not occur unless volatiles, such as H2O-rich fluids and/or melts, depress its solidus (e.g., Gallagher and Hawkesworth, 1992). It is noteworthy that metasomatized lithospheric peridotites, particularly those metasomatized by carbonate-rich melts or fluids, have considerable quantities of REE and low abundances of HFSE (e.g., Green and Wallace, 1988; Xu et al., 2003), although the composition of metasomatized SCLM is highly variable. Thus, their primitive mantle (PM)-normalized incompatible trace element diagrams often show characteristic negative Nb, Ta, Zr, Hf and Ti anomalies (e.g., Xu et al., 2003; Yang et al., 2007b) similar to those of arc-related basalts. However, these features are not consistent with those of most meta-mafic rock samples (Fig. 9). Despite many studied samples having concentrated Th/La ratios (~0.13–0.20) similar to that of average primitive continental arc basalt (CAB), they usually have lower Th/Ta and La/Sm ratios and a higher Nb/Th ratio (Fig. 11d–f). In 22

addition, CAB deviates clearly from the geochemical trends of the studied samples (Fig. 11d–f), suggesting that the meta-mafic rocks in the North Liaohe Group were unlikely to have been derived from a single metasomatized SCLM source.

6.3.2. Two-component mixing process

The meta-mafic rocks have high MgO (generally > 5.00 wt.% and up to 11.49 wt.%) and Mg# (up to 0.70) at basic silica contents (generally < 53.0 wt.%) (Table 1). These values differ from those of any crustal material or crust-derived melts (Rudnick and Gao, 2014), suggesting a mantle origin. Thus, the highly variable εNd(t), from -2.8 to +3.1 (Table 2), and the presence of inherited zircons with ages of 2.5–2.3 Ga (Fig. 3; e.g., Meng et al., 2014) indicate that the meta-mafic rocks might undergo a two-component mixing process (i.e., mantle and crustal components). It is noteworthy that crystal fractionation of a three-phase assemblage of olivine/clinopyroxene and plagioclase leads to weak correlations among SiO2, Al2O3 and Mg# (Fig. 8a, b). Consequently, the major elements are not appropriate for discriminating whether the meta-mafic rocks derive from two-component mixing, as described by Meng et al. (2014), Yuan et al. (2015) and Wang et al. (2016). In the following discussion, the trace element ratios (e.g., Th/La, Nb/Ta and Th/La) and isotopic data have been used to determine the two-component mixing process (e.g., Niu and Batiza, 1997), because these ratios are not fractionated from partial melting or fractional crystallization (e.g., Hoffmann, 1988) and useful to identify the end-member components effectively (e.g., Hawkesworth et al. 1995). 23

As shown in Fig. 11a–c, strong correlations between trace-element ratios in the meta-mafic rocks are reflective of two-component mixing. The negative correlation between εNd(t) and (La/Sm)N ratios (Fig. 12a) suggests that trace-element variations are not the result of simple differentiation of a parental magma, but are generated from assimilation of a crustal component with low εNd(t) and high LREE concentration. Most of the studied samples have highly varied Ce/Pb (31 of 37, 3.94–24.9) and Nb/U (59 of 64, 5.18–24.7) ratios falling between those of oceanic basalts (Sun and McDonough, 1989) and the upper continental crust (UCC; Rudnick and Gao, 2014), indicating that input of material from the UCC played a significant role in generating the meta-mafic rocks. Moreover, as clearly shown by Fig. 11d–f, contamination of the CC led to highly variable trace-element ratios, with positive correlations of Th/Ta and La/Sm versus Th/La, and negative correlation of Nb/Th versus Th/La. The mixing curves between trace element ratios can be either hyperbolic or linear (e.g., Niu and Batiza, 1997), and depend on the relative incompatibility between the two elements in the fractions. These hyperbolae constrain the nature of the mixing end members. Therefore, previous geochemical data of meta-mafic rocks have the highest εNd(t) (up to +4.23), lowest Th/La, Th/Ta and La/Sm ratios, and highest Nb/Th ratios should be the least-contaminated samples (Figs. 11d–f and 12a; sample YK12-2-2 in Yuan et al., 2015; sample 590HL1 in Wang et al., 2016). Overall, the suggested value of UCC (Rudnick and Gao, 2014) and most of the samples follow the mixing curves of Langmuir et al. (1978) (Fig. 11d–f). However, 24

some samples with high Th/La ratios and low Th/Ta and La/Sm ratios deviate clearly from these mixing curves. In addition, the Neoarchean basement rocks (e.g., syenogranite and monzogranite) found in the Anshan-Benxi area have more variable ranges of εNd(t) values (from +3.7 to -10.5) and Th/La (0.22–1.78) and Th/Ta (6.41–85.4) ratios (Wan et al., 2015), and thus cannot represent the tendencies of the meta-mafic rocks. These features suggest a specific mixing end-member from UCC. Hence, the field observation revealed that the meta-mafic rocks were contaminated by clastic xenoliths (i.e., feldspathic quartz-sandstone) with melting corrosion structures (Fig. 2b), which support continental detritus (i.e., sedimentary successions in the North Liaohe Group) as the main enriched end-member component. Due to a lack of detailed geochemical research on the sedimentary rocks in the North Liaohe Group, typical detritus from continental margins (A305, Kermadec-Hikurangi Margin, Gamble et al., 1996; DSDP Site 275, Ewart et al., 1998) were selected to simulate the mixing process. These continental detritus are in accordance with the geochemical trends of most studied samples (Fig. 11d–f), and the binary mixing modeling results indicate that < 50% bulk assimilation of continental detritus is required to explain the genesis of the meta-mafic rocks in the studied area (Fig. 12a). All of these factors suggest continental detritus as the primary involvement, and Archean basement rocks as a subordinate involvement, in the origin of the meta-mafic rocks.

6.3.3. The mantle source

As mentioned above, samples YK12-2-2 and 590HL1, which have low Th/La, 25

Th/Ta and La/Sm ratios and high Nb/Th ratios and εNd(t) values (Figs. 11d–f and 12), are the least-contaminated samples, and thus they preserve more information about the mantle source. They have E-MORB-like incompatible trace element patterns with low LaN/YbN and GdN/YbN ratios (Fig. 9) and high εNd(t), similar to depleted mantle at a comparable formation age of ca. 2.13 Ga (Fig. 12b). These characteristics preclude a long-term evolved and enriched SCLM source for the meta-mafic rocks in the North Liaohe Group (e.g., Yang et al., 2007b; Wang et al., 2008). Some studies have suggested that the meta-mafic rocks in the North Liaohe Group were generated by partial melting of young, depleted and subduction-related metasomatized lithospheric mantle (e.g., Meng et al., 2014; Yuan et al., 2015). However, two lines of evidence argue against this model. (1) These rocks have high εNd(t) and εHf(t) values (up to +4.23 and +9.58, respectively; Meng et al., 2014; Yuan et al., 2015), similar to those of depleted mantle. Mineral assemblages and geochemical compositions of mantle xenoliths from Paleozoic kimberlites show that an ancient and refractory lithospheric mantle underlying the NCC during the Paleozoic (Griffin et al., 1998; Zhang et al., 2004; Wu et al., 2006) formed at ca. 2.7 Ga and was replaced at ca. 1.95 Ga (Gao et al., 2002; Wu et al., 2006). During the Neoarchean (ca. 2.5 Ga), a mantle plume derived from the asthenospheric mantle produced widespread magmatism in the eastern NCC (Yang et al., 2008; Li and Wei, 2017), and may have provided small-degree melts, which might percolate to and modify the SCLM (e.g., McKenzie, 1989; Wang et al., 2008). Although the Precambrian SCLM beneath the NCC has not been studied directly, some research on 26

