講演者: Julien Vaucher (Midi-Pyrenees Observatory, France)
  題名: Rheology of recent lava flows in Cerberus, Mars
  日時: 2006年11月27日（月）17:00-18:30
  場所: 自然科学3号館6階セミナー室 609号室






The Cerberus plains were studied for evidence of recent volcanism
using images taken from orbit, and interactions among water, magma
and tectonic processes. There are three aqueous flood channels
emanating from a system of linear fissures. Recent eruptions of low
viscosity lavas were proposed to originate also from these fissures.
We present an interpretative map of the Cerberus area, based on a
roughness map from altimetric data and a morphologic analysis from
visible images. Ages of the most recent units were derived from
crater frequencies using images. The chronology of lava units is
discussed using a statistical approach. Our results confirm the
recent age (2 My) of the lavas and document the chronology of
volcanic episodes which suggest continuous volcanic activity over the
last 50 My. Lava viscosity is estimated, assuming their behavior as
Bingham fluid, as deduced from the geometrical parameters of the
leveed lava channels.  Rheological properties obtained (yield
strength = 15 Pa and viscosity = 0.1-100 Pa.s) are similar to those
of very fluid "hot-spot" basaltic (or ultra-mafic) flows on Earth,
but differ from other volcanic flows (Olympus, Ascraeus) on Mars.
This study confirms the recent volcanic and tectonic activity of the
Cerberus plains; it raises the question of its geodynamic origin and
has implications for the thermal history of Mars.