Deciphering shallow paleomagnetic inclinations: 1. Implications from correlation of Albian volcanic rocks along the Insular/Intermontane Superterrane boundary in the southern Canadian Cordillera

2003 ◽  
Vol 108 (B4) ◽  
Author(s):  
M. L. Haskin ◽  
R. J. Enkin ◽  
J. B. Mahoney ◽  
P. S. Mustard ◽  
J. Baker
Keyword(s):  
Volcanic Rocks ◽  
Canadian Cordillera

Development of late Paleozoic volcanic arcs in the Canadian Cordillera: an example from the Klinkit Group, northern British Columbia and southern Yukon

2003 ◽  
Vol 40 (7) ◽  
pp. 907-924 ◽  
Author(s):  
Renée-Luce Simard ◽  
Jaroslav Dostal ◽  
Charlie F Roots
Keyword(s):  
British Columbia ◽  
North America ◽  
Volcanic Rocks ◽  
Late Paleozoic ◽  
Canadian Cordillera ◽  
Alkali Basalts ◽  
The North ◽  
Pacific Margin ◽  
North American Craton ◽  
Arc Setting

The late Paleozoic volcanic rocks of the northern Canadian Cordillera lying between Ancestral North America to the east and the accreted terranes of the Omineca belt to the west record early arc and rift magmatism along the paleo-Pacific margin of the North American craton. The Mississippian to Permian volcano-sedimentary Klinkit Group extends discontinuously over 250 km in northern British Columbia and southern Yukon. The two stratotype areas are as follows: (1) in the Englishman Range, southern Yukon, the English Creek Limestone is conformably overlain by the volcano-sedimentary Mount McCleary Formation (Lower Clastic Member, Alkali-Basalt Member and Volcaniclastic Member), and (2) in the Stikine Ranges, northern British Columbia, the Screw Creek Limestone is conformably overlain by the volcano-sedimentary Butsih Formation (Volcaniclastic Member and Upper Clastic Member). The calc-alkali nature of the basaltic volcaniclastic members of the Klinkit Group indicates a volcanic-arc setting ((La/Yb)N = 2.77–4.73), with little involvement of the crust in their genesis (εNd = +6.7 to +7.4). Alkali basalts in the Mount McCleary Formation ((La/Yb)N = 12.5–17.8) suggest periodic intra-arc rifting events. Broadly coeval and compositionally similar volcano-sedimentary assemblages occur in the basement of the Mesozoic Quesnel arc, north-central British Columbia, and in the pericratonic Yukon–Tanana composite terrane, central Yukon, suggesting that they all represent pieces of a single long-lived, late Paleozoic arc system that was dismembered prior to its accretion onto Ancestral North America. Therefore, Yukon–Tanana terrane is possibly the equivalent to the basement of Quesnel terrane, and the northern Quesnel terrane has a pericratonic affinity.

Cross-strike potential-field anomalies in the Canadian Cordillera

2003 ◽  
Vol 40 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Frederick A Cook ◽  
C Elissa Lynn ◽  
Kevin W Hall
Keyword(s):  
Potential Field ◽  
Volcanic Rocks ◽  
Canadian Cordillera ◽  
Western Canada ◽  
Fraser River ◽  
Northern Limit ◽  
Linear Feature ◽  
Directional Filtering ◽  
Major Implication ◽  
Thrust Sheets

