Mesoproterozoic sedimentation, magmatism, and metamorphism in the southern part of the Grenville Province (western Quebec): U–Pb geochronological constraints

1995 ◽  
Vol 32 (12) ◽  
pp. 2103-2114 ◽  
Author(s):  
R. M. Friedman ◽  
J. Martignole
Keyword(s):  
The Other ◽  
High Grade ◽  
Metamorphic Zircon ◽  
Grenville Province ◽  
Plutonic Complex ◽  
Minimum Age ◽  
High Grade Metamorphism ◽  
The One ◽  
Geochronological Constraints ◽  
Age Range

U–Pb data provide new constraints on the age of sedimentation, metamorphism, magmatism, and deformation in the Grenville Province of western Quebec. A metapelite, an alaskitic gneiss, and an amphibolite were sampled within an area of 1 km2 in the Mont-Laurier terrane. The metapelite yielded detrital-metamorphic zircons that gave 207Pb/206Pb ages of ca. 1205–2200 Ma. The youngest detrital components, between 1210 and 1300 Ma and possibly as old as [Formula: see text] Ma, provide a maximum age range for the deposition of this rock. Data for the alaskitic gneiss suggest that it is either derived from an igneous (volcanic) protolith with a minimum age of ca. 1250 Ma and a maximum age of [Formula: see text] Ma, or is a dyke emplaced at ca. 1140–1170 Ma. The amphibolite yielded zircon interpreted as metamorphic, with a minimum age of 1118 Ma, and a maximum age not likely older than ca. 1160 Ma. Zircons from charnockites and monzonites of the Morin plutonic complex gave zircon igneous ages between ca. 1157 and 1165 Ma. High-grade metapelites of the Réservoir Cabonga terrane yielded metamorphic zircon ages of 1140-1160 Ma. Metamorphic monazites from both the Réservoir Cabonga and the Mont-Laurier terranes yielded ages of 1138−1182 Ma, interpreted as the crystallization age or the time that significant Pb loss ceased. These ages indicate that the two terranes underwent the same long-lasting metamorphic event. The overlap between ages of metamorphic zircons and monazites on the one hand and the age of anorthosite–charnockite magmatism on the other hand suggests a long-lasting high-grade metamorphism with heat contribution from crystallizing plutons. A posttectonic aplite dyke from the interior of the Mont-Laurier terrane gives a zircon minimum age of 1054 Ma, considered a minimum age for penetrative deformation in this part of the Grenville Province. Rutile ages of 945–955 Ma record cooling through about 400 °C in both the Réservoir Cabonga and the Mont-Laurier terranes.

Time of metamorphism beneath the Central Metasedimentary Belt boundary thrust zone, Grenville Orogen, Ontario: accretion at 1080 Ma?

1997 ◽  
Vol 34 (7) ◽  
pp. 1023-1029 ◽  
Author(s):  
H. Timmermann ◽  
R. A. Jamieson ◽  
N. G. Culshaw ◽  
R. R. Parrish
Keyword(s):  
Linear Array ◽  
High Grade ◽  
Granitoid Rock ◽  
Metamorphic Zircon ◽  
Grenville Province ◽  
Grade Metamorphism ◽  
Regional Tectonic ◽  
Thrust Zone ◽  
High Grade Metamorphism ◽  
Central Gneiss Belt

