Properties of the Proterozoic Geomagnetic Field and Geological Applications of Paleomagnetic Data from Rocks of the North American Midcontinent Rift PDF Download
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Author: Evgeniy V. Kulakov Publisher: ISBN: Category : Geophysics Languages : en Pages : 264
Book Description
Rocks of the North American Midcontinent rift (MCR) exposed in the Lake Superior area provide an excellent opportunity to use paleomagnetism as a means of studying the characteristics of geomagnetic field in Proterozoic and the history of the rift itself. The detailed paleomagnetic and paleointensity studies of different rock units associated with the MCR, including the 1108 Ma alkaline Coldwell Complex (Ontario, Canada), presumably 1107-1108 Ma basaltic flows of the Geordie Lake (Ontario, Canada) and Silver Mountain (Upper Michigan, USA), ~1095 Ma lava flows of the Portage Lake Volcanics (PLV) (Keweenaw Peninsula, Michigan), and ~1088 Ma lava flows of the Lake Shore Traps (LST) (Keweenaw Peninsula, Michigan) are presented. Paleomagnetic study of the Coldwell Complex indicates that the apparent asymmetry of geomagnetic reversal, recorded by many Keweenawan rocks is an artifact due to missing paleomagnetic record of an equator-ward plate motion in most MCR sequences. The result supports the validity of the geocentric axial dipole assumption for the ~1.1 Ga. Extrusive sequences exposed on the Keweenaw Peninsula revealed lower paleosecular variation than that recorded by 0-5 Ma lava flows, indicating that the Proterozoic field was more stable. Samples from the ~1088 Ma Lake Shore Traps yielded consistent paleofield values with a mean value of 26.3 ± 4.7 μ T, which corresponds to a virtual dipole moment of 5.9 ± 1.1 × 1022 Am2. The mean and range of paleofield values are similar to those of the recent Earth's magnetic field and incompatible with a "Proterozoic dipole low.". These results are consistent with a stable compositionally-driven geodynamo operating by the end of Mesoproterozoic. New high-quality paleomagnetic poles calculated for the ~1108 Ma Coldwell Complex and coeval extrusive rocks, and ~ 1094 Ma PLV indicate that North America was moving directly equator-ward with an approximately 20-25 cm/year rate between 1108 and 1094 Ma. However, the paleomagnetic data indicates a significant slowdown in motion between 1094 and 1088 Ma. This change in the plate tectonics regime coincides with a cessation of the MCR magmatism, which may indicate the beginning of renewed compression from the Grenville Front caused by continent-continent collision during the assemblage of the supercontinent Rodinia. New paleomagnetic data from the LST flows further confirm the idea of a primary nature of the MCR curvature in the Lake Superior area.
Author: Evgeniy V. Kulakov Publisher: ISBN: Category : Geophysics Languages : en Pages : 264
Book Description
Rocks of the North American Midcontinent rift (MCR) exposed in the Lake Superior area provide an excellent opportunity to use paleomagnetism as a means of studying the characteristics of geomagnetic field in Proterozoic and the history of the rift itself. The detailed paleomagnetic and paleointensity studies of different rock units associated with the MCR, including the 1108 Ma alkaline Coldwell Complex (Ontario, Canada), presumably 1107-1108 Ma basaltic flows of the Geordie Lake (Ontario, Canada) and Silver Mountain (Upper Michigan, USA), ~1095 Ma lava flows of the Portage Lake Volcanics (PLV) (Keweenaw Peninsula, Michigan), and ~1088 Ma lava flows of the Lake Shore Traps (LST) (Keweenaw Peninsula, Michigan) are presented. Paleomagnetic study of the Coldwell Complex indicates that the apparent asymmetry of geomagnetic reversal, recorded by many Keweenawan rocks is an artifact due to missing paleomagnetic record of an equator-ward plate motion in most MCR sequences. The result supports the validity of the geocentric axial dipole assumption for the ~1.1 Ga. Extrusive sequences exposed on the Keweenaw Peninsula revealed lower paleosecular variation than that recorded by 0-5 Ma lava flows, indicating that the Proterozoic field was more stable. Samples from the ~1088 Ma Lake Shore Traps yielded consistent paleofield values with a mean value of 26.3 ± 4.7 μ T, which corresponds to a virtual dipole moment of 5.9 ± 1.1 × 1022 Am2. The mean and range of paleofield values are similar to those of the recent Earth's magnetic field and incompatible with a "Proterozoic dipole low.". These results are consistent with a stable compositionally-driven geodynamo operating by the end of Mesoproterozoic. New high-quality paleomagnetic poles calculated for the ~1108 Ma Coldwell Complex and coeval extrusive rocks, and ~ 1094 Ma PLV indicate that North America was moving directly equator-ward with an approximately 20-25 cm/year rate between 1108 and 1094 Ma. However, the paleomagnetic data indicates a significant slowdown in motion between 1094 and 1088 Ma. This change in the plate tectonics regime coincides with a cessation of the MCR magmatism, which may indicate the beginning of renewed compression from the Grenville Front caused by continent-continent collision during the assemblage of the supercontinent Rodinia. New paleomagnetic data from the LST flows further confirm the idea of a primary nature of the MCR curvature in the Lake Superior area.
