The Group IV Rocks were collected from the Mae Suai area and the Wiang Pa Pao area. They are made up of meta-andesite/basalt and meta-diorite/gabbro. Both rock are foliated, and are made up mainly of amphibole,with subordinate plagioclase/quartz and zoisite/clinozoisite, and small amounts of titanite, opaque minerals, chlorite, biotite and prehnite. Relicts of orthopyroxene are present in the sample from the Wiang Pa Pao area. Amphibole pleochroism suggests that they are tremolite-actinolite series or hornblende. The Group IV Rocks have Zr/TiO2 and Nb/Y ratios in the ranges of 0.005-0.015 and 0.027-0.094, respectively,and are tholeiitic andesite/basalt. The representatives are chemically similar to the mid-ocean ridge basalt from Juan de Fuca Ridge, northeast Pacific Ocean, in terms of chondrite and N-MORB normalized multi-element patterns.