Abstract: Thermal evolution of the thrust system of French outer Alps: an overview from analytical data and modeling techniques

DEVILLE E

The outer parts of the western Alps constitutes a classical foreland fold-thrust belt including several tectonostratigraphic units (the Jura, the Molasse Basin and the Subalpine chains). These are largely overthrust by the Prealpine klippes issued from the inner zones of the Alpine orogenic wedge. All these units underwent a complex thermal history related to the polyphased kinematic evolution of the thrust system.

New ROCK-EVAL 6 pyrolysis analyses on field and well samples provided good calibration of the maturity of organic-rich rocks. Notably, these maturity data clearly image locally the deformation of the isomaturity surfaces, as well as extensive erosion processes in some places (notably in the Bornes area).

2D forward structural-thermal-maturity modeling using the THRUSTPACK program provided a reconstruction of the thermal history occurred within the thrust system.

The integration of the analytical data and the modeling results evidences several areas showing very different thermal evolutions vs. tectonic history:

(1) the Vercors area where the present day maturity distribution is mostly reached before thrust tectonics (as soon as Cretaceous), (2) The Molasse Basin the maturity paroxysm is attained progressively during the deposition of Oligocene-Aquitanian passive flexural sequences and during the Miocene thrust tectonics, (3) The Bornes massif where the present-day maturities are related to the tectonic setting of the Prealpine napes (now partly eroded) during Oligocene times, and (4) the Chartreuse area where the highest maturities are attained during the Miocene to Present thrust tectonics.

As such, the timing between maturation and trap development is very variable and obviously the still attractive areas appear as totally unexplored.

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