Figure F1. Bathymetric map of the eastern central Pacific showing the location of the Leg 205 drilling area (white box) in the Middle America Trench off Costa Rica. The white box shows the location of the map in Figure F2. The white circle denotes the location of the Leg 206 site. The map is modified after Vannucchi et al., (in press) based on a data compilation of C. Ranero.

Figure F2. Bathymetric map of the Middle America Trench off the Nicoya Peninsula, Costa Rica. The white box shows the location of the Leg 205 drilling area shown in Figure F3. Bathymetry is from Hydrosweep (Ranero and von Huene, 2000) and Simrad (E. Flueh, pers. comm. 2002) swath-mapping data combined with ETOPO5.

Figure F3. Bathymetric map of the Leg 205 drilling area showing Leg 205 (yellow dots) and 170 (white dots) drill sites. Seismic profiles are shown by the red (Fig. F25) (BGR-99-44; C. Reichert and C. Ranero, pers. comm., 2001) and yellow (CR-20; Shipley et al., 1992) lines. Leg 170 drill sites were based on seismic profile CR-20 (yellow line). Numbers along the BGR 99-44 seismic line are shotpoints. The white arrow gives the convergence direction (N30°E) and rate (88 mm/yr) (De Mets et al., 1990). The location of the map is shown in Figure F2; bathymetric contours are in meters. The bathymetric map is an integration of the compilation by Ranero and von Huene (2000) and Simrad data from E. Flueh (pers. comm., 2000).

Figure F4. Leg 205 Costa Rica drilling area (red box) (Fig. F3) and isochrons derived from seafloor magnetic anomalies (Barckhausen et al., 2001). Numbers indicate crustal age in million years. Tectonic boundaries, convergence direction and rate (arrow) (De Mets et al., 1990), and arc volcanoes (triangles) are shown. FS = Fisher Seamount, QSC = Quesada Sharp Contortion.

Figure F5. Summary of recovered lithology at drill sites on the incoming plate off Guatemala (DSDP Site 495) and Costa Rica (Site 1039) as well as on the Costa Rica margin (Sites 1040 and 1043). Note the similarity of incoming sediment sections at Sites 1039 and 495, as well as the repetition of the Site 1039 section below the décollement at Sites 1040 and 1043. Lithologic columns are modified from Kimura, Silver, Blum, et al. (1997).

Figure F6. Migrated multichannel seismic profile BGR-99-44 (C. Ranero and C. Reichert, pers. comm., 2001) across the Middle America Trench. Red lines = Leg 205 Sites 1253, 1254, and 1255. Thin black lines = Site 1039, 1040, and 1043 (Leg 170) locations (Kimura, Silver, Blum., et al., 1997). CMP = common midpoint.

Figure F7. Plot of cosmogenic ¹⁰Be vs. depth below seafloor at Site 1040. Produced by cosmic rays in the atmosphere and decaying with a 1.5-m.y. half-life, measurable ¹⁰Be enrichments are seen in sediments younger than 7–10 Ma. The underthrust sediments beneath the décollement (blue and purple) have high values typical of the incoming sediment section. Throughout the prism sediments of the upper plate, ¹⁰Be concentrations are very low, typical of sediments that are older than 3–5 Ma. Biostratigraphic (triangles) and magnetostratigraphic (x's) ages as well as sedimentation rates from Leg 170 cores (Kimura, Silver, Blum, et al., 1997) are shown on the right.

Figure F8. A. Heat flow measurements in the Leg 205 study area. Red box shows data projected onto a line (blue) across the Leg 205 and 170 drill sites which are shown below. The METEOR and Langseth and Silver (1996) data are from shallow penetration probes, and the Leg 170 data are from deeper penetration boreholes at Sites 1039, 1040, and 1043. B. Heat flow projected onto a line across the Legs 205 and 170 drill sites. The x-axis shows the distance from the deformation front.

