Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.483k&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 483
Other
1
Melting, Meteorite Craters, Point Impact, Quartz, Shock Waves, Breccia, Chemical Composition, Neutron Activation Analysis, Petrology, Structural Properties (Geology), X Ray Fluorescence
Scientific paper
The Ames structure in northwestern Oklahoma is evident in the form of a relatively circular, concentric, structural depression with a minimum diameter of approximately 15 km, on top of the Upper Ordovician Sylvan shale. The feature is covered by approximately 3000 m of sediments. It is marked by two concentric rims, an outer rim (comprising fractured and brecciated Arbuckle dolomite) that is approximately 1.5-3 km wide, and an inner 'ring' structure that seems to be the collapsed remnant of a structural uplift that consists of brecciated Precambrian granite and Arbuckle dolomite. The crater, which is sealed by Middle Ordovician Oil Creek shale, acts as a structural trap for hydrocarbons and is of local economic importance. We have begun studies of samples from several drill cores. No characteristic shock features were found in basement granite and fragmental breccia samples from the URC Bland #1-33. In these samples, deformation was found only in the form of local cataclasis of quartz or feldspar minerals and localized, possibly shearing-related, annealing. New samples were received from the following drill holes: Gamman 1-34, Dorothy 1-19, James 1-20, Wayne 1-32, Dixon 2-18, and Lloyd 1-17. The samples comprised mainly granitic basement, brecciated granite, and sediments, and were studied by optical microscopy, X-ray fluorescence analysis (major-element composition), and neutron activation analysis (trace-element composition). Breccias and melt breccias from the Gamman 1-24, Dixon 2-18, and Dorothy 1-19 drill holes were found to contain shocked quartz and K-feldspar with up to three sets of PDFs. The chemical composition of the fine-grained melt rock from Dorothy 1-19 is very similar to that of average granitic basement. The melt rock shows some differences in alkali contents and possibly some minor ad-mixture of dolomite; other melt rocks have a more pronounced carbonate component. Our findings confirm earlier reports of shocked quartz and provide further evidence for an impact origin of the Ames structure.
Koeberl Christian
Powell R. A.
Reimold Wolf Uwe
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