Foreland folding
Foreland folding
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前陆折叠
DOI：
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发表时间：
1952
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影响因子：
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通讯作者：
G. M. Lees
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文献类型：
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作者：
G. M. Lees
对前陆褶皱带的研究表明，沉积岩的覆盖起被动作用，并适应下方基底的运动。Buxtorf用来解释汝拉山构造的Abscherung理论所暗示的沿沉积盖层施加的侧向压力不被认为是可能的。造山是地球内部收缩的结果，在整个地质时代，这一原因造成的地壳压缩一直占主导地位。还介绍了在远离活跃山锋的盾构地区（如尼日利亚）压缩构造的例子。苏伊士湾和死海裂谷具有挤压和张拉双重特征，但前者更为重要。一个结晶基底复合体可以弯曲并形成背斜的核心，在某些情况下，很少或没有断层。委内瑞拉、苏门答腊和其他地区的石油勘探钻孔已经到达背斜核心的基底岩，并表明活动原理是基底的移动，而不是侧向压力产生的沉积盖层的剪切、无根褶皱。描述了不同类型的前陆褶皱的例子。侏罗山构造是由基底下的陡峭褶皱或断片构造形成的，沉积盖层在三叠纪盐的润滑作用下分离，褶皱成独立的格局。西南波斯山带是一个简单褶皱的例子，其背斜长可达250英里。阿萨姆邦被描述为织块褶皱的一个例子——强烈的逆冲断层背斜是由下方基底的逆冲褶皱产生的。西隆高原南侧的大弯曲。在喜马拉雅锋面和阿萨姆山脉之间，展示了一个表面上坚硬的结晶复合体如何弯曲成陡峭的弯曲，侵蚀表面如何向下弯曲到大约3万英尺的深度。特立尼达的粘土底涌泉背斜是在软粘土覆盖下陡折的表面表现，高压水和高压气作为促进粘土岩心向上挤压的介质。盐底辟背斜与圆形盐塞不同，其成因也与基底的挤压运动有关。在某些前陆带，基底岩的断裂、褶皱或弯曲程度与其他前陆带的刚性行为形成鲜明对比。沿着阿尔伯塔落基山脉前缘的巨大逆冲背斜，如特纳山谷，是基底断层片的结果。这个复杂的地带被推到一个绵延数百英里的坚硬的前陆带的沉积盖层上，直到基底岩石的最终露头。
Summary A study of foreland fold zones indicates that the cover of sedimentary rocks plays a passive role and accommodates itself to movements of the basement beneath. Lateral pressure exerted along a sedimentary cover from a thrust mountain front, such as is implied by the Abscherung theory of Buxtorf to explain the Jura Mountains structures, is not regarded as probable. Mountain building is the consequence of contraction of the interior of the earth and crustal compression from this cause has been dominant throughout revealed geological time. Examples of compression structures in shield areas far distant from active mountain fronts, as in Nigeria, are described. The Gulf of Suez and the Dead Sea rift valleys show evidence of both compressional and tensional features, but the former is the more important. A crystalline basement complex can flexure and form the cores of anticlines with, in some cases, little or no faulting. Oil exploration borings in Venezuela, Sumatra and elsewhere have reached basement rocks in the core of anticlines and have shown that the active principle is movement of the basement and not sheared, rootless folding in the sedimentary cover produced by lateral pressure. Examples of different types of foreland folding are described. The Jura Mountains structures are ascribed to steep folding or fault-slices in the basement below, the sedimentary cover having become detached as a result of the lubricating effect of the Triassic salt and folded into an independent pattern. The South-West Persian mountain belt is taken as an example of simple folding with long anticlines of up to 250 miles in individual length. Assam is described as an example of imbric folding— strongly thrust-faulted anticlines arising from thrust-folds in the basement below. The great flexure on the south flank of the Shillong plateau. between the Himalayan front and the Assam ranges, shows how an apparently rigid crystalline complex can be bent into a steep flexure and an erosion surface down-warped to a depth of about 30,000 feet. Clay diapir anticlines in Trinidad are the surface expression of steep folding below a cover of soft incompetent clays, with high-pressure water and gas acting as agents to promote the upward extrusion of the clay core. Salt diapir anticlines, as distinct from circular salt plugs, also owe their origin to compressional movements in their substratum. The degree to which basement rocks have been faulted, folded or flexed in some foreland zones is in marked contrast to more rigid behaviour in others. The great thrust-anticlines along the Rocky Mountain front in Alberta, such as Turner Valley, are the consequence of fault-slices in the basement. This complex zone is thrust on to the sedimentary cover of an unyielding foreland zone extending for hundreds of miles to the eventual outcrop of the basement rocks.