Chronology of the Red Wine alkaline province, central Labrador

1977 ◽  
Vol 14 (8) ◽  
pp. 1940-1946 ◽  
Author(s):  
Alan B. Blaxland ◽  
Laurence W. Curtis
Keyword(s):  
Red Wine ◽  
Early Stage ◽  
Regional Metamorphism ◽  
Strong Support ◽  
New Age ◽  
Igneous Rocks ◽  
Rift System ◽  
Alkaline Rocks ◽  
Plutonic Rocks ◽  
Basaltic Lavas

An 11-point Rb–Sr whole-rock isochron for the regionally metamorphosed Red Wine alkaline province gives an age of intrusion of 1345 ± 75 Ma (errors quoted at 2σ) and an initial 87Sr/86Sr ratio of (1.7021 ± 0.0103. Two 5-point mineral isochrons give ages of ~1000 Ma that represent metamorphic 'resetting' of the alkaline rocks. The whole-rock intrusion age compares closely with the early stage of magmatism in the Gardar Province of south Greenland where un-metamorphosed agpaitic igneous rocks, similar to those of the Red Wine Province, occur. In both provinces, alkaline plutonic rocks are associated, both spatially and chronologically, with thick sequences of continental sediments and basaltic lavas, and the new age data lend strong support to the supposition that the Gardar and Red Wine rocks are parts of the same pre-drift magmatic province and inferred rift system. The Gardar Province has, however, escaped the effects of the Grenville regional metamorphism which severely affected the Red Wine rocks.

New age data on the low-temperature regional metamorphism of Mt. Medvednica (Croatia)

2006 ◽  
Vol 49 (3) ◽  
pp. 207-221 ◽  
Author(s):  
Katalin Judik ◽  
Kadosa Balogh ◽  
Darko Tibljaš ◽  
Péter Árkai
Keyword(s):  
Low Temperature ◽  
Regional Metamorphism ◽  
New Age

scholarly journals Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

1992 ◽  
Vol 154 ◽  
pp. 49-59
Author(s):  
T Winther
Keyword(s):  
Open Systems ◽  
Early Stage ◽  
Rift System ◽  
Magma Chambers ◽  
Degree Of Contamination ◽  
Magma Reservoirs ◽  
Incompatible Elements ◽  
Low Degree ◽  
Alkaline Magmas ◽  
Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

Chapter 5.4b Marie Byrd Land and Ellsworth Land: petrology

2021 ◽  
pp. M55-2019-50 ◽  
Author(s):  
K. S. Panter ◽  
T. I. Wilch ◽  
J. L. Smellie ◽  
P. R. Kyle ◽  
W. C. McIntosh
Keyword(s):  
Trace Elements ◽  
Fractional Crystallization ◽  
High Pressures ◽  
Early Stage ◽  
Thermal Anomaly ◽  
Rift System ◽  
The West ◽  
Full Spectrum ◽  
West Antarctic Ice Sheet ◽  
West Antarctic

AbstractIn Marie Byrd Land and Ellsworth Land 19 large polygenetic volcanoes and numerous smaller centres are exposed above the West Antarctic Ice Sheet along the northern flank of the West Antarctic Rift System. The Cenozoic (36.7 Ma to active) volcanism of the Marie Byrd Land Volcanic Group (MBLVG) encompasses the full spectrum of alkaline series compositions ranging from basalt to intermediate (e.g. mugearite, benmoreite) to phonolite, peralkaline trachyte, rhyolite and rare pantellerite. Differentiation from basalt is described by progressive fractional crystallization; however, to produce silica-oversaturated compositions two mechanisms are proposed: (1) polybaric fractionation with early-stage removal of amphibole at high pressures; and (2) assimilation–fractional crystallization to explain elevated87Sr/86Sriratios. Most basalts are silica-undersaturated and enriched in incompatible trace elements (e.g. La/YbN>10), indicating small degrees of partial melting of a garnet-bearing mantle. Mildly silica-undersaturated and rare silica-saturated basalts, including tholeiites, are less enriched (La/YbN<10), a result of higher degrees of melting. Trace elements and isotopes (Sr, Nd, Pb) reveal a regional gradient explained by mixing between two mantle components, subduction-modified lithosphere and HIMU-like plume (206Pb/204Pb >20) materials. Geophysical studies indicate a deep thermal anomaly beneath central Marie Byrd Land, suggesting a plume influence on volcanism and tectonism.

