The Mesozoic Amdo micro-block and East Asian superconvergent tectonic system
Graphical abstract
Introduction
The assembly of the East Asian continent (EAC) involved multi-directional convergence of several micro-blocks from late Paleozoic to Mesozoic (Enkin et al., 1992, Gilder and Courtillot, 1997, Dong et al., 2008, Li et al., 2019). The late Paleozoic collisional orogenic stage formed the embryonic East Asian continent (EEA) (Carter et al., 2001, Ernst et al., 2007, Cocks and Torsvik, 2013, Guo et al., 2017a, Guo et al., 2017b, Zhao et al., 2018), known as the Indosinian Orogeny (Fromaget, 1934). Mesozoic amalgamation kinematics in East Asia is characterized by intracontinental orogeny (Li and Li, 2007, Li and Zhao, 2007, Zhang et al., 2008) and/or convergence of different micro-blocks or sub-blocks toward the EEA (Sengor, 1985, Zhang, 2001, Zhang, 2004, Oh, 2006, Kusky et al., 2007, Dong et al., 2008, Dong et al., 2018), forming three major suture zones termed as the Bangong-Nujiang subduction-collision zone to the southwest (Kapp et al., 2005, Liu et al., 2017a, Fan et al., 2018, Guo et al., 2019); the Paleo-Pacific subduction-accretion zone to the east (Suo et al., 2019, Suo et al., 2020,); and the Mongolia-Okhotsk subduction-collision zone to the north (Zorin, 1999, Fan et al., 2003, Sheldrick et al., 2020), together with some collision-derived, accretion-derived and rifting-derived micro-blocks (Li et al., 2018a) (Fig. 1a). This major deformational event is known as the Yanshanian Movement in East Asia (Wong, 1929, Dong et al., 2008). A better understanding of the Yanshanian epicontinental and intracontinental deformation and orogenesis requires detailed studies on the micro-blocks within the EAC.
The Bangong-Nujiang Suture Zone (BNSZ) formed through the subduction and closure of the Bangong-Nujiang Meso-Tethys Ocean (BNO) within the central Tibetan Plateau, and separates the Qiangtang Block (QTB) to the north and the Lhasa Block (LHB) to the south (Girardeau et al., 1984, Guynn et al., 2006a) (Fig. 1). This suture preserves the history of convergent regime of the micro-blocks that accreted northeastward toward the EAC during the late Mesozoic (Dewey et al., 1988, Kapp et al., 2007). The Amdo micro-block (ADB), located in the eastern segment of the BNSZ (Fig. 1b), is distinctly different in Mesozoic strata from the central-western sections of the BNSZ due to its unique Neoproterozoic and early Paleozoic basement (Xu et al., 1985, Guynn et al., 2006a, Guynn et al., 2006b, Guynn et al., 2012, Guynn et al., 2013, Wang et al., 2012a, Xie et al., 2013). It not only preserves the complete ophiolite suite derived from the BNO, but also provides a key region to study the transition of tectonic regimes within the intra-BNO (Coward et al., 1988, Lai and Liu, 2003).
The older basement of the ADB is composed of Neoproterozoic orthogneiss and Cambrian crystallization ages (Xie et al., 2010, Guynn et al., 2012), which were later intruded by voluminous Mesozoic granites (Harris et al., 1988, Yan et al., 2016a). It is generally agreed that the Jurassic granites are related to the northward subduction of the BNO (Sun et al., 2011, Li et al., 2017a). Sedimentary strata are mainly distributed around the ADB, but are absent in the interior of the ADB (Zhang et al., 2014). There are ophiolite outcrops on both the northern and southern sides of the micro-block (Lai and Liu, 2003, Sun et al., 2011, Bai et al., 2013). The crystalline basement has been subjected to metamorphism under high pressure (HP) granulite facies with a peak-metamorphic age of 191 Ma (Zhang et al., 2010, Zhang et al., 2014) and lower amphibolite facies with a peak-metamorphic age of 178 Ma (Guynn et al., 2013), respectively.
