Chronology, petrogenesis and heat sources for successive Carboniferous magmatic events in the southern-central Variscan Vosges Mts. (NE France)
Abstrakt
Plutonic bodies of the Central and Southern Vosges Mts. can be assigned to two major early Carboniferous magmatic events: a Visean Mg-K (c. 345 and 340-336 Ma) and younger S-type (329-322 Ma). New petrological, geochemical and Sr-Nd isotopic data highlight the existence of two groups of Mg-K intrusions that might be related to the nature of their primary magma sources, e.g.
CHUR-like and enriched mantle, which interacted with juvenile and mature crustal material, respectively. The differences between these two groups are explained by a geodynamic scenario involving deep subduction and relamination of the Saxothuringian continental crust under the Moldanubian Continent.
The relaminated radiogenic Saxothuringian material is thought to have been responsible for both dehydration melting of subducted crust and underlying metasomatised mantle thereby generating the Mg-K magma subsequently emplaced at middle crustal depth. During their ascent, the mafic magmas interacted with crustally-derived, felsic melts.
Significantly later (~10-15 m.y.) followed a widespread mid-crustal anatexis, generating voluminous granite intrusions from mixed crustal sources (paragneisses and/or immature felsic-intermediate metaigneous rocks mixed with Mg-K plutons). The principal heat source for such major melting event is related to the presence of Heat Producing Elements-rich Mg-K plutons which were responsible, after the time lag specified, for temperature increase at mid-crustal levels by in situ radiogenic heat production.
The current work underlines the importance of deep continental crust subduction and relamination for the magmatism and development of collisional orogens.