Hydrocarbon basins in SE Asia: understanding why they are there

Robert Hall SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK (e-mail: [email protected])

ABSTRACT: There are numerous hydrocarbon-rich sedimentary basins in Indone- sia, Malaysia and southern Thailand. Almost all these basins began to form in the Early Cenozoic, they are filled with Cenozoic sediments, most are rifted basins that are the product of regional extension, and they formed mainly on continental crust. Many different models have been proposed to account for their formation and age. Understanding basin development requires a better knowledge of the Mesozoic and Early Cenozoic history of Sundaland, which mainly lacks rocks of this age. Sundaland is a heterogeneous region, assembled from different continental blocks separated by oceanic sutures, in which there has been significant Mesozoic and Cenozoic deformation. It is not a ‘shield’ or ‘craton’. Beneath Sundaland there is a marked difference between the deep mantle structure west and east of about 100
E reflecting different Mesozoic and Cenozoic subduction histories. To the west are several linear high velocity seismic anomalies interpreted as subducted Tethyan oceans, whereas to the east is a broad elliptical anomaly beneath SE Asia indicating a completely different history of subduction. Throughout most of the Cretaceous there was subduction north of India, preceding collision with Asia. However, north of Australia the situation was different. Cretaceous collisions contributed to elevation of much of Sundaland. Subduction beneath Sundaland ceased in the Cretaceous after collision of Gondwana continental fragments and, during the Late Mesozoic and Paleocene, there was a passive margin surrounding most of Sunda- land. When Australia began to move northwards from about 45 Ma, subduction resumed at the Sunda Trench. Basins began to form as the region went into compression at the time of subduction initiation. There was widespread extension, broadly orthogonal to the maximum compressive stress but modified by pre-existing basement structure. After subduction resumed, the weakness of the Sundaland lithosphere, unusually responsive to changing forces at the plate edges, meant that the basins record a complex tectonic history.

KEYWORDS: sedimentary basins, Sundaland, subduction

INTRODUCTION processes, such as hinge rollback, or plate boundary changes following events elsewhere in the global plate system. There are numerous hydrocarbon-rich sedimentary basins in In this paper it is proposed that most of the basins began to and around the Sunda Shelf in Indonesia, Malaysia and south- form broadly synchronously in the Middle Eocene. It is argued ern Thailand, in the continental area described as Sundaland that they formed in response to breaking of the plate of which (Fig. 1). Almost all of these basins began to form in the Early Sundaland was part when new subduction systems were initi- Cenozoic, many are very deep and they are typically filled with ated around Sundaland. The considerable variation in the terrestrial and shallow-marine sediments. The basins formed on geometry, character and distribution of the basins, and their continental crust, although this crust has a complex character, subsequent histories, reflect two important features of Sunda- in terms of fabric and lithologies, and probably differs consid- land: the composite character of its basement and the weakness erably from older major continents. From a tectonic point of of its lithosphere. view the basins present two particular problems: exactly when did they begin to form and why? The two questions cannot be separated and it is not possible to identify a mechanism without BASIN FORMATION MODELS knowing the timing. The abundance of basins suggests a major driving force should be identifiable. There are several large A great deal has been written on the basins of the Sundaland tectonic causes that have been proposed or are feasible, region and a large number of models have been proposed to including effects of India–Asia collision, collisions at the SE account for the formation of some or all of the sedimentary Asian margins, regional extension due to subduction-related basins. It is not the intention of this paper to discuss the

Petroleum Geoscience, Vol. 15 2009, pp. 131–146 1354-0793/09/$15.00  2009 EAGE/Geological Society of London DOI 10.1144/1354-079309-830 132 R. Hall

Fig. 1. Geography of SE Asia and surrounding regions. Small black filled triangles are volcanoes from the Smithsonian Institution, Global Volcanism Program (Siebert & Simkin 2002), and bathymetry is simplified from the GEBCO (2003) digital atlas. Bathymetric contours are at 200 m, 3000 m and 5000 m. distribution and details of different basins, or basin models, and One of the problems in interpreting the causes of basin the reader is referred to reviews or special volumes (e.g. formation is identifying the ages of basin initiation. Dating the Williams et al. 1995; Howes & Noble 1997; Longley 1997; initiation of basin formation is problematical because the oldest Petronas 1999; Hall & Morley 2004; Doust & Sumner 2007) parts of the sequences are terrestrial, typically lack fossils and, in and papers cited below for this information. many cases, are observed only on seismic data. The older parts The basins have been classified in different ways and of many basins have not been sampled because they are too assigned to different categories. Many have been suggested to deep. It is possible that there is a progressive change in the age have originated as pull-apart basins due to strike-slip faulting of basin formation from the external parts of Sundaland, with (e.g. Davies 1984; Tapponnier et al. 1986; Polachan et al. 1991; basin initiation becoming younger towards the interior, but it Huchon et al. 1994; Cole & Crittenden 1997; Shaw 1997; appears more likely that subsidence began at approximately the Leloup et al. 2001). A few have been suggested to have a same time across most of Sundaland (Longley 1997; Hall & flexural origin (e.g. DeCelles & Giles 1996; Wheeler & White Morley 2004; Doust & Sumner 2007). More work is certainly 2002). Most authors have suggested that all or most basins are needed to try to date basin initiation more accurately, but the rifts (e.g. Burri 1989; Williams & Eubank 1995; Longley 1997; problems in doing this will not be overcome easily and ages will Wheeler & White 2002; Hall & Morley 2004; Doust & Sumner remain uncertain, because Upper Cretaceous and Paleocene 2007). sedimentary rocks are missing from most of Sundaland, prob- A variety of mechanisms have been suggested to account for ably reflecting widespread uplift and subsequent erosion after basin formation. Many authors link basin formation to India– the mid-Cretaceous. It is reasonably certain that rifting began Asia collision, either related to extrusion-related strike-slip almost everywhere except in Thailand in the Eocene, and the faulting (e.g. Huchon et al. 1994; Madon & Watts 1998; Leloup oldest proven rift sequences are Middle Eocene. Therefore, the et al. 2001; Tapponnier et al. 1986) or by driving extension (e.g. best estimate for basin initiation is suggested here to be about Cole & Crittenden 1997; Longley 1997). Many other authors 45 Ma. The ideas proposed below are not critically dependent have explicitly or implicitly linked basin formation to subduc- on this proposed age or the synchronicity of basin formation. tion. Some of the basins are described as forearc basins (e.g. Madon 1999), and many have been described as back-arc basins SUNDALAND LITHOSPHERE (e.g. Eubank & Makki 1981; Busby & Ingersoll 1995; Cole & Crittenden 1997; Barber et al. 2005), although it is not always The interior of SE Asia, particularly the Sunda Shelf (Fig. 1) clear if this term is being applied in a purely descriptive sense, and surrounding emergent, but topographically relatively low referring to their present setting, or a mechanistic sense, to areas of Sumatra, the Thai-Malay peninsula and Borneo are indicate they formed behind an active arc. Morley (2001) largely free of seismicity and volcanism, in marked contrast to suggested extension driven by subduction rollback to account its margins. This tectonically quiet region forms the continental for the formation of some Sundaland basins and Moulds (1989) core of Sundaland (Hall & Morley 2004). Sundaland extends proposed subduction-driven compression could account for north into Indochina, much of it was terrestrial for most of the extension of Sumatran and possibly other basins. Many authors Cenozoic and it formed an exposed landmass during the have noted the importance of pre-existing basement structures Pleistocene. Most of the shelf is flat, extremely shallow, with in influencing basin development (e.g. Hamilton 1979; Moulds water depths considerably less than 200 m. Seismicity (Cardwell 1989; Hutchison 1996a; Madon 1999; Hall & Morley 2004; & Isacks 1978; Engdahl et al. 1998) and GPS measurements Sapiie & Hadiana 2007). (Rangin et al. 1999; Michel et al. 2001; Bock et al. 2003; Simons Hydrocarbon basins in SE Asia 133 et al. 2007) indicate that a SE Asian or Sunda microplate is currently moving slowly relative to the Eurasian Plate. The Sunda Shelf is widely regarded as a stable area (e.g. Geyh et al. 1979; Tjia 1992; Hanebuth et al. 2000) and sea-level data from the region have been used in construction of global eustatic sea-level curves (e.g. Fleming et al. 1998; Bird et al. 2007), despite evidence of very young faulting and vertical movements (e.g. Bird et al. 2006). The present stability and the extensive shallow area of the Sunda Shelf has led to a widespread misconception that Sundaland was a stable area during the Cenozoic. It is often described as a shield or craton (e.g. Ben-Avraham & Emery 1973; Gobbett & Hutchison 1973; Tjia 1996; Parkinson et al. 1998; Barber et al. 2005), or plate (e.g. Davies 1984; Cole & Crittenden 1997; Replumaz & Tapponnier 2003; Replumaz et al. 2004), implying a rigid block with deformation concentrated at the edges during the Cenozoic. Some authors suggest Sundaland rotated clockwise as a block during the last Fig. 2. Sundaland at the end of the Cretaceous, modified after 8–10 million years (e.g. Rangin et al. 1999) or over a longer Metcalfe (1996), Barber et al. (2005) and Barber & Crow (2009). period (Replumaz et al. 2004). West Sumatra, West Burma and Indochina–East Malaya formed part However, the character of the Sundaland deep crust and of a Cathaysia block added to Eurasia during the Palaeozoic. mantle is quite different from nearby continental regions and Sibumasu was accreted along the Raub–Bentong suture in the Triassic. West Burma and West Sumatra were subsequently moved from cratons (Hall & Morley 2004; Hyndman et al. 2005; Currie along the Sundaland margin. The Woyla Arc was accreted in the & Hyndman 2006). Unlike the well-known shields or cratons Cretaceous. The Luconia block is interpreted here to be a Cathaysian (e.g. Baltic, Canadian, African, Australian), Sundaland is not fragment rifted from Asia and added to Sundaland during the underlain by a thick cold lithosphere that was stabilized in the Mesozoic. SW Borneo (Metcalfe 1990) and East Java–West Sulawesi Precambrian. There has been significant deformation during (Smyth et al. 2007) are interpreted to have been rifted from West the Cenozoic with formation of the sedimentary basins, as well Australia and added in the Late Cretaceous. as localized inversion and widespread elevation of mountains. There are numerous faults that have been active during the suggested elsewhere (Hall 2002; Hall & Morley 2004), this Cenozoic (e.g. Pubellier et al. 2005; Doust & Sumner 2007). means the entire region is likely to be unusually responsive to The Sundaland interior has high surface heat flow values, changing plate boundary forces. This weakness has been of typically greater than 80 mW m2. Doust & Sumner (2007) major importance in the initiation of the Sundaland sedimen- noted exceptionally elevated heat flow (>150 mW m2) and tary basins, and in their later histories. temperature gradients in the area that extends from the Central Sumatra Basin northward into the southern Gulf of Thailand SUNDALAND HISTORY BEFORE THE EOCENE with an unknown cause. At the Indonesian margins high heat flows reflect subduction-related magmatism but the hot interior The continental core of Sundaland was assembled from frag- of Sundaland mainly reflects upper crustal heat flow from ments (Fig. 2) that rifted from Gondwana during formation of radiogenic granites and their erosional products, the insulation different Tethyan oceans and this history is well described by effects of sediments and a large mantle contribution (Hall & Metcalfe (e.g. 1996, 1998). An Indochina–East Malaya block Morley 2004). Locally very high heat flows may reflect fluid separated from Gondwana in the Devonian and, by the movements in the upper crust. P- and S-wave seismic tomogra- Carboniferous, was at tropical low latitudes where a distinctive phy (Bijwaard et al. 1998; Ritsema & van Heijst 2000) also show Cathaysian flora developed. In contrast, Sibumasu separated the region is characterized by low velocities in the lithosphere from Gondwana in the Permian, and collided with Indochina– and underlying asthenosphere, in marked contrast to Indian East Malaya, already amalgamated with the South and North and Australian continental lithosphere to the NW and SE. Such China blocks, in the Triassic. Permian and Triassic granites of low mantle velocities are commonly interpreted in terms of the Thai–Malay Tin Belt are the products of subduction and elevated temperature, and this is consistent with regional post-collisional magmatism (Hutchison 1989). high heat flow, but they may also partly reflect the mantle The Mesozoic sedimentary record is very limited but sug- composition or elevated volatile contents. gests that much of Sundaland was emergent. Barber et al. (2005) Sundaland has been very far from stable (Hall & Morley suggested a complex shuffling of Cathaysian and Gondwana 2004) and it did not behave as a single rigid block during most blocks during the Late Palaeozoic and Early Mesozoic, possibly of the Cenozoic. The considerable evidence for a hetero- associated with important strike-slip faulting. During the Meso- geneous pattern of subsidence and elevation indicates signifi- zoic there were several episodes of granite magmatism, inter- cant internal deformation (Hall 1996, 2002; Hall et al. 2008). preted to have occurred at an Andean-type margin related to The upper mantle velocities and heat flow observations suggest northward subduction, during the Jurassic and Cretaceous the region is underlain by a thin and weak lithosphere (Hall & (McCourt et al. 1996). More continental fragments were added Morley 2004; Hyndman et al. 2005) that extends many hundreds to Sundaland in the Cretaceous (Fig. 3). The Kuching Zone of kilometres from the volcanic margins. Of critical importance (Hutchison 2005) includes rocks with Cathaysian affinities is the observation that such extensive regions of thin and hot suggesting an Asian origin and a subduction margin continuing lithosphere are weak (Hyndman et al. 2005; Currie & Hyndman south from East Asia at which ophiolitic, island arc and 2006) and have a total strength of similar magnitude to forces microcontinental crustal fragments were added during the acting at plate boundaries. When dry, plate boundary forces Mesozoic. may exceed the total lithosphere strength during compression Several important blocks were added in the Cretaceous. SW and, when wet, during both compression and extension. As Borneo is interpreted here to be a continental block rifted from 134 R. Hall

