AGU Fall Meeting - San Francisco

http://www.agu.org/meetings/fm07/

B16 Geomicrobiology and Environmental Biogeochemistry of Iron and Manganese Clara Chan, Woods Hole Oceanographic Institution Beth Orcutt, University of Southern California Iron and manganese are the most abundant redox active metals in Earth's crust, and thus are widely available for microbial energy generation. While Fe- and Mn-cycling microbes have long been recognized, recent work has provided great insight into their phylogenetic and physiological diversity, effects on environmental processes, roles in microbial ecology, and enzymatic pathways. In this session we aim to bring together researchers in geo- and biosciences to showcase the wide variety of lab-, field-, and computational-based approaches and to encourage dialogue between disciplines. Topics may include: What microbes oxidize and reduce Fe and Mn? What environments are they found in? What genes and proteins are involved? What is the geochemical/mineralogical state of Fe and Mn in the environment, and how do microbes affect this? What are tracers and biomarkers of Fe/Mn microbial activity and can we relate these to features in the rock record?

T04 The Behavior of Mid-Ocean Ridge Discontinuities (excerpt of full description) Robert A Dunn, University of Hawaii Scott M White, University of South Carolina The segmentation of mid-ocean ridges is thought to reflect the pattern of magma supply. How well magma supply corresponds to ridge-axis segmentation remains an open question. The purpose of this session is to bring together geophysical and geochemical data, geological mapping, and modeling studies in order to explore alternative ideas about segmentation from multiple perspectives. Whereas transform faults appear to be relatively long-lived and stationary features, so-called overlapping spreading centers (at faster-spreading ridges) and non-transform offsets (at slower-spreading ridges) exist on timescales of one million years or less and migrate along spreading segments at rates comparable to the local spreading rate. Contributions from recent studies of overlapping spreading centers are particularly invited, but the intent of this session is to address the linkage of tectonic and magmatic segmentation at a variety of spatial scales at ridge axis offsets. We welcome contributions that examine any aspect the tectonic or magmatic behavior of other kinds of ridge axis offsets, at present or in the past.

T11 Faults In The Ocean Crust: Perspectives From Geology And Geophysics Nicholas W Hayman, University of Texas Del Bohnenstiehl, North Carolina State University Faults in the oceanic crust play many roles: accommodating magmatic and tectonic strains at spreading centers, facilitating fluid flow along the ridge crest and outer-rise, and allowing the relative motions of plates along transform boundaries. Different approaches to studying ocean crustal faults include bathymetric analysis, earthquake and reflection seismology, ocean drilling, and geologic studies from submersible investigations. These diverse investigative techniques yield information at a range of temporal and spatial scales, which are challenging to integrate into a comprehensive model of oceanic fault development. Consequently, many processes and interactions involving seismicity, hydrogeology, and fault evolution remain poorly understood in oceanic settings. This session is intended to bridge disciplines to focus on open problems in ocean crustal faulting.

T19 The Generation Of Oceanic Lithospheric In Areas Of Low Effusive Magmatism - Where Has All The Crust Gone? Roger Searle, Durham University Eric Hellebrand, SOEST - University of Hawaii Maurice Tivey, Woods Hole Oceanographic Institution Benoit Ildefonse, CNRS - Université Montpellier 2 Recent years have seen increasing interest in the processes associated with the generation and early evolution of oceanic crust and lithosphere in regions of apparently low effusive volcanism and/or extensive detachment faulting. Such regions are mostly associated with low spreading rates such as the Gakkel Ridge and Southwest Indian Ridge, but also include the somewhat faster Mid-Atlantic Ridge at 12ºN - 17ºN, segment ends elsewhere on the Mid-Atlantic Ridge, the relatively fast spreading Parece Vela ridge in the Philippine Sea, and perhaps regions such as Pito Deep on the boundary of the Easter Microplate. The processes and related scientific questions include the degree of mantle melting, melt transport mechanisms, routes and final destinations of melt (e.g. is lack of effusive volcanism balanced by greater degrees of deep gabbro intrusions?); the nature and geometry of peridotite upwelling and incorporation into the lithosphere; the architecture and evolution of oceanic core complexes; early alteration of the crust/lithosphere; and the properties and bio-geo-chemical consequences of peridotite-hosted hydrothermal systems. A wide range of disciplines is involved in addressing these questions; we invite contributions from multi-disciplinary and multi-regional perspectives that are important for attaining solutions.

