Figure: Deep structure of Borneo. (a) NW-SE-NE transect, x–x′, showing long wavelength free-air gravity anomaly (see inset). (b) Uplift along transect from sub-plate temperature variation determined by calibrating seismic tomographic model shown in panel (d). Solid circles with vertical bars = air-loaded uplift, assuming that asthenosphere has ambient temperature of 1333+/-30 ◦C. (c) Topographic height along transect. Dashed line = mean sea level. (d) Vertical slice through seismic tomographic model of Schaeffer and Lebedev (2013). Gray polygon = regions where calculated temperature <1333 ◦C; dashed line = position of 1333 ◦C isothermal surface. Gray/black arrows = loci of two calculated geothermal profiles shown in panels (d) and (e). (e) Contour map = temperature as a function of shear wave velocities, Vs(z), and depth (Priestley and McKenzie, 2006). Gray/black circles = Vs(z) beneath central Borneo and Sunda Shelf, respectively (see arrows in panel d). (f) Pressure–temperature calculations. Gray/black circles = geothermal profiles beneath central Borneo and Sunda Shelf from Vs conversion scheme shown in panel (d). White circle = pressure and temperature estimates of primary melt for sample SBK13 with MgO number of 7.66 wt.% from Semporna peninsula (Macpherson et al., 2010). Pressures and temperatures were calculated using mafic thermobarometric method (Plank and Forsyth, 2016). Uncertainties in pressure and temperature estimates were determined for range of sample H2O and Fe oxidation contents (McNab et al., 2018; see body text). Dotted line projected to surface indicates mantle potential temperatures (T p ≈ 1380 ◦C). Pressure–temperature estimates are compared to anhydrous melt paths (gray polygon) calculated using Katz et al. (2013)’s formulation. Dashed line is their anhydrous solidus.