U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism

1977 ◽  
Vol 14 (10) ◽  
pp. 2316-2324 ◽  
Author(s):  
James M. Mattinson
Keyword(s):  
Volcanic Rocks ◽  
Primary Crystallization ◽  
Early Carboniferous ◽  
New Age ◽  
Crystalline Rocks ◽  
Thermal Event ◽  
Early Ordovician ◽  
Early Stages ◽  
Intrusive Rocks ◽  
Show Evidence

U–Pb measurements on minerals from the Burlington Peninsula indicate that volcanic rocks of the Grand Cove Group and the probably cogenetic Cape Brule porphyry have primary crystallization ages of 475 ± 10 Ma (Early Ordovician). Later intrusive rocks, including the Dunamagon granite, the Burlington granodiorite and the Seal Island Bight syenite were intruded between 445 and 435 Ma ago. The Grand Cove Group and the Cape Brule porphyry completely predate deformation and metamorphism of the eastern division of the Fleur de Lys Supergroup; the Seal Island Bight syenite, Burlington granodiorite, and Dunamagon granite were evidently emplaced during the early stages of this orogeny. The new age results therefore suggest that the orogeny is Taconic in the classic sense. Some of the isotope systems show evidence of a strong thermal event about 340 Ma ago (Early Carboniferous, Acadian). This event may have caused resetting of some of the Rb–Sr isochron ages recently reported for this area.

Tectonic evolution of southwestern Newfoundland as indicated by granitoid petrogenesis

1985 ◽  
Vol 22 (7) ◽  
pp. 1080-1092 ◽  
Author(s):  
Derek H. C. Wilton
Keyword(s):  
Fault Zone ◽  
Point Group ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Late Devonian ◽  
Partial Melt ◽  
Show Evidence ◽  
Partial Melts ◽  
Felsic Volcanic ◽  
Host Rocks

Four granitoid suites are recognized in the region of the Cape Ray Fault Zone of southwestern Newfoundland. The two oldest (Ordovician–Silurian (?)) suites represent partial melts of their enclosing host rocks. The Port aux Basques granite is modelled as a partial melt of the gneissic component of its host, Port aux Basques Complex. The Cape Ray granite forms a dominantly tonalitic terrane derived by partial melting of ophiolitic material. The Red Rocks granite and a megacrystic phase of the Cape Ray granite form coherent lines of geochemical descent from the parental tonalite but show evidence of some continental crust contamination.The Late Devonian Windowglass Hill granite is a subvolcanic equivalent of felsic volcanic rocks in the Windsor Point Group. Both units were derived as partial melts of continental crust.The post-tectonic, Late Devonian to Early Carboniferous Strawberry and Isle aux Morts Brook granites constitute the youngest granitoid suite in the region. These A-type granitoids were derived as partial melts of an underlying depleted granulitic (felsic) crust. The depleted nature of the source may have resulted from previous generation of the Windowglass Hill granite and Windsor Point Group. The only possible protolith for the granulitic source is Precambrian Grenvillian gneiss. The presence of this gneiss beneath the Cape Ray Fault Zone of southwestern Newfoundland implies that the complete series of lithologies is allochthonous.

New geochronological data on Palaeozoic igneous activity and deformation in the Severnaya Zemlya Archipelago, Russia, and implications for the development of the Eurasian Arctic margin

2006 ◽  
Vol 144 (1) ◽  
pp. 105-125 ◽  
Author(s):  
HENNING LORENZ ◽  
DAVID G. GEE ◽  
MARTIN J. WHITEHOUSE
Keyword(s):  
Early Carboniferous ◽  
High Arctic ◽  
Alternative Interpretation ◽  
Late Carboniferous ◽  
October Revolution ◽  
Early Ordovician ◽  
The North ◽  
Intrusive Rocks ◽  
Severnaya Zemlya ◽  
Severnaya Zemlya Archipelago