Previous studies mainly focused on the stratigraphy, petrology, isotopic geochronology and geochemistry (Guynn et al., 2006a, Guynn et al., 2006b, Guynn et al., 2012, Guynn et al., 2013, Zhang et al., 2010, Zhang et al., 2014, Chen et al., 2015), but several disputes exist, resulting in a lack of understanding of the evolution of ADB. Whether the missing magmatic arc on the northern side of the ADB was buried by some younger strata, or subducted northward with the LHB beneath the QTB, remains speculative (Guynn et al., 2006a; Liu et al., 2010, Liu et al., 2011a) proposed that the Amdo Jurassic plutons underwent magma mixing at 185 Ma and 175 Ma, and correlated these to mixing of crust-derived felsic magma with mantle-derived mafic magma. Furthermore, the tectonic offsetting of the Amdo ophiolites is also equivocal. Some scholars correlated these rocks to a typical island arc ophiolite (SSZ-type), which was formed in back-arc basin environment (Lai and Liu, 2003). However, others proposed that these rocks are part of oceanic crust formed in mid-ocean ridge or quasi mid-oceanic ridge environment (MOR-type) (Bai et al., 2013). In addition, the Mesozoic amalgamation history is also controversial. The peak-metamorphic age of 191 Ma for granulites indicates that the ADB deeply subducted beneath the QTB (Zhang et al., 2010, 2014); The P-T-t path shows that the Amdo gneiss experienced a tectono-thermal event related to the crustal thickening in a shortening setting at 178 Ma before the QTB-LHB collision (Guynn et al., 2013); The zircon and sphene U-Pb ages of 171 ± 6 Ma obtained by Xu et al. (1985) from the gneisses of the southern ADB may be related to the collision between the LHB and the QTB during the Early-Middle Jurassic; Many other scholars have suggested that the QTB-ADB and the LHB collided during the Early Cretaceous (Guynn et al., 2006a, Peng et al., 2011, Liu et al., 2017b).
Previous research in the ADB mostly focused on the magmatism and metamorphism with no detailed investigation on the structural aspects (Girardeau et al., 1984, Guynn et al., 2006b, Shi et al., 2012). In order to improve our understanding on the deformation history of the Amdo gneiss and the relation between Mesozoic magmatic rocks as well as the subduction of the BNO, in this paper, we present the results from a systematic field investigation and structural analysis in the ADB, and identify the deformation stages. We also integrate many petrological, isotopic geochronological and geochemical data of the Amdo magmatic and metamorphic rocks to reconstruct their tectonic settings and processes. Based on constraints from structural analysis, we discuss the response of various deformation events to magmatism and metamorphism in the ADB, as well as provide further insights into the tectonic evolution of the ADB in the context of multi-directional East Asian convergent tectonic system.
Section snippets
Strata and ophiolites around Amdo
The ADB is a roughly E-W-striking lenticular allochthonous micro-block, which is located on the eastern BNSZ between the QTB and the LHB (Xu et al., 1985, Zhu et al., 2011, Guynn et al., 2012). Its unique ancient basement distinguishes this block from the other terranes or micro-blocks around the BNSZ. The stratigraphic distribution of the ADB is nonuniform (Fig. 2a). The widely exposed Neoproterozoic Nyainrong Formation mainly comprises biotite plagioclase gneiss, amphibolite, diopside marble
Structural analysis
The major basement outcrops in the ADB are composed of highly deformed gneisses. From the late Mesozoic micro-block convergence to the Cenozoic India-Asia collision (Tapponnier and Molnar, 1976, Dong et al., 2008), the gneissic basement has experienced several tectonic events resulting in multi-stage deformation. However, the earlier gneisses, because of their high sensitivity to deformation, were replaced during the intensive late Mesozoic orogeny. Therefore, it is difficult to deduce the
Structural evidence for northward subduction polarity of the Amdo Ocean
The subduction polarity of the BNO has long remained controversial. For instance, Guynn et al. (2006a) proposed that the synchronous granitic magmatism and metamorphism of the ADB were related to the northward subduction of the oceanic lithosphere of the BNO. Zhu et al. (2013, 2016) suggested that it was related to the divergent double subduction of the BNO. Liu et al. (2011a) suggested that the Amdo island arc and QF back-arc deposition constituted within complete arc-basin system which
Conclusions
- (1)
Since the Mesozoic, the ADB has undergone five-stage deformation, as reflected in the NW-SE-striking tight folds, NE-SW-striking tight isoclinal folds, E-W-trending asymmetric folds, V-type conjugate strike-slip shear zones, and top-to-the-southwest thrust faults.
