On the Lu-Hf Isotope Geochemistry of Silicate Rocks   总被引：9，自引：0，他引：9  

Janne Blichert-Toft 《Geostandards and Geoanalytical Research》2001,25(1):41-56

This paper reviews the history (TIMS, hot‐SIMS, MC‐ICP‐MS), significance, geochemical behaviour and current uncertainties (λ¹⁷⁶ Lu, Hf‐Nd Bulk Silicate Earth) surrounding the Lu‐Hf isotope system, and thus marks two decades of its application to geochemical problems. An appendix further presents (a) improvements to the original chemistry protocol of Blichert‐Toft et al. (1997) for application to Mg‐rich samples and (b) a compilation of previously published and new Hf isotope determinations by MC‐ICP‐MS for a set of international rock reference materials. Prior to the advent of multiple‐collector plasma source mass spectrometry (MC‐ICP‐MS), routine analysis of the Lu‐Hf isotope system developed only slowly because of the extreme difficulty of measuring Hf isotope compositions with thermal ionisation mass spectrometry, caused by the very high first ionisation potential of Hf. However, Hf isotope compositions can be measured relatively easily using MC‐ICP‐MS and this new technique now provides reproducible measurements at high precision regardless of the matrix from which Hf is separated. Of the commonly used long‐lived radiogenic isotope systems, only the Sm‐Nd and Lu‐Hf isotope systems are unaffected by parent/daughter fractionations related to volatile nebular processes and core formation. While other systems (Rb‐Sr, U‐Th‐Pb, Re‐Os) may also be used to investigate the chemical evolution of the Earth, Moon, Mars and parent bodies of differentiated meteorites, the larger uncertainties in their bulk chemical and isotopic values limit their application to determine geochemical budgets and assess planetary mantle‐crust evolution. In the study of garnet‐bearing rocks, both for dating purposes and as an isotopic tracer for source provenance and mantle processes, the Lu‐Hf isotope system likewise is of major interest because of the high partition coefficient of Lu compared to Hf for garnet with respect to other minerals. Furthermore, the larger Lu/Hf fractionation compared to Sm/Nd during melting beneath ridges produces proportionally higher Lu/Hf in the residue and faster in‐growth of a radiogenic Hf isotopic signature (compared to Nd), which may help shed light on the dynamics of mantle melting. While the chemistry protocol and mass spectrometric technique for high‐precision Lu‐Hf isotope analysis have been resolved in satisfactory ways over the past five years, more accurate determination of the decay constant for ¹⁷⁶ Lu, at present known with a precision of only about 4%, still needs to be completed and a consensus reached on which value to use for future Lu‐Hf isotope studies. Although the current combined Lu‐Hf and Sm‐Nd Bulk Silicate Earth parameters are plagued by possible incompatibilities in chondrite selection and potential interlaboratory biases, a more accurate set of values may not be readily established owing to heterogeneities in the isotopic composition of chondrites that far exceed present analytical accuracy.  相似文献   

Present-day stress field and deformation in eastern Austria     

J. Reinecker  W. A. Lenhardt 《International Journal of Earth Sciences》1999,88(3):532-550

 We analysed fault plane solutions and borehole breakouts in the eastern part of the Eastern Alps and found a heterogeneous stress field which we interpret as a transition zone of three different stress provinces: the western European stress province with NW to NNW S_H orientation and mainly strike-slip faulting regime; the Adriatic stress province with a radial stress pattern and thrust faulting to strike-slip faulting regime; and the Dinaric-Pannonian stress province with NE S_H orientation and strike-slip faulting regime. The western Pannonian basin seems to be a part of the transition zone with WNW to NW S_H orientation. A stress regime stimulating strike-slip faulting prevails in the Eastern Alps. The south Bohemian basement spur as a major tectonic structure with a high rheological contrast to surrounding units has a strong influence on the stress field and exhibits the highest seismicity at its tip due to stress concentration. From a constructed vertical stress orientation profile we found stress decoupling of the Northern Calcareous Alps from the underlying European foreland. Both the Molasse and the Flysch-Helvetic zone are considered as candidates for decoupling horizons due to stress orientation observations and due to their rheological behaviour. From seismological and rheological data, we suggest a horizontal stress decoupling across the Eastern Alps caused by a weakened central Alpine lithosphere. Received: 3 July 1998 / Accepted: 4 April 1999  相似文献   

Rayleigh wave dispersion equation for a layered spherical earth with exponential function solutions in each shell     

Swarn Arora  S. N. Bhattacharya  M. L. Gogna 《Pure and Applied Geophysics》1996,147(3):515-536

We consider the second-order differential equations ofP-SV motion in an isotropic elastic medium with spherical coordinates. We assume that in the medium Lamé's parameters , r ^p and compressional and shear-wave velocities , r, wherer is radial distance. With this regular heterogeneity both the radial functions appearing in displacement components satisfy a fourth-order differential equation which provides solutions in terms of exponential functions. We then consider a layered spherical earth in which each layer has heterogeneity as specified above. The dispersion equation of the Rayleigh wave is obtained using the Thomson-Haskel method. Due to exponential function solutions in each layer, the dispersion equation has similar simplicity, as in a flat-layered earth. The dispersion equation is further simplified, whenp=–2. We obtain numerical results which agree with results obtained by other methods.  相似文献   

