HR: 1340h
AN: T23D-1658    [Abstracts]
TI: Thermal History of the Maladeta Pluton: Multiple Thermochronologic Controls on the Burial Heating and Exhumation of the Pyrenean Axial Zone
AU: * Metcalf, J R
EM: jrmetcal@syr.edu
AF: Department of Earth Sciences, Syracuse University 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Fitzgerald, P G
EM: pgfitzge@syr.edu
AF: Department of Earth Sciences, Syracuse University 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Baldwin, S L
EM: sbaldwin@syr.edu
AF: Department of Earth Sciences, Syracuse University 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AU: Muñoz, J A
EM: josep@geo.ub.es
AF: Group de Geodinàmica i Anàlisi de Conques, Departament de Geodinàmica i Geofisica, Universitat de Barcelona, Barcelona, 08028, Spain
AU: Schwabe, E
EM: easchwabe@syr.edu
AF: Department of Earth Sciences, Syracuse University 204 Heroy Geology Laboratory, Syracuse, NY 13244, United States
AB: The Pyrenees are a doubly vergent orogen that formed since the Late Cretaceous as a result of convergence between the European and Iberian plates. During convergence, normal faults were inverted, becoming thrust faults that, in the central Pyrenees, accommodated up to 165 km of shortening. The orogen comprises a central axial zone (AZ) of Hercynian basement, flanked north and south by fold and thrust belts, in turn flanked by the Aquitane and Ebro foreland basins. The AZ is a complex south-vergent duplex that culminates in an antiformal stack of three upper crustal basement thrust sheets. The Maladeta pluton, a Hercynian granitic massif intruded into Silurian-Carboniferous metasediments, lies within the Orri thrust sheet. New K-feldspar ⁴⁰Ar/³⁹Ar and apatite (U-Th)/He thermochronology combined with previous thermochronology and detailed structural studies of the Maladeta pluton provide a record of post-Hercynian cooling, relative Mesozoic tectonic stability, Late Cretaceous burial and heating, and rapid Cenozoic cooling and denudation. K-feldspar ⁴⁰Ar/³⁹Ar maximum ages from the highest elevations of the Maladeta pluton (2850m) are ~300 Ma, close to the age of intrusion, suggesting that the Maladeta cooled relatively quickly and remained near the surface or in the upper crust for most of the Mesozoic. This interpretation is consistent with geologic evidence that indicates the Maladeta pluton was part of thinned and extended continental crust, stretched between Iberia and Europe during Mesozoic time, on which marine sediments were deposited unconformably. K-feldspar ⁴⁰Ar/³⁹Ar multiple diffusion domain (MDD) thermal models from two samples at lower elevations in the Maladeta (1780m and 1400m) record heating beginning at ~80 Ma, reaching maximum temperatures of 270° to 280° C. We interpret this Cretaceous thermal event to represent burial of the Maladeta pluton as the Orri thrust sheet underthrust the Nogueres thrust sheet. This interpretation is consistent with the late Santonian (85.8 - 83.5 Ma) onset of convergence in the Pyrenees recorded by a significant regional unconformity. This Late Cretaceous burial and heating was followed by a period of rapid cooling, beginning at 50-60 Ma, and continuing to at least 30 Ma. Existing lower-temperature thermochronology data (apatite fission track, apatite (U-Th)/He), in addition to our (U-Th)/He ages from the Maladeta indicate extremely rapid cooling at 32-30 Ma due to erosional denudation, with the rate of cooling, and hence erosion, slowing from 30 Ma until ~15 Ma. This lower-temperature thermochronologic record is consistent with constraints from the new K-feldspar MDD models. Thus, we interpret the thermal record of the Maladeta pluton to represent cooling following intrusion during the Hercynian Orogeny, burial during deposition of Permian-Cretaceous sediments in an extensional basin, heating associated with crustal thickening due to thrusting during convergence between Iberia and Europe, and rapid cooling due to erosional denudation during the Cenozoic following the formation of the antiformal stack.
DE: 1140 Thermochronology
DE: 8108 Continental tectonics: compressional
DE: 8110 Continental tectonics: general (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting