Nous agissons comme contrôle qualité externe et incorruptible.Chacun peut nous faire des remontrances. Le devoir de résipiscence s'applique à tous.
Florian a écrit :> Bonjour,> > Comme par hasard, voilà une confirmation du positionnement de> l'australie et de l'antarctique à l'ouest de l'amérique du Nord il y a> 1.4 Ga, exactement comme le modèle de Maxlow le prévoit avant le Trias,> alors que l'océan Pacifique à plancher basaltique n'était pas encore> ouvert.> > Je n'ai pas encore lu l'article, mais le résumé mentionne aussi une> proximité entre Australie, Sibérie et Chine du sud qui semble> contradictoire dans les reconstitutions de Rodinia, mais colle aussi> parfaitement avec le modèle de Maxlow.> > <http://nachon.free.fr/Maxlow/Maxlowpacific.png>> > Par quel miracle un modèle *farfelu* collerait-il avec *toutes* les> données récentes tandis que le modèle actuel ne s'en accomode pas?> > La réponse est simple.> Il n'y a pas de miracle: quand le modèle est le bon, il fini *toujours*> par s'imposer.> > > Le résumé en anglais de l'article de Science du 11 juillet 2008:> > "The positions of Laurentia and other landmasses in the Precambrian> supercontinent of Rodinia are controversial. Although geological and> isotopic data support an East Antarctic fit with western Laurentia,> alternative reconstructions favor the juxtaposition of Australia,> Siberia, or South China. New geologic, age, and isotopic data provide a> positive test of the juxtaposition with East Antarctica: Neodymium> isotopes of Neoproterozoic rift-margin strata are similar; hafnium> isotopes of 1.4-billion-year-old Antarctic-margin detrital zircons match> those in Laurentian granites of similar age; and a glacial clast of> A-type granite has a uraniun-lead zircon age of 1440 million years, an> epsilon-hafnium initial value of +7, and an epsilon-neodymium initial> value of +4. These tracers indicate the presence of granites in East> Antarctica having the same age, geochemical properties, and isotopic> signatures as the distinctive granites in Laurentia."> > <http://www.sciencemag.org/cgi/content/short/321/5886/235>
Apprenez à lire l'anglais Lavau cela vous occupera bien jusqu'à la finde l'été:"The positions of Laurentia and other landmasses in the Precambriansupercontinent of *Rodinia are controversial*. Although geological andisotopic data support an East Antarctic fit with western Laurentia,alternative reconstructions favor the juxtaposition of Australia,Siberia, or South China."-- Florian "Toute vérité franchit trois étapes. D'abord elle est ridiculisée. Ensuite, elle subit une forte opposition. Puis, elle est considérée comme ayant toujours été une évidence." - Arthur Schopenhauer
HPP-01 General contributions to Precambrian geology Raimo Lahtinen, S. Wilde, J. PercivalThe Precambrian represents a large part of Earth's history and encompasses the formation of the Earth, onset of plate tectonics, irreversible oxidation of atmosphere and hydrosphere to the evolution of complex multicellular organisms, including the first animals. There is still a controversy as to when modern-style plate tectonics started. Subduction-type processes probably operated already during Neoarchean or earlier but eclogites and UHP rocks are rare before the Neoproterozoic era. The exponential decline of Earth's radiogenic heat production has affected the formation and evolution of continental crust, lithospheric mantle and the style of plate interaction. Crustal growth is dominantly a Precambrian phenomena and the net crustal mass input from (Meso- )Neoproterozoic to present seems to be only 10-20% or less. The Archaean-Proterozoic transition is one of several critical intervals in Earth history when the terrestrial systems were experiencing rapid, global-scale changes seen as world-wide occurrences of glaciation, red beds and carbon isotope excursions. The role of Precambrian supercontinents Kenorland, Nuna, Columbia and Rodinia is very important in understanding the mantle dynamics, crustal growth and hydroatmospheric evolution of the Earth system. For this general symposium, we invite presentations of the field aspects, petrology, geochemistry, structural geology and isotope geology of Precambrian geology and presentations of models bearing on the evolution of Precambrian lithosphere.HPP-04 From Rodinia to Nuna and beyond: Precambrian supercontinent reconstructions delving deeper in time Svetlana Bogdanova, David Evans, Mauro Cesar Geraldes, Hervé Théveniaut (IGCP 440 and IGCP 