the Neoarchean (ca. 2.5 Ga) meta-gabbro suggested that the SCLM of this period is enriched and has lower εNd(t) (from -0.23 to +1.85) and εHf(t) (from -11.6 to +6.9) values than those of the depleted mantle (Zhang et al., 2014). These geological evidence suggest that the SCLM beneath the eastern NCC was relatively evolved and enriched in the Paleoproterozoic era (ca. 2.1 Ga) when the meta-mafic rocks formed. (2) The least-contaminated samples (i.e., YK12-2-2 and 590HL1) exhibit negative Nb, Ta, Zr, Hf and Ti anomalies in PM-normalized incompatible trace element patterns, indicating that the mantle source was metasomatized by subduction-related fluids or melts; however, the degree of depletion is lower than that of subduction-zone basalt (Fig. 9). In addition, samples with moderate (Hf/Sm)PM and (Ta/La)PM ratios (0.72–0.99 and 0.79–0.82, respectively) show a clear trend from the area of depleted mantle to that of fluid-related subduction metasomatism, which is different from typical volcanic arc basalts extracted from a hydrated mantle source (La Flèche et al., 1998). These characteristics suggest that the quantity of subduction-related fluid may be limited, and this fluid may be insufficient to induce significant partial melting within the ancient and refractory continental lithospheric mantle beneath the eastern NCC. Therefore, the ca. 2.1 Ga meta-mafic rocks cannot be derived from partial melting of the CLM beneath the eastern NCC, and they were probably derived from partial melting of an asthenospheric mantle source beneath the continental lithospheric mantle in the eastern NCC. For mafic-ultramafic rocks, the concentrations and ratios (e.g., LREE/MREE or HREE) of REEs, which have increasing incompatibility from HREE to LREE, are 27

widely used to evaluate source compositions and the degree of partial melting (e.g., Aldanmaz et al., 2000; Xu et al., 2001; Yang et al., 2007b). After discerning and removing layers contaminated by CC, the least-contaminated samples (i.e., YK12-2-2 and 590HL1) have the highest εNd(t) values and the lowest La/Sm (Fig. 12a) and La/Yb (e.g., Th/La and εNd(t) vs. La/Yb diagrams, data not shown) ratios, showing the characteristics of the primary parental magma of the meta-mafic rocks. Generally, low La/Yb, La/Sm, Dy/Yb and Sm/Yb ratios suggest a relatively large degree of partial melting and/or melt generation in the spinel stability field, whereas high La/Yb, La/Sm, Dy/Yb and Sm/Yb ratios reflect a small degree of partial melting and/or garnet as the predominant residual phase (e.g., Aldanmaz et al., 2000; Yang et al., 2007b). In the Dy/Yb versus La/Yb diagram (Fig. 13), the meta-mafic rocks have relatively constant, low La/Yb and Dy/Yb ratios, indicating that a ~10% partial melt of spinel peridotite can explain the generation of the meta-mafic rocks and residual garnet, if any, is minor (e.g., Wang et al., 2016).

6.4. Tectonic implications

As discussed above, the meta-mafic rocks were generated from partial melting of depleted

asthenospheric

mantle,

which

was

metasomatized

by

limited,

subduction-related fluids and/or melts, then underwent shallow-level processes (e.g., fractional crystallization) and upper crustal contamination (i.e., Archean basement and continental detritus). Their trace element characteristics (e.g., low La/Yb and Dy/Yb ratios) suggest that melt generation occurred in the spinel stability field. 28

For decades, the tectonic evolution of the JLJB has been the subject of intense debate; two models have been proposed. (1) In the intra-continental rift opening and closing model, a ca. 2.2–1.9 Ga intra-continental rift separated the Nangrim and Longgang blocks and produced widespread A-type granitoids (i.e., Liaoji granites). Subsequently, voluminous sedimentary rocks and volcanic successions formed in the rift basin prior to rift closing (Zhang and Yang, 1988; Li et al., 2004, 2005, 2006, 2012; Luo et al., 2004, 2008; Li and Zhao, 2007; Wang et al., 2016). Zhao et al. (2012) and Zhao and Zhai (2013) proposed an upgraded model in which the JLJB underwent a rifting event at ca. 2.2–1.9 Ga to open an initial ocean, which formed the Longgang and Nangrim blocks from a single Archean Block, with subsequent oceanic plate subduction and collision at ca. 1.9 Ga. (2) In the arc-continent collision model, Bai (1993), Wang et al. (2011) and Meng et al. (2014) considered that the South and North Liaohe groups represented a back-arc basin. Faure et al. (2004), Li and Chen (2014) and Yuan et al. (2015) suggested an alternative tectonic setting, in which they interpreted the mafic rocks intruding into the South and North Liaohe groups as typical of a magmatic arc belt. The arc-continent collision occurred at ca. 1.85–1.95 Ga. The rift closure model can explain the presence of large volumes of A-type granites (Zhang and Yang, 1988; Hao et al., 2004; Lu et al., 2004a, 2006; Wang et al., 2017) and bimodal magmatism (Sun et al., 1993, 1996). In the rift closure model, rifting can eventually lead to rupture of the continental lithosphere, forming mafic rocks from asthenospheric or lithospheric mantle in the process (Thybo and Nielsen, 29

2009). Meanwhile, upwelling of hot basaltic magma from the mantle would heat the overlying granitoids and produce A-type granites (Li et al., 2008). However, some evidence presented in this study is not consistent with the rift closure model: (1) Mafic rocks from continental rifts commonly show geochemical features similar to those of OIB (Wilson, 1989; Li et al., 2006), whereas the meta-mafic rocks in the studied area have geochemical features similar to those of E-MORB (Figs. 9 and 10); (2) these mafic rocks are not derived from a long-term evolved and enriched SCLM, and are slightly depleted in some HFSEs (e.g., Ta, Nb, Zr, Hf and Ti), indicating a ca. 2.1 Ga ocean subduction event (Fig. 9); and (3) the depth of partial melting of the asthenospheric mantle that formed the mafic rocks occurred at shallow levels in the spinel stability field (Section 6.3.3). In addition, the mechanism and geodynamic source of rift closing is worthy of discussion. An alternative model is that an early magmatic arc collided with the Archean continent and formed the JLJB (Bai, 1993; Faure et al., 2004), and continuous studies have supported this hypothesis (e.g., Wang et al., 2011; Meng et al., 2014, 2017a, b; Li and Chen, 2014; Yuan et al., 2015; Li et al., 2017). Some studies consider the Paleoproterozoic meta-mafic rocks intruding into the Liaohe Group to be typical arc magmatism (e.g., Faure et al., 2004; Li and Chen., 2014; Yuan et al., 2015). However, present study provides several lines of evidence against this interpretation: (1) The igneous rocks in the Liaohe Group are composed mainly of basic and acidic rocks (cf. Sun et al., 1993, 1996; Lu et al., 2006; Meng et al., 2014; Li and Chen, 2014; Wang et al., 2017), in contrast to typical volcanic arc magmatism containing dominant 30

andesitic rocks (Wilson, 1989); (2) These basic rocks have a tholeiitic nature, inconsistent with typical arc basalts having a dominant calc-alkaline nature (Zhao et al., 2012; Zhao and Zhai, 2013; Meng et al., 2014; Yuan et al., 2015; Wang et al., 2016); (3) The meta-mafic rocks show geochemical affinity with E-MORB rather than with volcanic arc basalts (Figs. 9 and 10); (4) The incompatible element (e.g., Nb, Ta, Zr, Hf, Ti) concentrations of the meta-mafic rocks (i.e., samples YK12-2-2 and 590HL1) are higher than those of the typical subduction-zone basalt (Fig. 9; Tatsumi and Eggins, 1995), indicating limited metasomatism from subduction-related fluids and/or melts. Wang et al. (2011) and Meng et al. (2014) suggested that the meta-mafic rocks, which have geochemical features similar to those of typical island arc basalts, were formed in a back-arc tectonic setting. This study reintroduces that the Paleoproterozoic igneous and sedimentary rocks of the JLJB should be formed in a ca. 2.13 Ga back-arc basin; this interpretation supports the arc-continent collision model rather than the rift closure model. Furthermore, the back-arc basin opening and closing model can explain (1) meta-mafic rocks derived from asthenospheric mantle showing geochemical characteristics similar to both subduction-related fluids or melts and basalts from mid-oceanic ridges (Fig. 9); (2) the petrogenesis of large volumes of A-type granites (Sun et al., 2015) and bimodal magmatism (Shinjo and Kato., 2000); (3) geochemical variations of the metasedimentary rocks from the Laoling Group (Meng et al., 2017); and (4) the formation of ca. 1.9 Ga pelitic and mafic granulites, which require plate tectonic processes (e.g., subduction and continent-continent 31

collision) to bring the pelitic and mafic rocks to a middle-lower crustal depth from the Jingshan, South Liaohe and Ji’an groups (e.g., Zhou et al., 2008; Tam et al., 2011, 2012; Cai et al., 2017; Liu et al., 2017b). In summary, a newly tectonic evolution model for the Paleoproterozoic JLJB has been proposed: (1) Firstly, a ca. 2.18 Ga oceanic plate subduction event induced the back-arc basin opening, accompanied by the formation of the Liaoji granite; (2) subsequently, continental clast and carbonatite were extensively deposited in the back-arc basin, and the ca. 2.13 Ga mafic magma intruded into the sedimentary successions; (3) finally, subduction and arc-continent collision closed the back-arc basin and formed the JLJB in the period of ca. 1.9Ga. However, the related typical island arc magmatism, as direct evidence for the arc-continent collision model, still deserves to be researched carefully to test the validity of our hypothesis.

