Post by 1dave on Oct 4, 2016 11:53:11 GMT -5
Figure 3. Distribution of ca. 11–9 Ma high-K volcanic rocks in the Sierra Nevada and in the adjacent Walker Lane belt east of the Sierra Nevada range crest (revised from Pluhar et al., 2009); stratigraphy is described in Figure 4.
We propose herein that two distinct paleochannels (Cataract and Stanislaus) merged downstream into one (Cataract). Basal Stanislaus Group paleochannel fill consists of Table Mountain Latite (TML) lava, which erupted from fissures and was ponded to ~400 m thickness in the Sierra Crest graben-vent system (Fig. 2B).
Several TML lavas flowed down the Cataract paleochannel 130 km to Knight’s Ferry, shown at the westernmost edge of this figure, but the lavas that escaped down the paleochannel are <80 m thick (Gorny et al., 2009; Busby et al., 2013a).
The Eureka Valley Tuff includes trachydacite welded ignimbrites (Fig. 4) erupted from the Little Walker caldera (shown here); it is more extensive than the TML lavas because of the much greater mobility of pumice-rich pyroclastic flows (area shaded dark gray).
Along the Sierra Nevada crest (brown dashed line) and east of it, the distribution of high-K rocks was largely controlled by grabens, rather than paleochannels.
Inset: CR—Coast Ranges; GV—Great Valley; KM—Klamath Mountains; SCM—southern Cascade Mountains; SN—Sierra Nevada. Modified from King et al. (2007), Pluhar et al. (2009), and Busby et al. (2013a).
We propose herein that two distinct paleochannels (Cataract and Stanislaus) merged downstream into one (Cataract). Basal Stanislaus Group paleochannel fill consists of Table Mountain Latite (TML) lava, which erupted from fissures and was ponded to ~400 m thickness in the Sierra Crest graben-vent system (Fig. 2B).
Several TML lavas flowed down the Cataract paleochannel 130 km to Knight’s Ferry, shown at the westernmost edge of this figure, but the lavas that escaped down the paleochannel are <80 m thick (Gorny et al., 2009; Busby et al., 2013a).
The Eureka Valley Tuff includes trachydacite welded ignimbrites (Fig. 4) erupted from the Little Walker caldera (shown here); it is more extensive than the TML lavas because of the much greater mobility of pumice-rich pyroclastic flows (area shaded dark gray).
Along the Sierra Nevada crest (brown dashed line) and east of it, the distribution of high-K rocks was largely controlled by grabens, rather than paleochannels.
Inset: CR—Coast Ranges; GV—Great Valley; KM—Klamath Mountains; SCM—southern Cascade Mountains; SN—Sierra Nevada. Modified from King et al. (2007), Pluhar et al. (2009), and Busby et al. (2013a).
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