Intracratonic indentation of the Archean Slave Province into the Early Proterozoic Thelon Tectonic Zone of the Churchill Province, northwestern Canadian Shield

1990 ◽  
Vol 27 (12) ◽  
pp. 1699-1713 ◽  
Author(s):  
John B. Henderson ◽  
Peter H. McGrath ◽  
Reginald J. Theriault ◽  
Otto van Breemen
Keyword(s):  
Gravity Anomaly ◽  
Metamorphic Grade ◽  
Crustal Thickening ◽  
Positive Anomaly ◽  
The West ◽  
Tectonic Zone ◽  
Isostatic Rebound ◽  
Slave Province ◽  
Metamorphic Gradient ◽  
Middle Proterozoic

Some time between 1735 and 1840 Ma an intracratonic compression resulted in the indentation and consequent underthrusting of the eastern Thelon Tectonic Zone by the central Slave Province and part of the western Thelon Tectonic Zone. The wedge-shaped indentation involved major, transcurrent displacement on the McDonald and Bathurst fault systems. The affected region is characterized by (i) a prominent negative Bouguer gravity anomaly within the Slave Province between the faults and a smaller positive anomaly over the Thelon Tectonic Zone to the east, (ii) an easterly decreasing regional aeromagnetic field over the indenter, and (iii) an easterly increase in Proterozoic metamorphic grade. Rb–Sr dating of biotite shows a 1735 Ma "age plateau" in the eastern part of the wedge, whereas to the west the ages range between 2.0 and 2.5 Ga. Close coincidence between the margin of the 1735 Ma plateau, the metamorphic isograd pattern, and the negative gravity anomaly contours suggests a probable temporal and formative relationship between the metamorphic gradient, gravity anomaly, and the faults. Following indentation and resultant crustal thickening, isostatic rebound in the younger, weaker Thelon Tectonic Zone took place along older Thelon structures. In the older, stronger, structurally more homogeneous Slave Province, isostatic rebound was incomplete. A consequence of the indentation and rebound was crustal flexure to the east of the uplifted area, which resulted in the formation of the large structural basin, symmetrically disposed with respect to the indenting wedge, in which the originally more extensive Middle Proterozoic Thelon Formation is preserved.

Ages of detrital and metamorphic zircons and monazites from a pre-Taltson magmatic zone basin at the western margin of Rae Province

1994 ◽  
Vol 31 (8) ◽  
pp. 1353-1364 ◽  
Author(s):  
H. H. Bostock ◽  
O. van Breemen
Keyword(s):  
Isotope Geochemistry ◽  
Granulite Facies ◽  
Metamorphic Grade ◽  
Detrital Zircons ◽  
Ultramafic Rocks ◽  
Crustal Accretion ◽  
The West ◽  
Slave Province ◽  
Basin Formation ◽  
High Grade Metamorphism

The western edge of Rae Province, prior to indentation of Slave Province, is conceived as a compressional tectonic margin in which Archean plutonic rocks were intruded by syntectonic granites of 2.4–2.3 Ga age as a result of eastward subduction. Subsequently this margin was intruded by the 2.0–1.90 Ga granites that characterize the Taltson magmatic zone. The latter granites engulf remnants of a widespread supracrustal assemblage of lower granulite facies metamorphic grade, the age of which has heretofore been unknown. We use U–Pb zircon and monazite geochronology to limit the age of cessation of deposition of these metasediments in a pre-Taltson granite basin to between 2.13 and 2.09 Ga.Similarities in geochronology and isotope geochemistry between western Rae Province and Buffalo Head domain, together with the presence of mafic to ultramafic rocks both within the basin and along the western Rae margin, suggest that basin formation was by rifting. Influx of 2.15 Ga detrital zircons probably from the west, and high-grade metamorphism accompanying basin closure at 2.09 Ga, suggest an eastward (inward) movement of magmatism at that time. A second similar eastward migration of magmatism occurred in association with the Slave–Churchill collision (2.0–1.9 Ga). These relations suggest a complex record of crustal accretion within Buffalo Head and Chinchaga domains, the details of which remain to be established.

