Possible imprints of late Paleoproterozoic orogeny in the Dunhuang terrane, NW China: Constraints from igneous and metapelitic rocks

Highlights

• Ca. 1.86–1.82 Ga orogeny-related magmatic rocks are preserved in Dunhuang terrane.

• The metapelitic rock record ca. 1.81 Ga amphibolite-facies metamorphism.

• Late Paleoproterozoic subduction-collisional orogeny possibly occurred.

• The ca. 1.9–1.8 Ga geological record overprint ca. 440–360 Ma tectonothermal event.

Abstract

The Dunhuang terrane is a NEE trending tectonic belt confined by the Tarim Craton, Beishan Orogen, Alxa Block and Altyn Tagh Fault. To constrain the late Paleoproterozoic geotectonic background of this terrane, a synthetic research on petrology, geochemistry, zircon and monazite geochronology, and zircon Lu-Hf and whole-rock Nd isotopes of late Paleoproterozoic (ca. 1.9–1.8 Ga) igneous rocks and metapelites was conducted. The Sanweishan-Dongshuigou Na-rich rhyolite and granite formed at ca. 1.84–1.82 Ga exhibit enriched light rare earth elements (LREEs), depleted heavy rare earth elements (HREEs) and insignificant Eu anomalies, with low Y (3.44–6.39 ppm) and Yb (0.29–0.53 ppm) but relatively high Mg# (54.5–58.5) and Sr (368–643 ppm), and variable Cr (5.58–29.7 ppm) and Ni (2.82–15.6 ppm) contents, as well as negative to positive ε_Hf(t) (−6.1 to +6.4) values, indicating subduction-related arc magmatism accompanied by crustal-mantle interaction. The Shuwozi granitic gneiss crystallized at ca. 1.81 Ga displays S-type granite affinity (A/CNK > 1.1) and has low Sr/Y (1.0–1.3) and (Gd/Yb)_N (1.50–1.98) ratios, and negative ε_Hf(t) (−20.3 to −5.1) and ε_Nd(t) (−4.3) values, suggesting partial melting of crustal rocks at shallow crustal depth. The Hanxia amphibolite with protolith age of ca. 1.86–1.84 Ga is featured by depleted LREE and flat HREE patterns, insignificant Eu anomalies, low Nb/Ta (11.0–12.0), Ta/Yb (0.02–0.04), Th/Yb (0.01–0.04) and Th/Ta (0.7–1.3) but high Ti/V (22.9–26.7) ratios, and positive ε_Nd(t) (2.7–4.0) values, resembling depleted mantle-derived N-MORB- or BABB (back-arc-basin basalt) geochemical affinities. The metapelite, characterized by mineral assemblage of garnet, biotite, sillimanite, plagioclase, K-feldspar, quartz and rutile, documented ca. 1.81 Ga upper amphibolite-facies metamorphism with peak metamorphic P-T conditions being restricted to 690–810 °C and 5.3–6.4 kbar based on conventional geothermobarometry. These magmatic and metamorphic rocks were variously altered and deformed during Paleozoic (ca. 430–360 Ma) tectonothermal event. Integrated with published data, it can be inferred that the Dunhuang terrane underwent ca. 1.89–1.81 Ga subduction-collisional orogeny related to late Paleoproterozoic (ca. 2.0–1.8 Ga) global assembly of the Columbia supercontinent, similar as those recorded in the northern Tarim Craton, Alxa Block and Quanji massif, and then overprinted Paleozoic (ca. 440–360 Ma) orogenic process, corresponding to the previously proposed composite orogeny in the Dunhuang terrane.

Introduction

The global-scale Paleoproterozoic magmatism and metamorphism, widely documented in most of Archaean-Paleoproterozoic cratons around the world, led to the development of the Columbia/Nuna supercontinent (e.g., Wilde et al., 2002, Zhao et al., 2002, Zhao et al., 2005, Zhao et al., 2010, Rogers and Santosh, 2009, Zhai and Santosh, 2011). It has been suggested that plate tectonics might have initiated at late Paleoproterozoic of 2.1–1.8 Ga (e.g., Kröner, 1991), resulting in recycling of ancient crustal materials (e.g., Armstrong, 1991, Hawkesworth et al., 2010, Cawood et al., 2013). Therefore, the identification of late Paleoproterozoic orogenic-related magmatic and metamorphic rocks is crucial for reconstructing the configuration of the Columbia supercontinent and is also pivotal for understanding geological evolution of the Precambrian terranes.

