Geochronology of ophiolites of the Newfoundland Appalachians

1985 ◽  
Vol 22 (11) ◽  
pp. 1659-1670 ◽  
Author(s):  
G. R. Dunning ◽  
T. E. Krogh
Keyword(s):  
Oceanic Crust ◽  
Arctic Canada ◽  
Zircon Age ◽  
Mountain Belt ◽  
Single Zircon ◽  
Age Range ◽  
Zircon Fraction

Precise U/Pb zircon ages (2σ errors) are reported for four ophiolite complexes from the Newfoundland Appalachians.Zircons from trondhjemite from Blow Me Down Mountain, Bay of Islands Complex, give an age of [Formula: see text] (five points). Those from gabbro from Blow Me Down Brook give a minimum 207Pb/206Pb age of 480 Ma (one point), confirming that this is the age of the main plutonic episode. These data refute previously determined latest Cambrian U/Pb zircon and Sm/Nd (mineral–rock isochron) ages of 504 ± 10 and 505 Ma for the complex.Gabbro from the Betts Cove Complex yielded zircon that gives an age of [Formula: see text] (four points). This refutes the interpretation of an earlier U/Pb (zircon) age of 463 ± 6 Ma for a trondhjemite dyke as the age of the ophiolite. It was inconsistent with the presence of Arenigian graptolites in the overlying Snooks Arm Group.Two zircon ages from a pegmatitic and medium-grained trondhjemite of the Annieopsquotch Complex are [Formula: see text] (five points) and [Formula: see text] (two points). Zircon from trondhjemite of the Pipestone Pond Complex of central Newfoundland gives an age of [Formula: see text] (five points). Analysis of a single zircon fraction from the Coy Pond Complex gives a minimum 207pb/206pb age of 489 MaThe ages are comparable to those of the Lushes Bight Terrane, Newfoundland, the M'Clintock West Massif, Arctic Canada, and the Ballantrae Complex, Scotland, and together span 18 Ma of the Tremadocian and Arenigian stages. This short age range may imply that only young "hot" oceanic crust was emplaced and preserved in the Appalachian–Caledonian mountain belt.

scholarly journals New Pb-Pb Single Zircon Age Constraints on the Timing of Neoproterozoic Glaciation and Continental Break-up in Namibia

1996 ◽  
Vol 104 (4) ◽  
pp. 459-469 ◽  
Author(s):  
Hartwig E. Frimmel ◽  
Urs S. Klötzli ◽  
Pete R. Siegfried
Keyword(s):  
Zircon Age ◽  
Single Zircon ◽  
Neoproterozoic Glaciation ◽  
Break Up ◽  
Age Constraints

Rapid cooling history of a Neotethyan ophiolite: Evidence for contemporaneous subduction initiation and metamorphic sole formation

2019 ◽  
Vol 131 (11-12) ◽  
pp. 2011-2038 ◽  
Author(s):  
Osman Parlak ◽  
István Dunkl ◽  
Fatih Karaoğlan ◽  
Timothy M. Kusky ◽  
Chao Zhang ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Carbonate Platform ◽  
Alkali Basalts ◽  
Tholeiitic Magma ◽  
Subduction Initiation ◽  
Suprasubduction Zone ◽  
Isparta Angle ◽  
History Of ◽  
Ophiolitic Rocks ◽  
Age Range

