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121.
AbstractDuring the past 50 years, many geological and ore-deposit investigations have led to the discovery of the Fe–P–(Ti)-oxide deposits associated with mafic–ultramafic–carbonatite complexes in the Kuluketage block, northeastern Tarim Craton. In this paper, we discuss the genetic and ore-forming ages, tectonic setting, and the genesis of these deposits (Kawuliuke, Qieganbulake and Duosike). LA-ICP-MS zircon U–Pb dating yielded a weighted mean 206Pb/238U ages of 811?±?5?Ma, 811?±?4?Ma, and 840?±?5?Ma for Kawuliuke ore-bearing pyroxenite, Qieganbulake gabbro and Duosike ore-bearing pyroxenite, respectively. The CL images of the Kawuliuke apatite grains show core–rim structure, suggesting multi-phase crystallisation, whereas the apatite grains from Qieganbulake and Dusike deposits do not show any core–rim texture, suggesting a single-stage crystallisation. LA-ICP-MS apatite 207Pb-corrected U–Pb dating provided weighted mean 206Pb/238U ages of 814?±?21?Ma and 771?±?8?Ma for the Kawuliuke ores, and 810?±?7?Ma and 841?±?7?Ma for Qieganbulake and Duosike ores, respectively. The core–rim texture in apatite by CL imaging as well as two different ore-forming ages in the core and rim of the apatite indicate two metallogenic events for the Kawuliuke deposit. The first metallogenic period was magmatic in origin, and the second period was hydrothermal in origin. The initial ore-forming age of the Kawuliuke Fe–P–Ti mineralisation was ca 814?Ma and the second one was ca 771?Ma. On the other hand, the ore-forming ages of the Qieganbulake and Duosike deposits were ca 810?Ma and ca 841?Ma, respectively. Qieganbulake and Duosike deposits were of magmatic origin. Combined with previous geochronological data and the research on the tectonic background, we infer that the Kawuliuke, Qieganbulake and Duosike Fe–P–(Ti)-oxide deposits were formed in a subduction-related tectonic setting and were the product of subduction-related magmatism. 相似文献
122.
The consequences of wildfires are felt in susceptible communities around the globe on an annual basis. Climate change predictions in places like the south-east of Australia and western United States suggest that wildfires may become more frequent and more intense with global climate change. Compounding this issue is progressive urban development at the peri-urban fringe (wildland–urban interface), where continued infrastructure development and demographic changes are likely to expose more people and property to this potentially disastrous natural hazard. Preparing well in advance of the wildfire season is seen as a fundamental behaviour that can both reduce community wildfire vulnerability and increase hazard resilience – it is an important element of adaptive capacity that allows people to coexist with the hazardous environment in which they live. We use household interviews and surveys to build and test a substantive model that illustrates how social cohesion influences the decision to prepare for wildfire. We demonstrate that social cohesion, particularly community characteristics like ‘sense of community’ and ‘collective problem solving’, are community-based resources that support both the adoption of mechanical preparations, and the development of cognitive abilities and capacities that reduce vulnerability and enhance resilience to wildfire. We use the results of this work to highlight opportunities to transfer techniques and approaches from natural hazards research to climate change adaptation research to explore how the impacts attributed to the social components of social–ecological systems can be mitigated more effectively. 相似文献
123.
Statistical estimation of age of40Ar/40K ratios may be considered a result of convolution of uniform and normal distributions with different weights for different minerals. Data from Gul'shad Massif (Nearbalkhash, Kazakhstan, USSR) indicate that40Ar/40K ratios reflecting the intensity of geochemical processes can be resolved using convolutions. Loss of40Ar in bioties is shown whereas hornblende retained the original content of40Ar throughout the geological history of the massif. Results demonstrate that different estimation methods must be used for different minerals and different rocks when radiometric ages are employed for dating. 相似文献
124.
