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511.
512.
前寒武纪大陆地壳地质构造演化研究进展与问题 总被引:6,自引:0,他引:6
前寒武纪地质构造是地球系统科学研究的一个承前启后的重要组成部分,现存最古老的固体地球物质是38亿年前的大陆长英质岩石。以地质构造热事件为标志确认早中太古代已有30亿年年龄值的大陆克拉通化,而新太古代末大陆地壳已出现普遍的克拉通化。由深变质作用岩石测得的p-t值推断当时地温梯度与现今大陆稳定区相似,大规模的陆壳区断块已具基本刚性特征,使板块构造运动模式基本适用于太古宙地壳演化。古元古代末陆壳普遍隆升和遭剥蚀,陆壳生长作用导致形成大陆区块上的裂谷型坳拉槽系。中元古代起,世界约于18亿年前近乎同时出现不变质的沉积盖层,使前寒武纪明显必需划分为早、晚前寒武纪两大阶段。华北克拉通区是世界大陆克拉通地壳的组成部分,与世界各大陆克拉通演化有很好的可对比性,在前寒武纪超级大陆重建中有一定位置。在现今阶段研究基础上,对华北克拉通区提出了几个前瞻性的基础研究课题,应予深入探索。 相似文献
513.
华南的格林威尔造山带及其坍塌:在罗迪尼亚超大陆演化中的意义 总被引:24,自引:2,他引:22
吴根耀 《大地构造与成矿学》2000,24(2):112-123
华南的格林威尔造山运动始自约1200MaB.P.,在约1000~950MaB.P.扬子与湘赣—华夏微大陆发生碰撞 ,继之以岩石圈的拆沉作用和造山带的快速坍塌 ,在仰冲板片和下插板片上分别形成华南裂谷的北支和南支 ,部分地区可能有新生洋壳出现。裂谷以北地区的造山活动持续到约740MaB.P.,碰撞高原控制了长安冰期的沉积 ,至南沱冰期沉积时它已近剥蚀夷平。文章重塑了新元古代时华南裂谷的演化 ,探讨了它在罗迪尼亚超大陆裂解中的意义 相似文献
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Z. X. Li 《Geophysical Journal International》2000,142(1):173-180
A palaeomagnetic study of the Elgee Formation red siltstones and shales in the Palaeoproterozoic Kimberley Basin of northwestern Australia has been carried out. All seven sampling sites revealed an extremely stable magnetic remanence carried by haematite. The age of the formation is confined by precise SHRIMP U–Pb ages of early diagenetic xenotime from rocks both above and below it to be 1704 + 7/−14 Ma, but this may represent a minimum age. The youngest detrital zircon grains in the underlying formation provide a maximum age of 1786 ± 14 Ma for the formation. The extreme stability of the remanence, the dissimilarity of the remanent direction from expected younger palaeomagnetic directions, and the lack of regional overprint in the 1790 ± 4 Ma Hart Dolerite just north of the study region support a primary origin for the remanence. A marginally positive fold test also supports a primary origin. The mean direction of D = 92.2°, I = 14.9°, α 95 = 6.4° gives a palaeopole at 4.4°S, 210.0°E with dp = 3.3°, dm = 6.5°. This pole, a previously reported palaeopole from the Hart Dolerite and ca. 1700 Ma overprint poles from the Pilbara Craton all agree with palaeopoles of similar ages from the McArthur Basin of northern Australia. Palaeomagnetic results thus suggest that the North and West Australian cratons were possibly joined together by approximately 1.7 Ga. 相似文献
516.
近 2 0年来 ,在华北 ,扬子和华夏地块上已经获得较丰富的前寒武纪岩石古地磁和磁性地层资料 ,建立起三个地块的视极移轨迹。在此基础上 ,编制出 3个地块的初步年代磁性地层表 ,并尝试性地划分出 8个极性带 (或期 ) ,通过与全球的对比 ,似乎可以确立起 3~ 4个磁性地层的参考对比标志层。同时还利用极移轨迹的特殊现象———极环、拐点和极位分布等做为磁性地层研究的重要内容 ,进行了构造地层和年代地层的比较研究。结果表明古地磁学和磁性地层学对前寒武纪地质仍是重要的研究工具之一 相似文献
517.
