scholarly journals Igneous Rock Associations 25. Pre-Pliocene Andean Magmatism in Chile

2020 ◽  
pp. 65-82
Author(s):  
Veronica Oliveros ◽  
Pablo Moreno-Yaeger ◽  
Laura Flores
Keyword(s):  
Middle Eocene ◽  
Oceanic Lithosphere ◽  
Isotopic Signature ◽  
Trace Element Composition ◽  
Igneous Rocks ◽  
Physical Parameters ◽  
Magmatic Arc ◽  
The Andes ◽  
Majeure Partie ◽  
Dip Angle

Andean-type magmatism and the term ‘andesite’ are often used as the norm for the results of subduction of oceanic lithosphere under a continent, and the typical rock formed. Although the Andes chain occupies the whole western margin of South America, the most comprehensively studied rocks occur in the present-day Chilean territory and are the focus of this paper. Andean magmatism in this region developed from the Rhaetian-Hettangian boundary (ca. 200 Ma) to the present and represents the activity of a long-lived continental magmatic arc. This paper discusses Pre-Pleistocene volcanic, plutonic, and volcano-sedimentary rocks related to the arc that cover most of the continental mass of Chile (between the Pacific coast and the High Andes) between the latitudes of 18° and 50°S. They comprise most of the range of sub-alkaline igneous rocks, from gabbro to monzogranite and from basalt to rhyolite, but are dominated by the tonalite-granodiorite and andesite example members. Variations in the petrographic characteristics, major and trace element composition and isotopic signature of the igneous rocks can be correlated to changes in the physical parameters of the subduction zone, such as dip angle of the subducting slab, convergence rate and angle of convergence. Early Andean magmatic products (Jurassic to Early Cretaceous) are found along the Coastal Cordillera in the westernmost part of the Andes. The rock record of the subsequent stages (Late Cretaceous, Paleocene–Early Eocene, Middle Eocene–Oligocene, Miocene) is progressively shifted to the east, reflecting migration of the magmatic front towards the continent. Tectonic segmentation of the convergent margin, as attested by the magmatic record, may have occurred throughout the Andean life span but it is particularly evident from the Eocene onwards, where the evolution of the northern part of the Chilean Andes (north of 27°S latitude) is very different to that of the southern segment (south of 27°S latitude). RÉSUMÉLe magmatisme de type andin et le terme « andésite » sont souvent les appellations utilisées pour décrire les résultats de la subduction de la lithosphère océanique sous un continent, et la roche typique formée. Bien que la chaîne des Andes occupe toute la marge ouest de l'Amérique du Sud, les roches les plus étudiées se trouvent dans le territoire chilien actuel et sont l'objet de cet article. Le magmatisme andin dans cette région s'est développé depuis la limite rhéto-hettangienne (environ 200 Ma) jusqu'à aujourd'hui et représente l'activité d'un arc magmatique continental persistant. Cet article a pour sujet les roches volcaniques, plutoniques et volcano-sédimentaires du pré-Pléistocène liées à l'arc qui couvrent la majeure partie de la masse continentale du Chili (entre la côte du Pacifique et les Hautes Andes) entre les latitudes de 18° et 50°S. Elles comprennent la majeure partie de la gamme de roches ignées sous-alcalines, du gabbro à la monzogranite et du basalte à la rhyolite, mais sont dominées par des roches de type tonalite-granodiorite et andésite. Les variations des caractéristiques pétrographiques, de la composition des éléments majeurs et traces et de la signature isotopique des roches ignées peuvent être corrélées aux changements des paramètres physiques de la zone de subduction, tels que l'angle de pendage de la plaque plongeante, le taux de convergence et l'angle de convergence. Les premiers produits magmatiques andins (du Jurassique au Crétacé inférieur) se trouvent le long de la Cordillère de la Côte dans la partie la plus occidentale des Andes. La succession de roche des stades suivants (Crétacé supérieur, Paléocène – Éocène inférieur, Éocène moyen – Oligocène, Miocène) est progressivement déplacée vers l'est, reflétant la migration du front magmatique vers le continent. La segmentation tectonique de la marge convergente, comme l'attestent les enregistrements magmatiques, peut avoir eu lieu tout au long de la formation des Andes, mais elle est particulièrement évidente à partir de l'Éocène, où l'évolution de la partie septentrionale des Andes chiliennes (au nord de 27°S de latitude) est très différente de celle du segment méridional (sud de 27°S de latitude).

