Crustal structure of the Ruby Mountains and southern Carlin Trend region, Nevada, from magnetotelluric data     

Philip E. Wannamaker  William M. Doerner 《Ore Geology Reviews》2002,21(3-4)

We have collected about 150 magnetotelluric (MT) soundings in northeastern Nevada in the region of the Ruby Mountains metamorphic core complex uplift and southern Carlin mineral trend, in an effort to illuminate controls on core complex evolution and deposition of world-class gold deposits. The region has experienced a broad range of tectonic events including several periods of compressional and extensional deformation, which have contributed to the total expression of electrical resistivity. Most of the soundings reside in three east–west profiles across increasing degrees of core uplift to the north (Bald Mountain, Harrison Pass, and Secret Pass latitudes). One short cross-line was also taken to assess an east–west structure to the north of the northern profile. Model resistivity cross-sections were derived from the MT data using a 2-D inversion algorithm, which damps departures of model parameters from an a priori structure. Geological interpretation of the resistivity combines previous seismic, potential field and isotope models, structural and petrological models for regional compression and extension, and detailed structural/stratigraphic interpretations incorporating drilling for petroleum and mineral exploration. To first order, the resistivity structure is one of a moderately conductive, Phanerozoic sedimentary section fundamentally disrupted by intrusion and uplift of resistive crystalline rocks. Late Devonian and early Mississippian shales of the Pilot and Chainman Formations together form an important conductive marker sequence in the stratigraphy and show pronounced increases in conductance (conductivity–thickness product) from east to west. These increases are attributed to graphitization caused by Elko–Sevier era compressional shear deformation and possibly by intrusive heating. The resistive crystalline central massifs adjoin the host stratigraphy across crustal-scale, steeply dipping fault zones. The zones provide pathways to the lower crust for heterogeneous, upper crustal induced, electric current flow. Resistive core complex crust appears steeply bounded under the middle of the neighboring grabens and not to deepen at a shallow angle to arbitrary distances to the west. The numerous crustal breaks imaged with MT may contribute to the low effective elastic thickness (T_e) estimated regionally for the Great Basin and exemplify the mid-crustal, steeply dipping slip zones in which major earthquakes nucleate. An east–west oriented conductor in the crystalline upper crust spans the East Humboldt Range and northern Ruby Mountains. The conductor may be related to nearby graphitic metasediments, with possible alteration by middle Tertiary magmatism. Lower crustal resistivity everywhere under the profiles is low and appears quasi one-dimensional. It is consistent with a low rock porosity (<1 vol.%) containing hypersaline brines and possible water-undersaturated crustal melts, residual to the mostly Miocene regional extension. The resistivity expression of the southern Carlin Trend (CT) in the Pinon Range is not a simple lineament but rather a family of structures attributed to Eocene intrusion, stratal deformation, and alteration/graphitization. Substantial reactivation or overprinting by core complex uplift or Basin–Range extensional events seems likely. We concur with others that the Carlin Trend may result in part from overlap of the large Eocene Northeast Nevada Volcanic Field with Precambrian–Paleozoic deep-water clastic source rocks thickening abruptly to the west of the Pinon Range, and projecting to the north–northwest.  相似文献   

Milan: The city of constant renewal     

Anna Trono  Maria Chiara Zerbi 《GeoJournal》2002,58(1):65-72

Traditional models of urban development are no longer adequate to describe current metropolitan transformations. These are now at the centre of a debate concerning management and administration. In Italy, delays in resolving problems of urban and metropolitan government, despite the legal framework provided by Law 142/90, have weighed heavily on the larger urban areas of the country: Rome, Naples, Milan, which have not been able to tackle the issue of metropolitan government. Recent legislation, while not providing a pre-defined institutional solution, allows separate administrative districts to collectively establish metropolitan institutions of `variable geometry'. The Milan urban area is not one city, but a system of mutually-dependent cities, linked to each other and the rest of the world by a transport network still requiring much investment. The vitality of its economic structure (especially its small firms) is held back by seriously inadequate infrastructure and low external economic efficiency. The provincial capital may boast `historic centrality' but the most interesting potential for development is to be found on the periphery and in the administrative districts immediately surrounding it, in the recovery of derelict industrial areas and dormitory towns established in the 1950s and 1960s, especially to the north. Recovery of derelict areas, green areas, and better transport links within the urban area and with the outside world are the key elements in the reorganization of `Greater Milan'. In this situation of rapid transformation the most appropriate political strategies involve negotiated planning. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

