scholarly journals A SUÍTE CÓRREGO TAQUARI NO ANTICLINAL DE ITACAMBIRA, BACIA DO RIO MACAÚBAS (MG): MAGMATISMO BÁSICO TARDI-EDIACARANO (CA. 560 MA) NO DOMÍNIO EXTERNO DO ORÓGENO ARAÇUAÍ

2013 ◽  
Author(s):  
Maximiliano Martins ◽  
Marly Babinsk ◽  
Carlos Maurício Noce ◽  
Gláucia Nascimento Queiroga ◽  
Antônio Carlos Pedrosa-Soares ◽  
...  
Keyword(s):  
Small Population ◽  
Mafic Magmatism ◽  
Fold And Thrust Belt ◽  
Minas Gerais State ◽  
Facies Metamorphism ◽  
Escape Tectonics ◽  
Lateral Escape ◽  
Araçuaí Orogen ◽  
Method Show ◽  
Greenschist Facies Metamorphism

No setor central do cinturão de dobramentos e empurrões da Serra do Espinhaço, domínio externo ocidental do Orógeno Araçuaí, situa-se o Anticlinal de Itacambira onde foi identificado um conjunto de diques gabróicos, pouco deformados e metamorfisados na fácies xisto verde. Um desses diques, englobados na Suíte Metaígnea Córrego do Taquari, tem assinatura litoquímica de toleíito intraplaca, idade-modelo Sm-Nd (TDM) em torno de 1,8 Ga e épsilon Nd negativo. Deste dique extraiu-se grãos de zircão para datação pelo método U-Pb (SHRIMP). Alguns destes grãos são herdados e evidenciam assimilação de cristais de zircão do Paleoproterozóico e Mesoproterozóico. A maior parte dos grãos são cristais euédricos, magmáticos, e suas análises U-Pb resultaram na idade de 560 ± 6 Ma para a cristalização magmática da Suíte Córrego Taquari. Esta suíte registra um sítio transtensivo formado e preenchido pelo magma máfico no limiar dos estágios sincolisional e tardi-colisional do Orógeno Araçuaí, provavelmente relacionado ao início dos fenômenos de escape lateral que afetaram este orógeno.Palavras-chave: diques máficos, Ediacarano, Orógeno AraçuaíABSTRACT: THE CÓRREGO TAQUARI SUITE IN THE ITACAMBIRA ANTICLINE, MACAÚBAS RIVER BASIN, MINAS GERAIS STATE: LATE EDIACARAN (CA. 560 MA) MAFIC MAGMATISM IN THE EXTERNAL TECTONIC DOMAIN OF THE ARAÇUAÍ OROGEN. In the central sector of the Serra do Espinhaço fold-and-thrust belt, western tectonic domain of the Neoproterozoic Araçuaí orogen, occurs the Itacambira anticline where a swarm of Late Ediacaran metamafic bodies were recently discovered, the Córrego Taquari meta-igneous suite. Most of these bodies occur as dykes cutting across units of the Espinhaço Supergroup and Macaúbas Group, and show incipient deformation and low greenschist facies metamorphism. The lithochemical and Sm-Nd isotopic data (negative epsilon Nd and TDM model age around 1.8 Ga) point to a tholeiitic intraplate signature. Twenty two zircon grains, extracted from a sample of a gabbroic dyke and analysed by the U-Pb (SHRIMP) method, show a small population of Paleoproterozoic and Mesoproterozoic inherited grains, and a major population of magmatic euhedral crystals. The less discordant, euhedral zircon crystals yielded the U-Pb (SHRIMP) age of 560 ± 6 Ma for the magmatic crystallization age of the Córrego Taquari Suite. This mafic magmatism records a Late Ediacaran extensional episode, probably related to the beginning of the lateral escape tectonics that took place in the late collisional stage of the Araçuaí orogen.Keywords: mafic dykes, Ediacaran, Araçuaí Orogen

Novelties in Begonia (Begoniaceae) from the campos rupestres of Serra do Padre Ângelo, Minas Gerais, Brazil: a new species and a new record

Phytotaxa ◽  
2021 ◽  
Vol 510 (1) ◽  
Author(s):  
LUDOVIC JEAN CHARLES KOLLMANN ◽  
PAULO MINATEL GONELLA
Keyword(s):  
New Species ◽  
High Elevation ◽  
Iucn Red List ◽  
Minas Gerais ◽  
Small Population ◽  
Critically Endangered ◽  
Campos Rupestres ◽  
Rock Outcrops ◽  
Critically Endangered Species ◽  
Minas Gerais State

Begonia piranga (Begoniaceae) is a new narrowly endemic species from the campos rupestres of Serra do Padre Ângelo, a quartzitic massif in Conselheiro Pena, eastern Minas Gerais state, Brazil. Description, diagnosis, taxonomic comments, detailed illustrations, field photographs, and a provisional IUCN Red List Assessment are provided. The new species is considered Critically Endangered due to its restricted occurrence in high elevation rock outcrops, small population size, and decline in the quality of the habitat. Begonia vasconcelosiana, another Critically Endangered species, is also newly reported here for Serra do Padre Ângelo. These discoveries add to the increasing list of novelties from Serra do Padre Ângelo, reinforcing the urge for conservation actions to protect the endemic flora of this Serra and other areas of campos rupestres in eastern Minas Gerais state.