Fig. 3. Inferred position of the Late Jurassic and the Early Fig. 4. Depth slice at 300 km from the P-wave tomographic model Cretaceous Sundaland margin, adapted in part from Hamilton of Bijwaard & Spakman (2000). High velocities are represented by (1979), Parkinson et al. (1998) and Smyth et al. (2007). A suture blue and low velocities by red. The slice shows high velocity between pre-Cretaceous Sundaland and the SW Borneo block is anomalies parallel to present trenches, interpreted as subducted slabs assumed to be present beneath the Sunda Shelf. Its position is around Indonesia, and relatively low velocities beneath Sundaland. uncertain. The extent and boundaries of the Cathaysian Luconia block are also uncertain. The youngest Cretaceous suture runs from Java and through the Meratus Mountains of SE Borneo and to the lithologies and structure, which gave Sundaland at the begin- south and east of this is a continental fragment derived from western ning of the Cenozoic a highly complex basement fabric that Australia (Smyth et al. 2007). varies from area to area, and which includes profound and deep structural features that have been reactivated at different times in different ways. This complex basement structure is the the West Australian margin, and added to Sundaland in the second important influence on the formation and character of Early Cretaceous. The suture is suggested to run south from the the sedimentary basins of Sundaland. Natuna area along the structural lineament named the Billiton Depression (Ben-Avraham 1973; Ben-Avraham & Emery 1973) and originally interpreted by Ben-Avraham & Uyeda MANTLE STRUCTURE BENEATH SUNDALAND (1973) as a transform fault associated with Cretaceous opening of the South China Sea. After collision of the SW Borneo block P-wave and S-wave seismic tomography not only indicate the the Cretaceous active margin ran from Sumatra into West Java likely strength of the lithosphere but also display the mantle and continued northeast through SE Borneo into West structure beneath Sundaland (Widiyantoro & van der Hilst Sulawesi. The intra-oceanic Woyla Arc collided with the Sumat- 1997; Bijwaard et al. 1998; Ritsema & van Heijst 2000) from ran margin in the mid-Cretaceous, adding arc and ophiolitic which important insights into the subduction history of the rocks to the southern margin of Sumatra (Barber et al. 2005). region can be obtained. Tomographic depth slices of the upper Further east the Early Cretaceous active margin is marked by mantle (Fig. 4) reveal very clear, broadly curvilinear high Cretaceous high pressure–low temperature subduction-related velocity anomalies, mainly parallel to present trenches, inter- metamorphic rocks in Central Java, the Meratus Mountains of preted as the principal lithospheric slabs subducted during the SE Borneo and West Sulawesi (Parkinson et al. 1998). Further Late Cenozoic. However, of greater importance for interpreting fragments were added to Sundaland during the Late Cretaceous the older history are velocity contrasts in the lower mantle. At (Fig. 3) in East Java and West Sulawesi (Smyth et al. 2007; depths below 700 km there is a marked difference between the van Leeuwen et al. 2007). mantle structure west and east of about 100
E(Fig.5).Tothe Until recently, most authors (e.g. Metcalfe 1996) accepted west there are a series of linear high velocity anomalies trending that fragments rifted from the west Australian margin in the roughly NW–SE, interpreted as subducted remnants of Late Jurassic and Early Cretaceous had collided in West Burma Tethyan oceans by van der Voo et al. (1999). East of 100
E in the Cretaceous, or were uncertain about their present these anomalies no longer exist, and only the southernmost position. However, recent work suggests West Burma is not a anomaly can be traced eastwards. To the west of 100
Eisa block added in the Cretaceous, but has been part of SE Asia clear linear NW–SE-orientated high velocity anomaly, but to since the Early Mesozoic, possibly linked to West Sumatra the east the apparent continuation of the anomaly beneath SE (Barber & Crow 2009). The west Australian fragments are now Asia has a quite different appearance. It has a broad elliptical in Borneo, East Java and West Sulawesi. Outboard of the shape with a long axis orientated approximately NE–SW Meratus suture, East Java and West Sulawesi are underlain in that terminates at the edge of the west Pacific beneath the part by Archaean continental crust, and geochemistry (Elburg Philippines. et al. 2003) and zircon dating (Smyth et al. 2007; van Leeuwen North of India the linear anomalies have been interpreted as et al. 2007) indicate a west Australian origin. a series of subduction zones active during India’s northward The Cretaceous arrival of continental fragments contributed movement before collision with Asia (van der Voo et al. 1999; to crustal thickening, magmatism (see below), emergence and Aitchison et al. 2007). The high velocity anomaly in the lower widespread erosion of Sundaland during the Late Cretaceous mantle beneath Indonesia represents the accumulation of and Early Cenozoic, thus further diminishing the completeness subducted lithosphere, but indicates a completely different of the stratigraphic record. Of greater importance for basin subduction history. Replumaz et al. (2004) have suggested that development was the considerable variation in basement the lower mantle tomography reflects a large clockwise rotation Hydrocarbon basins in SE Asia 135

Cretaceous and Paleocene, except in West Sulawesi and Sumba. However, there was widespread granite magmatism across most of southern Sundaland in the Cretaceous, which unlike prod- ucts of older episodes (e.g. Hutchison 1989; Krähenbuhl 1991; Cobbing et al. 1992; McCourt et al. 1996) is not arranged in linear belts, and suggests crustal melting across a large region during a long period, rather than subduction-related plutonism.