7. Conclusion

Based on the detailed geological mapping at the 1:50,000 Scale, a systematic review of petrological, geochronological, geochemical and Sm-Nd isotopic studies of the meta-mafic rocks in the Liaodong Peninsula, combined with previous work, provided some important information on their source and petrogenesis, and tectonic evolution of the JLJB: 1. The large-scale meta-mafic rocks intruding into the North Liaohe Group are mainly composed of meta-diabase/gabbro and (garnet-bearing) amphibolite. Zircon U-Pb dating of seven samples suggests that they were emplaced at ca. 2130 Ma and 32

metamorphosed at ca. 1878 Ma. 2. Geochemical and whole-rock Nd isotopic data indicate that these meta-mafic rocks are derived from partial melting of a depleted asthenospheric mantle in the spinel stability field, which was metasomatized by limited subduction-related fluids and/or melts coupled with fractional crystallization and crustal contamination. 3. As a part of extensive Paleoproterozoic magmatism in the Liaodong Peninsula, it appears that the protolith of the meta-mafic rocks were formed in a ca. 2.1 Ga back-arc basin, subsequently closed at ca. 1.9 Ga to form the JLJB. 4. Determination of the intrusive age for the meta-mafic rocks reveals that the depositional age for the voluminous meta-sedimentary rock in the North Liaohe Group is older than ca. 2.1 Ga, rather than the 2.0–1.95 Ga reported as previous studies.

Acknowledgments

We thank the editor for editorial handling and comments, and two anonymous reviewers for their constructive comments. We are grateful to Professor Fukun Chen for his assistance in Nd isotopic analyses. We also thank Pinghua Liu, Chaohui Liu, Wei Wang and Lei Zou for their assistance in fieldwork. This work was supported by the National Natural Science Foundation of China (Grant no. 41430210), Chinese Geological Survey Bureau project (grant no. DD20160121), and Basic Scientific Foundation of CAGS (grant no. YYWF201703).

33

Reference

Aldanmaz, E., Pearce, J.A., Thirlwall, M.F., Mitchell, J.G., 2000. Petrogenetic evolution of late Cenozoic, post-collision volcanism in western Anatolia, Turkey. J. Volcanol. Geoth. Res. 102,

34

67–95. Andersen, T., 2002. Correction of common lead in U-Pb analyses that do not report 204Pb. Chem. Geol. 192 (1-2), 59–79. Bai, J., 1993. The Precambrian Geology and Pb-Zn Mineralization in the Northern Margin of North China Platform. Geological Publishing House, Beijing, pp. 47–89 (in Chinese with English abstract). Cai, J., Liu, F.L., Liu, P.H., Wang, F., Meng, E., Wang, W., Yang, H., Ji, L., Liu, L.S., 2017. Discovery of granulite-facies metamorphic rocks in the Ji’an area, northeastern Jiao–Liao–Ji Belt, North China Craton: metamorphic P–T evolution and geological implications. Precambr. Res. 303: 626–640. Chen, F.K., Hegner, E., and Todt, W., 2000, Zircon ages and Nd isotopic and chemical compositions of orthogneisses from the Black Forest, Germany: Evidence for a Cambrian magmatic arc. Int. J. Earth Sci. 88, 791–802. Chen, F.K., Li, X.H., Wang, X.L., Li, Q.L., Siebel, W., 2007. Zircon age and Nd-Hf isotopic composition of the Yunnan Tethyan belt, southwestern China. Int. J. Earth Sci. 96, 1179–1194. DePaolo, D. J., 1981. Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth Planet. Sc. Lett. 53, 189–202. Dong, C.Y., Ma, M.Z., Liu, S.J., Xie, H.Q., Liu, D.Y., Li, X.M., Wan, Y.S., 2012. Middle Paleoproterozoic crustal extensional regime in the North China Craton: New evidence from SHRIMP zircon U-Pb dating and whole-rock geochemistry of meta-gabbro in the Anshan-Gongchangling area. Acta Petrol. Sin. 28 (9), 2785–2792 (in Chinese with English 35

abstract). Ewart, A., Collerson, K.D., Regelous, M., Wendt, J.I., Niu, Y., 1998. Geochemical Evolution within the Tonga–Kermadec–Lau Arc–Back-arc Systems: the Role of Varying Mantle Wedge Composition in Space and Time. J. Petrol. 39, 331–368. Faure, M., Lin, W., Monie, P., Bruguier, O., 2004. Palaeoproterozoic arc magmatism and collision in Liaodong Peninsula (north-east China). Terra Nova 16, 75–80. Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical classification for granitic rocks. J. Petrol. 42, 2033–2048. Gallagher, K., Hawkesworth, C., 1992. Dehydration melting and the generation of continental flood basalts. Nature 258, 57–59. Gamble, J., Woodhead, J., Wright, I. and Smith, I., 1996. Basalt and sediment geochemistry and magma petrogenesis in a transect from oceanic island arc to rifted continental margin arc: the Kermadec-Hikurangi margin, SW Pacific. J. Petrol. 37, 1523–1546. Gao, S., Rudnickc, R.L., Carlson, R.W., McDonough, W.F., Liu, Y.S., 2002. Re-Os evidence for replacement of ancient mantle lithosphere beneath the North China craton. Earth Planet. Sc. Lett. 198, 307–322. Geisler, T., Pidgeon, R.T., Kurtz, R., Bronswijk, W.V., Schleicher, H., 2003. Experimental hydrothermal alteration of partially metamict zircon. Am. Mineral. 88, 1496–1513. Gibson, I.L., Kirkpatrick, R.J., Emmerman, R., Schmincke, H.U., Pritchard, G., Oakley, P.J., Thorpe, R.S., Marriner, G.F., 1982. The trace element composition of the lavas and dikes from a 3-km vertical section through the lava pile of Eastern Iceland. J. Geophys. Res. 87 (B8), 6532–6546. 36

Green, D.H., Wallace, M.E., 1988. Mantle metasomatism by ephemeral carbonatite melts. Nature 336, 459–62. Griffin, W.L., Zhang, A., O’Reilly, S.Y., Ryan, C.G., Flower, M.F.J., Chung, S.L., Lo, C.H., Lee, T.Y., 1998. Phanerozoic evolution of the lithosphere beneath the Sino-Korean Craton, Mantle Dynamics and Plate Interaction in East Asia. American Geophysical Union, Geodynamics Series 27, 107–126. Hao, D.F., Li, S.Z., Zhao, G.C., Sun, M., Han, Z.Z., Zhao, G.T., 2004. Origin and its constraint to tectonic evolution of Paleoproterozoic granitoids in the eastern Liaoning and Jilin province, North China. Acta Petrol. Sin. 20, 1409–1416 (In Chinese with English abstract). Hawkesworth, C.J., Lightfoot, P.C., Fedorenko, V.A., Blake, S., Naldrett, A.J., Doherty, W., Gorbachev, N.S., 1995. Magma differentiation and mineralization in the Siberian continental flood basalts. Lithos 34, 61–88. Hofmann, A.W., 1988. Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust. Earth Planet. Sc. Lett. 90, 297–314. Hoskin, P.W.O., Black, L.P., 2000. Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. J. Metamorph. Geol. 18, 423–439. Kelemen, P. B.., Hanghøj, K., Greene, A. R., 2014. One View of the Geochemistry of Subduction-Related Magmatic Arcs, with an Emphasis on Primitive Andesite and Lower Crust. In: Holland, H.D., Turekian, K.K. (Eds.), The Crust, Treatise on Geochemistry vol. 4. Elsevier, Oxford, pp. 1–58. Klein, E.M., Langmuir, C.H., 1987. Global correlations of ocean ridge basalt chemistry with axial depth and crustal thickness. J. Geophys. Res. 92, 8089–8115. 37

