27-11 Mesozoic Tectonic History of the North America Cordilleran Margin: A Case Study From the Tyaughton-Methow Basin, Southwestern British Columbia

Session: Evolution of Cordilleran-type orogenic systems

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Abstract:

The tectonic configuration of the Insular and Intermontane superterranes with respect to North America during the Mesozoic is a longstanding issue in Cordilleran tectonics. To discriminate between competing models of subduction polarity and terrane paleogeography, we focus on the sedimentary record of the Mesozoic Tyaughton-Methow basin of southwestern British Columbia. The Tyaughton-Methow basin is a 6-km-thick sequence of Upper Triassic to Cretaceous arc-derived sedimentary rocks located between the Insular and Intermontane superterranes. The position and age range of the basin make it a unique target for investigating potential changes in basin dynamics and sedimentary provenance related to Insular-Intermontane collision and assembly with North America. Previous work demonstrated that the Triassic and Jurassic portions of the basin record rifting and unroofing of a volcanic arc source to the east followed by input from both western- and eastern-arc sources by the Early Cretaceous. However, detrital zircon analytical work has been limited to middle Cretaceous samples in the upper part of the basin. We present preliminary geochronologic and geochemical analyses of zircons across five formations spanning the Upper Triassic to Early Cretaceous and explore the implications for provenance and subduction polarity during this time.

Preliminary detrital zircon U-Pb analyses were conducted on eleven samples across the Tyaughton, Nemaia, Tyox Pass, Teepee, and Potato Range formations. U-Pb analyses include a range of Mesozoic ages, with each sample yielding either bimodal or unimodal age populations between 231 and 135 Ma. These findings, alongside previous paleocurrent analyses and stratigraphic observations suggesting an eastern source throughout most of the basin’s history, point to Quesnellia and Stikinia as potential source terranes. Older Paleozoic and Proterozoic ages indicative of input from the craton interior were absent in the dataset, suggesting either a topographic barrier preventing inboard detritus from the craton or a large distance between the Intermontane terranes and North America throughout most of the Mesozoic. Lu-Hf and trace and rare earth element analyses were conducted on selected detrital samples across these age distributions to better constrain the source terrane geochemical fingerprints of the larger detrital system. We explore the depositional context and potential source terranes of these deposits, providing important insight into the tectonic configuration and paleogeographic evolution of the western North American margin throughout the Mesozoic.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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