* Laboratoire de Géologie Structurale et Appliquée,
Université de Savoie, B.P. 1104, 73011 Chambéry
Cedex, France.
** Laboratoire de Géodynamique, Université de Savoie,
B.P. 1104, 73011 Chambéry Cedex, France.
Abstract About 350 faults and slickenlines have been
measured in the western part of the Cimandiri Fault Zone on Java
Island. This fault zone trends N70°E and corresponds to the
limit of Southern Mountains and Cimandiri-Bandung area. The data
used in this study are mostly microfaults which range in length
from a few centimeters to a few meters.
On the basis of fault slip data, orientations of paleostresses
have been computed. Four strike-slip fault regimes have been identified.
Normal faulting seems to be associated with strike-slip regimes.
Our results of paleostress reconstruction using fault data from
Cimandiri Fault Zone support the hypothesis of stress reorientation
along a major strike-slip fault (Anderson 1951). The paleostress
directions enable us to deduce the main fault movement. The Cimandiri
Fault Zone is interpreted as a sinistral strike-slip fault zone.
The dynamic model initiated by Anderson (1951) and modified by
Price and Cosgrove (1990) explains the Cenozoic paleostress succession
in the Cimandiri Fault.
INTRODUCTION
The west Indoesian island arc results from the interaction
between Indo-Australian and Eurasian plates. In the Sunda arc
(Fig. 1) one may distinguish from the south to the north: (1)
the Indian Ocean Basin, (2) the Java Trench, (3) the Java-Sumatra
Outer Arc, partly submerged south of Java and represented by the
archipelago of Mentawai, southwest of Sumatra, (4) the magmatic
arc of Java-Sumatra and (5) the foreland basin of the Sunda continental
shelf represented by the Java Sea (Hamilton 1979). The Great Sumatran
dextral strikeslip fault is a major tectonic feature of the region
(Katili and Hehuwat 1967, Hamilton 1979). This fault induced a
pull-apart graben in the Sunda strait (Haryono 1988). The area
of this study is located eastward of the transitional zone between
the frontal subduction of Java and the oblique subduction zone
of Sumatra (Fig. 1).
Four distinct morphological and structural units can be distinguished
in West Java (van Bemmelen 1949, Fig. 1), which are, from the
north to the south: (1) the Northern Coastal Plain of West Java,
(2) the folded mountains of Bogor, (3) the Bandung Zone mostly
covered by recent olcanic products and (4) the Southern Mountains
of West Java.
The boundary between the Bandung Zone and the Southern Mountains
trends N70°E from the Gulf of Pelabuhanratu to the Bandung
area. This boundary is the Cimandiri Fault Zone (van Bemmelen
1949, Martodjojo 1984). It acted as a paleogeographical and structural
boundary during Cenozoic times (Martodjojo 1984). Evidence for
the continuation of this fault zone east of Bandung is lacking
(van Bemmelen 1949). Hamilton (1979) has identified in the Java
Sea a structural zone that connects the Cimandiri Fault Zone to
the Meratus Mountains south-east of Kalimantan (Fig. 1). Numerous
faults and folds can be observed near the fault zone (Sukamto
1975). The aims of this study are (1) to reconstruct the paleostress
fields using fault-slip data and (2) to analyse the movement along
the major fault and its implications.
