The fast evolution of a crustal hot zone at the end of a transpressional regime: the Saint-Tropez peninsula granites and related dykes (Maures Massif, SE France).

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Authors
Duchesne, J.C.
Liégeois, J.P.
Vander Auwera, J.
Bolle, O.
Bruguier, O.
Matukov, D.I.
Sergeev, S.A.
Discipline
Earth and related Environmental sciences
Subject
Geodynamics and mineral resources
Audience
Scientific
Date
2013Publisher
Elsevier
Metadata
Show full item recordDescription
Granite and dolerite occurring in the eastern unit of the Maures Massif (southern France Variscan belt) were  emplaced in the waning stage of the evolution of a dextral shear zone along the Gondwana border with  Laurasia.We present a geochronological and petro-geochemical study (major and trace elements, Sr Nd isotopes)  of (1) the foliated Moulin Blanc cordierite granite and related foliated dykes; (2) the equant Camarat granite and  dyke; and (3) the andesite basalt dolerite dykes (frequently mingled with leucogranite material at Pinet and  Capon tips) and cross-cutting leucogranitic dykes. Zircon and monazite dating of the Moulin Blanc granite gives  a crystallization age of 301±2 Ma. SHRIMP dating on zircons fromthe leucogranite component of a Pinet composite  dyke only reveals zircon core ages ofmainly 310±10 Ma (age ofmigmatization of the host gneiss). Undulating  contacts of dolerite dykes within the c. 300 Ma old Camarat granite suggest penecontemporary relationships  between the two intrusions. The age interval between the Moulin Blanc granite and the dolerite dykes would  thus be very short. TheMoulin Blanc pluton is formed bymingling andmixing ofmelts of granitic and dioritic composition,  the latter occurringmainly as microgranularmafic enclaves. Two other types of diorites are also identified  in the pluton. The foliated dykes are similar in composition to the Moulin Blanc granite, which confirms their  relationship to the main pluton. The Moulin Blanc granite is a typical example of a pluton formed by repeated recharges  coming from a deeper magma chamber. Formation of the Camarat dykes is controlled by hydrothermal  fluids that are responsible for the non-CHARAC behavior of trace elements. The Pinet and Capon leucogranite components  of the dolerite dykes have distinct geochemical signatures, different from the Camarat granite and dykes.  The cross-cutting leucogranitic dykes have much geochemical similarities with the Capon granite. The age of  similar dykes in the TanneronMassif supports the contemporaneity of Camarat granite and dolerites. The dolerite  geochemistrywas deeplymodified by alteration processes, but an andesite basalt composition is still recognizable  by using immobile element ratios. In a εNd vs. Sri diagram, all rocks plot close to a mixing hyperbola between a  depleted mantle component and a crustal component, characteristic of the Variscan crust in the French Massif  Central. There is a broad correlation between the NdTDM 2-stage model ages and the degree of fractionation of  the rocks. Modeling of dehydration melting in a range of P T conditions reveals that a variety of lithologies were  the source of the Saint-Tropez magmas: high-alumina and alkali-basalt amphibolites,metagraywackes, metapelites  and meta-arkoses. These sources were melted almost simultaneously at different levels in the crust. The calculated  critical dyke width required to transport the granitic melt by buoyancy is far too large compared to the observed  granitic dyke thicknesses. Therefore, tectonic processes and/ormelt overpressure must have played a role in the emplacement  mechanism. Thermo-mechanical constraints on mixing between mafic and felsic melts suggest that, in  the Pinet composite dykes, both melts should have mixed. The observed lack of mixing is interpreted as due to  quick cooling. The region was affected by a hot zone at the end of a transpressional regime.
Citation
Duchesne, J.C.; Liégeois, J.P.; Vander Auwera, J.; Bolle, O.; Bruguier, O.; Matukov, D.I.; Sergeev, S.A. (2013). The fast evolution of a crustal hot zone at the end of a transpressional regime: the Saint-Tropez peninsula granites and related dykes (Maures Massif, SE France).. , Lithos, Vol. 162-163, 195-220, Elsevier, DOI: http://dx.doi.org/10.1016/j.lithos.2012.12.019.Identifiers
Type
Article
Peer-Review
Yes
Language
eng
