Download or read book Some Aspects of the Structure and Magnetization of the Oceanic Crust written by Roi Granot and published by . This book was released on 2009 with total page 97 pages. Available in PDF, EPUB and Kindle. Book excerpt: The structure and magnetization of the oceanic crust reflect its tectonic and magmatic evolution since its initial formation. The magnetization of the crust also provides a record of the polarity reversals and strength of the Earth's geomagnetic field. In this dissertation I first describe absolute paleointensity measurements made on gabbroic rocks collected from the lower oceanic crust of the Troodos ophiolite, Cyprus. The resultant data-set provides a view into the geomagnetic field during the end of the Cretaceous normal polarity superchron (CNS, 120.6 to 83 million years ago). This data-set is then compared to the locally and globally existing data and predictions made by geodynamo numerical simulations. The results hint that the geomagnetic field had similar properties during times of frequent reversals and times of stable polarity. The second chapter of this dissertation is focused on the marine magnetic anomalies observed across the North Pacific fracture zones. Here I analyze archival and newly collected magnetic anomaly and bathymetric profiles measured across three fracture zones in the Cretaceous Quiet Zone (CNS in age). Forward and inverse modeling indicate that these anomalies arise from remanent magnetization, with enhanced remanence located on one side of each fracture zone. These long-duration enhanced zones require some long-lived asymmetry in crustal construction processes near ridge-transform intersections. The calculated magnetization contrasts provide long-term constraints on the properties of the geomagnetic field during the Cretaceous superchron. Finally, using seismic reflection and magnetic anomaly grids collected in the Adare Basin, Antarctica, I explore the kinematic evolution of the West Antarctic rift system during the Neogene. Correlation of the Adare seismic sequence to the closest drillholes and the Ross Sea seismic stratigraphy establishes the temporal framework of three regional tectonic events. Overall, minimal but significant extensional activity took place in the Adare Basin after seafloor spreading stopped. Comparison of the results with observations from the central and southern parts of the rift system suggests that a major change in plate motion took place in the middle miocene.

Download or read book Implications of Fine Scale Magnetics for the Structure and Evolution of Slowly Accreted Oceanic Crust written by and published by . This book was released on 1997 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The long range objective of this program is to understand the structure of oceanic crust created at slow-spreading ridges by investigating the patterns of magnetization that reside in the crust. The project seeks to investigate how crustal magnetic fields are related to the structural deformation history of oceanic crust formed in slow spreading environments and how magnetization may be used to predict the properties of the underlying crust. Scientific Objectives are: (1) Investigate the relationship between crustal magnetization and the tectonic structure and architecture of oceanic crust by comparing the magnetization patterns of crust created at 'inside corners' versus 'outside corners' of ridge segment offsets. (2) Investigate the relationship between crustal magnetization and cyclic magmatic and tectonic processes involved in crustal formation and how this magnetization signal varies with age. (3) Investigate along-axis variability in crustal magnetization within a ridge segment and compare with the ridge axis signal. (4) Map magnetic isochrons to provide temporal framework for other related studies e.g. investigate how crustal structure and seafloor morphology change with spreading rate.

Download or read book Modeling the Magnetic Structure of Oceanic Crust in the Gulf of California written by Christine Naomi Hanley and published by . This book was released on 1980 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Anomalous Magnetic Field of the World Ocean written by Alexander M. Gorodnitsky and published by CRC Press. This book was released on 1994-10-12 with total page 270 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book investigates the anomalous magnetic field of the ocean and its connection with geological structure, tectonic evolution of the oceanic lithosphere, and magnetic properties of different rock types in the oceanic crust. The book describes new instruments and techniques of gradient magnetic measurements with three sensors, as well as the new technique of processing and interpretating hydromagnetic data on the basis of adoptive filtration and reparametrization. The text provides unique data of geomagnetic surveys carried out by Russian research vessels in different regions of the World Ocean, including submersible apparatus and ingenious theoretical and experimental technology of the magnetic modeling and investigations of the nature of magnetic anomalies. The results of systems analysis of geochemical content and composition during the mid-oceanic ridge basalt are presented.