New U–Pb zircon and titanite data from the Muskoka domain, Grenville Province, Ontario, provide protolith and metamorphic ages for the southwestern Central Gneiss Belt. Discordant analyses from a migmatitic orthogneiss and its leucosome form a linear array with an upper intercept age of 1457 ± 6 Ma and a lower intercept age of 1064 ±18 Ma. U–Pb analyses on metamorphic zircon from an amphibolite yield a set of concordant analyses with an average 207Pb/206Pb age of 1079 ± 3 Ma. A weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the Central Metasedimentary Belt boundary thrust zone yielded a discordant array of analyses wth an upper intercept age of 1394 ± 13 Ma and a lower intercept age of 1066 ± 8 Ma. The charnockitic vein yielded concordant zircon ages of 1077 ± 2 Ma. The upper intercept ages are interpreted in terms of protolith crystallization, and the concordant and lower intercept ages as Grenviilian high-grade metamorphism and associated anatexis. We have found no evidence for a ca. 1190–1160 Ma metamorphic event in these rocks, as required by some regional tectonic interpretations. We conclude that emplacement of the Central Metasedimentary Belt over the Central Gneiss Belt, which caused high-grade metamorphism in the Muskoka domain, occurred at or shortly before ca. 1080 Ma, and that this marks the time of accretion of the Central Metasedimentary Belt to the southeast margin of Laurentia.

Geology and geochronology of Helikian magmatism, western Labrador

1981 ◽  
Vol 18 (7) ◽  
pp. 1211-1227 ◽  
Author(s):  
Christopher Brooks ◽  
Richard J. Wardle ◽  
Toby Rivers
Keyword(s):  
Volcanic Rocks ◽  
High Grade ◽  
Regional Mapping ◽  
Grenville Province ◽  
Felsic Volcanism ◽  
High Grade Metamorphism ◽  
Narrow Belt ◽  
Intrusive Suite ◽  
Magmatic History ◽  
Magma Series

The Shabogamo intrusive suite, a predominantly gabbroic magma series intrusive into a variety of Archean, Aphebian, and Helikian units in the Churchill and Grenville Provinces of western Labrador, is reliably dated at circa 1375 Ma using both the Rb/Sr and Sm/Nd methods on whole rocks and mineral separates. The suite is thus synchronous with Elsonian magmatism in Labrador, which is characterized by the intrusion of large volumes of gabbroic, anorthositic, and associated magma, and so invites petrogenetic correlations on a regional scale.Gabbros of the Shabogamo intrusive suite are emplaced into volcanics and volcaniclastics of the Blueberry Lake group, which are provisionally dated at 1540 ± 40 Ma. The volcanic rocks are therefore of similar age to, and probably correlative with, the upper Petscapiskau Group and Bruce River Group felsic volcanics, which occur further east in a narrow belt within the Grenville Foreland zone. The linear disposition of centres of felsic volcanism in the Grenville Foreland zone about 1500 Ma ago is suggestive of the development of a major ensialic rift at least 300 km in length at that time. A twofold magmatic history during the Helikian of this part of Labrador is now emerging from the field mapping and geochronological studies. Early extrusive felsic volcanism about 1500 Ma ago confined to a linear belt immediately north of the Grenville Province was followed by voluminous mafic magmatism (with emplacement of gabbroic, anorthositic, and associated rocks) occurring over a wide area both within and outside of the present location of the Grenville Province.Rb/Sr dating of Aphebian quartzofeldspathic schists from within the Grenville Province near Wabush – Labrador City shows that the high-grade metamorphism and development of a penetrative schistosity were Grenvillian features formed about 1000 Ma ago. This result effectively precludes the possibility of a Hudsonian metamorphic imprint, a feasible interpretation that was raised during regional mapping of the area.

scholarly journals Search for Archaean basement in the Caledonian fold belt of North-East Greenland

1994 ◽  
Vol 162 ◽  
pp. 129-133
Author(s):  
A.P Nutman ◽  
F Kalsbeek
Keyword(s):  
High Grade ◽  
Metamorphic Zircon ◽  
Fold Belt ◽  
Pb Isotope ◽  
Zircon Age ◽  
East Greenland ◽  
Early Proterozoic ◽  
North East ◽  
History Of ◽  
High Grade Metamorphism

SHRIMP U-Pb isotope data on zircon crystals from a gneiss sample near Danmarkshavn, where the presence of Archaean rocks has earlier been documented, show that the rock has undergone a complex history of igneous and metamorphic zircon growth. At least three generations of zircon are present with ages of c. 3000 Ma, c. 2725 Ma and 1967 ±8 Ma (2 α). Apparently the rock was formed from an Archaean protolith which underwent high grade metamorphism during the early Proterozoic. Another sample from the easternmost exposures of the Caledonian basement, collected further north, yielded only early Proterozoic zircons with an age of 1963 ± 6 Ma. Together with a SHRIMP U-Pb zircon age of 1974 ± 17 Ma reported earlier, these results give evidence of a major igneous and metamorphic event in North-East Greenland about 1965 Ma ago.

