Studies Of Xindi River Neoproterozoic Maflc-ultramafic Intrusions In Quruqtagh,XinJiang And Their Constraints On Breakup Of Rodinia Supercontinent

The various igneous rocks of the middle Neoproterozoic that are well developedin Quruqtagh have been received a gread deal of attention to many researchers overthe world. Tectonic environment of this period of magmatism is Rodinasupercontinent breakup event in the dynamics mechanism for the discussion ofgeological problems of vital importance. Three Neoproterozic mafic and ultramaficintrusions in Quruqtagh Xingdi River were selected for comprehensivestudies,detailed outcrop investigations,petrology,LA-ICP-MS ziron U-Pb dating,whole-rock precision geochemical and Hf isotopic,research mafic-ultramafic rock inthe mantle source region characteristics and magma evolurion process.Thus providenew constraints for the dynamics of the Quruqtagh Neoproterozoic evolution andtectonic setting of contention.Some achieves are as following:1. The main rock lithofacies of Xingdi No.Ⅰintrusions is gabbro,gabbro containa small amout of pyroxenite and olivine gabbro;Xingdi No.Ⅱintrusions mainlycomposed of pyroxene facies.peridotite facies and gabbro facies; Xingdi No.Ⅳintrusions is fine-grained diorite,local gabbro.2. The LA-ICP-MS zircon U-Pb geochronology studies have shown thatXingdi No.Ⅰgabbro age of728±3Ma (MSWD=0.77), central granite age of741±6.3M (MSWD=0.65), and edge granite age of729.4±2.6Ma (MSWD=1.3);Xingdi No.Ⅱassociated with the granite age of731±13Ma (MSWD=0.77),slightly later than the gabbro emplacement age. Xingdi No.Ⅳgabbro diorite age is737.8±6.4Ma (MSWD=0.47). The age of three Xingdi River mafic-ultramaficrock are both the middle Neoproterozoic.3,Three intrusions gabbro are both continental tholeiite series, enriched in largeion lithophile elements (LILE) and light rare earth elements (LREE), the loss of Nb,Ta, P and Ti, high-field strength elements (HFSE) and heavy REE (HREE). Xingdi No.Ⅱintrusions incompatible element enrichment and significant HREE fractionationis not obvious, compared Xingdi No.Ⅰand No.Ⅳ enriched in incompatible elementsthan the HREE fractionation is moderate. Xingdi No.Ⅳ gabbro diorite Hf isotope(εHf (t)=0.29~-23.78), indicating that the three rock source areas are enrichedcontinental lithospheric mantle, magma ascent to emplacement crystal fractionationand subjected to crustal contamination.4. During900-1000Ma the subduction transform the Quruqtagh continentallithosphere, reduce its solidus temperature, and subsequently induce a largeproportion partial melting of the continental lithosphere caused by the Mantle plumeheat conduction.By the impact of the global Rodinia supercontinent breakup event theNeoproterozoic medium-term Quruqtagh region of asthenospheric mantle upwell andcause the partial melting of the continental lithospheric mantle, and thus form theNeoproterozoic mafic-ultramafic rocks. In the early cracking process (820-800Ma),the thickness of the lithospheric mantle, the lithospheric mantle of low degree ofpartial melting, form Qieganbulake alkaline mafic-ultramafic-carbonatites.Duringcontinental breakup (-760Ma), with the asthenosphere upwelling, lithosphericthinning and the occurrence of a high proportion of partial melting, tholeiitic matter ofmafic magma differentiation and emplacement produce Xing II mafic-ultramaficintrusive complex, this period of mafic exhibited various degrees of Nb-Ta loss, haslow Nb/La ratio, may reflect the lithosphere (earth) contamination or recycling ofcontinental lithospheric mantle contribution; cracking advanced (730Ma):asthenosphere activity weakened, lithospheric cooling thickening, degree of partialmelting reduction, basaltic magma differentiation and emplacement produced with Iand IV rock mafic-ultramafic rock, magma underplating caused by overlying lowercrustal material dehydration melting, forming an accompanied granite (with I granite).