U–Pb zircon ages in supracrustal and plutonic rocks; North Spirit Lake area, Northwestern Ontario

1986 ◽  
Vol 23 (7) ◽  
pp. 967-977 ◽  
Author(s):  
F. Corfu ◽  
J. Wood
Keyword(s):  
Age Determination ◽  
Quartz Diorite ◽  
Lake Area ◽  
The North ◽  
Northwestern Ontario ◽  
Quartz Arenite ◽  
Two Generations ◽  
Minimum Age ◽  
Mafic Inclusion ◽  
Plutonic Rocks

The North Spirit Lake greenstone belt in the Sachigo Subprovince of the Superior Province comprises parts of three sequences of volcanic and sedimentary rocks; the main (youngest) is separated from the older sequences by an unconformity to disconformity. The belt is bounded by large granitoid batholiths and was metamorphosed under greenschist to, locally, hornblende–cordierite facies. U–Pb zircon dating was performed on volcanic, sedimentary, and plutonic rocks in order to establish an absolute chronology for the evolution of the area.A tuff breccia in the lowermost supracrustal sequence is dated at 3023 ± 2 Ma. Zircons from a tuff in the middle sequence show complex U–Pb relationships; although they do not allow a precise age determination, the data suggest that the tuff formed sometime between 2950 and 2800 Ma ago. Zircons from a quartz arenite, also in the middle sequence, yield a simple data pattern and define an age of [Formula: see text], suggesting derivation of the sediment from a uniform source of this age. A zircon analysis from a tonalitic clast in a conglomerate at the base of the upper sequence yields a minimum age of 2975 Ma. The clast may have had the same origin as the zircons in the quartz arenite. Another tonalitic clast from the same conglomerate yields a slightly older age of 3001 ± 3 Ma. No remnant of these tonalites can be recognized in the field, suggesting that they have been largely removed during subsequent erosional processes.Two subvolcanic intrusions from the upper sequence yield zircon ages of 2743 ± 2 and 2731 ± 2 Ma, respectively. A crystal tuff, also in the upper sequence, contains two generations of zircons: newly formed magmatic zircons, which date the extrusion of the tuff at 2735 ± 10 Ma, and older grains with a minimum age of 2862 Ma, which represent inherited zircons. This tuff was thus generated at least in part by anatectic melting of >2862 Ma crust.A quartz diorite from MacDowell Lake in the adjacent Berens River Subprovince yields an age of 2744 ± 2 Ma. A mafic inclusion in the quartz diorite contains amoeboidal, strongly fractured zircons, which point to an intercept age of about 2727 Ma. This age could either reflect a metamorphic event or represent a geologically meaningless mixed age.

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.

scholarly journals Employing Minimum age model (MAM) and Finite mixture modeling (FMM) for OSL age determination of two important samples from Ira Trench of North Tehran Fault

2016 ◽  
Vol 43 (1) ◽  
pp. 38-47 ◽  
Author(s):  
Morteza Fattahi ◽  
Mariam Heidary ◽  
Mohammad Ghasemi
Keyword(s):  
Age Determination ◽  
Mixture Modeling ◽  
Finite Mixture Modeling ◽  
The North ◽  
North Eastern ◽  
Minimum Age ◽  
Age Model ◽  
Osl Age ◽  
Mosha Fault

Abstract Ira trench site is in a point where, the surface trace of North Tehran Fault (NTF) joins the Mosha Fault (MF) in the north-eastern margin of Tehran and can provide important paleosismological information for Tehran. The Ira trench, were divided into 6 packages (I to VI), described, according to their composition, relative and absolute ages. Package I consists of units 23, 25, 26, 27, 28, 29, 30 and 31. The whole package I mainly belongs to Holocene, and provides essential constraints for the recent paleoearthquake activity of the EMF and NTF zone. Therefore, finding accurate ages for the units of this package is very important. Three colluvial wedges (units 23, 26, 28) are present between 20 and 36.5 m north in package I, which are assigned to 3 episodes of activity on Fault 13. Central age model (CAM) provided OSL ages of 35.0 ± 6.1, 7.3 ± 1.3, 6.4 ± 0.9 and 56 ± 6.5 ka for units 23, 26, 28 and 29, respectively. The conflicting ages of 56 ± 6.5 and 35.0 ± 6.1 ka (for units 23 and 29, respectively) as compared to the underlying younger units suggest that these ages are overestimated. MAM provided OSL ages of 13.1 ± 4.3 and 3.5 ± 0.4 ka for units 23 and 29, respectively. The contribution of the new statistical age model of sample IRA4 to the paleoseismic data is discussed.