AbstractThe Beyşehir-Hoyran Nappes, including Mesozoic carbonate platform rocks, deep-sea sediments, and ophiolite-related units, crop out extensively on the western limb of the Isparta Angle in the Central Taurides, Turkey. The ophiolite-related rocks are represented by variably serpentinized harzburgitic mantle tectonites, tectonically underlain by a subophiolitic metamorphic sole and mélange. The harzburgitic mantle tectonites and metamorphic sole are intruded by undeformed isolated dikes. Protoliths of the metamorphic sole are similar to within-plate alkali basalts and associated sediments. The isolated dikes were geochemically derived mainly from tholeiitic magma and, to a lesser extent, from alkaline magma. Five isolated dike samples yielded U-Pb ages ranging from 90.8 ± 1.6 Ma to 87.6 ± 2.1 Ma (zircon) and from 102.3 ± 7.4 Ma to 87.5 ± 7.9 Ma (titanite). Seven amphibolite samples yielded U-Pb age ranges of 91.1 ± 2.1–88.85 ± 1.0 Ma (zircon) and 94.0 ± 4.8–90.0 ± 9.4 Ma (titanite) and a 40Ar-39Ar age range of 93.7 ± 0.3–91.4 ± 0.4 Ma (hornblende). U-Pb and 40Ar-39Ar ages of mineral phases with different closure temperatures (∼900–500 °C) from the isolated dikes and metamorphic sole rocks are almost identical and overlapping within 1σ, suggesting that both the magmatic growth of oceanic crust and formation of metamorphic sole were contemporaneous and cooled very rapidly. Hence, all the data should be interpreted as the crystallization ages of the ophiolite and metamorphic sole pair. Genesis of suprasubduction zone–type oceanic crust, genesis and exhumation of the metamorphic sole, and postmetamorphic dike emplacement within the Inner Tauride Ocean can be best explained by subduction initiation and rollback processes during the Late Cretaceous based on petrological and geochronological data obtained from the ophiolitic rocks of the Beyşehir-Hoyran Nappes.

scholarly journals O STOCK NEFELINA-SIENÍTICO RIO PARDO, PROVÍNCIA ALCALINA DO SUL DO ESTADO DA BAHIA

2012 ◽  
Author(s):  
Rita da Cunha Leal Menezes ◽  
Herbet Conceição ◽  
Maria de Lourdes da Silva Rosa ◽  
Marco Antonio Galarza ◽  
Débora Correia Rios ◽  
...  
Keyword(s):  
Rare Earth ◽  
Trace Element ◽  
Nepheline Syenite ◽  
Crystallization Process ◽  
The South ◽  
Trace Element Contents ◽  
Single Zircon ◽  
Age Range ◽  
Fractional Crystallization Process ◽  
Zircon Evaporation

O Stock Nefelina-Sienítico Rio Pardo se localiza na porção sul do conjunto de intrusões alcalinas que constitui a Província Alcalina do Sul do Estado da Bahia. Esse corpo aflora numa área de 46 km2, sendo constituído por sienito, sienito com nefelina, nefelina sienito e sodalita sienito. A idade Pb-Pb obtida em monocristal de zircão para esse stock foi de 725 ± 2 Ma, a qual se insere no intervalo de idades para o magmatismo da parte sul dessa província alcalina (732 Ma a 720 Ma). Os dados litoquímicos obtidos para esse stock o posicionam na suíte alcalina subsaturada em SiO2 da Província Alcalina do Sul do Estado da Bahia. Os conteúdos de elementos traços asseguram sua afinidade anorogênica. Sua evolução, controlada por cristalização fracionada, se marca por acentuado enriquecimento em Na2O (até 15%) e Al2O3 (até 25%) e marcantes decréscimos em SiO2 (63% a 45%) e Elementos Terras Raras.Palavras-chave: nefelina sienito, idade Pb-Pb, Rio Pardo, BahiaABSTRACT: THE RIO PARDO NEPHELINE-SYENITIC STOCK, SOUTH BAHIA ALKALINE PROVINCE. The Rio Pardo nepheline-syenitic intrusion is located in the southern sector of the South Bahia Alkaline Province. It crops out over an area of 46 km2 and consists of syenite, nepheline-bearing syenite, nepheline syenite and blue-sodalite syenite. The Pb-Pb single-zircon evaporation age of 725 ± 2 Ma obtained for the Rio Pardo stock is in agreement with the age range (732 Ma to 720 Ma) for the southern part of province. Lithochemical data provide evidence to consider the Rio Pardo stock as a body of the SiO2 sub-saturated alkaline suite of the South Bahia Alkaline Province. Trace element contents indicate anorogenic afinity and the stock evolution, controlled by a fractional crystallization process, resulted in an outstanding enrichment of Na2O (up to 15%) and Al2O3 (up to 25%), and an important depletion of SiO2 (63% to 45%) and Rare Earth Elements.Keywords: nepheline syenite, Pb-Pb age, Rio Pardo, Bahia State.,

