40Ar/39Ar thermochronology of the Thor-Odin – Pinnacles area, southeastern British Columbia: tectonic implications of cooling and exhumation patterns

2016 ◽  
Vol 53 (10) ◽  
pp. 993-1009 ◽  
Author(s):  
D. van Rooyen ◽  
S.D. Carr
Keyword(s):  
British Columbia ◽  
Shear Zone ◽  
Late Cretaceous ◽  
Columbia River ◽  
Metamorphic Rocks ◽  
Structural Level ◽  
High Grade ◽  
Extensional Deformation ◽  
Structural Levels ◽  
Upper Boundary

The Thor-Odin dome is a basement-cored tectonothermal culmination in southern British Columbia, containing high-grade metamorphic rocks that were polydeformed during the Cordilleran orogenesis. A north–south 40Ar/39Ar thermochronology transect was carried out throughout a ∼7 km thick tilted section in the Thor-Odin dome and structurally overlying rocks to construct thermochronological histories using existing U–Pb geochronology data with new 40Ar/39Ar data and to determine the nature of the boundary between the dome and overlying rocks at Cariboo Alp. Hornblende cooling dates are ∼62–58 Ma at the highest structural level, ∼57–55 Ma in the middle, and ∼57–53 Ma at Cariboo Alp on the upper boundary of the dome. Muscovite and biotite cooling dates are ∼53–50.5 Ma; identical throughout the dome, margin, and overlying panel. The Cariboo Alp area separating the Thor-Odin dome from overlying rocks did not accommodate major post-cooling extensional deformation; rather, it is a Late Cretaceous to Paleocene compressional shear zone. These domains cooled at different rates from >700 to ca. 300 °C, with upper structural levels cooling at rates of ca. 20 °C/Ma and the lowest levels at rates in excess of 120 °C/Ma. All levels passed through the closure temperature for argon in biotite (here calculated to be 320–330 °C) together at ca. 52–51 Ma. Differential cooling rates are the result of interaction between northeast-directed compressional transport of rocks towards the foreland of the orogen overlapping with activity on the Columbia River fault zone, reflecting crustal-scale extension that reached a peak in the Eocene.

scholarly journals Deconstructing the Infrastructure: A Complex History of Diachronous Metamorphism and Progressive Deformation during the Late Cretaceous to Eocene in the Thor-Odin–Pinnacles Area of Southeastern British Columbia

2016 ◽  
Vol 43 (2) ◽  
pp. 103 ◽  
Author(s):  
Deanne Van Rooyen ◽  
Sharon D. Carr
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Normal Fault ◽  
Columbia River ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Basement Rocks ◽  
History Of ◽  
Complex Structural ◽  
Structural Levels

