Paleoproterozoic meta-carbonates from the central segment of the Trans-North China Orogen: Zircon U–Pb geochronology, geochemistry, and carbon and oxygen isotopes

doi:10.1016/j.precamres.2016.08.001

Precambrian Research

Volume 284, October 2016, Pages 14-29

https://doi.org/10.1016/j.precamres.2016.08.001 Get rights and content

Highlights

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The depositional age for the Wanzi Group is further constrained as 1.95–1.93 Ga and the Central Zanhuang Domain as 2.03–1.90 Ga.
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The protoliths of meta-carbonates were deposited in a proximal and shallow marine environment.
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The Wanzi Group was deposited in a forearc basin and the Central Zanhuang Domain was formed in a back-arc basin.
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The positive excursion of δ¹³C values in the Fuping area is possibly related to the Lomagundi or Jatulian Event.

Abstract

The Trans-North China Orogen (TNCO) represents one of the major Paleoproterozoic collisional orogens across the central part of the North China Craton. Here we investigate the meta-carbonates (marbles and calc-silicate rocks) from the Fuping and Zanhuang Complexes in the TNCO through a combination of detrital zircon U–Pb geochronology, geochemistry and stable isotopes (carbon and oxygen). The U–Pb ages obtained from detrital zircons in both sequences show age populations of 2.50–2.57 Ga, 2.2–2.4 Ga, 2.0–2.1 Ga and 1.85–1.90 Ga. The depositional age for the Wanzi Group in the Fuping Complex is further constrained as 1.95–1.93 Ga and the Central Zanhuang Domain (Zanhuang Complex) as 2.03–1.90 Ga. All samples show nearly flat REE patterns below the concentration level of 1 in the shale-normalized REE distribution diagram. The dolomite–calcite marbles from the Fuping Complex have δ¹³C values ranging from −0.31‰ to 3.65‰ and δ¹⁸O values vary from −9.12‰ to −2.96‰. The calc-silicate rocks from the Fuping Complex show wide variation of δ¹³C (−1.56‰ to 3.30‰) and δ¹⁸O (−12.89‰ to −5.84‰). Dolomite marbles from the Zanhuang Complex show low δ¹³C and δ¹⁸O values ranging from −3.31‰ to −3.69‰ and −12.98‰ to −13.59‰. The dolomite–calcite marbles from the Zanhuang Complex display δ¹³C and δ¹⁸O compositions of −2.68‰ to 1.44‰ and −11.77‰ to −7.76‰, respectively. The correlations between the isotopic results (δ¹³C and δ¹⁸O) and geochemical compositions (Mn, Sr, Mn/Sr, Mg/Ca, Ca/Sr and Fe/Sr) suggest that the dolomite marbles from the Zanhuang Complex are strongly disturbed and the calc-silicate rocks are moderately affected by the post-depositional processes. The salient lithological, geochemical and isotopic features imply that the protoliths of the meta-carbonates were formed in a proximal and shallow marine environment. The Wanzi Group was deposited in a forearc basin and the Central Zanhuang Domain was formed in a back-arc basin. The geochemical imprints and biospheres of the oceanic basin in the Fuping area were possibly affected by the Lomagundi or Jatulian Event, resulting in the positive excursion of δ¹³C values in the dolomite–calcite marbles. However, the back-arc basin in the Zanhuang area was formed after the 2.1–2.0 Ga rifting event, thus it was generated after the Jatulian Event, thus preserving normal δ¹³C values of marine carbonates.

Graphical abstract

Introduction

Meta-carbonate rocks with geological attributes of marine sediments are important components in Precambrian orogenic belts (Veizer et al., 1989, Huang and Buick, 2002, Singh et al., 2016). Their stratigraphic features as well as isotopic and geochemical data have been used as important clues to unravel the depositional environment, and post-depositional tectonic activities (Veizer et al., 1992, Hall and Veizer, 1996, Bau et al., 1999). Detrital zircon U–Pb dating can provide reliable geochronological constraints on the depositional age and provenance of impure meta-carbonate rocks (Tang et al., 2006, Tam et al., 2011, Fairey et al., 2013). The most extensively used tracers for the depositional environment are the stable isotopes (carbon and oxygen) and trace elements, which are controlled mainly by the primary features of the marine water and biosphere (Veizer et al., 1992, Kaufman and Knoll, 1995, Bau et al., 1999, Gaertner et al., 2011, Swart, 2015). Investigations combining detrital zircon U–Pb dating, geochemistry, C and O isotopes on meta-carbonates have been successfully applied to elucidate Precambrian tectonic processes (e.g. Tang et al., 2006, Hall et al., 2013, Paula-Santos et al., 2015).

