Gondwana

About: Gondwana is a research topic. Over the lifetime, 6078 publications have been published within this topic receiving 263050 citations. The topic is also known as: Gondwanaland.

The accretionary history of southern South America from the latest Proterozoic to the Late Palaeozoic: some palaeomagnetic constraints

Abstract: It is now accepted that southern South America was formed from several terranes of diverse origin and evolution. However, a detailed history of the accretionary processes has not been unravelled yet. Palaeomagnetism can play an important role in such an endeavour. Palaeomagnetic constraints on the tectonic evolution of this region in the Proterozoic and Palaeozoic are reviewed and discussed. Data from the Rio de la Plata craton suggest that this block was already attached to most major Gondwana blocks by the end of the Proterozoic and may have formed a single continental mass with Congo-Sao Francisco, West Nile and Arabia throughout most of the Vendian. A large ocean separating these cratons from Amazonia and West Africa, prior to Gondwana assembly, is supported by available palaeomagnetic data. To the west of the Rio de la Plata craton is the Pampia terrane. Despite lack of palaeomagnetic data, geological evidence supports a model of Early Cambrian collision between these blocks. An Early Ordovician magmatic arc, the Famatina-Eastern Puna belt, which had developed on the western margin of the already accreted Pampia terrane, shows a systematic pattern of large clockwise rotation that has been interpreted as representative of the whole terrane. The favoured tectonic model portrays a continental magmatic arc with a back-arc basin to the east that was closed when the terrane rotated. There is little doubt of a Laurentian origin for the Cuyania (Precordillera) terrane, given the amount and diversity of evidence, including palaeomagnetism. The tectonic mechanism for accretion and its timing are still controversial. New palaeomagnetic data from Late Ordovician rocks of Cuyania support the 'Laurentian plateau' hypothesis, which suggests that Cuyania was still linked to Laurentia well into the Ordovician. Nevertheless, these new data do not rule out the more generally favoured 'microcontinent model'. To the west of Cuyania is the Chilenia terrane, separated by a belt of ophiolites of Late Ordovician age. Very little is known about this terrane, although some U-Pb ages and Nd model ages point to a Laurentian origin for its basement. Lack of palaeomagnetic data precludes determining its kinematic evolution. The Arequipa-Antofalla block may actually be a composite terrane. Palaeomagnetic data obtained so far come exclusively from the southern Antofalla block. Recently acquired data in the western Puna of Argentina confirm the originally proposed distribution of Early Palaeozoic palaeomagnetic poles, which, despite several uncertainties, delineate a pattern of significant counterclockwise rotations with a possible anomaly in palaeolatitude for the late Cambrian. The data suggest a major tectonic discontinuity between the Eastern and Western Puna of Argentina in the Early Palaeozoic. Four palaeomagnetic poles of Devonian to Permian age from the North Patagonian Massif are consistent in position and age with the Gondwana apparent polar wander path, suggesting that both continental masses have not experienced major relative displacement since the Devonian. The data do not, however, rule out a restricted separation of Patagonia orthogonal to its northern boundary in the Early or Middle Palaeozoic and subsequent collision in the Late Palaeozoic. © The Geological Society of London 2005.

Provincias magmaticas acidas y evolucion tectonica de Gondwana: Andes chilenos (28-31°S)

Abstract: . The batholiths of the Andean Cordillera in the Atacama and Coquimbo Regions (28-31°S) reflect tectonic processes associated with the evolving margin of the Gondwana supercontinent. The batholiths consist of the Carbonilerous-Lower Permian Elqui Superunit which records the final assembly of Gondwana, and the Permian-Triassic (Lower Jurassic?) Ingaguas Superunit, which coincides with the period of stability of the supercontinent. These events are tied to those occurring along the Gondwana margin from Peru to Australia. The oldest Elqui unit, Guanta, is composed of calc-alkaline tonalites and granodiorites formed along an active continental margin. These granitoids are intruded by leucocratic peraluminous granitoids (Cochiguas and El Volcan units) derived from melting of variable crustal sources. Some of these granitoids have trace element signatures consistent with a high pressure residual mineralogy suggesting that they formed by melting of a thickened crust. All of the Elqui granitoids are mesozonal and show evidence of contemporaneous and post-emplacement deformation. Their uplift is contemporaneous with a compressional deformation (San Rafael Phase) in the Argentine foreland. The Ingaguas Superunit is an association of epizonal, post-collisional, intrusives which include granitoids derived from deep levels in a garnet-bearing thickened crust (Los Carricitos Unit) and hypersilicic, calc-alkaline to transitional A-type granites, indicating extensive crustal melting of a garnet-poor crust. These granites and the synchronous Pastos Blancos Rhyolites are part of the Choiyoi Magmatic Province which extends for more than 2,500 km along the Central and Southern Andes. Regional considerations suggest that the uplift of the Elqui Superunit and the San Rafael Phase could have resulted from the oblique collision of an allochthonous block to the west in the mid-Permian. This collision could explain crustal thickening and the termination of subduction and block rotations in the Argentine Frontal Cordillera. The removal of the inactive subducted plate would favor decompressional melting, generating large volumes of basalt that could accumulate at the base of the crust and produce the crustal melting that formed the Choiyoi Province. A similar Permian collision has also been suggested in the New England Fold 8elt in Australia. These collisions coincide with the end of the rapid movement of Gondwana relative to the South Pole. In the central part of the Gondwana margin from Patagonia to Antarctica, subduction continued until the Jurassic. 'Thermal blanketing' of the mantle by the stationary supercontinent resulted in accumulation of basaltic magmas at the crust-mantle boundary. The basaltic magmas accumulated below the collage of arc magmatic rocks and exotic blocks accreted in the Paleozoie produced extensive melting forming the Gondwana granite-rhyolite provinces. These events preceded the Jurassic dispersal of the Gondwana supercontinent in this region.

Palaeomagnetic Studies in the British Caledonides-VI Regional and Global Implications

Abstract: Summary Palaeozoic palaeomagnetic data from the British Isles are reviewed and are found to be consistent with erratic polar shift from the vicinity of 10° N, 180° E in the Ordovician to 0°, 145° E in the Siluro-Devonian and to 25° N, 160° E in the early Carboniferous. The Cambrian pole is less well established near 25° N, 170° E. The rates and times of shifts are discussed. World-wide palaeomagnetic data suggest the existence of three groups of continents in the Early and Middle Palaeozoic—the Gondwanan, Euramerican and Siberian groups—separated by large oceans which closed in the Late Palaeozoic along the lines of the Hercynides and Uralides. The data from Gondwana and Siberia are internally consistent and each may have been a single plate to which only peripheral slices were added subsequently. Data from Euramerica are less coherent. The most probable explanation seems to be that this group of continents was loosely-knit and consisted of the North American and the Baltic/Russian plates (which joined in the Silurian on the site of the Scandinavian Caledonides) and the British Isles sub-plate which joined in the Devonian (on previously unrecognized sutures lying in the present North Atlantic and North Sea respectively). This interpretation takes all the data at face value and assumes that time-coverage is adequate in all parts of the region. Alternatively, if time-coverage was not adequate, Britain might have been part of the North American plate, but further work is required to discriminate between these interpretations. Palaeomagnetic evidence from the British Isles also indicates that little or no closure has taken place across the British Caledonides since Early Ordovician time. If so the British Isles sub-plate may have been rotated in azimuth as well as being transported laterally before joining the Euramerican plate. Examples of rotation and remagnetization on a more local scale are cited, and are ascribed to tectonic and thermal effects of orogeny respectively. The Euramerica and Gondwana groups were already close together by early Carboniferous times, which is distinctly earlier than the Hercynian-Alleghenian orogenic belt which may mark their juncture. It may be generally true that large scale crustal drift, involving consumption of a large area of oceanic crust between two continents, significantly predates the orogenic belt which forms when the two continents have met. If this is so, large scale closure across the British Caledonides might have occurred in Precambrian or Cambrian time, but palaeomagnetic data are not yet adequate to evaluate this.