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Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta

Earth and Planetary Science Letters

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Abstract

UPb isotopic dating of single 1-3 ??g zircons from K/T distal ejecta from a site in the Raton Basin, Colorado provides a powerful new tool with which to determine both the time of the impact event and the age of the basement at the impact site. Data for the least shocked zircons are slightly displaced from the 544 ?? 5 Ma primary age for a component of the target site, white those for highly shocked and granular grains are strongly displaced towards the time of impact at 65.5 ?? 3.0 Ma. Such shocked and granular zircons have never been reported from any source, including explosive volcanic rocks. Zircon is refractory and has one of the highest thermal blocking temperatures; hence, it can record both shock features and primary and secondary ages without modification by post-crystallization processes. Unlike shocked quartz, which can come from almost anywhere on the Earth's crust, shocked zircons can be shown to come from a specific site because basement ages vary on the scale of meters to kilometers. With UPb zircon dating, it is now possible to correlate ejecta layers derived from the same target site, test the single versus multiple impact hypothesis, and identify the target source of impact ejecta. The ages obtained in this study indicate that the Manson impact site, Iowa, which has basement rocks that are mid-Proterozoic in age, cannot be the source of K/T distal ejecta. The K/T distal ejecta probably originated from a single impact site because most grains have the same primary age. ?? 1993.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Fingerprinting the K/T impact site and determining the time of impact by UPb dating of single shocked zircons from distal ejecta
Series title:
Earth and Planetary Science Letters
Volume
119
Issue:
3
Year Published:
1993
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Earth and Planetary Science Letters
First page:
425
Last page:
429