FIGURE CAPTIONS
Figure 1. Major physiographic features and active plate boundaries of the Woodlark Basin region. The stippled area encloses oceanic crust formed during the Brunhes Chron at spreading rates (labeled in mm/yr). MT and ST = Moresby and Simbo transform faults, respectively; DE = D’Entrecasteaux Islands. Inset, geographical location of the Woodlark Basin.
Figure 2. Topography of the Papuan Peninsula and bathymetry of the western Woodlark Basin showing relocated epicenters (black circles) and earthquake focal mechanisms from Abers et al. (1997). G = Goodenough Island, F = Fergusson Island, N = Normanby Island, R = Rossel Island, T = Tagula Island, MS = Moresby Seamount, MT = Moresby transform fault, M = Misima Island, W = Woodlark Island. Exploration wells Goodenough-1 and Nubiam-1 are labeled G-1 and N-1. The solid line is the landward boundary of oceanic crust and the thin double lines locate the spreading axes (Taylor et al., 1995).
Figure 3. Nested meridional sections at 151°34.5´E showing the (A) regional bathymetry and (B) local structures across the incipient conjugate margins (modified after Taylor et al., 1996). Leg 180 drill sites are depicted on the B section. VE = vertical exaggeration; M.S. = Moresby Seamount.
Figure 4. Stacked, migrated, and depth-converted 196-channel (EW95-1369) and 148-channel (EW95-1374) seismic sections collected with a 5-km streamer across the rift basin north of Moresby Seamount that is the locus of current deformation ahead of the Woodlark spreading center (the western tip of the neovolcanic zone is hatched in the inset). There is no vertical exaggeration. The bounding low-angle normal detachment wraps around Moresby Seamount and has a true dip of 27°± 3° toward 015°. Structure contours from 3 to 9 km depth are shown in the inset, with bathymetric contours labeled in hundreds of meters. The antithetic hanging wall normal fault dips south at 45°. On line EW95-1369 the planar detachment (curvi-planar in three dimensions) is imaged over the full depth extent of the seismogenic zone (3—9 km) determined from earthquake waveform inversion results (Abers et al., 1997). Miocene strata on the southern flank of the pre-rift forearc basin dip north at ~10% beneath the northern margin. Figure modified from Taylor et al., (unpubl. data) to show the location of Sites 1108, 1112, and 1113.
Figure 5. Stacked and migrated time section of 148-channel seismic line EW95-1366, located in Figure 7, on which Sites 1109—1111, 1114—1116, and 1118 were drilled. Common depth points (CDPs) are labeled 1—7 (in thousands). The top and bottom parts overlap by 100 CDPs (1.25 km). North is to the right.
Figure 6. Stacked and migrated time section of 196-channel seismic line EW95-1371, located in Figure 7, on which Site 1117 was drilled. CDPs are labeled 1—4 (in thousands). Four hundred CDPs equals 5 km. North is to the right.
Figure 7. Shaded relief map showing the locations of the Leg 180 drill sites and multichannel seismic tracks, plotted on a base map with 200-m bathymetric contours (thicker contours labeled every kilometer).
Figure 8. Multibeam bathymetry map (with 100-m contours and thicker contours labeled every kilometer) showing the locations of the Leg 180 drill sites in the vicinity of Moresby Seamount. Multichannel seismic tracks are plotted and labeled every 100 CDPs.
Figure 9. Lithology and correlation of Sites 1108, 1109, 1115, and 1118 from the footwall of the Woodlark rift basin.
Figure 10. Core photograph illustrating the transition facies from diabase, interpreted as a clast in conglomerate, overlain by shallow-marine conglomerates and limestone.
Figure 11. Sedimentation curves at Sites 1115 (solid line), 1109 (dashed line), 1118 (dotted line), 1108 (solid line upper right), 1114 (dashed line upper right), and 1116 (dotted line upper right), based on nannofossil (square) and planktonic foraminifer (circle) datum events, magnetic chron and subchron boundaries (triangle), and lithostratigraphic correlation (star). Symbols with arrows denote actual datum point can be above or below and older or younger than indicated by the symbols. Shown below are average sedimentation rates, calculated for intervals separated by vertical lines, and paleobathymetry, based on benthic foraminifers, at Sites 1115, 1109, and 1118. Broken lines indicate uncertainty in the placement of paleodepth boundaries. Unconformity represented by wavy line.
