Some of the islets in the eastern Beibu Gulf are covered by Quaternary volcano strata. The rock samples from these islets mainly consist of quartz tholeiites （at Shenjiandao）, olivine tholeiites （at Linshidao and X...Some of the islets in the eastern Beibu Gulf are covered by Quaternary volcano strata. The rock samples from these islets mainly consist of quartz tholeiites （at Shenjiandao）, olivine tholeiites （at Linshidao and Xieyang- dao） and alkali basalts （at Yangpubi and Jianshidao）, and basically represent four periods of the Quaternary volcanism of Hainan Island and its adjacent regions. Except for the samples from Shenjiandao, most of the Quaternary volcanics of these islets belong to alkali magma series. The trace element characteristics of all of these samples show they are OIB （oceanic island basalt） -like, which implies that their deep geodynamic setting may be related to a mantle plume. The Sr-Nd-Pb isotopic compositions show that the mantle source beneath the Quaternary strata can be regarded as a result of binary mixing between a depleted, DMM （de- pleted MORB mantle）-like source and an enriched mantle type 2 （EM2）. The EM2 may be originated from the Hainan mantle plume, and has been metasomatized by carbonaceous fluids released from ancient re- cycled oceanic crust at an asthenospheric mantle level. These features, together with typical trace element ratios, reflect that the parent magma was not subjected to crustal contamination during its ascent to the surface. This study provides further petrological and geochemical evidence for the existence of the Hainan mantle plume.展开更多
The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prosp...The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate.Based on 2D seismic reflection,we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin(ZJNB).The results show that sixty-nine sills and fourteen forced folds have been identified.The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface.The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca.0.2 Ma.The spatial and temporal occurrences of intrusions imply that the strong post-rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core-mantle boundary.Furthermore,these forced folds could produce several types of hydrocarbon traps,due to accommodation through bending and uplift of the overlying rock and free surface,but it is critical to evaluate the effect of such emplacement when setting exploration targets.展开更多
Based on the isotopic chronologic results of Cenozoic alkali basalts from the South China Sea, the characteristics of volcanic activi- ty of the South China Sea after spreading were studied. The potassium - argon ages...Based on the isotopic chronologic results of Cenozoic alkali basalts from the South China Sea, the characteristics of volcanic activi- ty of the South China Sea after spreading were studied. The potassium - argon ages of eight alkali basalt samples from the South China Sea, and the argon - argon ages of two samples among them are reported. Apparent ages of the whole rock are 3.80 to 7. 91 Ma with an average value of 5.43 Ma （potassium- argon, whole rock）, and there is little difference among samples at the same location, e. g. , 4. 76 - 5.78 Ma for location S（M-12. The argon - argon ages for the two samples are 6.06 and 4. 71 Ma, which lie within the age scope of potassium - argon method. The dating results indicate that rock-forming age is from late Miocene to Pliocene, which is consistent with erupting event for alkali basalts from adjacent regions of the South China Sea. Volcanic activities occur after the cessation of spreading of the South China Sea, which are controlled by lithospheric fault and the spreading center formed during the spreading period of the South China Sea. These dating results, combined with geochemical characteristics of these basalts, the published chronological data for the South China Sea and its adjacent regions, and the updated geophysical data near Hainan Island, suggest that after the cessation of spreading of the South China Sea, there occur widely distributing magmatic activities which primarily is alkali basalt, and the volcanic activity continues to Quaternary. The activity may be relative to Hainan mantle plume originated from core/mantle boundary.展开更多
The Qiongdongnan Basin(QDNB)is a rift basin located in the extension direction of the oceanic ridge of the Northwest Subbasin of the South China Sea.This basin is surrounded by Late Cenozoic Ocean Island Basalts(OIBs)...The Qiongdongnan Basin(QDNB)is a rift basin located in the extension direction of the oceanic ridge of the Northwest Subbasin of the South China Sea.This basin is surrounded by Late Cenozoic Ocean Island Basalts(OIBs)magmatism associated with the putative Hainan mantle plume.However,how the Hainan mantle plume has affected the QDNB has not been studied in detail.To reveal the crustal structure of the QDNB and the possible influence of the Hainan mantle plume,we conducted a wide-angle seismic exploration from Hainan Island across the QDNB to the Xisha Block,and obtained the crustal structure by travel-time tomography.The results show that the crustal stretching factors of the Northern and