La Flèche, M.R., Camire, G., Jenner, G.A., 1998. Geochemistry of post-Acadian, Carboniferous continental intraplate basalts from the Maritimes Basin, Magdalen islands, Quebec, Canada. Chem. Geol. 148, 115–136. Langmuir, C.H., Vocke, R.D., Hanson, G.N., 1978. A general mixing equation with application to Icelandic basalts. Earth Planet. Sc. Lett. 37, 380–392. Li, S.Z., Zhao, G.C., Sun, M., Han, Z.Z., Zhao, G.T., Hao, D.F., 2006. Are the South and North Liaohe Groups of North China Craton different exotic terranes? Nd isotope constraints. Gondwana Res. 9, 198–208. Li, S.Z., Han, Z.Z., Liu, Y.J., Yang, Z.S., Ma, R., 2001. Continental dynamics and regional metamorphism in the Liaohe Group. Geological Review 47 (1), 9–18 (in Chinese with English abstract). Li, S.Z., Suo, Y.H., Santosh, M., Dai, L.M., Liu, X., Yu, S., Zhao, S.J., Jin, C., 2013. Mesozoic to Cenozoic intracontinental deformation and dynamics of the North China Craton. Geol. J. 48, 543–560. Li, S.Z., Zhao, G.C., 2007. SHRIMP U–Pb zircon geochronology of the Liaoji granitoids: constraints on the evolution of the Paleoproterozoic Jiao-Liao-Ji belt in the Eastern Block of the North China Craton. Precambr. Res. 158, 1–16. Li, S.Z., Zhao, G.C., Santosh, M., Liu, X., Dai, L.M., Suo, Y.H., Tam, P.Y., Song, M.C., Wang, P.C., 2012. Paleoproterozoic structural evolution of the southern segment of the Jiao-Liao-Ji Belt, North China Craton. Precambr. Res. 200, 59–73. Li, S.Z., Zhao, G.C., Sun, M., Han, Z.Z., Luo, Y., Hao, D.F., Xia, X.P., 2005. Deformation history of the Paleoproterozoic Liaohe assemblage in the Eastern Block of the North China Craton. J. 38

Asian Earth Sci. 24, 659–674. Li, S.Z., Zhao, G.C., Sun, M., Wu, F.Y., Liu, J.Z., Hao, D.F., Han, Z.Z., Luo, Y., 2004. Mesozoic, not paleoproterozoic SHRIMP U-Pb zircon ages of two Liaoji Granites, eastern block, North China craton. Int. Geol. Rev. 46, 162–176. Li, X.H., Li, W.X., Li, Z.X., Liu, Y., 2008. 850–790 Ma bimodal volcanic and intrusive rocks in northern Zhejiang, South China: A major episode of continental rift magmatism during the breakup of Rodinia. Lithos 102, 341–357. Li, X.H., Li, Z.X., Wingate, M.T.D., Chung, S.L., Liu, Y., Lin, G.C., Li, W.X., 2006. Geochemistry of the 755Ma Mundine Well dyke swarm, northwestern Australia: Part of a Neoproterozoic mantle superplume beneath Rodinia? Precambr. Res. 146, 1–15. Li, X.H., Li, Z.X., Zhou, H.W., Liu, Y., Liang, X.R., 2002. U–Pb zircon geochronological, geochemical and Nd isotopic study of Neoproterozoic basaltic magmatism in western Sichuan: petrogenesis and geodynamic implications. Earth Sci. Front. 9, 329–338. Li, Z., Chen, B., 2014. Geochronology and geochemistry of the Paleoproterozoic meta-basalts from the Jiao-Liao-Ji Belt, North China Craton: Implications for petrogenesis and tectonic setting. Precambr. Res. 255, 653–667. Li, Z., Chen, B., Wei, C., 2017. Is the Paleoproterozoic Jiao-Liao-Ji Belt (North China Craton) a rift? Int. J. Earth. Sci. 106, 355–375. Li, Z., Wei, C., 2017. Two types of Neoarchean basalts from Qingyuan greenstone belt, North China Craton: Petrogenesis and tectonic implications. Precambr. Res. 292, 175–193. Liaoning Bureau of Geology and Mineral Resources (LBGMR), 1975a. 1:200000 Scale Regional Geology of Liaoyang, Liaoning Province (in Chinese). 39

Liaoning Bureau of Geology and Mineral Resources (LBGMR), 1975b. 1:200000 Scale Regional Geology of Yingkou City, Liaoning Province (in Chinese). Liaoning Bureau of Geology and Mineral Resources (LBGMR), 1975c. 1:200000 Scale Regional Geology of Yingkou County, Liaoning Province (in Chinese). Liaoning Bureau of Geology and Mineral Resources (LBGMR), 1976. 1:200000 Scale Regional Geology of Xiuyan, Liaoning Province (in Chinese). Liaoning Bureau of Geology and Mineral Resources (LBGMR), 1989. Regional Geology of Liaoning Province. Beijing: Geological Publishing House, 33–55 (in Chinese). Liu, D.Y., Nutman, A.P., Compston, W., Wu, J.S., Shen, Q.H., 1992. Remnants of >3800 Ma crust in the Chinese part of the Sino-Korean Craton. Geology 20, 339–342. Liu, F.L., Liu, C.H., Itano, K., Iizuka, T., Cai, J., Wang, F., 2017a. Geochemistry, U-Pb dating, and Lu-Hf isotopes of zircon and monazite of porphyritic granites within the Jiao-Liao-Ji orogenic belt: Implications for petrogenesis and tectonic setting. Precambr. Res. 300, 78–106. Liu, F.L., Liu, P.H., Wang, F., Liu, C.H., Cai, J., 2015. Progresses and overviews of voluminous meta-sedimentary series within the Paleoproterozoic Jiao-Liao-Ji orogenic/mobile belt, North China Craton. Acta Petrol. Sin. 31(10), 2816–2846 (in Chinese with English abstract). Liu, J.L., Ji, M., Shen, L., Guan, H.M., Davis, G.A., 2011. Early cretaceous extensional structures in the Liaodong Peninsula: Structural associations, geochronological constraints and regional tectonic implications. Sci. China Earth Sci. 54, 823–842. Liu, P.H., Liu, F.L., Liu, C.H., Wang, F., Liu, J.H., Yang, H., Cai, J., Shi, J.R., 2013. Petrogenesis, P-T-t path, and tectonic significance of high-pressure mafic granulites from the Jiaobei terrane, North China Craton. Precambr. Res. 233, 237–258. 40

Liu, P.H., Cai, J., Zou, L., 2017b. Metamorphic P-T-t path and its geological implications of the Sanjiazi garnet amphibolites from the northern Liaodong Penisula, Jiao-Liao-Ji belt: Constraints on phase equilibria and zircon U-Pb dating. Acta Petrol. Sin. 33, 2649–2674 (in Chinese with English abstract). Liu, Y.S., Gao, S., Hu, Z.C., Gao, C.G., Zong, K.Q., Wang, D.B., 2010. Continental and oceanic crust recycling-induced melt-peridotite interactions in the Trans-North China Orogen: U-Pb dating, Hf isotopes and trace elements in zircons from mantle xenoliths. J. Petrol. 51, 537–571. Lu, X.P., Wu, F.Y., Guo, J.H., Wilde, S.A., Yang, J.H., Liu, X.M., Zhang, X.O., 2006. Zircon U–Pb geochronological constraints on the Paleoproterozoic crustal evolution of the Eastern Block in the North China Craton. Precambr. Res. 146, 138–164. Lu, X.P., Wu, F.Y., Zhang, Y.B., Zhao, C.B., Guo, C.L., 2004a. Emplacement age and tectonic setting of the Paleoproterozoic Liaoji granites in Tonghua area, southern Jilin Province. Acta Petrol. Sin. 20, 381–392 (in Chinese with English abstract). Lu, X.P., Wu, F.Y., Lin, J.Q., Sun, D.Y., Zhang, Y.B., Guo, C.L., 2004b. Geochronological successions of the early Precambrian granitic magmatism in southern liaodong peninsula and its constraints on tectonic evolution of the North China Craton. Chinese Journal of Geology 39, 123–138. Ludwig, K.R., 2003. User's Manual for Isoplot 3.00. A Geochronological Toolkit for Microsoft Excel. Special Publication vol. 4a. Berkeley Geochronology Center, Berkeley, CA. Luo, Y., Sun, M., Zhao, G.C., Li, S.Z., Ayers, J.C., Xia, X.P., Zhang, J.H., 2008. A comparison of U-Pb and Hf isotopic compositions of detrital zircons from the North and South Liaohe 41

