The Panxi region is located in the frontal zone of positive squeezing subduction and side squeezing shearing between the Indian plate and the Eurasian plate. The long-period magnetotelluric (LMT) and broadband magne...The Panxi region is located in the frontal zone of positive squeezing subduction and side squeezing shearing between the Indian plate and the Eurasian plate. The long-period magnetotelluric (LMT) and broadband magnetotelluric (MT) techniques are both used to study the deep electrical conductivity structure in this region; magnetic and gravity surveys are also performed along the profile. According to the 2-D resistivity model along the Yanyuan-Yongshan profile, a high- conductivity layer (HCL) exists widely in the crust, and a high-resistivity block (HRB) exists widely in the upper mantle in general, as seen by the fact that a large HCL exists from the western Jinpingshan tectonic zone to the eastern Mabian tectonic zone in the crust, while the HRB found in the Panxi tectonic zone is of abnormally high resistivity in that background compared to both sides of Panxi tectonic zone. In addition, the gravity and magnetic field anomalies are of high value. Combined with geological data, the results indicate that there probably exists basic or ultrabasic rock with a large thickness in the lithosphere in the Panxi axial region, which indicates that fracture activity once occurred in the lithosphere. As a result, we can infer that the high-resistivity zone in the Panxi lithosphere is the eruption channel for Permian Emeishan basalt and the accumulation channel for basic and ultrabasic rock. The seismic sources along the profile are counted according to seismic record data. The results indicate that the most violent earthquake sources are located at the binding site of the HRB and the HCL, where the tectonic activity zone is generally acknowledged to be; however, the earthquakes occurring in the HCL are not so violent, which reflects the fact that the HCL is a plastic layer, and the fracture threshold of a plastic layer is low generally, making high stress difficult to accumulate but easy to release in the layer. As a result, a higher number of smaller earthquakes occurred in the HCL at Daliangshan tectonic zone, and violent earthquakes occurred at the binding site of high- and low-resistivity blocks at the Panxi tectonic zone.展开更多
The Panzhihua,Hongge,and Baima Fe-Ti-V oxide deposits in the Panzhihua-Xichang(Panxi) region are hosted in large layered mafic-ultramafic intrusions.The layered intrusions intrude either the Neoproterozoic Dengying Fo...The Panzhihua,Hongge,and Baima Fe-Ti-V oxide deposits in the Panzhihua-Xichang(Panxi) region are hosted in large layered mafic-ultramafic intrusions.The layered intrusions intrude either the Neoproterozoic Dengying Formation,composed mainly of limestone,or the Paleoproterozoic Hekou Formation,composed of meta-sedimentary-volcanic rocks.It remains unclear if the wall rocks have been involved during the fractionation of magmas and have affected the sequence of crystallization of Fe-Ti oxide.Volatiles and their C-H-O isotopic compositions of magnetite,apatite,clinopyroxene,and plagioclase of different types of ores from the three intrusions are analyzed using a technique of stepwise heating mass spectrometer to evaluate the role of wall rocks in the formation of Fe-Ti oxide ores.Volatiles released from magnetite are composed mainly of H 2 O and CO 2,whereas the other minerals are composed mainly of H 2 O,CO 2 and H 2.At 800-1200°C temperature interval,the average 13 C values of CO 2 of all the minerals from the three intrusions range from 7.7‰ to 13.5‰ and the average 18 O CO 2 values from 19.1‰ to 19.5‰,which are scattered in a mixed field with basalt and the two types of wall rocks as end-members,indicating that CO 2 from the wall rocks may have been involved in the magmas from which the three intrusions formed.At 400-800 C temperature interval,both 13 C values(13.7‰ to 17.9‰ on the average) and 18 O values(16.2‰ to 19.2‰ on the average) of CO 2 of all the minerals are lower than those for 800-1200 C temperature interval,and much closer to the values of the wall rocks.Abundant H 2 O released at the 400-800 C temperature interval has relatively low D values ranging from 90‰ to 115‰,also indicating the involvement of fluids from the wall rocks.The average bulk contents of volatiles released from magnetite of the Hongge,Baima,and Panzhihua intrusions are 4891,2996,and 1568 mm 3 STP/g,respectively,much higher than those released from other minerals in total,which are 382,600,and 379 mm 3 STP/g,respectively,indicating that magnetite crystallized from magmas with much more volatiles than other minerals.This can be interpreted as that crystallization of clinopyroxene and plagioclase in the early fractionation of magmas resulted in volatiles such as H 2 O that were eventually enriched in the residual magmas and,at the same time,fluids from the wall rocks may have been involved in the magmas and were trapped in magnetite,which crystallized later than clinopyroxene and plagioclase.展开更多
Ⅰ. DATA1. Terrestrial Heat FlowTo date, 13 reliable heat flow values have been obtained in the Panxi region and were published in Refs. [1, 2]. For use, these data were cited and synthesized in Table 1.
