The Camarat granite (Maures Massif, SE France): a tectonic marker of the late orogenic evolution of the South European Variscan Belt

<p>A significant portion of the Maures-Tanneron Massif (SE branch of the European Variscan Belt) is occupied by late orogenic, anatectic crustal granitoids that were emplaced at ca. 325-300 Ma (Upper Carboniferous)<sup>1,2</sup>. The Camarat granite<sup>3</sup> is one of the smallest representatives of these granitoids (~2.5 km<sup>2</sup>). It is a composite intrusion exposed in migmatitic gneisses of the Maures Massif, along the southern shore of the Saint-Tropez Peninsula. From west to east, it consists of an E-W strip of Ms-Bt-Crd leucogranite where coarse- and fine-grained facies are found in similar amounts, and two bodies of Bt-Ms leucogranite, dominantly coarse-grained.</p><p>Zircon and monazite from two samples of the Camarat granite have been analyzed by LA-ICP-MS for U-Pb dating. Sixteen monazite analyses from the fine-grained facies of the E-W granite strip give a Concordia age of 303.5 ± 1.8 Ma (2 S.E., MSWD = 0.9). Sixteen zircons from the coarse-grained facies of the easternmost intrusion provide a Concordia age of 304.6 ± 2.1 Ma (2 S.E., MSWD = 1.2). The two dates are identical within uncertainty and are considered to constrain crystallization of the Camarat granite at ~304 Ma (Kasimovian–Gzhelian limit).</p><p>Twenty-one measurements of the anisotropy of magnetic susceptibility (AMS) and direct textural quantifications through image analysis (IA) of 10 samples give agreeing results that reveal the fabric orientation in the Camarat granite. The foliation has a variable orientation, with a weighted average of N65°E/26°NNW for the AMS data and N77°E/17°NNW for the IA data (D = 10°). The lineation pattern is more homogeneous, displaying a consistent northerly shallow plunge (mean of N12°E/22°NNE vs. N22°E/20°NNE; D = 10°). The Camarat granite lineations are parallel to lineations in the gneissic country rocks. These were produced during the last Variscan tectonic event evidenced in the area, a partitioned transpression phase, localized along ca. N-S sinistral strike-slip shear zones<sup>4</sup>. It is proposed that the ascent of the Camarat granite was favoured by such strike-slip structures and that pull-aparts represent the sites of emplacement, as best exemplified by the E-W granite strip.</p><p>In the Corso-Sardinian Block, another portion of the SE Variscides formerly juxtaposed to the Maures-Tanneron Massif<sup>5</sup>, a model of progressive transition from orogen-parallel flow (late orogenic, Upper Carboniferous transpression) to orogen-perpendicular extension (post orogenic, Permian rifting) has been recently proposed<sup>6</sup>. Such a model may be extended to other areas of the SE Variscan Belt, in particular to the Maures-Tanneron Massif which is cut and bordered by ca. E-W Permian grabens<sup>7</sup>, implying that a ca. N-S direction of stretching, as recorded by the 304 Ma Camarat granite, was still prevailing in Permian times.</p><p> </p><ol><li>Duchesne et al., Lithos 162-163, 195-220 (2013). 2. Schneider et al., Geol. Soc. Spec. Pub. 405, 313-331 (2014). 3. Amenzou & Pupin, C. R. Acad. Sc. Paris (Série II) 303, 697-700 (1986). 4. Corsini & Rolland, C. R. Geoscience 341, 214-223 (2009). 5. Edel et al., Geol. Soc. Spec. Pub. 405, 333-361 (2014). 6. Casini et al., Tectonophysics 646, 65-78 (2015). 7. Toutin-Morin, Ann. Soc. géol. Nord 106, 183-187 (1987).</li> </ol>

A 50-year analysis of hydrological trends and processes in a Mediterranean catchment

The Réal Collobrier hydrological observatory in southeastern France, managed by Irstea since 1966, constitutes a benchmark site for regional hydro-climatology. Because of the dense network of stream gauges and raingauges available, this site provides a unique opportunity to evaluate long term hydro-meteorological Mediterranean trends. The main catchment (70 km2) and its sub-catchments are located in the Maures massif of Southeastern France, close to the Mediterranean coast. The vegetation is composed of forest mainly calcified on crystalline soils (maquis of heath, cork-oak, maritime pine and chestnut). Direct human influence has been negligible over the past 50 years. The land use/land cover has remained almost unchanged, with the notable exception of a wildfire in 1990 that impacted a small sub-catchment. Therefore changes in the hydrological response of the catchments are caused by changes in climate and/or physical conditions. This study investigates changes in observational data using up to 50-year daily series of precipitation and streamflow. The analysis used several climate indices describing distinct modes of variability, at inter-annual and seasonal time scales. Trends were assessed by the Mann-Kendall method. The analysis also used hydrological indices describing drought events based on daily data for a description of low flows, in particular in terms of timing and severity. The analysis shows that there is a marked tendency towards a decrease in the water resources of the Réal Collobrier catchment in response to climate trends, with a consistent increase in drought severity and duration. But the changes are variable among the sub-catchments.

U-Pb zircon age of 548 Ma for the leptynites (high-grade felsic rocks) of the central part of the Maures Massif. Geodynamic significance of the so-called leptyno-amphibolitic complexes of the Variscan belt of western Europe

U-Pb zircon and Rb-Sr geochronological, and Sm-Nd isotopic studies have been carried out on the so-called leptyno-amphibolitic complex of the central part of the Maures Massif. The emplacement of the protolith of the felsic end-member (« leptynites ») has been dated at 548 Ma, an age much older than those (lower Ordovician) previously obtained on other leptyno-amphibolitic complexes. Rb-Sr data obtained on whole rocks and on mineral separates give an age of 348 Ma for the amphibolite-facies metamorphism. Nd isotopes indicate that the amphibolites display clear-cut mantle-derived signatures, whereas a significant crustal contribution is recorded in the three analyzed felsic facies. One of these acidic terms can be interpreted in terms of a simple mixing between two components, respectively similar to the amphibolites and to the two other felsic samples. These latter involve another mantle source, distinct from that of the amphibolites, and comparable to that of continental alkali basalts. These data indicate that the central part of the Maures Massif and the southern Massif Central were possibly part of the same pre-Variscan structural unit. The lack of evidence for a clear genetic relationship between the respective protoliths of the two end-members of the leptyno-amphibolitic complex raises once again the problem of the geodynamic significance of these formations.