Groups: Constraints on the evolution of the Jiao-Liao-Ji Belt, North China Craton. Precambr. Res. 163, 279–306. Luo, Y., Sun, M., Zhao, G.C., Li, S.Z., Xu, P., Ye, K., Xia, X.P., 2004. LA-ICP-MS U-Pb zircon ages of the Liaohe Group in the Eastern Block of the North China Craton: constraints on the evolution of the Jiao-Liao-Ji Belt. Precambr. Res. 134, 349–371. Ma, L.J., Cui, Y.C., Liu, J.L., Zhang, J.B., 2007. Geochemical Characteristics and the Tectonic Setting of Amphibolites of the North Liaohe Group in Liaodong Area. Journal of Shanxi University (Natural Science Edition) 30 (4), 515–524 (in Chinese with English abstract). McKenzie, D., 1989. Some remarks on the movement of small melt fractions in the mantle. Earth Planet. Sc. Lett. 95 (1–2), 53–72. Meng, E., Liu, F.L., Liu, P.H., Liu, C.H., Yang, H., Wang, F., Shi, J.R., Cai, J., 2014. Petrogenesis and tectonic significance of Paleoproterozoic meta-mafic rocks from central Liaodong Peninsula, northeast China: Evidence from zircon U-Pb dating and in situ Lu-Hf isotopes, and whole-rock geochemistry. Precambr. Res. 247, 92–109. Meng, E., Wang, C.Y., Li, Y.G., Li, Z., Yang, H., Cai, J., Ji, L., Jin, M.Q., 2017. Zircon U–Pb–Hf isotopic and whole-rock geochemical studies of Paleoproterozoic metasedimentary rocks in the northern segment of the Jiao–Liao–Ji Belt, China: Implications for provenance and regional tectonic evolution. Precambr. Res. 298, 472–489. Miyashiro A., 1974. Volcanic rock series in island arcs and active continental margins. Am. J. Sci. 274 (4), 321–355. Niu, Y., Batiza, R., 1997. Trace element evidence from seamounts for recycled oceanic crust in the Eastern Pacific mantle. Earth Planet. Sc. Lett. 148, 471–483. 42

Niu, Y., O’Hara, M.J., 2008. Global Correlations of Ocean Ridge Basalt Chemistry with Axial Depth: a New Perspective. J. Petrol. 49, 633–664. Niu, Y.L., Regelous, M., Wendt, J.I., Batiza, R., O'Hara, M.J., 2002. Geochemistry of near-EPR seamounts: Importance of source vs. process and the origin of enriched mantle component. Earth Planet. Sc. Lett. 199, 327–345. Pearce, J., Cann, J., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth Planet. Sc. Lett. 19, 290–300. Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos 100, 14–48. Rudnick, R. L., Gao, S., 2014. The composition of the continental crust. In: Holland, H.D., Turekian, K.K. (Eds.), The Crust, Treatise on Geochemistry vol. 4. Elsevier, Oxford, pp. 1–51. Shinjo, R., Kato, Y., 2000. Geochemical constraints on the origin of bimodal magmatism at the Okinawa Trough, an incipient back-arc basin. Lithos 54 (3), 117–137. Show, D. M., 1970. Trace element fraction during anatexis. Geochim. Cosmochim. Ac. 34, 237–243. Staudigel, H., Plank, T., White, B., Schmincke, H.U., 1996. Geochemical fluxes during seafloor alteration of the basaltic upper oceanic crust: DSDP sites 417 and 418. In: Bebout, G.E., Scholl, S.W., Kirby, S.H., Platt, J.P. (Eds.), Subduction Top to Bottom. American Geophysical Union, Washington, D.C., pp. 19–38. Stern, R.J., Lin, P.N., Morris, J.D., Jackson, M.C., Fryer, P., 1990. Enriched back-arc basin basalts from the northern Mariana Trough: implications for the magmatic evolution of back-arc 43

basins. Earth Planet. Sc. Lett. 100, 210–225. Sun, F.J., Xu, X.S., Zou, H.B., Xia, Y., 2015. Petrogenesis and magmatic evolution of ~130 Ma A-type granites in Southeast China. J. Asian Earth Sci. 98, 209–224. Sun, M., Armstrong, R.L., Lambert, R.S.J., Jiang, C.C., Wu, J.H., 1993. Petrochemistry and Sr, Pb and Nd isotopic geochemistry of the paleoproterozoic kuandian complex, the eastern liaoning province, china. Precambr. Res. 62, 171–190. Sun, M., Zhang, L.F., Wu, J.H., 1996. The origin of the early Proterozoic Kuandian Complex: evidence from geochemistry. Acta Geol. Sin. 70 (3), 207–222 (In Chinese with English abstract). Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geological Society, London. Special Publications 42, 313–345. Tam, P.Y., Zhao, G.C., Liu, F.L., Zhou, X.W., Sun, M., Li, S.Z., 2011. Timing of metamorphism in the Paleoproterozoic Jiao-Liao-Ji Belt: New SHRIMP U-Pb zircon dating of granulites, gneisses and marbles of the Jiaobei massif in the North China Craton. Gondwana Res. 19, 150–162. Tam, P.Y., Zhao, G.C., Sun, M., Li, S.Z., Iizuka, Y., Ma, G.S.K., Yin, C.Q., He, Y.H., Wu, M.L., 2012. Metamorphic P-T path and tectonic implications of medium-pressure pelitic granulites from the Jiaobei massif in the Jiao-Liao-Ji Belt, North China Craton. Precambr. Res. 220, 177–191. Tatsumi, Y., Eggins, S.M., 1995. Subduction Zone Magmatism. Blackwell Science, Cambridge, p. 44

211. Thybo, H., Nielsen, C.A., 2009. Magma-compensated crustal thinning in continental rift zones. Nature 457, 873–876. Vermeesch, P., 2006. Tectonic discrimination diagrams revisited. Geochemistry Geophysics Geosystems 7, 466–480. Wan, Y.S., Ma, M.Z., Dong, C.Y., Xie, H.Q., Xie, S.W., Ren, P., Liu, D.Y., 2015. Widespread late Neoarchean reworking of Meso- to Paleoarchean continental crust in the Anshan-Benxi area, North China Craton, as documented by U-Pb-Nd-Hf-O isotopes. Am. J. Sci. 315, 620–670. Wan, Y.S., Song, B., Yang, C., Liu, D.Y., 2005. Zircon SHRIMP U–Pb geochronology of Archean rocks from the Fushun-Qingyuan area Liaoning Province and its geological significance. Acta Geol. Sin. 79 (1), 78–87. Wan, Y.S., Zhang, J.H., Williams, I.S., Liu, D.Y., Dong, C.Y., Fan, R.L., Shi, Y.R., Ma, M.Z., 2013. Extreme zircon O isotopic compositions from 3.8 to 2.5 Ga magmatic rocks from the Anshan area, North China Craton. Chem. Geol. 352, 108–124. Wang, H.C., Lu, S.N., Chu, H., Xiang, Z.Q., Zhang, C.J., Liu, H., 2011. Zircon U-Pb age and tectonic setting of meta-basalts of Liaohe Group in Helan area, Liao yang, Liaoning Province. Journal of Jilin University (Earth Science Edition) 41 (5), 1322–1334 (in Chinese with English abstract). Wang, X.P., Peng, P., Wang, C., Yang, S.Y., Söderlund, U., Su, X.D., 2017. Nature of three episodes of Paleoproterozoic magmatism (2180 Ma, 2115 Ma and 1890 Ma) in the Liaoji belt, North China with implications for tectonic evolution. Precambr. Res. 298, 252–267. Wang, X.C., Li, X.H., Li, W.X., Li, Z.X., Liu, Y., Yang, Y.H., Liang, X.R., Tu, X.L., 2008. The 45

