The Flinton Group: a late Precambrian metasedimentary succession in the Grenville Province of eastern Ontario

1980 ◽  
Vol 17 (12) ◽  
pp. 1685-1707 ◽  
Author(s):  
John M. Moore Jr. ◽  
Peter H. Thompson
Keyword(s):  
Regional Metamorphism ◽  
Grenville Province ◽  
Arc Volcanism ◽  
Late Precambrian ◽  
Granitic Intrusions ◽  
Group A ◽  
Eastern Ontario ◽  
Orogenic Cycle ◽  
Uplift And Erosion ◽  
Block Faulting

Clastic and carbonate metasediments, preserved in narrow synclines, have been correlated over an area of 2000 km2. These strata, the Flinton Group, lie unconformably on metamorphosed volcanic, clastic, and carbonate rocks, and on large granitic intrusions. The group, which comprises six formations, has undergone at least two major folding episodes and one main regional metamorphism of varying grade. The only post-Flinton intrusions are pegmatites at high grade and one tectonically emplaced ultramafic slice.Depositional environment ranged from fluvial to moderate-depth marine. Rapid facies changes, coupled with persistence of some units along strike and close relationships between facies and underlying lithology, point to local sources and local tectonic control of deposition basins. At the onset of sedimentation, a deeply weathered source terrain yielded mature basal redbeds, which were succeeded by less mature clastics as block faulting caused increase of relief between sources and basins. These facies passed offshore into finer, more reduced sediments. Deposition took place between 1050 and 1080 (±25) Ma ago, after arc volcanism, plutonism, uplift, and erosion, and before major regional metamorphism. All these events can be grouped within the Grenvillian orogenic cycle, spanning at least the interval 1300–1000 Ma and including, in eastern Ontario, the pre-Flinton Elzevirian Orogeny and post-Flinton Ottawan Orogeny.

Mineral parageneses and metamorphic reactions in metasedimentary enclaves from the Archaean Gneiss Complex of north-west India

1984 ◽  
Vol 48 (347) ◽  
pp. 195-209
Author(s):  
Ram. S. Sharma ◽  
Brian F. Windley
Keyword(s):  
Regional Metamorphism ◽  
Recrystallization Temperature ◽  
Prograde Metamorphism ◽  
Basement Complex ◽  
North West ◽  
Gneiss Complex ◽  
Two Generations ◽  
Orogenic Cycle ◽  
Banded Gneissic Complex ◽  
Partial Resorption

AbstractThree metasedimentary enclaves up to a kilometre in length of contrasting compositions within the polymetamorphic Banded Gneissic Complex (> 2580Ma) have been studied for their mineral parageneses and metamorphic conditions. The largest enclave, consisting of kyanite-chloritoid-muscovite schist with quartz or corundum, and kyanite-fuchsite-corundum ± diaspore, was metamorphosed at most under lower amphibolite conditions, and is thus not isofacial with the surrounding schists and gneisses (of the ‘basement’ complex) which reached sillimanite-grade metamorphism in the last orogenic cycle (Aravalli: 1650–950Ma Orogeny) in Rajasthan.The second enclave is a calc-silicate rock which occurs as a small lens. The presence of two generations of wollastonite which formed during different metamorphic events in the calcite-quartz-grossularite-anorthite-clinopyroxene assemblage indicates polymetamorphism.The third enclave is a metabasic rock which records a complete polymetamorphic history in discontinuous zones in garnet coexisting with hornblende-chlorite-plagioclase-quartz±epidote. To explain the garnet zoning a model involving partial resorption of early garnet during the initial recrystallization stage of superimposed regional metamorphism is preferred to the alternative based on a single prograde metamorphism and retrogression.The mineralogy of the calc-silicate and metabasic enclaves gives a recrystallization temperature of c. 700°C and a pressure in the range of 8–3 kbar during the second metamorphism.

Whole-Rock Rb/Sr Ages of Metamorphic Rocks from Northern Ellesmere Island, Canadian Arctic Archipelago. I. The Gneiss Terrain between Ayles Fiord and Yelverton Inlet

1975 ◽  
Vol 12 (1) ◽  
pp. 90-94 ◽  
Author(s):  
A. K. Sinha ◽  
Thomas Frisch
Keyword(s):  
Regional Metamorphism ◽  
Canadian Arctic ◽  
Ellesmere Island ◽  
Metamorphic Rocks ◽  
Canadian Arctic Archipelago ◽  
Fold Belt ◽  
Late Precambrian

The first Precambrian ages from the Northern Ellesmere Fold Belt are reported. Six rocks from the largest gneiss terrain in northern Ellesmere Island yield a Late Precambrian age (minimum 742 ± 12 m.y.) of regional metamorphism. Relatively high initial 87Sr/86Sr suggests that the rocks were derived from crustal materials.

