Figure F1. Schematic cross section of oceanic crust created by superfast seafloor spreading (after Karson et al., 2002). Approximate boundaries of seismic layers are given to the left. The black arrows show magma withdrawal in the subaxial magma chamber. The yellow arrows indicate deformation related to faulting, fracturing, and block rotation in the sheeted dikes and lower lavas.
Figure F2. Depth to axial low-velocity zone plotted against spreading rate, modified from Purdy et al. (1992) and Carbotte et al. (1997). Depth vs. rate predictions from two models of Phipps Morgan and Chen (1993) are shown, extrapolated subjectively to 200 mm/yr.
Figure F3. Age map of the Cocos plate and corresponding regions of the Pacific plate. Isochrons at 5-m.y. intervals have been converted from magnetic anomaly identifications according to the timescale of Cande and Kent (1995). Selected DSDP and ODP sites that reached basement are indicated by circles. The wide spacing of 10- to 20-Ma isochrons to the south reflects the extremely fast (200–210 mm/yr) full spreading rate.
Figure F4. Location of Guatemala basin MCS tracklines (bold) from the site survey conducted in March–April 1999. Gray shading shows normal magnetic polarity, based on digitized reversal boundaries (small circles, after Wilson, 1996). Anomaly ages: 5A = ~12 Ma, 5B = ~15 Ma, and 5D = ~17 Ma.
Figure F5. Bathymetry and site-survey track map for the primary site. Abyssal hill relief of up to 100 m is apparent in the southwest part of the area; relief to the northeast is lower and less organized. Line numbers 21–28 identify MCS lines for subsequent figures. Triangles show locations of OBHs recovered with data.
Figure F6. Bathymetry and track maps for alternative Site GUATB-01. Site GUATB-01 has very shallow depths and low relief, excluding seamounts, in contrast to Site ALIJOS (Fig. F7), which is slightly deep and has very high relief.
Figure F7. Bathymetry and track maps for Site ALIJOS, a surveyed site that is no longer under consideration for drilling.
Figure F8. Stacked, migrated section of MCS data from line 22, showing positions of primary drill Site GUATB-03C and alternate Site GUATB-03B. Crossing positions of lines 24–28 are labeled.
Figure F9. Stacked, migrated section of MCS data from line 27, showing the primary drill Site GUATB-03C and crossing positions of lines 21–23. The bright reflector at 5.5–5.7 s near the line 21 crossing may be a thrust fault, and site selection decisions avoided this feature.
Figure F10. One-dimensional velocity model based on inversion of refraction data. At shallow depths, separate inversions were performed on northeast and southwest data subsets, with slightly faster velocities found to the northeast where abyssal hill topography is very subdued. The Layer 2/3 boundary is present in the depth range 1.2–1.5 km. The velocity model of Detrick et al. (1998) for Site 504, also based on OBH refraction, is shown for comparison. Apparent differences are dominated by differences in the inversion techniques, but the differences at 1.3–1.7 km may be barely above uncertainties.
Figure F11. Underway geophysics plotted perpendicular to trackline for the Guatemala Basin sites. A. Magnetic anomaly, with negative anomaly (normal polarity) shaded and identifications labeled. B. Center-beam bathymetry. C. Free-air gravity anomaly.
Figure F12. Schematic cross section of drilling Scenario A, in which the reentry hole has two casing strings, a 20-in string that extends ~80 m into sediments and a 16-in string that extends ~20 m into basement.
Figure F13. Schematic cross section of drilling Scenario B, in which the reentry hole has three casing strings, a 20-in string that extends ~80 m into sediments, a 16-in string that extends ~20 m into basement, and a 133/8-in string that extends deeper into basement across an unstable zone. The existence of unstable zones is an unknown at this point, but such zones may be present and will be stabilized through the use of casing when feasible.