Day 1: The origin of diversity among primary magmas in arcs

James Gill: Earth Sciences Department, University of California, Santa Cruz, 1156 High Street, Santa Cruz CA 95064, USA

Tim Grove: Department of Earth, Atmospheric and Planetary Sciences (54-1220), Massachusetts Institute of Technology, Cambridge MA 02139 USA

Yoshiyuki Tatsumi: Institute for Research on Earth Evolution (IFREE), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka 237-0061, Japan

Richard Arculus: Department of Earth and Marine Sciences, Australian National University, Canberra ACT, Australia

M-Q1: What spectrum of arc magma compositions in continental and oceanic arcs is potentially in equilibrium with mantle peridotite ± pyroxenite? At what pressures, temperatures, H2O contents, and oxygen fugacities do these primary magmas form? From what combination of natural factors, laboratory methods, and sampling biases do uncertainties regarding the compositions and origins of primary arc magmas arise?

M-Q2: Which melting models for the mantle wedge are consistent with observations and what may cause a particular melting event in each case? In which set of circumstances could decompression melting, flux melting, dragging damp mantle across its solidus, and reactive flow be important? How would these different dynamic cases play roles in controlling magma compositions? Are the dynamics of melt formation, segregation, and ascent in the arc setting different from those at mid-ocean ridges and/or mantle plumes? If so, how?

M-Q3: Are there ‘global’ versus ‘local’ trends in mantle-derived arc parent magma compositions as there are for MORB? Is there systematic compositional variability among mantle-derived, parental arc magmas? Can mantle parameters be distinguished from slab-inherited signatures? If so, what are the most important mantle-related trends along and across arcs? Are there differences in mantle wedge composition and dynamics beneath the generally thicker and older lithospheres along continental margins, relative to oceanic arcs, that play important roles?

M-Q4: What is the spatial distribution of temperature and melt in the mantle wedge? Can geophysical observations and numerical models for mantle wedge dynamics be rationalized with regional and local patterns of mafic magma chemistry? When conflicts between models and observations occur, what are the most likely sources of these disconnects? What steps would most probably lead to more accurate models?

M-Q5: What are the mechanisms and the specific conditions that lead to arc magmas with adakitic signatures? What combination of subduction zone parameters, magmatic processes, and P-T-X conditions can lead to such magmas? Are slab-melt contributions a necessary condition, or may such magmas be generated by intra-crustal processes? How do adakitic magmas with plausibly different origins differ from each other? Can partial melting of subducted oceanic crust be rationalized with direct passage of such melts through the peridotitic mantle wedge? If not, how are such melts processed in the mantle?

The deadline f