Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: Implications for Archean–Paleoproterozoic Wilson cycle in the North China Craton

Journal Pre-proofs Neoarchean suprasubduction zone ophiolite discovered from the Miyun Com‐ plex: implications for Archean – Paleoproterozoic Wilson Cycle in the North China Craton M. Santosh, Pin Gao, Bing Yu, Cheng-Xue Yang, Sanghoon Kwon PII: DOI: Reference:

S0301-9268(20)30001-2 https://doi.org/10.1016/j.precamres.2020.105710 PRECAM 105710

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Precambrian Research

Received Date: Revised Date: Accepted Date:

1 January 2020 11 March 2020 17 March 2020

Please cite this article as: M. Santosh, P. Gao, B. Yu, C-X. Yang, S. Kwon, Neoarchean suprasubduction zone ophiolite discovered from the Miyun Complex: implications for Archean – Paleoproterozoic Wilson Cycle in the North China Craton, Precambrian Research (2020), doi: https://doi.org/10.1016/j.precamres.2020.105710

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Neoarchean

suprasubduction

zone

ophiolite

discovered from the Miyun Complex: implications for Archean – Paleoproterozoic Wilson Cycle in the North China Craton

M. Santosh1,2,3*, Pin Gao1, Bing Yu1, Cheng-Xue Yang1, Sanghoon Kwon4

1School

of Earth Sciences and Resources, China University of Geosciences

Beijing, Beijing 100083, P.R. China 2Department 3Yonsei

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

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

4Department

of Earth System Sciences, Yonsei University, Seoul 03722,

Republic of Korea

*Corresponding

author

e-mail:

[email protected];

[email protected]

Abstract The North China Craton (NCC) offers a window to Archean –

Paleoproterozoic crustal evolution. Following the amalgamation of microblocks during Neoarchean, the NCC witnessed another protracted Wilson cycle in the Paleoproterozoic with subductionaccretion-collision process. Here we report a newly identified suprasubduction zone ophiolite suite from the Miyun complex in the NCC where a rare and near-complete ophiolite succession is preserved including serpentinite, lherzolite, olivine clinopyroxenite, websterite, gabbro, dolerite, diorite, monzonite, metabasalts and trondhjemite, in association with Banded Iron Formation (BIF). The geochemical features of the suite are consistent with those of suprasubduction

ophiolite

complexes,

with

the

mafic

and

intermediate members displaying Island Arc Tholeiite (IAT) and MidOcean Ridge Basalt (MORB) affinity. Zircon grains from lherzolite define three groups of

207

Pb/206Pb weighted mean ages at 2500 ±

12 Ma marking the formation age, and 2237 ± 47 Ma, and 1843 ± 30 Ma representing subsequent thermal events. The majority of zircon grains in olivine clinopyroxenite, gabbro, and quartz monzonite yield

207

Pb/206Pb weighted mean ages of 2510 ± 19 Ma,

2495 ± 10 Ma, and 2486 ± 21 Ma respectively. Those from the trondhjemite show weighted mean age of 2476 ± 9.4 Ma. The compiled age data from all the rock types in the Miyun suite show two distinct age peaks at ca. 2486 Ma and 1832 Ma, corresponding to

the

timing

of

magma

differentiation

and

subsequent

metamorphism. The zircon Lu-Hf isotope data display distinct

positive ɛHf(t) values in the range 0.35 to 7.05, suggesting magma derived from Neoarchean to Paleoproterozoic depleted mantle (juvenile) source. The zircon TDM ages show a peak at 2670 Ma, confirming Neoarchean components. The timing of magma formation in the Miyun ophiolite is broadly identical to those of the other rare Neoarchean – early Paleoproterozoic ophiolite suites described from the NCC including those from Yishui and Zunhua. Furthermore, evidence from the recently reported Alaskan-type intrusions and arc root mafic-ultramafic complexes around Miyun complex with ages in the range of 2.4 to 2.0 Ga suggest continued subduction-related magmatic processes, with final collision in latest Paleoproterozoic at around 1.84 Ga. We propose that following the assembly of ancient microblocks along multiple zones of ocean closure marked by major greenstone belts of 2.6 to 2.5 Ga, and high-grade metamorphism along the margins of the microblocks during Archean – Paleoproterozoic transition, the NCC went through another major Wilson cycle from early to late Paleoproterozoic involving prolonged subduction, accretion and collision of larger crustal blocks and intervening arc complexes, leading to final cratonization.

Keywords: Suprasubduction zone ophiolite; Geochemistry and isotope geochronology; Microblock amalgamation; Precambrian plate tectonics; North China Craton

1. Introduction Ophiolites as remnants of oceanic crust and mantle preserved on continents or incorporated within orogenic belts are central to the models on plate tectonics and are key evidence for defining oceanic suture zones (Dewey and Bird, 1971; Miyashiro, 1975; Pearce et al., 1984; Kusky et al., 2001; Nicolas and Boudier, 2003; Pearce, 2008; Dilek and Furnes, 2011; Nicolas, 2012; Gillis et al., 2014; Santosh et al., 2016; Wang et al., 2019, among others). An early classification by Miyashiro (1975) grouped ophiolites into three classes based on the volcanic associations. A more recent definition by Dilek and Furnes (2011) divided ophiolites into subduction-related and subduction-unrelated types. The former includes three sub-types: continental margin (CM) type, mid-ocean ridge (MOR) type, and plume (P) type. The subduction-unrelated type is composed of suprasubduction-zone (SSZ) type, and volcanic arc (VA) type.

The opening of ocean basins through rifting and seafloor spreading, followed by closure of the ocean basin by subduction and eventual collision is termed as the Wilson cycle (Dewey et al., 1974; Rogers and Santosh, 2004). The concept was first introduced by Tuzo Wilson (1966) and is one of the most important elements in the plate tectonic paradigm. The Wilson Cycle and supercontinental cycle,

whereby continental fragments amalgamate into supercontinents on a global scale by closure of intervening ocean basins, are complementary processes. However, not all Wilson cycles generate supercontinents (Rogers and Santosh, 2004). As the remnants of oceanic subduction realm, ophiolites provide one of the best lines of evidence for testing models on Wilson cycle.

The North China Craton (NCC) is among the oldest cratons on the globe

preserving

important

records

of

Archean

to

late

Paleoproterozoic crustal evolution history (Zhao et al., 2005, Kusky et al., 2007; Santosh, 2010; Zhai and Santosh, 2011; Zhao and Zhai, 2013; Tang and Santosh., 2018a; Gao and Santosh, 2019; among others). Although ophiolite suites ranging in age from Proterozoic through early Paleozoic and Mesozoic – Cenozoic, including both SSZ types and intercontinental ocean basin type have been reported from various parts of China (Zhang et al., 2003a), those of Archean age are relatively rare and somewhat controversial. Kusky et al. (2001) reported the 2.5 Ga Dongwanzi ophiolite from the NCC. Polat et al. (2005) identified late Archean ophiolite remnants in the Wutai greenstone belt. Santosh et al. (2016) discovered a suprasubduction zone ophiolite from the Yishui complex located at the boundary of the Jiaoliao (JL) and Xuhuai (XH) microblocks NCC, which is also of late Archean age. In another recent study, Wang et al. (2019) identified a Neoarchean ophiolitic mélange from Zunhua

in the eastern Hebei province of the NCC.

In this study, we report a new finding of suprasubduction ophiolite sequence

composed

of

serpentinite-lherzolite-olivine

clinopyroxenite-olivine websterite-gabbro-diorite-monzonitetrondhjemite-banded iron formation (BIF, metamorphosed to banded magnetite quartzite - BMQ) from the Miyun complex along the boundary between the of Qianhuai (QH) and Jiaoliao (JL) microblocks in the NCC (Fig. 1). We present petrological, geochemical, zircon U-Pb and Lu-Hf isotope data on the various rock types from this suite. The Miyun ophiolite preserves the nearcomplete stratigraphy of a typical ophiolite suite and is therefore a rare example of a fully preserved Precambrian ophiolite succession from the NCC and elsewhere in the world. Our study confirms the existence of Neoarchean – early Paleoproterozoic subduction systems that brought together the ancient crustal blocks and intervening complexes leading to the final collision and cratonization of the NCC during late Paleoproterozoic.

2. Geological background and sampling Among the three Archean cratonic blocks in China (Tarim, North China and South China; Fig. 1, inset), the triangle-shaped NCC covers about 1.5 million sq. km with its boundaries marked by the Qilianshan Orogen in the west, Tianshan – Inner Mongolia –

Daxinganling Orogen in the north, and Qingling – Dabie ultrahighpressure metamorphic belt in the south (Fig. 1). The formation of the NCC during early Precambrian and its decratonization involving extensive lithospheric destruction during Mesozoic, with associated world-class metallogeny are topics of global interest (Bai, 1986; Zhao et al., 2005; Kusky and Li, 2003; Santosh., 2010; Zhai and Santosh, 2011; Zhao and Zhai, 2013; Liu et al., 2019; Gao and Santosh, 2019; Yang and Santosh, 2020; among others ).

