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.

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.

New Constraints on the Timing and History of Breccia Dikes in the Western San Juan Mountains, Southwestern Colorado

2019 ◽  
Vol 56 (4) ◽  
pp. 397-420
Author(s):  
David Gonzales
Keyword(s):  
Spatial Relationship ◽  
Metamorphic Rocks ◽  
San Juan ◽  
San Juan Mountains ◽  
Basement Rocks ◽  
Intrusive Rocks ◽  
Close Spatial Relationship ◽  
History Of ◽  
Proterozoic Basement ◽  
Structural Levels

In the western San Juan Mountains, clastic (breccia) dikes crop out in Paleozoic to Cenozoic rocks. The dikes are tabular to bifurcating masses up to several meters thick and are exposed on northwest or northeast trends for up to several kilometers. They are matrix- to clast-supported with angular to rounded pebble- to boulder-sized fragments that in most dikes are dominated by Proterozoic igneous and metamorphic rocks. U-Pb age analyses (n = 3) reveal a range of zircon ages in all samples with several containing high proportions of 1820 to 1390 Ma zircons. The majority of Proterozoic zircons are interpreted as direct contributions from basement rocks during breccia dike formation and emplacement. Field relations and U-Pb zircon analyses reveal that breccia dikes formed in intervals from 65 to 30 Ma (Ouray) and 27 to 12 Ma (Stony Mountain); some dikes are closely allied with mineralization. The dikes formed at depths over 500 meters where Proterozoic basement was fragmented, entrained, and transported to higher structural levels along with pieces of Paleozoic to Cenozoic rocks. A close spatial relationship exists between breccia dikes and latest Mesozoic to Cenozoic plutons. This is best exemplified near Ouray where clastic dikes share similar trends with ~65 Ma granodiorite dikes, and there is a clear transition from intrusive rocks to altered-brecciated plutons, and finally to breccia dikes. The preponderance of evidence supports breccia dike formation via degassing and explosive release of CO2-charged volatiles on deep fractures related to emplacement of 70 to 4 Ma plutons or mantle melts. In addition to breccia dikes, several post-80 Ma events in the region involved explosive release of volatile-charged magmas: 29-27 Ma calderas, ~25 Ma diatremes, and ~24 Ma breccia pipes. Causal factors for production of these gas-charged magmas remain poorly understood, but partial melting or assimilation of altered and metasomatized lithospheric mantle could have played a role.

Early Cenozoic resetting of potassium–argon dates and geothermal history of north Okanagan area, British Columbia

1981 ◽  
Vol 18 (8) ◽  
pp. 1310-1319 ◽  
Author(s):  
Wm. H. Mathews
Keyword(s):  
Vitrinite Reflectance ◽  
Volcanic Rocks ◽  
Blocking Temperature ◽  
Low Grade ◽  
High Grade ◽  
Basement Rocks ◽  
Thermal Changes ◽  
History Of ◽  
The Trinity ◽  
Early Cenozoic

Unmetamorphosed Early Eocene sediments and volcanic rocks of the Trinity Hills and Enderby Cliffs yield K–Ar dates of 42–49 Ma. These overlie high-grade gneisses yielding K–Ar ages on biotites, muscovites, and hornblende ranging from 47 to 60 Ma. The Eocene sediments and volcanics rest nearby on low-grade phyllites, greenstones, and schists yielding dates from 83 to 155 Ma. The gneiss dates are regarded as reset by some Late Cretaceous to earliest Cenozoic thermal event that did not affect, at least to the same degree, the nearby less metamorphosed basement rocks. A thermal history has been constructed to account for the decreasing apparent ages of biotite (assumed blocking temperature of 250 °C) with increasing depth below the sub-Eocene unconformity, for the greater ages of hornblende and muscovite in the same rocks (blocking temperatures of 500 and 350 °C), as well as for thermal changes associated with high vitrinite reflectance from coal at one site in the covering sediments. Very rapid stripping (something like 5 km in 12 Ma) is inferred for the areas of reset gneisses, but not for the schist areas, in early Cenozoic time.

