Crustal anatexis in continental subduction zones has great bearing on chemical differen-tiation of the continental crust at convergent plate boundaries.This was experimentally investigated for ultrahigh-pressure(UHP)metafelsic rocks at 0.5-3.0 GPa and 650-900℃.The results show that partial melting begins at about 750℃when pressure drops from 3.0 to 2.0 GPa,corresponding to de-compressional exhumation of the deeply subducted continental crust.As the pressure further decreases to 1.0 GPa,the partial melting degree reaches the maximum of～25％at 900℃.Partial melts produced in these experiments are rich in silica and alkali,and poor in iron,manganese and magnesium.As the degree of partial melting increases,the composition of partial melts gradually converges toward homo-geneous one.In the absence of free water,the partial melting of metafelsic rocks were triggered by the breakdown of hydrous minerals.At low temperatures of～750℃at 1.0-2.0 GPa,phengite dehydration melting occurs at first,giving rise to small amounts of felsic melts and peritectic K-feldspar.As the tem-perature rises up to 850-900℃,biotite begins to break down and gives rise to large amounts of felsic melts and peritectic minerals such as garnet,K-feldspar and orthopyroxene.It is noted that peritectic garnet is much different from anatectic garnet crystallized from anatectic melts and metamorphic gar-net formed through metamorphic dehydration reaction under subsolidus conditions.The peritectic gar-net is characterized not only by anhedral shapes with many multiphase crystal inclusions but also by compositions poor in spessartine and grossular but rich in almandine and pyrope.On the other hand,the anatectic garnets are characterized not only by euhedral shapes with few inclusions but also by compositions rich in grossular and spessartine but poor in almandine and pyrope.These observations provide experimental constraints on the origin of garnets in UHP metamorphic rocks,which have great bearing on understanding of anatectic metamorphism in collisional orogens.

Xu Luo;Qiong-Xia Xia;Yong-Fei Zheng;Wan-Cai Li

CAS Key Laboratory of Crust-Mantle Materials and Environments,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China;Center of Excellence in Comparative Planetology,Chinese Academy of Sciences(CAS),Hefei 230026,China;Department of Earth,Environmental and Planetary Sciences,Case Western Reserve University,Cleveland OH 44106,USA

地球科学学刊（英文版）

[1]Xu Luo;Qiong-Xia Xia;Yong-Fei Zheng;Wan-Cai Li-.An Experimental Study of Partial Melting of Metafelsic Rocks:Constraints on the Feature of Anatectic Melts and the Origin of Garnets in Collisional Orogens)[J].地球科学学刊（英文版）,2022(03):753-769

Metafelsic,Anatectic,Garnets,Orogens,metafelsic,phengite,anatectic,anhedral,spessartine,pyrope

Experimental,Study,Partial,Melting,Rocks,Constraints,Feature,Melts,Origin,Collisional,Crustal,anatexis,continental,subduction,zones,great,bearing,chemical,tiation,crust,convergent,plate,boundaries,This,was,experimentally,investigated,ultrahigh,pressure,UHP,rocks,GPa,results,show,that,partial,melting,begins,about,when,drops,from,corresponding,compressional,exhumation,deeply,subducted,further,decreases,degree,reaches,maximum,melts,produced,these,experiments,are,rich,silica,alkali,poor,iron,manganese,magnesium,increases,gradually,converges,toward,homo,geneous,In,absence,free,water,were,triggered,by,breakdown,hydrous,minerals,At,low,temperatures,dehydration,occurs,first,giving,small,amounts,peritectic,feldspar,rises,up,biotite,gives,large,such,orthopyroxene,It,noted,much,different,crystallized,metamorphic,formed,through,reaction,subsolidus,conditions,characterized,only,shapes,many,multiphase,inclusions,but,also,compositions,grossular,almandine,On,other,hand,garnets,euhedral,few,These,observations,provide,constraints,origin,which,have,understanding,metamorphism,collisional,orogens

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