Confronting Shear Bias: Magmatic Fabric Influence on Crustal Seismic Anisotropy

Frothingham, Michael G.; Mahan, K. H.; Schulte-Pelkum, V.; Gonçalves, Philippe; Zucali, Michele

doi:10.1130/abs/2022am-382432

Cited by 4 publications

(4 citation statements)

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“…We can look to seismic studies of the Earth's crust for confirmation. Some crustal seismic anisotropy is thought to result from the orientation of magmatic intrusions (Frothingham et al., 2023; Hammond, 2014) and fluid‐filled microcracks (Crampin, 1987; Crampin & Zatsepin, 1997; Elkibbi et al., 2005) that form parallel to the local maximum compressive stress (Gerst & Savage, 2004; Johnson, 2015). Within geophysically observable timescales, microscale crystallographic orientation is considered to be relatively static.…”

Section: Discussionmentioning

confidence: 99%

Melt Network Reorientation and Crystallographic Preferred Orientation Development in Sheared Partially Molten Rocks

Seltzer,

Peč,

Zimmerman

et al. 2023

Geochem Geophys Geosyst

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We investigated the co‐evolution of melt, shape, and crystallographic preferred orientations (MPOs, SPOs, and CPOs) in experimentally deformed partially molten rocks, from which we calculated the influence of MPO and CPO on seismic anisotropy. Olivine‐basalt aggregates containing 2 to 4 wt% melt were deformed in general shear at a temperature of 1,250°C under a confining pressure of 300 MPa at shear stresses of τ ≤ 175 MPa to shear strains of γ ≤ 2.3. Grain‐scale melt pockets developed a MPO parallel to the loading direction by γ < 0.4. At higher strains, the grain‐scale MPO remained parallel to the loading direction, while incipient sample‐scale melt bands formed at ∼20° to the grain‐scale MPO. An initial SPO and CPO were induced during sample preparation, with [100] and [001] axes girdled perpendicular to the long axis of the starting material. At the highest explored strain, a strong SPO was established subperpendicular to the loading direction, and the [100] axes of the CPO clustered nearly parallel to the shear plane. Our results demonstrate that grain‐scale and sample‐scale alignments of melt pockets are distinct. Furthermore, the melt and the solid microstructures evolve on different timescales: in planetary bodies, changes in the stress field will drive a relatively fast reorientation of the melt network and a relatively slow realignment of the crystallographic axes. Rapid changes to seismic anisotropy in a deforming partially molten aggregate are thus caused by MPO rather than CPO.

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Section: Discussionmentioning

confidence: 99%

Melt Network Reorientation and Crystallographic Preferred Orientation Development in Sheared Partially Molten Rocks

Seltzer,

Peč,

Zimmerman

et al. 2023

Geochem Geophys Geosyst

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“…As should be expected, the seismic structure of volcanic ocean islands can be very complex, resulting from pre‐existing boundaries, magma reservoirs, and a complex structure that may include structural (i.e., dipping interfaces or faulting) and/or intrinsic (i.e., mineral‐controlled) anisotropy. These effects on RF amplitude and arrivals are covered extensively in multiple studies (Frothingham et al., 2023; Schulte‐Pelkum & Mahan, 2014; Schulte‐Pelkum et al., 2020). This complexity can be observed at station HV.…”

Section: Resultsmentioning

confidence: 99%

Constraining the Lithospheric Discontinuity Structure Beneath Hawaiʻi Using Teleseismic Receiver Functions

