A càrrec de Joaquim JUEZ-LARRÉ (TNO - Geological Survey of the Netherlands, Països Baixos)
Organitzat conjuntament CSIC-UB

Dia: 06-04-2011
Hora: 12:00
Lloc: Sala d'actes de l'Institut Jaume Almera

Descripció:
In the last decades fission-track and (U-Th)/He thermochronometry in apatites and zircons have become an important tool for quantifying the cooling history of rocks as they pass through the upper crust. The Iberian Peninsula and the Central Andes are two exemplary areas where the use of low temperature thermochronology has provided remarkable new insights into their geological evolution.

Numerous thermochronological studies in Iberia report the resetting of many thermochronological systems of Variscan basement rocks during the break-up of Pangea (<200 Ma). Numerical modelling allows assessing the conditions under which rocks in the upper crust may have been thermally reset and the mechanisms likely involved. Active rifting combined with shallow magmatism, and to a lesser extent deep sedimentary burial, could have led to an increase of the geothermal gradient up to ~73 °C/km, and the reset of thermochronometers.

Over the last thirty years a plethora of models have been suggested in an attempt to explain how a plateau-type orogen formed at the leading edge of western South America. New thermochronological data from the Coastal Cordillera provide a new insight into the thermal and exhumation history of this forearc. Young apatite (U-Th)/He ages reveal a cooling event, never reported previously, between 40 and 50 Ma (Eocene). Two scenarios have been explore that can provide an explanation for the observed cooling; 1) forearc uplift and exhumation, and 2) changes in plate subduction dynamics. Erosion rates of 0.24 to 0.36 km/Myr, for a period of 10 Myr, are necessary to explain the cooling event. Alternatively, the subduction of a ridge could explain significant cooling by flat slab dewatering. Based on recent sea floor spreading reconstruction, we suggest the subduction of the Farallon-Phoenix ridge as a possible candidate. The subduction of this ridge can account for the cooling event at 40-50