U–Pb geochronology of Late Proterozoic rocks of the eastern Cobequid Highlands, Avalon Composite Terrane, Nova Scotia

1991 ◽  
Vol 28 (4) ◽  
pp. 504-511 ◽  
Author(s):  
Ronald Doig ◽  
J. Brendan Murphy ◽  
R. Damian Nance
Keyword(s):  
Nova Scotia ◽  
Shear Zones ◽  
Low Grade ◽  
Geochronological Data ◽  
Magmatic Arc ◽  
Late Precambrian ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
Orogenic Cycle ◽  
High Level

In the Cobequid Highlands of Nova Scotia, low-grade late Precambrian arc-related volcano-sedimentry rocks typical of the Avalon Composite Terrane overlie platformal metasedimentry rocks and are spatially associated with gneisses previously considered to be basement to both these units. U–Pb zircon dates of 580–587 Ma from an orthogneiss and an amphibolite are similar to the U–Pb zircon dates of 580–610 Ma from both syntectonic granites in ductile shear zones and high-level posttectonic plutons that intruded the Avalonian successions. Hence, the gneisses do not represent basement but are an integral part of the Avalonian orogenic cycle. The geochronological data indicate that penetrative fabrics in the gneisses, syntectonic granites, and volcano-sedimentary successions are penecontemporaneous (ca. 580–620 Ma) and not sequential, as previously interpreted. The gneisses have a metamorphic fabric (S1a), crystallized under amphibolite-facies conditions, and may represent the deeper roots of a late Precambrian magmatic arc. Fabrics within the deformed granite gneisses (S1b) are interpreted as reflecting crystallization within active ductile shear zones associated with intra-arc transtension and basin development. Fabrics in the volcano-sedimentary successions (S1c) are associated with deformation of the basin.

Evolution of regional metamorphism during back-arc stretching and subsequent crustal shortening in the 1.9 Ga Wopmay Orogen, Canada

1987 ◽  
Vol 321 (1557) ◽  
pp. 199-218 ◽  
Keyword(s):  
Regional Metamorphism ◽  
Thermal Relaxation ◽  
Time Interval ◽  
Magmatic Arc ◽  
Mineral Growth ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Continental Magmatic Arc ◽  
Uplift And Erosion ◽  
Structural Levels

The stratigraphic units, structural elements and metamorphic mineral assemblages of a regional metamorphic culmination in the 1.9 Ga Wopmay Orogen are exposed over greater than 30 km of composite structural depth, in a series of oblique sections produced by cross folding. Regional metamorphism developed continuously in three sequential, rapidly changing thermo-tectonic régimes within an evolving continental magmatic arc. At ca . 1900 Ma, stretching of intra-arc crust resulted in the accumulation of clastic sediment and bimodal volcanic rift-fill deposits. The onset (first stage) of regional metamorphism is marked by high- T low P mineral assemblages, condensed metamorphic zonal sequences and extensive areas of high-grade gneisses devoid of associated plutons. These features are interpreted in terms of a high thermal gradient related to stretching and thinning of the continental lithosphere. Five to ten million years after stretching, following deposition of a west-facing sedimentary prism, a suite of 1896—1878 Ma plutons was emplaced into the rift and margin deposits as they underwent subhorizontal shortening and deformation during the Calderian Orogeny. Thrusted and folded syn-orogenic foredeep deposits are also intruded by the syn-tectonic plutons. At high and intermediate structural levels, syn-tectonic metamorphic mineral growth and metamorphic zonal sequences which are spatially related to the plutons, document heat advection into the deforming marginal prism and mark a second stage of regional metamorphism related to the emplacement of the plutonic bodies. Inverted mineral isograds in autochthonous Proterozoic units beneath a basal décollement record downward thermal relaxation of isotherms following east-directed Calderian transport of the deformed, thickened, and still hot marginal prism over a relatively cold basement. Derivation of multi-point P - T trajectories from post-tectonic, poikiloblastic garnets charts metamorphic mineral growth during uplift and erosion of the internal zone, documenting the third (final) stage of regional metamorphism in Wopmay Orogen. The short erosional time interval (less than 11 Ma) between tectonic thickening and the end of uplift constrains the heat required for this last metamorphic stage to be inherited from the two preceding thermo-tectonic régimes: epicontinental stretching and the emplacement of the syn-tectonic plutonic suite.

