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Ancient Supercontinents and the Paleogeography of Earth
- 2021
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Samlingsverk (redaktörskap) (refereegranskat)abstract
- Ancient Supercontinents and the Paleogeography of Earth offers a systematic examination of Precambrian cratons and supercontinents. Through detailed maps of drift histories and paleogeography of each continent, this book examines topics related to Earth’s tectonic evolution prior to Pangea, including plate kinematics, orogenic development, and paleoenvironments. Additionally, this book discusses the methodologies used, principally paleomagnetism and tectonostratigraphy, and addresses geophysical topics of mantle dynamics and geodynamo evolution over billions of years. Structured clearly with consistent coverage for Precambrian cratons, this book combines state-of-the-art paleomagnetic and geochronologic data to reconstruct the paleogeography of the Earth in the context of major climatic events such as global glaciations. It is an ideal, up-to>date reference for geoscientists and geographers looking for answers to questions surrounding the tectonic evolution of Earth.
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| 2. |
- Buchan, Kenneth L., et al.
(författare)
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Rodinia : the evidence from integrated palaeomagnetism and U-Pb geochronology
- 2001
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Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 110:1-4, s. 9-32
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Tidskriftsartikel (refereegranskat)abstract
- Of many hundreds of well-defined palaeomagnetic poles that have been reported from cratons around the world in the 1700-500 Ma period, only a few are precisely dated. However, such ‘key' palaeopoles are a prerequisite for establishing rigorous palaeomagnetic reconstructions in order to chart the assembly, drift and breakup of the postulated late Precambrian supercontinent of Rodinia. Most key palaeopoles are derived from mafic dykes and sills that have been dated by U-Pb techniques. Most are from Laurentia, the largest and best studied of the continental fragments that are thought to have comprised Rodinia. Thirteen key Laurentia palaeopoles form an incomplete reference set that can be used for comparison with key palaeopoles from other cratons as they become available. Currently, there are four key palaeopoles for Baltica between 1700 and 500 Ma, although only one allows a direct comparison with a similar aged pole from Laurentia. The 1265 Ma match between Baltica and Laurentia is consistent with reconstructions in which Baltica is adjacent to present-day east Greenland, with the ca. 1700-1500 Ma Gothian and Labradorian belts aligned. Few key palaeopoles are yet available from other cratons. However, recent U-Pb dating of dykes, sills, or volcanic rocks in the Siberian, Australian and Kalahari cratons and in Coats Land of Antarctica constrains the ages of individual palaeopoles from each of these areas. Most of these are not key palaeopoles because they have not been conclusively demonstrated to be primary, or local tectonic rotations have not been ruled out. Nevertheless, they are useful in testing Rodinia reconstructions. In this paper, a U-Pb baddeleyite age is reported from the late Gardar magmatic rocks of southwest Greenland. Along with the previously published palaeopole for this unit, this age helps constrain the Mesoproterozoic location of southwest Greenland relative to North America.
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| 4. |
- Donadini, Fabio, et al.
(författare)
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Holocene geomagnetic paleointensities: A blind test of absolute paleointensity techniques and materials
- 2007
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Ingår i: Physics of the Earth and Planetary Interiors. - : Elsevier BV. - 0031-9201. ; 161:1-2, s. 19-35
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Tidskriftsartikel (refereegranskat)abstract
- Through several decades of research, absolute paleointensity estimates have been obtained from a wide range of rocks with varying ages, covering the last 3.45 Ga years. These paleointensity data are crucial to study the past geodynamo and the geological evolution of the Earth's deep interior. However, paleointensity data are often difficult to interpret, and on-going discussions concerning the past geomagnetic field invariably focus on data reliability, and which kind of material, and method, is best suited for absolute paleointensity experiments. In this paper we blind test paleointensity methods and materials using the new GEOMAGIA50 database that contains all available experimental information about published paleointensity estimates covering the last 50,000 years. Our analysis is built on simple comparisons of results obtained from different materials, and methodologies, to investigate their possible influence on the paleointensity estimate. We also study the effect of various numbers of samples, and dating accuracies. We focus on paleointensity estimates from the last 12,000 years, which includes the Holocene epoch. The advantage of this period is that data have been obtained from a wide array of methodological techniques as well as a wide selection of materials, including both natural ones (e.g. lava flows) and various archaeological artifacts. Our main observations are (i) that well-fired archaeological materials (bricks, potteries, clays, and ceramics) show the best correlation with the rest of the dataset, which we interpret to suggest that these data are the most reliable, and (ii) although paleointensity data obtained from lava flows are slightly more scattered, there is no evidence for paleointensity data from lavas to be significantly lower or higher than other data, irrespective of the methodology. (c) 2007 Elsevier B.V. All rights reserved.