Volcanic activity Throughout most of SE Asia, Upper Cretaceous and Paleocene rocks of all types are almost entirely absent. The evidence for Late Cretaceous and Early Cenozoic volcanic activity (Fig. 6) is almost entirely based upon K–Ar ages, mainly from whole-rock dating, and there are many reasons to be cautious about such ages (McDougall & Harrison 1988; Harland et al. 1990; Macpherson & Hall 2002; Villeneuve 2004), particularly in SE Asia where the effects of tropical weathering are superimposed Fig. 5. Depth slice at 1100 km from the P-wave tomographic model of Bijwaard & Spakman (2000). The slice shows the linear high on tectonically and thermally altered rocks, commonly with low velocity anomalies beneath India, in contrast to the deep wide high potassium contents. If these ages are accepted, they suggest an velocity anomaly beneath Sundaland. The line at about 100
Eis interval of significantly diminished volcanic activity, possibly interpreted to be the eastern end of the subduction zones north of post-collisional and often interpreted as not directly related to India. subduction, succeeded in many parts of the Sundaland margin by renewed abundant volcanism from the Middle Eocene, of a single SE Asian block since 40 Ma, as proposed in a which can be confidently linked to subduction. reconstruction of the India–Asia collision zone by Replumaz & Crow (2005) reviewed the record of Cenozoic volcanic Tapponnier (2003). However, there is no evidence from activity in Sumatra. No Upper Cretaceous rocks are known palaeomagnetism (Fuller et al. 1999) for the rotation or latitude (Page et al. 1979), but there are a small number of Paleocene change suggested by Replumaz & Tapponnier (2003) and the ages reported from boreholes, dykes and a few volcanic rocks, area of the anomaly extends significantly south of their recon- mainly basalts, which are mostly in south Sumatra (Bellon et al. structed position of the Java Trench. The geological history of 2004). The Paleocene Kikim Volcanics include volcanic brec- the region is also much more complex than that expected by cias, tuffs, and basaltic to andesitic lavas. De Smet & Barber rotation of a single rigid SE Asian plate (Hall et al. 2008). (2005) interpreted a period of erosion in Sumatra between the The reconstruction of Hall (2002) offers an alternative Late Cretaceous and Early Eocene, with some volcanic activity interpretation of the deep anomaly beneath SE Asia. Both the in the area of the Barisan Mountains, although they noted that upper and lower mantle reveal the importance of long-term the age of the volcanic rocks is poorly constrained. Middle to subduction at the Indonesian margins. However, most of what Upper Eocene volcanic rocks are known from a few parts of is observed in the mantle records the northward movement of West Sumatra (Crow 2005). They include subaerial pyroclastics Australia during the Cenozoic, which began to move at a and lavas interpreted as arc volcanics in Aceh, and volcaniclas- significant rate only from about 45 Ma (Royer & Sandwell tic sediments. K–Ar and zircon fission track ages are less than 1989). There is no evidence for a similar series of Tethyan 47 Ma. In Sumatra, prolonged erosion was followed in about oceans to those subducted north of India, consistent with the Middle Eocene by a resumption of volcanic activity which the absence of subduction during the Late Cretaceous and became widespread from the Late Eocene. Late Eocene to Paleocene. The position of the deep lower mantle anomaly fits Early Miocene volcanic activity is indicated by widespread and well with that expected from Indian–Australian lithosphere abundant volcanic rocks throughout Sumatra. subducted northward at the Java margin since about 45 Ma, and In Java there is an important Eocene unconformity and few proto-South China Sea lithosphere subducted southward at the exposures of older rocks. Central Java includes the most north Borneo trench since 45 Ma, with contributions from extensive area of basement rocks, the Lok Ulo Complex several other subduction zones within east Indonesia, such as (van Bemmelen 1949; Asikin et al. 1992). This is regarded as the those associated with the Sulu Arc, and the Sangihe Arc. The imbricated product of Cretaceous deformation (e.g. Parkinson difference in subduction history north of India compared to et al. 1998; Wakita 2000) at a subduction margin that extended that north of Australia, with the change occurring at about from West Java, through the Lok Ulo Complex, to the Meratus 100
E, is the third major feature relevant to the formation of Mountains. The youngest rocks from the Lok Ulo Complex the sedimentary basins of Sundaland. contain Campanian–Maastrichtian radiolaria with ages of 70–80 Ma (Wakita et al. 1994). The Lok Ulo Complex is IGNEOUS ACTIVITY FROM THE LATE overlain by the Eocene–Oligocene Karangsambung and CRETACEOUS TO EOCENE Totogan Formations, which include scaly clays with nummulitic limestone blocks, polymict conglomerates and basalt blocks, Typically, plate tectonic reconstructions have assumed subduc- interpreted as deep-water olistostromes (A.H. Harsolumakso, tion was underway at the Sunda Trench at least by the Early pers. comm. 2005) or mud diapirs (A.J. Barber, pers. comm. Eocene (e.g. Hall 1996, 2002) or from the Late Cretaceous (e.g. 2008). They lack abundant volcanic material but do contain Metcalfe 1996; Sribudiyani et al. 2003; Barber et al. 2005; large amounts of quartzose debris. In West Java the oldest Whittaker et al. 2007). There is abundant evidence for rocks are in the Ciletuh area where there are exposures of subduction-related magmatism since about 45 Ma from ‘pre–Tertiary’ (van Bemmelen 1949) peridotites, serpentinites Sumatra eastwards but, in contrast, there is little volcanic record and gabbros with chloritic schists interpreted as an ophiolitic in the expected position of the volcanic arc during the Late tectonic melange (e.g. Parkinson et al. 1998; Martodjojo et al. 136 R. Hall

Fig. 6. Distribution of (A) volcanic rocks and (B) minor intrusions in southern Sundaland with ages between 80 and 45 Ma. Sources are cited in the text. The shaded area is the position of the Early Cretaceous arc. The total number of dated rocks is small (63) but probably does reflect the abundance of Late Cretaceous to mid-Eocene volcanic activity.

1978). K–Ar dating provided few results due to alteration tuffs and greywackes (91 to 65 Ma) which rest unconformably (Schiller et al. 1991). A basalt pebble yielded a Late Cretaceous on the older rocks and have a molasse character (Yuwono et al. age, and a gabbro gave Paleocene to Middle Eocene ages. These 1988). These rocks are intruded by basaltic to dacitic dykes and rocks are probably overlain, although subsequently juxtaposed gabbroic to granitic stocks with K–Ar ages from 874Mato tectonically (Clements & Hall 2007), by the Middle Eocene 724 Ma, interpreted by Yuwono et al. (1988) to be Ciletuh Formation, which includes angular volcaniclastic subduction-related, based on their chemistry. The Manunggul material, ophiolitic and chert debris, rare amphibolites, blocks Formation passes transitionally into the Tanjung Formation of nummulitic limestones, and some volcaniclastic sandstones, (Yuwono et al. 1988) which consists predominantly of incorporated when incompletely lithified. They are interpreted quartzose clastic sediments and coals. This was originally as deposits of a deep-marine forearc setting (Schiller et al. 1991; interpreted to be Middle and Upper Eocene, but Bon et al. Clements & Hall 2007). In East Java there are a few, very small, (1996) interpreted the deepest part of the Tanjung Formation, exposures of basement greenschists and marbles (Smyth et al. dated from three wells, to be Upper Maastrichtian, based on 2007). The contact with overlying sedimentary rocks, including nannoflora previously regarded as reworked. They interpreted nummulitic limestones, is not exposed but is interpreted to the Maastrichtian–Paleocene sediments to be deposits of a be an unconformity. The oldest sedimentary rocks, in the passive margin, including minor Paleocene volcanic rocks, Nanggulan area, are fluviatile quartzose conglomerates and formed after the Cretaceous collision. North of the Meratus sandstones lacking volcanic debris. These terrestrial deposits Mountains, in the Kutai Basin, rifting that led to formation of pass rapidly up into Eocene marine deposits, which contain the Makassar Straits began in the Middle Eocene (Chambers & increasing amounts of volcaniclastic debris up-section. The Moss 1999; Moss & Chambers 1999) and the oldest Cenozoic stratigraphy indicates an important change in the Middle rocks resemble Upper Eocene quartzose clastic sequence in the Eocene, with initiation of volcanic activity after a prolonged Meratus Mountains. Upper Cretaceous volcanic rocks are period of emergence and erosion (Smyth et al. 2007). known from Kelian (Davies et al. 2008) in the Kutai Basin, In SE Borneo there is also a profound unconformity in the where an inlier of felsic volcaniclastics is surrounded by Eocene Meratus Mountains. The exposed basement includes ophiolites, terrestrial and shallow-marine sedimentary rocks. Zircons from Cretaceous volcaniclastic rocks (Sikumbang 1986, 1990; a pumice breccia have a U–Pb age of 67.80.3 Ma, considered Yuwono et al. 1988) and subduction-related high pressure–low to be the age of eruption (Davies, 2002). Detrital zircon temperature metamorphic rocks (Parkinson et al. 1998), which populations from the Kelian and Mahakam Rivers include were thrust together during a Late Cenomanian–Early Turonian Cretaceous ages from 126.3 to 67.6 Ma (Setiabudi et al. 2001). arc–continent collision (before c. 91 Ma). The Manunggul Throughout West Sulawesi, Upper Cretaceous formations Group (Sikumbang 1986) or Formation (Yuwono 1987; include material with an igneous provenance and record minor Yuwono et al. 1988) includes Upper Cretaceous volcanogenic volcanic activity (T.M. van Leeuwen, pers. comm., 2007). In Hydrocarbon basins in SE Asia 137 the Lariang and Karama area of West Sulawesi, the oldest Paleocene granites distributed across a very large area of Cenozoic sedimentary rocks rest in places on volcanic rocks Sundaland (Fig. 7). The majority of dated granites are Early and volcaniclastic sedimentary rocks that are mainly not well Cretaceous, and 215 of the 299 ages are older than 80 Ma. For dated and may be Cretaceous or Paleocene (Calvert 2000; obvious reasons there is little information from offshore, and Calvert & Hall 2007). In the northern part of West Sulawesi the there are some parts of Indochina for which there is little probable Campanian–Maastrichtian Latimojong Formation is information, such as Cambodia. None the less, it is difficult to composed dominantly of marine sedimentary rocks with basal- see linear belts that might be expected if they are subduction tic to dacitic flows (van Leeuwen & Muhardjo 2005) and there products, and many granites are far from probable subduction are volcaniclastic sandstones, tuffs and metabasites in the zones. Latimojong Mountains further south (A.J. Barber, pers. comm., Some granites could be part of an east-facing Andean 2007). Volcaniclastic rocks contain Precambrian to Cretaceous margin that continued south from South China. Cretaceous zircons and the youngest age population has U–Pb ages of granites are known in North China but it is still debated if they 80–120 Ma (van Leeuwen & Muhardjo 2005). In the southern were formed at a subduction margin (e.g. Lin & Wang 2006; Li part of West Sulawesi, similar rocks are dated in several & Li 2007; Yang et al. 2007). Jahn et al. (1976) argued that there places and assigned to a number of different formations. The was a Cretaceous (120–90 Ma) thermal episode in the SE China Balangbaru Formation (Hasan 1990, 1991) includes olisto- margin which may be related to west-directed Pacific subduc- stromes and turbidite fan deposits with a maximum age range tion. In South China, around Hong Kong, acid magmatism of Turonian to Maastrichtian age (91–65 Ma). The Marada ceased in the Early Cretaceous (Sewell et al. 2000) but mid- Formation (van Leeuwen 1981) is Campanian–Maastrichtian Cretaceous granites are reported from Vietnam (Nguyen et al. and includes distal turbidites which contain quartz, fresh 2004; Thuy et al. 2004) with youngest ages of 88 Ma. If this was feldspar and andesite fragments as well as volcanic flows or part of an Andean margin it is unclear if and where it continued sills. to the south. Unconformably above the Balangbaru Formation is the Alla The north–south belt of granites that follows the Thailand– or Bua Formation (Sukamto 1982, 1986; Yuwono 1987), Burma border is plausibly related to NE- or east-directed consisting of volcanic and intrusive rocks with K–Ar ages subduction of the Indian plate (e.g. Mitchell 1993; Barley et al. ranging from 65–58 Ma, interpreted as subduction-related 2003). Early Cretaceous granites continue south into the Malay (Elburg et al. 2002). This passes upwards into the marginal peninsula and Sumatra (Fig. 7A) and could be related to this marine coal-bearing siliciclastic rocks of the ?Lower–Middle subduction. Eocene Malawa Formation. Further east are the Middle to Granite magmatism in Borneo might be explained as the Upper Eocene Langi Volcanics (van Leeuwen 1981), which are product of flat-slab subduction from the west or south, but the predominantly andesitic volcanics with a typical arc geochem- positions of the Cretaceous arcs of southern Sundaland are well istry (Elburg et al. 2002); some volcaniclastic rocks in the lower known in Sumatra, Java and SE Borneo (Hamilton 1979; part contain zircons with a fission track age of 622 Ma. The Parkinson et al. 1998; Barber et al. 2005) and are far outboard of Langi Volcanics are intruded by a tonalite/granodiorite with a most of the granites. The Cretaceous granites in the Schwaner K–Ar age of 52–50 Ma and pass up into Upper Eocene Mountains (Williams et al. 1988) and western Sarawak (Tate limestones. 2001) have been interpreted as the product of Andean-type The interpretation of these sequences is not entirely clear. A magmatism associated with subduction dipping beneath post-collision passive margin setting has been suggested (Hasan Borneo. If SE Sundaland was rotated by 90
from its present 1990, 1991; Wakita et al. 1996) for the lower part of the position, as suggested by palaeomagnetic studies of Borneo Balangbaru Formation but igneous debris in the upper part is (Fuller et al. 1999), it is possible that the Schwaner granites suggested to be derived from a continental or magmatic arc and could be the product of subduction at the East Asian margin. may indicate a forearc setting (van Leeuwen 1981). The Alternatively, if SW Borneo is an accreted continental fragment geochemistry of the Paleocene and Lower Eocene igneous that originated in the south, it is possible that granite magma- rocks is generally interpreted to indicate a resumption of tism was associated with south-directed subduction during its subduction after Cretaceous collision, and Hasan (1990) inter- northward movement in the Early Cretaceous. preted a Late Paleocene–Early Eocene arc, but, if this was the The granites older than about 80 Ma may thus be explained case, the episode of subduction seems to have been short lived. by subduction of the Indian Plate or Pacific plates. However, All these rocks are overlain by sedimentary sequences typical of the younger granites in the area of Sumatra, Java and Borneo marginal and shallow marine conditions, including platform are less abundant and scattered across a wide area. A possible carbonates (Wilson et al. 2000), suggesting widespread rifting explanation is that they are products of collisional thickening. around the present Makassar Straits, which began in the Middle Further north in Sundaland, younger granites have been inter- Eocene (Moss & Chambers 1999; Calvert & Hall 2007). preted as the product of thickening following continental On Sumba there are Upper Cretaceous–Paleocene rocks of collision (Barley et al. 2003). It is suggested here that Late the Lasipu Formation resembling the deep-marine turbidites of Cretaceous and Paleocene, and possibly some of the wide- West Sulawesi in which there are some volcanic rocks (Burollet spread Early Cretaceous, granites of Borneo and the Sunda & Salle 1981). Abdullah et al. (2000) identified two calc- Shelf represent post-collisional magmatism following Creta- alkaline magmatic episodes by K–Ar dating, one Santonian– ceous accretion of the SW Borneo continental fragment or the Campanian (86–77 Ma) and the other Maastrichtian–Paleocene East Java–West Sulawesi continental fragment (see below). (71–56 Ma), which they interpreted as the result of subduction This would account for their widespread distribution. at the Sundaland margin producing an Andean magmatic arc. However, the area of volcanic activity is small. LATE CRETACEOUS TO MIDDLE EOCENE TECTONIC SETTING Widespread Cretaceous granite magmatism Many authors have assumed or implied that subduction at the In contrast to the paucity of volcanic rocks of Late Cretaceous Sundaland active margin was continuous through the Late and Early Cenozoic age, there are abundant Cretaceous and Mesozoic into the Cenozoic (e.g. Yuwono et al. 1988; Metcalfe 138 R. Hall