A Diagnostic Study of Explosive Development of Extratropical Cyclone over East Asia and West Pacific Ocean 总被引:9,自引:0,他引:9
ADiagnosticStudyofExplosiveDevelopmentofExtratropicalCycloneoverEastAsiaandWestPacificOcean¥JiaYiqin(贾逸勤)andZhaoSixiong(赵思雄)(... 相似文献
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福州盆地及其周围地区地壳深部结构与构造的初步研究 总被引:20,自引:4,他引:20
1986-1988年,福建省地震局在福州盆地及其周围地区完成了五条地震测深剖面:宁德-永春剖面;洪懒-宁德剖面;莲峰-福州(尚干)剖面;南平-永泰-平潭非纵剖面;并在宁德-古田-嵩口首次试验扇形剖面观测系统,结果表明,扇形剖面对确定断裂是有效的. 根据对地震波走时的正、反演计算,用理论地震图和射线追踪方法进一步修改和完善,得到了福州盆地及其周围地区地壳深部为高、低速相间的速度分布特征.地壳介质速度为6.40km/s,在中地壳普遍发育一层速度为5.80-5.90 km/s、厚度约5.0 km的低速层.Moho面深度30-33 km,福州盆地为一Moho面隆起区,隆起幅度达3.0 km.北西向断裂发育,其中,闽江断裂在纵剖面和扇形剖面均有明显的反映,并切割到Moho面2.0-3.0 km. 反射波谱频方法计算得到福州盆地地壳Q值仅120-150,比邻近地区明显偏低,中地壳低速层Q值为40-80,是一典型的低速-高导-低Q(高衰减)结构层,此层上界面埋深14-15 km,与居里面埋深较一致.这些结果为福州地区的地热资源远景预测和开发提供了地壳深部结构和某些地球物理场背景. 相似文献
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Ross M. Renner 《Mathematical Geology》1991,23(4):549-563
Given a compositional dataset in the absence of any prior information on any mixing process which may have formed it, a complete analysis of mixtures determines three distinct types of estimates in order. These are: (i) the estimate of the number of endmembers or fixed source compositions, of which all the sample compositions of the dataset must be approximate mixtures; (ii) the estimated compositions for each of these chosen number of endmembers; and (iii) the estimated contributions of each of these endmember estimates to each sample. Traditionally, the estimate for the number of endmembers has been assessed either by mapping or by inspection of the coefficients of determination between the observed and estimated variables. Mapping entails the plotting on a map of the region from which the samples were taken, either the contours of the contributions of each endmember to each sample, or some other portrayal of the distribution of endmember abundances. Because it requires the complete analysis, assessment by this method is too elaborate except for final confirmation and display. Alternatively, choosing a number of endmembers, which result in suitability high coefficients of determination for all or most variables, may account for elements which are not part of the conjectured mixing process or, worse, may result in the identification of endmembers which may never in fact have existed. Such an error is similar to overspecifying a multiple regression model. So, the obvious starting point from which to assess the validity, or otherwise choice of endmember numbers, is to examine the matrix of residuals. The differences between the logratio-transformed observed and estimated data form an array of residual logratios. A linear combination of these may be formed for each sample, which, under a random perturbation assumption, should follow a univariate normal distribution. Whether or not this scalar is normal can be readily tested. It can also be examined graphically for such desirable qualities as symmetry when the test for normality may be too severe. This procedure is employed to assess the decompositions of the U.S.G.S. Mid-Pacific data and the Nazca Plate Surface sediments.This paper was presented at the 18th Geochautauqua, Newark, Delaware, 13–14 October 1989. 相似文献
130.
滇西实验场两次中强地震前后尾波衰减的区域特征分析 总被引:9,自引:0,他引:9
本文在地方震尾波散理论模式的基础上,研究了1992年12月发生在滇西地震预报实验场永胜期纳地区的两次Ms5.4,5.1地震前后的序列地震尾波振幅衰减率β和尾波Q^-1值随时间和空间变化的衰减特征。结果表明,尾波衰减率在空间分布上表现出明显的小区域范围的非均匀性,在主震震中附近的近场区内,主震期间的β值是0.0076s^-1,相应的Qc^-1值是0.0056;余震期间的β值是0.0209s^-1,相 相似文献