Paleomagnetism of the Whitestone Anorthosite and Diorite, the Grenville Polar Track, and Relative Motions of the Laurentian and Baltic Shields

1975 ◽  
Vol 12 (2) ◽  
pp. 209-226 ◽  
Author(s):  
H. Ueno ◽  
E. Irving ◽  
R. H. McNutt
Keyword(s):  
Regional Metamorphism ◽  
Domain Theory ◽  
Slow Cooling ◽  
Grenville Province ◽  
The Third ◽  
Significant Difference ◽  
Before And After ◽  
Caledonian Orogeny ◽  
The Baltic ◽  
Cooling Model

The Whitestone anorthosite and diorite are situated in the Grenville Structural Province north of Parry Sound, Ontario. They are intruded into sediments and igneous rocks, the whole being metamorphosed to amphibolite facies. Aside from soft magnetizations due to the present field four magnetizations are present, two owing to hematite, the third mainly to magnetite, and a fourth of uncertain source. It is argued that these are thermoremanent magnetizations acquired during very slow cooling following regional metamorphism in the interval 1100 to 1000 m.y. A single-stage cooling model based on Neel's single domain theory is developed, which suggests that the hematite magnetizations were acquired during slow cooling at about 240 °C and the magnetite magnetizations at about 200 °C. The poles from Whitestone rocks fall among a group of poles from elsewhere in the Grenville Province. There are serious problems in integrating these Grenville poles with those from other parts of the Canadian Shield, and three possible ways of relating them are evaluated. Poles from Grenville-type rocks from the Baltic Shield are near to the Grenville poles after correction is made for the late Phanerozoic opening of the Atlantic, showing that the relative positions of Laurentian and Baltic Shields before and after the Caledonian orogeny were very similar. There is however a small but significant difference, and this is attributed to Caledonian diastrophism.

Paleomagnetism of the Lac St-Jean anorthosite and related rocks, Grenville Province, Quebec

1983 ◽  
Vol 20 (2) ◽  
pp. 246-258 ◽  
Author(s):  
K. L. Buchan ◽  
W. F. Fahrig ◽  
G. N. Freda ◽  
R. A. Frith
Keyword(s):  
North American ◽  
Regional Metamorphism ◽  
The Other ◽  
Central Portion ◽  
Grenville Province ◽  
Polar Wander ◽  
Thermal Demagnetization ◽  
The North ◽  
Apparent Polar Wander Path ◽  
Normal Polarity

Alternating field and thermal demagnetization study of the Lac St-Jean anorthosite and related rock units in the central portion of the exposed Grenville Province reveals two components of magnetization, one of reversed and the other of normal polarity. Both components are thought to have been acquired during the last regional metamorphism, which was sufficiently intense in this area (mostly amphibolite grade) to reset any earlier magnetization. Corresponding paleopoles at 193°W, 8°S (dm = 7.3°, dp = 4.6°) and 213°W, 19°S (dm = 10.5°, dp = 8.5°) lie along the 950–900 Ma segment of the recently calibrated Grenville track of the North American apparent polar wander path, a track that has thus far been defined largely by results from rock units of the western Grenville.

A major Aphebian–Helikian unconformity within the Central Mineral Belt of Labrador: definition of new groups and metallogenic implications

1978 ◽  
Vol 15 (12) ◽  
pp. 1954-1966 ◽  
Author(s):  
W. R. Smyth ◽  
B. E. Marten ◽  
A. B. Ryan
Keyword(s):  
Volcanic Rocks ◽  
Lava Flows ◽  
Grenville Province ◽  
Mafic Lava ◽  
Polyphase Deformation ◽  
Mineral Belt ◽  
Group A ◽  
Grenvillian Orogeny ◽  
Definition Of ◽  
Granitic Batholith

