Kate Selway

On the causes of electrical conductivity anomalies in tectonically stable lithosphere

Publisher: Springer Science and Business Media LLC

Date: 16-05-2014

DOI: 10.1007/S10712-013-9235-1

Towards an SDN network control application for differentiated traffic routing

Publisher: IEEE

Date: 06-2015

DOI: 10.1109/ICC.2015.7249251

Are xenoliths from southwestern Kaapvaal Craton representative of the broader mantle? Constraints from magnetotelluric modeling

Publisher: American Geophysical Union (AGU)

Date: 05-06-2021

DOI: 10.1029/2021GL092570

Abstract: Most of our knowledge of the composition and water content of the cratonic mantle comes from xenoliths found in alkaline magmatic rocks (e.g., kimberlites). However, it is debatable whether such mantle‐xenolith s les are representative of the mantle over larger lateral extents or only represent more local metasomatized conduits. To investigate this, we made 3D deterministic and 1D probabilistic models of magnetotelluric (MT) data from the southwestern Kaapvaal Craton and carried out quantitative interpretations. The results indicate that water content decreases with depth between 100 and 160 km, broadly matching the distribution of metasomatism inferred from garnet‐xenocrysts. Spatially pervasive phlogopite could exist for a colder geotherm (37 mW / m 2 ) whereas it is not required for the more likely geotherm of 40.2 mW / m 2 . Most water contents measured from xenolith s les agree with those calculated from the MT models within error, but the discrepancies between them suggest a local metasomatic control over xenolith water contents.

Thermochemical structure and evolution of cratonic lithosphere in central and southern Africa

Publisher: Springer Science and Business Media LLC

Date: 18-04-2022

DOI: 10.1038/S41561-022-00929-Y

Magnetotelluric constraints on subduction polarity

Publisher: Geological Society of America

Date: 09-2009

DOI: 10.1130/G30175A.1

MATE

Publisher: American Geophysical Union (AGU)

Date: 09-2020

DOI: 10.1029/2020GC009126

Magnetotelluric constraints on the tectonic setting of Grenville-aged orogenesis in central Australia

Publisher: Geological Society of London

Date: 2011

DOI: 10.1144/0016-76492010-034

Electrical discontinuities in the continental lithosphere imaged with magnetotellurics

Publisher: Wiley

Date: 31-10-2019

DOI: 10.1002/9781119249740.CH5

Melting of subducted sediments reconciles geophysical images of subduction zones

Publisher: Springer Science and Business Media LLC

Date: 26-02-2021

DOI: 10.1038/S41467-021-21657-8

Abstract: Sediments play a key role in subduction. They help control the chemistry of arc volcanoes and the location of seismic hazards. Here, we present a new model describing the fate of subducted sediments that explains magnetotelluric models of subduction zones, which commonly show an enigmatic conductive anomaly at the trenchward side of volcanic arcs. In many subduction zones, sediments will melt trenchward of the source region for arc melts. High-pressure experiments show that these sediment melts will react with the overlying mantle wedge to produce electrically conductive phlogopite pyroxenites. Modelling of the Cascadia and Kyushu subduction zones shows that the products of sediment melting closely reproduce the magnetotelluric observations. Melting of subducted sediments can also explain K-rich volcanic rocks that are produced when the phlogopite pyroxenites melt during slab roll-back events. This process may also help constrain models for subduction zone seismicity. Since melts and phlogopite both have low frictional strength, damaging thrust earthquakes are unlikely to occur in the vicinity of the melting sediments, while increased fluid pressures may promote the occurrence of small magnitude earthquakes and episodic tremor and slip.

Not All STEMI Patients Receive Timely Reperfusion: Considerations for Rural Emergency Departments

Publisher: Informa UK Limited

Date: 11-2021

DOI: 10.2147/JMDH.S337197

Electrical evidence of continental accretion

Publisher: American Geophysical Union (AGU)

Date: 2006

DOI: 10.1029/2005GL025328

Probing the southern African lithosphere with magnetotellurics: 2. linking electrical conductivity, composition, and tectonomagmatic evolution

Publisher: American Geophysical Union (AGU)

