Glass Microbeads in Analog Models of Thrust Wedges.

Taynara D'Angelo,Caroline J.S Gomes

doi:10.1590/0001-3765201720160291

Taynara D'Angelo, Caroline J.S Gomes

Open Access

https://doi.org/10.1590/0001-3765201720160291

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Abstract

Glass microbeads are frequently used in analog physical modeling to simulate weak detachment zones but have been neglected in models of thrust wedges. Microbeads differ from quartz sand in grain shape and in low angle of internal friction. In this study, we compared the structural characteristics of microbeads and sand wedges. To obtain a better picture of their mechanical behavior, we determined the physical and frictional properties of microbeads using polarizing and scanning electron microscopy and ring-shear tests, respectively. We built shortening experiments with different basal frictions and measured the thickness, slope and length of the wedges and also the fault spacings. All the microbeads experiments revealed wedge geometries that were consistent with previous studies that have been performed with sand. However, the deformation features in the microbeads shortened over low to intermediate basal frictions were slightly different. Microbeads produced different fault geometries than sand as well as a different grain flow. In addition, they produced slip on minor faults, which was associated with distributed deformation and gave the microbeads wedges the appearance of disharmonic folds. We concluded that the glass microbeads may be used to simulate relatively competent rocks, like carbonates, which may be characterized by small-scale deformation features.

Highlights

Several granular materials other than quartz sand have been employed to simulate compressive wedges under natural gravity conditions in analog models
We only present the progressive deformation of the medium basal friction models of each experimental series: the microbeads model “MB2” and the sand model “S2” (Fig. 3)
Our investigation showed that microbeads wedges and sand wedges produce slightly different deformation features when subjected to the same shortening conditions

Summary

Introduction

Several granular materials other than quartz sand have been employed to simulate compressive wedges under natural gravity conditions in analog models. These materials include wet clay (e.g., Eisenstadt and Sims 2005, Withjack et al 2007), glass microbeads, aluminum microspheres (Rossi and Storti 2003), water-saturated granular materials (Graveleau et al 2011), siliceous powder (Bonnet et al 2007), hemihydrate powder (CaSO4∙1⁄2H2O). Glass microbeads are commonly used to represent incompetent layers (e.g., mudstone, shale or a layer of high fluid pressure) between competent layers when simulating a multilayered rock package (e.g., Teixell and Koyi 2003, Panien et al 2005, 2006b, Ravaglia et al 2006) or a low-friction detachment (e.g., Turrini et al 2001, Massoli et al 2006, Malavieille 2010, Konstantinovskaya and Malavieille 2011). Viscous silicone putties are used to replicate ductile detachments; this material simulates a much lower strength, such as those that are commonly produced in evaporate layers

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