S32: Recycling of lower continental crust and implications for crustal and mantle geochemistry

Conveners:	Roberta Rudnick	(rudnick@geol.umd.edu)
	Andreas Stracke	(stracke@erdw.ethz.ch)
	Patrick O'Brien	(obrien@geo.uni-potsdam.de)

Traditionally, much of the geochemical thinking about crust-mantle interaction and recycling had focused on the most obvious form of such interaction, subduction of sediments. More recently, geochemical and geophysical evidence has come to light indicating that lowermost continental crust may also return to the mantle. This can happen in a number of ways including ìerosion" during subduction of rough oceanic crust, during continental crust subduction, by foundering of dense, eclogitic material produced during continental orogenesis and/or delamination of the base of the crust. Important questions in this context are: How might his process affect the bulk composition of mantle and crust? Can we recognize geochemical fingerprints of such lower-crustal material in recycled form? Does such material resurface only in intraplate magmas or is it also seen at mid-ocean ridges? These will be among the issues to be discussed in this symposium. In addition, we invite a broad range of contributions on the subject of continent subduction and the interaction of the continental crust with the mantle.

S33: Fluid-fluid equilibria in the crust

Conveners:	Axel Liebscher	(axel.liebscher@tu-berlin.de)
	Christoph Heinrich	(heinrich@erdw.ethz.ch)
Keynote:	Andreas Audétat	(Bayreuth) Victor-Moritz-Goldschmidt-Preis 2006, DMG

Fluids play a fundamental role in the geochemical and geophysical evolution of the Earth. Submarine hydrothermal systems link the chemistry of the oceans with that of the mantle and the oceanic crust. In volcanic systems magmatic fluids affect degassing and eruption style and transport volatile constituents like CO₂, sulfur and nitrogen species and halogens into the atmosphere. Fluid convection cells in volcanic systems that are fed by meteoric and/or oceanic water efficiently cool the systems and may result in economically important geothermal systems. Within the crust fluids may trigger partial melting, dehydration or alter and metasomatise pre-existing rocks. Around intrusions fluids are important constituents of contact metamorphism. Finally, hydrothermal fluids, which form in a variety of geologic environments, formed most of the Earth's ore deposits.

Geofluids are, however, usually not pure H₂O but contain significant quantities of dissolved components. Of these, dissolved salts like NaCl and KCl and volatile components like CO₂, CH₄ and different nitrogen, sulfur and hydrocarbon species are the most important ones. Depending on quality and quantity of the additional components, fluid immiscibility may prevail over large portions of crustal pressure and temperature conditions. Such fluid immiscibility or fluid phase separation is a very efficient way to fractionate and concentrate certain elements. Knowledge of the properties of fluid immiscibility is therefore necessary for any geochemical and geophysical study on the role of fluids in the diverse geological settings.?This interdisciplinary session intends to bring together scientists from the diverse geological subdisciplines that work on the various aspects of immiscibility of geofluids in crustal environments. It will draw the bow from low P-T hydrocarbon systems to high P-T metamorphic/magmatic environments, from field to experimental studies, and from basic to applied/economic geoscience. The session is predated by an MSA/GS Short Course on "Fluid-fluid equilibria in the crust - petrology, geochemistry, economy".

S34: Accessory minerals as tracers of crustal processes

Conveners:	Axel Gerdes	(gerdes@em.uni-frankfurt.de)
	Anders Schersten	(asch@geus.dk)
	Tony Kemp	(tony.kemp@bris.ac.uk
Keynote:	C. Hawkesworth,	(Bristol, U.K.)

This session seeks contributions that focus on understanding geological processes through the analysis of accessory minerals in igneous, sedimentary and metamorphic rocks.

Topics will include but are not limited to (i) the generation and evolution of continental crust, (ii) crustal melting and magmatic processes, (iii) high grade to ultra high grade metamorphism, (iv) accessory minerals as provenance indicators, (v) geochronology, (vi) thermometry, including trace element thermometry and (vii) new developments in analytical methods.

S35: Peralkaline magmatic systems

Conveners:	Gregor Markl	(markl@uni-tuebingen.de)
	Michael Marks	(michael.marks@uni-tuebingen.de)
	Ian Coulson	(Ian.Coulson@uregina.ca)
Keynote:	Roger Mitchell	(Thunder Bay, Canada)

Peralkaline rocks are typical members of both continental and oceanic magmatic provinces. Their origins are still intensely debated and involve fractionation from an alkali basaltic parent magma, crustal contamination of basaltic magmas and alkali metasomatism. The basaltic parent magma may have both asthenospheric and lithospheric contributions, but their respective importance is still unclear - or may vary from locality to locality. In the last few years, the enrichment of peralkaline rocks in some incompatible trace elements such as Ta, Nb, Zr or REE has gained considerable economic interest and the common occurrence of abiogenic hydrocarbons in some, specifically agpaitic, rocks has lead to an intensive scientific discussion about their origin (early vs. late-magmatic), the redox conditions in the source magmas and the chemical evolution of peralkaline melts in general.

S36: Formation and evolution of granitic magmas

Conveners:	Friedrich Finger	(Friedrich.Finger@sbg.ac.at)
	Stefan Jung	(jungs@staff.uni-marburg.de)
Keynote:	Tony Kemp	(Townsville, Australia)
	John Clemens	(Kingston University, UK)

Granites sensu lato represent an important geochemical reservoir within the earth¥s crust. However, despite decades of research, there are still a number of long standing fundamental problems regarding the origin and evolution of granitic rocks. These include the tectonothermal requirements for granite formation, the role of mantle components and magma mixing in granite petrogenesis etc...

This session shall bring together experts from a broad variety of research areas including elemental and isotope geochemistry, igneous and experimental petrology, and numeric modeling, to discuss and develop our current knowledge about granites. Topics will include but are not limited to (i) source rocks and granite types, (ii) P-T-fluid conditions during granite petrogenesis, (iii) addition of juvenile material to the continental crust during granite formation, (iv) petrogenetic mechanisms in various geodynamic settings, (v) interactions between mantle-derived precursors and felsic magmas and (vi) timescales of granite formation. We invite contributions addressing the geochemical and physical evolution of granite magmas (sensu lato), as deduced from theoretical studies, and field and laboratory investigations. Multi-disciplinary approaches are particularly welcome.

S37: The Oceanic crust - Magma chamber processes and high-temperature reactions

Conveners:	Juergen Koepke	(koepke@mineralogie.uni-hannover.de)
	Sumio Miyashita	(miyashit@geo.sc.niigata-u.ac.jp)
Keynote:	Damon A.H. Teagle	(NOCS, Southampton,UK)

This session is intended to bring together researchers working in the in-situ oceanic crust and on ophiolites to discuss the variety of chemical and physical processes related to MORB magma chambers beneath the ocean ridges. Topics will include: (1) shallow-level differentiation of MORB including related experimental studies, (2) formation of cumulate gabbros, (3) mantle-crust interactions, (4) the transition zone between gabbro and sheeted dikes, as recently drilled by IODP expedition 312, (5) reactions between gabbroic rocks and seawater-derived fluids at very high temperatures.

S38: The Oceanic crust - Hydrothermal processes

Conveners:	Colin W. Devey	(cdevey@ifm-geomar.de)
	W. Bach	(wbach@uni-bremen.de)
Keynote:	M. Tivey	(WHOI, USA)

Studying modern submarine hydrothermal systems provides important insights into the formation and development of seafloor vent sites, which have a global impact on the chemical composition of seawater and the alteration of the oceanic crust. The complex origin and evolution of hydrothermal systems is caused by diverse oceanic and tectonic settings, and complex hydrothermal circulation, which is a function of varying geochemical and geological conditions. The physico-chemical conditions and the alteration of the crust, the sulfide textures as well as the structure and the geological setting of the deposits can be studied in these natural laboratories. This symposium is intended to bring together a wide range of scientists working on specific aspects helping to reconstruct processes, reactions and the nature of the fluid flow paths in marine hydrothermal systems.

S39: The Oceanic crust - Bio-geochemistry of hydrothermal fluids

Conveners:	Richard Seifert	(seifert@geowiss.uni-hamburg.de)
	Andrea Koschinsky	(a.koschinsky@iu-bremen.de )
Keynote:	Dave Butterfield	(PMEL - Seattle, WA, USA)

Hydrothermal circulation plays a key role for the heat and mass transfer from the Earthís mantle and crust to the shallow subsurface and the water column. Information on subsurface processes are encoded in the physicochemical parameters of emanating fluids. New data from field campaigns, laboratory experiments, and rigorous theoretical modelling have considerably contributed to reading this record. Studies of organic compounds present in hydrothermal fluids and organisms thriving in hydrothermal environments have delivered insights into the evolution of early life in terms of prebiotic organic synthesis and chemoautotrophic life.

This session is aimed to combine diverse approaches addressing a wide variety of topics in organic and inorganic geochemisty of hydrothermal fluids to assist in a better understanding of the functioning and significance of hydrothermal systems in energy and mass transfer from the crust to the ocean.

We solicit papers that provide information from direct observations, modelling, or experimental results towards fingerprinting the geochemical processes in hydrothermal systems. Topics of emphasis include: physiochemical controls on fluid composition, supercritical fluid behaviour, catalytic reaction networks at high pressure and temperature, organometallic complexes in fluids, imprint of fluid composition on the vent fauna, abiotic formation of organic compounds, bio-geochemical processes in hydrothermal plumes, heat and mass transfer, and temporal evolution of hydrothermal systems.

S40: From field observation to experimental petrology and back in memory of Werner Schreyer

Conveners:	Walter Maresch	(walter.maresch@rub.de)
	Friedrich Seifert	(fritze.seifert@web.de)
	Ed Grew	(esgrew@maine.edu)
Keynote:	Barbara L. Dutrow	(University of Lousiana, USA)

Werner Schreyer combined astute observations in the field with precisely planned laboratory experiments, and thereby opened new avenues of research. His experimental work in the 1950's and 1960's in the MgO-Al₂O₃-SiO₂-H₂O system led him and his coworkers to lay the foundations for our modern understanding of the metamorphism of pelitic rocks at high and ultrahigh pressures. However, Werner's oeuvre spanned the whole spectrum from classical field work in structural geology to theoretical and experimental metamorphic petrology to detailed crystal chemistry and mineral physics of a wide range of minerals and their synthetic analogs. This symposium is keyed to Werner's seminal achievements in high-pressure and ultra-high-pressure metamorphism. Nevertheless, we welcome all contributions that will help to highlight the singular contributions of this respected scientist to petrology and mineralogy overall.