Southern Rises of the QDNB are estimated to be 1.3-2.0,indicating slight or moderate crustal thinning.Whereas,the crustal stretching factor in the Central Depression of the QDNB is estimated to be more than 3.0,which means that the crust has been hyperextended.Controlled by two detachment faults(F2 and F11),the upper and lower crust show brittle and ductile thinning,respectively.Three anomalous low-velocity conduits penetrating the crystalline crust are developed in the Songnan Uplift and the Southern Rise of the QDNB.Their P-wave velocities are 5.5-6.0 km s^(−1),which are significantly lower than those of the surrounding crust(6.0-6.8 km s^(−1)).The Late Cenozoic magmatic intrusions(e.g.,sills and dikes)and hydrothermal activities can be observed in the sedimentary strata above these low-velocity conduits.We interpret that the low-velocity conduits might be the crustal magmatic footprints of the Hainan mantle plume,due to the correlated distributions of OIB-type magmatism,the magmatic intrusion patterns,the deep structure of the Hainan mantle plume and the high heat flow of 95 mW m^(−2).Thus,we propose that the crustal structure of the QDNB is the product of crustal hyperextension in the rifting stage and subsequently affected by the Hainan mantle plume magmatism.This study provides a typical case for understanding the influence of a mantle plume on the continental crust with pre-existing rift structures.展开更多
The South China Sea(SCS)is the largest extensional basin in the western Pacific and was formed after rifting of the Euro-Asian continental margin.The nature of its underlying mantle remains enigmatic due to the lack o...The South China Sea(SCS)is the largest extensional basin in the western Pacific and was formed after rifting of the Euro-Asian continental margin.The nature of its underlying mantle remains enigmatic due to the lack of sampling of the seafloor’s igneous crust.The International Ocean Discovery Program Expedition 349 cored seafloor basalts of the southwestern(Site U1433)and eastern(Site U1431)SCS sub-basins.The recovered basalt samples exhibit different source lithologies and geochemistries.The Mg isotopic compositions of seafloor basalts from these sites were investigated to elucidate the origin of this large-scale mantle inhomogeneity.Results indicate that the Site U1431 basalts have a mantlelike averageδ^(26)Mg value of-0.27‰±0.06‰(2 SD;n=10).Together with inhomogeneous Sr-Nd-Pb-Hf isotopic compositions,the Site U1433 basalts have an averageδ^(26)Mg value(-0.20‰±0.06‰;2 SD;n=8)higher than those of the Site U1431 basalts and normal mantle.Their heavier Mg isotopic compositions and low206 Pb/204 Pb ratios(17.7)indicate that the Site U1433 basalts were affected by the re-melting of detached continental-arc lithosphere in the sub-ridge mantle.The coupling of Mg and Sr-Nd isotopes provides robust evidence that the mantle-likeδ^(26)Mg values of the Site U1431 basalts resulted from mixing between detached continental arc lithosphere and the nearby Hainan plume,with respective supra-and sub-normalδ^(26)Mg values.From the perspective of Mg isotope,the mantles of the southwestern and eastern sub-basins are compositionally inhomogeneous,with their mantle evolutionary histories being distinct.展开更多
The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that ...The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh ba-saltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cu-mulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.展开更多
基金The National Natural Science Foundation of China under contract Nos 41322036,41230960,40906034 and 41276003China Ocean Mineral Resources R&D Association (COMRA) under contract No.DY125-12-R-05+1 种基金China Postdoctoral Science Foundation under contract No.201104616the Taishan Scholar Program of Shandong Province
文摘Some of the islets in the eastern Beibu Gulf are covered by Quaternary volcano strata. The rock samples from these islets mainly consist of quartz tholeiites （at Shenjiandao）, olivine tholeiites （at Linshidao and Xieyang- dao） and alkali basalts （at Yangpubi and Jianshidao）, and basically represent four periods of the Quaternary volcanism of Hainan Island and its adjacent regions. Except for the samples from Shenjiandao, most of the Quaternary volcanics of these islets belong to alkali magma series. The trace element characteristics of all of these samples show they are OIB （oceanic island basalt） -like, which implies that their deep geodynamic setting may be related to a mantle plume. The Sr-Nd-Pb isotopic compositions show that the mantle source beneath the Quaternary strata can be regarded as a result of binary mixing between a depleted, DMM （de- pleted MORB mantle）-like source and an enriched mantle type 2 （EM2）. The EM2 may be originated from the Hainan mantle plume, and has been metasomatized by carbonaceous fluids released from ancient re- cycled oceanic crust at an asthenospheric mantle level. These features, together with typical trace element ratios, reflect that the parent magma was not subjected to crustal contamination during its ascent to the surface. This study provides further petrological and geochemical evidence for the existence of the Hainan mantle plume.
