Kinematic deformation model of the south-central subandean zone, Bolivia
Introduction
The study area is in the southern portion of the central Subandean zone of Bolivia (Fig. 1). It lies within the sedimentary prism of deformation where the contractional structures were generated by Oligocene to Early Miocene subduction of the Nazca plate under the South American plate. The Bolivian Subandean area is characterized as a thin-skinned thrust fold belt with inverted structures persisting for 50–100 km along strike in a broadly North-South direction (Fig. 1; Dunn et al., 1995; Hernández et al., 2002; Starck et al., 2002; McQuarrie et al., 2005). The ridges typically have elevations between 1300 and 2000 masl, while the intervening synclines lie at 600 to 800 masl.
The objective of this study is to build a regional structural model in the geological province of the south-central Bolivian Subandean region by generating a series of balanced and restored sections across the fold belt. The sections were constructed using the relationships that link the geometry of faults with the folds, all of that based on surface geological data, wells, 2D seismic and magnetotelluric information.
Section snippets
Geological background
The Oligocene to Early Miocene subduction of the Nazca plate produced a long-lived deformation and formed a large volcanic arc along the Pacific coast of South America (Ramos and Aleman, 2000; McQuarrie, 2002; Arriagada et al., 2006 and Ramos, 1999). Thrusting and folding occurred in all sequences causing significant shortening and uplift to create the Andean Mountains. Backarc and transported (piggyback) basins were formed within the high plateau and western sector of the Eastern mountain
Stratigraphy
The stratigraphic framework of the Phanerozoic in the southern Bolivian Subandean region is defined by four tectono-stratigraphic or tectono-sedimentary cycles (Sempéré, 1995). Tacsarian, Cordilleran, Subandean established by Suárez Soruco and López (1983), and the Andean cycle determined by Suárez Soruco (2000). The Andean cycle was subsequently subdivided into Andean I and II by Oller Veramendi (1992) (Fig. 2). The Andean cycle constitutes an important control element in the construction of
Data available
Integration of geological and geophysical information was the foundation for this study. Located within the Central Subandean area, 6 seismic sections (Fig. 4) with PSDM reprocessing and magneto-telluric (MT) data along with their respective interpretations were used as the main input to define the structural model. The MT method consists of passive measurements on the Earth's surface of the natural electromagnetic (EM) field. This EM field, generated by the impact of the solar wind on the
Structural observations, interpretation, restoration and balancing methods
The structural interpretation in the Subandean fold and thrust belts has many uncertainties, especially when the seismic quality is not optimal. Magnetotelluric data provides an independent geophysical tool to aid interpretation. For example, in areas where there is a resistance contrast between the reservoir and the overlying rocks, as it is the case for the Huamampampa and the Los Monos Formations, the MT data can help unraveling some of the complex internal deformation demonstrated by
Discussion
The geometry of the southern Subandean zone has been well-documented, especially in the frontal folds close to the foreland, with images of the predominant structural styles that have been identified on several seismic lines (Baby et al., 1992; Dunn et al., 1995; Blake et al., 1999; Ballard et al., 2018). However, many papers do not present the full dataset that has been used to build their interpretations. This paper displays and explains the raw data, especially the seismic and MT
Conclusions
A plausible structural model has been developed in the geological province of the Bolivian South-Central Subandean, identifying the main structural styles present in the area. The model has been restored and balanced in two dimensions along the structural sections. Although the interpretation has been validated from the geometrical point of view, alternative models could be generated from the available data.
Seismic imaging and geological surface mapping are the principal tools used in the
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank YPFB Chaco S.A. who permitted publishing these data.
The authors value the suggestions and comments from four colleagues: Dugmar Mendez, Diego Paredes (from 3D-GEO Pty Ltd), Nabil Chávez (from YPFB Chaco S.A.) and Elvira Pureza Gómez (from CNOOC International). We would also like to take this opportunity to thank Ph. D. Fernando Martinez for the invitation to submit this manuscript and, together with Ph. D. Andrés Folguera and other reviewers, for the effort and expertise that
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Structural styles of imbricate systems involving multiple detachments: An example from the Subandean fold-thrust belt, southern Bolivia
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