Amalgamation between the Yangtze and Cathaysia blocks in South China: Evidence from the ophiolite geochemistry

doi:10.1016/j.precamres.2020.105893

Precambrian Research

Volume 350, November 2020, 105893

https://doi.org/10.1016/j.precamres.2020.105893 Get rights and content

Highlights

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The Xiwan peridotites underwent an initial melt extraction at 1.8–2.1 Ga.
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The Fuchuan peridotites were formed by second stage melting of a depleted mantle induced by slab fluids.
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The ophiolites were formed in a subduction-related setting.

Abstract

Neoproterozoic ophiolites in the southeastern margin of the Yangtze Block record tectonic evolution of South China. The ∼1.0 Ga Xiwan ophiolite and the ca. 830 Ma Fuchuan ophiolite indicate a long-term assembly of the Yangtze and Cathaysia blocks during the Neoproterozoic time. Peridotites from the Xiwan ophiolite show high Al₂O₃ (1.24–2.67 wt%) and low MgO contents (39.61–44.26 wt%), similar to the abyssal and back-arc peridotites that experienced low degrees of partial melting. Their U-shaped REE patterns and HFSE enrichment indicate weak melt metasomatism. Whole rock ¹⁸⁷Re/¹⁸⁸Os (0.09–0.29) and ¹⁸⁷Os/¹⁸⁸Os ratios (0.11526–0.12193) yield a melt-extraction age of 1.8–2.1 Ga. However, peridotites from the Fuchuan ophiolite are more refractory and have low Al₂O₃ (0.51–0.95 wt%) and high MgO contents (43.99–48.24 wt%), similar to the forearc peridotites that underwent high degrees of melt extraction. Their ¹⁸⁷Re/¹⁸⁸Os (0.01–1.08) and ¹⁸⁷Os/¹⁸⁸Os (0.11852–0.12867) variations may have resulted from fluxed melting induced by the subduction-related fluids. The peridotites, in combination with the overlying mafic oceanic crustal rocks, suggest that the Xiwan and Fuchuan ophiolites are SSZ-type ophiolites which were formed in back-arc and forearc settings, respectively, followed by the collision between the Yangtze and Cathaysia blocks at ca. 830 Ma.

Introduction

Ophiolites in orogenic belts represent fragments of ancient oceanic lithosphere (Dewey and Bird, 1971, Nicolas, 1989, Lister and Forster, 2009, Dilek and Furnes, 2011), and record whole or part of geological history related to the tectonic evolution of oceanic basin during the Wilson cycle (Moores and Vine, 1971). They carry unique information of the disappeared oceans, thus are important for the paleo-plate reconstruction (Taylor and McLennan, 1995, Dilek and Furnes, 2011, Hébert et al., 2012, Kusky et al., 2018). A complete ophiolite succession includes, from bottom to top, mantle peridotite, ultramafic–mafic cumulate, isotropic gabbro, sheeted dike, pillow lava associated with minor plagiogranite that are overlain by pelagic sediments (Moores, 2002, Dilek and Robinson, 2003, Kusky, 2004, Pearce, 2014). Ophiolites are generally classified as supra-subduction zone (SSZ) and mid-ocean ridge (MOR) types (Dilek and Furnes, 2011, Pearce, 2014), and peridotite from the SSZ-type ophiolite is more refractory than that from the MOR-type ophiolite (Liu et al., 2019).

