scholarly journals Overlap assemblages: Laberge Group of the Whitehorse Trough, northern Canadian Cordillera

2021 ◽  
Author(s):  
D A Kellett ◽  
A Zagorevski
Keyword(s):  
Detrital Zircon ◽  
Middle Jurassic ◽  
Depositional Environment ◽  
Thermal Evolution ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Plutonic Complex ◽  
Time Histories ◽  
Regional Temperature ◽  
Temperature Time

The Laberge Group was deposited during the Early to Middle Jurassic in a marginal marine environment, in the northern Canadian Cordillera. It occurs as a narrow, elongated siliciclastic unit along more than 600 km of strike length, overlapping the Intermontane terranes of southern Yukon and northwestern British Columbia. The Laberge Group was deposited on the Late Triassic Stuhini and Lewes River groups, a volcano-plutonic complex of the Stikine terrane (Stikinia), and, locally, the Kutcho Arc. It is overlain by Middle Jurassic to Cretaceous clastic units. The variations in clast composition and detrital zircon populations among these units indicate major changes in depositional environment, basin extent, and sources during the latest Triassic to Middle Jurassic. Detrital zircon populations are dominated by near contemporary Stuhini-Lewes River arc grains, consistent with dissection of an active arc. Detrital rutile and muscovite data show rapid cooling and exhumation of metamorphic rocks during the Early Jurassic. Thermochronological data indicate that basin thermal evolution was domainal, with at least five regional temperature-time histories.

Provenance of Jurassic sedimentary rocks of south-central Quesnellia, British Columbia: implications for paleogeography

2004 ◽  
Vol 41 (1) ◽  
pp. 103-125 ◽  
Author(s):  
Nathan T Petersen ◽  
Paul L Smith ◽  
James K Mortensen ◽  
Robert A Creaser ◽  
Howard W Tipper
Keyword(s):  
Detrital Zircon ◽  
Middle Jurassic ◽  
Sedimentary Rocks ◽  
Source Area ◽  
Lower Jurassic ◽  
Early Jurassic ◽  
Late Triassic ◽  
Nd Isotopes ◽  
South Central ◽  
History Of

Jurassic sedimentary rocks of southern to central Quesnellia record the history of the Quesnellian magmatic arc and reflect increasing continental influence throughout the Jurassic history of the terrane. Standard petrographic point counts, geochemistry, Sm–Nd isotopes and detrital zircon geochronology, were employed to study provenance of rocks obtained from three areas of the terrane. Lower Jurassic sedimentary rocks, classified by inferred proximity to their source areas as proximal or proximal basin are derived from an arc source area. Sandstones of this age are immature. The rocks are geochemically and isotopically primitive. Detrital zircon populations, based on a limited number of analyses, have homogeneous Late Triassic or Early Jurassic ages, reflecting local derivation from Quesnellian arc sources. Middle Jurassic proximal and proximal basin sedimentary rocks show a trend toward more evolved mature sediments and evolved geochemical characteristics. The sandstones show a change to more mature grain components when compared with Lower Jurassic sedimentary rocks. There is a decrease in εNdT values of the sedimentary rocks and Proterozoic detrital zircon grains are present. This change is probably due to a combination of two factors: (1) pre-Middle Jurassic erosion of the Late Triassic – Early Jurassic arc of Quesnellia, making it a less dominant source, and (2) the increase in importance of the eastern parts of Quesnellia and the pericratonic terranes, such as Kootenay Terrane, both with characteristically more evolved isotopic values. Basin shale environments throughout the Jurassic show continental influence that is reflected in the evolved geochemistry and Sm–Nd isotopes of the sedimentary rocks. The data suggest southern Quesnellia received material from the North American continent throughout the Jurassic but that this continental influence was diluted by proximal arc sources in the rocks of proximal derivation. The presence of continent-derived material in the distal sedimentary rocks of this study suggests that southern Quesnellia is comparable to known pericratonic terranes.

Paleomagnetic evidence for displacement from the south of the Coast Plutonic Complex, British Columbia

1985 ◽  
Vol 22 (4) ◽  
pp. 584-598 ◽  
Author(s):  
E. Irving ◽  
G. J. Woodsworth ◽  
P. J. Wynne ◽  
A. Morrison
Keyword(s):  
British Columbia ◽  
Sierra Nevada ◽  
Lateral Displacement ◽  
Late Triassic ◽  
Time Range ◽  
Low Grade ◽  
Canadian Cordillera ◽  
Western Cordillera ◽  
Plutonic Complex ◽  
Coast Plutonic Complex

