GEOLEX

Summary of Citation: Aldape Park

Publication:
Clemens, D.M. and Wood, S.H., 1993, Radiometric dating, volcanic
   stratigraphy, and sedimentation in the Boise foothills,
   northeastern margin of the western Snake River Plain, Ada
   County, Idaho: Isochron/West, no. 59, p. 3-10

Usage in Publication:
Aldape Park Basalt

Modifications:	Geologic Province:	Dominant Lithology:
Named	Snake River basin	Basalt

Summary:
Probably named for park in Boise. Assigned to Miocene and Pliocene Idaho Group (revised). Occurs in northeast margin of western Snake River Plain near Boise, Ada Co, southwestern ID. Found exposed as aphyric, dated basalt flow in roadcut on Military Reserve Road, 43 deg 37' N, 116 deg 11' W, SW1/4, SE1/4, S2, T3N, R2E, Boise South 7.5' quad. Consists of thin basalts #1-4 (ascending) and basalt of Aldape Park (previous informal usage), together here named Aldape Park Basalt, based on chemical similarities markedly different from basalts within the underlying Miocene (11.3+/-0.3 Ma) Boise basalt volcanic assemblage [informal]. Each of the basalts has oxidized basal contacts and vesicular upper and lower crusts, varies from aphyric to slightly phyric, from vesicular to mostly nonvesicular, and lacks pillow structures. Total thickness of basalts <55 m. Basalts #1-4 lie between lower and upper portions of Miocene Terteling Springs Formation (first used) of Idaho Group. [Basalt of Aldape Park seems also contained within the Terteling Springs unit]. Age is Miocene, based on K-Ar date of 9.5+/-0.6 Ma by modified whole-rock analysis consistent with 10.1-8.8 Ma normal magnetic polarity #5 episode (La Brecque and others, 1977). Report includes geologic map and stratigraphic column.