Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang...Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang area. Many researchers have studied the geology, geochemistry and geophysics of this region, and many research achievements have been obtained from deep geophysical exploration of the region, especially using the magnetotelluric （MT） sounding technique. However,展开更多
Sparse felsic microgranitoid enclaves(FMEs)in the Shangshuiquan granite of the Zhangjiakou district,the north margin of the North China Craton,are fine-grained,dark-colored and exhibit subangular to subspherical shape...Sparse felsic microgranitoid enclaves(FMEs)in the Shangshuiquan granite of the Zhangjiakou district,the north margin of the North China Craton,are fine-grained,dark-colored and exhibit subangular to subspherical shapes.They share similar mineral assemblages,chemical compositions,and zircon Hf isotope compositions to the host granite.New zircon U-Pb geochronology reveals that the FMEs crystallized at 156-153 Ma,while the Shangshuiquan granite formed at ca.146 Ma.The FEMs are,therefore,10 to 7 Ma older than the host granite.Combined with petrological evidence,we suggest that the FMEs are fragments of rapidly crystalized magmas,which were captured by the younger Shangshuiquan magma.Magmas of the FMEs and Shangshuiquan granite originated from the same reservoir.The Shangshuiquan granite is the result of small batches of magma being built up incrementally,and the FMEs belong to the earlier batches of magma.The lifespan of the Shangshuiquan magma reservoir exceeds 10 Ma.FMEs derived from cogenetic fragments have the potential to offer critical information about the formation process and timescale of granitic plutons.展开更多
A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented fo...A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.展开更多
Based on data collected by deep seismic sounding carried out in 1999, a three-dimensional P wave velocity structure is determined with tomographic inversion. The tomographic result shows that there is a P wave low vel...Based on data collected by deep seismic sounding carried out in 1999, a three-dimensional P wave velocity structure is determined with tomographic inversion. The tomographic result shows that there is a P wave low velocity zone (LVZ) in the upper crust beneath the Tengchong volcanic area. The LVZ is in the depth of 7~8 km and may be a smgma chamber or a partial melting body. The result also shows that the LVZ is in the northeastern side of the Rehai hydrothermal field, which is located in another LVZ near the surface. The shallow LVZ may represent a well-developed fracture zone. The strong hydrothermal activity in Rehai area can attribute to the existence of fractures between two LVZs. These fractures are the channels for going upwards of the deep hot fluid.展开更多
Based on ALOS PALSAR images, time series deformation fields of the Agung w^lcann area were obtained using SBAS-InSAR in 2007 -2009. The time series deformation showed obvious inflation around the Agung volcano area, w...Based on ALOS PALSAR images, time series deformation fields of the Agung w^lcann area were obtained using SBAS-InSAR in 2007 -2009. The time series deformation showed obvious inflation around the Agung volcano area, which was positively correlated with time. We modeled the cumulated deformation interferogram based on Mogi point source and vertical prolate spheroid source. The deformation model indicated that the vertical prolate spheroid model fit the observed deformation reasonably well. The magma chamber was loc, ated beneath the eenter of the volcano at a depth of approximately 5 km beneath the summit.展开更多
The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered...The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered the unrest of the magma chamber.Based on geodetic data,we analyzed the volcanic activity according to the Global Position System(GPS)and leveling sites time-series and reestimated the location and volume change of magma chamber from 2002 to 2005.Meanwhile,we calculated the dilatational strain variations of the deep magma chamber resulting from coseismic deformations caused by the 1999 Mw7.0 and 2002 Mw7.3 Wangqing deep earthquakes and the 2011 Mw9.0 Tohoku-oki earthquake.Our results show:(1)Changbaishan has experienced four stages of unrest since 1999,and the biggest unrest of the shallow magma chamber occurred from 2002 to 2005;(2)the parameters of the shallow magma chamber simulated by the Mogi and Point Compound Dislocation Model(p DCM)show that the magma chamber is located in the northern part of the crater,with a depth of approximately 7 km.The volume of the magma chamber increased by 25-28×10^(6) m from 2002 to2005;(3)the strain variation beneath the Changbaishan volcano corresponding to the 1999 Wangqing earthquake was small.The 2002 Wangqing earthquake produced an expansion strain of about 4.4 nanostrain on the magma chamber at a depth of 550 km,and probably promoted the unrest of the Changbaishan volcano.The 2011 Tohoku earthquake induced the expansion of the shallow magma chamber and compression of the deep magma chamber.Although this event promoted shallow magma unrest,it inhibited deep magma unrest.This may explain why the Changbaishan did not show obvious unrest after the 2011 Tohoku earthquake.Therefore,more attention should be paid to earthquakes that can promote deep magma unrest in the Changbaishan volcano.展开更多
Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbai...Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.展开更多
Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plag...Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization.Although apatite inclusions have homogeneous intra-grain S and Cl compositions,there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase.Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An,FeO and Mg contents of the hosting plagioclase phenocryst.It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber,rather than by one major injection or by addition of mafic melt derived from different source region.Each primitive melt injection introduced essential ore-forming materials such as S and Cl,which were rapidly and effectively released to the coexisting fluids,causing mineralization.Once primitive melt injection stops,signaling the end of growth of underlying magma chamber,mineralization will cease quickly although the hydrothermal system can still survive for a long time.However,the later released fluids are relatively depleted in ore-forming materials,and thus have lower capability to generate mineralization.Accordingly,predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.展开更多
We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper level...We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper levels plutons are bounded by thick zone of migmatites with numerous melt filled shear bands which often overprinted by incipient charnockite.On the other hand in the mid-to-upper crustal levels plutons show relatively sharp contacts and truncates the adjoining basement.The plutons are composite which comprises voluminous intrusive monzodiorite,quartz-monzonite and porphyritic monzogranite in the central part and minor anatectic granites or diatexite at periphery.Numerous xenoliths,Mafic Magmatic Enclaves(MME),disrupted trains of synplutonic mafic dykes are found in both intrusive and anatectic facies.The plutons show magmatic as well as solid-state plastic fabrics defined by magmatic flow banding and C-S fabrics respectively.Crustal scale shear zone network comprising early melt filled NE trending hot ductile dextral shear bands and slightly later colder NW trending sinistral shear bands defined by rotation of mafic boudins,phenocrysts and C-S fabrics.The internal architecture of plutons is attributed to the crustal scale magma chamber processes where voluminous intrusive magmas emplaced into the crust caused reworking of surrounding basement resulting in production of anatectic magmas.Crystallization of voluminous intrusive magmas in the deep crust probably caused development of fractures to mantle depth causing decompression melting of mantle and resultant mafic magmas penetrated the crystallizing host in magma chambers.Field evidences together with published ages and Nd isotope data reveal a spatial link between late Archaean magmatic accretion,reworking and cratonization.展开更多
The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures invo...The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.展开更多
Lithium(Li)in geothermal waters along the India–Asia continental convergent margin is a potential Li resource and plays an important role in the Li budget and Li isotopic composition(δ^(7)Li)of rivers and oceans.How...Lithium(Li)in geothermal waters along the India–Asia continental convergent margin is a potential Li resource and plays an important role in the Li budget and Li isotopic composition(δ^(7)Li)of rivers and oceans.However,its origins and behavior remain unclear.Here,we systematically investigated theδ7Li,water(δ^(18)O andδ^(2)H)and helium(^(3)He/^(4)He)isotopes of 21 geothermal water samples as well as a series of shallow groundwater and river water samples from southern Tibet and the Himalayas.Theδ^(7)Li values of geothermal waters vary from+1.0‰to+14.3‰and are negatively correlated with the Li concentration(0.006–35.0 mg/L).For geothermal water with Li concentrations>5 mg/L,Li is sourced mainly from magmatic fluids exsolving from granitic magma chambers in the crust rather than the mantle,with contributions of 49.5%±3.2%to 85.5%±1.0%.Theδ^(7)Li values of these Li-rich