Geoelectric evidence for centripetal resurge of impact melt and breccias over central uplift of Araguainha impact structure

Abstract

We present fi ve profi les from electrical resistivity tomography (ERT), with surface constraints and gravity data, in the central uplift of the Araguainha impact structure in central Brazil. The central uplift, the overlying polymict breccias, and decameter-scale impact melt rocks are characterized by contrasting ranges of electrical resistivity. Our resistivity model provides empirical evidence that supports the existing model in which impact melt and breccias resurged toward the crater center in the fi nal stages of the cratering process. On the basis of our results from the fi rst use of ERT in impact cratering studies, we conclude that the deposition and fl ow of impact melt and breccias over the central uplift were infl uenced by the geometry of the lithologic boundaries in the central uplift.

Impact ejecta emplacement on terrestrial planets

“…2F,G) and Martian (Fig. 6F-I) and terrestrial (Tong et al, 2010) craters and impact melt ponds within and outside of the crater rim region of all terrestrial planets (Figs. 2A-D, 5B-D, 6H).…”

Geophysical Studies of Impact Craters

“…The total gravity anomaly produced by any target structure is independent of source depth (from Gauss's theorem); hence, integrals of the total gravity anomaly can be used for mass excess/deficit calculations. This means that gravity data can also be used to estimate the total excess or missing mass below surface Figure 14.1 Left-hand figure is a tomographic model of electrical resistivity at Araguainha Crater (also see Plate 33); righthand figure is Bouguer gravity and its relationship with surface outcrop (from Tong et al (2010) The dimensions of the smallest body that can be resolved with each geophysical method are shown in parentheses. Resolution can also be adversely affected by survey design, noise and modelling approach adopted.…”

“…Some of the sediments are overturned, and duplications within the sedimentary layer are responsible for the thickening of these strata (Lana et al, 2008). A suite of resistivity and gravity data were acquired across the central crater with the aim of obtaining a geological model of the structure below the surface (Tong et al, 2010). These data revealed some intriguing resistivity anomalies, most notably a low-resistivity zone (LRZ) dipping underneath the granitic core which, at the surface, corresponds to the impact breccias ( Fig.…”

“…If impact breccias do lie beneath the central uplift at Araguainha, then this is the first such observation at a terrestrial crater, and has implications for central crater formation. Tong et al (2010) postulated that there was a resurge of impact breccias during crater formation and that the resurge was influenced by crater floor topography and the geometry of the sedimentary and granitic units. The Araguainha impact structure has a crater diameter of 40 km and, hence, might be expected to have a central gravity high (Table 14.1).…”

“…The observation that the granitic core is associated with a gravity low (Fig. 14.1) indicates that the central uplift has been strongly fractured (Tong et al, 2010).…”