- (2)
The initial active NE-SW-striking collision occurred between the ADB and the QTB at 191 Ma, triggering Deformation D1. The slab rollback of the BNO south of the ADB caused the back-arc spreading in the QTB interior, forming a new
CRediT authorship contribution statement
Run-Hua Guo: Investigation, Conceptualization, Resources, Methodology, Writing – original draft. San-Zhong Li: Supervision, Funding acquisition, Writing – review & editing. Jie Zhou: Supervision, Writing – review & editing. Yi-Ming Liu: Investigation, Formal analysis. Sheng-Yao Yu: Resources, Funding acquisition. Yu-Hua Wang: Investigation, Formal analysis. Lin Liu: Conceptualization, Resources. M. Santosh: Writing – review & editing.
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 are thankful to Associate Editor Andrea Festa and two anonymous referees for their helpful comments which helped in improving our manuscript. This research was financially funded by National Key Research and Development Program of China (No. 2017YFC0601401), National Natural Science Foundation of China (Nos. 91958214, 41802232, 41702050), Fundamental Research Funds for the Central Universities (Nos. 202012015, 202072017), Qingdao National Laboratory for Marine Science and Technology (Nos.
References (134)
- et al.
Middle triassic volcanic rocks in the northern Qiangtang (central Tibet): geochronology, petrogenesis, and tectonic implications
Tectonophysics
(2016) - et al.
Late Triassic island-arc-back-arc basin development along the Bangong-Nujiang Suture Zone (central Tibet): Geological, geochemical and chronological evidence from volcanic rocks
Lithos
(2015) - et al.
Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane, central Tibet
Gondwana Res.
(2017) - et al.
Multiple deformations along the Honam shear zone in southwestern Korea constrained by Rb-Sr dating of synkinematic fabrics: implications for the Mesozoic tectonic evolution of northeastern Asia
Lithos
(2006) - et al.
The dynamic evolution of the palaeozoic geography of eastern Asia
Earth Sci. Rev.
(2013) - et al.
Tectonic evolution of the Qinling orogen, China: Review and synthesis
J. Asian Earth Sci.
(2011) - et al.
Late Paleozoic-Mesozoic subduction-related magmatism at the southern margin of the Siberian continent and the 150 million-year history of the Mongol-Okhotsk Ocean
J. Asian Earth Sci.
(2013) - et al.
Late Jurassic adakitic granodiorite in the Dong Co area, northern Tibet: Implications for subduction of the Bangong-Nujiang oceanic lithosphere and related accretion of the southern Qiangtang terrane
Tectonophysics
(2016) - et al.
Late Mesozoic calc-alkaline volcanism of post-orogenic extension in the northern Da Hinggan mountains, northeastern China
J. Volcanol. Geoth. Res.
(2003) - et al.
Deep-seated lithospheric geometry in revealing collapse of the Tibetan Plateau
Earth Sci. Rev.
(2018)
U-Pb geochronology of basement rocks in central Tibet and paleogeographic implications
J. Asian Earth Sci.
SHRIMP U-Pb zircon ages of pyroclastic rocks in the Bansong Group, Taebaeksan Basin, South Korea and their implication for the Mesozoic tectonics
Gondwana Res.
Thermo-mechanical controls of flat subduction: insights from numerical modeling
Gondwana Res.
Geochronological and geochemical constraints on the petrogenesis of Mesozoic high-K granitoids in the central Korean Peninsula
Gondwana Res.
Early Cretaceous sedimentary evolution of the northern Lhasa Block terrane and the timing of initial Lhasa Block-Qiangtang Block collision
Gondwana Res.
Early Jurassic tectonism occurred within the Basu metamorphic complex, eastern central Tibet: Implications for an archipelago-accretion orogenic model
Tectonophysics
An Andean-type retro-arc foreland system beneath northwest South China revealed by SINOPROBE profiling
Earth Planet. Sci. Lett.
Structural and geochronological constraints on the Mesozoic tectonic evolution of the North Dabashan zone, South Qinling, central China
J. Asian Earth Sci.
Geochronology, geochemistry, and zircon Hf isotopic compositions of Mesozoic intermediate-felsic intrusions in central Tibet: Petrogenetic and tectonic implications
Lithos
Two-stage collision-related extrusion of the western Dabie HP-UHP metamorphic terranes, central China: Evidence from quartz c-axis fabrics and structures
Gondwana Res.
