Paleomagnetic, Geochemical, and Geochronological Evidence for Reconstructing a Paleochannel of the Tuolomne River, Sierra Nevada, CA.
Abstract
Previous studies have used paleochannel-filling volcanics both to reconstruct the paleogeomorphology of the Sierra Nevada, CA and as tilt markers and piercing points to reveal uplift and faulting, respectively. Using archival samples, we paleomagnetically, geochemically, and geochronologically confirm the existence of a Miocene lava-filled paleo-channel of the ancestral Tuolomne River (or a tributary) that flowed south-by-southwestwards from the eruptive source at the Little Walker Caldera at the western edge of the Great Basin, across the present crest of the Sierra Nevada, to Rancheria Mountain, overlooking Hetch Hetchy, CA. Normal polarity trachyandesites of the Table Mountain formation, dated here at ~10.4 Ma, the 9.4 Ma reversed-polarity Tollhouse Flat member of Eureka Valley Tuff, and arc-volcano-affinity andesitic units of Relief Peak Formation fill the former channel(s) at Rancheria Mountain, but existing maps suggest that they have been completely stripped from the 30-km stretch between Hetch Hetchy and the Little Walker Caldera - by glacial and fluvial erosion. However, the detailed paleomagnetic directions and other data provide clear correlation, supporting reconstruction of the ~10.4 Ma paleochannel and its use as a tilt marker. New geologic mapping demonstrates several generations of fill and incision into the paleochannel at Rancheria Mountain. In at least one case, younger units are inset lower down into the incising paleochannel.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMGP43A0792R
- Keywords:
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- 1599 General or miscellaneous;
- GEOMAGNETISM AND PALEOMAGNETISM