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81 results on '"Bland, PA"'

1. Large impact cratering during lunar magma ocean solidification

Author

Miljković, K, Wieczorek, MA, Laneuville, M, Nemchin, A, Bland, PA, Zuber, MT, Miljković, K, Wieczorek, MA, Laneuville, M, Nemchin, A, Bland, PA, and Zuber, MT

Abstract

AbstractThe lunar cratering record is used to constrain the bombardment history of both the Earth and the Moon. However, it is suggested from different perspectives, including impact crater dating, asteroid dynamics, lunar samples, impact basin-forming simulations, and lunar evolution modelling, that the Moon could be missing evidence of its earliest cratering record. Here we report that impact basins formed during the lunar magma ocean solidification should have produced different crater morphologies in comparison to later epochs. A low viscosity layer, mimicking a melt layer, between the crust and mantle could cause the entire impact basin size range to be susceptible to immediate and extreme crustal relaxation forming almost unidentifiable topographic and crustal thickness signatures. Lunar basins formed while the lunar magma ocean was still solidifying may escape detection, which is agreeing with studies that suggest a higher impact flux than previously thought in the earliest epoch of Earth-Moon evolution.

Published
2021

2. Large impact cratering during lunar magma ocean solidification

Author

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Miljković, K, Wieczorek, MA, Laneuville, M, Nemchin, A, Bland, PA, Zuber, Maria, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Miljković, K, Wieczorek, MA, Laneuville, M, Nemchin, A, Bland, PA, and Zuber, Maria

Abstract

The lunar cratering record is used to constrain the bombardment history of both the Earth and the Moon. However, it is suggested from different perspectives, including impact crater dating, asteroid dynamics, lunar samples, impact basin-forming simulations, and lunar evolution modelling, that the Moon could be missing evidence of its earliest cratering record. Here we report that impact basins formed during the lunar magma ocean solidification should have produced different crater morphologies in comparison to later epochs. A low viscosity layer, mimicking a melt layer, between the crust and mantle could cause the entire impact basin size range to be susceptible to immediate and extreme crustal relaxation forming almost unidentifiable topographic and crustal thickness signatures. Lunar basins formed while the lunar magma ocean was still solidifying may escape detection, which is agreeing with studies that suggest a higher impact flux than previously thought in the earliest epoch of Earth-Moon evolution.

Published
2021

3. Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization

Author

Muxworthy, AR, Bland, PA, Davison, TM, Moore, J, Collins, GS, Ciesla, FJ, and Science and Technology Facilities Council (STFC)

Subjects
Geochemistry & Geophysics, PARENT BODY, DARK INCLUSION, Science & Technology, BASIN-FORMING IMPACTS, SHOCK METAMORPHISM, EARLY SOLAR-SYSTEM, SUSCEPTIBILITY, Physics::Geophysics, 0201 Astronomical And Space Sciences, 0403 Geology, Physical Sciences, REVERSAL CURVE DIAGRAMS, 0402 Geochemistry, Astrophysics::Earth and Planetary Astrophysics, CARBONACEOUS CHONDRITES, FIELD, REMANENT MAGNETIZATION
Abstract

We conducted a paleomagnetic study of the matrix of Allende CV3 chondritic meteorite, isolating the matrix’s primary remanent magnetization, measuring its magnetic fabric and estimating the ancient magnetic field intensity. A strong planar magnetic fabric was identified; the remanent magnetization of the matrix was aligned within this plane, suggesting a mechanism relating the magnetic fabric and remanence. The intensity of the matrix’s remanent magnetization was found to be consistent and low (~6 μT). The primary magnetic mineral was found to be pyrrhotite. Given the thermal history of Allende, we conclude that the remanent magnetization formed during or after an impact event. Recent mesoscale impact mode ling, where chondrules and matrix are resolved, has shown that low-velocity collisions can generate significant matrix temperatures, as pore-space compaction attenuates shock energy and dramatically increases the amount of heating. Non-porous chondrules are unaffected, and act as heat-sinks, so matrix temperature excursions are brief. We extend this work to model Allende, and show that a 1km/s planar impact generates bulk porosity, matrix porosity, and fabric in our target that match the observed values. Bimodal mixtures of a highly porous matrix and nominally zero-porosity chondrules, make chondrites uniquely capable of recording transient or unstable fields. Targets that have uniform porosity, e.g., terrestrial impact craters, will not record transient or unstable fields. Rather than a core dynamo, it is therefore possible that the origin of the magnetic field in Allende was the impact itself, or a nebula field recorded during transient impact heating.

Published
2017

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