The camptonites of Platja Fonda are intrusive into Cambro-Ordovician metasediments and late Variscan granitoids. They appear as decimetre to centimetre thick sub-horizontal dykes following a fracture system, with dilation nearly orthogonal to their strike. The largest dykes have zoned structure, with chilled margins at both borders grading to porphyritic camptonites towards the centre, whereas the latest thinner dykes are intrusive into the porphyritic camptonites and their texture is almost aphyric. The macrocrysts of the porphyritic camptonites are interpreted as phenocrysts according to their chemistry and conditions of formation with respect to the crystals in the groundmass. They are mainly of kaersutite and of subordinate diopside-augite. Whole-rock major-element compositions reveal the existence of two types of camptonites: the predominant, sodi-potassic and the subordinate, slightly potassic. Other geochemical differences between the two types are minimal. The potassic camptonites are found as isolated dykes, but the potassic tendency exists in the latest thinner dykes that cross-cut earlier sodi-potassic camptonites and show small amount of normative leucite. Both types do not seem to be related by fractional crystallization and could represent slightly different alkaline melts, which would have been formed by partial melting of a metasomatized mantle. Increasing participation of the incongruent breakdown of calcic amphibole and phlogopite during the genesis of the most potassic camptonites is suggested. These camptonites in general, and specifically the potassic ones, have the lowest SiO2, the highest CaO and the lowest Mg numbers of all known camptonites in the Catalan Coastal Ranges.
- Intrusion mechanism