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vol.38 issue3PETROGRAPHY AND CARTOGRAPHY OF CONTACT AUREOLE OF THE MARIQUITA GRANODIORITE (TOLIMA DEPARTMENT, COLOMBIAN CENTRAL CORDILLERA) author indexsubject indexarticles search
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Boletin de Geología

Print version ISSN 0120-0283

Abstract

RODRIGUEZ G., Gabriel  and  CETINA T., Lina María. PETROGRAPHIC AND CHEMICAL CHARACTERIZATION OF OCEANIC CRUST ROCKS FROM THE COMPLEJO QUEBRADAGRANDE AND COMPARISON WITH THE DIABASAS DE SAN JOSÉ DE URAMA UNIT. bol.geol. [online]. 2016, vol.38, n.3, pp.15-29. ISSN 0120-0283.  http://dx.doi.org/10.18273/revbol.v38n3-2016001.

The Complejo Quebradagrande unit is formed by "lithological blocks" of sedimentary rocks of marine origin, arc vulcanites (tuffs, andesites and basalts) and oceanic crust "blocks" (basalts and diabases). It is limited to the East by the San Jeronimo fault that separates it from the Complejo Cajamarca unit and to the West by the Silvia-Pijao fault that separates it from the Complejo Arquia unit. The "blocks" of oceanic crust are represented by diabases, variolitic basalts and deformed diabases and basalts, with intergranular, ophitic-subophitic and variolitic textures, mainly composed of plagioclase and clinopyroxene and, as accessory minerals, titanite and opaques. The diabases and basalts of the Complejo Quebradagrande unit are basic rocks with SiO2 values between 44.95% and 50.80%, high concentrations of MgO in the range between 8.9 and 5.42%, Fe2O3 varies between 14.83 and 7.98%, CaO contents are high between 7.55% and 13.2%, values of TiO2 in the majority of samples are between 1 and 2%, low ratio of alkalis vs SiO2 (0.03 to 0.10 wt %) and low K2O values between 0.07% and 0.47%. The rocks correspond to the high in Mg tholeiitic series, little differentiated and of subalkaline affinity, and have greater than 30 Zr/Nb ratios, (La/Sm) N less than 1 and rare earths patterns that suggest affinity with N-MORB type basalts, except two samples (VR-364R and VR-384R) that exhibited patterns similar to the E-MORB. The rocks of the Complejo Quebradagrande unit differ from the Diabasas de San Jose de Urama unit in that the rocks of the latter have Zr/Nb values between 10 and 15, and that the ratios (La/Sm) N present values greater and lower than 1, with flat rare earths patterns similar to type T-MORB basalts. These results suggest that the rocks of these two units correspond to different, not contemporary oceanic crusts, with associated arc rocks that present a difference in the chemical composition, that are not correlatable, except for samples VR-364R and VR-384R, which exhibit a geochemical similarity with the Diabasas de San José de Urama unit.

Keywords : Colombia; Complejo Quebradagrande; Diabasas de San José de Urama unit; "diabasic" textures; geochemistry.

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