Palaeopole for the 69 Ma Prospector Mountain stock: a critique of the Carmacks/‘Baja BC’ transport estimate for Yukon, Canada

Symons, D. T. A.; Kawasaki, Kazuo; McCausland, Phil J.A.; Hart, Craig J.R.

doi:10.1093/gji/ggw398

Cited by 3 publications

(7 citation statements)

References 64 publications

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“…The décollement modeled herein aligns with an interpretation of relatively small amounts of shortening across the Intermontane terranes and Selwyn basin, as suggested by the geological and structural interpretations (e.g., Cecile & Cook, ; Gordey, ; Cecile, Cook, & Snowdon, ; Gordey et al, ) and the paleomagnetism of plutonic rocks (e.g., Symons et al, , , , ). However, the décollement could be part of a structure, now hidden, postulated to be located in or east of the eastern margin of Selwyn basin (Enkin, Johnston, et al, ), which accommodated a component of large (>1,500 km, not including 430 km of displacement on the Tintina fault) displacements including terminal docking of the Intermontane terranes and related formation of the Mackenzie Mountains fold and thrust belt (Johnston, ).…”

Section: Discussionsupporting

confidence: 84%

“…Shortening in the Selwyn Mountains (Figure ) is estimated to be in excess of 150 km, but constraint on the timing is bracketed by deformed Late Triassic (Norian) sedimentary rocks intruded by undeformed middle Cretaceous plutonic rocks (~93–98 Ma) (Cecile, , ; Cecile et al, ). These estimates are lower than those from the paleomagnetism of Cretaceous‐ and Eocene‐aged plutonic rocks, which suggest that less than ~800 km of northward displacement of the Intermontane terranes (e.g., 650 ± 450 km, Symons et al, , ; 780 ± 730 km, McCausland et al, ) was accompanied by 305 ± 125 km of ENE‐WSW shortening across Selwyn basin and the Mackenzie Mountains (Symons et al, , , ). Approximately two thirds of the related terrane rotations are interpreted to have occurred between the middle Cretaceous and Early Eocene, with the remainder post‐54 Ma (Symons et al, , , ).…”

Section: Discussionmentioning

confidence: 93%

“…Low‐temperature (U‐Th)/He thermochronology from Neoproterozoic strata implies that regional compressional, associated with the Laramide deformation event (Aitken & Cook, ), resulted in shortening and uplift of the Mackenzie Mountains fold and thrust belt between the Albian (middle Cretaceous) and Paleocene (Powell, ; Powell et al, ). The paleomagnetism of Late Cretaceous plutonic rocks suggests that at that time, the Intermontane terranes were <800 km to the south of their present position (e.g., McCausland et al, ; Symons et al, ), as supported by geological evidence (e.g., Gabrielse et al, ; Wyld et al, ). An alternative hypothesis (commonly known as Baja British Columbia , Irving, ), based primarily on the paleomagnetism of the Late Cretaceous Carmacks Group (e.g., Enkin, ), but supported by detrital zircon analysis (e.g., Matthews et al, ), suggests that the Intermontane terranes and parts of the Cordilleran hinterland to which they were attached experienced ~1,500 km of northward translation from the latest Cretaceous (~70 Ma) to the Paleocene.…”

Section: Tectonic Development Of the Northern Cordilleramentioning

confidence: 87%

“…The degree of tilting of plutons and their host rocks within the Intermontane terranes and Selwyn basin during displacement on the décollement, especially near to where it shallows and deformation is focused in the Mackenzie Mountains fold and thrust belt (Figure ), and also during subsequent displacement on the Tintina and related faults is difficult to constrain in an exact way. However, it is commonly inferred on the basis of hornblende geobarometry and/or local geological relationships that many of the region's middle to Late Cretaceous plutons have not been significantly tilted since emplacement (e.g., Harris et al, , ; McCausland et al, ; Symons et al, , ; Symons & McCausland, ). For example, the Prospector Mountain stock (PM, Figure a) is inferred by Symons et al () to have not been tilted, but the intrusion is shown to be faulted along with the Late Cretaceous Carmacks Group volcanic rocks it intrudes (Ryan et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…However, it is commonly inferred on the basis of hornblende geobarometry and/or local geological relationships that many of the region's middle to Late Cretaceous plutons have not been significantly tilted since emplacement (e.g., Harris et al, , ; McCausland et al, ; Symons et al, , ; Symons & McCausland, ). For example, the Prospector Mountain stock (PM, Figure a) is inferred by Symons et al () to have not been tilted, but the intrusion is shown to be faulted along with the Late Cretaceous Carmacks Group volcanic rocks it intrudes (Ryan et al, ). Layered rocks of the Carmacks Group, present as outliers to the west of the Tintina fault, show a broad range of dips and azimuths both locally and regionally (e.g., Gordey & Ryan, ; Payne et al, ; Tempelman‐Kluit, , , ).…”

Section: Discussionmentioning

confidence: 99%

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The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

