GEOCHEMICAL CHARACTERISTICS OF BASALTIC ROCKS FROM THE WUKSI VOLCANIC CHAIN, CASCADE RANGE NEAR LA PINE

The Wuksi volcanic chain is located on the east flank of the high cascades and is approximately 20 km south-southwest of Mt. Bachelor, and 50 km southwest of Bend, Oregon. The 10-km long chain is defined by five topographic highs consisting of cinder cones and a tuff cone; lava flow fields lie between the topographic highs. Age is constrained to older than 6.8 ka by pumice and ash from Mt. Mazama and younger than 18-22 ka inferred from contact relationships with Suttle Lake Advance drift deposits. Field investigation shows the tuff cone is one of the oldest units. Some lava flows are cut by the crater walls of maars; some lava flows are present within the craters of maars; some maars may be younger than the lava flows. Tuff-cone deposits contain abundant highly vesiculated juvenile glass; little juvenile material has been found in the maar deposits. Stream-rounded cobbles form accidental inclusions in the tuff cone, maar deposits, and some of the basalt flows and are derived from underlying poorly consolidated sedimentary rocks. Angular blocks of vesiculated basalt are also present as accidental inclusions and are geochemically distinct from rocks of the Wuksi volcanic chain.

Thirty seven lava and scoria samples have been analyzed via XRF and results show a narrow silica range from 51.2- to 52.4 wt.% and a total alkali content from 4.05-4.42 wt%. Samples cluster in two groups: one is basaltic (65% of the samples) and the other basaltic andesite (35% of all samples) (La Bas et al. (1986)). Grouping is also apparent in titanium content which decreases with increasing silica content.

We will present our geochemical data of the Wuksi volcanic chain and compare it to nearby eruptive centers at Mt. Bachelor and Newberry volcano.