The Trans-North China Orogen (TNCO) welding the Eastern and Western Blocks in the North China Craton (NCC) is one of the major Paleoproterozoic collisional orogenic belts in the NCC, and exposes accreted and metamorphosed sedimentary sequences and associated rocks which have been interpreted as remnants of ancient oceanic crust (Zhao and Zhai, 2013, and references therein). However, the origins of these rocks in terms of their depositional history in forearc/foreland basin/trench, back-arc environments remain controversial (Wu et al., 1989, Sun et al., 1992, Zhao et al., 2005, Zhao et al., 2007, Zhao et al., 2012, Xia et al., 2006, Faure et al., 2007, Wang, 2009, Liu et al., 2011, Liu et al., 2012a, Liu et al., 2012b, Liu et al., 2014, Santosh et al., 2015a). Paleoproterozoic meta-carbonate rocks are well preserved in the basement terranes of the TNCO, including the Fuping Complex, Zanhuang Complex, Lüliang Complex, Wutai Complex and Zhongtiao Complex (Fig. 1). Investigations on the detrital zircon record, geochemistry and stable isotopes of these rocks are critical to elucidating the depositional age and environment. In this study, we present zircon U–Pb geochronological, geochemical and isotopic (carbon and oxygen isotopes for calcite and dolomite) data on a suite of impure marbles and calc-silicate rocks from the Fuping and Zanhuang Complexes which are two representative basement terranes located within the central segment of the TNCO. The objective of this study is to constrain the depositional age and environment for the meta-sedimentary sequences in the Fuping and Zanhuang Complexes, use the results to gain insights into the Paleoproterozoic tectonic processes in the NCC.

Section snippets

Regional geology and sample description

As the largest and oldest craton in China, the NCC has been traditionally sub-divided into the Western Block, Eastern Block and TNCO (Fig. 1; e.g. Zhao et al., 2005, Zhao et al., 2012, Zhao and Zhai, 2013, Santosh et al., 2015a). The Western Block was formed by the amalgamation of the Yinshan Block and the Ordos Block along the E–W trending Inner Mongolia Suture Zone at 1.95–1.92 Ga (or known as the Khondalite Belt, e.g. Santosh, 2010, Tsunogae et al., 2011, Santosh et al., 2012), and the

Whole rock geochemistry

Thirteen representative fresh samples (five dolomite–calcite marbles and four calc-silicate rocks from Fuping Complex, two dolomite–calcite marbles and two dolomite marbles from Zanhuang Complex) were chosen for major and trace element analyses. The rock samples were initially reduced to avoid surface alteration and then powered to 200-mesh. Contents of major elemental oxides were measured by X-ray fluorescence (XRF) spectrometry (PW4400) and trace elements were measured by PE300D inductive

Major and trace elements

The five dolomite–calcite marbles from Fuping Complex show constant MgO (19.95–20.75 wt.%), CaO (28.35–30.10 wt.%) and Mg/Ca values (0.58–0.62). These dolomite–calcite marbles are impure with variable SiO₂ contents (1.80–6.82 wt.%), in accordance with the petrological observations that show the occurrence of silicic minerals (phlogopite and muscovite). K₂O and Al₂O₃ concentrations are low (0.05–0.41 wt.% and 0.10–1.30 wt.%, respectively). The dolomite–calcite marbles have variable trace element

Effects of diagenesis and metamorphism

For Precambrian meta-carbonate rocks, processes including diagenesis, fluid–rock interaction and metamorphism may affect the primary geochemical and isotopic features (Veizer et al., 1989, Jacobsen and Kaufman, 1999, Melezhik and Fallick, 2003, Tang et al., 2006). Diagenetic and metamorphic processes result in the enrichment of Mn and depletion of Sr, and for rocks that have not been affected by later events, Mn/Sr ratio lower than 10 is suggested (Brand and Veizer, 1980, Veizer, 1983, Guan and

Conclusions

(1)
The correlations between the isotopic results (δ¹³C and δ¹⁸O) and geochemical composition (Mn, Sr, Mn/Sr, Mg/Ca, Ca/Sr and Fe/Sr) suggest that the dolomite marbles from the Zanhuang Complex were strongly disturbed and that the calc-silicate rocks were moderately affected by the post-depositional processes. The dolomite–calcite marbles display the primary geochemical features without post-depositional effects.
(2)
The protoliths of the impure marbles and calc-silicate rocks are marine carbonates.

Acknowledgements

We thank Prof. Guochun Zhao and reviewers Dr. Qiong-Yan Yang and an anonymous referee for their constructive comments and suggestions. This work forms part of the PhD research of Li Tang at the China University of Geosciences Beijing and the University of Tsukuba. We thank Xin-Kai Hu, Xue-Ming Teng, Tatsuya Koizumi, Akito Hiraga, Xiao-Fang He and Shan-Shan Li for their help during the field and analyses. This study was jointly supported through the Foreign Expert grant from China University of

