T143 Insights into Cordilleran Tectonics and Magmatism from the Sedimentary Record

Tuesday, 12 October 2021
8:00 AM - 12:00 PM
Portland Ballroom 255 (Hybrid Room)

DETRITAL ZIRCON RECORD OF CORDILLERAN MAGMATISM AS PRESERVED BY JURASSIC-PALEOCENE FOREARC AND FORELAND BASINS OF THE NORTH AMERICAN CORDILLERA

Paper number: T143-5
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Abstract

Compilations of detrital zircon (DZ) data from North American Cordilleran basins effectively subdue variability in DZ distributions that is commonly observed in studies of more limited geographic and/or temporal extent, allowing for the investigation of magmatic and sedimentary processes acting at the orogen-scale. We present a compilation of 830 DZ samples (>100,000 individual ages from 70 studies of forearc and foreland strata) to address the Jurassic-Paleocene history of Cordilleran magmatism, placing emphasis on 251-56 Ma grains that we infer to be uniquely derived from the arc (herein “arc-derived grains”). We compare detrital age distributions against >1,000 igneous zircon U-Pb ages from magmatic rocks. Results show that the forearc and foreland DZ records are excellent proxies for arc magmatism because they provide space- and time-integrated records of crystallization that are commonly obscured in igneous records. The DZ distributions show that arc magmatism was continuous throughout Mesozoic and earliest Cenozoic time, with presumably lower-volume magmatism during the Triassic and Early Jurassic (~251-174 Ma), episodic high-volume magmatism beginning in the Middle Jurassic and continuing through the Late Cretaceous (~174-66 Ma), and low-volume magmatism during the Paleocene (until ~56 Ma). However, DZ distributions are spatially and temporally variable across the basins. The forearc is dominated (>80%) by arc-derived grains, whereas the foreland is dominated (>80%) by grains >251 Ma. The dominance of arc-derived grains in the forearc supports that the arc was its dominant source of sediment, with rapid delivery via fluvial processes. The dominance of >251 Ma grains in the foreland demonstrates that rocks exposed in the Cordilleran hinterland and fold-thrust belt were the primary sources of sediment to the foreland. However, proportions of arc-derived grains in the foreland are highly variable, reflecting variations in the topography separating the arc and foreland and highlighting the important role of ash-fall processes in zircon delivery. Overall, the DZ distributions illustrate that Cordilleran basin-fills are reliable long-term archives of zircon production, and by extension, arc activity.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-366504

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