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《中国科学院地质与地球物理研究所2006年论文摘要集》 2007年
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Variation in peak P-T conditions across the upper contact of the UHP terrane,Dabieshan,China:gradationai or abrupt?

【摘要】:正The Southern Dabieshan Terrane(SDT) has previously been divided into high-pressure (HP) and ultrahigh-pressure(UHP) terranes,and its regional extent and the tectonic nature of its boundaries are hotly debated topics.In this study,an eclogite-bearing area of 100 km2 near Taihu is mapped in detail,and divided into Northern,Middle and Southern Zones on the basis of lithological characteristics.The Northern Zone consists of epidote-biotite gneiss and eclogite blocks,the Middle Zone includes granitic gneiss,biotite gneiss,eclogites and amphibolite,and the Southern Zone is composed mainly of garnet-bearing mica schist.The eclogites occur mainly as lens or blocks in the Northern and Middle Zones.The peak P-T conditions for 61 eclogite samples across the area are estimated using the Grt-Cpx Fe2+-Mg thermometers and the Grt-Cpx-phe barometers.The results indicate three different P-T regions:2.82-4.09 GPa/759-942℃in the Northern Zone,and 2.00-3.54 GPa/641-839℃in the granitic gneiss and 1.38-2.36 GPa/535-768℃in the biotite gneiss from the Middle Zone.Combined with the spatial distribution of eclogites across the area,the P-T values for eclogites increase continuously from the south to the north, defining a reference "geotherm" of 5℃km-1.However,some unreasonable apparent gradients can be established along two S-N profiles across the area,and display a P-T difference between the Northern and Middle zones.On the basis of the average P-T data for eclogites across the area, a gap of at least 0.3 GPa/20℃exist between the Northern and Middle zones.By contrast,the P-T values of eclogites from the Middle zone show a coherent pattern with transitional characteristics from HP in the south to UHP in the north.We suggest that the SDT was a coherent slab during subduction,and was broken up by a major fault during exhumation,which was formed under ultrahigh-pressure metamorphic conditions.

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1 ;Variation in peak P-T conditions across the upper contact of the UHP terrane,Dabieshan,China:gradationai or abrupt?[A];中国科学院地质与地球物理研究所2006年论文摘要集[C];2007年
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