geothermal waters are relatively homogeneous and comparable to those of bulk granitic rocks.They are mainly controlled by the Li isotopic compositions of granitic magmatic fluids(−2.6‰to+5.6‰),and the dissolution of primary minerals and the precipitation of secondary minerals with minimal Li isotopic fractionation during high-temperature(174±5℃ to 315±6℃)water–granite interactions at deep geothermal reservoirs(4.4–7.9 km).For geothermal waters with Li concentrations<5 mg/L,Li originates primarily from water–granitic rock interactions(dominated by biotite dissolution)at 106±3℃ to 207±10℃,contributing approximately 85%±16%of the total Li.An integrated dissolution–precipitation–mixing model suggests that highδ^(7)Li values in Li-depleted samples result from preferential incorporation of ^(6)Li into secondary minerals at lower reservoir temperatures within shallower reservoirs(2.7–5.2 km)and mixing of shallow groundwater during the ascent of geothermal waters.This study provides new insights into the fluid geochemistry of crustal granitic magma chambers and highlights that Li-rich geothermal waters in Tibet are controlled by the existence of crustal granitic magma chambers and the scale of faults.展开更多
The trachyandesite lavas from Heikongshan volcano of the Tengchong volcanic cluster,Yunnan Province contain relatively abundant mafic and ultramafic small xenoliths comprising mainly gabbro,pyroxenite and rare lherzol...The trachyandesite lavas from Heikongshan volcano of the Tengchong volcanic cluster,Yunnan Province contain relatively abundant mafic and ultramafic small xenoliths comprising mainly gabbro,pyroxenite and rare lherzolites,all less than 2.5 cm in size.Gabbro xenoliths are characterized by"open"texture represented by relatively abundant vesicles and ground-mass fillings,while pyroxenite xenoliths are characterized by equigranular and poikilitic texture.Their mineral compositions(clinopyroxene±orthopyroxene±plagioclase)are similar to those of phenocrysts in lavas,and their equilibration temperature(1000-1125°C)is consistent with the crystallization temperature of the phenocrysts(998-1108°C).Thus,the textures and compositions of these xenoliths are different from those of lower crustal and mantle xenoliths,and were derived from the magma chamber.Among them,the gabbroic xenoliths come from the crystal-bubble-liquid zone at the top of the magma reservoir,while the pyroxenite xenoliths come from the cumulates in the bottom of magma reservoir.The studied single lherzolite xenolith with porphyroclastic texture has similar mineral compositions to the mantle xenoliths from eastern China,and is considered to be of upper mantle origin.It was brought into magma reservoir by replenishment magma,and might have experienced a cooling event before eruption.The formation of xenoliths in trachyandesite flows largely reflects the ascent,storage,evolution and eruption processes of magma.展开更多
In this study,we present an artificial neural network(ANN)-based approach for travel-time tomography of a volcanic edifice under sparse-ray coverage.We employ ray tracing to simulate the propagation of seismic waves t...In this study,we present an artificial neural network(ANN)-based approach for travel-time tomography of a volcanic edifice under sparse-ray coverage.We employ ray tracing to simulate the propagation of seismic waves through the heterogeneous medium of a volcanic edifice,and an inverse modeling algorithm that uses an ANN to estimate the velocity structure from the“observed”travel-time data.The performance of the approach is evaluated through a 2-dimensional numerical study that simulates i)an active source seismic experiment with a few(explosive)sources placed on one side of the edifice and a dense line of receivers placed on the other side,and ii)earthquakes located inside the edifice with receivers placed on both sides of the edifice.The results are compared with those obtained from conventional damped linear inversion.The average Root Mean Square Error(RMSE)between the input and output models is approximately 0.03 km/s for the ANN inversions,whereas it is about 0.4 km/s for the linear inversions,demonstrating that the ANN-based approach outperforms the classical approach,particularly in situations with sparse ray coverage.Our study emphasizes the advantages of employing a relatively simple ANN architecture in conjunction with second-order optimizers to minimize the loss function.Compared to using first-order optimizers,our ANN architecture shows a~25%reduction in RMSE.The ANN-based approach is computationally efficient.We observed that even though the ANN is trained based on completely random velocity models,it is still capable of resolving previously unseen anomalous structures within the edifice with about 5%anomalous discrepancies,making it a potentially valuable tool for the detection of low velocity anomalies related to magmatic intrusions or mush.展开更多
基金the National Natural Science Foundation of China(grants No.41504061 and 41674078)the National Key Research and Development Project of China(grant No. 2016YFC0600302)
文摘Objective The Gaoligongshan oblique collisional orogen is located in the southern section of the Hengduan Mountains, and belongs to one of the main Late Yanshanian-Himalayan oblique collisional orogens in the Sanjiang area. Many researchers have studied the geology, geochemistry and geophysics of this region, and many research achievements have been obtained from deep geophysical exploration of the region, especially using the magnetotelluric （MT） sounding technique. However,
基金funded by the National Natural Science Foundation of China (Grant Nos. 42373072, 42003032)the Open Project of Weihai Key Laboratory of Energy and Mineral Resources Investigation and Evaluation (Grant No. LDKF-2023WH-05)the China Geological Survey Project (Grant Nos. DD20190166, DD20190570 and DD20190159)
文摘Sparse felsic microgranitoid enclaves(FMEs)in the Shangshuiquan granite of the Zhangjiakou district,the north margin of the North China Craton,are fine-grained,dark-colored and exhibit subangular to subspherical shapes.They share similar mineral assemblages,chemical compositions,and zircon Hf isotope compositions to the host granite.New zircon U-Pb geochronology reveals that the FMEs crystallized at 156-153 Ma,while the Shangshuiquan granite formed at ca.146 Ma.The FEMs are,therefore,10 to 7 Ma older than the host granite.Combined with petrological evidence,we suggest that the FMEs are fragments of rapidly crystalized magmas,which were captured by the younger Shangshuiquan magma.Magmas of the FMEs and Shangshuiquan granite originated from the same reservoir.The Shangshuiquan granite is the result of small batches of magma being built up incrementally,and the FMEs belong to the earlier batches of magma.The lifespan of the Shangshuiquan magma reservoir exceeds 10 Ma.FMEs derived from cogenetic fragments have the potential to offer critical information about the formation process and timescale of granitic plutons.
文摘A systematic account of micro-textures and a few compositional profiles of plagioclase from high-alumina basaltic aa lava erupted during the year 1994-1995, from Barren Island Volcano, NE India ocean, are presented for the first time. The identified micro-textures can be grouped into two categories： （i） Growth related textures in the form of coarse/fine-sieve morphology, fine-scale oscillatory zoning and resorption surfaces resulted when the equilibrium at the crystal-melt interface was fluctuated due to change in temperature or H20 or pressure or composition of the crystallizing melt; and （ii） morphological texture, like glomerocryst, synneusis, swallow-tailed crystal, microlite and broken crystals, formed by the influence of dynamic behavior of the crystallizing magma （convection, turbulence, degassing, etc.）. Each micro-texture has developed in a specific magmatic environment, accordingly, a first order magma plumbing model and crystallization dynamics are envisaged for the studied lava unit. Magma generated has undergone extensive fractional crystallization of An-rich plagioclase in stable magmatic environment at a deeper depth. Subsequently they ascend to a shallow chamber where the newly brought crystals and pre-existing crystals have undergone dynamic crystallization via dissolution-regrowth processes in a convective self- mixing environment. Such repeated recharge-recycling processes have produced various populations of plagioclase with different micro-textural stratigraphy in the studied lava unit. Intermittent degassing and eruption related decompression have also played a major role in the final stage of crystallization dynamics.
基金State Natural Science Foundation of China (D49974020), Joint Seismological Science Foundation of China (199110) and Project (95-11-01-06) during Ninth Five-Year Plan from China Seismological Bureau.
文摘Based on data collected by deep seismic sounding carried out in 1999, a three-dimensional P wave velocity structure is determined with tomographic inversion. The tomographic result shows that there is a P wave low velocity zone (LVZ) in the upper crust beneath the Tengchong volcanic area. The LVZ is in the depth of 7~8 km and may be a smgma chamber or a partial melting body. The result also shows that the LVZ is in the northeastern side of the Rehai hydrothermal field, which is located in another LVZ near the surface. The shallow LVZ may represent a well-developed fracture zone. The strong hydrothermal activity in Rehai area can attribute to the existence of fractures between two LVZs. These fractures are the channels for going upwards of the deep hot fluid.