Zhao et al. (2001) divided the NCC into three major domains: the Western Block (WB), Eastern Block (EB), and the intervening Trans – North China Orogen (TNCO) (Fig. 1). Kusky and Li (2003) believed that the Archean NCC was composed of two major blocks separated by Central Orogenic Belt (COB).

Zhao et al. (2005)

further demarcated the Western Block as a collage of the Yinshan Block to the North and Ordos Block to the south, separated by the Khondalite Belt, which was subsequently designated as the Inner Mongolia Suture Zone (Santosh, 2010).

In deviation to these

popular models, Zhai and Santosh (2011) proposed that the Archean NCC was a collage of several microblocks including the Qianhuai Block (QH), Jiaoliao Block (JL), Xuchang Block (XCH), Xuhuai Block (XH), Alashan Block (ALS), Ordos Block (OR), Jining Block (JN) (Fig. 1). These microblocks are surrounded by Archean greenstone belts which are considered to represent zones of

multiple ocean closure.

Several Archean – Paleoproterozoic

‘complexes’ occur in between, such as the Wutai complex (WT), Fuping complex (FP), Lüliang complex (LL), and Zanhuang complex (ZH), among others, many of which represent subduction-related arcs (Tang and Santosh, 2018a; Gao and Santosh, 2019) (Fig. 1).

The Miyun complex is located to the north of Beijing, in the northeastern part of the NCC, along the boundary between the TNCO and EB (Fig. 1), where the major rock types exposed are Archean-Paleoproterozoic basement and 2.6-2.7 Ga greenstone belt (Fig. 1). The Archean metamorphic rocks are classified as the Miyun group, which are subdivided into the Shachang formation, Weiziyu formation, and Dacao formation from older to younger (Bureau of Geology and Mineral Resources of Beijing, 1991).

Our discovery of the ophiolite suite comes from a large open cast mine - the Shachang iron mine in the Shachang village, 16 km east of Miyun country (Fig. 2a). The major rock types in this area are grouped as the Archean Shachang formation, which are covered by Quaternary sediments, and Jurassic volcano-sedimentary rocks including tuffaceous breccia, with siltstone occurring in the northeast (Fang et al., 2016). Some Mesoproterozoic granitoid intrusions also occur in the area.

In the abandoned iron mine in Shachang, several open cast mining levels expose fresh vertical rock sections (Fig. 2b), as well as in the surrounding hillocks. We carried out detailed field work and sample collection during three field sessions which led to the reconstruction of a near-complete succession of the ophiolite including serpentinite, lherzolite, websterite, olivine bearing pyroxenite, gabbro, quartz monzonite, trondhjemite and BIF, together with highly dismembered metabasalts and dolerite. All the rocks are deformed and metamorphosed and have been sliced up as thrust sheets leading to repetitive packages of the rock suites similar to duplex structure in accretionary prisms. The serpentinite and lherzolite are greenish, containing altered coarse grains of olivine and occur as dismembered layers or fragmented blocks (Fig. 3a). Grayish green gabbro is the main section of the ophiolite with massive structure, coarse to medium texture in irregular contact with pyroxenite, monzonite, and trondhjemite (Fig. 3b, 3c, and 3d). The pyroxenite is dark greenish, coarse to medium grained, and occurs as dismembered layers at the base of the gabbro (Fig. 4a and 4b). The diorite is gray and medium-grained (Fig. 4c). The monzonite is leucocratic, medium grained and contains clots of amphiboles (Fig. 4d). The trondhjemite occurs as large, several meters thick sheets and is white colored with coarse to medium grained plagioclase and quartz (Fig. 4e). The BIF occurs as 5 to 8 meters thick layers and show alternating bands of magnetite and quartz (Fig. 4f). The

metabasalts associated with BIF bands are greenish, fine grained and altered with abundant chlorite and epidote. Thin (few cm thick) fine grained dolerite dykes occur as fragmented remnants.

The various rock types can be broadly divided into the following units: ultramafic unit, gabbroic complex which is the major unit, volcanic unit, and pelagic sediments (BIF). The sample locations and other salient details are given in Table 1. The ultramafic and cumulate rocks at the base of the Miyun ophiolite succession include serpentinite,

lherzolite,

olivine

clinopyroxenite,

and

olivine

websterite. Above this occurs the major unit including gabbro and diorite, together with monzonite, quartz monzonite, trondhjemite and dolerite dykes. The overlying volcanic unit comprising fine-grained metabasalts has been nearly completely removed as mine waste. Several thick bands of metamorphosed BIF which were tectonically deformed and intensely folded constitute the uppermost unit and are the main ore in the iron mine.

Due to government regulations on environmental protection, rapid land reclamation work is in progress in the area following mining operations for iron, which unfortunately is fast covering up the ophiolite sequence. Many of the lower units of the ophiolite succession were found to be already covered up with landfill during

our subsequent field visits. This rare and near-complete ophiolite suite of Miyun complex face the fate of being totally covered up in the near future.

3. Analytical techniques 3.1 Petrology Polished thin sections were prepared for petrographic study at the Peking University. Representative thin sections of all the rock types including serpentinite, lherzolite, olivine pyroxenite, gabbro, diorite, and trondhjemite were studied in detail using a petrological microscope at the China University of Geosciences Beijing.

3.2 Geochemistry The least altered and homogeneous portions of rock samples were crushed and powdered to 200 mesh for geochemical analyses after detailed petrographic observation. These were analyzed for wholerock major, trace, and rare earth element (REE) abundances using inductively coupled plasma atomic emission spectrometry (ICP-AES; Thermo Jarrel-Ash ENVIRO II) and ICP mass spectrometry (ICPMS; Perkin-Elmer Optima 3000) at the Activation Laboratories, Ltd., Canada. Analytical uncertainties range from 1 to 3% (Kim et al., 2012).

3.3 Zircon geochronology Zircon separation was performed at the Yu'neng Geological and Mineral Separation Survey Centre, Langfang City, Hebei Province, China, from crushed rock samples using magnetic and density separation methods. This was followed by handpicking of zircon grains under a binocular microscope. The grain morphology was studied using a binocular microscope under reflected light. The zircon grains were mounted onto an epoxy resin disk and polished to expose the internal texture and were examined under transmitted and reflected light. Suitable domains for U-Pb and Lu-Hf analyses were marked on the grains based on Cathode Luminescence (CL) images.

Zircon U-Pb analyses were carried out at the National Key Laboratory of Continental Dynamics of Northwest University, Xi’an following the analytical procedures described by Yuan et al. (2004). A laser ablation inductively coupled plasma spectrometer (LA-ICPMS) with the laser spot diameter and frequency of 30 μm and 10 Hz, respectively, was used. Standard zircon 91500 was employed for data correction and silicate glass NIST was used to optimize the instrument (Morel et al., 2008). The NIST 610 as an external standard and 29Si as an internal standard were also employed to

calibrate the U-Th-Pb concentration. The raw data were processed using the GLITTER program to calculate isotopic ratios and ages of 207

Pb/206Pb, 206Pb/238U, 207Pb/235U, respectively. And using the Errors

are quoted at the 2σ level. Concordia diagrams and weighted mean calculations were made using Isoplot 4.15 (Ludwig, 2003).

Zircon Lu-Hf analyses were performed on the same domains of the grains that are large enough for analyses from where U–Pb data were collected. The analysis was conducted using an ESI NWR193 laser-ablation microprobe, attached to a Neptune plus multicollector ICP–MS at the National Key Laboratory of Continental Dynamics of Northwest University, Xi’an, China. Instrumental conditions and data acquisition were as described by Wu et al. (2006) and Hou et al. (2007). The beam diameter was 40 μm depending on the size of the ablated domains. Helium was used as a carrier gas to transport the ablated sample from the laser-ablation cell to the ICP-MS torch via a mixing chamber mixed with Argon. In order to correct the isobaric interferences of 176Lu and 176

Lu/175Lu = 0.02658 and

176

176

Yb on

176

Hf,

Yb/173Yb = 0.796218 ratios were

determined (Chu et al., 2002). For instrumental mass bias correction, Yb isotope ratios were normalized to 172Yb/173Yb of 1.35274 (Chu et al., 2002) and Hf isotope ratios to

179

Hf/177Hf of 0.7325 using an

exponential law. The mass bias behavior of Lu was assumed to follow that of Yb, mass bias correction protocols followed those

described in Wu et al. (2006) and Hou et al. (2007). Zircon GJ1 was used as the reference standards during our analyses, with a weighted mean 176Hf/177Hf ratio of 0.282007 ± 0.000007 (2σ, n=36). This value is not distinguishable from a weighted mean

176

Hf/177Hf

ratio of 0.282000 ± 0.000005 (2σ) using a solution analysis method by Morel et al. (2008). The Hf depleted mantle model ages and Hf crustal model ages were also computed.

