Petrogenesis And Magma Source Of The Mafic-ultramafic Complex In The Northeast Of Tarim Plate

Permian magmatite distributes in Tarim Plate and surrounding area extensively,the complicated structure and lithic varity are always the discussing foucs in Beishan area of northeast of Tarim plate .The studying degree on the Permian mafic-ultramafic complex is superficial by forefathers. The classical rock bodies in north of Zhongposhan area and Gubaoquan area are selected and studied on petrology, crystal chemistry, rare-earth elements, trace elements and Nd,Sr, Pb isotopes in detail. It analysis the magmatic processing, magmatic character, mantle source character and probably formation mechanism of the mafic-ultramafic complex rock bodies in this area by using modern petrologyical theory. According to them, the mafic-ultramafic complex rocks are divided into Cu,Ni deposit series and Fe deposit series .It also studied the Geo-chemical characteristic of the two parts in detail, the mainly developments are as following:1 .The Permian magmatite of Beishan area in xinjiang located confinented sprending , mantle raising continental plate tectonic sysem , the sprending movement is the same as ridge-basin area of western American, and belongs to mid-plate sprending environment.2.The U-Pb harmonic age of the rock body in northern Zhongposhan is 274±4Ma, MSWD=0.273. It belongs to early Permian.3. The olive types is chrysolite ; the clinopyroxene types are augite , diopside , enstatite and baikalite; the plagiogranite types are labradorite and bytownite, in mafic-ultramafic rock bodies of northern Zhongposhan area and Gubaoquan area, but the two parts are different from enstenite types, the former is hypersthene, the latter is bronite.4. The confact zone of the two rock bodies universal suffered migmatization, the LIL elements exhibited abnormal change in the primitive mantle partition curve. The sample almost exhibited different degree positive correlation in La/Nb^Si, K₂O/P₂O₅～SiO₂, Zr^Th> Nd^Y, Th/Yb^Ta/Yb and Ce/Nb^Th/Nb relative drawings. All of these illustrated that the crust materals joined in the rock bodies of northern Zhongposhan and Gubaoquan in the course of magma evoluation processing. They underwent different degree assimilation contamination.5.The rock bodies of the two parts happened fractional crystallization on olive, climopyroxene, plasiogranite. In rock body of north Zhongposhan, the order ofcrystallization on olive are pyroxene-peridotite, olive-gabbroite, bojite, norite-gabbroite; the order of crystallization on climopyroxene are olive-gabbroite, pyroxene-peridotite, norite-gabbroite, bojite, panorthosite; the order of crystallization on plagiogranite are olive-gabbroite, norite-gabbroite, bojite, pyroxene-peridotite, panorthosite. In the rock body of Gubaoquan , the order of crystallization on olive are pyroxene-allivalite, olive-gabbroite, gabbroite; the order of crystallization on climopyroxene are olive-gabbroite, pyroxene-allivalite, gabbroite; the order of crystallization on plagiogranite are olive-gabbroite, pyroxene-allivalite, gabbroite.6. The content of MgO primitive magma in northern Zhongposhan and Gubaoquan rock bodies are 13.26%, 8.77% respectively; The former is picrite magma ,which has poor magnesium content, The latter belongs to basaltic magma,which riched in magnesium.7.The characteristic of rare-earth elements ,trace elements and Nd^ S^ Pb isotopes show that the magma orignited from the depleted mantle, and other components magma joined in,which source originated from rheosphere. They have a close relationship with the mantle plume. It presumpted that the source materials originated from the rheosphere, and was brought in it, and partly melted.8. On the light of vening rules or mineraliztion in Beishan of Xjiang, the mafic-ultramafic rocks are divided into Fe series and Cu% Ni series. The characteristic of Cu> Ni series are as follows: 1) Rock association is bojite, norite-gabbroite, olive-gabbroite, pyroxenite, pyroxene- peridotite, peridotite; 2) It is low in SiO2> A12O3> CaO> FeO+Fe2O3> Na2O+K2O> MnO, TiO2, P2O5 and high MgO ; 3) It belongs to tholeiite series. 4) It is riched in Mg# and high ratio on Mg/Fe; 5) rare-earth elements partition curve displayed flat type is like E-MORB; 6) Nd(t) value range from 6.89 to 8.09, has a relative stable domain. The characteristic of Fe series are as follows: 1) Rock association is hornblende-dolerite, biotite- dolerite, gabbro- dolerite, dolerite, gabbroite, olive-gabbroite; 2) It is high in content of SiO2> A12O3^ CaO> FeO+Fe2O3^ Na2O+K2O> MnO> TiO2, P2O5 and high MgO ; 3) It belongs to transition series of tholeiite and calc-alkaline; 4) It is poor in Mg# and low ratio on Mg/Fe; 5) rare-earth elements partition curve displayed fiat type is like N-MORB; 6) Nd(t> value range from -1.29 to 6.80, has a dispersible domain.