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| 2. |
- Bibikova, E. V., et al.
(författare)
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Sarmatia-Volgo-Uralia junction zone: Isotopic-geochronologic characteristic of supracrustal rocks and granitoids
- 2009
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Ingår i: Stratigraphy and Geological Correlation. - 0869-5938. ; 17:6, s. 561-573
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Tidskriftsartikel (refereegranskat)abstract
- The geochronologic (U-Pb isotopic system of zircons) and isotopic-geochemical (Sm-Nd isotopic system of the bulk rock) studies were performed along the profile extending from the eastern Sarmatia (in the west) to the Middle Volga megablock of Volgo-Uralia (in the east), i.e., across the entire junction zone for dating the integration of Sarmatia and Volgo-Uralia, representing two segments of the East European Craton. It is established that the examined rocks are characterized by the Paleoproterozoic Nd isotopic model age, which varies from 2.1 and 2.4 Ga, except for some samples indicating a similar age of the crust through the entire Sarmatia-Volgo-Uralia junction zone. The highly metamorphosed complexes of the granulite and amphibolite facies constituting the southwestern margin of Volgo-Uralia are Paleoproterozoic, not Archean, in age, contrary to previous views. Two Early Paleoproterozoic lithotectonic complexes are defined in Volgo-Uralia: South Volga metasedimentary and Tersa metasedimentary-volcanogenic. The obtained data confirm the asynchronous integration of individual segments into the East European Craton: the integration of Sarmatia and Volgo-Uralia approximately 2100-2000 Ma ago was followed by the conjunction of this newly-formed continent with Fennoscandia ca. 1800 Ma ago.
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| 3. |
- Bogdanova, Svetlana, et al.
(författare)
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Assembly and Breakup of Rodinia (Some results of IGCP project 440)
- 2009
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Ingår i: Stratigraphy and Geological Correlation. - 0869-5938. ; 17:3, s. 259-274
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Forskningsöversikt (refereegranskat)abstract
- The principal results of project 440 "Assembly and Breakup of Rodinia" of the International Geological Correlation Programme (IGCP) are reviewed in this work. A map of that supercontinent compiled using geological and paleomagnetic data describes global paleogeography 900 Ma ago. The assembly of Rodinia, which comprised most of Precambrian continental blocks, lasted ca. 400 m.y. (from 1300 to 900 Ma). Its breakup presumably triggered by mantle superplume took place between 830 and 650 Ma. The correlation between tectonic events in different continental blocks is considered. Some problems concerning the Rodinia reconstruction and history, e.g., the slow growth of juvenile crust and effects of mantle-plume events during the amalgamation period and of glaciations at the breakup time, are discussed. The latter caused changes in the biosphere and climate, whereas postglacial periods stimulated progress in biota evolution.
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| 10. |
- Johansson, Ake, et al.
(författare)
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A revised geochronology for the Blekinge Province, southern Sweden
- 2006
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Ingår i: GFF. - 2000-0863. ; 128, s. 287-302
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Tidskriftsartikel (refereegranskat)abstract
- Zircon grains from nine samples of metavolcanic rocks, gneisses, granitoids and migmatites from the Blekinge Province in southeasternmost Sweden have been dated by U-Pb using ion microprobe. The results suggest that most of the Blekinge bedrock was formed within a narrow time interval of 1.77-1.75 Ga, including the Vastana supracrustal formation and 'coastal gneisses' previously dated to c. 1.70 Ga. One sample, the 1.81 Ga Nattraby gneissic granite, appears to represent a sliver of slightly older proto-crust. An age of c. 1.75 Ga for an aplitic granite crosscutting the deformed Tving granitoids in eastern Blekinge brackets their deformation to between 1.77 and 1.75 Ga, whereas zircon grains of similar age from a migmatite neosome at Lindo may be inherited, making the result inconclusive. Thin metamorphic zircon overgrowths and resetting of the U-Pb system in titanite indicate a regional tectonothermal event at 1.45 to 1.40 Ga, accompanying the intrusion of the Karlshamn-type granites. The crust of the Blekinge Province thus was formed at 1.77-1.75 Ga from relatively juvenile sources in a subduction-related environment along the southern edge of Fennoscandia. It was deformed and partly uplifted relative to the undeformed TIB-1 granitoids of the Smaland block further north, prior to the intrusion of the Karlshamn-type granites at 1.45 Ga.
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| 11. |
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| 12. |
- Li, Z. X., et al.
(författare)
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How not to build a supercontinent: A reply to JDA Piper
- 2009
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268. ; 174:1-2, s. 208-214
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The hypothesized existence of a Neoproterozoic supercontinent called Rodinia is based on a series of geological and paleomagnetic observations, with details about the configuration and evolution of this supercontinent still a matter for debate. Regrettably, we found that the comment by Piper (this volume) lacks scientific objectiveness. The 'Palaeopangaea' that he promotes is, in our view, based on incorrect application of paleomagnetic data, and is not supported by geological evidence. (C) 2009 Elsevier B.V. All rights reserved.
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