The Neoproterozoic Jiangnan Fold Belt is a suture zone that represents the assembly between the Yangtze and Cathaysia blocks. Two ophiolite suites have been recognized at the Xiwan and Fuchuan regions in the eastern segment of the Jiangnan Fold Belt (Figs. 1 and 2a). Zircon U-Pb dating revealed that they were formed at ∼1.0 Ga and ∼830 Ma, respectively (Li et al., 1994, Li et al., 2017, Ding, 2008, Gao et al., 2009, Zhang et al., 2012a, Zhang et al., 2013, Wang et al., 2015a, Sun et al., 2018). The Xiwan ophiolite is classified as an SSZ-type ophiolite, which was proposed to have been formed in various tectonic settings, including forearc basin (Sun et al., 2018), back-arc basin (Zhou et al., 1989, Li et al., 1997, Wang et al., 2015a), island arc (Xing, 1990, Chen et al., 1991), as well as ridge-subduction (Zhang et al., 2015). Similarly, the Fuchuan ophiolite also displays subduction-related lithological and geochemical features (Ding, 2008, Zhang et al., 2012a, Sun et al., 2018). The coeval bimodal dike swarms, gabbro, spilite, granite and sedimentary sequences suggest that the Fuchuan ophiolite was probably formed in forearc (Zhang et al., 2013) or back-arc settings (Zhang et al., 2012a, Sun et al., 2018). Compared with basaltic to granitic rocks, peridotite can provide direct information for formation age, petrological and geochemical features, as well as evolutionary history of the mantle source (Irvine et al., 2001, Yuan et al., 2007, Schulte et al., 2009, Harvey et al., 2010, Liu et al., 2012, Liu et al., 2019, Ionov et al., 2015, Hu et al., 2020). Although extensive studies have been carried out on the mafic rocks of the ophiolites in the eastern Jiangnan Fold Belt, the mantle peridotites have not been well addressed. The nature of the mantle source, the tectonic settings and emplacement dynamics of the ophiolites are still unclear.

In this paper, we present whole-rock major and trace elements and Re-Os isotopes for the mantle peridotites from the above two sets of ophiolites, as well as zircon U-Pb ages for the granite and gabbro from the Fuchuan ophiolite. The new results show that the Xiwan and Fuchuan ophiolites are SSZ-type ophiolites which were formed in back-arc and forearc settings, respectively. The mantle peridotites underwent variable degrees of depletion and metasomatism, and indicate the multistage assembly of South China.

Section snippets

Regional geology

South China comprises the Yangtze Block to the northwest and the Cathaysia Block to the southeast, which were amalgamated together along the Jiangnan Fold Belt during the Neoproterozoic (Fig. 1; Zhao and Cawood, 2012). The fold belt consists of the late Mesoproterozoic to early Neoproterozoic sedimentary and volcanic rocks that underwent strong deformation and greenschist facies metamorphism (Zhao et al., 2011, Wang et al., 2013a). The late Mesoproterozoic sequences, such as the Tieshajie

Zircon U-Pb dating

Representative zircon grains were separated using heavy liquid and magnetic techniques, mounted in epoxy, polished, coated with gold, and photographed in transmitted and reflected light. Cathodoluminescence (CL) images were used to reveal internal structures so as to select zircon grains for U-Pb dating. U-Pb isotopic ratios were measured using the Cameca IMS 1280 large-radius SIMS at the Institute of Geology and Geophysics (IGG), Chinese Academy of Sciences (CAS), Beijing. Analytical

Zircon U-Pb ages

Two samples from the granites and gabbros in the Fuchuan ophiolite were selected for zircon separation. Zircons from the granite sample SHE7 are subhedral to euhedral, colorless and transparent, 90–230 µm long with aspect ratios of 1:1–1:4. Most grains show unzoned or faintly zoned interiors surrounded by oscillatory-zoned rims, indicating magmatic origin. Some zircons contain rounded and faintly zoned core (Fig. 4a). They display high U (140–631 ppm) and Th concentrations (36–220 ppm) with

The effect of serpentinization

Serpentinization is ubiquitous in ultramafic rocks, and converts olivine and pyroxene to serpentine and magnetite, and changes whole rock geochemical compositions (Rudnick and Walker, 2009). Peridotites from the Xiwan and Fuchuan ophiolites underwent strong serpentinization as indicated by their lithologies (Fig. 3) and high loss on ignition (11.08–15.51 wt%; Table 2), which resulted in collateral losses in MgO (Snow and Dick, 1995, Paulick et al., 2006, Kodolányi et al., 2012). It should be