4. Results 4.1 Petrology The polished thin sections of representative samples collected from the iron mine were studied under a petrological microscope. All the rocks have undergone low to medium grade metamorphism (greenschist to amphibolite facies). 4.1.1 Serpentinite The basal serpentinite is rarely exposed in the Shachang mine, and our sample MMY 6-45 is from a disrupted band beneath the pyroxenite layer. The rock is dark greenish black and fine grained, and under thin section, serpentine (70-80%) and altered olivine (510%), occur together with accessory magnetite (Fig. 5a). The serpentinization shows typical mesh-type structure composed of tiny residual olivine grains traversed by reticulated veins of

serpentinite. Thin calcite veins occur along some fractures.

4.1.2 Lherzolite The lherzolite occurs as disrupted blocks in the bottom unit of the ophiolite. The rock is grayish-green and partly altered. A representative sample (MMY 6-1) is composed of clinopyroxene (20-25%), orthopyroxene (20-25%), phlogopite (25-30%) and olivine (15-20%), with magnetite as the accessory mineral (Fig. 5b). The phlogopite forms metasomatic filling between the early olivine and pyroxene. Olivine grains are broken and highly altered, with phlogopite forming along the cracks.

In some thin sections,

orthopyroxene is largely unaltered and occurs as coarse (2-3 mm) subhedral grains. 4.1.3 Olivine clinopyroxenite and websterite The clinopyroxenite (MMY 6-3A,3B,4) is dark green and coarse grained with clinopyroxene as the major mineral showing cumulate texture, with minor olivine grains.

The major minerals in the

websterite (MMY 6-2) are orthopyroxene (35-40%), clinopyroxene (35-40%), minor olivine (~5%) and zoisite (~5%). The orthopyroxene and clinopyroxene are medium-grained (0.2–1.5 mm) with idiomorphic grains. Zoisite dark bluish and fine-grained (Fig.5c).

4.1.4 Gabbro and diorite The gabbro-diorite association in the central unit is the major exposed rock type in the mine. The gabbro is dark-colored, coarse to medium-grained, and slightly foliated. The diorite is also coarse to medium grained with obvious foliation in hand specimen. A representative gabbro sample (MMY 6-8) is composed of plagioclase (35-40%), clinopyroxene (25-35%), and orthopyroxene (15-20%), with magnetite as accessories. The plagioclase is a tabular subhedral, showing polysynthetic twinning (Fig. 5d). Mineralogically, the rock corresponds to norite. 4.1.5 Quartz monzonite The monzonite is coarse to medium-grained and light grayish. In thin-section (MMY6-13), the rocks are composed of plagioclase (2530%), K-feldspar (10-15%), clinopyroxene (30-35%), hornblende (10-15%) and quartz (5%) (Fig. 5e). The clinopyroxene is partly altered. The plagioclase and K-feldspar show subhedral texture. Hornblende is slightly pleochroic, with a subhedral and granular texture and grain size of about 0.5 to 0.7mm. 4.1.6 Trondhjemite, metabasalts and dolerite The trondhjemite (samples MMY 6-14,15, 16) is strikingly white colored and medium to coarse grained and is composed of plagioclase (45-50%) and quartz (40-45%), with accessory minerals

including rutile, zircon and Fe-Ti oxides (up to 10%). The plagioclase laths are medium-grained (0.2–1 mm) and display polysynthetic twinning, with subhedral morphology. Quartz is fine to mediumgrained (0.1–1 mm) and shows anhedral morphology with wavy extinction.

The upper sequence of metabasalts has been largely removed as mine waste while recovering the closely associated BIF bands. These rocks are greenish and fine grained, composed of altered plagioclase, hornblende and chlorite, with high modal content of epidote. Fine grained and dark grayish-green fragmented dykes of dolerite occur within the gabbro and in thin section, these rocks are composed of plagioclase and hornblende with relict clinopyroxene.

4.1.6 Banded Iron Formation (BIF) The BIF constitutes the uppermost layer, but has been intensely deformed, folded and faulted and occur intermixed with the other lithologies as bands and layers ranging up to several meters thick. The rock has been metamorphosed to banded magnetite quartz (BMQ) although the original fine-scale layering with alternating bands of magnetite and quartz is often preserved (Fig. 5f). Brownish hematite is also associated.

4.2 Geochemistry A total of eighteen representative samples of the different rock types from

the

ophiolite

suite

(serpentinite,

lherzolite,

olivine

clinopyroxenite, olivine websterite, gabbro, diorite, monzonite, and trondhjemite) were analyzed for major, trace and rare earth elements, and the results are given in Supplementary Table 1. The samples used for geochemical analyses were carefully selected from relatively fresh and homogenous portions and altered domains were avoided.

4.2.1 Major and trace elements Major element oxides data of the ophiolite suit are projected on Total alkalis versus SiO2 (TAS) plot (Le Maitre, 1989) where the rocks show a large spread falling in the fields of peridot gabbro, gabbro, diorite, monzonite, and granite due to the large variation in SiO2 contents (39.20-73.55 wt.%) (Fig. 6a). The plots broadly define a magmatic evolution trend from ultramafic through mafic to felsic, with the diorite, monzonite, and trondhjemite probably representing the fractional crystallization products from a parent basaltic magma. The ultramafic rocks display sub-alkaline nature, whereas the gabbro and diorite are sub-alkaline and alkaline. Based on CIPW norm calculation from the bulk chemical data, we use the Ol-OpxCpx classification diagram (Streckeisen,1976), where the ultramafic

rocks (Fig. 6b) correspond to lherzolite (MMY 6-1), olivine clinopyroxenite (MMY 6-3A, 3B, 4) and olivine websterite (MMY 62).

In the Harker’s binary plots, the rocks from the Miyun ophiolite suite define a clear differentiation trend for most elements except for a few which show dispersed plots. Major element oxides like Fe2O3, MnO, MgO, CaO display moderate to strong negative trends against SiO2, whereas K2O and Na2O show positive trend (Fig. 7). The Al2O3 content in most of the ultramafic and mafic rocks are generally high (except for one sample), and some of these are similar to that of mantle peridotite.

On the AFM diagram (Beard,1986) (Fig. 8a), most of the gabbro and diorite samples fall in the tholeiitic basalt field and the monzonite falls in the calc-alkaline field. The gabbro and diorite fall in the arcrelated non-cumulative field whereas the lherzolite, olivine clinopyroxenite, and olivine websterite fall in the arc-related maficultramafic cumulate fields (except one sample which has higher FeOT value due to high modal content of magnetite).

In the TiO2-Al2O3-K2O triangular diagram (Fig. 8b), most of the gabbro, diorite and monzonite samples fall in the island arc and orogenic basalt field boundary. Geochemically, the gabbro and

diorite correspond to island arc tholeiite (IAT), and one gabbro and all monzonite samples plot in the field of oceanic arc basalt in TiO2MnO-P2O5 triangular diagram (Fig. 8c).

In the V vs. Ti diagram (Fig. 9a), all the rocks fall in the MORB field. The Th/Yb ratios range from 0.14 to 1.72 and Nb/Yb values are in the range of 1.09 to 20.46, with the rocks defining an evolution trend from EMORB mantle array to crust-mantle interaction (Fig. 9b; Pearce, 2008). The rocks from the ophiolite suite (except BIF) are characterized by high Mg# (27.81 to 75.24) with most of the ultramafic-mafic samples corresponding to mantle melts, and the intermediate and felsic rocks indicating interaction with crust (Heilimo et al., 2010) (Fig. 9c). On the (La/Yb)N VS (Yb)N diagram, the rocks plot in the field of island arc magmas (Martin, 1986) (Fig. 9d)

The Miyun samples show a wide range of total REE from 16.7-272.9 ppm. The two monzonites and three olivine clinopyroxenite samples contain moderate to high total REE (>100 ppm), whereas the other samples (excluding BIF) show low ΣREE (16.7-78.7 ppm). The ultramafic, mafic and intermediate rocks in the suite (lherzolite, olivine

clinopyroxenite,

olivine

websterite,

gabbro,

diorite,

monzonite) show either slight depletion or enrichment of LREE on the chondrite normalized REE patterns. The diorite exhibits

relatively narrow variation in LREE when compared to the gabbros and ultramafic samples (Fig. 10a). Overall, there is no marked REE fractionation in these rocks. The trondhjemite shows an obvious enrichment of LREE and also depletion of HREE with clearly positive Eu and negative Sm anomalies. In Fig. 10a, the MORB and OIB data from Sun and McDonough (1989) and Aldanmaz et al. (2008) and the Yishui ophiolite data from Santosh et al. (2016) are also plotted for comparison. The gabbros and diorites exhibit compositional similarity to E-MORB and N-MORB with patterns to the MORB from Neotethyan Ophiolite in western Turkey (Aldanmaz et al., 2008). Most of the trends from the Miyun suite are markedly similar to those of the Archean Yishui ophiolite (light yellow field on Figure 10a).