Figure 12. Calcium carbonate content plotted vs. depth at Site 1115. Note the downward decrease in carbonate content to 400 mbsf.
Figure 13. Digital photomicrograph. Plane-polarized light. Crystal vitric tuff, with abundant angular, fresh pipe vesicle glass shards in a glassy matrix (Sample 180-1118A-38R-3, 128—130 cm).
Figure 14. Digital photomicrograph. Plane-polarized light. A pumiceous rock containing phenocrysts of hornblende within a glassy groundmass. Occurs as a granule-size clast within a sandy silty claystone (Sample 180-1108B-12R-5, 50—53 cm).
Figure 15. Digital photomicrograph. Viewed under crossed nicols. A well-rounded clast of fresh glassy basalt with plagioclase and biotite microphenocrysts, set in a calcitic matrix including volcanic and metamorphic grains (Sample 180-1115C-12R-4, 144—148 cm).
Figure 16. Digital photomicrograph. Viewed under crossed nicols . A subrounded clast of basalt with plagioclase microphenocrysts (right); an acidic clast (left), and a clast of serpentinite (lower). The matrix is calcareous, with quartz and feldspar grains (Sample 180-1108B-3R-CC, 0—4 cm).
Figure 17. Correlated lithologic logs of Sites 1114, 1116, and 1117 from the footwall of the Woodlark rift basin. See site summaries for discussion.
Figure 18. Digital photomicrograph. Angular fragment of calc-schist, surrounded by glassy basalt and silicic fragments, set in a sparry calcite cement (Sample 180-1116A-13R-2, 25—27 cm).
Figure 19. Occurrence of volcanogenic ash layers at Sites 1118, 1109, and 1115 shown in terms of thickness (gray pattern) and number of volcanogenic ash layers (black pattern) for Pliocene—Pleistocene time. Note: the spiky nature of the peaks of volcaniclastic input are in part artifacts of variable core recovery. Refer to the visual core descriptions on the CD-ROM for details of recovery.
Figure 20. Physical properties data for Sites 1108, 1109, 1111, 1114, 1115, 1116, and 1118. A. Porosity data, as measured from discrete index property samples. Dashed lines show the depth of the regional unconformity at the northern sites. B. Porosity data, with depth shifts as follows: Site 1108: 500 m added to mbsf depths above 165 mbsf (the location of a fault zone), 700 m added below 165 mbsf; 750 m added to Site 1114 data; and 1000 m added to Site 1116 data. Data below the unconformities at Sites 1109, 1115, and 1118 are not shown because of the unknown hiatus. See text for discussion.
Figure 21. Magnetic susceptibility for Sites 1118, 1109, and 1115 aligned with respect to the location of the Top Mammoth datum (interpolated from biostratigraphy at Site 1109).
Figure 22. Magnetic susceptibility for Sites 1118, 1109, and 1115 plotted as a function of time. Given the accuracy of the age data, the transition from low-amplitude to high-amplitude magnetic susceptibility is approximately coeval across the sites.
Figure 23. Photograph of hand specimen of gabbro fragment showing coarse-grained, nonlaminated nature. No layering was apparent at the scale of the recovered material (Sample 180-1117A-13R-1, 19—23 cm).
Figure 24. Plots of diabases and metadiabases from Sites 1109, 1114, 1117 and 1118 where they were recovered in situ. Samples from the other holes are normalized to values from Site 1109 (presumed closest to pristine diabase). av. = average.
Figure 25. Plot of diabase and metadiabase samples from talus samples at Sites 1108, 1111, and 1114 normalized to the average values for unaltered diabase from Site 1109. Key: 1 = foliated, epidote-rich schist in Hole 1111A (Sample 180-1111A-16R-CC, 8—15 cm); 2 = metadiabase pebble in sediments of Hole 1108B (Sample 180-1108B-47R-CC, 1—3 cm); 3 = nonfoliated metadiabase in Hole 1114A (Sample 180-1114A-36R-2, 40—42 cm); 4 = foliated metadiabase pebble in Hole 1114A (Sample 180-1114A-36R-1, 70—72 cm).
