The Study of Dalabute Ophiolitic in Western Junggar, Xinjiang

Abstract: This dissertation is object on Dalabute ophiolitic in Western Junggar,Xinjiang. Systemic researching the character of ophiolitic of rock combination、petrology、petrochemistry、geochemistry、tectonic setting、formtive age、emplacement mechanisms、tectonic significance and so on.1.It is composed of different tectonic blocks which come from ophiolitic,and chaotic matrixes which are slice serpentinite.The metaperidotites、cumulate complex、basic volcanic rock of Dalabute ophiolitic m(?)lange are more developmental,Siliceousrock and the scale of dike swarm which stand for spreading mechanism are small,plagiogranite apophysis interweave gabbro.The position of serpentinite is lowest,gabbro、diabase and basalt accumulate on the serpentinite,and siliceousrock cover with basalt.Although succession of strata is demolished,the combination of ophiolitic are integrated.The rocks are intensively deformation、pervasive metamorphose、cataclasis、zoisitization、uralitization and mylonitizaion.2.The metaperidotites of Dalabute ophiolitic m(?)lange,show low TiO_2、Al_2O_3、CaO and total alkali,high MgO,Mg~#,and have lowΣREE,enriched LREE,the rare earth element distribution patterns appear "凹" or "U",they are depletion pyrolite form primitive mantle which had undergone part melting.Basic rock show high MgO,low MgO,A1_2O_3、K_2O、P_2O_5andω(Na_2O)>ω(K_2O).The geochemical of basic rock characteristic of lowΣREE,depleted in LREE and HREE flat,unfractionated in HSF elements indicates that they are similar to a normal mid-ocean basalt(N-MORB),meanwhile,samples are showing distinguishable enrichment in large-ion lithophile elements(LILE),depeletion in Nb and Ta.They are indicate that the magma root depletion mantle,showing that it related with subdution.3.Combine the character of Dalabute ophiolitic of geochemistry with tectonic discrimination diagrams,it is reasonable suggest that the Dalabute ophiolitic was formed in a back-arc basin setting.4.Zircon U—Pb dating of gabbro from Dalabute ophiolite,give the age of 391.1±6.8Ma,MSWD=0.97(95%confidence),indicating a Middle Devonian age of Dalabute ophiolite.5.Carboniferous stratum of both sides of Dalabute fault have some close characteristics,and the Dalabute rupture is not important boundary of lithofacies、biology combinnation、metamorphism、magmatic activity,showing that Dalabute fault was not suture belt after ocean basin closed,it may be a deep fault formed along witn the extention of back-arc basin,providing a channel for mafic magma intrusion,or a nappe structure with the closure of back-arc basin.6.The time of Dalabute ophiolitic came into being correspond with the ocean basin began to eliminate,it was new oceanic crust after oceanic crust beginning to subducted which induced back-arc basin was unclosed.Finally,Dalabute ophiolitic adhered to land after extrusion mechanism.7.Sedimentary basin beside Dalabute ophiolitic m(?)lange belong to a stratigraphic division,correcting a conclusion that the Dalabute ophiolitic m(?)lang was served as a borderline to two stratigraphic divisions…
Key words: Dalabute ophiolitic; petrology; geochemistry; tectonic setting; Middle Devonian; emplacement mechanisms and tectonic significance; Western Junggar; Xinjiang

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