Geochronology of Archean and Proterozoic Rocks in the Southern District of Keewatin

1975 ◽  
Vol 12 (1) ◽  
pp. 95-114 ◽  
Author(s):  
R. K. Wanless ◽  
K. E. Eade
Keyword(s):  
Volcanic Rocks ◽  
Southern District ◽  
Quartz Monzonite ◽  
Minimum Age ◽  
First Time ◽  
Hurwitz Group ◽  
Age Determinations

Rb–Sr and U–Pb dating techniques have been utilized to identify and date Archean supracrustal rocks within the Churchill structural province in regions where K–Ar age determinations have recorded only the effects of younger Hudsonian orogeny. The age of emplacement of Archean granodiorite has been established at 2550 m.y., a determination that also provides a minimum age for volcanic rocks intruded by the granodiorite.The overlying Proterozoic Hurwitz Group volcanic rocks have been dated for the first time at 1808 ± 35 m.y. (Upper Aphebian). A post-Hurwitz Group quartz monzonite pluton intruded the granodiorite gneiss at 1772 ± 22 m.y. and the age of the post-tectonic Nueltin Lake Granite has been established at 1700 ± 16 m.y. (Paleohelikian).It is concluded that the Hurwitz Group cannot be correlated with the Huronian succession in Ontario as the Hurwitz Group rocks are 300 to 400 m.y. younger than the Huronian strata.

Potassium–Argon Age Determinations of Metamorphic and Plutonic Rocks in the Yukon Crystalline Terrane

1975 ◽  
Vol 12 (11) ◽  
pp. 1895-1909 ◽  
Author(s):  
D. J. Tempelman-Kluit ◽  
R. K. Wanless
Keyword(s):  
Volcanic Rocks ◽  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Retrograde Metamorphism ◽  
Acid Volcanic ◽  
Quartz Monzonite ◽  
Plutonic Rocks ◽  
Dyke Swarms ◽  
Age Determinations

Forty-four new potassium–argon age determinations on minerals of metamorphic and igneous rocks from the Yukon Crystalline Terrane define the timing of the three most recent thermal events affecting this region. The oldest, 160 to 170 Ma ago, involved weak retrograde metamorphism of igneous and metamorphic rocks and coincides with the intrusion of batholiths of pink quartz monzonite. The next event, 90 to 100 Ma ago, reflects the emplacement of batholiths of the Coffee Creek quartz monzonite suite. The youngest thermal episode, 50 to 60 Ma ago, marks the time when the Nisling Range alaskite, with its porphyry dyke swarms and explosive acid volcanic rocks, was emplaced and when the K–Ar system of the Ruby Range Batholith was thermally reset. The data provide a younger limit to the age of the oldest Mesozoic plutonic rocks, the Klotassin suite, but they do not define its time of emplacement.

Geology and Geochronology of the Wollaston Lake Fold Belt in Northwestern Manitoba

1975 ◽  
Vol 12 (10) ◽  
pp. 1749-1759 ◽  
Author(s):  
W. Weber ◽  
R. K. Anderson ◽  
G. S. Clark
Keyword(s):  
Igneous Rocks ◽  
Lake Area ◽  
Fold Belt ◽  
Rock Series ◽  
Granitic Gneiss ◽  
Metasedimentary Rocks ◽  
Continental Deposits ◽  
Quartz Monzonite ◽  
Minimum Age ◽  
Hurwitz Group

Recent studies in the northeastern extension of the Wollaston fold belt in Manitoba suggest that Aphebian metasedimentary rocks of the southern Churchill province comprise a geosynclinal facies that is conformably overlain by a platform facies. A possible period of emergence and embryonic Hudsonian tectonism separates this lower sequence from a blanket of continental deposits, which is probably of large regional extent and includes part of the Hurwitz Group in the District of Keewatin.Rubidium–strontium total-rock isochron ages have been obtained for five rock units in the Kasmere Lake area of Manitoba. The ages reveal that the metasedimentary rocks of the Wollaston fold belt are bounded to the east by an Archean complex comprising a differentiated hypersthene-bearing rock series having a minimum age of 2745 ± 124 Ma (87Rb = 1.39 × 10−11 yr−1) and a quartz monzonite unit having a minimum age of 2636 ± 163 Ma.Hudsonian igneous rocks are mostly syn- to post-kinematic. The age of 1855 ± 62 Ma for a quartz monzonite of batholithic dimension coincides with the ages of similar syntectonic Hudsonian intrusions in the Northwest Territories. The age of 1800 ± 60 Ma obtained from a pelitic gneiss unit is a minimum age for the Hudsonian metamorphism and dates the end of the Hudsonian orogeny in this part of the Churchill province. An age of 1941 ± 25 Ma for a granitic gneiss along the western margin of the Wollaston fold belt indicates early or pre-Hudsonian magmatic activity.

