Genesis Of Mantle Peridotite In The Luobusha,Tibet—The Study Of Scientific Drilling Core(LSD-1)

Found in diamond and other UHP minerals in mantle peridotite and chromite in the Yarlung Zangbo suture zone in southern Tibet, causing domestic and international concern. This thesis is through the systematic research of a length of approximately 1500m drilling core in Luobusha chromite District, to discriminate the genetic type and tectonic environment of Luobusha chromite District mantle peridotite.The drilling of LSD-1, located in the southern edge of the Luobusha chromite district, which at the contact of south side of the block and the Triassic. The lithology of drilling core: harzburgite, lens dunite, Iherzolite, layered dunite and pyroxenite. The length of harzburgite is about 870 m; the length of lens dunite is about 300 m; the length of Iherzolite is about 10 m; the length of layered dunite is about 183 m; the length of pyroxenite is about 115 meters. A few of disseminated chromite can be observed in harzburgite between 1100-1200m.The component of minerals of harzburgite:olivine (75%-90%), orthopyroxene (5%-20%), clinopyroxene (<5%) and Cr-spinel (1%-2%); the component of minerals of dunite:olivine (95%-99%), orthopyroxene (1%-4%), clinopyroxene (<3%) and Cr-spinel (1%-2%); the component of minerals of Iherzolite:olivine (80%-90%), orthopyroxene (5%-10%), clinopyroxene (<10%) and Cr-spinel (1%-2%); the component of minerals of layered dunite:olivine (95%-98%) and Cr-spinel (1%-2%); the component of minerals of pyroxenite:clinopyroxene.Through detailed field observations and core catalog, according to the characteristics of the petrography, mineralogy, geochemistry and isotope data analysis, and achieved the following progress:1. There are two sets of mineral assemblages in the mantle peridotite, and not formed at the same time. Over 1500 electron microprobe data statistics shows that there is some variation of mineral composition and its mineral particles, shape and output relations in the mantle peridotite2. The diagram of primitive mantle-normalized REE of mantle peridotite shows two types:LREE enrichment and LREE depletion, and these two types unconstrainted by these two mineral assemblages.3. The mantle peridotite is the production by the the effects of the minerals and geochemistry of the late SSZ tectonic environment, the composition of mantle peridotite is different from the primitive mantle.4. Re-Os isotope data instruct mantle peridotite experienced five partial melting events.5. Layered dunite is the production of rock-melt reaction.