Download or read book Seismic and Magnetic Constraints on the Structure of Upper Oceanic Crust at Fast and Slow Spreading Ridges written by Stefan Anthony Hussenoeder and published by . This book was released on 1998 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt: The upper ocean crust contains a comprehensive record of the shallow geological processes active along the world's mid-ocean ridge system. This thesis examines the magnetic and seismic structure of the upper crust at two contrasting ridges-the fast spreading East Pacific Rise (EPR) and the slow spreading Mid-Atlantic Ridge (MAR)-to build a more complete understanding about the roles of volcanic emplacement, tectonic disruption and hydrothermal alteration in the near-ridge environment. A technique that inverts potential field measurements. directly from an uneven observation track is developed and applied to near-bottom magnetic data from the spreading segments north of the Kane transform on the MAR. It is concluded that the central anomaly magnetization high marks the locus of focused volcanic emplacement. A cyclic faulting model is proposed to explain the oscillatory magnetization pattern associated with discrete blocks of crust being transported out of the rift valley between intensely altered fault zones. Seismic waveform and amplitude analyses of the magma sill along the EPR reveal it to be a thin (

Download or read book Magnetization of Oceanic Crust Near Selected Areas of Hydrothermal Activity on the Mid Atlantic and Gorda Ridges written by Anita L. Wooldridge and published by . This book was released on 1990 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Seismic and Magnetic Constraints on the Structure of Upper Oceanic Crust at Fast and Slow Spreading Ridges written by and published by . This book was released on 1998 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Magnetization of the Oceanic Crust Thermoremanent Magnetization Or Chemical Remanent Magnetization written by C. A. Raymond and published by . This book was released on 1987 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: We propose a model in which chemical remanent magnetization (CRM) acquired within the first 20 m.y. of crustal evolution may account for 80% of the bulk natural remanent magnetization of older basalts. The CRM of the crust is acquired as the original thermoremanent magnetization (TRM) is lost through low-temperature alteration. The CRM intensity and direction are controlled by the post emplacement polarity history. This model explains several independent observations observations concerning the magnetization of the oceanic crust. The model accounts for amplitude and skewness discrepancies observed in both the intermediate-wavelength satellite field and the short-wavelength sea surface magnetic anomaly pattern. It also explains the decay of magnetization away from the spreading axis and the enhanced magnetization of the Cretaceous Quiet Zones, while predicting other systematic variations with age in the bulk magnetization of the oceanic crust. The model also explains discrepancies in the anomaly skewness parameter observed for anomalies of Cretaceous age. Our study also indicates varying rates of TRM decay in very young crust which depicts the advance of low-temperature alternation through the magnetize layer.

Download or read book Using Magnetic Methods to Better Understand the Thermal Structure of Fast spread Lower Ocean Crust at Pito Deep written by Sarah May Maher and published by . This book was released on 2021 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: More than 30% of oceanic crust is formed at fast-spreading ridges, but there remains much to learn about how the lower, gabbroic crust is accreted and cooled. This is partially due to conflicting evidence from direct and indirect studies of the lower crust and ophiolite analogues, leading to two end-member models for gabbroic crust formation which have different predictions for the thermal structure of the crust. The gabbro glacier model asserts the majority of heat is lost through the upper crust via hydrothermal circulation while the gabbroic crust cools conductively off-axis. The sheeted sills model requires efficient cooling throughout the crust within 2-3 km of the spreading center via deep hydrothermal circulation. These models are testable using magnetic techniques. As the lower ocean crust cools, magnetic minerals will lock in the magnetic field direction. If the crust is cooling during a magnetic reversal, the boundary between polarity intervals acts as a proxy isotherm in the lower crust. The slope of that isotherm will distinguish between the gabbro glacier model, which should have shallow isotherms dipping away from the ridge, and the sheeted sills model, where isotherms would steeply dip near the ridge. A 2017 cruise to Pito Deep, a tectonic exposure in fast-spread crust, recorded near-bottom magnetic data and collected oriented gabbroic samples to document a polarity boundary in the lower crust. This thesis developed a magnetic inversion technique to incorporate near-bottom anomaly data from multiple platforms over steep escarpments to identify the location of the polarity boundary at depth. Results show a large offset of the polarity boundary between the dike and gabbroic layers, implying that the gabbroic layer remains hotter for an extended period off-axis. Using oriented samples from a 1x1 km study area, I verified the location of a polarity boundary which remains horizontal for a minimum of 8 km off-axis. Finally, I use samples with multiple polarity components to determine a cooling rate in gabbroic crust. Our results are incompatible with deep hydrothermal cooling within 2-3 km of the spreading center, and instead promote the idea of slow cooling within 8 km of the spreading center.