scholarly journals Magmatism of the Weddell Sea rift system in Antarctica: Implications for the age and mechanism of rifting and early stage Gondwana breakup

2020 ◽  
Vol 79 ◽  
pp. 185-196 ◽  
Author(s):  
Teal R. Riley ◽  
Tom A. Jordan ◽  
Philip T. Leat ◽  
Mike L. Curtis ◽  
Ian L. Millar
Keyword(s):  
Early Stage ◽  
Weddell Sea ◽  
Rift System

Rb/Sr Ages and a profile of initial Sr87/Sr86 ratios for plutonic rocks across the Yukon Crystalline Terrane

1976 ◽  
Vol 13 (2) ◽  
pp. 319-330 ◽  
Author(s):  
P. C. Le Couteur ◽  
D. J. Tempelman-Kluit
Keyword(s):  
Quartz Diorite ◽  
Igneous Rocks ◽  
Slow Cooling ◽  
Precambrian Rocks ◽  
Quartz Monzonite ◽  
Plutonic Complex ◽  
Coast Plutonic Complex ◽  
Plutonic Rocks

Nine Rb/Sr apparent ages are reported for igneous rocks of the Yukon Crystalline Terrane. The oldest age (144 m.y.) is from the Triassic? Klotassin quartz diorite and is thought to be a hybrid age that probably reflects the effects of younger intrusives on rocks at least 190 m.y. old. Five ages of about 100 m.y. presumably reflect the cooling of the Coffee Creek quartz monzonite. K/Ar ages for this event are slightly younger than the Rb/Sr ages, suggesting slow cooling. Rb/Sr ages of 53 and 67 m.y. were obtained for the Ruby Range batholith and an age of 61–67 m.y. for the Nisling Range alaskite. The Rb/Sr ages obtained generally confirm recently determined K/Ar ages. There is a regional decrease in initial Sr87/Sr86 ratios, southwestward across the Yukon Crystalline Terrane. This may mean that Precambrian rocks extend under the Yukon Crystalline Terrane, but are absent under the adjoining Coast Plutonic Complex.

The Genesis of Oligoclase in Certain Schists

1933 ◽  
Vol 70 (12) ◽  
pp. 529-541 ◽  
Author(s):  
F. J. Turner
Keyword(s):  
Chemical Composition ◽  
Bulk Composition ◽  
Regional Metamorphism ◽  
Slight Modification ◽  
Igneous Rocks ◽  
Calcic Plagioclase ◽  
Irregular Distribution ◽  
Thermal Metamorphism

The mineralogical changes in green schists and related quartzofelspathic schists of sedimentary origin are discussed, and the following conclusions are reached as to the conditions of formation of oligoclase in these rocks:—(1) Oligoclase normally appears as a product of dynamothermal metamorphism at relatively high grades such as prevail in the zones of almandine and perhaps kyanite. It is accompanied either by deeply-coloured hornblende, hornblende and biotite, or biotite and muscovite, according to the chemical composition of the rocks in which it occurs.(2) Sodic oligoclase containing 10 per cent to 15 per cent of anorthite may occur with pale aluminous hornblende in green schists lying within the more strongly metamorphosed portion of the chlorite zone. The rocks in question are low in potash and have been formed by reconstitution, at a higher grade, of chlorite-epidotealbite-schists containing calcite. This oligoclase-hornblende association is not to be confused with the actinolite-epidote-albite-chlorite assemblage which is formed at any grade within the zone of chlorite, by direct reconstitution of basic igneous rocks without change in bulk composition and in the absence of CO2. A slight modification of Tilley’s subdivision of the green schist facies of Eskola is therefore introduced.(3) A zone of oligoclase representing a grade of metamorphism higher than that attained in the biotite zone, may be recognized for quartzo-felspathic schists of appropriate composition and for many green schists, in areas of progressive regional metamorphism. In the latter case, blue-green hornblende often accompanied by biotite is also present.(4) Oligoclase or more calcic plagioclase and deeply-coloured hornblende form readily during purely thermal metamorphism of only medium grade in the absence of stress. This accounts for the irregular distribution of both these minerals in districts where purely thermal and regional metamorphism have both occurred during the same period of orogeny.

