Early Proterozoic Ductile Reworking of Archean Basement in the Central Laramie Range: A Complex Response to the Cheyenne Belt, Trans-Hudson and Central Plains Orogens

1998 ◽  
pp. 219-221
Author(s):  
R. L. Bauer ◽  
D. A. Gresham ◽  
J. D. Edson
Keyword(s):  
Central Plains ◽  
Early Proterozoic ◽  
Cheyenne Belt ◽  
Complex Response ◽  
Laramie Range ◽  
Archean Basement

Postcollisional cooling of the Penokean orogen in east-central Minnesota

1993 ◽  
Vol 30 (5) ◽  
pp. 913-917 ◽  
Author(s):  
Daniel K. Holm ◽  
Timothy B. Holst ◽  
Daniel R. Lux
Keyword(s):  
Lake Superior ◽  
Tectonic Activity ◽  
East Central ◽  
Early Proterozoic ◽  
Granite Emplacement ◽  
Internal Zone ◽  
Basement Gneiss ◽  
Rhyolitic Volcanism ◽  
Archean Basement ◽  
Collisional Orogeny

New 40Ar/39Ar thermochronologic data from the internal zone of the Penokean orogen in east-central Minnesota indicate rapid cooling from mid-crustal temperatures. Early Proterozoic metamorphosed cover rocks yield concordant hornblende and biotite plateau ages of ~ 1755 Ma. Underlying Archean basement gneiss yields concordant muscovite and biotite plateau ages of ~ 1705 Ma. These are some of the oldest cooling ages recorded in rocks buried during the 1830–1860 Ma Penokean collisional orogeny. Cooling was coeval with regional rhyolitic volcanism and granite emplacement, suggesting a period of tectonic activity in this region during mid to late 1700 Ma. Based on similarities with Phanerozoic extensional regimes, we suggest, preliminarily, that these data might be explained by a previously unrecognized major extensional episode in the Lake Superior region.

U–Pb geochronology in the Trans-Hudson Orogen, northern Saskatchewan, Canada

1987 ◽  
Vol 24 (3) ◽  
pp. 407-424 ◽  
Author(s):  
W. R. Van Schmus ◽  
M. E. Bickford ◽  
J. F. Lewry ◽  
R. Macdonald
Keyword(s):  
Granitic Rocks ◽  
Early Proterozoic ◽  
Tectonic Events ◽  
Northern Saskatchewan ◽  
High Grade Metamorphism ◽  
The One ◽  
Relationship Of ◽  
The Relationship ◽  
Orogenic Events ◽  
Archean Basement

We have obtained U–Pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern Trans-Hudson Orogen in northern Saskatchewan. These data constrain the timing of early Proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the Trans-Hudson Orogen to other early Proterozoic orogens in North America.With one exception, all units studied so far yield zircon ages of 1890–1835 Ma, most of which are systematically earlier than previously reported Rb–Sr isochron ages on the same or similar units, suggesting open-system behavior in the Rb–Sr systems. Five metarhyolites, from volcanic sequences in the La Ronge domain, Glennie domain, and Hanson Lake block, give ages ranging from 1888 to 1876 Ma. Most of the plutons we dated, ranging from gneissic syntectonic tonalites and granodiorites to less-deformed late intrusions such as the Wathaman batholith and other smaller bodies, yield ages of 1870–1850 Ma, apparently constraining peak plutonic activity to about 1860 ± 10 Ma ago. The youngest unit found is a small discordant pluton with an age of 1836 ± 7 Ma. The concordance of ages of volcanics on the one hand and of plutons on the other suggests that domainal distinctions are mainly lithotectonic rather than temporal.Zircons from the Sahli charnockitic granite in the Hanson Lake block yield equivocal results. Discordia upper and lower intercepts for the Sahli granite suggest that granitic rocks at least 2500 Ma old were subjected to high-grade metamorphism about 1800–1900 Ma ago, with substantial resetting of zircons. Reworked Archean basement is thus present in this domain, supporting previously reported Rb–Sr isochron data from the Sahli granite. No other indications of Archean basement in the Trans-Hudson Orogen are documented, although one sample from the adjacent Peter Lake domain shows that it consists of Archean continental crust.Zircon ages in the range 1890–1835 Ma from this part of the Trans-Hudson Orogen are similar to those obtained from igneous units of the Penokean and Wopmay orogens, in North America, and from the Svecofennian Orogen, suggesting essential synchroneity of igneous and tectonic events in these four major orogens during major Proterozoic continental assembly.

