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Alpine-Himalayan Orogens |
Geologisch Instituut, Universiteit van Amsterdam, Nieuwe Prinsengracht 130, Amsterdam, Netherlands
The Betic Cordilleras, the Alpine south-east flank of Spain, lie between the exposed, Hercynian and older rocks of the continental Spanish block and the oceanic basin of the western Mediterranean. To the south-west the Alpine orogen curves sharply across the Straits of Gibraltar into the Rif Mountains (see Choubert & Faure-Muret, this volume, pp. 37-46), but to the north-east, beyond the Balearic Islands, the orogen appears to be truncated at the margin of the western Mediterranean basin.
If the Balearic Islands are included, the Betic orogen stretches NE-SW for 1000 km approximately in a straight line. The south-east margin, with the western Mediterranean basin, is not well known. The north-west margin of the External zone (see below) with the Spanish Meseta is broadly gradational: the Alpine structures gradually disappear. Between these margins the orogen varies from 50 km to 200 km in width, averaging 120 km.
Segment: throughout this article detailed data relate to the Internal zone in a specific segment (see Fig. 1), which is some 65 km long and within which the zone averages 75 km in width. The External zone is described only in outline.
Zones: two zones—External and Internal—are recognized. The External zone mainly consists of non-metamorphic Triassic, Jurassic, Cretaceous and Tertiary sediments and contrasts strongly with the Internal zone, which is for the greater part built of metamorphosed Triassic and older rocks. No rocks older than (Permo-) Triassic have been found in the External zone, and horizontal translations of the order of those known to
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