STRATIGRAPHIC RELATIONS AND SOURCE AREAS OF ASH-FLOW SHEETS OF THE BLACK MOUNTAIN AND STONEWALL MOUNTAIN VOLCANIC CENTERS, NEVADA.

The paper presents evidence for new stratigraphic correlations and source-area assignments for certain ash-flow units of the Black Mountain and Stonewall Mountain volcanic centers in southern Nevada. These new interpretations are based on field relations, trace element and paleomagnetic 'fingerprinting,' and radiometric age data. Some ash flows that were previously thought to have erupted from the Black Mountain center are now related to the slightly younger Stonewall Mountain center. As a result, the volumes of two of the members of the Thirsty Canyon Tuff have been reduced by approximately one-half, and the probable time span over which the Black Mountain volcanic center was active has been appreciably shortened.