GRC Transactions, Vol. 40, 2016

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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.

KeywordsColombia, 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

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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).

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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.

This var ie ty of ages impacts the resulting

Figure 2. Location of study area. Upper image represents the geotectonic map of Colombia with geodetic displacement measurements representing interaction with the northwestern sector of Colombia (Trenkamp, 2002).

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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 lavas were highly fractured. The samples of metagabbro from the La Reina Quarry did not show microstructures that indicated the kinematics of the fault, contrary to macro-scale observations, where a well-conserved kinematics is apparent (Figures 13 and 14).

The relation between the Santa Rosa fault and the thermal seeps of San Vicente was not possible to study, due to the structural complexity and high vegetation cover of the area, not allowing the associations at depth between this deformation and fluid-supply systems to be observed.

Santa Rosa Fault – Striation

In the La Reina quarry sector, striation mea-surements were made on the Chinchiná - Santa Rosa metagabbro, highlighting normal dextral faulting. A pa-leostress tensor for this area was found in a compressive regime with σ1 in direction NNW-SSE and σ3 in direction NW-SE (Figure 3).

In the La Telaraña sector, measurements for striation were made on the andesitic - dactic of the Paramillo de Santa Rosa lavas. In this area there is a paleostress tensor in a dextral transcurrent regime with σ1 sense in the E-W direction and σ3 in N-S direction (Figure 3).

The Sector Gualí-Romeral II (situated northwest of the Volcano Nevado of the Ruiz in the Azufrado Valley) is influenced by the Palestina, Santa Rosa, and Villamaría - Termales faults. Here, recent lavas have strong jointing and high argillic alteration with vuggy silica formation. In this area there is a transcurrent regime with dextral sense and a slight dip with σ1 in the WNW-ESE direction and σ3 in the NNE-SSW direction (Figure 3).

Santa Rosa Fault – Joints

According to our interpretation of the stereogram jointing pattern of the Santa Rosa fault in the study area, it was established that the area has a NE-SW main trend and is subordinate NW-SE (and to a lesser extent, N-S), possibly generated by the faults present in the area (Pales-tina, Villamaría-Termales, Santa Rosa, and San Jerónimo). Observing the jointing trends, a structural control related to the Santa Rosa, Palestina, and Villamaría-Termales faults has been identified to the northwest of the Nevado del Ruiz volcano in the area of Azufrado Valley. In the sector of the Molinos river and La Telaraña, one structural control related to the Santa Rosa fault can be observed. Finally, in the area of the La Reina quarry, orientations are associated with NNE-SSW with the San Jerónimo fault (Figure 4).

Figure 3. Map showing the stereogram of striations across of Santa Rosa fault.

Figure 4. Map showing the stereogram of joints across of Santa Rosa fault.

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La Telaraña Fault – Striation

The La Telaraña fault in the sector of the Tigrera is influenced by the San Jeronimo and Laguna Baja faults to the west, and by the Santa Rosa fault to the east. The stress regime here is compressive, with a dextral compo-nent heading with σ1 in the NW-SE direction and σ3 in the NNE-SSW direction (Figure 5).

La Telaraña – Joints

The corresponding joint system for this fault in the sector of the Tigrera has a main structural control with an orientation NE-SW, and another subordinated with orienta-tion NW-SE. In the sector of the township Fermín López, the main structural control has an orientation WNW-ESE, and the subordinated has an orientation NE-SW (Figure 6).

Conclusions

According to our results, the current field efforts are associated with a transcurrent environment in which faults such as the Santa Rosa and La Telaraña faults are oriented obliquely to compression, with no apparent dip component.

At a microscopic scale, the rocks of the Upper Cretaceous earlier ages (Cajamarca Complex schists and Santa Rosa metagabbro) were deformed under a ductile regime, which is evident in fish-type structures and drag folds observed in Cajamarca Complex schists. These rocks are mylonitized, showing that the Santa Rosa fault affected depths corresponding to ductile field deformation of these bodies of rock, which were then exposed at the surface by subsequent tectonic events, tenuously distorting these lithologies and other rocks of recent ages (cataclasis). This could indicate that the fault has had reactivations.

The density of fracturing is moderated, presenting mainly two families of joints in the NW – SE and NE – SW directions.

Rocks with cataclastic deformation can be good conductors of fluids due to high porosity, as evident in the Fermin Lopez sector.