Metamorphic evolution and zircon geochronology of early Proterozoic granulites in the Aravalli Mountains of northwestern India

2005 ◽  
Vol 142 (3) ◽  
pp. 287-302 ◽  
Author(s):  
A. B. ROY ◽  
ALFRED KRÖNER ◽  
P. K. BHATTACHAYA ◽  
SANJEEV RATHORE
Keyword(s):  
Granite Gneiss ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Granulite Metamorphism ◽  
History Of ◽  
Single Zircon ◽  
Northwest India ◽  
Orogenic Cycle ◽  
Age Range ◽  
Rock Association

Granulites including a charnockite suite, mafic granulites, pelitic granulites, metanorite dykes and their retrograde varieties occur as discontinuous shear zone-bounded bodies within the Archaean basement comprising a granite gneiss–amphibolite–metasedimentary rock association in the central part of the Aravalli Mountains, northwest India. The entire suite, named the Sandmata Complex, preserves a complex history of tectonothermal evolution. Except for their strongly foliated margins, the granulite bodies are largely massive. Partial melting in the ‘country rocks’ led to the development of migmatite gneisses close to the contact of the granulite, a feature not as common in the rocks further away from the granulite contact. Geothermobarometry of massive granulites indicates Tmax>900°C and Pmax∼7.5 kbar. The retrograde granulites, which formed at lower amphibolite/upper greenschist-facies conditions, experienced channelized hydration reactions concomitant with shearing. These rocks locally appear as hornblende–biotite-bearing foliated granulite with or without Cpx or Opx. The rocks seem to have followed an inverse PTt path and have undergone an earlier phase of near-isobaric cooling. Our single zircon Pb–Pb ages indicate that the exhumation of granulites to the shallower amphibolite-facies levels with concomitant melting in the country rocks took place between 1690 Ma and 1621 Ma. Assuming that the granulite-facies metamorphism took place at around 1725 Ma, we relate the entire process of granulite metamorphism and exhumation covering an age range between 1725 and 1621 Ma to the rift basin opening stages of the Delhi Orogenic cycle that culminated at c. 1450 Ma.

scholarly journals Remnants of Mesoarchaean oceanic crust in the Tartoq Group, South-West Greenland

2011 ◽  
Vol 23 ◽  
pp. 57-60 ◽  
Author(s):  
Kristoffer Szilas ◽  
Vincent J. Van Hinsberg ◽  
Alexander F. M. Kisters ◽  
Thomas F. Kokfelt ◽  
Anders Scherstén ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Structural Data ◽  
Zircon Age ◽  
Joint Project ◽  
New Model ◽  
West Greenland ◽  
Mineral Potential ◽  
South West ◽  
Metavolcanic Rocks ◽  
Minimum Age

The Tartoq Group is located in the Sermiligaarsuk fjord region in South-West Greenland in an area of approximately 20 × 50 km (Fig. 1). The Tartoq Group consists of several discrete, fault-bound blocks of metavolcanic rocks, surrounded by Archaean tonalite-trondhjemite-granodioritetype (TTG) gneisses. A zircon age of 2996.3 ± 5.9 Ma of a TTG intrusion provides a minimum age for the formation of the Tartoq Group (Fig. 2). The metavolcanic rocks probably show the lowest degree of metamorphism found anywhere in the Archaean craton of Greenland. Here we present a new model for the origin of the metavolcanic rocks of the Tartoq Group based on geochemical, metamorphic and structural data. The samples used for this study were collected by the Geological Survey of Denmark and Greenland (GEUS) in 2009 and 2010. The study is part of a joint project between the Greenland Bureau of Minerals and Petroleum and GEUS on the mineral potential of south-western Greenland.