Urban cloverleaves: origin, aesthetics, and contradictions of the Slussen, Stockholm

2021 ◽  
pp. 1-14
Author(s):  
Álvaro Clua Uceda
Keyword(s):  
Traffic Engineering ◽  
City Centre ◽  
Compact City ◽  
The Baltic Sea ◽  
Southern District ◽  
Stockholm Archipelago ◽  
The Baltic ◽  
First Time ◽  
Historic City ◽  
Different Levels

On 11 October 1935, the inauguration of the Slussen urban cloverleaf took place in front of the excited citizens of Stockholm. It had the attributes of a pure traffic machine taken from the most advanced traffic engineering publications, and it expressed the optimistic cultural modernism that five years ago the Stockholm International Exhibition had promoted.1 This urban cloverleaf was made of translucent glass, reinforced concrete, metallic handrails, and reflective tiles and was meant to solve, in one single gesture, the complex urban link between the Lake Mälaren and the Baltic Sea, between Gamla Stan – the historic city centre – and Södermalm – the southern district built on top of the 35-metre-high plateau [1]. The solution made difficult urban compromises between the foothills of the Brunkeberg topography, the smooth water surfaces of the Stockholm archipelago, the architecture of the historic urban tissue, and the demands of a complex articulated mobility. Boats, goods, suburban trains, subways, trams – later buses – pedestrians, cyclists, and automobiles finally converged on this place at different levels, completing the intricacies of a threedimensional geometry which, for the first time in history, was inserted into a compact city.

A Discussion on global tectonics in Proterozoic times - Late Proterozoic cratonization in southwest Saudi Arabia

1976 ◽  
Vol 280 (1298) ◽  
pp. 517-527 ◽  
Keyword(s):  
Saudi Arabia ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Granulite Facies ◽  
Greenschist Facies ◽  
Arabian Shield ◽  
Granulite Facies Metamorphism ◽  
Quartz Monzonite ◽  
Facies Metamorphism ◽  
Global Tectonics

Early cratonal development of the Arabian Shield of southwestern Saudi Arabia began with the deposition of calcic to calc-alkalic, basaltic to dacitic volcanic rocks, and immature sedimentary rocks that subsequently were moderately deformed, metamorphosed, and intruded about 960 Ma ago by dioritic batholiths of mantle derivation (87Sr/86Sr = 0.7029). A thick sequence of calc-alkalic andesitic to rhyodacitic volcanic rocks and volcanoclastic wackes was deposited unconformably on this neocraton. Regional greenschistfacies metamorphism, intensive deformation along north-trending structures, and intrusion of mantle-derived (87Sr/86Sr = 0.7028) dioritic to granodioritic batholiths occurred about 800 Ma. Granodiorite was emplaced as injection gneiss about 785 Ma (87Sr/86Sr = 0.7028- 0.7035) in localized areas of gneiss doming and amphibolite to granulite facies metamorphism. Deposition of clastic and volcanic rocks overlapped in time and followed orogeny at 785 Ma. These deposits, together with the older rocks, were deformed, metamorphosed to greenschist facies, and intruded by calc-alkalic plutons (87Sr/86Sr = 0.7035) between 600 and 650 Ma. Late cratonal development between 570 and 550 Ma involved moderate pulses of volcanism, deformation, metamorphism to greenschist facies, and intrusion of quartz monzonite and granite. Cratonization appears to have evolved in an intraoceanic, island-arc environment of comagmatic volcanism and intrusion.