Rubidium–strontium ages of Archean and Proterozoic rocks in the Nejanilini and Great Island domains, Churchill Province, northern Manitoba, Canada

1988 ◽  
Vol 25 (2) ◽  
pp. 246-254 ◽  
Author(s):  
G. S. Clark ◽  
D. C. P. Schledewitz
Keyword(s):  
Granitic Rocks ◽  
Granitic Magma ◽  
Initial Ratio ◽  
Early Proterozoic ◽  
Metasedimentary Rocks ◽  
Field Evidence ◽  
Southern District ◽  
Island Group ◽  
Minimum Age ◽  
Archean Basement

Rubidium–strontium whole-rock ages are reported from the Nejanilini – Great Island area in northeastern Manitoba. This area is part of an extensive zone of Archean basement that was metamorphosed and intruded by granitic magma during the Proterozoic; it extends into Saskatchewan and southern District of Keewatin, Northwest Tertitories. An age of 2577 ± 42 Ma (1σ error) for the extensive Nejanilini granulite massif (Nejanilini domain), considered one of the oldest rock units in the area, is interpreted as a minimum age for late Archean granulite-facies metamorphism. A minimum age of 2052 ± 41 Ma (initial ratio 0.7150) for quartz–feldspar porphyry that intrudes the Seal River volcanic suite constrains the age of these volcanics and could represent a partially reset Archean age. Early Proterozoic quartzite and metagreywacke of the Great Island Group unconformably overlies the quartz–feldspar porphyry. These metasedimentary rocks, which are probably correlative with the Daly Lake Group (Saskatchewan) or the Hurwitz Group (southern District of Keewatin), give an age of 1885 ± 85 Ma, with an initial ratio of 0.7093. The age records the time of closure of the Rb–Sr isotopic system subsequent to early Proterozoic metamorphism. The age and initial ratio are consistent with published results for other, possibly correlative, metasedimentary rocks in this zone. Modelling the Rb–Sr isotopic data constrains the time of sedimentation to between ca. 2100 and 2000 Ma ago. Syn- to late-kinematic, early Proterozoic granite to granodiorite batholiths, which intruded metasedimentary rocks of the Great Island Group, may largely be the product of melting of Archean basement, based on field evidence and high initial 87Sr/86Sr ratios. The Caribou Lake porphyritic quartz monzonite gives an age of 1795 ± 35 Ma, with an initial 87Sr/86Sr ratio of 0.7084. High initial ratios seem to typify early Proterozoic granitic rocks in this remobilized craton.

Structure of the Early Proterozoic Hurwitz Group in the Tavani area, Keewatin, Northwest Territories

1991 ◽  
Vol 28 (7) ◽  
pp. 1078-1095 ◽  
Author(s):  
Adrian F. Park ◽  
Steven Ralser
Keyword(s):  
Northwest Territories ◽  
Structural Study ◽  
Local Response ◽  
Structural Domains ◽  
Structural Pattern ◽  
Early Proterozoic ◽  
Hurwitz Group ◽  
Archean Basement

A structural study of the Early Proterozoic Hurwitz Group has been carried out in the Tavani area, approximately 80 km southwest of Rankin Inlet, District of Keewatin, Northwest Territories. The Hurwitz Group, in the Tavani area, consists of orthoquartzites of the Kinga Formation (Whiterock Lake Member) and quartz-feldspar arenites and litharenites of the Tavani Formation. More localized lithologies include siltstone, sandstones, breccia, and shales beneath the Whiterock Lake Member and conglomerate, shales, and shale-clast breccias within the Tavani Formation.Open, northeast-trending folds dominate the Hurwitz Group, although overturned folds and easterly trending structures are developed locally. Later northwest-trending faults complicate the northeast-trending structural pattern. Three structural domains are defined: north of the Wilson River, the Whiterock Syncline, and the Last Lake belt. The interrelationship of folding and faulting creates distinctive patterns in each domain, though overall, folding is demonstrated to be a local response to basement faulting, including reactivation of Archean structures. An overall north–south compressive regime is envisaged in which heterogeneities in the Archean basement are responsible for local peculiarities.

The first data on possible Mezozoic magmatism within the Western slope of the Southern Urals

2018 ◽  
pp. 24-34
Author(s):  
A. O. Khotylev ◽  
N. B. Devisheva ◽  
Al. V. Tevelev ◽  
V. M. Moseichuk
Keyword(s):  
Southern Urals ◽  
Western Slope ◽  
Isotopic Age ◽  
The Southern Urals ◽  
Early Proterozoic ◽  
Carbonate Formations ◽  
Two Bodies

Within the Western slope of the Southern Urals, there are plenty of basite dyke complexes of Riphean to Vendian among Precambrian terrigenous-carbonate formations. In metamorphic formations of the Taratash complex (Archean to Early Proterozoic, the northern closure of the Bashkirian meganticlinorium) there was observed the andesitic dyke with isotopic age of 71±1 Ma (U-Pb SHRIMP II on zircons) and near Bakal two bodies of gabbroids with zircons of similar ages were found. These are the first evidence of possible Mezozoic magmatism in this region.

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