The camptonites in the multiple intrusion of Platja Fonda (Girona, NE Spain): mechanisms of intrusion and geochemistry

Abstract

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 SiO 2 , the highest CaO and the lowest Mg numbers of all known camptonites in the Catalan Coastal Ranges.

Reactivation of Magma Pathways: Insights From Field Observations, Geochronology, Geomechanical Tests, and Numerical Models

“…While geochemical variations within multi‐dykes have been widely studied (e.g., Ehlers & Ehlers, 1977; Esteve et al., 2014; Gibson & Walker, 1963; Kanaris‐Sotiriou & Gibb, 1985; Sun et al., 2013), literature on the mechanics of their formation is lacking. Indeed, it is commonly assumed that multi‐dykes form either because the initial dyke did not have time to solidify completely before the subsequent injection, or because the solidified dyke or its chilled margin were weaker than the host rock it intruded (Ehlers & Ehlers, 1977; Esteve et al., 2014; Gudmundsson, 1984; Guppy & Hawkes, 1925; Marinoni & Gudmundsson, 2000; Platten, 2000; Walker, 1992).…”

Post‐collisional alkaline lamprophyre magmatism in northern Iran: Implications from whole‐rock geochemistry and mineral compositions

“…The REE of alkaline lamprophyres avg . composition of camptonite samples after Rock (1991) and Esteve et al (2014) have plotted in Figure 10c for a compression.…”

“…(c) Chondrite‐normalized REE patterns and (d) primitive mantle‐normalized spider diagrams for the Shanderman lamprophyres (Sun & McDonough, 1989). For comparison, the CI‐chondrite‐normalized REE patterns for the camptonite lamprophyres are shown; dashed red line (Rock, 1991) and purple thick line (Esteve et al, 2014).…”