峨眉山大火成岩省幔源岩浆底侵作用的地壳响应：来自大老包花岗岩的年代学和热模拟证据

Mantle-derived magmas underplating and its effect on the crust in the Emeishan large igneous province: Evidence from geochronological study and numerical simulation of Dalaobao granites

峨眉山大火成岩省中红格铁矿区的大老包花岗岩侵入到含矿基性一超基性杂岩，花岗岩主要为黑云母二长花岗岩。通过对大老包黑云母二长花岗岩的锆石LA-ICP—MS U-Pb年龄测定，获得大老包花岗岩形成时代为255．1±3．6Ma。该研究结果与前人通过红格东侧的矮郎河高铝花岗岩的u-Pb测年得到的花岗岩成岩时代（255．2±3．6Ma）结果一致，表明大老包花岗质岩体与矮郎河高铝花岗岩是同阶段的，可能是二叠纪峨眉山大火成岩省岩浆活动晚期的产物。这一成岩时代晚于攀枝花铁矿成矿时代（～260Ma）。通过本文得到的大老包花岗岩的形成时代和前人测得的二叠纪峨眉山大火成岩省主体岩浆的活动时间，笔者基于国际上最新的下地壳热区模型进行数值模拟，认为峨眉山大火成岩省幔源岩浆底侵过程中可以导致下地壳发生部分熔融，大老包花岗岩可能是峨眉山大火成岩省喷发过程中底侵的玄武质岩浆在4Myr内部分熔融下地壳形成的。

The Hongge Dalaobao granitic stock in the Emeishan large igneous province, SW China, shows spatical association with the giant Fe-Ti-V deposit-bearing mafic-lutramafic intrusion. This granitic intrusion is composed of medium- to fine-grained biotite monzonitic granite. In situ ziron LA-ICP-MS U-Pb age indicates that the age of monzogranite is 255.1 ± 3.6Ma, which is consistent with the ages （255.2 ± 3.6Ma） by zircon U-Pb of peraluminous granites from Ailanghe. The ages show Dalaobao granites are related to the upwelling of the Emeishan plume. The age is 4Myr younger than the main stage （ ～ 260Ma） of the Emeishan volcanism. Based on the deep crustal hot zones, the results of numerical simulation show that the partial melting of deep crust and the Dalaobao granites magmatism are triggered by conductive heating of the mantle-driven magma. Key words Emeishan Large igneous province; Pan-Xi area; Hongge granites ; Age of magmatic intrusion