The North China Craton （NCC） is the largest and oldest one among the worldwide cratons. It preserves important imprints of the Earth＇s early history, including crust formation, stabilization and reworking. The Yins...The North China Craton （NCC） is the largest and oldest one among the worldwide cratons. It preserves important imprints of the Earth＇s early history, including crust formation, stabilization and reworking. The Yinshan Block （YB） constitutes the northwestern part of NCC, and contains extensive exposure of Archean rocks （Fig. 1）.展开更多
The 2.5 Ga Guyang greenstone belt is a major lithological unit in the northwestern part of the North China Craton.Komatiites have recently been identified to occur within the lower part of the meta-volcanic sedimentar...The 2.5 Ga Guyang greenstone belt is a major lithological unit in the northwestern part of the North China Craton.Komatiites have recently been identified to occur within the lower part of the meta-volcanic sedimentary sequence of the greenstone belt.The biggest komatiite near Guyang has been mapped out,which is 500 m long and 50 m wide lenticular block.Re-Os isotopic compositions of 9 samples were analyzed to date the komatiites.The Os contents are from 0.88 to 2.63 ppb,identical with typical komatiites,and slightly lower than the normal mantle.The 187Os/188Os ratios are from 0.1115 to 0.1197,which are lower enough to exclude the origin of Phanerozoic magma as widely developed in adjacent areas.The calculated Re depletion model ages(TRD) are from 1346 to 2454 Ma,among them the oldest age of 2454 Ma gives the minimum evaluation for the formation age of the Guyang komatiite.Therefore,the komatiites are a part of the Guyang greenstone belt,indicating high degree melting of mantle during～2.5 Ga crustal growth event.展开更多
基金financially supported by the Natural Science Foundation of China(grants No.41572174 and 41202138)
文摘The North China Craton （NCC） is the largest and oldest one among the worldwide cratons. It preserves important imprints of the Earth＇s early history, including crust formation, stabilization and reworking. The Yinshan Block （YB） constitutes the northwestern part of NCC, and contains extensive exposure of Archean rocks （Fig. 1）.
基金supported by the National Natural Science Foundation of China(40730315,40721062 and 40642023)
文摘The 2.5 Ga Guyang greenstone belt is a major lithological unit in the northwestern part of the North China Craton.Komatiites have recently been identified to occur within the lower part of the meta-volcanic sedimentary sequence of the greenstone belt.The biggest komatiite near Guyang has been mapped out,which is 500 m long and 50 m wide lenticular block.Re-Os isotopic compositions of 9 samples were analyzed to date the komatiites.The Os contents are from 0.88 to 2.63 ppb,identical with typical komatiites,and slightly lower than the normal mantle.The 187Os/188Os ratios are from 0.1115 to 0.1197,which are lower enough to exclude the origin of Phanerozoic magma as widely developed in adjacent areas.The calculated Re depletion model ages(TRD) are from 1346 to 2454 Ma,among them the oldest age of 2454 Ma gives the minimum evaluation for the formation age of the Guyang komatiite.Therefore,the komatiites are a part of the Guyang greenstone belt,indicating high degree melting of mantle during～2.5 Ga crustal growth event.
