Textural analyses of peridotites drilled by Oman Drilling Project for reconstruction of the orientation of mantle flow
Abstract
Oman Ophiolite is the biggest ophiolite that preserves structures of crustal section including volcanic rocks, sheeted dikes, gabbro and mantle section consisting of peridotites. Oman Drilling Project has drilled cores penetrating the section from lower crust to upper mantle including Crust-Mantle Transition Zone. Structural characteristics within peridotites of 3 holes at BA site corresponding to upper mantle section have been described during the Oman Drilling Project Phase 2 from 5th August to 3rd September, 2018 on D/V Chikyu. The peridotites consist of intensely serpentinized harzburgites and dunites containing elongated and aligned pyroxene grains. In this study, we analyze peridotite textures of BA site and perform electron backscatter diffraction (EBSD) to understand the characteristics of the uppermost mantle flow.
Variously deformed textures ranging from protogranular to protomylonite exhibited by elongated pyroxene grains are observed in every core. Dip angles of elongated pyroxene are different for each core, but nearly constant regardless of the depth. Pyroxene and olivine grains in protomylonitic peridotites are intensely elongated, showing kink bands and wavy extinction at thin section scale. In protogranular peridotites, pyroxene grains have rounded shapes, and few of them show kink bands or wavy extinction. Crystallographic preferred orientations (CPOs) of olivine have been measured by the EBSD. For all samples, J-index is in the range between 2 and 4, whereas P-wave velocity anisotropies are at around 8 %. Fabric Index Angles (FIA; Michibayashi et al., 2016) are in the range between 52 and 85, indicating that CPO types are classified to A or D type. Furthermore, the strength of the olivine CPO and the pattern of P-wave anisotropy vary within 20 cm section. These variations may show the localization of deformation during mantle flow.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T21D0369K
- Keywords:
-
- 1032 Mid-oceanic ridge processes;
- GEOCHEMISTRY;
- 1037 Magma genesis and partial melting;
- GEOCHEMISTRY;
- 8140 Ophiolites;
- TECTONOPHYSICS;
- 8416 Mid-oceanic ridge processes;
- VOLCANOLOGY