Cretaceous Meteorite Impact-Induced Initial Subduction: Records of highly Siderophile Element Abundances and Re-Os Isotopes in Ophiolites

Compiled global ophiolite data reveal that Cretaceous ophiolites exhibit broaden variations in Re-187/Os-188 and Os-187/Os-188 values, increases in Re concentrations and thus Re/Os ratios in all peridotites and chromitites, and additional increased PPGE/IPGE (Pd-subgroup platinum-group element (PGE)/Ir-subgroup PGE) ratios in chromitites and dunites relative to pre-Cretaceous ophiolites. These compositional changes in Cretaceous ophiolites, which mostly formed in subduction initiation settings, cannot be attributed solely to involvement of subducting or previously subducted crustal materials. Here, the author proposes a Cretaceous meteorite impact model that led to impact- induced disruption of oceanic lithosphere, asthenosphere upwelling, subduction initiation at edges of laterally spreading anomalies. High-pressure and high-temperature conditions during the impacts caused melting of the meteorites and the ambient crustal and mantle rocks, producing hybrid melts containing partially un-melted fragments. Crustal materials contributed to the elevated Os-187/Os-188 values, Re and Re/Os ratios, whereas the undifferentiated meteorite accounted for the increases in the PPGE/IPGE and decreased Os-187/Os-188 ratios. Shock pressure and super-reduced phases were likely generated by this process and were subsequently transported into the newly formed mantle peridotites and chromitites of future ophiolites. The remaining meteoritic and lithospheric fragments most likely sank deeper and were distributed widely in the convecting mantle to produce the observed global compositional heterogeneities.

Automated summary

Compiled global ophiolite data suggests that compositional variations in Cretaceous ophiolites are primarily attributed to a Cretaceous meteorite impact model. This impact disrupted the oceanic lithosphere and initiated subduction, resulting in changes in the composition of peridotites and chromitites. The impact also produced high-pressure and high-temperature conditions, causing melting of meteorites and surrounding rocks, and the distribution of fragments throughout the mantle.