Petrogenesis of the alkaline lamprophyre cluster between Molí d’en Ponç and Collet de la Cidereda (eastern Catalonian Coastal Ranges, NE Iberia)

Abstract

This work focuses on the cretaceous camptonite cluster between Molí d’en Ponç and Collet de la Cidereda, eastern Montseny massif from the Catalan Coastal Ranges (NE Iberian Peninsula). These post-orogenic lamprophyres (~ 79 Ma) crosscut Palaeozoic and late Variscan granitoids. Their intrusion is related to the opening of the Bay of Biscay. Thus, they belong to the Late Cretaceous Iberian Alkaline Igneous Province. The studied cluster comprises two sills displaying a N110-N140-trending direction and subvertical dikes that intrude the camptonite sills or the granodioritic host rock. DyN/YbN ratios ≥ 2.4 show that the primary melts of the studied camptonites were generated at pressures higher than ~ 2.5 GPa (~ 80 km) on the garnet stability field close to the transition to the spinel stability field. The more evolved melts, corresponding to sodic alkaline basalts, were subjected to within-plate enrichment and fractional crystallization processes. The olivine antecrysts and microlites correspond to forsterite (Fo74 to Fo88). They do not show peridotitic mantle source composition and some are in equilibrium with sulfides. The clinopyroxene antecrysts correspond to diopside (Mg# 75–80) and do not show peridotitic mantle source composition. The forsterite, diopside, and kaersutite antecrysts display compositional oscillatory variations related to mixing processes associated with ascending successive magma pulses. The higher concentrations of Mn in forsterite and diopside microlites from the groundmass, compared to the antecrysts, are consistent with a more evolved composition of the ascending magma. The pressure estimation obtained from diopside antecryst cores (~ 1 GPa) supports the stagnation of ascending magma in the lower crust or the transitional boundary between the lower crust and upper mantle. The pressure obtained from clinopyroxene antecryst rims is ~ 0.28 GPa.