Recrystallisation textures in zircons generated by ocean-floor and eclogite facies metamorphism: a cathodoluminescence and U-Pb SHRIMP study with constraints from REE elements.

Abstract

Eclogites formed during the Eo-alpine metamorphic event are common within the ophiolitic unit of the Mulhacén complex, which forms part of the Betic Cordillera in southeastern Spain. A detailed study with cathodoluminescence (CL) images of zircon from these eclogites has revealed three types of domains, confirmed by some differences in their REE patterns and ages. There are a) igneous domains, with oscillatory zoning, yielding an Early to Middle Jurassic age, dating the crystallization of the basic protolith, and b) two different types of recrystallized metamorphic domains, one with grey homogeneous CL images, mainly clustering around the Late Jurassic, and the other with bright clouded CL images, ranging down to a Late Cretaceous to Paleocene age. These two types of recrystallized areas in the zircon are interpreted as having formed during the ocean-floor and the Eo-alpine metamorphism, in eclogite-facies conditions, respectively. We contend that processes of metamorphic recrystallization, which are more pervasive in the internal part of the zircon crystals than at their edge, was facilitated by oceanic fluids that circulated through them and were located in their vesicles, forming fluid inclusions