scholarly journals THE ETHICS OF PRESCRIBING OFF-LABEL DRUGS IN CHILDREN.THE DILEMMA OF SILDENAFIL

2015 ◽  
Vol 64 (2) ◽  
pp. 126-130
Author(s):  
Laszlo-Zoltan Sztankovszky ◽  
◽  
Magdalena Iorga ◽  
Cristian Gheonea ◽  
Georgiana Russu ◽  
...  
Keyword(s):  
Pediatric Cardiology ◽  
The Other ◽  
Off Label Use ◽  
Off Label ◽  
Other Hand ◽  
Widespread Phenomenon ◽  
The One ◽  
Age Range ◽  
Label Use

The off-label prescription means that medicines are administered by an unlicensed route, in an unlicensed formulation or dosage or to a child below the stated age range. The use of drugs in an off-label or unlicensed manner to treat children is widespread. Because many prescribed treatments for children have not been adequately tested in children, this population of patients remains a vulnerable one. On the one hand, prescribing off-label use drugs in children determines a lot of controversies but, one the other hand, without this possibility, could be deprived of a chance to be treated. The paper presents the widespread phenomenon of off-label us drugs in children, reflecting in scientific studies in USA and Europe. An important focus is on Romanian statistic of Sildenafil prescription and on dilemmatic use of it in pediatric cardiology unit.

Monazite as a metamorphic chronometer, south of the Grenville Front, western Quebec

1993 ◽  
Vol 30 (5) ◽  
pp. 1056-1065 ◽  
Author(s):  
Fiona Childe ◽  
Ronald Doig ◽  
Clément Gariépy
Keyword(s):  
Cooling Rate ◽  
Closure Temperature ◽  
High Grade ◽  
Grenville Province ◽  
Abrupt Transition ◽  
Grade Metamorphism ◽  
Tectonic Transport ◽  
High Grade Metamorphism

Monazite was utilized as a chronometer to examine the effects of high-grade metamorphism across the Parautochthonous Belt and Allochthon Boundary Thrust of the Grenville Province in western Quebec. This study, in addition to previous geo-chronological studies, indicates an Archean component in the gneisses, which is consistent with the presence of more than one set of peak metamorphic conditions.Single-grain monazite analyses from metasedimentary gneisses from four locations within the Parautochthonous Belt yielded Grenvillian U–Pb dates of 1000 ± 5 to 1006 ± 2 Ma. The location farthest to the northwest, 45 km southeast of the Grenville Front, included monazite with a distinct Archean signature. Southeast of this point an Archean signature was not detected in the monazite. At 70 km southeast of the Grenville Front, monazite yielded two discrete ages of 1005 ± 2 and 1020 ± 3 Ma. Xenotime from one location indicated that the closure temperature of this mineral may be equivalent to that of monazite (725 ± 25 °C).Monazite from the Allochthon Boundary Thrust, 135 km southeast of the Grenville Front, yielded 207Pb/206Pb dates of 1049–1092 Ma, indicating earlier cooling than rocks closer to the Grenville Front. The monazite age was combined with that of rutile from the same location to determine a cooling rate of 2 °C/Ma following cooling through the closure temperature of monazite. The abrupt transition from Archean to Grenvillian ages some 45 km southeast of the Grenville Front is consistent with tectonic transport in the form of northwest-directed thrusting.

Translation of Human Rights Law according to Local Context: A Solution to Child Marriage in Africa?