The Severnaya Zemlya Archipelago, located close to the continental edge of the Kara Shelf in the Russian high Arctic, represents, together with northern Tajmyr, the exposed Neoproterozoic and Palaeozoic part of the North Kara Terrane. This terrane has been interpreted as an independent microcontinent or part of a larger entity, such as Arctida or Baltica, prior to collision with Siberia in Late Carboniferous time. A major stratigraphic break, the Kan'on (canyon) River Unconformity, separates folded Late Cambrian from Early Ordovician successions in one area, October Revolution Island. New geochronological U–Th–Pb ion-microprobe data on volcanic and intrusive rocks from this island constrain the age of an important magmatic episode in the earliest Ordovician. A tuff, in association with Tremadocian fossils, overlying the Kan'on River Unconformity, has been dated to 489.5 ± 2.7 Ma. The youngest rocks beneath the unconformity are of the Peltura minor Zone, and the latter has been dated previously, in western Avalonia, to 490.1+1.7−0.9 Ma. Thus, little time is available for the tectonic episode recorded by the unconformity, and the similarities in radiometric dates may indicate problems with the correlation of faunal markers for the Cambrian–Ordovician boundary across palaeo-continents. The other extrusive and intrusive rocks which have been related to Early Ordovician rifting in the Severnaya Zemlya area yield ages from 489 Ma to 475 Ma. An undeformed granite, cutting folded Neoproterozoic successions on neighbouring Bol'shevik Island has been dated to 342 ± 3.6 Ma and 343.5 ± 4.1 Ma (Early Carboniferous), in accord with evidence elsewhere of Carboniferous strata unconformably overlying the folded older successions. This evidence conflicts with the common interpretation that the structure of the Severnaya Zemlya Archipelago originated during the collision of the North Kara Terrane with Siberia in Late Carboniferous time. An alternative interpretation is that Severnaya Zemlya was located in the Baltica foreland of the Caledonide Orogen and that the eastward-migrating deformation of the foreland basin reached the area of the archipelago in latest Devonian to Early Carboniferous time. This affinity of the North Kara Terrane to Baltica is further supported by 540–560 Ma xenocrysts in Ordovician intrusions on October Revolution Island, an age which is characteristic of the Timanide margin of Baltica.

Problème de la limite Précambrien–Cambrien: étude radiochronologique par la méthode U–Pb sur zircons du volcan du Jbel Boho (Anti-Atlas marocain)

1977 ◽  
Vol 14 (12) ◽  
pp. 2771-2777 ◽  
Author(s):  
J. Ducrot ◽  
J. R. Lancelot
Keyword(s):  
Volcanic Rocks ◽  
Lower Paleozoic ◽  
Thermal Event

A 534 ± 10 Ma age has been obtained on zircons from Jbel Boho volcano by the U–Pb method; previous assumptions of older ages for the Anti-Atlas Infracambrien (Morocco) cannot be maintained. This formation belongs to the lower Paleozoic. A slight thermal event has affected the volcanic rocks during Variscan (or Hercynian) times and induced opening of the K–Ar and Rb–Sr systems; but the U–Pb system of the zircons has not been affected. These U–Pb data are further reasons to raise the Precambrian – Cambrian boundary to an age of 550–560 Ma.

Identifying Early Carboniferous bimodal volcanic rocks and geochemical characteristics in the Atengtao Mountain, Yili Block (Chinese western Tianshan)

2018 ◽  
Vol 53 ◽  
pp. 148-162 ◽  
Author(s):  
Zuopeng Wang ◽  
Yongjun Li ◽  
Lili Tong ◽  
Gaoxue Yang ◽  
Pengfei Ren ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Geochemical Characteristics ◽  
Western Tianshan

Magmatic evidence for Late Carboniferous-Early Permian slab breakoff and extension of the southern Mongolia collage system in Central Asia

