The Experts below are selected from a list of 2721 Experts worldwide ranked by ideXlab platform
M. C. Osácar - One of the best experts on this subject based on the ideXlab platform.
-
Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)
International Journal of Earth Sciences, 2017Co-Authors: A. M. Casas-sainz, T. Román-berdiel, B. Oliva-urcia, C. García-lasanta, J. J. Villalaín, L. Aldega, S. Corrado, C. Caricchi, C. Invernizzi, M. C. OsácarAbstract:Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (including structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and Paleomagnetism, and paleothermometry) is used to define thrusting conditions, deformation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal displacement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside striations) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k _max/ k _int plane in sites with strong shear deformation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong deformation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels.
Tristan Van Leeuwen - One of the best experts on this subject based on the ideXlab platform.
-
micromagnetic tomography for Paleomagnetism and rock magnetism
Journal of Geophysical Research, 2021Co-Authors: Lennart V De Groot, Richard J Harrison, Karl Fabian, Annemarieke Beguin, Martha E Kosters, David Cortesortuno, Chloe M L Jansen, Tristan Van LeeuwenAbstract:Our understanding of the past behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g. (volcanic) rocks. Bulk rock samples, however, often contain magnetic grains that differ in chemistry, size and shape; some of them record the Earth’s magnetic field well, others are unreliable. The presence of a small amount of adverse behaved magnetic grains in a sample may already obscure important information on the past state of the geomagnetic field. Recently it was shown that it is possible to determine magnetizations of individual grains in a sample by combining X-ray computed tomography and magnetic surface scanning measurements. Here we establish this new Micromagnetic Tomography (MMT) technique and make it suitable for use with different magnetic scanning techniques, and for both synthetic and natural samples. We acquired reliable magnetic directions by selecting subsets of grains in a synthetic sample, and we obtained rock-magnetic information of individual grains in a volcanic sample. This illustrates that MMT opens up entirely new venues of paleomagnetic and rock-magnetic research. MMT’s unique ability to determine the magnetization of individual grains in a nondestructive way allows for a systematic analysis of how geological materials record and retain information on the past state of the Earth’s magnetic field. Moreover, by interpreting only the contributions of known magnetically well-behaved grains in a sample MMT has the potential to unlock paleomagnetic information from even the most complex, crucial, or valuable recorders that current methods are unable to recover.
Benjamin P Weiss - One of the best experts on this subject based on the ideXlab platform.
-
reply to comment on pervasive remagnetization of detrital zircon host rocks in the jack hills western australia and implications for records of the early dynamo
Earth and Planetary Science Letters, 2016Co-Authors: Benjamin P Weiss, Adam C Maloof, Nicholas L Swansonhysell, Mark T Harrison, Joseph L Kirschvink, Bruce E Watson, Robert S Coe, Sonia M Tikoo, Jahandar RamezaniAbstract:Determining the history of Earth's dynamo prior to the oldest known well-preserved rock record is one of the ultimate challenges in the field of Paleomagnetism. Tarduno et al. (2015) argued that detrital zircons contain records of an active dynamo dating back to 4.2 billion years ago (Ga), 700 million years earlier than previously identified (Biggin et al., 2011 and Tarduno et al., 2010). However, this extraordinary claim requires evidence that the zircons have not been remagnetized during the intervening time since their formation. Weiss et al. (2015) argued that such evidence had yet to be provided, a conclusion that we find still firmly holds.
-
lightning remagnetization of the vredefort impact crater no evidence for impact generated magnetic fields
Journal of Geophysical Research, 2012Co-Authors: Benjamin P Weiss, Stuart Gilder, Laurent Carporzen, Anne Pommier, R J HartAbstract:[1] The Vredefort impact crater in South Africa is one of the oldest and largest craters on Earth, making it a unique analog for planetary basins. Intense and randomly oriented remanent magnetization observed in surface samples at Vredefort has been attributed to impact-generated magnetic fields. This possibility has major implications for extraterrestrial Paleomagnetism since impact-generated fields have been proposed as a key alternative to the dynamo hypothesis for magnetization on the Moon and asteroids. Furthermore, the presence of single-domain magnetite found along shock-generated planar deformation features in Vredefort granites has been widely attributed to the 2.02 Ga impact event. An alternative hypothesis is that the unusual magnetization and/or rock magnetic properties of Vredefort rocks are the products of recent lightning strikes. Lightning and impact-generated fields can be distinguished by measuring samples collected from below the present surface. Here we present a paleomagnetic and rock magnetic study of samples from two 10 m deep vertical boreholes. We show that the magnetization at depth is consistent with a thermoremanent magnetization acquired in the local geomagnetic field following the impact, while random, intense magnetization and some of the unusual rock magnetic properties observed in surface rocks are superficial phenomena produced by lightning. Because Vredefort is the only terrestrial crater that has been proposed to contain records of impact-generated fields, this removes a key piece of evidence in support of the hypothesis that Paleomagnetism of the Moon and other extraterrestrial bodies is the product of impacts rather than past core dynamos.
