Metamorphism and deformation of blueschist belts and their tectonic implications, North Qilian Mountains, China

Hanquan, Wu; Yimin, Feng; Song, Shuguang

doi:10.1111/j.1525-1314.1993.tb00169.x

Cited by 116 publications

(8 citation statements)

References 14 publications

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“…The Early Neoproterozoic event recorded in the north Qaidam Mountains and the adjacent Qilian terrane suggests that they may share a common Neoproterozoic history with the south China block rather than the north China block. This argues against the suggestion that north Qaidam Mountains-Qilian terrane is a fragment split off from the north China craton during Neoproterozoic to early Paleozoic times (e.g., Wu et al, 1993). Nevertheless, because of thorough overprinting during early Paleozoic metamorphism, as discussed below, it is diffi cult to constrain the details of the Neoproterozoic event based on the present data.…”

Section: The Early Neoproterozoic Tectonothermal Eventcontrasting

confidence: 60%

Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: Evidence from zircon U-Pb geochronology

Zhang

Mattinson

Meng

et al. 2008

Geological Society of America Bulletin

170

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High-grade gneisses of the north Qaidam high-pressure/ultrahigh-pressure metamorphic terrane enclose minor eclogites and ultramafi c rocks. In combination with petrological data, sensitive high-resolution ion microprobe U-Pb geochronology on the granulitized gneisses in the Luliangshan and Xitieshan, western north Qaidam Mountains, reveals a polyphase tectonothermal history including Early Neoproterozoic and Early Paleozoic events. The rocks investigated are two granulite-facies paragneisses and one orthogneiss that both surround garnet peridotite in the Luliangshan, and two paragneisses that enclose eclogite in the Xitieshan. The inherited zircon cores from paragneiss and orthogneiss yield ages between ca. 1000 Ma and ca. 2500 Ma, representing Mesoproterozoic to Archaean source material for these gneisses. A ca. 900 Ma age obtained from one orthogneiss and one paragneiss is interpreted as the age of simultaneous Early Neoproterozoic magmatism and metamorphism. This Early Neoproterozoic tectonothermal event is similar in age to the Jinning orogeny, which is commonly recognized in the metamorphic basement of the south China block, and suggests that the north Qaidam Mountains have an affi nity to the south China block. Early Paleozoic metamorphism is recorded in all gneiss samples. In conjunction with cathodoluminescence imagery and mineral inclusions, U-Pb dating of zircons reveals two Early Paleozoic age groups: ca. 450 Ma represents the age of high-pressure granulite metamorphism (Grt + Rt inclusions in zircon; kyanite porphyroblasts), whereas ca. 425 Ma refl ects the time of medium-pressure, granulite-facies metamorphism (Pl + Sil inclusions in zircon) and associated anatexis during decompression. The ages obtained suggest that the granulitefacies metamorphism lasted for ~25 m.y. and was related to the Early Paleozoic continental collision between the Qilian and Qaidam blocks, and to subsequent thermal relaxation and exhumation.

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Section: The Early Neoproterozoic Tectonothermal Eventcontrasting

confidence: 60%

Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: Evidence from zircon U-Pb geochronology

Zhang

Mattinson

Meng

et al. 2008

Geological Society of America Bulletin

170

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“…1 and 3). This includes eclogite and UHP metamorphism of continental and oceanic material exposed in the Altyn Tagh Range and North Qaidam (Sobel and Arnaud, 1999;Zhang et al, 2005;Yin et al, 2007b;Menold et al, 2009;Song et al, 2014), early Paleozoic arc-related granitoids throughout northern Tibet, Cambrianaged ophiolites including supra-subduction zone ophiolites (Song et al, 2013), ophiolitic mélange dispersed throughout the Qilian Shan, and early Paleozoic blueschist and eclogite in the northern Qilian Shan and Altyn Tagh Range (e.g., Wu et al, 1993;Liu et al, 2006;Song et al, 2006Song et al, , 2007Zhang et al, 2007;Xiao et al, 2009;Cheng et al, 2016;Fig. 1).…”

Section: Tectonic Models For the Qilian Orogenmentioning

confidence: 99%

Tectonic evolution of the Qilian Shan: An early Paleozoic orogen reactivated in the Cenozoic