Bikou basalts in the northwestern Yangtze block, South China: Remnants of 820-810 Ma continental flood basalts? Geol. Soc. Am. Bull. 120, 1478–1492. Wang, X.P., Peng, P., Wang, C., Yang, S.Y., 2016. Petrogenesis of the 2115 Ma Haicheng mafic sills from the Eastern North China Craton: Implications for an intra-continental rifting. Gondwana Res. 39, 347–364. Wilson, M., 1989. Igneous Petrogenesis. Kluwer Academic Publishers, London, pp. 8. Winchester, J.A., Floyd, P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chem. Geol. 20, 325–343. Wood, D.A., Joron, J.L., Treuil, M., 1979. A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings. Earth Planet. Sc. Lett. 45 (2), 326–336. Wu, F.Y., Li, Q.L., Yang, J.H., Kim, J.N., Han, R.H., 2016. Crustal growth and evolution of the Rangnim Massif, northern Korean Peninsula. Acta Petrol. Sin. 32 (10), 2933–2947(in Chinese with English abstract). Wu, F.Y., Walker, R.J., Yang, Y.H., Yuan, H.L., Yang, J.H., 2006. The chemical-temporal evolution of lithospheric mantle underlying the North China Craton. Geochim. Cosmochim. Ac. 70, 5013–5034. Wu, F.Y., Xu, Y.G., Zhu, R.X., Zhang, G.W., 2014. Thinning and destruction of the cratonic lithosphere: A global perspective. Sci. China Earth Sci. 44 (11), 2358–2372 (in Chinese). Wu, F.Y., Zhao, G.C., Wilde, S.A., Sun, D.Y., 2005. Nd isotopic constraints on crustal formation in the North China Craton. J. Asian Earth Sci. 24, 523–545. Wu, Y.B., Zheng, Y.F., 2004. Genesis of zircon and its constraints on interpretation of U–Pb age. 46

Chin. Sci. Bull. 49 (15), 1554–1569. Xu, W., Liu, F.L., Liu, C.H., 2017. Petrogenesis and geochemical characteristics of the North Liaohe metabasic rocks, Jiao-Liao-Ji orogenic belt and their tectonic significance. Acta Petrol. Sin. 33 (9), 2743–2757 (in Chinese with English abstract). Xu, X.S., O'Reilly, S.Y., Griffin, W.L., Zhou, X.M., 2003. Enrichment of upper mantle peridotite: petrological, trace element and isotopic evidence in xenoliths from SE China. Chem. Geol. 198, 163–188. Xu, Y.G., Menzies, M.A., Thirlwall, M.F., Xie, G.H., 2001. Exotic lithosphere mantle beneath the western Yangtze craton: Petrogenetic links to Tibet using highly magnesian ultrapotassic rocks. Geology 29 (9), 863–866. Yang, J.H., Sun, J.F., Chen, F., Wilde, S.A., Wu, F.Y., 2007b. Sources and petrogenesis of late triassic dolerite dikes in the Liaodong Peninsula: Implications for post-collisional lithosphere thinning of the eastern North China Craton. J. Petrol. 48 (10), 1973–1997. Yang, J.H., Wu, F.Y., Chung, S.L., Lo, C.H., Wilde, S.A., Davis, G.A., 2007a. Rapid exhumation and cooling of the Liaonan metamorphic core complex: Inferences from Ar-40/Ar-39 thermochronology and implications for Late Mesozoic extension in the eastern North China Craton. Geol. Soc. Am. Bull. 119, 1405–1414. Yang, J.H., Wu, F.Y., Wilde, S.A., Zhao, G.C., 2008. Petrogenesis and geodynamics of Late Archean magmatism in eastern Hebei, eastern North China Craton: Geochronological, geochemical and Nd-Hf isotopic evidence. Precambr. Res. 167, 125–149. Yang, J.H., Wu, F.Y., Xie, L.W., Liu, X.M., 2007c. Petrogenesis and tectonic implications of Kuangdonggou syenites in the Liaodong Peninsula, east North China Craton; Constraints 47

from in-situ zircon U-Pb ages and Hf isotopes. Acta Petrol. Sin. 23, 263–276 (in Chinese with English abstract). Yu, J.J., Yang, D.B., Feng, H., Lan, X., 2007. Chronology of amphibolite protolith in Haicheng of southern Liaoning: evidence from LA-ICP-MS zircon U-Pb dating. Global Geology 26(4), 391–396 (in Chinese with English abstract). Yuan, L.L., Zhang, X.H., Xue, F.H., Han, C.M., Chen, H.H., Zhai, M.G., 2015. Two episodes of Paleoproterozoic mafic intrusions from Liaoning province, North China Craton: Petrogenesis and tectonic implications. Precambr. Res. 264, 119–139. Zhai, M.G., 2014. Multi-stage crustal growth and cratonization of the North China Craton. Geosci. Front. 5, 457–469. Zhang, H.F, Sun, M., Zhou, M.F., Fan, W.M., Zhou, X.H., Zhai, M.G., 2004. Highly heterogeneous Late Mesozoic lithospheric mantle beneath the North China Craton: evidence from Sr-Nd-Pb isotopic systematics of mafic igneous rocks, Geol. Mag. 141, 53–62. Zhang, Q.S., Yang, Z.S., 1988. Early Crust and Mineral Deposits of Liaodong Peninsula, China. Geological Publishing House, Beijing (in Chinese with English abstract). Zhang, X.H., Yuan, L.L., Xue, F.H., Zhai, M.G., 2014. Neoarchean metagabbro and charnockite in the Yinshan block, western North China Craton: Petrogenesis and tectonic implications. Precambr. Res. 255, 563–582. Zhao, G.C., Cao, L., Wilde, S.A., Sun, M., Choe, W.J., Li, S.Z., 2006. Implications based on the first SHRIMP U–Pb zircon dating on Precambrian granitoid rocks in North Korea. Earth Planet. Sc. Lett. 251, 365–379. Zhao, G.C., Cawood, P.A., Wilde, S.A., Sun, M., 2002. Review of global 2.1–1.8 Ga orogens: 48

implications for a pre-Rodinia supercontinent. Earth Sci. Rev. 59, 125–162. Zhao, G.C., Cawood, P.A., Li, S.Z., Wilde, S.A., Sun, M., Zhang, J., He, Y.H., Yin, C.Q., 2012. Amalgamation of the North China Craton: Key issues and discussion. Precambr. Res. 222–223, 55–76. Zhao, G.C., Sun, M., Wilde, S.A., Li, S.Z., 2005. Late Archean to Paleoproterozoic evolution of the North China Craton: key issues revisited. Precambr. Res. 136, 177–202. Zhao, G.C., Zhai, M.G., 2013. Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Res. 23, 1207–1240. Zhou, X.W., Zhao, G.C., Wei, C.J., Geng, Y.S., Sun, M., 2008. EPMA, U-Th-Pb monazite and SHRIMP U-Pb zircon geochronology of high-pressure pelitic granulites in the Jiaobei massif of the North China Craton. Am. J. Sci. 308, 328–350.

49

Figure Captions

Fig. 1. (a) Tectonic framework of NCC (Zhao et al., 2005); (b) Simplified geological map of central Liaodong Peninsula illustrating the distribution of mafic rocks in the Liaohe Group (modified from LBGMR, 1975a, b, c, 1976). The rough boundary between NLH and SLH is adapted from Wang et al. (2011); NCC—North China Craton; KB—Khondalite Belt;

50

TNCO—Trans North-Central Orogen; JLJB—Jiao-Liao-Ji Belt; NLH—North Liaohe Group; SLH—South Liaohe Group.

Fig. 2. (a) Meta-diabase showing concordant intrusive contact with marble of the Dashiqiao Formation; (b) Meta-diabase as a dyke intruding into marble of the Gaojiayu Formation; (c) Intrusive contact relationship between the dyke-like meta-gabbro and phyllitic slate of the Langzishan Formation; (d) Felsic clastic rocks with melting corrosion structures found within meta-diabase; (e) Photomicrograph showing enlarged gabbroic-ophitic texture of altered diabase; (f) Photomicrograph showing ophitic texture of meta-diabase; (g) Photomicrograph of amphibolite; and (h) Photomicrograph of gneissic amphibolite. Pl-plagioclase; Hbl-hornblende; Act- actinolite; Mag-magnetite; Ttn-titanite.

