Virtual Field Trip—Group 2
Sierra Blanca Igneous Complex Lava Flow
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Geologic Overview for the Lava Flow
This field trip stop was at a road cut about 3 miles west of Alto at the fork of Eagle Lake Road and Ski Apache Road. It is located in the Angus quadrangle of Lincoln County, New Mexico. The lava flow is andesitic, thick, and coarsely porpyhritic, and flowing in an easterly direction. The lava flow originated from the east flank of Sierra Blanca.
Sierra Blanca was part of a group of stratovolcanoes that formed between 26 and 38 million years ago (Late Eocene to Oligocene time). These volcanoes were formed from the action of plate tectonics, specifically a subduction zone to the west. Based on published data Dr. Chamberlin estimates this lava flow is about 38–33 million years old.
This geologic feature shows:
- Large porpyhritic plagioclase crystals
- That the flow was affected by hydrothermal actions because of the different colors of the lava flow
- Zonation within large crystals reflecting changes in the magma as the crystal was forming
- Infilling of the vesicles with carbonate
A panoramic image of this stop is available
(when the image loads, drag your cursor on the image left or right to view the entire field stop)