安徽大别、苏北和山东胶南是世界上第三个发现含柯石英榴辉岩的地区。在关于苏鲁皖超高压变质带大地构造背景的学术讨论中,其时代问题成为当前争论的焦点。本文用锆石U-Pb法得到碧溪岭榴辉岩体谐和图上交点年龄2774.5±24Ma以及t(~(207)Pb/~(206)Tb)平均表面年龄2662Ma,提供了榴辉岩的原岩和超高压变质作用可能形成于晚太古代的信息;并用多硅白云母Ar-Ar法测得661.7±13Ma的退变质年龄,也表明本区榴辉岩可能是前寒武纪的产物;此外,还测得围岩大别群斜长片麻岩中的白云母以及榴辉岩中晚期交代的普通角闪石的Ar-Ar等时线年龄分别为192.55±3.85和230.70±4.61Ma,代表后榴辉岩(posteclogite)的印支期区域动力变质作用改造年龄。笔者对已报道的榴辉岩Sm-Nd年龄的地质意义进行了讨论,并指出了含石榴子石Sm-Nd矿物等时线定年法潜在的弊端。 相似文献
518.
我国早前寒武纪地层研究进展、问题和建议 总被引:1,自引:2,他引:1
主要介绍自1996年以来我国早前寒武纪地层研究的新进展、存在问题和今后工作的建议。新进展主要包括三个方面:正确认识早前寒武纪地层研究的复杂性和工作难度;在学术思想和工作方法方面取得的新进展;在研究具体的早前寒武纪地层中取得新进展。在了解存在问题的基础上,提出今后工作的8点建议。 相似文献
519.
LIU Yongsheng GAO Shan WANG Xuance HU Shenghong & WANG Jianqi . State Key Laboratory of Geological Processes Mineral Resources China University of Geosciences Wuhan China . Key Laboratory of Continental Dynamics Department of Geology Northwest University Xi’an China 《中国科学D辑(英文版)》2005,48(8):1106-1119
Hofmann[1] found that the depleted mantle (DM) and bulk continental crust (BCC) are simply compen-satory in terms of many elements and elemental ratios. High-field-strength elements (HFSE) (e.g., Zr, Hf, Nb, Ta and Ti) are immobile and thus useful to track the primary features of the ancient mafic volcanics. It has been long considered that Nb-Ta behave as identical twins during magmatic processes, based on their matching atomic radii and valence state and hence coherent geochemical affi… 相似文献
520.
Stratigraphical and biological significance of negative carbon isotopic anomalies in the basal Cambrian series of Guizhou Province 总被引:2,自引:0,他引:2
The early Early Cambrian strata within the bounds of Guizhou Province are almost predominated by black shale deposition. Recently, however, the authors have found a section consisting of a set of mudstones interbedded with limestones at the basement of the Cambrian at Yingping, Fuquan County,Guizhou Province, which provides favorable conditions for the study of marine geochemical characteristics of the early Early Cambrian. The characteristics of intense negative carbon isotopic anomalies near the Precambrian/Cambrian boundary at Yingping, Fuquan County, Guizhou Province, can be correlated with those of global carbon isotopic anomalies at the same time on a global scale, corresponding to the intense negative carbon isotopic anomalies near the Neoproterozoic/Cambrian boundaries at the bottom of the Xiaowaitoushan Member, Huize, Yunnan Province, at the top of the Tsagaan 0loom Formation of Mongolia and at the top of the Salarmy Gol Formation of Siberia, as well as those observed in southwestern United States, Iran, Amman, Poland, Newfoundland, the Great Britain, Canada, etc. Negative carbon isotopic anomalies can be used as the important basis for the division of the Precambrian/Cambrian boundaries.There have been found 8 m-thick black shales and cherts below the intense negative carbon isotopic anomalies in this profile. In the black shales there have been found large amounts of fossils such as Bradoricla,gernus Archotuba, indicating that during the period of sedimentation of black shales under anaerobic conditions there would be large quantities of organic species living in the sea. But in the section of grayish-green mudstones interbedded with limestones with intense negative carbon isotopic anomalies almost no organic fossil has been found. This may imply that the anaerobic event seems to have little bearing on the mass extinction near the Precambrian/Cambrian boundary, whereas the intense negative carbon isotopic anomaly event appears to be more closely related to the mass extinction occurring near the Precambrian/Cambrian boundary. 相似文献