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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Magnetic evidence for slow seafloor spreading during the formations of the Newfoundland and Iberian margins
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Magnetic evidence for slow seafloor spreading during the formations of the Newfoundland and Iberian margins

机译：纽芬兰和伊比利亚边缘形成期间缓慢海底扩散的磁性证据

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There is considerable debate concerning the nature and origin of the thin crust within the ocean-continent transition (OCT) zones of many passive non-volcanic continental margins, located between thinned continental and true oceanic crust. This crust is usually found to be underlain by upper mantle material of 7.2-7.4 km/s velocity at shallow depths (1-2 km). It has been proposed that such crustal material could have originated either by exhumation of upper mantle material during rifting of continents or by slow seafloor spreading. One of the examples of occurrence of such a crust are the conjugate margins of Newfoundland and Iberia. Here we present an interpretation of magnetic data from these regions to show that their OCT zones are underlain by crustal material formed by slow seafloor spreading (6.7 mm/yr) soon after Iberia separated from the Grand Banks of Newfoundland in the late Jurassic. Similarities in the magnetic anomalies and velocity distributions from these regions with those from the Sohm Abyssal Plain, a region lying immediately south of the Newfoundland Basin and formed by seafloor spreading at a similar rate of spreading, give further support to such an interpretation. The idea that these regions were formed by unroofing of upper mantle during rifting of Iberia from Newfoundland may be likely but the presence of weak magnetic anomalies in these regions, which bear all the characteristics of seafloor spreading anomalies, makes it difficult to ignore the possibility that these regions could be underlain by oceanic crust formed during slow seafloor spreading. The similarities in velocity structure and the presence of small amplitude magnetic anomalies both across this pair of conjugate margins of the North Atlantic and that of the Labrador Sea suggest that this OCT velocity structure may be the norm rather than the exception across those passive non-volcanic margins where the initial seafloor spreading was slow. Furthermore, the existence of similar velocity distributions along a few active spreading centers raises the possibility of formation of similar crust across slow spreading ridges.
机译：在稀薄大陆和真实洋壳之间的许多被动非火山大陆边缘的海陆过渡带（OCT）区域内，关于薄壳的性质和成因存在很多争论。通常发现该地壳是浅层深度（1-2公里）以7.2-7.4 km / s速度的上地幔物质包裹的。已经提出，这种地壳物质可能是由于大陆裂谷期间上地幔物质的发掘或海底缓慢扩散而产生的。发生这种地壳的例子之一是纽芬兰和伊比利亚的共轭边缘。在这里，我们对这些地区的磁数据进行了解释，以显示在伊比利亚在侏罗纪晚期从纽芬兰大河岸分离后不久，由缓慢的海底扩散（6.7毫米/年）形成的地壳物质支撑着它们的OCT带。这些区域的磁异常和速度分布与索姆深渊平原的磁异常和速度分布相似，索姆深渊平原位于纽芬兰盆地以南，由海床以相似的扩展速度扩展形成，为这种解释提供了进一步的支持。这些区域可能是从纽芬兰（Newfoundland）分离伊比利亚（Iberia）期间由上地幔顶开形成的想法，但是这些区域中存在弱磁异常，这些异常具有海底扩散异常的所有特征，因此很难忽略以下可能性：这些区域可能被缓慢的海底扩散过程中形成的洋壳所覆盖。在北大西洋和拉布拉多海的这对共轭边缘，速度结构的相似性和小振幅磁异常的存在表明，这种OCT速度结构可能是正常的，而不是那些被动非火山的异常最初海底扩散缓慢的边缘。此外，沿着几个活动扩展中心存在相似的速度分布，增加了在缓慢扩展的脊上形成相似的地壳的可能性。

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