Figure F9. Strontium isotope ratios from pore water samples from Site 1039 are indicated by data points and the solid line, with the dashed line showing the strontium seawater curve appropriate to the sediment age. Note the basal pore water trend toward modern seawater composition, with values greater than Miocene seawater, indicating a strong seawater component in basement fluids. Similar variations are seen in calcium and strontium concentration data.

Figure F10. Structures and geochemical anomalies at Site 1040A.

Figure F11. Pore pressures determined from consolidation tests for Site 1040 (Leg 170) and compaction ratios after Saffer (in press). The very sharp gradient in barium concentrations across the base of the décollement indicates limited vertical diffusion or advection (after Kastner, pers. comm., 2002).

Figure F12. Schematic of a CORK-II installation for monitoring fluid flow, flow rates, pressure, and temperature. ROV = remotely operated vehicle, RCB = rotary core barrel.

Figure F13. Portion of multichannel seismic profile BGR 99-44 across Sites 1253 and 1039. Figure F25 shows the BGR 99-44 seismic profile across all drill sites. Vertical exaggeration is ~1.6.

Figure F14. Bathymetric map of the Leg 205 drilling area (Ranero et al., 2000b) showing the location of ODP Site 1253 and its projected position at 17 Ma, the approximate age of the white tephra recovered at 398.8 mbsf. The inset shows the 8-cm-thick altered ash over and underlain by laminated clay-rich sediments.

Figure F15. Composite diagram showing selected logging data annotated with physical property measurements on the cores, petrologic observations, and paleomagnetic and rock magnetism results. Petrologic and magnetic results are reported in the core reference frame, wherein Subunit 4B was curated at a depth of 450 mbsf. Logging data show that Subunit 4B begins at a depth of ~460 mbsf. Correlations between core and logging intervals are shown as solid lines to indicate major boundaries (bottom of Subunit 4A and top of Subunit 4B) or as dashed lines to indicate subunit boundaries identified petrologically. Labeled zones at the base of the petrologic section indicate the following observations: (1) location of the cryptocrystalline horizon of basaltic texture; (2) greater number of magmatic contacts; (3) more veins or voids filled with holo- and cryptocrystalline groundmass/altered glass, clay and zeolites; (4) up to 5% degree of alteration within 1 m of Section 205-1253A-37R-1 and higher abundance of voids filled with clays and zeolites ending in an homogeneous microcrystalline gabbro; (5) increasing number of centimeter scale fractures and veins; and (6) very homogeneous microcrystalline to fine-grained gabbro with very weak magmatic contacts. Also indicated are the positions of the two OsmoSamplers (OS).

Figure F16. Core photograph and thin section photomicrographs from Subunit 4A. A. Close-up photograph of microcrystalline to fine-grained homogeneous holocrystalline gabbro (interval 205-1253A-8R-2 [Piece 2, 45–60 cm]). B. Microcrystalline gabbro observed within Subunit 4A. C. Completely altered primary mineral, replaced by clay (thin section 10-A; Sample 205-1253A-7R-1, 130–133 cm; 414.6 mbsf). D. Olivine, completely altered to clay (thin section 13-C; Sample 205-1253A-8R-1, 24–27 cm; 416.24 mbsf). E. Olivine, mostly replaced by clay (thin section 13-D; Sample 205-1253A-8R-1, 24–27cm; 416.24 mbsf). F.ŻAltered plagioclase, replaced by a mixture of clay and isotropic secondary products (thin section 13-E; Sample 205-1253A-8R-1, 24–27 cm; 416.24 mbsf). Mag = magnetite, Pl = plagioclase, Ilm = ilmenite, Ol = olivine.

Figure F17. Core photograph and thin section photomicrographs from Core 205-1253A-17R, in the upper part of Subunit 4B. A. 4-mm-wide vein with glassy margin and zeolite filling (Sample 205-1253A-17R-2, 100–117 cm). B. Photomicrograph in cross-polarized light (XPL) taken with a blue filter at 5x magnification, showing microcrystalline gabbro (Sample 205-1253A-17R-2, 108–111 cm). C. Photomicrograph showing zeolites, probably mesolite or thomsonite (thin section 27-E; Sample 205-1253A-17R-2, 108–111 cm; 478.18 mbsf). Cpx = clinopyroxene, Pl = plagioclase.

