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Kinematic and Deformative Analysis for the Santa Rosa and La Telaraña Faults

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Kinematic and Deformative Analysis for the Santa Rosa and La Telaraña Faults GRC Transactions, Vol. 40, 2016 Kinematic and Deformative Analysis for the Santa Rosa and La Telaraña Faults Lucrecia Acosta Ospina and Jaider A. Quintero Loaiza Dewhurst Group, L.L.C. Keywords Colombia, Andes, Nevado del Ruiz, microstructure, kinematics, structural geology, faulting, Santa Rosa fault, La Telaraña fault, geothermal ABSTRACT This study was aimed at analyzing the kinematics and deformation associated with the NE – SW striking Santa Rosa and La Telaraña faults located west of the Nevado del Ruiz volcano (VNR) in Colombia. Paleo-stresses for both structures show a compressive regime mainly in the NW – SE direction, and an almost vertical intermediate stress causing predominantly dextral slip; this is evident from striated surfaces, showing kinematic components with a dip in a slightly normal-type. The microstructures along the Santa Rosa Fault establish the presence of ductile deformation in some areas, evidence mainly in the Paleozoic units such as schist belonging to the Cajamarca Complex, where fish-like structures with developing shear dextral bands, dynamic recrystallization of quartz and carbonates, and superimposed brittle deformation (cataclasis) can be observed. In younger lithologies, including Ruiz lavas, Paramillo of Santa Rosa lavas, and Rio Claro ignimbrite, a cataclastic deformation was observed in all units related to both faults, as well as a system of larger NE – SW joints, and a subordinate series of NW – SE to E –W joints, with centimetric to metric scale cataclasis. Introduction Structural analysis in the exploration of geothermal resources is crucial for the interpretation of different geologi- cal processes that have occurred in a particular area. These analyses provide insight into the evolution of the terrain and areas prone to geothermal fluid flow along faults and fractures. Knowledge these deformation characteristics allows us to understand the dynamics of the associated geothermal systems and thus make projections for future resource exploitation. The permeability structure associated with a fault depends strongly on the architecture of the fault (that is, the core of the fault usually made up of cataclasites, breccias, and/or fault gouges), and the area of damage proximal to a fault consisting of intense fracturing (Gudmundsson, et al., 2001). The study area ranges in altitude from 1700m to 4000m above sea level. The area is characterized by steep topography and is considered a tropical to temperate climate typified by high rainfall and dense vegetation. Because of the climatic conditions (extreme weathering) few rock outcrops exist where geological data can be reliably collected. Theoretical Framework The study area is comprised of the northern part of the Department of Tolima, on its borders with the southern part of the Department of Caldas and the Nevado del Ruiz volcano, as well as an area in the southwest of the Department of Caldas and in the northeast Risaralda Department, specifically along the western flank of the Central Cordillera. The 425 Acosta Ospina and Quintero Loaiza study is bounded on the west by the Romeral fault system and on the east by the Palestina fault. The Lithologies range in age from Paleozoic to Quaternary. Methodology Four stages of preparation were carried out in order to develop a systematic and sequential work. First Stage: Literature review of structural studies of the Colombian Andes, in particular the Central Cordillera. Methodologies used, evolutionary tectonic models proposed for the Central Cordillera, and existing interpretation of kinematic data were all examined. A collection of geological maps (at a scale of 1:25000) belonging to EPM-CHEC’s (Empresas Públicas de Medellín – Central Hidroeléctrica de Caldas) geothermal project was also analyzed; different sec- tors were chosen in a geological section of the trace of Santa Rosa and La Telaraña faults (NE – SW). Subsequently, satellite images were analyzed with Digital Elevation Models (DEM) obtained from the Shuttle Radar Topography Mission (SRTM) from NASA. Aerial photography files belonging to EPM-CHEC between the departments of Caldas and Risaralda were also reviewed. With this data collection, sites and routes were chosen to carry out the field studies and sampling required for development work. Second Stage: Fieldwork aimed to find outcrops along highways, roads, and drainages. Data collection included joints, foliation, stretch marks, fault planes, and lineations, and a geomorphological analysis was performed in the selected field site. Third Stage: Data processing (of features such as joints, stretch marks, and structures) with Win-Tensor 5.0.5 soft- ware (Delvaux and Sperner, 