Characterization of bedrock in the northern cordillera real of ecuador along the La Sofía fault
We describe the bedrock along a road cut that follows the Colombia-Ecuador border in the northernmost part of the Cordillera Real of Ecuador. The study area straddles the La Sofía Fault, which has an orientation of 213°/78°W. We carried out a detailed lithologic description and structural analysis o...
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| Natura: | bachelorThesis |
| Lingua: | eng |
| Pubblicazione: |
2020
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| Accesso online: | http://repositorio.yachaytech.edu.ec/handle/123456789/270 |
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Aggiungi Tag | Riassunto: | We describe the bedrock along a road cut that follows the Colombia-Ecuador border in the northernmost part of the Cordillera Real of Ecuador. The study area straddles the La Sofía Fault, which has an orientation of 213°/78°W. We carried out a detailed lithologic description and structural analysis of the study area. The lithologies found were: meta-sediments, orthogneisses, intrusive units (granodiorites, granites) and Quaternary volcanic rocks. The western side of the fault, and along the trace of the fault zone, is characterized by orthogneisses intercalated with foliated, coarse-grained intrusive rocks. This side of the fault shows a high grade of dynamic metamorphism due to the presence of mylonitic zones. At the eastern side of the fault, granodiorites and granites appear intercalated with meta-sedimentary rocks (schists, phyllites, slates, quartzites), which generally have a systematic behavior: the further from the fault towards the east, the lower the grade of meta-sedimentary rocks. The protoliths of the meta-sedimentary rocks were pelites and arenites, and they formed pendants and enclaves that represent the basement into which the surrounding plutons were intruded. Leucosomes and dikes cut the mylonite zones, and in some cases also appear deformed and sheared. Thus, it suggests that the deformation event that created the mylonitic rocks was synchronous with the time were the arc magmatism was active. Brittle deformation is characterized by widespread small fault zones with one larger fault zone interpreted as the main slip plane. Brittle and ductile deformation geometries are almost identical. Both fabrics have a sub vertical dip and a SW to NE trend. This suggests that brittle regime of deformation was using the pre-existing ductile fabric. We interpret that Quaternary deformation of the La Sofía fault re-activated the inherited structural fabrics resultant from the Mesozoic deformation. The inmaturity of the fault also suggests that it has not accrued a large amount of displacement, consistent with Quaternary estimates for the age of the North Andean Sliver (NAS). |
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