CALIFORNIA’S OPHIOLITE RIMMED GREAT VALLEY: JURASSIC/CRETACEOUS BOUNDARY IMPACT BASIN DEFORMED BY ~145 MA OF E-W SHORTENING AND AT LEAST 30 MA OF NW-SE RIGHT-LATERAL SHEAR?

Speculation that circular to elliptical segments of exposed lithospheric mantle belts may mark rims of large terrestrial impact basins suggests that the ophiolite rimmed Sulu Sea, Loyalty and Yucatan basins could be impact basins resulting from middle Miocene, late Eocene and K/Pg boundary mantle excavating hypervelocity impacts on Earth [1]. Considered together, these basins show progressively greater degrees of deformation with age, consistent with cumulative effects of plate tectonics. Older impact basins will be increasingly difficult to recognize as originally circular to elliptical belts of surface exposed mantle become progressively deformed, dis-membered and/or incorporated into sutures. Note that: 1) ophiolites rimming the Great Valley (GV) are of various Jurassic and older ages; while 2) oldest Great Valley Group (GVG) sedimentary rocks are ~J/K boundary in age [2]. This suggests the GV may be a large deformed J/K boundary impact basin, the present shape resulting from integrated deformation at the Western North American active margin over the last 145 Ma. Said deformation may include 145 Ma of E-W shortening, at least 30 Ma of GV axis parallel right-lateral shear and some period of pre-accretionary (before 100 Ma) erosive subduction [3].

Taking undeformed basin diameter as ~700 km, consistent with curvature of the southern Sierra Nevada arc east of the Kings River and Kaweah ophiolites and with current basin extent, and taking maximum excavation depth as ~5% final crater diameter [4], impact excavation of mantle rock from depths of up to ~35 km on oceanic lithosphere is plausible. It remains to be determined if the J/K boundary impact basin hypothesis for the GV is consistent with earliest ophiolite obduction timing. If so, a look into possible correlation with J/K boundary global extinction events and impact ejecta horizons [5] plus tsunami deposits [6] may be warranted.

1) Olds, P., Journal of Earth Science, 2019. 30(3): p. 451-459. 2) Surpless, K.D., et al., Geology, 2006. 34(1): p. 21-24. 3) Wakabayashi, J., Tectonophysics, 2012. 568: p. 230-247. 4) O'Keefe, J.D. and T.J. Ahrens, JGR: Planets, 1993. 98(E9): p. 17011-17028. 5 ) Rampino, M.R. and K. Caldeira, Geoscience Frontiers, 2017. 8(6): p. 1241-1245. 6) Schnyder, J., F. Baudin, and J.-F. Deconinck, Sedimentary Geology, 2005. 177(3-4): p. 209-227.