The mid-Cretaceous Spuzzum and Porteau plutons of the Coast Plutonic Complex of British Columbia have two magnetizations, A and B. The A magnetization (eight sites, 83 specimens, D = 30.3°, I = 56.7°, α95 = 4.9°, paleolatitude = 37 ± 5°N, paleopole 65.0°N, 14.9°W, A95 = 6.2°) is considered to have been acquired in the age range 105–90 Ma. This result differs from the field established for cratonic North America in this time range. The difference could be caused either by previously undetected tilting about a horizontal axis of the plutons, or by their rotation about a vertical axis and lateral displacement relative to the craton. Previously observed mid-Cretaceous magnetizations from other rock units from the western Canadian Cordillera and the Cascades of Washington, United States, are similarly discordant with respect to the craton. This similarity over such a large area indicates that, although local undetected tilting could be partly responsible, it is unlikely to be the prime cause, and we argue therefore that lateral displacement and rotation have occurred. It would seem that much of the western part of the Canadian Cordillera has moved north by about 2400 km and rotated clockwise since the mid-Cretaceous. The paleolatitude of the southern Coast Plutonic Complex of British Columbia is statistically identical to that recently observed (39 ± 3°N) for three plutons from the Central Sierra Nevada of California, which raises the possibility that the two complexes were much closer together at the time of their emplacement than at present. The second magnetization called B (four sites, 27 specimens, D = 5.1°, I = 67.6°, α95 = 4.7°, paleopole 86.5°N, 51.2°W) is parallel to the mid-Tertiary field, as previously determined from nearby intrusions, and is considered to be an overprint acquired during regional heating and low-grade metasomatism. Some earlier paleomagnetic studies of mid-Cretaceous rocks from the Coast Plutonic Complex indicated either an absence of displacement or uncertain evidence for it, and we attribute this to the nonrecognition, in this earlier work, of similar magnetically stable overprints of Tertiary age. Overprints in several Triassic rock units in the western Cordillera are parallel to the A magnetization, indicating that the mid-Cretaceous and the mid-Tertiary probably were periods of severe magnetic overprinting in British Columbia. Mid-Cretaceous and Late Triassic results from the western Cordillera of British Columbia are systematically different, indicating that movements relative to the craton occurred between these times.

The Canadian Cordillera, the Hellenides, and the Sea-Floor Spreading Theory

1972 ◽  
Vol 9 (6) ◽  
pp. 709-743 ◽  
Author(s):  
Jean Dercourt
Keyword(s):  
Pacific Ocean ◽  
Oceanic Crust ◽  
Continental Margin ◽  
Middle Jurassic ◽  
Late Jurassic ◽  
Late Triassic ◽  
Canadian Cordillera ◽  
Transform Faults ◽  
Sea Floor ◽  
Sea Floor Spreading

The theory of plate tectonics is applied to the tectonic evolution of the Hellenides and the Canadian Cordillera. In the Hellenides a Tethyan zone of sea-floor spreading developed within the continental crust during Triassic time and functioned until the end of the Middle Jurassic. It led to the formation of two plates, each with continental and oceanic segments, that were separated in some places by accreting plate margins and in others by transform faults. In Late Jurassic time the mid-Tethyan ridge became inactive as new ridges developed in the Atlantic Ocean. From Late Jurassic to Recent time, Tethyan oceanic crust largely disappeared under one of the cratons. The chronology of tectonic events in the Hellenides corresponds well with that of sea-floor spreading in the Atlantic.Four periods of sea-floor spreading were involved in the formation of the Canadian Cordillera: (1) a Silurian? to Early Devonian period when an Archeo-Pacific Ocean separated the Canadian craton with a stable sedimentary margin from a volcanic archipelago; (2) a Middle Devonian to Permian period when the extinct volcanic archipelago was bounded to the west by a spreading Paleo-Pacific Ocean, and to the east by a tectonic contact which was consuming Archeo-Pacific oceanic crust; part of this crust was obducted over the continental margin; (3) a Late Triassic to Middle Jurassic period when a second volcanic archipelago separated a spreading Neo-Pacific Ocean from the continental margin; and (4) a Late Jurassic to Recent period where spreading occurred in both the Atlantic and Pacific Oceans, subjecting the second volcanic archipelago and the continental margin to major tectonism; since the Paleocene, the Cordillera has slid towards the NNW along transform faults.

scholarly journals Detrital zircon provenance of the Late Triassic Songpan-Ganzi complex: Sedimentary record of collision of the North and South China blocks: Comment and Reply: REPLY

Geology ◽  
2006 ◽  
Vol 34 (1) ◽  
pp. e107-e108
Author(s):  
A. L. Weislogel ◽  
S. A. Graham ◽  
E. Z. Chang ◽  
J. L. Wooden ◽  
G. E. Gehrels ◽  
...  
Keyword(s):  
South China ◽  
Detrital Zircon ◽  
Late Triassic ◽  
Sedimentary Record ◽  
The North ◽  
North And South

The provenance of Middle Jurassic sandstones in the Scotian Basin: petrographic evidence of passive margin tectonics 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin. 2Geological Survey of Canada Contribution 20110319.