2018 ◽  
Vol 5 (1) ◽  
Author(s):  
Isabela Warioba
Keyword(s):  
Human Rights ◽  
Protective Role ◽  
The Other ◽  
Local Context ◽  
Child Marriage ◽  
Human Rights Law ◽  
Local Conditions ◽  
Minimum Age ◽  
The One ◽  
Child Brides

In Africa, despite decades of campaigns to restrict child marriage through legislation and the adoption of minimum age laws, the practice is still very common and the continent is predicted to have the largest global share of child brides by the year 2050. This begs the question whether human rights law, as it stands, is the appropriate strategy against child marriage. On the one hand, law can create an “enabling environment” and strengthen those who seek the elimination of child marriage; but, on the other hand, vigorous enforcement of such legislation may result in counter-intuitive effects, leaving the girls more vulnerable instead of the law fulfilling its protective role. This article uses a socio-legal approach to argue that the solution to child marriage might lie in a form of translation and enforcement of human rights. It makes a case for the need for human rights to be translated according to local conditions in order to deal effectively with child marriage in Africa. In this case, “translation” refers to the reinterpretation and reframing of human rights in line with specific local conditions, leading towards assimilation and acceptance while maintaining its core foundations.

Paleoproterozoic reworking of an Archean thrust fault in the Hearne domain, Western Churchill Province: U–Pb geochronological constraints

2005 ◽  
Vol 42 (7) ◽  
pp. 1313-1330 ◽  
Author(s):  
K MacLachlan ◽  
W J Davis ◽  
C Relf
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Lake Area ◽  
High Grade ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
Geochronological Constraints ◽  
Basement Deformation ◽  
And Control

The nature, timing and control of Archean crustal architecture on the distribution of Proterozoic reworking in Western Churchill Province are investigated in the Yathkyed Lake area, central Nunavut. The Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains, respectively, in the hanging wall and footwall. Metamorphism and deformation in the hanging wall are ca. 2.66–2.50 Ga. Two episodes of metamorphism are recorded in a foliated granodiorite in the footwall, at 1818+5–2 and 1827 ± 5.6 Ma. The latter age is interpreted as the time of amphibolite-facies metamorphism and deformation in the footwall. A crosscutting dyke provides a minimum age of 1818 ± 2 Ma for this metamorphism and deformation. The TSZ is dominated by dextral oblique-slip shear fabrics. A suite of leucogranite dykes provide a maximum age of 1816 ± 2 Ma for dextral shearing. Dextral deformation is bracketed between 1815 ± 2 and 1811 ± 1 Ma, the ages of two other granitoid dykes. In an area of low dextral strain, there are proto-sheath folds related to Neoarchean thrusting. Paleoproterozoic transtensional shearing in the TSZ was localized along a preexisting late Archean thrust fault. The prior existence of this structure resulted in localization of penetrative Paleoproterozoic deformation in its footwall. This domain of high-grade Proterozoic deformation was uplifted in a regional, antiformal, metamorphic culmination, in part, by dextral-normal shearing along the TSZ. Penetrative basement deformation at depth played a role in transmitting farfield stresses related to the Trans-Hudson Orogen into its hinterland.

scholarly journals Persistence of melt-bearing Archean lower crust for >200 m.y.—An example from the Lewisian Complex, northwest Scotland

Geology ◽  
2019 ◽  
Vol 48 (3) ◽  
pp. 221-225 ◽  
Author(s):  
Richard J.M. Taylor ◽  
Tim E. Johnson ◽  
Chris Clark ◽  
Richard J. Harrison
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

Abstract Geochronological data from zircon in Archean tonalite–trondhjemite–granodiorite (TTG) gneisses are commonly difficult to interpret. A notable example is the TTG gneisses from the Lewisian Gneiss Complex, northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at ca. 2.7 Ga and ca. 2.5 Ga, with intermediate ages reflecting variable Pb loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace-element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchean ages, they exhibit subtle but key step changes in trace-element compositions that are difficult to ascribe to diffusive resetting, but that are consistent with emplacement of regionally extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 m.y. or more during the Neoarchean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace-element compositions consistent with derivation from a mafic source, and they define a well-constrained U-Pb zircon age of ca. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence of melt-bearing lower crust for hundreds of millions of years was probably the norm during the Archean.

