# Mediterranean detachment zones : thermicity vs heritage.

Loic Labrousse, Benjamin Huet, Laetitia Le Pourhiet, Laurent Jolivet, Evgenii Burov

► To cite this version:

Loic Labrousse, Benjamin Huet, Laetitia Le Pourhiet, Laurent Jolivet, Evgenii Burov. Mediterranean detachment zones: thermicity vs heritage. 19th EGU General Assembly, 2017, Vienne, Austria. pp.13018. hal-03552754

HAL Id: hal-03552754

https://hal.science/hal-03552754

Submitted on 3 Feb 2022

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# Mediterranean detachment zones : thermicity vs heritage.

Loic Labrousse (1), Benjamin Huet (2), Laetitia Le Pourhiet (1), Laurent Jolivet (3), and Evgenii Burov (1)

(1) UPMC, ISTEP, PARIS, France (loic.labrousse@upmc.fr), (2) Geologische Bundesanstalt, VIENNA, Austria, (3) ISTO, Université d'Orléans, ORLEANS, France

Even if the seminal comprehensive descriptions of Metamorphic Core Complexes (MCCs) in the American Cordillera mentionned lower plates constituted of gneiss and intruded by granites (e. g. Snake Range, Whipple Mountains), the actual definition of MCCs : « Cordilleran metamorphic core complexes appear to be bodies from the middle crust that have been dragged out from beneath fracturing and extending upper crustal rocks, and exposed beneath shallow-dipping (normal slip) faults of large areal extent » {as in Lister & Davis, 1989, Journal of Structural Geology, v. 11, pp. 65-94} refers to rocks exhumed from the middle crust whatever their thermal history. The fundamental property of this middle crust resides in its ability to flow laterally toward the forming dome, to accommodate stretching of the upper plate and preserve a relatively flat moho. Even though thermal reequilibration can induce weakening of the lower crust, a similar strength profile can also be inherited from pre-extension evolution of the continental crust and promote development of the original structure of MCCs : their detachment. In order to unravel the rheological meaning of detachments, we propose here a review of extensional shear zones described as detachments in the Mediterranean realm, and establish a three end-members typology with « hot MCCs » as one end-member, and two cold MCC end-members with a weak middle crust due to stacking of high pressure metapelitic nappes or a strong upper crust responsible for the strength contrast exaggeration between the upper and lower crust. New fully coupled thermo-mechanical modeling experiments together with a review of comparable published results allow to test this three end-member typology and determine the critical strength contrast for the perennial development of a detachment zone. A 1000 ratio between the strength at the brittle-ductile transition and the strength at the base of the crust seems a boundary value between localized extensional modes and distributed modes. An exaggeration of one order of magnitude (100 to 1000) of the strength contrast between the upper and lower crust appears to be sufficient to promote the development of a MCC, whatever the cause of this exaggeration. For large Mediterranean Core Complexes (Menderes, Cyclades, Betics for instance) evolution through time is also compatible with a progressive prevalence of thermicity over herited contrasts.