The Study Of Magma Mixing Of Dongquangebi Granite In East Of The South Tianshan, Xinjiang

The rock-body studied in this paper lies in the north edge of the South Tian orogenic belt,which intruded into the Kumishi Yushugou-Tonghuashan ophiolite tectonic mixtite belt.Through the systematic overall study of macroscopical rock characteristics, petrographycharacteristics, geochemistry characteristics and chronology, the progresses we made is asfollows:1. Dongquangebi pluton is mainly made up host-rock porphyaceous biotite monzoniticgranite and mafic microgranular enclaves. The mafic microgranular enclaves are mainlydiorite.2. The Dongquangebi pluton has the typic petrographic character of magmatic mixingand petrogeochemistry character. The mafic microgranular enclaves, which have typicigneous-texture, develop lopsided texture of minerals, such as the peritectic structure of quartz,the augen quartz and the potassium feldspar ingotism which has the edge of melanocraticmineral, acicular hollow apatite, he xenocrysts of potassium feldspar in enclaves, the rapakivitexture of plagioclase in potassium feldspar, the very complex zone structure of plagioclase inenclaves and host-rock, the ocellar texture of titanite-plagioclase. The mafic microgranularenclaves and host-granite presents well linear relation in Huck diagram and magmatic mixingtrend in the TFeO-MgO diagram.3. The host-granite, which is charactered by quasi-aluminous rock, high-k calc-alkalineseries and high Mg#, is rich in large ion lithophile element (LILE) and light rare earth element(LREE) and present to be loss in high field-strength element (HFSE) and heavy rare earthelement (HREE). It indicates in the ACF diagram that the type of the host-granite is I-typegranite. In a word, the host-granite of Dongquangebi pluton belongs to I-type granite which ismetaluminous, high Mg#and high-k calc-alkaline.4. SHRIMP zircon U-Pb dating of host-rock porphyraceous biotite monzonitic graniteindicates that the weighted mean206Pb/238U age of it is305±1Ma. The Dongquangebi pluton,which is in the post-collision tectonic setting, indicates that the residual sea basin of the SouthTianshan has been closed before the late carboniferous. We imply that the time of the closing of residual sea basin of the South Tianshan is from late early carboniferous to the early periodof late Carboniferous.5. The residual minerals of source region which balance with host-granite of Dongquan-gebi pluton are amphibolite, garnet, pyroxene and plagioclase (a little). The press of formingthe rock is1.0~1.3GPa. The source region of the rock is calc-alkali and high-k calc-alkalineandesitic amphibolite. Because the K-rich rocks of the lower crust occur partial meltingresulting from the magma underplating, the generatedk-rich felsic magma and mafic magmaoccur the magma mixing, generating the granitic magma with the high Mg#, Cr and Ni. Themafic microgranular enclaves are the incomplete mixing products of felsic magma and maficmagma.6. Dongquangebi pluton is magma-mixing type granite by the mixing of acidic magma ofthe crust source and basic magma of the mantle source, which indicates the continental crustalgrowth of the South Tianshan by the way of the joining of the mantle material in the lateCarboniferous.