Paleomagnetism of Permian Basins in Morocco - A Contribution to Late Paleozoic Geodynamivs in the Western Mediterranean
Palaeontology
Final Report Abstract
The configuration of Pangea in the early Permian is still not unequivocally accepted and hinges on the interpretation of the paleomagnetic data from Laurasia and Gondwana for the late Paleozoic and on the question whether paleomagnetic data for Adria are representative for Gondwana. Whereas the early Permian paleomagnetic dataset for Laurasia is considered rather robust this is not true for Gondwana. However, taking the paleomagnetic data for both continents at face value and comparing the paleolatitudes for their northern and southern margins a continental overlap of about 1000km results in a conventional Wegnerian Pangea (A) reconstruction, calling for an alternative Pangea reconstruction (Pangea B) where Gondwana is positioned roughly 3000km further to the east. Since there is a general agreement, however, that the break-up of Pangea and the opening of the Atlantic ocean started from a classical Pangea A configuration, a major megashear zone is required along which Gondwana can be transferred into the pre-break-up configuration. This model is strongly debated and the existence of such an intracontinental shear system questioned. However, there is conclusive paleomagnetic evidence for major block rotations of early Permian age in the western Mediterranean, which could be taken as evidence for the activity of such a shear zone but it is unclear, whether the (a) Permian basins of Morocco have also been part of this shear zone and whether the (b) quality of the Permian paleomagnetic data from Morocco, playing a key role in this debate, are of sufficiently high quality for reliable paleogeographic reconstructions. Addressing these two points described above, this project targeted the early Permian basins of the Morocco Meseta. Du ring two field campaigns, 994 samples from 15 late Paleozoic basins and two late Paleozoic plutons were collected at 152 locations and later analyzed rock and paleomagnetically. Ten of these basins yield coherent results and based on stability tests and the presence of geomagnetic reversals these are interpreted tobe of primary origin e.g. of early Permian age. Resulting virtual geomagnetic pole positions (VGPs) are strung out along a NE-SW trending small circle exceedng 60° in width and intersecting the early Permian segment of the reference apparent polar wander path{APWP) for Gondwanan, The associated rotation pole is located in Morocco, diagnostic for significant vertical axis block rotations within the Meseta which are interpreted tobe syndepositional and can be related to intra-Pangean strike slip faulting. The resulting paleolatitudes based on inclination data independent of the studied rock types position the Morocoon Meseta close to the paleo-equator allowing a Pangea A-Type configuration with no continental overlap. Furthermore, our new data questions the validity of the continental coherence of the Adriatic microplate and Gondwana in the early Permian.
Publications
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Paleomagnetism of Permian basins in Morocco – a contribution to Late Paleozoic geodynamics in the Western Mediterranean, Köln.
Weissbrodt, V., V. Bachtadse, H. Saber & A. Ronchi
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Tectonic imprints in Permian paleomagnetic data of Morocco. Earth-Science Reviews, 254, 104787.
Weissbrodt, Vinzenz; Bachtadse, Valerian; Kirscher, Uwe; Saber, Hafid; Liu, Yebo & Ronchi, Ausonio
