Gaëtan Rimmelé

Correlation of syn-orogenic tectonic and metamorphic events in the Cyclades, the Lycian nappes and the Menderes massif : Geodynamic implications

The recent discovery of HP-LT parageneses in the basal unit of the Lycian nappes and in the Mesozoic cover of the Menderes massif leads us to reconsider and discuss the correlation of this region with the nearby collapsed Helle-nides in the Aegean domain. Although similarities have long been pointed out by various authors, a clear correlation has not yet been proposed and most authors insist more on differences than similarities. The Menderes massif is the eastern extension of the Aegean region but it has been less severely affected by the Aegean extension during the Oligo-Miocene. It would thus be useful to use the structure of the Menderes massif as an image of the Aegean region before a significant extension has considerably reduced its crustal thickness. But the lack of correlation between the two regions has so far hampered such comparisons. We describe the main tectonic units and metamorphic events in the two regions and propose a correlation. We then show possible sections of the two regions before the Aegean extension and discuss the involvement of continental basement in the Hellenic accretionary complex. In our interpretation the Hellenic-Tauric accretionary complex was composed of stacked basement and cover units which underwent variable P-T histories. Those which were not exhumed early enough later followed a high-T evolution which led to partial melting in the Cyclades during post-orogenic extension. Although the Menderes massif contains a larger volume of basement units it does not show significant evidence for the Oligo-Miocene migmatites observed in the center of the Cyclades suggesting that crustal partial melting is strictly related to post-orogenic extension in this case.

Raman mapping and numerical simulation of calcium carbonates distribution in experimentally carbonated Portland-cement cores

The spatial distribution of CaCO 3 polymorphs formed during the experimental carbonation of water saturated Portland-cement cores (30 mm in diameter), with supercritical CO 2 at 90 °C and 30 MPa, has been investigated using Raman microspectrometry on polished sample sections and X-ray microdiffraction. The three calcium carbonate polymorphs (calcite, aragonite and vaterite) were clearly distinguished using both techniques and their distribution along the main CO 2 diffusion direction could be mapped at the millimetre scale using a dynamic line-scanning Raman mapping tool. The calcium carbonate 2D distribution clearly shows that vaterite, the least stable of the three CaCO 3 polymorphs, is mostly located in a 500 μm wide ring ahead of the carbonation zone. This feature indicates that vaterite is the first CaCO 3 polymorph to crystallize within the cement sample in the course of the carbonation process. The presence of a vaterite front indicates that local mineral-solution equilibration can be slower than species transport, even above ambient conditions, and that kinetics cannot be ignored in the cement carbonation process. By using calcite and vaterite precipitation kinetic data from the literature and assuming water-mineral kinetics based on the Transition State Theory, the vaterite front inferred from Raman mapping is reproduced with a purely diffusive 1D transport code.

Structural evolution of Andros (Cyclades, Greece): a key to the behaviour of a (flat) detachment within an extending continental crust

Abstract The continental crust extends in a brittle manner in its upper part and in more distributed (ductile) manner in its lower part. During exhumation of HP metamorphic rocks, brittle features superimpose on earlier ductile ones as a result of the progressive localization of deformation. The islands of Tinos and Andros are part of the numerous metamorphic core complexes exhumed in the Aegean domain. They illustrate two steps of a gradient of finite extension along a transect between Mt. Olympos and Naxos. This study confirms the main role of boudinage as an initial localizing factor at the brittle–ductile transition and emphasizes the continuum of strain from ductile to brittle during exhumation. Early low-angle semi-brittle shear planes superimpose onto precursory ductile shear bands, whereas steeply dipping late brittle planes develop by progressive steepening of structures or sliding across en echelon arrays of veins. The comparison between Tinos and Andros allows us to propose a complete dynamic section of the Aegean extending continental crust and emphasizes that the strain localization process depends on both its rheological stratification and its compositional heterogeneity.

The wide distribution of HP-LT rocks in the Lycian Belt (Western Turkey): implications for accretionary wedge geometry

Abstract In SW Turkey, Fe-Mg-carpholite has recently been recognized in the basal metasediments of the Lycian Nappes, which overthrust the Menderes Massif on its southern flank. This high-pressure-low-temperature (HP-LT) metamorphic index mineral was widely found in the Bodrum peninsula region. Our new metamorphic and structural data on similar carpholite-bearing rocks found farther north in several klippen of the Lycian Nappes located on top of the Menderes Massif show that HP-LT rocks in SW Turkey occur over a distance of >200 km in both north-south and east-west directions, thus indicating a wide HP-LT metamorphic belt. The deformation pattern from the Bodrum peninsula to Çivril, all along the contact between the Lycian Nappes and the Menderes Massif, reveals the role played by major top-to-the-NE shear zones contemporaneous with exhumation of the Lycian HP-LT rocks. This deformation shows an oblique direction of opposite shear sense relative to the earlier southward translation of the Lycian Nappes over the Menderes Massif, for which top-to-the-south displacements are preserved in the upper units of the Lycian Nappes on the Bodrum peninsula, as well as at the base of the Lycian nappe klippen located farther north. The widespread distribution of well-preserved Fe-Mg-carpholite-bearing rocks in the Lycian Nappes has implications for the geometry of the accretionary wedge responsible for HP-LT metamorphism in SW Turkey.