The Guanxian-Anxian fault zone in the Longmen Shan,Sichuan,China,exhibits long-term creep-slip but ruptured during the 2008 Wenchuan earthquake,challenging the view that creeping faults rarely generate strong earthqua...The Guanxian-Anxian fault zone in the Longmen Shan,Sichuan,China,exhibits long-term creep-slip but ruptured during the 2008 Wenchuan earthquake,challenging the view that creeping faults rarely generate strong earthquakes.To investigate the transition from creep-slip to stick-slip,we analyzed fault rocks from the WFSD-3,using microstructural observations,XRD,μXRF,Raman spectroscopy,and quartz grain size statistics.Fault rocks show intense foliation,pressure-solution structures,and abundant clay minerals,reflecting long-term aseismic creep.At the interface between black and gray fault gouges at~1249.98 m,microstructures indicate stick-slip behavior,including truncated grains,angular fragments,and finer grain sizes.Here,clay content drops sharply while strong minerals(quartz,feldspar,calcite,dolomite)increase.Elemental mapping shows Al and K enriched in black gouge,whereas Ca and Si in gray gouge;Raman spectroscopy indicates possible graphitization;the finest quartz grains occur in black gouge.These features mark co-seismic principal slip zone of the Wenchuan earthquake.We propose that fluid-driven transformation of strong minerals into clays facilitates creep-slip,whereas localized precipitation of strong minerals strengthens the fault,causing stress accumulation and controlling the creep-slip to stick-slip transition.This mechanism has implications for reassessing seismic hazards of creeping faults.展开更多
Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experie...Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experienced significant seismic events,particularly along its northern boundary,highlighting the recurrent seismic activity in the Kyrgyz Republic.The Issyk-Ata fault,stretching 120 km from west to east in the northern Tien Shan,bounds from the north a young,growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression.This region is susceptible to strong earthquakes,posing a significant threat to the Chui region and Bishkek,the capital city with over a million residents.The youngest fault in the area is the Issyk-Ata fault,traversing the southern part of Bishkek,where modern construction has obscured its features.This study integrates remote sensing,detailed fieldwork,and paleoseismological investigations to map and analyze surface ruptures,quantify vertical displacements,and assess seismic hazards along the Issyk-Ata fault.Using optically stimulated luminescence and radiocarbon dating,we determined ages for documented paleoseismic events,placing two ancient earthquakes in the Holocene.Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1.In the Dzhal area,geological and geomorphological analysis yielded a longterm fault-slip rate of 1.15 mm/a.The Issyk-Ata fault shows variable rupture behavior,with distinct segments demonstrating different seismic characteristics and histories of activity.This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.展开更多
Understanding diagenetic processes plays a crucial role in evaluating the quality of tight reservoirs.In this study,we aimed to examine diagenetic facies and thereby assess reservoir quality by conducting an integrate...Understanding diagenetic processes plays a crucial role in evaluating the quality of tight reservoirs.In this study,we aimed to examine diagenetic facies and thereby assess reservoir quality by conducting an integrated analysis of porosity,petrology,permeability,mineralogy,mercury injection,and stable isotopic data in core samples from the Permian Shan 2 and He 1 members(Shan 2—He 1 Mbr)in China's Ordos Basin.Early compaction and precipitation of diagenetic minerals have significantly reduced primary pore space in these members,although certain sandstones have retained anomalously high porosity.These high-porosity reservoirs have been shaped by many factors,with dissolution identified as the predominant mechanism.Detailed petrographic observations and assessments of the primary minerals,the minerals'genesis,and associated diagenetic processes revealed seven distinct diagenetic facies differentiated by their sand-grain populations,types of cementation,clay matrix contents,and volcanic tuffaceous sediment(VTS).The main interstitial fillings consist of VTS,clay minerals,quartz overgrowths,and calcite(ferrocalcite).Clasts and VTS-dissolved sandstone have mainly formed Class I reservoirs with highly unstable grains and good secondary pores resulting from the dissolution of the grains and VTS.VTS tight sandstone,siliceous cementation tight sandstone,illite-siliceous cementation tight sandstone,and calcite cementation tight sandstone have formed Class II reservoirs with high rates of interstitial filling and cementation.Sandstone tightly cemented by illite has poor reservoir properties and has mainly formed Class III reservoirs.This classification underscores the critical importance of understanding diagenesis,diagenetic facies,and especially the diagenetic features of VTS for accurately assessing reservoir quality.A comprehensive understanding of these factors may facilitate more effective hydrocarbon exploration and exploitation in this area.展开更多
