Download or read book Seismic and Numerical Constraints on the Formation and Evolution of Ocean Lithosphere written by Hannah F. Mark and published by . This book was released on 2019 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis explicates aspects of the basic structure of oceanic lithosphere that are shaped by the processes that form the lithosphere. The strength of lithospheric plates relative to the underlying mantle enables the surface plate motions and plate boundary processes that characterize plate tectonics on Earth. Surprisingly, we have a relatively poor understanding of the physical mechanisms that make the lithosphere strong relative to the asthenosphere, and we lack a reference model for ordinary lithospheric structure that can serve as a baseline for comparing geophysical observations across locations. Chapters 2 and 3 of this thesis investigate the seismic structure of a portion of the Pacific plate where the simple tectonic history of the plate suggests that its structure can be used as a reference model for oceanic lithosphere. We present measurements of shallow azimuthal seismic anisotropy, and of a seismic discontinuity in the upper mantle, that reflect the effects of shear deformation and melting processes involved in the formation of the lithosphere at mid-ocean ridges. Chapter 4 uses numerical models to explore factors controlling fault slip behavior on normal faults that accommodate tectonic extension during plate formation.
Download or read book Seismic and Numerical Constraints on the Formation and Evolution of Oceanic Lithosphere written by Hannah F. Mark and published by . This book was released on 2019 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis explicates aspects of the basic structure of oceanic lithosphere that are shaped by the processes that form the lithosphere. The strength of lithospheric plates relative to the underlying mantle enables the surface plate motions and plate boundary processes that characterize plate tectonics on Earth. Surprisingly, we have a relatively poor understanding of the physical mechanisms that make the lithosphere strong relative to the asthenosphere, and we lack a reference model for ordinary lithospheric structure that can serve as a baseline for comparing geophysical observations across locations. Chapters 2 and 3 of this thesis investigate the seismic structure of a portion of the Pacific plate where the simple tectonic history of the plate suggests that its structure can be used as a reference model for oceanic lithosphere. We present measurements of shallow azimuthal seismic anisotropy, and of a seismic discontinuity in the upper mantle, that reflect the effects of shear deformation and melting processes involved in the formation of the lithosphere at mid-ocean ridges. Chapter 4 uses numerical models to explore factors controlling fault slip behavior on normal faults that accommodate tectonic extension during plate formation.
Download or read book Geophysical and Geochemical Constraints on the Evolution of Oceanic Lithosphere from Formation to Subduction written by Gregory William Horning and published by . This book was released on 2017 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis investigates the evolution of the oceanic lithosphere in a broad sense from formation to subduction, in a focused case at the ridge, and in a focused case proximal to subduction. In general, alteration of the oceanic lithosphere begins at the ridge through focused and diffuse hydrothermal flow, continues off axis through low temperature circulation, and may occur approaching subduction zones as bending related faulting provides fluid pathways. In Chapter 2 1 use a dataset of thousands of microearthquakes recorded at the Rainbow massif on the Mid-Atlantic Ridge to characterize the processes which are responsible for the long-term, high-temperature, hydrothermal discharge found hosted in this oceanic core complex. I find that the detachment fault responsible for the uplift of the massif is inactive and that the axial valleys show no evidence for faulting or active magma intrusion. I conclude that the continuous, low-magnitude seismicity located in diffuse pattern in a region with seismic velocities indicating ultramafic host rock suggests that serpentinization may play a role in microearthquake generation but the seismic network was not capable of providing robust focal mechanism solutions to constrain the source characteristics. In Chapter 3 I find that the Juan de Fuca plate, which represents the young/hot end-member of oceanic plates, is lightly hydrated at upper crustal levels except in regions affected by propagator wakes where hydration of lower crust and upper mantle is evident. I conclude that at the subduction zone the plate is nearly dry at upper mantle levels with the majority of water contained in the crust. Finally, in Chapter 4 I examine samples of cretaceous age serpentinite sampled just before subduction at the Puerto Rico Trench. I show that these upper mantle rocks were completely serpentinized under static conditions at the Mid-Atlantic Ridge. Further, they subsequently underwent 100 Ma of seafloor weathering wherein the alteration products of serpentinization themselves continue to be altered. I conclude that complete hydration of the upper mantle is not the end point in the evolution of oceanic lithosphere as it spreads from the axis to subduction.
Download or read book Seismic Constraints on the Processes and Consequences of Secondary Igneous Evolution of Pacific Oceanic Lithosphere written by Helen Shao-Hwa Feng and published by . This book was released on 2016 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis examines the structure of Pacific oceanic lithosphere that has been modified by post-formation magmatism in order to better understand the processes of secondary magmatic evolution of the lithosphere, which can have global-scale implications for oceanic and atmospheric chemistry. In the western Pacific, widespread Cretaceous magmatism has modified oceanic lithosphere over hundreds of millions of square kilometers. Seismic models of the upper crust from within the Jurassic Quiet Zone and the crust and upper mantle near the Mariana Trench reveal crust that is locally thickened via focused extrusive volcanism and crust that is modestly but uniformly thickened over broad regions. These distinct modes of magmatic emplacement suggest the operation of both focused and diffuse modes of melt transport through the lithosphere. Analysis of seismic observations from Guaymas Basin, in the Gulf of California, endeavor to advance our understanding of sill-driven alteration of sediments, an important consequence of secondary magmatism. We show that seismically imaged physical disruption to sediments due to igneous sill intrusion can be related to changes in sediment physical properties that reflect alteration processes. We also show how sill thickness can be estimated, enabling alteration intensity to be related to sill thickness in a variety of settings.