Application of bandpass and directional filtering to potential-field maps of western Canada has led to the discovery of regionally extensive anomalies crossing the northwest strike of Cordilleran structures. The most prominent of these, the Steamboat–Fraser trend, is a north–south-striking feature that projects from the foreland belt in northeastern British Columbia, where it becomes subparallel to anomalies east of the Mackenzie Mountains, southward to the northern limit of the Fraser River strike-slip fault, a distance of about 600 km. Within the hinterland of the Cordillera, the trend appears to spatially correlate with the margins of some Tertiary volcanics. The northeasternmost, and thus most cratonward, Tertiary volcanics are located on the northern projection of the trend. The trend may thus be interpreted as either late, post-orogenic intrusives (e.g., dikes and related volcanic rocks) that are only partially exposed, as pre-orogenic (pre-Mesozoic) features (e.g., faults, dikes) in the crust that were overridden by the Cordilleran thrust sheets, or a combination of these. Although it is not possible to determine which of these (pre- or post-orogenic) is appropriate for the trend, the eventual choice has important implications for the structure and evolution of this part of the Cordillera. If the source of the anomalies is pre-orogenic, a major implication is that Precambrian Shield rocks would be present at depth beneath the southern Canadian Cordillera as far west as the Fraser River fault. Alternatively, if the source is post-orogenic, it represents an anomalously linear feature that has no obvious expression on the surface other than a poorly defined spatial correlation with the margins of some Tertiary volcanics.

The Anvil aureole, an atypical mid-Cretaceous culmination in the northern Canadian Cordillera

1990 ◽  
Vol 27 (3) ◽  
pp. 344-356 ◽  
Author(s):  
J. M. Smith ◽  
P. Erdmer
Keyword(s):  
Country Rock ◽  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Canadian Cordillera ◽  
South Fork ◽  
Upper Proterozoic ◽  
Tectonic History ◽  
South Central ◽  
Upper Paleozoic ◽  
Peak Metamorphism

The mid-Cretaceous Anvil batholith, in south-central Yukon near Faro, intrudes Upper Proterozoic to upper Paleozoic strata of the Cordilleran outer miogeocline. From previous work, it was unclear whether biotite, andalusite–staurolite, and garnet isograds near the pluton resulted from pre-Devonian regional metamorphism and subsequent arching in a structural culmination or from mid-Cretaceous instrusion. The present study has documented biotite, andalusite, staurolite, garnet, and sillimanite isograds concentric to the pluton. Prophyroblast–matrix relationships indicate that peak metamorphism occurred during intrusion, which took place under approximately 3 kbar (300 MPa) pressure and heated country rock to temperatures of 600°–620 °C. The metamorphism is thus compatible with a deep, mid-Cretaceous event. Regional uplift of 10 km is implied by the metamorphic minerals. From cogenetic relationships between some phases of the Anvil batholith and the nearby South Fork volcanic rocks, regional uplift appears to have been completed in a few million years in the mid-Cretaceous. The uncharacteristic aureole suggests that mid-Cretaceous events in this region are atypical of the Cordillera and may reflect a unique tectonic history or position in the orogen.

U-Pb zircon age constraint for late Neoproterozoic rifting and initiation of the lower Paleozoic passive margin of western Laurentia

2002 ◽  
Vol 39 (2) ◽  
pp. 133-143 ◽  
Author(s):  
Maurice Colpron ◽  
James M Logan ◽  
James K Mortensen
Keyword(s):  
Volcanic Rocks ◽  
Passive Margin ◽  
Canadian Cordillera ◽  
Lower Paleozoic ◽  
Zircon Age ◽  
Continental Breakup ◽  
North American Cordillera ◽  
The North ◽  
Windermere Supergroup ◽  
Late Neoproterozoic

A concordant U–Pb zircon age of 569.6 ± 5.3 Ma from synrift volcanic rocks of the Hamill Group, southeastern Canadian Cordillera, provides the first direct U–Pb geochronologic constraint on timing of latest Neoproterozoic rifting along western Laurentia. This age confirms a previous estimate of 575 ± 25 Ma for timing of continental breakup, as derived from the analysis of tectonic subsidence in lower Paleozoic miogeoclinal strata of the North American Cordillera. It also corresponds to the timing of passive margin deposition in the "underlying" Windermere Supergroup of the northern Cordillera, as determined by chemostratigraphic correlations. These timing relationships imply a different breakup history for the northern, as compared to the southern, Cordillera. We propose a model that attempts to explain this paradox of Cordilleran geology. The earlier Neoproterozoic (Windermere-age) rifting event probably records breakup of a continental mass from northern Laurentia followed by development of a passive margin. Accordingly, the Windermere Supergroup of the southern Canadian Cordillera was deposited in an intracontinental rift. The second Neoproterozoic rifting (Hamill–Gog) is interpreted to indicate continental breakup and establishment of a passive margin along western Laurentia.

