U–Pb age constraints for the magmatic and tectonic evolution of the Pontiac Subprovince, Quebec

1993 ◽  
Vol 30 (9) ◽  
pp. 1970-1980 ◽  
Author(s):  
J. K. Mortensen ◽  
K. D. Card
Keyword(s):  
Tectonic Evolution ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Volcanic Zone ◽  
Volcanic Arcs ◽  
The North ◽  
Intrusive Rocks ◽  
History Of ◽  
Tonalitic Gneiss ◽  
Age Constraints

New U–Pb zircon, titanite, and monazite ages help constrain the history of magmatism and tectonism within the Pontiac Subprovince of western Quebec. The Pontiac Subprovince resembles other metasedimentary belts of the Superior Province; however, the stratigraphic relationships between the dominantly sedimentary rocks of the Pontiac and the adjacent, volcanic-dominated Abitibi belt to the north and west remain controversial. Volcanic rocks of the Belleterre volcanic zone in the southern part of the Pontiac Subprovince have been interpreted by other workers as klippen of Abitibi strata that were thrust southward onto the Pontiac Subprovince. However, volcanic rocks in the Belleterre zone give crystallization ages of 2689–2682 Ma, which are younger than any extrusive rocks dated thus far from the Abitibi belt. Single detrital zircon grains from Pontiac sedimentary rocks give ages as young as 2683 Ma, indicating that the sediments are similar in age, or younger than, the volcanic units. The volcanic rocks probably represent distal facies of small volcanic arcs deposited within a large turbidite basin.The Lac des Quinze tonalitic gneiss body gives U–Pb zircon and titanite ages of 2695 ± 1 Ma and 2673 ± 4 Ma, respectively. Although the gneiss may represent basement to the supracrustal units, field relationships indicate that it was tectonically juxtaposed against the supracrustal package. Alkaline intrusive rocks in the Pontiac Subprovince yield U–Pb ages that overlap with the youngest ages obtained from the volcanic units. This attests to a very short-lived cycle of sedimentation and arc magmatism, followed by late tectonic and posttectonic alkaline plutonism.

ARCHAEAN SEDIMENTARY ROCKS OF NORTH SPIRIT LAKE AREA, NORTHWESTERN ONTARIO

1965 ◽  
Vol 2 (6) ◽  
pp. 622-647 ◽  
Author(s):  
J. A. Donaldson ◽  
G. D. Jackson
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Sole Source ◽  
Lake Area ◽  
Red Lake ◽  
Sedimentary Sequences ◽  
The North ◽  
Northwestern Ontario ◽  
History Of ◽  
Granitoid Rocks

Archaean sedimentary rocks of the North Spirit Lake area show little evidence of having been derived predominantly from associated Archaean volcanic rocks. Instead, compositions of the sediments reflect significant sedimentary and (or) granitoid provenance. A remarkably high content of clastic quartz in thick units of sandstone and conglomerate suggests either reworking of older quartzose sediments, or reduction of the labile constituents in quartz-rich granitoid rocks through prolonged weathering and rigorous transport. Observations for other sedimentary sequences in the region between Red Lake and Lansdowne House suggest that the North Spirit sediments are not unique in the Superior Province. Quartzose sandstones commonly are regarded as atypical of the Archaean, but such rocks arc abundant in northwestern Ontario. Frameworks of many Archaean greywackes actually are richer in quartz than typical greywackes from numerous Proterozoic and Phanerozoic sequences.The concept of rapidly rising volcanic arcs as the sole source of Archaean sedimentary detritus is rejected for the North Spirit area. The volcanies, rather than representing relicts of protocontinents, probably record events removed from initial volcanism in the history of the earth by one or more orogenic cycles. Major unconformities may therefore exist not only between sedimentary and volcanic units, but also between these units and older granitoid rocks.

Chilliwack composite terrane in northwest Washington: Neoproterozoic–Silurian passive margin basement, Ordovician–Silurian arc inception

2010 ◽  
Vol 47 (10) ◽  
pp. 1347-1366 ◽  
Author(s):  
E. H. Brown ◽  
G. E. Gehrels ◽  
V. A. Valencia
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Complex Problem ◽  
Late Ordovician ◽  
Detrital Zircons ◽  
Passive Margin ◽  
Early Paleozoic ◽  
Intrusive Rocks ◽  
History Of ◽  
Detrital Zircon Ages