509)Accurate descriptions of pre-Pangean paleogeographic reconstructions will be essential for understanding the role of supercontinents in mantle dynamics, as well as providing the boundary conditions for studies in global climate and hydroatmospheric chemistry of the evolving Earth system. Much recent work has advanced our perception of the Neoproterozoic supercontinent Rodinia, although some important questions remain unresolved. Rodinia's predecessor, the Paleoproterozoic supercontinent Nuna (or Columbia), is only beginning to take form. This symposium of the co-operating IGCP Projects 440 (Rodinia Assembly and Break-up) and 509 (Paleoproterozoic Supercontinents and Global Evolution) welcomes presentations of new tectonostratigraphic and paleomagnetic results bearing on Rodinia, Nuna, and earlier reconstructions, which are bound together both in their geological evolution and the methods we use to discover them.HPP-05 Evolution of Archean crust Yildirim Dilek, Harald Furnes, Maarten de WitThe role of plate tectonics in the evolution of Phanerozoic and Proterozoic crust is well established, but is a subject of debate regarding the Archean history. Crustal growth and differentiation through punctuated events (i.e. emplacement of mantle 'super-plumes') versus continuous subduction processes and whether Archean crust was too weak and mobile to behave as in rigid plates are fundamental questions in geodynamics. The occurrence of boninites, adakites, Mg-andesites, and ophiolites in some of the Archean greenstone belts suggests that Phanerozoic-like subduction zone tectonics may have been operating as early as 3.8 Ga. Specific questions to explore include the nature of magmatic and tectonic accretion of Archean continental crust and cratonization processes; sources of mantle magmatism; geodynamic evolution of greenstone belts, oceanic crust, and Archean ocean basins; and, the operation of plume activities and subduction processes in the Archean. This session is designed to evaluate the diverse dataset from the Archean rock record in order to address these questions and to better understand the nature and tempo of those processes involved in development of the Archean crust and their implications for the planetary evolution.HPP-06 The evolving Earth system through Archaean-Palaeoproterozoic transition Victor A. Melezhik, David A.D. Evans, Ariel Anbar (IGCP509, ICDP FAR-DEEP, Kaapvaal Drilling Project, ABDP)The Archaean-Proterozoic transition is one of several critical intervals in Earth history when the terrestrial systems were experiencing rapid, global-scale changes. The sequence of events includes the first global icehouse event, oxidation of the atmosphere and emergence of an aerobic world, and global perturbations in the carbon cycle, all representing the greatest challenge to life on Earth since its beginning. Overall, there is incomplete understanding of the timing, cause(s) and specifically the biological consequences with respect to the most profound change in surface environments during the early history of planet Earth. This session invites presentations of recent data and models bearing on the operation and interactions of various terrestrial systems leading to emerging modern-style geodynamics, irreversible oxidation of atmosphere and hydrosphere, drastic modification in ocean chemistry and isotope geochemistry, climatic instability and biological innovations including changes in C, S, P and N cycling. The invitation is also extended in to the understanding of extraterrestrial impacts on various terrestrial systems throughout this important period of Earth history.HPP-07 Late Neoproterozoic orogenic belts and assembly of Gondwana Bernard Bingen, Joachim Jacobs, Alan S. Collins, Giulio Viola, Mark A. Smethurst, Daud Jamal Invited speakers: Sergei Pisarevsky, Alan CollinsSupercontinent Gondwana formed at the end of the Neoproterozoic, by assembly of Austral cratons, along Pan-African – Brasiliano orogenic belts. The Pan-African – Brasiliano system has multiple branches through Australia, India, Antarctica, Africa and South America, and qualifies as one of the largest orogenies that has affected planet Earth. Improved reconstruction of this orogenic cycle, and evaluation of its impact on Phanerozoic Earth history requires global and regional studies, integrating innovative geological mapping, stratigraphy, tectonics, geochronology, geochemistry, isotope geochemistry, petrology, geophysics, and paleomagnetism.
