青山群火山岩是华北克拉通破坏期间最具代表性的地幔或地壳熔融产物,记录了华北深部地质演化的重要信息。本文对胶东青山群基性火山岩进行了40Ar/39Ar定年和岩石地球化学分析,结合前人报道的胶东青山群酸性火山岩资料,发现:(1)基性火山...青山群火山岩是华北克拉通破坏期间最具代表性的地幔或地壳熔融产物,记录了华北深部地质演化的重要信息。本文对胶东青山群基性火山岩进行了40Ar/39Ar定年和岩石地球化学分析,结合前人报道的胶东青山群酸性火山岩资料,发现:(1)基性火山岩喷发年龄为122～113Ma,早于青山群酸性火山岩(110～98Ma);(2)基性和酸性火山岩显示了不同的元素和同位素地球化学特征。岩石成因分析表明,基性火山岩为交代富集地幔部分熔融作用的产物,而酸性火山岩为古老下地壳和中生代底侵岩浆的熔融产物(Ling et al.,2009)。因此,胶东地区青山群火山岩记录了岩浆熔融源区从地幔向下地壳的转变。这与长时间尺度的岩石圈减薄过程中热能由地幔向地壳传递过程相吻合,而不同于地壳拆沉作用所预测的岩浆演化趋势。展开更多
To unravel the forces and better understand the processes that drive continental rifting, and to understand the role of sedimentation in promoting the rifting process, we compare;the different geological features of t...To unravel the forces and better understand the processes that drive continental rifting, and to understand the role of sedimentation in promoting the rifting process, we compare;the different geological features of two narrow rifts, the Salton Trough and Death Valley, California. According to our models, the Moho is 22 km deep to the southwest of the Salton Sea on US-Mexico border and it deepens to 30 km in the region west of the Salton Trough. In Death Valley, the Moho is 24 km deep in the central part of the basin and it deepens to 32 km outside of the basin. The dome shaped Moho in both rifts is suggested to be primarily the product of magmatic activity in the lower crust and upper mantle. Death Valley is narrow rift in the initial stage of rifting with several sedimentary basins 2 - 4 km deep. In Death Valley magmatic (thermal) forces appears to drive the rifting process. The Salton Trough is wider than Death Valley and is moving toward sea floor spreading. The depth of the sedimentary basins ranges from 8 - 10 km and a combination of thermal and sedimentation appears to drive rifting processes in the Salton Trough.展开更多
We use receiver function, gravity, and magnetic data to image the deep structures of central Death Valley. Receiver function analysis suggests the Moho is 24 km deep in the central part of the basin and deepens to 33 ...We use receiver function, gravity, and magnetic data to image the deep structures of central Death Valley. Receiver function analysis suggests the Moho is 24 km deep in the central part of the basin and deepens to 33 km to the east and 31 km to the west. The estimated lower crustal density is 2900 kg/m3, which suggests a gabbroic composition, whereas the upper crustal density, excluding basin sediments, is estimated to average 2690 kg/m3 or approximately a quartzofeldspathic composition. We modeled the magnetic sources as upper crustal to suggest a relatively shallow Curie depth in this region of high heat flow. We developed models to test the hypothesis that a low-density, non-magnetic body (magma or fluid-rich material?) within the lower crust at a depth of 15 km could coincide with the location of the Death Valley bright spot imaged on a deep seismic reflection profile. Those models suggest that if there is a low density region in the mid to lower crust in the area of the bright spot, then the region is also likely to be underplated by mafic or ultramafic materials which may have contributed to heating, uplift, and thinning of the crust during extension.展开更多
文摘青山群火山岩是华北克拉通破坏期间最具代表性的地幔或地壳熔融产物,记录了华北深部地质演化的重要信息。本文对胶东青山群基性火山岩进行了40Ar/39Ar定年和岩石地球化学分析,结合前人报道的胶东青山群酸性火山岩资料,发现:(1)基性火山岩喷发年龄为122～113Ma,早于青山群酸性火山岩(110～98Ma);(2)基性和酸性火山岩显示了不同的元素和同位素地球化学特征。岩石成因分析表明,基性火山岩为交代富集地幔部分熔融作用的产物,而酸性火山岩为古老下地壳和中生代底侵岩浆的熔融产物(Ling et al.,2009)。因此,胶东地区青山群火山岩记录了岩浆熔融源区从地幔向下地壳的转变。这与长时间尺度的岩石圈减薄过程中热能由地幔向地壳传递过程相吻合,而不同于地壳拆沉作用所预测的岩浆演化趋势。
文摘To unravel the forces and better understand the processes that drive continental rifting, and to understand the role of sedimentation in promoting the rifting process, we compare;the different geological features of two narrow rifts, the Salton Trough and Death Valley, California. According to our models, the Moho is 22 km deep to the southwest of the Salton Sea on US-Mexico border and it deepens to 30 km in the region west of the Salton Trough. In Death Valley, the Moho is 24 km deep in the central part of the basin and it deepens to 32 km outside of the basin. The dome shaped Moho in both rifts is suggested to be primarily the product of magmatic activity in the lower crust and upper mantle. Death Valley is narrow rift in the initial stage of rifting with several sedimentary basins 2 - 4 km deep. In Death Valley magmatic (thermal) forces appears to drive the rifting process. The Salton Trough is wider than Death Valley and is moving toward sea floor spreading. The depth of the sedimentary basins ranges from 8 - 10 km and a combination of thermal and sedimentation appears to drive rifting processes in the Salton Trough.
文摘We use receiver function, gravity, and magnetic data to image the deep structures of central Death Valley. Receiver function analysis suggests the Moho is 24 km deep in the central part of the basin and deepens to 33 km to the east and 31 km to the west. The estimated lower crustal density is 2900 kg/m3, which suggests a gabbroic composition, whereas the upper crustal density, excluding basin sediments, is estimated to average 2690 kg/m3 or approximately a quartzofeldspathic composition. We modeled the magnetic sources as upper crustal to suggest a relatively shallow Curie depth in this region of high heat flow. We developed models to test the hypothesis that a low-density, non-magnetic body (magma or fluid-rich material?) within the lower crust at a depth of 15 km could coincide with the location of the Death Valley bright spot imaged on a deep seismic reflection profile. Those models suggest that if there is a low density region in the mid to lower crust in the area of the bright spot, then the region is also likely to be underplated by mafic or ultramafic materials which may have contributed to heating, uplift, and thinning of the crust during extension.
