Table of Content

30 March 2013, Volume 35 Issue 1

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Research Paper

SEISMOLOGICAL STUDY ON BEHAVIORS OF PRESENT-DAY MOVEMENT OF ARCUATE TECTONIC BELT IN SOUTHEAST YUNNAN

HU Nan, HAN Zhu-jun

2013, 35(1):  1-21.  DOI: 10.3969/j.issn.0253-4967.2013.01.001

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The accurate relocations of small earthquakes during 1990-2011 on the arcuate tectonic belt in southeast Yunnan (23°N to 25°N,101°E to 103°E) are obtained by hypo2000 and double difference algorithm using Pg and Sg phase readings of 721 earthquakes recorded by Yunnan Earthquake Network Center.The RMS residual decreases to 0.45 from 1.43 with an average precision of about 1.4km horizontally and 1.9km vertically after relocation. Then we collected the waveform data of the study region during 2007-2012 and calculated the focal mechanisms of 148 small earthquakes with the method of the maximum amplitude ratio between Pg and Sg. Focal mechanism result shows that the number of nodal planes representing normal strike-slip is almost twice of that of the reverse strike-slip,which demonstrates that the dominant movement on the arcuate tectonic belt is normal strike-slip currently. Relocation of small earthquakes greatly improves the definition of the seismic images on the faults that generate them. According to the relocated focal depths,the Qujing Fault and Shiping-Jianshui Fault dip southwest,and the Honghe Fault dips northeast,which are in accord with the fault geometric characteristics revealed by crustal velocity profiles. According to this,the rollback of Sumatra-Myanmar trench has already brought a deep effect on the arcuate tectonics in southeast Yunnan,the compression caused by the slip of Sichuan-Yunnan rhombic block towards SSE may be weakened. So the tensile stress in SWW-NEE direction plays a more important role in present-day activities of the arcuate tectonics compared to the compressive stress in SSE-NNW direction,which can also be deduced from the characteristics of focal mechanism parameters. A transtensional zone may be emerging from the arcuate tectonics in southeast Yunnan.

USING DEFORMATION TERRACES TO CONFINE THE SHORTENING AND UPLIFT OF THE LONGQUAN ANTICLINE

LI Kang, XU Xi-wei, TAN Xi-bin

2013, 35(1):  22-36.  DOI: 10.3969/j.issn.0253-4967.2013.01.002

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Located at east of the Longmen Mountains Thrust,the Longquan anticline is a foreland uplift of Sichuan foreland basin. Three terraces have formed along the Kaijiang River across the Longquan anticline. According to optically stimulated luminescence (OSL) and ¹⁴C samples,the age of the terrace T₁ and T₂ is 4.6ka and (11.7?0.4)ka,respectively. With growing of the anticline,terrace surfaces deformed obviously,which is characterized by folding scarps.The longitudinal profiles of the terraces at the Kaijiang River have been measured by differential GPS.We interpret the subsurface fault and fold geometries using petroleum seismic reflection profiles,our data suggest that the Longquan anticline grows laterally through kink-band migration and depth-to-detachment is about 6 kilometers.The cumulative shortening along the direction of tectonic transport is estimated to be 0.8km. We can confine that the crustal shortening and the uplift rate in late Pleistocene is (1.36?0.41)mm/a and(0.64?0.19)mm/a. India colliding with Eurasia results in the strong resistance from the South China block against the E to SEE extrusion of Bayan Har block,most of the energy has released in the form of uplifting of Longmen Mountains,and part,by the decollement,has been transferred to form the Longquan anticline.The 12 May 2008 Wenchuan earthquake (M_W=7.9) of China occurred in the Longmen Shan thrust belt and is a consequence of the ongoing uplift process of the eastern margin of Tibetan plateau. After the earthquake,stress was reduced on the northern section and increased on the southern section of Longquan Fault.The event clearly illustrates that the Longquan anticline and the Longmen Shan thrust belt is an integral whole.The mechanism of uplift of Longquan Mountains provides some evidence for the orogenic model of brittle crustal thickening in the eastern Tibet Plateau.

