Abstract

Cooling-rate estimates of 150-350 °C/m.y., suggesting magnitudes of uplift and exhumation of ∼15-20 km at rates of 5-10 km/m.y., are proposed for the final stage of the orogenic development in a major part of the Betic Cordilleras. The results are based on a combination of radiometric and paleontological dates. Six isotopic chronometers (muscovite and biotite whole-rock Rb-Sr, muscovite and biotite 40Ar/39Ar, biotite K-Ar, and whole-rock Rb-Sr) yield analytical ages between 23 and 18.5 Ma for rocks from Alpine nappe complexes. Nappe-sealing marine sedimentary rocks contain early Miocene foraminifera and nannoplankton indicating minimum ages of 18-15.5 Ma. The very high estimates of cooling and uplift-exhumation rates suggest tectonic unroofing, which is tentatively connected geodynamically to lithospheric slab detachment and concomitant diapirism in the upper mantle, and extensional tectonics in the crustal section.

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