Dehydration melting of UHP eclogite and paragneiss in the Dabie orogen: Evidence from laboratory experiment to natural observation  

作　　者：LIU Qiang WU Yao 

机构地区：[1]Faculty of Earth Sciences, China University of Geosciences [2]State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences

出　　处：《Chinese Science Bulletin》2013年第35期4390-4396,共7页

基　　金：supported by the National Key Basic Research Program from the MOST(2009CB825003);the National Natural Science Foundation of China(40802046 and 41272078);the Fundamental Research Funds for the Central Universities,China University of Geosciences(Wuhan)(CUG120121)

摘　　要：Dehydration melting of subducted continental crust is significant during exhumation,and its study from both experimental and petrological observations is of great importance to our understanding of continental geodynamics.Dehydration melting experiments were carried out on ultrahigh-pressure(UHP)eclogite from Bixiling in the Dabie orogen using a piston cylinder at 1.5–3.0GPa and 800–950°C to investigate partial melting of eclogite induced by phengite breakdown.The phengite-bearing eclogite started to melt at T 800–850°C and P=1.5–2.0 GPa and produced about 3%granitic melt.The products of dehydration melting vary with temperature and pressure.Such results provide valuable constraints on the micro-texture related to partial melting of UHP rocks in the Dabie-Sulu orogenic belt.Three types of polyphase inclusions were identified in garnet from the Shuanghe UHP eclogite.K-feldspar and quartz inclusions are interpreted to represent the products of segregation and crystallization of minor amounts of melt that formed during dehydration melting of phengite by the inferred reaction Phengite+Omphacite±Quartz→Amphibole±Garnet+Melt(K-feldspar+Quartz±Plagioclase).Polyphase inclusions of phengite and K-feldspar+Quartz inclusions were also found in zoisite/clinozoisite and garnet from the Shuanghe garnet-bearing paragneiss.These polyphase inclusions provide evidence for a continuous process from sub-solidus dehydration to partial melting within the UHP gneissic rocks.The compositional variation of garnets demonstrates that breakdown of epidote-group minerals may have played a crucial role during dehydration melting reaction of phengite.The Ti-in-zircon thermometry and Si content of phengite in zircon suggest that partial melting would occur at 783–839°C and 2.0–2.5 GPa.Therefore,both experimental results and petrological observations indicate that dehydration melting and fluid activity within the Dabie UHP rocks at micro-scale are controlled by the breakdown of phengite.Dehydration melting of subducted continental crust is significant during exhumation, and its study from both experimental and petrological observations is of great importance to our understanding of continental geodynamics. Dehydration melting experi- ments were carried out on ultrahigh-pressure （UHP） eclogite from Bixiling in the Dabie orogen using a piston cylinder at 1.5-3.0 GPa and 800-950℃ to investigate partial melting of eclogite induced by phengite breakdown. The phengite-bearing eclogite started to melt at T≤800-850℃ and P=1.5-2.0 GPa and produced about 3% granitic melt. The products of dehydration melting vary with temperature and pressure. Such results provide valuable constraints on the micro-texture related to partial melting of UHP rocks in the Dabie-Sulu orogenic belt. Three types of polyphase inclusions were identified in garnet from the Shuanghe UHP eclogite. K-feldspar and quartz inclusions are interpreted to represent the products of segregation and crystallization of minor amounts of melt that formed during dehydration melting of phengite by the inferred reaction Phengite＋Omphacite＋Quartz Amphibole_＋Garnet＋Melt （K-feldspar＋Quartz＋Plagioclase）. Polyphase inclusions of phengite and K-feldspar＋Quartz inclusions were also found in zoisite/clinozoisite and garnet from the Shuanghe garnet-bearing paragneiss. These polyphase inclusions pro- vide evidence for a continuous process from sub-solidus dehydration to partial melting within the UHP gneissic rocks. The com- positional variation of garnets demonstrates that breakdown of epidote-group minerals may have played a crucial role during de- hydration melting reaction of phengite. The Ti-in-zircon thermometry and Si content of phengite in zircon suggest that partial melting would occur at 783-839℃ and 2.0-2.5 GPa. Therefore, both experimental results and petrological observations indicate that dehydration melting and fluid activity within the Dabie UHP rocks at micro-scale are controlled by the breakdown of phengite.

关 键 词：脱水熔融实验 超高压榴辉岩 实验证据 副片麻岩 大别山 实验室 自然观 多硅白云母 

分 类 号：P588.3[天文地球—岩石学] P588.34[天文地球—地质学]