Bitterroot — 2 Comments

  1. At 470km, this is on trend with Great Basin anomaly, separated by Snake River plain trend. And you’ve restored this one more or less directly north of that. This might suggest this anomaly is also less than ~40 million years old? There is an “ignimbrite flareup” like incident in, perhaps slightly east of the central Cascade crest in latest Oligocene.

  2. A reference for the above.
    Sigloch, Karin, Nadine McQuarrie, and Guust Nolet. “Two-stage subduction history under North America inferred from multiple-frequency tomography.” Nature Geoscience 1.7 (2008): 458-462.
    Feature appears to me to correspond to the steep portion of their N1 anomaly, which they connect to modern plate boundary. Deeper N2/S2 anomalies are estimated to be < c. 45 million years (which corresponds closely to detrital zircon maximumm depositional age of first sediments to be incorporated in Olympic subduction complex 44.72 ± 0.21 Ma; Eddy, Clark, and Polenz, 2017.

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