U-Th-Pb geochronology of the Coast Mountains batholith in north-coastal British Columbia: Constraints on age and tectonic evolution

George E. Gehrels, M. Rusmore, G. Woodsworth, M. Crawford, C. Andronicos, L. Hollister, J. Patchett, M. Ducea, R. Butler, K. Klepeis, C. Davidson, R. Friedman, J. Haggarf, B. Mahoney, W. Crawford, D. Pearson, J. Girardi

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225 Scopus citations


Previously published and new U-Pb geochronologic analyses provide 313 zircon and 59 titanite ages that constrain the igneous and cooling history of the Coast Mountains batholith in north-coastal British Columbia. First-order findings are as follows: (1) This segment of the batholith consists of three portions: a western magmatic belt (emplaced into the outboard Alexander and Wrangellia terranes) that was active 177-162 Ma, 157-142 Ma, and 118-100 Ma; an eastern belt (emplaced into the inboard Stikine and Yukon-Tanana terranes) that was active ca. 180-110 Ma; and a 100-50 Ma belt that was emplaced across much of the orogen during and following mid-Cretaceous juxtapo sition of outboard and inboard terranes. (2) Magmatism migrated eastward from 120 to 80 (or 60) Ma at a rate of 2.0-2.7 km/Ma, a rate similar to that recorded by the Sierra Nevada batholith. (3) Magmatic flux was quite variable through time, with high (>35-50 km3/Ma per km strike length) flux at 160-140 Ma, 120-78 Ma, and 55-48 Ma, and magmatic lulls at 140-120 Ma and 78-55 Ma. (4) High U/Th values record widespread growth (and/or recrystallization) of metamorphic zircon at 88-76 Ma and 62-52 Ma. (5) U-Pb ages of titanite record rapid cooling of axial portions of the batholith at ca. 55-48 Ma in response to east-side-down motion on regional extensional structures. (6) The magmatic history of this portion of the Coast Mountains batholith is consistent with a tectonic model involving formation of a Late Jurassic-earliest Cretaceous magmatic arc along the northern Cordilleran margin; duplication of this arc system in Early Cretaceous time by >800 km (perhaps 1000-1200 km) of sinistral motion (bringing the northern portion outboard of the southern portion); high-flux magmatism prior to and during orthogonal mid-Cretaceous terrane accretion; low-flux magmatism during Late Cretaceous-Paleocene dextral transpressional motion; and high-flux Eocene magmatism during rapid exhumation in a regime of regional crustal extension.

Original languageEnglish (US)
Pages (from-to)1341-1361
Number of pages21
JournalBulletin of the Geological Society of America
Issue number9-10
StatePublished - 2009

ASJC Scopus subject areas

  • Geology


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