The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of ...The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.展开更多
The formation and growth mechanisms of Mid-Ocean Ridges(MOR)are relatively well known,whereas those of back-arc spreading ridges are comparatively less known because geophysical,geochemical,and morphological data are ...The formation and growth mechanisms of Mid-Ocean Ridges(MOR)are relatively well known,whereas those of back-arc spreading ridges are comparatively less known because geophysical,geochemical,and morphological data are scarce and of low density.Here we present a high-resolution bathymetry of the Marsili Seamount(MS;1 Ma-3 ka),which represents the inflated spreading ridge of the 2 Ma old Marsili back-arc basin associated to the subduction of the Ionian Sea below the Calabrian Arc and Tyrrhenian Sea.MS is 70 km long,30 km wide,and its height reaches about 3000 m from surrounding seafloor.Our new digital bathymetric model has a 5 m grid cell size resolution and covers the MS bathymetry from-1670 mbsl to the top at-491 mbsl.We conduct morphometric and morphological analyses of the bathymetry and recognize landforms due to volcanic,tectonic,hydrothermal and gravity processes.MS consists of volcanoes related to fissural and central-type activity,this latter located at the northern and southern tips of the main dike swarms.Dike swarms represent the surface expression of different ridge segments whose strikes are controlled by the larger scale back-arc spreading processes and by the local occurrence of an active hydrothermal field.This latter develops in a flat area between two partly overlapping ridge segments where historical volcanism and extensional processes concentrate.Such ridges represent the embryonic stage of the formation of transform-like faults.Central volcanoes,the northern of which is characterized by a caldera,form at the tips of MS because the decrease in width of the major volcanic fissures promotes vent localization associated with the formation of sill-like reservoirs from which central-type vents may develop.Gravity processes affecting the MS flanks are due to shallow seafloor sliding.Caldera collapses affecting the northernmost central-type polygenic volcano must be included in the evaluation of the hazard related to potential tsunami.Inward dipping faults characterize the MS eastern flank suggesting a moderately asymmetric growth of the spreading ridge possibly associated with the eastward opening of the Marsili back-arc.The Marsili back-arc spreading rate is similar to those of MOR slow spreading ridges.However,the MS morphology resembles that of fast spreading ridges.These two features also characterize more extended back-arc spreading ridges(e.g.the Mariana in Western Pacific).We conclude that,independently from the spatial scale,the increase in the ridge accretion rate is related to the progressive addition of a subduction-related component to a pure spreading mantle source.展开更多
As relics of ancient ocean lithosphere,ophiolites are the most important petrological evidence for marking the sutures and also play a key role in reconstructing plate configuration.They also provide valuable windows ...As relics of ancient ocean lithosphere,ophiolites are the most important petrological evidence for marking the sutures and also play a key role in reconstructing plate configuration.They also provide valuable windows for studying crustal accretion and mantle processes occurring at modem ocean ridges.Abundant ophiolites are distributed along the Yarlung-Tsangpo suture and represent the relics of ocean lithosphere of the Neo-Tethys.They are characterized by an incomplete litho-stratigraphy,of which the mantle section is much thicker than the crustal section.Ocean crustal rocks outcropped in the Yarlung-Tsangpo ophiolites are much thinner than normal ocean crusts(~7 km)or even absent.Tectonic settings from which the Yarlung-Tsangpo ophiolites originated remain highly controversial,although an origin of the supra-subduction zone is prevailing.Moreover,their incomplete litho-stratigraphy has been commonly attributed to tectonic dismemberment during the late-stage emplacement after their formation.Nevertheless,such an incompleteness resembles the ocean lithosphere generated at modem ultraslow spreading ridges,such as the Southwest Indian Ridge(SWIR).In this paper,we present several lines of evidence that support the formation of the Yarlung-Tsangpo ophiolites at ultraslow spreading ridges,during which detachment faults were developed.This suggests that the Yarlung-Tsangpo ophiolites might represent the ocean core complexes(OCC)in the Neo-Tethys Ocean.The OCC with high topography in the seafloor were clogged in the trench and preserved as ophiolites through Indo-Eurasia collision.The clogging resulted in the demise of an old subduction and a new subduction was re-initiated beneath the clogged OCC.展开更多
The study“Archean cratonic mantle recycled at a mid-ocean ridge”on abyssal peridotites from the Southwest Indian Ridge(SWIR)[1]has received wide attention,which may challenge our Africa continental rift at∼135 Ma a...The study“Archean cratonic mantle recycled at a mid-ocean ridge”on abyssal peridotites from the Southwest Indian Ridge(SWIR)[1]has received wide attention,which may challenge our Africa continental rift at∼135 Ma and the subsequent opening/growth of the South Atlantic Ocean(Fig.1b).That is,the eastward Nazca plate subduction beneath South America and E-mail address:yaoling.niu@foxmail.com(Y.Liu).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
Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floo...Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floor.These bathymetric highs may be subducted,and such processes are commonly referred to as ridge subduction.Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics,they also play an important role in the generation of arc magmatism,material recycling,the growth and evolution of continental crust,the deformation and modification of the overlying plates,and metallogenesis at convergent plate boundaries.Therefore,these events have attracted widespread attention.The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window,and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt(OIB)or a mid-oceanic ridge basalt(MORB)-type rock suite,and is closely associated with Au mineralization.Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct,to typically collide with arcs or continents or to induce flat subduction(low angle of less than 10°)due to the thickness of their underlying normal oceanic crust(>6–7 km)and high topography.However,the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic.On the eastern side of the Pacific Ocean,aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents,which may cause a magmatic gap.But slab melting can occur and adakites,or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing.Cu-Au mineralization is commonly associated with such flat subduction events.On the western side of the Pacific Ocean,however,aseismic ridges and oceanic plateaus are subducted at relatively high angles(>30°).These subduction processes can generate large scale eruptions of basalts,basaltic andesites and andesites,which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge.In addition,some inactive arc ridges are subducted beneath Southwest Japan,and these subduction processes are commonly associated with the production of basalts,high-Mg andesites and adakites and Au mineralization.Besides magmatism and Cu-Au mineralization,ridge subduction may also trigger subduction erosion in subduction zones.Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events,clarifying the associated geodynamic mechanisms,quantifying subduction zone material recycling,establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization,establishing criteria to recognize pre-Cenozoic ridge subduction,the onset of modernstyle plate tectonics and the growth mechanisms for Archean continental crust.展开更多
基金The National Natural Science Foundation of China under contract Nos 41176053,41076029,91028002 and 41176046Dayang 115 under contract No.DYXM-115-02-3-01
文摘The Moho interface provides critical evidence for crustal thickness and the mode of oceanic crust accretion. The seismic Moho interface has not been identified yet at the magma-rich segments （46°-52°E） of the ultra- slow spreading Southwestern Indian Ridge （SWIR）. This paper firstly deduces the characteristics and do- mains of seismic phases based on a theoretical oceanic crust model. Then, topographic correction is carried out for the OBS record sections along Profile Y3Y4 using the latest OBS data acquired from the detailed 3D seismic survey at the SWIR in 2010. Seismic phases are identified and analyzed, especially for the reflected and refracted seismic phases from the Moho. A 2D crustal model is finally established using the ray tracing and travel-time simulation method. The presence of reflected seismic phases at Segment 28 shows that the crustal rocks have been separated from the mantle by cooling and the Moho interface has already formed at zero age. The 2D seismic velocity structure across the axis of Segment 28 indicates that detachment faults play a key role during the processes of asymmetric oceanic crust accretion.
文摘The formation and growth mechanisms of Mid-Ocean Ridges(MOR)are relatively well known,whereas those of back-arc spreading ridges are comparatively less known because geophysical,geochemical,and morphological data are scarce and of low density.Here we present a high-resolution bathymetry of the Marsili Seamount(MS;1 Ma-3 ka),which represents the inflated spreading ridge of the 2 Ma old Marsili back-arc basin associated to the subduction of the Ionian Sea below the Calabrian Arc and Tyrrhenian Sea.MS is 70 km long,30 km wide,and its height reaches about 3000 m from surrounding seafloor.Our new digital bathymetric model has a 5 m grid cell size resolution and covers the MS bathymetry from-1670 mbsl to the top at-491 mbsl.We conduct morphometric and morphological analyses of the bathymetry and recognize landforms due to volcanic,tectonic,hydrothermal and gravity processes.MS consists of volcanoes related to fissural and central-type activity,this latter located at the northern and southern tips of the main dike swarms.Dike swarms represent the surface expression of different ridge segments whose strikes are controlled by the larger scale back-arc spreading processes and by the local occurrence of an active hydrothermal field.This latter develops in a flat area between two partly overlapping ridge segments where historical volcanism and extensional processes concentrate.Such ridges represent the embryonic stage of the formation of transform-like faults.Central volcanoes,the northern of which is characterized by a caldera,form at the tips of MS because the decrease in width of the major volcanic fissures promotes vent localization associated with the formation of sill-like reservoirs from which central-type vents may develop.Gravity processes affecting the MS flanks are due to shallow seafloor sliding.Caldera collapses affecting the northernmost central-type polygenic volcano must be included in the evaluation of the hazard related to potential tsunami.Inward dipping faults characterize the MS eastern flank suggesting a moderately asymmetric growth of the spreading ridge possibly associated with the eastward opening of the Marsili back-arc.The Marsili back-arc spreading rate is similar to those of MOR slow spreading ridges.However,the MS morphology resembles that of fast spreading ridges.These two features also characterize more extended back-arc spreading ridges(e.g.the Mariana in Western Pacific).We conclude that,independently from the spatial scale,the increase in the ridge accretion rate is related to the progressive addition of a subduction-related component to a pure spreading mantle source.