DISCUSSION OF SEISMOGENIC STRUCTURE OF THE JUNE 24,2012 NINGLANG-YANYUAN M_S5.7 EARTHQUAKE

CHANG Zu-feng, YANG Sheng-yong, ZHOU Qing-yun, ZHANG Yan-feng, XIE Ying-qing

2013, 35(1):  37-49.  DOI: 10.3969/j.issn.0253-4967.2013.01.003

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The June 24th 2012 Ninglang-Yanyuan M_S 5.7 earthquake happened at 30km northwest of the Lijiang-Xiaojinhe Fault, a region seismically active in history and prone to earthquake in northwestern Yunnan. Tectonics in the earthquake region is complex,where two groups of faults are developed,trending NW and NE,respectively,and distributed in a chessboard pattern. Field survey results reveal that there are the NW-trending Yongning Fault and the NE-trending Rigulu-yanwa Fault developed near the epicenter,both are active in late Pleistocene.The Yongning Fault,composed of Wenquan Fault,Yongning Fault,and Alaao Fault,shows obvious fault landforms and clear linear features on satellite imagery.The fault has played an obvious control role in the development of the Yongning Quaternary Basin and Lugu Lake Basin,with several hot springs developed along the fault. Several tributaries of Qiansuo River run along the fault,and there are dextral displacements observed in many parts of the rivers along the fault,such as between Baqi and Haiyijiao,Shancuo village east of Rigulu. Near Alaao,the fault offset the late Pleistocene deposit on the T₂ terrace,and the latest TL age of the offset stratum is (21.19±1.80)ka,indicating it is a normal with dextral strike-slip,late Pleistocene active fault.The Rigulu-Wayan Fault has played a noticeable control role in the development of the Tertiary Basins such as Wayan,Rigulu,and Lijiazui and the Quaternary Basin of Yongning. It offset the mid Pleistocene and the upper Pleistocene strata. Between Zhongwadu and Lijiazui,several streams were synchronously displaced left-laterally. There are obvious signs showing the fault was active in the late Pleistocene,dominated by sinistral strike-slip. According to the focal mechanism solutions,the Ninglang-Yanyuan M_S 5.7 earthquake is of normal faulting with dextral strike-slip,the attitude of the NW nodal plane is basically consistent to the Yongning Fault,and the seismic rupture pattern is identical to the kinematical characteristic of Yongning Fault.The major axis of the isoseismals,the linear distribution of intensity Ⅷ anomaly sites and the direction of tectonic ground fissures are all consistent to the strike of Yongning Fault. Through analysis,it is believed that Yongning Fault is the seismogenic fault of Ninglang-Yanyuan M_S 5.7 earthquake. Furthermore,the 1996 Lijiang M7.0 earthquake,the 1976 Zhongdian M5.5 earthquake and this M5.7 earthquake all have apparent normal dip-slip component. These earthquakes are located in the periphery of the neo-tectonic uplift of Haba Snow Mountain and Yulong Snow Mountain. Based on analyses of regional topography,the normal faulting in this area is most likely related to the gravitational potential energy resulting from the big topography contrast.