1996; Soeria-Atmadja et al. 1994, 1998; Abdullah et al. 2000; Sribudiyani et al. 2003) with an Andean magmatic arc stretching from Sumatra to West Sulawesi. Most granite magmatism in Indonesia that could be associated with an Andean-margin is older than 80 Ma. Furthermore, as observed above, there is little evidence of volcanic activity in Sumatra, none in Java, very little in SE Borneo, and only in West Sulawesi and Sumba can a case be made for subduction-related volcanic activity. Vol- canic rocks are mainly flows or sills associated with deep- marine turbidites, and some volcaniclastic debris could be reworked from older arc rocks. The arc itself is not seen. Volcanic activity had ceased by the end of the Eocene in SW Sulawesi, although probably continued into the Oligocene further north; its distribution in time and space suggests that it was localized and intermittent, and radiometric age dates and stratigraphic information suggest little or no volcanism between 30 and 19 Ma (T.M. van Leeuwen, pers. comm. 2007). The arguments for subduction-related volcanic activity are based on the subduction-character of the geochemistry, but the subduc- tion signature could simply reflect post-collisional magmatism (Macpherson & Hall 2002). However, even if there was subduction beneath Sumba and West Sulawesi this does not require subduction in other parts of the Indonesian margin. In contrast, some authors have either explicitly suggested that parts of the Sundaland margin were passive from the Late Cretaceous to the Eocene, or implied a passive margin by identifying Cenozoic resumption of subduction (e.g. Hamilton 1979; Hasan 1990, 1991; Daly et al. 1991; Bon et al. 1996; Carlile & Mitchell 1994; Wakita et al. 1996; Parkinson et al. 1998). Parkinson et al. (1998) suggested that subduction ceased in the Cretaceous after collision of a Gondwana continental fragment that is now beneath most of West Sulawesi. Carlile & Mitchell (1994) surmised that a collision of the Woyla Arc in Sumatra was connected to collision and ophiolite emplacement in the Meratus Mountains. The age and character of volcanic and sedimentary rocks from SE Borneo and Sulawesi are consistent with a major change in regime at about 90 Ma following collision. Smyth et al. (2005, 2007) have shown that there is a continental crust beneath the Southern Mountains of East Java, and Smyth et al. (2007) proposed that a continental fragment collided in the Cretaceous and terminated subduction. The ages of radiolaria in accreted deep-marine sediments in Central Java show the youngest subduction-related rocks are about 80 Ma. It is therefore suggested here that subduction ceased all around the south Sundaland margin in the Late Cretaceous, at about 90 to 80 Ma (Fig. 8), and was not resumed until the Middle

Fig. 7. Distribution of Cretaceous granites in southern Sundaland. There may be more Cretaceous granites offshore beneath the Sunda Shelf, based on personal communications from oil company geolo- gists. (A) Granites older than 110 Ma, suggested to be the age of docking of the SW Borneo block. (B) Granites with ages between 110 and 80 Ma, suggested to be the age of docking of the East Java–West Sulawesi block. (C) Cretaceous to Paleocene granites. The shaded area is the position of the Early Cretaceous arc. Unfilled squares on (A) are Cretaceous but with no precise age (ESCAP 1994; Koning 2003). All other samples are radiometrically dated (Kirk 1968; Gobbett & Hutchison 1973; Pupilli 1973; Patmosukismo & Yahya 1974; Garson et al. 1975; Bignell & Snelling 1977; Haile et al. 1977; Beckinsale et al. 1979; Ishihara et al. 1980; Putthapiban & Gray 1983; Putthapiban 1984, 1992; van de Weerd et al. 1987; Darbyshire & Swainbank 1988; Williams et al. 1988, 1989; Yuwono et al. 1988; Seong 1990; Krähenbuhl 1991; Cobbing et al. 1992; Nakapadungrat & Puttapiban 1992; Amiruddin & Trail 1993; Charusiri et al. 1993; de Keyser & Rustandi 1993; Nakapadungrat & Maneenai 1993; Pieters & Sanyoto 1993; Pieters et al. 1993; Supriatna et al. 1993; Wikarno et al. 1993; Dunning et al. 1995; Dirk 1997; Hartono 1997; Utoyo 1997; Nguyen et al. 2004; Cobbing, 2005). Hydrocarbon basins in SE Asia 139