2021 ◽  
Author(s):  
Hai Zhou ◽  
Guochun Zhao ◽  
Donghai Zhang
Keyword(s):  
Subduction Zones ◽  
Volcanic Rocks ◽  
Early Carboniferous ◽  
Ocean Basin ◽  
Magma Source ◽  
Central Asian ◽  
Slab Rollback ◽  
Slab Breakoff ◽  
Subduction Fluids ◽  
Arc Setting

<p>Oceanic subduction and its last underthrusted part can both triggers arc-like magmatism. As the existence of multi-subduction zones in the Central Asian Orogenic Belt, controversy still surrounds on when and especially how the subduction of the (Paleo-Asian Ocean) PAO terminated. We present geochronological, geochemical, and Lu-Hf isotopic data for a suite of basalt-andesites, dacite-rhyolites and later trachyandesite-mugearitic dykes from the Khan-Bogd area in the Gobi Tianshan Zone (GTZ) of the southern Mongolia. U-Pb dating of zircons indicate the basalt-andesites and dacite-rhyolites were formed at ~334-338 Ma, and the dykes at ~300 Ma. These Early Carboniferous volcanic rocks display high U/Th, Ba/Th, low La/Sm and variable Zr/Nb ratios, implying the involvement of subduction fluids or sediment melt. They display arc geochemical features such as calc-alkaline and metaluminous nature and positive Ba and U and negative Nb, Ta and Ti anomalies. Moreover, their continental geochemical signals (e.g. positive Pb, K anomalies) and some old captured zircons implying a continental arc setting. Comparatively, the ~300 Ma dykes are characterized by high alkaline contents, which are common for coeval (~320-290 Ma) and widespread post-subductional granites there. Given a mainly crust-derived magma source for those granites, these dykes likely reflect a mantle disturbance due to: (1) their relative low SiO<sub>2 </sub>(51.71-55.85 wt. %) and high Mg# (40.3-67.3) values, and (2) positive zircon Ɛ<sub>Hf</sub>(t) (most > 12). Considering a slab rollback model during the Carboniferous and Triassic, the mantle disturbance was possibly induced by the oceanic slab breakoff. Combined with previous work, this ~320-290 Ma slab breakoff-induced extension marks the closure of a wide secondary ocean (North Tianshan-Hegenshan ocean) north of the main ocean basin of the PAO. This research was financially supported by NSFC Projects (41730213, 42072264, 41902229, 41972237) and Hong Kong RGC GRF (17307918).</p>

Dosage du potassium, de l'uranium, du radium et du thorium, par spectrometrie gamma dans les laves d'Auvergne, du Velay et de la province sicilienne

1963 ◽  
Vol S7-V (2) ◽  
pp. 218-231 ◽  
Author(s):  
Jean Louis Cheminee ◽  
Daniel Nordemann
Keyword(s):  
Hydrothermal Alteration ◽  
Volcanic Rocks ◽  
Statistical Dependence ◽  
Direct Proportion ◽  
Radioactive Elements ◽  
Spectrometry Analysis ◽  
Functional Relations ◽  
South Central ◽  
Intrusive Rocks ◽  
Radioactive Minerals

Abstract Fifty samples of volcanic rocks from south-central France, ranging from basalts to rhyolites, were subjected to gamma spectrometry analysis for the purpose of determining the proportions and relationships of the constituent radioactive elements. Zircon, sphene and apatite generally contained less thorium and uranium than the less abundant accessory minerals such as allanite, monazite and xenotime. Results of the analysis also show that the percentage of radioactive minerals is greater in the acidic lavas than in the intrusive rocks, suggesting that the latter were subjected to hydrothermal alteration. The percentage of potassium varies in direct proportion to the variation in the percentage of silica. The increase in thorium as a function of silica is more rapid than that of uranium. Graphically, no correlation exists between the percentage of radium and silica. The concentrations of uranium and thorium do not vary independently but seem to have a statistical dependence whose functional relations are not yet apparent.

