Abstract

RODRIGUEZ G., GABRIEL  and  ARANGO, MARÍA ISABEL. BARROSO FORMATION: A THOLEIITIC VOLCANIC ARC AND SAN JOSE DE URAMA DIABASES: A T-MORB TYPE ACCRETIONARY PRISM IN THE NORTHERN SEGMENT OF WESTERN CORDILLERA OF COLOMBIA. Bol. cienc. tierra [online]. 2013, n.33, pp.17-38. ISSN 0120-3630.

In the North Segment of Cordillera Occidental between Cauca-Almaguer and Dabeiba-Pueblo Rico faults outcrop two volcanic units. These were gathered in previous works named Formación Barroso. However these units are actually from different age and geotechnical environment which is called San José de Urama Diabases y Barroso Formation. San José de Urama Diabases correspond to tectonic blocks and bodies of diabase and pillow basalt with ophitic, subophitic, intersertal, intergranular and variolitic textures, from tholeiitic series in low-K, with a trace elements pattern and REE from a mantle source T- MORB type. To this unit was obtained an age by using Ar-Ar method in total rock of 155.1 ±11.2 M.a locating it in upper Jurassic - lower Cretaceus understanding it as a basament of North Segment of Cordillera Occidental Barroso Formation outcrops in the eastern edge of North Segment of Cordillera Occidental. This belongs to a sedimentary volcanic unit assembled by basalts and andesites with porphyritic and amygdalars textures linked to agglomerates, tuffs and packs of marine sedimentary rocks interspersed and discordant upon volcanic rocks. Barroso Formation vulcanite falls into tholeiitic series and calco alkaline medium-K. The behavior of rare earth elements and trace elements are part of rocks created in an arc formed by subduction. It also has a plutonic component represented at least by Sabanalarga Batholith, Buriticá Tonalite and gabbro minor bodies. The obtained ages allow us to propose that volcanic-plutonic arc was formed between 88 and 115 Ma (Turonian-Aptian) at the boundary between oceanic and continental crusts of the northern Andes.

Keywords : Barroso Formation; San José de Urama Diabases; Cordillera Occidental.

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