With the super-wide band magnetoteiluric sounding data of the JUong （吉隆）-Cuoqin （措勤） profile （named line 800） which was completed in 2001 and the Dingri （定日）-Cuomai （措迈） profile （named line 900） wh...With the super-wide band magnetoteiluric sounding data of the JUong （吉隆）-Cuoqin （措勤） profile （named line 800） which was completed in 2001 and the Dingri （定日）-Cuomai （措迈） profile （named line 900） which was completed in 2004, we obtained the strike direction of each MT station by strike analysis, then traced profiles that were perpendicular to the main strike direction, and finally obtained the resistivity model of each profile by nonlinear conjugate gradients （NLCG） inversion. With these two models, we described the resistivity structure features of the crust and the upper mantle of the center-southern Tibetan plateau and its relationship with Yalung Tsangpo suture： the upper crust of the research area is a resistive layer with resistivity value range of 200-3 000 Ω.m. The depth of its bottom surface is about 15-20 km generally, but the bottom surface of resistive layer is deeper in the middle of these two profiles. At llne 900, it is about 30 km deep, and even at line 800, it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km, and a conductive layer is beneath it with resistivity even less than 5 Ω.m. This conductive layer is composed of individual conductive bodies, and at the south of the Yalung Tsangpo suture, the conductive bodies are smaller with thickness about 10 km and lean to the north slightly. However, at the north of the Yalung Tsangpo suture, the conductive bodies are larger with thickness about 30 km and also lean to the north slightly. Relatively, the conductive bodies of line 900 are thinner than those of line 800, and the depth of the bottom surface of line 900 is also shallower. At last, after analyzing the effect factors to the resistivity of rocks, it was concluded that the very conductive layer was caused by partial melt or connective water in rocks. It suggests that the middle and lower crust of the center-southern Tibetan plateau is very thick, hot, flabby, and waxy.展开更多
ABSTRACT Using data from 17 coupled models and nine sets of corresponding Atmospheric Model Intercomparison Project （AMIP） results, we investigated annual and seasonal variation biases in the upper 50 m of the sout...ABSTRACT Using data from 17 coupled models and nine sets of corresponding Atmospheric Model Intercomparison Project （AMIP） results, we investigated annual and seasonal variation biases in the upper 50 m of the south-central equatorial Pacific, with a focus on the double-ITCZ bias, and examined the causes for the amplitude biases by using heat budget analysis. The results showed that, in the research region, most of the models simulate SSTs that are higher than or similar to observed. The simulated seasonal phase is close to that observed, but the amplitudes of more than half of the model results are larger than or equal to observations. Heat budget analysis demonstrated that strong shortwave radiation in individual atmospheric models is the main factor that leads to high SST values and that weak southward cold advection is an important mechanism for maintaining a high SST. For seasonal circulation, large surface shortwave radiation amplitudes cause large SST amplitudes.展开更多
South-central Chile has some potential mineral resources including radioactive and rare earth elements (REE) minerals. This study reports some basic characteristics of the mineralogy of a radioactive-rare earth elemen...South-central Chile has some potential mineral resources including radioactive and rare earth elements (REE) minerals. This study reports some basic characteristics of the mineralogy of a radioactive-rare earth elements occurrence, related to a pegmatitic outcrop “Vertientes Pegmatite” hosted on Paleozoic granitic rocks of the South Coastal Batholith and discusses potential areas for REE deposits, particularly beach placers along the coastline of the BioBío region. In this pegmatite, X-ray diffraction analysis shows uranium-bearing minerals such as coffinite and metaschoepite, along with microcline, anorthoclase, albite, quartz and illite. Through optical microscopy and electron probe micro-analyzer (EPMA), rare earth minerals (monazite and xenotime) and radioactive minerals (thorite and thorium silicate ± uranium) were identified. Additionally, granitic rocks of the South Coastal Batholith around this pegmatite show rare earth minerals (monazite and allanite).展开更多
Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and the...Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and their basement. In order to provide an overview of exploratory potential, the stream sediments that are part of several gold placers in the northwest area of the BioBío region are analyzed, which have been registered on the basis of empirical evidence from artisanal mining activities. The overview consists of two goals: 1) determine the presence of auriferous occurrences (stream sediments and basement) and 2) identify potentially favorable areas to find gold placer deposits. Through optical microscopy this study characterized the metallic and non-metallic mineralogy of the basement, along with geochemical analyses of stream sediments and surrounding rocks of the placer deposits. The geochemical results show two sectors with high precious metal contents in sediments (up to 24 ppm of Au and 8 ppm of Ag) and two rocky outcrops with Au (757 and 41 ppb). Additionally, there are depressions in the study area that have received large amounts of sediments (reaching up to 170 m-thick), which are favorable places for the accumulation of auriferous sediments from nearby valleys due to the tectonic and structural conditions where they are located. Then, these results show an exploratory potential for gold placers and can be useful to delineate future exploration strategies in the Coastal Range of south-central Chile.展开更多
Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Earl...Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end,giving way to shortening and Andean growth from the Late Cretaceous onward.Nevertheless,there are disagreements regarding the timing and nature of this transition to Andean orogenesis.To address these issues,we conducted geochronologic(U-Pb and^(40)Ar/&(39)Ar),sedimentologic,and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area(Principal Cordillera,Chile,36°S).From our findings and prior analyses,we propose the following tectono-stratigraphic evolution of the region.(1)Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin.(2)After a~40 Myr hiatus,fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian.Whereas the Colimapu Formation displays evidence of syndepositional shortening,the Plan de los Yeuques Formation exhibits synextensional growth strata.Contrary to other studies,our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous.We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening,followed by extension.(3)After a~20 Myr hiatus,middle Eocene to early Miocene(Lutetian-Aquitanian)accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin.(4)Finally,major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene.This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina.In terms of the transition to early Andean deformation,we propose that structural deformation did not generate a major,regional-scale fold-thrust belt during the late Albian-Santonian.Modest extension,tectonic quiescence,or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.展开更多
Based on studies of the water content of the early Cretaceous Feixian high-magnesium basalts in the eastern part of the North China Craton(NCC),it has been suggested that the early Cretaceous lithospheric mantle of th...Based on studies of the water content of the early Cretaceous Feixian high-magnesium basalts in the eastern part of the North China Craton(NCC),it has been suggested that the early Cretaceous lithospheric mantle of the eastern NCC was highly hydrous([1,000 ppm,H2O wt.)and that this high water content had significantly reduced the viscosity of the lithospheric mantle and provided a prerequisite for the destruction of the NCC.The eastern part of the NCC had undergone multistage subduction of oceanic plates from the south,north,and east sides since the early Paleozoic,and these events may have caused the strong hydration of the NCC lithospheric mantle.To determine which subduction had contributed most to this hydration,we measured the water contents of the peridotite xenoliths hosted by the early Cretaceous high-magnesium diorites of Fushan in the southcentral part of the Taihang Mountains.Our results demonstrate that the water content of the early Cretaceous lithospheric mantle beneath the south part of the Taihang Mountains was*40 ppm and significantly lower than that of the contemporary lithospheric mantle beneath the eastern part of the NCC.Thus,the hydration of the early Cretaceous lithospheric mantle of the eastern part of the NCC can be ascribed to the subduction of the Pacific plate from the west side.Thus,the main dynamic factor in the destruction of the NCC was likely the subduction of the Pacific plate.展开更多
基金This paper is supported by Ministry of Land and Resources (No. 2001010202)Ministry of Education (No. 0211)the Focused Subject Program of Beijing (No. XK104910598).
文摘With the super-wide band magnetoteiluric sounding data of the JUong （吉隆）-Cuoqin （措勤） profile （named line 800） which was completed in 2001 and the Dingri （定日）-Cuomai （措迈） profile （named line 900） which was completed in 2004, we obtained the strike direction of each MT station by strike analysis, then traced profiles that were perpendicular to the main strike direction, and finally obtained the resistivity model of each profile by nonlinear conjugate gradients （NLCG） inversion. With these two models, we described the resistivity structure features of the crust and the upper mantle of the center-southern Tibetan plateau and its relationship with Yalung Tsangpo suture： the upper crust of the research area is a resistive layer with resistivity value range of 200-3 000 Ω.m. The depth of its bottom surface is about 15-20 km generally, but the bottom surface of resistive layer is deeper in the middle of these two profiles. At llne 900, it is about 30 km deep, and even at line 800, it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km, and a conductive layer is beneath it with resistivity even less than 5 Ω.m. This conductive layer is composed of individual conductive bodies, and at the south of the Yalung Tsangpo suture, the conductive bodies are smaller with thickness about 10 km and lean to the north slightly. However, at the north of the Yalung Tsangpo suture, the conductive bodies are larger with thickness about 30 km and also lean to the north slightly. Relatively, the conductive bodies of line 900 are thinner than those of line 800, and the depth of the bottom surface of line 900 is also shallower. At last, after analyzing the effect factors to the resistivity of rocks, it was concluded that the very conductive layer was caused by partial melt or connective water in rocks. It suggests that the middle and lower crust of the center-southern Tibetan plateau is very thick, hot, flabby, and waxy.
基金supported by the Global Change Research Great Scientific Research Plan Program: "Development and Evaluation of High Resolution Climate Models" (Grant No.2010CB951904)the National Natural Science Foundation of China (Grant Nos.41075059 and 41023002)
文摘ABSTRACT Using data from 17 coupled models and nine sets of corresponding Atmospheric Model Intercomparison Project （AMIP） results, we investigated annual and seasonal variation biases in the upper 50 m of the south-central equatorial Pacific, with a focus on the double-ITCZ bias, and examined the causes for the amplitude biases by using heat budget analysis. The results showed that, in the research region, most of the models simulate SSTs that are higher than or similar to observed. The simulated seasonal phase is close to that observed, but the amplitudes of more than half of the model results are larger than or equal to observations. Heat budget analysis demonstrated that strong shortwave radiation in individual atmospheric models is the main factor that leads to high SST values and that weak southward cold advection is an important mechanism for maintaining a high SST. For seasonal circulation, large surface shortwave radiation amplitudes cause large SST amplitudes.