Crustal velocity structure from SAREX, the Southern Alberta Refraction Experiment

2002 ◽  
Vol 39 (3) ◽  
pp. 351-373 ◽  
Author(s):  
Ron M Clowes ◽  
Michael JA Burianyk ◽  
Andrew R Gorman ◽  
Ernest R Kanasewich
Keyword(s):  
Velocity Structure ◽  
Data Interpretation ◽  
Crustal Thickening ◽  
Tectonic Zone ◽  
Crustal Layer ◽  
Crustal Velocity ◽  
Crustal Velocity Structure ◽  
Southern Alberta ◽  
Magmatic Underplating ◽  
Lower Crustal

Lithoprobe's Southern Alberta Refraction Experiment, SAREX, extends 800 km from east-central Alberta to central Montana. It was designed to investigate crustal velocity structure of the Archean domains underlying the Western Canada Sedimentary Basin. From north to south, SAREX crosses the Loverna domain of the Hearne Province, the Vulcan structure, the Medicine Hat block (previously considered part of the Hearne Province), the Great Falls tectonic zone, and the northern Wyoming Province. Ten shot points along the profile in Canada were recorded on 521 seismographs deployed at 1 km intervals. To extend the line, an additional 140 seismographs were deployed at intervals of 1.25–2.50 km in Montana. Data interpretation used an iterative application of damped least-squares inversion of traveltime picks and forward modeling. Results show different velocity structures for the major blocks (Loverna, Medicine Hat, and Wyoming), indicating that each is distinct. Wavy undulations in the velocity structure of the Loverna block may be associated with internal crustal deformation. The most prominent feature of the model is a thick (10–25 km) lower crustal layer with high velocities (7.5–7.9 km/s) underlying the Medicine Hat and Wyoming blocks. Based on data from lower crustal xenoliths in the region, this layer is interpreted to be the result of Paleoproterozoic magmatic underplating. Crustal thickness varies from 40 km in the north to almost 60 km in the south, where the high-velocity layer is thickest. Uppermost mantle velocities range from 8.05 to 8.2 km/s, with the higher values below the thicker crust. Results from SAREX and other recent studies are synthesized to develop a schematic representation of Archean to Paleoproterozoic tectonic development for the region encompassing the profile. Tectonic processes associated with this development include collisions of continental blocks, subduction, crustal thickening, and magmatic underplating.

scholarly journals The country rocks of Devonian magmatism in the North Patagonian Massif and Chaitenia

2018 ◽  
Vol 45 (3) ◽  
pp. 301 ◽  
Author(s):  
Francisco Hervé ◽  
Mauricio Calderón ◽  
Mark Fanning ◽  
Robert Pankhurst ◽  
Carlos W. Rapela ◽  
...  
Keyword(s):  
Metamorphic Grade ◽  
Oceanic Island ◽  
Detrital Zircons ◽  
Island Arc ◽  
Ultramafic Rocks ◽  
The West ◽  
Metasedimentary Rocks ◽  
The North ◽  
The Andes ◽  
Late Neoproterozoic

Previous work has shown that Devonian magmatism in the southern Andes occurred in two contemporaneous belts: one emplaced in the continental crust of the North Patagonian Massif and the other in an oceanic island arc terrane to the west, Chaitenia, which was later accreted to Patagonia. The country rocks of the plutonic rocks consist of metasedimentary complexes which crop out sporadically in the Andes on both sides of the Argentina-Chile border, and additionally of pillow metabasalts for Chaitenia. Detrital zircon SHRIMP U-Pb age determinations in 13 samples of these rocks indicate maximum possible depositional ages from ca. 370 to 900 Ma, and the case is argued for mostly Devonian sedimentation as for the fossiliferous Buill slates. Ordovician, Cambrian-late Neoproterozoic and “Grenville-age” provenance is seen throughout, except for the most westerly outcrops where Devonian detrital zircons predominate. Besides a difference in the Precambrian zircon grains, 76% versus 25% respectively, there is no systematic variation in provenance from the Patagonian foreland to Chaitenia, so that the island arc terrane must have been proximal to the continent: its deeper crust is not exposed but several outcrops of ultramafic rocks are known. Zircons with devonian metamorphic rims in rocks from the North Patagonian Massif have no counterpart in the low metamorphic grade Chilean rocks. These Paleozoic metasedimentary rocks were also intruded by Pennsylvanian and Jurassic granitoids.

The geology and evolution of the Pinchi Fault Zone at Pinchi Lake, central British Columbia

1977 ◽  
Vol 14 (6) ◽  
pp. 1324-1342 ◽  
Author(s):  
I. A. Paterson
Keyword(s):  
Fault Zone ◽  
Subduction Zones ◽  
High Pressures ◽  
Metamorphic Grade ◽  
Fault System ◽  
Late Triassic ◽  
Transform Fault ◽  
The West ◽  
Early Mesozoic ◽  
Complex Fault

