X-ray fluorescence (XRF) analysis of Ubehebe Hills and related basalts, Northern Death Valley, California

Abstract

An olivine-bearing basalt flow in the Death Valley Wash (37.05175°N, 117.45295°W) underlies the 3.3 Ma Mesquite Spring tuff. Based on its stratigraphic position, the basalt flow was correlated with the 3.7±0.2 Ma basalt of Ubehebe Hills found 10 km to the south; however, there are three other olivine-bearing basalt flows older than 3.3 Ma and closer to Death Valley Wash. A 4.2±0.3 Ma olivine-basalt is found 5 km to the west on the east slope of the Last Chance Range. Two basalt flows in the Grapevine Mountains with dates of 7.5±0.3 Ma and 7.4±0.4 Ma are found 8 km southeast and 8 km north, respectively. Determining the source of the Death Valley Wash basalt will help elucidate Death Valley Late Miocene-Pliocene paleogeography and stratigraphy. Samples were collected from the five outcrops and analyzed by x-ray fluorescence (XRF). Major element concentrations indicate that all samples are basalt (47.6-51.88% SiO2). Trace element data (Zr/Ba vs Ce/Y) confirms that the Death Valley Wash basalt is the 3.7 Ma basalt of Ubehebe Hills. The source of the asthenosphere-dominated magma that produced the basalt of Ubehebe Hills is unknown. The 7.4-7.5 Ma basalt in the Grapevine Mountains has a different asthenosphere-dominated magma source. The suspected source of the 4.2 Ma basalt on the east flank of the Last Chance Range was the Saline Range to the west; however, the XRF data indicate an altogether different, lithosphere-dominated, magma source that is similar to basalts in the northern Last Chance Range. XRF analysis of basalts of northern Death Valley suggests that the basalt of Ubehebe Hills erupted into a narrow, north-south trending sedimentary basin and a similar source for basalts throughout the Last Chance Range and, possibly, the Saline Range.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016