Abstract: Combined Fission Track Analysis and Tectonic Modeling of the West Iberian Margin

STAPEL, GERCO, PAUL ANDRIESSEN, and SIERD CLOETINGH

We compiled data on the West Iberian margin to investigate the thermal history and tectonics of the Lusitanian basin (Portugal). The Lusitanian basin records the opening of the North Atlantic during the Mesozoic and was subjected to Alpine compression during the Cenozoic. To constrain the Mesozoic and Cenozoic denudation episodes we analyzed 40 fission track samples consisting of both a regional coverage of the Variscan basement and selected vertical profiles. We applied forward tectonic modeling to an extensive seismic data set covering the majority of the Lusitanian basin that was recently re-interpreted and depth converted by GEUS Copenhagen. Furthermore, free air gravity and bathymetry were used in conjunction with well data to constrain the large-scale structure of the margin.

Our regional forward tectonic modeling suggests that the main extension leading to continental breakup was located West of the present-day shelf break during the Early Cretaceous. Subsidence analysis of the Lusitanian basin records two earlier stretching phases during the Triassic Jurassic followed by Early Cretaceous hiatuses. This general picture is consistent with the fission track data that suggest, with the assumption of a 30 C/km geotherm, a phase of Late Mesozoic cooling at a rate of about 30 m/Ma. Because our fission track data constrain the Cenozoic cooling rates of about 200 m/Ma quite well, we are able to discuss in our paper the implications of our analyses for the Mesozoic and Cenozoic mass balance of the West Iberian margin.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria