Tectonic evolution of the western Mediterranean during the Late Paleozoic

点击翻译按钮获取中文摘要

Varieties of reconstructions for the Late Paleozoic Pangea supercontinent - ranging from Pangea A1 and A2 to Pangea B and C - have stirred a vivid debate within the paleomagnetic community since the late `70s [see Van der Voo, 1993b and references therein]. When choosing a Wegener type configuration (Pangea A1) in the Permian, paleogeographic reconstructions based on paleomagnetic data result in major continental overlaps between Gondwana and Laurasia. These overlaps can be eliminated by shifting Gondwana along lines of latitude to the east with respect to Laurasia by about 3000 km, which maintains the coherence of the paleomagnetic poles. This modification results in an alternative configuration of Pangea called Pangea B [Irving, 1977], which markedly differs from the Wegenerian Pangea A1 and places South America (and Africa) adjacent to the southern margin of Europe. Since the opening of the Atlantic Ocean in Early Jurassic times started from a Pangea A1 configuration, major dextral shear should have occurred between Gondwana and Laurasia prior to the Early Jurassic. Based on a recently published paleogeographic map [Muttoni et al., 2003], the supposed location of this dextral shear zone must lie within the Mediterranean realm and form part of a great-scale shear zone active during the Late Paleozoic as previously envisaged by Arthaud and Matte [1977]. However, it is fair to say that Pangea B and its tectonic implications have not been widely accepted by the Earth sciences community, essentially because ¿there is no plausible geological evidence that would account for a megashear system of such magnitude¿, as opined by McElhinny and McFadden [2000] referring to the Pangea B to Pangea A transformation. This is one of the main arguments against the general acceptance of Pangea B despite its compatibility with the well established megashear model of Arthaud and Matte [1977]. The project proposed here is designed to magnetically identify declination patterns in Permian rocks which are of local and regional extent and to derive rotational movements of continental blocks in southern Europe and northern Africa as implied by the megashear model of Arthaud and Matte [1977]. Main targets for this study comprise Permian to Triassic continental sedimentary rocks and volcanic rocks in Sardinia, Corsica, southern France and Spain. At a later stage of the project, these studies will be extended to the northern margin of Africa. Standard rockmagnetic and petrographic investigations as well as numerical age determinations of the sampled rocks will also be carried out.