0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapp...0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapponnier et al.,2001;Meyer et al.,1998).The northwest-trending mountain ranges in the Qilian Shan(“Shan”means“Mountain”in Chinese)have significantly influenced this deformation(Zheng et al.,2013).展开更多
The north-trending Liupan Shan （六盘山） is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and e...The north-trending Liupan Shan （六盘山） is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identi- fy the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the pa- leomagnetic polarity zones of the Huating （华亭） Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.ln of the Geomagnetic Polar- ity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distribu- tions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.展开更多
Many small mountain glaciers have been reported undergoing strong shrinkage, and it is therefore important to understand how they respond to climate change. The availability of topographic maps from 1962, Landsat TM i...Many small mountain glaciers have been reported undergoing strong shrinkage, and it is therefore important to understand how they respond to climate change. The availability of topographic maps from 1962, Landsat TM imagery from 1990 and ASTER（Advanced Spaceborne Thermal Emission and Radiometer） imagery from 2006 and field investigation of some glaciers allow a comprehensive analysis of glacier change based on glacier size and topography on Mt. Bogda. Results include：（1） an overall loss of a glacierized area by 31.18±0.31 km^2 or 21.6% from 1962 to 2006,（2） a marked dependence of glacier area shrinkage on initial size, with smaller glaciers experiencing higher shrinkage levels,（3） the disappearance of 12 small glaciers,（4） a striking difference in area loss between the southern and northern slopes of 25% and 17%, respectively. A subset of the investigated glaciers shows that the area 57.45±0.73 km2 in 1962 reduced to 54.79±0.561 km^2 in 1990 and 48.88±0.49 km^2 in 2006, with a relative area reduction of 4.6% during 1962-1990, and 10.8% during 1990-2006. The corresponding volume waste increased from 6.9% to 10.2%. Three reference glaciers were investigated in 1981 and revisited in 2009. Their terminus experienced a marked recession. Meteorological data from stations around Mt. Bogda reveals that glacier shrinkage is correlated with winter warming and an extension of the ablation period. Precipitation on the northwest side of the range shows a marked increase, with a slight increase on the southeast side.展开更多
Endemic to China, the Emei Shan Liocichla(Liocichla omeiensis) is considered globally vulnerable by the IUCN because of its small, declining population and fragmented range. The species has been recorded in only a few...Endemic to China, the Emei Shan Liocichla(Liocichla omeiensis) is considered globally vulnerable by the IUCN because of its small, declining population and fragmented range. The species has been recorded in only a few mountainous forests in south-central Sichuan and in the extreme northeast of Yunnan Province. We summarized the basic eco-biology information on its habitat,breeding, winter habits and behavior, voice, population status, research and conservation.展开更多
The Yingxiu-Beichuan fault zone(YBFZ)has long been active and experienced repeated large earthquakes.The physicochemical properties of the deep fault zone(>1000 m)are the key to understanding the deformation mechan...The Yingxiu-Beichuan fault zone(YBFZ)has long been active and experienced repeated large earthquakes.The physicochemical properties of the deep fault zone(>1000 m)are the key to understanding the deformation mechanism of large earthquakes.This study uses rock magnetic,microstructural,and geochemical analyses of representative samples exposed in FZ1681 within the Wenchuan Earthquake Fault Scientific Drilling borehole 2(WFSD-2)cores.Fault gouge and fault breccia have higher magnetic susceptibility values than wall rocks,and they contain abundant paramagnetic minerals and small quantities of magnetite and monoclinic pyrrhotite.The magnetite and monoclinic pyrrhotite in the fault gouge were mainly formed by coseismic frictional heating,indicating that large earthquakes with frictional heating temperatures of~500-900℃once occurred in the YBFZ.The seismogenic and coseismic environment was reducing with a relatively high sulfur content.The monoclinic pyrrhotite in the fault breccia was formed mainly by low-temperature hydrothermal fluid.This indicates that the fault zone experienced reducing and low-temperature(<400℃)hydrothermal fluid with a relatively high sulfur content after the earthquake.The YBFZ,which experiences frequent large earthquakes,is weakly oxidizing environment at different depths,but the effect of the low-temperature hydrothermal fluid is weaker at depth.展开更多
基金supported by the National Natural Science Foundation of China(42230312,42272270,42172262,42372266)the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(2024ZD1000500)the China Geological Survey Project(DD20240041).
