Geochemistry of Axial Lavas from Intra-Transform Spreading Centers of the Valdivia F.Z. System, Chile Ridge

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This combined program will conduct a detailed geophysical and geochemical study of the Northern Chile Ridge and Valdivia Fracture Zone intra-transform spreading centers. A 40-day field program will use SeaBeam 2000, magnetics, and gravity to map the detailed geomorphology of the axial region out to the Brunhes-Matuyama magnetic reversal boundary. The neo-volcanic zone will be sampled at ~125 sites by dredging and wax coring; lavas recovered will be analyzed by electron microprobe, ICP-MS, DCP, and mass spectrometry for major element, trace element, and Pb-Nd-Sr isotopic characteristics. The combined data set for the Northern Chile Ridge will be used to investigate the relationship of axial depth, crustal structure and lava composition with thermal effects associated with large- offset transform faults. The Valdivia F.Z. data set will be used to further investigate the extent and variability of anomalous geochemical features of the Southeast Pacific discovered in previous studies of the Southern Chile Ridge (i.e., DUPAL isotopic signatures and MORB with subduction zone trace element characteristics) and to extend on-going studies of relationships between Pacific mid-ocean ridge basalt chemistry and axial depth to deeper ridge segments.