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271.
哈尔里克山早古生代岩浆弧的初步确定——来自塔水河一带花岗质岩体锆石SHRIMP U-Pb测年的证据 总被引:20,自引:3,他引:20
哈尔里克山南坡塔水河一带花岗质岩体的锆石SHRIMPU-Pb定年结果显示:钾长花岗岩中的锆石8个测点的206Pb/238U加权平均年龄为(462±9)Ma;花岗闪长岩中的锆石8个测点的206Pb/238U加权平均年龄为(447±11)Ma;石英闪长岩中的锆石8个测点的206Pb/238U加权平均年龄为(448±7)Ma。这些年龄值是在哈尔里克古生代复合岛弧带首次获得的中—晚奥陶世中酸性侵入岩的时代,为探讨该古生代复合岛弧带的构造发展历史提供了新的资料。 相似文献
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274.
“中央造山带”早古生代缝合带及构造分区概述 总被引:15,自引:2,他引:15
“中央造山带”是夹持于中国塔里木、华北和扬子克拉通之间的近东西向延展的(局部为北东向和北西向)显生宙造山系统。该造山带中包括了库地-喀拉塔什、红柳沟-肃北-北祁连、南阿尔金-滩间山、昆中、朱阳关-夏馆和商州-丹凤6条早古生代缝合带。被缝合带所围限的前寒武纪地质构造单元包括中阿尔金-祁连-金吉地块、柴达木地块、北秦岭地块和东、西昆仑2个变质地体。南秦岭原为扬子克拉通的北部边缘,但卷入了显生宙造山带,成为中央造山带的一部分。对上述6条早古生代缝合带和6个前寒武纪地质构造单元的特点进行了概略总结,并阐述了各地质构造单元中的构造地层系统和热-构造事件的年代格架。 相似文献
275.
新疆西天山达巴特铜矿床地质特征和成矿时代研究 总被引:18,自引:1,他引:18
本文通过对西天山地区比较典型的达巴特斑岩铜钼矿床矿石中辉钼矿Re-Os的直接定年研究,结合区域地质演化和其他年代学资料,探讨了西天山赛里木和博罗科努地区斑岩铜多金属成矿带的成矿地球动力学背景和成矿机制。结果显示达巴特矿床中辉钼矿Re-Os年龄为301±20Ma,表明成矿作用发生于晚石炭世。矿床形成于别珍套—科古琴石炭纪岛弧带,成岩成矿与石炭纪巴音沟洋壳向南的俯冲作用密切相关,可能的成矿机制是由于洋壳向南对赛里木隆起带陆壳基底的俯冲,岛弧基底断裂系向北逆冲,导致一系列与斑岩矿床有关的中酸性岩浆活动,区域深大断裂为岩浆的上侵提供了条件。 相似文献
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277.
Sébastien Joannin Frédéric Quillévéré Christophe Lécuyer François Martineau 《Quaternary Research》2007,67(2):264-274
Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ18O and δ13C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ18O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova. 相似文献
278.
The Ratcliff Site in southwestern Virginia lies in a small second-order stream valley filled with approximately 3.5 m of organic-rich deposits that contain bones of mammoth, mastodon, deer (or antelope), logs, and plant macrofossils. Radiocarbon analyses indicate the age of the organic-rich sediment ranges from > 44,000 to 29,100 14C yr BP, a time period with no fossil remains reported in this region of the Appalachians. Analyses of field observations, textural data, organic carbon content, and plant macrofossils indicate that the organic-rich sediments contain interbedded standing-water and debris-flow deposits. Up to 6 m of oxidized debris-flow sediments bury the organic-rich sediments. The presence of Rubus parviflorus (Thimble Berry) throughout the deposit indicates the site had a boreal environment from > 44,000 to 29,100 14C yr BP. Plant macrofossil evidence indicates the uplands had stands of spruce/jack-pine forests while the valley contained ponds and associated wetlands. Three debris flows occurred at the site between approximately 38,000 and 29,000 14C yr BP, suggesting a recurrence interval for major storms of approximately 3000 yr, even though the apparent stability of the boreal environment implies a climate not conducive to catastrophic rainstorms. This conflicting combination of features suggests that during the middle Wisconsinan this area experienced generally cool climates, dominated by polar air masses, but was punctuated by relatively brief warm periods marked by incursions of tropical air masses. 相似文献
279.
Economic transition in central and eastern Europe (CEE) has had a particularly strong impact on industrial cities and regions. Following their economic collapse, most of them are now confronted with serious problems such as high unemployment and vast ecological damage. The paper presents findings from a pan European research project that investigated the problems of these cities and regions as well as the strategies being adopted to cope with structural change. It examines the differences in approaches and addresses the question whether existing EU policy is suitable for supporting the redevelopment of old industrial cities and regions in CEE countries. The paper concludes with recommendations for future directions in policy making. 相似文献
280.