On the primitive mantle (Sun and McDonough, 1989) normalized multi-element spider diagram, the ultramafic and mafic samples show negative Nb and Ta anomalies and flat HREE. The monzonite lacks any Y anomaly. Also, the trondhjemite shows highly negative K anomaly and flat HREE with feeble positive Y anomalies (Fig. 10b). Most gabbro and diorite samples display compositional ranges broadly similar to E-MORB. The ultramafic samples including lherzolite and olivine clinopyroxenite also exhibit patterns similar to that of the gabbro and diorite, but with relatively lower HREE and more negative anomalies of Ta and Nb, as well as a positive

anomaly of Sr.

4.3 Geochronology 4.3.1 Zircon morphology and U-Pb geochronology Seven samples including lherzolite, olivine clinopyroxenite, gabbro, and trondhjemite were chosen for zircon separation and U-Pb as well as Lu-Hf analyses. The U-Pb analytical data are given in Supplementary Table 2.

Zircon grains from lherzolite sample MMY 6-1 are mostly colorless or light brown. They show irregular morphology with a length of around 100 μm, and length to width ratio of 1:1 to 2:1. In CL images (Fig.11a), they do not display any distinct core-rim structures. More than half of the grains show broken euhedral terminations with the remaining part showing banded zoning. Other grains possess chaotically zoned and sector zoned cores, with few cores showing clear magmatic oscillatory zoning. A total of 28 analyses were carried out on both magmatic domains and metamorphic domains of the zircon grains. The Th and U show variable contents ranging from 18.15 to 587.74 ppm and 34.87 to 1047.8 ppm respectively. The Th/U ratios show range from 0.03 to 1.17, with the higher values of the cores indicating magmatic crystallization (Supplementary

Table 2). The 28 analyses form three age groups within analytical error, with 207Pb/206 Pb spot ages ranging from 1811 to 2135 Ma. The concordant spots of the younger age group yield

207

Pb/206Pb

weighted mean age of 1843 ± 30 Ma (MSWD = 0.27; N = 8), the second group yield 207Pb/206Pb weighted mean age of 2237 ± 47 Ma (MSWD = 5.3; N = 6) and the older group yield 207Pb/206Pb weighted mean age of 2500 ± 12 Ma (MSWD = 1.02; N = 9) (Fig. 12a).

Zircon grains from the olivine clinopyroxenite sample MMY 6-3 are mostly colorless or light brown. They show elliptical morphology with a length of around 100 μm, and length to width ratio of 1:1 to 2:1. In CL images (Fig. 11b), they show relict cores of various sizes, bordered by thick brighter rims, which are considered to be metamorphic overgrowth. The cores show banded zoning. Some grains are not zoned and homogeneous. A total of 27 analyses were carried out on both magmatic core domains and metamorphic rim domains. The Th and U show variable contents ranging from 23.74 to 306.09 ppm and 25.57 to 627.56 ppm respectively. The Th/U ratios range from 0.17 to 2.27, the higher values in the cores corresponding to magmatic crystallization (Supplementary Table 2). The 27 analyses yield

207

Pb/206 Pb spot ages ranging from 2099 to

2582 Ma, and the concordant spots define

207

Pb/206 Pb weighted

mean age of 2495 ± 10 Ma (MSWD = 0.98; N = 11) (Fig. 12b). A slightly older concordant zircon grains show an age of 2582 Ma.

Zircon grains from gabbro sample MMY 6-8 are mostly colorless or light brown. They show long prismatic or slightly elliptical morphology with length in the range of 120-180 μm, and length to width ratio of 1:1 to 2:1. In CL images (Fig. 11c), some grains show core-rim structures with a dark core and light overgrowth mantles, which

are

considered

to

be

the

result

of

metamorphic

recrystallization. More than half of the grains are broken euhedral crystals. A total of 20 analyses were carried out on both magmatic core domains and metamorphic rim domains from zircon grains. The Th and U show variable contents ranging from 15.02 to 116.26 ppm and 15.67 to 180.59 ppm respectively. The Th/U ratios show a range of 0.59 to 1.25, the higher values of the core domains corresponding to growth from magma (Supplementary Table 2). The 20 spots show 207

Pb/206Pb ages ranging from 2222 to 2551 Ma, among which the

concordant spots yield 207Pb/206Pb weighted mean age of 2510 ± 19 Ma (MSWD = 0.21; N = 15) (Fig. 12c). Another group of concordant zircon grains shows ages around 2.3 Ga.

Zircon grains from quartz monzonite sample MMY 6-13 are mostly colorless or light brown. They are subhedral to oval with a length of around 100 μm, and length to width ratio of 1:1 to 2:1. In CL images (Fig. 11d). Most grains display distinct core-rim structures with bright rims around darker cores, typical of metamorphic overgrowth. The

relict cores show clear oscillatory zoning. A total of 17 analyses were carried out on both magmatic core domains and metamorphic rim domains and the results show Th and U ranging from 26.98 to 412.72 ppm and 25.84 to 520.24 ppm respectively. The Th/U ratios show a wide range from 0.59 to 2.26, with the cores displaying generally higher values (Supplementary Table 2). The U-Pb data define

207

Pb/206Pb ages ranging from 2403 to 2541 Ma. The

concordant spots yield 207Pb/206Pb weighted mean age of 2486 ± 21 Ma (MSWD = 1.19; N = 11) (Fig. 13a).

Zircon grains from trondhjemite sample MMY 6-14 are mostly colorless or light brown. They show subhedral to elliptical morphology with length from 100 to 150 μm and length to width ratio of 1:1 to 2:1. In CL images (Fig. 11e), they display distinct core-rim structures with lighter overgrowth rims, indicating metamorphic overgrowth around magmatic grains. The magmatic cores show distinct oscillatory zoning. A total of 54 analyses were made on both magmatic core domains and metamorphic rim domains from zircon grains. The Th and U rage from 24.36 to 749.54 ppm and 32.99 to 431.89 ppm respectively. The Th/U ratios are in the range of 0.52 to 2.06, with higher values for the core domains (Supplementary Table 2). The 54 analyses yield

207

Pb/206Pb ages ranging from 2400 to

2530 Ma, with the concordant spots showing a 207Pb/206Pb weighted mean age of 2476 ± 9.4 Ma (MSWD = 3.9; N = 54) (Fig. 13b).

4.3.2 Zircon Lu-Hf geochronology In situ Hf isotope analyses were carried out on zircon grains on the same spots or immediately adjacent domains from where the U–Pb data were gathered. A total of 33 zircon grains were analyzed for LuHf isotopes and the results are presented in Table 2 and plotted in Fig. 14a, with the TDM age showing a peak at 2670 Ma (Fig. 14b). Five zircon grains from lherzolite (MMY 6-1) show initial

176

Hf/177Hf

ratios of 0.2813209 to 0.2814032, with markedly positive εHf(t) values in the range of 4.4 to 5.7 (average 4.8) computed using the 207

Pb/206Pb age of individual zircon spots (2481–2512 Ma). The Hf

depleted model ages (TDM) are between 2572 to 2652 Ma (mean 2615 Ma (Fig. 14a).

Five zircon grains from olivine clinopyroxenite (MMY 6-3) show initial

176

Hf/177Hf ratios of 0.281275 to 0.2814716, with markedly

positive εHf(t) values in the range of 2.5 to 7.0 (average 5.1) computed using the

207

Pb/206Pb age of individual zircon spots

(2457–2522 Ma). The Hf depleted model ages (TDM) are between 2543 Ma and 2722 Ma (mean 2604 Ma) (Fig. 14a).

Only two zircon grains were analyzed from gabbro sample (MMY 68) due to small size and scarcity of grains, and the initial

176

Hf/177Hf

ratios of 14 to 0.2813712, with markedly positive εHf(t) values in the range of 2.6 to 5.9 (average 4.6) computed using the

207

Pb/206Pb

age of individual zircon spots (2509–2551 Ma). The Hf depleted model ages (TDM) are between 2607 Ma and 2735 Ma (mean 2657 Ma) (Fig. 14a).