在"数字国土工程"中我区地学数据库建设的现状及发展趋势     

张梅  胡凤翔 《内蒙古地质》2002,(2)

近年来,在国土资源部的高度重视下,我区相继建立了一系列地学数据库。这些地学数据库的建立不仅为地矿行业提供了基础性数据,也加速了"数字国土工程"和国土资源信息化建设的步伐。随着信息技术的高速发展,利用地理信息系统(GIS)将各类地学数据有机地结合起来,形成地学数据应用与管理系统,最终通过网络服务于社会,必将是各类地学数据发展的必然趋势。  相似文献   

Impact of oasis establishment on underground environment in salinized sandy lands     

赵元杰  张鹤年  买买堤艾堤  孙永强 《中国科学D辑(英文版)》2002,45(Z1)

The salinized sandy lands are the important reclaimable reserve wastelands in thesouth area of the Xinjiang Uygur Autonomous Region of China. But it is necessary that the eco-logical environment of the area is not destroyed by action of oasis development. The main factor tohinder oasis development is land salinization. Rational oasis establishment rebuilds wastelandswith lower productivity and utilization efficiency for the growth of agriculture, forestry, and stock raising. The results of surveying sub-soil environment of Aimugaike. Awati oasis in Hotian County ofthe Xinjiang Uygur Autonomous Region show that the underground water and soil environment arenot deteriorated under the rational management and administration, which could be coordinatedfor obtaining economic and environmental benefit. During the oasis establishment period from1997 to 1999, the plowland area has reached 166.7 hm2, and the seed cotton yield per unit areahas reached 2250 kg @ hm-2, the area of timber forest and active sand break forest has reached 20hm2, the area of fruit trees is 71.5 hm2; and the soil moisture has decreased from 22.07% to18.12%. In the first year of oasis establishment, the soil type has changed salt soil into light saltsoil, in the second year the soil has been out of salt harm; and the content of soil organic matter intopsoil has increased obviously.  相似文献   

Water availability for the greening of Kuwait     

Majda Khalil Suleiman  Mahdi Saleh Abdal 《Limnologica》2002,32(4):322-328

Water resources for agricultural development and landscape enhancement in Kuwait are very scarce; the quality is saline (brackish), and the soil texture is sandy, incapable of holding nutrients and moisture. Most of the rainfall in Kuwait either evaporates due to the high temperatures or percolates through the soil. The rainfall is not sufficient to recharge the underground water supply. A variety of alternative water sources have been studied, including seawater desalination and wastewater treatment. Wastewater treatment proved to be convenient due to the relatively low salinity detected in the treated water. Furthermore, the amount of wastewater is expected to increase as more residential areas are connected to the sewage system as the population increases.

The development of a greenery plan for Kuwait requires intensive water management. This goal can be achieved through manpower training in landscape development, selection of plants tolerant to arid environments, usage of appropriate irrigation and drainage systems, promotion of greenery programs within public and the governmental agencies for their direct participation in urban area beautification, and extension of wastewater treatment techniques.  相似文献   

天山西部中山带积雪变化趋势与气温和降水的关系——以巩乃斯河谷为例   总被引：12，自引：9，他引：12  

张丽旭  魏文寿 《地理科学》2002,22(1):67-71

根据位于巩乃斯河谷的天山积雪雪崩研究站近30年来的年最大雪深、月平均气温、月降水量观测记录，用平均差值法、最小二乘法、自回归滑动平均法检验了天山西部中山带积雪、冷季降水、冷季平均气温的变化趋势，结果表明，天山西部中山带积雪呈增加趋势，近30年来年平均增加1.43%，与青藏高原、南极大陆及格陵兰冰盖表面积雪积累增加相一致。天山西部中山带冷季气温和降水的变化趋势也是增加的，其中冷季降水平年平均增加0．12％，而冷季气温升高了0．8℃，积雪与冷季气温之间存在着弱的负相关关系，而与冷季降水呈显著的正相关关系。积雪的增加主要是因为气候变暖引起的冷季降水的增加对积雪增加的贡献大于由于冷季气温升高而造成积雪减少的贡献的结果。  相似文献   

