scholarly journals Uraniferous Granitoid Rocks From the Superior Province of northwestern Ontario

1982 ◽  
Author(s):  
F W Breaks
Keyword(s):  
Superior Province ◽  
Northwestern Ontario ◽  
Granitoid Rocks

U–Pb geochronology of the central Uchi Subprovince, Superior Province

1993 ◽  
Vol 30 (6) ◽  
pp. 1179-1196 ◽  
Author(s):  
F. Corfu ◽  
G. M. Stott
Keyword(s):  
Large Scale ◽  
Regional Scale ◽  
Early Period ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Granitoid Rocks ◽  
Age Patterns ◽  
Tectonic Development ◽  
Greenstone Belts ◽  
Multiple Episodes

U–Pb zircon and titanite ages for rocks of the central Uchi Subprovince in northwestern Ontario indicate a late Archean magmatic and tectonic development spanning over 200 Ma. An early period at 2900–2800 Ma formed volcano-plutonic complexes, presumably linked to 3.1–2.8 Ga terrains of the northwestern Superior Province. A later period of southward growth by magmatic and tectonic accretion occurred at 2750–2710 Ma and was concluded by large scale compression and plutonism at 2700 Ma.The oldest 2890–2860 and 2840–2820 Ma components occur in the Pickle Lake and Meen–Dempster greenstone belts and as gneisses in the Seach–Achapi and the Lake St. Joseph batholiths in northern and central sectors of the region. Together with distinct 2750–2740 Ma volcano-plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion. Plutons of 2730–2710 Ma age are intrusive into these older, northern domains, whereas their volcanic counterparts compose the Lake St. Joseph and Miminiska – Fort Hope greenstone belts to the south. Late-tectonic to posttectonic granitoid rocks intruded a region extending from the northern Berens River Subprovince to the southern English River Subprovince at 2700 Ma. These plutons were cut by regional scale faults formed by residual north-northwest directed shortening. The timing of this movement seems to be recorded by titanite ages of 2690–2670 Ma. Reactivation of the same faults may account for Proterozoic Pb loss observed in some of the zircon populations. The age patterns are consistent with crustal growth along a continental margin in a north-dipping subduction environment.

Orthoquartzite pebbles in Archean conglomerate, North Spirit Lake, northwestern Ontario

1977 ◽  
Vol 14 (9) ◽  
pp. 1980-1990 ◽  
Author(s):  
J. A. Donaldson ◽  
Richard W. Ojakangas
Keyword(s):  
Greenstone Belt ◽  
Sedimentary Rocks ◽  
Canadian Shield ◽  
Superior Province ◽  
Lake Area ◽  
Definite Evidence ◽  
The North ◽  
Northwestern Ontario ◽  
Form Part ◽  
Quartz Grains

An Archean conglomerate in the North Spirit Lake area of northwestern Ontario contains rare orthoquartzite pebbles. Detailed study of these pebbles shows that mineralogically they are very mature, consisting of as much as 99.8 percent quartz and a heavy mineral suite of zircon, tourmaline, and apatite. Textures are typically bimodal, characterized by rounded sand-sized quartz grains set in a 'matrix-cement' of thoroughly recrystallized finer quartz grains. These orthoquartzite pebbles provide the first definite evidence for local tectonic stability of the Canadian Shield before deposition of the immature sedimentary rocks that form part of an Archean (>2.6 Ga) greenstone belt of the Superior Province.

Shallow crustal sounding in the Superior Province by audio frequency magnetotellurics

1978 ◽  
Vol 15 (11) ◽  
pp. 1701-1711 ◽  
Author(s):  
A. Koziar ◽  
D. W. Strangway
Keyword(s):  
Pore Space ◽  
High Resistivity ◽  
Conducting Layer ◽  
Superior Province ◽  
Audio Frequency ◽  
Magnetotelluric Soundings ◽  
Northwestern Ontario ◽  
Greenstone Belts ◽  
Very High ◽  
Made In

Audio frequency magnetotelluric soundings in the frequency range of 10 Hz to 10 kHz have been carried out over a section of the Superior Province of the Precambrian Shield in northwestern Ontario. Measurements were made in the English River sub-province, which is mainly a gneissic belt. Resistivity values over gneissic rocks and granitic intrusives were found to be generally very high. Resistivity values over greenstone belts were lower. In addition, there was a distinct conductive layering to the crust that was independent of the surface rock type.At the surface there is a thin conducting layer due to water in the surface soils and fractured rocks. Below a few tens of metres, the resistivity rises to values typically between several thousand and 100 000 ohm∙m. This is undoubtedly due to the presence of massive, unfractured rock with little water content. Beyond a depth of 7 km the resistivity drops sharply to values of 100–1000 ohm∙m. One explanation of this drop is the presence of small amounts of trapped pore-space fluids.