Structural geology of the Lardeau Group near Trout Lake, British Columbia: implications for the structural evolution of the Kootenay Arc

1992 ◽  
Vol 29 (6) ◽  
pp. 1305-1319 ◽  
Author(s):  
Moira T. Smith ◽  
George E. Gehrels
Keyword(s):  
British Columbia ◽  
Shear Zone ◽  
Structural Evolution ◽  
Strike Slip ◽  
Ductile Deformation ◽  
Lower Paleozoic ◽  
Trout Lake ◽  
Facies Metamorphism ◽  
Dextral Strike Slip ◽  
Greenschist Facies Metamorphism

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic eugeoclinal strata present in the Kootenay Arc in southeastern British Columbia. It is in fault contact with lower Paleozoic miogeoclinal strata for all or some of its length along a structure termed the Lardeau shear zone. The Lardeau Group was deformed prior to mid-Mississippian time, as manifested by layer-parallel faults, folds, and evidence for early greenschist-facies metamorphism. Regional constraints indicate probable Devono-Mississippian timing of orogeny, and possible juxtaposition of the Lardeau Group over miogeoclinal strata along the Lardeau shear zone at this time. Further ductile deformation during the Middle Jurassic Columbian orogeny produced large folds with subhorizontal axes, northwest-striking foliation and faults, and orogen-parallel stretching lineations. This deformation was apparently not everywhere synchronous, and may have continued through Late Jurassic time northeast of Trout Lake. This was followed by Cretaceous(?) dextral strike-slip and normal movement on the Lardeau shear zone and other parallel faults. While apparently the locus of several episodes of faulting, the Lardeau shear zone does not record the accretion of far-travelled tectonic fragments, as sedimentological evidence ties the Lardeau Group and other outboard units to the craton.

scholarly journals The tectono-metamorphic evolution of a dismembered ophiolite (Tinos, Cyclades, Greece)

1996 ◽  
Vol 133 (3) ◽  
pp. 237-254 ◽  
Author(s):  
Yaron Katzir ◽  
Alan Matthews ◽  
Zvi Garfunkel ◽  
Manfred Schliestedt ◽  
Dov Avigad
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Subduction Zone ◽  
Sea Water ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Model Calculations ◽  
Facies Metamorphism ◽  
Greenschist Facies Metamorphism

AbstractThe six exposures of the Upper tectonic Unit of the Cycladic Massif occurring on the island of Tinos are shown to comprise a metamorphosed dismembered ophiolite complex. The common stratigraphic section consisting of tens-of-metres- thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low-angle normal faults. All rock types show evidence of a phase of regional greenschist-facies metamorphism, which in the case of the phyllites is accompanied by penetrative deformation. The greenschist-facies metamorphism in gabbros is preceded by high temperature sea-floor amphibolite-facies alteration, whereas in the serpentinites, the antigorite + forsterite greenschist-facies assemblage overprinted an earlier low temperature lizardite serpentinite. Trace element patterns of the mafic phyllites and a harzburgitic origin of meta-serpentinites suggest a supra subduction zone (SSZ) affinity for the ophiolitic suite. ρ18O values of phyllites, gabbros and serpentinites range from 6 to 15%o. Model calculations indicate that such values are consistent with low temperature (50–200°C) alteration of parent rocks by sea-water at varying water/rock ratios. This would agree with the early low temperature mineralogy of the serpentinites, but the early high temperature alteration of the gabbros would require the presence of 18O-enriched sea-water.The following overall history is suggested for Tinos ophiolitic slices. (1) Oceanic crust was generated at a supra-subduction zone spreading centre with high temperature alteration of gabbros. (2) Tectonic disturbance (its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites) brought the already cooled ultramafics into direct contact with sea-water and caused low-T serpentinization. (3) Tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite. (4) Regional metamorphism of all the ophiolite components at greenschist-facies conditions (−450°C) overprinted the early alteration mineralogy. It was probably induced by continued thrusting and piling up of nappes. The Tinos ophiolite, dated as late Cretaceous and genetically related to other low pressure rock-units of the same age in the Aegean, differs in age and degree of dismemberment and metamorphism from ophiolites in mainland Greece.

scholarly journals Thermochronological evidence for late Proterozoic (Vendian) cooling in southwest Wedel Jarlsberg Land, Spitsbergen

1998 ◽  
Vol 135 (1) ◽  
pp. 63-69 ◽  
Author(s):  
M. MANECKI ◽  
D. K. HOLM ◽  
J. CZERNY ◽  
D. LUX
Keyword(s):  
Geological Mapping ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Variable Intensity ◽  
Late Proterozoic ◽  
Facies Metamorphism ◽  
History Of ◽  
Greenschist Facies Metamorphism

Two Proterozoic terranes with different metamorphic histories are distinguished from geological mapping in southwestern Wedel Jarlsberg Land: a northern greenschist facies terrane and a southern amphibolite facies terrane which has been overprinted by greenschist facies metamorphism. To better characterize the tectonothermal history of these terranes we have obtained new 40Ar/39Ar mineral dates from this area. A muscovite separate from the northern terrane yielded a Caledonian plateau age of 432±7 Ma. The southern terrane yielded significantly older 40Ar/39Ar ages with three muscovite plateau dates of 584±14 Ma, 575±15 Ma, and 459±9 Ma, a 484±5 Ma biotite plateau date, and a 616±17 Ma hornblende plateau date. The oldest thermochronological dates are over 300 Ma younger than the age of amphibolite facies metamorphism and therefore probably do not represent uplift-related cooling. Instead, the Vendian dates correlate well with a regionally widespread magmatic and metamorphic/thermal resetting event recognized within Caledonian complexes of northwestern Spitsbergen and Nordaustlandet. The apparent Ordovician dates are interpreted to represent partial resetting, suggesting that late Caledonian greenschist facies overprinting of the southern terrane was of variable intensity.

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