内蒙古中部苏尼特左旗富钾花岗岩锆石SHRIMP U-Pb年龄   总被引：12，自引：3，他引：12  

石玉若  刘敦一简平　张旗张福勤  苗来成施光海  张履桥陶华 《地质通报》2005,24(5):424-428

精确的锆石SHRIMP U-Pb年龄测定表明,内蒙古苏尼特左旗富钾花岗岩的结晶年龄分别为423Ma±8Ma和424Ma±10Ma.综合区域资料,认为该年龄代表了内蒙古中部志留纪期间发生弧-陆碰撞事件的时限.  相似文献   

库车坳陷下侏罗统沉积特征及砂体展布   总被引：6，自引：0，他引：6       下载免费PDF全文

张惠良  寿建峰  陈子料  王少依  杨晓宁  皮学军  蔡振忠 《古地理学报》2002,4(3):47-58

库车坳陷位于塔里木盆地北部，北缘是南天山山前断裂带，南缘是塔北隆起，呈NEE向展布，东西长250km，南北宽20－60km，面积约21170km^2。下侏罗统自下而上发育阿合组、阳霞组。对吐格尔明、克孜勒努尔、库车河剖面及依南2井岩芯观察发现，阿合组和阳霞组按其岩性特征均可以划分为5个岩性段，各个岩性段在全具有对比性。还可分出4类和17个亚类岩相。阿合组细砂岩以上的粗碎屑岩含量为80％以上；阳霞组细砂岩以上的碎屑岩含量为50％－60％。砂岩厚度占总地层厚度的50％－60％以上，是油气勘探的重要目的层系。以吐格尔明剖面为代表的依南2井以东地区的阿合组和阳霞组岩矿特征基本相似，以克孜勒努尔地区为代表的依南2井以西地区有较大差异，即阳霞组长石含量几乎为零。两区共同点是以岩屑砂岩为主，成分成熟度低，结构成熟度中等，岩屑含量较高。从岩性组合、沉积构造、微观岩石成分、结构和砂体形态等方面的综合分析认为，辫状三角洲沉积体系是该区阿合组和阳霞组的主要沉积体系。阿合组砂体纵向上以多个辫状三角洲平原上的辫状分流河道砂岩加积复合为主，横向上指状镶嵌叠置呈东西向展布。阳霞组第3岩性段砂体纵向上以多个辫状三角洲前缘上的水下辫状分流河道砂岩加积复合为主，横向上指状镶嵌叠置也呈东西向展布。第2、4、5岩性段砂体以河道滞流砂岩侧砂为主，横向叠瓦状叠置呈东西向展布。  相似文献   

鄂尔多斯盆地中部地区下古生界碳酸盐岩生烃潜力探讨   总被引：4，自引：0，他引：4  

李贤庆  侯读杰  胡国艺  唐友军  谢增业  张爱云 《矿物岩石地球化学通报》2002,21(3):152-157

下古生界高成熟－过成熟碳酸盐岩的生烃潜力一直是困扰我国海相地层油气评价和勘探的重要问题，至今尚未得到很好的解决。本采用有机岩石学和有机地球化学方法，系统剖析了鄂尔多斯盆地中部地区下古生界碳酸盐岩的基本特征及其生烃潜力。结果表明，鄂尔多斯盆地中部地区发育下古生界海相碳酸盐岩，烃源岩厚度较大，有机质丰度较低，有机质类型主要为I型和Ⅱ型，有机质热演化已达到过成熟阶段，这套烃源岩是该区重要的有效气源岩，具有较好的生烃潜力，可为中部大气田提供良好的气源条件。  相似文献   

Ludlow (Silurian) stromatoporoid biostromes from Gotland, Sweden: facies, depositional models and modern analogues   总被引：1，自引：0，他引：1  

