SEMAIL OPHIOLITE: CRATER RIM SEGMENT AND COURSE EJECTA FROM CENOMANIAN-TURONIAN BOUNDARY HYPERVELOCITY IMPACT EVENT? OPHIOLITE OBDUCTION BY IMPACT CRATERING?

Elliptical to circular segments of exposed mantle were recently speculated to mark rims of large impact basins on Earth: The Sulu Sea, Loyalty and Yucatan basins possibly corresponding to middle Miocene, late Eocene and K-Pg boundary mantle excavating impact events (1). Similarly, the Semail Ophiolite suggests such a circular rim segment of an originally ~500 km diameter impact basin before subduction of its NE rim at the active Makran trench. For large impact basins on the rocky planets, maximum excavation depths are estimated to be ~5% final basin diameters (2) in this case implying ejecta source depths of up to ~25 km, a number roughly consistent with observed thicknesses of crust plus mantle sections (3) and with depths of burial due to overthrusting (obduction) implied by the exhumed metamorphic sole (4). Peak metamorphism timing of the metamorphic sole is within uncertainty of the CT boundary at ~94 Ma (5,6). Further study of peak obduction timing correlation with CT global extinction plus anoxic events (7) and a search for proximal and distal CT boundary ejecta plus tsunami deposits (8) may be warranted.

1) Olds, P. 2019 JES v. 30, no. 3, p. 451-459

2) O'Keefe, J.D. & Ahrens, T.J. 1993 JGR Planets v. 98, no. E9, p. 17011-17028

3) Aldega et al. 2017 Marine & Petroleum Geology v. 84, p. 18-33

4) Cowan et al. 2014 Geol Soc London Spec Pub v. 392, no. 1, p. 155-175

5) Hacker et al. 1996 Tectonics v. 15, no. 6, p. 1230-1247

6) Roberts et al. 2016 Geoscience Frontiers v. 7, no. 4, p. 609-619

7) Wan et al. 2003 Palaeogeography, Palaeoclimatology, Palaeoecology v. 199, n. 3-4, p. 283-298

8) Monteiro et al. 2001 caev, p.3129.