基金supported by the National Key Research and Development Project(2019YFA0708500)the National Natural Science Foundation of China(No.42202170 and U20B6001)。
文摘The transportation of magma in sedimentary basins often occurs through extensive dyke-sill networks.The role of sills on the plumbing system in rifted margins and the impact of sills on hydrocarbon reservoirs of prospective sedimentary basins has long been an area of great industrial interest and scientific debate.Based on 2D seismic reflection,we present data on how the sills emplaced to form a magmatic plumbing system of the volcanic system for the Zhongjiannan Basin(ZJNB).The results show that sixty-nine sills and fourteen forced folds have been identified.The distribution and geometry of the sills suggest that magma flowed from west to east and then ascended to near the surface.The onlap relationship of the forced folds indicates that the timing of magmatic activities can be constrained at ca.0.2 Ma.The spatial and temporal occurrences of intrusions imply that the strong post-rift magmatism in ZJNB was associated with the Hainan mantle plume arising from the core-mantle boundary.Furthermore,these forced folds could produce several types of hydrocarbon traps,due to accommodation through bending and uplift of the overlying rock and free surface,but it is critical to evaluate the effect of such emplacement when setting exploration targets.
基金The Special Basic Research Fund for Central Public Research Institutes (First Institute of Oceanograpgy,State Oceanic Administration)under contract No.GY02 -2008G38the Special Plan of Science and Technology Generalship in Qingdao under contract No.05-2 -JC-79the Special Project of Technical Foundational Work and Social Public Welfare Research under contract No.2003DIB3J114
文摘Based on the isotopic chronologic results of Cenozoic alkali basalts from the South China Sea, the characteristics of volcanic activi- ty of the South China Sea after spreading were studied. The potassium - argon ages of eight alkali basalt samples from the South China Sea, and the argon - argon ages of two samples among them are reported. Apparent ages of the whole rock are 3.80 to 7. 91 Ma with an average value of 5.43 Ma （potassium- argon, whole rock）, and there is little difference among samples at the same location, e. g. , 4. 76 - 5.78 Ma for location S（M-12. The argon - argon ages for the two samples are 6.06 and 4. 71 Ma, which lie within the age scope of potassium - argon method. The dating results indicate that rock-forming age is from late Miocene to Pliocene, which is consistent with erupting event for alkali basalts from adjacent regions of the South China Sea. Volcanic activities occur after the cessation of spreading of the South China Sea, which are controlled by lithospheric fault and the spreading center formed during the spreading period of the South China Sea. These dating results, combined with geochemical characteristics of these basalts, the published chronological data for the South China Sea and its adjacent regions, and the updated geophysical data near Hainan Island, suggest that after the cessation of spreading of the South China Sea, there occur widely distributing magmatic activities which primarily is alkali basalt, and the volcanic activity continues to Quaternary. The activity may be relative to Hainan mantle plume originated from core/mantle boundary.
基金supported by the National Natural Science Foundation of China (Grant Nos. 42076071, 42006071, 41576041)the Key Research and Development Plan of Hainan Province (Grant No. ZDYF2020198)+1 种基金the Rising Star Foundation of the South China Sea Institute of Oceanology (Grant Nos. NHXX2017DZ0101, NHXX2019DZ0201)Special Research Assistant Project of Chinese Academy of Sciences.