Growth rates of pterobranchs and the lifespan of graptolites

Paleobiology ◽  
1993 ◽  
Vol 19 (4) ◽  
pp. 459-475 ◽  
Author(s):  
Susan Rigby ◽  
P. Noel Dilly
Keyword(s):  
Environmental Stress ◽  
Water Column ◽  
Growth Rates ◽  
Life Tables ◽  
Taxonomic Significance ◽  
Utica Shale ◽  
Minimum Age ◽  
First Time

Pterobranchs are the closest living relatives of graptolites. Their skeleton is constructed from the same material, and in a homologous manner. Growth rates of the pterobranch Cephalodiscus gracilis are described for the first time and, along with rhabdopleuran growth rates, they are used to estimate the amount of time invested by a graptolite colony in growing its rhabdosome. This is a measure of minimum age. The significance of age calculations is shown for individuals and large communities of graptoloids. Large individuals can be shown to be much older than the time it would have taken them to settle through seawater and so it is shown that graptoloids moved up, as well as down, through the water column. Life tables constructed for biserial graptoloids from the Utica shale in Quebec, Canada, suggest that these graptoloids died from constant environmental stress. Graptoloid length can thus be a function of environment and should only cautiously be considered to be of taxonomic significance.

scholarly journals New data on the ecological peculiarities and the distribution in Bulgaria of the vulnerable habitat F3.1d Balkan-Anatolian submontane genistoid scrub from the European Red List of Habitats

Hacquetia ◽  
2019 ◽  
Vol 18 (2) ◽  
pp. 271-287
Author(s):  
Georgi Kunev ◽  
Rossen Tzonev
Keyword(s):  
Vegetation Type ◽  
Volcanic Rocks ◽  
Habitat Type ◽  
Life Forms ◽  
Plant Life Forms ◽  
Area Of Occupancy ◽  
Floristic Elements ◽  
First Time ◽  
Floristic Structure ◽  
East Mediterranean Region

Abstract The study presents new data on the habitat dominated by the species complex of Genista lydia/G. rumelica in Bulgaria. It is based on 129 phytocoenological relevés and provides information on the chorology, ecology and floristic structure of these communities. This habitat type occupies substrates composed by different volcanic rocks. The floristic structure is very rich in species. The phytogeographical relationships with the East Mediterranean region are considerable, which is proved by the high occurrence of floristic elements with Mediterranean or sub-Mediterranean origin. The plant life-forms analysis demonstrates that the therophytes, geophytes and chamephytes prevail in their floristic structure, which is also typical for the shrub communities in this region. During the field study this vegetation type has been mapped and its total area of occupancy has been calculated. For a first time it is proposed this habitat to be divided into three habitat sub-types due to the established differences in the environmental factors. Some recommendations have been proposed on the conservation management and also complements on the habitat‘s descriptions in EUNIS habitat classification.

scholarly journals Gold-hosting supracrustal rocks on Storø, southern West Greenland: lithologies and geological environment

2007 ◽  
Vol 13 ◽  
pp. 41-44 ◽  
Author(s):  
Christian Knudsen ◽  
Jeroen A.M. Van Gool ◽  
Claus Østergaard ◽  
Julie A. Hollis ◽  
Matilde Rink-Jørgensen ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Quartz Veins ◽  
Rock Types ◽  
Minimum Age ◽  
Arc Setting ◽  
Basic Volcanic ◽  
Back Arc ◽  
Different Sources

A gold prospect on central Storø in the Nuuk region of southern West Greenland is hosted by a sequence of intensely deformed, amphibolite facies supracrustal rocks of late Mesoto Neoarchaean age. The prospect is at present being explored by the Greenlandic mining company NunaMinerals A/S. Amphibolites likely to be derived from basaltic volcanic rocks dominate, and ultrabasic to intermediate rocks are also interpreted to be derived from volcanic rocks. The sequence also contains metasedimentary rocks including quartzites and cordierite-, sillimanite-, garnet- and biotite-bearing aluminous gneisses. The metasediments contain detrital zircon from different sources indicating a maximum age of the mineralisation of c. 2.8 Ga. The original deposition of the various rock types is believed to have taken place in a back-arc setting. Gold is mainly hosted in garnet- and biotite-rich zones in amphibolites often associated with quartz veins. Gold has been found within garnets indicating that the mineralisation is pre-metamorphic, which points to a minimum age of the mineralisation of c. 2.6 Ga. The geochemistry of the goldbearing zones indicates that the initial gold mineralisation is tied to fluid-induced sericitisation of a basic volcanic protolith. The hosting rocks and the mineralisation are affected by several generations of folding.