Conclusions

(1)
The peridotites from the ∼1.0 Ga Xiwan ophiolite are chemically similar to the abyssal and back-arc peridotites, and experienced partial melting at 1.8–2.1 Ga. The peridotites from the ∼830 Ma Fuchuan ophiolite are akin to the forearc peridotites, and represent a more refractory depleted mantle source after two stages of partial melting.
(2)
Both the Xiwan and Fuchuan ophiolites are SSZ-type ophiolites that were formed in back-arc and forearc settings, respectively. The united South China Craton was

Declaration of Competing Interest

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

Acknowledgments

We thank Prof. Zhu-Yin Chu for his assistance in Re-Os isotope analyses and Dr. Wen-Jun Hu for his constructive comments that helped to clarify our discussion. Two anonymous reviewers are highly appreciated for their helpful comments. This work was substantially supported by the National Nature Science Foundation of China (41773027 and 41973031) and MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences.

References (134)

H. Becker
Re-Os fractionation in eclogites and blueschists and the implications for recycling of oceanic crust into the mantle
Earth Planet. Sci. Lett.
(2000)
A.D. Brandon et al.
¹⁹⁰Pt-¹⁸⁶Os and ¹⁸⁷Re-¹⁸⁷Os systematics of abyssal peridotites
Earth Planet. Sci. Lett.
(2000)
A. Büchl et al.
Os mobilization during melt percolation: the evolution of Os isotope heterogeneities in the mantle sequence of the Troodos ophiolite
Cyprus. Geochim. Cosmochim. Acta
(2004)
J. Chen et al.
Crustal evolution of southeastern China: Nd and Sr isotopic evidence
Tectonophysics
(1998)
X. Chen et al.
Neoproterozoic chromite-bearing high-Mg diorites in the western part of the Jiangnan orogen, southern China: geochemistry, petrogenesis and tectonic implications
Lithos
(2014)
J. Chesley et al.
Large-scale mantle metasomatism: a Re-Os perspective
Earth Planet. Sci. Lett.
(2004)
J. Gao et al.
Adakitic signature formed by fractional crystallization: An interpretation for the Neo-Proterozoic meta-plagiogranites of the NE Jiangxi ophiolitic mélange belt, South China
Lithos
(2009)
S. Gao et al.
Re-Os evidence for replacement of ancient mantle lithosphere beneath the North China craton
Earth Planet. Sci. Lett.
(2002)
G. Gruau et al.
The origin of U-shaped rare earth patterns in ophiolite peridotites: assessing the role of secondary alteration and melt/rock reaction
Geochim. Cosmochim. Acta
(1998)
M.R. Handler et al.
The persistence of off-cratonic lithospheric mantle: Os isotopic systematics of variably metasomatised southeast Australian xenoliths
Earth Planet. Sci. Lett.
(1997)

J. Harvey et al.

Ancient melt extraction from the oceanic upper mantle revealed by Re-Os isotopes in abyssal peridotites from the Mid-Atlantic ridge

Earth Planet. Sci. Lett.

(2006)

J. Harvey et al.

Unravelling the effects of melt depletion and secondary infiltration on mantle Re-Os isotopes beneath the French Massif Central

Geochim. Cosmochim. Acta

(2010)

R. Hébert et al.

The Indus-Yarlung Zangbo ophiolites from Nanga Parbat to Namche Barwa syntaxes, southern Tibet: first synthesis of petrology, geochemistry, and geochronology with incidences on geodynamic reconstructions of Neo-Tethys

Gondwana Res.

(2012)

D.A. Ionov et al.

Post-Archean formation of the lithospheric mantle in the central Siberian craton: Re-Os and PGE study of peridotite xenoliths from the Udachnaya kimberlite

Geochim. Cosmochim. Acta

(2015)

J.C. Lassiter et al.

Constraints from Os-isotope variations on the origin of Lena Trough abyssal peridotites and implications for the composition and evolution of the depleted upper mantle

Earth Planet. Sci. Lett.

