Petrogenesis of intermediate-acid intrusive rocks and enclaves in Tongling area and the application of mineral thermobarometry
LEI Min1,WU Cai-lai1,GAO Qian-ming2,GUO He-ping2,LIU Liang-gen2,GUO Xiang-yan2,GAO Yuan-hong1,CHEN Qi-long1 and QIN Hai-peng1(1.Institute of Geology,CAGS,Beijing 100037,China;2.No.321 Geological Party,Anhui Bureau of Geology and Mineral Resources,Tongling 244033,China)
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 1 357℃ and 1.783 GPa for pyroxene cumulate,1 228℃ and 1.430 GPa for hornblende cumulate,1 214℃ 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,1 096～1 043℃ 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.
【Fund】： 国家财政部科学专项(140102);; 国家自然科学基金资助项目(49772106 40472034 40672049);; 中国地质调查局项目(1212010918007 1212010818090 1212010611803 1212010711816)
【CateGory Index】： P588.12
【CateGory Index】： P588.12