Download or read book The Lithosphere written by Irina Artemieva and published by Cambridge University Press. This book was released on 2011-07-28 with total page 795 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presenting a coherent synthesis of lithosphere studies, this book covers a range of geophysical methods (seismic reflection, refraction, and receiver function methods; elastic and anelastic seismic tomography; electromagnetic and magnetotelluric methods; thermal, gravity and rheological models), complemented by petrologic and laboratory data on rock properties. It also provides a critical discussion of the uncertainties, assumptions, and resolution issues that are inherent in the different methods and models of the lithosphere. Multidisciplinary in scope, global in geographical extent, and covering a wide variety of tectonics settings across 3.5 billion years of Earth history, this book presents a comprehensive overview of lithospheric structure and evolution. It is a core reference for researchers and advanced students in geophysics, geodynamics, tectonics, petrology, and geochemistry, and for petroleum and mining industry professionals.
Download or read book Composition Deep Structure and Evolution of Continents written by R.D. van der Hilst and published by Elsevier Science. This book was released on 1999-11-05 with total page 341 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ensemble of manuscripts presented in this special volume captures the stimulating cross-disciplinary dialogue from the International Symposium on Deep Structure, Composition, and Evolution of Continents, Harvard University, Cambridge, Massachusetts, 15-17 October 1997. It will provide an update on recent research developments and serve as a starting point for research of the many outstanding issues. After its formation at mid-oceanic spreading centers, oceanic lithosphere cools, thickens, and subsides, until it subducts into the deep mantle beneath convergent margins. As a result of this continuous recycling process oceanic lithosphere is typically less than 200 million years old (the global average is about 80 Myr). A comprehensive, multi-disciplinary study of continents involves a wide range of length scales: tiny rock samples and diamond inclusions may yield isotope and trace element signatures diagnostic for the formation age and evolution of (parts of) cratons, while geophysical techniques (e.g., seismic and electromagnetic imaging) constrain variations of elastic and conductive properties over length scales ranging from several to many thousand kilometers. Integrating and reconciling this information is far from trivial and, as several papers in this volume document, the relationships between, for instance, formation age and tectonic behavior on the one hand and the seismic signature, heat flow, and petrology on the other may not be uniform but may vary both within as well as between cratons. These observations complicate attempts to determine the variations of one particular observable (e.g., heat flow, lithosphere thickness) as a function of another (e.g., crustal age) on the basis of global data compilations and tectonic regionalizations. Important conclusions of the work presented here are that (1) continental deformation, for instance shortening, is not restricted to the crust but also involves the lithospheric mantle; (2) the high wavespeed part of continental lithospheric mantle is probably thinner than inferred previously from vertically travelling body waves or form global surface-wave models; and (3) the seismic signature of ancient continents is more complex than expected from a uniform relationship with crustal age.
Download or read book Formation and Evolution of the Eastern Black Sea Basin written by Caroline L. Scott and published by . This book was released on 2009 with total page 0 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 Shear Wave Velocity Structure and Evolution of Old Oceanic Lithosphere written by Lexine Black and published by . This book was released on 2015 with total page 89 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although plate tectonic theory was first proposed in the early 1900's, the very nature and process of tectonic plate formation is actively debated today, with arguments for simple conductive cooling and growth with advancing seafloor age versus arguments presented for the influence of mantle dynamic sources. Could the plate tectonic system and mantle convection cycle be linked via buoyancy forces and flow in the asthenosphere, which catalyze plate formation and growth? Seafloor subsidence values for ages less than 80 Ma are satisfied by the half-space conductive cooling model, but these parameters deviate from the linearly described model for older seafloor. There is a paucity of data from old seafloor to address this discrepancy. I investigate the lithospheric structure of a section of 150-160 Ma seafloor in the northwestern Pacific using Rayleigh wave phase velocity data. My results indicate high velocities of 4.7 km/s + 0.07 km/s in the upper lithosphere that extend to ~65 km depth. I observe a negative velocity gradient with a minimum of 4.30 + 0.09 km/s at 150 km depth. The lithosphere-asthenosphere boundary, defined by the negative velocity gradient below the high velocity lid, occurs at 90 km + 35 km. The highest velocities in my study region are higher than previous studies of 5-9 Ma seafloor, but similar to studies of 100 Ma seafloor. High velocities in the 150 Ma seafloor I studied are similar to velocities typically observed in the upper lithosphere of Archean cratons. This similarity suggests that continental evolution is a complex process of multi-layered growth whereas the evolution of oceanic lithosphere is a simple, single layer process of growth. Half space cooling may be sufficient to explain the evolution process but alternative models of interaction with dynamic mantle sources cannot be ruled out.
Download or read book The Formation and Evolution of Africa written by Douwe J. J. van Hinsbergen and published by Geological Society of London. This book was released on 2011 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: The African continent preserves a long geological record that covers almost 75% of Earth's history. The Pan-African orogeny (c. 600-500 Ma) brought together old continental kernels (West Africa, Congo, Kalahari and Tanzania) to form Gondwana and subsequently the supercontinent Pangaea by the late Palaeozoic. The break-up of Pangaea since the Jurassic and Cretaceous, primarily through opening of the Central Atlantic, Indian, and South Atlantic oceans, in combination with the complicated subduction history to the north, gradually shaped the African continent. This volume contains 18 contributions that discuss the geology of Africa from the Archaean to the present day.
Download or read book Processes of Magmatic and Tectonic Accretion of Oceanic Lithosphere at Mid ocean Ridges written by Anke Dannowski and published by . This book was released on 2009 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Geophysical Journal written by and published by . This book was released on 1988 with total page 688 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vols. 11 and 13 includes the Proceedings of the 2nd, 3rd, International Symposium on Geophysical Theory and Computers, Rehovoth, Israel, etc., 1965-66.
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1992 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Processes of Magmatic and Tectonic Accretion of Oceanic Lithosphere at Mid ocean Ridges written by Anke Dannowski and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mantle Convection and Surface Expressions written by Hauke Marquardt and published by John Wiley & Sons. This book was released on 2021-07-07 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: A multidisciplinary perspective on the dynamic processes occurring in Earth's mantle The convective motion of material in Earth's mantle, powered by heat from the deep interior of our planet, drives plate tectonics at the surface, generating earthquakes and volcanic activity. It shapes our familiar surface landscapes, and also stabilizes the oceans and atmosphere on geologic timescales. Mantle Convection and Surface Expressions brings together perspectives from observational geophysics, numerical modelling, geochemistry, and mineral physics to build a holistic picture of the deep Earth. It explores the dynamic processes occurring in the mantle as well as the associated heat and material cycles. Volume highlights include: Perspectives from different scientific disciplines with an emphasis on exploring synergies Current state of the mantle, its physical properties, compositional structure, and dynamic evolution Transport of heat and material through the mantle as constrained by geophysical observations, geochemical data and geodynamic model predictions Surface expressions of mantle dynamics and its control on planetary evolution and habitability The American Geophysical Union promotes discovery in Earth and space science for the benefit of humanity. Its publications disseminate scientific knowledge and provide resources for researchers, students, and professionals.
Download or read book Experimental and Seismological Constraints on the Rheology Evolution and Alteration of the Lithosphere at Oceanic Spreading Centers written by Brian J. DeMartin and published by . This book was released on 2006 with total page 212 pages. Available in PDF, EPUB and Kindle. Book excerpt: (Cont.) Experimental results coupled with geomechanical models indicate that pervasive grain boundary cracking occurs in mantle peridotite when it is uplifted to within 4 km of the seafloor. Whereas faults provide the high-permeability pathways necessary to sustain high-temperature fluid circulation, grain boundary cracks form the interconnected network required for pervasive alteration of the oceanic lithosphere. This thesis provides fundamental constraints on the rheology, evolution, and alteration of the lithosphere at oceanic spreading centers.
Download or read book Upper Crustal and Lithosphere Asthenosphere Boundary Seismic Structure of 0 75 Ma Old Normal Oceanic Lithosphere in the Equatorial Atlantic Ocean written by Pranav Audhkhasi and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Previous studies on upper oceanic crust have been limited to young lithosphere and wide-angle seismic data, which lacks resolution in the upper crust. The oceanic lithosphere-asthenosphere boundary (LAB) has been studied extensively by seismological studies, but also suffers from low vertical resolution. The TransAtlantic ILAB experiment collected multi-channel seismic reflection data over oceanic lithosphere aged 0-75 Ma formed at the slow-spreading Mid-Atlantic Ridge in the Equatorial Atlantic Ocean. Analysis of upper crust by means of seismic imaging and high-resolution tomography indicates the top of the crust (Layer 2A) is never sealed from 0-75 Ma and hydrothermal systems continue in older oceanic crust. Most of the evolution happens within the first 4 Myr, beyond which intensity of hydrothermal circulation reduces and sediment cover increases. Layer 2A/2B boundary is a lava/dyke contact at the ridge-axis and a hydrothermal alteration front away from the ridge-axis. Co-located heatflow data from the LITHOS experiment supports the possibility of large hydrothermal cells in older oceanic crust. The LAB is imaged throughout on lithosphere aged 2-75 Ma. From 2-47 Ma, there is evidence of a LAB channel decoupling the lithospheric mantle from the asthenospheric mantle with the lithosphere being 25 km thick at 2 Myr and 72 km thick at 47 Myr. However from 49-75 Myr, a single LAB reflection is imaged implying possible disruption of the base of the channel due to adjacent Cameroon Volcanic Line. Strong evidence of mantle thermal anomaly comes from the LAB being shallower and an uplifted lithosphere.