The Thor-Odin dome is a basement-cored tectonothermal culmination in southern British Columbia containing high-grade metamorphic rocks that were polydeformed in the Late Cretaceous to Eocene. The rocks south of the Thor-Odin dome that extend ca. 20 km to the Pinnacles culmination and Whatshan batholith comprise a heterogeneous tract of polydeformed medium- to high-grade metamorphic rocks and host the South Fosthall pluton near the base of the structural section. They lie in the footwall of the Columbia River fault (CRF) zone, a moderately east-dipping, ductile-brittle, normal fault that was active after ca. 55 Ma and reactivated periodically up to 30 Ma. This tract of rocks has been interpreted as a mid-crustal zone that was exhumed and cooled during Eocene extension or, alternatively, a mid-crustal channel that was bounded at the top by the CRF and was active during the Late Cretaceous to Eocene. However, the timing of metamorphism, deformation, anatexis in basement rocks, and intrusion of leucogranite plutons reveals that there are four tectonothermal domains within the tract that each experienced metamorphism, deformation and cooling at different times. These rocks record Cretaceous metamorphism and cooling in the upper structural levels and three stages of progressive metamorphism and penetrative deformation that migrated into deeper crustal levels in the Paleocene and Eocene producing a complex structural section that was exhumed in part due to motion on the Columbia River fault zone, and in part due to NE-directed transport over a basement ramp.RÉSUMÉLe dôme de Thor-Odin correspond à une culmination tectonothermique d’un noyau de socle dans le sud de la Colombie-Britannique renfermant des roches métamorphiques de haute intensité polydéformées entre le Crétacé supérieur et l’Éocène. Les roches au sud du dôme de Thor-Odin qui s’étendent sur environ 20 km jusqu’à la culmination des Pinnacles et du batholite de Whatshan sont constituées d’une bande hétérogène de roches polydéformées à faciès métamorphique d’intensité moyenne à élevée qui constitue l’encaissant du pluton de South Fosthall près de la base de la colonne structurale. Elles se trouvent dans l'éponte inférieure de la zone de faille de la rivière Columbia (CRF), une faille normale à pendage modéré vers l’est, ductile-fragile, qui a été active après 55 Ma environ et a été réactivée périodiquement jusqu'à 30 Ma. Cette bande de roches a été interprétée comme une zone de mi-croûte qui a été exhumée et a refroidi durant l’extension éocène ou alors comme un canal mi-crustal qui a été limité au sommet par la CRF, et qui a été actif de la fin du Crétacé jusqu’à l’Éocène. Toutefois, la chronologie du métamorphisme, de la déformation, de l’anatexie dans les roches du socle, et de l'intrusion de plutons de leucogranite, montre qu'il existe quatre domaines tectonothermiques pour chaque bande qui ont subit du métamorphisme, de la déformation et du refroidissement à différents moments. Ces roches exhibent un métamorphisme et un refroidissement crétacé dans les niveaux structuraux supérieurs et trois stades de métamorphisme progressif et de déformation pénétrative qui ont migré dans les niveaux crustaux profonds au Paléocène et à l’Eocène constituant ainsi une colonne structurale complexe qui a été exhumée en partie en raison du mouvement de la zone de faille de Columbia River, et en partie en raison du transport vers le N.-E. sur une rampe de socle.

Formation pressures of eclogites from the Franciscan complex, California, from quartz-in-garnet elastic barometry

2020 ◽  
Author(s):  
Miguel Cisneros ◽  
Whitney Behr ◽  
John Platt
Keyword(s):  
Growth Conditions ◽  
Temporal Variations ◽  
Garnet Growth ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Franciscan Complex ◽  
Spatio Temporal ◽  
Santa Catalina Island ◽  
Structural Levels ◽  
Similar Peak

<p>The spatial, temporal, and pressure-temperature (P-T) relationships among high-pressure metamorphic rocks from within subduction complexes have key implications for their exhumation mechanisms and the rheological properties of the subduction interface. Structural, age, and P-T relationships among exhumed rocks may indicate, for example, (1) melange-style mixing during subduction and exhumation or (2) progressive underplating and coherent exhumation.  Melange-style subduction ‘channels’ should exhibit a range of peak metamorphic grades in incorporated blocks, whereas coherent underplating may result in similar peak P-T conditions among blocks, especially from similar structural levels. Determining P-T conditions of high grade blocks is key for understanding these subduction zone endmembers, but constraining formation pressures of high grade blocks such as eclogites has historically been challenging for petrologists due to the lack of suitable barometers.</p> <p>In this study, we compare pressure conditions recorded by spatially and temporally variant high-grade eclogite blocks from the Franciscan Complex in California. We use quartz-in-garnet elastic barometry, a technique that can reliably provide growth P conditions of garnets, to determine formation pressures of eclogites from sections of the northern (Jenner Beach, Ring Mountain, and Junction School) and the southern Fransican Complex (Santa Catalina Island). Multiple eclogite blocks from Jenner Beach are analyzed, and single eclogite blocks from the other localities. By comparing  garnet growth conditions from within a single outcrop and between distinct outcrops, we evaluate the local and regional spatial distribution of P conditions recorded by eclogites. Preliminary data from > 100 quartz-in-garnet inclusion pressures suggests that eclogites from the northern Franciscan record similar garnet growth conditions (~1.5 - 1.9 GPa), and pressures recorded on Santa Catalina Island differ slightly (~1.2 - 1.3 GPa). We use these results to address spatio-temporal variations of peak P recorded by eclogites and its implications for exhumation of the Franciscan complex, and further discuss how quartz-in-garnet pressures compare with conventional thermobarometry techniques.</p>

scholarly journals Quantitative finite strain analysis of high-grade metamorphic rocks within the Mae Ping shear zone, western Thailand