The Central Mineral Belt of Labrador consists of a belt of supracrustal rocks that occupies the northern foreland region of the Grenville Province of the Canadian Shield. Recent mapping in this belt has shown that the Proterozoic Croteau Group consists of two distinct sequences separated by an observed angular unconformity. It is therefore proposed that the name Croteau Group be abandoned and that the lower, Aphebian, marine sequence of sandstone, dolostone, slate, argillite, and mafic volcanic rocks be named the Moran Lake Group and that the upper, Helikian, continental sequence of conglomerate, tuffaceous sandstone, and a calc-alkalic volcanic assemblage be named the Bruce River Group.The Moran Lake Group underwent polyphase deformation, which has been assigned to the Hudsonian Orogeny, prior to deposition of the Bruce River Group around 1474 Ma. The Bruce River Group was intruded by a large granitic batholith, the Otter Lake Granite, for which a preliminary Rb–Sr isochron age of 1445 Ma has been obtained; this age correlates with the Elsonian magmatic event, an event well documented in northern Labrador. The Seal Lake Group, a Neohelikian (1278 Ma) sequence of quartzites, conglomerates, and intercalated mafic lava flows, was unconformably deposited upon the Bruce River Group and the Otter Lake Granite. During the Grenvillian Orogeny, the Bruce River and Seal Lake Groups were deformed together into a major easterly trending syncline. Deformation and metamorphism decrease across these groups to the north.The Bruce River Group forms part of the Labrador uranium area and hosts 14 known uranium occurrences. Occurrences are concentrated in the basal sandstones and conglomerates of the group, above the Aphebian–Helikian unconformity, and in ignimbrites and acid tuffs near the top of the group. No uranium occurrences are known from the Moran Lake Group except in fault-related fractures below the unconformity.

Potassium–Argon Dating of Slates from the Meguma Group, Nova Scotia

1973 ◽  
Vol 10 (7) ◽  
pp. 1059-1067 ◽  
Author(s):  
P. H. Reynolds ◽  
E. E. Kublick ◽  
G. K. Muecke
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Atlantic Canada ◽  
Plate Tectonic ◽  
Thermal Metamorphism ◽  
Argon Dating ◽  
Granitic Intrusion ◽  
Minimum Age ◽  
Granitic Intrusions ◽  
Orogenic Events

Recent reconstructions of the geologic evolution of Atlantic Canada based on plate-tectonic models have aroused new interest in the timing of orogenic events on both sides of the Atlantic. K–Ar apparent ages ranging from 332–403 m.y. are reported for 15 whole-rock slate and hornfels samples from the Halifax Formation of the Meguma Group. Four biotite concentrates from spatially associated granitic intrusions yield K–Ar ages of 364–369 m.y. A minimum age of about 390 m.y. for the regional metamorphic event is deduced from the whole-rock slate data. Granitic intrusion at approximately 367 m.y. profoundly affected the argon clock in many Halifax slates and resulted in its partial resetting even in slates which do not display mineralogic or textural effects of superimposed thermal metamorphism. The 390 m.y. minimum age for regional metamorphism supports suggestions by other workers that the currently widely-accepted 395 m.y. date for the Devonian–Silurian boundary may need revision.

Late Archean evolution of the Nain Province, Nain, Labrador: imprint of a collision

1996 ◽  
Vol 33 (9) ◽  
pp. 1325-1342 ◽  
Author(s):  
J. N. Connelly ◽  
B. Ryan
Keyword(s):  
Regional Metamorphism ◽  
Granulite Facies ◽  
Boundary Zone ◽  
Critical Position ◽  
The North ◽  
Ductile Shearing ◽  
Granitic Intrusions ◽  
Corroborative Evidence ◽  
Geochronological Evidence ◽  
Nain Plutonic Suite

Archean gneisses of the Nain Province in the Nain area, Labrador, comprise narrow septa between intrusions of the Mesoproterozoic Nain Plutonic Suite. This region occupies a critical position between the northern (Saglek) and southern (Hopedale) blocks of the Nain Province, which experienced distinct thermotectonic histories until the late Archean. Field and geochronological evidence are indicative of a strong late Archean thermotectonic overprint that is absent from most of the remainder of the Nain Province. Archean gneisses were intruded by granites and mafic dykes at 2578 ± 3 and [Formula: see text], respectively, and subsequently subjected to amphibolite- to granulite-facies regional metamorphism and ductile shearing at ca. 2550 Ma; granite veins and dykes related to the Nain Plutonic Suite were emplaced at ca. 1310 Ma. The Archean events are interpreted to represent the juxtapositioning and final docking of Saglek and Hopedale blocks to form a single, stable cratonic mass during the late Archean. Corroborative evidence indicates that the collisional boundary zone could extend at least 200 km to the north and 150 km to the south of Nain. This late Archean junction may have subsequently been exploited by several Paleoproterozoic granitic intrusions and some members of the Mesoproterozoic Nain Plutonic Suite.

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