Chapter 14 Cambrian-Ordovician history

1997 ◽  
Vol 17 (1) ◽  
pp. 257-271 ◽  
Author(s):  
W. Brian Harland
Keyword(s):  
Late Ordovician ◽  
Early Cambrian ◽  
The South ◽  
Thermal Event ◽  
Early Ordovician

Cambrian-Ordovician history is well documented in Svalbard with late Early Cambrian faunas and a range of Ordovician faunas to provide a basis for correlation. Not so extensive as Vendian, the rocks crop out in four areas: (i) only slightly deformed strata in the youngest Hecla Hoek (Oslobreen) Group in northeastern Svalbard yield especially rich Early to Mid-Ordovician faunas, (ii) The Hornsundian Geosyncline in south Spitsbergen with more variable facies and tectonic complications also exhibits Early Cambrian and Canadian strata, (iii) The Bjornoya succession reveals a marked hiatus between Vendian and Early and Mid-Ordovician strata, (iv) In western Svalbard the lack of Cambrian and Early Ordovician strata marks a distinct Mid Ordovician tectono-thermal event to be followed by ?Late Ordovician and Early Silurian strata. Indeed the above four areas correspond to distinct terranes which, having different affinities especially with areas in Greenland, give evidence of relatively distant areas and environments of formation. Evidence of Cambro-Ordovician volcanism is not recorded.Figure 14.1 lists the successions in the four areas mentioned according to the classification of rock units as abstracted from chapters 6, 7, 8, 9, 10 and 11, where their regional settings may be found. The outcrops are plotted on Fig. 14.2. The northeastern Svalbard strata are separated by Hinlopenstretet. This waterway divides Ny Friesland and Olav V Land in Spitsbergen from northwestern Nordaustlandet and occupies a syncline, but the successions although differently named are essentially continuous. In southern Spitsbergen the fjord Hornsund separates the successions to the south in Sorkapp Land

The Duck Pond and Boundary Cu–Zn deposits, Newfoundland: new insights into the ages of host rocks and the timing of VHMS mineralization

2010 ◽  
Vol 47 (12) ◽  
pp. 1481-1506 ◽  
Author(s):  
Vicki McNicoll ◽  
Gerry Squires ◽  
Andrew Kerr ◽  
Paul Moore
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Isotopic Data ◽  
Sulphide Ores ◽  
Intrusive Rocks ◽  
Felsic Volcanic ◽  
Host Rocks ◽  
Felsic Volcanic Rocks

The Duck Pond Cu–Zn–Pb–Ag–Au deposit in Newfoundland is hosted by volcanic rocks of the Cambrian Tally Pond group in the Victoria Lake supergroup. In conjunction with the nearby Boundary deposit, it contains 4.1 million tonnes of ore at 3.3% Cu, 5.7% Zn, 0.9% Pb, 59 g/t Ag, and 0.9 g/t Au. The deposits are hosted by altered felsic flows, tuffs, and volcaniclastic sedimentary rocks, and the sulphide ores formed in part by pervasive replacement of unconsolidated host rocks. U–Pb geochronological studies confirm a long-suspected correlation between the Duck Pond and Boundary deposits, which appear to be structurally displaced portions of a much larger mineralizing system developed at 509 ± 3 Ma. Altered aphyric flows in the immediate footwall of the Duck Pond deposit contained no zircon for dating, but footwall stringer-style and disseminated mineralization affects rocks as old as 514 ± 3 Ma at greater depths below the ore sequence. Unaltered mafic to felsic volcanic rocks that occur structurally above the orebodies were dated at 514 ± 2 Ma, and hypabyssal intrusive rocks that cut these were dated at 512 ± 2 Ma. Some felsic samples contain inherited (xenocrystic) zircons with ages of ca. 563 Ma. In conjunction with Sm–Nd isotopic data, these results suggest that the Tally Pond group was developed upon older continental or thickened arc crust, rather than in the ensimatic (oceanic) setting suggested by previous studies.

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