The geochemistry of the igneous rocks is consistent with a rift tectonic
setting where the mafic rocks have an ocean island basalt (OIB)
source and a lower crust contaminant and the ignimbrites come from
crustalmelts (Kleiman and Salvarredi, 2001). According to the latter authors,
this Triassic bimodal magmatism is produced by basaltic underplating
in an increasingly extensional tectonic regime coupled with an
exceptionally high geothermal gradient due to the preceding subduction
and the stationary period of Gondwana, that supplied enough
heat to melt a young and warm crust. This geodynamic setting could
launch a hydrothermal activity at regional scale producing the abundant
fluorite ore deposits of the SRM. This origin is supported by the Sm/Nd
isochrone age of 216–194 Ma. Besides, the low initial 143Nd/144Nd
(0.512182) in the analyzed fluorite suggests an enriched mantle source
and thus the involvement of the crust in their genesis (Rollinson, 1993).