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.

Geochronology and geochemistry of felsic rocks in an Archean volcanic–plutonic suite in the Wabigoon belt, northwestern Ontario

1979 ◽  
Vol 16 (10) ◽  
pp. 1978-1987 ◽  
Author(s):  
J. M. Wolff ◽  
J. H. Crocket
Keyword(s):  
Lake Area ◽  
Northwestern Ontario ◽  
Metavolcanic Rocks ◽  
Magma Sources ◽  
Minimum Age ◽  
Grid Index ◽  
High Alkali ◽  
Geochemical Studies ◽  
Upper Third ◽  
Felsic Rocks

Selected rock units of an Archean volcanic–plutonic assemblage from the Kakagi Lake area, northwestern Ontario, were sampled for geochronological and geochemical studies. The units sampled were felsic metavolcanic rocks from the upper third of the sequence (Middle Felsic Group) and a felsic pluton (the Stephen Lake stock) intruded into these metavolcanics. A Rb/Sr whole rock isochron from the Stephen Lake stock yielded an age of 2534 ± 96 Ma with an initial 87Sr/86Sr ratio of 0.7015. This date is interpreted as a minimum age for the end of volcanism in the Kakagi Lake area, and the low initial ratio indicates that older sialic material was not a significant contributor to the Stephen Lake magma.Major and trace element (Rb, Sr, Ba, Zr, Y, Ce) compositions show that the Kakagi Lake felsic metavolcanics are similar to high-alkali andesite and depleted siliceous volcanics as recognized by Condie. Geochemical indicators such as K/Rb, the potash index, and the Rb/Sr thickness grid index suggest that the Stephen Lake pluton is not simply the intrusive equivalent of the felsic metavolcanics, but that different magma sources are probably required.

U–Pb zircon ages for the Rice Lake area, southeastern Manitoba

1989 ◽  
Vol 26 (1) ◽  
pp. 23-30 ◽  
Author(s):  
A. Turek ◽  
R. Keller ◽  
W. R. Van Schmus ◽  
W. Weber
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Quartz Diorite ◽  
Granitic Rocks ◽  
Lake Area ◽  
The South ◽  
Metasedimentary Rocks ◽  
The North ◽  
Felsic Volcanic ◽  
Felsic Volcanic Rocks

The Archean Rice Lake greenstone belt in southeastern Manitoba is made up of mafic to felsic volcanic rocks and associated intrusive and metasedimentary rocks. The belt is flanked to the north by the Wanipigow River granitic complex and to the south by the Manigotagan gneissic belt. The Ross River quartz diorite pluton is intrusive into the centre of the greenstone belt. U–Pb zircon ages indicate a major volcanic and plutonic event in the area at 2730 Ma. Ages for two volcanic units of the Rice Lake Group are 2731 ± 3 and 2729 ± 3 Ma. The Ross River pluton yields an age of 2728 ± 8 Ma and the Gunnar porphyry gives an age of 2731 ± 13 Ma; both intrude rocks of the Rice Lake Group. Granitic rocks of the Wanipigow River granitic complex give ages of 2731 ± 10 and 2880 ± 9 Ma, while a post-tectonic granite in the Manigotagan gneissic belt has an age of 2663 ± 7 Ma.

Preliminary Rb–Sr geochronology of the Rice Lake – Beresford Lake area, southeastern Manitoba

1968 ◽  
Vol 5 (6) ◽  
pp. 1373-1380 ◽  
Author(s):  
A. Turek ◽  
Z. E. Peterman
Keyword(s):  
Greenstone Belt ◽  
San Antonio ◽  
Regional Metamorphism ◽  
Quartz Diorite ◽  
Lake Area ◽  
Quartz Veins ◽  
Minimum Age ◽  
Basic Rocks

A Rb–Sr geochronologic study of rocks of the Rice Lake – Beresford Lake area, southeastern Manitoba, shows that gold-quartz veins containing sericite and fuchsite were emplaced at 2720 ± 185 m.y. ago (λ87Rb = 1.39 × 10−11 yr−1). The mineralization postdates, and thus provides a minimum age for, the Rice Lake Group as well as for the successively younger intrusive basic rocks, quartz diorite plutons, and the San Antonio Formation. A whole-rock isochron for the potassic granite that lies north of the greenstones indicates an age of 2550 ± 80 m.y., with an initial 87Sr/86Sr of 0.7031 ± 0.0021, which we also consider as the age of regional metamorphism. This is in agreement with a metamorphic age of 2490 ± 90 m.y., as registered by phyllites from the Rice Lake Group. The gneisses and granites that lie south of the greenstone belt are older than 2630 m.y., as determined by a cross-cutting pegmatite. Because the northern granite is younger than the gold-quartz veins, extensive prospecting of the northern granite for gold-quartz mineralization is not likely to be fruitful unless there was a still younger, but presently unrecognized, period of mineralization.

