Geochemical Characteristics And Formation Environment Of Tuerkubantao Ophiolitic Mélange In Xinjiang

This paper researched the exposed basic-ultrabasic tectonic blocks and basalt ofTuerkubantao ophiolitic mélange in detail. We established the petrosal assemblage type ofophiolitic mélange, through detail set and construction after summarizing research. Andsystemic researching the character of oPhiolitie of mineralogy, Petrology, Petrochemistry,geochemistry, tectonic setting, formative age, tectonic significance and so on.1. The initial sequence of the ophiolitic is reconstructed. Completely developedophiolitic mélange from bottom to the upwards occur sequences: peridotiteâ†'cumulates(gabbros and pyroxenites)â†'basic lava(basalts)â†'pyroclastic rock and tufa, and showssome siliceous rock and flysch formation. Missing formed of Sheeted dikes in extensionalenvironment.2. The mineralogys and mineral compositions of olivine, orthopyroxene, monoclinicpyroxene and chromium spinel of metamorphic peridotite, indicated to be similar to mineralcharacters of mantle peridotite.3. Geochemistry of metamorphic peridotite show low Al2O3, CaO, TiO2and, highMgO and Mg#, represents the depleted mantle rock of partial melting of the primitivemantle.4. Geochemistry of cumulates show high Al2O3, CaO, MgO and Fe2O3，low total alkali,especially K2O, similar to which oceanic tholeiite and island arc basalt. Trace element showlow∑REE, slightly enrichment of LREE and HREE flat, indicates that they are similar to aarc-basalt, meanwhile, samples are showing distinguishable enrichment in large-ion lithophileelements(LILE), depeletion in Nb and Ta. They are showed that it related with subdution.5. Combing the features of geochemistry with tectonic discrimination diagrams ofbasalts, which similar to normal mid-ocean ridge basalts (N-MORB) and island arc basalts,it is reasonable suggest that the Tuerkubantao ophiolitie was formed in a back-arc basinsetting.6.This paper measured the zircon age of gabbro was380.0±2.2Ma (MSWD=0.24), andon the basis of previous studies of the chronology, indicating a Middle-late Devonian eraage of Tuerkubantao ophiolite.7.The Sr-Nd isotopic compostions of cumulates are characterized by higher initial Srisotopic ratios(0.704677～0.705773), lower initial Nd isotopic ratios（0.5130～0.5133）, andthe Pb isotopic have Dupal isotopic untypical anomaly(â–³Sr>50，△7/4Pb＞3，△8/4Pb>10),suggest a mixing source of magmas with the properties of the depleted mid-ocean ridge basalt mantle end-member (DMM) and EMII enriched mantle endmemher in Tuerkubantaoophiolite.8. ophiolitic is probably on behalf of the back-arc basin system on the northern side ofthe paleoasian ocean in the late Paleozoic, showing that the region located in island arcenvironment in associated with subduction of the paleoasian ocean during the late Paleozoic.