Science Opportunities - Basic Research Opportunities in Earth Science - page 56

Science Opportunities
The next decade will see discoveries derived from the rapidly expanding
capabilities to observe both ancient and modern continental processes at a new
level of detail. Particularly promising are the recent advances in dating
capabilities and the ability to image structures deep within the Earth, allowing the
temporal record obtained from geologic and geochemical studies to be correlated
with ever more accurate knowledge of the Earth's three-dimensional structure.
Surface Processes, Climate, and Tectonics
What were once thought to be one-way forcing functions are now recognized
to act in both directions, with feedback coupling continental tectonics, erosion
processes, climate, and the composition of the atmosphere and oceans. The onset
of the Indian monsoon and the desertification of sub-Saharan Africa can be
related to the uplift of Tibet; the melting of midcrustal rocks and topographic
collapse of mountain belts can be related to rapid denudation rates at the surface;
and carbon sequestration in the oceans and atmospheres can be related to the
formation and destruction of passive continental margins that are sites of
carbonate deposition. These strong interdependencies are only beginning to be
investigated, and the long-term evolutionary effects are very poorly known.
Recent calculations suggest that current plate tectonics may be subducting up to
an order of magnitude more water into the mantle than is being released out of the
mantle by surface volcanism; taken at face value, the model implies that the
oceans are draining back into the planet at the present time. This controversial
example illustrates the unprecedented opportunities for basic research on the
coupling of Earth processes from the mantle through the crust and into the oceans
and atmosphere.
Active Deformation
The global forces that drive surficial motions are rooted in the mantle, but
the processes of crustal deformation are governed by the ductility, fracture, and
friction of rocks. These properties are not simple functions of thermodynamic
state; rather, their variation is coupled in a complex way to the evolution of stress
and strain. A more complete picture of the stress distribution and deformation
mechanisms will require the combination of neotectonic studies with laboratory-
based rock mechanics, earthquake seismology, and tectonic