大陆碰撞成矿论
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本文为国家自然科学重点基金(编号 40730419)、杰出青年基金(编号 40425014)、国家科技支撑计划项目(编号 2006BAB01A08)、地质调查项目(编号 1212010818096)资助的成果。


Metallogensis of Continental Collision
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    摘要:

    基于经典的板块构造而建立的成矿理论已日臻完善, 完好地解释了增生造山成矿作用及汇聚边缘成矿系统发育机制,但却无法解释碰撞造山成矿作用及大陆碰撞带成矿系统。通过对青藏高原碰撞造山与成矿作用的详细研究,并与中国秦岭和其它碰撞造山带综合对比,本文系统提出了一套全新的大陆碰撞成矿理论,简称“大陆碰撞成矿论”,初步阐明了大陆碰撞带成矿系统和大型矿床的成矿动力背景、深部作用过程和形成机制。该理论认为,伴随大陆三段式碰撞过程而发育的主碰撞陆陆汇聚环境、晚碰撞构造转换环境和后碰撞地壳伸展环境,是大陆碰撞带成矿系统和大型矿床的主要成矿构造背景。对应于三段式碰撞而在深部出现的俯冲板片断离、软流圈上涌和岩石圈拆沉过程,是导致大规模成矿作用的异常热能驱动力。伴随三段式碰撞而分别出现的压张交替或压扭/张扭转换的应力场演变,是驱动成矿系统形成发育的构造应力机制。大陆碰撞产生的不同尺度的高热流、不同起源的富金属流体流、不同级次的走滑-剪切-拆离-推覆构造系统和张性裂隙系统, 是形成成矿系统和大型矿床的主导因素。成矿金属在碰撞形成的壳/幔混源高fO2岩浆-热液系统、地壳深熔低fO2岩浆-热液系统、剪切变质-富CO2流体系统以及逆冲推覆构造驱动的区域卤水系统和浅位岩浆房诱发的对流循环流体系统中,伴随成矿金属的积聚与淀积是形成大型矿床的关键机制。“大陆碰撞成矿论”还强调, 完整的大陆碰撞过程可以引发三次大规模成矿作用, 形成一系列标示性的大型矿床:在主碰撞陆陆汇聚成矿期,大陆碰撞引发地壳加厚与深熔, 产生富W-Sn壳源花岗岩, 形成花岗岩型Sn-W矿床; 大陆俯冲板片断离诱发软流圈上涌, 产生富金属的壳/幔混源花岗闪长岩, 形成岩浆-热液型或叠合型Pb-Zn-Mo-Fe矿床; 大陆碰撞从变质地体排挤出富CO2流体, 在剪切带形成造山型Au矿, 从造山带排泄出建造流体,在前陆盆地形成MVT型Zn-Pb矿。在晚碰撞构造转换成矿期,大规模走滑断裂系统诱发壳幔过渡带和富集地幔减压熔融,其岩浆在浅部地壳岩浆房出溶成矿流体, 分别形成斑岩型Cu(-Mo-Au)矿床和碳酸岩型REE矿床;深切岩石圈的剪切作用与下地壳变质产生含Au富CO2流体,形成造山型Au矿;逆冲推覆构造驱动地壳流体长距离迁移汇聚、走滑拉分导致流体大量排泄和充填,形成 Pb-Zn-Cu-Ag矿。在后碰撞地壳伸展成矿期,新生下地壳部分熔融产生富金属、富水、高fO2埃达克质岩浆浅成侵位和流体出溶,产生斑岩型Cu矿;中上地壳部分熔融层(岩浆房)驱动地热流体系统,在地热区发育热泉型Cs-Au矿,在构造拆离带形成热液脉型Pb-Zn-Sb和Sb-Au矿。

    Abstract:

