FAULTING ON THE EASTERN RIM OF THE HUYGENS IMPACT BASIN, MARS

Well preserved dendritic valley neworks as well as other topographic features on the eastern rim of Huygens impact basin are instrumental in identifying fault patterns and styles here and serve as ideal surface markers that record both vertical and horizontal movements of the Martian crust. Analysis of HR imagery acquired from the ESA Mars Express orbiter indicates a diversity of faults including graben/horst, strike-slip, and thrust faults.

Crustal extension resulted in the formation of one graben-horst system, striking east-west (GH) and a second graben striking southeast (G). The graben floor of GH is covered with smooth plains materials that are connected with low-lying areas to the north and east. Several stream valleys empty into the valley formed by GH. GH and G are near radial to Huygens as are a number of other grabens outside the study area and most likely formed due to crustal adjustments after the impact basin formed.

Strike-slip faults offset stream valleys as well as fault related ridges at several locations. A ridge associated with the northern normal fault of G2 is displaced approximately 9 km along a right-lateral strike-slip fault (SS1). A stream valley along the same fault shows a displacement of 2.5 km. Strike along SS1 changes to a more easterly direction in the southern part of the study area and movement here appears to be accommodated by a thrust fault.

A northwest-striking fault (NWSF) trends oblique to GH and G and parallels SS1 and 2. It appears to have dip-slip component (upthrown to the southwest) as well as a right- lateral strike-slip component as it offsets two major stream valleys. The upthrown block is dissected by a number of valley networks that downcut through the exposed fault scarp.

North of GH thrust faults form mare-like wrinkle ridges whose scarps strike northwest. Stream valleys are offset vertically where they cross the scarps. Thrust fault scarps show a down to the southwest sense of displacement. Stream valleys intersecting the scarps flowed to the east-northeast and trend across the scarps without interruption or diversion. No incision into the scarps is evident. Thus the thrust fault scarps post date the time of active stream flow.

Cross-cutting relationships between the stream valleys and the faults permit the construction of a chronologic sequence for the eastern Huygens rim.