Herr,

Delph

2023

JGR Solid Earth

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The Hawaiian Islands represent the youngest portion of the long‐lived Hawaiian‐Emperor Seamount chain sourced from hotspot volcanism on the northwesterly moving Pacific plate. Despite being one of the best studied hotspots on Earth, our understanding of the lithospheric discontinuity structure of Hawaiʻi is inhibited by a lack of a long‐term distributed broadband seismic network and lithospheric‐scale imaging of other oceanic hotspots. In this study, we analyze 3,530 teleseismic waveforms from 1,130 events recorded at 47 stations to compute P‐wave radial receiver functions. We then incorporate an elevation correction to adaptive common conversion point stacking to create a 3D discontinuity volume of the lithospheric structure associated with an ocean island hotspot. We find a positive amplitude conversion consistently at ∼12 km below sea level, likely representing the crust‐mantle transition below much of the island. However, this conversion occurs at only ∼6 km below Kīlauea, where local tomography images a zone of high P‐wave velocities (>7 km/s) within the crust and deformation of olivine phenocrysts within a magmatic reservoir is thought to occur. At this location, seismicity also extends vertically to 35 km depth before merging with an interpreted sill complex at ∼40 km. We interpret this anomalously shallow high amplitude discontinuity as an olivine‐dominated magmatic reservoir with an estimated maximum 5% melt over the resolution of our data at crustal depths. This represents the shallow seismic signature of a much more extensive magma system extending to depth. These images provide a better understanding of the magmatic structure associated with oceanic hotspot volcanoes.

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“…Another important debate is related to the question of how the NAFZ continues in the crust and lithosphere. To shed light on this issue, we investigate the depth‐variation in anisotropic parameters that may result from a change in the dominant mineralogy at different depth layers including upper, lower crust and mantle (Bernard & Behr, 2017; Frothingham et al., 2023). These microscale variations can strongly control the regional lithospheric strength and depth distribution of strain.…”

Section: Discussionmentioning

confidence: 99%

Depth‐Dependent Anisotropy Along Northwest Segment of the North Anatolian Fault Zone: Evidence for Paleo‐Tectonic Structures Contributing to Overall Complexity

Keleş,

Eken,

Licciardi

et al. 2024

JGR Solid Earth

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The North Anatolian Fault Zone (NAFZ) is a prominent tectonic structure with a significant impact on the observed active deformation in Türkiye. Detailed knowledge of the seismic anisotropy in the crust and mantle along this nascent shear deformation zone provides insights into the kinematics associated with past and present tectonic events. We employed teleseismic earthquakes observed by the Dense Array North Anatolia seismic network to map 3‐ D variations in crustal and mantle anisotropy in/around the NW segment of the NAFZ. To achieve this, we first performed a harmonic decomposition analysis of P‐receiver functions. The results were then used as a priori information to conduct an anisotropic receiver function inversion with the Neighborhood Algorithm that enabled imaging of the actual orientation and geometry of anisotropic structures. SKS splitting measurements are further used to make a comparison between the anisotropic behavior of crustal and mantle structures. Crustal anisotropy parameters estimated in our analyses/models well identify the signature of deformation caused by accumulated strain in the earthquake cycle through the strike of shallow cutting faults in the brittle crust beneath the NAFZ. Diffuse intense anisotropic energy at lower crustal depths was attributed to lattice preferred orientation of crystals or partially molten lenses elongated along the shear direction. Strong harmonic energy variations beneath the northern part of the Istanbul Zone likely reflect imprints of LPO‐originated frozen fabric at shallow depths (0–20 km) associated with the palaeotectonic Odessa Shelf, Intra‐Pontide Suture Zones or remnants of the Tethys Ocean.

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Confronting Shear Bias: Magmatic Fabric Influence on Crustal Seismic Anisotropy

Cited by 4 publications

References 0 publications

Melt Network Reorientation and Crystallographic Preferred Orientation Development in Sheared Partially Molten Rocks

Melt Network Reorientation and Crystallographic Preferred Orientation Development in Sheared Partially Molten Rocks

Constraining the Lithospheric Discontinuity Structure Beneath Hawaiʻi Using Teleseismic Receiver Functions

Depth‐Dependent Anisotropy Along Northwest Segment of the North Anatolian Fault Zone: Evidence for Paleo‐Tectonic Structures Contributing to Overall Complexity

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