TECTONIC MAP OF THE OCCATOR CRATER: A FLOOR FRACTURED CRATER ON CERES

The Dawn spacecraft’s Framing Camera (FC) provided the first images of Ceres’ surface. Geologic analyses were performed on FC mosaics from Approach (1.3 km/px), Survey (415 m/px), the High Altitude Mapping Orbit (HAMO - 140 m/px), and the Low Altitude Mapping Orbit (35 m/px), including clear filter and color images and digital terrain models derived from stereo images.

Several of the impact craters on Ceres have patterns of fractures on their floors. Occator crater has several sets of fractures associated with it, including: 1) Linear floor fractures; 2) Circumferential floor fractures encircling its central pit; 3) Circumferential fractures near the crater rim; and 4) Circumferential fractures in the ejecta blanket. While the ejecta fractures are consistent with formation due to differential compaction, many of the floor fractures are similar to those found within a class of lunar craters referred to as Floor-Fractured Craters (FFCs),

Lunar FFCs are characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures [1]. Models for their formation have included both floor uplift due to magmatic intrusion below the crater, and floor shallowing due to viscous relaxation. The depth versus diameter relationship of the FFCs is distinctly shallower than the same association for other lunar craters, and topographic analysis supports the hypotheses that the floor fractures form due to shallow magamatic intrusion under the crater [2]. Similar topographic analyses performed on Ceres FFCs, including Occator, are also consistent with a shallow intrusion fracture formation mechanism.

However, a pattern of fractures found in SW Occator is more consistent with formation due to asymmetrical domal uplift. These fractures show apparent broad outer arc extension, with at least two central peaks. A transition to radial faulting with distance from the center is consistent with the change in stress orientation that occurs at the edge of a dome.

References: [1] Schultz P. (1976) Moon, 15, 241-273. [2] Jozwiak L.M. et al. (2015) JGR 117, doi: 10.1029/ 2012JE004134.

Acknowledgements: Support of the Dawn Instrument, Operations, and Science Teams is gratefully acknowledged. This work is supported by grants from NASA through the Dawn project, and from the German and Italian Space Agencies.