Timing and duration of melting in the mid orogenic crust: Constraints from U–Pb (SHRIMP) data, Muskoka and Shawanaga domains, Grenville Province, Ontario

2004 ◽  
Vol 41 (11) ◽  
pp. 1339-1365 ◽  
Author(s):  
Trond Slagstad ◽  
Michael A Hamilton ◽  
Rebecca A Jamieson ◽  
Nicholas G Culshaw
Keyword(s):  
High Grade ◽  
Field Observations ◽  
Ion Microprobe ◽  
Melt Crystallization ◽  
Geochronological Data ◽  
Grenville Province ◽  
Deformational History ◽  
High Grade Metamorphism ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt

The Central Gneiss Belt in the Grenville Province, Ontario, exposes metaplutonic rocks, orthogneisses, and minor paragneisses that were deformed and metamorphosed at crustal depths of 20–35 km during the Mesoproterozoic Grenvillian orogeny. We present sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon data from eight samples of migmatitic orthogneiss, granite, and pegmatite from the Muskoka and Shawanaga domains that constrain the age and duration of partial melting in the mid orogenic crust. Our results support earlier interpretations that the protoliths to these migmatitic orthogneisses formed at ca. 1450 Ma. Emplacement and crystallization of granite and pegmatite in the Shawanaga domain took place at ca. 1089 Ma, apparently coevally with deformation and high-grade metamorphism. Leucosomes in the Muskoka and Shawanaga domains yield ages of 1067 and 1047 Ma, respectively, interpreted as the ages of melt crystallization. The geochronological data and field observations suggest that melt was present at the mid-crustal level of the Grenville orogen during a significant part of its deformational history, probably at least 20–30 million years. By analogy with modern orogens, the amount and duration of melting observed in the Muskoka and Shawanaga domains may have had an impact on the orogenic evolution of the area.

Persistence of melt-bearing Archean lower crust for >200 m.y.— An example from the Lewisian Complex, northwest Scotland

2020 ◽  
Author(s):  
Tim Johnson ◽  
Rich Taylor ◽  
Chris Clark
Keyword(s):  
Trace Element ◽  
Lower Crust ◽  
Mafic Magma ◽  
High Grade ◽  
Trace Element Data ◽  
Metamorphic Zircon ◽  
Geochronological Data ◽  
Zircon Age ◽  
Gneiss Complex ◽  
High Grade Metamorphism

<p><strong>Geochronological data in zircon from Archaean tonalite–trondhjemite–tonalite (TTG) gneisses is commonly difficult to interpret. A notable example are TTG gneisses from the Lewisian Gneiss Complex (LGC), northwest Scotland, which have metamorphic zircon ages that define a more-or-less continuous spread through the Neoarchaean, with no clear relationship to zircon textures. These data are generally interpreted to record discrete high-grade events at c. 2.7 Ga and c. 2.5 Ga, with intermediate ages reflecting variable Pb-loss. Although ancient diffusion of Pb is commonly invoked to explain such protracted age spreads, trace element data in zircon may permit identification of otherwise cryptic magmatic and metamorphic episodes. Although zircons from the TTG gneiss analyzed here show a characteristic spread of Neoarchaean ages, they exhibit subtle but key step changes in trace element compositions that are difficult to ascribe to diffusive resetting, but which are consistent with emplacement of regionally-extensive bodies of mafic magma. These data suggest suprasolidus metamorphic temperatures persisted for 200 Myr or more during the Neoarchaean. Such long-lived high-grade metamorphism is supported by data from zircon grains from a nearby monzogranite sheet. These preserve distinctive trace element compositions suggesting derivation from a mafic source, and define a well-constrained U–Pb zircon age of c. 2.6 Ga that is intermediate between the two previously proposed discrete metamorphic episodes. The persistence for hundreds of millions of years of melt-bearing lower crust was probably the norm during the Archaean.</strong></p>

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