Special Seminar:

Dr. Brian Hampton, Michigan State University

"A detrital record of arc accretion, exhumation, and basin development in the North American Cordillera, southern Alaska"

Wednesday, 10 September
12 noon - 12:55pm
Dillman 320

A reception with snack will follow in the Dow 6th Floor Atrium

Please join us to learn about Alaskan tectonics, rather than Alaskan politics!  Instead of scouring the detritus of political machinations for insight into current events, we will see the history of Alaskan tectonic movement from its own detritus, and the record it leaves as well as the geologic insight it provides.


The detrital record of Mesozoic island arc accretion along the North American Cordillera is preserved in a discontinuous belt of clastic marine strata that are exposed inboard of the Wrangellia island arc from southwestern Alaska to Washington State.  In southern Alaska, synorogenic deposits of the Upper Jurassic-Cretaceous Kahiltna assemblage contain the stratigraphic record of Wrangellia island arc accretion.  U-Pb detrital zircon ages combined with detailed stratigraphic constraint from the Kahiltna assemblage reveal a distinct temporal and spatial trend in regional exhumation and basin-fill evolution during Jurassic-Cretaceous time. LA-ICPMS analysis of detrital zircon grains from a >250-km-long transect of the Kahiltna basin reveal a U-Pb age distribution of primarily Mesozoic age grains (74%) with less abundant Paleozoic (11%), and Precambrian (15%) age grains.  Preexisting biostratigraphic constraint from the Kahiltna basin together with a minimum crystallization age (maximum depositional age) from each of the 8 samples allows for the study of upsection changes in provenance within the Kahiltna assemblage, which, ultimately reflect a distinct pattern of exhumation and erosion along the margins of the basin during island arc accretion.  A comparison of detrital zircon age distribution through time in the Kahiltna assemblage reveals three distinct stages of exhumation and basin development that include: (1) An initial Late Jurassic (latest Oxfordian) stage during which detrital zircon grains were derived solely from Late Triassic-Late Jurassic igneous sources of the oceanic Wrangellia composite terrane (Mz-100%-Pz-0%-Pc-0%), (2) an Early Cretaceous (Barremian-Aptian) stage during which detritus was derived primarily from Precambrian, Devonian-Mississippian, and Late Triassic-Jurassic source areas of the continental margin, as well as Late Triassic-Cretaceous arc sources of the oceanic Wrangellia composite terrane (Mz-76%-Pz-12%-Pc-12%); and, (3) an Early Cretaceous (Albian) stage that is represented by zircon age populations that reflect a large component of Precambrian and Ordovician-Silurian sources of the continental margin, as well as Cretaceous sources of the Wrangellia composite terrane (Mz-19%-Pz-22%-Pc-59%).  A comparison of along-strike detrital trends from throughout southern Alaska are consistent with a model favoring northward progression of exhumation, erosion, and deposition in a series of syncollisional basins during oblique collision  of the oceanic Wrangellia composite terrane to the Cordilleran continental margin during Late Jurassic-Early Cretaceous time.



For more information about this talk , please contact the Department Geological and Mining Engineering and Sciences—487-2531


BACK to News