At Pinchi Lake, the Pinchi Fault Zone separates the early Mesozoic Takla Group to the east from the late Paleozoic Cache Creek Group to the west. Between these regions a complex fault system involves a series of elongate fault-bounded blocks of contrasting lithology and metamorphic grade. These blocks consist of: (a) highly deformed aragonite–dolomite limestone and blueschist, (b) pumpellyite–aragonite greenstone, (c) a harzburgite–gabbro–diabase–basalt ophiolite sequence, (d) serpentinized alpine ultramafite, and (e) Cretaceous (?) conglomerate. The blueschist probably formed at 8–12 kbar (8 × 105–12 × 105 kPa) and 225–325 °C during a penetrative early deformation which was closely followed by a later deformation associated with a Late Triassic uplift and cooling event. The ophiolite sequence is overlain by Late Triassic sediments which locally contain aragonite suggesting that at least part of the Takla Group may have also undergone high pressure – low temperature metamorphism.The evolution of the 450 km fault zone is discussed and a model is proposed which involves right lateral transform faulting on the Pinchi Fault and underthrusting along northerly dipping subduction zones during the Late Triassic. The blueschist formed at high pressures in such a subduction zone and leaked to the surface in zones of low pressure along an active transform fault.

scholarly journals Crustal velocity structure of the Superior and Grenville provinces of the southeastern Canadian Shield

1997 ◽  
Vol 34 (8) ◽  
pp. 1167-1184 ◽  
Author(s):  
S. Winardhi ◽  
R. F. Mereu
Keyword(s):  
Greenstone Belt ◽  
Velocity Structure ◽  
Canadian Shield ◽  
Crustal Thickening ◽  
Surface Velocity ◽  
Data Set ◽  
Tectonic Zone ◽  
Near Surface ◽  
Abitibi Greenstone Belt ◽  
Sudbury Structure

The 1992 Lithoprobe Abitibi–Grenville Seismic Refraction Experiment was conducted using four profiles across the Grenville and Superior provinces of the southeastern Canadian Shield. Delay-time analysis and tomographic inversion of the data set demonstrate significant lateral and vertical variations in crustal velocities from one terrane to another, with the largest velocity values occurring underneath the Central Gneiss and the Central Metasedimentary belts south of the Grenville Front. The Grenville Front Tectonic Zone is imaged as a southeast-dipping region of anomalous velocity gradients extending to the Moho. The velocity-anomaly maps suggest an Archean crust may extend, horizontally, 140 km beneath the northern Grenville Province. Near-surface velocity anomalies correlate well with the known geology. The most prominent of these is the Sudbury Structure, which is well mapped as a low-velocity basinal structure. The tomography images also suggest underthrusting of the Pontiac and Quetico subprovinces beneath the Abitibi Greenstone Belt. Wide-angle PmP signals, indicate that the Moho varies from a sharp discontinuity south of the Grenville Front to a rather diffuse and flat boundary under the Abitibi Greenstone Belt north of the Grenville Front. A significant crustal thinning near the Grenville Front may indicate post-Grenvillian rebound and (or) the extensional structure of the Ottawa–Bonnechere graben. Crustal thickening resulting from continental collision may explain the tomographic images showing the Moho is 4–5 km deeper south of the Grenville Front.

Le batholite de De Pas, Nouveau-Québec : infrastructure composite d'arc magmatique protérozoïque

1998 ◽  
Vol 35 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Jacques Martelain ◽  
Maurice Chenevoy ◽  
Marc Bélanger
Keyword(s):  
Rare Earth ◽  
Source Area ◽  
Major Elements ◽  
Amphibolite Facies ◽  
Crustal Thickening ◽  
Granitic Magma ◽  
Common Source ◽  
The West ◽  
Southeastern Part ◽  
Field Evidence

The De Pas Batholith, in New Quebec, is a mass of granitoids elongated in a N-S direction, covering 7000 km2 in the southeastern part of the Archean Rae province. It is located between the Paleoproterozoic New Quebec Orogen in the West and the Torngat Orogen in the East. The batholith is composed, in its south half, of two parallel plutonic units: a charnockitic intrusion in the West, enclosed in granulitic gneisses, and a granitic unit in the East intruding an Archean orthogneiss complex migmatized at amphibolite facies grade. Field evidence indicates that the charnockitic unit is younger than the granitic unit. Both plutonic units are differentiated. The granitic unit ranges in composition from pyroxenite and diorite to the dominant porphyritic granodiorite. The charnockitic unit varies from norite to the dominant porphyritic opdalite. Late intrusive granites are present. The granitic unit and charnockitic unit show calc-alkalic evolutionary trends, granodioritic for the the granitic unit and monzonitic for the charnockitic unit. Similar major elements patterns suggest a common source area. Compatible trace element and heavy rare earth abundances are similar in both units. However, incompatible elements (Rb, Th, and U) and light rare earth are less abundant in the charnockitic unit. This poverty in certain large-ion lithophile elements and high field strength elements is a primary characteristic of the charnockitic magma. The overall geochemical characteristics of the De Pas Batholith are similar to those of a plutonic arc in a subduction setting. Only the late granites show evidence of a collisional setting. The differences in trace elements of the granitic unit and the charnockitic unit might be explained by contrasting styles of contamination of the magmas by continental materials in different intrusive conditions and geological settings. The granitic magma was intruded into Archean (?) crust of amphibolite facies, with which the granitic unit was in physical equilibrium. The charnockitic magma crystallised in the deeper granulitic crust, poor in highly lithophile elements. The De Pas Batholith occurs in the hinterland of the New Quebec Orogen, and represents an early subductional magmatic arc formed in two stages separated by a period of crustal thickening in the arc zone.