U—Pb single zircon data of granitoids from the High Tatra Mountains (Slovakia): implications for the geodynamic evolution

2000 ◽  
Vol 91 (1-2) ◽  
pp. 235-243 ◽  
Author(s):  
Ulrike Poller ◽  
Wolfgang Todt
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Tatra Mountains ◽  
Geodynamic Evolution ◽  
Zircon Age ◽  
Granite Intrusion ◽  
Asthenospheric Mantle ◽  
Subducted Oceanic Crust ◽  
Single Zircon ◽  
High Tatra Mountains

New U/Pb results by cathodoluminescence-controlled single zircon dating of rocks from the High Tatra Mountains (Slovakia) constrain ages for the protolith at 2Ga for the granitoids and 3 Ga for the Koncistá migmatite. Concordant single zircon ages date the intrusion of the migmatite precursor at 3567 Ma and the migmatisation at 332 ± 5 Ma. The intrusion of this precursor corresponds with the major granite intrusion in the Western Tatra Mountains. The geodynamic scenario at this time is described as slab detachment of subducted oceanic crust at the active continental margin of Gondwana. The resulting upwelling of asthenospheric mantle brought enough heat for the anatexis of old metasediments and the production of new H- to S-type granites. High Tatra diorites have an intrusion age of 341 ± 5 Ma, constrained by a concordant single zircon age. This age marks the beginning of the Variscan collision of the two convergent continents Laurasia and Gondwana. The intrusion of granites in the High Tatra was confirmed by concordant data at 314 ± 4 Ma, documenting the final stage of the Variscan continent collision.

Zircon age range and sources of alkaline rocks from the Kurgusul intrusion, Kuznetsk Alatau: The first U-Pb (SHRIMP II) and Sm-Nd isotope data

2014 ◽  
Vol 459 (2) ◽  
pp. 1576-1581 ◽  
Author(s):  
V. V. Vrublevskii ◽  
I. F. Gertner ◽  
P. A. Tishin ◽  
T. B. Bayanova
Keyword(s):  
Zircon Age ◽  
Nd Isotope ◽  
Alkaline Rocks ◽  
Isotope Data ◽  
Age Range

scholarly journals Enigmatic Red Beds Exposed at Point of Rocks, Cimarron National Grassland, Morton County, Kansas

2015 ◽  
pp. 1-16
Author(s):  
Jon J. Smith ◽  
Brian F. Platt ◽  
Greg A. Ludvigson ◽  
Robert S. Sawin ◽  
Craig P. Marshall ◽  
...  
Keyword(s):  
Detrital Zircon ◽  
Copper Oxides ◽  
Red Beds ◽  
Zircon Age ◽  
Copper Sulfides ◽  
Jurassic System ◽  
Basin Formation ◽  
Single Zircon ◽  
Cimarron River ◽  
Marker Beds

Point of Rocks, a high-relief bluff overlooking the Cimarron River valley in Morton County, Kansas, is capped by distinct white beds of Neogene Ogallala Formation calcrete that overlie red beds of shale, siltstone, and sandstone. These unfossiliferous red beds are currently assigned to the Jurassic System; however, their age has long been debated due to a lack of marker beds, index fossils, and nearby correlative outcrops. As a result, geologists over the years have assigned the rocks to systems ranging from the Permian to the Cretaceous. In this study, four stratigraphic sections were measured in the red beds and three bulk samples were collected to determine the uranium-lead age distributions of detrital zircon (DZ) populations. Red-bed strata composed of fissile shale and sandstone are interpreted as alluvial overbank deposits, while dominantly trough cross-bedded and planar-laminated sandstones are interpreted as tidally influenced fluvial deposits. Detrital zircon age peaks can be grouped into at least seven subpopulations with a youngest single zircon age of 263.8 ± 12.1 Ma, a more conservative age of 293.0 ± 6.95 Ma based on the youngest grouping of three grain ages overlapping at 2σ, and a complete absence of Mesozoic age zircons. In addition, copper oxides along partings and fractures suggest that the red beds once hosted copper sulfides, a common constituent of regional Permian-Triassic red beds. The DZ data--in conjunction with the identification of the Permian Day Creek Dolomite marker bed in logs of nearby drilling tests--strongly suggest that the enigmatic red beds cropping out at the base of Point of Rocks should be assigned to the Guadalupian Big Basin Formation, the uppermost Permian unit in Kansas.

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