RAMAN GEOTHERMOMETRY CONSTRAINTS ON PEAK METAMORPHIC TEMPERATURES OF MARBLES FROM THE JARARA FORMATION, GUAJIRA PENINSULA, COLOMBIA

We apply Raman spectroscopy of carbonaceous materials (RSCM) to refine peak metamorphic temperatures for calcitic marbles in the Cretaceous-age Jarara formation, Guajira Peninsula, Colombia. Sediments of the Jarara Formation were deposited at the Cretaceous margin of South America as the intraoceanic island arc approached. The collision and reversal of subduction in the Late Cretaceous-Paleocene resulted in shortening of the Jarara Formation. Regional metamorphism associated with this shortening altered the Jarara Formation into a sequence of phyllites, schists, gneisses, and marbles with peak metamorphic conditions generally highest in the south and decreasing to the north. The marbles of the Jarara formation have mineralogically distinct layers and are intensely ductility deformed, characterized by isoclinal folds and fold interference patterns. We determined the mineralogy of the layers to locate areas with carbonaceous material (CM) by SEM/EDS, XRD, and confocal microscopy. Layers containing CM are mostly calcite with disseminated micron-scale quartz, while the layers with quartz lenses and sericite largely lack CM. The marbles are generally CM-poor and the CM is fine-grained (< 2 microns). Raman imaging facilitated the identification of CM grains encased in or beneath calcite grains. Using the methods of Kouketsu et al. (2014), we calculate peak metamorphic temperatures of 323-288°C (average = 309°C) and 339-298°C (average = 312°C) from two different samples. These temperatures suggest greenschist facies conditions and are consistent with the pervasive ductile deformation observed in these rocks. In this presentation, we successfully determined peak metamorphic temperature of CM-poor marbles using RSCM and suggest that this technique can be applied more widely across the Guajira Peninsula to characterize regional temperature gradients.