Two komatiitic pyroclastic units, Superior Province, northwestern Ontario: their geology, petrography, and correlation

1991 ◽  
Vol 28 (9) ◽  
pp. 1455-1470 ◽  
Author(s):  
Stephen J. Schaefer ◽  
Penelope Morton
Keyword(s):  
Explosive Volcanism ◽  
Pyroclastic Rock ◽  
Superior Province ◽  
Metasedimentary Rocks ◽  
The North ◽  
Northwestern Ontario ◽  
Volcanic Breccia ◽  
Metavolcanic Rocks ◽  
Volcaniclastic Rocks ◽  
Lapilli Tuff

Two Archean komatiitic pyroclastic rock units occur on opposite sides of the Quetico Fault in northwestern Ontario. The eastern unit, the Dismal Ashrock, is located 3 km north of Atikokan, Ontario, on the north side of the Quetico Fault within the Wabigoon Subprovince of the Superior Province. It is part of a suprascrustal sequence, the Steep Rock Group. The Grassy Portage Bay ultramafic pyroclastic rock unit (GUP) is located 100 km to the west, on the south side of the Quetico Fault, and is part of an overturned succession comprising mafic metavolcanic rocks, GUP, and metasedimentary rocks. The Dismal Ashrock dips steeply, is little deformed, has undergone greenschist metamorphism, and is divided into komatiitic lapilli tuff, komatiitic volcanic breccia, komatiitic volcaniclastic rocks, and a mafic pillowed flow. GUP outcrops form an arcuate fold interference pattern, are strongly deformed, and have undergone amphibolite metamorphism. GUP is divided into komatiitic lapilli tuff and komatiitic volcanic breccia. Both pyroclastic units contain cored and composite lapilli, evidence for explosive volcanism. Locally, some of the lapilli fragments are highly vesicular (up to 30% by volume), greater than reported for any other komatiites. Other fragments show no vesicularity. The low vesicularity of some of the pyroclasts and, in the case of the Dismal Ashrock, their association with pinowed lava flows may indicate explosive hydrovolcanic activity. The Dismal Ashrock and GUP are high in MgO, Cr, and Ni and are unusually enriched in Fe, Ti, Zr, Mn, P, Ba, Nb, Rb, and Sr compared with other komatiites. These unique geochemical compositions are not understood at this time.

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.

Age structure and orogenic significance of the Berens River composite batholiths, western Superior Province

1998 ◽  
Vol 35 (10) ◽  
pp. 1089-1109 ◽  
Author(s):  
Fernando Corfu ◽  
Denver Stone
Keyword(s):  
Age Structure ◽  
Greenstone Belt ◽  
Biotite Granite ◽  
Superior Province ◽  
Northwestern Ontario ◽  
Peraluminous Granites ◽  
Granitic Intrusions ◽  
Age Patterns ◽  
Greenstone Belts ◽  
Intrusive Activity

The Berens River area of northwestern Ontario is underlain mainly by Archean felsic plutonic rocks, which enclose minor supracrustal and gneissic enclaves and merge with the greenstone-belt-rich Uchi Subprovince to the south. U-Pb geochronology using zircon and monazite shows that the batholiths evolved mainly between 2750 and 2690 Ma by sequential and essentially continuous intrusive activity into an older substratum composed of 3000-2800 Ma volcanic and tonalitic crust. There is a broad, but not strict, compositional transition from early biotite tonalite and hornblende tonalite, progressing with time towards a greater abundance of hornblende granodiorite to granite, and finally to late biotite granite, rare peraluminous granites, and sanukitoid (dioritic, monzodioritic to granitic) plutons. The tonalite suites were predominantly synvolcanic. The late granitic intrusions postdated volcanism, but were largely synchronous with the main compressional events that caused widespread sedimentation, deformation, and metamorphism in other parts of the region. The age patterns and compositional features of the batholiths and the spatial and temporal links between their evolution and those of the supracrustal sequences in the greenstone belts of the region are consistent with mechanisms of magma generation and emplacement at converging plate margins.

Sign in / Sign up

Export Citation Format

Share Document