(2014)

L. Li et al.

Geochemistry and tectonic implications of late Mesoproterozoic alkaline bimodal volcanic rocks from the Tieshajie Group in the southeastern Yangtze Block

South China. Precambrian Res.

(2013)

L. Li et al.

Ca. 830 Ma back-arc type volcanic rocks in the eastern part of the Jiangnan orogen: implications for the Neoproterozoic tectonic evolution of South China Block

Precambrian Res.

(2016)

L. Li et al.

Geochronology and geochemistry of volcanic rocks from the Jingtan Formation in the eastern Jiangnan orogen, South China: Constraints on petrogenesis and tectonic implications

Precambrian Res.

(2018)

W.X. Li et al.

Obduction-type granites within the NE Jiangxi ophiolite: implications for the final amalgamation between the Yangtze and Cathaysia Blocks

Gondwana Res.

(2008)

X.H. Li et al.

Geochemical and Sm-Nd isotopic study of Neoproterozoic ophiolites from southeastern China: petrogenesis and tectonic implications

Precambrian Res.

(1997)

X.H. Li et al.

Precise ²⁰⁶Pb/²³⁸U age determination on zircons by laser ablation microprobe-inductively coupled plasma-mass spectrometry using continuous linear ablation

Chem. Geol.

(2001)

X.H. Li et al.

Neoproterozoic granitoids in South China: crustal melting above a mantle plume at ca. 825 Ma?

Precambrian Res.

(2003)

X.H. Li et al.

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

(2008)

X.H. Li et al.

Amalgamation between the Yangtze and Cathaysia Blocks in South China: constraints from SHRIMP U-Pb zircon ages, geochemistry and Nd-Hf isotopes of the Shuangxiwu volcanic rocks

Precambrian Res.

(2009)

G. Lister et al.

Tectonic mode switches and the nature of orogenesis

Lithos

(2009)

C.Z. Liu et al.

Mesozoic accretion of juvenile sub-continental lithospheric mantle beneath South China and its implications: geochemical and Re-Os isotopic results from Ningyuan mantle xenoliths

Chem. Geol.

(2012)

C.Z. Liu et al.

Limited recycling of crustal osmium in forearc mantle during slab dehydration

Geology

(2018)

Q. Ma et al.

Triassic ‘‘adakitic” rocks in an extensional setting (North China): melts from the cratonic lower crust

Lithos

(2012)

W.F. McDonough et al.

The composition of the Earth

Chem. Geol.

(1995)

T. Meisel et al.

Osmium isotopic compositions of mantle xenoliths; a global perspective

Geochim. Cosmochim. Acta

(2001)

Y. Niu et al.

The origin of abyssal peridotites: a new perspective

Earth Planet. Sci. Lett.

(1997)

H. Paulick et al.

Geochemistry of abyssal peridotites (Mid-Atlantic Ridge, 15°20’ N, ODP Leg 209): implications for fluid/rock interaction in slow spreading environments

Chem. Geol.

(2006)

A.H. Peslier et al.

Os isotopic systematics in mantle xenoliths; age constraints on the Canadian Cordillera lithosphere

Chem. Geol.

(2000)

Y. Rolland et al.

Jurassic back-arc and Cretaceous hot-spot series in the Armenian ophiolites: implications for the obduction process

Lithos

(2009)

R.L. Rudnick et al.

Interpreting ages from Re-Os isotopes in peridotites

Lithos

(2009)

R.F. Schulte et al.

Chemical and chronologic complexity in the convecting upper mantle: evidence from the Taitao ophiolite, southern Chile

Geochim. Cosmochim. Acta

(2009)

M. Sharma et al.

The concentration and isotopic composition of osmium in the oceans

Geochim. Cosmochim. Acta

(1997)

J.E. Snow et al.

Os isotopes and highly siderophile elements (HSE) in the Ligurian ophiolites

Italy. Earth Planet. Sci. Lett.

