Rift thermal inheritance in the SW Alps (France): insights from RSCM thermometry and 1D thermal numerical modelling
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Published:2023-01-04
Issue:1
Volume:14
Page:1-16
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ISSN:1869-9529
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Container-title:Solid Earth
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language:en
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Short-container-title:Solid Earth
Author:
Célini NaïmORCID, Mouthereau FrédéricORCID, Lahfid Abdeltif, Gout ClaudeORCID, Callot Jean-PaulORCID
Abstract
Abstract. Conceptual models of orogenic accretionary prisms assume that peak
temperatures (Tmax) increase towards the internal domains as crustal
rocks are accreted from the lower to the upper plate. However, the recognition
of pre-orogenic heating events in mountain belts questions the magnitude of
thermal overprint during nappe stacking. Using Raman spectroscopy on carbonaceous material (RSCM) to calculate Tmax, we have investigated
the thermal record of Lower Jurassic to Eocene strata exposed along six
stratigraphic sections at the front of the Digne Nappe (SW Alps), from the
Devoluy Massif to the Castellane Arc. Our results highlight two groups of
depth-dependent temperatures: (1) a regionally extensive and constant
Tmax up to 300–330 ∘C measured in the Jurassic succession and
(2) regionally variable lower temperatures (<150 ∘C)
recorded either in the Upper Mesozoic or the syn-orogenic sequence.
Modelling shows that the highest palaeotemperatures were achieved during the
Early Cretaceous (∼ 130 Ma), associated with the
Valaisan–Vocontian rifting, while the lowest Tmax reflect post-rift
thermal relaxation in the Alpine foreland basin. This study provides a
striking new example where mid-crustal palaeotemperatures measured in
sediments accreted from the downgoing plate are inherited. An estimated peak
thermal gradient of 80–90 ∘C km−1 requires a crustal thickness of 8–10 km during the Early Cretaceous, hence placing constraints for tectonic
reconstruction of rift domains and geophysical interpretation of current
crustal thickness in the SW Alps. These results call for the careful
interpretation of palaeothermal data when they are used to identify past
collisional thermal events. Where details of basin evolution are lacking,
high-temperature records may be misinterpreted as syn-orogenic, which can in
turn lead to an overestimation of both orogenic thickening and horizontal
displacement in mountain belts.
Funder
Agence Nationale de la Recherche
Publisher
Copernicus GmbH
Subject
Paleontology,Stratigraphy,Earth-Surface Processes,Geochemistry and Petrology,Geology,Geophysics,Soil Science
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