基金supported by the Special Earthquake Research ProjectChina Earthquake Administration(201208009)
文摘Based on ALOS PALSAR images, time series deformation fields of the Agung w^lcann area were obtained using SBAS-InSAR in 2007 -2009. The time series deformation showed obvious inflation around the Agung volcano area, which was positively correlated with time. We modeled the cumulated deformation interferogram based on Mogi point source and vertical prolate spheroid source. The deformation model indicated that the vertical prolate spheroid model fit the observed deformation reasonably well. The magma chamber was loc, ated beneath the eenter of the volcano at a depth of approximately 5 km beneath the summit.
基金support from the National Key Research and Development Program of China(2018YFC1503601)Scientific Research Fund of Institute of Seismology and Institute of Crustal Dynamics,China Earthquake Administration(IS201926297)。
文摘The major earthquakes often trigger unrest of surrounding volcanic magma chambers.In recent years,three major earthquakes occurred around the Changbaishan volcano,but it was unclear whether these earthquakes triggered the unrest of the magma chamber.Based on geodetic data,we analyzed the volcanic activity according to the Global Position System(GPS)and leveling sites time-series and reestimated the location and volume change of magma chamber from 2002 to 2005.Meanwhile,we calculated the dilatational strain variations of the deep magma chamber resulting from coseismic deformations caused by the 1999 Mw7.0 and 2002 Mw7.3 Wangqing deep earthquakes and the 2011 Mw9.0 Tohoku-oki earthquake.Our results show:(1)Changbaishan has experienced four stages of unrest since 1999,and the biggest unrest of the shallow magma chamber occurred from 2002 to 2005;(2)the parameters of the shallow magma chamber simulated by the Mogi and Point Compound Dislocation Model(p DCM)show that the magma chamber is located in the northern part of the crater,with a depth of approximately 7 km.The volume of the magma chamber increased by 25-28×10^(6) m from 2002 to2005;(3)the strain variation beneath the Changbaishan volcano corresponding to the 1999 Wangqing earthquake was small.The 2002 Wangqing earthquake produced an expansion strain of about 4.4 nanostrain on the magma chamber at a depth of 550 km,and probably promoted the unrest of the Changbaishan volcano.The 2011 Tohoku earthquake induced the expansion of the shallow magma chamber and compression of the deep magma chamber.Although this event promoted shallow magma unrest,it inhibited deep magma unrest.This may explain why the Changbaishan did not show obvious unrest after the 2011 Tohoku earthquake.Therefore,more attention should be paid to earthquakes that can promote deep magma unrest in the Changbaishan volcano.
基金Key Project from China Earthquake Administration and the Project (95-11-02-01) from Ministry of Science and Technology (2001DIA10003).
文摘Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFC0600310)the National Natural Science Foundation of China(Grant Nos.41872083 and 41702091)+2 种基金the Program of the China Geological Survey(Grant No.DD20160024-07)the China Fundamental Research Funds for the Central Universities(Grant No.2652018133)the 111 Project of the Ministry of Science and Technology(Grant No.BP0719021)。
文摘Saindak is one of the typical porphyry Cu deposits(PCDs)in the Chagai magmatic arc in Pakistan.Ore-forming porphyries at Saindak PCD are mainly composed of tonalite.Here,we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization.Although apatite inclusions have homogeneous intra-grain S and Cl compositions,there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase.Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An,FeO and Mg contents of the hosting plagioclase phenocryst.It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber,rather than by one major injection or by addition of mafic melt derived from different source region.Each primitive melt injection introduced essential ore-forming materials such as S and Cl,which were rapidly and effectively released to the coexisting fluids,causing mineralization.Once primitive melt injection stops,signaling the end of growth of underlying magma chamber,mineralization will cease quickly although the hydrothermal system can still survive for a long time.However,the later released fluids are relatively depleted in ore-forming materials,and thus have lower capability to generate mineralization.Accordingly,predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system.
基金funded by Department of Science and Technology(DST),Govt.of India funded project ESS/16/297/2007.
