峨眉火成岩省岩浆矿床成矿作用与地幔柱动力学过程的耦合关系

GENETIC LINKS OF MAGMATIC DEPOSITS IN THE EMEISHAN LARGE IGNEOUS PROVINCE WITH DYNAMICS OF MANTLE PLUME

峨眉火成岩省位于扬子地块西部,为中二叠世末地幔柱活动产物。迄今为止,峨眉火成岩省已发现超大型V-Ti磁铁矿矿床4处,大中型岩浆硫化物型Ni-Cu-(PGE)矿床近10处。这些矿床的含矿镁铁-超镁铁岩体为260Ma±,与峨眉山玄武岩为同一地幔柱的产物。系统归纳和分析上述两类含矿镁铁-超镁铁岩体在空间分布、岩体规模、岩石组合和造岩矿物组成等方面存在明显的差异:可以分为内带和外带,内带以巨厚的峨眉山玄武岩、大型层状岩体和众多小型镁铁-超镁铁岩体、低Ti玄武岩、碱性岩体和丰富的成矿作用为标志。外带则玄武岩厚度降低,以高-Ti玄武岩为主,很少有侵入岩体。在对这两类岩浆矿床的分布及其与低Ti和高Ti玄武岩地质和地球化学联系的归纳和分析基础上,结合对杨柳坪Ni-Cu-(PGE)硫化物矿床成矿过程与峨眉山玄武岩岩浆起源和演化相互关系的研究结果,认为峨眉山火成岩省这些不同类型的矿床是地幔柱动力学过程不同阶段的产物。V-Ti磁铁矿矿床的形成于高Ti玄武岩浆有关,主要受控于岩浆的分离结晶作用;而Ni-Cu-(PGE)硫化物矿床成矿主要取决于3个因素:高程度的部分熔融,下地壳同化混染和分离结晶。Ni-Cu-(PGE)硫化物矿床是地幔柱活动早期阶段的产物,而V-Ti磁铁矿矿床则形成则晚于岩浆硫化物矿床。

The Emeishan large igneous province in the western Yangtze Block was resulted from a mantle plume at end of the Middle Permian. Four super-large V-Ti-magnetite deposits and 10 large-medium Ni-Cu-（PGE） sulfide deposits have been explored in the Emeishan large igneous province. Precise age data indicated that these ore-bearing mafic-ultramafic intrusions were produced by the same mantle plume that caused the Emeishan flood basalts at 260 Ma ＋. The maficultramafic intrusion hosting V-Ti-magnetite deposits and Ni-Cu-（PGE） sulfide deposits are distinguished in localization, scale, rock-assemblages, components of rock-forming minerals. The Emeishan large province can be divided to Inner- and Outer-Zones. The Inner-Zone is marked by large thickness of the Emeishan flood basalts, large laYered intrusions, mafic-ultrmafic intrusive bodies, low-Ti basalts, alkaline intrusions, and various mineralizations related to the mantle plume. The basalts become thinner and consist of high-Ti basalts in the Outer-Zone where fewer mafic-ultramafic bodies are exposed. Special and geochemical relationship between the two type of magmatic deposits and high- and low-Ti basalts,the study on petrogenetic links between the Ni-Cu-（PGE） sulfide deposits and the Emeishan flood basalts in the Yangliuping area indicate that the magmatic deposits formed in different dynamic stages of the mantle plume. The V-Ti-magnetite deposits are associated with the high-Ti basaltic magmas and related to fractional crystallization. In contrast, the Ni-Cu-（PGE） sulfide mineralization may be related to either the high- or low-Ti basaltic magmas and controlled by three factors, high degree partial melting of upper mantle, contamination of the lower crust, and fractional crystallization. The NiCu-（PGE） sulfide deposits were formed earlier than the V-Ti-magnetite deposits.