about 45 Ma (Royer & Sandwell 1989). Hence, there is no requirement for subduction beneath Indonesia and, indeed, the only way in which subduction could have been maintained during the Late Cretaceous and Early Cenozoic is to propose a hypothetical spreading centre between Australia and Sundaland which moved northward until it was subducted (e.g. Whittaker et al. 2007). Ridge subduction is often suggested to produce slab windows associated with volumetrically or compositionally unusual magmatism (e.g. Thorkelson & Taylor 1989; Hole et al. 1995; Thorkelson 1996; Gorring & Kay 2001). A slab window should have swept westward beneath Java and Sumatra during the Late Cretaceous and Paleocene according to the Whittaker et al. (2007) model, but there is no evidence for it; indeed, as observed above, there is no magmatism of this age in Java, and almost none in Sumatra. Thus, the new view proposed here of the large-scale tectonic setting during the Late Cretaceous and Early Cenozoic between India and SE Asia is that it was markedly different in the west compared to the east. West of about 100
E, India was moving rapidly northward and was yet to collide with Asia. East of about 100
E, there was no subduction. Australia was still far to the south and, although Australia–Antarctica separation had begun in the Cretaceous, the rate and amount was small until the Eocene. The difference between east and west implies a broadly transform boundary between the Indian and Australian Fig. 8. Reconstruction for the Late Cretaceous after collision of the plates at about 100
E. Such a feature is supported by anomaly SW Borneo block (SWB), and the later addition of the East Java (EJ) ages on the unsubducted Indian Plate in the Wharton Basin and West Sulawesi (WS) blocks (shaded dark) which terminated south of Sumatra where there are large distances between subduction beneath Sundaland. The inferred positions of these blocks on the West Australian margin in the Late Jurassic at about anomalies across fracture zones indicating northward transform 155 Ma are shown by the numbered codes (SWB155, WS155 and offset of the Late Cretaceous to Eocene spreading centre of EJ155). A transform or very leaky transform spreading centre is c. 1700 km (anomaly 28) at 90
E and a further c. 1100 km inferred to have separated the Indian and Australian Plates between (anomaly 28) between 90
E and 100
E (Sclater & Fisher 1974) 80 and 45 Ma as India moved rapidly northwards. or a total of c. 2000 km (anomaly 28) between the end Cretaceous spreading centre west of 90
E and that east of Eocene, at about 45 Ma. The very limited amount of volcanic 100
E (Royer & Sandwell 1989). Similar large offsets are activity between 90 and 45 Ma is interpreted as localized suggested to have continued north on the now subducted post-collisional magmatism, with the exception of West boundary between the Indian and Australian Plates (Fig. 8). Sulawesi and Sumba where there was some west-directed At the beginning of the Cenozoic there was no northward subduction. subduction, and Sundaland is interpreted to have been an A similar scenario can be inferred for the north side of the elevated continent due to the Cretaceous collisions of conti- Sundaland promontory. Deep-marine sediments of the nental blocks. South of Sumatra and Java, east of about 100
E, Cretaceous–Eocene Rajang Group form much of the Central it is suggested that there was a passive margin. This passive Borneo Mountains and Crocker Ranges in north Borneo and margin continued all round eastern Sundaland, which was have been widely interpreted as deposits of an active margin separated from South China by the proto-South China Sea. The (Haile 1969, 1974; Hamilton 1979; Holloway 1982; Hutchison margins changed from passive to active in the Eocene as 1973, 1989, 1996a, b; Williams et al. 1988, 1989). According to Australia began to move rapidly north. South-directed subduc- Hutchison (1996b), deposition of Rajang Group sediments was tion began beneath north Borneo while north-directed subduc- terminated by a Sarawak orogeny suggested to represent an tion began south of Sumatra and Java. intra-Eocene collision between a Balingian–Luconia and the Schwaner Mountains continents. In contrast, Moss (1998) EOCENE RESUMPTION OF SUBDUCTION AND presented evidence that the Rajang Group sediments were ITS CONSEQUENCES deposited at a passive margin. Thus, an alternative interpreta- tion of the Late Cretaceous to Eocene setting is that the Only from about 45 Ma did Australia begin to separate signifi- Sarawak ‘orogeny’ marks the Middle Eocene initiation of cantly from Antarctica, and to move rapidly northwards, and subduction of the proto-South China Sea beneath northern this caused subduction to resume at the Sundaland margins. Borneo, at the former passive margin, rather than a collision. The resumption of subduction initiated an active margin on the The new subduction zone dipped towards the southeast and south side of Sundaland forming the Sunda Arc, and another was active from the Eocene until the Early Miocene (e.g. Tan & active margin on the north side of Sundaland in north Borneo. Lamy 1990; Hazebroek & Tan 1993; Hall 1996; Hutchison et al. In most of Sumatra, volcanic activity became widespread from 2000). the Middle Eocene (Crow 2005). In Java, volcanic activity Furthermore, considering tectonics at a much larger scale, began in the Middle Eocene to form an arc that ran the length although there is good evidence from magnetic anomalies south of the island (Hall & Smyth 2008; Smyth et al. 2008; Clements of India for its rapid northward movement in the Late et al. 2009). In Sulawesi the Langi andesitic volcanics (van Cretaceous and Early Cenozoic, and hence subduction to the Leeuwen 1981; Elburg et al. 2002) may represent a Middle to north of India, the magnetic anomalies south of Australia Late Eocene episode of subduction-related volcanism. On indicate very slow separation of Australia and Antarctica until Sumba there was a significant episode of Eocene to Oligocene 140 R. Hall volcanism (Abdullah et al. 2000). The Sunda Arc continued east this resembles the situation south of India at the present day into the Pacific (Hall 2002). (Martinod & Molnar 1995). In this case, it is easier to deform Subduction also resumed on the north side of the Sundaland continental Asia than break the plate (Stern 2004). In the two promontory at about 45 Ma, and an active margin ran from other cases, either an Atlantic-type passive margin evolves over Sarawak east towards the Philippines (Hall 1996, 2002). In a long period to form a trench or, in the other, the continent north Borneo, in the Eocene to Early Miocene, there was collapses towards the ocean, producing back-arc extension and southeast-directed subduction (Hall & Wilson 2000; Hutchison subduction, resembling the Mediterranean. The result depends et al. 2000) and the Crocker Fan (van Hattum et al. 2006) on the brittle and ductile strength of the passive margin, the formed above the subduction zone at the active margin. There negative buoyancy of the oceanic lithosphere, and the horizon- was relatively little Eocene to Early Miocene subduction-related tal body forces between continent and ocean. Mart et al. (2005) magmatism (Kirk 1968; Hutchison et al. 2000; Prouteau et al. also experimented with analogue models, but in a centrifuge, 2001) in Borneo, probably because the proto-South China Sea and suggested that lateral density differences at continental narrowed westwards (Hall 1996, 2002). margins may influence the initiation of subduction. However, the most important effect was the initiation of McKenzie (1977), Mueller & Phillips (1991) and Toth & widespread rifting throughout Sundaland leading to subsidence Gurnis (1998) all included inclined pre-existing faults in their and accumulation of vast amounts of sediment in sedimentary models, but Mueller & Phillips (1991) differed in their estimate basins. It is suggested here that this rifting was a response to the of resisting stresses on the faults and consequently found regional stresses imposed on Sundaland during the breaking of subduction initiation to be very unlikely. McKenzie (1977) and the plate which was required in order to begin subduction. Toth & Gurnis (1998) agreed on the magnitude of the stresses required, but McKenzie (1977) concluded that ridge-push SUBDUCTION INITIATION forces were insufficient to cause subduction initiation, whereas Toth & Gurnis (1998) argued that they were sufficient, and that Starting subduction is widely considered to be a very difficult combined with additional forces from adjacent subduction process (McKenzie 1977; Mueller & Phillips 1991) for which zones, subduction initiation is not difficult and expected to be the dynamics remain poorly understood (Cloetingh et al. 1982; common in the Western Pacific. Observations around SE Asia Toth & Gurnis 1998), and has been described as a fundamental, where there are numerous young subduction zones that have yet poorly understood, process (Hall et al. 2003) or as one of initiated in the last 15 Ma, including the Manila, Negros, the unresolved problems of plate tectonics (Regenaur-Lieb et al. Cotobato, North Sulawesi and Philippine Trenches (e.g. 2001). None the less, the process must occur regularly and Cardwell et al. 1980; Karig 1982; Hall 1996, 2002), support this continuously, since long-lived subduction zones disappear and conclusion. All have developed at the boundaries between new ones form in other places (Toth & Gurnis 1998). Since ocean crust and thickened arc crust, typically at the edges of McKenzie’s (1977) demonstration that creating trenches is small basins, where there is both a topographic and buoyancy difficult, the problem has been investigated theoretically using contrast. numerical and analogue modelling, and most studies have concentrated on breaking a plate in two types of tectonic setting: within an oceanic plate and at a passive continental SETTING OF BASIN FORMATION margin. There is still considerable uncertainty. It is generally agreed Features that have been identified in different models as that the stresses required to initiate subduction are very large important or critical were present during the Eocene at the (McKenzie 1977; Cloetingh et al. 1982; Mueller & Phillips 1991) Sundaland margins, including pre-existing dipping faults, bathy- and, therefore, there have been many suggestions that oceanic metric and buoyancy contrasts, weak serpentinized zones, lithosphere may break at pre-existing zones of weakness, such and probable considerable sediment loads. Early Cretaceous as transform faults and fracture zones (Toth & Gurnis 1998; Sundaland had been surrounded by active margins and Karig Hall et al. 2003), especially those that are serpentinized (Hilairet (1982) identified former subduction zone margins which he et al. 2007). Lateral buoyancy contrasts may also be important, called ‘deactivated continental or arc margins’ to be likely sites such as might be found at the edges of large oceanic plateaux of subduction initiation. At about 45 Ma, Australia began to (Niu et al. 2003). In numerical modelling the assumption of separate rapidly from Antarctica, hence increasing ridge-push rheology is important; a non-Newtonian viscosity may make stresses on the Sundaland margin. SE Asia today, and during subduction initiation easier (Billen & Hirth 2005) and conver- the Cenozoic, has been the site of exceptionally high rates of gence rate is also a significant factor (Hall et al. 2003; Billen & sediment supply (e.g. Milliman et al. 1999; Hall & Nichols 2002; Hirth 2005). Suggate & Hall 2003; Hall & Morley 2004), and it is likely that All modelling confirms that old passive margins are difficult much of Sundaland was elevated following Cretaceous colli- to turn into subduction zones. Increasing the age of passive sions. Thus, a considerable sediment load at the Sundaland margin does not make it easier to initiate subduction (Cloetingh margins is probable. et al. 1982) and the negative buoyancy of old oceanic litho- It is not easy to identify the consequences of subduction sphere is insufficient in itself to lead to trench formation. Again, initiation on the region from the present limited understanding pre-existing weaknesses may be important (Cohen 1982) and of the process and, therefore, the following scenario is some- faults may be reactivated if convergence is oblique (Erickson what speculative. I suggest that in the Middle Eocene, the 1993). Sediment loading of young lithosphere may play a part Sundaland region went into regional compression as Australia (Cloetingh et al. 1982), and sediment loading over long periods attempted to move north (Fig. 9). This would have meant (c. 100 Ma) may trigger subduction (Regenaur-Lieb et al. 2001). approximate N–S compression and, in consequence, approxi- Water may play an important role in weakening young litho- mately E–W extension, causing basins to form. The local sphere beneath a sediment load (Regenaur-Lieb et al. 2001). extension direction varied considerably, initially because of Faccenna et al. (1999) described three scenarios based on variations in basement fabric and, later, because once subduc- analogue modelling. The first produces only folding of oceanic tion began, these were augmented by other forces around lithosphere and no subduction is initiated at the passive margin; Sundaland due to the different types and orientations of plate Hydrocarbon basins in SE Asia 141

Fig. 9. The situation just before and just after subduction began beneath Sundaland at about 45 Ma. The initiation of subduction required the plate to be broken at the Sundaland continental margin and it is suggested that compression induced broadly E–W extensional stresses, which were locally re-orientated by basement structures. After subduction was initiated, plate edge forces became increasingly important. boundaries. There has been little work on topographic effects reactivation of different structures in the various basins at as subduction begins, although Toth & Gurnis (1998) showed different times, and resulting in changing orientations of faults, that in their models a long wavelength depression developed on multiple episodes of extension, and inversion. For example, the the overriding plate with a wavelength of c. 400 km. All the extension direction observed in the Nam Con Son and Cuu models, numerical and analogues, have used simple and typical Long basins is likely to reflect an interaction of the regional strengths for different types of lithosphere but, as summarized stresses imposed by subduction initiation, basement structures above, Sundaland is not typical (Hall & Morley 2004) and there in the Vietnam margin, slab-pull forces due to southeast- is a very large region of weak lithosphere extending more than directed subduction of the proto-South China Sea, and far-field 900 km to the north of the Sunda Trench (Hyndman et al. 2005; effects of India–Asia convergence. The tectonic development Currie & Hyndman 2006) where plate boundary forces are of SE Asia in the last 45 Ma (Hall 2002), involving subduction, greater than the strength of the plate in compression. hinge movements, arc and microcontinent collisions, and new Thus, once subduction had started it is likely that stresses in ocean basin formation, led to a complex and frequently different parts of Sundaland varied considerably, leading to changing distribution of forces at the Sundaland margin; Hall & 142 R. Hall

