Changes

===Permian-Triassic Boundary (251 Ma)===

===Permian-Triassic Boundary (251 Ma)===

The beginning of the Mesozoic was marked by the end of the transitional stage from the Pangea B to Pangea A configurations (Irving, 1977; Morel and Irving, 1981; Muttoni et al., 1996; Torq et al., 1997; Bachtadse et al., 2002; Irving, 2005; Angiolini et al., 2007). The change in the configuration of Pangea required a west to east translation of Laurasia of some 3000 km (1864 mi) with respect to Gondwana (Figure 6). The dextral movement was accommodated along a lithospheric shear zone which runs from the subduction zone of Panthalassa eastward to a triple junction joining this shear zone, the Neo-Tethys ridge, and the subduction of Paleo-Tethys below the southern margin of Laurasia. This triple junction was located along the northern margin of the Tethys, close to southern Europe (Muttoni et al., 2009b).

The beginning of the Mesozoic was marked by the end of the transitional stage from the Pangea B to Pangea A configurations (Irving, 1977; Morel and Irving, 1981; Muttoni et al., 1996; Torq et al., 1997; Bachtadse et al., 2002; Irving, 2005; Angiolini et al., 2007). The change in the configuration of Pangea required a west to east translation of Laurasia of some 3000 km (1864 mi) with respect to Gondwana ([[:file:M106Ch01Fig06.jpg|Figure 6]]). The dextral movement was accommodated along a lithospheric shear zone which runs from the subduction zone of Panthalassa eastward to a triple junction joining this shear zone, the Neo-Tethys ridge, and the subduction of Paleo-Tethys below the southern margin of Laurasia. This triple junction was located along the northern margin of the Tethys, close to southern Europe (Muttoni et al., 2009b).

Northern Gondwana was characterized by the development of a mature passive margin along the Neo-Tethys Ocean, which started to open with a time-transgressive trend beginning in Carboniferous time (Al-Belushi et al., 1996; Garzanti and Sciunnach, 1997). Oceanic crust began forming as early as Early Permian time (Garzanti, 1999; Angiolini et al., 2003; Metcalfe 2006). The opening of the Neo-Tethys was responsible for the northward flight of the peri-Gondwanan blocks: in Early Triassic time these continental blocks were moving northward toward the southern margin of Asia. These blocks include a number of minor, semi-independent blocks such as Apulia, Taurides, Iran (NW and Central), Sanandaj Sirjian, Heland, and Northern Tibet (Ruban et al., 2007). In detail, Iran was crossing the equator (Muttoni et al., 2009b) before its docking to Eurasia, which gave rise to the Cimmerian orogeny. In contrast, to the east most of the blocks were still located south of the equator. The different velocities of the peri-Gondwanan blocks were probably controlled by the presence of roughly N-S trending transform faults, which defined portions of the Neo-Tethys oceanic ridge characterized by different rates of spreading. The existence of a complex network of oceanic branches during the opening of the Neo-Tethys has been suggested by Sengor (1990), who interpreted the peri-Gondwanan blocks as three independent ribbons migrating northward.

Northern Gondwana was characterized by the development of a mature passive margin along the Neo-Tethys Ocean, which started to open with a time-transgressive trend beginning in Carboniferous time (Al-Belushi et al., 1996; Garzanti and Sciunnach, 1997). Oceanic crust began forming as early as Early Permian time (Garzanti, 1999; Angiolini et al., 2003; Metcalfe 2006). The opening of the Neo-Tethys was responsible for the northward flight of the peri-Gondwanan blocks: in Early Triassic time these continental blocks were moving northward toward the southern margin of Asia. These blocks include a number of minor, semi-independent blocks such as Apulia, Taurides, Iran (NW and Central), Sanandaj Sirjian, Heland, and Northern Tibet (Ruban et al., 2007). In detail, Iran was crossing the equator (Muttoni et al., 2009b) before its docking to Eurasia, which gave rise to the Cimmerian orogeny. In contrast, to the east most of the blocks were still located south of the equator. The different velocities of the peri-Gondwanan blocks were probably controlled by the presence of roughly N-S trending transform faults, which defined portions of the Neo-Tethys oceanic ridge characterized by different rates of spreading. The existence of a complex network of oceanic branches during the opening of the Neo-Tethys has been suggested by Sengor (1990), who interpreted the peri-Gondwanan blocks as three independent ribbons migrating northward.