Paleomagnetism of Permian Basins in Morocco - A Contribution to Late Paleozoic Geodynamivs in the Western Mediterranean

摩洛哥二叠纪盆地的古地磁——对西地中海晚古生代地球动力学的贡献

• 批准号: 374919867
• 负责人: Professor Dr. Valerian Bachtadse
• 金额: --
• 依托单位: Sektion Geophysik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/374919867?language=en
• 关键词: Paleomagnetism; Permian; Basins; Morocco; Contribution

The exact configuration of Pangea during Permian times is still a matter of debate. Espe-cially the question whether the continental overlap of more than 1.000km between Gondwana and Laurentia in classical Pangea reconstructions which are based on paleomagnetic data is still debated in a very controversial way. Accepting this continental misfit as real ,the overlap can be overcome by shifting Gondwana some 3000km to the east (Pangea B). This move does not violate the fundamental laws of paleomagnetism, but requires a mega shear zone in order to transfer Gondwana into the Pangea A configuration prior to the opening of the Atlantic ocean. Although, recent paleomagnetic studies in Sardinia and the Toulon- basin have demonstrated that such a mega-shear zone might have existed it has not been generally accepted and opponents of Pangea B have argued that the continental overlap is an artifact and due to inclination shallowing, a post sedimentary process by which the paleomagnetic inclination is flattened and the paleolatitude at which the magnetization has been acquired is falsified signifi-cantly. Applying a blanket correction for inclination shallowing to all sedimentary paleomagnetic data used for palaeogeographic reconstructions reduces rmoves the overlap but whether this procedure is appropriate is not clear. The Permo-Carboniferous sedimentary basins of Morocco, especially of the Meseta, play a key role for Pangea reconstructions. High quality paleomagnetic data for Gondwana for Permian times are rather scarce and paleomagnetic studies of the sedimentary and volcanic rocks exposed here have very high potential to significantly improve this situation and to lead to a more robust paleogeographic reconstruction. The stratigraphy of many of these basins is controlled by red beds of various grain sizes and intercalated volcanic rocks which achieve significant thicknesses. By careful and detailed paleo- and rock magnetic studies it is possible to identify the carriers of magnetization in these red beds (pigmentary and/or sedimentary hematite) and by the use of competing methods to determine the degreeof inclination shallowing, if any, in the latter. Comparison of the mean directions obtained for sediments to those from volcanic rocks directly below or above the sediments allows a test of the reliabilty of these methods. Parallel to the analysis of inclination data, the study aims at identification of rotational movements of the Permian basins comparable to the ones observed in Sardinia and southern France. The identification of rotations about vertical axis will yield additional support to the existence of a mega shear zone and declinations taken together with high quality inclination data will allow a robust reconstruction of Gondwana during Permian times.

二叠纪时期盘古大陆的确切构造仍然是一个有争议的问题。特别是在古地磁资料重建的古大陆重建中，冈瓦纳大陆和劳伦大陆之间是否存在1000 km以上的大陆重叠，至今仍存在很大争议。如果承认这种大陆错位是真实的，那么这种重叠可以通过将冈瓦纳大陆向东移动约3000公里（盘古大陆B）来克服。这一移动并不违反古地磁学的基本定律，但需要一个巨大的剪切带，以便在大西洋开放之前将冈瓦纳转变为盘古大陆A的配置。虽然最近在撒丁岛和土伦盆地的古地磁研究表明，这样一个巨型剪切带可能已经存在，但它并没有被普遍接受，泛大陆B的反对者认为大陆重叠是人为的，由于倾斜变浅，沉积后的过程，通过该过程，古地磁倾角变平，并且已经获得磁化的古纬度被显著地伪造，尖锐地。对所有用于古地理重建的沉积古地磁数据应用倾斜变浅的覆盖层校正减少了重叠，但这种程序是否合适尚不清楚。摩洛哥的石炭纪-二叠纪沉积盆地，特别是梅塞塔盆地，在泛大陆重建中起着关键作用。冈瓦纳二叠纪时期的高质量古地磁数据是相当稀缺的，这里暴露的沉积岩和火山岩的古地磁研究有很大的潜力，显着改善这种情况，并导致更强大的古地理重建。这些盆地中的许多盆地的地层学受不同粒度的红层和厚度相当大的火山岩夹层的控制。通过仔细和详细的古地磁和岩石磁学研究，有可能确定这些红层中的磁化载体（颜料和/或沉积赤铁矿），并通过使用竞争方法来确定后者的倾斜变浅程度（如果有的话）。将沉积物的平均方向与沉积物正下方或正上方火山岩的平均方向进行比较，可以检验这些方法的可靠性。平行的倾斜数据的分析，研究的目的是识别二叠纪盆地的旋转运动在撒丁岛和法国南部观察到的。围绕垂直轴的旋转的识别将产生额外的支持，一个大剪切带的存在和高质量的倾斜数据一起采取的磁偏角将允许在二叠纪时期的冈瓦纳强大的重建。