Inherited and Environmentally Induced Differences in Mutation Frequencies Between Wild Strains of Sordaria fimicola From “Evolution Canyon”

Genetics ◽  
1998 ◽  
Vol 149 (1) ◽  
pp. 87-99
Author(s):  
Bernard C Lamb ◽  
Muhammad Saleem ◽  
William Scott ◽  
Nina Thapa ◽  
Eviatar Nevo
Keyword(s):  
Genetic Variation ◽  
Spontaneous Mutation ◽  
The South ◽  
Natural Genetic Variation ◽  
The North ◽  
Ascospore Germination ◽  
Evolution Canyon ◽  
Two Generations ◽  
Wild Strains ◽  
Sordaria Fimicola

Abstract We have studied whether there is natural genetic variation for mutation frequencies, and whether any such variation is environment-related. Mutation frequencies differed significantly between wild strains of the fungus Sordaria fimicola isolated from a harsher or a milder microscale environment in “Evolution Canyon,” Israel. Strains from the harsher, drier, south-facing slope had higher frequencies of new spontaneous mutations and of accumulated mutations than strains from the milder, lusher, north-facing slope. Collective total mutation frequencies over many loci for ascospore pigmentation were 2.3, 3.5 and 4.4% for three strains from the south-facing slope, and 0.9, 1.1, 1.2, 1.3 and 1.3% for five strains from the north-facing slope. Some of this between-slope difference was inherited through two generations of selfing, with average spontaneous mutation frequencies of 1.9% for south-facing slope strains and 0.8% for north-facing slope strains. The remainder was caused by different frequencies of mutations arising in the original environments. There was also significant heritable genetic variation in mutation frequencies within slopes. Similar between-slope differences were found for ascospore germination-resistance to acriflavine, with much higher frequencies in strains from the south-facing slope. Such inherited variation provides a basis for natural selection for optimum mutation rates in each environment.

scholarly journals Mineralogy, mineral chemistry and thermobarometry of post-mineralization dykes of the Sungun Cu–Mo porphyry deposit (Northwest Iran)

2020 ◽  
Vol 12 (1) ◽  
pp. 764-790
Author(s):  
Amin Allah Kamali ◽  
Mohsen Moayyed ◽  
Nasir Amel ◽  
Fadaeian Mohammad ◽  
Marco Brenna ◽  
...  
Keyword(s):  
Active Continental Margin ◽  
Mineral Chemistry ◽  
Quartz Diorite ◽  
Alkaline Magmatism ◽  
Porphyry Deposit ◽  
Average Percentage ◽  
The North ◽  
Northwestern Iran ◽  
Subduction System ◽  
Late Stages

AbstractThe Sungun copper–molybdenum porphyry deposit is located in the north of Varzaghan, northwestern Iran. The Sungun quartz-monzonite is the oldest mineralized intrusive body in the region and was emplaced during the Early Miocene. Eight categories of the late and unmineralized dykes, which include quartz diorite, gabbrodiorite, diorite, dacite, microdiorite and lamprophyre (LAM), intrude the ore deposit. The main mineral phases in the dykes include plagioclase, amphibole and biotite, with minor quartz and apatite and secondary chlorite, epidote, muscovite and sericite. The composition of plagioclase in the quartz diorite dykes (DK1a, DK1b and DK1c) varies from albite-oligoclase to andesine and oligoclase to andesine; in the diorite, it varies from andesine to labradorite; in the LAM, from albite to oligoclase; and in the microdiorite (MDI), it occurs as albite. Amphibole compositions are consistent with classification as hornblende or calcic amphibole. Based on their AlIV value (less than 1.5), amphibole compositions are consistent with an active continental margin affinity. The average percentage of pistacite (Ps) in epidotes formed from alteration of plagioclase and ferromagnesian minerals is 27–23% and 25–30%, respectively. Thermobarometric studies based on amphibole and biotite indicate approximate dyke crystallization temperature of 850–750℃, pressure of 231–336 MPa and high fO2 (>nickel-nickel-oxide buffer). The range of mineral compositions in the postmineralization dyke suite is consistent with a genetic relationship with the subduction of the Neotethys oceanic crust beneath the continental crust of the northwest part of the Central Iranian Structural Zone. Despite the change from calc-alkaline to alkaline magmatism, the dykes are likely related to the late stages of magmatic activity in the subduction system that also generated the porphyry deposit.