Five zircon grains from quartz monzonite (MMY 6-13) show initial 176

Hf/177Hf ratios of 0.2812464 to 0.281363, with positive εHf(t)

values in the range of 0.3 to 5.5 (average 2.9) computed using the 207

Pb/206Pb age of individual zircon spots (2469–2504 Ma). The Hf

depleted model ages (TDM) are between 2591 Ma and 2787 Ma (mean 2717 Ma) (Fig. 14a).

Four zircon grains from trondhjemite (MMY 6-3) show initial 176

Hf/177Hf ratios of 0.2812912 to 0.281260, with markedly positive

εHf(t) values in the range of 1.5 to 6.5 (average 3.2) computed using the 207Pb/206Pb age of individual zircon spots (2474–2521 Ma). The Hf depleted model ages (TDM) are between 2567 Ma and 2741 Ma (mean 2683 Ma) (Fig. 14a).

5. Discussion 5.1 Rare preservation of a near-complete ophiolite succession Typical ophiolite assemblage includes serpentinized ultramafic rock, mafic intrusive complex, mafic lava, and marine sediment, representing fragments of oceanic crust and upper mantle, and reflecting magmatic differentiation in convergent margins (Kusky and Zhai, 2012; Dilek and Furnes, 2011; Santosh et al., 2016). Since ophiolites are usually emplaced at the surface, they are mixed with other rock types and tectonically destroyed or eroded, with less chance for older ophiolite suites to survive in ancient cratonic terranes. Therefore, the discovery of Archean ophiolites are of prime importance, and the findings have often led to debates and controversies (e.g., Kusky et al., 2001, Karson, 2001; Zhang et al., 2003a, b; Zhai et al., 2002, Zhao et al., 2007; Kusky and Zhai, 2012).

In the NCC, Kusky et al.（2001）reported one of the world’s oldest ophiolite complexes from the Dongwanzi area in northeastern Zunhua structural belt and dated the gabbros in the suite as ca. 2.50 Ga. Li et al. (2002) reported another ophiolite in southwestern Zunhua structural belt and considered that this occurrence preserves deeper parts of the Dongwanzi ophiolite complexes

reported by Kusky et al. (2001).

In a more recent study, Santosh et al. (2016) discovered a relatively well-preserved suprasubduction zone ophiolite succession from the Yishui complex, which is composed of lherzolite, pyroxenite, noritic and hornblende gabbro, leucogranite sheets, metavolcanic bands, and banded formation. They presented detailed petrologic, geochemical and geochronological data on various lithologies from this suite which indicate that the ophiolite was emplaced in the Neoarchean and represents the destructed oceanic lithosphere between Jiaoliao (JL) and Xuhuai microblocks in the NCC.

In

another study, Wang et al. (2019) described Neoarchean ophiolitic mélange from the Zunhua complex.

The above studies reveal the preservation of rare Neoarchean to early Paleoproterozoic ophiolites along the boundaries of various crustal blocks or microblocks in the NCC, attesting to subduction tectonics along convergent margins.

In the present study, the following salient features of the newly reported Miyun suite argue in favor of a typical ophiolite succession.

1) The lithological assemblage including serpentinite-lherzolite – olivine clinopyroxenite – olivine websterite – gabbro – diorite –

monzonite – trondhjemite – metabasalts – banded iron formation represents a typical oceanic crust and mantle section. Although there are compositional differences between some of the typical modern ophiolite suites such as those in Oman (Boudier and Nicolas, 1985), due to later deformation and metamorphism, the Miyun succession is broadly comparable with the definition of ophiolite given by Penrose field conference (1972).

2) Geochemically, the ultramafic rocks in this study correspond to peridotite mantle source. The gabbro-diorite suite defines an island arc tholeiite affinity with trace element discrimination identifying a MORB source, evolving into EMORB with limited crust-mantle interaction. 3) The REE patterns of the rocks from the Miyun ophiolite suite display mostly flat trends that are similar to OIB and E-MORB. Most of the geochemical features of the Miyun suite are closely similar to the Archean Yishui ophiolite suite reported by Santosh et al. (2016) as well as the Neo-Tethyan ophiolites in western Turkey. The geochemical trends displayed by gabbro and diorite suggest fractional crystallization of magma from a mantle source. The rocks show a crust-mantle interaction trend (Fig. 8b) and fall in the domains of mantle melts, or those that interacted with arc crust-reworked crust (Fig. 8c and 8d), suggesting subductionrelated setting. Dilek and Furnes (2011) classified the ophiolite to

subduction-related and subduction-unrelated types, and the Miyun suite in this study shows a close correlation with subduction-related, suprasubduction type as seen in the MORB normalized patterns (Fig. 15).

Combining the above features, we suggest that the Miyun ophiolite suite represents the remnants of suprasubduction ophiolite sourced from mantle magmas, emplaced in a subduction-related setting, and subsequently metamorphosed during the final continental assembly of the NCC.

5.2 Formation age and tectonic setting In this study, we obtained zircon U-Pb ages from the major rock types in the ophiolite suite from the Miyun complex. The lherzolite yielded three groups of

207

Pb/206Pb weighted mean ages at 2500 ±

2237 ± 47 Ma, and 1843 ± 30 Ma, the oldest of which compares with the ages from other rocks types in the suite, and younger ones correlate with subsequent thermal events. The majority of the concordant zircons from olivine clinopyroxenite show

207

Pb/206Pb

weighed mean age at 2495 ± 10 Ma with an older grain dated as 2582 Ma. The older zircon population of the gabbro yield 207Pb/206Pb weighted mean age at 2510 ± 19 Ma. The concordant zircon grains from quartz monzonite show

207

Pb/206Pb weighted mean age at

2486 ± 21 Ma, indicating a slightly younger rock, following magma

differentiation. The zircon grains from trondhjemite also show a similar age of 2476 ± 9.4 Ma.

The Lu-Hf isotope data of zircons is a good tracer to explore the magma sources and crustal evolution. In this study, the zircon ɛHf(t) values in all the rocks are distinctly positive, ranging between 0.3 and 7.0, and yield single-stage model ages (TDM) from 2544 to 2787 with the peak at 2670 Ma. The ɛHf(t) values of zircon grains in hornblendite, gabbro and leucogranite from the Yishui ophiolite (Santosh et al., 2016), are also dominantly positive, in the range of 0 to 5, based on which Neoarchean juvenile input was inferred. Liu et al. (2019) reported zircon Lu-Hf isotopes data of trondhjemite, metagabbro, pyroxenite and charnockite from Huangyang and Gaoling regions from Miyun area, where also, except for one grain, all the others show positive ɛHf(t) values in the range of 0.5 to 11.7. Wang et al. (2019) also reported positive ɛHf(t) values from zircon grains in biotite-plagioclase gneiss and syenogranite from the Zunhua ophiolite. Plots in the ɛHf(t) vs. age diagram (Fig. 14) clearly indicate that the magmas in all these cases were derived from depleted mantle (juvenile) source, contributing to new crustal additions associated with subduction in a multiple convergent regime.

The Miyun complex and surrounding region which fall along the

margin of the Eastern Block of the NCC at the junction with the Trans-North China Orogen seem to preserve important records of a subduction system that was initiated during late Neoarchean – early Paleoproterozoic

and

continued

to

late

Paleoproterozoic,

culminating in collision. We show the geographical distribution of some related rock suites and their compiled age data histograms in Fig. 16. 207

The Miyun ophiolite of present study shows peak

Pb/206Pb ages 2486 Ma and 1832 Ma corresponding to the timing

of the mantle magma differentiation and subsequent metamorphism. The Zunhua ophiolite mélange occurs to the east of our study area and the age data reported from here by Wang et al. (2019) show a peak at 2462 Ma, similar to the peak age for the Miyun ophiolite. Han et al. (2018) reported an Alaskan-type ultramafic intrusion from the Miyun complex, immediately north of our study area, in which zircon

207

Pb/206Pb ages of serpentinite, olivine orthopyroxene and

anthophyllite glimmerite indicate magma generation during 2300 to 2000 Ga and metamorphism at 1.84 Ga. Liu et al. (2019) obtained zircon

207

Pb/206Pb age of 2481 Ma, 2449 Ma and 2464 Ma from

metagabbro, pyroxenite, and trondhjemite from a mafic-ultramafic complex metamorphosed under high-grade (granulite facies) conditions, representing the root of a continental arc, to the NW of our present study area. In a regional tectonic framework, all the above rock types represent suprasubduction zone sequences, with Miyun and Zunhua representing accreted suites at the upper level,

the Alaskan-type ultramafic complex denoting slab melting and melt-peridotite interaction in the underlying mantle wedge, and the metamorphosed

mafic-ultramafic

intrusion

representing

differentiated slab melts underplated beneath the arc root (Fig. 17). The ages ranging from ca. 2500 to 2000 Ma among these suites indicate magmatic processes in a long-lasting subduction system, culminating in collision and metamorphism at ca. 1.84 Ga associated with the final assembly of continental blocks and cratonization of the NCC. The nearly 700 m.y. of subduction and accretion is analogous to that in the Central Asian Orogenic Belt, where multiple subduction and prolonged and accretion lasted for more than 800 m.y. (Xiao and Santosh, 2014)

The peak magmatic age of 2462 Ma from the Miyun ophiolite is identical to the peak age of 2478 Ma reported from the ophiolites in Yishui along the southern margin if the Jiao-Liao block, indicating that multiple subduction zones operated almost coevally along the margins of the various microblocks in the NCC.