Olof Sandström  Steve Kershaw† 《Sedimentology》2002,49(3):379-395

Stacked stromatoporoid‐dominated biostromes of the Ludlow‐age Hemse Group (Silurian) in eastern Gotland, Sweden, are 0·5–5 m thick and a few tens of metres to >1 km in lateral extent. They form one of the world's richest Palaeozoic stromatoporoid deposits. This study compiles published and new data to provide an overall facies model for these biostromes, which is assessed in relation to possible modern analogues. Some biostromes have predominantly in‐place fossils and are regarded as reefs, but lack rigid frameworks because of abundant low‐profile non‐framebuilding stromatoporoids; other biostromes consist of stromatoporoid‐rich rudstones interpreted here as storm deposits. Variation between these two `end‐members' occurs both between interlayered biostromes and also vertically and laterally within individual biostromes. Such variation produces problems of applying established reef classification terms and demonstrates the need for the development of terminology that recognizes taphonomic destruction of reef fabrics. An approach to such terminology is found in all four categories of a recent biostrome classification scheme that are easily recognized in the Hemse biostrome facies: autobiostromes (>60% in place); autoparabiostromes (a mixture of in‐place and overturned reef‐building organisms, 20–60% in place); parabiostromes (builders are overturned and damaged, <20% in place); and allobiostromes (transported and detrital reef material, nothing in place). These categories provide a broad taphofacies scheme for the Hemse biostromes, which are mostly autoparabiostrome to allobiostrome. The biostromes developed on crinoidal grainstone sheets and expanded laterally across relatively flat substrates in a marine setting of low siliciclastic input. Planar erosion surfaces commonly terminate biostrome tops. Three broadly similar modern analogues are identified, each of which has elements in common with the Hemse biostromes, but none of which is an exact equivalent: (a) laterally expanded and coalesced back‐barrier patch reefs behind the Belize barrier, an area influenced by limited accommodation space; (b) a hurricane‐influenced shelf, interpreted for Grand Cayman, where reef cores consist of rubble and lack substantial framework; the wide distribution of rounded pebbles and cobbles of stromatoporoids in the Hemse biostromes most probably resulted from hurricanes; (c) coral carpets in 5–15 m water depth of the northern Red Sea, where lateral expansion of low‐diversity frames dominated by Porites coral has produced low‐profile biostromes up to 8 m thick and several km long. Such carpets accumulated large amounts of carbonate, with little export, as in the Hemse biostromes, although the latter did not build frameworks because of the nature of growth of the stromatoporoids. The notable lack of algae in the Hemse biostrome facies is also a feature of Red Sea coral carpets; nevertheless, coral carpets are ecologically different. Hemse biostromes lack evidence of a barrier reef system, although this may not be exposed; the facies assemblage is consistent with either a storm/hurricane‐influenced mid‐ to upper ramp or back‐barrier system.  相似文献   

Continental crust and lithospheric mantle interaction beneath North China: isotopic evidence from granulite xenoliths in Hannuoba, Sino-Korean craton   总被引：40，自引：0，他引：40  

Xinhua Zhou  Min Sun  Guohui Zhang  Shaohai Chen 《Lithos》2002,62(3-4):111-124

Mafic granulite and pyroxenite xenoliths from Cenozoic alkaline basalts at Hannuoba, Hebei Province, North China have been selected for a systematic geochemical and Sr–Nd–Pb isotopic study, which provides a unique opportunity to explore nature of the lower crust and the interaction between the continental crust and lithospheric mantle beneath an Archean craton. The major, compatible and incompatible elements and radiogenic isotopes of these xenoliths suggest great chemical heterogeneity of the lower crust beneath the Hannuoba region. Petrological and geochemical evidences indicate a clear cumulate origin, and most likely, they are related to basaltic underplating in different geological episodes. However, the Sr–Nd–Pb isotopic compositions of the xenoliths reveal a profound enriched source signature (EM I) with some influence of EM II, which implies that some portion of pre-existing, old metasomatized subcontinental lithospheric mantle could have played an important role in their genesis. It is suggested that the interaction between continental crust and subcontinental mantle as manifested by basaltic underplating would be closely related to regional tectonic episodes and geodynamic processes in the deep part of subcontinental lithospheric mantle.  相似文献   

The “boudinage” question in the High-Ardenne Slate Belt (Belgium): a combined structural and fluid-inclusion approach     

