Neoarchean decoupling of upper- and mid-crustal tectonothermal domains in the southeast Slave Province: evidence from the Walmsley Lake area

2005 ◽  
Vol 42 (6) ◽  
pp. 869-894 ◽  
Author(s):  
S Cairns ◽  
C Relf ◽  
K MacLachlan ◽  
W J Davis
Keyword(s):  
High Strain ◽  
Amphibolite Facies ◽  
Lake Area ◽  
Structural Topology ◽  
Crustal Shortening ◽  
Rock Types ◽  
Slave Province ◽  
Crustal Transect ◽  
Thermomechanical Modeling ◽  
Tectonothermal Event

The Walmsley Lake area of the southeastern Slave Province, Northwest Territories, exposes a crustal transect from greenschist through to upper amphibolite facies. Two tectonothermal crustal domains are proposed based on disparate tectonic histories and rock types. Within the upper tectonothermal domain, D1 deformation reached lower amphibolite facies prior to 2614 Ma and associated M1 metamorphic conditions outlasted D1. Peak M2 conditions reached middle amphibolite facies prior to 2603 Ma and outlasted D2 deformation. Deformation style and metamorphic sequencing during these two pre-2600 Ma events are consistent with regional crustal shortening and thickening in the upper tectonothermal domain. At mid-crustal levels in the lower tectonothermal domain, a third tectonothermal event (D3–M3) produced uppermost amphibolite-facies peak metamorphic conditions, transposed preexisting fabrics to shallow dips, and produced a subhorizontal foliation and recumbent folds at ca. 2583 Ma. D3 structures are not present in the upper tectono thermal domain, however, evidence of M3 heating is locally displayed in rocks at the base of the upper tectonothermal domain. Upper and lower domains were structurally decoupled during the D3–M3 event. In rare places where the zone between the two domains outcrops, it comprises a narrow high-strain zone. The metamorphic and structural topology of the Walmsley Lake area is consistent with the topology predicted from thermomechanical modeling and modern observations of gravitational accommodation in structurally thickened crust.

Temporal distribution of granitoid plutonic rocks in the Archean Slave Province, northwest Canadian Shield

1992 ◽  
Vol 29 (10) ◽  
pp. 2186-2199 ◽  
Author(s):  
O. van Breemen ◽  
W. J. Davis ◽  
J. E. King
Keyword(s):  
Continental Margin ◽  
Temporal Distribution ◽  
Lake Area ◽  
Margin Setting ◽  
General Terms ◽  
Slave Province ◽  
Age Variation ◽  
Granitoid Rocks ◽  
Plutonic Rocks ◽  
Granitoid Gneisses

Granitoid rocks in the Slave Province consist of 4.0–2.8 Ga granitoid gneisses that predate the 2.71–2.65 Ga volcanic and turbiditic rocks of the Yellowknife Supergroup and 2.70–2.58 Ga granitoid plutons that intrude the Yellowknife Supergroup. U–Pb zircon ages and Nd and Pb isotopic data indicate that the older granitoids are restricted to the western part of the Slave Province. Granitoid gneisses in the eastern Slave Province, previously suspected to predate the Yellowknife Supergroup, are similar in age to the volcanic rocks.In this paper, the results of a detailed geochronological study of plutonic rocks of the Contwoyto Lake – Nose Lake area of the northcentral Slave Province are reviewed and integrated with the available age data base for plutonic rocks elsewhere in the Slave Province. The data indicate that the timing of the later (<2.7 Ga) plutonism is bimodal, consisting of two distinct magmatic periods separated by approximately 20 Ma of apparent magmatic quiescence. The first period was synvolcanic, dating from 2695 to 2650 Ma. The second period, during which more than 80% of the granitoids presently exposed in the Slave Province were intruded, lasted from 2625 to 2580 Ma, spanning the major Archean deformation events, Syndeformation granitoids, with ages between 2625 and 2595 Ma, are dominantly diorite and tonalité in composition. Late- to post-deformation granitoid rocks, with ages between 2605 and 2580 Ma, range in composition from megacrystic biotite granodiorite to two-mica granite. In general terms, the compositions of the granitoid plutons vary in time from dominantly metaluminous to more strongly peraluminous.Present data show no obvious regional age variation among the younger granitoid rocks across the province. This apparent absence of diachroneity has important implications for models interpreting the magmatism as having evolved in a continental-margin setting, because the extent of contemporaneous plutonism is more than 400 km across strike, considerably broader than in most Mesozoic continental-margin batholiths.

