The south-Pyrenean thrust sequence and thermal history in the eastern Jaca basin (W-central southern Pyrenees)
Résumé
The Jaca basin is a thrust-sheet top basin transported southward and
underlain by basement and cover thrusts separated by a Triassic décollement.
Basin-fill upper Cretaceous to lower Oligocene synorogenic sequences
record a southward depocenter migration, while growth strata
date a shift of deformation from the mid-Eocene in the N to the early
Miocene in the S (S-Pyrenean front). However, the deep geometry and
kinematic relationships between the cover and basement thrusts remain
non-consensual. We present a new structural and kinematic interpretation
for the eastern Jaca basin, based on subsurface structural maps and
cross-sections constructed using industrial seismic reflection profiles.
Raman Spectroscopy of Carbonaceous Material (RSCM), vitrinite reflectance
and apatite fission track (AFT) thermochronology data give
further constraints for the restoration of the deformation and burialexhumation
sequence. We define 3 main basement thrusts under the
northern part of the basin, from N to S the Broto, Fiscal and Guarga
thrusts. The study also clarifies the deep structure of the cover thrusts
and their links with these basement thrusts and those located more to
the north in the Axial Zone (AZ), which altogether define the timing of
the basement thrust sequence as follows : the Lakoura-Eaux Chaudes
thrust system (northern AZ) active up to the end Bartonian, the Gavarnie
(central AZ) and Broto thrusts during the Priabonian-Rupelian and
the Fiscal and Guarga thrusts during the late Oligocene-early Miocene.
AFT results in the basin fill and AZ date the exhumation of the basin
to the late Oligocene-early Miocene, in relation to the Fiscal-Guarga
thrusting. AFT partial reset argues for a maximum burial < 6 km for
the base of the Eocene detrital sequence (Hecho Group turbidites). By
contrast, RSCM and vitrinite thermometry at the same level indicates
Tmax around 180°C, locally up to 240°C, attesting to a temperature anomaly
possibly related to transient fluid circulation.