Seismic anisotropy of the lithospheric mantle beneath Marie Byrd Land, West Antarctica: Constraints from peridotite xenoliths

2020 ◽  
Author(s):  
Seth Kruckenberg ◽  
Vasileios Chatzaras
Keyword(s):  
Lithospheric Mantle ◽  
Seismic Anisotropy ◽  
P Wave ◽  
Spinel Peridotite ◽  
Seismic Structure ◽  
West Antarctica ◽  
The West ◽  
West Antarctic ◽  
Peridotite Xenoliths ◽  
Static Conditions

<p>Constraining the seismic structure of the West Antarctic mantle is important for understanding its viscosity structure, and thus for accurately predicting the evolution of the West Antarctic Ice Sheet.  Seismic anisotropy, which is the dependence of seismic velocities on the propagation and polarization direction of seismic waves, is a valuable tool for understanding mantle deformation and flow.  We provide petrological and microstructural data from a suite of 44 spinel peridotite xenoliths entrained in Cenozoic (1.4 Ma) basalts of 7 volcanic centers located in Marie Byrd Land, West Antarctica.  Equilibration temperatures obtained from three different calibrations of the two-pyroxene geothermometer and the olivine-spinel Fe-Mg exchange geothermometer range from 780°C to 1200°C, calculated at a pressure of 1500 MPa.  This range of temperatures corresponds to extraction depths between 39 and 72 km, constraining the source of the xenoliths within the lithospheric mantle above the low velocity zone modelled by seismic studies.</p><p>The Marie Byrd Land xenoliths are fertile with average clinopyroxene mode that ranges between 15 and 24%.  Based on their modal composition, xenoliths are predominantly classified as lherzolites (n=30), with lesser occurrences of harzburgite (n=4), wehrlite (n=3), dunite (n=3), olivine websterite (n=1), websterite (n=1), and clinopyroxenite (n=2).  Petrological data suggest that the xenoliths have been affected by various degrees of partial melting as well as by reaction with silicate melts or fluids.  For example, clinopyroxenes in the more fertile lherzolites and wehrlites show a constant TiO<sub>2</sub> concentration at 0.65 wt% and 0.8 wt% over a range of olivine Mg# values, while TiO<sub>2</sub> decreases rapidly with increasing Mg#, down to 0.01 wt% in the more refractory harzburgites and dunites.  The observed trend is interpreted to indicate a refertilization process.  Microstructures also indicate multiple episodes of reactive melt percolation under either static conditions or during the late stages of deformation.  Pyroxenes may enclose rounded olivine grains in crystallographic continuity with neighbouring grains, cross-cut the subgrain boundaries of olivine grains, or show an interstitial habit, either forming cuspate-shaped grains in olivine triple junctions or films along olivine-olivine grain boundaries.  Olivine shows a range of crystallographic preferred orientation (CPO) patterns, including the A-type, axial-[010], axial-[100], and B-type.  Pyroxenes have weaker but not random CPOs with [001] axes having similar orientation to olivine [100] axes in the majority of the xenoliths.  Calculated P and S waves anisotropy is variable (2–12%) and increases with olivine fraction but decreases with both increasing ortho- or clinopyroxene content.  P-wave anisotropy is correlated with the strength of olivine CPO expressed with the M-index and increases with increasing strength of the orthopyroxene CPO, but seems to be less correlated with the strength of the clinopyroxene CPO.</p>

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

2021 ◽  
pp. M56-2020-16
Author(s):  
V. Chatzaras ◽  
S. C. Kruckenberg
Keyword(s):  
Upper Mantle ◽  
Mantle Xenoliths ◽  
P Wave ◽  
West Antarctica ◽  
Seismic Properties ◽  
West Antarctic ◽  
Peridotite Xenoliths ◽  
Melt Percolation ◽  
Supplementary Material ◽  
Reactive Melt

AbstractWe 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

Proterozoic lithosphere in Marie Byrd Land, West Antarctica: Re–Os systematics of spinel peridotite xenoliths

2003 ◽  
Vol 196 (1-4) ◽  
pp. 131-145 ◽  
Author(s):  
Monica R. Handler ◽  
Richard J. Wysoczanski ◽  
John A. Gamble
Keyword(s):  
Spinel Peridotite ◽  
West Antarctica ◽  
Peridotite Xenoliths

Active subglacial volcanism in West Antarctica as assessed by airborne geophysics: Distribution and context

2020 ◽  
Author(s):  
Donald Blankenship ◽  
Enrica Quatini ◽  
Duncan Young
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Rift System ◽  
West Antarctica ◽  
The West ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Subglacial Volcanism

<p>A combination of aerogeophysics, seismic observations and direct observation from ice cores and subglacial sampling has revealed at least 21 sites under the West Antarctic Ice sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogenous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially underrepresented. Unsurprisingly, the sites of active subglacial volcanism we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea to Siple Coast lithospheric transition.</p>

scholarly journals The internal origin of the west-east asymmetry of Antarctic climate change