A Gravel Outwash/Deformation till Continuum, Skalafellsjokull, Iceland     

David J. A. Evans 《Geografiska Annaler: Series A, Physical Geography》2000,82(4):499-512

A stratigraphic sequence exposed by river erosion in the foreland of Skalafellsjokull, southern Iceland, displays five lithofacies documenting glaciofluvial deposition followed by glaciotectonic disturbance and subglacial deformation. Lithofacies 1a and 1b are glaciotectonically thrust glaciofluvial outwash and subglacial deformation till respectively from an early advance of Skalafellsjokull. Lithofacies 2, massive gravels and clast–supported diamictons, documents the deposition of glaciofluvial outwash in the proto–River Skala prior to overriding by Skalafellsjokull during the Little Ice Age. During overriding, lithofacies 2 was glaciotectonically disturbed and now possesses the clast fabric and structural characteristics of G _B (non–penetratively deformed) and G _A (penetratively deformed) type glaciotectonites. A shear zone separates lithofacies 2 from overlying lithofacies 3, the latter possessing the clast fabric signature of a D _A (dilatant) type deformation till although it was originally deposited as a discontinuous diamicton within a glaciofluvial sequence, probably as a hyperconcentrated flow, and appears to have been at least partially derived from underlying materials by glaciotectonic cannibalization. Lithofacies 4 is a glaciofluvial deposit comprising two coarseningupward sequences of gravel and diamicton. These facies have been overprinted with G _B glaciotectonite and D _A?B (dilatant to non–dilatant) deformation till structures and clast fabrics recording a vertical progression towards more pervasively deformed material. The sequence is capped by lithofacies 5, a two–tiered deformation till possessing the characteristics of D _A and D _B horizon subglacial tills previously reported from Icelandic glacier snouts. The whole sequence comprising lithofacies 2–5 represents a gravel outwash/deformation till continuum displaying variable strain signaturesproduced in response to stress induced by the overriding of Skalafellsjokull during the Little Ice Age. These signatures are dictated by the sediment rheology and a vertical strain profile for the sediment pile during glacier overriding is reconstructed.  相似文献   

黄河流域水资源利用与经济增长脱钩及影响因素分解     

李汝资  白昳  周云南  黄淑琪  晏振宁  李英姿  赵宏波 《地理科学》2023,43(1):110-118

水资源是黄河流域生态保护和高质量发展的最大刚性约束,识别流域水资源利用变化驱动因素具有重要意义。首先从结构视角测度黄河流域水足迹变化,进而基于Tapio脱钩模型与Kaya-LMDI分解模型,解析水足迹与经济增长脱钩状态,并从技术效应、结构效应、规模效应、禀赋效应、城市化效应和人口效应识别水资源利用变化驱动因素。研究发现：(1)黄河流域水足迹总体呈现上升趋势,农业水足迹占比高达85%,用水结构与产业结构倒挂问题突出。(2)黄河流域上下游水资源量与水足迹空间分布不匹配,中下游面临更严重水资源约束。(3)水足迹与经济增长关系主要表现为弱脱钩,但2015—2019年各省区开始向强脱钩转变。(4)规模效应、城市化效应和人口效应对水足迹变化起拉动作用,技术效应、结构效应和禀赋效应对水足迹变化起抑制作用,但仍有提升潜力,各省区影响因素存在一定差异。为此,需要强化水资源利用技术研发与推广,推动农业集约式发展,提升农业用水效率,进一步优化产业结构和新型城镇化建设,缓解水资源约束困境,推动黄河流域经济高质量发展。  相似文献   

我国城镇化对二氧化碳排放的影响机理研究     

胡雷 《气候变化研究进展》2016,12(4):341-347

本文首先从规模、结构和效率3个方面在理论上分析我国城镇化对二氧化碳排放的影响机理。并利用1978-2012年的数据,采用对数迪氏平均指数分解方法（LMDI）量化分析规模效应、结构效应和技术效应的影响程度。结果表明：城镇化导致的经济增长是人均二氧化碳排放增加的主要拉动因素;而城镇化过程中结构调整是人均二氧化碳排放的主要拉低因素;城镇化过程中技术效应拉低了人均二氧化碳的排放,但与结构效应相比影响效果较小。研究认为：城镇化带来的结构变化的影响越来越重要,成为降低碳排放的最大因素,目前技术效应正在发挥作用,但是作用有限,如果要实现低碳城镇化,需要提高能源使用效率来发挥技术效应的作用。  相似文献   