战略环境评价若干问题研究   总被引：7，自引：2，他引：7  

董德明  赵文晋  王宪恩  房春生 《地理科学》2002,22(5):615-618

分析了传统环境影响评价制度的不足，回顾了战略环境评价的研究与实践进展，阐述了战略环境评价与环境可持续发展的关系，并对以实现环境可持续发展为目标的战略环境评价体系所存在的问题进行了分析。  相似文献   

河南省区域经济发展差异及其时空格局研究   总被引：63，自引：1，他引：63  

胡良民  苗长虹  乔家君 《地理科学进展》2002,21(3):268-274

河南省是我国第一人口大省。 80年代以来 ,经济迅速发展 ,总量水平在全国的位次不断上升 ,但区域经济差异也发生了显著变化。本文以计量统计分析为基础 ,探讨了河南省区域经济差异变化的时间特征、区域经济差异的空间格局及其变化过程 ,分析了区域经济发展与区域环境条件之间的关系 ,提出了调控河南省区域经济差异的政策建议。  相似文献   

河北南部地区资源、环境、发展初析   总被引：3，自引：0，他引：3  

吴凯 《地理科学进展》2002,21(5):477-483

河北南部地区山前平原区农业气候条件适于夏玉米的生长 ,黑龙港地区适于棉花的生长。本区水资源匮乏 ,地下水超采严重。浅层地下水超采模数为 8.0 1× 1 0 4 m3/( km2 ·a) ,深层地下水为 2 .5 8× 1 0 4 m3/( km2·a)。全区水资源利用的综合边际效益以廊坊市最高 ( 2 6.68元 /t) ,保定市最低 ( 1 4.85元 /t) ,两者之比为 1 .80。区内地下水降落漏斗与地面沉降等环境地质灾害频繁 ,1 998年浅层地下水漏斗区面积为 0 .5 4× 1 0 4 km2 ,深层地下水为 1 .5 9× 1 0 4 km2。地下水、粮食和蔬菜受到农药残留、过量化肥的污染。本区 2 0 1 0水平年外流域调水将占可供水量的 2 3.9% ,但缺水率仍达 36.2 %。若全区通过发展工程节水 (提高综合节水率 3.2 % )、实施适水种植 (冬小麦播种面积下调 7% ) ,利用水分胁迫处理 (减少一次灌溉 )等节水措施 ,则比 1 999年节水 1 7.2 %。  相似文献   

湘桂黔滇藏红色岩溶风化壳发育模式   总被引：11，自引：0，他引：11  

李德文  崔之久  刘耕年 《地理学报》2002,57(3):293-300

基于对湘，桂、黔，滇，藏等地岩溶区红色风化壳的野外和室内研究，从表生地貌学，粘土矿物学和地球化学角度分析红色石灰土性质与地貌演化的关系，提出红色岩溶风化壳发育的二阶段模式；1）地貌夷平-风化物质积累阶段，在地貌演化过程中溶蚀残余物质不断积累，最后在夷平面上形成厚层连续的泥质风化壳，夷平面的地貌水文条件有利于粘粒的形成和保存，但限制了富铝化作用的有效进行，造就了岩溶风化壳粘粒含量高，富铝化程度低的特点，这与研究区23个红色岩溶风化壳剖面化学，粒度特征和粘土矿物组合特点一致。2）地貌切割-风化壳淋溶阶段，原始夷平面上的风化壳大多呈灰色，只有在构造隆升和地表微切割导致地下水位降低，淋溶条件开始改善的情况下，风化壳才有可能枞根本上转为红色。  相似文献