et al. 2017

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The Qilian Shan, located along the northeastern margin of the Tibetan Plateau, has experienced multiple episodes of tectonic deformation, including Neoproterozoic continental breakup, early Paleozoic subduction and continental collision, Mesozoic extension, and Cenozoic intracontinental orogenesis resulting from the India-Asia collision. In the central Qilian Shan, pre-Mesozoic ophiolite complexes, passive-continental margin sequences, and strongly deformed forearc strata were juxtaposed against arc plutonic/ volcanic rocks and ductilely deformed crystalline rocks during the early Paleozoic Qilian orogen. To better constrain this orogen and the resulting closure of the Neoproterozoic-Ordovician Qilian Ocean, we conducted an integrated investigation involving geologic mapping, U-Th-Pb zircon and monazite geochronology, whole-rock geochemistry, thermo barometry, and synthesis of existing data sets across northern Tibet. The central Qilian Shan experienced two phases of arc magmatism at 960-870 Ma and 475-445 Ma that were each followed by periods of protracted continental collision. Integrating our new data with previously published results, we propose the following tectonic model for the Proterozoic-Paleozoic history of northern Tibet. (1) Early Neoproterozoic subduction accommodated the convergence and collision between the South Tarim-Qaidam and North Tarim-North China continents. (2) Late Neoproterozoic rifting partially separated a peninsular Kunlun-Qaidam continent from the southern margin of the linked Tarim-North China craton and opened the Qilian Ocean as an embayed marginal sea; this separation broadly followed the trace of the earlier Neoproterozoic suture zone. (3) South-dipping subduction along the northern margin of the Kunlun-Qaidam continent initiated in the Cambrian, first developing as the Yushigou supra-subduction zone ophiolite and then transitioning into the continental Qilian arc. (4) South-dipping subduction, arc magmatism, and the convergence between Kunlun-Qaidam and North China continued throughout the Ordovician, with a trenchparallel intra-arc strike-slip fault system that is presently represented by high-grade metamorphic rocks that display a pervasive right-lateral shear sense. (5) Counterclockwise rotation of the peninsular Kunlun-Qaidam continent toward North China led to the closure of the Qilian Ocean, which is consistent with the right-lateral kinematics of intra-arc strike-slip faulting observed in the Qilian Shan and the westward tapering mapview geometry of Silurian flysch-basin strata. Continental collision at ca. 445-440 Ma led to widespread plutonism across the Qilian Shan and is recorded by recrystallized monazite (ca. 450-420 Ma) observed in this study. Our tectonic model implies the parallel closure of two oceans of different ages along the trace of the Qilian suture zone since ca. 1.0 Ga. In addition, the Qilian Ocean was neither the Proto-nor Paleo-Tethys (i.e., the earliest ocean separating Gondwana from Laurasia), as previously suggested, but was rather a relatively sm...

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“…Zhang et al, 2017c;Song et al, 2017), strikes NW-SE and extends for more than 1000 km. The NQOB consists of two ophiolite belts, volcanic and granitic rocks, high pressure (HP) metamorphic rocks, and accretionary complexes and was regarded as a suture zone between the Alxa terrane and the Central Qilian block (Wu et al, 1993;Wang et al, 2005;Song et al, 2007Song et al, , 2013Song et al, , 2014aZhang et al, 2007;J.X. Zhang et al, 2017a;Y.Q.…”

Section: Geological Backgroundmentioning

confidence: 99%

Early Paleozoic collision-related magmatism in the eastern North Qilian orogen, northern Tibet: A linkage between accretionary and collisional orogenesis

Kusky

Wilde

et al. 2018

GSA Bulletin

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Collision-related magmatism in accretionary-to-collisional orogens records a tectonic transition from early subductionaccretionary processes to collisional orogenesis, and also plays a significant role in continental growth. Here, we present an integrated study of field observations, geochemistry, whole-rock Rb-Sr and Sm-Nd isotopes, and zircon U-Pb ages and Lu-Hf isotopes for the Laohushan mafic to felsic magmatic rocks related to initial collision between the Alxa terrane and the Central Qilian block along the North Qilian orogenic belt, northeastern Tibet. The Laohushan magmatic rocks are dominated by quartz diorites (ca. 426 Ma), with minor tonalites enclosing dioritic enclaves (ca. 430 Ma) and hornblendite xenoliths (ca. 448 Ma), and some coeval dolerite dikes (ca. 427 Ma) intruded into the accretionary complex. The quartz diorites are characterized by light rare earth element (LREE)-and large ion lithophile element (LILE)-enrichment but have high field strength element (HFSE)-depleted trace element patterns and negative initial ε Nd (-1.6 to-2.9) and positive zircon initial ε Hf (+3.0 to +6.2) values. The dioritic enclaves are also characterized by LREE-enriched and HFSE-depleted patterns and have mostly negative initial ε Nd (-9.2 to +0.03) but positive zircon initial ε Hf (+3.0 to +5.9) values. These geochemical and isotopic features, together with isotopic mixing calculations, suggest that the quartz diorites were likely derived from partial melting of the lower crust dominated by accreted mafic oceanic rocks with minor sediments, whereas the dioritic enclaves originated from underplated mantlederived magmas mixed with crust-derived melts. The hornblendite xenoliths have high MgO, Cr, and Ni contents, positive Th, U, and Pb anomalies, and negative Nb, Ta, and Ti anomalies. They have negative initial ε Nd (-2.8), near chondritic zircon initial ε Hf (-0.4 to +1.4) values and an Archean Nd model age (T DM = 2.74 Ga), suggesting that the hornblendites were likely produced by partial melting of subcontinental lithospheric mantle peridotite that was metasomatized by subduction-related melts beneath the Archean-Proterozoic Alxa terrane. We propose that partial melting of the lower crust of the early Paleozoic North Qilian orogenic belt was in response to slab breakoff and asthenospheric upwelling during the initial stage of collisional orogenesis. This study demonstrates that heterogeneous magma sources, involving accretionary materials (i.e., accreted oceanic crust and sediments) and various mantle-derived components, were mixed to form the collision-related magmatic rocks. It also highlights the significance of collisionrelated magmatism in continental growth and stabilization of newly-assembled crust in accretionary-to-collisional orogens.

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Metamorphism and deformation of blueschist belts and their tectonic implications, North Qilian Mountains, China

Cited by 116 publications

References 14 publications

Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: Evidence from zircon U-Pb geochronology

Polyphase tectonothermal history recorded in granulitized gneisses from the north Qaidam HP/UHP metamorphic terrane, western China: Evidence from zircon U-Pb geochronology

Tectonic evolution of the Qilian Shan: An early Paleozoic orogen reactivated in the Cenozoic

Early Paleozoic collision-related magmatism in the eastern North Qilian orogen, northern Tibet: A linkage between accretionary and collisional orogenesis

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