文摘The Guanxian-Anxian fault zone in the Longmen Shan,Sichuan,China,exhibits long-term creep-slip but ruptured during the 2008 Wenchuan earthquake,challenging the view that creeping faults rarely generate strong earthquakes.To investigate the transition from creep-slip to stick-slip,we analyzed fault rocks from the WFSD-3,using microstructural observations,XRD,μXRF,Raman spectroscopy,and quartz grain size statistics.Fault rocks show intense foliation,pressure-solution structures,and abundant clay minerals,reflecting long-term aseismic creep.At the interface between black and gray fault gouges at~1249.98 m,microstructures indicate stick-slip behavior,including truncated grains,angular fragments,and finer grain sizes.Here,clay content drops sharply while strong minerals(quartz,feldspar,calcite,dolomite)increase.Elemental mapping shows Al and K enriched in black gouge,whereas Ca and Si in gray gouge;Raman spectroscopy indicates possible graphitization;the finest quartz grains occur in black gouge.These features mark co-seismic principal slip zone of the Wenchuan earthquake.We propose that fluid-driven transformation of strong minerals into clays facilitates creep-slip,whereas localized precipitation of strong minerals strengthens the fault,causing stress accumulation and controlling the creep-slip to stick-slip transition.This mechanism has implications for reassessing seismic hazards of creeping faults.
基金financial support of the Faculty Research Grant project of the American University of Central Asia(AUCA)supported by the Ministry of Education of the Republic of Korea and the National Research Foundation of Korea(NRF-2023S1A5B5A16080131)。
文摘Geodetic observations over the past several decades identify the Tien Shan as a prominent and active intracontinental mountain belt,characterized by a meridional shortening rate of up to 20 mm/a.The region has experienced significant seismic events,particularly along its northern boundary,highlighting the recurrent seismic activity in the Kyrgyz Republic.The Issyk-Ata fault,stretching 120 km from west to east in the northern Tien Shan,bounds from the north a young,growing anticline demarcating the foothills of the Kyrgyz Range and the Chui depression.This region is susceptible to strong earthquakes,posing a significant threat to the Chui region and Bishkek,the capital city with over a million residents.The youngest fault in the area is the Issyk-Ata fault,traversing the southern part of Bishkek,where modern construction has obscured its features.This study integrates remote sensing,detailed fieldwork,and paleoseismological investigations to map and analyze surface ruptures,quantify vertical displacements,and assess seismic hazards along the Issyk-Ata fault.Using optically stimulated luminescence and radiocarbon dating,we determined ages for documented paleoseismic events,placing two ancient earthquakes in the Holocene.Magnitude estimates suggest seismic events with magnitudes ranging from 6.6 to 7.1.In the Dzhal area,geological and geomorphological analysis yielded a longterm fault-slip rate of 1.15 mm/a.The Issyk-Ata fault shows variable rupture behavior,with distinct segments demonstrating different seismic characteristics and histories of activity.This variability necessitates comprehensive seismic hazard modeling to better understand and mitigate potential risks in the region.
基金supported by the National Natural Science Foundation of China:Tethys Dynamics(Grant No.92255302)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA14010201)the China Scholarship Council(Grant No.202206400023).
文摘Understanding diagenetic processes plays a crucial role in evaluating the quality of tight reservoirs.In this study,we aimed to examine diagenetic facies and thereby assess reservoir quality by conducting an integrated analysis of porosity,petrology,permeability,mineralogy,mercury injection,and stable isotopic data in core samples from the Permian Shan 2 and He 1 members(Shan 2—He 1 Mbr)in China's Ordos Basin.Early compaction and precipitation of diagenetic minerals have significantly reduced primary pore space in these members,although certain sandstones have retained anomalously high porosity.These high-porosity reservoirs have been shaped by many factors,with dissolution identified as the predominant mechanism.Detailed petrographic observations and assessments of the primary minerals,the minerals'genesis,and associated diagenetic processes revealed seven distinct diagenetic facies differentiated by their sand-grain populations,types of cementation,clay matrix contents,and volcanic tuffaceous sediment(VTS).The main interstitial fillings consist of VTS,clay minerals,quartz overgrowths,and calcite(ferrocalcite).Clasts and VTS-dissolved sandstone have mainly formed Class I reservoirs with highly unstable grains and good secondary pores resulting from the dissolution of the grains and VTS.VTS tight sandstone,siliceous cementation tight sandstone,illite-siliceous cementation tight sandstone,and calcite cementation tight sandstone have formed Class II reservoirs with high rates of interstitial filling and cementation.Sandstone tightly cemented by illite has poor reservoir properties and has mainly formed Class III reservoirs.This classification underscores the critical importance of understanding diagenesis,diagenetic facies,and especially the diagenetic features of VTS for accurately assessing reservoir quality.A comprehensive understanding of these factors may facilitate more effective hydrocarbon exploration and exploitation in this area.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(No.2019QZKK0901)the State Key Laboratory of Earthquake Dynamics(No.LED2023B04)+1 种基金the National Natural Science Foundation of China(Nos.42272242,W2411033,W2521003)the Science and Technology Plan of Gansu Province(No.22JR11RA088)。
文摘0 INTRODUCTION The Qilian Mountain Belt,at the forefront of the Tibetan Plateau's expansion,offers key insights into the plateau's tectonic deformation(Zuza et al.,2018;Zheng et al.,2010;Zhang et al.,2004;Tapponnier et al.,2001;Meyer et al.,1998).The northwest-trending mountain ranges in the Qilian Shan(“Shan”means“Mountain”in Chinese)have significantly influenced this deformation(Zheng et al.,2013).