RESEARCH ON LATE QUATERNARY ACTIVITY OF THE SOUTHEASTERN SEGMENT OF GANZI-YUSHU FAULT ZONE

SHI Feng, LI An, YANG Xiao-ping, XU Xi-wei, HE Hong-lin

2013, 35(1):  50-63.  DOI: 10.3969/j.issn.0253-4967.2013.01.004

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Taking tectonic geomorphology of southeastern Ganzi-Yushu Fault zone as the research object,and based on remote sensing interpretation,the paper investigates the late Quaternary activity of the southeastern segment of Ganzi-Yushu Fault zone through trenching and detailed field investigation on several typical sites. We analyze the landscapes and calculate the late Quaternary slip rates along the fault zone at the sites in Shengkang township,Renguo township,Cuoa township,and Ria township,respectively.The horizontal and vertical slip rates are (7.6?0.5)mm/a and (1.1?0.1)mm/a at Shengkang township,(8.0?0.3)mm/a and (1.1?0.1)mm/a at Renguo township. And horizontal slip rate of Cuoa township is (10.3?0.4)mm/a.The horizontal and vertical slip rates of Ria township are (10.8?0.8)mm/a and (1.1?0.1)mm/a,respectively. Both trenches at Renguo township and Cuoa township have revealed several paleoearthquake events. Though there are some differences in fault tectonic styles revealed between the two trenches,the fault motion on this segment is of strike-slip with a certain amount of thrust component on the whole. Associated with the analysis of paleoearthquake events and slip rate,it is found that the southeastern Ganzi-Yushu Fault zone is subject to intensive activity since late Quaternary,especially since Holocene.

QUATERNARY FAULTS OF THE QIANLIYAN UPLIFT IN THE NORTHERN SOUTH YELLOW SEA

SHEN Zhong-yan, ZHOU Jian-ping, GAO Jin-yao, WU Zhao-cai, YANG Chun-guo, TAO Chun-hui, YANG Yong, ZHANG Tao

2013, 35(1):  64-74.  DOI: 10.3969/j.issn.0253-4967.2013.01.005

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By far,there have been only a few neotectonic studies of the Qianliyan Uplift. In recent years,we have gathered multi-channel seismic data covering the whole uplift. After interpretation,we recognized three major Quaternary faults/fault zones. They are the South Boundary Fault Zone(SBFZ),F₃,and F₂ from south to north,respectively. These faults are almost parallel each other and trend northeastward.The SBFZ on most sections has been active at least since the middle Pleistocene; some segments of SBFZ are active since the Early Pleistocene.The latest activity of F₂ is in the Early Pleistocene while that of the F₃ is in the Middle-Early Pleistocene.The deformation intensity of SBFZ varies along strike and is well correlated with the curvature of the fault trace, that is,big curvature correlates with big deformation intensity. This correlation implies a NW maximum principal stress that may be caused by the relative convergence of the Philippine Sea Plate and the Euro-Asia Plate.The map of earthquake epicenters (≥M_S 3.0) shows that there are several earthquakes distributed roughly along the SBFZ.Considering the relative intense deformation of SBFZ,we propose that great attention should be paid to the seismic risk of SBFZ.

THE EVOLUTION OF HYDROGEN ISOTOPE IN LOW-MEDIUM TEMPERATURE GEOTHERMAL SYSTEMS OF CONVECTIVE TYPE

LIN Xu-dong, XU Jian-dong

2013, 35(1):  75-84.  DOI: 10.3969/j.issn.0253-4967.2013.01.006

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Low-medium temperature geothermal system of convective type has a very important significance in clarifying the regional tectonic activity,the formation of geothermal resource,as well as water-rock interaction and useful element enrichment mineralization. Water as a heat carrier,its isotopic variation is the premise for studying water-rock interaction and tracing the source of geothermal water. In this article,we have gathered 167 δD data in geothermal water and local cold spring water in China. Then,we overlay the location of geothermal field on the regional active fault system in order to figure out the spatial relationship between geothermal spring and regional active fault.The results show that 1) 91.11% of geothermal water locates near the Quaternary fault; 2) δD value of geothermal water is lower than local cold spring water. This δD variation is further studied in this article. According to kinetic fractionation theory,this phenomenon is caused by the H-D isotopic fraction in water during water recycle in the crust.The mechanism is a process that separates H-D isotopes from each other by their mass during unidirectional processes (water circulation),while the degree of fractionation is dependent on temperature and the routine length. For convection geothermal systems in active tectonic zones,there are plenty of fractures and fissures. In this way,water can make deep circulation in convection geothermal system. During the circulation,the H-D isotopes can gather enough heat quantity and enough routine to fraction. On the basis of above analysis,we have modeled the geothermal water H-D fraction in convection geothermal systems as raised by White (1968).As a secondary reason,the H-D isotopic exchange between water and kaoline/montmorillonite can also reduce the δD in geothermal water.

