| 1. |
- Bispo-Santos, Franklin, et al.
(författare)
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Columbia revisited : paleomagnetic results from the 1790 Ma colider volcanics (SW Amazonian Craton, Brazil)
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 164:1-2, s. 40-49
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to improve our understanding of the Paleoproterozoic geodynamic evolution, a paleomagnetic study was performed on 10 sites of acid volcanic rocks of the Colider Suite, southwestern Amazonian Craton. These rocks have a well-dated zircon U-Pb mean age of 1789 +/- 7 Ma. Alternating field and thermal demagnetization revealed northern (southern) directions with moderate to high upward (downward) inclinations. Rock magnetism experiments and magnetic mineralogy show that this characteristic magnetization is carried by Ti-poor magnetite or by hematite that replaces magnetite by late-magmatic cleuteric alteration. Both magnetite and hematite carry the same characteristic component. The mean direction (Dm = 183.0 degrees, Im = 53.5 degrees, N = 10, alpha(95) = 9.8 degrees, K = 25.2) yielded a paleomagnetic pole located at 298.8 degrees E, 63.3 degrees S (alpha(95) = 10.2 degrees, K = 23.6), which is classified with a quality factor Q = 5. Paleogeographic reconstructions using this pole and other reliable Paleoproterozoic poles suggest that Laurentia, Baltica, North China Craton and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1790 Ma ago. This is reinforced by geological evidence which support the existence of the supercontinent Columbia in Paleoproterozoic times.
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| 2. |
- Bispo-Santos, Franklin, et al.
(författare)
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Tectonic implications of the 1419 Ma Nova Guarita mafic intrusives paleomagnetic pole (Amazonian Craton) on the longevity of Nuna
- 2012
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 196-197, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- The Nuna supercontinent was probably assembled in the Paleoproterozoic, but its paleogeography and the timing for its demise are still a matter of debate. A paleomagnetic and geochronological study carried out on the Mesoproterozoic Nova Guarita dyke swarm (northern Mato Grosso State, SW Amazonian Craton) provides additional constraints on the duration of this supercontinent. Paleomagnetic AF and thermal treatment revealed south/southwest (northeast) magnetic directions with downward (upward) inclinations for nineteen analyzed sites. These directions are carried by PSD magnetite with high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the progressive acquisition of isothermal remanence in selected samples. A positive contact test with the host granite in one of the studied dykes further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at Dm = 220.5°, Im = 45.9° (α95 = 6.5°, K = 27.7), which yielded a paleomagnetic pole located at 245.9°E, 47.9°S (A95 = 7.0°). 40Ar/39Ar dating carried out on biotites from four analyzed dykes yielded well-defined plateau ages with a mean of 1418.5 ± 3.5 Ma. The Nova Guarita pole precludes a long-lived Nuna configuration in which Laurentia, Baltica, North China, and Amazonia formed a long and continuous block as previously proposed for the Paleoproterozoic. It is nevertheless fully compatible with a SAMBA (Amazonia-Baltica) link at Mesoproterozoic times.
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| 3. |
- D’Agrella-Filho, Manoel S., et al.
(författare)
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A new 1.42 GA paleomagnetic pole from the Amazonian craton : implications for the Columbia supercontinent configuration
- 2011
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Ingår i: Proceedings of Second Biennial Meeting of Latinmag.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Paleomagnetic studies carried out on the 1.42 Ga Indiavaí mafic intrusive rocks, that crop out in the SW Mato Grosso State provides a great opportunity to test the proposed paleogeographic models for Columbia. Paleomagnetic AF and thermal treatment revealed south/southwest magnetic directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional magnetic tests, including thermomagnetic curves, hysteresis loops and the IRM acquisition curves. A different magnetization obtained for host mafic rocks from the basement ca. 10 km NW away from the Indiavaí intrusive, further attests to the primary origin of the characteristic magnetic component. A mean site direction was calculated at Dm=209.8°, Im=50.7° (α95=8.0°, K=22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95=8.6°). Comparison of this pole with other paleomagnetic poles of similar age from Baltica and Laurentia provides evidence for a link of north-northeastern Amazonian craton, southwestern Baltica and Laurentia, as previously suggested from the similar Mesoproterozoic geological evolution of their margins.
