Geology Reference
In-Depth Information
Figure 8.34. An oblique Galileo image of two dark-
oored craters
within the bright zone of Memphis Facula
(Fig. 8.37)
. The dark
oors
could represent material implanted from the impact, or perhaps
material brought to the surface by the impact. Crater Chrysor (left
side) is 6 km in diameter; crater Aleyn is 12 km across (NASA Galileo
PIA01607).
Figure 8.36. Ganymede crater Neith is about 160 km in diameter and
is a dome crater; the dome is ~45 km across and is surrounded by
rugged terrain. The crater rim is barely visible and is located along
the outer boundary of a relatively smooth, circular area (indicated by
arrows), assumed to be the crater
floor, which in turn surrounds the
rugged terrain (NASA Galileo PIA01658).
Figure 8.35. A Voyager 2 image in Galileo Regio showing the 344 km
in diameter palimpsest Memphis Facula (NASA Voyager 2, FDS
20637.02).
Figure 8.37. Sets of furrows on Ganymede, such as these in Galileo
Regio, could be related to large impact events; also visible are several
central-pit craters. The area shown is about 650 km across (NASA
Voyager 2 546J2
-
001).
onto the surface. Higher-resolution Galileo images sup-
port this general view in some areas, as outlined in
Fig. 8.38
, but the emphasis is much more on tectonic
processes than on cryovolcanism. For example, the boun-
dary between dark and bright terrain in Uruk Sulcus
(Fig. 8.39)
shows highly fractured tilt-blocks of bright
terrain cutting across the dark terrain. This style of tec-
tonic resurfacing was diagrammed by Bob Pappalardo
and colleagues in 2004
(Fig. 8.40)
.
Most of the tectonic structures on Ganymede indicate
extensional processes, as re
ected in the grabens and
deformed impact craters cut by faults
(Fig. 8.41)
.Inaddi-
tion, strike
-
slip deformation is seen
(Fig. 8.42)
,including
en échelon fault patterns. Global extension of the litho-
sphere might have taken place as a result of liquid water
freezing, much like the expansion of ice in a soda can.
