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New ties between the Alexander Terrane and Wrangellia and implications for North America Cordilleran evolution

Steve Israel, Luke Beranek, Richard M. Friedman and James L. Crowley
New ties between the Alexander Terrane and Wrangellia and implications for North America Cordilleran evolution
Lithosphere (May 2014) 6 (4): 270-276

Abstract

Two large tectonic terranes, Alexander and Wrangellia, at the northwestern margin of North America, have long been considered exotic to each other and the rest of the northern Cordillera. Pennsylvanian plutons tie the two terranes together, but their seemingly dissimilar geological character led most workers to believe the two evolved separately before and after the Pennsylvanian. New chemical abrasion zircon U-Pb geochronology, whole-rock geochemistry, and other geological evidence from Paleozoic magmatic rocks in Yukon, Canada, suggest that the terranes evolved together by the late Paleozoic and that the Alexander terrane partially forms the basement to a portion of Wrangellia.Large ca. 363 Ma gabbro complexes have non-arc geochemical signatures and intrude both terranes. Volcanic rocks near the base of northern Wrangellia are ca. 352 Ma and have back-arc to N-MORB geochemical signatures. At higher stratigraphic levels, Wrangellia contains abundant Mississippian to Pennsylvanian arc volcanic and volcaniclastic rocks (Skolai arc). Similar-aged arc/back-arc rocks are found in the southern part of Wrangellia (Sicker arc) and are interpreted as the southern extension of the Skolai arc.We propose that the gabbros represent the initiation of extension through an arc located at the margin of the Alexander terrane (Skolai/Sicker arc system). Extension progressed enough to deposit basalts within a back-arc basin setting. Subduction reversal closed the basin and rejuvenated the arc in the Pennsylvanian. Collision of the arc with the Alexander terrane led to exhumation and deposition of conglomerates unconformably on top of the gabbros.The evolution of the Alexander terrane and Wrangellia proposed here is broadly similar to the Late Devonian plate tectonic history along the northwestern Laurentian margin and is likely part of the same chain of arcs/back-arcs.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 6
Serial Issue: 4
Title: New ties between the Alexander Terrane and Wrangellia and implications for North America Cordilleran evolution
Affiliation: Yukon Geological Survey, Whitehorse, YT, Canada
Pages: 270-276
Published: 20140512
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 38
Accession Number: 2014-039285
Categories: GeochronologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Yukon Geological Survey Contrib. No. 017
Illustration Description: illus. incl. strat. col., 3 tables, geol. sketch map
N60°00'00" - N62°00'00", W141°00'00" - W136°00'00"
Secondary Affiliation: Memorial University of Newfoundland, CAN, CanadaUniversity of British Columbia, CAN, CanadaBoise State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201424
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