Tectonic evolution of the western Mediterranean during the Late Paleozoic

对晚古生代泛大陆超大陆的各种重建——从泛大陆A1和A2到泛大陆B和C——自70年代末以来在古地磁界激起了一场生动的争论[见Van der Voo， 1993b及其参考文献]。在选择二叠纪Wegener型构造（Pangea A1）时，基于古地磁资料的古地理重建结果表明，冈瓦纳与劳拉亚大陆之间存在主要的大陆重叠。这些重叠可以通过将冈瓦纳沿着纬度线相对于劳亚大陆向东移动约3000公里来消除，这保持了古磁极的一致性。这种改变导致了另一种盘古大陆的构造，称为盘古大陆B [Irving， 1977]，它与魏格伦盘古大陆A1明显不同，并将南美洲（和非洲）置于欧洲南缘附近。由于早侏罗世大西洋的开放始于泛大陆A1构造，因此早侏罗世之前冈瓦纳和劳亚之间应该发生了主要的右旋切变。根据最近发表的一份古地理地图[Muttoni等人，2003]，这个右侧剪切带的假定位置必须位于地中海范围内，并且是araud和Matte[1977]先前设想的晚古生代活动的大规模剪切带的一部分。然而，公平地说，泛大陆B和它的构造含义并没有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型盆地系统”，正如McElhinny和McFadden[2000]在提到泛大陆B到泛大陆a的转变时所认为的那样。这是反对普遍接受泛大陆B的主要论据之一，尽管它与Arthaud和Matte[1977]建立的巨gashear模型兼容。这里提出的项目旨在从磁学上识别二叠纪岩石的赤纬模式，这种模式具有局部和区域范围，并推导出欧洲南部和北非大陆块体的旋转运动，这是由Arthaud和Matte[1977]的大gashear模型所暗示的。主要研究对象为撒丁岛、科西嘉岛、法国南部和西班牙的二叠纪至三叠纪陆相沉积岩和火山岩。在项目的后期阶段，这些研究将扩展到非洲北部边缘。标准的岩石磁学和岩石学调查以及取样岩石的数值年龄测定也将进行。

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.