The Chinese continent mainly consists of the North China Craton, the Tarim Craton and the South China Craton, which was amalgamated together through several Phanerozoic orogenic belts (Fig. 1a) (e.g., Zhao et al., 2005, Zhao and Cawood, 2012, Zhai et al., 2005). The late Paleoproterozoic subduction-collisional events in the North China Craton intensively occurred at 2.0–1.8 Ga, manifested as a series of high-pressure and ultra-high-temperature metamorphism (Kusky and Li, 2003, Zhao et al., 2005, Santosh et al., 2007, Zhai and Santosh, 2011, Zhang et al., 2016; and references therein). The Tarim Craton also widely documented the late Paleoproterozoic tectonothermal event, characterized by 2.0–1.9 Ga metamorphism, anatexis and magmatism (Shu et al., 2011, Xin et al., 2011, Xin et al., 2013, Long et al., 2012, Long et al., 2015, Ge et al., 2013a, Ge et al., 2013b, Ge et al., 2014, Xu et al., 2013). In the South China Craton, the late Paleoproterozoic collisional orogen at 2.0–1.85 Ga have been identified in the Huangtuling, Lengshui and Kongling complexes (Zhang et al., 2006, Sun et al., 2008, Wu et al., 2008, Guo et al., 2014, Wang et al., 2015). In addition, the late Paleoproterozoic metamorphism and anatexis also happened in the microcontinent of Oulongbuluke Block between the North Qaidam HP-UHP metamorphic belt and the Qilian Block (Chen et al., 2009, Yu et al., 2017).

The Dunhuang terrane, located in the junction of the Tarim Craton, Mt. Qilian, Alxa Block and Beishan Orogen (Fig. 1b), has been traditionally considered to be part of the Tarim Craton (Mei et al., 1997, Mei et al., 1998, Zhang et al., 2011, Meng et al., 2011) or North China Craton (Huang et al., 1980, Zhang et al., 1997), or a microcontinent within Central Asian Orogenic Belt (Ren et al., 1999). However, recent studies show that this terrane underwent regional Silurian-Devonian metamorphism (Zong et al., 2012, He et al., 2014, Zhao et al., 2016, Zhao et al., 2019a, Wang et al., 2016a, Wang et al., 2017a, Wang et al., 2017b, Wang et al., 2018a, Wang et al., 2018b, Pham et al., 2018, Zhang et al., 2020) and Silurian-Triassic magmatism (Zhang et al., 2009, Zhang et al., 2020, Zhu et al., 2014, Zhu et al., 2020, Wang et al., 2016b, Wang et al., 2016c, Wang et al., 2017c, Zhao et al., 2017, Shi et al., 2019, Xu et al., 2019, Feng et al., 2020), but locally preserved imprints of Archean-Paleoproterozoic tectonothermal events (Zhang et al., 2012a, Zhang et al., 2013a, He et al., 2013, Zhao et al., 2013, Zhao et al., 2015a, Zhao et al., 2015b, Zhao et al., 2019b, Zhao et al., 2019c, Zong et al., 2013, Yu et al., 2014, Wang et al., 2013a, Wang et al., 2013b, Wang et al., 2014, Wang et al., 2017d). With regard to the Archean-Paleoproterozoic geological processes, most investigations focus on crustal growth and evolution of the Dunhuang terrane in Archean Era (Zhang et al., 2013a, Zhao et al., 2013, Zhao et al., 2015a, Zhao et al., 2015b, Zong et al., 2013). It has been proposed that the Dunhuang terrane documented late Paleoproterozoic collisional and post-collisional event, marked by ca. 1.85–1.82 Ga mafic high-pressure granulite (Zhang et al., 2012a, Zhang et al., 2013a) and ca. 1.79–1.73 Ga A-type granite (Yu et al., 2014, Wang et al., 2017d, Zhao et al., 2019c), respectively. Nevertheless, the late Paleoproterozoic tectonic setting and orogenic processes, as well as the origin/affinity of the Precambrian complex within the Dunhuang terrane remain ambiguous for lacking of systematic and synthetical studies on magmatic and metamorphic rocks. The late Paleoproterozoic (1.9–1.8 Ga) mafic-felsic magmatic and metapelitic rocks have been recognized in the Dunhuang terrane, which will provide concrete constraints on the late Paleoproterozoic geological evolutionary history.

In this paper, we present whole-rock geochemical, zircon U-Pb geochronological, zircon Lu-Hf and whole-rock Nd isotope data for late Paleoproterozoic igneous rocks, as well as mineralogical, and zircon and monazite U-Pb geochronological data for late Paleoproterozoic metapelite from the Dunhuang terrane, NW China. This study aims to: (1) constrain the timing of late Paleoproterozoic magmatism and metamorphism; (2) ascertain the nature and magma source of late Paleoproterozoic igneous rocks; (3) determine the P-T conditions of late Paleoproterozoic metamorphism; and (4) synthetically reveal late Paleoproterozoic geological evolutionary history of the Dunhuang terrane and compare with its adjacent areas.