Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile

Geodynamic evolution and tectonostratigraphic terranes of northwestern Argentina and northern Chile

proposed, in part, because of the recent collection of geochronologic data indicating a 550 Magranulite forming event in East Gondwana and the observa...

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proposed, in part, because of the recent collection of geochronologic data indicating a 550 Magranulite forming event in East Gondwana and the observation that the apparent polar wander path for Gondwana does not form a spatially and temporally coherent pattern until roughly the same time. The Kuunga orogeny may have resulted from the collision between Australia and Antarctica with the rest of Gondwana. Gondwana assembly: the view from southern Africa and east Gondwana Wilson T.J., Grunow A.M. & Hanson R.E., JournalofGeodynamics, tectonism in 1997, 23/3-4 (263-286).Neoproterozoic-Cambrian Africa, Antarctica and formerly adjacent parts of East Gondwana records the final assembly of the Gondwana supercontinent. Here we compile recent data regarding the timing and kinematics of tectonism for critical parts of southern Africa and East Gondwana, focusing on the period between -650-500 Ma, and integrate these data into a regional framework in order to investigate aspects of the assembly of this portion of Gondwana. We use this information to address the following questions. What cratons remained coherent continental blocks between Rodinia break-up and Gondwana assembly? What were the configurations of Neoproterozoic-Cambrian oceans that separated these coherent blocks? When did the cratons reassemble into the Gondwana supercontinent?. Geodynamic evolution and tectonostratigrapbic terranes of northwestern Argentina and northern Chile Bahlburg H. & Herve F., Geological Society ofAmerica Bulletin, 1997, 109/7 (869-884).In Ordovician time, Gondwana in the area of northwestern Argentina and northern Chile had a west-facing active margin. The evolution of this margin culminated in the Ocloyic orogeny at the end of Ordovician time. This orogeny was caused by the collision of the allochthonous Arequipa-Antofalla terrane with this margin. The early Paleozoic evolution of northwestern Argentina and northern Chile contrasts markedly with the accretionary history of central Argentina and central Chile, where the Precordillera and Chilenia terranes docked in the Late Ordovician and Late Devonian periods, respectively. Results from an inspection of the available stratigraphic and geochronological data on sedimentary, volcanic, and plutonic units of the southern Central Andes of northern Chile and northwestern Argentina are described. Demembrement ante-mesozoique de la chaine varisque d’Europe occidentale et d’Afrique du Nord: role essentiel des grands decrochements transpressifs dextres accompagnant la rotation-translation horaire de I’Afrique durant le Stephanien (The Variscan ‘puzzle’ in western Europe and Africa: fits and effects of the Stephanian transpressive faulting during the clockwise late Paleozoic wandering of Gondwana)

Bard J.-P., Cotnptes Rendus - Academic des Sciences, Serie II. Sciencesde la Terre et des Planetes, 1997,324/9 (693-704).1n western Europe and North-Africa, the continental Stephanian is a period of major dextral transpressive faulting associated with the large clockwise rotation-translation of Africa (Gondwana) towards North America. This is the first reason why this belt has been strongly fragmented in numerous exotic segments before new redistributions during the circum-Mediterranean Alpine erogenic processes. This paper attempts to rebuild the ‘puzzle’ just before and after the Stephanian. There is an abridged English version.

GEOPHYSICS Estimates of the Earth’s spin (geographic) axis relative to Gondwana from glacial sediments and paleomagnetism Smith A.G., Earth-Science Reviews, 1997, 42/3 (161-179)The ice centres of the Permo-Carboniferous and late Ordovician glaciation of Gondwana have been quantitatively estimated. Their positions relative to the inferred mean paleomagnetic poles are not significantly different from those of the Quatemary ice centres relative to the present-day geographic poles. These data suggest it is unnecessary to postulate that the Paleozoic Earth had marked non-dipole components in the geomagnetic field, or that the average of the dipole axis was significantly different from the geographic axis or that there was a significantly different tilt to the geographic axis. The short-lived late Ordovician ice age is tentatively attributed to equally short episodes of faulting within Gondwana. These are believed to have created transient highlands which converted a previously snow-free summer climate into one in which snow could accumulate and build ice caps. Once the faulting ceased the topography decayed and the climate reverted to its previous snow-free summer state.

ENERGY SOURCES Rank and petrographic characters of Gondwana (Lower Permian) coal of Peninsular India Chakrabarti NC., Indian Minerals, 1996, 50/l-2 (41-52).Detailed study of coal from the major Gondwana (Lower Permian) basins of India has brought out certain differences in petrographic as well as rank characters. However, coal in general follows the ‘normal’ coalification trend. A lateral variation in composition and rank of coal in these basins is attributed to differential palaeodepositional environment and thermal gradient influencing the diagenetic processes in the basins of deposition. The conditions favoured formation of high-inertinite and low-rank non-caking coal. Coking propensity is found to be dependent on both rank and petrographic composition.

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