Cretaceous accretionary–collision complexes in central Indonesia
K. Wakita
Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305, Japan Received 26 April 1999; accepted 15 January 2000
Abstract
The geology of Cretaceous accretionary –collision complexes in central Indonesia is reviewed in this paper. The author and his colleagues have investigated the Cretaceous accretionary–collision complexes by means of radiolarian biostratigraphy and meta-
morphic petrology, as well as by geological mapping. The results of their work has revealed aspects of the tectonic development of the Sundaland margin in Cretaceous time. The Cretaceous accretionary–collision complexes are composed of various tectonic units
formed by accretionary or collision processes, forearc sedimentation, arc volcanism and back arc spreading. The tectonic units consist of chert, limestone, basalt, siliceous shale, sandstone, shale, volcanic breccia, conglomerate, high PT and ultra high P metamorphic
rocks and ultramafic rocks dismembered ophiolite. All these components were accreted along the Cretaceous convergent margin of the Sundaland Craton. In the Cretaceous, the southeastern margin of Sundaland was surrounded by a marginal sea. An immature
volcanic arc was developed peripherally to this marginal sea. An oceanic plate was being subducted beneath the volcanic arc from the south. The oceanic plate carried microcontinents which were detached fragments of Gondwanaland. Oceanic plate subduction caused
arc volcanism and formed an accretionary wedge. The accretionary wedge included fragments of oceanic crust such as chert, siliceous shale, limestone and pillow basalt. A Jurassic shallow marine allochthonous formation was emplaced by the collision of continental
blocks. This collision also exhumed very high and ultra-high pressure metamorphic rocks from the deeper part of the pre-existing accretionary wedge. Cretaceous tectonic units were rearranged by thrusting and lateral faulting in the Cenozoic era when successive
collision of continental blocks and rotation of continental blocks occurred in the Indonesian region. q 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
The Indonesian region includes components which record various tectonic scenarios, i.e. oceanic plate subduction,
sediment accretion, back arc rifting, forearc basin develop- ment, continental accretion and collision, lateral fault
displacement, thrust movement and metamorphic rock exhumation.
In this paper, the author will review the structure and tectonic history of the Cretaceous accretionary–collision
complexes in Indonesia. He and his colleagues have investigated the zone since 1992 under a cooperative
project between the Geological Survey of Japan, Univer- sity of London, Research and Development Centre for
Geotechnology, and Geological Research and Develop- ment Centre, Bandung. The author and his colleagues
published and reported their research results on the geology and tectonics of each complex. Here the author will try to
subdivide the tectonic elements in the complex in order to describe the characteristic elements, and will explain the
Cretaceous tectonics in the central Indonesian region as a whole.
2. Outline of geology
The main lithotectonic components of the central Indo- nesian
region comprise
pre-Tertiary accretionary
complexes, continental fragments, ophiolite massifs and island arcs which are distributed between the western
margin of the Sundaland craton and the north and north- eastern margins of the Australian craton Fig. 1. They are
formed by subduction, accretion and collision processes from the Cretaceous to present.
The Cretaceous accretionary–collisional complexes in central Indonesia are assemblages of tectonically disrupted
rocks and formations generated by various processes. They are distributed mainly in West and Central Java, South and
Central Sulawesi, and West and South Kalimantan Asikin, 1974; Sukamto, 1975, 1978, 1982, 1986; Ketner et al., 1976;
Sikumbang,
1986; Suparka,
1988; Sikumbang
and Heryanto, 1994; Heryanto et al., 1994; Wakita et al.,
1994a,b, 1996, 1998; Miyazaki et al., 1996, 1998; Wakita, 1997; Parkinson et al., 1996, 1998. The major complexes
are the Luk Ulo Complex of Central Java Asikin, 1974, the Bantimala Complex of South Sulawesi Sukamto, 1982 and
Journal of Asian Earth Sciences 18 2000 739–749
1367-912000 - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 6 7 - 9 1 2 0 0 0 0 0 0 2 0 - 1
www.elsevier.nllocatejseaes
the Meratus Complex of South Kalimantan Sikumbang, 1986 Fig. 2. These complexes are composed of similar
lithological components, including radiolarian chert, pillow basalt, clastic sedimentary rocks, low-grade schist and
pelite-matrix melange Fig. 3.
The Luk Ulo Complex Asikin, 1974; Ketner et al., 1976; Suparka, 1988; Wakita et al., 1994a is exposed in the
Karangsambung area of Central Java Fig. 2. The complex is an assemblage of E–W trending tectonic blocks
composed of crystalline schist, phyllite, marble, rhyolite, dacite, mafic and ultramafic rocks, limestone, chert, silic-
eous shale, shale, sandstone and conglomerate, occurring as tectonic slices and fault-bounded blocks Fig. 3. The
complex is unconformably overlain by the Eocene Karang- sambung Formation.
The Bantimala Complex is located about 40 km NE of Ujung Pandang in South Sulawesi Fig. 2. The Bantimala
Complex Sukamto, 1975, 1978, 1982, 1986; Wakita et al., 1994b, 1996; Miyazaki et al., 1996; Parkinson et al., 1998
is a tectonic assemblage of slabs and blocks consisting of sandstone, shale, conglomerate, chert, siliceous shale,
basalt, ultramafic rocks, schist, schist breccia and felsic intrusive rocks Fig. 3. The tectonic slabs are oriented
NW–SE and dip steeply to the east. Stratigraphic and struc- tural relationships among the components are unclear,
except for that between schist and chert. The ages of the components range from Jurassic to Late Cretaceous. The
oldest lithotectonic unit is a Jurassic shallow marine forma- tion, the Paremba Sandstone. The complex is unconform-
ably overlain by Palaeocene volcanic rocks and younger formations.
The Meratus Complex is distributed in the Meratus and Bobaris Mountains of SE Kalimantan and in Pulau Laut
Fig. 2. The complex is a tectonic assemblage of slabs and blocks consisting of high-pressure metamorphic rocks,
ultramafic rocks and polymict melange comprising clasts of chert, limestone and basalt within shale matrices Sikum-
bang, 1986; Sikumbang and Heryanto, 1994; Heryanto et
K. Wakita Journal of Asian Earth Sciences 18 2000 739–749 740
Fig. 1. Distribution of Asian terranes and Cretaceous accretionary–collision complexes in central Indonesia. Cretaceous accretionary–collision complexes are distributed along the eastern and southern margins of Sundaland, which is located at the southeastern margin of the amalgamated Asian continent. Modified
from Metcalf, 1990.
al., 1994; Wakita et al., 1998. The ages of components of the complex range from Jurassic to early Late Cretaceous
Fig. 3. These rocks are unconformably overlain by Late Cretaceous volcanic rocks and turbidite, such as the Pitap
Alino and Haruyan Pudak Formations. All these Meso- zoic rocks are unconformably covered by Eocene and
younger formations.
Similar complexes crop out in the Latimojong, Barru and Pompangeo areas, Sulawesi, and the Ciletuh and Jiwo Hills
areas in Java. In the Sintang area of West Kalimantan, the Late Cretaceous Selangkai Group includes Cretaceous
radiolarian chert, schist and limestone as olistoliths within turbidite-olistostrome sequences. These olistoliths are
remnants of a former accretionary wedge similar to that which generated the Luk Ulo and Meratus Complexes.
The components of these complexes can be subdivided into accretionary units, collisional units, volcanic arc units,
ophiolitic units, forearc basin units, intrusive and effusive units and cover formations, which reflect differing origins
and tectonic histories.
3. Accretionary units
