HR: 17:15h
AN: V32H-06    [PDF]
TI: Origins of Newberry Volcano, Central Oregon: A Cascade Backarc, High Lava Plains, Basin and Range Shield Volcano?
AU: * Rowe, M C
EM: rowem@geo.orst.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331
AU: Kent, A J
EM: adam.kent@science.oregonstate.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331
AU: Nielsen, R L
EM: nielsenr@geo.orst.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331
AU: Wallace, P J
EM: pwallace@darkwing.uoregon.edu
AF: Department of Geological Sciences, University of Oregon, Eugene, OR 97403
AU: Donnelly-Nolan, J M
EM: jdnolan@usgs.gov
AF: Volcano Hazards Program, U.S. Geological Survey, MS 910, 345 Middlefield Rd., Menlo Park, CA 94025
AB: Newberry Volcano, located 60 km east of the central Oregon High Cascades resides in a complex tectonic and volcanic region. Understanding the petrogenesis of Newberry Volcano is important to understanding the regional geological framework because of its location at the confluence of the back-arc of the Oregon Cascades, the northern end of the Basin and Range, and the western end of the High Lava Plains (HLP). The latter province includes a NW trend of propagating rhyolitic volcanism whose youngest expression appears to be Newberry. A clear understanding of Newberry's relation to the Cascades is also important due to a scarcity of backarc volcanism in this region. The first goal of this study is to evaluate the range of composition of the primary magmas that make up the parent magma array for this system to evaluate the diversity of mantle materials involved and the degree of melting. This study uses major- and trace-element data from primitive basalts ($>$ 8 wt % MgO, $>$ Fo\# 80) and melt inclusions, coupled with volatile elements (Cl, S, CO$_{2}$, and H$_{2}$O) from high-alumina olivine tholeiite (HAOT) lavas from Newberry Volcano, the HLP, the northern Basin and Range volcanics, and the Oregon Cascades in an attempt to evaluate the primitive compositions and melting dynamics at Newberry. Using this data we hope to discern Newberry's relative importance and relation to the surrounding volcanic regions. Preliminary melt inclusion data from Newberry and surrounding regions suggests that Newberry is slightly enriched in Ba (up to 750 ppm), K$_{2}$O (1 wt %), and Rb (24 ppm) relative to samples collected from the adjacent Basin and Range volcanics and the HLP. Also significant is that Nb and Ta are relatively depleted in the Newberry melt inclusions with K/Nb ranging from 600 to 1135 whereas the samples from the Basin and Range and HLP vary from 400-570 and 180-245, respectively. This, coupled with the Ba enrichment may suggest that a subduction-related fluid component is present in the mantle source region of Newberry magmas that is absent from the Basin and Range and HLP. Additionally, Cl concentrations in melt inclusions from several Newberry samples range from 200 to 1600 ppm, similar to values for primitive basalts in the High Cascades and much higher than values for magmas from the Basin and Range and HLP. The Cascades have been interpreted as a hot, dry arc and yet an apparent subduction-related fluid signature is observed as far as 300 km inland from the trench. Therefore, this data, while not conclusive, may have important ramifications for dehydration and fluid migration models beneath young, hot volcanic arcs.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting