Effects of melt-percolation, refertilization and deformation on upper mantle seismic anisotropy: constraints from peridotite xenoliths, Marie Byrd Land, West Antarctica

Abstract

We report on the petrology, microstructure, and seismic properties of 44 peridotite xenoliths extracted from the upper mantle beneath Marie Byrd Land (MBL), West Antarctica. The aim of this work is to understand how melt-rock reaction, refertilization, and deformation affected the seismic properties (velocities, anisotropy) of the West Antarctic upper mantle, in the context of MBL tectonic evolution and West Antarctic Rift System formation. Modal compositions, mineral major element compositions, microstructures, and crystallographic preferred orientations (CPOs) provide evidence for diachronous reactive melt percolation and refertilization. Olivine shows three main CPO patterns, the A-type, axial-[010], and axial-[100] texture types. Average seismic properties of the MBL mantle lithosphere are mainly controlled by the strength of olivine crystallographic texture. Reactive melt percolation and refertilization likely modified seismic velocities and anisotropy, as is suggested by a systematic decrease in maximum P-wave and S-wave anisotropies with increasing modal abundance of pyroxene. At larger spatial scales, the seismic properties of the MBL mantle xenoliths are dominated by the anisotropy resulting from the A-type olivine CPO. Variations between individual volcanic centers, however, attest to spatial variations in the mantle structure, potentially related to 3-D deformation and the prolonged tectonic history of MBL.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5315261

Shear Wave Splitting Across Antarctica: Implications for Upper Mantle Seismic Anisotropy

“…Previous studies in continental settings, including Antarctica (e.g., Accardo et al., 2014; Barklage et al., 2009; Graw & Hansen, 2017), have assumed that the commonly occurring A‐type fabric (e.g., Bernard et al., 2019), which promotes the alignment of the olivine fast axis with the direction of maximum shear, provides the primary contribution to seismic anisotropy. This assumption has been recently corroborated for Marie Byrd Land (MBL) in West Antarctica by Chatzaras and Kruckenberg (2021), who determined that the A‐type fabric is a primary contributor to upper mantle anisotropy by analyzing xenoliths from seven volcanic centers in western and central MBL.…”

An introduction to the geochemistry and geophysics of the Antarctic mantle

“…In the latter case, is considering short-term and long-term viscosity sufficient or does viscosity need to be considered as a function of loading frequency (Lau et al 2021)? A consistent description of viscosity must consider deformation at the microscopic scale from observations on mantle xenoliths (Chatzaras and Kruckenberg 2021) and laboratory experiments (e.g. Hansen et al 2016).…”

Microstructural Relationship between Olivine and Clinopyroxene in Ultramafic Rocks from the Red Hills Massif, Dun Mountain Ophiolite

“…Discovering the detailed melt status is helpful for recovering the mantle kinematics. Both melt-rock reactions and melt flow injection are common during mantle evolution progress [17,20,[61][62][63][64]. Previous studies in the Red Hills Massif have indicated that the Ellis Stream Complex is influenced by partial melting under high temperature (>1000 • C) conditions [18,32,36,41].…”

“…This difference was probably due to the two pyroxenes experiencing respective evolutionary progress, as mentioned in Section 5.1. Clinopyroxene-saturated melt occurred during both syn-and post-kinematics, possibly leading to incoherent olivine and clinopyroxene CPOs [17,62,81]. The clinopyroxene-dominant melt veins injected peridotites and became solid and subsequent shearing bent the veins.…”

“…Although the solid second phase may inhibit the development of the olivine crystallographic preferred orientation (CPO) [7,8], wehrlites in different areas and geological environments can generate various olivine CPO types (B, E, and AG-type; [9][10][11]). In comparison, (010) [001] is the most common clinopyroxene CPO type [12][13][14] whereas it is not dominant in wehrlite or other peridotite types [15][16][17]. (Olivine) clinopyroxenites are usually banded or veined in natural outcrops [18][19][20].…”