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| 4. |
- D'Agrella-Filho, Manoel S., et al.
(författare)
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The 1420 Ma Indiavaí Mafic Intrusion (SW Amazonian Craton): Paleomagnetic results and implications for the Columbia supercontinent
- 2012
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Ingår i: Gondwana Research. - : Elsevier BV. - 1342-937X .- 1878-0571. ; 22:3-4, s. 956-973
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Tidskriftsartikel (refereegranskat)abstract
- The configuration and the timing of assembly and break-up of Columbia are still matter of debate. In order to improve our knowledge about the Mesoproterozoic evolution of Columbia, a paleomagnetic study was carried out on the 1420 Ma Indiavaí mafic intrusive rocks that crosscut the polycyclic Proterozoic basement of the SW Amazonian Craton, in southwestern Mato Grosso State (Brazil). Alternating field and thermal demagnetization revealed south/southwest ChRM directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional rock magnetic tests, including thermomagnetic data, hysteresis data and the progressive acquisition of isothermal remanent magnetization. Different stable magnetization components isolated in host rocks from the basement 10 km NW away to the Indiavaí intrusion, further support the primary origin of the ChRM. A mean of the site mean directions was calculated at Dm = 209.8°, Im = 50.7° (α95 = 8.0°, K = 22.1), which yielded a paleomagnetic pole located at 249.7°E, -57.0°N (A95 = 8.6°). The similarity of this pole with the recently published 1420 Ma pole from the Nova Guarita dykes in northern Mato Grosso State suggests a similar tectonic framework for these two sites located 600 km apart, implying the bulk rigidity of the Rondonian-San Ignacio crust at that time. Furthermore these data provide new insights on the tectonic significance of the 1100-1000 Ma Nova Brasilândia belt –a major EW feature that cuts across the basement rocks of this province, which can now be interpreted as intracratonic, in contrast to previous interpretation. From a global perspective, a new Mesoproterozoic paleogeography of Columbia has been proposed based on comparison of these 1420 Ma poles and a 1780 Ma pole from Amazonia with other paleomagnetic poles of similar age from Baltica and Laurentia, a reconstruction in agreement with geological correlations.
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| 5. |
- 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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| 6. |
- Salminen, Johanna, et al.
(författare)
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Congo-São Francisco craton in Paleoproterozoic-Mesoproterozoic supercontinent Nuna
- 2024
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Ingår i: Precambrian Research. - 0301-9268. ; 406
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Tidskriftsartikel (refereegranskat)abstract
- The location of the Congo-São Francisco (CSF) craton, one of the largest cratons in Proterozoic paleogeography, has been poorly constrained for the supercontinent Nuna interval (ca. 1800–1300 Ma). Initial models of Nuna suggested that the CSF craton was part of the Atlantica continent, together with Amazonia, West Africa, and perhaps Río de la Plata, as a separate continental block from other Nuna constituents. In other Nuna models the CSF craton has been placed adjacent to Baltica and Siberia, the core of Nuna, based mainly on ages of mafic magmatism and sparse paleomagnetic data. Through a geochemical, geochronological and paleomagnetic study of the WNW-trending Virei mafic dykes, which extend outward from the Mesoproterozoic Kunene Igneous Complex in southwest Angola, we provide a U-Pb baddeleyite age of 1385 ± 5 Ma, geochemical signatures, and a robust Mesoproterozoic paleomagnetic pole to test the CSF craton's placement within Nuna. Including our new pole with quality-filtered poles from the other cratons during the Nuna interval, we propose a refined Nuna model with (1) southwest Congo / west Siberia cratonic connection at 1700–1500 Ma, (2) proximity of Amazonia and West Africa cratons, and (3) connection of southwest Congo craton with northwest West Africa at 1380 Ma. Our proposed 1500–1380 Ma reconstructions are further supported by matching large igneous province (LIP) records from these crustal blocks. The new 1385 Ma Virei pole, when considered relative to an earlier CSF pole at ca. 1500 Ma, requires substantial azimuthal rotation (∼85°) of CSF in the intervening time interval. To accommodate both the matching LIP records and paleomagnetic data from CSF and neighboring cratons in Nuna, we propose an interval of transform motion near the supercontinent's periphery prior to more widespread mid-Mesoproterozoic supercontinental breakup.
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