Mesozoic tectono-magmatic response in the East Asian ocean-continent connection zone to subduction of the Paleo-Pacific Plate
Earth Sci. Rev.
SHRIMP U-Pb zircon geochronology of the Liaoji granitoids: Constraints on the evolution of the Paleoproterozoic Jiao-Liao-Ji Belt in the Eastern Block of the North China Craton
Precambrian Res.
Closure of the Proto-Tethys Ocean and Early Paleozoic amalgamation of microcontinental blocks in East Asia
Earth Sci. Rev.
Zircon U-Pb age and Hf isotopic compositions of Mesozoic granitoids in southern Qiangtang, Tibet: Implications for the subduction of the Bangong-Nujiang Tethyan Ocean
Gondwana Res.
Mesozoic intraplate tectonism of East Asia due to flat subduction of a composite Yanshanian slab
Earth Sci. Rev.
Cretaceous structures in the Duolong region of central Tibet: Evidence for an accretionary wedge and closure of the Bangong-Nujiang Neo-Tethys Ocean
Gondwana Res.
Diachronous closure of the Shuanghu Paleo-Tethys Ocean: constraints from the Late Triassic Tanggula arc-related volcanism in the East Qiangtang subterrane, Central Tibet
Lithos
A new concept on tectonic correlation between Korea, China and Japan: histories from the late Proterozoic to Cretaceous
Gondwana Res.
Amount of Asian lithospheric mantle subducted during the India/Asia collision
Gondwana Res.
Evidence for southward subduction of the Mongol-Okhotsk oceanic plate: Implications from Mesozoic adakitic lavas from Mongolia
Gondwana Res.
Melt/mantle mixing produces podiform chromite deposits in ophiolites: Implications of Re-Os systematics in the Dongqiao Neo-tethyan ophiolite, northern Tibet
Gondwana Res.
Mesozoic-Cenozoic basin inversion and geodynamics in East China: A review
Earth Sci. Rev.
Eastward tectonic migration and transition of the Jurassic-Cretaceous Andean-type continental margin along Southeast China
Earth Sci. Rev.
Timing of mylonitization in the Funatsu shear zone within Hida belt of southwest Japan: Implications for correlation with the shear zones around the Ogcheon belt in the Korean Peninsula
Gondwana Res.
1:250000 Kulangmikti County, regional geological survey report of the People's Republic of China
Characteristics and zircon SHRIMP U-Pb dating of the Amdo trachyte, Tibet, China
Geol. Bull. China
1:250000 Amdo County, regional geological survey report of the People's Republic of China
Understanding Mesozoic accretion in Southeast Asia: significance of Triassic thermotectonism (Indosinian Orogeny) in Vietnam
Geology
Two phases of Mesozoic north-south extension in the eastern Altyn Tagh range, northern Tibetan Plateau
Tectonics
The structure of the 1985 Tibet geotraverse, Lhasa Block to Golmud
Philos. Trans. R. Soc. Lond. A. Math. Phys. Sci.
Constraints on absolute motion and plate interaction inferred from Cenozoic igneous activity in the western United States
Am. J. Sci.
The tectonic evolution of the Tibetan Plateau
Philos. Trans. R. Soc. Lond. A. Math. Phys. Sci.
The Yanshan orogeny and late Mesozoic multi-plate convergence in East Asia—Commemorating 90th years of the “Yanshan Orogeny”
Sci. China Earth Sci.
Jurassic tectonic revolution in China and new interpretation of the “Yanshan Movement”
Acta Geol. Sin. - English Ed.
Age and evolution of late Mesozoic metamorphic core complexes in southern Siberia and northern Mongolia
J. Geol. Soc.
Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction
Geology
Paleomagnetic constraints on the geodynamic history of the major blocks of China from the Permian to the present
J. Geophys. Res. Solid Earth
Permo-Triassic collision, subduction-zone metamorphism, and tectonic exhumation along the East Asian continental margin
Annu. Rev. Earth Planet. Sci.
Reconstructing in space and time the closure of the middle and western segments of the Bangong-Nujiang Tethyan Ocean in the Tibetan Plateau
Int. J. Earth Sci.
Observations et réflexions sur la géologie stratigraphique et structurale de l’Indochine
Bull. Soc. Geol. Fr.
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