| 青城子矿区黑云母和石榴石的地球化学及变质作用的P-T条件探讨 |
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| GEOCHEMISTRY OF BIOTITES AND GARNETS FROM METAMORPHIC ROCKS AND DISCUSSION ON METAMORPHISM P-T CONDITIONS IN QINGCHENGZI MINING DISTRICT |
| The chemical compositions and oxygen, hydrogen and silicon stable isotope compositions of biotites and garnets from metamorphic rocks in Qingche-ngzi mining district are studied in detail.The main elements of biotites and garnets show that the biotites are mainly ferribiotites and the garnets are mainly almandites. The ferrian coefficients of biotites and garnets are very high and vary in different rock layers. From lower strata to upper strata, the Si and Al components of biotites decrease and Ca and Mg components increase which reflects in the diagrams of (Ca + Mg)-(Si + Al)-(Fe + Mn), Mg-Al-(Fe + Mn) and Al-K-(Fe + Mg + Mn + Ti) of biotites and are compared to those of the metamorphic rocks.The contents of minor mineralizing elements such as Pb and Zn in biotites are very high: Pb 72.8-900.8 ppm and Zn 0-1754.3 ppm. While those in garnets are a little lower. The contents of minor basic elements such as Co, Ni, Cr, V, Ba and Cd are also very high both in biotites and garnets, which may be an indication of their relation to submarine volcanic substance. Also, the trace elements and their ratios show a regular variation in different rock layers.The oxygen and hydrogen isotope compositions of biotites and garnets are analyzed. From those data, we calculated the δ18OH2O and δDDH2O values of metamorphic water. The δ18OH2O values are 15.0‰-16.9‰ and δDH2O valuesare -63‰--81‰ or a little higher. The δ18O values of coexisting biotites andgarnets show that the oxygen isotope equilibration was disturbed by later geological events. The silicon isotopes of biotites and garnets are analyzed for the first time. The δ30Si values in biotites and garnets from schistand are -0.3‰--0.6‰ and -0.9%--1.1‰ respectively. The δ30Si valuephlogopite from the marble is 0.9‰ which is very different from those of biotites garnets in schist. These results show that the silicon substance sources of of biotite and pholgopite are different from each other.Maybe the biotites was formed from rotting kaolinitic clay or related to the submarine volcanic substance while the phlogopite was formed from bedded chert in marble.The coexisting minerals and the chemical compositions and Fe2+ and Mg distribution coefficient (KD) of biotite and garnet show that the metamor-phism grade is up to epidote amphibolite facies or amphibolite facies with the P-T conditions of P>0.35-0.5 GPa and r = 620-660℃. The mineralization has a close relation with the regional metamorphism. |
| JIANG Shao-yong,DING Ti-ping,WAN De-fang,WEI Ju-ying.1992.GEOCHEMISTRY OF BIOTITES AND GARNETS FROM METAMORPHIC ROCKS AND DISCUSSION ON METAMORPHISM P-T CONDITIONS IN QINGCHENGZI MINING DISTRICT[J].Acta Geoscientica Sinica,13(1):71-84. |
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