V10 From the Arc to the Back-Arc: Linking Geochemical and Geophysical Observations with Geodynamic Models of the Mantle Wedge Paul Hall, Boston University Stephane Escrig, Harvard University Back-arc basins (BABs) are complex tectonic environments in which oceanic crust is created at a spreading center (back-arc spreading center, BASC) in close proximity to a subduction zone. This juxtaposition results in strong spatial gradients in both geochemical and geophysical observables, providing a unique window on geodynamic and petrogenetic processes in the upper mantle. This session seeks to highlight progress in our understanding of mantle flow and melting in the mantle wedge by considering differences between arcs and BASCs, as well as between BASCs and normal mid-ocean ridges. Questions of interest include: What is the nature of the slab-derived component that contributes to arc and BASC magmatism (e.g., hydrous fluids, melts)? What is the distribution of this component within the wedge, and by what mechanism is it transported? What constraints do seismic attenuation and velocity studies provide regarding the presence of water, melt and fine-scale structure in the mantle wedge beneath BABs? How does plate kinematics (e.g., subduction angle, subduction rate, arc-back-arc separation, back-arc spreading rate) affect mantle flow and melting in arcs and BASCs? Contributions from geochemistry, petrology, seismology, geophysics, geodynamics and mineral physics are encouraged, as are contributions from researchers working in relevant Ridge and Margins focus sites (e.g., Lau Basin, Izu-Bonin-Mariana).

V12 Spreading Ridge Interactions with Hotspots, Subduction Zones, and Transforms John Chadwick, University of North Carolina Mike Perfit, University of Florida Randy Keller, Oregon State University This session will focus on the magmatic, geochemical, and tectonic phenomena that occur where active spreading ridges (mid-ocean ridges, back-arc spreading centers) interact with hotspots, subduction zones, and transform faults. Spreading ridges influence and are influenced by interactions with other plate boundaries or hotspots. The complex and dynamic interactions include unusual volumes, locations, and styles of magmatism, mixing of magmas and sources between the different regimes, and complex tectonic effects. Geochemical tracers and enhanced magmatic volumes typical of hotspots can be found along ridges tens or hundreds of kilometers from the interacting hotspot. Subduction of an active ridge can create slab windows beneath the overriding plate leading to forearc volcanism near the triple junction, and arc-affinity lavas have been found along near-trench mid-ocean ridges. The proximity of a ridge to a major transform can dramatically alter the volume and geochemical characteristics of ridge magmas including the generation of silicic lavas or enriched MORB at ridge-transform intersections. We invite contributions from all areas of research aimed at a better understanding of the effects of interactions between spreading ridge systems and other major tectonic features.

V35 Seafloor Hydrothermal Systems Related to Volcanic Arcs David Butterfield, University of Washington Wolfgang Bach, University of Bremen Hydrothermal venting at back-arc spreading centers and at submerged island-arc volcanoes display both similarities and differences when compared to systems found on mid-ocean ridges, with differences attributed to a range of factors including the composition of the substrate (basalt, andesite, rhyolite, dacite), contributions of magmatic volatiles to the hydrothermal system, and the depth and structure of the substrate. For example, recent studies in the southwest Pacific (Lau Basin, Manus Basin, Kermadec and Mariana Arcs) are providing evidence for volatile input (based on both alteration assemblages and vent fluid compositions). This session seeks contributions on any topic related to submarine volcanic arc hydrothermal systems.