Whole-rock geochemical, zircon U-Pb geochronological and Sr-Nd-Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high S...Whole-rock geochemical, zircon U-Pb geochronological and Sr-Nd-Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high SiO2 （73.19-77.68 wt%） and Na20＋K20 （6.53-8.98 wt%） contents, with enrichment in Rb, Th, U, Pb and LREE, and depletion in Nb, Ta, P and Ti. Three rhyolite samples, one rhyolite porphyry sample, and one volcanic breccia sample yield weighted mean 206pb/23SU ages of 135.1±1.2 Ma, 116.5±1.1 Ma, 121.9±1.0 Ma, 118.1±0.9 Ma and 116.9±1.4 Ma, respectively. All these rocks have moderate （STSr/S6Sr）i values of 0.704912 to 0.705896, slightly negative eNd（t） values of -1.4 to -0.1, and positive Cur（t） values of 3.7 to 8. Their zircon Hf and whole-rock Nd isotopic model ages range from 594 to 1024 Ma. These results suggest that the Early Cretaceous volcanic rocks were originated from melting of subducted oceanic crust and associated sediments during the closure of the Mongol-Okhotsk Ocean.展开更多
The Wenquan molybdenum deposit is associated with a Triassic granite in this area.The Wenquan granite is enriched in LILE and LREE,poor in HFSE,and has significantly higher contents of alkali(K2O+Na2O) and Sr,Ba than ...The Wenquan molybdenum deposit is associated with a Triassic granite in this area.The Wenquan granite is enriched in LILE and LREE,poor in HFSE,and has significantly higher contents of alkali(K2O+Na2O) and Sr,Ba than those of the island arc volcanic rocks.These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series.Studies of major elements,trace elements,REEs and chronology of the Wenquan pluton show that,in the geodynamic transition stage of continent-continent convergence to extension,the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma,and the Wenquan pluton was formed by mixing of the two magmas.Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma,and an Re-Os isochron age of 214.4±7.1 Ma.These ages are close to K-Ar ages(223 to 226 Ma) and a SHRIMP zircon U-Pb age(223±7 Ma) for the Wenquan granite within the error range,but relatively younger.This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion,and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt(QOB) after continental collision be-tween the North China Block(NCB) and the South China Block(SCB).This process is also corre-sponding to the geological events of metamorphism and deformation in South Qinling,closure of the Mian-Lue oceanic basin,and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks.The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered sig-nificant crustal thickening and exhumation of subducted slab.In the late Triassic,the tectonic setting was transformed to the transition stage from collision to extension.Materials from the asthenospheric mantle would ascend into the root of the lower crust,which could induce partial melting of the lower crust and generate Mo-enriched granitic magma.The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization.The Mo deposits in the QOB are mainly formed in two episodes,namely 220± Ma and 140± Ma.The two episodes of metal-logenesis were developed in the tectonic transition settings from compression to extension,but they were in the different stages of the tectonic evolution.The occurrence of the Wenquan Mo-bearing plu-ton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB.Therefore,it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.展开更多
基金supported by the resource compensation of Heilongjiang Province(Grant Nos.SDK2010-25)the Special Scientific Research Fund of Public Welfare Profession of China(Grant Nos.201211008)
文摘Whole-rock geochemical, zircon U-Pb geochronological and Sr-Nd-Hf isotopic data are presented for the Early Cretaceous volcanic rocks from the northern Da Hinggan Mountains. The volcanic rocks generally display high SiO2 （73.19-77.68 wt%） and Na20＋K20 （6.53-8.98 wt%） contents, with enrichment in Rb, Th, U, Pb and LREE, and depletion in Nb, Ta, P and Ti. Three rhyolite samples, one rhyolite porphyry sample, and one volcanic breccia sample yield weighted mean 206pb/23SU ages of 135.1±1.2 Ma, 116.5±1.1 Ma, 121.9±1.0 Ma, 118.1±0.9 Ma and 116.9±1.4 Ma, respectively. All these rocks have moderate （STSr/S6Sr）i values of 0.704912 to 0.705896, slightly negative eNd（t） values of -1.4 to -0.1, and positive Cur（t） values of 3.7 to 8. Their zircon Hf and whole-rock Nd isotopic model ages range from 594 to 1024 Ma. These results suggest that the Early Cretaceous volcanic rocks were originated from melting of subducted oceanic crust and associated sediments during the closure of the Mongol-Okhotsk Ocean.
基金Supported by the National Basic Research Program of China(Grant No.2006CB403502)National General Investigation Program of China(Grant No.1212010631007)+3 种基金National Natural Science Foundation of China(Grant No.40872071)Foundation of State Key Laboratory of Ore Deposit Geochemistry,Chinese Academy of Sciences(Grant No.20060)Foundation of Educational Bureau of Shaanxi Province Foundation(Grant No.07JK414)Foundation of State Key Laboratory for Mineral Deposits Research,Nanjing University(Grant No.14-08-1)
文摘The Wenquan molybdenum deposit is associated with a Triassic granite in this area.The Wenquan granite is enriched in LILE and LREE,poor in HFSE,and has significantly higher contents of alkali(K2O+Na2O) and Sr,Ba than those of the island arc volcanic rocks.These geochemical characteristics are similar to post-collisional granites in high K calc-alkaline series.Studies of major elements,trace elements,REEs and chronology of the Wenquan pluton show that,in the geodynamic transition stage of continent-continent convergence to extension,the partial melting of the enriched lithospheric mantle generated the basaltic magma and triggered the partial melting of the thickened lower crust which produceded the acidic magma,and the Wenquan pluton was formed by mixing of the two magmas.Molybdenite Re-Os isotopic dating gave Os model ages of 212.7±2.6 Ma to 215.1±2.6 Ma with a weighted mean of 214.1±1.1 Ma,and an Re-Os isochron age of 214.4±7.1 Ma.These ages are close to K-Ar ages(223 to 226 Ma) and a SHRIMP zircon U-Pb age(223±7 Ma) for the Wenquan granite within the error range,but relatively younger.This implies that the Mo mineralization occurred in a late stage of the magmatic intrusion,and the metallogenesis took place in the transition stage from syn-collision to post-collision in the tectonic setting of the Qinling Orogenic Belt(QOB) after continental collision be-tween the North China Block(NCB) and the South China Block(SCB).This process is also corre-sponding to the geological events of metamorphism and deformation in South Qinling,closure of the Mian-Lue oceanic basin,and exhumation of the Dabie-Sulu ultrahigh-pressure metamorphic rocks.The large-scale continent-continent collision between NCB and SCB in the middle Triassic triggered sig-nificant crustal thickening and exhumation of subducted slab.In the late Triassic,the tectonic setting was transformed to the transition stage from collision to extension.Materials from the asthenospheric mantle would ascend into the root of the lower crust,which could induce partial melting of the lower crust and generate Mo-enriched granitic magma.The ore-forming elements enriched in the fluid derived from the condensation and fraction of the magma resulted in the Mo mineralization.The Mo deposits in the QOB are mainly formed in two episodes,namely 220± Ma and 140± Ma.The two episodes of metal-logenesis were developed in the tectonic transition settings from compression to extension,but they were in the different stages of the tectonic evolution.The occurrence of the Wenquan Mo-bearing plu-ton indicates that the Triassic tectonic-magmatic belt of Western Qinling is another favorable region for Mo mineralization in the QOB.Therefore,it is significant to pay more attention to evaluation of the ore-forming potentiality in the Triassic granites in Western Qinling.