EFFECT ANALYSIS AND PRELIMINARY ESTIMATION OF VOLCANO LAKE OUTBURST FLOOD MAXIMUM FLOW OF CHANGBAISHAN TIANCHI VOLCANO

LIU Jun-qing, SUN Ji-cai, WU Cheng-zhi, LI Ke

2013, 35(1):  85-91.  DOI: 10.3969/j.issn.0253-4967.2013.01.007

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The active volcano-Changbaishan Tianchi Volcano in China,has an urgent eruption danger at present. There have been several eruptions in the past. In recent years,ground deformation and earthquake monitoring stations were established in the Changbaishan Volcano area,and the monitoring data show that the magma underground has triggered earthquake swarm activities and led to ground deformation. A lot of research results show that Changbaishan Tianchi Volcano is in an early unrest stage at present,the future eruption risk is increasing. The volcano disaster is very complicated.The determinants include volcano eruption pattern, crater position and magma ingredients. To the Changbaishan Tianchi Volcano,once it erupts in the future,in addition to generating volcano mud flow,debris flow and ash cloud,the flooding dam overflow caused will be the most influential and worst secondary disaster. Changbaishan Tianchi Volcano Lake is one of the highest volcano lakes in the world,with a lake area 10km²,depth 371m,water volume 2 billion m³,once it bursts,it will cause huge economic loss and people death to the downstream region. This article elaborates the topography and hydrology and watershed characteristics of Changbaishan Tianchi volcano. Using the hydraulic formula,we estimate the volcano lake dam-break model and analyze maximum volcano lake outburst flood flow and the flood evolution process to downstream area under the different conditions.The conclusion shows that,if the volcano lake dam collapses by half,the Er-Dao town will be flooded,and the downstream Baishan reservoir will suffer a serious threat from the floodwaters.

MEAN STRESS FIELD INFERRED FROM THE TOTAL SEISMIC MOMENT RELEASED BY EARTHQUAKES

SHENG Shu-zhong, WAN Yong-ge, XU Zhi-guo, BU Yu-fei, WU Ye, LI Ying-qiu

2013, 35(1):  92-100.  DOI: 10.3969/j.issn.0253-4967.2013.01.008

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In this paper,we present a method which allows to calculate the mean stress field according to the total seismic moment released by earthquakes.The exact method is as follows: First,we calculate the scalar seismic moment released by each earthquake according to the statistical relationship between earthquake magnitude and its seismic moment; Second,we calculate the seismic moment tensor released by each earthquake according to the relationship between focal mechanism solution and seismic moment tensor; Then,we can get the total seismic moment tensor released in a specific time period of the study area; Finally,we calculate the eigenvector and eigenvalue of the total seismic moment tensor,the obtained eigenvector is corresponding to the mean stress field direction released by the study area. We tested the method by using the synthetic focal mechanism to which random error was added and with the focal mechanism data of Tangshan aftershock zone.The testing results show that,the released stress field of the study area obtained by our method is in consistency with the regional stress field. So our method can be applied to solve regional stress field.The more focal mechanism data used,the more stable the result would be,and closer to the real regional stress field. One of the advantages of this method is that it uses magnitude as the weight of each earthquake,so the contribution difference of the earthquake size in the stress field inversion can be better reflected. Another advantage is that it does not need to know which nodal plane of the focal mechanism is the real fault plane when we calculate stress field.

