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102nd Annual Meeting of the Cordilleran Section, GSA, 81st Annual Meeting of the Pacific Section, AAPG, and the Western Regional Meeting of the Alaska Section, SPE (8–10 May 2006)

Paper No. 5
Presentation Time: 10:00 AM

A TRIASSIC LINK BETWEEN YUKON-TANANA TERRANE AND NORTH AMERICA: NEW DETRITAL ZIRCON AGE, GEOCHEMICAL, AND BIOSTRATIGRAPHIC DATA


BERANEK, Luke P., Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, Canada and MORTENSEN, James K., Earth and Ocean Sciences, The Univ of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4, lberanek@eos.ubc.ca

New detrital zircon age and whole-rock geochemical data from conodont age-constrained Triassic sedimentary rocks in Yukon imply that the strata represent an overlap assemblage linking the pericratonic Yukon-Tanana Terrane (YTT) to western North America by the Early Mesozoic. A Triassic overlap assemblage in the northern Cordillera has two profound implications: (1) most or all of the Slide Mountain ocean closed by the Triassic, causing accretion of YTT up to 50 m.y. before its previously assumed Early Jurassic convergence with North America; and (2) Triassic sediments, containing western-derived detritus from YTT, are traditionally associated with the Cordilleran passive margin in Yukon and must be redefined as deposits within a foreland basin that formed to the east of YTT.

Specifically, the Early Triassic (Smithian) type section of the Jones Lake Formation, eastern Yukon, contains Early Mississippian (345 Ma) detrital zircons, consistent with U-Pb ages of the Simpson Range Plutonic Suite (345-355 Ma) of YTT. These ages are younger than other dated Paleozoic igneous units within the Selwyn Basin (all >362 Ma). Whole-rock geochemical data from the Jones Lake Formation also suggest a minor mafic component in the sediment, possibly reflecting input from the Slide Mountain ocean basin.

Middle Triassic (Ladinian) sedimentary rocks of the western Selwyn Basin exposed along the Sa Dena Hes mine road and in the 99 Mile Creek area, southeastern Yukon, contain Ladinian (236, 242 Ma), mid-Permian (265-270 Ma) and late Mississippian (320-334 Ma) detrital zircons. U-Pb ages closely resemble the Mississippian Tatlmain Plutonic Suite (336-340 Ma) and the Permian Klondike Schist metavolcanic rocks and Sulphur Creek orthogneiss suite (252-264 Ma) of YTT.

Late Triassic (Norian) rocks exposed at Clinton Creek, northwest of Dawson in western Yukon, contain mid-Permian (262-280 Ma) and late Mississippian (320-340 Ma) detrital zircons. Late Paleozoic grains are slightly older than those observed in the Klondike or Sulphur Creek units; however Late Mississippian ages compare favorably with plutonic suites of YTT.

Session No. 3

T6. GSA: New Insights into the Origin and Evolution of the Northern Cordilleran Pericratonic Terranes I
Monday, 8 May 2006: 7:55 AM-11:20 AM
Geological Society of America Abstracts with Programs. Vol. 38, No. 5, p.5
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