Significance of “gneissic” rocks in the Liscomb Complex, Nova Scotia

2010 ◽  
Vol 47 (6) ◽  
pp. 927-940 ◽  
Author(s):  
J. V. Owen ◽  
R. Corney ◽  
J. Dostal ◽  
A. Vaughan
Keyword(s):  
Igneous Rocks ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
High Grade ◽  
Peraluminous Granite ◽  
Isotopic Signatures ◽  
Conventional View ◽  
Basement Rocks ◽  
Mineral Assemblages ◽  
Intrusive Rocks

The Liscomb Complex comprises Late Devonian intrusive rocks (principally peraluminous granite) and medium- to high-grade metamorphic rocks (“gneisses”) that collectively are hosted by low-grade (greenschist facies) metasediments of the Cambro-Ordovician Meguma Group. The conventional view that these “gneisses” contain high-grade mineral assemblages and represent basement rocks has recently been challenged, and indeed, some of the rocks previously mapped as gneisses, particularly metapelites, have isotopic compositions resembling the Meguma Group. Amphibole-bearing enclaves in the Liscomb plutons, however, are isotopically distinct and in this regard resemble xenoliths of basement gneisses in the Popes Harbour lamprophyre dyke, south of the Liscomb area. Metasedimentary enclaves with Meguma isotopic signatures can contain garnets with unzoned cores (implying high temperatures) that host high-grade minerals (prismatic sillimanite, spinel, and (or) corundum) and are enclosed by retrograde-zoned rims. These features are interpreted here as having formed during and following the attainment of peak temperatures related to Liscomb magmatism. The amphibole-bearing meta-igneous rocks described here contain cummingtonite or hornblendic amphibole and occur as enclaves in granodioritic to tonalitic plutons. They are mineralogically, texturally, and isotopically distinct from Meguma metasediments and at least some of the plutonic rocks that enclose them, so remain the most likely candidate for basement rocks in the Liscomb Complex.

Les bassins sedimentaires du nord de la Corse; essai de synthese stratigraphique et apercu tectonique

1964 ◽  
Vol S7-VI (3) ◽  
pp. 322-333
Author(s):  
Roland Delcey ◽  
Jean Claude Limasset ◽  
Pierre Routhier
Keyword(s):  
Metamorphic Rocks ◽  
Pillow Lavas ◽  
Tectonic History ◽  
Basement Rocks ◽  
Structural Nature ◽  
History Of

Abstract The Saint Florent, Balagne, and Francardo basins of northern Corsica, surrounded by Paleozoic granitic and metamorphic rocks, are occupied by Permian to Triassic arkosic clastics and rhyolite overlain by dolomitic limestones, Jurassic limestones and spilite pillow lavas, Cretaceous flysch and overlying Globotrunca marly and sandy limestones, Eocene arkosic clastics, Nummulite limestone, and flysch. Although the paleogeographic history of the three basins differs in details, it was essentially the same in major features. The tectonic history, however, differed considerably depending on the structural nature of the underlying basement rocks of the basins. Presence of nappes of distant origin is suspected from relationships of the Cretaceous flysch and the Paleozoic schists east of Francardo.

scholarly journals Late Cretaceous to Paleocene Tectonometamorphic Evolution of the Blanchard River Assemblage, Southwest Yukon: New Insight into the Terminal Accretion of Insular Terranes in the Northern Cordillera

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Lianna Vice ◽  
H. Daniel Gibson ◽  
Steve Israel
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Northern Coast ◽  
Coast Mountains ◽  
Tectonic Events ◽  
Western Cordillera ◽  
History Of ◽  
Northwestern North America

Abstract The Intermontane-Insular terrane boundary stretches over 2000 kilometers from British Columbia to Alaska in the western Cordillera. Juxtaposed between these terranes is a series of Jura-Cretaceous basinal and arc assemblages that record a complicated and contested tectonic evolution related to the Mesozoic-Paleocene accretionary history of northwestern North America. In southwest Yukon, west-verging thrust faults facilitated structural stacking of the Yukon-Tanana terrane over these basinal assemblages, including the Early Cretaceous Blanchard River assemblage. These previously undated compressional structures are thought to be related to the final collapse of the Jura-Cretaceous basins and the tectonic burial of the Blanchard River assemblage resulting in amphibolite facies metamorphism. New in situ U-Th-Pb monazite ages record at least three tectonic events: (1) the tectonic burial of the Blanchard River assemblage to amphibolite facies conditions between 83 and 76 Ma; (2) peak burial was followed by regional exhumation at ca. 70-68 Ma; and (3) intense heating and ca. 63-61 Ma low-pressure contact metamorphism attributed to the intrusion of the voluminous Ruby Range suite, which is part of the northern Coast Mountains batholith. The tectonometamorphic evolution recorded in the Blanchard River assemblage can be correlated to tectonism within southwest Yukon and along the length of the Insular-Intermontane boundary from western British Columbia through southwestern Yukon and Alaska. In southwest Yukon, these results suggest an asymmetric final collapse of Jura-Cretaceous basins during the Late Cretaceous, which relates to the terminal accretion of the Insular terranes as they moved northward.