Hayward

2019

Tectonics

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A new approach to the 3D inversion and interpretation of gravity data is applied to the crustal architecture of the northern Cordillera of Canada and Alaska. The technique models the distribution and depth extent of rocks with systematic density contrasts, such as sedimentary or intrusive rocks. In the northern Cordillera, the geometry of low-density zones, primarily associated with middle to Late Cretaceous granitic intrusions, and Neoproterozoic and Cretaceous sedimentary rocks, is defined. Variation in the depth extent of these zones delimits a surface, interpreted herein as a regional décollement syntectonic with, or postdating, middle Cretaceous intrusions, but predating and displaced~430 km by the Eocene-aged Tintina fault. The décollement trends N35°E and shallows from a depth of~15-20 km beneath Selwyn basin tõ 11 km beneath the Mackenzie Mountains. Here surface faults echo the décollement geometry, linked to fold and thrust belt development between the middle Cretaceous and Paleocene. The décollement continues southward for an unknown distance into northern British Columbia, but the Liard line represents a structural discontinuity between the fold and thrust belts of the Mackenzie Mountains and northern Rocky Mountains. The décollement's northwestern extent is broadly defined by surface faults in the northern Ogilvie Mountains. However, prior to Tintina fault displacement, the décollement was likely connected to a fold and thrust belt and related décollement in east-central Alaska. Estimates of post-middle Cretaceous exhumation suggest regional tectonic modification of the décollement, possibly including the presently active detachment inferred for the weak lower crust.HAYWARD 307

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Section: Discussionsupporting

confidence: 84%

Section: Discussionmentioning

confidence: 93%

Section: Tectonic Development Of the Northern Cordilleramentioning

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

Hayward

2019

Tectonics

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Jurassic location of the Yukon-Tanana Terrane from paleomagnetism of the folded Mississippian Tatlmain Batholith and Ragged Stock

Symons

Kawasaki

2019

Geophysical Journal International

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Summary The extensive Yukon-Tanana terrane of the northern Canadian Cordillera has been considered controversially to be part of the allochthonous ‘Baja B.C.’ microcontinent or of the para-autochthonous North American cratonic margin during the Mesozoic. Paleomagnetic methods have isolated a very-stable Early Jurassic thermochemical remanent remagnetization in the terrane's felsic Tatlmain batholith and mafic Ragged stock after correction for: 1) rotation from northeast-plunging anticlinal deformation; 2) northerly dipping tectonic tilt of the host rocks; and, 3) northwestward regional translation on the adjacent Tintina transcurrent fault zone. The resulting 196 ± 6 Ma Tatlmain and Ragged paleopoles are 64.9° N, 44.8° E (A95 = 5.9°) and 64.2° N, 58.5° E (A95 = 7.7°), respectively. The YTT paleopoles support para-autochthonous tectonic models that have the YTT: 1) accreting to North America by the Early Jurassic; 2) undergoing non-significant orogen-perpendicular shortening by mid-Early Cretaceous from thrust-faulting; and, then 3) undergoing significant orogen-parallel northward translation of ∼500 km from mid-Early Cretaceous to the Eocene. In contrast, the paleopoles for Stikinia and Quesnellia of the Intermontane Belt show progressive northwestward translation relative to North America by ∼1000 km and a rotation of ∼55° cw since mid-Early Cretaceous. We speculate that ∼500 km of the northward translation is related to dextral motion on the Tintina and Northern Rocky Mountain Trench fault in British Columbia, and that the clockwise rotation is related to upper crustal tectonics in both Yukon and southern British Columbia.

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Evidence for early glaciation of southeastern Beringia

Savidge¹

2020

Can. J. Earth Sci.

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Between the Klondike Plateau and Yukon–Tanana highlands of Yukon and Alaska, respectively, current maps explain glaciated alpine locales and periglacial areas in terms of localized Pliocene–Pleistocene montane ice caps, alpine glaciers, and periglacial changes. However, this region’s plateau topography is populated with long undulating ridges having wide flattened tops; it contrasts with relief of other regions of northwestern North America also affected by ice caps, cryoplanation, and erosion over similar duration during the same epochs. This region has received minimal research and appears to present a new opportunity for resolving outstanding glaciological and stratigraphy issues. The glaciological history is reviewed, placing particular emphasis upon the low-elevation ridges within the “unglaciated” region, suggesting that those ridges are relict arête/cirque remnants. Sites of subalpine glacial grooving and mountaintop planing are also identified, and a conglomeratic red bed containing erratic clasts is described. All indications point to the “unglaciated” region having been glaciated before late Pliocene. Two working hypotheses are proposed: (1) The landscape once supported a range of young mountains that became glaciated then overridden and pared to a plateau by an ice sheet. (2) Following deglaciation, an extended period of paraglacial activity removed most of the former drift and excised new valleys to give the region an unglaciated appearance, which thereafter became modified into its present state by local montane/alpine glaciations, interglacial cryoplanation, periglacial gelifraction, and erosion. In addition to Pliocene–Pleistocene glaciations, a northeastward advancing Miocene ice sheet seems plausible and, on the basis of paleographic considerations and lithology, a Cretaceous glaciation evidently is also not out of the question.

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Palaeopole for the 69 Ma Prospector Mountain stock: a critique of the Carmacks/‘Baja BC’ transport estimate for Yukon, Canada

Cited by 3 publications

References 64 publications

The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

Jurassic location of the Yukon-Tanana Terrane from paleomagnetism of the folded Mississippian Tatlmain Batholith and Ragged Stock

Evidence for early glaciation of southeastern Beringia

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