Metamorphism Of Mafic Granulite And Neoarchean Crustal Evolution In Quruqtagh,Xinjiang

The origin and evolution throughout be attached great importance to geologist at homeland or abroad, and it always is a hot frontier topic in science. Kuluketage block located in the northeastern margin of the Tarim block, and it has a old precambrian basemen with large scale and intact ancient tectonic magmatic evolution information, hence it’s a most important windows to research the precambrian geological evolution of Tarim block. The 1:5000 regional geological survey found the archaean granulites for the first time, and will provid some most important information for the crustal evolution of the Kuluketage.The main conclusions of this paper are as follows:1)Based on the detailed petrographic observation,combined with the structure of metamorphic reaction, the basic granulite class divided into three stages of metamorphic mineral assemblage. Progred metamorphism stage in the early period(M1): Shape of inclusions in garnet, variable intracrystalline mineral combination for diopside Ⅰ + plagioclaseⅠ+ quartz; Peak metamorphism stage(M2), and it’s mineral assemblage is garnet+ plagioclaseⅡ+ diopsideⅡ+ hyperstheneⅠ, medium pressure granulite facies metamorphism; Decompression retrograde stage(M3), and it’s early stage performanced typical “the white circles” structure, mineral assemblage is plagioclaseⅢ+ hyperstheneⅢ+hornblende + diopsideⅢ, the later period of decompression retrograde stage possible mineral assemblage is plagioclaseⅢ+amphibole. The 3 stages of metamorphic mineral assemblage can be inferred that mafic granulite metamorphic stage is reached through into the medium-pressure granulite facies, after a typical buck retrograde metamorphic stage, the same as the granulite facies metamorphism and the late stage, continue to lower amphibolite facies, with a clockwise P-T path, represents the earth dynamics process of.tectonic thickening then rapid uplift.2)Pomegranate two pyroxene hornblende plagioclase granulite in two groups: a group of harmonic harmonic U-Pb age older was 2531+13Ma, may represent the two pyroxene amphibolite granulite; second groups of Concordia age 2388 + 49 Ma, the group of age may record a magmatic events of the period. Secondly, the sample contains 2712+46Ma, 2742+46Ma magmatic event information; in addition, the weighted sample with three zircon age of metamorphic zircon is 1927+26Ma, consistent with the regional metamorphic event 1.8-1.9Ga.3)Pomegranate two pyroxene hornblende plagioclase granulite Hf isotopic data indicate that: ~2.5Ga is an important period for the Kuluketage block crustal growth, remelting magma may be derived from mantle sources of biomass for new or old crust. ~1.9Ga is a high-grade metamorphism of granulite facies metamorphism, crustal source rocks, causing the remelting, as an important crustal reworking event.4)The protolith of the mafic granulite is basic igneous rocks, with the REE patterns type slightly flat, slightly LREE enrichment,enrichment of large ion lithophile elements(lile) Rb, Ba, Sr, and loss of high field strength elements(HFSE) Th, Nb, Ta, P,just similar to the characteristics of island arc basalt.Combined with the basalt’s tectonic discrimination diagrams, indicating that mafic granulite protolith formation in an island arc environment. ~2.5Ga zircon εHf> 0, indicating the protolith of mafic granulite is derived from depleted mantle, combined with the geochemical characteristics which indicate that during the magmas ascending experienced significant crustal contamination, no significant fractional crystallization.