An identification has been made of some shoshonitic intrusive rocks in central Hainan Island recently. These rocks are K-rich (K2O=2.9%―5.1%, K2O/Na2O=0.95―2.12), distinctly enriched in LILE and LREE, strongly deple...An identification has been made of some shoshonitic intrusive rocks in central Hainan Island recently. These rocks are K-rich (K2O=2.9%―5.1%, K2O/Na2O=0.95―2.12), distinctly enriched in LILE and LREE, strongly depleted in Nb, Ta, and moder- ately depleted in Sr and Ti, with (87Sr/86Sr)i = 0.70859―0.71425 and ε Nd(t) = (?2.77―?7.49). They were derived from an EMⅡ-type mantle source. The enrichment process is related to metasomatism of depleted mantle caused by a great amount of fluid-melt released from oceanic crust and terri- genous sediments at great depth (eclogite facies) during the subduction of the South China plate under the Indochina-South China Sea plate in the Carbon- iferous–Early Permian. A SHRIMP U-Pb zircon dating yields a crystallization age of 272±7 Ma for the sho- shonitic intrusions, which is coeval with the strongly peraluminous granites found in central Hainan Island. These two kinds of rocks generally possess syn-intrusion ductile deformation structures. Thus they are considered to have been generated during the early stage (syn-thrust phase) of a post-collisional event. The primary magma of shoshonitic rocks was produced at a depth > 80 km by decompression- dehydration melting of previously enriched litho- spheric mantle wedge, phlogopite-bearing garnet peridotite, which was in turn caused by the break-off of a descendent slab and upwelling of a hot as- thenosphere. The rising of melts was accompaniedby crustal contamination and crystallization fractiona- tion (AFC). Combining with other related data, it is proposed that the southwards subduction and amal- gamation of the South China plate with the Indo- China-South China Sea plate took place at ca. 287- 278 Ma, which was a part of the convergence proc- ess of the Pangea supercontinent. The suture zone was probably located along the line of Song Ma-Beibu Gulf-north margin of the Yunkai Moun- tains-Wuyi Mountains.展开更多
The late Precambrian algal megafossils, Chuaria-Tawuia assemblage, were found for the first time in Bed 6 of the Shilu Group, Hainan Island, South China. Consequently. the geological age of the iron-ore deposits of th...The late Precambrian algal megafossils, Chuaria-Tawuia assemblage, were found for the first time in Bed 6 of the Shilu Group, Hainan Island, South China. Consequently. the geological age of the iron-ore deposits of the Shilu Group can be determined and placed into the Qingbaikou System. This meaningful discovery offers sufficient evidence for settling the protracted dispute over the ore-forming age of the Shilu iron deposits, and will be of great help for better understanding the evolutional history of geology and tectonics, as well as the further ore-prospecting of the Shilu-type iron-deposits both in the island and South China.展开更多
基金the National Land and Resources Great Survey Projects （Grant Nos. 200013000127, 200113900018, 200313000041） the National National Natural Science Foundation of China （Grant Nos. 40572052 , 40373014）+1 种基金 the 0pen Foundation of State Key Laboratory for Endogenous Mineral Deposits Research, Nanjing University the New Era Higher-Level Qualified Scientists and Engineers Foundation, Hubei Province.
文摘An identification has been made of some shoshonitic intrusive rocks in central Hainan Island recently. These rocks are K-rich (K2O=2.9%―5.1%, K2O/Na2O=0.95―2.12), distinctly enriched in LILE and LREE, strongly depleted in Nb, Ta, and moder- ately depleted in Sr and Ti, with (87Sr/86Sr)i = 0.70859―0.71425 and ε Nd(t) = (?2.77―?7.49). They were derived from an EMⅡ-type mantle source. The enrichment process is related to metasomatism of depleted mantle caused by a great amount of fluid-melt released from oceanic crust and terri- genous sediments at great depth (eclogite facies) during the subduction of the South China plate under the Indochina-South China Sea plate in the Carbon- iferous–Early Permian. A SHRIMP U-Pb zircon dating yields a crystallization age of 272±7 Ma for the sho- shonitic intrusions, which is coeval with the strongly peraluminous granites found in central Hainan Island. These two kinds of rocks generally possess syn-intrusion ductile deformation structures. Thus they are considered to have been generated during the early stage (syn-thrust phase) of a post-collisional event. The primary magma of shoshonitic rocks was produced at a depth > 80 km by decompression- dehydration melting of previously enriched litho- spheric mantle wedge, phlogopite-bearing garnet peridotite, which was in turn caused by the break-off of a descendent slab and upwelling of a hot as- thenosphere. The rising of melts was accompaniedby crustal contamination and crystallization fractiona- tion (AFC). Combining with other related data, it is proposed that the southwards subduction and amal- gamation of the South China plate with the Indo- China-South China Sea plate took place at ca. 287- 278 Ma, which was a part of the convergence proc- ess of the Pangea supercontinent. The suture zone was probably located along the line of Song Ma-Beibu Gulf-north margin of the Yunkai Moun- tains-Wuyi Mountains.
文摘The late Precambrian algal megafossils, Chuaria-Tawuia assemblage, were found for the first time in Bed 6 of the Shilu Group, Hainan Island, South China. Consequently. the geological age of the iron-ore deposits of the Shilu Group can be determined and placed into the Qingbaikou System. This meaningful discovery offers sufficient evidence for settling the protracted dispute over the ore-forming age of the Shilu iron deposits, and will be of great help for better understanding the evolutional history of geology and tectonics, as well as the further ore-prospecting of the Shilu-type iron-deposits both in the island and South China.
