Tectonic evolution of the western Mediterranean during the Late Paleozoic

从盘古大陆A1和A2到盘古大陆B和C，对晚古生代盘古超大陆的各种重建自20世纪70年代末以来在古地磁学界引起了激烈的争论[参见货车der Voo，1993 B及其参考文献]。当选择Wegener型配置（盘古大陆A1）在二叠纪，古地理重建古地磁数据的基础上，在冈瓦纳和劳亚大陆之间的主要大陆重叠。这些重叠可以通过将冈瓦纳大陆相对于劳亚大陆沿沿着向东移动约3000公里来消除，这保持了古磁极的一致性。这种变化导致了另一种盘古大陆的构型，称为盘古大陆B [欧文，1977]，它明显不同于韦格纳盘古大陆A1，并将南美洲（和非洲）与欧洲南缘相邻。由于早侏罗世大西洋的打开是从泛大陆A1构造开始的，因此早侏罗世之前冈瓦纳和劳亚大陆之间应该发生了主要的右旋剪切。根据最近出版的古地理图[Muttoni等人，2003年]，假定该右旋剪切带的位置必须位于地中海范围内，并形成Arthaud和Matte [1977年]先前设想的晚古生代期间活动的大规模剪切带的一部分。然而，可以公平地说，盘古B及其构造含义尚未被地球科学界广泛接受，主要是因为没有合理的地质证据可以解释如此巨大的巨震系统，正如McElhinny和McFadden [2000]所认为的那样，指的是盘古B到盘古A的转变。这是反对泛大陆B被普遍接受的主要论点之一，尽管它与Arthaud和Matte [1977]建立的巨震模型是兼容的。这里提出的项目旨在用磁力识别二叠纪岩石中具有局部和区域范围的地壳运动模式，并推导出Arthaud和Matte [1977]的巨震模型所暗示的南欧和北方非洲大陆块体的旋转运动。本研究的主要目标包括撒丁岛、科西嘉、法国南部和西班牙的二叠纪至三叠纪大陆沉积岩和火山岩。在该项目的后期阶段，这些研究将扩大到非洲北方边缘。还将进行标准的岩石磁学和岩相学调查以及对取样岩石进行数字年龄测定。

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.