Date: 03-2022

DOI: 10.1029/2021JB023105

Abstract: The tectonic history of southern Africa includes Archean craton formation, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. These processes left behind a compositional trail that can be observed in xenoliths and measured by geophysical methods. The abundance of kimberlites in southern Africa makes it an ideal place to test and calibrate mantle geophysical interpretations that can then be applied to less well‐constrained regions. Magnetotellurics (MT) is a particularly useful tool for understanding tectonic history because electrical conductivity is sensitive to temperature, bulk composition, accessory minerals, and rock fabric. We produced three‐dimensional MT models of the southern African mantle taken from the SAMTEX MT data set, mapped the properties of ∼36,000 garnet xenocrysts from Group I kimberlites, and compared the results. We found that depleted regions of the mantle are uniformly associated with high electrical resistivities. The conductivity of fertile regions is more complex and depends on the specific tectonic and metasomatic history of the region, including the compositions of metasomatic fluids or melts and the emplacement of metasomatic minerals. The mantle beneath the ∼2.05 Ga Bushveld Complex is highly conductive, probably caused by magmas flowing along a lithospheric weakness zone and precipitating interconnected, conductive accessory minerals such as graphite and sulfides. Kimberlites tend to be emplaced near the edges of the cratons where the mantle below 100 km depth is not highly resistive. Kimberlites avoid strong mantle conductors, suggesting a systematic relationship between their emplacement and mantle composition.

Constraining upper mantle viscosity using temperature and water content inferred from seismic and magnetotelluric data

Publisher: American Geophysical Union (AGU)

Date: 08-2022

DOI: 10.1029/2021JB023824

Abstract: Mantle viscosity controls a variety of geodynamic processes such as glacial isostatic adjustment (GIA), but it is poorly constrained because it cannot be measured directly from geophysical measurements. Here we develop a method that calculates viscosity using empirical viscosity flow laws coupled with mantle parameters (temperature and water content) inferred from seismic and magnetotelluric (MT) observations. We find that combining geophysical constraints allows us to place significantly tighter bounds on viscosity estimates compared to using seismic or MT observations alone. In particular, electrical conductivity inferred from MT data can determine whether upper mantle minerals are hydrated, which is important for viscosity reduction. Additionally, we show that rock composition should be considered when estimating viscosity from geophysical data because composition directly affects seismic velocity and electrical conductivity. Therefore, unknown composition increases uncertainty in temperature and water content, and makes viscosity more uncertain. Furthermore, calculations that assume pure thermal control of seismic velocity may misinterpret compositional variations as temperature, producing erroneous interpretations of mantle temperature and viscosity. Stress and grain size also affect the viscosity and its associated uncertainty, particularly via their controls on deformation regime. Dislocation creep is associated with larger viscosity uncertainties than diffusion creep. Overall, mantle viscosity can be estimated best when both seismic and MT data are available and the mantle composition, grain size and stress can be estimated. Collecting additional MT data probably offers the greatest opportunity to improve geodynamic or GIA models that rely on viscosity estimates.

Numerical constraints on heat flux variations and lithospheric thinning associated with passage of the Iceland plume beneath Greenland

Publisher: Wiley

Date: 16-12-2020

DOI: 10.1002/ESSOAR.10505370.1

Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift

Publisher: Seismological Society of America (SSA)

Date: 07-09-2016

DOI: 10.1785/0220160112

A small, unextractable melt fraction as the cause for the low velocity zone

Publisher: Elsevier BV

Date: 07-2019

DOI: 10.1016/J.EPSL.2019.04.012

Water content of the Tanzanian lithosphere from magnetotelluric data

Publisher: Elsevier BV

Date: 02-2014

DOI: 10.1016/J.EPSL.2013.11.024

Author Correction: Thermochemical structure and evolution of cratonic lithosphere in central and southern Africa

Publisher: Springer Science and Business Media LLC

Date: 16-01-2023

DOI: 10.1038/S41561-023-01124-3

Constraints on volumes and patterns of asthenospheric melt from the space‐time distribution of seamounts

Publisher: American Geophysical Union (AGU)

Date: 25-07-2017

DOI: 10.1002/2017GL074098

The uppermost mantle seismic velocity structure of West Antarctica from Rayleigh wave tomography

Publisher: Elsevier BV

Date: 09-2019

DOI: 10.1016/J.EPSL.2019.06.024

A simple 2-D explanation for negative phases in TE magnetotelluric data

Publisher: Oxford University Press (OUP)