2016 ◽  
Vol 109 (2) ◽  
Author(s):  
Peekamon Ponmanee ◽  
Pitsanupong Kanjanapayont ◽  
Bernhard Grasemann ◽  
Urs Klötzli ◽  
Montri Choowong
Keyword(s):  
Shear Zone ◽  
Finite Strain ◽  
Strain Analysis ◽  
Metamorphic Rocks ◽  
High Grade

Structural and stratigraphic setting of the Downie slide, Columbia River valley, British Columbia

1980 ◽  
Vol 17 (6) ◽  
pp. 698-709 ◽  
Author(s):  
Richard L. Brown ◽  
John F. Psutka
Keyword(s):  
British Columbia ◽  
Shear Zone ◽  
Columbia River ◽  
River Valley ◽  
Axial Plane ◽  
Western Slope ◽  
Second Phase ◽  
Main Body ◽  
The North ◽  
Slide Mass

The Downie slide is a late to postglacial rockslide situated on the western slope of the Columbia River valley about 70 km north of Revelstoke, British Columbia. It attains a maximum thickness of 270 m and is estimated to involve 1.5 × 109 m3 of rock and debris. The head of the slide is bounded by a nearly vertical escarpment reaching heights of more than 125 m; its lateral boundaries are defined by a prominent east–west trending scarp on the south and a more subdued linear northeast trending ridge on the north. The toe forms the west bank of the Columbia River in this area.The slide occurs within a compositionally anisotropic formation of high-grade pelitic and semipelitic schists and psammites. The main shear zone at the base of the slide is located in pelitic schists. Minerals in the rock of the shear zone have been mechanically crushed and locally reduced to a fine-grained gouge.Three distinct phases of deformation are recognized in the Downie slide region. The location and attitude of the second and third fold phases and their associated fabrics controlled the external geometry of the slide.Along the western slopes of this part of the Columbia River valley the second phase of deformation has been dominant. Within the formation that contains the slide, bedding is extensively deformed by tight to isoclinal second phase minor folds that exhibit a penetrative axial plane foliation. At Downie slide this foliation dips approximately 20° eastward towards the Columbia River, and nearly parallels the slope of the hillside; the basal shear zone of the slide developed parallel to the axial plane foliation.West of the slide, third phase major and minor folds have been superimposed on the second phase geometry, but they die out eastward, and are of only minor significance within the main body of the slide. The eastern limit of major superposition coincides with the head scarp of the slide. The slide mass broke away along the hinge zone of the first major monoclinal flexure fold associated with this front of phase 3 folding.Late fracturing probably influenced the position of the northern and southern lateral boundaries of the slide.

U – Pb age constraints for the lithotectonic evolution of the Grenville Province along the Mauricie transect, Quebec

1997 ◽  
Vol 34 (3) ◽  
pp. 299-316 ◽  
Author(s):  
David Corrigan ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
High Grade ◽  
Isotopic Age ◽  
Grenville Province ◽  
Zircon Age ◽  
South Central ◽  
Continental Arc ◽  
Structural Levels ◽  
Age Constraints