Fig. 3. (a–g) Zircon U-Pb concordia diagrams, representative cathodoluminescence (CL) and transmitted light images and (h) binned frequency histograms of zircon ages for the meta-mafic rocks intruding into the North Liaohe Group from the Helan area, Liaodong Peninsula. The diameters of all yellow circles represent 32 μm.

Fig. 4. Chondrite-normalized rare earth element (REE) patterns of zircons in the meta-mafic rocks intruding into the North Liaohe Group from the Helan area, Liaodong Peninsula. Chondrite-normalized value is from Sun and McDonough (1989).

Fig. 5. Plots of selected major and trace elements versus Zr for the meta-mafic rocks to evaluate 51

the mobility of these elements under different geochemical conditions during alteration and metamorphism. Previous data are from Meng et al. (2014), Yuan et al. (2015) and Wang et al. (2016).

Fig. 6. (a) Zr/TiO2 versus Nb/Y (Winchester and Floyd, 1977) and (b) TFeO/MgO versus SiO2 (Miyashiro, 1974) diagrams for classification of the meta-mafic rocks in the North Liaohe Group

Fig. 7. (a) Chondrite-normalized REE patterns and (b) primitive mantle (PM)-normalized trace element diagrams for the meta-mafic rocks intruding into the North Liaohe Group. The chondrite, PM normalized values and enriched mid-ocean ridge basalt (E-MORB) are from Sun and McDonough (1989). The data for upper and lower continental crust (UCC and LCC) are from Rudnick and Gao (2014).

Fig. 8. Variations of selected oxides, trace elements and elemental ratios plotted against Mg# for the meta-mafic rocks from the Liaodong Peninsula. Previous data sources are the same as for Fig. 5. Calculation of Mg# for all samples is based on Mg# = Mg/(Mg+Fe2+) and Fe2+/total Fe = 0.85. Pl: plagioclase; Cpx: clinopyroxene; Ol: olivine; Ap: apatite; Fe-Ti: Fe-Ti oxides.

Fig. 9. Comparison of PM-normalized incompatible trace element spidergrams for the meta-mafic rocks of the North Liaohe Group with those of OIB, E-MORB, normal-MORB (N-MORB), UCC, LCC and subduction zone basalts. OIB, E-MORB and N-MORB are from Sun and McDonough (1989). UCC and LCC are from Rudnick and Gao (2014). The subduction zone basalts are limited 52

by “average” low-K and high-K basalts from Tatsumi and Eggins (1995). YK12-2-2 and 590HL1, considered to be the least-contaminated samples (Section 6.3.2), are from Yuan et al. (2015) and Wang et al. (2016), respectively.

Fig. 10. (a) Ti-Sm-V (Vermeesch, 2006) and (b) Nb/Yb-Th/Yb (Pearce, 2008) discrimination plots for the meta-mafic rocks of the North Liaohe Group, Liaodong Peninsula. Previous data sources are the same as for Fig. 5, and the sources of samples YK12-2-2 and 590HL1 are the same as in Fig. 9.

Fig. 11. (a–c) Correlations between Lu/Hf and other trace-element ratios suggesting a two-component mixing process for the meta-mafic rocks of the North Liaohe Group. (d–f) Variations of Th/Ta, Nb/Th, and La/Sm with Th/La used to constrain the source and end-member components of the meta-mafic rocks. CAB-average primitive continental arc basalt (Kelemen et al., 2014); UCC-upper continental crust (Rudnick and Gao, 2014). Samples A305 and 275 of continental detritus are from Gamble et al. (1996) and Ewart et al. (1998), respectively. The sources of samples YK12-2-2 and 590HL1 are the same as in Fig. 9. Calculation of mixing curves is based on Langmuir et al. (1978).

Fig. 12. Plots of εNd(t) versus (a) (La/Sm)N and (b) t (Ma) for the meta-mafic rocks intruding into the North Liaohe Group. The sources of samples YK12-2-2 and 275-2 are provided in Fig. 9 and Fig. 11, respectively. The mixing line is determined by simple binary mixing and assimilation-fractional crystallization (AFC) processes (Depaolo, 1981) with DNd = 0.0915 (Wang 53

et al., 2008). Tick marks on the simple mixing line represent 20% increments. The depleted mantle evolutionary curve is from Wu et al. (2005).

Fig. 13. La/Yb versus Dy/Yb diagram showing the source compositions and degree of partial melting of the meta-mafic rocks intruding into the North Liaohe Group. The melt curves for garnet (Grt) lherzolite, garnet-facies amphibole (Amp) lherzolite and spinel (Sp) lherzolite are based on non-modal batch melting equations (Show, 1970). Data sources: normative weight fractions of minerals and melt modes (Yang et al., 2007b); Mineral-melt distribution coefficients (http://earthref.org/)

Table Captions

Table 1. Major (wt%) and trace (ppm) elements for the meta-mafic rocks intruding into the North Liaohe Group Mg#=Mg/(Mg+Fe2+), assuming Fe2+/total Fe=0.85. Total iron as Fe2O3.

Table 2. Sm-Nd isotopic compositions of the Paleoproterozoic meta-mafic rocks in Helan area,

54

Liaodong Peninsula. The 147Sm/144Nd and 143Nd/144Nd ratios at the present time are 0.1967 and 0.512638 for chondrite, and 0.2137 and 0.51315 for depleted mantle, respectively. The 147Sm/144Nd ratio is 0.118 for crust. λ147Sm=6.54×10-12a-1.