IN addition to vanadium titano-magnetite, lead-zinc ore is also one of the mineral resources with great exploring potentiality in the Panxi region of Sichuan Province, China. In the carbonate rock strata of theSinian ...IN addition to vanadium titano-magnetite, lead-zinc ore is also one of the mineral resources with great exploring potentiality in the Panxi region of Sichuan Province, China. In the carbonate rock strata of theSinian Dengying Formation which account for about 3.5%-11.4% of the total thickness of the strataexposed in the Panxi region there are quite a number of the Pb-Zn deposits that account for 53.4% of thetotal Pb-Zn ore reserve in the whole region. Furthermore, some large Pb-Zn deposits such as the Tianbaoshan Pb-Zn deposit in Huili, the Daliangzi Pb-Zn deposit in Huidong and the Yinchanggou Pb-Zn deposit in Ningnan are also hosted in the Sinian Dengying Formation. Why? Previous studies indicated that the high background values of Pb and Zn, favorable lithofacies andpaleogeographic conditions and good ore-hosting structures made the Sinian Dengying Formation a pre-展开更多
The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background o...The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in China's Mainland and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block's interior. In this paper, the three-dimensional (3D) P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai-Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north-south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by low- velocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan-Dian and Songpan-Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan-Ganzi Block and the sub-block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80-120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background for the area's strong earthquake activity.展开更多
基金supported by National High-Tech R&D Program of China (Grant 2014AA06A612)the project of the China Geological Survey (Grants 1212011220263,1212010914049 and 1212011121273)
文摘The Panxi region is located in the frontal zone of positive squeezing subduction and side squeezing shearing between the Indian plate and the Eurasian plate. The long-period magnetotelluric (LMT) and broadband magnetotelluric (MT) techniques are both used to study the deep electrical conductivity structure in this region; magnetic and gravity surveys are also performed along the profile. According to the 2-D resistivity model along the Yanyuan-Yongshan profile, a high- conductivity layer (HCL) exists widely in the crust, and a high-resistivity block (HRB) exists widely in the upper mantle in general, as seen by the fact that a large HCL exists from the western Jinpingshan tectonic zone to the eastern Mabian tectonic zone in the crust, while the HRB found in the Panxi tectonic zone is of abnormally high resistivity in that background compared to both sides of Panxi tectonic zone. In addition, the gravity and magnetic field anomalies are of high value. Combined with geological data, the results indicate that there probably exists basic or ultrabasic rock with a large thickness in the lithosphere in the Panxi axial region, which indicates that fracture activity once occurred in the lithosphere. As a result, we can infer that the high-resistivity zone in the Panxi lithosphere is the eruption channel for Permian Emeishan basalt and the accumulation channel for basic and ultrabasic rock. The seismic sources along the profile are counted according to seismic record data. The results indicate that the most violent earthquake sources are located at the binding site of the HRB and the HCL, where the tectonic activity zone is generally acknowledged to be; however, the earthquakes occurring in the HCL are not so violent, which reflects the fact that the HCL is a plastic layer, and the fracture threshold of a plastic layer is low generally, making high stress difficult to accumulate but easy to release in the layer. As a result, a higher number of smaller earthquakes occurred in the HCL at Daliangshan tectonic zone, and violent earthquakes occurred at the binding site of high- and low-resistivity blocks at the Panxi tectonic zone.
基金supported by the Main Direction Program of Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No. KZCX2-YW-Q04-06)National Basic Research Program of China (Grant No. 2011CB808903)+1 种基金National Natural Science Foundation of China (Grant No. 41073030)Hundred Talents Program of the Chinese Academy of Sciences to CYW
文摘The Panzhihua,Hongge,and Baima Fe-Ti-V oxide deposits in the Panzhihua-Xichang(Panxi) region are hosted in large layered mafic-ultramafic intrusions.The layered intrusions intrude either the Neoproterozoic Dengying Formation,composed mainly of limestone,or the Paleoproterozoic Hekou Formation,composed of meta-sedimentary-volcanic rocks.It remains unclear if the wall rocks have been involved during the fractionation of magmas and have affected the sequence of crystallization of Fe-Ti oxide.Volatiles and their C-H-O isotopic compositions of magnetite,apatite,clinopyroxene,and plagioclase of different types of ores from the three intrusions are analyzed using a technique of stepwise heating mass spectrometer to evaluate the role of wall rocks in the formation of Fe-Ti oxide ores.Volatiles released from magnetite are composed mainly of H 2 O and CO 2,whereas the other minerals are composed mainly of H 2 O,CO 2 and H 2.At 800-1200°C temperature interval,the average 13 C values of CO 2 of all the minerals from the three intrusions range from 7.7‰ to 13.5‰ and the average 18 O CO 2 values from 19.1‰ to 19.5‰,which are scattered in a mixed field with basalt and the two types of wall rocks as end-members,indicating that CO 2 from the wall rocks may have been involved in the magmas from which the three intrusions formed.At 400-800 C temperature interval,both 13 C values(13.7‰ to 17.9‰ on the average) and 18 O values(16.2‰ to 19.2‰ on the average) of CO 2 of all the minerals are lower than those for 800-1200 C temperature interval,and much closer to the values of the wall rocks.Abundant H 2 O released at the 400-800 C temperature interval has relatively low D values ranging from 90‰ to 115‰,also indicating the involvement of fluids from the wall rocks.The average bulk contents of volatiles released from magnetite of the Hongge,Baima,and Panzhihua intrusions are 4891,2996,and 1568 mm 3 STP/g,respectively,much higher than those released from other minerals in total,which are 382,600,and 379 mm 3 STP/g,respectively,indicating that magnetite crystallized from magmas with much more volatiles than other minerals.This can be interpreted as that crystallization of clinopyroxene and plagioclase in the early fractionation of magmas resulted in volatiles such as H 2 O that were eventually enriched in the residual magmas and,at the same time,fluids from the wall rocks may have been involved in the magmas and were trapped in magnetite,which crystallized later than clinopyroxene and plagioclase.
