The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Crat...The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Craton(WDC).However,3.0-2.7 Ga geological records are missed in the CDB.This study identified the 2.85 Ga gabbroic xenoliths within the Closepet batholith in the CDB.The~2.85 Ga inherited zircons and zircon Hf model ages in CDB further provide evidence for this significant magmatic event.The gabbroic xenoliths are characterized by E-MORB REE patterns and Nb,Ta,and Ti depletions,together with high radiogenic isotopic signatures,including zircon Hf(ε_(Hf)(t)_(min)=-3.2),whole-rock Nd(ε_(Nd)(t)=-0.8-0.7),and Pb isotopes(κ=4.9-7.9),indicating derivation from a slightly enriched mantle source.Additionally,they have high Nb(4.41 to 4.73 ppm),low Ti/V(23.4 to 22.5),and elevated Th/Yb(0.38 to 0.61).All these suggest a subduction-related back-arc basin setting.Coupled with widespread early Neoarchean subduction-related igneous rocks in the DC,the 2.85 Ga gabbroic magmatism signifies that the DC had transitioned into a tectonic stage dominated by lateral movement of continental blocks around 2.85 Ga,corresponding to global~2.85 Ga magmatic events.展开更多
This study provides new evidence for a significant Neoproterozoic tectono-thermal event in the southern Dharwar Craton,based on U-Pb dating of rutile and monazite from metamorphic rocks of the Sargur Group.Trace eleme...This study provides new evidence for a significant Neoproterozoic tectono-thermal event in the southern Dharwar Craton,based on U-Pb dating of rutile and monazite from metamorphic rocks of the Sargur Group.Trace element analysis of rutile in garnet-bearing amphibolite,amphibolite,garnet-bearing staurolite-kyanite schist,and grunerite-garnet schist suggests that their protoliths were primarily basaltic rocks,sediments with mafic component,pelitic sediments,and mixed sediments with both mafic and felsic components,respectively.Rutile U-Pb ages of 625±22 Ma(garnet-bearing amphibolite),752±5.1 Ma(amphibolite),836±4 Ma to 663±26 Ma(garnet-bearing staurolite kyanite schist)and 860±13 Ma(grunerite-garnet schist),along with a monazite U-Pb age of 789±4.4 Ma(garnet-bearing staurolite kyanite schist),record a significant Neoproterozoic(860-625 Ma)tectono-thermal event along the southern margin of the western Dharwar Craton.This event is most likely associated with aborted rift-related alkaline magmatism along the northern margin of the Southern Granulite Terrane(SGT)and the southern margin of the Dharwar Craton.Given the lack of direct evidence for the assembly of the Rodinia supercontinent in the Dharwar Craton and SGT,this Neoproterozoic event is unlikely to be related to the breakup of Rodinia.展开更多
Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,co...Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,coesite pseudomorphs and other UHP minerals.It is the largest oceanic-type UHP metamorphic belt reported so far.It has formed due to northward subduction of the Tianshan Paleo-Ocean.U-Pb dating of metamorphic rims of zircons from a coesite-bearing garnet-phengite schist yields a peak UHP metamorphic ages of 320±3.7 Ma.Combined with ages of 233–226 Ma obtained from rims of zircons from retrograded eclogites,a long retrograde metamorphic evolution(>70 Ma)has been revealed.According to phase equilibria modeling,the P-T paths of both coesite-bearing eclogites and garnet-phengite schists are characterized by thermal relaxation,i.e.,the metamorphic temperature peak lags behind the pressure peak,indicating that the UHP rocks experienced slow and long heating and decompression during exhumation in the subduction channel.On the basis of the field observation that a small amount of eclogite lenses is wrapped in large volumes of metapelites,and the similar P-T paths of both rock types,we propose that the exhumation of the UHP eclogites from southwestern Tianshan,China,may have resulted from the exhumation of large volumes of low-density metapelites,which carried the denser eclogites to the Earth’s surface.展开更多
基金financially supported by the National Natural Science Foundations of China(41890831,41421002)the MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University(201210133)。
文摘The Dharwar Craton(DC)in India consists of three distinct Archean blocks.Previous research suggests that the Central Dharwar Block(CDB)experienced a geological history(3.3-2.5 Ga)comparable to the Western Dharwar Craton(WDC).However,3.0-2.7 Ga geological records are missed in the CDB.This study identified the 2.85 Ga gabbroic xenoliths within the Closepet batholith in the CDB.The~2.85 Ga inherited zircons and zircon Hf model ages in CDB further provide evidence for this significant magmatic event.The gabbroic xenoliths are characterized by E-MORB REE patterns and Nb,Ta,and Ti depletions,together with high radiogenic isotopic signatures,including zircon Hf(ε_(Hf)(t)_(min)=-3.2),whole-rock Nd(ε_(Nd)(t)=-0.8-0.7),and Pb isotopes(κ=4.9-7.9),indicating derivation from a slightly enriched mantle source.Additionally,they have high Nb(4.41 to 4.73 ppm),low Ti/V(23.4 to 22.5),and elevated Th/Yb(0.38 to 0.61).All these suggest a subduction-related back-arc basin setting.Coupled with widespread early Neoarchean subduction-related igneous rocks in the DC,the 2.85 Ga gabbroic magmatism signifies that the DC had transitioned into a tectonic stage dominated by lateral movement of continental blocks around 2.85 Ga,corresponding to global~2.85 Ga magmatic events.
