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The Features Of Gangtangcuo Granite And Its Geological Significance In Tibet Qiangtang Area

Posted on:2010-03-22Degree:MasterType:Thesis
Country:ChinaCandidate:F ZhangFull Text:PDF
GTID:2230360272987801Subject:Structural geology
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Gangtangcuo granite in Tibet Qiangtang area is composed by early mid-coarse grained porphyritic biotite monzogranite (T3γβa) rock unit and mid-fine grained porphyritic monzogranite (T3γβb) and late (including tourmaline) mid-fine grained porphyritic monzogranite (T3γβb) composite rock; rock outcrops with Xueshui river rock for the contact between the intrusive contact, a total area of rough open 149km2, the study area is acidic intrusive rocks in the main body of the rock unit.In the rock unit, the mid-coarse grained porphyritic biotite giant adamellite (T3γβa) formed early contains a large number of black micro-fine-grained quartz diorite and stripe pack of K-feldspar porphyroblast giant. Through the study of thermodynamics crystallography, we get a conclusion that the giant stripe K-feldspar porphyroblast in the rock unit is formed by magma mixing, the results of two feldspar thermometer temperature measurement showed that temperature of porphyroblast crystallization is 954~773℃from the center to the edge, Therefore, the early formation of rock unit in Gangtangcuo granite is formed by magma mixing.The petrology and geochemistry of Gangtangcuo granite as follows: the rock unit in early formation, A / CNK> 1, Rb, Th, K, Nd and Sm strongly enriched, Ba, Nb, Sr and Ti strongly lost, which react the characteristics of shell source; the average ofΣREE is more than 250, chondrite REE curve rightist "V"-shaped, negative abnormal EU, light, strong HREE fractionation for high-K calc-alkaline peraluminous granite.the rock unit in late formation, A / CNK> 1.1, Rb, U, K and P strongly enriched, Ba, Nb, Sr and Ti strongly lost, the average ofΣREE is about 33, chondrite distribution curve standardization rightist "V" font, but the light and heavy rare earth fractionation weak, which react the characteristics of the crust-mantle mixed-source, the geochemical characteristics of rock unit showed that the sets are strongly peraluminous high-K calc-alkaline series granite.Zircon U-Pb isotope dating shows that the Gangtangcuo granite rock of the early crystallization unit emplacement age is 210~225Ma, the late rock dating data exit a large deviation, needed further study. Comparative study of regional integration through the Gangtangcuo granite geochemical tectonic discrimination diagrams drawn that Gangtangcuo granite rock is formed in the early collision course with the subduction of continental plates during the proliferative marginal environment, and the late rock unit is the formed in in the collision orogeny process of syn-collision with the structure after the environment.
Keywords/Search Tags:Gangtangcuo granite, peraluminous granite, stripe K-feldspar, syn-collision
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