Subduction-related magmatism of late Ordovician age in eastern England

1993 ◽  
Vol 130 (5) ◽  
pp. 647-656 ◽  
Author(s):  
T. C. Pharaoh ◽  
T. S. Brewer ◽  
P. C. Webb
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Late Ordovician ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Geochemical Composition ◽  
Magmatic Arc ◽  
Hypabyssal Intrusions ◽  
Deep Boreholes ◽  
Intrusive Suite

AbstractDeep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the Caledonian basement in eastern England. The isotopic compositions of these rocks reveal that many of them are of late Ordovician age (440–460 Ma), and their geochemical compositions suggest calc–alkaline affinities. The intermediate (diorite-tonalite) plutonic rocks are associated with a prominent northwest–southeast trending belt of aeromagnetic anomalies extending from Derby to St Ives, Hunts., which is interpreted to work the plutonic core of a calc-alkaline magmatic arc. It is inferred that this arc was generated by the subduction of oceanic lithosphere, possibly from the Tornquist Sea, in a south or southwest direction beneath the Midlands Microcraton in late Ordovician times. The age and geochemical composition of concealed Ordovician volcanic rocks in eastern England, and hypabyssal intrusions of the Midlands Minor Intrusive Suite in central England, is compatible with such a hypothesis.

The Peninsular Ranges Batholith: an insight into the evolution of the Cordilleran batholiths of southwestern North America

1988 ◽  
Vol 79 (2-3) ◽  
pp. 105-121 ◽  
Author(s):  
L. T. Silver ◽  
B. W. Chappell
Keyword(s):  
Baja California ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Radiometric Dating ◽  
Island Arcs ◽  
Magmatic Arc ◽  
Metasedimentary Rocks ◽  
Basaltic Composition ◽  
Peninsular Ranges ◽  
General Aspects

ABSTRACTThe Peninsular Ranges Batholith of southern and Baja California is the largest segment of a Cretaceous magmatic arc that was once continuous from northern California to southern Baja California. In this batholith, the emplacement of igneous rocks took place during a single sequence of magmatic activity, unlike many of the other components of the Cordilleran batholiths which formed during successive separate magmatic episodes. Detailed radiometric dating has shown that it is a composite of two batholiths. A western batholith, which was more heterogeneous in composition, formed as a static magmatic arc between 140 and 105 Ma and was intrusive in part into related volcanic rocks. The eastern batholith formed as a laterally transgressing arc which moved away from those older rocks between 105 and 80 Ma, intruding metasedimentary rocks. Rocks of the batholith range from undersaturated gabbros through to felsic granites, but tonalite is the most abundant rock throughout. Perhaps better than elsewhere in the Cordillera, the batholith shows beautifully developed asymmetries in chemical and isotopic properties. The main gradients in chemical composition from W to E are found among the trace elements, with Ba, Sr, Nb and the light rare earth elements increasing by more than a factor of two, and P, Rb, Pb, Th, Zn and Ga showing smaller increases. Mg and the transition metals decrease strongly towards the E, with Sc, V and Cu falling to less than half of their value in the most westerly rocks. Oxygen becomes very systematically more enriched in18O from W to E and the Sr, Nd and Pb isotopic systems change progressively from mantle values in the W to a more evolved character on the eastern side of the batholith. In detail the petrogenesis of the Peninsular Ranges Batholith is not completely understood, but many general aspects of the origin are clear. The exposed rocks, particularly in the western batholith, closely resemble those of present day island arcs, although the most typical and average tonalitic composition is distinctly more felsic than the mean quartz diorite or mafic andesite composition of arcs. Chemical and isotopic properties of the western part of the batholith indicate that it formed as the root of a primitive island arc on oceanic lithosphere at a convergent plate margin. Further E, the plutonic rocks appear to have been derived by partial melting from deeper sources of broadly basaltic composition at subcrustal levels. The compositional systematics of the batholith do not reflect a simple mixing of various end-members but are a reflection of the differing character of the source regions laterally and vertically away from the pre-Cretaceous continental margin.

Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes

1993 ◽  
Vol 130 (6) ◽  
pp. 835-846 ◽  
Author(s):  
S. R. Noble ◽  
R. D. Tucker ◽  
T. C. Pharaoh
Keyword(s):  
Volcanic Rocks ◽  
Igneous Rocks ◽  
Calc Alkaline ◽  
Nd Isotopes ◽  
Nd Isotope ◽  
Magmatic Arc ◽  
The North ◽  
Basement Rocks ◽  
Continental Arc ◽  
Lower Palaeozoic

AbstractThe U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

Geological Correlation Between Northern Cyprus And Southern Anatolia

2021 ◽  
Author(s):  
Yucel Yilmaz
Keyword(s):  
Carbonate Platform ◽  
Middle Eocene ◽  
Source Region ◽  
Oceanic Lithosphere ◽  
Late Eocene ◽  
Central Anatolia ◽  
Late Cenozoic ◽  
Ophiolitic Mélange ◽  
South Central ◽  
Northern Cyprus

The island of Cyprus constitutes a fragment of southern Anatolia separated from the mainland by left-oblique transtension in late Cenozoic time. However, a geological framework of offset features of the south-central Anatolia, for comparison of Cyprus with a source region within and west of the southeastern Anatolian suture zone, has not yet been developed. In this paper, I enumerate, describe, and compare a full suite of potentially correlative spatial and temporal elements exposed in both regions. Northern Cyprus and south-central Anatolia have identical tectonostratigraphic units. At the base of both belts, crop out ophiolitic mélange-accretionary complex generated during the northward subduction of the NeoTethyan Oceanic lithosphere from the Late Cretaceous until the end of middle Eocene. The nappes of the Taurus carbonate platform were thrust above this internally chaotic unit during late Eocene. They began to move as a coherent nappe pile from that time onward. An asymmetrical flysch basin was formed in front of this southward moving nappe pile during the early Miocene. The nappes were then thrust over the flysch basin fill and caused its tight folding. Cyprus separated from Anatolia in the Pleistocene-Holocene when, transtensional oblique faults with dip-slip components caused the development of the Adana and Iskenderun basins and the separation of Cyprus from Anatolia.

Initiation of Iapetus subduction under Irish Avalonia

1997 ◽  
Vol 134 (2) ◽  
pp. 213-218 ◽  
Author(s):  
BRIAN McCONNELL ◽  
JOHN MORRIS
Keyword(s):  
Early Stage ◽  
Oceanic Lithosphere ◽  
Igneous Rocks ◽  
Trace Element Geochemistry ◽  
Plate Tectonic ◽  
Element Geochemistry ◽  
Volcanic Origin ◽  
Volcanic Arc ◽  
Lower Ordovician ◽  
Minimum Age

The Dowery Hill Member of metamorphosed basalt, dolerite and siltstone is here recognized as the oldest exposed volcanic unit of the Lower Ordovician Ribband Group, with a minimum age of early Arenig. Peperites and resedimented hydroclastic breccia demonstrate a volcanic origin for the basalts. The igneous rocks are tholeiitic, with a trace element geochemistry indicative of a subduction-modified fertile mantle source, which we interpret as recording an early stage of volcanic arc evolution. The member is therefore the oldest known component of the volcanic arc generated by subduction of Iapetus oceanic lithosphere under southeastern Ireland. Subduction started earlier than predicted by current plate tectonic models, and these should be re-evaluated.

scholarly journals ORÓGENO ARAÇUAÍ: SÍNTESE DO CONHECIMENTO 30 ANOS APÓS ALMEIDA 1977

2013 ◽  
Author(s):  
Antônio Carlos Pedrosa-Soares ◽  
Carlos Maurício Noce ◽  
Fernando Flecha de Alkmim ◽  
Luiz Carlos da Silva ◽  
Marly Babinski ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Detrital Zircon ◽  
Volcanic Rocks ◽  
Oceanic Lithosphere ◽  
Continental Rift ◽  
Passive Margin ◽  
Iron Formation ◽  
Calc Alkaline ◽  
Magmatic Arc ◽  
Araçuaí Orogen