I. Kenis  M. Sintubin  Ph. Muchez  E. A. J. Burke 《Tectonophysics》2002,348(1-3)

  相似文献   

中朝地台东北缘地区的地震层析成像   总被引：24，自引：5，他引：24       下载免费PDF全文

卢造勋  蒋秀琴  潘科  白云  姜德录  肖立萍  刘建华  刘福田  陈辉  何建坤 《地球物理学报》2002,45(3):338-351

根据中朝地台东北缘地区 (东经 1 1 7°0 0′— 1 2 6°0 0′ ,北纬 36°0 0′— 44°0 0′) 1 980— 1 997年的 380 0 0余条P波走时数据 ,利用正交投影法重建了该区地壳和上地幔的三维速度结构 .通过分析及同人工地震测深剖面的详细对比 ,证明了成像结果的可靠性 .结果表明 :中朝地台东北缘地区地壳上地幔介质存在显著的横向不均匀性 ,直至 1 2 0km深度处依然明显 ;地壳上部的速度图像清楚地反映了不同岩石单元的分布与该区不同性质的基岩分布基本吻合 ;从上、中地壳的速度图像中发现了研究区存在海城、朝阳、义县、丹东南、唐山等几个低速异常区(即速度逆反层区 ) ,其中海城、唐山、朝阳等地区的壳内低速层已由深地震测深资料所证实 ;研究区陆地发生的几次强震均发生于壳内低速层上方的高速脆性介质内 ,而渤海发生的强震 ,此现象不明显 ,但都发生于横向介质速度显著突变的位置 ;在地壳不同深度上发现了普兰店至山海关横跨渤海的北西向低速异常带 ;地震层析二维速度图像与深地震测深资料的对比表明 ,研究区利用地震层析成像技术 ,在一定条件下可以获得与人工地震测深相似的效果  相似文献   

四川江油-北川地区下石炭统灰岩的古地磁研究     

李学森  吴汉宁  黄宝春  李秋实  张小浩  李林 《地球物理学进展》2002,17(3):406-413

对采于四川北部江油 北川地区 (31.4°N ,10 4 .3°E)下石炭统 39个采点的 334块灰岩标本进行了较为系统的古地磁学研究 ,结果表明 ,标本中剩磁方向具有明显的双分量特征 ,低温 (10 0～ 30 0℃ )分量在地理坐标系下与现代地磁场方向基本一致 ,且不能通过褶皱检验 ,应是现代地磁场的重磁化 ,中温 (30 0～ 4 80℃ )反极性分量在地层坐标系中具有高负倾角的特征 ,其形成可能与早侏罗世岩层的褶皱弯曲有关 .  相似文献   

Is there any detachment in the Lower Dolpo (western Nepal)?Y a-t-il un détachement dans le bas Dolpo (Népal occidental) ?     

Rodolfo Carosi  Chiara Montomoli  Dario Visonà 《Comptes Rendus Geoscience》2002,334(12):933-940

A structural transect in the Lower Dolpo highlights that the deformation and metamorphism of the Tibetan Zone (TZ) increase toward the bottom of the sequence. The contact with the underlying HHC is marked by a metamorphic jump from amphibolite facies in the carbonatic rocks of the upper part of the HHC to greenschist facies marbles in the TZ. Moreover, the HHC and the TZ show different metamorphic histories. The contact zone shows a strain increase accompanied by asymmetric folds with a top-to-the-northeast vergence, connected to a down-to-the-northeast tectonic transport. The contact is interpreted as an extensional shear zone, connected to the South Tibetan Detachment System. To cite this article: R. Carosi et al., C. R. Geoscience 334 (2002) 933–940.  相似文献   

长江中下游晚中生代中基性岩的铅同位素特征:富集地幔的证据   总被引：33，自引：3，他引：33  

闫峻  陈江峰  喻钢  钱卉  周泰禧 《高校地质学报》2003,9(2):195-206

长江中下游东段庐枞、怀宁、繁昌、铜陵和宁芜地区的中基性岩属于碱性系列 ,具有高的U ,Th含量和Th/Pb ,U/Pb比值 ,分别平均为 2 .82× 10 -6,9.5 6× 10 -6和 0 .6 35 ,0 .184。样品的初始铅同位素 (130Ma)组成为 :(2 0 6Pb/ 2 0 4Pb) i=17.6 5～ 18.6 0 ,(2 0 7Pb/ 2 0 4Pb) i=15 .4 2～ 15 .5 0 ,(2 0 8Pb/ 2 0 4Pb) i=37.6 7～ 38.0 4。形成中基性岩的原始岩浆来源于富集的岩石圈地幔 ,具有EMⅠ和EMⅡ ,且以EMⅡ为主的特征。和长江中下游西段黄石地区以及大别地块西南部玄武岩的比较表明 ,长江中下游地区岩石圈地幔高的Th/Pb和U/Pb比值可能和俯冲板片析出流体的交代有关。晚中生代时期 ,华北板块岩石圈地幔以EMⅠ特征为主 ,华南板块岩石圈地幔以EMⅡ特征为主 ,岩石圈地幔性质的区域性分布与印支期扬子板块深俯冲事件密切相关。虽然中国东部新生代玄武岩因岩石圈大规模减薄表现了亏损特征 ,但残留的富集岩石圈地幔在中国东部新生代玄武岩的Pb同位素中仍有所反映  相似文献