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KT Boundary Chromites Determined to be Terrestrial: Cr Isotopic Evidence for Excavation and Ejection of Mafic/Ultramafic Rocks by the KT Boundary Impact
Author(s) -
OLDS Peter,
SANBORN Mathew E.,
TEAGUE Tim,
YIN Qingzhu
Publication year - 2017
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.13163
Subject(s) - ultramafic rock , mafic , geology , impact crater , geochemistry , crust , ejecta , mantle (geology) , mineralogy , astrobiology , physics , quantum mechanics , supernova
Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on ∼35 km thick continental crust (DePaolo et al., 1983; Montanari et al., 1983; Hildebrand and Boynton, 1988, 1990). Evidence for mafic/ultramafic target rocks was reinforced by discovery of chromites, some with shock planar deformation features (PDF), in impact layer samples from sites in southern Colorado and eastern Wyoming (Bohor et al., 1990). However, until now it was unclear whether the chromites originated with an impactor or with terrestrial target rocks. To this end, high‐precision 54 Cr/ 52 Cr isotope ratios were measured on KT boundary chromites along with known terrestrial chromites. We find a terrestrial 54 Cr/ 52 Cr ratio in KT boundary chromites from impact layer samples collected at the above sites over the last several years (Fig. 1). Ejected terrestrial chromites suggest the impact sampled terrestrial mafic and/or ultramafic target rocks not known to exist in the Chicxulub target area.