Fluid flow in cataclastic thrust fault zones in sandstones, Sub-Andean Zone, Southern Bolivia

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Abstract

The Bolivian Sub-Andean Zone (SAZ) corresponds to a Neogene thrust system that affects an about 10-km thick Palaeozoic to Neogene siliciclastic succesion. The analysis of macro and microstructures and cement distribution in thrust fault zones shows that they are sealed by quartz at depths > ~ 3 km, due to local silica transfer by pressure-solution/precipitation activated at temperatures >70-90 °C. At shallower depths, faults have remained open and could be preferential drains for lateral flow of carbonate-bearing fluids, as shown by the occurence of carbonate cements in fractures and their host-sandstone. Due to decreasing burial, resulting from foothill erosion during fault activity, critically buried fault segments can be affected by non-quartz-sealed structures that post-date initial quartz-sealed structures. The integration of textural, fluid inclusion and isotopic data shows that carbonates precipitated at shallow depth (<3 km), low temperature (<80 °C) and relatively late during the thrusting history. Isotopic data also show that precipitation occured from the mixing of gravity-driven meteoric water with deeper formation water bearing carbonate carbon derived from the maturation of hydrocarbon source rocks (Silurian and Devonian shales). The combined microstructural and isotopic analyses indicate that: (i) fluid flow in fault zones often occured with successive pulses derived from different or evolving sources and probably related to episodic fault activity, and (ii) at a large-scale, the faults have a low transverse permeability and they separate thrust sheets with different fluid histories. © 2001 Elsevier Science B.V. All rights reserved.

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Labaume, P., Sheppard, S. M. F., & Moretti, I. (2001). Fluid flow in cataclastic thrust fault zones in sandstones, Sub-Andean Zone, Southern Bolivia. Tectonophysics, 340(3–4), 141–172. https://doi.org/10.1016/S0040-1951(01)00144-5

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