A detrital record of Mesozoic island arc accretion and exhumation in the North American Cordillera: U-Pb geochronology of the Kahiltna basin, southern Alaska

Brian A. Hampton, Kenneth D. Ridgway, George E Gehrels

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

The stratigraphic record of Mesozoic arc accretion in the North American Cordillera is preserved in a discontinuous belt of clastic strata that are exposed inboard (cratonward) of the allochthonous Wrangellia composite terrane in southern Alaska, western Canada, and Washington State. LA-ICPMS analyses of eight samples (n = 714 detrital zircon grains) collected at different stratigraphic intervals from the Jurassic-Cretaceous Kahiltna assemblage in southern Alaska reveals a bulk U-Pb age distribution of Precambrian-Mesozoic age grains (Mz 74%, Pz 11%, Pc 15%). A comparison of U-Pb ages from older to younger stratigraphic intervals within the Kahiltna assemblage reveals three stages of exhumation and basin development during arc accretion. Stages include (1) an initial Late Jurassic-Early Cretaceous pre/early collisional phase during which detritus was derived almost solely from Middle-Late Jurassic and Early Cretaceous magmatic sources of the outboard Wrangellia composite terrane (Mz 100%, Pz 0%, Pc, 0%), (2) a second Early Cretaceous syncollisional phase that reflects the introduction of Paleozoic and Precambrian detritus from the inboard Intermontane belt (Mz 84%, Pz 11%, Pc 5%) and an upsection increase in older detrital zircon grains compared to Mesozoic age grains (Mz 65%, Pz 11%, Pc 24%), and (3) a final Early-Late Cretaceous late/postcollisional phase that represents continued detrital contributions from Precambrian-Mesozoic source areas (Mz 19%, Pz 22%, Pc 59%) located inboard and outboard of the Kahiltna basin. Similar bulk trends in detrital zircon age populations have been reported from along-strike, age-equivalent strata of the Gravina belt (Mz 74%, Pz 20%, Pc 6%) in southeastern Alaska suggesting that similar provenance trends may exist in basins along this >2000 km -long collisional zone.

Original languageEnglish (US)
Article numberTC4015
JournalTectonics
Volume29
Issue number4
DOIs
StatePublished - 2010

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Geochronology
geochronology
island arcs
cordillera
exhumation
island arc
accretion
Cretaceous
strata
Precambrian
basin
zircon
Jurassic
arcs
detritus
terrane
intervals
trends
composite materials
Composite materials

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

A detrital record of Mesozoic island arc accretion and exhumation in the North American Cordillera : U-Pb geochronology of the Kahiltna basin, southern Alaska. / Hampton, Brian A.; Ridgway, Kenneth D.; Gehrels, George E.

In: Tectonics, Vol. 29, No. 4, TC4015, 2010.

Research output: Contribution to journalArticle

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abstract = "The stratigraphic record of Mesozoic arc accretion in the North American Cordillera is preserved in a discontinuous belt of clastic strata that are exposed inboard (cratonward) of the allochthonous Wrangellia composite terrane in southern Alaska, western Canada, and Washington State. LA-ICPMS analyses of eight samples (n = 714 detrital zircon grains) collected at different stratigraphic intervals from the Jurassic-Cretaceous Kahiltna assemblage in southern Alaska reveals a bulk U-Pb age distribution of Precambrian-Mesozoic age grains (Mz 74{\%}, Pz 11{\%}, Pc 15{\%}). A comparison of U-Pb ages from older to younger stratigraphic intervals within the Kahiltna assemblage reveals three stages of exhumation and basin development during arc accretion. Stages include (1) an initial Late Jurassic-Early Cretaceous pre/early collisional phase during which detritus was derived almost solely from Middle-Late Jurassic and Early Cretaceous magmatic sources of the outboard Wrangellia composite terrane (Mz 100{\%}, Pz 0{\%}, Pc, 0{\%}), (2) a second Early Cretaceous syncollisional phase that reflects the introduction of Paleozoic and Precambrian detritus from the inboard Intermontane belt (Mz 84{\%}, Pz 11{\%}, Pc 5{\%}) and an upsection increase in older detrital zircon grains compared to Mesozoic age grains (Mz 65{\%}, Pz 11{\%}, Pc 24{\%}), and (3) a final Early-Late Cretaceous late/postcollisional phase that represents continued detrital contributions from Precambrian-Mesozoic source areas (Mz 19{\%}, Pz 22{\%}, Pc 59{\%}) located inboard and outboard of the Kahiltna basin. Similar bulk trends in detrital zircon age populations have been reported from along-strike, age-equivalent strata of the Gravina belt (Mz 74{\%}, Pz 20{\%}, Pc 6{\%}) in southeastern Alaska suggesting that similar provenance trends may exist in basins along this >2000 km -long collisional zone.",
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