Petrography and geochemistry of ejecta from the Sudbury impact event |
| |
| Authors: | Matthew S Huber Iain McDonald Christian Koeberl |
| |
| Institution: | 1. Department of Lithospheric Research, University of Vienna, , A‐1090 Vienna, Austria;2. School of Earth and Ocean Sciences, Cardiff University, , Cardiff, CF10 3AT UK;3. Natural History Museum, , A‐1010 Vienna, Austria |
| |
| Abstract: | Ejecta from the Connors Creek site in Michigan (500 km from the Sudbury Igneous Complex SIC]), the Pine River site in western Ontario (650 km from the SIC), and the Coleraine site in Minnesota (980 km from the SIC) were petrographically and geochemically analyzed. Connors Creek was found to have approximately 2 m of ejecta, including shocked quartz, melt droplets, and accretionary lapilli; Pine River has similar deposits about 1 m in thickness, although with smaller lapilli; Coleraine contains only impact spherules in a 20 cm‐thick layer (impact spherules being similar to microkrystites or microtektites). The ejecta transition from chaotic deposits of massively bedded impactoclastic material with locally derived detritus at Connors Creek to a deposit with apparently very little detrital material that is primarily composed of melt droplets at Pine River to a deposit that is almost entirely composed of melt spherules at Coleraine. The major and trace element compositions of the ejecta confirm the previously observed similarity of the ejecta deposits to the Onaping Formation in the SIC. Platinum‐group element (PGE) concentrations from each of the sites were also measured, revealing significantly elevated PGE contents in the spherule samples compared with background values. PGE abundances in samples from the Pine River site can be reproduced by addition of approximately 0.2 wt% CI chondrite to the background composition of the underlying sediments in the core. PGE interelement ratios indicate that the Sudbury impact event was probably caused by a chondritic impactor. |
| |
| Keywords: | |
|
|