Possible extension of the Midcontinent Rift in west Texas and eastern New Mexico

1994 ◽  
Vol 31 (4) ◽  
pp. 709-720 ◽  
Author(s):  
Donald C. Adams ◽  
G. Randy Keller
Keyword(s):  
New Mexico ◽  
Lake Superior ◽  
Igneous Rocks ◽  
Rift System ◽  
Central Basin ◽  
Midcontinent Rift ◽  
Sacramento Mountains ◽  
Midcontinent Rift System ◽  
Southern Oklahoma ◽  
Igneous Activity

The Midcontinent Rift System forms one of the most prominent gravity features in North America. The recognized geophysical anomaly extends in an arc from southern Oklahoma to Lake Superior and then into southern Michigan. The Midcontinent Rift System was active between 1185–1010 Ma, as indicated in the Lake Superior region by age determinations on intrusive igneous rocks. We suggest that the period of formation of the Midcontinent Rift was also a time of extensive igneous activity in Texas and New Mexico. This activity is represented by intrusions beneath the Central basin platform (Texas and New Mexico), intrusions which crop out at the Pajarito Mountain in the Sacramento Mountains (New Mexico), a basaltic debris flow in the Franklin Mountains (Texas), basalt flows at Van Horn (Texas), and the Crosbyton geophysical anomaly (east of Lubbock, Texas). These bodies and other bodies located by geophysical anomalies and wells drilled into mafic Precambrian rocks may be related to the Midcontinent Rift System. Alternatively this magmatism could be related to Grenville age tectonics in Texas. The mafic igneous rocks in this area form a 530 km diameter Middle Proterozoic igneous province, which formed between 1070 and 1220 Ma. Comparison of the Midcontinent Rift System and its extensions proposed here with the Mesozoic and Cenozoic African rift systems indicates that these features are of comparable scale and complexity.

The distinction of analcime from leucite in rocks by X-ray methods

1931 ◽  
Vol 22 (132) ◽  
pp. 469-476 ◽  
Author(s):  
F. A. Bannister
Keyword(s):  
Isotropic Material ◽  
Igneous Rocks ◽  
North African ◽  
X Ray ◽  
Ray Methods ◽  
Basaltic Lavas

Since W. Lindgren first detected the presence of microphenocrysts of analcime in basalt, many observers have recorded this mineral as a constituent of igneous rocks, but there is some difficulty in distinguishing between analcime and glass and between analcime and leucite in thin rock-sections. For instance, H. Rosenbusch identified the interstitial colourless isotropic material in monchiquites as glass, whereas L. V. Pirsson showed it to be analcime. H.S. Washington showed that basalts from Sardinia, previously thought to be leueitic, contain phenocrysts of analcime. A. Lacroix also found, in his study of north African basaltic lavas, that in many cases so-called leucite-lavas actually contain analcime and not leucite.

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.

A lacustrine record of the early stage of the Miocene Climatic Optimum in Central Europe from the Most Basin, Ohře (Eger) Graben, Czech Republic

2014 ◽  
Vol 151 (6) ◽  
pp. 1013-1033 ◽  
Author(s):  
TOMÁŠ MATYS GRYGAR ◽  
KAREL MACH ◽  
PETR SCHNABL ◽  
PETR PRUNER ◽  
JIŘÍ LAURIN ◽  
...  
Keyword(s):  
Current Knowledge ◽  
Early Stage ◽  
Sedimentary Environment ◽  
Magnetic Polarity ◽  
Early Miocene ◽  
Rift System ◽  
Age Model ◽  
Climatic Optimum ◽  
The Stability ◽  
Lake Deposits

AbstractThis study reports on a ~ 150 m thick macrofossil-barren sequence of siliciclastic sediments from a Burdigalian age (Early Miocene) freshwater lake. The lake was located within an incipient rift system of the Most Basin in the Ohře (Eger) Graben, which was part of the European Cenozoic Rift System, and had an original area of ≈ 1000 km2. Sediments from the HK591 core that cover the entire thickness of the lake deposits and some of the adjacent stratigraphic units were analysed by X-ray fluorescence spectroscopy (a proxy for element composition) and magnetic polarity measurement. The element proxies were subjected to frequency analysis, which provided estimated sedimentation rates, and allowed for sediment dating by magnetostratigraphy and orbital tuning of the age model. Based on the resulting age model and the known biostratigraphy, the lake was present between 17.4 and 16.6 Ma, which includes the onset of the Miocene Climatic Optimum in the latest Early Miocene. The identification of orbital forcing (precession, obliquity and short eccentricity cycles) confirms the stability of the sedimentary environment of the perennial lake in an underfilled basin. The dating allowed the sediment record to be interpreted in the context of the current knowledge of the European climate during that period. The stability of the sedimentary environment confirms that precipitation was relatively stable over the period recorded by the sediments.

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