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Abstract Subduction zone accretionary prisms are commonly modeled as elastic structures where permanent deformation is accommodated by faulting and folding of otherwise elastic materials, yet accretionary prisms may exhibit other deformation styles over relatively short time scales. In this study, we use 6.5‐year (2014–2021) Sentinel‐1 interferometric synthetic aperture radar (InSAR) time‐series of post‐seismic deformation in the Makran accretionary prism of southeast Pakistan to characterize non‐linear viscoelastic deformation within an active accretionary prism on short timescales (months to years). We constructed a series of 3‐D finite‐element models of the Makran subduction zone, including an accretionary prism, and constrained the elastic thickness of the upper wedge and the flow‐law parameters (power‐law exponent, activation enthalpy, and pre‐exponential constant) of the lower wedge through forward model fits to the InSAR time‐series. Our results show that the prism is elastically thin (8–12 km) and the non‐linear viscoelastic relaxation of the deep portions of the prism alone can sufficiently explain the post‐seismic surface deformation. Our best fitting flow‐law parameters (n = 3.76 ± 0.39,Q = 82.2 ± 37.73 kJ mol−1, andA = 10−3.36±4.69) are consistent with triggering of low temperature dislocation creep within fluid‐saturated siliciclastic rocks. We believe that the fluids necessary for this weakening originate from sedimentary underplating and/or the presence the hydrocarbons. The presence of power‐law rheology within the lower wedge impacts the estimated plate coupling and the stress state in the subduction system, with respect to the conventional elastic wedge model, and hence should to be considered in future earthquake cycle models.
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Calcite Twinning in Mollusk Shells and Carrara Marble
Abstract Mollusk shells protect the animals that form and inhabit them. They are composites of minerals and organics, with diverse mesostructures, including nacre, prismatic calcite, crossed‐lamellar aragonite, and foliated calcite. Twins, that is, crystals mirror symmetric with respect to their coherent interface, occurring as formation or deformation twins, are observed in all mollusk shell mesostructures but never within calcite prisms. Here, nanotwins and microwins within single calcite prisms are observed in different shells. Using Polarization‐dependent Imaging Contrast (PIC) mapping with 20–60 nm resolution, twins are observed to be 0.2–3 µm thick layers of differently oriented and colored crystals with respect to the main prism crystal. Multiple twins are interspersed with the prism crystal, parallel to one another, and similarly oriented. When comparing images of calcite prisms and twins obtained by PIC mapping and by Electron Back‐Scattered Diffraction (EBSD), the images correspond precisely. All twins are e‐twin types, with 127° angular distance betweenc‐axes. E‐twins are the most common deformation twins in geologic calcite, as also observed here in Carrara marble. Location of all twins near the outer surface of all shells and e‐twin type both suggest that twins within calcite prisms in mollusk shells result from deformation twinning.
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- Award ID(s):
- 2220274
- PAR ID:
- 10441470
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 34
- Issue:
- 35
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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