S68: Chemical and physical weathering of basalt on the Earth, Moon, and Mars

Conveners:	Susan L. Brantley	(brantley@essc.psu.edu)
	Joe Michalski	(michalskijoe@gmail.com)
	Libby Hausrath	(emh191@psu.edu)
Keynote:	Doug Ming	(Houston)

Basalt is the most common primary rock type on the surfaces of silicate planets in our Solar System. Therefore physical and chemical weathering of basaltic material is a key component of most planetary geologic processes. New insights from terrestrial weathering studies and a wealth of new spacecraft data provide a basis for reevaluating both fundamental and environmentally specific aspects of weathering. This symposium will address basalt weathering across a broad spectrum of topics including terrestrial basalt weathering, weathering on Mars from in-situ (rover), orbital and meteorite observations, and lunar space weathering. Participants are invited to contribute results from field, modeling, experimental, spectroscopic, or remote sensing studies addressing the often inseparable mineralogical, geochemical, physical, and biological aspects of basalt weathering.

S69: Geochemical constraints on the topographic evolution of Cenozoic orogens

Conveners:	Andreas Mulch	(mulch@geowi.uni-hannover.de)
	Todd Ehlers	(tehlers@umich.edu)
Keynote:	P.C. Chamberlain	(Stanford)

Significant advancements in quantifying the rates and timing of Cenozoic mountain building and surface processes provide previously unavailable constraints on the tectonic evolution of many of the major mountain belts on Earth. As the topographic evolution of mountain ranges is a direct reflection of the complex interplay between tectonic forces and climatic processes in orogenic belts, this session will address how methods such as low-temperature thermochronology, stable isotope paleoaltimetry, and radiogenic isotope tracers quantify links and feedbacks among climate, tectonics and surface processes. We encourage field and modeling studies that aim at understanding the relationships among uplift and exhumation histories, topography development and erosional history of orogens on intermediate or long time scales. This session welcomes studies that focus on advancements made using individual techniques as well as interdisciplinary approaches that provide new constraints for competing tectonic models.

S70: In-situ cosmogenic nuclides: Advances in methodology and applications

Conveners:	Tibor Dunai	(Tibor.Dunai@ed.ac.uk)
	Fred Phillips	(phillips@nmt.edu)
Keynote:	John Stone	(Seattle)

Terrestrial cosmogenic nuclides (TCN) provide quantitative constraints on the evolution of Earth's surface. The last decade has seen an explosion in the use of the workhorse nuclides, ¹⁰Be and ²⁶Al, to disciplines such as glacial chronology. This has gone hand-in-hand with the refinement of analysis/interpretation of hitherto less commonly-used isotopes, ³He, ²¹Ne and ³⁶Cl, and the development of new isotopes, e.g. ¹⁴C and ⁵³Mn. These developments offer opportunities for more sophisticated and ambitious applications which are driving development of more complex interpretive strategies and models. The resultant range of quantitative constraints on near surface earth processes now extends well beyond the exposure age versus steady state erosion rate options. This session seeks to tap into these recent developments to provide a flavour of the new applications of TCN and exciting discoveries in Earth Surface Processes using TCN. Furthermore we solicit papers on methodological work at the foundations of the techniques, such as refinement of production rates, decay constants, and issues of scaling, to name but a few. This session is co-sponsored by CRONUS-EU and CRONUS-Earth.

S71: Geochemical and model-driven approaches to determining reaction rates at the Earth's surface

Conveners:	Kate Maher	(kmaher@usgs.gov)
	Matt Fantle	(mfantle@geosc.psu.edu)
Keynote:	Carl Steefel	(Lawrence Berkeley Laboratory, California)

The objective of the session is to highlight the determination of reaction rates using a combination of geochemical measurements and numerical modeling techniques, in low-temperature, natural environments such as soils and marine sediments. While the determination of rates in natural systems is important, it is also critical to consider rates determined under experimental conditions and the scaling of these experiments to natural systems. This session will stress the application of various data, from elemental to isotopic, combined with numerical modeling approaches, from simple box to complex reactive transport.

