This study investigates the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean.We first calculated the relative distance between the So...This study investigates the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean.We first calculated the relative distance between the Southwest Indian Ridge (SWIR) and relevant hotspots on the basis of models of plate reconstruction,and then calculated the corresponding excess magmatic anomalies of the hotspots on the basis of residual bathymetry and Airy isostasy.The results reveal that the activities of the Marion hotspot can be divided into three main phases:interaction with the paleo-Rodrigues triple junction (73.6-68.5 Ma),interaction with the SWIR (68.5-42.7 Ma),and intra-plate volcanism (42.7-0 Ma).These three phases correspond to the formation of the eastern,central,and western parts of the Del Cano Rise,respectively.The magnitude and apparent periodicity of the magmatic volume flux of the Marion hotspot appear to be dominated by the hotspot-ridge distance.The periodicity of the Marion hotspot is about 25 Ma,which is much longer than that of the Hawaii and Iceland hotspots (about 15 Ma).展开更多
The hydrothermal vent in Area A （37.78°S, 49.65°E） is the first active hydrothermal vent discovered on the Southwest Indian Ridge （SWlR）. Heat source and adequate bulk permeability are two necessary fact...The hydrothermal vent in Area A （37.78°S, 49.65°E） is the first active hydrothermal vent discovered on the Southwest Indian Ridge （SWlR）. Heat source and adequate bulk permeability are two necessary factors for the formation of a hydrothermal vent. Along the SWIR 49.3°E to 51.2°E, the gravity-derived crustal thickness is up to 9.0 km, much thicker than the average thick- ness of the global oceanic crust. This characteristic indicates that the magma supply in this area is robust, which is possibly af- fected by a hotspot. The large-scale residual mantle Bouguer anomalies （RMBA） reveal prominent negative-gravity anomalies between the first-order ridge segment （from Indomed to Gallieni, 46.0°E to 52.0°E） and the Marion-Del Cano-Crozet region. These anomalies indicate the channel of the hotspot-ridge interaction. The tomography data corrected with theoretical thermal model indicate that the low-velocity anomalies corresponding to this channel can reach the base of the lithosphere. Near the hydrothermal vent area, the topography and crustal thickness at the off-axis area are extremely asymmetrical. South of the SWIR, the high topography corresponds to the thinning crustal thickness. The residual isostatic topography anomalies indicate that Area A is a deviation from the local isostatic equilibrium, similar to the characteristics of the transform fault inside corner. The forward profiles of the magnetic data indicate that the thinning magnetic layer at the south side of Area A corresponds to the shallow, high-velocity area revealed by the OBS, which is the result of tectonic extension of a detachment fault. The active tectonic processes in Area A can provide sufficient crustal permeability to the hydrothermal circulation and may form massive sulfide deposits.展开更多
基金supported by SOA Funds for Young Scientists(Grant Nos.1084-10)Special Funding for the Basic Scientific Research(Grant Nos.JG0706and JG0716)
文摘This study investigates the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean.We first calculated the relative distance between the Southwest Indian Ridge (SWIR) and relevant hotspots on the basis of models of plate reconstruction,and then calculated the corresponding excess magmatic anomalies of the hotspots on the basis of residual bathymetry and Airy isostasy.The results reveal that the activities of the Marion hotspot can be divided into three main phases:interaction with the paleo-Rodrigues triple junction (73.6-68.5 Ma),interaction with the SWIR (68.5-42.7 Ma),and intra-plate volcanism (42.7-0 Ma).These three phases correspond to the formation of the eastern,central,and western parts of the Del Cano Rise,respectively.The magnitude and apparent periodicity of the magmatic volume flux of the Marion hotspot appear to be dominated by the hotspot-ridge distance.The periodicity of the Marion hotspot is about 25 Ma,which is much longer than that of the Hawaii and Iceland hotspots (about 15 Ma).
基金supported by the National Natural Science Foundation of China(Grant No.41106049)Special Funding for the Basic Scientific Research(Grant No.JT1106)
文摘The hydrothermal vent in Area A （37.78°S, 49.65°E） is the first active hydrothermal vent discovered on the Southwest Indian Ridge （SWlR）. Heat source and adequate bulk permeability are two necessary factors for the formation of a hydrothermal vent. Along the SWIR 49.3°E to 51.2°E, the gravity-derived crustal thickness is up to 9.0 km, much thicker than the average thick- ness of the global oceanic crust. This characteristic indicates that the magma supply in this area is robust, which is possibly af- fected by a hotspot. The large-scale residual mantle Bouguer anomalies （RMBA） reveal prominent negative-gravity anomalies between the first-order ridge segment （from Indomed to Gallieni, 46.0°E to 52.0°E） and the Marion-Del Cano-Crozet region. These anomalies indicate the channel of the hotspot-ridge interaction. The tomography data corrected with theoretical thermal model indicate that the low-velocity anomalies corresponding to this channel can reach the base of the lithosphere. Near the hydrothermal vent area, the topography and crustal thickness at the off-axis area are extremely asymmetrical. South of the SWIR, the high topography corresponds to the thinning crustal thickness. The residual isostatic topography anomalies indicate that Area A is a deviation from the local isostatic equilibrium, similar to the characteristics of the transform fault inside corner. The forward profiles of the magnetic data indicate that the thinning magnetic layer at the south side of Area A corresponds to the shallow, high-velocity area revealed by the OBS, which is the result of tectonic extension of a detachment fault. The active tectonic processes in Area A can provide sufficient crustal permeability to the hydrothermal circulation and may form massive sulfide deposits.