The Araçuaí Fold Belt was defined as the southeastern limit of the São Francisco Craton in the classicalpaper published by Fernando Flávio Marques de Almeida in 1977. This keystone of the Brazilian geologicliterature catalyzed important discoveries, such as of Neoproterozoic ophiolites and a calc-alkaline magmaticarc, related to the Araçuaí Belt and paleotectonic correlations with its counterpart located in Africa (the WestCongo Belt), that provided solid basis to define the Araçuaí-West-Congo Orogen by the end of the 1990thdecade. After the opening of the Atlantic Ocean in Cretaceous times, two thirds of the Araçuaí-West-CongoOrogen remained in the Brazil side, including records of the continental rift and passive margin phases ofthe precursor basin, all ophiolite slivers and the whole orogenic magmatism formed from the pre-collisionalto post-collisional stages. Thus, the name Araçuaí Orogen has been applied to the Neoproterozoic-Cambrianorogenic region that extends from the southeastern edge of the São Francisco Craton to the Atlantic coastlineand is roughly limited between the 15º and 21º S parallels. After 30 years of systematic geological mappingtogether with geochemical and geochronological studies published by many authors, all evolutionary stagesof the Araçuaí Orogen can be reasonably interpreted. Despite the regional metamorfism and deformation, thefollowing descriptions generally refer to protoliths. All mentioned ages were obtained by U-Pb method onzircon. The Macaúbas Group records rift, passive margin and oceanic environments of the precursor basinof the Araçuaí Orogen. From the base to the top and from proximal to distal units, this group comprises thepre-glacial Duas Barras and Rio Peixe Bravo formations, and the glaciogenic Serra do Catuni, Nova Auroraand Lower Chapada Acauã formations, related to continental rift and transitional stages, and the diamictitefreeUpper Chapada Acauã and Ribeirão da Folha formations, representing passive margin and oceanicenvironments. Dates of detrital zircon grains from Duas Barras sandstones and Serra do Catuni diamictitessuggest a maximum sedimentation age around 900 Ma for the lower Macaúbas Group, in agreement withages yielded by the Pedro Lessa mafic dikes (906 ± 2 Ma) and anorogenic granites of Salto da Divisa (875 ±9 Ma). The thick diamictite-bearing marine successions with sand-rich turbidites, diamictitic iron formation,mafic volcanic rocks and pelites (Nova Aurora and Lower Chapada Acauã formations) were depositedfrom the rift to transitional stages. The Upper Chapada Acauã Formation consists of a sand-pelite shelfsuccession, deposited after ca. 864 Ma ago in the proximal passive margin. The Ribeirão da Folha Formationmainly consists of sand-pelite turbidites, pelagic pelites, sulfide-bearing cherts and banded iron formations,representing distal passive margin to oceanic sedimentation. Gabbro and dolerite with plagiogranite veinsdated at ca. 660 Ma, and ultramafic rocks form tectonic slices of oceanic lithosphere thrust onto packagesof the Ribeirão da Folha Formation. The pre-collisional, calc-alkaline, continental magmatic arc (G1 Suite,630-585 Ma) consists of tonalites and granodiorites, with minor diorite and gabbro. A volcano-sedimentarysuccession of this magmatic arc includes pyroclastic and volcaniclastic rocks of dacitic composition datedat ca. 585 Ma, ascribed to the Palmital do Sul and Tumiritinga formations (Rio Doce Group), depositedfrom intra-arc to fore-arc settings. Detrital zircon geochronology suggests that the São Tomé wackes (RioDoce Group) represent intra-arc to back-arc sedimentation after ca. 594 Ma ago. The Salinas Formation, aconglomerate-wacke-pelite association located to northwest of the magmatic arc, represents synorogenicsedimentation younger than ca. 588 Ma. A huge zone of syn-collisional S-type granites (G2 Suite, 582-560Ma) occurs to the east and north of the pre-collisional magmatic arc, northward of latitude 20º S. Partialmelting of G2 granites originated peraluminous leucogranites (G3 Suite) from the late- to post-collisionalstages. A set of late structures, and the post-collisional intrusions of the S-type G4 Suite (535-500 Ma) andI-type G5 Suite (520-490 Ma) are related to the gravitational collapse of the orogen. The location of themagmatic arc, roughly parallel to the zone with ophiolite slivers, from the 17º30’ S latitude southwardssuggests that oceanic crust only developed along the southern segment of the precursor basin of the Araçuaí-West-Congo Orogen. This basin was carved, like a large gulf partially floored by oceanic crust, into the SãoFrancisco-Congo Paleocontinent, but paleogeographic reconstructions show that the Bahia-Gabon cratonicbridge (located to the north of the Araçuaí Orogen) subsisted since at least 1 Ga until the Atlantic opening.This uncommon geotectonic scenario inspired the concept of confined orogen, quoted as a new type ofcollisional orogen in the international literature, and the appealing nutcracker tectonic model to explain theAraçuaí-West-Congo Orogen evolution. 

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