Thermal evolution of early passive margins formation and consequences on their geophysical signature
Résumé
Many large-scale dynamic processes, from continental rifting
to plate subduction, are intimately linked to metamorphic reactions.
This close relation between geodynamic processes and
metamorphic reactions is, in spite of appearances, yet poorly understood.
For example, during extension processes, rocks will be
exposed to important temperature, pressures and stress changes.
Meanwhile less attention has been paid to other important aspects
of the metamorphic processes. When reacting rocks expand and
contract, density and volume changes will set up in the surrounding
material.
While several tectonic models are proposed to explain the formation
of extensive basins and passive margins ( simple shear
detachment mantle exhumation .... ) a single thermal model
(McKenzie, 1978), as a kind of dogma, is used to understanding
and modeling the formation and evolution of sedimentary basins.
The study of the thermal evolution, coupled with other tectonic
models, and its consequences have never been studied in detail,
although the differences may be significant. And it is clear that
the petrological changes associated with changes in temperature
conditions, influence changes reliefs.
Constrained by the new field data of north Pyrenean basins on
thermal evolution of pre-rift and syn-rift sediments, we explore
the petrological changes associated to different thermal evolution
and the consequences on the subsidence of the basins. We will
also present numerical models quantifying mineralogical and physical
changes inside the whole lithosphere during rifting processes.
In the light of these models, we discuss the consequences of different
thermal evolution on the subsidence processes as well as on
gravimetry and seismic velocities signature of passive margins.