花岗质岩浆侵位对围岩裂隙发育和热结构影响的数值模拟  

Numerical modelling of fracture development and thermal structure of host rocks during emplacement of granitic magma

作　　者：卢靖雯 王勤[1,2] 刘春 LU Jingwen;WANG Qin;LIU Chun(School of Earth Sciences and Engineering,Nanjing University,Nanjing,Jiangsu 210046.China;State Key Laboratory for Mineral De posits Research,Nanjing University,Nanjing,J iangsu 210046,China)

机构地区：[1]南京大学地球科学与工程学院,江苏南京210046 [2]内生金属矿床成矿机制研究国家重点实验室,江苏南京210046

出　　处：《地质学报》2022年第10期3619-3638,共20页Acta Geologica Sinica

基　　金：国家自然科学基金委杰出青年基金项目(编号41825006)资助的成果。

摘　　要：岩浆侵位会引起围岩的接触变质作用和变形,虽然围岩中的破裂提供了流体活动和元素迁移的重要通道,但是大多数岩浆侵位模型忽略了围岩中热对流的影响。本文总结了岩浆侵位的数值模拟原理和常用模拟方法,然后使用离散元软件MatDEM建立了二维的双层围岩模型和均质围岩模型,用孔隙密度流法模拟花岗质岩浆侵位和冷却过程中岩浆与围岩之间的流-固-热-力耦合过程。结果表明岩浆侵位过程中围岩的裂隙发育和热对流对接触变质晕具有重要影响,围岩的裂隙发育和热传输模式可分为三个阶段:(1)岩浆侵位初期的挤压力使围岩中产生广泛分布的、呈径向展布的剪裂隙,围岩以热传导和孔隙渗流为主导;(2)在持续的孔隙流体压下,径向裂隙连通形成主干张性断裂并向上扩展,成为熔/流体迁移的重要通道以及伟晶岩型和热液型矿床的成矿空间,通道流和局部热对流控制了围岩的热传输;(3)在岩浆侵位后期,岩浆房附近围岩中的孔隙流体压增大,在侵入体与围岩的接触带形成大量张裂,加强了变质晕内的热对流,有助于矽卡岩型矿床的形成。与只有热传导的模型对比,热对流使围岩中变质晕的宽度减小。接触变质晕的几何形态受侵入体的形态控制,但是变质晕宽度在空间上有显著差异。本研究为重建岩浆侵位过程中的变质-变形-成矿作用提供了新方法。Emplacement of granitic magma causes contact metamorphism and brittle deformation in host rocks.These fractures provide important pathways for fluid activity and element migration.However,most magma emplacement models ignored the influence of thermal convection.Here we summarize numerical simulation principles of magma emplacement and compare different simulation methods.Using the MatDEM discrete element software,we establish a double-layer host rock model and a homogeneous host rock model.The pore-density flow method of MatDEM was applied to simulate the fluid-solid-heat-stress coupling process during intrusion and cooling of granitic magma.The results reveal three stages of the fracture development and heat transfer patterns during magma emplacement.(1)During initial intrusion,compression of magma produces the widespread,radial distribution of shear fractures in host rocks.Heat conduction and infiltration are dominant in host rocks.(2)Under continuous pore fluid pressure,the radial shear fractures are connected and form major extensional fractures,which become important pathways of melt and fluids and provide space for pegmatitic and hydrothermal ore deposits.Channel flow and localized thermal convection control heat transportation in host rocks.(3)In the last stage,increase of the pore fluid pressure in host rocks around the magma chamber triggers large amounts of tensile fractures,which enhance the thermal convection in the contact aureole and promoting skarn-type mineralization.Compared with the thermal conduction model,initial thermal convection will decrease the width of the contact aureole.The geometric shape of a contact aureole is controlled by the shape of intrusion,but its width shows remarkable spatial variations.Our modeling results provide a new way to reconstruct metamorphism,deformation and mineralization during magma emplacement.

关 键 词：岩浆侵位 接触变质晕 裂隙发育 热传导 热对流 数值模拟 

分 类 号：P612[天文地球—矿床学]