Paleo‐Tethyan Oceanic Crust Subduction in the Eastern Section of the East Kunlun Orogenic Belt: Geochronology and Petrogenesis of the Qushi'ang Granodiorite

Abstract

The Qushi'ang granodiorite (QSG) is located at the central east of the ophiolitic melange belt in the East Kunlun Orogenic Belt (EKOB) in the northern margin of the Qinghai‐Tibetan Plateau. LA‐MC‐ICP‐MS zircon U–Pb dating suggests that the granodiorite and mafic microgranular enclaves (MMEs) crystallized 246.61±0.62 and 245.45±0.9 Ma ago, respectively. Granodiorite, porphyritic diorite, and MMEs are metaluminous and medium‐K calk ‐ alkaline series, with island‐arc magma features, such as LILE enrichment and HFSE depletion. The porphyritic diorite has high Cr (13.50 ppm to 59.01 ppm), Ni (228.53 ppm to 261.29 ppm), and Mg# (46–54). Granodiorite and porphyritic diorite have similar mineral compositions and evolved major and trace elements contents, particularly Cr and Ni, both of which are significantly higher than that in granites of the same period. The crystallization age of MMEs is close to that of granodiorite, and their major and trace elements contents are in‐between porphyritic diorite and granodiorite. The results suggest that the original mafic magma, which was the product of mantle melting by subduction process, intruded into the lower crust (Kuhai Rock Group), resulting in the formation of granodiorite. Countinous intrusion of mafic magma into the unconsolidated granodiorite formed MMEs and porphyritic diorite. The granodiorite reformed by late‐stage strike‐slip faulting tectonic event indicates that the strike‐slip fault of Middle Kunlun and the collision of the Bayanhar block with East Kunlun were later than 246 Ma. Therefore, the formation of the QSG not only indicates the critical period of evolution of East Kunlun but also represents the tectonic transition from oceanic crust subduction to slab breaking.

Zircon U–Pb geochronology, Hf isotopes, and whole‐rock geochemistry of Hongshuihe Early to Middle Triassic quartz diorites and granites in the Eastern Kunlun Orogen, NW China: Implication for petrogenesis and geodynamics

“…Comparing with the 244‐Ma Balugou granitic rocks (Ding et al, ), 247–249‐Ma Wulonggou granodiorite (Ding et al, ), and 246‐Ma Xiaoyakou granites (Ding et al, ), nearly 80 km away, the Hongshuihe granitoids may have a strong relationship with those Triassic magmatic rocks in temporal and spatial distribution, as well as other similar granitic rocks in the MKL (e.g., Qushi'ang granodiorite, Asiha diorite, Manzhang'gang granodiorite, and Kaerqueka granodiorite; Chen et al, ; Li, Sun, et al, ; Ren et al, ; Yao et al, ). The Early–Middle Triassic granitic intrusions from Hongshuihe area are critically important in understanding the Late Palaeozoic–Early Mesozoic petrogenesis of granites and tectonic evolution of MKL discussed below.…”

“…(2) 250 Ma (Chen et al, 2011); (3) Balugou granite, 244 Ma ; (4) Naomuhun granodiorite, 261 Ma (Xiong et al, 2012); (5) South Dulan granodiorite, 250 Ma (Huang et al, 2014); (6) Yuegelu granodiorite, 242 Ma (Liu et al, 2004); (7) 253 Ma (Chen et al, 2011); (8) Wulonggou granodiorite, 248 Ma; Xiaoyakou granite, 246 Ma (Ding et al, 2015). The extent of Figure 2 is also shown [Colour figure can be viewed at wileyonlinelibrary.com] Jurassic clastic and carbonate sedimentary and some granitic intrusions emplaced between the Late Palaeozoic to early Mesozoic in the central part (Chen et al, 2017;Ding et al, 2014).…”

“…Late Palaeozoic magmatic rocks, mostly monzonite granite and granodiorite, are widespread (Jiang et al, ). The SKL within the M.KLB and S.KLB‐AFM is characterized by widespread Precambrian to Jurassic clastic and carbonate sedimentary and some granitic intrusions emplaced between the Late Palaeozoic to early Mesozoic in the central part (Chen et al, ; Ding et al, ).…”

“…The EKO was previously described as a Late Palaeozoic orogen, but recent research indicates that it was a composite orogen (Chen et al, 2017;Ding et al, 2015). The EKO evolved tectonically from Early Palaeozoic to Cenozoic (Chen et al, 2017;Ding et al, 2014;Jiang et al, 1992;Liu et al, 2005;Mo et al, 2007).…”

“…The data-point error ellipses are 68.3% confidence. Red solid line circles of CL images are the location of U-Pb age analyses, and blue dashed lines are the locations of Hf isotope analysis spots [Colour figure can be viewed at wileyonlinelibrary.com] Asiha diorite, Manzhang'gang granodiorite, and Kaerqueka granodiorite;Chen et al, 2017;Li, Sun, et al, 2012;Ren et al, 2016;Yao et al, 2017). The Early-Middle Triassic granitic intrusions from Hongshuihe area are critically important in understanding the Late Palaeozoic-Early Mesozoic petrogenesis of granites and tectonic evolution of MKL discussed below.…”