The making and unmaking of a supercontinent: Rodinia revisitedJoseph G. Meerta, Corresponding Author Contact Information, E-mail The Corresponding Author and Trond H. Torsvikba Department of Geological Sciences, University of Florida, 241 Williamson Hall, PO Box 11210, Gainesville, FL 32611, USAb Academy of Sciences (VISTA), c/o Geodynamics Center, Geological Survey of Norway, Leif Eirikssons vei 39, Trondheim 7491, NorwayAbstractDuring the Neoproterozoic, a supercontinent commonly referred to as Rodinia, supposedly formed at ca. 1100 Ma and broke apart at around 800–700 Ma. However, continental fits (e.g., Laurentia vs. Australia–Antarctica, Greater India vs. Australia–Antarctica, Amazonian craton [AC] vs. Laurentia, etc.) and the timing of break-up as postulated in a number of influential papers in the early–mid-1990s are at odds with palaeomagnetic data. The new data necessitate an entirely different fit of East Gondwana elements and western Gondwana and call into question the validity of SWEAT, AUSWUS models and other variants. At the same time, the geologic record indicates that Neoproterozoic and early Paleozoic rift margins surrounded Laurentia, while similar-aged collisional belts dissected Gondwana. Collectively, these geologic observations indicate the breakup of one supercontinent followed rapidly by the assembly of another smaller supercontinent (Gondwana). At issue, and what we outline in this paper, is the difficulty in determining the exact geometry of the earlier supercontinent. We discuss the various models that have been proposed and highlight key areas of contention. These include the relationships between the various ‘external’ Rodinian cratons to Laurentia (e.g., Baltica, Siberia and Amazonia), the notion of true polar wander (TPW), the lack of reliable paleomagnetic data and the enigmatic interpretations of the geologic data. Thus, we acknowledge the existence of a Rodinia supercontinent, but we can place only loose constraints on its exact disposition at any point in time.Author Keywords: Rodinia; Paleomagnetism; Gondwana; Supercontinent; True polar wanderArticle Outline1. Introduction2. Paleomagnetic constraints on the Neoproterozoic supercontinent2.1. 1100–900 Ma: Laurentia and Baltica2.2. 1100–900 Ma: Amazonian craton (AC)2.3. 1100–900 Ma: Kalahari craton2.4. 1100–900 Ma: Congo–Sao Francisco (CSF) craton2.5. 1075–990 Ma Siberian craton2.6. India 1100–1000 Ma3. True polar wander?4. The breakup of Rodinia: 800–700 Ma5. 580 Ma and younger reconstructions6. ConclusionsAcknowledgementsAppendix A. Euler poles (clockwise)ReferencesFig. 1. The ‘traditional’ model of Rodinia adopted from [Dalziel, 1997] and [Torsvik et al., 1996]. The model posits two rifting events, one along the present-day western margin of Laurentia sometime between 800 and 700 Ma, and a second along the present-day eastern margin of Laurentia between 600 and 550 Ma.Fig. 2. (a) Proposed APWP for Laurentia based on poles listed in Table 1. Individual poles (on all figures) are keyed to their numbered entry (key ages are listed on the figure) in the table. Note: shaded group of poles labeled “W” are poles used by [Weil et al., 1998] to constrain the direction of the North American APWP. (b) Proposed APWP for Baltica (assumed north poles) from 1070 to 930 Ma based on the entries in Table 1. (c) Baltica poles rotated to the Laurentian APWP (shaded) using the fit of [Bullard et al., 1965] (rotated 38° clockwise about an euler pole located at 88°N, 27°E). Inset figure shows the continental reconstruction (all inset figures show a North pole projection: Laurentia fixed). (d) Baltica poles rotated to the Laurentian APWP (shaded) using the fit of [Piper, 1987] (rotated 66.5° clockwise about an euler pole at 80.5°N, 274°E). Inset figure shows the continental reconstruction (e) Baltica poles rotated to the Laurentian APWP (shaded) using the fit of [Torsvik et al., 1996] (rotated 50° clockwise about an euler pole located at 72°N, 43°E). Inset figure shows the continental reconstruction and (f) Baltica poles rotated to the Laurentian APWP (shaded) using an alternative fit (this study; rotated 35° clockwise about an euler pole located at 70°N, 211°E). Inset figure shows the continental reconstruction.
À propos de ggl.ulaval.ca, comment Florian explique l'imagehttp://www.ggl.ulaval.ca/personnel/bourque/s1/1.13.gif dans http://www.ggl.ulaval.ca/personnel/bourque/s1/magnetisme.terr.html , qui indique que l'Europe et l'Amérique du Nord étaient proches au Jurassique, éloignés au Permien, moins éloignés au Carbonifère ? Non fiabilité du paléomagnétisme et incompétence des géologues paléomagnéticiens ?