张宣金矿密集区基底及成矿作用年代学研究进展   总被引：3，自引：0，他引：3  

李怀坤  陆松年  李惠民  杨春亮 《地球学报》1999,20(2):169-176

张宣地区是华北地台北缘著名的金矿密集区之一,分布着规模不等的金矿床（点）百余处。区内前寒武纪基底呈双层结构模式：其下层结构是由厘定后的桑干杂岩组成,主体是太古宙晚期－元古宙初期的深成花岗质片麻岩,含规模不等和时代更老的各类表壳岩包体;上层结构是时代上可能和邻区集宁岩群相当的艾家沟岩组孔兹岩系。和基底有关的金矿主要与下层结构关系密切。Ａｕ丰度１０倍于地壳克拉克值的初始地壳,是该区形成金矿密集区的物质基础。精确的单颗粒锆石Ｕ－Ｐｂ年代学研究表明,区内重要金矿床小营盘金矿在吕梁运动期１８００Ｍａ左右的退变质作用过程中有一期重要矿化作用;而著名的东坪金矿则形成于其赋矿围岩石英二长岩就位之后约６０Ｍａ的３５０Ｍａ的海西早期。  相似文献   

塔里木沙漠公路不同地貌部位的产式沙障阻沙特征   总被引：6，自引：1，他引：5  

黄强  雷加强 《干旱区地理》2000,23(3):227-232

对塔里木沙漠公路不同地貌部位的高立式沙障的阻沙效果分析表明：垄间平地路段高立式沙障可以在２￣３年内有效阻止防沙体系外的沙子进入体系内,不但能有效阻止体系外风沙流进入体系内,而且降低了体系外沙丘移入体系内的速度;垄体、垭口和过渡区路段的高立式沙障,仅在短时间内有效阻止体系外风沙流进入体系内,不能使体系外沙丘移入体系内的速度降低;垄间新月型沙丘（链）路段的高立式沙障能明显降低体系外沙丘移入体系内的速度  相似文献   

Cosmogenic10Be: A critical view on its widespread dominion in geosciences     

D. Lal 《Journal of Earth System Science》2000,109(1):181-186

The radionuclide¹⁰Be (half-life = 1.5my), produced naturally in the Earth’s atmosphere by nuclear interactions of cosmic rays, was sought in ocean sediments in the late fifties, considering its potential usefulness as a radiotracer for dating sediments.¹⁰Be was discovered independently by two groups, one in India and the other in the USA, and used only for dating marine sediments and manganese nodules until the seventies. Subsequently, as a result of a technical advance resulting in the improvement in the sensitivity of measurement of¹⁰Be by about a factor of 10⁶, there was a global rush to measure this nuclide in most materials participating in the physical, chemical and biological processes in the dynamic geosphere. This paper outlines the reasons for this “isotope rush”, and the lessons learned from these studies. I also present my personal views of the special attractive features of this nuclide on the one hand, and on the other, the pitfalls or the wrong message this nuclide could convey!  相似文献   

LASER PROBE ~(40)Ar/ ~(39)Ar DATING OF MICAS ON THE DEFORMED ROCKS FROM ALTYN FAULT AND ITS TECTONIC IMPLICATIONS,WESTERN CHINA     

Liu Yongjiang    Ye Huiwen    Ge Xiaohong    Liu Junlai    Pan Hongxun    Chen Wen  WT  ”BX 《地学前缘》2000,(Z1)

LASER PROBE ~(40)Ar/ ~(39)Ar DATING OF MICAS ON THE DEFORMED ROCKS FROM ALTYN FAULT AND ITS TECTONIC IMPLICATIONS,WESTERN CHINAtheNationalNaturalScienceFundCommittee (NO .4 9772 157)  相似文献   

Sr–Nd isotope ratios of gabbroic and dioritic rocks in a Cretaceous-Paleogene granite terrain, Southwest Japan     

Shigeru Iizumi  Teruyoshi Imaoka and  Hiroo Kagami 《Island Arc》2000,9(1):113-127

Abstract Whole‐rock chemical and Sr and Nd isotope data are presented for gabbroic and dioritic rocks from a Cretaceous‐Paleogene granitic terrain in Southwest Japan. Age data indicate that they were emplaced in the late Cretaceous during the early stages of a voluminous intermediate‐felsic magmatic episode in Southwest Japan. Although these gabbroic and dioritic rocks have similar major and trace element chemistry, they show regional variations in terms of initial Sr and Nd isotope ratios. Samples from the South Zone have high initial ⁸⁷Sr/⁸⁶Sr (0.7063–0.7076) and low initial Nd isotope ratios (?_Nd, ?2.5 to ?5.3); whereas those from the North Zone have lower initial ⁸⁷Sr/⁸⁶Sr (usually less than 0.7060) and higher Nd isotope ratios (?_Nd, ?0.8 to + 3.3). Regional variations in Sr and Nd isotope ratios are similar to those observed in granitic rocks, although gabbroic and dioritic rocks tend to have slightly lower Sr and higher Nd isotope ratios than granitic rocks in the respective zones. Limited variations in Sr and Nd isotope ratios among samples from individual zones may be attributed partly to a combination of upper crustal contamination and heterogeneity of the magma source. Contamination of magmas by upper crustal material cannot, however, explain the observed Sr and Nd isotope variations between samples from the North and South Zones. Between‐zone variations would reflect geochemical difference in magma sources. The gabbroic and dioritic rocks are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE), showing similar normal‐type mid‐ocean ridge basalt (N‐MORB) normalized patterns to arc magmas. Geochronological and isotopic data may suggest that some gabbroic and dioritic rocks are genetically related to high magnesian andesite. Alternatively, mantle‐derived mafic or intermediate rocks which were underplated beneath the crust may be also plausible sources for gabbroic and dioritic rocks. The magma sources (the mantle wedge and lower crust) were isotopically more enriched beneath the South Zone than the North Zone during the Cretaceous‐Paleogene. Sr and Nd isotope ratios of the lower crustal source of the granitic rocks was isotopically affected by mantle‐derived magmas, resulting in similar initial Sr and Nd isotope ratios for gabbroic, dioritic and granitic rocks in each zone.  相似文献   

