Lithogenesis And Metallogeny Of The West Namcuo Ophiolite, Tibet

Ophiolite have Indicative function to the plate movement and the chromite ores which consist in the ophiolite is the scarce mineral type to our country, so the study to the ophiolite have great significance. West Namcuo located in the central of Lhasa plate, east paragraph of Laguocuo-Jiali ophiolite belt which is situated between Bangongcuo-Nujiang suture and Yarlung zangbo River suture; the ophiolite in west Namcuo distributing in disorder, but it have complete rock type; the mantle peridotite class, the cumulate rocks class, the magnesium iron sheet diked swarm class, the volcano miscellaneous rock class, the radiolarian silicalite and so on expose in research district.The ophiolite in the study area is degree is scarce, it's lithogenesis environment and structural unit belonging there is great controversy; also minerals in the area are newly discovered deposits, research the metallogeny of the ophiolite have great significance for prospecting.This article according to gathered information from field work and laboratory study, analysis of the group and geochemical characteristics and so on of the ophiolite in the area; then debate with every unit of the ophiolite in the west Namcuo, the lithogenesis environment and magmatic source area. Combining the feature of tectonic evolution in the area, Propose new geological basis and geological cognition of the tectonic evolution of the weste Namcuo area. In addition, study on the mineral characteristics in the metal ores which associated with ophiolites in the study area, such as chromite, nickel, and compare metallogeny of the ophiolite in other area, analyze the causes of ophiolites in the minerals in the study area. The main results are as follows:?1? The ophiolitic rocks in the west Namcuo, including four units as the mantle peridotite class, the cumulate rocks class, the magnesium iron sheet diked swarm class, the volcano miscellaneous rock class, the radiolarian silicalite and tuff Rock and so on as associated products.?2? Ophiolite of study area from the bottom to the top of its element content with a gradual process; explain the order of the Ophiolite very well.?3? Previous research data and the study of the basalt dating data collected fossils in the Radiolarian cherts then concluded that West Namco Ophiolite formed roughly at the late Jurassic.?4? Through a series graphic processing of geological data which from basalt rocks, understand the West Namcuo Ophiolite similar to the subduction zone on the back-arc basin, generated by the mid-ocean ridge dilatation. Associate regional geological event occurred found that Middle-North Gangdise magmatic arc was not unified in the Mesozoic, Middle-North Gangdise northern extension was formed a back-arc basin in Jurassic, and cut closed prior to Early Cretaceous.?5? The chromite in research district was generated by dive plate dive melting while water and CO₂ in the plate was lossn, formed heat flow into mantle, led to mantle material melting point reduced, then promote mantle olive rock of melting, and after once or number times melting process like this, led to chrome rich set, eventually formed chromite.?6? Through compared research found that petrology and petrochemistry characteristics of nickel deposit in research district have great different from previously found of several nickel deposit type in our country, maybe it is a new nickel deposit mine mode.