0000000000114450
AUTHOR
Virginia Toy
Does second phase content control the evolution of olivine CPO type and deformation mechanisms? A case study of paired harzburgite and dunite bands in the Red Hills Massif, Dun Mountain Ophiolite
Abstract We have examined the microstructures and crystallographic preferred orientations (CPOs) of six “paired” harzburgite and dunite samples from a small (~ 1 km2) area in the Ellis Stream Complex, Red Hills Massif, Dun Mountain ophiolite belt in New Zealand. Here, banded peridotites with isoclinal folds, E-W striking vertical foliations and vertical lineations are inferred to result from shear on vertical planes that overprint previous mantle structures. The samples contain five different olivine CPOs: typically known as A, C, D, E and AG-types. The co-located harzburgite and dunite of each pair show different CPOs (e.g., A vs E type). In each pair, dunite generally has larger grain siz…
Seismic anisotropy and its impact on imaging the shallow Alpine Fault : an experimental and modeling perspective.
The transpressional Alpine Fault in New Zealand has created a thick shear zone with associated highly anisotropic rocks. Low seismic velocity zones (LVZ) and high seismic reflectivity are recorded in the Alpine Fault Zone, but no study has explored the underlying physical rock parameters of the shallow crust that control these observations. Protomylonites are the volumetrically dominant lithology of the fault zone. Here we combine experimental measurements of P‐wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged. Numerical models that account for the porosity‐free real samples' fabric elastic tensors f…
The estimation of porosity in Japan Trench plate boundary using low-resolution X-ray computed tomography (XCT) images and laboratory measurements
Abstract. X-ray computed tomography (XCT) is an advanced imaging technique that has been increasingly used in the past years because it can provide valuable information on internal structures of a rock sample in a non-invasive manner. The maximum resolution of lab-based XCT facilities is ~0.5 μm, which might be sufficient to capture macropores in some rocks (i.e., sandstone), but will result in underestimation of porosity in clay-rich sediments containing micro-and nano-scale pores. Furthermore, such high-resolution XCT facilities are quite expensive and not ubiquitous. In this study, we introduce a new methodology based on the K-means clustering algorithm to process of low-resolution XCT i…
Fracture Shape and Orientation Contributions to P-Wave Velocity and Anisotropy of Alpine Fault Mylonites
P-wave anisotropy is significant in the mylonitic Alpine Fault shear zone. Mineral- and texture-induced anisotropy are dominant in these rocks but further complicated by the presence of fractures. Electron back-scattered diffraction and synchrotron X-ray microtomography (micro-CT) data are acquired on exhumed schist, protomylonite, mylonite and ultramylonite samples to quantify mineral phases, crystal preferred orientations, microfractures and porosity. The samples are composed of quartz, plagioclase, mica and accessory garnet, and contain 3-5% porosity. Based on the micro-CT data, the representative pore shape has an aspect ratio of 5:2:1. Two numerical models are compared to calculate the…