The Chilliwack composite terrane in northwest Washington is part of an assemblage of mid-Paleozoic arc terranes extending from California to Alaska. Some terranes bear evidence of exotic origin, whereas others apparently formed proximal to western Laurentia, posing a complex problem in unraveling the Paleozoic accretionary history of the Cordillera. In our proposed broader definition, the Chilliwack composite terrane includes the volcanic and sedimentary East Sound and Chilliwack groups, and the plutonic and metamorphic Turtleback and Yellow Aster complexes. New zircon ages indicate that the plutonic and volcanic rocks are mutually related as parts of the same arc complex and that its inception was as old as Late Ordovician to Silurian, older than most other parts of the mid-Paleozoic terrane assemblage. Basement to the arc complex is a passive margin assemblage of metamorphosed quartzose sandstone and calc-silicate rock of the Yellow Aster Complex, bracketed in age by ca. 1000 Ma detrital zircons and 418 Ma intrusive rocks. This association of paragneiss basement and overlying and (or) intruding arc resembles that of older parts of the extensive Yukon–Tanana terrane in the northern Cordillera. Detrital zircon ages support a western Laurentian pericratonic origin for the paragneiss basement and the overlying arc. However, an early to mid-Paleozoic connection of this assemblage to the exotic outboard Alexander terrane is also indicated, based on (1) Mesoproterozoic and early Paleozoic detrital zircons in Devonian sedimentary rocks of the arc, and also in certain other pericratonic Devonian terranes and strata of the miogeocline; (2) Late Ordovician – Silurian igneous ages; and (3) an earliest Devonian or older metamorphic age of the basement paragneiss.

New U–Pb and Ar/Ar isotopic age constraints on the timing of Eocene magmatism, Fort Fraser and Nechako River map areas, central British Columbia

2001 ◽  
Vol 38 (4) ◽  
pp. 679-696 ◽  
Author(s):  
Nancy C Grainger ◽  
Michael E Villeneuve ◽  
Larry M Heaman ◽  
Robert G Anderson
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Core Complex ◽  
The North ◽  
Intrusive Rocks ◽  
Volcanic Suite ◽  
Stratigraphic Nomenclature ◽  
Age Constraints ◽  
Western Portion ◽  
Extensional Setting

Twenty-three new, precise, Eocene U–Pb and 40Ar/39Ar age determinations for calc-alkaline volcanic rocks of the Ootsa Lake Group and associated intrusive rocks, widespread in the Nechako Plateau in central British Columbia, constrain the timing of the Eocene magmatism to 53.2–47.6 Ma, with a local duration of as little as 2–3 million years. The new dates show that magmatism in the study area is partly coeval with that responsible for the Babine Igneous Suite – Newman Volcanic Suite (53–50 Ma) to the north, and for the Endako Group (51–45 Ma), which overlies the Ootsa Lake Group; however, locally the three magmatic suites are distinct in age and (or) the strata record a magmatic hiatus of as much as 7.5 million years. The ages generally young from north to south (52–47 Ma) along the western portion of the study area. The Babine Igneous Suite – Newman Volcanic Suite represents the oldest member of this series. However, in the east, the Ootsa Lake Group volcanic rocks are generally older (53–51 Ma). The anomalously older ages may be related to the interaction of magmatism and formation of a nearby and coeval core complex, which ongoing studies show was uplifted at about the same time during the Eocene. Felsic plutonism associated with the Ootsa Lake Group occurred between 50.5 and 47.3 Ma. These plutons were emplaced in an extensional setting along north-northeast-trending faults. The new dates, stratigraphic relationships, and suggested correlations of Eocene strata in the study area with that to the west and north require a revision of the stratigraphic nomenclature for the Ootsa Lake and Endako groups.

scholarly journals IV.—The Volcanic History of Ireland

1874 ◽  
Vol 1 (5) ◽  
pp. 205-210
Author(s):  
Edward Hull
Keyword(s):  
Volcanic Rocks ◽  
Central Valley ◽  
Short Description ◽  
Lower Carboniferous ◽  
Volcanic History ◽  
The North ◽  
History Of ◽  
Similar Materials ◽  
Considerable Intensity

Carboniferous Period.—The Lower Carboniferous rocks, both of the North of England, of Scotland, and of Ireland, afford examples of contemporaneous volcanic action of considerable intensity. The so-called “toad-stones” of Derbyshire, and the great sheets of melaphyre, porphyrite, and ashes of the central valley of Scotland, forming the Kilpatrick, Campsie, and Dairy Hills, appear to have been erupted over the bed of the same sea as that in which were poured out similar materials in County Limerick, forming the well-known Carboniferous volcanic rocks of “the Limerick Basin.” These rocks have been already so fully described by several observers, that I shall confine myself to a very short description, such as is essential to the brief history of volcanic action which I am here endeavouring to draw up.

Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part II: Tectonic evolution and geomechanical model

1983 ◽  
Vol 20 (9) ◽  
pp. 1355-1373 ◽  
Author(s):  
Erich Dimroth ◽  
Lazlo Imreh ◽  
Normand Goulet ◽  
Michel Rocheleau
Keyword(s):  
Tectonic Evolution ◽  
Anisotropic Plate ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Normal Fault ◽  
Geomechanical Model ◽  
Southwestern Part ◽  
South Central ◽  
Central Segment ◽  
Volcanic Terrain

In this paper, we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the Archean Abitibi and Bellecombe belts. Volcanism in the Abitibi Belt created a very thick, anisotropic plate composed of competent volcanic rocks and broken by the Duparquet–Destor break. The depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings, and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole. The Cadillac break, a normal fault, separated the Abitibi and Bellecombe belts. The latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic–mafic flows.North–south compression of the volcanic terrain during the Kenoran Orogeny produced a set of flexure folds, F1, that curve around the consolidated cores of central volcanic complexes generally in an easterly direction. Synclinoria nucleated at the deeply subsident depocenters of the upper diverse division. Further north–south flattening and subvertical stretching produced the east-trending F2 folds, their axial-plane schistosity S2, and local superposed schistosities S3 and S4. Southward verging recumbent folds suggest that the Bellecombe Belt simultaneously was pulled northward below the Abitibi Belt. During the orogeny, the Duparquet–Destor and Cadillac breaks were transformed to thrust faults; the Duparquet–Destor break also shows minor (< 3 km) right-lateral strike slip. Diapiric rise of late- to post-kinematic plutons locally distorted earlier schistosities.

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.

Rb–Sr geochronology and metamorphic history of Proterozoic to early Archean rocks north of the Cape Smith Fold Belt, Quebec

1987 ◽  
Vol 24 (4) ◽  
pp. 813-825 ◽  
Author(s):  
Ronald Doig
Keyword(s):  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Iron Formation ◽  
Fold Belt ◽  
Metasedimentary Rocks ◽  
Metamorphic History ◽  
The North ◽  
Basement Rocks ◽  
History Of ◽  
Wide Zone

The Churchill Province north of the Proterozoic Cape Smith volcanic fold belt of Quebec may be divided into two parts. The first is a broad antiform of migmatitic gneisses (Deception gneisses) extending north from the fold belt ~50 km to Sugluk Inlet. The second is a 20 km wide zone of high-grade metasedimentary rocks northwest of Sugluk Inlet. The Deception gneisses yield Rb–Sr isochron ages of 2600–2900 Ma and initial ratios of 0.701–0.703, showing that they are Archean basement to the Cape Smith Belt. The evidence that the basement rocks have been isoclinally refolded in the Proterozoic is clear at the contact with the fold belt. However, the gneisses also contain ubiquitous synclinal keels of metasiltstone with minor metapelite and marble that give isochron ages less than 2150 Ma. These ages, combined with low initial ratios of 0.7036, show that they are not part of the basement, as the average 87Sr/86Sr ratio for the basement rocks was about 0.718 at that time.The rocks west of Sugluk Inlet consist mainly of quartzo-feldspathic sediments, quartzites, para-amphibolites, marbles, and some pelite and iron formation. In contrast to the Proterozoic sediments in the Deception gneisses, these rocks yield dates of 3000–3200 Ma, with high initial ratios of 0.707–0.714. These initial ratios point to an age (or a provenance) much greater than that of the Archean Deception gneisses. The rocks of the Sugluk terrain are intruded by highly deformed sills of granitic rocks with ages of about 1830 Ma, demonstrating again the extent and severity of the Proterozoic overprint. The eastern margin of this possibly early Archean Sugluk block is a discontinuity in age, lithology, and geophysical character that could be a suture between two Archean cratons. It is not known if such a suturing event is of Archean age, or if it is related to the deformation of the Cape Smith Fold Belt.Models of evolution incorporating both the Cape Smith Belt and the Archean rocks to the north need to account for the internal structure of the fold belt, the continental affinity of many of the volcanic rocks, the continuity of basement around the eastern end of the belt, and the increase in metamorphism through the northern part of the belt into a broad area to the north. The Cape Smith volcanic rocks may have been extruded along a continental rift, parallel to a continental margin at Sugluk. Continental collison at Sugluk would have thrust the older and higher grade Sugluk rocks over the Deception gneisses, produced the broad Deception antiform, and displaced the Cape Smith rocks to the south in a series of north-dipping thrust slices.

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