(2000)

L. Shu et al.

Tectonic evolution of the eastern Jiangnan region, South China: new findings and implications on the assembly of the Rodinia supercontinent

Precambrian Res.

(2019)

Z.M. Sun et al.

Formation of the Neoproterozoic ophiolites in southern China: new constraints from trace element and PGE geochemistry and Os isotopes

Precambrian Res.

(2018)

B. Taylor et al.

Back-arc basin basalt systematics

Earth Planet. Sci. Lett.

(2003)

M. Teklay

Neoproterozoic arc-back-arc system analog to modern arc-back-arc systems: evidence from tholeiite-boninite association, serpentinite mudflows and across-arc geochemical trends in Eritrea, southern Arabian-Nubian shield

Precambrian Res.

(2006)

R.J. Walker et al.

Os, Sr, Nd, and Pb isotope systematics of Southern African peridotite xenoliths: implications for the chemical evolution of subcontinental mantle

Geochim. Cosmochim. Acta

(1989)

C.Z. Wang et al.

Timing and tectonic setting of the ophiolite in northeast Jiangxi: Constrains from zircon U-Pb age, Hf isotope and geochemistry of the Zhangshudun gabbro

Acta Petrol. Mineral.

(2015)

D. Wang et al.

Unraveling the Precambrian crustal evolution by Neoproterozoic conglomerates, Jiangnan orogen: U-Pb and Hf isotopes of detrital zircons

Precambrian Res.

(2013)

J. Wang et al.

History of Neoproterozoic rift basins in South China: implications for Rodinia breakup

Precambrian Res.

(2003)

W. Wang et al.

Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China

Precambrian Res.

(2013)

X.L. Wang et al.

Geochemistry of the Meso- to Neoproterozoic basic-acid rocks from Hunan Province, South China: implications for the evolution of the western Jiangnan orogen

Precambrian Res.

(2004)

X.L. Wang et al.

Geochronology and Hf isotopes of zircon from volcanic rocks of the Shuangqiaoshan Group, South China: implications for the Neoproterozoic tectonic evolution of the eastern Jiangnan orogen

Gondwana Res.

(2008)

X.S. Wang et al.

Early Neoproterozoic multiple arc-back-arc system formation during subduction-accretion processes between the Yangtze and Cathaysia blocks: new constraints from the supra-subduction zone NE Jiangxi ophiolite (South China)

Lithos

(2015)