SEISMIC HAZARD ANALYSIS OF THE SICHUAN-YUNNAN REGION,WESTERN CHINA

WANG Fan, SHEN Zheng-kang, WANG Min, WANG Yan-zhao, TAO Wei

2013, 35(1):  101-112.  DOI: 10.3969/j.issn.0253-4967.2013.01.009

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As the southeastern margin of the Tibetan plateau,the Sichuan-Yunnan region is carved by ample tectonic active faults. Many strong earthquakes have taken place in the past,and some of which resulted in massive damages and great losses of human lives. In this study we attempt to estimate the seismic hazard potential using two different approaches. Our first approach follows Kagan and Jackson(1994)and uses earthquake catalog data to estimate the mid- to long-term spatial probability of strong earthquakes,based on the assumption that earthquake likelihood is proportional to the intensity and quantity of past events. A retrospective test shows that the model offers reasonable ‘forecasts’ statistically over the last 37 years,based on the catalog data of previous 470 years for model constraints. Our second approach is to use secular geodetic strain rate deduced from GPS velocity data to constrain earthquake probability model,assuming that likelihood of strong earthquakes is spatially proportional to the geodetic strain rate. A retrospective test of the model with earthquake occurrence of the past 30 years shows that the model 'forecasted poorly,but did reasonably well when comparing with the catalog data of the past 500 years,suggesting that the geodetic strain rate obtained at the decade scale may still be a good indicator of long-term earthquake activity in the region,but only at a time scale of hundreds of years.

STUDY ON RELOCATION AND ACTIVITY CHARACTERISTIC OF SMALL EARTHQUAKES IN PUBUGOU RESERVOIR AREA

ZHANG Yong-jiu, XIE Rong-hua, ZHANG Zhi-wei, HU Xian-ming

2013, 35(1):  113-124.  DOI: 10.3969/j.issn.0253-4967.2013.01.010

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The small earthquakes in and around Pubugou reservoir area are relocated by the double-difference method,and the earthquake properties of two cluster regions near water area are also analyzed.The 1834 earthquakes in the study area from 14 October 2006 to 31 December 2011 are relocated, and we have gotten 1708 earthquake relocation results eventually,amounting to 93.1% of the total. After the relocation,the RMS average value of arrival time residual decreases from 0.93s to 0.21s,the average error is 0.5km in EW direction,0.6km in NS direction,and 2.9km in vertical direction.The epicenter distribution is more concentrated,and the dominant distribution is also more obvious,the cluster region of small earthquakes distributes in the middle part of reservoir area,near to and downstream of the dam.The average focal depth is 9.2km. Earthquakes with focal depths less than 10km amount to 59% of relocation results,and those within 15km amount to 72%,the deepest focal depth is 33.1km.According to spatial distribution of relocation results,we divide the study area into four main regions (A,B,C and D) to discuss respectively.The evolutions of earthquake activities with time show that the variation of earthquake activities in region C and D is relativity larger than that in region A and B; the earthquakes of region C and D are highly centralized,and the focal depth is obviously shallow. With respect to the origin time of earthquakes,the earthquakes in region A and B occurred randomly in 24 hours of a day,which is accord with the time characteristic of natural earthquakes,while the occurrence time of earthquakes in region C and D had obvious regularity,most of them occurred in daytime,and focused on pre- and post 12'clock at noon and 18'clock in the afternoon.The results of field survey show that the seismic cluster area in region C is in accord with the construction sites of Ya'an-Xichang expressway and new Hanyuan county,and the cluster in region D is in accord with the quarry of Kaergou and Jialiega which are all near the reservoir dam. By synthesis analysis,we think that small earthquakes of region C and D may not be tectonic earthquakes; moreover,most of them occurred before November 2009,a time before the impoundment of Pubugou reservoir. So the earthquakes are not related with the impoundment either,but possibly the explosion ones caused by all kinds of construction.