Pre-Grenvillian evolution and Grenvillian overprinting of the Parautochthonous Belt in Key Harbour, Ontario: U–Pb and field constraints

1994 ◽  
Vol 31 (3) ◽  
pp. 583-596 ◽  
Author(s):  
David Corrigan ◽  
Nicholas G. Culshaw ◽  
Jim K. Mortensen
Keyword(s):  
High Strain ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Orogeny ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
High Metamorphic Grade ◽  
Harbour Area ◽  
East West

The Parautochthonous Belt in the region of Key Harbour, Ontario, is composed of Early Proterozoic migmatitic para- and orthogneiss and Mid-Proterozoic granitoids, which were reworked during the Grenville orogeny. Grenvillian deformation is localized into anastomosing arrays of high-strain shear zones enclosing elongate bands and lozenges of rock subjected to lower and near-coaxial strain. Crosscutting relationships preserved in the low-strain domains document two pre-Grenvillian plutonic and tectonometamorphic events, which are bracketed in age by U–Pb zircon geochronology. A 1694 Ma leucogranite intrudes, and provides a minimum age for, high metamorphic grade gneisses formed during an earlier tectonometamorphic event (D1–M1). The leucogranite was intruded by mafic dykes, deformed, and metamorphosed at uppermost amphibolite facies during D2–M2, before the emplacement of Mid-Proterozoic granitoids at ca. 1450 Ma. Following the emplacement of gabbro dykes and pods at ca. 1238 Ma, the area was overprinted by granulite to uppermost amphibolite facies metamorphism (Grenvillian), for which monazites provide a minimum age of ca. 1035 Ma. Titanite U–Pb ages of 1003 – 1004 Ma record cooling through 600 °C. A regionally important swarm of east–west-trending posttectonic pegmatite dykes dated by U–Pb zircon at 990 Ma provides a minimum age for Grenvillian ductile deformation. The present data support the contention that the Parautochthonous Belt in the Key Harbour area consists in part of reworked midcontinental crust of Early to Mid-Proterozoic age.

Provenance of Mesozoic and Cenozoic sediments from the Labrador and western Greenland continental margins

1978 ◽  
Vol 15 (11) ◽  
pp. 1850-1860 ◽  
Author(s):  
Roger Higgs
Keyword(s):  
Amphibolite Facies ◽  
Igneous Rocks ◽  
Continental Margins ◽  
Low Grade ◽  
Baffin Island ◽  
Source Areas ◽  
Rock Types ◽  
Local Abundance ◽  
Principal Source ◽  
Cenozoic Sediments

Forty-two Cretaceous and Paleocene sand samples from offshore Labrador and onshore western Greenland were examined petrographically. The sands were found to be mineralogically and texturally immature, reflecting rapid erosion and transportation from local, high-relief source areas. The principal source-rock types were acidic plutonics and amphibolite-facies metasediments and metavolcanics. Basic igneous rocks provided minor quantities of detritus, whereas contributions from sedimentary and low-grade-metamorphic sources were negligible. Cretaceous and Paleocene sediment transport was essentially perpendicular to the axis of the 'Labrador–Baffin rift system.In view of the apparent local abundance of amphibolite-facies supracrustal rocks during the Cretaceous and Paleocene, extensive post-Paleocene denudation in Labrador, Baffin Island, and western Greenland is invoked to account for the present scarcity of such rock types.

Lead- and sulfur-isotope ratios from the Great Slave Lake area, Canada

1968 ◽  
Vol 5 (5) ◽  
pp. 1269-1276 ◽  
Author(s):  
D. K. Robertson ◽  
G. L. Cumming
Keyword(s):  
Lead Isotope ◽  
Sulfur Isotope ◽  
Isotope Ratios ◽  
Ore Deposits ◽  
Lake Area ◽  
Iron Sulfides ◽  
Tectonic Event ◽  
Slave Province ◽  
Great Slave Lake ◽  
Lead Line

Lead- and sulfur-isotope ratios have been determined for some galenas and iron sulfides from two regions around Yellowknife, Northwest Territories. For the ore deposits, sulfur-isotope ratios are close to the meteoritic value or slightly positive. Lead-isotope ratios fall into two groups, one derived from a source with Th/U = 4.3 and μ = 9–11, and the other from a source with Th/U = 3.5 and μ = 9.0. The ratios fall on an anomalous lead line, which indicates one event of great antiquity (approximately 4000 m.y.), and another about 2800 m.y. ago.Other sulfide samples from areas around Great Slave Lake, primarily outside the ancient (2800 m.y.) Slave Province, indicate events at 2800 m.y. and 1550 m.y., the latter date probably representing the time of the last major tectonic event in the Slave Province. Sulfur-isotope ratios for these samples vary from +1‰ to −13‰ relative to the meteoritic value, suggesting that these leads may have been remobilized by thermal metamorphism, and recombined with crustal sulfur enriched in 32S.

scholarly journals Rb/Sr whole rock age determinations from the western part of the 0stfold basement complex, SE Norway

