THE PROTOGONOS: A LONG LIVED MAGMATIC ARC ALONG THE NORTHERN MARGIN OF GONDWANA-LAND AND ITS DISRUPTION DURING THE HERCYNIAN OROGENY

The Hercynian Orogenic Belt occupies a 8000 km long swath from the Carpathians to the Huastecan Belt in Mexico and a 1000 km wide swath from the North Sea to the Sahara. Its formation took place in the late Carboniferous and resulted in the final amalgamation of Pangaea. The pre-collisional palaeogeography and formation of this complex and re-deformed belt is still debated.

This study focuses on European and African parts of this orogenic belt and uses a methodology of comparative anatomy of orogens to resolve its evolution. Every orogenic belt has its own organs represented by distinct rocks assemblages. Magmatic arc, fore-arc and back-arc regions are basic body parts of an orogenic belt. These body parts may not be developed properly in every orogenic belt but the most common feature among all these is the magmatic arc marking the former plate boundary. Properly-identified and well-dated magmatic rocks can be used as indicators of geodynamic environments, and even as reliable witnesses of geodynamic evolution. To identify the magmatic arcs, the intermediate and felsic magmatic rocks, namely granodiorites, diorites, andesites, granites, and rhyolites are used. For this purpose, geological maps of the relevant regions were digitized and mapped as one geological map. ~2700 high quality isotopic age data were collected from the literature. 1138 of them are interpreted as products of a single magmatic arc which had been active from the Ediacaran to the late Carboniferous on the northern margin of Gondwana-Land. The fragments of this magmatic arc repositioned according to the displacements on the major transcurrent faults at that time. For this purpose, Pangaea B reconstruction template is used to replace the tectonic units. This magmatic arc is herein named “Protogonos” (=the first born). Magnetic anomaly maps and structural trend lines are used as supplements in identifying the extent and evolution of Protogonos. Therefore, our geological reconstruction shows that the Pangaea B model seems more appropriate for the early Permian which then shifted to Pangaea A model at the end of the Permian as palaeomagnetically supported. This invalidates former geological arguments against Pangaea B.