CLAYS IN PALEOWEATHERING PROCESSES: STUDY OF A TYP ICAL WEATHERING PROFILE IN THE HERCYNIAN BASEMENT IN THE MONTES DE

ABSTRACT: A series of weathered Paleozoic slates was studied in an area southwest of the Montes de Toledo mountain range where the weathered slates are overlain by a rafia formation and show three weathering levels. The fresh slate (at 30 m depth) is composed offerrous chlorite, mica, quartz and feldspars. Inthe lowest part of the weathering profile the ferrous chlorite begins to evolve to smectite, and in the intermediate level, all the chlorite has been transformed into smectite. In the upper level (in contact with the rafia formation), the smectites volve to kaolinite, and the micas, which are unaffected atgreater depths, begin to evolve to vermiculite, and there has been segregation of the free iron oxyhydroxides producing red, ochre and white zones. Two principal weathering processes, separated intime but superimposed, have been identified. According to Sole & Llopis (1952) the Iberian Hercynian Massif ( IHM) is the oldest geologic basement in the Iberian peninsula, lying within the western half (Fig. 1). Because of its age, the IHM has been affected by the Hercynian orogeny (360-290 million years ago) and consequently the rocks (mostly granites, granodiorites, gneisses, mica-schists, lates, greywackes, quartzites and limestones) are metamorphosed and folded. Structurally it is defined by a series of blocks separated by old fractures, which were reactivated during th