Date: 31-01-2012

DOI: 10.1111/J.1365-246X.2011.05312.X

Magnetotelluric investigation of the Vestfold Hills and Rauer Group, East Antarctica

Publisher: American Geophysical Union (AGU)

Date: 04-2016

DOI: 10.1002/2015JB012677

Grain size reduction by plug flow in the wet oceanic upper mantle explains the asthenosphere's low seismic Q zone

Publisher: Elsevier BV

Date: 08-2023

DOI: 10.1016/J.EPSL.2023.118232

Thick lithosphere, deep crustal earthquakes and no melt

Publisher: Oxford University Press (OUP)

Date: 16-12-2016

DOI: 10.1093/GJI/GGV492

Surface wave imaging of the weakly extended Malawi Rift from ambient-noise and teleseismic Rayleigh waves from onshore and lake-bottom seismometers

Publisher: Oxford University Press (OUP)

Date: 04-2017

DOI: 10.1093/GJI/GGX133

Identifying the lithospheric structure of a Precambrian orogen using magnetotellurics

Publisher: Elsevier BV

Date: 02-2009

DOI: 10.1016/J.PRECAMRES.2008.09.010

The seismic mid-lithosphere discontinuity

Publisher: Elsevier BV

Date: 03-2015

DOI: 10.1016/J.EPSL.2014.12.029

The relationship between Kimberlitic magmatism and electrical conductivity anomalies in the mantle

Publisher: American Geophysical Union (AGU)

Date: 15-09-2022

DOI: 10.1029/2022GL099661

Abstract: Kimberlites are igneous rocks whose formation remains enigmatic due to their severely altered nature, highly variable compositions and rapid ascent through the lithosphere. The spatiotemporal distribution of kimberlites suggests that mantle metasomatism may play an essential role in their emplacement. Since the magnetotelluric (MT) method is sensitive to metasomatic mantle modification in the forms of interconnected minerals and water, we compiled MT models from Australia, Brazil, Botswana, Canada, Namibia, South Africa and the USA, calculated water content variations and compared them to the distribution of kimberlites. Results indicate that kimberlites mostly ascend through hydrated/metasomatized lithosphere and avoid both dry and heavily metasomatized lithosphere. Diamondiferous kimberlites preferentially occur on moderately metasomatized lithosphere, with the diamondiferous rate increasing with the degree of metasomatism in Archean terranes and decreasing in Proterozoic terranes. These results link geophysical observations of mantle metasomatism to kimberlite magmatism and will improve mineral systems models for diamond exploration.

Probing the southern African lithosphere with magnetotellurics-part I: model construction

Publisher: American Geophysical Union (AGU)

Date: 03-2022

DOI: 10.1029/2021JB023117

Abstract: The Southern African Magnetotelluric Experiment (SAMTEX) involved the collection of data at over 700 sites in Archean to Proterozoic southern Africa, spanning features including the Kalahari Craton, Bushveld Complex, and voluminous kimberlites. Here, we present the first 3D inversions of the full SAMTEX data set. In this paper, we focus on assessing the robustness of the 3D models by comparing two different inversion codes, jif3D and ModEM , and two different subsets of the data, one containing all acceptable data and the other containing a smaller selection of undistorted, high‐quality data. Results show that the main conductive and resistive features are imaged by all inversions, including deep resistive features in the central Kaapvaal Craton and southern Congo Craton and a lithospheric‐scale conductor beneath the Bushveld Complex. Despite this, differences exist between the jif3D and ModEM inverse models that derive mainly from the differences in regularization between the models, with jif3D producing models that are very smooth laterally and with depth, while ModEM produces models with more discrete conductive and resistive features. Analysis of the differences between these two inversions can provide a good indication of the model resolution. More minor differences are apparent between models run with different subsets of data, with the models containing all acceptable data featuring higher wavelength conductivity variations than those run with fewer stations but also demonstrating poorer data fit.