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 ΤΗE PELAGONIAN NAPPE PILE IN NORTHERN GREECE AND FYROM. STRUCTURAL EVOLUTION DURING THE ALPINE OROGENY: A NEW APROACH

2017 ◽  
Vol 43 (1) ◽  
pp. 276 ◽  
Author(s):  
Ad. Kilias ◽  
W. Frisch ◽  
A. Avgerinas ◽  
I. Dunkl ◽  
G. Falalakis ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Late Jurassic ◽  
Structural Evolution ◽  
Shear Zones ◽  
Low Grade ◽  
Northern Greece ◽  
Alpine Orogeny ◽  
Clastic Sediments ◽  
History Of ◽  
Structural Levels

The geometry of kinematics and the deformation history of the Pelagonian nappe pile during the Alpine orogeny have been studied in Northern Greece and FYROM. Deformation was started in Middle-Late Jurassic time and was initially associated with ocean-floor subduction followed by ophiolites obduction, nappe stacking and duplication of the Pelagonian continent. The footwall Pelagonian segment from top to bottom was metamorphosed under greenschist to amphibolit facies conditions and a relative high pressure (T = 450o to 620o C and P = 12,5 to 8 kb). Blueschist facies metamorphic assemblages of Late Jurassic age are immediately developed between both hangingwall and footwall Pelagonian segments. Transgressive Late Jurassic-Early Cretaceous neritic limestones and clastic sediments on the top of the obducted ophiolites are maybe related to extension and basins formation simultaneously with the nappe stacking and metamorphism at the lower structural levels of the Pelagonian nappes. Contractional tectonics and nappe stacking continued during the Albian-Aptian time. Simultaneously retrogression and pressure decreasing taken place at the tectonic lower Pelagonian footwall segment. Low grade mylonitic shear zones, possible related to extension, are developed during Late Cretaceous time simultaneously with basins formation and sedimentation of neritic Late Cretaceous to Paleocene limestones and flysch. Intense shortening and imbrication under semi-ductile to brittle conditions occurred during Paleocene to Eocene time resulting the onset of the dome like formation of the footwall Pelagonian segment. The next stages of deformation from Oligocene to Quaternary are related to brittle extension and the final uplift and configuration of the Pelagonian nappe pile.

Geology of the Nemo Lakes belt, northern Valhalla Range, southeast British Columbia

1981 ◽  
Vol 18 (5) ◽  
pp. 944-958 ◽  
Author(s):  
Randall R. Parrish
Keyword(s):  
British Columbia ◽  
Large Scale ◽  
Phase 1 ◽  
Normal Fault ◽  
Columbia River ◽  
Ultramafic Rocks ◽  
Phase 2 ◽  
Metasedimentary Rocks ◽  
The North ◽  
Gneiss Complex

High-grade metasedimentary rocks, probably of both early Paleozoic and late Paleozoic – Triassic ages, underlie an area termed the Nemo Lakes belt between Slocan and Arrow Lakes in the northern Valhalla Range, southeastern British Columbia. The rocks have experienced two possibly related periods of major folding. Phase 1, accompanied and outlasted by metamorphism at P–T conditions of 5.0–6.8 kbar (500–680 MPa) and 630–680 °C, involved emplacement of ultramafic rocks, major faulting, and folding. Phase 2 involved large-scale inclined to upright folds which were dominantly south-verging, deforming the phase 1 fabric. Both phases probably occurred in the Middle to Late Jurassic, as part of the Columbian Orogeny.Rocks lithologically and structurally similar to those of the Nemo Lakes belt are found across the Rodd Creek fault near the Columbia River and extend the general continuity of the belt into the Shuswap metamorphic complex.Plutonic rocks, some of which bracket the movement on the Rodd Creek fault, the southern extension of the Columbia River fault zone, range in age from Middle Jurassic to EoceneIn the valley of Slocan Lake, a major normal fault is postulated on structural and metamorphic grounds and may be related to the north–south arching of the Valhalla gneiss complex. It is suggested that this arching and uplift, which followed phase 2 deformation, produced both the fault and a zone of cataclasis on the eastern side of the complex, and gave rise to its domal shape.

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