PALEOMAGNETIC EVIDENCE FOR POLYGENETIC BASALTIC VOLCANISM IN BIG PINE VOLCANIC FIELD, CALIFORNIA

Basaltic volcanoes are typically monogenetic, with eruptions that last about a decade (e.g., Paricutin). However, polygenetic basaltic volcanoes have been recognized in some basaltic volcanic fields (e.g., Cima, CA; Pisgah Crater, CA) with multiple eruptions over hundreds to thousands of years. Identifying whether volcanoes are polygenetic or monogenetic is significant for evaluating volcanic hazards from individual volcanoes. Using a combination of field mapping and paleomagnetic techniques, we are assessing the nature of volcanism at single volcanoes in the Big Pine volcanic field (BPVF), eastern California. The BPVF comprises at least nine scoria cones and associated basaltic flows. Reconnaissance mapping of a volcanic center directly south of Taboose Creek in the northwestern portion of the BPVF reveals four distinct basaltic flow units that erupted from closely spaced vents. Three of the flow units have identical phenocryst (ol+cpx) assemblages whereas the fourth flow unit contains granitic xenoliths and orthopyroxene xenocrysts, suggesting the eruption of different magma batches. Drill cores from the different flow units were collected for paleomagnetic analysis and demagnetized using low temperature and alternating field techniques at the Caltech Paleomagnetics Laboratory. The results from one site were excluded due to suspected remagnetization from lightning strikes, leaving a total of four mean site directions, one from each flow unit. The different flow units show a systematic change in the mean site directions that correlates with stratigraphic order, suggesting that these different flow units record secular variation of the magnetic field and erupted over an interval of 100 to 1000 years, and, in turn, suggesting that individual basaltic volcanoes in BPVF may be polygenetic.