References Auzende, J.-M, V. Ballu, R. Batiza> D. seagoing processing laboratory as well. Flg.2 is the general data processing flow diagram

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2 in the last few years. This super-fast spreading segment EPR fers a great opportunity to study the fundamental aspects crustalorigin at oceanic spreading centers. The full spreading rate along this ridge segment is mm/year. Previous studies have revealed an extremely narrow, elevated ridge axis, hydrothermal venting temperatures 400CC, magma chambers as shallow as -900 m and fresh, glassy basalt at many submersible dive locations (e.g., Lonsdale, 1989; Detrick et al., 1993; Cormier and Macdonald, 1994; Fujioka et al., 1995; Feely et al.,in press). [TAMU]2 data shows us the distribution and variation in tectonic and volcanic activity along die ridge. Hie data qualify has been excellent - the images are like photographs. We have observed that overlapping spreading exists at various scales all along the ridge. We have found numerous axial rifts, extensive volcanic flows on the ridge flanks and mammoth f-ridge lava flows. Normal faulting is most extensively developed at the base the elevated 2 to 4 mile wide axial ridge. Apparently the axial ridge crest is sufficiently hot and plastic so that brittle faulting doesn't become the dominant tectonic expression until the newly formed crust has moved a mile or two away from the ridge axis. Instrumentation and Data Processing [TAMU]2 is a long range side sacn sonar system with new capabilities for simultaneous seafloor swath imaging and bathymetric mapping. It contains ll/12khz and 72kHz sonar arrays and can collect data in swaths from 100m to 30kms. Data binning is selectable more than 8,000 pixels per ping or swath (currently maximum number bin is set to 8,192, only because programming convinence). Bathymetry is obtained by phase interferometry using complex demodulation the received signal, which produces 12 bit 'inphase' and 'quadrature* values for each two channels on either side the towfish at the rate 20k sets per second. Fig. 1 shows a schematic concept die [TAMU]2 towfish underway observation. An extremely versatile stware system, based in part on NASA's ELAS stware, has been developed for shorebased image processing and map production. All this capability are now transferred to the seagoing processing laboratory as well. Flg.2 is the general data processing flow diagram onboard/onshore laboratory. All the survey lines are shown in Fig.3. The collocated images (backscatter imagery and bathymetry) with unprecedented resolution, c.a. 12m x 12m bin size, provide us an entirely new perspective the seafloor, particularly discussion on the tectonic evolution the ridge system. New findings from imagery and bathymetry the Data processing for the SEPR data set is stillon going, so we cannot present final results here. The following are new findings from the [TAMU]2 imagery and bathymetry. (1) smaller scale axial grabens (a few tens meters wide) are ubiquitous all along the axis, which has been anticipated as an extrapolation from the previous works (Lonsdale, 1989), i.e. existence higher order discontinuity or segmentation in finer scale, (2) axial asymmetry volcanic activity is evident even on the central axial domain, actually symetrical axial dome shape is rare, (3) f-ridge volcanism (even within the surveyed narrow strip) is quite active and shows different types lava flow pattern, e.g. eruptions from small conical mounds, intensive lava floods covering wide area and lava patches smaller than the flood but bounded by faults, (4) existence PDS fault system, named after Primary and Definitive Structuring fault, is clearly recognizable from the imagery, ten very subtle in the bathymetry, as piece-wise continuous (concealed or interruptted by axial flank eruptions) normal fault system, which we posturate as a key mechnism controlling and associating to some tectonic features, such as the origin the tectonic fabric, asymmetric volcanic eruptions on the axial flanks, effective cause magma re-distribution along a segment Figures 4a and 4b show great improvement resolution in the (TAMU]2 data than in the multi-narrow beam swath mapping systems, such as Seabeam2000. References Auzende, J.-M, V. Ballu, R [TAMU]2 Batiza> D.

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