Distribution of Fusulinaceans in the Western Canadian Cordillera

1971 ◽  
Vol 8 (2) ◽  
pp. 259-278 ◽  
Author(s):  
J. W. H. Monger ◽  
C. A. Ross
Keyword(s):  
Volcanic Rocks ◽  
Canadian Cordillera ◽  
Crustal Movements ◽  
Clastic Rocks ◽  
Western Cordillera ◽  
Local Environments ◽  
Upper Paleozoic ◽  
Biogeographic Provinces ◽  
The Family ◽  
Part Time

Fusulinacean faunas in Upper Paleozoic lithological sequences containing volcanic rocks in the western Canadian Cordillera form two assemblages based on geographic association of genera. One assemblage, in Permian strata, is dominated by genera of the family Schwagerinidae and occupies belts in the eastern and western parts of the western Cordillera. This assemblage is associated with brachiopods, bryozoans, horn corals, and crinoids and is in limestones interbedded with clastic rocks and volcanic rocks of variable composition. The other Permian assemblage is dominated by genera of the family Verbeekinidae and occupies a central belt where it occurs with crinoid detritus and algae in thick, regionally extensive limestones associated with cherts, basalt, and ultramafic rocks. The less-well documented Pennsylvanian fusulinaceans appear to occupy similar belts. Because fossils of both assemblages are at least in part time equivalent, their distribution may well be due to differing local environments. In addition, or alternatively, this diversity may be brought about by major crustal movements juxtaposing originally isolated biogeographic provinces.

Introduction to the special issue of Canadian Journal of Earth Sciences: The Nechako NATMAP Project of the central Canadian Cordillera

2001 ◽  
Vol 38 (4) ◽  
pp. 485-494 ◽  
Author(s):  
Lambertus C Struik ◽  
Donald G MacIntyre
Keyword(s):  
Volcanic Rocks ◽  
Mineral Deposits ◽  
Future Research ◽  
Canadian Cordillera ◽  
Special Issue ◽  
Volcanic Arc ◽  
Mountain Ranges ◽  
Crustal Thinning ◽  
Line Spacing ◽  
Central Cordillera

The Canadian Cordillera in central British Columbia has seen the Mesozoic subduction of an oceanic terrane; the amalgamation of volcanic-arc terranes; continued intermittent Mesozoic compression and magmatism; and Tertiary wrenching, extension and magmatism. Except in its northernmost mountain ranges, the area is extensively covered in glacial drift and thin veneers of Tertiary volcanic rocks. In 1994, a group of scientists and technologists believed they could understand that cover, see through it, and discover the components of that collision and extensional orogen. They would apply modern techniques of isotopic and paleontological geochronology; lake-sediment, till, and plant geochemistry; detailed gravity, magnetic, radiometric, paleomagnetic, and electromagnetic surveys; and isotopic and trace element lithochemistry, as they conducted extensive bedrock and surficial mapping. This special issue summarizes a cross-section of the scientific contributions derived from that mapping conducted under the auspices of the Nechako NATMAP Project. It demonstrates the absolute necessity of applying modern isotopic and paleontologic geochronology to understand the Phanerozoic geology of the Cordillera. It emphasizes the necessity of detailed aeromagnetic surveys (500 m or less line spacing) in looking through covered terranes at anything more than 1 : 250 000 scale. And, it shows the immense utility of applying various geochemical techniques to solve geological problems and establish baselines for future research and economic development. Bedrock and surficial mapping in the central Cordillera, using these and other techniques, have established the nature and timing of Mesozoic crustal growth, Tertiary crustal thinning, and the associated formation of mineral deposits.

