Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in thr...Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.展开更多
Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimen...Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.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
基金funded by the National Natural Science Foundation of China under Grant Nos.41972313 and 41790453by the Engineering Research Center of Geothermal Resources Development Technology and Equipment,Ministry of Education,Jilin University,China.
文摘Changbaishan,an intraplate volcano,is characterized by an approximately 6 km wide summit caldera and last erupted in 1903.Changbaishan experienced a period of unrest between 2002 and 2006.The activity developed in three main stages,including shield volcano(basalts),cone-construction(trachyandesites to trachytes with minor basalts),and caldera-forming stages(trachytes to comendites).This last stage is associated with one of the more energetic eruptions of the last millennium on Earth,the 946 CE,VEI 7 Millennium Eruption(ME),which emitted over 100 km^(3) of pyroclastics.Compared to other active calderas,the plumbing system of Changbaishan and its evolution mechanisms remain poorly constrained.Here,we merge new whole-rock,glass,mineral,isotopic,and geobarometry data with geophysical data and present a model of the plumbing system.The results show that the volcano is characterized by at least three main magma reservoirs at different depths:a basaltic reservoir at the Moho/lower crust depth,an intermediate reservoir at 10-15 km depth,and a shallower reservoir at 0.5-3 km depth.The shallower reservoir was involved in the ME eruption,which was triggered by a fresh trachytic melt entering a shallower reservoir where a comenditic magma was stored.The trachytes and comendites originate from fractional crystallization processes and minor assimilation of upper crust material,while the less evolved melts assimilate lower crust material.Syn-eruptive magma mingling occurred during the ME eruption phase.The magma reservoirs of the caldera-forming stage partly reactivate those of the cone-construction stage.The depth of the magma storage zones is controlled by the layering of the crust.The plumbing system of Changbaishan is vertically extensive,with crystal mush reservoirs renewed by the replenishment of new trachytic to trachyandesitic magma from depth.Unlike other volcanoes,evidence of a basaltic recharge is lacking.The interpretation of the signals preceding possible future eruptions should consider the multi-level nature of the Changbaishan plumbing system.A new arrival of magma may destabilize a part of or the entire system,thus triggering eruptions of different sizes and styles.The reference model proposed here for Changbaishan represents a prerequisite to properly understand periods of unrest to potentially anticipate future volcanic eruptions and to identify the mechanisms controlling the evolution of the crust below volcanoes.
文摘Water-rich clay to sand suspensions show a shear rate dependent flow behavior and knowledge of the appropriate rheological model is relevant for sedimentological, industrial and hydraulic studies. We present experimental rheological measurements of water-rich(40 to 60 wt%) clay to silt(population A) and silt to sand(population B) suspensions mixed in different proportions. The data evidence a shear rate dependent shear thinning-shear thickening transition. At lower shear rates, the suspensions organize in chains of particles, whereas at higher shear rates, these chains disrupt so increasing the viscosity. The viscosity, consistency and yield stress decrease as the A+B fraction decreases as the content of B particles increases. This behavior reflects the competing effects of the lubrication and frictional processes as a function of particle size and water content. Transitional flows form by the incorporation of small amounts of the finer fraction while ‘oceanic floods’ form at the estuary of rivers and the submarine debris-flows increase their velocity by incorporating water. The critical Reynolds number of the studied suspensions is ～2000±100 suggesting that the grainsize plays a major role in the laminar to turbulent transition. Our results have implications for the modeling of sediment flows and the hazard related to floods.
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.