The NCC preserves crustal records dating from Paleoarchean, and recent models consider that in the early Precambrian, the craton was composed of several microblocks separated by intervening ocean basins (Zhai and Santosh, 2011). These microblocks were welded by 2.75–2.6 Ga and ∼2.5 Ga granite-greenstone belts,

marking one of the earlier Wilson cycles in the NCC (Tang and Santosh, 2018b). The lithological assemblages in the greenstone belts include volcano-sedimentary sequences, subduction-collision related granitoids and bimodal volcanic rocks interlayered with minor komatiites and calc-alkalic volcanic rocks.

The volcano-

sedimentary successions and granitoids in the late Neoarchean granite-greenstone belts display formation ages of 2.60–2.48 Ga, followed by metamorphism at 2.52–2.47 Ga. As summarized by Tang and Santosh (2018b), the first phase of cratonization in the NCC during Neoarchean involved two stages of tectonic processes along the 2.75–2.6 Ga and ∼2.5 Ga greenstone belts, the former involving

plume–arc

interaction

process,

and

the

latter

characterized by oceanic lithospheric subduction, with or without arc-plume interaction. A recent study on the Wutai complex in NCC revealed that the accreted oceanic crust in this region, overlain by sulfidic BIF layers, is as old as 2.9 Ga (Gao and Santosh, 2019), suggesting

that

the

subduction

system

operated

since

Mesoarchean. There is clear evidence for continental collision during Archean – Paleoproterozoic transition with ca. 2.5 Ga highgrade metamorphism under high-pressure and high-temperature conditions as recorded from granulite facies assemblages distributed along the boundaries of the microblock boundaries (e.g., Yang et al., 2016; Tang et al., 2019). This marks the culmination of an early Wilson cycle that involved multiple ocean closure along

microblock boundaries (Zhai and Santosh, 2011). Subsequently, the amalgamated larger crustal blocks and the arc complexes in between started assembling, in a more modern-style plate tectonic process generating the latest Neoarchean – Early Paleoproterozoic Miyun, Zunhua and Yishui type ophiolites, and several other early Paleoproterozoic supracrustal sequences including the Fangmayu Alaskan type intrusions, and subduction-related underplated arc root mafic-ultramafic complexes. This subduction system ended by the final assembly of crustal blocks and accretion of the intervening arc complexes during the latest Paleoproterozoic, accompanied by high-grade metamorphism ranging up to high-pressure and ultrahigh temperature conditions, marking the final cratonization of the NCC.

6. Conclusion  The

newly

identified

serpentinite,

lherzolite,

olivine

clinopyroxenite, olivine websterite, gabbro, dolerite, diorite, monzonite, trondhjemite, metabasalt, and BIF association from the Miyun complex in this study represents the remnants of a typical suprasubduction zone ophiolite sequence  Geochemical features of the ultramafic rocks indicate mantle source magma. The gabbro and diorite display MORB and IAT characteristics. The rocks show E-MORB affinity with a crust-

mantle interaction trend, with typical features of an arc-related system.  Zircon U-Pb analyses yielded

207

Pb/206Pb weighted mean ages

of 2500 ± 12 Ma, 2237 ± 47 Ma and 1843 ± 30 Ma for lherzolite, 2495 ± 10 Ma for olivine clinopyroxenite, 2510 ± 19 Ma for gabbro, 2486 ± 21 Ma for quartz monzonite, 2476 ± 9.4 Ma for trondhjemite. The oldest zircon grain in gabbro show 207Pb/206Pb age of 2582 Ma. The combined zircon U-Pb age data show peaks at 2486 Ma and 1832 Ma corresponding to magma emplacement

and

differentiation,

and

subsequent

metamorphism. Zircon Lu-Hf data show markedly positive ɛHf(t) values in all cases, ranging from 0.35 to 7.02 with the peak of the TDM age of 2670 Ma, suggesting Neoarchean depleted mantle (juvenile) source.  The occurrence of similar ophiolite suites in other parts of the NCC, particularly along the margins of microblocks, together with other suprasubduction zone complexes surrounding the Miyun area suggest that a major subduction system prevailed during Paleoproterozoic with the Wilson cycle culminating in collisional orogeny in late Paleoproterozoic, marking the final cratonization of the NCC.

Acknowledgments We thank Prof. Guochun Zhao, Editor-in-Chief and two anonymous referees for

their encouraging comments that helped in improving this paper. We are grateful to our team members Haidong Liu and Yuesheng Han for accompanying us during field work and sample collection. Sanghoon Kwon appreciates the partial support by the NRF-2017R1A6A1A07015374 (Multidisciplinary study for assessment of large earthquake potentials in the Korean Peninsula) and NRF-2019R1A2C1002211 through the National Research Foundation of Korea funded by the Ministry of Science and ICT, Korea. This study was funded by Foreign Expert grant from the China University of Geosciences Beijing, China, and from the Shaanxi 100 Talent programme fund from NW University, Xi’an to M. Santosh

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from Yishui Complex in the North China Craton. Gondwana Research. 38, 1-27. Tang, L., and Santosh, M., 2018a. Neoarchean-Paleoproterozoic terrane assembly and Wilson cycle in the North China Craton: an overview from the central segment of the Trans-North China Orogen. Earth-science reviews. 182, 1-27. Tang, L., Santosh, M., 2018b. Neoarchean granite-greenstone belts and related ore mineralization in the North China Craton: An overview. Geoscience Frontiers 9, 751-768. Tang, L., Santosh, M., Tsunogae, T., 2019. Petrology, phase equilibria modelling and zircon U-Pb geochronology of garnetbearing charnockites from the Miyun area: Implications for microblock amalgamation of the North China Craton. Lithos 324-325, 234-245. Wilson, J. T., 1966. Did the Altantic close and then re-open?. Nature. 211,676-681. Wu, F. Y., Yang, Y. H., Xie, L. W., 2006. Hf isotopic compositions of the standard zircons and baddeleyites used in U-Pb geochronology. Chem. Geol. 234, 105–126. Wang, J. P., Li, X. W., Ning, W. B., Kusky, T. M., Wang, L., Polat, A., and Deng, H., 2019. Geology of a Neoarchean suture: Evidence from Zunhua ophiolitic mélange of the Eastern Hebei Province, North China Craton. The Geology Society of America. doi.org/10.1130/B35138.1

Xiao, W.J., Santosh, M., 2014. The western Central Asian Orogenic Belt:

A window to accretionary orogenesis and continental

growth. Gondwana Research 25, 1429-1444. Yang, C.X., Santosh, M., 2020. Ancient deep roots for Mesozoic world-classs gold deposits in the north China craton: an integrated genetic perspective. Geoscience Frontiers 11, 203214. Yang, Q.Y., Santosh, M., Tsunogae, T., 2016.

High-grade

metamorphism during Archean–Paleoproterozoic transition associated with microblock amalgamation in the North China Craton:

Mineral

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zircon

geochronology. Lithos 263, 101-121. Yuan, H. L., Gao, S., Liu, X. M., Li, H. M., Gunther, D., Wu, F. Y., 2004. Accurate U-Pb age and trace element determination of zircon by laser ablation-inductively coupled plasmamass spectrometry. Geostand. Geoanal. Res. 28, 353–370. Zhao, C. H., 1989. The atk diagram of basic-intermediate volcanic rocks and tectonic environment. Geological Science and Technology Information. 4, 1-5. Zhao, G. C., Wilde, S. A., Cawood, P. A., and Sun. M., 2001. Archean blocks and their boundaries in the North China Craton:

lithological, geochemical, structure and P-T path constraints and tectonic evolution. Precambrian Research. 107, 45-73. Zhao, G. C., Sun, M., Wilde, S. A., and Li, S. Z., 2005, Late Archean to Paleoproterozoic evolution of the North China Craton: key issues revisited. Precambrian Research. 136, 177-202. Zhao, G. C., Wilde, S. A., Li, S. Z., Sun, M., Grant, M. L., Li, X. P., 2007. U-Pb zircon age constrants on the Dongwanzi ultramaficmafic body, North China Craton, confirm it is not an Archean ophiolite. Earth and Planetary Science Letters, 255, 85-93. Zhai, M. G., Zhao, G. C., and Zhang, Q., 2002. Is the Dongwanzi complex an Archean ophiolite. Science. 295, 923-923. Zhang, Q., Ni, Z. Y., and Zhai, M. G., 2003a. Comment on Archean Ophiolite in Eastern Hebei. Earth Science Frontiers (China University of Geoscience, Beijing). 10(4), 429-437. ( in Chinese with English abstract). Zhang, Q., Zhou, G. Q., and Wang, Y., 2003b. Distribution of Chinese ophiolite, age, and its forming environment. Acta Petrologica Sinica. 19 (1), 1-8. (in Chinese with English abstract) Zhai, M. G., and Santosh, M., 2011. The early Precambrian odyssey of the North China Craton: A synoptic overview. Gondwana Research. 20, 6-25. Zhao, G. C., and Zhai, M, G., 2013. Lithotectionic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Research. 23, 1207-1240.

