Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of Anchorage quadrangle, and southwest corner of Healy quadrangle, Alaska

Abstract

TV VOLCANIC ROCKS, UNDIFFERENTIATED (Paleocene to Miocene, uppermost part may be as young as Pleistocene)--0ver 1,500-m-thick sequence of felsic to mafic subaerial volcanic rocks and related shallow intrusives. Lower part of sequence consists of small stocks, irregular dikes, lenticular flows, and thick layers of pyroclastic rocks; made up dominantly of medium-to fine-grained, generally medium-gray quartz latite, rhyolite, and latite. A few dikes and intercalated flows of brown andesite are also present. Rocks of the lower part of the sequence, occurring mostly in the upper Talkeetna River area, are interpreted to be vent facies deposits and near vent deposits of stratovolcanos. The upper part of the sequence consists of gently dipping brown andesite and basalt flows interlayered with minor amounts of tuffs. A few lenses of fluviatile conglomerate are also present. Locally, at Yellowjacket Creek for instance, the feeder dikes of the mafic flows make up more than half the volume of the underlying country rocks. According to E. M. MacKevett, Jr. (oral commun., 1975), the andesite and basalt flows are lithologically identical to the basal andesites of the Wrangell Lava in eastern Alaska.