基金supported by the National Natural Science Foundations of China(Grant Nos:41890831 and 42172214)the MOST Special Fund from the State Key Laboratory of Continental Dynamics,Northwest University.
文摘This study provides new evidence for a significant Neoproterozoic tectono-thermal event in the southern Dharwar Craton,based on U-Pb dating of rutile and monazite from metamorphic rocks of the Sargur Group.Trace element analysis of rutile in garnet-bearing amphibolite,amphibolite,garnet-bearing staurolite-kyanite schist,and grunerite-garnet schist suggests that their protoliths were primarily basaltic rocks,sediments with mafic component,pelitic sediments,and mixed sediments with both mafic and felsic components,respectively.Rutile U-Pb ages of 625±22 Ma(garnet-bearing amphibolite),752±5.1 Ma(amphibolite),836±4 Ma to 663±26 Ma(garnet-bearing staurolite kyanite schist)and 860±13 Ma(grunerite-garnet schist),along with a monazite U-Pb age of 789±4.4 Ma(garnet-bearing staurolite kyanite schist),record a significant Neoproterozoic(860-625 Ma)tectono-thermal event along the southern margin of the western Dharwar Craton.This event is most likely associated with aborted rift-related alkaline magmatism along the northern margin of the Southern Granulite Terrane(SGT)and the southern margin of the Dharwar Craton.Given the lack of direct evidence for the assembly of the Rodinia supercontinent in the Dharwar Craton and SGT,this Neoproterozoic event is unlikely to be related to the breakup of Rodinia.
基金supported by the National Basic Research Program of China(2009CB825007)the National Natural Science Foundation of China(41121062 and41272069)
文摘Recent progress in the study of the UHP metamorphic belt in southwestern Tianshan,China,is summarized in this paper.This about 80-km-long and over 10-km-wide UHP belt has been recognized by the discovery of coesite,coesite pseudomorphs and other UHP minerals.It is the largest oceanic-type UHP metamorphic belt reported so far.It has formed due to northward subduction of the Tianshan Paleo-Ocean.U-Pb dating of metamorphic rims of zircons from a coesite-bearing garnet-phengite schist yields a peak UHP metamorphic ages of 320±3.7 Ma.Combined with ages of 233–226 Ma obtained from rims of zircons from retrograded eclogites,a long retrograde metamorphic evolution(>70 Ma)has been revealed.According to phase equilibria modeling,the P-T paths of both coesite-bearing eclogites and garnet-phengite schists are characterized by thermal relaxation,i.e.,the metamorphic temperature peak lags behind the pressure peak,indicating that the UHP rocks experienced slow and long heating and decompression during exhumation in the subduction channel.On the basis of the field observation that a small amount of eclogite lenses is wrapped in large volumes of metapelites,and the similar P-T paths of both rock types,we propose that the exhumation of the UHP eclogites from southwestern Tianshan,China,may have resulted from the exhumation of large volumes of low-density metapelites,which carried the denser eclogites to the Earth’s surface.