Figure captions Figure 1 Geological and tectonic framework of the North China Craton, showing the basement rocks, crustal blocks, arc complexes, and greenstone belts. The Precambrian ophiolite locations are also shown (modified from Zhao et al., 2005 and Santosh, 2010; the classification scheme of microblocks is from Zhai and Santosh, 2011; locations of the complexes are from Zhao et al., 2001; locations of the ophiolite complexes are from Kusky and Zhai, 2012, Santosh et al., 2016 and Wang et al., 2019).

Figure 2 (a) Geological map and sample locations of the Miyun area (modified after Bureau of geology and mineral resources of Hebei province, 1989). (b) Google earth map of Shachang iron mine.

Figure 3 Representative field photographs. (a) Serpentinite; (b) pyroxenite and gabbro; (c) gabbro and monzonite; (d) gabbro and trondhjemite. Figure 4 Representative field photographs. (a) and (b) Pyroxenite; (c) diorite; (d) monzonite; (e) trondhjemite; (f) BIF-Banded Iron Formation. Figure 5 Representative photomicrographs of the rocks analyzed in this study. (a) Serpentinite showing reticulate structure with Srp + Ol (MMY 6-45); (b) highly altered lherzolite with olivine + orthopyroxene

+ clinopyroxene + phlogopite (MMY 6-1); (c) slightly altered websterite with orthopyroxene + clinopyroxene + zoisite (MMY 6-2) ; (d) gabbro with orthopyroxene + clinopyroxene + plagioclase (MMY 6-8) ; (e) altered quartz monzonite with hornblende + plagioclase + K-feldspar (MMY 6-13) ; (f) BIF under reflected light (MMY 6-20). Mineral abbreviations: Spr- Serpentine; Cpx- clinopyroxene; OlOlivine; Phl- phlogopite; Zo- zoisite; Pl- plagioclase; Opxorthopyroxene; Kfs- K-feldspar; Hbl- hornblende; Qtz- quartz; MtMagnetite. Figure 6 (a) Total alkalis versus SiO2 (TAS) plot (Le Maitre, 1989). (b) classification diagram by Ol-Opx-Cpx for ultramafic rocks MMY 6-1,2,3A,3B,4 (Streckeisen,1976).

Figure 7 Major oxide plots against SiO2 on Harker's binary diagrams. Figure 8 (a) AFM diagram. Field of cumulate and non-cumulate mafic-ultramafic rocks are from Beard (1986). (b) TiO2*10-Al2O310K2O triangular diagram indicating magma source of mafic and intermediate volcanic rocks, I-oceanic basalt; II-continent basalt, IIIisland arc and orogenic basalt (after Zhao, 1989). (c) TiO2/10-MnOP2O5 triangular diagram (after Mullen, 1983). Figure 9 (a) Ti vs V/1000 plot (after Shervais, 1982) (b) Th/Yb vs Nb/Yb (Pearce, 2008) binary plot for the ophiolite suit. (c) Mg# versus SiO2 (modified after Heilimo et al., 2010) for characterizing the ophiolite suits. (d) (La/Yb)N versus (Yb)N plot (Martin, 1986)

characterizing of the studied rocks. Figure 10 (a) Chondrite normalized REE diagram and (b) Primitive mantle normalized trace element abundance patterns (Sun and McDonough, 1989). The field of Archean Yishui ophiolite is from Santosh et al. (2016) and that western Turkey is from Aldanmaz et al. (2008). Figure 11 Representative Cathodoluminescence (CL) images of zircon grains from (1) MMY 6-1, lherzolite; (2) MMY 6-3, olivine clinopyroxenite; (3) MMY 6-8, gabbro; (4) MMY 6-13, quartz monzonite; (5) MMY 6-14, trondhjemite. Zircon U–-Pb ages (Ma) and εHf(t) values are also shown. The smaller yellow circles indicate spots of LA-ICP-MS U–-Pb dating, whereas the larger red circles represent locations of Hf isotopic analyses. Figure 12 (a) U-Pb Concordia plots of zircon U–Pb analyses from lherzolite, sample MMY 6-1; (b) U-Pb Concordia plots of zircon U– Pb analyses from olivine clinopyroxenite, sample MMY 6-3; (c) UPb Concordia plots of zircon U–Pb analyses from gabbro, sample MMY 6-8. Figure 13 (a) U-Pb Concordia plots of zircon U–Pb analyses from quartz monzonite, sample MMY 6-13; (b) U-Pb Concordia plots of zircon U–Pb analyses from trondhjemite, sample MMY 6-14;

Figure 14 Zircon Hf isotopic evolution diagram compared with the previous study. CHUR- Chondritic Uniform Reservoir. Previous data

include hornblendite, gabbro, and leucogranite from Santosh et al. (2016); trondhjemite, metagabbro, pyroxenite and charnockite from Liu et al. (2019); biotite – plagioclase – quartz gneiss and syenogranite from Wang et al. (2019). (b) TDM Kernel density distribution of age data. Figure

15

Mid-ocean-ridge-basalt

(MORB)-normalized multi-

element diagrams (the subduction-unrelated and related patterns, the normalizing value from Dilek and Furnes, 2011). Abbreviations: IAT- Island Arc Tholeiite; MOR- Mid-Ocean Ridge; Cont. – Continent; PP- Plume Proximal; PD- Plume Distal; TP- Trench Proximal; SSZSuprasubduction zone; BA-FA- Backarc to Forearc; OBA- Oceanic Backarc; CBA- Continental Backarc; Volc.- Volcanic.

Figure 16 Geographical distribution of suprasubduction zone complexes around Miyun complex as reported in this study and other publications, together with zircon U-Pb data plots from these locations using the Kernel density distributions. The previous studies include serpentinite, olivine orthopyroxene and anthophyllite glimmerite from Han et al. (2018); metamorphosed mafic-ultramafic complex from a differentiated arc root from Liu et al. (2019); and biotite – plagioclase – quartz gneiss and syenogranite from ophiolitic mélange reported by Wang et al. (2019). Figure 17 Schematic tectonic model illustrating the early Paleoproterozoic

subduction

system

that

generated

the

suprasubduction zone complexes in Miyun and surrounding regions including ophiolites (this study), ophiolitic mélange (Wang et al., 2019), arc root mafic-ultramafic complex (Liu et al., 2019) and Alaskan-type ultramafic complex (Han et al., 2018).

Table captions Table1 Summary of location, rock type sand general mineralogy of samples in this study from the Miyun ophiolite complex.

Table 2 Zircon Lu-Hf data on ophiolite lithologies from the Miyun ophiolite complex.

Table 1. Summary of location, rock type sand general mineralogy of samples in this study from the Miyun ophiolite complex. Sample No.

