By mcasuring the Sm-Nd and Rb-Sr isotopiccompositions of harzburgite and gabbro from Shimianophiolite suite, we got the whole rock Sm-Nd isochron age of(938 ± 30) Ma (2σ), and the e Nd of 7.6 ± 0.8 (2σ), w...By mcasuring the Sm-Nd and Rb-Sr isotopiccompositions of harzburgite and gabbro from Shimianophiolite suite, we got the whole rock Sm-Nd isochron age of(938 ± 30) Ma (2σ), and the e Nd of 7.6 ± 0.8 (2σ), which showsthat the ophiolite was formed at the Early Neoproterozoic.The obvious change (0.70209-0.70708) of Isr values of theophiolite is caused by the meteoric hydrothermal alteration.The high εNd values indicate that the primitive magma wasderived from the intense depleted mantle rescrvoir. It is sug-gested that this area was in a back-arc basin environmentduring the Early Neoproterozic.展开更多
The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthqu...The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.展开更多
The first independent Te deposit discovered in China occurs at northern plunging end ofDashuigou thermal dome(diapiric granite)in centrel part of Daduhe ductile shear zone.The deposit isrepresented by an assemblage of...The first independent Te deposit discovered in China occurs at northern plunging end ofDashuigou thermal dome(diapiric granite)in centrel part of Daduhe ductile shear zone.The deposit isrepresented by an assemblage of Te,Bi,Se,Au,Ag and Cu,in which Te is a main mineralizing element.The orebody occurs as vein form,oblique to Triassic metamiorphic rocks.Studies of mineralogy,fluid inclu-sion and stable isotope geochemistry suggest that Te has been concentrated during the early period ofmineralization,and mineralization fluid may be related to hydrothermal solution from granitic magma and meteoricwater is consequent upon the fluid in the late period of Au mineralization.Preliminary study suggests thatDashuigou deposit represents a type of independent mesothermal Te deposit,which is mostly related to granitichydrothermal origin.展开更多
Debris flow is an abrupt phenomenon of earth surface movement and typical disaster in mountainous areas with steep terrace, quantity of loose soil and abundant surface runoff. Intense rainfall and rainstorm easily tri...Debris flow is an abrupt phenomenon of earth surface movement and typical disaster in mountainous areas with steep terrace, quantity of loose soil and abundant surface runoff. Intense rainfall and rainstorm easily triggered debris flows and generated huge losses. The disastrous debris flows, on July 4, 2013 at the gullies of Hou, Heilinzi and Xiongjia in Shimian County, Sichuan Province, resulted in 18 casualties and endangering Shimian city with a population of 50,000. These debris flows were characterized by low viscosity with only 0.9% - 1.4% clay soil of less than 0.05mm, density of 1.77 - 1.84 t/m<sup>3</sup>, velocity of 4.4 - 13.5m/s and discharge of 827 - 1248 m<sup>3</sup>/s, respectively, and also delivered sediment of 16.8 × 10<sup>4</sup>m<sup>3</sup>, 12.7 - 13.5 × 10<sup>4</sup> m<sup>3</sup>, 20.5 × 10<sup>4</sup>m<sup>3</sup> out of the outlet, respectively. These three events all generated a hazard chain, which involved in flash flood, channelized debris flow, dammed lake and outburst flood. The threshold conditions of debris flow blocking Nanya River and forming this hazard chain are that the unit width peak discharge and the deposition volume in river channel are more than 37.0 m<sup>3</sup>/s and 4500 m<sup>3</sup>, respectively. These debris flows were initiated by intense rainfall with the antecedent rainfall of over 52 mm and triggering rainstorm of over 36 mm/h. And, the property losses and casualties mainly originated from impacting and scouring, burying and blocking, highway destructing and river channel rising. The irrational location of constructions and the destruction of under-standard prevention constructions were responsible for loss worsening. It was strongly recommended for mitigating that hazards reassessment, integrated control, emergency plan and integrated risk management were made at mountainous urban areas, especially in high-hazard areas.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant No.49972024).
