Regional-scale Cretaceous albitization in the Pyrenees: evidence from <i>in situ</i> U–Th–Pb dating of monazite, titanite and zircon

Abstract

Abstract: Albitization is a common metasomatic process active in various geodynamic contexts. In the northern Pyrenees, there are several occurrences of albitites but, until now, only one occurrence has been dated (117 Ma, Ar–Ar dating). This paper presents new U–Th–Pb ages for several albitite occurrences throughout the Pyrenees to test whether they are contemporaneous and, if so, to specify the regional extent of the albitization event. Ages obtained from large euhedral titanite and monazite grains from distinct albitites are 110 ± 8 and 98 ± 2 Ma, respectively. The zircon U–Th–Pb isotopic system did not record this Cretaceous metasomatic event, even when grains were selected in metasomatically Zr-enriched rocks or in hydrothermal structures (millimetre-sized veins cross-cutting granitoids). We argue that the total time span of 20 Ma recorded by albitites corresponds to a long-lived hydrothermal system that was active during the rotation of Iberia around Europe, along the North Pyrenean Fault. Because albitization and talc mineralization have the same spatial and temporal distribution in the Pyrenees, we argue that these two metasomatic phenomena are two independent records of this single, regional-scale, long-lived hydrothermal system.