HR: 0800h
AN: T11B-0375    [Abstracts]
TI: Contrasting Protoliths of Cretaceous Metamorphic Rocks from the Luk Ulo Accretionary Wedge Complex of Central Java, Indonesia
AU: * Kadarusman, A
EM: adek@geotek.lipi.go.id
AF: Institut fuer Mineralogie und Kristallchemie, Universitaet Stuttgart, Azenbergstr. 18, Stuttgart, 70174 Germany
AU: Massone, H
EM: h-j.massone@mineralogie.uni-stuttgart.de
AF: Institut fuer Mineralogie und Kristallchemie, Universitaet Stuttgart, Azenbergstr. 18, Stuttgart, 70174 Germany
AU: Permana, H
EM: permana@geotek.lipi.go.id
AF: Research Center for Geotechnology, (Indonesian Institute of Sciences) LIPI, Jl. Sangkuriang, Bandung, 40135 Indonesia
AU: Munasri, A
EM: munasri@geotek.lipi.go.id
AF: Karangsambung Information and Conservation Center of Earth, LIPI, Komplek LIPI, Karangsambung, Kebumen, 54353 Indonesia
AB: Rocks of the Lok Ulo Accretionary Complex crop out over a small (<100 km²) area in the Karangsambung residency of Central Java. They are part of Cretaceous accretionary wedge complexes in Central Indonesia, which are distributed sporadically in an arc extending from southwest and central Java to southeast Kalimantan and southern Sulawesi. The Lok Ulo complex consists of various types of rocks occurring as tectonic slabs in a black-shale matrix tectonic melange. The slabs are composed of a dismembered ophiolite, sedimentary rocks, and crystalline schists and gneisses. Detailed work on all the various metamorphic rock types in the Lok Ulo complex will be the focus of the study. Our investigations already show that the metamorphic rocks have two different kinds of protoliths and differ in P-T evolution as well. The first group (called `oceanic plate protolith') consists of fine-grained metabasites with metapelitic intercalations ranging from greenschist to amphibolite facies. High-pressure rocks such as eclogite, partially containing lawsonite, jadeite-glaucophane schist and blueschist crop out in a thin zone between the low-grade schists and a serpentinite zone along Kali Muncar. They are associated with a succession of metabasalt, serpentinite, chert and red limestone as common constituents of an ophiolite. The second group (called `continental crustal protolith') consists of low to high grade medium pressure metapelites, calc-silicate rocks, and metagranites (gneisses, quartzites, marbles, felsic granulites), and minor bimodal low grade metavolcanic. These rocks are presumably associated with a monotonous sequence of metapelites from the chlorite zone up to the garnet zone exposed in the northern and eastern part of the Karangsambung area (e.g. Kali Loning). Our findings suggest that the metamorphic rocks from the Lok Ulo complex are not the simple result of subduction metamorphism along the Indo-Australian oceanic plate (margin of the Sundaland craton) in the early Cretaceous as previously thought. The observed presence of low to high grade schists and gneisses of continental supracrustal parentage point to an early involvement of continental crust during the collisional event at least in the Karangsambung area (eastern part of the subduction zone).
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3660 Metamorphic petrology
DE: 8104 Continental margins: convergent
DE: 9320 Asia
SC: Tectonophysics [T]
MN: Fall Meeting 2005