Discovery of the Ordovician arc-type gabbros in Nanpingxueshan area,West Kunlun orogenic belt,and its geological significance
The Early Paleozoic magmatic rocks in the western Kunlun orogenic belt preserve crucial information regarding the evolution of Proto-Tethys tectonics within the region.Our research group recently recognized the Ordovician gabbros in the Nanpingxueshan area,on the southern West Kunlun orogenic belt.LA-MC-ICPMS zircon U-Pb dating results indicate that the gabbro was formed during the Early Ordovician(476～471 Ma).The gabbro exhibits high Al2O3(14.32％～16.91％)and TiO2(1.20％～2.53％),low P2O5(0.22％～0.55％)and alkali(Na2O+K2O=4.03％～5.84％),and variable SiO2(52.27％～56.65％)and MgO(2.98％～7.59％).Some samples exhibit Nb-enriched signatures,with relatively high SiO2(53.08％～56.86％),low MgO(2.98％～6.05％),high TiO2(1.48％～2.54％)and Nb(7.64×10-6～14.08×10-6).All samples are characterized by enrichment of large ion lithophile elements(LILEs;Rb,Th,U,K)and light rare earth elements,while depleted in Nb,Ta,Sr.These features are typical of island arc magmatic rocks.Isotopically,the gabbros are depleted inεNd(t)values(2.84～4.04).Based on their similar geochemical characteristics,we hypothesize that the Ordovician gabbros were originated by partial melting of the depleted mantle metasomatized by melts from subducted slabs.Based on regional geological characteristics,we propose that the unique assemblages of continental arc gabbros(530 Ma),Nb-enriched arc-like gabbros(476～471 Ma),and OIB-type pillow basalts(465 Ma)in the Mazar-Tianshuihai terrane are associated with the back-arc extension environment resulting from the retreat of subducted Proto-Tethys oceanic slab.
Early PaleozoicOrdovician gabbroProto-Tethys OceanWest Kunlun orogenic beltNanpingxueshan area
万方数据
维普