1981 ◽  
Vol 29 ◽  
pp. 119-128
Author(s):  
B. Hageskov ◽  
S. Pedersen
Keyword(s):  
High Strain ◽  
Amphibolite Facies ◽  
Basement Complex ◽  
Se Norway ◽  
Age Determinations

Rb/Sr whole rock age determinations on granitic orthogneisses in the western part of the 0stfold base­ment complex have yielded ages in the range 1380-1015 m.y. The ages obtained indicate that the regional multiple fold structures, formed by superimposition of folds with E-W trending, vertical to steeply northwards dipping axial surfaces on older folds with N-S axial surfaces, are younger than 1320 m.y. Intrusion of basic dykes (the Kattsund dykes), and the subsequent ductile high strain deformation in the Oslofjorden region are younger than 1225 m.y. It is suggested that the last amphibolite facies metamor­phism in the area, which is associated with the high strain deformation, occurred about 1015 m.y. ago.

scholarly journals Neoproterozoic pegmatite from Skoddefjellet, Wedel Jarlsberg Land, Spitsbergen: Additional evidence for c. 640 Ma tectonothermal event in the Caledonides of Svalbard

2012 ◽  
Vol 33 (1) ◽  
pp. 1-17 ◽  
Author(s):  
Jarosław Majka ◽  
Alexander Larionov ◽  
David Gee ◽  
Jerzy Czerny ◽  
Jaroslav Pršek
Keyword(s):  
Electron Microprobe ◽  
Regional Metamorphism ◽  
Amphibolite Facies ◽  
The Other ◽  
Clear Distinction ◽  
Metasedimentary Rocks ◽  
Facies Metamorphism ◽  
Shrimp Zircon ◽  
Tectonothermal Event

Neoproterozoic pegmatite from Skoddefjellet, Wedel Jarlsberg Land, Spitsbergen: Additional evidence forc. 640 Ma tectonothermal event in the Caledonides of SvalbardNeoproterozoic (c. 640 Ma) amphibolite facies metamorphism and deformation have been shown recently to have affected the Isbjørnhamna and Eimfjellet Complex of Wedel Jarlsberg Land in southwestern Spitsbergen. New SHRIMP zircon U-Pb andin situelectron microprobe monazite and uraninite U-Th-total Pb ages are presented here on a pegmatite occurring within the Isbjørnhamna metasedimentary rocks. Although the dated zircons are full of inclusions, have high-U contents and are metamict and hence have experienced notable Pb-loss, the new Cryogenian ages are consistent with the age of regional metamorphism of the host metasediments, providing additional evidence for a clear distinction of the Southwestern Province from the other parts of the Svalbard Caledonides.

Tectonic stacking of metamorphic zones in Cheticamp River area, Cape Breton Highlands, Nova Scotia

1984 ◽  
Vol 21 (11) ◽  
pp. 1229-1244 ◽  
Author(s):  
D. Craw
Keyword(s):  
High Strain ◽  
Amphibolite Facies ◽  
Lower Limbs ◽  
Low Grade ◽  
Metamorphic Peak ◽  
Cape Breton ◽  
Gneiss Complex ◽  
Show Evidence ◽  
Penetrative Foliation ◽  
Very High

Metabasic and quartzo-feldspathic schists and gneisses of the Cheticamp River area can be subdivided into three north–south-trending metamorphic belts. The westernmost belt, the low-grade belt, has been metamorphosed to transitional greenschist–amphibolite facies with development of one penetrative foliation. The central medium-grade belt has been metamorphosed to amphibolite facies with development of two penetrative foliations. The eastern high-grade belt has been metamorphosed to amphibolite facies accompanied by development of strong gneissic segregation and nonanatectic migmatite leucosomes during formation of two penetrative foliations.Deformation has been inhomogeneous in each of these belts. Most rocks in each belt show evidence of post-tectonic porphyroblast growth. However, deformation continued after the metamorphic peak in localized zones. Very high strain occurred in many of these zones during and after the metamorphic peak, so that early formed fold axes were rotated towards the stretching direction. Locally, dynamically recrystallized mylonite has formed. The three belts were juxtaposed under waning metamorphic conditions by relative movement on these high-strain zones. The schist and gneiss complex thus consists of stacked metamorphic zones with the lowest grade rocks lying at the bottom of the stack. Stacking occurred by east to west thrusting of tight macroscopic ductile folds whose lower limbs have been sheared off.There are many lithologic similarities between the three metamorphic belts. The rocks may have been derived from the same protolith and have since been variably deformed and metamorphosed before later juxtaposition. There is no evidence for involvement of an older "basement complex" in the stacking tectonics in the studied area.The schist and gneiss complex has been intruded by post-tectonic plutonic rocks, and locally affected by post-metamorphic brittle deformation.

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