The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline serie...The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline series. They are characterized by LREE and LILEs enrichment, and HFSE depletion with slightly negative Eu anomalies (Eu/Eu*=0.62-0.90). The initial 87Sr/86Sr ratios are in range from 0.711458 to 0.717461, and εNd values vary from -9.4 to -12.3, distinct from those of the contemporaneous granodiorites mantle-derived from the Southeastern Hunan Province (SEH) (87Sr/86Sr(i)=0.707962～0.710396, εNd(t)=-6.98～-2.30). By contrast, such signatures are roughly similar to those of the neighboring other Mesozoic granitic plutons (Eu/Eu*=0.30-0.70; 87Sr/86Sr >0.710; εNd = -12 to -16) in South China Block (SCB), which have been interpreted as the remelting products of Precambrian basement. The Proterozoic lower-middle crust is an important contributor to the petrogenesis of these early Mesozoic granodiorites in the NEH. An intracontinental extension setting is present in the northeastern Hunan Province at that time due to the demand of enough thermal transfer.展开更多
Major elements, trace elements and sulfur, oxygen isotopic compositions of the main intrusions were studied in Yueshan area. The fact that intrusions enriched in Th and Sr, and depleted in Rb and Ba in this area, sugg...Major elements, trace elements and sulfur, oxygen isotopic compositions of the main intrusions were studied in Yueshan area. The fact that intrusions enriched in Th and Sr, and depleted in Rb and Ba in this area, suggests that the original magma roots in alkali basalt magma of upper mantle, with deep characteristics. It can be seen that the diagenesis environments are the island arc and active continental margin areas from the lg τ to lg σ diagram of intrusions. With the increase of SiO2, Fe2O3, MnO and P2O5 decrease, which shows that the magma of Yueshan area endured crystal fractionation of ferromanganese mineral and apatite in early evolution stage. With the further rise and evolution of magma, magma composition of calcium increased, meanwhile enriched in Zr, and depleted in Nb and Ta. This indicates that crustal component is gradually added, the assimilation and contamination occur between magma and crustal material, which includes the magma evolving, from calc-alkaline series to alkaline series. The results show that crystal fractionation, assimilation and contamination are the main evolution law of magma in this area.展开更多
基金This project was jointly supported by China National Natural Science Foundation(Grant No.40334039)CAS Knowledge Innovation Project(Grant No.KZCX1-102)CAS Key Laboratory ofIsotope Geochronology and Geochemistry(Grant No.GIGCX-03-01)
文摘The early Mesozoic granodiorites (ca.165 Ma) in the northeastern Hunan Province (NEH) have SiO2=65.4-69.65%, K2O/Na2O=0.95-1.38 and K2O+Na2O>6%, A/CNK=0.96-1.13 and belong to metaluminous high-K calc-alkaline series. They are characterized by LREE and LILEs enrichment, and HFSE depletion with slightly negative Eu anomalies (Eu/Eu*=0.62-0.90). The initial 87Sr/86Sr ratios are in range from 0.711458 to 0.717461, and εNd values vary from -9.4 to -12.3, distinct from those of the contemporaneous granodiorites mantle-derived from the Southeastern Hunan Province (SEH) (87Sr/86Sr(i)=0.707962～0.710396, εNd(t)=-6.98～-2.30). By contrast, such signatures are roughly similar to those of the neighboring other Mesozoic granitic plutons (Eu/Eu*=0.30-0.70; 87Sr/86Sr >0.710; εNd = -12 to -16) in South China Block (SCB), which have been interpreted as the remelting products of Precambrian basement. The Proterozoic lower-middle crust is an important contributor to the petrogenesis of these early Mesozoic granodiorites in the NEH. An intracontinental extension setting is present in the northeastern Hunan Province at that time due to the demand of enough thermal transfer.
基金Project(2012zzts010)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(20091100704)supported by the Special Funds for Scientific Research of Land and Natural Resources,China
文摘Major elements, trace elements and sulfur, oxygen isotopic compositions of the main intrusions were studied in Yueshan area. The fact that intrusions enriched in Th and Sr, and depleted in Rb and Ba in this area, suggests that the original magma roots in alkali basalt magma of upper mantle, with deep characteristics. It can be seen that the diagenesis environments are the island arc and active continental margin areas from the lg τ to lg σ diagram of intrusions. With the increase of SiO2, Fe2O3, MnO and P2O5 decrease, which shows that the magma of Yueshan area endured crystal fractionation of ferromanganese mineral and apatite in early evolution stage. With the further rise and evolution of magma, magma composition of calcium increased, meanwhile enriched in Zr, and depleted in Nb and Ta. This indicates that crustal component is gradually added, the assimilation and contamination occur between magma and crustal material, which includes the magma evolving, from calc-alkaline series to alkaline series. The results show that crystal fractionation, assimilation and contamination are the main evolution law of magma in this area.
