Tectonostratigraphy-volcanic of Gajah-Ijo-Menoreh Tertiary volcanic formations in Kulon Progo mountain area, Yogyakarta-Indonesia

Abstract

Kulon Progo Mountains areas are formed by three Tertiary volcanic bodies that formed during Oligocene-Miocene times. Each volcano shows different tectonic control and stratigraphic result. This research conducted through interpretations of volcanic bodies, construction of stratigraphic columns, construction of geological cross-sections, supported by lithological-structural data from the field and some previous researchs. There are four volcanism periods in Kulon Progo Mountains, namely Late Eocene Volcanism, Early Oligocene Volcanism/Gajah, Late Oligocene Volcanism/Ijo and Late Miocene Volcanism/Menoreh. Gajah shape shows there are collaps volcano at the southern part and it was happened before Ijo emerge. Volcanism of the Eocene-Gajah-Ijo period is related to the Palaeogene extensional rifting period. Ijo volcano covers the southern part of Gajah Volcano. Menoreh volcano emerges at Late Miocene and covers Gajah volcano and Jonggrangan Formation. Menoreh Volcanism is related to the period of Neogene Compressional Wrench that produces a sinistral fault with left-stepping left lateral fault pattern.