Author: L. Tauxe Publisher: Springer Science & Business Media ISBN: 0306481286 Category : Science Languages : en Pages : 302
Book Description
Paleomagnetic data are useful in many applications in Earth Science from determining paleocurrent directions to analyzing the long-term behavior of the geomagnetic field. In this book, an attempt has been made to draw together the various principles and practices within paleomagnetism in a consistent and up-to-date manner. It includes many practical examples that illustrate various applications of paleomagnetism. A companion software package implements the theory explained in the text. Audience: This volume is aimed at professional Earth Scientists using paleomagnetic data for their research. It is also suitable for use as a text book for students in courses with a paleomagnetic content. In addition, this volume will be of value to other professionals with an interest in the analysis of vector and tensor data in general.
Author: Michael W. McElhinny Publisher: Elsevier ISBN: 0080513468 Category : Science Languages : en Pages : 407
Book Description
Paleomagnetism is the study of the fossil magnetism in rocks. It has been paramount in determining that the continents have drifted over the surface of the Earth throughout geological time. The fossil magnetism preserved in the ocean floor has demonstrated how continental drift takes place through the process of sea-floor spreading. The methods and techniques used in paleomagnetic studies of continental rocks and of the ocean floor are described and then applied to determining horizontal movements of the Earth's crust over geological time. An up-to-date review of global paleomagnetic data enables 1000 million years of Earth history to be summarized in terms of the drift of the major crustal blocks over the surface of the Earth. The first edition of McElhinny's book was heralded as a "classic and definitive text." It thoroughly discussed the theory of geomagnetism, the geologic reversals of the Earth's magnetic field, and the shifting of magnetic poles. In the 25 years since the highly successful first edition of Palaeomagnetism and Plate Tectonics (Cambridge, 1973) the many advances in the concepts, methodology, and insights into paleomagnetism warrant this new treatment. This completely updated and revised edition of Paleomagnetism: Continents and Oceans will be a welcome resource for a broad audience of earth scientists as well as laypeople curious about magnetism, paleogeography, geology, and plate tectonics. Because the book is intended for a wide audience of geologists, geophysicists, and oceanographers, it balances the mathematical and descriptive aspects of each topic. - Details the theory and methodology of rock magnetism, with particular emphasis on intrepreting crustal movements from continental and oceanic measurements - Outlines Earth history for the past 1000 million years, from the Rodinia super-continent through its breakup and the formation of Gondwana to the formation and breakup of Pangea and the amalgamation of Eurasia - Provides a comprehensive treatment of oceanic paleomagnetism - Provides a set of color pateogeographic maps covering the past 250 million years - Written by two internationally recognized experts in the field
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Abstract : Understanding the geomagnetic field direction and strength (e.g., paleomagnetism and paleointensity, respectively) recorded by Precambrian rocks is essential to obtain insight into the nature and evolution of the Earth's early geodynamo and for constraining models of planetary evolution. Major milestones of our planet's history, such as beginning of plate tectonics, development of the atmosphere and life, took place during the first four billion years. However, the available data on the Earth's magnetic field in the Precambrian are very limited, especially the information about the field intensity which represents one of the most challenging aspect of paleomagnetic research. Many Precambrian rocks are not suitable for paleointensity determinations with the most commonly used Thellier double-heating method because of their geological and experimental alteration. Complementing the Precambrian paleomagnetic and paleointensity database and improving alternative paleointensity techniques is essential to better our understanding of the Earth. This dissertation presents the results of investigations of the Precambrian geomagnetic field direction and strength, and