2020 ◽  
Vol 6 (24) ◽  
pp. eaaz1490
Author(s):  
Sang-Yoon Jun ◽  
Joo-Hong Kim ◽  
Jung Choi ◽  
Seong-Joong Kim ◽  
Baek-Min Kim ◽  
...  
Keyword(s):  
Climate Change ◽  
Anthropogenic Factors ◽  
Observation Data ◽  
Austral Winter ◽  
West Antarctica ◽  
The West ◽  
Asymmetric Mode ◽  
West Antarctic ◽  
Surface Climate ◽  
The Antarctic

Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although this asymmetric feature is well recognized, its origin remains poorly understood. Here, by analyzing observation data and multimodel results, we show that a west-east asymmetric internal mode amplified in austral winter originates from the harmony of the atmosphere-ocean coupled feedback off West Antarctica and the Antarctic terrain. The warmer ocean temperature over the West Antarctic sector has positive feedback, with an anomalous upper-tropospheric anticyclonic circulation response centered over West Antarctica, in which the strength of the feedback is controlled by the Antarctic topographic layout and the annual cycle. The current west-east asymmetry of Antarctic surface climate change is undoubtedly of natural origin because no external factors (e.g., orbital or anthropogenic factors) contribute to the asymmetric mode.

Chapter 7.5 Active subglacial volcanism in West Antarctica

2021 ◽  
pp. M55-2019-3
Author(s):  
Enrica Quartini ◽  
Donald D. Blankenship ◽  
Duncan A. Young
Keyword(s):  
Ice Sheet ◽  
Ice Cores ◽  
Rift System ◽  
West Antarctica ◽  
The West ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Subglacial Volcanism

AbstractA combination of aerogeophysics, seismic observations and direct observation from ice cores, and subglacial sampling, has revealed at least 21 sites under the West Antarctic Ice Sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogeneous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially under-represented. Unsurprisingly, the sites of active subglacial volcanism that we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal-thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea–Siple Coast lithospheric transition.

Overview of West Antarctic tectonic evolution from ~500 Ma to the present

2021 ◽  
Author(s):  
Tom Jordan ◽  
Teal Riley ◽  
Christine Siddoway
Keyword(s):  
Tectonic Evolution ◽  
Weddell Sea ◽  
East Antarctica ◽  
Rift System ◽  
West Antarctica ◽  
The West ◽  
Magmatic Arc ◽  
West Antarctic ◽  
The Pacific ◽  
Tectonically Active

<p>West Antarctica developed as the tectonically active margin separating East Antarctica and the Pacific Ocean for almost half a billion years. Its dynamic history of magmatism, continental growth and fragmentation are recorded in sparse outcrops, and revealed by regional geophysical patterns. Compared with East Antarctica, West Antarctica is younger, more tectonically active and has a lower average elevation. We identify three broad physiographic provinces within West Antarctica and present their overlapping and interconnected tectonic and geological history as a framework for future study: 1/ The Weddell Sea region, which lay furthest from the subducting margin, but was most impacted by the Jurassic initiation of Gondwana break-up. 2/ Marie Byrd Land and the West Antarctic rift system which developed as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin. 3/ The Antarctic Peninsula and Thurston Island which preserve an almost complete magmatic arc system. We conclude by briefly discussing the evolution of the West Antarctic system as a whole, and the key questions which need to be addressed in future. One such question is whether West Antarctica is best conceived as an accreted collection of rigid microcontinental blocks (as commonly depicted) or as a plastically deforming and constantly growing melange of continental fragments and juvenile magmatic regions. This distinction is fundamental to understanding the tectonic evolution of young continental lithosphere. Defining the underlying geological template of West Antarctica and constraining its linkages to the dynamics of the overlying ice sheet, which is vulnerable to change due to human activity, is of critical importance.</p>

Reduced perchlorate in West Antarctica snow during stratospheric ozone hole

2017 ◽  
Vol 29 (3) ◽  
pp. 292-296 ◽  
Author(s):  
T.Z. Crawford ◽  
Alexandria D. Kub ◽  
Kari M. Peterson ◽  
Thomas S. Cox ◽  
Jihong Cole-Dai
Keyword(s):  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Stratospheric Ozone Depletion ◽  
West Antarctica ◽  
The West ◽  
West Antarctic Ice Sheet ◽  
West Antarctic ◽  
Apparent Correlation ◽  
Antarctic Snow ◽  
Perchlorate Concentration

AbstractSnowpit samples collected at the West Antarctic Ice Sheet (WAIS) Divide location in January 2013 were analysed to investigate the levels and variations of perchlorate concentrations in Antarctic snow. During 2008–12, the perchlorate concentration in WAIS Divide snow ranged between 6–180 ng l–1 and followed a seasonal cycle. The highest concentrations appeared in the autumn, and the lowest in winter and spring. No apparent correlation was observed between perchlorate and nitrate or chloride concentrations in snow. Since perchlorate is believed to form in the atmosphere when chlorine species are oxidized in reactions involving ozone, perchlorate concentrations were hypothesized to be high during the spring, based on the assumption that stratospheric ozone depletion enhances tropospheric perchlorate production. The data show that perchlorate concentrations in snow were sharply reduced during stratospheric ozone depletion events; the evidence, therefore, does not support the hypothesis. Instead, the results suggest a stratospheric origin of perchlorate in Antarctic snow.

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