基金supported by the National Natural Science Foundation of China (Nos. 41290253, 40772116)the National Basic Research Program of China (973 Projects) (Nos.2010CB83340, 2013CB955904)
文摘The north-trending Liupan Shan （六盘山） is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identi- fy the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the pa- leomagnetic polarity zones of the Huating （华亭） Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.ln of the Geomagnetic Polar- ity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distribu- tions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.
基金supported by the Initial Funding of Doctor Scientific Research (No. LZCU-BS2013-06)the Project of Humanities and Social Sciences from the Ministry of Education of China (No. 13YJC790009)+2 种基金the National Basic Research Program of China (No. 2013CBA01801)the National NaturalScience Foundation of China (No. 41471058)the Funds for the Creative Research Groups of China (No. 41121001)
文摘Many small mountain glaciers have been reported undergoing strong shrinkage, and it is therefore important to understand how they respond to climate change. The availability of topographic maps from 1962, Landsat TM imagery from 1990 and ASTER（Advanced Spaceborne Thermal Emission and Radiometer） imagery from 2006 and field investigation of some glaciers allow a comprehensive analysis of glacier change based on glacier size and topography on Mt. Bogda. Results include：（1） an overall loss of a glacierized area by 31.18±0.31 km^2 or 21.6% from 1962 to 2006,（2） a marked dependence of glacier area shrinkage on initial size, with smaller glaciers experiencing higher shrinkage levels,（3） the disappearance of 12 small glaciers,（4） a striking difference in area loss between the southern and northern slopes of 25% and 17%, respectively. A subset of the investigated glaciers shows that the area 57.45±0.73 km2 in 1962 reduced to 54.79±0.561 km^2 in 1990 and 48.88±0.49 km^2 in 2006, with a relative area reduction of 4.6% during 1962-1990, and 10.8% during 1990-2006. The corresponding volume waste increased from 6.9% to 10.2%. Three reference glaciers were investigated in 1981 and revisited in 2009. Their terminus experienced a marked recession. Meteorological data from stations around Mt. Bogda reveals that glacier shrinkage is correlated with winter warming and an extension of the ablation period. Precipitation on the northwest side of the range shows a marked increase, with a slight increase on the southeast side.
基金supported by projects of the Sichuan Provincial Science&Technology Department(2011JYZ008)the Sichuan Provincial Education Department(11ZA155)Leshan Normal University(Z1158)
文摘Endemic to China, the Emei Shan Liocichla(Liocichla omeiensis) is considered globally vulnerable by the IUCN because of its small, declining population and fragmented range. The species has been recorded in only a few mountainous forests in south-central Sichuan and in the extreme northeast of Yunnan Province. We summarized the basic eco-biology information on its habitat,breeding, winter habits and behavior, voice, population status, research and conservation.
基金supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project(2024ZD1000500)the National Natural Science Foundation of China(42172262 and 42372266)+1 种基金the China Geological Survey(DD20240041)the Fundamental Research Funds of the Institute of Geomechanics(DZLXJK202516).
文摘The Yingxiu-Beichuan fault zone(YBFZ)has long been active and experienced repeated large earthquakes.The physicochemical properties of the deep fault zone(>1000 m)are the key to understanding the deformation mechanism of large earthquakes.This study uses rock magnetic,microstructural,and geochemical analyses of representative samples exposed in FZ1681 within the Wenchuan Earthquake Fault Scientific Drilling borehole 2(WFSD-2)cores.Fault gouge and fault breccia have higher magnetic susceptibility values than wall rocks,and they contain abundant paramagnetic minerals and small quantities of magnetite and monoclinic pyrrhotite.The magnetite and monoclinic pyrrhotite in the fault gouge were mainly formed by coseismic frictional heating,indicating that large earthquakes with frictional heating temperatures of~500-900℃once occurred in the YBFZ.The seismogenic and coseismic environment was reducing with a relatively high sulfur content.The monoclinic pyrrhotite in the fault breccia was formed mainly by low-temperature hydrothermal fluid.This indicates that the fault zone experienced reducing and low-temperature(<400℃)hydrothermal fluid with a relatively high sulfur content after the earthquake.The YBFZ,which experiences frequent large earthquakes,is weakly oxidizing environment at different depths,but the effect of the low-temperature hydrothermal fluid is weaker at depth.
