Metallogensis of continental collision

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 oreforming metals occurring in the crustal-mantle high f o2 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 CO2 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.