MULTI-POINT DISLOCATION IN STICK-SLIP PROCESS

LI Pu-chun, LIU Li-qiang, GUO ling-li, LIU Pei-xun

2013, 35(1):  125-137.  DOI: 10.3969/j.issn.0253-4967.2013.01.011

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By using a newly developed distributed multi-channel transient signal acquisition system,the spatial distribution of arrival time and direction of the first motion of the acoustic emissions (AE) along the fault under near field conditions was well studied. With the high frequency strain recording system,the stress distributions along the fault were well characterized and the focal dislocation behavior during stick-slip was studied as well.The experiment was conducted in a biaxial servo-control loading system. Analysis shows that for each sudden stress drop event,the corresponding focal dislocation consists of a few smaller sub-dislocations and each sub-dislocation results in its own AE event and stress change. Besides,it can be proved that each sub-dislocation may correspond to multiple sources rather than point source,the evidences of which can be found in the heterogeneity of the spatial distribution of the first motion and the strain field along fault. Our study indicates that the multi-dislocation during stick-slip under near field conditions is very complicated. By the result of our study,it is more convenient to understand the complication of focal process. Besides,it could provide an evidence for the uncertainty of in-situ earthquake focus and the high contradiction rate of earthquake mechanism solutions.

APPLICATION OF SUB-PIXEL IMAGE CORRELATION TO NEAR FIELD GROUND DEFORMATION MEASUREMENTS OF WENCHUAN EARTHQUAKE

LIU Yun-hua, SHAN Xin-jian, QU Chun-yan, SONG Xiao-gang, ZHANG Gui-fang

2013, 35(1):  138-150.  DOI: 10.3969/j.issn.0253-4967.2013.01.012

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The distribution and characteristic of ground deformation is a key issue in geodesy,which brings insight into the geometry of the ruptured fault and seismic hazard assessment in the future in the surrounding areas. It also provides better constraint conditions for geophysical inversion. Compared with field research,satellite imagery regularly provides detailed and spatially comprehensive images and is a most valuable alternative especially for the study in remote areas. So,observing seismic rupture is urgent after earthquake. InSAR is useful for measuring ground displacement,but the technique has severe limitations that are mainly due to data decorrelation and signal saturation,and it does not generally provide measurements in the near-fault area where large displacements occur. In this paper,the sub-pixel correlation method and SPOT image are used to map the Wenchuan earthquake rupture and to identify the faults activated by the earthquake. A computation is introduced of the inverse projection matrices for which a rigorous resampling is proposed. Image registration and correlation is achieved with an iterative unbiased processor that estimates the phase plane in the Fourier domain for subpixel shift detection,then the earthquake deformation field is derived.The results indicate that the Wenchuan earthquake produced at least surface ruptures on two faults along the Longmenshan Fault,the main rupture named Beichuan-Yinxiu rupture zone(Longmenshan town-Gaochuan in this map)and the secondary rupture named Hanwang rupture zone.The former is characterized by dextral-slip thrusting with a horizontal displacement of 4～6m in average and a dextral-slip displacement of 1～3m near Gaochuan town.The latter is characterized by pure thrusting,with horizontal displacement 1～2m in average. There is no obvious ground rupture along Wenchuan-Maoxian Fault.The research indicates that sub-pixel correlation using optical image can be a powerful complement to differential radar interferometry,which can measure ground displacement near the fault zone.The study also shows that earthquake displacement fields can be calculated by remote sensing technology.The surface rupture can be traced and the meizoseismal area can be located by this method. Compared with field research,satellite imagery regularly provides detailed and spatially comprehensive images and is a most valuable alternative especially for the study in remote areas.

