T65 Tectonics of the Northwest Cordillera II: A Session in Honor of the Career Contributions of Ned Brown, Jim Monger, and Glenn Woodsworth

Sunday, 19 October 2014
1:00 PM - 5:00 PM
116/117

MESOZOIC TO CENOZOIC TECTONIC ASSEMBLY OF THE NORTHERN CORDILLERAN COAST BELT: INSIGHT FROM SOUTHWEST YUKON

Paper number: T65-13
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

The magmatic, structural and metamorphic history of the Coast belt of the western North American Cordillera has long been attributed to the tectonic interaction between the Insular and Intermontane terranes. Generally stated, this history consists of: initial Jurassic accretion, extension and formation of Jura-Cretaceous basins between the Insular and Intermontane terranes and sinistral translation, mid-Cretaceous compression and closure of the basins followed by extensive orogen-parallel dextral translation and Eocene extension, all occurring during episodic Jurassic to Paleocene magmatism.

The northern extension of the Coast belt occurs in southwest Yukon where it is truncated by the mainly Eocene and younger Denali fault. New U-Pb geochronology on zircons from magmatic and detrital sources along with up-to-date bedrock mapping indicates a multi-stage magmatic and tectonic interaction similar to what has been observed in other parts of the orogen, with some minor differences. The overall tectonic model for the northern Coast belt needs to account for: 1) formation of a Latest Triassic arc along the edges of the Insular terranes; 2) formation of Jura-Cretaceous basins along the outboard margin of the Intermontane terranes and the inboard margin of the Insular terranes and possible links across the basins; 3) Latest Jurassic to Early Cretaceous closure of the basins and obduction of the Triassic arc on to the Intermontane terranes; 4) continued Late Cretaceous to Paleocene compression with southwestward directed (today’s coordinates) movement of the Intermontane terranes over the Jura-Cretaceous sediments; 5) Eocene cooling, exhumation; and 6) up to 470 km of dextral displacement along the Denali fault.

The structural evolution is punctuated by and are therefore constrained by magmatic episodes that include; Latest Triassic (216-204 Ma), Early Cretaceous (124-116 Ma), Late Cretaceous (78-74 Ma), Paleocene (64-55 Ma) and Eocene (48-45 Ma).