COMPOSITIONAL POPULATIONS RECORDED IN AEOLIAN BASALTIC SAND DUNES: USING BASALTIC DUNES IN HAWAII TO UNDERSTAND AEOLIAN PROCESSES ON MARS

The present-day surface of Mars has been shaped significantly by aeolian processes. A product of those long-term processes are dark, basaltic sand dunes. While we can observe the presence of the dunes, the transport distance and ultimate source of those dune sediments is still a subject of debate. Most aeolian sand dunes on Earth are composed of felsic materials and, consequently, our understanding of aeolian sediment source, transport distance and deposition are based on felsic minerals. To understand transport of basaltic materials on Mars, we need to understand the behavior of those materials on Earth. The Ka’u Desert in Volcanoes National Park in Hawaii is one of the few places on the Earth where basaltic aeolian sand dunes form. We collected sands from 11 aeolian sand dunes along with samples from potential sediment sources (the Keanakako’i tephra formation, nearby cinder cones, basaltic flow tops, etc.) to investigate whether or not we could use the composition of various phases in the sand to determine the source(s) contributing to dune formation. For each sand and tephra sample, we separated and analyzed olivine, smooth basaltic glass, frothy basaltic glass, and lithic grains for major element abundances using the EDS detector on a Phenom ProX SEM. We also powdered and analyzed cinder cone and basaltic flow top for major element abundances by XRF. Between 30 and 80 grains of each phase were measured per sand sample, and the average composition of each grain was calculated from a minimum of three analytical points. Most of the olivine in the sand dunes can be traced back to specific layers within the Keanakako’i tephra; some layers have extremely Mg-rich olivine (Fo>92) whereas other layers are more moderate (Fo = 82-92). Both smooth and frothy basaltic glass compositions demonstrate different dunes have different glass sources: some dunes have high-Mg glasses (MgO= 10-14 wt. %) while other dunes have low-Mg glasses (MgO = 6-10 wt. %). Most Keanakako’i glasses analyzed thus far are similar to the low-Mg glasses, signifying that there must be a separate, yet-to-be identified source for the high-Mg glasses. Based on data collected thus far, compositional variations in olivine and glass sand grains are useful tools to trace sand grains back to their sources.