2012 ◽  
Vol 49 (12) ◽  
pp. 1463-1477 ◽  
Author(s):  
Gang Li ◽  
Georgia Pe-Piper ◽  
David J.W. Piper
Keyword(s):  
Early Cretaceous ◽  
Middle Jurassic ◽  
Mineral Chemistry ◽  
Passive Margin ◽  
Heavy Minerals ◽  
Late Triassic ◽  
Cape Breton Island ◽  
Grand Banks ◽  
Meguma Terrane ◽  
Geomorphological Evolution

The tectonic and geomorphological evolution of the Scotian margin and its hinterland is poorly known between Late Triassic rifting and the Early Cretaceous progradation of major deltas. This study determined sedimentary provenance of Middle Jurassic Mohican Formation sandstones from three wells using heavy minerals and mineral chemistry. Indicator minerals such as xenotime, altered ilmenite, and varietal types of garnet and tourmaline are similar to those in Hauterivian–Barremian sandstones in the western Scotian Basin, which are almost exclusively derived from the Meguma terrane. The wells adjacent to the Canso Ridge have more zircon and less ilmenite, indicating a greater contribution of polycyclic reworking, but with an ultimate source in the Meguma terrane. Zircon and ilmenite were likely derived in part from Carboniferous sandstones in eastern mainland Nova Scotia and Cape Breton Island. Any river drainage from the inboard terranes of the Appalachians either was diverted through the Fundy Basin or entered the easternmost Scotian Basin, where the Mohican Formation is 5.5 km thick, along the linear continuation of the southwest Grand Banks transform. Such sediment did not reach the Canso Ridge, suggesting that the Cobequid–Chedabucto fault zone in Orpheus graben was not a significant physiographic feature. This tectonically controlled paleogeography in the Middle Jurassic is quite different from that during active rifting in the Late Triassic – Early Jurassic. Middle Jurassic quiescence was followed in the Tithonian – Early Cretaceous by renewed tectonic uplift associated with rifting of Grand Banks from Iberia and Labrador from Greenland.

Global carbon isotope signal in the Middle Triassic on Svalbard

2021 ◽  
Author(s):  
Victoria S. Engelschiøn ◽  
Øyvind Hammer ◽  
Fredrik Wesenlund ◽  
Jørn H. Hurum ◽  
Atle Mørk
Keyword(s):  
Carbon Isotope ◽  
Depositional Environment ◽  
Middle Triassic ◽  
Barents Sea ◽  
Water Productivity ◽  
Sedimentary Environment ◽  
The Arctic ◽  
Late Triassic ◽  
Triassic Boundary ◽  
Thin Sections

<p>Several carbon isotope curves were recently published for the Early and Middle Triassic in Tethys. Recent work has also been done on the Early Triassic of Svalbard, but not yet for the Middle Triassic. This work is the first to measure δ<sup>13</sup>C for different Middle Triassic localities on Svalbard, which was then part of the Boreal Ocean on northern Pangea. Our aim is to understand the controls on the Svalbard carbon isotope curve and to place them in a global setting.</p><p>Correlating Triassic rocks around the world is interesting for several reasons. The Triassic Period was a tumultuous time for life, and the Arctic archipelago of Svalbard has shown to be an important locality to understand the early radiation of marine vertebrates in the Triassic. Much effort is also made to understand the development of the Barents Sea through Svalbard’s geology.</p><p>Carbon isotope curves are controlled by depositional environment and global fluctuations. Global factors such as the carbon cycle control the long-term carbon isotopic compositions, while short-term fluctuations may reflect the origin of organic materials in the sediment (e.g. algal or terrestrial matter), stratification of the water column, and/or surface water productivity. Carbon isotopes can therefore be useful to understand the depositional environment and to correlate time-equivalent rocks globally.</p><p>The dataset was collected through three seasons of fieldwork in Svalbard with localities from the islands Spitsbergen, Edgeøya and Bjørnøya. Detailed stratigraphic sampling has resulted in high-resolution δ<sup>13</sup>C curves. These show three strong transitions; 1) on the boundary between the Early and Middle Triassic, 2) in the middle of the formation and 3) at the Middle and Late Triassic boundary. Several Tethyan localities show a possibly similar Early-Middle Triassic signal. Current work in progress is sedimentological analysis by thin sections and X-ray fluorescence spectroscopy (XRF) to further understand the sedimentary environment.</p>

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