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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 4. (April)

First Page: 658

Last Page: 658

Title: Summary of the Geologic Mapping Program by the Division of Geological and Geophysical Surveys (DGGS) in McGrath Quadrangle, Alaska: ABSTRACT

Author(s): T. K. Bundtzen, W. G. Gilbert, J. T. Kline, D. N. Solie

Article Type: Meeting abstract

Abstract:

From 1977-84, DGGS completed 1:63,360-scale geologic mapping of the McGrath quadrangle in western Alaska. Rock units in the study area range in age from lower Paleozoic to recent. The geologic history of this region has integrated stratigraphy, igneous activity, and mineral resources. From Cambro-Ordovician to Middle Devonian time, the Nixon Fork and Dillinger assemblages were deposited as coeval platform continental margin facies. Upper Devonian through Lower Jurassic shallow to deep-water sedimentary-volcanic facies of the Mystic assemblage overlie both older sequences. All three may have been offset right laterally from the Selwyn basin in northwestern Canada along the Tintina and other faults in central Alaska.

Upper Jurassic to Lower Cretaceous flysch of the Black Clastic sequence was structurally juxtaposed against the Dillinger and Mystic assemblages, probably during mid-Cretaceous compression related to terrane accretion in southern Alaska. Upper Cretaceous Kuskokwim Group flysch was deposited over Nixon Fork assemblage rocks in an extensional environment in the westernmost portion of the quadrangle.

A series of calc-alkaline intrusive and extrusive rocks ranging in age from Late Cretaceous to middle Tertiary intrude and overlie older, layered lithologies. Significant metalliferous epigenetic, stockwork, and skarn deposits are related to these igneous rocks near Farewell and McGrath. Middle Tertiary coal-bearing arenaceous sediments have been deposited in structural troughs related to the Farewell fault system. Offset solutions along the Farewell fault suggest up to 60 km of right-lateral offset since the Cretaceous. At least four Pleistocene and one late Tertiary(?) glaciations have advanced northward from the Alaska Range.

The DGGS efforts have resulted in the release of eight geologic maps and an extensive geochemistry survey of the entire quadrangle. A comprehensive summary of the geology and mineral resources of the entire quadrangle is in process. The poster session will also summarize university graduate studies of mineral deposits, igneous petrology, and stratigraphy.

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