Figure 26. Plot of major and trace elements of diabases and metadiabases from Sites 1108, 1109, 1111, 1114, 1117, and 1118 normalized to E-MORB using the values of Sun and McDonough (1989).
Figure 27. Close-up photograph of highly sheared gabbro with a well developed foliation plane and shear bands (Sample 180-1117A-9R-1, 24—32 cm).
Figure 28. Core photograph of the fault gouge recovered at Site 1117. This shows soft, light- colored clayey material that contains talc, chlorite, calcite, ankerite, and serpentine. This material is consistent with intense shearing and hydrothermal alteration of underlying deformed gabbro.
Figure 29. Schematic cross section showing the increasing proportion (circles) of strike-slip and oblique-slip faults toward the Moresby Seamount. Note that oblique- and strike-slip faults at Sites 1109 and 1115 occur in the pre-rift sequence.
Figure 30. Estimated thermal gradients (in °C/km) from Leg 180. Confidence in data is discussed in the text.
Figure 31. Plot of dissolved Ca, Mg, and SiO2 at northern Woodlark Rise sites. The shapes of the Ca and Mg profiles reflect the effects of carbonate diagenesis and a variable extent of alteration of volcanic matter in the upper portion of the sedimentary column of each site. Deeper downhole, alteration of volcanics exerts a more dominant control on pore-water profiles. Large increases in dissolved Ca result primarily from alteration of plagioclase whereas depletion of Mg reflects its uptake during authigenic smectite formation. The dissolved SiO2 profiles depict a downhole progression including dissolution of volcanic ash in the upper sedimentary column, and WST reactions deeper downhole. Particularly elevated SiO2 concentrations deep in Site 1118 are attributable to an abundance of fresh to slightly altered volcanic matter in higher porosity sediments.
Figure 32. Biogeochemical profiles in sediments from the Woodlark Basin, Leg 180: A. Total bacterial populations at Sites 1109, 1115, and 1118. The solid curve represents a general regression line of bacterial numbers vs. depth in deep-sea sediments (Parkes et al., 1994), with 95% upper and lower prediction limits shown by dashed curves. Sulfate, ammonia, and methane depth profiles at Sites (B) 1118, (C) 1109, and (D) 1115. Unconformity at each site represented by wavy line. E. C1/C2 ratios at Sites 1108, 1109, 1115, and 1118.
Figure 33. Natural gamma ray from the triple-combo runs in Holes 1114A, 1118A, 1109D, and 1115C.
Figure 34. Neutron porosity and density porosity from the triple-combo runs in Holes 1114A, 1118A, 1109D, and 1115C.
Figure 35. Photoelectric effect (PEFL) from the triple-combo runs in Holes 1114A, 1118A, 1109D, and 1115C.
Figure 36. Sonic velocity (Vp)from the array sonic tool in Holes 1114A, 1118A, 1109D, and 1115C.
Figure 37. This dynamically normalized, double pass FMS image from Site 1115 shows well defined, flat-lying, conductive clayey layers interbedded with thin (~10 cm), resistive sandy or carbonate-rich beds, which are characteristic of the stratigraphy observed in FMS images from each of the three hanging wall drill sites (1109, 1115, and 1118). The dashed lines mark the Pad 1 azimuth trace of each FMS pass. The FMS images are oriented from 0° to 360° from geographic north.
Figure 38. Statically normalized FMS image (left) and tadpole plot (right) from Site 1114. Sinusoidal fit to dipping beds (dashed) and fractures (solid) are used to measure dips and dip directions, which are shown on the tadpole plot. Dominant bed dips are ~30° oriented northwest, while dominant fracture dips are ~50° to ~60° oriented north within the same interval.
Figure 39. Bed and fracture dip direction distributions from Site 1114. A, B. Histograms of bed and fracture dip directions. C, D. Rose diagrams of bed and fracture strikes. The two main populations consist of beds that strike northeast and fractures that strike just north of east.
Figure 40. Depth converted multichannel seismic (MCS) traces at Sites 1118 and 1109, displayed with the lithostratigraphic columns. The MCS data in time, spanning the two sites, is shown correlated with depth. CMP = common midpoint. TWT = two-way traveltime. Lithologic patterns as in Figure 9.