Week 4 - Martian volcanism:
of volcanic constructs:
- formed primarily from flows.
- steeper upper slopes and shallower lower
- characterized by collapse caldera (large
than typical on earth).
- dome shaped.
- more viscous magma?
- lowland paterae:
- even lower angel slopes than shield volcanoes
- complex summit calderas.
- Alba Patera is one of the better known ones.
- highland paterae:
- same as lowland except also characerized
by complex radiating channel systems.
Note - what volcanic forms common on earth
seem to be missing on Mars?
Are pyroclastic deposits evident on Mars:
- the erodability of many of the volcanic structures
- deposits with great lateral mobility (400km
for Alba Patera!) also indicates so.
- morphology indicates these were debris flows,
not air fall.
Samples from Mars
- fell in France in 1852.
- an olivine cumulate (dunite), Frankel (1996)
- microscopic bubles of gas with content similar
that of the atmospher of Mars (Frankel, 1996)
- how did atmospheric gases get trapped in
- first example found near Nakhla, Eygpt.
- a pyroxene cumulate.
- named after Shergotty, India.
- basaltic, volcanic.
SNC - meteorites
from Mars. 12 or so 'suspected' Martian meteorites are known.
What are cumulates?
"On Mars, low gravity and low atmospheric
pressure at the surface result in a crustal bulk density profile
different from other planets (Wilson & Hed, 1994), which means
that magma reservoirs are predicted to be deeper than on earth
by a factor of four." Head & Coffin, 1997, Large Igneous
Provinces: A Planetary Perspective; in Geophysical Monograph 100,
American Geophysical Union, p. 420.
How did cumulates get excavated? How did fluid
inclusion samples of Martian atmosphere get incorporated?
One distinctive aspect of Martian volcanoes
are the large calderas. For Mons Olympus the caldera complex is
80 km across. What are the implications of this large size for
One interesting 'problem' is that the flows
that should be associated with large scale caldera collapse are
not really evident!
Are some Martian flows komatiites?
- ultramafic and very fluid flows.
- require a greater percentage of partial melt
- since Mars is a smaller body, it overall
has less heat content and might be expected to have had smaller
percentages of partial melt. However, the lithostatic gradient
is also less, because of Mar's smaller mass, and this can increase
the ease of partial melting by reducing the inhibiting effect
of pressure on partial melting.
- tend to be sulfur rich.
Why might Martian volcanism
Cooling rates - how does a lava flow cool?
- transfer of heat to atmosphere and or hydrosphere
by complex processes.
- radiative blackbody cooling.
- Mars is colder.
- however, with less of an atmosphere cooling
rates could be slower..
Historical evolution of volcanism
- earlier ash flows and lava plains
- later bulges and shield volcanoes up until
maybe 300 million years ago (see handout).
- may be relationship between changing degree
of recycling fluids in crust and diminishment of pyroclastic
Why are the three Tharsis volcanoes
in a line?
What controls how high martian volcanos can
In depth and recent source on Martian volcanism:
Peter Cattermole, 1996, Planetary Volcanism, Wiley.
Reading for next time:
A. D. Fortes, Discriminating Between Models for the
Formation of the Northern Lowlands of Mars.
Head and Wilson, 2002, Tharsis Radial graben systems
as a surface manifestation of plume related dike intrusion complexes
... JGR. Don't read in detail, but
focus on abstract and diagrams. Spend an hour and see what you
can learn in that time.