NSF Forms - Ridge 2000 Program

Figure 1: From Martinez & Taylor [Martinez and Taylor, 2002], with the addition of newly
discovered ventfields during the R2K expeditions. Map and axial profiles of the Lau spreading center.
a, Map view of the bathymetry. b, Along-axis depth profile (black line) and distance of the spreading
centers from the volcanic front (red line). Green areas labeled AMCR indicate where axial magma
chamber reflectors have been observed. Blue triangles show known active hydrothermal sites, which
have their names next to them. c, Across-axis area (dots) and spreading rate variations (red line). A–T,
Australia–Tonga spreading rates. A–N, Australia–Niuafo’ou spreading rates. d, Adjusted mantle
Bouguer anomaly (aMBA; red line) and free-air anomaly (black line).. e, Map view of the adjusted
mantle Bouguer anomaly. Warm colors indicate relatively thin crust, and cool colors relatively thick
crust. Panels a and e have a tectonic interpretation showing location of the boundary (ticked line)
between the older crust of the basin (1) and various outlined crustal domains (2–4) associated with the
Lau spreading centers (white lines). Dashed line indicates arc volcanic front of the Tofua arc.
spreading rate is slowest, the Valu Fa Ridge (VFR) is shallow with a prominent axial high, limited
faulting, thick crust and a bright axial magma chamber (AMC) reflector [Morton and Sleep, 1985;
Turner et al., 1999 – see Fig. 1]. Towards the north, as spreading rates increase, ridge depth
descends from 1700 to 3300 m, there is a well developed rift valley, the crust thins, and the AMC
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