Morley (2004) illustrated these changing forces in a schematic are thanked for suggestions and comments on some of the ideas in way for different intervals during the Cenozoic and Figure 9 this paper. shows the possible forces that influenced basin formation and orientation of local extensional stresses just before and just REFERENCES after subduction began. The subsequent development of the basins, including such features as relative age and sedimentary Abdullah, C.I. Rampnoux, J.–P. Bellon, H. Maury, R.C. & Soeria-Atmadja, R. fill, importance of continental rift inheritance for source and 2000. The evolution of Sumba Island (Indonesia) revisited in the light of reservoir distribution, and heat flow histories, is described and new data on the geochronology and geochemistry of the magmatic rocks. Journal of Asian Earth Sciences, 18, 533–546. discussed elsewhere (e.g. Williams et al. 1995; Howes & Noble Aitchison, J.C. Ali, J.R. & Davis, A.M. 2007. When and where did India and 1997; Longley 1997; Petronas 1999; Hall & Morley 2004; Doust Asia collide? Journal of Geophysical Research, 112, B05423, DOI: 10.1029/ & Sumner 2007). 2006JB004706. Amiruddin & Trail, D.S. 1993. Geology of the Nangapinoh Sheet area, Kalimantan. Geological Research and Development Centre, Bandung, Indonesia. CONCLUSIONS Asikin, S. Handoyo, A. Busono, H. & Gafoer, S. 1992. Geology of the Kebumen Quadrangle, Jawa, 1:100,000. Geological Research and Development Centre, Although it is now widely accepted that the Sundaland basins Bandung, Indonesia. are dominantly extensional, the origin of the extensional forces Barber, A.J. & Crow, M.J. 2009. The structure of Sumatra and its implications remains uncertain. McKenzie-type models are widely applied, for the tectonic assembly of Southeast Asia and the destruction of Paleotethys. Island Arc, 18, 3–20. but the setting of SE Asian basins is very different from Barber, A.J. Crow, M.J. & Milsom, J.S.(eds) 2005. Sumatra: Geology, Resources intra-continental rifts like the North Sea, or passive margins like and Tectonic Evolution. Geological Society, London, Memoir, 31. those of the Atlantic, where such models were developed and Barley, M.E. Pickard, A.L. Zaw, K. Rak, P. & Doyle, M.G. 2003. Jurassic to work well. India–Asia collision was not the cause of basin Miocene magmatism and metamorphism in the Mogok metamorphic belt formation. Even if the indentor model is accepted, the timing and the India–Eurasia collision in Myanmar. Tectonics, 22, DOI: 10.1029/ of basin initiation is earlier than major movements on the 2002TC001398. Beckinsale, R.D. Suensilpong, S. Nakapadungrat, S. & Walsh, J.N. 1979. strike-slip faults and there are many other counter arguments Geochronology and geochemistry of granite magmatism in Thailand in discussed elsewhere (e.g. Morley 2002; Hall & Morley 2004; relation to a plate tectonic model. Journal of the Geological Society, London, 136, Hall et al. 2008). The collision is often identified as a cause in 529–540. rather a mystical manner with no clear indication of what was Bellon, H. Maury, R.C. Sutanto, Soeria-Atmadja, R. Cotten, J. & Polvé, M. happening, or where India was in relation to SE Asia. Further- 2004. 65 m.y.-long magmatic activity in Sumatra (Indonesia), from more, there is now doubt about the timing of India–Asia Paleocene to Present. Bulletin de la Société géologique de France, 175, 61–72. Ben-Avraham, Z. 1973. Structural framework of the Sunda Shelf and vicinity. PhD collision which may be significantly younger than previously thesis, Massachusetts Institute of Technology and Woods Hole Oceano- accepted. Basin formation was well underway before the end graphic Institute. Eocene age for continent–continent collision proposed by Ben-Avraham, Z. & Emery, K.O. 1973. Structural framework of Sunda Shelf. Aitchison et al. (2007). American Association of Petroleum Geologists Bulletin, 57, 2323–2366. Most of the models proposed for basin formation could be Ben-Avraham, Z. & Uyeda, S. 1973. The evolution of the China Basin and right in the sense that all could apply somewhere in the the Mesozoic paleogeography of Borneo. Earth and Planetary Science Letters, 18, 365–376. Sundaland region. The regional compression proposed here Bignell, J.D. & Snelling, N.J. 1977. K–Ar ages on some basic igneous rocks would cause extension by pure or simple shear, but a variety of from peninsular Malaysia and Thailand. Bulletin of the Geological Society of different local stress systems may result from other influences, Malaysia, 8, 89–93. such as local basement structure, reactivated faults, shape of the Bijwaard, H. & Spakman, W. 2000. Nonlinear global P-wave tomography by continental margin, type of crust on each side of the new plate iterated linearized inversion. Geophysical Journal International, 141, 71–82. boundary, and locally weak or strong layers within the litho- Bijwaard, H. Spakman, W. & Engdahl, E.R. 1998. Closing the gap between regional and global travel time tomography. Journal of Geophysical Research, sphere. The composite character of the Sundaland lithosphere 103, 30 055–30 078. means that all of these could apply and local principal stresses Billen, M.I. & Hirth, G. 2005. Newtonian versus non-Newtonian upper could vary considerably around the region. mantle viscosity: Implications for subduction initiation. Geophysical Research It is most likely that the plate broke by a tear propagating Letters, 32, DOI: 10.1029/2005GL023457. through the region from an existing plate boundary. This Bird, M.I. Pang, W.C. & Lambeck, K. 2006. The age and origin of the Straits suggests a west to east propagation of the tear from North of Singapore. Palaeogeography, Palaeoclimatology, Palaeoecology, 241, 531–538. Bird, M.I. Fifield, L.K. Teh, T.S. Chang, C.H. Shirlaw, N. & Lambeck, K. Sumatra eastwards. However, this is speculative, and the 2007. An inflection in the rate of early mid-Holocene eustatic sea-level rise: character and orientation of plate boundaries at the Pacific end A new sea-level curve from Singapore. Estuarine, Coastal and Shelf Science, 71, of the system are not known. The weakness of the lithosphere 523–536. in the region means that many basins did not subsequently have Bock, Y. Prawirodirdjo, L. & Genrich, J.F. et al. 2003. Crustal motion in simple histories. Many are characterized by changing stresses, Indonesia from Global Positioning System measurements. Journal of reflected, for example, in multiple episodes of extension and Geophysical Research, 108, 2367, DOI: 10.1029/2001JB000324. Bon, J. Fraser, T.H. Amris, W. Stewart, D.N. Abubakar, Z. & Sosromihardjo, different directions of extension. This is due to changing S. 1996. A review of the exploration potential of the Paleocene Lower balance of forces at plate edges and their interaction with Tanjung Formation in the South Barito Basin. Indonesian Petroleum Associ- basement fabric, all driven by multiple subduction-related ation, Proceedings 25th Annual Convention, 25, 69–79. processes. Subduction has been the most important influence Burollet, P.F. & Salle, C. 1981. A contribution to the geological study of on SE Asia for all of its history, and still is. Sumba (Indonesia). In: Indonesian Petroleum Association, Proceedings 10th Annual Convention, 331–344. The author is grateful to the University of London Central Research Burri, P. 1989. Hydrocarbon potential of Tertiary intermontane basins in Fund, the Royal Society and the Natural Environment Research Thailand. In: Thanasuthipitak, T. & Ounchanum, P. (eds) Proceedings of the Council for support, but especially to the consortium of oil International Symposium on Intermontane Basins: Geology and Resources, Chiang companies who have supported projects in SE Asia for many years. Mai, Thailand, 3–12. Thanks to colleagues in Indonesia at the Pusat Survei Geologi Busby, C.J. & Ingersoll, R.V. (eds) 1995. Tectonics of Sedimentary Basins. Bandung, Lemigas, Indonesian Institute of Sciences, and Institut Blackwell Science, Cambridge. Teknologi Bandung, and many colleagues, friends and students in Calvert, S.J. 2000. The Cenozoic geology of the Lariang and Karama regions, western the UK, Europe and SE Asia. Theo van Leeuwen and Tony Barber Sulawesi, Indonesia. PhD thesis, University of London. Hydrocarbon basins in SE Asia 143