New U–Pb zircon and monazite ages on 12 samples from the Mauricie transect in Quebec provide constraints on the lithologic and tectonic evolution of the south-central Grenville Province. From lowest to highest structural levels, the Mékinac, Shawinigan, and Portneuf – St. Maurice domains are identified on the basis of protolith age, tectonic overprint, and plutonism. The structurally highest Portneuf – St. Maurice domain consists of remnants of an island arc (Montauban Group) that was deformed and metamorphosed before and during the intrusion of continental arc plutons (La Bostonnais complex). A tonalitic orthogneiss yielding a [Formula: see text] zircon age suggests that most of the structurally underlying Mékinac and Shawinigan domains consist of orthogneisses that may be high-grade equivalents of the La Bostonnais complex. A voluminous metasedimentary unit occurring in the Shawinigan domain (St. Boniface unit) was deposited between ca. 1.18 and 1.09 Ga, precluding any correlation with the ca. 1.45 Ga Montauban Group. Two suites of anorthosite–mangerite–charnockite–granite (AMCG) plutonic rocks are identified on the basis of field relationships and isotopic age. A megacrystic granite belonging to the "older" AMCG suite yielded a [Formula: see text] zircon age. Three plutons from the "younger" suite yielded ages of [Formula: see text], 1059 ± 2, and 1056 ± 2 Ma. The Mékinac and Shawinigan domains, excluding the younger AMCG plutons, were penetratively deformed at granulite to uppermost amphibolite facies during west-northwest-directed thrusting between 1.15 and 1.09 Ga. At ca. 1.09 Ga, a transition from contraction to oblique extension resulted in the juxtaposition of the "cold" Portneuf – St. Maurice domain with the "hot" Shawinigan domain, along the Tawachiche shear zone. Oblique extension may have been active from ca. 1.09 to 1.04 Ga and was contemporaneous with emplacement of the younger AMCG suite.

Early Tertiary resetting of potassium–argon dates in the Kootenay Arc, southeastern British Columbia

1983 ◽  
Vol 20 (5) ◽  
pp. 867-872 ◽  
Author(s):  
W. H. Mathews
Keyword(s):  
British Columbia ◽  
Upper Mantle ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Thermal Event ◽  
Grade Metamorphism ◽  
Early Tertiary ◽  
Common Control ◽  
High Grade Metamorphism

K–Ar analyses of rocks in the central Kootenay Arc indicate a Paleocene (or slightly earlier) thermal event, locally reaching 350 °C, that has reset this isotope clock. The area of resetting is nearly coincident with a north–south belt, 20 km wide, of metamorphic rocks resulting from an earlier (mid-Jurassic?) thermal event with temperatures reaching an estimated 625 °C. The strata involved in both high-grade metamorphism and resetting seem not to have been uplifted more than older weakly metamorphosed strata to the east. The mid-Jurassic? and Paleocene thermal events appear to be distinct in time from one another, but may both be related to some common control in the deeper crust or upper mantle.

Unravelling the enigmatic Grampian Shear Zone: In-situ monazite and titanite U-Pb analysis of the juxtaposed Badenoch and Grampian Groups

2021 ◽  
Author(s):  
Lewis Evason ◽  
Anna Bird ◽  
Eddie Dempsey ◽  
Kit Hardman ◽  
Martin Smith ◽  
...  
Keyword(s):  
Shear Zone ◽  
Major Elements ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Icp Ms ◽  
Wide Range ◽  
Caledonian Orogeny ◽  
Detailed Picture ◽  
Spot Analysis

<p>The Grampian Shear Zone (GSZ) represents a highly deformed tectonostratigraphic contact between the Proterozoic metamorphic rocks of the Dalradian Group from the underlying high grade metamorphic Neoproterozoic rocks of the Badenoch Group within the Grampian Highlands. The nature (tectonic suture or palaeo-unconformity), age and structure of the GSZ and indeed the underling Badenoch Group are poorly constrained. Previous studies of the GSZ and synkinematic (intruded during shearing) pegmatites found therein, yielded metamorphic/deformation (and magmatic) ages ranging from c.a. 808 to 440 M. This study reinvestigates this shearzone using in-situ (within section) petrochonological analysis on a range of U-Pb and Rb-Sr chronometers – Monazite, zircon, titanite, rutile and mica. Carrying out this analysis in-situ and using a variety of minerals allows us to directly date deformation fabrics over a wide range of deformation temperatures, giving us a far more detailed picture of the events recorded within these rocks. Large monazite grains (≥100μm) were mapped using in-situ LA-ICP-MS to show within grain variation of major elements and REEs. Monazite U-Pb spot analysis from the GSZ has yielded ages ranging from 784.11 ± 1.2Ma to 442.58 ± 0.58Ma. The same analysis was performed on a sample from the Grampian group which yielded an age of 441.34 ± 037Ma. In addition to this monazite data, in-situ U-Pb Titanite analysis from the Badenoch Group gave ages of 526.96 ± 1.33 Ma from a metabasite sample, with a metasedimentary sample giving a range of titanite U Pb ages from 540 to 460Ma. These age ranges show that the Badnoch Group and the GSZ have recorded a complex polyorogenic history relative to the “simple” overlying Dalradian metasediments. We propose that the Grampian Shear Zone represents a deep-seated Knoydartian (808 to 784Ma) age shear zone within the meso-Neoproterozoic Badenoch Group. This shear zone was then reactivated during the Grampian phase of the Caledonian Orogeny resulting in the tectonic emplacement of the Dalradian metasediments above the Badenoch group.</p>