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Development of a mid-Neoproterozoic arched rift in eastern South China as a response to the Rodinia breakup
2023, Precambrian Research
The initial time (before or after ∼ 820 Ma) and geodynamic mechanism (bottom-up rising mantle plume or top-down deep subduction) of Rodinia breakup remain unresolved. This issue has impacted our current understanding of the tectonic evolution of South China. Some scholars believe that separation of the South China Craton (SCC) from the Rodinia supercontinent and contemporary SCC rifting began at ca. 860 Ma and was induced by a subduction-related extension event. In addition, other researchers consider that the SCC rifting occurred after ca. 820 Ma. We show that renewed Rodinia breakup within or along the margin of South China occurred ca. 820–740 Ma, which is supported by early studies and our newly obtained U–Pb zircon ages of 755.4 ± 1.0 and 801.6 ± 5.2 Ma from basalts and mafic intrusive bodies in an arched (arc-shaped) belt. Major elemental variations and calculated datasets for the rift-related igneous rocks suggest a mantle plume origin for the dated rocks, which indicates that the SCC rifting was driven by a rising mantle plume and formed several rifts. This arched belt, including < 820 Ma sedimentary and igneous rocks within it, may well have been the eastern part of the original Nanhua Rift, i.e., the prototype of the Nanhua Rift should be a “T” shape. Owing to a barren magmatic area at the “T” junction, the Nanhua Rift must have split into the Nanhua Rift and arched rift. We suggest that the first stage of rifting event during 860–825 Ma may occurred in the interior Yangtze or Cathaysia Block and was associated with a subduction-related extension event.
Early Neoproterozoic (∼840 Ma) assemblage in South China and the southern extension of the Jiangshan-Shaoxing zone: Records from the Zhoutan and Shenshan igneous rocks in central Jiangxi
2022, Precambrian Research
Citation Excerpt :
Wang et al. (2018b) have identified 860–830 Ma high-Mg intermediate and high-Si adakitic, arc-like basaltic and andesitic, and high-Nb and Nb-enriched mafic rocks within the Chencai Complex, and proposed an early Neoproterozoic arc–trench setting until ca. 830 Ma. Available data show that the volcanic rocks, granitoids, and associated ophiolite suites (e.g., Zhangshudun and Fuchuan ophiolites) in the eastern segment mainly formed at 960–830 Ma (e.g., Ding et al., 2008; Li et al., 2008a; Zhang et al., 2010, 2012b; Wang et al., 2015, 2019b; Cui et al., 2017; Sun et al., 2018; Li and Zhao, 2020). In the central and western segments, the main rock-units include the ∼ 870–820 Ma Lengjiaxi and overlying 810–720 Ma Banxi groups and their equivalents, which are separated by an angular unconformity, as well as the associated Neoproterozoic igneous rocks (e.g., Wang et al., 2007, 2020a; Zhao et al., 2011, 2013; Zhao and Cawood, 2012; Zhang et al., 2013b; Ma et al.,2016; Zhang and Wang, 2016, 2020; Deng et al., 2019; Yao et al., 2019; Yang et al., 2020; Shu et al., 2021).
The amalgamation process and suture boundary of the Yangtze and Cathaysia blocks have been in hot dispute and attracted considerable attention. Overall, controversies remain on where the closure boundary of the Paleo-Huanan Ocean was and how the Jiangshan-Shaoxing fault southwesterly extended. This paper presents a set of new geochronological, geochemical and Nd isotopic data for the igneous rocks from the Zhoutan and Shenshan groups in Central Jiangxi. The Zhoutan amphibolites formed during the Neoproterozoic (∼850–830 Ma) and experienced the Silurian (∼430 Ma) metamorphism. They have low SiO₂ (49.5–52.9 wt%), Al₂O₃ (13.48–14.38 wt%), and TiO₂ (0.99–1.57 wt%) contents and K₂O/Na₂O values (<1.0), and show E-MORB-resembling REE and PM-normalized pattern, with Nb/La of 0.59–0.88. Their ε_Nd(t) values range from + 4.8 to + 5.9, and they were originated from a slab fluid-modified E-MORB-like mantle source. The high-Mg meta-andesite and -dacite rocks from the Zhoutan Group and Lower Shenshan subgroup yield zircon U–Pb mean ages of 850–837 Ma and exhibit 61.4–75.2 wt% SiO₂ and 2.0–4.1 wt% MgO. They are enriched in LILEs and depleted in HFSEs, with Nb/La = 0.21–0.42 and ε_Nd(t) = − 3.1 to − 8.9. These high-Mg volcanic rocks were derived from a sediment- modified wedge source. The Shenshan Group is likely to be an equivalent of the Yingyangguan volcano-sedimentary sequence that was split into Lower (853–830 Ma) and Upper (810–740 Ma) subgroups. The Zhoutan and Lower Shenshan igneous rocks formed in a fore-arc setting at the Neoproterozoic period in response to the westward consumption of the Paleo-Hunan Ocean. The Jiangshan–Shaoxing suture extends southwardly into the Yingyangguan area across the Zhoutan–Yangtian area near to the Chenzhou-Linwu fault.

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Amalgamation between the Yangtze and Cathaysia blocks in South China: Evidence from the ophiolite geochemistry

Highlights

Abstract

Introduction

Section snippets

Regional geology

Zircon U-Pb dating

Zircon U-Pb ages

The effect of serpentinization

Conclusions

Declaration of Competing Interest

Acknowledgments

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