Abstract

RODRIGUEZ-ESQUIVEL, Carlos Ernesto  and  SANCHEZ-QUINONEZ, Carlos Alberto. Evidence of low grade metamorphism and petrographic characterization of the El Hígado Formation, South of Huila, Colombia. Bol. geol. [online]. 2021, vol.43, n.1, pp.77-97.  Epub Jan 01, 2021. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v43n1-2021004.

The El Hígado Formation is a Middle Ordovician unit that has been the subject of studies focused primarily on its fossil content since it was proposed. In this work, a petrographic analysis was carried out that allowed to report characteristics of the original sediment factory, and the evidence of metamorphism conditions and hydrothermalism that the rocks was undergone. The new uplift of the stratigraphic column in the type section evidences the changes in the exposure of the outcrops. The characterization of the clay minerals present in the rocks by means of X-ray diffraction provided the necessary information, as did the petrographic analysis, to establish the changes at the mineralogical level that the rocks experienced during burial. In the pelitic rocks is where evidence of foliation was found with petrography, indicating that the rocks suffered regional metamorphism effects. With the determination of the illite’s crystallinity index, it was corroborated that the El Hígado Formation reached conditions where metamorphism occurs when exposed to temperatures above 300°C, between the limits of the high anquizone and the epizone, being consistent with the foliation found. In those rocks that were affected by the intrusion of dykes of Jurassic age, there was an alteration in the crystallinity index values, but not in their textural or compositional characteristics, as evidenced by petrographic and XRD analysis. With the data mentioned above, the rocks were classified considering the degree of metamorphism that affects them.

Keywords : El Hígado Formation; Metamorphism; Paleozoic in Colombia; Middle Ordovician; Illite’s crystallinity index; Colombian Central Cordillera.

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