Petrogenetic constraints of the La Quinta Formation igneous rocks, Serranía del Perijá, northern Colombian Andes

Abstract

La Quinta Formation is a Triassic-Jurassic volcano-sedimentary unit that crops out along both flanks of the Serranía de Perijá, in Cesar and La Guajira departments of Colombia, and Zulia state in Venezuela. It is mainly composed of red clastic sedimentary rocks (siltstones, sandstones, and minor conglomerates), interbedded with volcanic rocks and cut by small stocks. The volcanic horizons are mainly formed by rhyolitic tuffs and lava flows (basalts and andesites).   Andesites and basalts are constituted by plagioclase, clinopyroxene, biotite, magnetite, apatite, and zircon, whereas rhyolites and tuffs are formed by plagioclase, ß quartz, biotite, and sanidine. EMPA analyses revealed that plagioclase display varying compositions from labradorite-andesine in intermediate and basic rocks to oligoclase in rhyolites. Besides, clinopyroxene from basalts was classified as augite, and several hydrothermal mineral phases were also recognized, such as epidote, Ca-zeolites, and andradite-grossular. Using ILMAT (ilmenite-magnetite) geothermometer, temperature and oxygen fugacity conditions of 700-730°C and +1.2 ∆NNO were determined for dolerite.   Whole-rock geochemistry results evidence that La Quinta Formation volcanic rocks belong to the sub-alkaline (calc-alkaline) series, displaying compositions from basaltic andesites to rhyolites. Chondrite normalized REE and incompatible elements spidergrams show typical features of subduction-related magmatism and depict three groups of rocks (basic, intermediate, and acid) with contrasting geochemical behaviors. Hence, each group could have formed during single magmatic events associated with different magmatic suites. Nevertheless, the three groups have features that suggest a genesis related to an Andean-type supra-subduction zone, which agrees with the regional tectonic assemblage during Triassic-Jurassic times.