中国陆壳演化、多块体拼合造山与特色成矿的关系

矿产资源的种类、时空分布、形成演化与成岩作用和大地构造格局密切相关。中国地质构造复杂,成矿条件多样(发育裂谷成矿、碰撞成矿、地幔柱成矿、低温成矿等特色成矿系统),矿床类型比较齐全,如大宗矿产(铁、铝、铜、钾盐)短缺,小宗矿产中盛产稀土元素(REE)、钨、锡、钼矿。中国早前寒武纪矿床相对较少,燕山期成矿集中爆发。这种矿产资源分布格局与中国大陆地壳的性质与演化、多块体拼合造山格局之间的内在联系尚待深入揭示。本文基于对中国陆壳演化、陆块与造山带组成格局和多块体拼合造山的系统分析总结,试图阐明中国成矿特色与其内在联系,从陆壳形成与造山带演化的宏观视角来研究中国大陆成矿特色、成矿物质时空分布规律,其特色包括:(1)中国陆壳的地台区与造山带区质量比约3∶7(全球陆壳地台区占69.6%),太古界面积小且支离破碎,地壳固化时间晚且运动频繁强烈,因此难以形成巨型条带状铁建造(BIF)富铁矿床、太古代火山岩块状硫化物型(VMS)铜锌矿带和元古代内克拉通裂谷有关的扎伊尔-赞比亚巨型铜矿。(2)环绕中朝-塔里木和扬子板块的增生造山带由老到新依次形成,并镶接于古板块边缘,使中国大陆逐渐增生扩展,导致火山岩型、与岩浆岩类和沉积岩系有关的大型矿床空间上向板块边缘推移,时间上越来越新,地壳演化成矿作用和矿床类型越来越多样化。(3)中亚成矿域以古生代多陆块拼合造山、中新生代陆内造山与山盆体系构成独特的地质构造格局。既发育增生造山阶段的弧环境相关矿床(蛇绿岩型铬铁矿、斑岩铜矿、VMS),也发育与碰撞造山有关的矿床(造山型金矿、石棉、滑石、白云母)、地幔柱叠置造山带背景下的岩浆铜镍矿和后碰撞陆内岩石圈伸展相关的大陆环境矿床(斑岩钼矿、热液金矿、伟晶岩型稀有金属矿)。(4)青藏高原(特提斯成矿域)系特提斯洋长期增生演化、印度-欧亚大陆碰撞的产物。其成矿条件优越,具有多期成矿作用、多矿种和多类型的复合成矿系统特点。形成了蛇绿岩套型铬铁矿、密西西比河谷型(MVT)铅锌矿和独具特色的碰撞环境超大型斑岩铜钼矿。(5)我国东部环太平洋成矿域,伴随晚中生代克拉通性质的根本转变及岩石圈明显的减薄过程与破坏,在华北克拉通周缘发生大规模的岩浆活动和强烈的金、铜、钼和轻稀土等成矿作用。不同时期的造山带干涉叠加使得南岭地区盛产花岗岩有关的钨、锡、钼矿,具有叠加改造成矿、大器晚成的鲜明成矿特色。由于中国成矿特色与大陆地壳演化密切相关,中国的找矿勘探部署必须立足于中国大陆演化与多块体拼合造山的基本地质事实,方能取得好的勘查效果。中国大陆小陆块拼合造山成矿还存在诸多未解之谜,文末提出了当前成矿学面临的一系列科学问题,对于今后我国找矿战略选区具有借鉴意义。

Links of collage orogenesis of multiblocks and crust evolution to characteristic metallogeneses in China

The style, spatial-temporal distribution, formation and evolution of mineral resources are closely related to the nature and evolution of the crust and the development of the tectonic framework. Due to the complexity of geological settings in Chinese continent, various types of metallogenic systematics are well developed, such as Proterozoic rift, collision, plume, low-temperature metallogenic systematics. China is rich in Mo, W, Sn and REE but short of Cu, high-grade Fe, Al and sylvite. It also lacks of Early Precambrian mineral deposits, and has the outbreak of Yanshanian mineralization. The relationship between these characteristics of mineralization, the formation and evolution features of small continental blocks in China, and accretionary collage of microcontinents is still unclear. In this paper, we try to summarize and reveal the formation and evolution features of small continental blocks in China, the double-directions accretionary collage orogenesis in Central Asian Orogenic Belt (CAOB), and the evolution of Proto-Paleo-New Tethyan Ocean and succeden continent-arc collision orogenic belt as well as decraton of North China Craton (NCC) during Late Mesozoic, and their relationship to mineralizations. The features are as follows:(1) The mass ratio of platform over orogens in Chinese continent (about 3:7) is smaller than that of the bulk Earth (about 7:3). And China has the separated and small areas of Archean crust. The consolidation of the Chinese continental crust also took place over 500~1000Myr later than the shield areas elsewhere in the world. All these features resulted in the lack of rich BIF deposits, Archean giant VMS Cu-Zn deposits and Proterozoic rift-related Zambia-style giant Cu deposits. (2) We conclude the characteristics of the metallogenesis and their connection with the styles, evolution and overlapping of orogens along the North China, Tarim and Yangtze platforms and crustal evolution. The continental crust of China was formed through the accretion of several blocks. With the old masifs as the core and the orogen system of different ages as the margins, it progressively accreted and grew outwards, leading to the migration of volcanic intrusive activies, sites of sedimentation and related mineralization towards the margins of the old orogen and basin with the progress of time. (3) The Central Asian Orogenic Belt has experienced the Paleozoic accretionary collage of microcontinents, and Mesozoic-Cenozoic intra-continental orogenesis and basin-and-mountain system, thus the CAOB can host arc-related mineral deposits (e.g. ophiolite chromite deposit, porphyry Cu-Au-Mo deposit and volcanic-host massive sulfide deposit), collision-related ore deposits (e.g. orogenic gold deposit, and asbestos, talc and mica deposits), ore deposits related to unusual overlapping CAOB by Early Permian Tarim plume (magmatic Cu-Ni-Co deposit), and intra-continent extensional environment (such as, porphyry Mo deposit, hydrothermal Au deposit and pegamatite rare metals, sandstone U and sylvite deposits). (4) Numerous large- and super-large porphyry Cu-Au-Mo deposits, MVT Pb-Zn and ophiolite Cr deposits are generated in the evolution of Proto-Paleo-New Tethyan oceanic subduction along the Qilian, Kunlen to Bangongcuo-Nujiang and Yarlung Zangbo sutures and the process of the India-Asia continental collision in the Qinghai-Tibetan orogen. (5) Crustal movements in China, especially in East China, were ubiquitious, frenquent and rather strong, and these chacteristics are rarely seen in other parts of the world. The massive magmatism and Au, Cu, Mo and light rare earth elements deposits around the NCC occurred in the Late Mesozoic, accompanied with the significant change in the nature of NCC and the decraton of North China lithosphere. A large number of world-class W, Sn and Mo deposits occured with high-evolved granitoids in the highly mature East China continent, related to the polycyclic nature of the tectonism, magmatism, and sedimentation in China. As all the metallogenic features are genetically associated with the evolution of continental crust and multi-stage orogens, the exploration plans in China shoud pay much more attention to the evolution features of small continental blocks, and accretionary collage of microcontinents. Finally, we suggest several significant questions in the areas of continental metallogeny and the futher exploration in China.