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Volume 27 (1) - 2004

IETTO A. & IETTO F.

Age and history of the weathering of granitoids in southern Calabria (Italy)

Pages 37-45

Abstract

The main outcrops of granitoid rock in the Italian peninsula are to be found in Calabria or, to be more precise, in Southern Calabria. The literature which, up to now, has studied the weathering process of these rocks, even though limited to the Serre mountains, has always implicitly or explicitly stated that these occurred in an environment with a «Mediterranean climate» and, consequently, during the Pleistocene, taking into account the climatic variations of this period. This assumption is the basis from which the various stages of maturity of these processes have been studied area by area, adopting the classic methods of analysis or proposing some new techniques. Our recent studies enable us to state that the beginning of the weathering process in Calabrian granitoids dates back at least to the pre-Tortonian and that the present outcrops of granitic alterithes are the erosive residual of more ancient mantles. Consequently, the degree of maturity that can now be observed in different outcrops depends essentially on the extent of the superficial erosive processes. The stratigrafic columns do not show the degree of maturity that the weathering has reached but the immaturity of the deepest levels of the more ancient mantles that progressively emerge. The areas with more mature alterith outcrops are, however, those which are more protected from the erosive stripping. In the two principal mountain chains of southern Calabria it can be observed that: a) on the promontory of Mt. Poro, between Vibo Valentia and Tropea, the granitoids are covered by Tortonian transgressive sediments made up of very fossiliferous sandstones and calcarenites. The basic conglomerate elements are all in an advanced phase of spheroidal weathering; b) in the Serre mountains, the granitoids do not have a sedimentary covering and so it can be supposed that their continental outcrops have never been interrupted from the Miocene to today. Also here, the weathering mantles are the thickest to be found in the whole of Calabria (up to 40-45 m). The Pleistocene uplift of the mountain chain has been estimated to be of about 0,6-0,8mm/year on average. At the same time an intensity of 800-1000 tn/km2 is estimated for the erosive stripping. Therefore, the weathering of Calabrian granitoids was already mature in the Miocene.

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