| 1. |
- Patten, C. G. C., et al.
(författare)
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Multi-source and multi-stage metal mobilization during the tectonic evolution of the Central Lapland Greenstone Belt, Finland : implications for the formation of orogenic Au deposits
- 2023
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 58:3, s. 461-488
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Tidskriftsartikel (refereegranskat)abstract
- Precambrian greenstone belts are prospective terrains for orogenic Au deposits worldwide, but the sources of Au, base metals, metalloids, and ligands enriched within the deposits are still debated. Metamorphic devolatilization is a key mechanism for generating Au-rich hydrothermal fluids, but the respective role of the metavolcanic and metasedimentary rocks present within these belts in releasing ore-forming elements is still not fully understood. The Central Lapland Greenstone Belt (CLGB), Finland, one of the largest Paleoproterozoic greenstone belts, hosts numerous orogenic Au deposits and is composed of variably metamorphosed volcanic and sedimentary rocks. Characterization of element behavior during prograde metamorphism highlights that (1) metavolcanic rocks release significant Au, As, Sn, Te, and possibly S; (2) metasedimentary rocks release significant S, C, Cu, As, Se, Mo, Sn, Sb, Te, and U, but limited Au; and (3) metakomatiite releases C and possibly Au. Throughout the CLGB metamorphic evolution, two main stages are identified for metal mobilization: (1) prograde metamorphism at ~ 1.92–1.86 Ga, promoting the formation of typical orogenic Au deposits and (2) late orogenic evolution between ~ 1.83 and 1.76 Ga, promoting the formation of both typical and atypical orogenic Au deposits. The complex lithologic diversity, tectonic evolution, and metamorphic history of the CLGB highlight that metal mobilization can occur at different stages of an orogenic cycle and from different sources, stressing the necessity to consider the complete dynamic and long-lasting evolution of orogenic belts when investigating the source of Au, ligands, metals, and metalloids in orogenic Au deposits.
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| 2. |
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| 3. |
- Pesonen, LJ, et al.
(författare)
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Palaeomagnetic configuration of continents during the Proterozoic
- 2003
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 375:1-4, s. 289-324
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Forskningsöversikt (refereegranskat)abstract
- Palaeomagnetic data are used to study the configurations of continents during the Proterozoic. Applying stringent reliability criteria, the positions of the continents at 12 times in the 2.45- to 1.00-Ga period have been constructed. The continents lie predominantly in low to intermediate latitudes. The sedimentological indicators of palaeoclimate are generally consistent with the palaeomagnetic latitudes, with the exception of the Early Proterozoic, when low latitude glaciations took place on several continents. The Proterozoic continental configurations are generally in agreement with current geological models of the evolution of the continents. The data suggest that three large continental landmasses existed during the Proterozoic. The oldest one is the Neoarchaean Kenorland, which comprised at least Laurentia, Baltica, Australia and the Kalahari craton. The protracted breakup of Kenorland during the 2.45- to 2.10-Ga interval is manifested by mafic dykes and sedimentary rift-basins on many continents. The second 'supercontinental' landmass is Hudsonland (also known as Columbia). On the basis of purely palaeomagnetic data, this supercontinent consisted of Laurentia, Baltica, Ukraine, Amazonia and Australia and perhaps also Siberia, North China and Kalahari. Hudsonland existed from 1.83 to ca. 1.50-1.25 Ga. The youngest assembly is the Neoproterozoic supercontinent of Rodinia, which was formed by continent-continent collisions during similar to 1.10-1.00 Ga and which involved most of the continents. A new model for its assembly and configuration is presented, which suggests that multiple Grenvillian age collisions took place during 1.10-1.00 Ga. The configurations of Kenorland, Hudsonland and Rodinia depart from each other and also from the Pangaea assembly. The tectonic styles of their amalgamation are also different reflecting probable changes in sizes and thicknesses of the cratonic blocks as well as changes in the thermal conditions of the mantle through time. (C) 2003 Elsevier B.V. All rights reserved.
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| 4. |
- Buchan, K. L., et al.
