This paper reports the systematic studies of geochemistry on the meta sedimentary rocks, felsic gneisses and amphibolites of the Kongling complex from the Archean high grade terrain of the Yangtze craton. It shows t...This paper reports the systematic studies of geochemistry on the meta sedimentary rocks, felsic gneisses and amphibolites of the Kongling complex from the Archean high grade terrain of the Yangtze craton. It shows that the amphibolites originated from a weakly depleted mantle resource. Nb negative anomaly, negative ε (Nd, t ) and the t DM ages which older than their isochron ages of the TTG gneisses imply the possible existence of the crust older than round about 2.7 Ga in the region. Three types of meta sedimentary rocks are identified from the Kongling complex. The first type originated from the juvenile crust with the features of the first cycle sedimentary rocks. Cratonic sedimentary rocks characterize the second type. Mobilization of REE and other elements resulted from partial melting during the migmatization is found in the third type of meta sedimentary rocks. Apart from the early TTG gneisses, some of the mafic rocks are also expected to be the source rocks of the first type of para rocks. The deposition times of the first and second type paragneisses are closed in the Neoarchean of about 2.7 Ga and the early period of Proterozoic respectively, and the period when cratonization of the Yangtze continental block completed is referred to be earlier than the Mesoproterozoic. Nd isotopic tracing on the magma sources of the Jinning granitic rocks in the region reveals that the major part of the Kongling basement is Neoarchean.展开更多
The Neo-Archean Sonakhan Greenstone Belt(SGB) located in the north-eastern fringes of Bastar craton,Central India, is dominated by Basalts, Andesites, Dacites and Rhyolites association. Partial melting modeling on the...The Neo-Archean Sonakhan Greenstone Belt(SGB) located in the north-eastern fringes of Bastar craton,Central India, is dominated by Basalts, Andesites, Dacites and Rhyolites association. Partial melting modeling on the SGB metabasalts indicates that these rocks were derived by20% melting of spinel peridotite. Fractional crystallisation modeling with REE reveal that the most evolved samples represent the product of fractional crystallization of least evolved magma with 35% plagioclase, 35% clinopyroxene,20% olivine, 5% magnetite and 5% ilmenite as fractionating minerals with 40% remaining magma. Depletion of HFSE with reference to the LILE and LREE/HFSE ratios and Nb, Zr anomalies in the multi-element diagram of the mafic rocks of SGB indicate Island arc magmatic setting.The enriched Th/Yb values further substantiate that the mantle arrays were modified by subduction-related fluids or melts. The general conclusions drawn indicate that the metabasalts from the SGB were formed as a result of subduction of an intraoceanic lithosphere in a fore-arc suprasubduction zone environment.展开更多
Single zircons from two trondhjemitic gneisses and two clastic metasedimentary rocks without Eu anomaly of the Kongling high-grade metamorphic terrain are dated by the in situ SHRIMP U-Pb method. The results show that...Single zircons from two trondhjemitic gneisses and two clastic metasedimentary rocks without Eu anomaly of the Kongling high-grade metamorphic terrain are dated by the in situ SHRIMP U-Pb method. The results show that the trondhjemitic magma emplaced at 2947-2903 Ma. Concordant age of as old as 3.3 Ga is present in the detrital zircons from the clastic metasedimentary rocks. Together with the depleted mantle Nd model age (TDM =3.2-3.3 Ga) of the clastic metasedimentary rocks, this documents the presence of Paleoarchean continental crust in the Yangtze craton.展开更多
Sm Nd isotopic compositions of associated amphibolites, TTG gneisses and granitic gneisses from the Archean Kongling Complex of the Yangtze Craton, South China are systematically analyzed. The results show that the am...Sm Nd isotopic compositions of associated amphibolites, TTG gneisses and granitic gneisses from the Archean Kongling Complex of the Yangtze Craton, South China are systematically analyzed. The results show that the amphibolites and TTG gneisses have a similar age of ca. 2 700 Ma, which well agrees with zircon U Pb dating of previous studies. However, their ε Nd ( t ) are different, suggestive of possible dissimilarity in source composition.展开更多
文摘This paper reports the systematic studies of geochemistry on the meta sedimentary rocks, felsic gneisses and amphibolites of the Kongling complex from the Archean high grade terrain of the Yangtze craton. It shows that the amphibolites originated from a weakly depleted mantle resource. Nb negative anomaly, negative ε (Nd, t ) and the t DM ages which older than their isochron ages of the TTG gneisses imply the possible existence of the crust older than round about 2.7 Ga in the region. Three types of meta sedimentary rocks are identified from the Kongling complex. The first type originated from the juvenile crust with the features of the first cycle sedimentary rocks. Cratonic sedimentary rocks characterize the second type. Mobilization of REE and other elements resulted from partial melting during the migmatization is found in the third type of meta sedimentary rocks. Apart from the early TTG gneisses, some of the mafic rocks are also expected to be the source rocks of the first type of para rocks. The deposition times of the first and second type paragneisses are closed in the Neoarchean of about 2.7 Ga and the early period of Proterozoic respectively, and the period when cratonization of the Yangtze continental block completed is referred to be earlier than the Mesoproterozoic. Nd isotopic tracing on the magma sources of the Jinning granitic rocks in the region reveals that the major part of the Kongling basement is Neoarchean.
文摘The Neo-Archean Sonakhan Greenstone Belt(SGB) located in the north-eastern fringes of Bastar craton,Central India, is dominated by Basalts, Andesites, Dacites and Rhyolites association. Partial melting modeling on the SGB metabasalts indicates that these rocks were derived by20% melting of spinel peridotite. Fractional crystallisation modeling with REE reveal that the most evolved samples represent the product of fractional crystallization of least evolved magma with 35% plagioclase, 35% clinopyroxene,20% olivine, 5% magnetite and 5% ilmenite as fractionating minerals with 40% remaining magma. Depletion of HFSE with reference to the LILE and LREE/HFSE ratios and Nb, Zr anomalies in the multi-element diagram of the mafic rocks of SGB indicate Island arc magmatic setting.The enriched Th/Yb values further substantiate that the mantle arrays were modified by subduction-related fluids or melts. The general conclusions drawn indicate that the metabasalts from the SGB were formed as a result of subduction of an intraoceanic lithosphere in a fore-arc suprasubduction zone environment.
基金Ministry of Science and Technology of China (Grant No.1999043202), the National Natural Science Foundation of China (Grant Nos. 49625305, 49573183, 49673184, 49794043), the Northwest University, the Ministry of Education of China and the Australian Res
文摘Single zircons from two trondhjemitic gneisses and two clastic metasedimentary rocks without Eu anomaly of the Kongling high-grade metamorphic terrain are dated by the in situ SHRIMP U-Pb method. The results show that the trondhjemitic magma emplaced at 2947-2903 Ma. Concordant age of as old as 3.3 Ga is present in the detrital zircons from the clastic metasedimentary rocks. Together with the depleted mantle Nd model age (TDM =3.2-3.3 Ga) of the clastic metasedimentary rocks, this documents the presence of Paleoarchean continental crust in the Yangtze craton.
文摘Sm Nd isotopic compositions of associated amphibolites, TTG gneisses and granitic gneisses from the Archean Kongling Complex of the Yangtze Craton, South China are systematically analyzed. The results show that the amphibolites and TTG gneisses have a similar age of ca. 2 700 Ma, which well agrees with zircon U Pb dating of previous studies. However, their ε Nd ( t ) are different, suggestive of possible dissimilarity in source composition.