Updating the International Seafarers' Code: Recent Developments

1997 ◽  
Vol 12 (3) ◽  
pp. 341-363 ◽  
Author(s):  
George P. Politakis
Keyword(s):  
State Control ◽  
Private Placement ◽  
Hours Of Work ◽  
Recent Developments ◽  
Labour Standards ◽  
Minimum Age ◽  
Changing Practices ◽  
Working And Living Conditions ◽  
First Time ◽  
Core Issues

AbstractMaritime labour matters have traditionally been of particular importance as far as the ILO's standard-setting function is concerned. To date, the ILO has adopted a total of 39 conventions and 30 recommendations-a body of labour standards known as the International Seafarer's Code-addressing the specific problems related to the working and living conditions of seafarers. The 84th (Maritime) session of the International Labour Conference, held in October 1996, undertook to revise core issues of this body of standards in the light of rapidly changing practices and needs of the maritime sector. This article traces briefly the negotiating history and highlights some of the most salient aspects of the new conventional instruments such as the setting of the minimum age for seafarers at 16 years, the adoption of a convention for the first time on labour inspection, the establishment of daily and weekly limitations on hours of work, the extension of port state control (as provided for in ILO Convention 147) in matters concerning hours of work and manning, or the recognition of private placement services for seafarers.

scholarly journals The main pulse of the Siberian Traps expanded in size and composition

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
L. E. Augland ◽  
V. V. Ryabov ◽  
V. A. Vernikovsky ◽  
S. Planke ◽  
A. G. Polozov ◽  
...  
Keyword(s):  
Volcanic Activity ◽  
Volcanic Rocks ◽  
West Siberia ◽  
Main Pulse ◽  
Environmental Consequences ◽  
Siberian Traps ◽  
Minimum Age ◽  
Area North ◽  
Permian Mass Extinction ◽  
Compositional Diversity

AbstractEmplacement of large volumes of (sub)volcanic rocks during the main pulse of the Siberian Traps occurred within <1 m.y., coinciding with the end-Permian mass extinction. Volcanics from outside the main Siberian Traps, e.g. Taimyr and West Siberia, have since long been correlated, but existing geochronological data cannot resolve at a precision better than ~5 m.y. whether (sub)volcanic activity in these areas actually occurred during the main pulse or later. We report the first high precision U-Pb zircon geochronology from two alkaline ultramafic-felsic layered intrusive complexes from Taimyr, showing synchronicity between these and the main Siberian Traps (sub)volcanic pulse, and the presence of a second Dinerian-Smithian pulse. This is the first documentation of felsic intrusive magmatism occurring during the main pulse, testifying to the Siberian Trap’s compositional diversity. Furthermore, the intrusions cut basal basalts of the Taimyr lava stratigraphy hence providing a minimum age of these basalts of 251.64 ± 0.11 Ma. Synchronicity of (sub)volcanic activity between Taimyr and the Siberian Traps imply that the total area of the Siberian Traps main pulse should include a ~300 000 km2 area north of Norilsk. The vast aerial extent of the (sub)volcanic activity during the Siberian Traps main pulse may explain the severe environmental consequences.

The Lower Ordovician Brachiopod Syntrophla sp., cf. S. arethusa (Billings 1862) from South Catcher Pond, Northeastern Newfoundland

1973 ◽  
Vol 10 (3) ◽  
pp. 427-430 ◽  
Author(s):  
A. J. Boucot
Keyword(s):  
North American ◽  
Volcanic Rocks ◽  
Lower Ordovician ◽  
First Time

The Lower Ordovician North American Province brachiopod genus Syntrophia is recognized for the first time from northern Newfoundland. It occurs together with other Lower Ordovician fossils (trilobites and conodonts) in a limestone lens interbedded with volcanic rocks that may belong to the Lush's Bight Group.

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