    The metallogenesis theory, based and constructed on the classic plate tectonics, has been coming to its perfection and can better explain the evolution mechanism of accretion orogenic metallogenesis and converged margin mineralization. The theory, however, fails to interpret both the collisional orogenic metallogenesis and continental collision mineralization. This study proposed a new, systematical metallogenesis theory of continental collision, herein simply named "The Metallagenesis of Continental Collision (MCC)", after the detailed research of the collisional orogeny and metallogenesis in the Tibet-Qinghai Plateau and the comparison with the Qinling orogenic belt and other collisional orogenic belts. It is suggested in the theory that the main-collisional intracontinental accretion settings, the late-collisional transitional settings, and post-collisional crustal extension setting in response to the three-stage collisional processes, are the dominant metallogenic environments of the continental collision metallogenesis and large-scale deposits. Subducted slab breakoff, asthenosphere upswelling and lithosphere dismantling and subsiding process occurring at depth in response to the three-stage collision constituted the abnormal thermal energy driving force which was responsible for large-scale mineralization. Meanwhile, the stress field evolution of transpressional and trantensional alternation or transform accompanied the three-stage collision provided the tectonic stress mechanism for the development of metallogenic system. The leading factors for the formation of metallgonesis and large-scale deposits were high-temperature fluid flows of different extents, metal-rich fluids of various origins, strike-slip -incision-detachment-thrusting structure system of various levels, as well as tensile fracture systems, all triggered by the continental collision. The crucial mechanisms for the formation of large deposits were the accumulation and sedimentation of ore-forming metals occurring in the crustal-mantle high fO2 magmatic and thermal system during the collision, fO2 magmatic-hydrothermal system during crustal anatexis, shearing metamorphic CO2-rich fluid system, as well as brine system deriving from thrusting tectonics and convection system triggered by shallow magma chamber. The MCC also put emphasis on that the whole continent collision might have triggered the three large-scale mineralizations and formed a series of indicative of large deposits. Crustal thickening and anatexis due to continental collision produced W-Sn-rich A-type granite and then formed greisen-type Sn-W deposits. Asthenosphere upwelling induced by the continental subduction slab produced metal-rich crustal-mantle mixed granodiorite, resulting in the formation of magmatic-hydrothermal-type or superimposed-type Pb-Zn-Mo-Fe deposits. CO2-rich fluid derived from metamorphic bodies due to continental collision resulted in the formation of orogeny-type Au deposits along the shearing zones while the ore-forming fluids derived from the orogenic belt formed MVT-type Zn-Pb deposits in the foreland basins. During the metallogenic period of late-collisional transform, large-scale strike-slip faulting gave rise to depressurization melting in the crust and mantle transitional zone and the enriched mantle. The exsolution of magma from the shallow crustal magma chamber produced ore-forming fluids, resulting in the formation of the porphyry-type Cu-(Mo-Au) deposits and carbonatite-type REE deposits respectively, while the Au-rich CO2 fluid derived from incising lithosphere and crustal metamorphism caused the formation of the orogeny-type Au deposits. Thrusting structure drove crustal fluid migrate and accumulated, while strike-slip pulling-apart resulted in large amount of fluids to excrete and fill, thus forming orogenic-type Pb-Zn-Cu-Ag deposits. During the post-collisional crustal extension period, shallow emplacement and fluid exsolution of the newly-born adakitic magma, resulting from the lower crust and rich in metals, water and high fO2, formed porphyry copper deposits; partial melting (magma chamber)of the middle and upper crust drove geothermal fluid system, and formed hot spring-type Cs-Au deposits in the geothermal areas, and hydrothermal vein-type Pb-Zn-Sb and Sb-Au deposits in the tectonic detachment belt.

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引用本文

侯增谦.2010.大陆碰撞成矿论[J].地质学报,84(1):30-58.
HOU Zengqian.2010. Metallogensis of Continental Collision[J]. Acta Geologica Sinica,84(1):30-58.

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  • 收稿日期:2009-09-12
  • 最后修改日期:2009-11-17
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