稀有金属成矿全球时空分布与大陆演化

花岗岩是大陆地壳的主要组成,是陆壳的特征性物质。花岗岩的形成及演化往往伴随着金属元素的不断富集和广泛的成矿作用,进而形成与之相关的大陆成矿体系。稀有金属成矿是大陆成矿体系的重要内容,毫无疑问,与花岗岩有关的稀有金属成矿作用是大陆演化的直接产物,因此,稀有金属成矿学是大陆动力学的研究内容之一。花岗伟晶岩是锂、铍、钽最重要的成矿母岩,碱性岩(花岗岩、伟晶岩和碳酸岩)与铌、锆等成矿作用有关。全球稀有金属成矿时代集中在太古代3.0~2.6Ga、古元古代1.8Ga、新元古代1.0~0.9Ga、古生代450~400Ma、早中生代250~200Ma、晚中生代160~130Ma和新生代中新世35~10Ma,直接反映了稀有金属成矿与超大陆演化重大事件具有密切的成因关系。最古老的稀有金属成矿作用始于乌尔-诺基兰超大陆,形成了现今分布于北美、非洲南部、西澳等地的重要钽成矿带,其它时期成矿作用相继对应于哥伦比亚超大陆、罗迪尼亚超大陆、冈瓦纳超大陆和潘吉亚超大陆聚合、裂解作用,并终结于新生代发生的印度板块与亚洲板块的碰撞作用。值得关注的是,稀有金属矿物与稀有金属成矿总是共演化,锂辉石、锂电气石、绿柱石和铌铁矿-钽铁矿等几种重要的稀有金属矿物最早出现的时代都在太古代3.0~2.6Ga。

Global tempo-spatial distribution of rare-metal mineralization and continental evolution

Granites constitute as major and typical components the continental crust.Making thesignificant rare-metal enrichments and consequently tempo-spatially wide mineralization,granite-forming processes constructthe continental metallogenic system.Granite-relatedrare-metal mineralization certainly originating from continental evolution is thus logicallycharacterizedinto the continental metallogeny.Granitic pegmatites are considered the most important sources for lithium,beryllium and tantalum,meanwhile alkaline rocks(including granites,pegmatites and carbonatites)mostly contributed to niobium and zirconium mineralization.Based on compiled geochronological data,global distribution ages of rare-metal mineralization span mainly in Archean(3.0~2.6 Ga)、Paleoproterozoic(~1.8 Ga)、Neoproterozoic(1.0~0.9 Ga)、Paleozoic(450~400 Ma)、early Mesozoic(250~200 Ma)、late Mesozoic(160~130 Ma)and Miocene in Cenozoic(35~10 Ma),directly linking supercontinental cycling events and synchronous rare-metal mineralization.The earliest rare-metal mineralization was recorded in Ur-Kenorland supercontinent,forming important lithium-cesium-tantalum-type pegmatite provinces particularly in northern America,southern Africa and western Australia.Other dominant metallogenic events successively correspond to assembly-breakup of Columbia,Rodinia,Gondwana and Pangea continents,and most likely ended during the Cenozoic collision between India-Asia blocks.Interestingly,rare metals display co-evolution between minerals and mineralization,as the case of the first record of spodumene,elbaite,beryl and columbite-tantalite in Archean(3.0~2.6 Ga).