Geochemistry of the northern Cache Creek terrane and implications for accretionary processes in the Canadian Cordillera

2010 ◽  
Vol 47 (1) ◽  
pp. 13-34 ◽  
Author(s):  
Joseph M. English ◽  
Mitchell G. Mihalynuk ◽  
Stephen T. Johnston
Keyword(s):  
Volcanic Rocks ◽  
Minor Component ◽  
Oceanic Lithosphere ◽  
Ocean Basin ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Basaltic Rocks ◽  
Subducting Plate ◽  
A Minor ◽  
Collisional Orogenesis

The northern Cache Creek terrane in the Canadian Cordillera includes a subduction complex that records the existence of a late Paleozoic – Mesozoic ocean basin and provides an opportunity to assess accretionary processes that involve the transfer of material from a subducting plate to an upper plate. Lithogeochemical data from basaltic rocks indicate that the northern Cache Creek terrane is dominated by two different petrogenetic components: (1) a dominant suite of subalkaline intrusive and extrusive rocks mostly of arc affinity and (2) a volumetrically less significant suite of alkaline volcanic rocks of within-plate affinity. The subalkaline intrusive and extrusive rocks constitute a section of oceanic lithosphere that is interpreted to have occupied a fore-arc position during the Late Triassic and Early Jurassic before it was accreted during collisional orogenesis in the Middle Jurassic. Alkaline volcanic rocks in the northern Cache Creek terrane are stratigraphically associated with carbonate strata that contain Tethyan fauna that are exotic with respect to the rest of North America; together, they are interpreted as remnants of oceanic seamounts and (or) plateaux. The volcanic rocks are a minor component of the carbonate stratigraphy, and it appears that the majority of the volcanic basement was either subducted completely at the convergent margin or underplated at greater depth in the subduction zone. In summary, accretion in the northern Canadian Cordillera occurred principally by the accretion of island arcs and emplacement of fore-arc ophiolites during collisional orogenesis. The transfer of oceanic sediments and the upper portions of oceanic seamounts from the subducting plate to an accretionary margin accounts for only small volumes of growth of the upper plate.

The Eocene–Oligocene magmatic hiatus in the south-central Canadian Cordillera: a capture of the Kula Plate by the Pacific Plate?

2008 ◽  
Vol 45 (1) ◽  
pp. 69-82 ◽  
Author(s):  
Jaroslav Dostal ◽  
J Duncan Keppie ◽  
B Neil Church ◽  
Peter H Reynolds ◽  
Cheryl R Reid
Keyword(s):  
Volcanic Rocks ◽  
Pacific Plate ◽  
North American Plate ◽  
Volcanic Complex ◽  
Canadian Cordillera ◽  
Continental Flood Basalts ◽  
The North ◽  
South Central ◽  
The Pacific ◽  
Back Arc

The Tertiary (Paleogene and Neogene) geological record in south-central Canadian Cordillera is dominated by the 350–400 km wide, lower Eocene volcanic arc and the overlying Miocene–Recent back-arc lavas that are separated by a hiatus in magmatic activity between 48 and 24 Ma. In the Black Dome area (~240 km north of Vancouver), the Eocene volcanic rocks are mainly continental margin calc-alkaline andesite and dacite, resulting from the melting of a juvenile mafic source at the base of the crust. In contrast, the Miocene volcanic rocks resemble continental flood basalts. Both Eocene and Miocene rocks from the Black Dome volcanic complex have high positive εNd values (+7.2 to +7.4 and +6.4 to +7.6, respectively) and low initial Sr isotopic ratios (0.702 516 – 0.703 528 and 0.703 376 – 0.703 392, respectively) comparable to modern oceanic basalts. The onset of the hiatus in magmatism at 48 Ma coincides with capture of the Kula Plate by the Pacific Plate resulting in a change in convergence direction with the North American Plate from orthogonal to margin-parallel. The margin-parallel motion is inferred to have removed a 50–100 km sliver of the Eocene forearc that formed the boundary between the Pacific and subducted Kula Plate. Reinitiation of arc magmatism at 24 Ma is related to subduction of the Farallon and associated plates and it superimposed back-arc tholeiitic magmatism on top of the Eocene arc.

