Thermal evolution, rate of exhumation, and tectonic significance of metamorphic rocks from the floor of the Alboran extensional basin, western Mediterranean

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doi: 10.1029/98TC02204
Author(s): Platt, J. P.; Soto, J. I.; Whitehouse, M. J.; Hurford, A. J.; Kelley, S. P.
Author Affiliation(s): Primary:
University College London, Department of Geological Sciences, London, United Kingdom
Universidad de Granada, Spain
Swedish Museum of Natural History, Sweden
Open University, United Kingdom
Volume Title: Tectonics
Source: Tectonics, 17(5), p.671-689. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0278-7407 CODEN: TCTNDM
Note: In English. 81 refs.; illus., incl. 3 tables, sketch map
Summary: High-grade metamorphic rocks drilled at Ocean Drilling Program Site 976 in the Alboran Sea show a PT path characterized by decompression from about 1050 MPa (40 km depth) to 350 MPa (13 km depth) accompanied by an increase in temperature from about 550°±50°C to 675°±25°C. The Ar/Ar dating on muscovite and apatite fission track analysis indicate that the final stage of exhumation and cooling occurred very rapidly in the interval 20.5-18 Ma, which coincides with the initiation of sedimentation in the Alboran Sea basin. The Alboran Sea formed by Miocene extension on the site of a Late Cretaceous? to Paleogene contractional orogen, and extension coincided with thrusting in the peripheral parts of the Betic-Rif arc, which surrounds the basin on three sides. Thermal modeling of the PT path was carried out with the aim of constraining geodynamic models for the formation of the basin. Variables considered in the modeling included (1) the thickness and thermal gradient of the postorogenic lithosphere; (2) the radiogenic heat production in the thickened crust; (3) the time gap (pause) between the end of contractional tectonics and the start of extension; (4) removal of lithospheric mantle below 125, 75, or 62.5 km; and (5) the rate of extension. The only combinations of variables that produce modeled PT paths with the observed characteristics involve high radiogenic heat production combined with a significant postcontractional pause (to produce high temperatures in rocks initially at 40 km depth), removal of lithosphere below 62.5 km (to produce further heating during decompression), extension by a factor of 3 in 6 m.y. (to delay the attainment of the maximum temperature until the rocks reached shallow depths), and final exhumation and cooling in about 3.3 m.y. (to satisfy radiometric and petrological constraints). This gives a maximum of about 9 m.y. for exhumation from 40 km depth to the surface. Lithospheric stretching in response to plate-boundary forces such as trench rollback, without removal of lithosphere, cannot explain the late onset of heating and the high temperatures reached by these rocks. Removal of lithosphère at depths significantly greater than 62.5 km cannot explain the combination of high temperatures reached by these rocks and the shallow depth at which they attained the maximum temperature. Only a combination of significant postcollisional radiogenic heating, then whole-sale removal of lithospheric mantle below the orogenic crust, followed by rapid stretching can explain the observed PT path. These results appear to support some form of lithospheric delamination as the primary cause for the formation of the Alboran Sea basin. Copyright 1998 by the American Geophysical Union.
Year of Publication: 1998
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 18 Geophysics, Solid-Earth; Absolute age; Alboran Basin; Alboran Sea; Ar/Ar; Biotite; Cenozoic; Compression tectonics; Cores; Exhumation; Extension tectonics; Geodynamics; Geologic barometry; Geologic thermometry; Heating; High temperature; High-grade metamorphism; Mediterranean Sea; Metamorphic rocks; Metamorphism; Mica group; Muscovite; Nesosilicates; Orthosilicates; P-T conditions; Petrography; Plate collision; Plate tectonics; Sheet silicates; Silicates; Tectonics; Temperature; Thermal history; U/Pb; West Mediterranean; Zircon; Zircon group
Coordinates: N350000 N380000 W0010000 W0050000
Record ID: 1999012179
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.