The spacing between joint families is very variable as they go from centimetric to metric scale. Joint gaps are centimetric scale (up to 3 cm), cooling joints were not considered when determining the paleo-stress tensor because of its non-tectonic nature, even though they enable interconnections of deeper tectonic structures with reservoirs. The joints in the NE – SW direction are continuous, while joints in the NW – SE direction are cut by the above-mentioned family joint.

Many of the joints are filled with carbonates, silica, chlorite, sericite, epidote and sulfurs that represent fossil hy-drothermal circulation. In thin sections it was possible to determine the composition of the fractures (Figure 7, Figure 14). Some of the them are fissured by tectonism and others are not fissured and crossing the others, evidence that there has been hydrothermal circulation through time.

The relationship of this fault with the thermal seeps of San Vicente and Santa Rosa is unclear, since there is no obvious connection between such systems, due to the structural complexity of the sector. However, the Santa Rosa Fault could serve as a fluid supply channel because jointing and cataclasis represent areas of high porosity and permeability which would allow fluid flow to the other structural systems in E – W to NW – SE to the Campoalegrito Fault, where hot springs emerge.

The relation of the Santa Rosa Fault with Botero Lodoño thermal systems could be associated with the extensional kinematics of different faults in the area, thus creating an enabling environment for the circulation of fluids due to dila-tational nature.

Figure 5. Map showing the stereogram of striations across of La Telaraña fault.

Figure 6. Map showing the stereogram of joints across of La Telaraña fault.

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There is evidence of geomorpho-logical deformation on the Río Claro ignimbrite and the Quaternary deposits, associated to Santa Rosa and La Telaraña Faults.

Petrography and Microtectonic Analysis

The rocks described in the petrog-raphy correspond to:

Cajamarca ComplexNereidas samples: Quartz-chlorite

schist with carbonates and muscovites. Protolith: Marl; Facies: Green schist; Metamorphic degree: Low; Textures: Lepidoblastic, granoblastic, low mylonitic texture.

Molinos samples: Quartz-actinolite schist with tremolite and Clinozoisite-zoisite; Protholith: Basic (igneous); Facies: high green schist turning into anfibolite facies; Metamorphic degree: Low-medium; Textures: nematoblastic, granoblastic.

1mm

Figure 7. Nereidas sample. Dextral micro-faulting (upper right image) in schist, fracture filled of muscovite and chlorite. Interbedded quartz-plagioclase and carbonates in grano-

blastic texture with chlorite and muscovite in lepidoblastic texture.

Figure 9. Molinos sample. Actinolite-tremolite with relict amphibole in a nematoblastic

texture with dynamic metamorphism imposed. Significant presence of opaques.

Figure 8. Molinos sample. Mylonitic dextral deformation in schist. Nematoblastic texture in

actinolite - tremolite along with granoblastic texture in quartz-plagioclase and epidote.

Deformed saussuritized plagioclase in ductile zone with dextral sense, demonstrating the basic

igneous protolith rock (lower image).

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Nevado del Ruiz LavasAzufrado: Porphyritic andesite with

two pyroxenes. Hypocrystalline, porphyritic, inequigranular, fine grained.

Figure 10. Azufrado sample. Poikilitic texture of clinopyroxene in zoned plagioclase.

No tectonic structure in the image.

Figure 11. Azufrado sample. Glomeroporphyritic tex-ture of bytownite plagioclase and clinopyroxene, many of the latter twinned, baveno twinning in augite in the

center of the image. No tectonic structure in the image.

Figure 12. Azufrado sample. Cataclasis in clinopyroxene.

Chinchiná-Santa Rosa Metagabbro

La Reina Quarry. Rock: Metagabbro; textures: Holocrystalline, phaneritic, inequi-granular, medium grained with dynamic metamorphism.

Figure 13. La Reina quarry sample. Plagioclase in granoblastic disposal, alteration to saussurite from pla-gioclase (basic protolithic evidence) intercalated with

relict hornblende in nematoblastic texture. No tectonic structure in the image.

Figure 14. La Reina quarry sample. Fracture filled with chlorite and Clinozoisite-zoisite in relict hornblende.

No tectonic structure in the image.

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Acknowledgments

Dewhurst Group, Stratigraphy Research Institute (IIES in Spanish), University of Caldas, CHEC-EPM, M.Sc. Gustavo Hincapié Jaramillo and God.

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