Petrogenesis of Haidewula Diabase,Eastern Kunlun Orogenic Belt and Its Geological Implications
The timing of the closure of the A'nyemaqen ocean,which was a branch of Paleo-Tethys ocean at the East Kunlun orogenic belt(EKOB),is still a subject of debate.In this study,it presents zircon U-Pb geochronology,whole-rock elemental geochemistry and Sr-Nd isotopic data on the Haidewula diabase in the eastern section of the EKOB.Zircon LA-ICP-MS U-Pb isotope dating reveals that the Haidewula diabase formed at 238±2 Ma.The diabase is characterized by low MgO(2.76%-6.34%)contents,as well as relatively high TiO2(1.75%-2.46%)and Fe2O3T(8.88%-12.30%)contents.The diabase shows enrichment in incompatible elements,but is relatively depleted in Nb,Ta,Sr,and Ti.All these geochemical characteristics imply that the diabase is a production of island arc magmatic activity.Additionally,the diabase displays enriched and uniform Sr-Nd isotopic compositions((87Sr/86Sr)i= 0.711 61-0.712 95,εNd(t)=-3.2 to-2.8).Based on the geochemical characteristics and isotopic compositions,it suggests that the Haidewula diabase was derived from partial melting of an enriched mantle,which had undergone metasomatism induced by the fluid released from the subducting slab,and had experienced some degree of crustal contamination during migration through continental crust.Combing our results and previous studies on Middle Permian-Triassic basic igneous rocks in the EKOB,it proposes that the northward subduction of the A'nyemaqen ocean lasted to the end of the Middle Triassic(238 Ma);the closure of the A'nyemaqen ocean happened during early Late Triassic;then,the tectonic environment of the eastern section of the EKOB transited into post-collisional extension no later than 228 Ma.
East Kunlun orogenic belttectonic evolutionTriassicdiabasepetrogenesispetrology
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