Complex cinder cone eruptive sequence at O’Neill Crater,

San Francisco Volcanic Field

Beth SchreckNorthern Arizona University

Mentor: Dr. Nancy Riggs

IntroductionThe San Francisco Volcanic Field - 4,700 km2, over 600

volcanoes, 6 Ma to presentBasaltic volcanism characteristicsChanges in vent activityLava breaching and raftingPost-rafting activity

http://facweb.bhc.edu/academics/science/harwoodr/rhweb/thesis/index.htm

Project GoalsO’Neill CraterWhy was there no

cone re-growth with further eruption?

Cinder cone models currently too simplistic

Cinder cones on Mars may have complex morphology

SP Crater photo courtesy WA Duffield

http://facweb.bhc.edu/academics/science/harwoodr/rhweb/thesis/FullThesis/index.htm

DataData collection at

O’Neill CraterField workSamples collected

for thin section and Optically Stimulated Luminescence dating

AnalysisThin sectionsRock crushing and lab workMappingGeologic principles

ResultsGoal: eruptive

history of O’Neill crater

Chronology based on field analysis:

1. Cone-building stage

2. Continued eruption breached cone

3. Extrusion of dacite dome

ResultsDacite dome

extrusion complexInjection of basaltic-

andesiteEruption triggered

dacite

basaltic-andesite

ResultsBasaltic-andesite

eruption continuesEvidence from rocks

collectedQuestion still needs

to be answeredNew thin section

made

dacite fragment

basaltic-andesite

AcknowledgmentsDr. Nancy RiggsNAU Space Grant ProgramMy family

Questions?

http://facweb.bhc.edu/academics/science/harwoodr/rhweb/thesis/index.htm