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| Journal of the Geological Society |  |
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Original Article |
1 1Research School of Earth Sciences at UCL-Birkbeck, London WC1E 6BT, UK (e-mail: John.Platt@ucl.ac.uk)
2 2Department of Earth Sciences, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
3 3Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
4 4Department of Earth Science and Engineering, Imperial College of Science, Technology and Medicine, Prince Consort Road, London SW7 2BP, UK
The Ronda peridotite in the Betic Cordillera of southern Spain is a relic of the sub-orogenic lithospheric mantle that was exhumed during earliest Miocene time from about 66 km depth. Overlying crustal rocks show an apparently coherent metamorphic zonation from high-pressure granulite-facies rocks at the contact to unmetamorphosed rocks 5 km higher in the structural sequence, indicating drastic tectonic thinning of the whole orogenic crust during exhumation. P–T paths from the peridotite and its crustal envelope indicate decompression with rising temperature to shallow depths. U–Pb ion microprobe dating of zircon, Ar/Ar dating of hornblende, Ar/Ar laserprobe dating of muscovite and biotite, and fission-track analysis of zircon and apatite reveal that cooling was extremely rapid in the interval 21.2–20.4 Ma. One-dimensional thermal modelling of the array of P–T–time paths indicates that an asthenospheric heat source at an initial depth of about 67.5 km is required to explain heating during exhumation, and that the main period of exhumation lasted 5 Ma, starting at around 25 Ma. Exhumation must therefore have directly followed removal of most, but not all, of the lithospheric mantle beneath the Betic orogen, and was coeval with a period of late orogenic extension that profoundly modified the crustal structure and created the present-day Alboran Sea in the western Mediterranean.
KEYWORDS: Betic Cordillera, absolute age, exhumation, thermobarometry, extensional tectonics
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