新疆北部可可托海地区阿拉尔复式花岗岩体形成机制的探讨OA

The Aral composite granitic pluton in the Koktokay area of northern Xinjiang is composed of different intrusive units.This study obtained LA-ICP-MS zircon U-Pb isotopic ages of 217.3±3.8 Ma,218.6±2.4 Ma,and 216.5±6.3 Ma for the medium-to fine-grained biotite monzogranite,medium-grained porphyritic two-mica syenogranite,and medium-to coarse-grained porphyritic two-mica syenogranite,respectively.The rocks are characterized by high silicon,low titanium,enrichment in potassium and aluminum,and depletion in magnesium;strong negative Eu anomalies(δEu=0.30～0.72);enrichment in large-ion lithophile elements(LILEs)such as Rb,Th,and U,and rare earth elements(REEs)such as La,Ce,Nd,and Sm,while being depleted in Ba,Nb,Sr,P,and Ti.They belong to typical low-Ba and low-Sr granites,indicating that the pluton was likely the product of low-degree partial melting of crustal sources.The n(176Hf)/n(177Hf)ratios of the medium-grained porphyritic two-mica syenogranite and the medium-to coarse-grained porphyritic two-mica syenogranite are 0.282642～0.282800 and 0.282675～0.282763,respectively.Their εHf(t)values range from-0.02 to 5.73 and from 1.03 to 4.37,respectively,and their second-stage Hf model ages(TDM2)are 759～1052 Ma and 827～993 Ma,respectively.This suggests that the magmas were likely derived from the partial melting of Precambrian microcontinental block crustal materials,with the involvement of mantle-derived components.Integrating regional data,it is proposed that during the Triassic period,a large mid-to deep-crustal magma chamber might have existed in the Altay Orogenic Belt.This magmatic activity involved the supply of mantle-derived magmas and underwent complex magmatic evolution processes,including assimilation of crustal materials and magma mixing.The heat source for this activity was likely related to the Siberian super mantle plume.