岩浆Cu-Ni-PGE硫化物矿床的克拉通边缘成矿模型

摘要

Basing on the global distribution of magmatic Ni-Cu-PGE suliide deposits and the relationship between this type deposits and large igneous provinces (LIPs), we suggested that the location of magmatic Ni-Cu-PGE sulfide deposits is related to lithospheric architecture. At crustal levels, this relationship is manifested by a close proximity to craton and paleocraton margins. Deposits are associated with mafic-ultramafic rocks and many show a close spatial and temporal relationship with coeval igneous magmation. A craton-margin model for the genesis of magmatic Ni-Cu-PGE sulfide deposits is proposed, and there are five steps for the formation of this type deposits: ①The generation of high-volume ultramafic melts in the mantle. ②The flowage of hot mantle or magma towards the craton margin. ③The passage of magma through the lithosphere. ④The tectonics and interaction between magma and crustal rocks. ⑤The eruption of magma and the deposition of minerals. The advantages of the craton margin for the formation of magmatic Ni-Cu-PGE sulfide deposits were summarized: ① Zones of thinner lithosphere are more likely adjacent to and along the cratonic margins, this provides a natural focus for mantle plume flow along the base of the SCLM, followed by localized decompression melting of the plume in the zones of thinner lithosphere. ② Margins of cratons are prone to focusing strain during regional tectomsm, providing points of dilation along active structures in the craton margins area. ③ Deposits along or slightly internal to paleocraton margins internal to a continent may be better protected from uplift and erosion during subsequent orogenesis.v%对比分析了世界范围内岩浆Cu-Ni-PGE硫化物矿床的空间分布,以及其与大火成岩省(LIPs)的成因联系,认为此类矿床的产出位置与岩石圈结构关系密切.这种密切关系表现在此类矿床主要分布在克拉通边缘或古克拉通边缘；矿床与铁镁质-超铁镁质岩石关系密切,表现在许多矿床与基性-超基性火山岩浆作用间具有密切的的时空联系.构建了岩浆Cu-Ni-PGE硫化物矿床的(古)克拉通边缘成矿模型,认为此类矿床形成需要5个作用过程:①地幔中大规模超镁铁质熔体的产生.②大规模超镁铁质熔体朝克拉通边缘运移.③地幔熔体穿过岩石圈.④地幔熔体与地壳物质间相互作用.⑤岩浆喷发及矿质堆积成矿.概括了克拉通边缘三方面的成矿优越性:①克拉通内部岩石圈厚大,边缘岩石圈相对薄弱,这就促使了地幔柱熔体顺陆下岩石圈地幔(SCLM)基底发生侧向运移.②克拉通边缘是大地构造运动的应力集中区,这就使得沿克拉通边缘分布的转换断层将在局部变异,形成地球物理障.③顺克拉通边缘分布的矿床或位于大陆内古克拉通边缘的矿床具有更好的保存条件,免遭了造山后因差异抬升而形成的剥蚀作用的破坏.