GPS coordinates

Rock type

Assemblage

MMY-6/1 MMY6/3A,3B MMY-6/4

Ultramafic rock

Opx Cpx Ol

Ultramafic rock

Opx Cpx Ol

Ultramafic rock

MMY-6/2

Websterite

MMY-6/5

monzonite

Opx Cpx Ol Opx Cpx Ol Zo Mag Opx Pl Kfs

MMY-6/6

Diorite

Opx Cpx Hbl

MMY-6/9

Diorite

Opx Cpx

MMY-6/11

Diorite

Opx Cpx

Diorite

Opx Cpx

Gabbro

Opx Cpx Pl

Gabbro

Opx Cpx Pl Opx Cpx Pl Opx Pl Kfs Qtz

MMY-6/14

Gabbro Quartz monzonite Trondhjemite

MMY-6/15

Trondhjemite

Pl Qtz

MMY-6/16

Trondhjemite

Pl Qtz

MMY-6/20

BIF

Qtz Mag

MMY-6/21

Felsic dyke

Qtz Pl Bt

MMY 6-30

Ultramafic rock

Cpx Pl

MMY 6-31

BIF

Qtz Mag

MMY 6-32

BIF

Qtz Mag

MMY 6-45

Serpentinite

Srp

MMY-6/12 MMY-6/7 MMY-6/8 MMY-6/10 MMY-6/13

Locality

Shachan g iron mine at Shouyun national mine park

N

E

40°22′

117°01′

31.65″

04.45″

Pl Qtz Bt

Table 2. Zircon Lu-Hf data on ophiolite lithologies from the Miyun ophiolite complex. Sp A 2 176Yb/ 2σ 2σ 2σ ɛH ɛH 176 176 176 Hf/ Lu/ Hf/ ot ge σ 177 f(0 f(t 177 177 177 Hf Hf Hf Hfi ( No ) ) M . a) M M Y6108 M M Y6123 M M Y6125 M M Y6127 M M Y6130 M M Y6307 M M Y6308 M M Y6313 M M Y6321 M M Y6332 M M Y6809 M

C

2 σ

T 2 D σ

(M TDMa)

2 σ

2 5 0 9

1 9

M

( M a) 26 8 09 5

24 81

3 0.0114 7 60

0.00 0039

0.000 0.00 303 0001

0.281 351

0.00 0032

0.281 336

50. 3

4.9

1 . 2

25 13

3 0.011 4 383

0.00 0063

0.000 0.00 360 0002

0.281 0.00 321 0051

0.281 304

51. 3

4.4

1 . 9

26 1 52 3 6

2 5 4 4

3 0

24 31

3 0.004 6 823

0.00 0084

0.000 0.00 168 0002

0.281 0.00 372 0039

0.281 364

49. 5

4.7

1 . 4

25 1 72 0 3

2 4 6 2

2 3

25 06

3 0.004 5 842

0.00 0033

0.000 0.00 139 0001

0.281 0.00 349 0032

0.281 343

50. 3

5.7

1 . 2

25 8 99 5

2 5 2 7

1 9

24 88

3 0.047 4 354

0.00 0734

0.001 0.00 848 0031

0.281 0.00 403 0059

0.281 315

48. 4

4.3

2 . 2

26 1 43 6 5

2 5 2 3

3 7

24 64

3 0.007 4 826

0.00 0154

0.000 0.00 277 0006

0.281 0.00 398 0041

0.281 385

48. 6

6.2

1 . 5

25 1 43 0 9

2 4 8 1

2 4

25 08

3 0.0139 3 93

0.00 0240

0.000 0.00 472 0004

0.281 275

0.00 0039

0.281 252

52. 9

2.5

1 . 5

27 1 22 0 5

2 5 5 6

2 3

25 22

3 0.0126 4 49

0.00 0304

0.000 0.00 507 0013

0.281 395

0.00 0055

0.281 371

48. 7

7.0

2 . 1

25 1 62 4 8

2 5 3 1

3 3

24 82

3 0.0496 3 12

0.00 1324

0.001 0.00 887 0060

0.281 472

0.00 0053

0.281 382

46. 0

6.5

2 . 0

25 1 50 5 0

2 4 9 7

3 3

24 57

3 0.023 3 211

0.00 1248

0.000 0.00 863 0041

0.281 0.00 354 0059

0.281 314

50. 1

3.5

2 . 2

26 1 42 6 0

2 4 9 8

3 6

25 22

3 0.041 7 205

0.00 0476

0.001 0.00 156 0014

0.281 0.00 301 0045

0.281 245

52. 0

2.6

1 . 7

27 1 35 2 4

2 5 6 9

2 8

25

3 0.021

0.00

0.000 0.00

0.281 0.00

0.281

-

5.9

1

26 1

2

2

M Y6811 M M Y6818 M M Y6819 M M Y6820 M M Y613 06 M M Y613 10 M M Y613 13 M M Y613 26 M M Y613 31 M M Y614 01 M M Y614 03 M M

51

9

25 12

297

0188

597

0003

3 0.026 7 825

0.00 0516

0.000 0.00 773 0016

25 09

3 0.019 9 182

0.00 0077

25 25

3 0.0250 6 31

24 90

349

0042

320

50. 3

. 6

30 1 3

5 6 8

5

0.281 0.00 364 0038

0.281 327

49. 8

5.2

1 . 4

26 1 22 0 4

2 5 3 6

2 3

0.000 0.00 578 0005

0.281 0.00 303 0034

0.281 276

51. 9

3.3

1 . 3

26 9 91 1

2 5 5 0

2 0

0.00 0476

0.000 0.00 695 0011

0.281 371

0.00 0035

0.281 338

49. 5

5.9

1 . 3

26 9 07 4

2 5 4 3

2 1

3 0.0095 4 15

0.00 0037

0.000 0.00 289 0002

0.281 363

0.00 0027

0.281 349

49. 8

5.5

1 . 0

25 7 91 2

2 5 1 2

1 6

24 81

3 0.0259 3 09

0.00 0356

0.000 0.00 751 0007

0.281 295

0.00 0036

0.281 260

52. 2

2.1

1 . 3

27 9 14 6

2 5 3 3

2 1

24 86

3 0.0239 3 42

0.00 0338

0.000 0.00 851 0009

0.281 246

0.00 0035

0.281 206

54. 0

0.3

1 . 3

27 9 87 4

2 5 5 3

2 1

25 04

3 0.0242 3 48

0.00 0232

0.000 0.00 869 0008

0.281 332

0.00 0041

0.281 290

50. 9

3.7

1 . 5

26 1 73 1 2

2 5 4 2

2 5

24 69

3 0.0137 5 75

0.00 0146

0.000 0.00 500 0005

0.281 301

0.00 0068

0.281 278

52. 0

2.5

2 . 6

26 1 88 8 4

2 5 1 8

4 1

24 90

3 0.038 3 537

0.00 0187

0.001 0.00 083 0006

0.281 0.00 354 0037

0.281 303

50. 1

3.9

1 . 4

26 1 57 0 2

2 5 2 7

2 3

25 05

3 0.012 3 352

0.00 0103

0.000 0.00 365 0002

0.281 0.00 302 0028

0.281 285

52. 0

3.6

1 . 1

26 7 78 6

2 5 4 3

1 7

24 93

3 0.0267 4 12

0.00 0190

0.000 0.00 878 0006

0.281 296

0.281 254

52. 2

2.2

2 . 0

27 1 22 4 2

2 5 4

3 2

0.00 0052

Y614 12 M M Y614 16 M M Y614 20 M M Y614 27 M M Y614 36 M M Y614 36 M M Y614 46 M M Y614 51 M M Y614 54

4

25 05

3 0.0191 5 83

0.00 0338

0.000 0.00 587 0007

0.281 295

0.00 0041

0.281 267

52. 2

2.9

1 . 5

27 1 03 1 0

2 5 4 9

2 4

24 88

3 0.006 8 832

0.00 0085

0.000 0.00 238 0003

0.281 0.00 321 0043

0.281 309

51. 3

4.1

1 . 6

26 1 45 1 6

2 5 2 3

2 6

25 02

3 0.034 5 084

0.00 0274

0.000 0.00 924 0004

0.281 0.00 413 0038

0.281 368

48. 1

6.5

1 . 4

25 1 67 0 5

2 5 1 7

2 3

24 81

3 0.036 4 921

0.00 0055

0.001 0.00 057 0004

0.281 0.00 291 0037

0.281 241

52. 4

1.5

1 . 4

27 1 41 0 2

2 5 3 9

2 3

24 69

3 0.0308 6 42

0.00 0162

0.000 0.00 869 0006

0.281 332

0.00 0041

0.281 291

50. 9

3.0

1 . 5

26 1 72 1 1

2 5 1 4

2 5

24 78

3 0.0333 5 87

0.00 0126

0.000 0.00 965 0006

0.281 303

0.00 0034

0.281 257

52. 0

2.0

1 . 3

27 9 19 4

2 5 3 1

2 1

24 74

3 0.0443 6 16

0.00 1340

0.001 0.00 270 0027

0.281 339

0.00 0045

0.281 279

50. 7

2.7

1 . 7

26 1 91 2 5

2 5 2 2

2 8

24 99

3 0.036 5 295

0.00 0232

0.001 0.00 021 0003

0.281 0.00 294 0039

0.281 246

52. 3

2.0

1 . 5

27 1 34 0 7

2 5 5 1

2 4

Declaration of competing interest

The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

Highlights  Discovery of a suprasubduction zone ophiolite suite with nearcomplete stratigraphy  Geochemical features suggest mantle source and MORB-IAT setting  Age peaks at 2486 Ma and 1832 Ma correspond to emplacement and metamorphism  Markedly positive ɛHf(t) values suggest Neoarchean depleted mantle (juvenile) source.  Evaluation of Archean- Paleoproterozoic subduction system in the NCC