文摘We present results of field studies for magmatic processes of 2.57-2.52 Ga calc-alkaline plutonic bodies from three corridors in the eastern Dharwar craton(EDC)corresponding to different crustal levels.At deeper levels plutons are bounded by thick zone of migmatites with numerous melt filled shear bands which often overprinted by incipient charnockite.On the other hand in the mid-to-upper crustal levels plutons show relatively sharp contacts and truncates the adjoining basement.The plutons are composite which comprises voluminous intrusive monzodiorite,quartz-monzonite and porphyritic monzogranite in the central part and minor anatectic granites or diatexite at periphery.Numerous xenoliths,Mafic Magmatic Enclaves(MME),disrupted trains of synplutonic mafic dykes are found in both intrusive and anatectic facies.The plutons show magmatic as well as solid-state plastic fabrics defined by magmatic flow banding and C-S fabrics respectively.Crustal scale shear zone network comprising early melt filled NE trending hot ductile dextral shear bands and slightly later colder NW trending sinistral shear bands defined by rotation of mafic boudins,phenocrysts and C-S fabrics.The internal architecture of plutons is attributed to the crustal scale magma chamber processes where voluminous intrusive magmas emplaced into the crust caused reworking of surrounding basement resulting in production of anatectic magmas.Crystallization of voluminous intrusive magmas in the deep crust probably caused development of fractures to mantle depth causing decompression melting of mantle and resultant mafic magmas penetrated the crystallizing host in magma chambers.Field evidences together with published ages and Nd isotope data reveal a spatial link between late Archaean magmatic accretion,reworking and cratonization.
基金supported by IIMAS and the Geophysics Institute,both at UNAMmaterial support from both institutions.This research did not receive any specific grant from funding agencies in the public,commer-cial,or nonprofit sectors.
文摘The remaining fault scarps of a collapsed structure at 32 ka,named Tetelzingo crater,that included Citlaltépetl(CT)volcano,and the associated gravity field,are the basis of a reconstruction of the structures involved.The gravity field is obtained from the GGMplus model,from which 3D inversions at resolutions of 1000,500,and 250 m are performed.Low-gravity anomalies are associated with Sierra Negra(4580 m)and Citlaltépetl(5521 m)volcanoes,as well as with the Chichimeco Dome Complex(~4000 m)(CDC).They are located within a SW-NE anomaly that serves as a constraint to the reconstruction.The associ-ated Bouguer anomaly appears as a continuous low-gravity surface;however,its vertical derivative Dz shows that the sources of those three structures are separated.The fault scarps are complemented with inferred trajectories that suggest the existence of two volcanoes before the collapse at 32 ka:Citlaltépetl and the Ancestral Teteltzingo.Density cross-sections identify three stratified magmatic deposits under the summit of CT.On the summit of CT,there is an anomalous concentration of high-density materials,attributed to the presence of domes and lava flows,which mask the position of the volcano’s chimney.The existence of the Ancestral Teteltzingo volcano(ATE)is inferred NE of CT from the associated density distribution;CDC is at the center of the ATE struc-ture and is interpreted as a resurgent activity at<8 ka.Sierra Negra volcano(SN)shows low-density distributions in and around its summit,contradicting the idea that this is an extinct volcano.
基金supported by the National Natural Science Foundation of China(Grant Nos.42102292,42272294,92047202,and 42271091)Key Laboratory of Synergetic Control and Joint Remediation for Soil&Water Pollution,Ministry of Ecology and Environment(GHBK-2023-02)+2 种基金the GDAS'Project of Science and Technology Development(2022GDASZH-2022010104)Evaluation of Rare Earth Resources in Important Metallogenic Areas of Guangdong Province under the Geological Exploration and Urban Geology of Guangdong Province(2024-26)the High-level University Special Fund(G03050K001).
