2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 117-12
Presentation Time: 9:00 AM-6:00 PM


JARET, Steven, JACOBSEN, S.B., and PETAEV, Michail I., Department of Earth & Planetary Sciences, Harvard University, Cambridge, MA 02138, sjaret@fas.harvard.edu

Gardnos (Norway, 60°40’N, 9°00’E) is a 5-6 km impact structure in crystalline target rocks [1, 2]. Field work in 2010 identified the first known injection dike into the Gardnos Breccia of the crater floor. While most mineral grains in the Gardnos Breccia show no shock metamorphic effects, equivalent mineral grains in the dike show textures indicative of higher shock. Specifically, biotite in the dike shows severe kinking visible in both plane- and cross-polarized light, anomalous interference figures, and the development of planar microstructures which have an amphibole-like symmetry. Similar textures in biotite have been reported at the Reis structure [3].

A combination of field relationships and this difference in petrographic shock textures allows for a determination of the relative timing of events after impact: 1) shock deformation of the uppermost units, 2) brecciation (but not shock deformation) of the crater floor, and then 3) injection of the more strongly shocked material into the unshocked Gardnos Breccia.

[1] French et al., (1997), Geochim. Cosmochim. Acta, 61, 873-904 [2] Kalleson et al. (2010), Meteorit. Planet. Sci, 45, 798-827. [3] Schneider (1972), Contr. Mineral. and Petrol., 37, 75—85

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 117--Booth# 342
Impact Cratering on the Earth, Moon, and Planets: Remote, Field, and Lab Studies (Posters)
Minneapolis Convention Center: Hall C
9:00 AM-6:00 PM, Monday, 10 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 307

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