The Bandung Basin is located on axis of the Sunda arc in the West Java, Indonesia. This basin is underlain by dominant late Cenozoic volcanics. Lava samples were corrected from Quaternary Sunda and Tangkuban Perahu volcanoes and volcanics underlying these. Age of the lavas have been dated by K-Ar method to be ca. 4.1 Ma-ca. 0.04 Ma. Lavas are basalt to dacite in composition, and SiO₂ contents range 51-63 wt.%. Both tholeiitic and calc-alkaline suites exist, and K₂O 1evel covers medium-K to high-K suites. We used trace element for the estimation of primary basalt compositions. Model calculations using primary magma incompatible element contents examined the degree of partial melting of the source mantle occurred over the life of the suites. Continuous cooling of the mantle wedge was estimated, and a resurgence of degree of melting seems to have occurred between ca. 1.1 and ca. 0.6 Ma. Axial uplift took place in the Sunda arc during the period. This tectonic event may have been induced by a kinematic change in the subduction of the Indian-Australian Plate beneath the Sunda arc, which also affected the melting state of the upper mantle beneath the area.

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High pressure and temperature experiments have been done in the KMg₃AlSi₃O₁₀(OH)₂(phlogopite; Ph)-KMn₃AlSi₃O₁₀(OH)₂ (manganese phiogopite; MnPh) system under 1, 10, and 20 kbar at 750°C under NNO buffer conditions. The phases coexisting with phlogopite at 1 kbar include leucite, olivine, pyroxenoid, and manganese oxide. At 10 kbar, the equilibrium phases include phiogopite, olivine, manganese oxide, pyroxenoid, leucite and melt. At 20 kbar, they are phlogopite, olivine, pyroxenoid, manganese oxide and melt. The extent of solid solution of manganese phlogopite systematically increases with the increase of pressure and extent of solid solution being 17, 37, and 43 mol.% at 1, 10 and 20 kbar respectively.

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