The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province.LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba ...The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province.LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8±1.6 and 246.5±1.3 Ma,coeval with peraluminous granites of the Qinzhou Bay Granitic Complex.The studied rhyolites and dacites are characterized by high SiO_(2),K_(2)O,and Al_(2)O_(3),and low MgO,CaO,and P_(2)O_(5) contents and are classified as high-K calc-alkaline S-type rocks,with A/CNK=0.98-1.19.The volcanic rocks are depleted in high field strength elements,e.g.,Nb,Ta,Ti,and P,and enriched in large ion lithophile elements,e.g.,Rb,K,Sr,and Ba.Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions(ε_(Hf)(t)=-29.1 to-6.9),source discrimination indicators and high calculated Ti-in-zircon temperatures(798-835℃)reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S-type silicic magma.The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo-Tethys Ocean in this region,as the associated subduction would have generated an extensional setting in which the mantle-derived upwelling and volcanic activity occurred.展开更多
To show paleontological characteristics of the Olenekian-Anislan boundary beds in the Russian Far East, a review of new data on the Upper Olenekian and Lower Anisian biostratigraphy of South Primorye is given on the b...To show paleontological characteristics of the Olenekian-Anislan boundary beds in the Russian Far East, a review of new data on the Upper Olenekian and Lower Anisian biostratigraphy of South Primorye is given on the basis of five sections： Golyi Cape, Petrovka River, Zhitkov Peninsula, Tchernyschew Bay and Atlasov Cape, using new ammonoid, brachiopod and conodont findings. The most representative ammonoid assemblage at the base of the Anisian was discovered in the Ussuriphyllites amurensis Zone （10.6 m thick） of the Atlasov Cape Section： Parasageceras sp. nov., Prionitidae gen. et sp. nov. , Ussuriphyllites amurensis （Kiparisova） （dominant）, Megaphyllites atlasoviensis Zakharov, Leiophyllites praematurus Kiparisova, Leiophyllites sp. , Ussurites sp. , Paradanubites sp. indet., Paracrochordiceras sp. nov., Prohungarites popowi Kiparisova, Arctohungarites primoriensis Zakharov, A. solimani （Toula）, Salterites sp. indet. （gigantic shell）, and Tropigastrites sublachontanus Zakharov. Conodonts Neospathodus cf. homeri （Bender） were found in the lower part of the Ussuriphyllites amurensis Zone of the Atlasov Cape. The Atlasov Cape seems to be one of the very promising sections of the Russian Far East for detailed investigation of the Olenekian-Anisian boundary.展开更多
基金supported by the Guangxi Natural Science Foundation Program(Grant Nos.2021GXNSFAA220077,2021GXNSFBA220063)the Natural Science Foundation of China(Grant No.42073031)。
文摘The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province.LA-ICP-MS zircon U-Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8±1.6 and 246.5±1.3 Ma,coeval with peraluminous granites of the Qinzhou Bay Granitic Complex.The studied rhyolites and dacites are characterized by high SiO_(2),K_(2)O,and Al_(2)O_(3),and low MgO,CaO,and P_(2)O_(5) contents and are classified as high-K calc-alkaline S-type rocks,with A/CNK=0.98-1.19.The volcanic rocks are depleted in high field strength elements,e.g.,Nb,Ta,Ti,and P,and enriched in large ion lithophile elements,e.g.,Rb,K,Sr,and Ba.Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions(ε_(Hf)(t)=-29.1 to-6.9),source discrimination indicators and high calculated Ti-in-zircon temperatures(798-835℃)reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S-type silicic magma.The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo-Tethys Ocean in this region,as the associated subduction would have generated an extensional setting in which the mantle-derived upwelling and volcanic activity occurred.
文摘To show paleontological characteristics of the Olenekian-Anislan boundary beds in the Russian Far East, a review of new data on the Upper Olenekian and Lower Anisian biostratigraphy of South Primorye is given on the basis of five sections： Golyi Cape, Petrovka River, Zhitkov Peninsula, Tchernyschew Bay and Atlasov Cape, using new ammonoid, brachiopod and conodont findings. The most representative ammonoid assemblage at the base of the Anisian was discovered in the Ussuriphyllites amurensis Zone （10.6 m thick） of the Atlasov Cape Section： Parasageceras sp. nov., Prionitidae gen. et sp. nov. , Ussuriphyllites amurensis （Kiparisova） （dominant）, Megaphyllites atlasoviensis Zakharov, Leiophyllites praematurus Kiparisova, Leiophyllites sp. , Ussurites sp. , Paradanubites sp. indet., Paracrochordiceras sp. nov., Prohungarites popowi Kiparisova, Arctohungarites primoriensis Zakharov, A. solimani （Toula）, Salterites sp. indet. （gigantic shell）, and Tropigastrites sublachontanus Zakharov. Conodonts Neospathodus cf. homeri （Bender） were found in the lower part of the Ussuriphyllites amurensis Zone of the Atlasov Cape. The Atlasov Cape seems to be one of the very promising sections of the Russian Far East for detailed investigation of the Olenekian-Anisian boundary.