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Ocean Plate Stratigraphy of a long-lived Precambrian subduction-accretion system: The Wutai Complex, North China Craton
2021, Precambrian Research
Ocean Plate Stratigraphy (OPS) is the travelogue of the oceanic lithosphere from its birth at the Mid Ocean Ridge to its demise at the subduction zone in convergent plate margins. Here we present an OPS succession preserved onland in the Wutai Complex of the North China Craton (NCC), representing a prolonged subduction-accretion-collision system and continental growth during the Neoarchean-Paleoproterozoic. The OPS succession in Wutai includes metabasalts and banded iron formation representing the pelagic sequences together with intercalated metacarbonates. Phyllite, greenschist, and mica schist represent the hemipelagic sequence. Quartzite and conglomerate correspond to the turbidite sequence, with a progressive southward accretion towards a magmatic arc in the north. We present results from petrological, geochemical, zircon U-Pb, REE, and Lu-Hf studies from representative rocks in the OPS sequence of the Wutai Complex. The trace elements including the rare-earth element (REE) data of the metabasalt show transitional features between normal mid-ocean ridge basalt (N-MORB) and enriched mid-ocean ridge basalt (E-MORB). The REY (lanthanide elements and Y) data of the banded iron formation (BIF), greenschists, and phyllite suggest the interaction of high-temperature hydrothermal fluids and seawater. Magmatic zircon grains from the quartzite show ²⁰⁶Pb/²⁰⁷Pb upper intercept age of 2443 ± 21 Ma, whereas zircon grains in the phyllite show upper intercept age of 2494 ± 32 Ma, with minor xenocrysts with older ages of 2726 ± 46 Ma and 2672 ± 48 Ma. Zircon grains in the metaconglomerate show upper intercept age of 2569 ± 32 Ma. Those from the siliceous and intercalated bands in the BIF yield upper intercept ages of 2583 ± 34 Ma and 2524 ± 49 Ma. The zircon Lu-Hf data on zircon grains from the BIF, phyllite, quartzite, and metaconglomerate all show positive εHf(t) values (+1.3 to +7.4) in the range of depleted mantle to new crust, suggesting Neoarchean intra oceanic arc subduction. Combined with the zircon U-Pb and Hf isotopic data previously reported from the Wutai Complex, we infer the following four tectonic evolution stages: ca. 2800 Ma subduction initiation, ca. 2750–2300 Ma arc-accretionary complex, ca. 2300–2100 Ma back-arc rifting, and ca.1900–1750 Ma arc-continent collision. The metavolcanics and part of the metasedimentary rock assemblages in the Wutai Complex represent a deformed and dismembered OPS sequence generated through northward subduction and closure of the Wutai Ocean.
Neoarchean to Paleoproterozoic tectonothermal evolution of the North China Craton: Constraints from geological mapping and Th-U-Pb geochronology of zircon, titanite and monazite in Zanhuang Massif
2021, Precambrian Research
Citation Excerpt :
These zircon grains may have experienced partial lead loss which is similar to our re-assessment of the quality of data from hydrothermally altered zircons reported by Tang et al. (2016). These ages have no geological meaning (Wan et al., 2011; Geng et al., 2018; Wang et al., 2017a). The zircon grains of sample 2019XT-2–1 are mostly subhedral, prismatic or oval in shapes, with length of ~ 100–180 μm and width of ~ 50–100 μm.
The North China Craton (NCC) consists of Neoarchean to Paleoproterozoic basement, with rare Eo-Paleoarchean crustal relicts. However, the Precambrian tectonothermal evolution of the Central Orogenic Belt (COB) of the NCC is still hotly debated. In this contribution, we present new results of field-based litho-structural analysis, Th-U-Pb geochronology of accessory minerals including zircon, titanite and monazite from paragneiss and marble in a passive margin sequence in the Zanhuang Massif of the COB. Field studies show that two generations of deformation events occurred in the Zanhuang Massif. The earlier deformation is widely distributed in the entire Zanhuang Massif and developed with a top-to-SE shear sense resulting in foliation of the micaschist, metavolcanic rock, marble and paragneiss. The latter deformation is locally occurred in the central Zanhuang Massif and developed with a top-to-SW shear sense represented by the faulting and folding events which are similar to the fold-and-thrust structures of accretionary wedge during the formation of Zanhuang mélange. Zircons from paragneiss yield single-peak age populations with mean ages of 2.52 and 2.51 Ga, and a metamorphic age of 1.84 Ga. Zircon ages from marble are divided into four groups including a main peak of 2.54 Ga, two older groups of 2.77–2.82 and 2.60–2.70 Ga, and a younger metamorphic age of 1.81 Ga. Titanites from paragneiss and marble yield mean metamorphic ages between 1.94 and 1.88 Ga, representing an earlier thermal event. Monazites from paragneiss yield an isochron age of 1.80 Ga, representing a later thermal event. Based on our new litho-structural observations and geochronological data, coupled with previous studies, we suggest that the paragneiss and marble from the marble-siliciclastic unit represent the passive margin sequence, and were mainly deposited at 2.51–2.50 Ga. In addition, the Zanhuang Massif has experienced two tectonothermal events at ca. 1.94–1.88 Ga and ca. 1.83–1.80 Ga, which are widely distributed in the entire NCC, but gradually become weaker from north to south.

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Paleoproterozoic meta-carbonates from the central segment of the Trans-North China Orogen: Zircon U–Pb geochronology, geochemistry, and carbon and oxygen isotopes

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Regional geology and sample description

Whole rock geochemistry

Major and trace elements

Effects of diagenesis and metamorphism

Conclusions

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