The tectonic evolution of the East Kunlun Orogen, northern Tibetan Plateau: A critical review with an integrated geodynamic model

Abstract

The East Kunlun Orogen is an integral component of the northern Qinghai-Tibet plateau. Here we synthesize the geologic, geochemical, geochronological and stratigraphical dataset and propose an integrated geodynamic model to illustrate the tectonic evolution of this orogen. This review also provides important insights on the complex Phanerozoic plate tectonic processes. We envisage the protracted multi-stage accretion and collision of a collage of terranes during the subduction and closure of the South Kunlun and Anemaqen oceans, from the Neoproterozoic to Early Mesozoic. The East Kunlun orogen is tectonically divided into the North Kunlun Terrane (NKT), South Kunlun Terrane (SKT), Muz Tagh-Anemaqen Terrane (MAT) and Hoh Xil-Bayan Har Terrane (HBT) from the north to south, of which evolution can be divided into six stages from Late Neoproterozoic-Early Mesozoic age (550 Ma–200 Ma): I. ca. 540–481 Ma; II. ca. 481–424 Ma; III. ca. 424–370 Ma; IV. ca. 370–271 Ma (magmatic gap); V ca. 271–224 Ma; and VI. ca. 224–201 Ma.The NKT, as an active continental margin initiated at ca. 450 Ma as a consequence of backarc ocean lithosphere subduction in the late Ordovician-middle Silurian (Stage II). The closure of back arc basin led to an oblique collision between the NKT and SKT during the early-middle Silurian (Stage II), and to a post-collisional environment in the late Silurian-middle Devonian (Stage III). The SKT and MAT developed as a young island arc, both carrying large amounts of ocean island arc granitoids (OAGs) and SSZ (supra-subduction zone) type ophiolites together with island arc tholeiite (IAT), as a consequence of bidirectional subduction of Proto-Tethys Ocean (Stage I). During the collision between SKT and NKT, the SKT transformed from a young island arc into a mature island arc With thickening crust, and the granitoids geochemically evolved from the OAGs to CAGs (continental arc granitoids)-WPGs (within-plate granitoids) in the late Ordovician-middle Silurian (Stage II). The collision between SKT and MAT probably occurred after the middle Devonian (Stage III), as evidenced from the absence of the upper Devonian strata in the SKT. The SKT and MAT is interpreted as an exotic terrane that has been accreted onto the continental margin and contributed significantly to the continental growth in this orogenic belt. A magmatic quiescence occurred during ca. 370–270 Ma (Stage IV) associated with subduction polarity reversal. A new subduction zone initiated at the southern margin of the MAT after the middle Permian (Stage V), which subsequently resulted in extensively development of calc-alkaline granitoids in the NKT, SKT and MAT. The progressive chronology change of granitoids from NKT to further south maybe the joint results of flat subduction and slab rollback which make magmatism center retrograde migrate towards the trench. The final closure of the Anemaqen Ocean might have occurred in the Late Triassic (Stage VI) as indicated by the upper Triassic Babaoshan terrestrial molasse formation and development of CAGs and WPGs in the HBT, which resulted in the accretion of the North Qiang-Tang microcontinent.