文摘The Qiongdongnan Basin(QDNB)is a rift basin located in the extension direction of the oceanic ridge of the Northwest Subbasin of the South China Sea.This basin is surrounded by Late Cenozoic Ocean Island Basalts(OIBs)magmatism associated with the putative Hainan mantle plume.However,how the Hainan mantle plume has affected the QDNB has not been studied in detail.To reveal the crustal structure of the QDNB and the possible influence of the Hainan mantle plume,we conducted a wide-angle seismic exploration from Hainan Island across the QDNB to the Xisha Block,and obtained the crustal structure by travel-time tomography.The results show that the crustal stretching factors of the Northern and Southern Rises of the QDNB are estimated to be 1.3-2.0,indicating slight or moderate crustal thinning.Whereas,the crustal stretching factor in the Central Depression of the QDNB is estimated to be more than 3.0,which means that the crust has been hyperextended.Controlled by two detachment faults(F2 and F11),the upper and lower crust show brittle and ductile thinning,respectively.Three anomalous low-velocity conduits penetrating the crystalline crust are developed in the Songnan Uplift and the Southern Rise of the QDNB.Their P-wave velocities are 5.5-6.0 km s^(−1),which are significantly lower than those of the surrounding crust(6.0-6.8 km s^(−1)).The Late Cenozoic magmatic intrusions(e.g.,sills and dikes)and hydrothermal activities can be observed in the sedimentary strata above these low-velocity conduits.We interpret that the low-velocity conduits might be the crustal magmatic footprints of the Hainan mantle plume,due to the correlated distributions of OIB-type magmatism,the magmatic intrusion patterns,the deep structure of the Hainan mantle plume and the high heat flow of 95 mW m^(−2).Thus,we propose that the crustal structure of the QDNB is the product of crustal hyperextension in the rifting stage and subsequently affected by the Hainan mantle plume magmatism.This study provides a typical case for understanding the influence of a mantle plume on the continental crust with pre-existing rift structures.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA22050101 and XDB42020302)the National Natural Science Foundation of China(91858206 and 41876040)+2 种基金the Laboratory for Marine GeologyQingdao Pilot National Laboratory for Marine Science and Technology(MGQNLM-TD201806)the Taishan Scholars Program of Shandong Province(tsqn201909157)。
文摘The South China Sea(SCS)is the largest extensional basin in the western Pacific and was formed after rifting of the Euro-Asian continental margin.The nature of its underlying mantle remains enigmatic due to the lack of sampling of the seafloor’s igneous crust.The International Ocean Discovery Program Expedition 349 cored seafloor basalts of the southwestern(Site U1433)and eastern(Site U1431)SCS sub-basins.The recovered basalt samples exhibit different source lithologies and geochemistries.The Mg isotopic compositions of seafloor basalts from these sites were investigated to elucidate the origin of this large-scale mantle inhomogeneity.Results indicate that the Site U1431 basalts have a mantlelike averageδ^(26)Mg value of-0.27‰±0.06‰(2 SD;n=10).Together with inhomogeneous Sr-Nd-Pb-Hf isotopic compositions,the Site U1433 basalts have an averageδ^(26)Mg value(-0.20‰±0.06‰;2 SD;n=8)higher than those of the Site U1431 basalts and normal mantle.Their heavier Mg isotopic compositions and low206 Pb/204 Pb ratios(17.7)indicate that the Site U1433 basalts were affected by the re-melting of detached continental-arc lithosphere in the sub-ridge mantle.The coupling of Mg and Sr-Nd isotopes provides robust evidence that the mantle-likeδ^(26)Mg values of the Site U1431 basalts resulted from mixing between detached continental arc lithosphere and the nearby Hainan plume,with respective supra-and sub-normalδ^(26)Mg values.From the perspective of Mg isotope,the mantles of the southwestern and eastern sub-basins are compositionally inhomogeneous,with their mantle evolutionary histories being distinct.
基金Special Plan Project of Science and Technology Generalship in Qing-dao (Grant No.05-2-JC-79)Special Project of Technical Foundational Work and Social Public Welfare Research (Grant No. 2003DIB3J114)
文摘The whole rock K-Ar ages of basalts from the South China Sea basin vary from 3.8 to 7.9 Ma, which suggest that intra-plate volcanism after the cessation of spreading of the South China Sea (SCS) is comparable to that in adjacent regions around the SCS, i.e., Leiqiong Peninsula, northern margin of the SCS, Indochina block, and so on. Based on detailed petrographic studies, we selected many fresh ba-saltic rocks and measured their major element, trace element, and Sr-Nd-Pb isotope compositions. Geochemical characteristics of major element and trace element show that these basaltic rocks belong to alkali basalt magma series, and are similar to OIB-type basalt. The extent of partial melting of mantle rock in source region is very low, and magma may experience crystallization differentiation and cu-mulation during the ascent to or storing in the high-level magma chamber. Sr-Nd-Pb isotopic data of these basaltic rocks imply an inhomogeneous mantle below the South China Sea. The nature of magma origin has a two end-member mixing model, one is EM2 (Enriched Mantle 2) which may be originated from mantle plume, the other is DMM (Depleted MORB Mantle). Pb isotopic characteristics show the Dupal anomaly in the South China Sea, and combined with newly found Dupal anomaly at Gakkel ridge in Arctic Ocean, this implies that Dupal anomaly is not only limited to South Hemisphere. In variation diagrams among Sr, Nd and Pb, the origin nature of mantle below the SCS is similar to those below Leiqiong peninsula, northern margin of the SCS and Indochina peninsula, and is different from those below north and northeast China. This study provides geochemical constraints on Hainan mantle plume.
