Petrography and geochemistry of the Golero’s Rhyolite Unit north of Valledupar city, Cesar, Colombia

The Golero’s Rhyolite is a lithological unit of heterogeneous composition, consisting of basaltic, dacitic, andesitic and rhyolitic volcanic rocks that outcrops on the eastern and southern flank of the Sierra Nevada de Santa Marta, northwestern tip of South America. The study area comprises the rural area north of Valledupar City, Cesar, Colombia. The objective of this re-search is to analyze petrographically and geochemically the volcanic rocks of the Golero’s Rhyolite Unit north of the city of Valledupar, Cesar, Colombia. For the execution of the research, we initially proceeded with a compilation of cartographic information at a scale of 1:25,000, where lithological and structural characteristics were identified; later, field trips and collection of 22 samples for compositional and textural classification, selecting 9 specimens for micropetrographic and geochemical analysis (X-ray fluorescence). Macroscopic and microscopic petrographic analysis evidences that they consist of aphanitic matrix composed mostly of plagioclase, with porphyritic inequigranular and sometimes bimodal inequigranular texture or grain size distribution, in general there are euhedral to subhedral plagioclase minerals, epidote altering the plagioclase, subhedral hornblende, subhedral feldspar, anhedral quartz, and in smaller proportion hematite, magnetite and calcite in veinlets. Within the elements variation diagrams the samples are located in the same crystallization sequence, suggesting that they are part of the same magmatism and fractionation of the rocks from SiO2 values of 44.63 wt% to 63.07 wt %; (basalts to dacites). The rocks of the Golero’s Rhyolite Unit were generated from a calc-alkaline magma in an intraplate tectonic environment, possibly influenced by oceanic islands (OIA) product of continental rifting.