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Oblique Convergence as a Driving Mechanism for Protracted Exhumation, Basin Development, and along-Strike Sedimentation during Island Arc Collision: A Case Study from Southern Alaska

Hampton, Brian 1
1 Geological Sciences, Michigan State University, East Lansing, MI.

Late Cenozoic examples of island arc collision (e.g. Taiwan, Trinidad, Venezuela) have aided in our understanding of exhumation, basin development, and sediment dispersal in moderately- to highly-oblique convergent margin settings. However, in older mountain belts, often the timing, location, and duration of collision can only be inferred from stratigraphic and provenance trends from sedimentary basin that developed during suturing events. In the case of the North American Cordillera, Mesozoic island arc collision is recorded in a discontinuous belt (>2000-km-long) of clastic strata that are exposed inboard (cratonward) of the allochonous Wrangellia composite terrane (composite island arc) from southern Alaska to Washington State. In southern Alaska, synorogenic strata of the Upper Jurassic-Cretaceous Kahiltna assemblage are located in the suture zone between the Wrangellia composite terrane and pericratonic Intermontane belt. Stratigraphic constraint and provenance trends from the Kahiltna assemblage, including U-Pb detrital zircon geochronology, reveal distinct temporal and spatial trends in regional exhumation and basin development during Jurassic-Cretaceous arc collision. U-Pb detrital zircon geochronology from base-to-top of the Kahiltna assemblage reveal an age distribution of primarily Mesozoic age grains (Mz-74%) with less abundant Paleozoic (Pz-11%), and Precambrian (Pc-15%) age grains. A comparison of detrital zircon ages from older to younger stratigraphic intervals within the Kahiltna assemblage reveals three distinct stages of exhumation and basin development that are interpreted to represent: (1) An initial Late Jurassic-Early Cretaceous stage during which detritus was derived almost solely from Middle-Late Jurassic igneous sources of the Wrangellia composite terrane (Mz-100%-Pz-0%-Pc-0%) and deposited in a retroarc foreland basin, (2) an Early Cretaceous stage that reflects a transition to sedimentation in a remnant ocean basin setting and the first introduction of Paleozoic and Precambrian age detritus from pericratonic source areas (Mz-84%-Pz-11%-Pc-5%; Mz-59%-Pz-12%-Pc-29%), and finally,
3 an Early to Late Cretaceous stage that reflects a transition to a collisional foreland basin that was characterized by continued detrital contributions from inboard and outboard source areas and a relative decrease in Mesozoic arc source areas and increased in Precambrian and Paleozoic pericratonic sources (Mz-46%-Pz-16%-Pc-38%).

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009