Lake and inland dunes as interconnected Systems: The story of Lake Tresssee and an adjacent dune field (Schleswig-Holstein, North Germany)

The Holocene ◽  
2020 ◽  
pp. 095968362098168
Author(s):  
Christian Stolz ◽  
Magdalena Suchora ◽  
Irena A Pidek ◽  
Alexander Fülling
Keyword(s):  
Water Level ◽  
Bronze Age ◽  
Environmental Changes ◽  
High Water ◽  
Alluvial Fan ◽  
Water Levels ◽  
Lake Area ◽  
Dune Field ◽  
The North ◽  
Sand Drift

The specific aim of the study was to investigate how four adjacent geomorphological systems – a lake, a dune field, a small alluvial fan and a slope system – responded to the same impacts. Lake Tresssee is a shallow lake in the North of Germany (Schleswig-Holstein). During the Holocene, the lake’s water surface declined drastically, predominately as a consequence of human impact. The adjacent inland dune field shows several traces of former sand drift events. Using 30 new radiocarbon ages and the results of 16 OSL samples, this study aims to create a new timeline tracing the interaction between lake and dunes, as well, as how both the lake and the dunes reacted to environmental changes. The water level of the lake is presumed to have peaked during the period before the Younger Dryas (YD; start at 10.73 ka BC). After the Boreal period (OSL age 8050 ± 690 BC) the level must have undergone fluctuations triggered by climatic events and the first human influences. The last demonstrable high water level was during the Late Bronze Age (1003–844 cal. BC). The first to the 9th century AD saw slightly shrinking water levels, and more significant ones thereafter. In the 19th century, the lake area was artificially reduced to a minimum by the human population. In the dunes, a total of seven different phases of sand drift were demonstrated for the last 13,000 years. It is one of the most precisely dated inland-dune chronologies of Central Europe. The small alluvial fan took shape mainly between the 13th and 17th centuries AD. After 1700 cal. BC (Middle Bronze Age), and again during the sixth and seventh centuries AD, we find enhanced slope activity with the formation of Holocene colluvia.

Overburden geochemical signature of the Lac des Iles platinum group element deposit, northwestern Ontario, Canada

2007 ◽  
Vol 44 (8) ◽  
pp. 1151-1168 ◽  
Author(s):  
Peter J Barnett
Keyword(s):  
Mineral Exploration ◽  
Shallow Groundwater ◽  
Soil System ◽  
Near Surface ◽  
Rock Fragments ◽  
The North ◽  
Northwestern Ontario ◽  
Airborne Contamination ◽  
The Many ◽  
Lac Des Iles

Many previously published studies of the behaviour of Pt and Pd in till and soils have been done in areas of complex stratigraphy or very thin overburden cover, making the interpretation of soil results difficult because of the many variables associated with these settings. At the Lac des Iles mine site in northwestern Ontario, there are excellent exposures of the overburden in a series of exploration trenches. Glacial dispersal trains can be observed in till (C horizon) geochemistry (e.g., Ni, Cr, Cu, and Co). Regional geochemical dispersal trains of elements, such as Ni, Cr, Mg, and Co associated with the North Lac des Iles intrusion, can be detected for about 4 km beyond the western margin of the Mine Block intrusion. Entire dispersal trains range from 5 to 7 km in length and about 1 to 2 km in width. The dispersal of North Lac des Iles intrusion rock fragments tends to mask the response of the Mine Block intrusion. Dispersal trains of Pt and Pd are not well defined and tend to be very short, <1 km in length, due to the initial low concentrations of these elements in C-horizon till samples from the Lac Des Iles area. An exception to this is the Pd dispersal train originating from the high-grade zone that is up to 3 km long. Pd, Pt, Ni, and Cu appear to be moving both within and out of the soil system downslope into surface and shallow groundwater. It is suggested that these elements, to varying degrees, are moving in solution. Airborne contamination from mine operations of the humus has adversely affected the ability to determine the effectiveness of humus sampling for mineral exploration at Lac des Iles. The airborne contamination likely influences the geochemical results from surface water, shallow groundwater, and near-surface organic bog samples, particularly for the elements Pd and Pt.

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