文摘South-central Chile has some potential mineral resources including radioactive and rare earth elements (REE) minerals. This study reports some basic characteristics of the mineralogy of a radioactive-rare earth elements occurrence, related to a pegmatitic outcrop “Vertientes Pegmatite” hosted on Paleozoic granitic rocks of the South Coastal Batholith and discusses potential areas for REE deposits, particularly beach placers along the coastline of the BioBío region. In this pegmatite, X-ray diffraction analysis shows uranium-bearing minerals such as coffinite and metaschoepite, along with microcline, anorthoclase, albite, quartz and illite. Through optical microscopy and electron probe micro-analyzer (EPMA), rare earth minerals (monazite and xenotime) and radioactive minerals (thorite and thorium silicate ± uranium) were identified. Additionally, granitic rocks of the South Coastal Batholith around this pegmatite show rare earth minerals (monazite and allanite).
文摘Many gold placers located in the Coastal Range of south-central Chile have been exploited commercially during the past decades;nevertheless and until now, there are not any exploration studies of these placers and their basement. In order to provide an overview of exploratory potential, the stream sediments that are part of several gold placers in the northwest area of the BioBío region are analyzed, which have been registered on the basis of empirical evidence from artisanal mining activities. The overview consists of two goals: 1) determine the presence of auriferous occurrences (stream sediments and basement) and 2) identify potentially favorable areas to find gold placer deposits. Through optical microscopy this study characterized the metallic and non-metallic mineralogy of the basement, along with geochemical analyses of stream sediments and surrounding rocks of the placer deposits. The geochemical results show two sectors with high precious metal contents in sediments (up to 24 ppm of Au and 8 ppm of Ag) and two rocky outcrops with Au (757 and 41 ppb). Additionally, there are depressions in the study area that have received large amounts of sediments (reaching up to 170 m-thick), which are favorable places for the accumulation of auriferous sediments from nearby valleys due to the tectonic and structural conditions where they are located. Then, these results show an exploratory potential for gold placers and can be useful to delineate future exploration strategies in the Coastal Range of south-central Chile.
基金founded by ANID,Fondecyt Regular projects 1151146,and 1200428founded by ANID,National Doctoral Scholarship.
文摘Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end,giving way to shortening and Andean growth from the Late Cretaceous onward.Nevertheless,there are disagreements regarding the timing and nature of this transition to Andean orogenesis.To address these issues,we conducted geochronologic(U-Pb and^(40)Ar/&(39)Ar),sedimentologic,and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area(Principal Cordillera,Chile,36°S).From our findings and prior analyses,we propose the following tectono-stratigraphic evolution of the region.(1)Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin.(2)After a~40 Myr hiatus,fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian.Whereas the Colimapu Formation displays evidence of syndepositional shortening,the Plan de los Yeuques Formation exhibits synextensional growth strata.Contrary to other studies,our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous.We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening,followed by extension.(3)After a~20 Myr hiatus,middle Eocene to early Miocene(Lutetian-Aquitanian)accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin.(4)Finally,major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene.This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina.In terms of the transition to early Andean deformation,we propose that structural deformation did not generate a major,regional-scale fold-thrust belt during the late Albian-Santonian.Modest extension,tectonic quiescence,or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.
基金supported by the National Natural Science Foundation of China(91014007 and 41225005)
文摘Based on studies of the water content of the early Cretaceous Feixian high-magnesium basalts in the eastern part of the North China Craton(NCC),it has been suggested that the early Cretaceous lithospheric mantle of the eastern NCC was highly hydrous([1,000 ppm,H2O wt.)and that this high water content had significantly reduced the viscosity of the lithospheric mantle and provided a prerequisite for the destruction of the NCC.The eastern part of the NCC had undergone multistage subduction of oceanic plates from the south,north,and east sides since the early Paleozoic,and these events may have caused the strong hydration of the NCC lithospheric mantle.To determine which subduction had contributed most to this hydration,we measured the water contents of the peridotite xenoliths hosted by the early Cretaceous high-magnesium diorites of Fushan in the southcentral part of the Taihang Mountains.Our results demonstrate that the water content of the early Cretaceous lithospheric mantle beneath the south part of the Taihang Mountains was*40 ppm and significantly lower than that of the contemporary lithospheric mantle beneath the eastern part of the NCC.Thus,the hydration of the early Cretaceous lithospheric mantle of the eastern part of the NCC can be ascribed to the subduction of the Pacific plate from the west side.Thus,the main dynamic factor in the destruction of the NCC was likely the subduction of the Pacific plate.