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| 5. |
- Elming, Sten-Åke, et al.
(författare)
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Paleo-Mesoproterozoic Nuna supercycle
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 499-548
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Bokkapitel (refereegranskat)abstract
- We review models of the Precambrian supercontinent Nuna (c.1.80–1.20 Ga) and present a new model of the Nuna life-cycle. We explore the option where Amazonia−West Africa and Congo−São Francisco cratons were not a part of Nuna but form a cluster of cratons named Atlantica. Nuna was finally assembled at c.1.65 Ga, encompassing Laurentia, Baltica, Siberia, proto-Australia, North China, and India. The break up of Nuna is here suggested to have started at c.1.3 Ga with Australian cratons moving away from Laurentia. Varying drift rates and length between coeval poles from separate cratons support the operation of modern style plate tectonics during the Nuna supercycle. Moreover, if there was no link between Nuna and the Atlantica cratons, the size of Nuna might not meet the criteria for a supercontinent, but should be regarded as a huge landmass.
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| 6. |
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| 7. |
- Evans, David A.D., et al.
(författare)
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An expanding list of reliable paleomagnetic poles for Precambrian tectonic reconstructions
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 605-639
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Bokkapitel (refereegranskat)abstract
- We present a compilation of reliable Precambrian paleomagnetic poles from three successive international workshops (in years 2009, 2014, 2017), comprising paleomagnetists specializing in Precambrian tectonic reconstructions. The working groups compiled lists of two global classes of poles, published through the end of 2017. “Grade-A” results are judged to provide essential constraints on tectonic reconstructions; “Grade-B” poles are judged to be suggestive of high-quality, but not yet demonstrated to be primary, or perhaps lacking precise geochronologic or other constraints. Our catalog documents a resurgence of high-quality data acquisition in recent years, and highlights specific cratons and time intervals that are most lacking in the data needed to reconstruct those blocks through supercontinental cycles.
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| 8. |
- Knudsen, Mads Faurschou, et al.
(författare)
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Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr
- 2008
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 272:1-2, s. 319-329
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Tidskriftsartikel (refereegranskat)abstract
- All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMACIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We Subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (Be-10 and C-14). This comparison generally lends Support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, Suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This Study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr, and that similar to 4.10(22) Am-2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur. (C) 2008 Elsevier B.V. All rights reserved.
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| 9. |
- Meert, Joseph G., et al.
(författare)
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The magnificent seven : A proposal for modest revision of the Van der Voo (1990) quality index
- 2020
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Ingår i: Tectonophysics. - : Elsevier. - 0040-1951 .- 1879-3266. ; 790
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Tidskriftsartikel (refereegranskat)abstract
- Thirty years ago, Rob Van der Voo proposed an elegant and simple system for evaluating the quality of paleomagnetic data. As a second-year Ph.D. student, the lead author remembers Rob waxing philosophical about the need to have an appropriate, but not overly rigid evaluation system. The end result was a 7-point system that assigned a (1) or (0) for any paleomagnetic result based on objective criteria. The goal was never to reject or blindly accept any particular result, but merely to indicate the degree of quality for any paleomagnetic pole. At the time, the global paleomagnetic database was burgeoning and it was deemed useful to rank older paleomagnetic results with the newer data being developed in modern laboratories. Van der Voo's, 1990 paper launched a silent revolution in paleomagnetism. Researchers began to evaluate their data against those seven criteria with the anticipation that reviewers would be similarly critical.Today, paleomagnetism is a mature science. Our methods, analyses, and results are more sophisticated than they were 30 years ago. Therefore, we feel it is appropriate to revisit the Van der Voo (1990) criteria in light of those developments. We hope to honor the intention of the original paper by keeping the criteria simple and easy to evaluate while also acknowledging the advances in science. This paper aims to update the criteria and modernize the process. We base our changes on advances in paleomagnetism and geochronology with a faithful adherence to the simplicity of the original publication. We offer the “Reliability” or “R” index as the next generation of the Van der Voo “Quality” or “Q” index. The new R-criteria evaluate seven different information items for each paleomagnetic pole including age, statistical requirements, identification of magnetic carriers, field tests, structural integrity, presence of reversals and an evaluation for possible remagnetization.
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