40Ar/39Ar thermochronometric constraints on the tectonic evolution of the Clachnacudainn complex, southeastern British Columbia

1999 ◽  
Vol 36 (12) ◽  
pp. 1989-2006 ◽  
Author(s):  
Maurice Colpron ◽  
Raymond A Price ◽  
Douglas A Archibald
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Tectonic Evolution ◽  
Thermal Evolution ◽  
Hanging Wall ◽  
Closure Temperature ◽  
Widespread Distribution ◽  
Early Tertiary ◽  
Intrusive Rocks ◽  
Structural Levels

40Ar/39Ar thermochronometry from the Clachnacudainn complex indicates that the thermal evolution of the complex was controlled primarily by the intrusion of granitoid plutons in mid- and Late Cretaceous times. Hornblendes from the eastern part of the complex cooled below their Ar closure temperature (ca. 500°C) shortly after intrusion of the mid-Cretaceous plutons; those from the western part of the complex have latest Cretaceous cooling dates, indicating cooling of these hornblendes after intrusion of the leucogranite plutons at ca. 71 Ma. Micas from the southern Clachnacudainn complex exhibit a pattern of progressive cooling toward lower structural levels, where Late Cretaceous and younger intrusions occur. The occurrence of Late Cretaceous - Paleocene mica cooling dates in both the hanging wall and footwall of the Standfast Creek fault refutes the hypothesis that there has been significant Tertiary extensional exhumation of the Clachnacudainn complex along the Standfast Creek fault. Furthermore, the widespread distribution of Late Cretaceous - Paleocene mica cooling ages suggests that an important volume of Late Cretaceous - early Tertiary intrusive rocks must be present in the subsurface beneath the Clachnacudainn complex.

GEOLOGY OF PART OF THE NORTHERN CASCADES IN SOUTHERN BRITISH COLUMBIA

1967 ◽  
Vol 4 (6) ◽  
pp. 1199-1228 ◽  
Author(s):  
K. C. McTaggart ◽  
R. M. Thompson
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Regional Metamorphism ◽  
Fault Zones ◽  
Late Paleozoic ◽  
Fraser River ◽  
High Grade ◽  
The Third ◽  
Serpentine Belt ◽  
Main Fault

The late Paleozoic(?) Hozameen Group consists of four divisions composed of various proportions of ribbon chert, basic lavas (now greenstones), limestone, and argillite, totalling at least 20 000 ft in thickness. In late Paleozoic or Triassic time, these rocks were metamorphosed to form the Custer Gneiss, a high-grade migmatitic complex of layered gneiss and schist. A second episode of high-grade regional metamorphism in Late Cretaceous time is associated with the emplacement of the Spuzzum Intrusions. This was followed by the Yale Intrusions (mainly foliated granodiorite), deposition of Eocene conglomerate and sandstone, and intrusion of Chilliwack batholithic rocks (mainly tonalite), which are partly of Miocene age. Several periods of deformation, some associated with the orogenies mentioned above, produced fold axes trending northwest, northeast, and northerly. The area contains three main fault zones. One separates the Custer Gneiss from its overlying cover of Hozameen rocks. A second, the Hozameen fault, separates the Hozameen beds from Mesozoic formations to the east and contains the 'serpentine belt'. The third, the Fraser River fault zone, is represented by the Hope and Yale faults.

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