| 1. |
- 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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| 2. |
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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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| 3. |
- 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. |
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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. |
- 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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| 7. |
- 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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| 8. |
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| 9. |
- Nisca, Dan H., et al.
(författare)
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The lycksele structure, a huge ring formation in Northern Sweden : result of an impact?.
- 2000
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Ingår i: S T A R (Online). - 1548-8837. ; 38
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The current database of impact structures in Fennoscandia reveals 28 proven impact craters of various ages and sizes. Recently, we started to search for large and old impact structures, which may show traces of the impact in their shape or in their rocks and minerals and which can be diagnostically identified through the masking effects of postimpact deformations. Since we are dealing with strongly eroded and often deformed structures, the classical criteria for proving an impact origin are not tenable. Through a combined analysis of topography, drainage, gravity, magnetic, and petrophysical data, a circular structure has been identified in northern Sweden. The structure is characterized by a circular system of faults, arc-shaped contacts between rocks, and a circular distribution of granitic intrusions. The fault zone at the edges is defined from gradients in the gravity data, from magnetic data by arc-shaped anomalies, and from topographic data by an arc-shaped relief, which is also reflected in the drainage pattern. The zone is characterized by vertical faults that also cut the granitic intrusions at the edge of the formation, and from interpretation of gravity data an uplift of high density rocks (about 2850 kg/m(exp 3)) is indicated in the central part. The age of granites and pegmatites ranges from 1.82 to 1.78 Ga. Therefore, based on age data and on paleomagnetic results of various generations of dikes that cut and are truncated by the structure, the age of the formation lies within 1.80-1.26 Ga. The rocks have not been studied petrologically to see if any traces of shock metamorphism can be found. At present, four models for the origin of the structure are possible: (1) basement doming, (2) meteorite impact, (3) large buried pluton, or (4) fault-bounded block. An impact origin, however, seems most plausible.
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| 10. |
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| 11. |
- Pesonen, Lauri J., et al.
(författare)
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Precambrian supercontinents and supercycles—an overview
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 1-50
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Bokkapitel (refereegranskat)abstract
- There is ample evidence that supercontinent cycles on Earth have been operating since the Late Paleoproterozoic. Evidence for the supercontinent cyclicity arises from multidisciplinary observations from geology, geochronology, geophysics (e.g., paleomagnetism, seismology, heat flow), isotope geology, and geochemistry. This overview summarizes current views of Precambrian supercontinent episodicity or cyclicity. In addition, paleogeographic reconstructions based on global key paleomagnetic poles and kinematic models of Paleo-Mesoproterozoic Nuna supercycle, Meso-Neoproterozoic Rodinia supercycle, and the Phanerozoic Gondwana/Pangea supercycle are explored. The lifecycle of supercontinents is tested by geological, geophysical, and geochemical data coupled with secular evolution trends of Earth. Results suggest that (1) supercontinent cyclicity has a characteristic (quasi-) period of ~700–500 million years, supported by planetary secular evolutionary trends, but other periods are also present; (2) supercontinents Nuna, Rodinia, and Gondwana/Pangea have different configurations and secular evolutionary trends possibly due to different tectonic styles of assembly; (3) globally averaged plate velocity during the Precambrian reveals a wave-like pattern with peaks and lows corresponding with features in several secular evolution indices including the distribution of U−Pb ages, passive margins, metamorphic events, tectonic proxies, and magmatic activity; (4) the data suggest three tectonomagmatic lulls during the Proterozoic, but the proposed Mesoproterozoic quiescent period, coined as “boring billion” years of Earth history (1.8–0.8 Ga) appears to be seen mainly by atmospheric and biospheric data rather than tectonomagmatic activity; and (5) tectonic processes driving supercontinent cyclicity are interactive, with feedbacks from all six spheres of the Earth—the geosphere, cryosphere, hydrosphere, biosphere, atmosphere, and magnetosphere.
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| 12. |
- Pesonen, Lauri J., et al.
(författare)
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Preface
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. xv-xvi
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 13. |
- Pisarevsky, Sergei A., et al.
(författare)
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Mesoproterozoic paleogeography : Supercontinent and beyond
- 2014
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 244, s. 207-225
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Tidskriftsartikel (refereegranskat)abstract
- A set of global paleogeographic reconstructions for the 1770–1270 Ma time interval is presented here through a compilation of reliable paleomagnetic data (at the 2009 Nordic Paleomagnetic Workshop in Luleå, Sweden) and geological constraints. Although currently available paleomagnetic results do not rule out the possibility of the formation of a supercontinent as early as ca. 1750 Ma, our synthesis suggests that the supercontinent Nuna/Columbia was assembled by at least ca. 1650–1580 Ma through joining at least two stable continental landmasses formed by ca. 1.7 Ga: West Nuna (Laurentia, Baltica and possibly India) and East Nuna (North, West and South Australia, Mawson craton of Antarctica and North China). It is possible, but not convincingly proven, that Siberia and Congo/São Francisco were combined as a third rigid continental entity and collided with Nuna at ca.1500 Ma. Nuna is suggested to have broken up at ca. 1450–1380 Ma. West Nuna, Siberia and possibly Congo/São Francisco were rigidly connected until after 1270 Ma. East Nuna was deformed during the breakup, and North China separated from it. There is currently no strong evidence indicating that Amazonia, West Africa and Kalahari were parts of Nuna.