走滑断裂活动导致地应力解耦的机理研究——以龙门山断裂带东北段为例     

丰成君  张鹏  戚帮申  郭长宝  孟静  孙东生  王苗苗  牛琳琳  谭成轩  陈群策 《大地测量与地球动力学》2017,37(10):1003-1009

2008年汶川MS8.0地震后,沿龙门山断裂带系列水压致裂地应力测量结果表明,断裂带东北段(茂县-绵竹连线东北侧)北川、平武及广元等地浅表层最大主应力方向与区域应力场相比发生了25°~69°不等的偏转,亦称地应力解耦。初步分析认为,龙门山断裂带东北段的右旋走滑活动直接导致了区域内最大主应力方向的解耦,且最大主应力方位向偏转角度与断裂右旋走滑活动量正相关。为合理解释这一现象,探讨走滑断裂活动导致地应力解耦的机理,本文采用二维有限元数值模拟方法,选取汶川MS8.0地震断裂(龙门山中央断裂)上的同震右旋走滑位移作为边界条件,首先模拟了龙门山断裂带东北段右旋走滑活动产生的扰动应力特征,之后结合断裂带附近典型钻孔地应力测量结果,叠加该扰动应力作用,从力学机理上深入剖析断裂右旋走滑活动产生的扰动应力对区域应力场(或初始应力场)的影响,并对其附近不同构造部位最大主应力方向偏转现象进行定量解释。初步结果表明：1) 走滑断裂活动导致地应力解耦主要是通过断裂滑动产生的扰动应力对区域应力场的附加影响实现的;2) 在固定的断裂活动长度和摩擦强度情况下,走滑断裂活动导致区域最大主应力方向偏转角度基本与活动断裂走滑位移量呈正比;3) 受汶川MS8.0地震影响,龙门山断裂带大致以茂县-绵竹为界,西南侧的宝兴-映秀-汶川一带最大主应力方向偏转角度很小,基本与区域应力场一致,而东北侧的北川-平武-广元一带则发生角度不等的偏转,3个地区最大主应力方向平均偏转角度分别为65°、56°和29°,该角度与龙门山断裂带东北段同震右旋走滑位移量呈正相关。  相似文献   

测震台站综合防雷系统建设及效能评价   总被引：2，自引：0，他引：2       下载免费PDF全文

瞿旻  霍祝青  戴波  单菡  王大伟 《地震工程学报》2015,37(2):619-622,628

介绍雷害对测震台站的危害方式,总结测震台站的综合防雷基本措施,包括地网改造、配电防雷、信号与通信防雷、布线规划与整理,创新地提出特定条件下安装退耦器以提高防雷效果。通过对比计算台基噪声与观测系统标定结果,研究综合防雷系统接入测震台站观测系统后对数据质量的影响,以进行防雷效能评价。  相似文献   

2000—2019年江西省能源消费碳排放变化及其影响因素          下载免费PDF全文

陈燕玲  王投婧  占明锦  秦建成 《气象与减灾研究》2022,45(1):38-45

基于能源消耗数据,采用IPCC碳核算方法和LMDI分解模型,探讨了2000—2019年江西省一次能源消费碳排放的变化及其主要影响因素,并通过Tapio脱钩模型进一步分析了经济增长与能源碳排放脱钩特征。结果表明： 1） 一次能源碳排放量整体呈上升趋势,碳排放强度总体呈下降趋势,其中2015年以后碳排放量年均增长速度放缓、碳排放强度下降速度加快。2） 对碳排放量增加起促进作用的因素为人口效应、经济产出效应和能源结构效应,其中经济产出效应的作用最为显著;起抑制作用的要素为能源强度效应,能源替代效应不明显。与2000—2015年仅能源强度效应使碳排放量下降的情况不同,2015—2019年能源强度效应、能源替代效应和能源结构效应均使碳排放量下降,其中能源强度效应贡献率比2000—2015年高3倍。3） 经济增长与能源消费碳排放量以弱脱钩为主,其中2016—2019年脱钩弹性呈逐渐减小趋势。  相似文献   

长三角城市经济增长与资源环境压力的脱钩效应     

胡美娟  孙萍  李在军  侯兵 《世界地理研究》2022,31(3):538-548

实现资源环境压力与经济增长的有效脱钩是经济、资源、环境、社会、人口等要素协调可持续发展的重要途径。在构建资源环境压力评价指标体系的基础上,运用脱钩理论、结构分解模型分析2000—2017年长三角地区城市经济增长与资源环境压力脱钩关系及驱动效应,以期促进长三角区域一体化发展与生态文明建设进程。研究发现：①长三角城市经济增长整体尚未完全摆脱“自然消耗增加型”模式,且区域内部城市差异较大,大部分发达城市人均资源环境压力持续降低,其它城市资源环境压力仍随经济增长而加剧;②随着时间的延续,整体上大部分城市的经济增长速度快于资源环境压力增速,全区以弱脱钩类型占绝对优势,强脱钩区域范围先扩大后缩小,中心地区的城市实现了良好的脱钩状态,仅少数边缘地市资源环境压力依然呈现较快增长趋势,未实现有效脱钩;③结构分解模型表明经济增长效应是资源环境压力增加的直接效应,且边缘欠发达城市的经济驱动效应强于核心发达城市,而经济发达城市的人口驱动效应高于欠发达城市,技术效应驱动了资源环境压力的明显下降,总体呈现出南高北低的分布格局。  相似文献