Calvert, S.J. & Hall, R. 2007. Cenozoic evolution of the Lariang and Karama Doust, H. & Sumner, H.S. 2007. Petroleum systems in rift basins – a regions, North Makassar Basin, western Sulawesi, Indonesia. Petroleum collective approach in Southeast Asian basins. Petroleum Geoscience, 13, Geoscience, 13, 353–368. 127–144. Cardwell, R.K. & Isacks, B.L. 1978. Geometry of the subducted lithosphere Dunning, G.R. Macdonald, A.S. & Barr, S.M. 1995. Zircon and monazite beneath the Banda Sea in eastern Indonesia from seismicity and fault plane U–Pb dating of the Doi Inthanon core complex, northern Thailand: solutions. Journal of Geophysical Research, 83, 2825–2838. implications for extension within the Indonesian orogen. Tectonophysics, 251, Cardwell, R.K. Isacks, B.L. & Karig, D.E. 1980. The spatial distribution of 197–215. earthquakes, focal mechanism solutions and subducted lithosphere in the Elburg, M. van Leeuwen, T. Foden, J. & Muhardjo. 2002. Origin of Philippines and northeast Indonesian islands. In: Hayes, D.E. (ed.) The geochemical variability by arc–continent collision in the Biru area, South- Tectonic and Geologic Evolution of Southeast Asian Seas and Islands. American ern Sulawesi (Indonesia). Journal of Petrology, 43, 581–606. Geophysical Union, Geophysical Monograph, 23, 1–35. Elburg, M. van Leeuwen, T. Foden, J. & Muhardjo. 2003. Spatial and Carlile, J.C. & Mitchell, A.H.G. 1994. Magmatic arcs and associated gold and temporal isotopic domains of contrasting igneous suites in western and copper mineralization in Indonesia. Journal of Geochemical Exploration, 50, northern Sulawesi, Indonesia. Chemical Geology, 199, 243–276. 91–142. Engdahl, E.R. van der Hilst, R. & Buland, R. 1998. Global teleseismic Chambers, J.L.C. & Moss, S.J. 1999. Depositional modelling of rift episodes earthquake relocation with improved travel times and procedures for depth and inversion in the Kutai Basin, Kalimantan, Indonesia. Petroleum Explo- determination. Seismological Society of America Bulletin, 88, 722–743. ration Society of Australia Journal, 27, 9–24. Erickson, S.G. 1993. Sedimentary loading, lithospheric flexure, and subduc- Charusiri, P. Clark, A.H. Farrar, E. Archibald, D. & Charusiri, B. 1993. tion initiation at passive margins. Geology, 21, 125–128. Granite belts in Thailand: evidence from the 40Ar/39Ar geochrono- ESCAP. 1994. Geological Map of Cambodia 1:500,000. United Nations Econ- logical and geological syntheses. Journal of Southeast Asian Earth Sciences, 8, omic and Social Commission for Asia and the Pacific, Bangkok. 127–136. Eubank, R.T. & Makki, A.C. 1981. Structural geology of the Central Sumatra Clements, B. & Hall, R. 2007. Cretaceous to Late Miocene stratigraphic and back-arc basin. In: Indonesian Petroleum Association, Proceedings 10th Annual tectonic evolution of West Java. Paper IPA07-G-037, presented at the Convention, 153–196. Indonesian Petroleum Association, 31st Annual Convention. Faccenna, C. Giardini, D. Davy, P. & Argentieri, A. 1999. Initiation of Clements, B. Hall, R. Smyth, H.R. & Cottam, M.A. 2009. A new interpreta- subduction at Atlantic-type margins: Insights from laboratory experiments. tion of Java’s structure. Petroleum Geoscience, 15, 159–174. Journal of Geophysical Research, 104, 2749–2766. Cloetingh, S. Wortel, M.J.R. & Vlaar, N.J. 1982. Evolution of passive Fleming, K. Johnston, P. Zwartz, D. Yokoyama, Y. Lambeck, K. & Chappell, continental margins and initiation of subduction zones. Nature, 297, J. 1998. Refining the eustatic sea-level curve since the last glacial maximum 139–142. using far- and intermediate-field sites. Earth and Planetary Science Letters, 163, Cobbing, E.J. 2005. Granites. In: Barber, A.J. Crow, M.J. & Milsom, J.S. (eds) 327–342. Sumatra: Geology, Resources and Tectonic Evolution. Geological Society London, Fuller, M. Ali, J.R. Moss, S.J. Frost, G.M. Richter, B. & Mahfi, A. 1999. Memoirs, 31, 54–62. Paleomagnetism of Borneo. Journal of Asian Earth Sciences, 17, 3–24. Cobbing, E.J. Pitfield, P.E.J. Darbyshire, D.P.F. & Mallick, D.I. J. 1992. The Garson, M.S. Young, F.B. Mitchell, A.H.G. & Tait, B.A.R. 1975. The geology of granites of the South-East Asian tin belt. Overseas Memoir of the British the tin belt in peninsular Thailand around Phuket, Phangnga and Takua Geological Survey, 10. Pa. Institute of Geological Sciences, London, Overseas Division, Memoir, Cohen, C.R. 1982. Model for a passive to active continental margin transition; 1. implications for hydrocarbon exploration. American Association of Petroleum GEBCO. 2003. IHO–UNESCO, General Bathymetric Chart of the Oceans, Digital Geologists Bulletin, 66, 708–718. Edition 2003. World Wide Web Address: www.ngdc.noaa.gov/mgg/gebco. Cole, J.M. & Crittenden, S. 1997. Early Tertiary basin formation and the Geyh, M.A. Kudrass, H.R. & Streif, H. 1979. Sea-level changes during the development of lacustrine and quasi-lacustrine/marine source rocks on the late Pleistocene and Holocene in the Straits of Malacca. Nature, 278, Sunda Shelf of SE Asia. In: Fraser, A.J. Matthews, S.J. & Murphy, R.W. 441–443. (eds) Petroleum geology of SE Asia. Geological Society, London, Special Gobbett, D.J. & Hutchison, C.S. (eds) 1973. Geology of the Malay Peninsula Publications, 126, 147–183. (West Malaysia and Singapore). Wiley-Interscience, New York. Crow, M.J. 2005. Tertiary volcanicity. In: Barber, A.J. Crow, M.J. & Milsom, Gorring, M.L. & Kay, S.M. 2001. Mantle processes and sources of Neogene J.S. (eds) Sumatra: Geology, Resources and Tectonic Evolution. Geological Society, slab window magmas from southern Patagonia, Argentina. Journal of London, Memoirs, 31, 98–119. Petrology, 42, 1067–1094. Currie, C.A. & Hyndman, R.D. 2006. The thermal structure of subduction Haile, N.S. 1969. Geosynclinal theory and the organizational pattern of the zone back arcs. Journal of Geophysical Research, 111, B08404, DOI: 10.1029/ North-west Borneo geosyncline. Quarterly Journal of the Geological Society of 2005JB004024. London, 124, 171–194. Daly, M.C. Cooper, M.A. Wilson, I. Smith, D.G. & Hooper, B.G.D. 1991. Haile, N.S. 1974. Borneo. In: Spencer, A.M. (ed.) Mesozoic–Cenozoic orogenic Cenozoic plate tectonics and basin evolution in Indonesia. Marine and belts. Geological Society, London, Special Publications, 4, 333–347. Petroleum Geology, 8, 2–21. Haile, N.S. McElhinny, M.W. & McDougall, I. 1977. Palaeomagnetic data and Darbyshire, D.P.F. & Swainbank, I.G. 1988. Southeast Asia granite project – radiometric ages from the Cretaceous of West Kalimantan (Borneo), and geochronology of a selection of granites from Burma. Natural Environment their significance in interpreting regional structure. Journal of the Geological Research Council, Isotope Geology Centre Open File Report, 88/6. Society, London, 133, 133–144. Davies, A.G.S. Cooke, D.R. Gemmell, J.B. Van Leeuwen, T. Cesare, P. & Hall, C.E. Gurnis, M. Sdrolias, M. Lavier, L.L. & Muller, R.D. 2003. Hartshorn, G. 2008. Hydrothermal breccias and veins at the Kelian gold Catastrophic initiation of subduction following forced convergence across mine, Kalimantan, Indonesia: Genesis of a large epithermal gold deposit. fracture zones. Earth and Planetary Science Letters, 212, 15–30. Economic Geology, 103, 717–757. Hall, R. 1996. Reconstructing Cenozoic SE Asia. In: Hall, R. & Blundell, D.J. Davies, G.S. 2002. Geology and genesis of the Kelian gold deposit, East Kalimantan, (eds) Tectonic Evolution of SE Asia. Geological Society, London, Special Indonesia. PhD thesis, University of Tasmania. Publications, 106, 153–184. Davies, P.R. 1984. Tertiary structural evolution and related hydrocarbon Hall, R. 2002. Cenozoic geological and plate tectonic evolution of SE Asia occurrences, North Sumatra basin. In: Indonesian Petroleum Association, and the SW Pacific: computer-based reconstructions, model and anima- Proceedings 13th Annual Convention, 19–50. tions. Journal of Asian Earth Sciences, 20, 353–434. De Celles, P.G. & Giles, K.A. 1996. Foreland basin systems. Basin Research, 8, Hall, R. & Nichols, G. 2002. Cenozoic sedimentation and tectonics in 105–124. Borneo: climatic influences on orogenesis. In: Jones, S.J. & Frostick, L. de Keyser, F. & Rustandi, E. 1993. Geology of the Ketapang Sheet area, Kalimantan, (eds) Sediment Flux to Basins: Causes, Controls and Consequences. Geological 1:250,000. Geological Research and Development Centre, Bandung, Indo- Society, London, Special Publications, 191, 5–22. nesia. Hall, R. & Morley, C.K. 2004. Sundaland Basins. In: Clift, P. Wang, P. Kuhnt, de Smet, M.J. & Barber, A.J. 2005. Tertiary stratigraphy. In: Barber, A.J. W. & Hayes, D.E. (eds) Continent–Ocean Interactions within the East Asian Crow, M.J. & Milsom, J.S. (eds) Sumatra: Geology, Resources and Tectonic Marginal Seas. AGU Geophysical Monograph, 149, 55–85. Evolution. Geological Society, London, Memoirs, 31, 86–97. Hall, R. & Smyth, H.R. 2008. Cenozoic arc processes in Indonesia: identifi- Dirk, M.H.J. 1997. Penelitian batuan Granitik Batang Alai–Barabai–Hulu cation of the key influences on the stratigraphic record in active volcanic Sungai Tengah, Kalsel. Laporan Tahunan Proyek Kajian dan Informasi Geologi arcs. In: Draut, A.E. Clift, P.D. & Scholl, D.W. (eds) Formation and Tematik Tahun Anggaran 1996/1997. Puslitbang Geologi, Deparrment Applications of the Sedimentary Record in Arc Collision Zones. Geological Society Pertambangan dan Energi, Bandung, 1. of America Special Publication, 436, 27–54. 144 R. Hall

