Petrogenesis of intermediate-acid intrusive rocks and enclaves in Tongling are a and the application of mineral thermobarometry
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    Abstract:

    Mesozoic intermediate-acid intrusive rocks in Tongling area can be divided into two magmatic series, namely the shoshonitic series and the high-potassium (K)calc-alkaline series. The shoshonitic series is characterized by the association of pyroxene monzodiorites (PMD)+monzonites(Mz)+quartz monzonites(QM), whereas the high-potassium calc-alkaline series has the association of gabbro-diorite (GBD)+quartz monzodiorites (QMD)+granodiorites(GD). Rocks of these two series have a similar mineral association composed of feldspar, pyroxene, hornblende, biotite, potassium feldspar and quartz, but the content of these minerals is different. The cumulate enclaves such as pyroxene cumulate, hornblende cumulate and hornblende gabbro in the shoshonitic series rocks are composed mainly of pyroxene and hornblende and subordinately of spinel, feldspar, apatite and phlogopite, while micro-diorite enclaves, mafic quartz monzodiorite enclaves and mica-enriched enclaves in the high-potassium calc-alkaline series are mainly comprised of feldspar, hornblende and biotite. Taking into account the preconditions for the application of thermobarometry, the authors calculated the pressure and temperature conditions for the formation of the intrusive rocks and enclaves. The calculated results of all enclaves and intrusive rocks show that their average temperatures and pressures are 1357℃ and 1783 GPa for pyroxene cumulate, 1228℃ and 1.430 GPa for hornblende cumulate, 1214℃ and 1.300 GPa for hornblende gabbro cumulate, 889℃ and 0.413 GPa for micro-diorite enclave, 887℃ and 0.114 GPa for mafic quartz monzodiorite enclaves, 1096~1043℃ and 0.167~0.115 GPa for shoshonitic series, and 844~784℃ and 0.211~0.193 GPa for high-potassium (K) calc-alkaline series, respectively. If these pressure values are converted into the depth according to 3.3 kbar/km, their corresponding depths are 45~65 km for all cumulate enclaves, 12~15 km for micro-diorite enclaves and about 4 km for mafic quartz monzodiorite enclaves, 4~6 km for shoshonitic series and 6~7 km for high-potassium(K) calc-alkaline series, respectively. Combined with petrologic and geochemical studies of all enclaves and two series of intrusive rocks, the authors believe that all cumulate enclaves were derived from crystallization differentiation of the mafic magma in the deep magma chamber, the micro-diorite enclaves came from the mixing between evolved magma from the deep magma chamber and crustal partial melt in the shallow magma chamber, the mafic quartz monzodiorite enclaves might have been the marginal facies of early intrusive body, and the mica-enriched enclaves were probably relics of crustal partial melting.

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雷 敏,吴才来,高前明,国和平,刘良根,郭祥炎,郜源红,陈其龙,秦海鹏,2010,铜陵地区中酸性侵入岩及其包体的成因和矿物温压计的应用[J].岩石矿物学杂志,29(3):271~288. LEI Min, WU Cai_lai, GAO Qian_ming, GUO He_ping, LIU Liang_gen, GUO Xiang_yan, GAO Yuan_hong, CHEN Qi_long, QIN Hai_peng,2010,Petrogenesis of intermediate-acid intrusive rocks and enclaves in Tongling are a and the application of mineral thermobarometry[J]. Acta Petrologica et Mineralogica,29(3):271~288.

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