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

盘古大陆在二叠纪时期的确切形状仍然是一个有争议的问题。特别是在基于古地磁资料的古盘古重建中，冈瓦那和劳伦西亚之间的大陆重叠是否超过1.000公里的问题仍然存在很大争议。承认这种大陆错位是真实的，这种重叠可以通过将冈瓦那向东移动约3000公里来克服(泛古大陆B)。这一举动并不违反古地磁的基本规律，但需要一个巨型剪切带，以便在大西洋开放之前将冈瓦那转变为盘古A构型。尽管撒丁岛和土伦盆地最近的古地磁研究表明，可能存在这样的巨型剪切带，但仍未被普遍接受，泛古大陆B的反对者认为，大陆重叠是一种人工产物，由于倾斜变浅，是沉积后的一种过程，通过这种过程，古地磁倾角被展平，获得磁化的古纬度被显著证伪。对用于古地理重建的所有沉积古地磁数据进行倾角变浅的全面校正可以减少重叠，但这种方法是否合适尚不清楚。摩洛哥的石炭-二叠纪沉积盆地，特别是梅塞塔盆地，对盘古大陆的重建起着关键作用。冈瓦那地区二叠纪高质量的古地磁资料相当稀缺，而对这里暴露的沉积和火山岩的古地磁研究具有极大的潜力来显著改善这种情况，并导致更强有力的古地理重建。其中许多盆地的地层由不同粒度的红层和夹层火山岩控制，这些火山岩达到了显著的厚度。通过仔细和详细的古和岩石磁学研究，有可能确定这些红层(色素和/或沉积赤铁矿)中的磁化载体，并通过使用相互竞争的方法来确定后者的倾斜变浅程度(如果有的话)。将沉积物的平均方位与沉积物正下方或上方的火山岩的平均方位进行比较，可以检验这些方法的可靠性。在分析倾角数据的同时，这项研究的目的是确定二叠纪盆地的旋转运动，可与在撒丁岛和法国南部观察到的旋转运动相媲美。确定围绕垂直轴的旋转将为巨型剪切带的存在提供额外的支持，而倾角与高质量的倾角数据结合在一起，将使冈瓦那在二叠纪期间得到强有力的重建。

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.