CRATERS OF THE SOUTHWEST BOTH YOUNG AND OLD, SMALL AND LARGE: METEOR CRATER, AZ AND SANTA FE, NM

With the paucity of impact sites on Earth compared to planets with older surfaces, the field geologist is not able to view impact breccias, ejecta outcrops, and central peaks. The southwestern United States has two impact sites in Meteor Crater and Santa Fe where these features can be examined. The two craters differing remarkably in nearly every aspect (Table 1) provides a variety of features and geologic histories.

Meteor Crater is well-studied over the past century (guidebook: Kring 2007). To generate interest in a 1-day field trip to Santa Fe on Saturday, May 12th, current knowledge of the Santa Fe impact structure is presented here.

Shatter cones were observed in 2006 (McElvain et al. 2007) and verified by petrography (Fackelman et al. 2008). Impact models suggest that shatter cones form directly under the transient crater (Baratoux & Melosh 2003). The orientation of Santa Fe shatter cones (Fackelman) combined with the pattern of float and proposed vertical erosion (> 2 km) lead us to suggest that a large outcrop of shatter cones may be under the central peak of the original crater.

Breccias are found ~18 km ESE of the shatter cones, but these breccias are associated with fault breccias outlining the Picuris-Pecos Fault. There is much debate about the timing and potential reactivation(s) of this fault (Bauer & Rasler 1995; Fankhauser & Erslev 2004; Cather et al. 2007), but these fault breccias in Proterozoic metagranites and schists provide excellent comparisons to a 2nd breccia found in several localities to the west of the shatter cones. This Breccia Type 2 (Wright et al. 2010) are also clasts in the proposed fault breccias, which indicates several brecciation events took place. No glass is observable 100’s of Ma after impact, and the matrix of Breccia Type #2 has been replaced by hematite and silica due to aqueous alteration. Petrography and SEM images of shatter cones and breccias, along with field images, will be shown along with those from other terrestrial impact sites for comparison.

	Meteor Crater, AZ	Santa Fe, NM
diameter	1.2 km	not known but > 6-13 km
crater?	yes	no rim, crater
age of impact	~50 ka	1.2 Ga - 330 Ma; perhaps 700 Ma (prelim. Ar-Ar)
age of target	Permian sandstone, limestone	1.2 Ga metagranites, schists
ejecta?	impact breccias throughout	none
central peak?	too small of a crater	shatter cones may indicate remnant central peak