2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 56
Presentation Time: 1:30 PM-5:30 PM


TAYLOR, Stephen B.1, TEMPLETON, Jeffrey1, BUDNICK, Jeffrey1, DRURY, Chandra, FISHER, Jamie1 and RUNYAN, Summer3, (1)Earth and Physical Science Dept, Western Oregon University, 345 N. Monmouth Ave, Monmouth, OR 97361, (2)University Computing Services, Western Oregon University, Monmouth, OR 97361, taylors@wou.edu

Newberry Volcano of central Oregon is located in a complex, extensional tectonic setting. Fracture systems converging near the volcanic center include the Brothers (west-northwest trending), Tumalo (north-northwest), and Walker Rim (northeast) fault zones. Newberry covers greater than 1600 sq. km and is associated with over 400 basaltic cinder cones and fissure vents (Holocene-Late Pleistocene). The large number of cinder cones provides a robust data set from which to conduct spatial analyses of vent distribution patterns and quantitatively test for structural controls on magma emplacement.

Newberry cone positions (n=296) were compiled from digital geologic maps and statistically analyzed using GIS. Cone locations were further subdivided into northern (n=149) and southern (n=147) domains to test for mutually independent relations between the three fault zones. Observed cone patterns were tested for randomness and spatial anisotropy using a combination of quadrat analysis (Komogorov-Simirnov test) and comparative-distribution analysis via Monte Carlo simulations. The latter employed the “line-azimuth” and “point-density” techniques of Lutz (1986) and Zhang and Lutz (1989). Statistically significant cone-distribution patterns were subsequently compared to fault trends to assess the degree to which magma emplacement was guided by regional tectonic stress fields.

Results of the K-S tests reject the null hypothesis at the 95% confidence interval, documenting that Newberry cinder cones are not randomly distributed. The Monte Carlo-based analyses identify four significant cone alignments in the southern domain (dominant azimuth directions = 10-15, 30-35, 325-330, 355), and three in the northern (85, 310, 345). Fault segment analysis reveals three dominant azimuthal trends in the region: 310-325 (Brothers fault zone), 330-340 (Tumalo fault zone), and 45-50 (Walker Rim). The above results suggest that the Brothers and Tumalo fault zones had a detectable control on cinder-cone emplacement in both the northern and southern domains, whereas the Walker Rim is poorly correlated to significant cone-alignment patterns. Cinder cone alignments with azimuthal trends of 10-15, 30-35, and 85 suggest additional control by structural conditions other than those represented by mapped surface faults.