The authors studied zircon LA-ICP-MS U-Pb dating,the zircon Hf isotope and geochemistry of acidic volcanic rocks in Baiyingaolao Formation of Keyouzhongqi area,Inner Mongolia,and discussed the chronology,source region...The authors studied zircon LA-ICP-MS U-Pb dating,the zircon Hf isotope and geochemistry of acidic volcanic rocks in Baiyingaolao Formation of Keyouzhongqi area,Inner Mongolia,and discussed the chronology,source region and tectonic setting of the volcanic rocks in the studied area. The clear oscillatory zoning of zircons indicates a typical magmatic origin,and the results of dating show that the volcanic rocks of Baiyingaolao Formation were formed in Early Cretaceous( 121. 5 ± 1. 0 Ma). The features of major and trace elements show that the rocks are alkali-rich,poor in calcium and magnesium with enrichment in LILEs like Th,U,K and Gd and depletion in HFSEs,e. g. Nb,Ta,Sr and Ti. The fact implies that they were the products of partial melting of the crust. εHf( t) =( +6.30--+9.06) and TDM2= 600--835 Ma,suggest the magma originated from partial melting of the young crust. Combined with the evolution of regional tectonic structure,the authors conclude that the acidic volcanic rocks of Baiyingaolao Formation may be formed under the extensional environment related to the subduction of Paleo-Pacific Plate.展开更多
It has been debated whether there was southward movement of the South China Block （SCB） during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks （-88...It has been debated whether there was southward movement of the South China Block （SCB） during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks （-88 Ma） of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval （〉 500℃） from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E （N = 19, A95 = 3.9°）, and the scatter SB = 9.0. The Fisher distri- bution of virtual geomagnetic poles （VGPs） and the consistence of S8 with the expected value at the 95% confidence level in- dicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path （APWP） curve, suggests no obvious southward movement of the sampling site during the Cretaceous.展开更多
文摘The authors studied zircon LA-ICP-MS U-Pb dating,the zircon Hf isotope and geochemistry of acidic volcanic rocks in Baiyingaolao Formation of Keyouzhongqi area,Inner Mongolia,and discussed the chronology,source region and tectonic setting of the volcanic rocks in the studied area. The clear oscillatory zoning of zircons indicates a typical magmatic origin,and the results of dating show that the volcanic rocks of Baiyingaolao Formation were formed in Early Cretaceous( 121. 5 ± 1. 0 Ma). The features of major and trace elements show that the rocks are alkali-rich,poor in calcium and magnesium with enrichment in LILEs like Th,U,K and Gd and depletion in HFSEs,e. g. Nb,Ta,Sr and Ti. The fact implies that they were the products of partial melting of the crust. εHf( t) =( +6.30--+9.06) and TDM2= 600--835 Ma,suggest the magma originated from partial melting of the young crust. Combined with the evolution of regional tectonic structure,the authors conclude that the acidic volcanic rocks of Baiyingaolao Formation may be formed under the extensional environment related to the subduction of Paleo-Pacific Plate.
基金supported by National Natural Science Foundation of China (Grant Nos. 40634024 and40821091)
文摘It has been debated whether there was southward movement of the South China Block （SCB） during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks （-88 Ma） of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval （〉 500℃） from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E （N = 19, A95 = 3.9°）, and the scatter SB = 9.0. The Fisher distri- bution of virtual geomagnetic poles （VGPs） and the consistence of S8 with the expected value at the 95% confidence level in- dicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path （APWP） curve, suggests no obvious southward movement of the sampling site during the Cretaceous.
