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Potential of pressure solution for strain localization in the Baccu Locci Shear Zone (Sardinia, Italy)

Casini, Leonardo and Funedda, Antonio (2014) Potential of pressure solution for strain localization in the Baccu Locci Shear Zone (Sardinia, Italy). Journal of structural geology, Vol. 66 , p. 188-204. ISSN 1873-1201. eISSN 0191-8141. Article.

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DOI: 10.1016/j.jsg.2014.05.016

Abstract

The mylonites of the Baccu Locci Shear Zone (BLSZ), Sardinia (Italy), were deformed during thrusting along a bottom-to-top strain gradient in lower greenschist facies. The microstructure of metavolcanic protoliths shows evidence for composite deformation accommodated by dislocation creep within strong quartz porphyroclasts, and pressure solution in the finer grained matrix. The evolution of mylonite is simulated in two sets of numerical experiments, assuming either a constant width of the deforming zone (model 1) or a narrowing shear zone (model 2). A 2-5 mm y-1 constant-external-velocity boundary condition is applied on the basis of geologic constraints. Inputs to the models are provided by inverting paleostress values obtained from quartz recrystallized grain-size paleopiezometry. Both models predict a significant stress drop across the shear zone. However, model 1 involves a dramatic decrease in strain rate towards the zone of apparent strain localization. In contrast, model 2 predicts an increase in strain rate with time (from 10-14 to 10-12 s-1), which is consistent with stabilization of the shear zone profile and localization of deformation near the hanging wall. Extrapolating these results to the general context of crust strength suggests that pressure-solution creep may be a critical process for strain softening and for the stabilization of deformation within shear zones.

Item Type:Article
ID Code:4769
Status:Published
Refereed:Yes
Uncontrolled Keywords:Mylonite, rheology, numerical modeling, Gamma-ray, spectrometry, variscan, paleopiezometry
Subjects:Area 04 - Scienze della terra > GEO/03 Geologia strutturale
Divisions:001 Università di Sassari > 01-a Nuovi Dipartimenti dal 2012 > Scienze della Natura e del Territorio
Publisher:Elsevier
ISSN:1873-1201
eISSN:0191-8141
Deposited On:05 Nov 2010 10:21

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