The Geochemical Composition And Tectonic Environment Of Ophiolite In Shigatse And Serpentine In The Island Arc Of IBM Central Section

The formation of the ophiolite’s concept experiences a long time. Eventually forms the concept that widely recognized now. Ophiolite is not a kind of rock or mineral, but a combination of a series of orderly arranged rocks. It is also called the suite of ophiolite. A complete ophiolite has a whole rock sequence, from bottom to top respectively:ultramafic rock, gabbro, sheeted basaltic dikes, a volcanic sequence, and a sedimentary cover. Not all ophiolites have the complete sequence, and not just found this combination sequence must be an ophiolite. Some are rocks rando mLy grouped together. This needs evidences from geochronology, geochemistry and petrology. From the global tectonic ophiolite can be divided into two broad categories. One is associated with subduction. It includes the type of super subduction zone (SSZ) and volcanic arc. Another is not associated with subduction. It includes the type of Continental margin (CM) ophiolites, Mid-ocean-ridge (MOR) ophiolites and Plume-type (P) ophiolites. In this paper, the samples all belong to the first type.This paper carries out detailed research about the ophiolite of Shigatse in Tibet and serpentine in the island arc of IBM central from mineralogy, petrology, geochemistry and U-Pb dating. As a result, samples of peridotite, basalt and siliceous rocks collected from Shigatse may belong to the same ophiolite. The slide pyroxene collected from Bailang is generated by continental crust, and not an ophiolite. The figure of REE from peridotite shows that it produces in SSZ environment. The geochemical characteristics of siliceous rocks show that they are biogenic and not hydrothermal genesis. Almost all peridotites in the central of IBM island arc are serpentinized. Comparing the peridotites from IBM island arc and ODP, found that not only the sea water severely affects the serpentinization of peridotites, but the speed of subduction and submarine topography also have certain influence to it. It needs to do further research. Comparing the peridotites from Shigatse and IBM island arc, found that their variation trend of trace element and REE is similar. But the element content of the former is more depleted. May both be homologous.