THE YUSHU EARTHQUAKE TRIGGERED LANDSLIDE HAZARD EVALUATION BASED ON WEIGHT OF EVIDENCE METHOD

XU Chong, XU Xi-wei, YU Gui-hua

2013, 35(1):  151-164.  DOI: 10.3969/j.issn.0253-4967.2013.01.013

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2036 landslides were triggered by the 2010 Yushu earthquake from aerial photographs and remote sensing images interpreting,verified by selected field checking. In this paper,twelve factors that influence landslide occurrence,including distance from main co-seismic surface ruptures,peak ground acceleration (PGA),elevation,slope angle,slope aspect,slope curvature,slope position,distance from drainages,lithology,distance from faults,distance from roads,normalized difference vegetation index (NDVI),are selected as landslide hazard evaluation factors. Two types of landslide hazard index map are derived using two "weight of evidence" methods based on Geographical Information Systems (GIS) technology.The success rate of Add-"weight of evidence" method is 80.32%,and the success rate of Subtract-"weight of evidence" method is 80.19%,both are satisfactory.The resulting hazard evaluation maps are divided into five categories, i.e.extremely high,high,moderate,low,and extremely low,respectively.The landslide hazard maps can be used to identify and delineate unstable hazard-prone areas. It can also help planners to choose favourable locations for development schemes,such as infrastructures,buildings,road construction,and environmental protection.

A PILOT SURVEY AND PRELIMINARY ANALYSIS OF EARTHQUAKE DISASTER COGNITIVE LEVEL AMONG THE POPULACE IN BEIJING

WEI Ben-yong, SU Gui-wu, CHEN Biao, ZHANG Wen-jia

2013, 35(1):  165-176.  DOI: 10.3969/j.issn.0253-4967.2013.01.014

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This paper analyzes the features of public earthquake disaster cognition by the methods of questionnaire survey in Beijing. The results show that at present,the public cognitive ability of earthquake disaster in the studied area is not ideal and part of the populace could not effectively identify earthquake rumors in Beijing. However,most of the public could accurately master the knowledge and skills of the emergency evacuation in and recue after an earthquake in Beijing. Public awareness of protection against and mitigation of earthquake disasters are continually enhanced. The public hope to master more knowledge of earthquake prevention and disaster reduction. Moreover,most of public could realize the importance of self-aid and mutual aid among neighbors,communities and departments. The public features of earthquake disaster cognition show an obvious group difference in Beijing.the cognitive level of female is inferior to that of the male in Beijing,and public cognitive level shows a gradually increased tendency with age. The public education levels have significant effect on their cognitive levels. The more the knowledge gained by the populace,the higher the cognitive levels are. Furthermore,the public education level might be the basic influencing factor. Except for strengthening the publicity of the knowledge and skills of earthquake prevention and disaster reduction by traditional electronic media,the school education and modern communication,such as internet,cell phone,are also the effective publicity ways,to which more attention should be paid. In addition,due to the limited conditions,there are still rooms to improve in this study,in which the sampling method is the main one. Compared to the probability sampling,the sample representation of non-probability sampling used in this paper might be insufficient,which might inevitably have some effects on the results of this study.

Monograph review

⁴⁰Ar/³⁹Ar GEOCHRONOLOGY OF SUPERGENE ALUNITE-GROUP MINERALS

YANG Jing, ZHENG De-wen, WU Ying

2013, 35(1):  177-187.  DOI: 10.3969/j.issn.0253-4967.2013.01.015

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Recently the successful application of laser heating ⁴⁰Ar/³⁹Ar dating to supergene alunite-group minerals demonstrates the applicability of the method to dating minerals existing in the oxidation zones of sulfur rich ore deposits. Laser-heating ⁴⁰Ar/³⁹Ar method not only reduces the amount of samples,but also the system background level; In addition,⁴⁰Ar/³⁹Ar step-heating dating method can test for the presence of hypogene contaminants,the excess/inherited Ar,and the multiple generations of supergene minerals. Although problems remain in isotopic dating of supergene alunite-group minerals,the systematic sampling and reasonable analysis process,combined with a variety of detection methods,can yield meaningful weathering ages,which will provide a new approach for the research on the timing of continental weathering,the formation of oxidization zones,and climatic desiccation of Northwest China.