Figure F18. Core photograph and photomicrograph from Sample 205-1253A-25R-1 (Piece 9, 57.5–63.5 cm; 513 mbsf). A. Chilled margin of cryptocrystalline basalt including voids filled with zeolites and clay (interval 205-1253A-25R-1, 58–63 cm). B. Photomicrograph in cross-polarized light (XPL) taken with a blue filter at 5x magnification showing cryptocrystalline groundmass (Sample 205-1253A-25R-1, 57.5–63.5cm). Cpx = clinopyroxene.

Figure F19. Composite diagram showing fracture distribution within the igneous units, core recovery and a summary of petrologic observations, and detailed FMS images for the depths at which OsmoSamplers (OS) 1 and 2 were installed.

Figure F20. A. Photomicrograph showing the zeolite stilbite as a cavity filling in Section 205-1253A-33R-1, in lower part of Subunit 4B. B. Vein up to 0.5 cm wide filled with pale green clay in interval 205-1253A-42R-2, 72–101 cm. The interior of the vein shows a lighter color, which could be zeolites. The sample in B was taken for microbiological studies at the interval immediately adjacent to the bottom of part B. pl = plagioclase.

Figure F21. Composite diagram of pore fluid chemical data from Legs 205 and 170, measured just above and below the gabbro sill (Subunit 4A). Dashed horizontal line = depth of the sill at Hole 1039C for comparison.

Figure F22. Hole 1253A borehole installation showing subseafloor depths for OsmoSamplers, screens, packers, and casing strings. This figure is not to scale.

Figure F23. Location of Site 1254. Open circles = drill sites occupied during Leg 205, closed circles = drill sites occupied during Leg 170. Bathymetric map is an integration of the compilation by Ranero and von Huene (2000) and Simrad data from E. Flueh (pers. comm., 2000). LWD = logging while drilling.

Figure F24. Portion of multichannel seismic profile BGR 99-44 across Sites 1254 and 1040. Figure F3 shows the BGR 99-44 seismic profile across all drill sites. Vertical exaggeration is 1.7. CMP = common midpoint.

Figure F25. Summary of results at Hole 1254A. Composite view of structural and geochemical results from Hole 1254A with identification of major structural elements.

Figure F26. Photograph of the lithologic boundary between forearc prism sediments (Subunit P1B), represented here as darker claystone (interval 205-1254A-15R-2, 128–145 cm) and the underthrust sediment (Subunit U1A), which is shown here as a lighter, more silt-rich claystone.

Figure F27. Photograph of deformed hemipelagic sediments (Subunit U1A) within the lowermost décollement zone (interval 205-1254A-16R-1, 96–100 cm), demonstrating that the lithologic boundary does not coincide with the base of the décollement.

Figure F28. Photograph of a fault gouge (Riedel shear) developed by brittle shearing in a zone in the hemipelagic sediments of Subunit U1A (interval 205-1254A-16R-2, 23–32 cm) of discrete deformation.

Figure F29. Location of Site 1255. Red circle = the drill site occupied during Leg 205, black circles = the drill sites occupied during Leg 170. The bathymetric map is an integration of the compilation by Ranero and von Huene (2000) and Simrad data from E. Flueh (pers. comm., 2000).

Figure F30. Portion of multichannel seismic profile BGR 99-44 across Sites 1255 and 1043. Figure F24 shows the BGR 99-44 seismic profile across all drill sites. Vertical exaggeration is 1.7. CMP = common midpoint.

Figure F31. Hole 1253A borehole installation showing subseafloor depths for OsmoSamplers, screens, packers, and casing strings. This figure is not to scale.