Abstract: Compressive Interaction of Siberian and North American Plates, Bering Strait Region, Alaska

C. L. Sainsbury, Edward Bloomstein

Detailed geologic mapping, airborne magnetics, and distribution of mineral deposits demonstrate that presently the Chukotsky and the Seward Peninsulas are part of a continuous geologic province. "Jamming" together of the Siberian and western Alaskan part of the North American plates is documented by (1) intense eastward thrusting of rocks older than Late Cretaceous across the entire Seward Peninsula, (2) folding and reverse faulting of rocks of the Cretaceous basin east of the Seward Peninsula, and (3) cutting off of the Brooks Range by the zone of eastward thrusting that includes the west tip of the Lisburne Peninsula.

Initial interaction between the Siberian and western Alaskan plates may have begun in the Jurassic, with outpouring of mafic, chrome, and platinum-rich volcanic rocks that lie beneath the volcaniclastic sediments of the Cretaceous basin. Distribution of alkalic and younger intrusive rocks of dioritic to monzonitic composition suggests interaction between mantle material and possible oceanic crust around the margins of the Cretaceous basin, and the alkalic rocks are highly discordant with trends of intrusive rocks of the Seward Peninsula west of the margins of the Cretaceous basin.

Blueschist-facies rocks developed from mafic rocks that include Precambrian basalts and gabbroic intrusive rocks of possible Cretaceous age suggest fossil subduction zones which are still preserved on the Seward Peninsula, or slices of mantle material carried up during thrusting along the Collier thrust belt.

Mineral deposits of the Seward Peninsula which may be related to plate margins include uranium-thorium deposits associated with alkalic rocks, and tin deposits of Latest Cretaceous or Early Tertiary age associated with undeformed two-mica granites west of the belts of blueschist rocks. The large and important placer gold deposits are related principally to the distribution of the York Slate of late Precambrian age, with secondary control by nearness to granitic and mafic intrusive rocks, and degree of deformation by thrusting of the York Slate.

AAPG Search and Discovery Article #90966©1977 Alaska Geological Society 1977 Symposium, Anchorage, Alaska