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| 14. |
- Salminen, Johanna, et al.
(författare)
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The Precambrian drift history and paleogeography of Baltica
- 2021
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Ingår i: Ancient Supercontinents and the Paleogeography of Earth. - : Elsevier. ; , s. 155-205
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Bokkapitel (refereegranskat)abstract
- We review paleomagnetic data and paleoclimatological indicators of Baltica and its subcratons. Between Neoarchean and middle Mesoproterozoic Karelia and Kola, and later the united Baltica were located mostly at the latitudes between 35°N and 35°S. Location of Baltica oscillated between high latitudes and the equator at late Mesoproterozic–Neoproterozoic. Drift velocities of the separate cratons between Neoarchean and middle Proterozoic are lower than the velocities of the united Baltica at late Paleoproterozoic–middle Mesoproterozoic. At Late Mesoproterozoic–Neoproterozoic Baltica shows high velocity peaks, which correlate temporarily with the ones obtained for Laurentia and can be ascribed to true polar wander. Increase in drift rates correlate temporarily with orogenies related to the formation of the supercontinents Nuna and Rodinia and in smaller scale to the crustal growth of Baltica. Based on the results, we review possible nearest neighbors for the Kola and Karelia in the Superia supercraton and for Baltica in the Nuna and Rodinia supercontinents.
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| 15. |
- Söderlund, Ulf, et al.
(författare)
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Emplacement ages of Paleoproterozoic mafic dyke swarms in eastern Dharwar craton, India : Implications for paleoreconstructions and support for a ∼30° change in dyke trends from south to north
- 2019
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268. ; 329, s. 26-43
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Tidskriftsartikel (refereegranskat)abstract
- Large igneous provinces (LIPs) and especially their dyke swarms are pivotal to reconstruction of ancient supercontinents. The Dharwar craton of southern Peninsular India represents a substantial portion of Archean crust and has been considered to be a principal constituent of Superia, Sclavia, Nuna/Columbia and Rodinia supercontinents. The craton is intruded by numerous regional-scale mafic dyke swarms of which only a few have robustly constrained emplacement ages. Through this study, the LIP record of the Dharwar craton has been improved by U-Pb geochronology of 18 dykes, which together comprise seven generations of Paleoproterozoic dyke swarms with emplacement ages within the 2.37–1.79 Ga age interval. From oldest to youngest, the new ages (integrated with U-Pb ages previously reported for the Hampi swarm) define the following eight swarms with their currently recommended names:NE–SW to ESE–WNW trending ca. 2.37 Ga Bangalore-Karimnagar swarm.N–S to NNE–SSW trending ca. 2.25 Ga Ippaguda-Dhiburahalli swarm.N–S to NNW–SSE trending ca. 2.22 Ga Kandlamadugu swarm.NW–SE to WNW–ESE trending ca. 2.21 Ga Anantapur-Kunigal swarm.NW–SE to WNW–ESE trending ca. 2.18 Ga Mahbubnagar-Dandeli swarm.N–S, NW–SE, and ENE–WSW trending ca. 2.08 Ga Devarabanda swarm.E–W trending 1.88–1.89 Ga Hampi swarm.NW–SE ca. 1.79 Ga Pebbair swarm. Comparison of the arcuate trends of some swarms along with an apparent oroclinal bend of ancient geological features, such as regional Dharwar greenstone belts and the late Archean (ca. 2.5 Ga) Closepet Granite batholith, have led to the hypothesis that the northern Dharwar block has rotated relative to the southern block. By restoring a 30° counter clockwise rotation of the northern Dharwar block relative to the southern block, we show that pre-2.08 Ga arcuate and fanning dyke swarms consistently become approximately linear. Two possible tectonic models for this apparent bending, and concomitant dyke rotations, are discussed. Regardless of which deformation mechanisms applies, these findings reinforce previous suggestions that the radial patterns of the giant ca. 2.37 Ga Bangalore-Karimnagar dyke swarm, and probably also the ca. 2.21 Ga Anantapur-Kunigal swarm, may not be primary features.
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| 16. |
- Thunehed, Hans, et al.
(författare)
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Lycksele structure in northern Sweden: Result of an impact?
- 2000
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Ingår i: Large meteorite impacts and planetary evolution II. - Boulder, Colo : Geological Society of America. - 0813723396 ; , s. 125-30
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The Lycksele structure in northern Sweden is a large circular structure with a diameter of approximately 130 km. The structure has been defined from a combined analysis of topography, gravity, and magnetic data and is characterized by a circular system of faults, arc-shaped contacts between rocks, a quasi-circular system of downfaulted lowdensity granitic rocks, and an uplift of high-density rocks in the center. On the basis of ages of granite intrusions and a thrust zone that is cut by faults of the ring, together with paleomagnetic data, the age of the structure is between 1.80 and 1.26 Ga. The Bouguer gravity anomaly is similar to that associated with other known large impact structures on Earth. The rim of the structure, defined from the gravity gradients, magnetic data, and topography, is not restricted to specific rock types but cuts regional geologic structures as well as smaller intrusions, which may be expected for an impact structure in Precambrian deformed target rocks. Therefore, an impact origin seems most plausible for this structure, but to confirm this idea we need identifications of shock metamorphic features in the rocks.
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