the results of a methodological study of the pseudo-Thellier experimental protocol for absolute paleointensity determination. Detailed paleomagnetic and rock magnetic observations were performed on rocks emplaced ~1100 Ma during the formation of the North-American Mid-Continent Rift. The identification of three independent paleomagnetic directions in the Baraga and Marquette dikes and their comparison to the Mesoproterozoic Apparent Polar Wonder Path (the so-called Logan loop) permitted the estimation of the relative timescale for their intrusion (Chapter 2). The Shaw paleointensity results on the dikes from Baraga and Marquette areas yielded consistent intensity values of ~14.4 μT and ~20.4 μT corresponding to a VDM of ~2 x 1022 Am2 and 3.3 x 1022 Am2, respectively. The detailed paleomagnetic analysis of the ~1094 Ma Greenstone flow, one of the largest large flows on the planet, was applied to evaluate the various scenarios of emplacement and cooling of the flow and to assess the paleosecular variation of the geomagnetic field (Chapter 3). The results of an experimental study using the combination of the pseudo-Thellier and Shaw experimental protocols on synthetic and natural magnetite-bearing samples suggest that the calibrated pseudo-Thellier method can xii provide absolute paleointensity estimates for Precambrian rock equivalent to the results from conventional heating methods (Chapter 4). The paleointensity values (2-3 x 1022Am2) obtained from the Baraga and Marquette dikes are low in comparison to the average field strength value (~8.0 x 1022 Am2) for the last 10 Myr but agree with some low paleointensity determinations from other Precambrian rocks. These results suggest that the Baraga-Marquette dikes intruded during a period where the geomagnetic field was weak. However, a possibility of underestimating the field strength due to the presence of thermochemical remanent magnetization cannot be ruled out.
Author: Lisa Tauxe Publisher: Univ of California Press ISBN: 0520946375 Category : Nature Languages : en Pages : 506
Book Description
More than 400 years ago William Gilbert said, "The Earth itself is a great magnet." Today, we know that it is also a great magnetic tape recorder. This work is a comprehensive, up-to-date textbook on extracting and using rock and paleomagnetic data in archaeological, geological, and geophysical applications. Designed for students and professionals with knowledge of college level physics and some background in earth sciences, it describes both the theory and the practice of paleomagnetism, covering topics such as the basics of magnetism, geomagnetic fields, how rocks become magnetized, and the various ways of analyzing the magnetism of rocks. The book uses the companion PmagPy software package. An appendix contains a brief introduction to Python, an easy-to-use, cross-platform, and most important, free programming environment in which PmagPy programs are written.
Author: Kenneth P. Kodama Publisher: John Wiley & Sons ISBN: 1118384156 Category : Science Languages : en Pages : 343
Book Description
This book describes the paleomagnetism of sediments and sedimentary rocks, how sediments and sedimentary rocks become magnetized, and how the physical and chemical processes involved can affect the accuracy of paleomagnetism. Topics covered include depositional and post-depositional remanence acquisition, the detection and correction of compaction-caused inclination shallowing, reduction diagenesis of magnetic minerals, chemical remagnetization, and rotation of remanence by grain-scale rock strain. The book also has a chapter on environmental paleomagnetism, including examples of the new technique of high-resolution rock magnetic cyclostratigraphy and its application to sedimentary sequences. By emphasising the accuracy of sedimentary paleomagnetism and the magnitude of post-depositional processes that can affect it, the book will be invaluable in the geologic interpretation of sedimentary paleomagnetic data. Paleomagnetism of Sedimentary Rocks will be welcomed by paleomagnetists, students of paleomagnetism and all Earth scientists who use sedimentary paleomagnetic data in their research. Additional resources for this book can be found at: www.wiley.com/go/kodama/paleomagnetism.
Author: Evgeniy V. Kulakov
Author: Evgeniy V. Kulakov
Author: L. Tauxe
Author: Michael W. McElhinny
Author: 
Author: Lisa Tauxe
Author: Peter C. Lippert
Author: M.W. McElhinny
Author: Rob Van der Voo
Author: Kenneth P. Kodama
Author: