Cordilleran Andes and marginal Andes: A review of Andean geology north of the Arica elbow (18°s)

Mégard, François

doi:10.1029/gd018p0071

Cited by 76 publications

(71 citation statements)

References 70 publications

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“…As for most Late Cretaceous -Paleogene accretions in Ecuador (Jaillard et al, 1997;Reynaud et al, 1999), the accretion of the Raspas oceanic plateau occurred without obduction. In this model, underthrusting of parts of accreted oceanic terranes might contribute to the crustal thickening of the upper plate in this part of the Andes, as already suggested by Megard (1987Megard ( , 1989 in Ecuador and further documented in Colombia by Weber et al (2002).…”

Section: Discussionmentioning

confidence: 69%

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

et al. 2002

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The Raspas Metamorphic Complex of southwestern Ecuador is regarded as the southernmost remnant of oceanic and continental terranes accreted in the latest Jurassic -Early Cretaceous. It consists of variably metamorphosed rock types. (1) Mafic and ultramafic rocks metamorphosed under high-pressure (HP) conditions (eclogite facies) show oceanic plateau affinities with flat REE chondrite-normalized patterns, eNd 150 Ma ranging from + 4.6 to 9.8 and initial Pb isotopic ratios intermediate between MORB and OIB. (2) Sedimentary rocks metamorphosed under eclogitic conditions exhibit LREE enriched patterns, strong negative Eu anomalies, Rb, Nb, U, Th, Pb enrichments, low eNd 150 Ma values (from À 6.4 to À 9.5), and high initial 87 Sr/ 86 Sr and 206,207,208 Pb/ 204 Pb isotopic ratios suggesting they were originally sediments derived from the erosion of an old continental crust. (3) Epidote-bearing amphibolites show N-MORB affinities with LREE depleted patterns, LILE, Zr, Hf and Th depletion, high eNd 150 Ma (> + 10) and low initial Pb isotopic ratios. The present-day well defined internal structure of the Raspas Metamorphic Complex seems to be inconsistent with the formerly proposed interpretation of a ''tectonic mélange''. The association of oceanic plateau rocks and continent-derived sediments both metamorphosed in HP conditions suggests that the thin edge of the oceanic plateau first entered the subduction zone and dragged sediments downward of the accretionary wedge along the Wadatti -Benioff zone. Subsequently, when its thickest part arrived into the subduction zone, the oceanic plateau jammed the subduction processes, due to its high buoyancy. In Ecuador and Colombia, the latest Jurassic -Early Cretaceous suture involves HP oceanic plateau rocks and N-MORB rocks metamorphosed under lower grades, suggesting a composite or polyphase nature for the latest Jurassic -Early Cretaceous accretionary event. D

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Section: Discussionmentioning

confidence: 69%

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

et al. 2002

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“…As placas de Nazca e da Antártica e o septo do Chile que as separa entraram em subducção, e este processo foi responsável pela edificação de cadeias acrescionárias muito típicas, estreitas e lineares, orientadas norte-sul, e ainda pela criação e deformação de ambientes relacionados aos arcos, e o retrabalhamento do embasamento fortemente estruturado. Os vários picos de atividade orogênica são quase contínuos desde o Triássico Superior, consoante os esquemas de Mégard (1987) e Hervé et ai. (1987), entre os mais destacados.…”

Section: Figura 5 -Os Diferentes 'Terrenos "Acrescionados àS Margens unclassified

America Do Sul: Quatro Fusões, Quatro Fissões E O Processo Acrescionário Andino

Neves

1999

RBG

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SOUTH AMERICA: FOUR FUSIONS, FOUR FISSIONSAND THE ANDEAN ACCRECIONARY PROCESSThe aim of this article is try to interpret -as a first approximation-the evolution of the South American continent from the point of view of the Supercontinents Theory of the new Global Tectonics. It is preliminarly reiterated that the individualization of this lithospheric segment as a continent (geotectonic sense) is a fact younger than 100 Ma old, although we know about a crustal evolutionary history -as participant of other continental configurations as older as 3.5 Ga. Most of those previous continental configurations were larger in size than this now presented. Four major processes of (super)continental agglutination are being identified and they will be described, three of them Precambrian in age in the upper part of the Proterozoic eras (Paleoproterozoic, Mesoproterozoic and Neoproterozoic). The last of these agglutination processes took place in Early Mesozoic times, after a long and complex Paleozoic history of accretions and interior collisions. Following each of these agglutinantion events there were wide processes of continental break up (taphrogenesis) and dispersion ( drift) of the descendant lithospheric segments, as result of the dissipation of heat from astenospheric realms. The last process of dispersion, after the Triassic continental collage (Pangea supercontinent) is still under way, in terms of the present grouwth of the Atlantic Ocean. Só, it hás partially been coeval of the concurrent accretionary processes in the Andean Chain, which are somehow leading to a future continental agglutination (when of the disappearance of The Pacific and Caribbean oceanic segments). Such development of these two different and concurrent processes (at the western and eastern margin) is the responsible for the present shape and concept of the continent, which hás to be understood just as a particular instance (and configuration) of an ongoing complex evolutionary trajectory of this continental lithospheric segment.Keywords: fusion, fission, collage, supercontinent, Brasiliano, taphrogenesis RESUMO O objetivo deste artigo é tentar interpretar -em primeira aproximação -a evolução do continente Sul-Americano do ponto de vista da Teoria dos Supercontinentes da nova Tectônica Global. Preliminarmente é reiterado que a individualização deste segmento litosférico como continente (sentido geotectônico) é um fato novo, mais jovem que 100 Ma, ainda que nós saibamos de uma história crustal evolutiva tão velha quanto 3,5 Ga, como participante de outras configurações continentais. A maioria destas configurações continentais prévias foram maiores em dimensões que a atualmente apresentada. Quatro processos maiores de aglutinação (super) continental são identificados e aqui descritos, três deles de idade pré-cambriana, da parte superior das eras do Proterozóico (Paleoproterozóico, Mesoproterozóico e Neoproterozóico). O último destes processos de aglutinação teve lugar no início do Permiano, após uma complexa e longa história de colagens e ...

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“…Spreading and subsidence have lead to a thinning of the continental crust. The fact that the two subfields of ore deposits in the central Peruvian marginal basin (stage lie) are slightly more radiogenic than those near the magmatic arc in northern Chile Megard (1987) (stages lib and lid) could be attributed to segmentation factors, i.e., to systematic differences in the crust and/or upper mantle along the orogene. However, the considerable spread in the 206 Pb/ 204 Pb ratios of the Peruvian deposits makes it more reasonable to assume that the spread and the relatively increased 206 Pb/ 204 Pb ratios are the result of different amounts of upper crustal contamination of MORB material.…”

Section: Metal Sources In the Different Geotectonic Positionsmentioning

confidence: 99%

Metal Sources in Stratabound Ore Deposits in the Andes (Andean Cycle) — Lead Isotopic Constraints

Fontboté

Gunnesch

Baumann

1990

Stratabound Ore Deposits in the Andes

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Cordilleran Andes and marginal Andes: A review of Andean geology north of the Arica elbow (18°s)

Cited by 76 publications

References 70 publications

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

America Do Sul: Quatro Fusões, Quatro Fissões E O Processo Acrescionário Andino

Metal Sources in Stratabound Ore Deposits in the Andes (Andean Cycle) — Lead Isotopic Constraints

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