Geology Reference
In-Depth Information
Figure 6.18. A computer-generated oblique view of Maat
Mons, a 500 km diameter by 6 km high volcano in Atla Regio,
showing extensive lavas that
flowed from the
anks; the
vertical scale has been exaggerated ×23 to enhance detail in
topography. A 23 km in diameter impact crater and its ejecta
melt
flow-lobe are visible in the foreground (NASAMagellan
P-40175).
Figure 6.19. This ~20 km in diameter caldera in the Aphrodite Terra
area displays a series of concentric fractures outlining the zone of
subsidence and radial lava
Figure 6.20. This series of domes is found east of Alpha Regio; the
domes average 25 km across and their steep margins represent
emplacement of viscous lavas, possibly of silicic composition (NASA
Magellan P-37125).
flows that extend beyond the depression.
Note also the widely spaced concentric fractures beyond the lava
flows (NASA Magellan F-MIDR O6N227).
which are probably calderas. Coronae are considered to
represent crustal deformation resulting frommantle plumes
or upwelling
Complex ridged terrain formed by crustal deformation
under both extensional and compressional processes
(Fig. 6.26)
. This terrain, found mostly in highland regions,
makes up some 30% of the surface and is characterized
by features called tesserae (from the Greek referring to
four corners). Tesserae consists of tile-like blocks of crust
cut by ridges and troughs 10
-
20 km apart, which are
often transected by younger, broad grabens
(Fig. 6.26)
.
Embayment and superposition of plains units show
”
In addition to coronae, tectonism indicative of both
extension and compression is common on Venus. Sets
of parallel rugged ridge-belts, as in Lavinia Planitia, and
mare ridges in plains re
ect regional compression
(Fig. 6.24)
, while troughs, broad grabens, and complex
chasmata
(Fig. 6.25)
indicate extensional tectonism.
“
hot spots.