Geological and geochemical evidence for variable magmatism and tectonics in the southern Canadian Cordillera: Paleozoic to Jurassic suites, Greenwood, southern British Columbia

2001 ◽  
Vol 38 (1) ◽  
pp. 75-90 ◽  
Author(s):  
J Dostal ◽  
B N Church ◽  
T Hoy
Keyword(s):  
British Columbia ◽  
Middle Triassic ◽  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Deep Ocean ◽  
Island Arc ◽  
Canadian Cordillera ◽  
South Central ◽  
Upper Paleozoic ◽  
Paleozoic Rocks

The Paleozoic and early Mesozoic rocks of the Greenwood mining camp in southern British Columbia are a part of the Quesnel terrane in the eastern part of the Intermontane Belt of the Canadian Cordillera. Upper Paleozoic rocks include the Knob Hill Group composed of oceanic tholeiitic basalts (with (La/Yb)n [Formula: see text] 0.4–1.2), associated with deep ocean sedimentary rocks and serpentinites; the Attwood Group that comprises island-arc tholeiites (with (La/Yb)n [Formula: see text] 1–4 and positive εNd values), clastic sedimentary rocks and limestones; and a unit of oceanic gabbros with (La/Yb)n < 0.5. These lithologically defined units occur as tectonically emplaced slivers of oceanic crust probably produced during the closure of the Slide Mountain basin during the Permian. They are unconformably overlain by Middle Triassic calc-alkaline volcanic and sedimentary rocks of the Brooklyn Group. The Brooklyn Group volcanic rocks have characteristics of mature island-arc rocks, including (La/Yb)n [Formula: see text] 2.5–4.5 and positive εNd values. The Paleozoic rocks are crosscut by a 200 million years old granodioritic intrusion containing zircon with an Early Proterozoic inheritance age (~2.4 Ga). By inference, southern Quesnellia may have been well offshore from the ancestral North American margin in the Mississippian, in close proximity to the margin by the Middle Triassic, and contiguous with it by the Early Jurassic. It is suggested that the complex tectonic history of extension and contraction of the southern Canadian Cordillera during the post Middle Jurassic can be extended in south-central British Columbia as far back as the upper Paleozoic.

TEM/AEM characterization of fine-grained clay minerals in very-low-grade rocks: Evaluation of contamination by empa involving celadonite family minerals

1996 ◽  
Vol 54 ◽  
pp. 694-695
Author(s):  
Gejing Li ◽  
D. R. Peacor ◽  
D. S. Coombs ◽  
Y. Kawachi
Keyword(s):  
Electron Microscopy ◽  
Volcanic Rocks ◽  
Analytical Electron Microscopy ◽  
Metamorphic Rocks ◽  
New Mineral ◽  
Chemical Compositions ◽  
Low Grade ◽  
Fine Grained ◽  
Depth Analysis ◽  
Mineral Aggregates

Recent advances in transmission electron microscopy (TEM) and analytical electron microscopy (AEM) have led to many new insights into the structural and chemical characteristics of very finegrained, optically homogeneous mineral aggregates in sedimentary and very low-grade metamorphic rocks. Chemical compositions obtained by electron microprobe analysis (EMPA) on such materials have been shown by TEM/AEM to result from beam overlap on contaminant phases on a scale below resolution of EMPA, which in turn can lead to errors in interpretation and determination of formation conditions. Here we present an in-depth analysis of the relation between AEM and EMPA data, which leads also to the definition of new mineral phases, and demonstrate the resolution power of AEM relative to EMPA in investigations of very fine-grained mineral aggregates in sedimentary and very low-grade metamorphic rocks.Celadonite, having end-member composition KMgFe3+Si4O10(OH)2, and with minor substitution of Fe2+ for Mg and Al for Fe3+ on octahedral sites, is a fine-grained mica widespread in volcanic rocks and volcaniclastic sediments which have undergone low-temperature alteration in the oceanic crust and in burial metamorphic sequences.

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