55

56

57

58

59

60

61

62

63

64

65

66

67

68

Table 1 Major (wt%) and trace (ppm) elements for the MNLH Loc

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

N40°5

atio

E123° 1′26″

E123° 5′19″

E123° 5′01″

E123° 4′48″

E123° 1′15″

E123° 7′08″

E123° 2′30″

E123° 4′03″

E123° 1′19″

E123° 3′18″

E123° 5′36″

E123° 2′05″

E123° 7′13″

E123° 8′22″

E123° 3′47″

E123° 3′55″

16KD 18′39″

D100 26′43″

D100 25′59″

D100 25′44″

D205 22′38″

D301 25′30″

D302 24′53″

D303 25′07″

D304 25′57″

D403 20′41″

D500 23′45″

D501 22′47″

D502 23′37″

D504 21′28″

P12-1 23′22″

P12-1 23′12″

68-1-

2-2

9-5

9-7

0-1

7-2

6-1.1

8-2

4-2

3-2

5-1

2-2

9-1

8-4

0-1b

6-1b

Sam n wt% ple SiO

49.59

48.94

49.55

50.83

50.82

49.67

51.07

51.18

49.48

46.68

49.36

50.05

49.76

52.58

TiO

51.16 3 0.56

1.44

1.38

1.64

1.60

0.69

1.36

0.86

1.46

1.30

1.19

2.33

0.89

1.16

1.74

1.45

Al2

10.21

13.85

14.39

13.28

14.13

14.70

13.39

15.33

14.11

13.72

15.89

14.95

14.71

13.01

12.26

13.48

Fe2 O3

11.21

13.88

13.40

15.25

14.25

9.65

15.14

10.05

16.03

15.14

13.59

17.58

11.25

12.21

16.68

15.01

MnT O3

0.20

0.16

0.15

0.22

0.15

0.14

0.19

0.14

0.18

0.21

0.21

0.23

0.16

0.16

0.20

0.17

Mg O

11.49

6.96

5.82

6.15

5.78

9.17

6.49

7.62

6.02

6.34

8.03

2.77

8.04

8.10

4.16

4.85

2

53.90

2

Ca O

10.46

7.85

9.35

7.55

8.96

11.07

10.28

10.65

5.50

10.25

10.74

6.47

11.23

9.38

8.55

6.49

Na2 O

1.62

3.24

2.83

1.92

2.83

2.60

1.88

3.44

2.26

1.51

1.78

4.87

1.76

2.03

0.61

2.39

K2O O

1.25

1.06

1.37

1.80

0.75

0.41

0.62

0.33

0.73

0.74

0.50

0.64

1.01

1.23

1.08

0.54

P2O

0.07

0.15

0.14

0.18

0.17

0.07

0.12

0.08

0.15

0.11

0.09

0.26

0.07

0.08

0.16

0.15

LOI

1.64

0.74

1.79

1.56

0.50

0.49

0.94

0.95

1.86

0.98

1.17

0.28

1.10

2.44

1.49

1.05

Tota

99.87

98.92

99.56

99.10

99.95

99.81

99.95

100.52

99.48

99.66

99.87

99.74

100.27

99.56

99.51

99.35

Mg l

0.70

0.54

0.50

0.48

0.49

0.69

0.50

0.64

0.47

0.49

0.58

0.27

0.62

0.61

0.37

0.43

5

ppm # Li

6.18

8.64

8.07

16.60

5.85

4.55

9.47

3.86

36.3

11.2

15.9

8.35

3.47

25.6

10.4

11.9

Be

1.30

0.85

0.79

0.96

0.94

0.39

0.64

0.59

1.18

0.68

0.41

1.13

0.44

0.66

1.05

1.18

Sc

48.9

34.8

36.5

36.5

37.5

37.0

40.0

37.9

41.1

40.7

44.6

32.3

42.5

34.7

41.6

40.8

V

212

251

249

278

274

191

304

227

289

306

295

303

240

299

305

282

Cr

1580

300

340

234

277

178

124

101

14.3

128

290

1.44

391

458

3.07

13.6

Co

44.9

60.7

46.9

55.4

49.0

39.1

61.7

42.9

44.9

58.5

55.0

42.2

48.1

57.0

54.3

54.0

Ni

168

102

70.1

72.9

56.6

20.6

45.4

28.1

9.19

58.1

112

16.4

55.5

52.1

6.40

8.89

Ga

14.2

19.8

19.9

19.8

20.6

13.2

20.7

27.4

22.8

19.8

19.0

24.1

17.0

19.7

21.1

21.5

Rb

25.9

48.3

63.9

87.0

20.1

8.49

19.9

9.29

24.3

26.3

29.3

15.4

33.4

60.8

29.3

15.2

Sr

71.3

157

216

150

315

335

225

342

267

292

229

247

285

223

246

245

Y

20.8

29.6

27.5

32.2

31.8

14.1

26.2

22.2

32.3

25.8

20.8

43.7

17.0

17.7

35.1

31.9

Zr

64.4

137

122

144

139

51.1

87.4

76.4

161

98.1

65.1

201

60.4

87.4

177

166

Nb

4.98

8.04

7.46

9.21

8.52

3.54

5.97

4.64

8.85

5.78

3.02

10.7

3.42

5.01

9.34

9.12

Cs

0.54

3.72

2.77

1.33

0.44

0.39

0.36

0.29

0.82

0.59

1.28

0.54

0.86

3.01

0.54

0.75

Ba

95.9

165

249

481

151

176

181

59.5

335

306

75.9

116

223

231

495

179

La

8.21

15.7

15.0

17.7

14.7

5.62

9.32

11.8

17.8

6.63

4.78

13.7

6.35

9.82

15.3

17.6

Ce

18.2

33.8

32.8

38.1

34.7

13.7

21.5

24.3

37.1

17.1

11.4

35.7

14.0

21.1

33.4

37.4

Pr

2.40

4.49

4.30

4.97

4.80

1.67

3.01

3.14

4.99

2.60

1.78

4.90

1.95

2.79

4.65

4.84

Nd

10.6

19.6

18.4

21.4

21.3

7.29

13.7

13.5

20.8

12.6

8.80

22.9

9.00

12.1

20.7

20.6

Sm

2.53

4.97

4.66

5.37

5.45

2.01

3.74

3.35

5.21

3.62

2.78

6.44

2.42

3.26

5.47

5.04

Eu

0.71

1.56

1.51

1.57

1.69

0.66

1.46

1.37

1.45

1.32

1.08

2.10

1.05

1.12

1.73

1.50

Gd

2.87

5.13

4.59

5.10

5.17

2.10

3.87

3.34

5.12

4.32

3.64

7.04

2.69

3.31

6.40

5.16

Tb

0.50

0.96

0.90

1.02

1.02

0.42

0.77

0.64

1.01

0.77

0.65

1.36

0.52

0.61

1.11

0.98

Dy

3.36

5.65

5.34

6.00

5.96

2.58

4.69

3.96

6.01

4.75

3.90

8.25

3.13

3.53

6.59

5.82

Ho

0.74

1.10

1.03

1.17

1.16

0.51

0.93

0.87

1.31

1.05

0.85

1.82

0.69

0.74

1.43

1.28

Er

2.09

3.35

3.07

3.50

3.44

1.57

2.84

2.41

3.52

2.87

2.34

5.00

1.84

1.91

3.98

3.49

Tm

0.31

0.49

0.46

0.52

0.51

0.23

0.43

0.36

0.53

0.43

0.35

0.75

0.28

0.27

0.59

0.53

Yb

2.14

3.11

2.91

3.27

3.23

1.48

2.72

2.27

3.34

2.77

2.18

4.79

1.77

1.74

3.86

3.40

Lu

0.33

0.49

0.46

0.52

0.51

0.24

0.43

0.36

0.54

0.45

0.35

0.77

0.27

0.27

0.60

0.54

Hf

2.02

3.76

3.49

3.97

3.92

1.62

2.74

2.09

3.96

2.71

1.84

5.08

1.70

2.42

4.21

4.14

Ta

0.46

0.57

0.53

0.63

0.57

0.26

0.41

0.39

0.75

0.48

0.28

0.87

0.30

0.44

0.75

0.75

Pb

4.45

1.36

1.64

18.5

3.16

2.07

3.12

4.14

2.93

7.05

17.5

2.47

1.65

10.5

4.52

4.00

Th

2.54

3.40

3.26

3.89

3.55

1.61

1.71

2.99

6.86

2.39

0.80

3.54

1.46

2.82

4.72

6.15

U

0.96

1.04

0.94

1.20

1.05

0.37

0.52

0.48

0.87

0.38

0.19

0.72

0.32

0.54

0.80

1.21

2+

2+

Mg#=Mg/(Mg+Fe ), assuming Fe /total Fe=0.85. Total iron as Fe2O3.

69

Table 2 Sm-Nd isotopic composition of the MNLH in Helan area, Liaodong Peninsula. 147

Sm/144Nd

143

Nd/144Nd

2δ

εNd(t)

TDM1 (Ma)

TDM2 (Ma)

0.511954

9

-1.5

2998

2678

0.1517

0.511983

7

-0.5

2851

2598

20.6

0.1547

0.512134

14

1.7

2611

2427

2.16

7.83

0.1667

0.512223

15

0.1

2986

2551

2130

3.40

13.7

0.1500

0.511838

9

-2.8

3117

2788

D4033-2

2130

3.55

12.4

0.1737

0.512328

15

0.2

3110

2541

D5012-2

2130

6.85

24.4

0.1700

0.512234

9

-0.6

3172

2607

D5048-4

2130

3.80

14.1

0.1629

0.512320

5

3.1

2478

2315

Sample

Age(Ma)

Sm(ppm)

Nd(ppm)

D1002-2

2130

4.67

18.4

0.1533

D1009-7

2130

5.32

21.2

D2050-1

2130

5.27

D3017-2

2130

D3038-2

The

147

Sm/144Nd and

143

Nd/144Nd ratios at the present time are 0.1967 and 0.512638 for chondrite, and 0.2137 and 0.51315 for depleted

mantle, respectively. The 147Sm/144Nd ratio is 0.118 for crust. λ147Sm=6.54×10-12a-1.

70

Highlights: 1. The Paleoproterozoic meta-mafic rocks from the Jiao-Liao-Ji Belt were emplaced at ca. 2130 Ma and metamorphosed at ca. 1878 Ma. 2. These rocks are generated from a depleted asthenospheric mantle metasomatized by limited subduction-related fluids and/or melts. 3. They are parts of Paleoproterozoic magmatism and formed in a back-arc basin, which closed at ca. 1.9 Ga to form the Jiao-Liao-Ji Belt.

71