Petrogenesis And Metallogenesis Of Post-collisional Mantle-derived Orthomagmatic Deposits In East Tianshan,Xinjiang

Eastern Tianshan is a major district hosting extensive Late Paleozoic mantle-derived magmatism of China,and hosts a series of mafic-ultramafic intrusions and associated orthomagmatic deposits,including Ni-Cu sulfide deposit,Fe-Ti-V deposit and CuNi-VTiFe composite deposit.The petrogenesis and metallogenesis of orthomagmatic deposits of eastern Tianshan plays a key role in the research of regional tectonic magmatism,regional metallogeny,as well as mineral resource exploration.Thus,three major types of orthomagmatic deposits,including Ni-Cu sulfide deposit,Fe-Ti-V oxide deposit and CuNi-VTiFe composite deposit,are chosen for object in this dissertation.The characteristics of chronology,petrology,mineralogy,geochemistry and isotope geochemistry are investigated for the purpose as follow:(1)genetic relationship between tectonic magmatism and orthomagmatic deposits;(2)regional metallogenic regularity of orthomagmatic deposits;(3)metallogenic mechanisms of orthomagmatic deposits in the eastern Tianshan;(4)providing the basis for regional orthomagmatic deposits exploration.On the basis of the systematically research of orthomagmatic deposit in the eastern Tianshan,some conclusion has been drawn:(1)The eastern Tianshan had stepped into a compression-extension transitional stage of post-collision at the Late Carboniferous,producing a series of Fe-Ti-V oxide deposits,and stepped into post-collisional extension stage at the Early Permian,producing a series of Ni-Cu sulfide deposits and the Xiangshanxi NiCu-FeTiV composite deposit,respectively.(2)The Late Carboniferous mantle-derived magmatism produced a series of Fe-Ti-V oxide deposits,which mainly distributed along the northern margin of the Central Tianshan massif,minor occur on the southern margin of the Harlik island arc.(3)The Late Carboniferous Fe-Ti-V oxide deposits of eastern Tiashan are mainly hosted in the layered gabbroic intrusions,which are composed of olivine gabbro,gabbor,hornblende gabbro and anorthosite.The primary magma derived from enriched lithospheric mantle and is metallogenic elements enriched,while the parental magma had experienced extensively fractional crystallization at deeper magma chamber process,inducing metallogenic elements further enriched.The formation of anorthositic rocks induced the ore materials fractionated from the rock-forming minerals,leading to the formation of Fe-Ti-V oxide deposit.(4)The Early Permian Ni-Cu sulfide deposits are formed during the post-collisional extension stage.The upwelling of large scale asthenospheric mantle induced by slab break off controlled the distribution of Ni-Cu sulfide deposits in the eastern Tianshan.The basin-shaped deposits mainly occur in the Kangguer ductile shear zone,while the dyke-shaped deposits mainly distribute on the tectonic units north and south to the Kangguer ductile shear zone.(5)The metallogenesis of the Xiangshanxi NiCu-FeTiV composite deposit is associated with successively emplacement of hornblende gabbro and lherzolite.The first intrusive phase is highly differentiated hornblende gabbro,enriched in volatile components and metallogenic elements,while the second intrusive phase is low differentiated ultramafic rock.The interaction between these two pulses of magma induced physico-chemical change,not only induced accumulation of Fe-Ti oxide but also segregation of Ni-Cu sulfide,leading to the formation of the Xiangshanxi NiCu-FeTiV composite deposit.(6)The Fe-Ti-V oxide deposits are mainly associated with the Late Carboniferous highly differentiated layered gabbro,hosting low Fo olivine and low An plagioclase,and characterized by extremely high Cu/Ni ratio.The Ni-Cu sulfide deposits are mainly hosted in the Early Permian siliceous enriched mafic-ultramafic intrusions,which are characterized by occurrence of abundant orthopyroxene and low-An plagioclase.The An value of plagioclase from ultramafic rocks is an important index in mineralization assessment,and could indicate the scale of deposits.