文摘Lithium(Li)in geothermal waters along the India–Asia continental convergent margin is a potential Li resource and plays an important role in the Li budget and Li isotopic composition(δ^(7)Li)of rivers and oceans.However,its origins and behavior remain unclear.Here,we systematically investigated theδ7Li,water(δ^(18)O andδ^(2)H)and helium(^(3)He/^(4)He)isotopes of 21 geothermal water samples as well as a series of shallow groundwater and river water samples from southern Tibet and the Himalayas.Theδ^(7)Li values of geothermal waters vary from+1.0‰to+14.3‰and are negatively correlated with the Li concentration(0.006–35.0 mg/L).For geothermal water with Li concentrations>5 mg/L,Li is sourced mainly from magmatic fluids exsolving from granitic magma chambers in the crust rather than the mantle,with contributions of 49.5%±3.2%to 85.5%±1.0%.Theδ^(7)Li values of these Li-rich geothermal waters are relatively homogeneous and comparable to those of bulk granitic rocks.They are mainly controlled by the Li isotopic compositions of granitic magmatic fluids(−2.6‰to+5.6‰),and the dissolution of primary minerals and the precipitation of secondary minerals with minimal Li isotopic fractionation during high-temperature(174±5℃ to 315±6℃)water–granite interactions at deep geothermal reservoirs(4.4–7.9 km).For geothermal waters with Li concentrations<5 mg/L,Li originates primarily from water–granitic rock interactions(dominated by biotite dissolution)at 106±3℃ to 207±10℃,contributing approximately 85%±16%of the total Li.An integrated dissolution–precipitation–mixing model suggests that highδ^(7)Li values in Li-depleted samples result from preferential incorporation of ^(6)Li into secondary minerals at lower reservoir temperatures within shallower reservoirs(2.7–5.2 km)and mixing of shallow groundwater during the ascent of geothermal waters.This study provides new insights into the fluid geochemistry of crustal granitic magma chambers and highlights that Li-rich geothermal waters in Tibet are controlled by the existence of crustal granitic magma chambers and the scale of faults.
基金supported by the Special Fund for China Earthquake Research(Grant No.200708-27)
文摘The trachyandesite lavas from Heikongshan volcano of the Tengchong volcanic cluster,Yunnan Province contain relatively abundant mafic and ultramafic small xenoliths comprising mainly gabbro,pyroxenite and rare lherzolites,all less than 2.5 cm in size.Gabbro xenoliths are characterized by"open"texture represented by relatively abundant vesicles and ground-mass fillings,while pyroxenite xenoliths are characterized by equigranular and poikilitic texture.Their mineral compositions(clinopyroxene±orthopyroxene±plagioclase)are similar to those of phenocrysts in lavas,and their equilibration temperature(1000-1125°C)is consistent with the crystallization temperature of the phenocrysts(998-1108°C).Thus,the textures and compositions of these xenoliths are different from those of lower crustal and mantle xenoliths,and were derived from the magma chamber.Among them,the gabbroic xenoliths come from the crystal-bubble-liquid zone at the top of the magma reservoir,while the pyroxenite xenoliths come from the cumulates in the bottom of magma reservoir.The studied single lherzolite xenolith with porphyroclastic texture has similar mineral compositions to the mantle xenoliths from eastern China,and is considered to be of upper mantle origin.It was brought into magma reservoir by replenishment magma,and might have experienced a cooling event before eruption.The formation of xenoliths in trachyandesite flows largely reflects the ascent,storage,evolution and eruption processes of magma.
文摘In this study,we present an artificial neural network(ANN)-based approach for travel-time tomography of a volcanic edifice under sparse-ray coverage.We employ ray tracing to simulate the propagation of seismic waves through the heterogeneous medium of a volcanic edifice,and an inverse modeling algorithm that uses an ANN to estimate the velocity structure from the“observed”travel-time data.The performance of the approach is evaluated through a 2-dimensional numerical study that simulates i)an active source seismic experiment with a few(explosive)sources placed on one side of the edifice and a dense line of receivers placed on the other side,and ii)earthquakes located inside the edifice with receivers placed on both sides of the edifice.The results are compared with those obtained from conventional damped linear inversion.The average Root Mean Square Error(RMSE)between the input and output models is approximately 0.03 km/s for the ANN inversions,whereas it is about 0.4 km/s for the linear inversions,demonstrating that the ANN-based approach outperforms the classical approach,particularly in situations with sparse ray coverage.Our study emphasizes the advantages of employing a relatively simple ANN architecture in conjunction with second-order optimizers to minimize the loss function.Compared to using first-order optimizers,our ANN architecture shows a~25%reduction in RMSE.The ANN-based approach is computationally efficient.We observed that even though the ANN is trained based on completely random velocity models,it is still capable of resolving previously unseen anomalous structures within the edifice with about 5%anomalous discrepancies,making it a potentially valuable tool for the detection of low velocity anomalies related to magmatic intrusions or mush.