Download or read book The Structure of Oceanic Crust written by Timothy John Henstock and published by . This book was released on 1993 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Seismic and Magnetic Constraints on the Strucutre of Upper Oceanic Crust and Fast and Slow Spreading Ridges written by Stefan Anthony Hussenoeder and published by . This book was released on 1998 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Fate of Marine Magnetic Anomalies in Subduction Zone written by Hanjin Choe and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this study is to understand the causes of the decaying seafloor spreading magnetic anomalies on subducting oceanic crust. We investigate the magnetization of the oceanic crust both before and after subduction and extend our initial study area from the Japan-Kuril subduction zone to other subduction zones to try to generalize our observations. Before subduction, a 20% loss of magnetization between the outer-rise and the trench occurs in old seafloor, caused by rejuvenated hydrothermal circulations and alteration of magnetic minerals. Conversely, such a loss of magnetization is not observed for the young seafloor because the flexure remains very limited. After subduction, both exhibit a fast decay of magnetization due to thermal demagnetization of titanomagnetite (Tc:150-350°C) in the extrusive basalt, followed by a much slower one due to thermal demagnetization of magnetite (Tc: 580 °C) in the deeper crust. However, the fast decay is more rapidly achieved in the young seafloor due to differences in the thermal structure. Overall, the magnetic anomalies in subducting oceanic crust decay as an effect of flexure, normal faulting and hydrothermal alteration before subduction, and thermal demagnetization of the different magnetic minerals after subduction. The seawater injected in the oceanic crust before subduction is trapped by the sediment cover after entering subduction and may significantly heat up the slab through thermal blanketing, adding to the thermal gradient and possibly heat released by serpentinization of the mantle wedge. The speed of thermal demagnetization is modulated by the lithospheric thickness, hydration rate, and therefore the age of the seafloor.

Download or read book Geophysical Investigations of the Nicaraguan Rise written by Ben Nnaemeka Nwaochei and published by . This book was released on 1981 with total page 160 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1989 with total page 984 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Treatise on Geophysics written by and published by Elsevier. This book was released on 2015-04-17 with total page 5604 pages. Available in PDF, EPUB and Kindle. Book excerpt: Treatise on Geophysics, Second Edition, is a comprehensive and in-depth study of the physics of the Earth beyond what any geophysics text has provided previously. Thoroughly revised and updated, it provides fundamental and state-of-the-art discussion of all aspects of geophysics. A highlight of the second edition is a new volume on Near Surface Geophysics that discusses the role of geophysics in the exploitation and conservation of natural resources and the assessment of degradation of natural systems by pollution. Additional features include new material in the Planets and Moon, Mantle Dynamics, Core Dynamics, Crustal and Lithosphere Dynamics, Evolution of the Earth, and Geodesy volumes. New material is also presented on the uses of Earth gravity measurements. This title is essential for professionals, researchers, professors, and advanced undergraduate and graduate students in the fields of Geophysics and Earth system science. Comprehensive and detailed coverage of all aspects of geophysics Fundamental and state-of-the-art discussions of all research topics Integration of topics into a coherent whole

Download or read book Earth Resources written by and published by . This book was released on 1986 with total page 760 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Collected Reprints written by and published by . This book was released on 1970 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: