Mesozoic mélange formation in Indonesia - with special reference to Jurassic mélange of Japan

Author : Koji Wakita
Publication : Bulletin of the Geological Society of Malaysia
Page : 19-30
Volume Number : 43
Year : 1999

Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 19 – 30

Mesozoic mélange formation in Indonesia – with special reference to Jurassic mélanges of Japan


Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki, 305-8567, Japan


Abstract: Cretaceous mélange is distributed in Central Java, South Sulawesi, and South Kalimantan in Indonesia. It consists predominantly of polymict clasts in muddy matrices. Geologic relationships were investigated by means of stratigraphy, palaeontology, structural geology, petrology and geochemistry, in order to elucidate the origin of the mélange in the three regions.

Mélange of the Luk-Ulo Complex in Central Java mainly consists of high pressure type metamorphic rocks, bedded chert, siliceous shale, sandstone and shale, ultramafic rocks, basalt, limestone and rhyolite. The mélange is unconformably covered by the Eocene Karangsambung Formation.

Mélange of the Bantimala Complex in South Sulawesi is mainly composed of clasts of high-pressure type metamorphic rocks, ultramafic rocks, basalt, bedded chert and sandstone within muddy matrices. The mélange is intruded by Palaeogene diorite.

Mélange of the Meratus Complex in South Kalimantan consists of bedded chert, ultramafic rocks, schist, sandstone and shale. The mélange is unconformably overlain by Eocene strata.

The protoliths of the sedimentary clasts include representatives of “Oceanic Plate Stratigraphy (OPS)”. The OPS was originally deposited on oceanic plate, and travelled from the oceanic ridge to subduction trench, and was incorporated within an accretionary wedge. The OPS was dismembered during the accretionary process, which included tectonic mixing, diapiric injection and submarine sliding. The fragments of schist and ultramafic rocks were derived from blocks exhumed following micro continental collision. Additionally, fabrics related to Cenozoic faulting overprinted the already complicated structures of these mélanges.

The Jurassic mélange of the Mino terrane in central Japan is representative of a subduction-related mélange along the circum-Pacific margin. Most of the protoliths are similar to those of the mélanges of Indonesia. The Jurassic mélange of the Mino terrane is composed of fragments of OPS ranging in age from Permian to earliest Cretaceous. These components were dismembered during the processes of offscraping and underplating within an accretionary wedge.

A major difference in Mesozoic mélanges of Indonesia and that of Japan is the presence of metamorphic and ultramafic clasts. The metamorphic and ultramafic clasts were incorporated within the mélanges during microcontinental collision. The mélange of the Mino terrane was generated during the accretionary processes during oceanic plate subduction, while the Mesozoic mélanges in Indonesia were generated by the collisional process as well as the accretionary process.