Volcanic and tectonic evolution of the Cascade Volcanic Arc, central Oregon

Abstract

From 22 to 0 Ma, σ3 in the Cascade arc rotated clockwise from approximately N–S to E–W. σ1 rotated from subhorizontal to vertical at about 7 Ma, producing an extensional stress regime at 7–0 Ma. Rotation of σ1 and σ3 was likely a response to decreasing influence of ENE to NE compression at the Juan de Fuca plate‐North American plate (JDFP‐NAP) boundary relative to N‐S compression and attendant continental extension produced at the Pacific plate (PP)‐North American plate boundary. Decreases in orthogonal convergence rate, convergence angle, and length of the convergent margin relative to the NAP‐PP transform boundary caused the stress rotations. Volcanic production decreased by a factor of 3 from the interval 35–17 Ma to 16.9–7.4 Ma, probably reflecting a decrease in convergence rate. Volcanic production increased at 7.4–0 Ma even though convergence rate continued to decrease. The extensional stress regime at 7–0 Ma promoted mafic volcanism that caused the increased volcanic production. Volcanic production is therefore a function of convergence rate and upper plate stress regime. The volcanic front migrated progressively eastward from 35 to 0 Ma as the volcanic belt narrowed. The narrowing was caused primarily by steepening slab dip at depths greater than 100 km. Eastward migration was likely caused by decreasing shallow (0–100 km) slab dip resulting from thinning of the NAP. Uplift of the Western Cascades province in the early Pliocene may have been caused by vigorous flow into the mantle wedge accommodating an increase of free rollback rate of the subducted plate at 4 Ma.

Coevolution of volcanic catchments in Japan

“…These conditions are in the same range of our study (aridity index: 0.281-0.826; annual precipitation: 1513-3305 mm), which allows the two studies to be compared. Studies addressing the tectonic uplift in the western Cascades suggests that the portions of the landscape are uplifted during the early Pliocene (5.3-3.6 Ma; Priest, 1990); and the cross section of the western Cascades suggested that the rate of tectonic uplift is on the order of 700 m in the period (Conrey et al, 2002), which corresponds to 350-500 m in the Quaternary. The rates of tectonic uplift of our catchments, ranging from 250 to 1000 m, suggests some of our study catchments are more dynamic than the catchments in the Oregon Cascades.…”

Hydrogeology of the McKinney Butte Area: Sisters, Oregon

“…The Green Ridge fault (the major fault in the Green Ridge fault zone) marks the eastern boundary of the High Cascades axial graben (Allen, 1966;Priest, 1990) and is responsible for the tremendous amount of groundwater discharging to Metolius Spring at the headwaters of the Metolius River (Gannett et al, 2003). Chemical analysis suggests that the water discharged from Metolius Spring includes a large component of deep regional 9 groundwater, implying vertical permeability along the Green Ridge escarpment (Gannett et al, 2003).…”

“…The fault zone in the area between Bend and Sisters has been previously referred to as the Tumalo fault zone (Priest, 1990) and the Sisters fault zone (Sherrod et al, 2004). Wellik (2008) Butte .…”

“…Spring River is located at the western edge of the Shukash structural basin in the southern part of the upper Deschutes Basin. Metolius Spring, the headwaters of the Metolius River, occurs along the Green Ridge fault, which marks the eastern edge of the High Cascades graben (Allen, 1966;Priest, 1990). Vertical movement along the Green Ridge fault system is estimated to be over 600 m (Conrey, 1985).…”

“…Figure 46a shows water temperature of a spring as a function of the discharge elevation, and Figure 46b shows the relationship between spring temperatures corrected for GPE dissipation and recharge elevation obtained from oxygen isotope analysis. The plus signs show the mean annual surface temperature as a function of elevation at seven climate stations in or near the current study area for the period from 1961-1990(Oregon Climate Service, 2008 (Table 22). The dashed lines in Figure 46 bracket the range of expected surface temperatures as a function of elevation.…”