New K–Ar ages of shield lavas from Waianae Volcano, Oahu, Hawaiian Archipelago     

H. Guillou  J. Sinton  C. Laj  C. Kissel  N. Szeremeta 《Journal of Volcanology and Geothermal Research》2000,96(3-4)

A geochronological study utilized the unspiked potassium–argon (K–Ar) technique to obtain ages from the two main volcanic members of the shield stage of the Waianae Volcano, HI. These new dates are further constrained using a combination of stratigraphic relationships, magnetostratigraphy and major element geochemistry. Exposed shield lavas encompass 0.85 Ma, with reliably dated tholeiitic lavas from the main shield ranging from 3.93±0.08 to 3.54±0.04 Ma, and a later shield stage ranging in age from 3.57±0.04 to 3.08±0.04 Ma. These data suggest that the total extent of Waianae shield activity was significantly more than 1 Ma. The age of faulting in two flank zones is constrained to be about 3.4 Ma. Preliminary estimates of lava accumulation rates vary from about 0.3 to 2.0 mm/a; calculated rates show no systematic variation with location in the volcano or with time.  相似文献   

粤西阳春中生代钾玄质侵入岩及其构造意义:Ⅰ.岩石学和同位素地质年代学   总被引：45，自引：7，他引：38  

李献华  周汉文  刘颖  李寄嵎  陈正宏  于津生  桂训唐 《地球化学》2000,29(6):513-520

粤西阳春地区马山二长岩的岩石化学组成特征为典型的钾玄质岩石,岗尾、轮水石英二长岩和花岗闪长岩属酸性一偏中性的钾玄质系列岩石(少数样品为高钾钙碱性岩石),而石菉花岗闪长岩则为典型的钙碱性系列岩石,这些岩体在岩石化学演化趋势上存在显著的差异,不属于同一个岩石成因系列.40Ar-39Ar和Rb-Sr同位素定年结果表明,马山和岗尾岩体的形成年龄分别为(164±2)Ma和(154±1)Ma.阳春地区从中侏罗世到早白垩世期间发生了3次主要的岩浆活动,从早到晚岩浆的K富集程度逐渐降低,岩浆岩成分从钾玄质系列过渡到钙碱系列.  相似文献   

内蒙古喀喇沁堆晶岩捕虏体和寄主闪长岩的同位素年龄   总被引：14，自引：0，他引：14  

邵济安  张任祜  韩庆军  张履桥  乔广生  桑海清 《地球化学》2000,29(4):331-336

喀喇沁地区们于大兴安岭中生代构造岩浆岩带与华北克拉通交汇部位。研究区的闪长岩侵入到太古宙基底中。闪长岩中含有二辉岩、辉长岩、苏长岩、角闪岩、斜长岩等不同组分的镁铁质－超镁铁堆晶岩捕虏体和基性麻粒岩捕虏体,它们是幔源玄武质岩浆底侵作用的产物。分别用Ｒｂ－Ｓｒ法、Ｋ－Ａｒ法和Ａｒ－Ａｒ法,对堆晶岩捕虏体及其寄主岩全岩或单矿物进行了详细的同位素地质年代学研究,共获得各种年龄数据８件,橄榄辉石岩的全岩Ｒｂ  相似文献   

A complete and easily accessible means of calculating surface exposure ages or erosion rates from Be and Al measurements     

Greg Balco  John O. Stone  Nathaniel A. Lifton  Tibor J. Dunai 《Quaternary Geochronology》2008,3(3):174-195

We codify previously published means of calculating exposure ages and erosion rates from ¹⁰Be and ²⁶Al concentrations in rock surfaces, and present a single complete and straightforward method that reflects currently accepted practices and is consistent with existing production rate calibration measurements. It is intended to enable geoscientists, who wish to use cosmogenic-nuclide exposure age or erosion rate measurements in their work to: (a) calculate exposure ages and erosion rates; (b) compare previously published exposure ages or erosion rate measurements on a common basis; (c) evaluate the sensitivity of their results to differences between published production rate scaling schemes. The method is available online at http://hess.ess.washington.edu.  相似文献   

长岛地质遗迹成因与综合评价   总被引：4，自引：0，他引：4  

朱远峰  尹延鸿  朱志伟  于洪社 《海洋地质与第四纪地质》2005,25(4):115-120

对世界罕见的海洋地质遗迹--黄渤海分界线砾脊、海蚀栈道等成因进行了探讨.综合评价认为,长岛是开展海洋动力沉积作用和新生代以来全球气候与海平面变化研究的极佳基地;13处主要地质遗迹的美学价值半定量评价表明高观赏度者达69%.  相似文献