With mineral-melt thermobarometers, reconstruction of P-T-depth history of magmas can be established for volcanic rocks. The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositional range resulting from little or no fractional crystallization or crustal assimilation and shows evidence of rapid magma ascent. The established thermodynamic model covers the pathway from the magma source depth to the eruption. The model shows that the pillow lava originated at the depths of ~85-100 km by fluid ascent from a stagnant slab. This range corresponds to the depth that encompasses the uppermost asthenosphere to the lowermost lithosphere corresponding to the upper garnet to the lower spinel stability fields of the mantle. Subsequently, the melt rose to ~66-71 km depth where a primary magma reservoir was generated possibly due to existence of a possible local discontinuity within the upper mantle. The magma uprose rapidly from ~61 to ~20 km or even to a shallower depth with crystallization of dendritic clinopyroxene and titanomagnetite, due to dehydration of magma. Magma ascent slowed down near the surface possibly due to the volcanic channel split into two or more toward the vents. The model can be applied to other volcanic areas composed of less evolved rocks.