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TitleThe tectonic setting and origin of Cretaceous batholiths within the North American Cordillera: the case for slab failure magmatism and its significance for crustal growth
AuthorHildebrand, R S; Whalen, J B
SourceGeological Society of America, Special Paper no. 532, 2017 p. 1-113,
Alt SeriesNatural Resources Canada, Contribution Series 20170131
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
AreaMexico; United States of America
Subjectsstructural geology; tectonics; general geology; batholiths; magmatic arcs; crustal thickness; magmatic rocks; plutons; subduction; subduction zones; rock geochemistry; isotopic studies
Illustrationslocation maps; diagrams; graphs; tables; plots
ProgramGEM2: Geo-mapping for Energy and Minerals Western Cordillera, Regional porphyry transitions
Released2017 10 03
AbstractIn the standard model, Cordilleran-type batholiths form beneath volcanic arcs in thickened crust, but our survey of modern and ancient continental arcs revealed most to be regions of normal to thinned crust, not zones of crustal thickening. This suggested to us that the standard batholithic paradigm is fl awed. In order to better understand the batholiths, we explored (1) the 100 - 84 Ma La Posta and Sierran Crest magmatic suites of the Peninsular Ranges and Sierran batholiths, which formed after the 100 Ma Oregonian event due to closure of the Bisbee-Arperos seaway; (2) plutons and batholiths emplaced into the metamorphic hinterland of the 124 - 115 Ma Sevier event, which occurred in the Great Basin sector of the United States but, due to younger meridional transport, are now exposed in the Omineca belt and Selwyn Basin of Canada; and (3) Late Cretaceous-early Cenozoic intrusive rocks, such as the Coast, Idaho, and Boulder batholiths, which intruded a metamorphic hinterland during and after the Laramide event. The dominance of synto postdeformational emplacement and the distinctive slab failure-type geochemistry indicate that most, but not all, Cretaceous plutons within Cordilleran batholiths formed during and after arc-continent collision as the result of slab failure. We interpret whole-rock geochemistry, as well as radiogenic and stable isotopes,
to indicate that slab failure magmas involve only minor amounts of crust and are derived mainly from plagioclase-absent melting of garnet-bearing rocks in the mantle. Some suites, such as the <100 Ma Oregonian Sierran and Peninsular Ranges batholiths, have evolved Nd and Sr isotopes compatible with old enriched subcontinental lithospheric mantle. The well-known 0.706 87/86Sri isopleth appears to separate rocks of Oregonian slab failure from rocks of older arc magmatism and is probably unrelated to any obvious crustal break; instead, it refl ects involvement of old subcontinental lithospheric mantle in the slab failure magmas. To expand our fi ndings
we examined the geochemistry of Cenozoic slab window and Precambrian tonalitetrondhjemite-granodiorite suites and found them to share many similarities with the Cretaceous slab failure rocks.
Summary(Plain Language Summary, not published)
Granitoid batholiths, long interpreted as arc magmatism, constitute a volumetrically major component of the NA Cordillera and host a significant proportion of its mineral endowment. This paper presents a new controversial interpretation of granite batholiths as being post-collisional products of oceanic slab breakoff.

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