(författare)
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Comparing the drift of Laurentia and baltica in the Proterozoic : the importance of key palaeomagnetic poles
- 2000
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 319:3, s. 167-198
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Tidskriftsartikel (refereegranskat)abstract
- Key palaeomagnetic poles are defined as those which pass basic reliability criteria and are precisely and accurately dated. They allow a more rigorous analysis of Precambrian continental drift and continental reconstructions than the traditional apparent polar wander path (APWP) approach using mostly non-key poles. Between ca. 2.45 and 2.00 Ga in the early Palaeoproterozoic, key poles define the drift of the Archaean Superior craton of Laurentia, yielding a result that is quite unlike the drift interpreted in earlier studies using the APWP method. There are no early Palaeoproterozoic key poles for the other Archaean cratons that amalgamated to form Laurentia and Baltica prior to 1.8 Ga, so that a rigorous test of early Palaeoproterozoic reconstruction models is not possible. Key poles from Laurentia between ca. 1.46 and 1.267 Ga and Baltica between 1.63 and 1.265 Ga help to define, in a preliminary fashion, the early Mesoproterozoic drift of the two shields. The key pole age match at ca. 1.265 Ga is consistent with Baltica located adjacent to eastern Greenland, and geological considerations suggest that the most reasonable fit aligns the Labradorian belt of Laurentia with the Gothian belt of Baltica. Although there is limited support from non-key poles and key poles that are not matched in age for such a fit as early as ca. 1.8 Ga, no rigorous assessment will be possible until a match in key pole ages is achieved. In the late Mesoproterozoic to Neoproterozoic, Laurentia's drift is reasonably well documented by seven key poles between 1.235 and 0.73 Ga. There are no key poles in this period from Baltica, however, so that a ≈90° clockwise rotation of Baltica relative to Laurentia between 1.265 and 1.0 Ga, widely used in the literature, cannot be confirmed.
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| 5. |
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| 6. |
- Elming, Sten-åke, et al.
(författare)
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Drift history of Fennoscandia
- 2009
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Ingår i: A continent revealed. - Cambridge : Cambridge University Press.
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Luoto, T., et al.
(författare)
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New palaeoproterozoic palaeomagnetic data from Central and Northern Finland indicate a long-lived stable position for Fennoscandia
- 2023
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Ingår i: Geophysical Journal International. - : Oxford Univ Press. - 0956-540X .- 1365-246X. ; 235:2, s. 1810-1831
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Tidskriftsartikel (refereegranskat)abstract
- The Svecofennian gabbro intrusions coincide temporally with the global 2100-1800 Ma orogens related to the amalgamation of the Mesoproterozoic supercontinent Nuna. We provide a new reliable 1891-1875 Ma palaeomagnetic pole for Fennoscandia based on rock magnetic and palaeomagnetic studies on the Svecofennian intrusions in central Finland to fill gaps in the Palaeoproterozoic palaeomagnetic record. By using the new pole together with other global high-quality data, we propose a new palaeogeographic reconstruction at 1885 Ma. This, together with previous data, supports a long-lived relatively stable position of Fennoscandia at low to moderate latitudes at 1890-1790 Ma. Similar stable pole positions have also been obtained for Kalahari at 1880-1830 Ma, Siberia at 1880-1850 Ma, and possibly India at 1980-1775 Ma. A new reconstruction at the beginning of this period indicates the convergence of several cratons at 1885 Ma in the initial stages of the amalgamation of the Nuna supercontinent at low to moderate latitudes. The close proximity of cratons at low to moderate latitudes is further supported by global and regional palaeoclimatic indicators. Stable position of several cratons could indicate a global period of minimal apparent drift at ca. 1880-1830 Ma. Before this period, the global palaeomagnetic record indicates large back-and-forth swings, most prominently seen in the high-resolution 2020-1870 Ma Coronation loops of the Slave craton. These large back-and-forth movements have been explained as resulting from an unstable geomagnetic field or basin- or local-scale vertical-axis rotations. However, the most likely explanation is inertial interchange true polar wander (IITPW) events, which is in line with the suggestion of large amplitude true polar wander events during the formation of the supercontinent.
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| 8. |
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| 9. |
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| 10. |
- Pesonen, L. J., et al.
(författare)
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Catalogue of palaeomagnetic directions and poles from Fennoscandia : Archaean to tertiary
- 1991
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Ingår i: Tectonophysics. - 0040-1951 .- 1879-3266. ; 195:2-4, s. 151-207
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Tidskriftsartikel (refereegranskat)abstract
- Palaeomagnetic data from Fennoscandia ranging from the Archaean to the Tertiary have been compiled into a catalogue. The data are presented in table format, listing Precambrian data according to tectonomagmatic blocks and Late Precambrian-Phanerozoic data according to geological periods. Each pole is graded with the modified Briden-Duff classification scheme. The catalogue (complete to the end of 1988) contains 350 entries from 31 tectonomagmatic blocks and/or geological periods. Normal and reversed polarity data are listed separately to allow polarity asymmetries to be studied. Each entry also has an indexed abstract summarizing relevant information, such as the age of the rock, the age of the natural remanent magnetization and the basis for the assigned reliability grade. All the data are stored in the palaeomagnetic data bank, which will be updated annually with new data. The catalogue is the basic source of data for the microcomputer-based palaeomagnetic database for Fennoscandia now being compiled.
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