S72: New isotope tracers of chemical weathering

Conveners:	Albert Galy	(albert00@esc.cam.ac.uk)
	Bernard Bourdon	(bourdon@erdw.ethz.ch)

Understanding the complexity of chemical weathering processes warrants the development of new sophisticated methods based on isotope geochemistry. In this session, we will focus on the isotopic systems that are successfully applied to the study of chemical weathering: non-traditional stable isotopes, systems involving radioactive isotopes. The variations in the stable isotope composition of elements such as Li, B, Mg, Si, Ca, Cu, Fe, Zn, etc have been shown to be impact on areas such as biogeochemistry, hydrology, the marine and continental sedimentary cycle; all of them having some implications on weathering. The contrasting chemical behaviour of some radioactive parent-daughter pairs such as Rb-Sr, U-Th, Th-Ra or Lu-Hf is also increasingly applied to the study of weathering. This session will examine recent advances in these areas of research including experimental, theoretical and field studies, and the quantification of continent-ocean fluxes related to chemical weathering.

S73: Advances in using isotopic tracers for groundwater studies

Conveners:	Don Porcelli	(don.porcelli@earth.ox.ac.uk)
	Dave Hilton	(drhilton@ucsd.edu)

A wide variety of isotopic and chemical tracers are now available to understand the rates and patterns of groundwater transport and the processes of water/rock interaction within the aquifer. This includes radiogenic isotopic variations that reflect source regions and can be used to trace flow patterns, cosmogenic nuclides and noble gases that record the last?interactions with the atmosphere, and recently developed stable isotope fractionations that may reveal aquifer chemical processes. This session will bring together presentations of novel uses of traditional tracers, as well as the development and application of new methods.

S74: The impact of plants on Earth-surface cycling and preservation of elements

Conveners:	Louis A. Derry	(lad9@cornell.edu)
	Oliver A. Chadwick	(oac@geog.ucsb.edu)

Plants acquire a variety of elements from soils, litterfall and decomposition recycle those components to the soil surface. Groundbreaking work by Lucas et al., 1992 demonstrated the potential importance of plant cycling in modifying soil secondary mineral composition. Initial work in this area relied on inference as much as specific measurement. Recent work has employed elemental and isotopic tracers to better understand the role of plants in affecting movement of elements among the lithosphere, biosphere, and hydrosphere. Papers will highlight both the processes by which plants create these excursions from predicted elemental behavior and the overall impact that they have in modifying local to global flows of elements.

S75: Continental-scale Earth surface geochemical mapping - Recent progress and future directions. Sponsored by IAGC

Conveners:	Clemens Reimann	(Clemens.Reimann@ngu.no)
	Marty Goldhaber	(mgold@usgs.gov)
Keynotes:	Patrice de Caritat	(CRC LEME, Geoscience Australia)
	Galina Kashulina	(Kola Science Centre)

Continental-scale geochemical mapping is required to recognize and understand the importance of large-scale geochemical processes, human impacts on natural element distributions, and the role of chemical elements in the distribution of endemic diseases. During the last 10 years, large domains in Northern Europe have been mapped at ever decreasing sample densities: e.g., 1 site/300km² in the Kola Project, 1 site/1000 km² in the Barents Project, 1 site/2500 km² in the Baltic Soil Survey, and 1 site/5000 km² for the Geochemical Atlas of Europe. China has made a major investment in regional geochemical surveys for mineral exploration and medical geology purposes. New programs in North America and Australia will commence sampling for continental-scale geochemical mapping in 2007. Low-density geochemical mapping results in the construction of robust geochemical maps of large areas at reasonable cost. Such maps contain important new information and politically vital reference data about the varying levels of chemical elements in the surface environment at the regional and continental scales. It appears that major natural factors influencing the distribution of chemical elements in the surface environment (e.g. landscape, climate, weathering, the role of vegetation, and biogeochemical element cycles) are not sufficiently recognized and are under-researched at these geospatial scales. The anthropogenic impact on the natural environment cannot be reliably documented and understood without continental-scale geochemical maps. This symposium will review recent advances in geochemical mapping, present results from continental-scale geochemical surveys, and discuss the challenges facing continental-scale geochemical mapping in the future.