Albitization profiles related to the Variscan basement, a case study of the Catalan Costal Ranges and the Eastern Pyrenees (NE Iberia)

Abstract

Widespread albitization has been recorded on Variscan granitoids of the Catalan Coastal Ranges (CCR) and the Eastern Pyrenees. Field observations suggest that albitization display a profile-like shape beneath Triassic, Cretaceous and Paleocene unconformities, decreasing in intensity forward the internal areas of the pristine granitoids. Petrographic, cathodoluminescence, SEM, microprobe and geochemical analyses show that albitization of Ca-plagioclase occurs as a pseudomorphic dissolution-reprecipitation mechanism and is mainly accompanied by biotite chloritization and Feoxides precipitation, giving a characteristic red-pink colour to the Na-metasomatized rock. Palaeomagnetic data suggest a Triassic age for the Fe-oxides and so for albitization. Triassic severe environmental conditions are characterized by high atmospheric and oceanic CO2 levels and global warming, besides acidification and salinisation of marine waters. All these features, possibly coupled with the granitoids long-lasting exposure due to smooth palaeoreliefs, could have played a major role in the development of these unusual shallow albitization profiles during Triassic times.