西藏错那洞穹隆早古生代岩浆成因:来自锆石U-Pb年代学及地球化学特征的证据OACHSSCD

The Cuonadong gneiss dome is situated on the southern flank of the Tethyan Himalaya,adjacent to the South Tibetan Detachment System(STDS).It exhibits a tripartite structure comprising a core,a mantle,and a rim.The core is composed of granitic gneiss and leucogranite,intruded by numerous pegmatite veins.The mantle consists of a suite of intensely metamorphosed and deformed two-mica schist,while the rim is primarily composed of low-grade metamorphosed sedimentary sequences.Geochronological results indicate that zircons from the granitic gneiss exhibit magmatic zircon characteristics with corresponding Th and U contents,yielding a weighted mean age of 500.8±3.5 Ma(n=24,MSWD=0.04),which represents the crystallization age of the granitic gneiss.The granitic gneiss is characterized by high silica,peraluminous,and alkali-rich compositions.It shows pronounced fractionation between light and heavy rare earth elements(enriched in LREE and depleted in HREE),a negative Eu anomaly,and depletion in Ti,Nb,and Ta.The Nb/Ta ratios range from 8.54 to 10.60,significantly lower than the mantle-derived magma ratio(17±1),indicating typical crustal signatures.Its age is essentially consistent with the core gneisses of other domes within the North Himalayan Gneiss Domes(NHGD),identifying it as a product of Pan-African to Early Paleozoic orogenesis.Integrating regional Early Paleozoic magmatic activity and Cenozoic doming-related metamorphic events,the formation of the Early Paleozoic granitic gneiss was controlled by orogenic processes related to the subduction of the Proto-Tethys oceanic slab beneath the Gondwana continent.The granitic gneiss of the Cuonadong dome also records metamorphism and anatexis events subsequent to the Cenozoic India-Eurasia continental collision orogeny.