-
Paleomagnetism of lonar impact crater india
Earth and Planetary Science Letters, 2008Co-Authors: K L Louzada, Benjamin P Weiss, Adam C Maloof, S T Stewart, Nicholas L Swansonhysell, Adam S SouleAbstract:article i nfo Lonar crater, India, is the best preserved terrestrial impact crater formed in basalt and is a unique terrestrial analogue for small, simple craters on terrestrial planets and the Moon. We investigated the paleomagnetic and rock-magnetic properties of the 1.88 km diameter crater in order to understand the effect of impacts on magnetization in target rocks. The magnetization in the Lonar basalts consists of an original 65 Ma Deccan magnetization and a recent overprint. We constrained the timing of magnetization acquisition at Lonar using a combination of conglomerate tests on ejecta deposit clasts and fold tests on the overturned and jumbled rim fold. In some areas, the recumbent rim fold is preserved and can be approximated as a horizontal cylindrical fold. In other areas, substantial vertical axis rotation may have occurred where tear zones developed during folding. We observed only subtle effects from the impact on the rock-magnetic properties of Lonar materials, which include a slightly elevated coercivity in shocked ejecta blocks. We show that Paleomagnetism can provide a constraint on shock heating in the absence of petrographic evidence of shock (in this case, b187±15 °C). At Lonar, viscous (and/or chemical) remanent magnetization acquired in the b50 kyr subsequent to crater formation has obscured any evidence of shock remanent magnetization. We also find no evidence of shock demagnetization or the presence of intense impact-induced or impact- amplified transient magnetic fields that have been proposed around larger impact structures.
David L Shuster - One of the best experts on this subject based on the ideXlab platform.
-
Paleomagnetism of rumuruti chondrites suggests a partially differentiated parent body
Earth and Planetary Science Letters, 2020Co-Authors: P Rochette, C Cournede, Jerome Gattacceca, David L ShusterAbstract:Abstract Different types of magnetic fields were at work in the early solar system: nebular fields generated within the protoplanetary nebula, solar fields, and dynamo fields generated within the solar system solid bodies. Paleomagnetic studies of extraterrestrial materials can help unravel both the history of these magnetic fields, and the evolution of solar system solid bodies. In this study we studied the Paleomagnetism of two Rumuruti chondrites (PCA 91002 and LAP 03639). These chondrites could potentially bear the record of the different fields (solar, nebular, dynamo fields) present during the early solar system. The magnetic mineralogy consists of pseudo-single domain pyrrhotite in LAP 03639 and pyrrhotite plus magnetite in PCA 91002. Paleomagnetic analyses using thermal and alternating field demagnetization reveal a stable origin trending component of magnetization. Fields of 12 μT or higher are required to account for the magnetization in PCA 91002, but the timing and exact mechanism of the magnetization are unconstrained. In LAP 03639, considering various chronological constraints on the parent body evolution and on the evolution of the different sources of magnetic field in the early solar system, an internally-generated (dynamo) field of ∼5 μT recorded during retrograde metamorphism is the most likely explanation to account for the measured magnetization. This result indicates the existence of an advecting liquid core within the Rumuruti chondrite parent body, and implies that, as proposed for CV and H chondrites, this chondritic parent body is partially differentiated.
A. M. Casas-sainz - One of the best experts on this subject based on the ideXlab platform.
-
Multidisciplinary approach to constrain kinematics of fault zones at shallow depths: a case study from the Cameros–Demanda thrust (North Spain)
International Journal of Earth Sciences, 2017Co-Authors: A. M. Casas-sainz, T. Román-berdiel, B. Oliva-urcia, C. García-lasanta, J. J. Villalaín, L. Aldega, S. Corrado, C. Caricchi, C. Invernizzi, M. C. OsácarAbstract:Thrusting at shallow depths often precludes analysis by means of structural indicators effective in other geological contexts (e.g., mylonites, sheath folds, shear bands). In this paper, a combination of techniques (including structural analysis, magnetic methods, as anisotropy of magnetic susceptibility and Paleomagnetism, and paleothermometry) is used to define thrusting conditions, deformation, and transport directions in the Cameros–Demanda thrust (North Spain). Three outcrops were analyzed along this intraplate, large-scale major structure having 150 km of outcropping length, 30 km of maximum horizontal displacement, and 5 km of vertical throw. Results obtained by means of the different techniques are compared with data derived from cross sections and stratigraphic analysis. Mixed-layer illite–smectite and vitrinite reflectance indicating deep diagenetic conditions and mature stage of hydrocarbon generation suggests shallow depths during deformation, thus confirming that the protolith for most of the fault rocks is the footwall of the main thrust. Kinematic indicators (foliation, S/C structures, and slickenside striations) indicate altogether a dominant NNW movement of the hanging wall in the western zone and NE in the eastern zone of the thrust, thus implying strain partitioning between different branches of the main thrust. The study of AMS in fault rocks (nearly 400 samples of fault gouge, breccia, and microbreccia) indicates that the strike of magnetic foliation is oblique to the transport direction and that the magnetic lineation parallelizes the projection of the transport direction onto the k _max/ k _int plane in sites with strong shear deformation. Paleomagnetism applied to fault rocks indicates the existence of remagnetizations linked to thrusting, in spite of the shallow depth for deformation, and a strong deformation or scattering of the magnetic remanence vectors in the fault zone. The application of the described techniques and consistency of results indicate that the proposed multidisciplinary approach is useful when dealing with thrusts at shallow crustal levels.
