Basaltic volcanism in the northeastern part of the Zuni lava field is related to a north-northeast trending regional fracture system. This is shown by elongation of centers and their alignment. However, .the fractures do not control the direction of lava tubes.
There are three distinct stages of volcanic activity common to the Zuni lava field:
1) early pyroclastic eruptions,
2) quiescent flows or fissure eruptions
3) late pyroclastic eruptions.
Evidence for the first stage is sometimes lacking, but the second and third stages can always be seen.
The basalts range from weakly tholeiitic to alkali in nature. Potassium content varies from 0.31 to 1 .33 percent in the lava field. There is a strong positive correlation between potassium and strontium content. The rocks can be divided into alkalic and tholeiitic basalts on this basis.
The Bandera Crater basalts have an initial 87Sr/86Sr ratio of 0.703 indicating a mantle origin.
The surface expression of lava tubes is a series of collapse depressions, usually sinuous. ·Lava tubes are not present in all of the basalt flows, but are found in both alkalic and tholeiitic basalts. The flows with large grains have no significant lava tube development.
Complete collapse of lava tube may not occur because:
1) rafted blocks support roof sections,
2) rubble from collapsed sections fills the tube in collapsed sections,
3) braided patterns result in central pillars which support large roofs.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Wolfgang Eugene Elston
Second Committee Member
J. Paul Fitzsimmons
Third Committee Member
Albert Masakiyo Kudo
Causey, James Douglas. "Geology, Geochemistry And Lava Tubes In Quaternary Basalts, Northeastern Part Of Zuni Lava Field, Valencia County, New Mexico." (1970). https://digitalrepository.unm.edu/eps_etds/312