An experimental study of dehydration melting of phengite-bearing eclogite at 1.5―3.0 GPa  

作　　者：LIU Qiang1,2, JIN ZhenMin1,2 & ZHANG JunFeng1,2 1 State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China 2 Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China 

出　　处：《Chinese Science Bulletin》2009年第12期2090-2100,共11页

基　　金：Supported by National Natural Science Foundation of China(Grant Nos.40802046and90714005);National Basic Research Program of China(Grant No.2009CB825003);State Key Laboratory of GPMR Foundation(Grant No.200610)

摘　　要：Dehydration melting experiments were performed on ultrahigh-pressure eclogite from Bixiling in the Dabie orogen at 1.5―3.0 GPa and 800―950℃ using piston cylinder apparatus. The results show that (1) eclogite with ~5% phengite started to melt at T≤800―850℃ and P = 1.5―2.0 GPa and produced about 3% granitic melt; (2) the products of dehydration melting of phengite-bearing eclogite vary with temperature and pressure. Fluid released from dehydration of phengite and zoisite leads to partial melting of eclogite and formation of plagioclase reaction rim around kyanite at pressures of 1.5―2.0 GPa and temperatures of 800―850℃; (3) phengite reacted with omphacite and quartz and produced oligoclase, kyanite and melt at elevated temperatures. Oligoclase is the primary reaction product produced by partial melting of phengite in the eclogite; and (4) the dehydration melting of phengite-bearing eclogite at pressures of 1.5―3.0 GPa and temperatures ≥900 ℃ results in formation of garnets with higher molar fraction of pyrope (37.67 wt.%―45.94 wt.%). Potassium feldspar and jadeite occur at P = 2.4―3.0 GPa and T≥900 ℃ , indicating higher pressure and fluid-absent conditions. Our results constrain the solidus for dehydration melting of phengite-bearing eclogite at pressures of 1.5―3.0 GPa. Combining experi- mental results with field observations of partial melting in natural eclogites, we concluded that phengite-bearing eclogites from the Dabie-Sulu orogen were able to partially molten at P = 1.5―2.0 GPa and T = 800―850℃ during exhumation. The ultrahigh-high pressure eclogites would have experienced partial melting in association with metamorphic phase transformation under different fluid conditions.Dehydration melting experiments were performed on ultrahigh-pressure eclogite from Bixiling in the Dabie orogen at 1.5--3.0 GPa and 800--950℃ using piston cylinder apparatus. The results show that （1） eclogite with -5% phengite started to melt at T≤800--850℃ and P = 1.5--2.0 GPa and produced about 3% granitic melt; （2） the products of dehydration melting of phengite-bearing eclogite vary with temperature and pressure. Fluid released from dehydration of phengite and zoisite leads to partial melting of eclogite and formation of plagioclase reaction rim around kyanite at pressures of 1.5--2.0 GPa and temperatures of 800--850℃; （3） phengite reacted with omphacite and quartz and produced oligoclase, kyanite and melt at elevated temperatures. Oligoclase is the primary reaction product produced by partial melting of phengite in the eclogite; and （4） the dehydration melting of phengite-bearing eclogite at pressures of 1.5--3.0 GPa and temperatures ≥900℃ results in formation of garnets with higher molar fraction of pyrope （37.67 wt.%--45.94 wt.%）. Potassium feldspar and jadeite occur at P = 2.4--3.0 GPa and T≥900℃, indicating higher pressure and fluid-absent conditions. Our results constrain the solidus for dehydration melting of phengite-bearing eclogite at pressures of 1.5--3.0 GPa. Combining experi- mental results with field observations of partial melting in natural eclogites, we concluded that phengite-bearing eclogites from the Dabie-Sulu orogen were able to partially molten at P= 1.5--2.0 GPa and T= 800--850℃ during exhumation. The ultrahigh-high pressure eclogites would have experienced partial melting in association with metamorphic phase transformation under different fluid conditions.

关 键 词：超高压榴辉岩 脱水熔融实验 水白云母 反应压力 部分熔融 大别造山带 苏鲁造山带 反应产物 

分 类 号：P579[天文地球—矿物学]