西藏南木林地区达那古火山机构中花岗岩大地构造意义OA北大核心CSTPCD

The newly discovered Dana ancient volcanic edifice in the Nanmulin area of Xizang provides a window for exploring the lithofacies composition of continental volcanic edifice and its tectonic significance.This study con-ducts geological profile measurements and petrographic studies on the Dana ancient volcanic edifice,and conducts zircon LA-ICP-MS U-Pb dating and the whole-rock geochemical analysis for the porphyric monzonitic granite which intrusived into volcanic channel laterly.The results show that the zircon U-Pb age of the porphyric monzonitic gran-ite is 54.0±1.4 Ma,with high silicon(SiO2=71.03％～75.88％),high potassium and low sodium(K2O/Na2O=1.45～1.79),rich alkali(ALK=8.97％～9.67％),and low titanium(TiO2=0.17％～0.37％)characteristics.The A/CNK value ranges from 0.95 to 1.00,and the Rittman index(σ)ranges from 2.45 to 3.38,belonging to the quasi-aluminous and calc-alkaline rock series.Enrichment of light rare earth elements and relative depletion of heavy rare earth elements(LREE/HREE=7.60～9.78),with obvious differentiation characteristics,(La/Sm)N=2.85～4.21;Large ion lithophilic elements such as Rb,Th,U(LILE)and incompatible elements are relatively enriched,while high field strength elements such as Nb,Ta,P,Ti(HFSE)are relatively depleted,exhibiting typ-ical geochemical properties of subduction arc or crustal magmatic rocks.Based on the above geological information,it is indicated that the Dana ancient volcanic edifice was formed before 54 Ma,and the porphyric monzonitic granite was formed in the tectonic background of the active continental margin during the India-Eurasia collision.Under the action of mantle-derived magma intrusion,the middle and lower crust melted,and then the magma differentiated and ascended to infiltrate and crystallize in the volcanic channel.