We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fa...We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fault systems;and 2) fluids in the upper crust that have been released from that magmatic body. The absence of a magmatic body and fluids at the location of fossil spreading centers along the Sand Hill and Algodones faults ndicated by little or no seismic activity in those areas. We show several lines of evidence to point out that both melt and fluids related to the seismic activity. In particular, receiver function analysis, Vp/Vs ratios, and tomographic data reveal low velocity zones coincide with the location of the active spreading centers. High Vp/Vs ratios and low velocity zones in the lower crust and upper mantle attributed to melt inclusion, while low Vp/Vs ratios in the upper crust are attributed water inclusions. Frequency-mag- nitude distributions characterized by high b-values in southern California;high b-values have also been associated with crustal fluids. A crustal scale model developed from the receiver functions, gravity, and magnetic data supports the existence of a magmatic intrusion within about 20 km of the surface southwest of the Salton Sea, that intrusion extends for 70 km in a SW-NE direction.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
The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of...The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of this basin, we have incorporated receiver function, gravity, and aeromagnetic data to construct new subsurface crustal scale models. Receiver function analysis suggests the Moho is 20 km deep to the southwest of the Salton Sea and deepens to 32 km in the region east of the Salton Trough and dome in shape. Crustal modeling shows that the density of the lower crust is 2950 kg/m3, which is an indication for gabbroic com- position, while the density of the upper crust varies from 2500 kg/m3 to 2600 kg/m3 and the depth of sedi- mentary and meta-sedimentary rocks appears to be 8 - 10 km. Most magnetic anomalies show shallow relief and are low amplitude with some exceptions in the marginal areas, suggesting the absence of shallow buried mafic intrusions and deep basement. Our models show a magmatic body to the southwest of the Salton Sea at depth of about 18 km and extend in SW-NE direction for about 90 km, We expect this magmatic body (mix- ture of lower crust and upper mantle material) is responsible for crustal thinning, stretching and rifting, ac- cording to the crustal models this body doesn’t exist in the north region of Salton Trough, thus, no further propagate of the rift is expected in the north.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
文摘We interpret seismic activity in the active spreading centers of the Salton Trough to indicate 1) a magmatic intrusion in the lower crust beneath the active Brawly, Cerro Prieto, Imperial, Elsinore, and San Jacinto fault systems;and 2) fluids in the upper crust that have been released from that magmatic body. The absence of a magmatic body and fluids at the location of fossil spreading centers along the Sand Hill and Algodones faults ndicated by little or no seismic activity in those areas. We show several lines of evidence to point out that both melt and fluids related to the seismic activity. In particular, receiver function analysis, Vp/Vs ratios, and tomographic data reveal low velocity zones coincide with the location of the active spreading centers. High Vp/Vs ratios and low velocity zones in the lower crust and upper mantle attributed to melt inclusion, while low Vp/Vs ratios in the upper crust are attributed water inclusions. Frequency-mag- nitude distributions characterized by high b-values in southern California;high b-values have also been associated with crustal fluids. A crustal scale model developed from the receiver functions, gravity, and magnetic data supports the existence of a magmatic intrusion within about 20 km of the surface southwest of the Salton Sea, that intrusion extends for 70 km in a SW-NE direction.
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.
文摘The Salton Trough of southwestern California is inferred to be an incipient ocean basin, and is a polyphase basin with significant extension in addition to dextral shear. To further explore the origin and evolution of this basin, we have incorporated receiver function, gravity, and aeromagnetic data to construct new subsurface crustal scale models. Receiver function analysis suggests the Moho is 20 km deep to the southwest of the Salton Sea and deepens to 32 km in the region east of the Salton Trough and dome in shape. Crustal modeling shows that the density of the lower crust is 2950 kg/m3, which is an indication for gabbroic com- position, while the density of the upper crust varies from 2500 kg/m3 to 2600 kg/m3 and the depth of sedi- mentary and meta-sedimentary rocks appears to be 8 - 10 km. Most magnetic anomalies show shallow relief and are low amplitude with some exceptions in the marginal areas, suggesting the absence of shallow buried mafic intrusions and deep basement. Our models show a magmatic body to the southwest of the Salton Sea at depth of about 18 km and extend in SW-NE direction for about 90 km, We expect this magmatic body (mix- ture of lower crust and upper mantle material) is responsible for crustal thinning, stretching and rifting, ac- cording to the crustal models this body doesn’t exist in the north region of Salton Trough, thus, no further propagate of the rift is expected in the north.
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.
