A Structural and Heavy Mineral Study of an Upper Jurassic and Cretaceous Sedimentary Section to Constrain the Upper Mesozoic Tectonic Development of South-Central Alaska

Jason Altekruse

University of California, Geology Department

Davis, California

[email protected]

The Alaska Range suture zone marks the boundary between the lower Mesozoic continental margin of North America and a Paleozoic to lower Mesozoic island-arc assemblage.  Recently published stratigraphic and detrital zircon studies of the upper Jurassic and Cretaceous clastic sedimentary section in the suture zone document a transition in the marine section from solely island-arc derived sediment in the upper Jurassic to lower Cretaceous, to a combination of continental and island-arc material in the middle Cretaceous reflecting proximity of the island-arc to the continental margin.  Additionally, a Late Cretaceous nonmarine sedimentary section, locally in profound angular unconformity with the underlying marine section, is interpreted to reflect the final stage in the development of the suture zone.

The purpose of this study is to constrain the tectonic and paleogeographic development of south-central Alaska during the upper Mesozoic.  Specifically: (1) make a preliminary comparison of the heavy mineral assemblages in two Late Cretaceous nonmarine sections separated by the McKinley Fault,  (2) constrain the paleogeographic position of the island-arc assemblage with respect to the continental margin during the upper Mesozoic using heavy mineral provenance analysis to compliment existing detrital zircon data, and (3) use structural analysis to compare the deformational history of the marine and nonmarine sections, to determine if deformation of the marine section was widespread before nonmarine deposition.  This combination of structural and heavy mineral analysis will compliment ongoing studies and further constrain the history of basin development in southern Alaska and the tectonic development of south-central Alaska.