Uplift of the central transantarctic mountains

Publisher: Springer Science and Business Media LLC

Date: 17-11-2017

DOI: 10.1038/S41467-017-01577-2

Abstract: The Transantarctic Mountains (TAM) are the world’s longest rift shoulder but the source of their high elevation is enigmatic. To discriminate the importance of mechanical vs. thermal sources of support, a 550 km-long transect of magnetotelluric geophysical soundings spanning the central TAM was acquired. These data reveal a lithosphere of high electrical resistivity to at least 150 km depth, implying a cold stable state well into the upper mantle. Here we find that the central TAM most likely are elevated by a non-thermal, flexural cantilever mechanism which is perhaps the most clearly expressed ex le anywhere. West Antarctica in this region exhibits a low resistivity, moderately hydrated asthenosphere, and concentrated extension (rift necking) near the central TAM range front but with negligible thermal encroachment into the TAM. Broader scale heat flow of east-central West Antarctica appears moderate, on the order of 60–70 mW m −2 , lower than that of the U.S. Great Basin.

A 3D lithospheric electrical resistivity model of the Gawler Craton, Southern Australia

Publisher: Informa UK Limited

Date: 03-2007

DOI: 10.1179/174327507X167037

Magnetotelluric Constraints on the Temperature, Composition, Partial Melt Content, and Viscosity of the Upper Mantle Beneath Svalbard

Publisher: American Geophysical Union (AGU)

Date: 05-2020

DOI: 10.1029/2020GC008985

Magnetotelluric evidence for massive sulphide mineralization in intruded sediments of the outer Vøring Basin, mid-Norway

Publisher: Elsevier BV

Date: 06-2017

DOI: 10.1016/J.TECTO.2017.04.011

Upper mantle meltdistribution from petrologicallyconstrained magnetotellurics

Publisher: American Geophysical Union (AGU)

Date: 07-2019

DOI: 10.1029/2019GC008227

Abstract: Three parameters: temperature, hydrogen content, and the presence of partial melt, are the dominant controls on the rheology of the convecting upper mantle. As such, they determine the dynamics that control plate tectonics and continental evolution. Since hydrogen depresses the peridotite solidus temperature, these parameters are strongly linked petrologically. We have developed a genetic algorithm code to statistically assess the likelihood that a section of upper mantle contains partial melt. This code uses magnetotelluric observations and petrological constraints on composition and solidus temperatures and allows for uncertainties in the geotherm and the electrical conductivity structure. We have applied this code to the convecting upper mantle beneath (1) a stable continent (the Superior Craton) (2) a hot spot (Tristan da Cunha) (3) stable, old oceanic lithosphere (the northwest Pacific Ocean) and (4) young oceanic lithosphere (adjacent to the East Pacific Rise). Results show that the volume of melt in the convecting upper mantle is heterogeneous. The highest melt proportions are beneath the hot spot while little to no melt is required in the other regions. All regions show low water contents (generally wt ppm in olivine) in the shallow convecting upper mantle, making it unlikely that water causes a large or sharp viscosity contrast between the lithosphere and the convecting mantle. Results differ significantly for different experimental olivine hydrogen conductivity models, highlighting the importance of reconciling these experimental constraints.

The uppermost mantle seismic velocity and viscosity structure of central West Antarctica

Publisher: Elsevier BV

Date: 08-2017

DOI: 10.1016/J.EPSL.2017.05.016

Negligible effect of hydrogen content on plate strength in East Africa

Publisher: Springer Science and Business Media LLC

Date: 06-2015

DOI: 10.1038/NGEO2453

Grain size reduction by plug flow in the wet oceanic upper mantle explains the asthenosphere's low seismic Q zone

Publisher: Wiley

Date: 31-08-2022

DOI: 10.1002/ESSOAR.10512275.1

Electrical conductivity of the lithosphere-asthenosphere system

Publisher: Elsevier BV

Date: 04-2021

DOI: 10.1016/J.PEPI.2021.106661

University Of Oslo

Location: Norway

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University Of South Australia

Location: Australia

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Macquarie University

Location: Australia

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Discovery Projects - Grant ID: DP0988263

Start Date: 2009

End Date: 12-2013

Amount: $338,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP220100709

Start Date: 12-2022

End Date: 11-2025

Amount: $490,000.00

Funder: Australian Research Council

ARC Future Fellowships - Grant ID: FT150100541

Start Date: 2017

End Date: 12-2022

Amount: $648,852.00

Funder: Australian Research Council

Special Research Initiatives - Grant ID: SR200100008

Start Date: 08-2021

End Date: 12-2027

Amount: $20,000,000.00

Funder: Australian Research Council