碰撞造山带斑岩型矿床的深部约束机制  

The constraints from deep processes on the porphyry metallogenesis in collisional orogens.

作　　者：罗照华[1] 卢欣祥[1] 陈必河[1] 黄凡[1] 杨宗锋[1] 王秉璋[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2008年第3期447-456,共10页Acta Petrologica Sinica

基　　金：国家重点基础发展规划项目(2002CB412603);国家科技支撑计划重点项目(2006BAB07808);河南省地质矿产重大科技攻关计划项目(26417)资助

摘　　要：在印度-亚洲大陆碰撞过程中,俯冲板片断离触发了幔源岩浆底侵作用、下地壳部分熔融和冈底斯岩基带以及同岩基斑岩的产生。在此过程中,幔源岩浆分离结晶的产物、下地壳岩石部分熔融残余和地壳分异过程中下沉的镁铁质块体,构成了加厚下地壳。随着造山岩石圈的冷却和加厚下地壳重力不稳定性的增加,岩石圈拆沉作用触发了后碰撞斑岩型岩浆活动。与此相应,碰撞造山带斑岩型矿床可以形成于同碰撞和后碰撞两个不同的构造阶段。同碰撞成矿作用发生于岩基带形成时期,成矿物质主要来自于底侵幔源岩浆及更深部的含矿流体,其触发机制是俯冲板片的断离。后碰撞成矿作用发生于加厚下地壳冷却之后,成矿物质主要来自于新生矿源层和更深部的含矿流体,其触发机制为岩石圈拆沉作用。在同碰撞构造阶段,伴随着幔源岩浆的底侵作用,深部流体和幔源岩浆所含的成矿物质被注入到岩基岩浆中,与从岩基岩浆源区萃取的成矿物质汇聚在一起,一部分受岩基热的驱使上升成矿。由于流体中成矿元素的浓度强烈依赖于压力,另一部分成矿元素则滞留在难熔残余中形成新的矿源层。当发生岩石圈拆沉作用时,由此矿源层部分熔融形成的斑岩岩浆将相对富含成矿物质,导致碰撞造山带第二次成矿作用大爆发。The Cenozoic collision of the Indian-Asian continents has induced break-off of the subducted slab, the later has in turn triggered underplating of the mantle-derived magma, partial melting of the lower crust and production of the Gangdese batholiths belt and the co-batholithic porphyries. In this process, the underplated mantle-derived magma, the remnant from partial melting of the lower crust and the sinking mafic blocks differentiated from the crust composed the thickened mafic lower crust. Due to cooling of the orogenic lithosphere and hence increasing of the gravitational instability of the thickened lower crust, the lithosphere delamination has triggered post-collision porphyritic magmatism. Corresponding to magmatism, two types of porphyritic mineral deposits produced in the two tectonic stages： syn-collisional and post-collisional. The syn-collisional metallogenesis took place when the batholiths belt is formed under triggering of breaking-off of the subducted slab. The ore-forming materials came from the underplated mantle-derived magma and the deeper ore-bearing fluids. In the syn-collisional stage, a part of the ore-forming materials resolved in the deeper fluids and the mantle-derived magma are injected into the batholitic magma in terms of underplating of the mantle-derived magma. These metals together with that extracted from the source of the batholiths magma ascended to form deposits under driving of the heat from the batholiths magma. However, the other part of the ore-forming materials would be detained in the refractory remnants and induce to form a new ore source bed, because the solubility of the ore-forming elements in the fluids strongly depends upon pressure. Ones the lithosphere delamination takes place, the partial melt from this source should contain more ore-forming materials and hence induces explosion of the second period of metallogenesis in the collision orogen.

关 键 词：碰撞造山带 斑岩型矿床 深部过程 岩石圈拆沉作用 矿源层 

分 类 号：P588.132[天文地球—岩石学] P611.13[天文地球—地质学]