文摘Ⅰ. DATA1. Terrestrial Heat FlowTo date, 13 reliable heat flow values have been obtained in the Panxi region and were published in Refs. [1, 2]. For use, these data were cited and synthesized in Table 1.
文摘IN addition to vanadium titano-magnetite, lead-zinc ore is also one of the mineral resources with great exploring potentiality in the Panxi region of Sichuan Province, China. In the carbonate rock strata of theSinian Dengying Formation which account for about 3.5%-11.4% of the total thickness of the strataexposed in the Panxi region there are quite a number of the Pb-Zn deposits that account for 53.4% of thetotal Pb-Zn ore reserve in the whole region. Furthermore, some large Pb-Zn deposits such as the Tianbaoshan Pb-Zn deposit in Huili, the Daliangzi Pb-Zn deposit in Huidong and the Yinchanggou Pb-Zn deposit in Ningnan are also hosted in the Sinian Dengying Formation. Why? Previous studies indicated that the high background values of Pb and Zn, favorable lithofacies andpaleogeographic conditions and good ore-hosting structures made the Sinian Dengying Formation a pre-
基金supported by China earthquake scientific array exploration Southern section of North South seismic belt(201008001)Northern section of North South seismic belt(20130811)+1 种基金National Natural Science Foundation of China(41474057)Science for Earthquake Resllience of China Earthquake Administration(XH15040Y)
文摘The special seismic tectonic environment and frequent seismicity in the southeastern margin of the Qinghai-Tibet Plateau show that this area is an ideal location to study the present tectonic movement and background of strong earthquakes in China's Mainland and to predict future strong earthquake risk zones. Studies of the structural environment and physical characteristics of the deep structure in this area are helpful to explore deep dynamic effects and deformation field characteristics, to strengthen our understanding of the roles of anisotropy and tectonic deformation and to study the deep tectonic background of the seismic origin of the block's interior. In this paper, the three-dimensional (3D) P-wave velocity structure of the crust and upper mantle under the southeastern margin of the Qinghai-Tibet Plateau is obtained via observational data from 224 permanent seismic stations in the regional digital seismic network of Yunnan and Sichuan Provinces and from 356 mobile China seismic arrays in the southern section of the north-south seismic belt using a joint inversion method of the regional earthquake and teleseismic data. The results indicate that the spatial distribution of the P-wave velocity anomalies in the shallow upper crust is closely related to the surface geological structure, terrain and lithology. Baoxing and Kangding, with their basic volcanic rocks and volcanic clastic rocks, present obvious high-velocity anomalies. The Chengdu Basin shows low-velocity anomalies associated with the Quaternary sediments. The Xichang Mesozoic Basin and the Butuo Basin are characterised by low- velocity anomalies related to very thick sedimentary layers. The upper and middle crust beneath the Chuan-Dian and Songpan-Ganzi Blocks has apparent lateral heterogeneities, including low-velocity zones of different sizes. There is a large range of low-velocity layers in the Songpan-Ganzi Block and the sub-block northwest of Sichuan Province, showing that the middle and lower crust is relatively weak. The Sichuan Basin, which is located in the western margin of the Yangtze platform, shows high-velocity characteristics. The results also reveal that there are continuous low-velocity layer distributions in the middle and lower crust of the Daliangshan Block and that the distribution direction of the low-velocity anomaly is nearly SN, which is consistent with the trend of the Daliangshan fault. The existence of the low-velocity layer in the crust also provides a deep source for the deep dynamic deformation and seismic activity of the Daliangshan Block and its boundary faults. The results of the 3D P-wave velocity structure show that an anomalous distribution of high-density, strong-magnetic and high-wave velocity exists inside the crust in the Panxi region. This is likely related to late Paleozoic mantle plume activity that led to a large number of mafic and ultra-mafic intrusions into the crust. In the crustal doming process, the massive intrusion of mantle-derived material enhanced the mechanical strength of the crustal medium. The P-wave velocity structure also revealed that the upper mantle contains a low-velocity layer at a depth of 80-120 km in the Panxi region. The existence of deep faults in the Panxi region, which provide conditions for transporting mantle thermal material into the crust, is the deep tectonic background for the area's strong earthquake activity.