基金the National Science Fund for Distinguished Young Scholars(Grant No.42025201)。
文摘As relics of ancient ocean lithosphere,ophiolites are the most important petrological evidence for marking the sutures and also play a key role in reconstructing plate configuration.They also provide valuable windows for studying crustal accretion and mantle processes occurring at modem ocean ridges.Abundant ophiolites are distributed along the Yarlung-Tsangpo suture and represent the relics of ocean lithosphere of the Neo-Tethys.They are characterized by an incomplete litho-stratigraphy,of which the mantle section is much thicker than the crustal section.Ocean crustal rocks outcropped in the Yarlung-Tsangpo ophiolites are much thinner than normal ocean crusts(~7 km)or even absent.Tectonic settings from which the Yarlung-Tsangpo ophiolites originated remain highly controversial,although an origin of the supra-subduction zone is prevailing.Moreover,their incomplete litho-stratigraphy has been commonly attributed to tectonic dismemberment during the late-stage emplacement after their formation.Nevertheless,such an incompleteness resembles the ocean lithosphere generated at modem ultraslow spreading ridges,such as the Southwest Indian Ridge(SWIR).In this paper,we present several lines of evidence that support the formation of the Yarlung-Tsangpo ophiolites at ultraslow spreading ridges,during which detachment faults were developed.This suggests that the Yarlung-Tsangpo ophiolites might represent the ocean core complexes(OCC)in the Neo-Tethys Ocean.The OCC with high topography in the seafloor were clogged in the trench and preserved as ophiolites through Indo-Eurasia collision.The clogging resulted in the demise of an old subduction and a new subduction was re-initiated beneath the clogged OCC.
基金supported by the National Natural Science Foundation of China(91958215,91014003,41130314,41630968,and U1606401)Shandong Basic Research Office(WSR2023018)the Ministry of Education 111 Project(B18048)。
文摘The study“Archean cratonic mantle recycled at a mid-ocean ridge”on abyssal peridotites from the Southwest Indian Ridge(SWIR)[1]has received wide attention,which may challenge our Africa continental rift at∼135 Ma and the subsequent opening/growth of the South Atlantic Ocean(Fig.1b).That is,the eastward Nazca plate subduction beneath South America and E-mail address:yaoling.niu@foxmail.com(Y.Liu).
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.
基金supported by the National Natural Science Foundation of China(Grant Nos.41630208 and 91855215)the National Key R&D Program of China(Grant No.2016YFC0600407)+3 种基金the Strategic Priority Research Program(A)of the Chinese Academy of Sciences(Grant No.XDA2007030402)the Key Program of the Chinese Academy of Sciences(Grant No.QYZDJ-SSWDQC026)the Key Program of Guangzhou City(Grant No.201707020032)No.IS-2873 from GIGCAS。
文摘Modern oceans contain large bathymetric highs(spreading oceanic ridges,aseismic ridges or oceanic plateaus and inactive arc ridges)that,in total,constitute more than 20–30%of the total area of the world’s ocean floor.These bathymetric highs may be subducted,and such processes are commonly referred to as ridge subduction.Such ridge subduction events are not only very common and important geodynamic processes in modern oceanic plate tectonics,they also play an important role in the generation of arc magmatism,material recycling,the growth and evolution of continental crust,the deformation and modification of the overlying plates,and metallogenesis at convergent plate boundaries.Therefore,these events have attracted widespread attention.The perpendicular or high-angle subduction of mid-ocean spreading ridges is commonly characterized by the occurrence of a slab window,and the formation of a distinctive adakite–high-Mg andesite–Nb-enriched basalt-oceanic island basalt(OIB)or a mid-oceanic ridge basalt(MORB)-type rock suite,and is closely associated with Au mineralization.Aseismic ridges or oceanic plateaus are traditionally considered to be difficult to subduct,to typically collide with arcs or continents or to induce flat subduction(low angle of less than 10°)due to the thickness of their underlying normal oceanic crust(>6–7 km)and high topography.However,the subduction of aseismic ridges and oceanic plateaus occurred on both the western and eastern sides of the Pacific Ocean during the Cenozoic.On the eastern side of the Pacific Ocean,aseismic ridges or oceanic plateaus are being subducted flatly or at low angles beneath South and Central American continents,which may cause a magmatic gap.But slab melting can occur and adakites,or an adakite–high-Mg andesite–adakitic andesite–Nb-enriched basalt suite may be formed during the slab rollback or tearing.Cu-Au mineralization is commonly associated with such flat subduction events.On the western side of the Pacific Ocean,however,aseismic ridges and oceanic plateaus are subducted at relatively high angles(>30°).These subduction processes can generate large scale eruptions of basalts,basaltic andesites and andesites,which may be derived from fractional crystallization of magmas originating from the subduction zone fluid-metasomatized mantle wedge.In addition,some inactive arc ridges are subducted beneath Southwest Japan,and these subduction processes are commonly associated with the production of basalts,high-Mg andesites and adakites and Au mineralization.Besides magmatism and Cu-Au mineralization,ridge subduction may also trigger subduction erosion in subduction zones.Future frontiers of research will include characterizing the spatial and temporal patterns of ridge subduction events,clarifying the associated geodynamic mechanisms,quantifying subduction zone material recycling,establishing the associated deep crustal and mantle events that generate or influence magmatism and Cu-Au mineralization,establishing criteria to recognize pre-Cenozoic ridge subduction,the onset of modernstyle plate tectonics and the growth mechanisms for Archean continental crust.