Nd and Sr isotopic constraints on the petrogenesis of the west side of the northern Coast Mountains batholith, Alaskan and Canadian Cordillera

1991 ◽  
Vol 28 (6) ◽  
pp. 939-946 ◽  
Author(s):  
Scott D. Samson ◽  
P. Jonathan Patchett ◽  
William C. McClelland ◽  
George E. Gehrels
Keyword(s):  
Late Cretaceous ◽  
Crustal Thickening ◽  
Northern Coast ◽  
Crustal Material ◽  
The West ◽  
Crustal Component ◽  
Coast Mountains ◽  
Early Proterozoic ◽  
Depleted Mantle ◽  
Wrangellia Terrane

Nd and Sr isotopic ratios are reported from 15 samples of plutons of the northern Coast Mountains batholith (CMB), between. the Alexander–Wrangellia terrane and the Stikine terrane of southeastern Alaska. Samples of plutons that are part of the Late Cretaceous – Eocene CMB suite have a range in initial εNd of −3.0 to −0.2 and 87Sr/86Sr of 0.70494–0.70607. There is no correlation of isotopic ratio with age, lithology, or geographic location of these plutons. Two plutons that are probably older than the bulk of the CMB plutons have present-day εNd values of −6.8 and −2.6.The Late Cretaceous – Eocene plutons have Nd depleted-mantle model ages (tDM) of 620–1070 Ma. These data indicate that the northern CMB must contain a significant component of old, evolved continental crust. The presence of an old crustal component is further demonstrated by inherited zircons of average Early Proterozoic age contained in some plutons. The mid to Late Proterozoic tDM ages of the CMB plutons are therefore a result of a mixture of Early Proterozoic crustal material with. younger, juvenile crust. The most likely source of this old crustal component is the Yukon–Tanana terrane, a fragment composed of ancient crustal material that occurs within and directly to the west of the northern CMB. The juvenile component is probably a combination of material derived from the mantle and from anatexis of the surrounding juvenile terranes. Crustal anatexis may have occurred as a result of the intrusion of mafic melts related to subduction along the outboard margin of the Alexander–Wrangellia terrane, by crustal thickening due to the underthrusting of the Alexander–Wrangellia terrane beneath the Yukon–Tanana and Stikine terranes, or by a combination of both processes.

The Pontiac problem, Quebec–Ontario, in the light of gravity data

1987 ◽  
Vol 24 (9) ◽  
pp. 1916-1919 ◽  
Author(s):  
J. Kalliokoski
Keyword(s):  
Gravity Anomaly ◽  
Greenstone Belt ◽  
Gravity Data ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Iron Formation ◽  
Bouguer Gravity ◽  
The West ◽  
Abitibi Greenstone Belt ◽  
Uplifted Block

A belt of Archean quartzose metasedimentary gneisses with minor mafic volcanic rocks (the Pontiac Group) lies south of the Blake River and older Archean mafic volcanic rocks of the Abitibi Greenstone Belt, and is separated from them by the Larder Lake – Cadillac Break. To the west of the Pontiac Group, on strike, is the Archean Larder Lake Group of turbidite conglomerate, argillite, limestone, and iron formation with abundant mafic flows and intrusions. These strata also lie south of the Larder Lake – Cadillac Break and south of the Blake River and older Archean mafic volcanic rocks. The western contact between the Pontiac and Larder Lake groups is covered by a narrow north–south strip of Proterozoic Cobalt sedimentary rocks. On the basis of gravity work that compares the Bouguer gravity anomaly gradient across the Cadillac Break with that across the west margin of the Pontiac Group, it is proposed that the Larder Lake and Pontiac groups are separated by a north–south fault and that the Pontiac Group represents a lithologically distinct uplifted block. The Pontiac block may be an Archean terrane.

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