文摘By mcasuring the Sm-Nd and Rb-Sr isotopiccompositions of harzburgite and gabbro from Shimianophiolite suite, we got the whole rock Sm-Nd isochron age of(938 ± 30) Ma (2σ), and the e Nd of 7.6 ± 0.8 (2σ), which showsthat the ophiolite was formed at the Early Neoproterozoic.The obvious change (0.70209-0.70708) of Isr values of theophiolite is caused by the meteoric hydrothermal alteration.The high εNd values indicate that the primitive magma wasderived from the intense depleted mantle rescrvoir. It is sug-gested that this area was in a back-arc basin environmentduring the Early Neoproterozic.
基金This work is jointly supported by the National Natural Science Foundation of China(No.41904057)the National Key Research and Development Program of China(No.2018YFC1503402).
文摘The Shimian area of Sichuan sits at the junction of the Bayan Har block.Sichuan-Yunnan rhombic block,and Yangtze block,where several faults intersect.This region features intense tectonic activity and frequent earthquakes.In this study,we used local seismic waveform data recorded using dense arrays deployed in the Shimian area to obtain the shear wave splitting parameters at 55 seismic stations and thereby determine the crustal anisotropic characteristics of the region.We then analyzed the crustal stress pattern and tectonic setting and explored their relationship in the study area.Although some stations returned a polarization direction of NNW-SSE.a dominant polarization direction of NW-SE was obtained for the fast shear wave at most seismic stations in the study area.The polarization directions of the fast shear wave were highly consistent throughout the study-area.This orientation was in accordance with the direction of the regional principal compressive stress and parallel to the trend of the Xianshuihe and Daliangshan faults.The distribution of crustal anisotropy in this area was affected by the regional tectonic stress field and the fault structures.The mean delay time between fast and slow shear waves was 3.83 ms/km.slightly greater than the values obtained in other regions of Sichuan.This indicates that the crustal media in our study area had a high anisotropic strength and also reveals the influence of tectonic complexity resulting from the intersection of multiple faults on the strength of seismic anisotropy.
文摘The first independent Te deposit discovered in China occurs at northern plunging end ofDashuigou thermal dome(diapiric granite)in centrel part of Daduhe ductile shear zone.The deposit isrepresented by an assemblage of Te,Bi,Se,Au,Ag and Cu,in which Te is a main mineralizing element.The orebody occurs as vein form,oblique to Triassic metamiorphic rocks.Studies of mineralogy,fluid inclu-sion and stable isotope geochemistry suggest that Te has been concentrated during the early period ofmineralization,and mineralization fluid may be related to hydrothermal solution from granitic magma and meteoricwater is consequent upon the fluid in the late period of Au mineralization.Preliminary study suggests thatDashuigou deposit represents a type of independent mesothermal Te deposit,which is mostly related to granitichydrothermal origin.
文摘Debris flow is an abrupt phenomenon of earth surface movement and typical disaster in mountainous areas with steep terrace, quantity of loose soil and abundant surface runoff. Intense rainfall and rainstorm easily triggered debris flows and generated huge losses. The disastrous debris flows, on July 4, 2013 at the gullies of Hou, Heilinzi and Xiongjia in Shimian County, Sichuan Province, resulted in 18 casualties and endangering Shimian city with a population of 50,000. These debris flows were characterized by low viscosity with only 0.9% - 1.4% clay soil of less than 0.05mm, density of 1.77 - 1.84 t/m<sup>3</sup>, velocity of 4.4 - 13.5m/s and discharge of 827 - 1248 m<sup>3</sup>/s, respectively, and also delivered sediment of 16.8 × 10<sup>4</sup>m<sup>3</sup>, 12.7 - 13.5 × 10<sup>4</sup> m<sup>3</sup>, 20.5 × 10<sup>4</sup>m<sup>3</sup> out of the outlet, respectively. These three events all generated a hazard chain, which involved in flash flood, channelized debris flow, dammed lake and outburst flood. The threshold conditions of debris flow blocking Nanya River and forming this hazard chain are that the unit width peak discharge and the deposition volume in river channel are more than 37.0 m<sup>3</sup>/s and 4500 m<sup>3</sup>, respectively. These debris flows were initiated by intense rainfall with the antecedent rainfall of over 52 mm and triggering rainstorm of over 36 mm/h. And, the property losses and casualties mainly originated from impacting and scouring, burying and blocking, highway destructing and river channel rising. The irrational location of constructions and the destruction of under-standard prevention constructions were responsible for loss worsening. It was strongly recommended for mitigating that hazards reassessment, integrated control, emergency plan and integrated risk management were made at mountainous urban areas, especially in high-hazard areas.