2003) was carried out to obtain stress tensors for each sector. Similarly, a microstructural and lithological analysis was conducted on thin sections from the Cajamarca Complex, ancient and recent Nevado del Ruiz volcano lavas, the Paramillo of Santa Rosa lavas and Santa Rosa meta-gabbros (Gomez-Cruz et al, 2010). Fourth Stage: Development and delivery of a final report. Regional Geological Framework The geological units that make up the Central Cordillera in the area of interest are comprised of metamorphic Pa- leozoic units similar to the Cajamarca complex. Cajamarca complex rocks range from green schist to amphibolite facies and form the core of the central mountain range (Gonzalez, 1993). There is also the early cretaceous Quebradagrande Complex (Maya and Gonzalez, 1995), which is a bimodal unit, sedimentary in the east and volcanic in the west. The units in the survey area are covered with the most recent pyroclastic deposits and lava flows produced by volcanoes Santa Isabel, Nevado Del Ruiz, Cerro Bravo, and Paramillo of Santa Rosa (Figure 1). Figure 1. Regional geological map of the VNR area. Cajamarca Complex (Pes, Pq, Pev), Quebradagrande Complex (Ksc-Kvc), Stock of Chinchiná-Santa Rosa (Kgd), andesitic-dacitic porphyry-(P?lda), lava flows, Río Claro ignimbrite (Qirc) Quaternary deposits. (Amended of González, 2001 by Mejía 2012). 426 Acosta Ospina and Quintero Loaiza Regional Tectonic Framework The northwest of South America is characterized by a wide deformation zone, in the Colombian Andes, correspond- ing to the Andean block (Kellogg et al., 1985), which is generated by the convergence of the Caribbean, Nazca, and South American plates and the Panama-Choco Block, collectively resulting in the “Andean orogeny” (Duque-Caro, 1990). Ego et al (1996) determined that in the North Block of the Andes (is a region that constitutes an ancient continental margin characterized by the Cauca – Romeral fault system) there are at least two major domains of stress with different orientations. The same author mentioned that south of latitude 5°N to the stress tensor has maximum compression in the direction E-W, while north of this latitude, the maximum compression has a NW-SE direction. Colmenares and Zoback (2011) identified two large provinces with homogeneous tensors within the block of the Colombian Andes. In the northern region (approximately north of 4°N latitude) the direction of maximum compression is generally NW-SE, while South 4°N, the orientation of the maximum compression is EW. The transition zone between these two tectonic domains is between 4 and 5 degrees north latitude (Ego et al., 1996; Cortes and Angelier, 2005). The Nevado del Ruiz Volcano is located within this area with a maximum compression EW to NW-SE. In southwestern Colombia, Guzman et al. (1998) posit a stress tensor with a varying direction of NNE-SSW to NE-SW. The transfer of these stresses to the conti- nent causes the differential reactivation of fault systems parallel to the Andes and, in general terms, a transpressional domain (Toro and Oso- rio, 2005). The study area is structurally influenced by N – S to NNE – SSW striking, which coincides with the orientation of the Andean chain, and oblique fault systems striking NW – SE and E –W to NE – SW (Figure 2). The Santa Rosa and La Telaraña faults, which are the main object of this study, are de- scribed below. Results Structural analysis defining the paleostress tensor was performed for the three sectors where there are striations associated with the Santa Rosa and La Telaraña faults. Santa Rosa fault was determined with a normal dextral transcurrent kinematics character. The La Telaraña fault clearly appears to be dextral without any com- ponent dip. Lithologies along the Santa Rosa fault vary in age, from Paleozoic to recent. La Telaraña’s fault striation were found only in recent lithologies, main- ly in the Paramillo of Santa Rosa lavas. Figure 2. Location of study area. Upper image represents the geotectonic map of Colombia with geodetic This variety of displacement measurements representing interaction with the northwestern sector of Colombia (Trenkamp, ages impacts the resulting 2002). 427 Acosta Ospina and Quintero Loaiza compression directions, presenting a cumulative deformation associated with the Santa Rosa, Palestina, San Jerónimo, and NW-SE transversal faults. Microstructures are observed in the samples taken from the Nereidas area. There, Cajamarca Complex schists pres- ent dextral strike micro-faulting (Figure 7), and slight mylonitization and fish-type structures in some muscovites show dextral kinematics. In the Molinos river area, the Cajamarca Complex schists present dextral mylonitic deformation and fish-type structures and indicate ductile deformation in some plagioclase and amphibole (tremolite-actinolite), (Figures 8 and 9). In the Azufrado Valley, pyroxene-andesite
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