Hall, R. & Wilson, M.E.J. 2000. Neogene sutures in eastern Indonesia. Journal Krähenbuhl, R. 1991. Magmatism, tin mineralization and tectonics of the of Asian Earth Sciences, 18, 787–814. Main Range, Malaysian Peninsula: Consequences for the plate tectonic Hall, R. van Hattum, M.W.A. & Spakman, W. 2008. Impact of India– model of Southeast Asia based on Rb–Sr, K–Ar and fission track data. Asia collision on SE Asia: the record in Borneo. Tectonophysics, 451, Bulletin of the Geological Society of Malaysia, 29, 1–100. 366–389. Leloup, P.H. Arnaud, N. & Lacassin, R. et al. 2001. New constraints on the Hamilton, W. 1979. Tectonics of the Indonesian region. USGS Professional Paper structure, thermochronology, and timing of the Ailao Shan–Red River 1078. shear zone, SE Asia. Journal of Geophysical Research, 106, 6683–6732. Hanebuth, T. Stattegger, K. & Grootes, P.M. 2000. Rapid flooding of the Li, Z.-X. & Li, X.-H. 2007. Formation of the 1300 km-wide intracontinental Sunda Shelf: A late glacial sea-level record. Science, 288, 1033–1035. orogen and postorogenic magmatic province in Mesozoic South China: A Harland, W.B. Armstrong, R.L. Cox, A.V. Craig, L.E. Smith, A.G. & Smith, flat-slab subduction model. Geology, 35, 179–182. D.G. 1990. A Geologic Time Scale 1989. Cambridge University Press, Lin, W. & Wang, Q. 2006. Late Mesozoic extensional tectonics in the North Cambridge. China block: a crustal response to subcontinental mantle removal? Bulletin Hartono, U. 1997. Petrologi Batuan Gunungapi dan Ultrabasa, Daerah de la Société Géologique de France, 177, 287–297. Pegunungan Meratus, Kalsel. Laporan Tahunan Proyek Kajian dan Informasi Longley, I.M. 1997. The tectonostratigraphic evolution of SE Asia. In: Fraser, Geologi Tematik Tahun Anggaran 1996/1997. Puslitbang Geologi, Depart- A.J. Matthews, S.J. & Murphy, R.W. (eds) Petroleum Geology of Southeast Asia. ment Pertambangan dan Energi, Bandung, 1. Geological Society, London, Special Publications, 126, 311–339. Hasan, K. 1990. The Upper Cretaceous flysch succession of the Balangbaru Formation, Macpherson, C.G. & Hall, R. 2002. Timing and tectonic controls in the Southwest Sulawesi, Indonesia. PhD thesis, University of London. evolving orogen of SE Asia and the western Pacific and some implications Hasan, K. 1991. Upper Cretaceous flysch succession of the Balangbaru for ore generation. In: Blundell, D.J. Neubauer, F. & von Quadt, A. (eds) Formation, Southwest Sulawesi. In: Indonesian Petroleum Association, Proceed- The Timing and Location of Major Ore Deposits in an Evolving Orogen. Geological ings 20th Annual Convention, 183–208. Society, London, Special Publications, 204, 49–67. Hazebroek, H.P. & Tan, D.N.K. 1993. Tertiary tectonic evolution of the NW Madon, M.B. 1999. Plate tectonic elements and the evolution of Southeast Sabah continental margin. Bulletin of the Geological Society of Malaysia, 33, Asia. In: The Petroleum Geology and Resources of Malaysia. Petronas, Kuala 195–210. Lumpur, 59–76. Hilairet, N. Reynard, B. Wang, Y.B. Daniel, I. Merkel, S. Nishiyama, N. & Madon, M.B. & Watts, A.B. 1998. Gravity anomalies, subsidence history and Petitgirard, S. 2007. High-pressure creep of serpentine, interseismic defor- the tectonic evolution of the Malay and Penyu Basins (offshore Peninsular mation, and initiation of subduction. Science, 318, 1910–1913. Malaysia). Basin Research, 10, 375–392. Hole, M.J. Saunders, A.D. Rogers, G. & Sykes, M.A. 1995. The relationship Mart, Y. Aharonov, E. Mulugeta, G. Ryan, W. Tentler, T. & Goren, L. 2005. between alkaline magmatism, lithospheric extension and slab window Analogue modelling of the initiation of subduction. Geophysical Journal formation along continental destructive plate margins. In: Smellie, J.L. (ed.) International, 160, 1081–1091. Volcanism Associated with Extension at Consuming Plate Margins. Geological Martinod, J. & Molnar, P. 1995. Lithospheric folding in the Indian Ocean and Society, London, Special Publications, 81, 265–285. the rheology of the oceanic plate. Bulletin de la Société Géologique de France, Holloway, N.H. 1982. The stratigraphic and tectonic evolution of Reed Bank, 166, 813–821. North Palawan and Mindoro to the Asian mainland and its significance in Martodjojo, S. Suparka, S. & Hadiwasastra, S. 1978. Status Formasi Ciletuh the evolution of the South China Sea. American Association of Petroleum dalam evolusi Jawa Barat. Geologi Indonesia, 5, 29–38. Geologists Bulletin, 66, 1357–1383. McCourt, W.J. Crow, M.J. Cobbing, E.J. & Amin, T.C. 1996. Mesozoic and Howes, J.V.C. & Noble, R.A. (eds) 1997. Proceedings of the International Cenozoic plutonic evolution of SE Asia: evidence from Sumatra, Conference on Petroleum Systems of SE Asia & Australia, 21–23 May Jakarta, Indonesia. In: Hall, R. & Blundell, D.J. (eds) Tectonic Evolution of SE Asia. Indonesia. Indonesian Petroleum Association, Jakarta, Indonesia. Geological Society, London, Special Publications, 106, 321–335. Huchon, P. Lepichon, X. & Rangin, C. 1994. Indo-China peninsula and the McDougall, I. & Harrison, T.M. 1988. Geochronology and Thermochronology by the collision of India and Eurasia. Geology, 22, 27–30. 40Ar/39Ar Method. Oxford Monographs on Geology and Geophysics, Hutchison, C.S. 1973. Tectonic evolution of Sundaland: a Phanerozoic Oxford. synthesis. Bulletin of the Geological Society of Malaysia, 6, 61–86. McKenzie, D.P. 1977. The initiation of trenches: A finite amplitude instabil- Hutchison, C.S. 1989. Geological Evolution of South-East Asia. Oxford Mono- ity. In: Talwani, M. & Pitman, W.C. (eds) Island Arcs, Deep Sea Trenches and graphs on Geology and Geophysics, Clarendon Press, Oxford. Back-Arc Basins. American Geophysical Union, Washington DC, Maurice Hutchison, C.S. 1996a. South-East Asian Oil, Gas, Coal and Mineral Deposits. Ewing Series, 105, 57–61. Oxford Monographs on Geology and Geophysics, Oxford Science Publi- Metcalfe, I. 1990. Allochthonous terrane processes in Southeast Asia. cations, Clarendon Press, Oxford. Philosophical Transactions of the Royal Society of London, A331, 625–640. Hutchison, C.S. 1996b. The ‘Rajang Accretionary Prism’ and ‘Lupar Line’ Metcalfe, I. 1996. Pre-Cretaceous evolution of SE Asian Terranes. In: Hall, R. Problem of Borneo. In: Hall, R. & Blundell, D.J. (eds) Tectonic Evolution & Blundell, D.J. (eds) Tectonic Evolution of SE Asia. Geological Society, of SE Asia. Geological Society, London, Special Publications, 106, London, Special Publications, 106, 97–122. 247–261. Metcalfe, I. 1998. Palaeozoic and Mesozoic geological evolution of the SE Hutchison, C.S. 2005. Geology of North-West Borneo. Elsevier, Amsterdam, Asian region: multidisciplinary constraints and implications for biogeogra- The Netherlands. phy. In: Hall, R. & Holloway, J.D. (eds) Biogeography and Geological Evolution Hutchison, C.S. Bergman, S.C. Swauger, D.A. & Graves, J.E. 2000. A of SE Asia. Backhuys Publishers, Leiden, The Netherlands, 25–41. Miocene collisional belt in north Borneo: uplift mechanism and isostatic Michel, G.W. Yu, Y.Q. & Zhu, S.Y. et al. 2001. Crustal motion and block adjustment quantified by thermochronology. Journal of the Geological Society, behaviour in SE Asia from GPS measurements. Earth and Planetary Science London, 157, 783–793. Letters, 187, 239–244. Hyndman, R.D. Currie, C.A. & Mazzotti, S.P. 2005. Subduction zone Milliman, J.D. Farnsworth, K.L. & Albertin, C.S. 1999. Flux and fate of backarcs, mobile belts, and orogenic heat. GSA Today, 15, 4–10. fluvial sediments leaving large islands in the East Indies. Journal of Sea Ishihara, S. Sawata, H. Shibata, K. Terashima, S. Arrykul, S. & Sato, K. 1980. Research, 41, 97–107. Granites and Sn–W deposits of peninsular Thailand. In: Ishihara, S. & Mitchell, A.H.G. 1993. Cretaceous–Cenozoic tectonic events in the western Takenouchi, S. (eds) Granitic magmatism and related mineralization. Mining Myanmar (Burma)–Assam region. Journal of the Geological Society, London, Geology Special Issue, Society of Mining Geologists of Japan, 8, 223–242. 150, 1089–1112. Jahn, B.-M. Chen, P.Y. & Yen, T.P. 1976. Rb–Sr ages of granitic rocks in Morley, C.K. 2001. Combined escape tectonics and subduction rollback– southeastern China and their tectonic significance. Geological Society of backarc extension: a model for the Tertiary rift basins in Thailand, Malaysia America Bulletin, 87, 763–776. and Laos. Journal of the Geological Society, London, 158, 461–474. Karig, D.E. 1982. Initiation of subduction zones: Implications for arc Morley, C.K. 2002. A tectonic model for the Tertiary evolution of strike-slip evolution and ophiolite development. In: Leggett, J.K. (ed.) Trench-Forearc faults and rift basins in SE Asia. Tectonophysics, 347, 189–215. Geology. Geological Society, London, Special Publications, 10, 563–576. Moss, S.J. 1998. Embaluh group turbidites in Kalimantan: evolution of a Kirk, H.J.C. 1968. The igneous rocks of Sarawak and Sabah, Geological Survey remnant oceanic basin in Borneo during the Late Cretaceous to Palaeo- Borneo Region, Malaysia, Bulletin, 5. gene. Journal of the Geological Society, London, 155, 509–524. Koning, T. 2003. Oil and gas production from basement reservoirs: examples Moss, S.J. & Chambers, J.L.C. 1999. Tertiary facies architecture in the Kutai from Indonesia, USA and Venezuela. In: Petford, N. & McCaffrey, K.J.W. Basin, Kalimantan, Indonesia. Journal of Asian Earth Sciences, 17, 157–181. (eds) Hydrocarbons in Crystalline Rocks. Geological Society, London, Special Moulds, P.J. 1989. Development of the Bengkalis depression, central Sumatra Publications214, 83–92. and its subsequent deformation – A model for other Sumatran Grabens? Hydrocarbon basins in SE Asia 145

In: Indonesian Petroleum Association, Proceedings 18th Annual Convention, 217– Royer, J.-Y. & Sandwell, D.T. 1989. Evolution of the eastern Indian Ocean 246. since the Late Cretaceous: constraints from Geosat altimetry. Journal of Mueller, S. & Phillips, R.J. 1991. On the initiation of subduction. Journal of Geophysical Research, 94, 13 755–13 782. Geophysical Research, 96, 651–665. Sapiie, B. & Hadiana, M. 2007. Mechanism of some rift basins in the western Nakapadungrat, S. & Maneenai, D. 1993. The Phuket, Phangnga and Takua Indonesia. In: Indonesian Petroleum Association, 10th Annual Convention, 1–10. Pa tin-field, Thailand. Journal of Southeast Asian Earth Sciences, 8, 359–368. Schiller, D.M. Garrard, R.A. & Prasetyo, L. 1991. Eocene submarine fan Nakapadungrat, S. & Puttapiban, P. 1992. Granites and associated minerali- sedimentation in southwest Java. In: Indonesian Petroleum Association, Proceed- zation in Thailand. In: Proceedings of a National Conference on Geologic Resources ings 20th Annual Convention, 125–182. of Thailand: Potential for future development (Supplementary volume), 153– Sclater, J.G. & Fisher, R.L. 1974. Evolution of the East Central Indian Ocean, 171. with emphasis on the tectonic setting of the Ninetyeast Ridge. Geological Nguyen, T.T.B. Satir, M. Siebel, W. & Chen, S. 2004. Granitoids in the Dalat Society of America Bulletin, 85, 683–702. zone, southern Vietnam: age constraints on magmatism and regional Seong, K.T. 1990. K–Ar dating of micas from granitoids in the Kuala geological implications. International Journal of Earth Sciences, 93, 329–340. Lumpur – Seramban area. Bulletin of the Geological Society of Malaysia, 26, Niu, Y.L. Hara, M.J. & Pearce, J.A. 2003. Initiation of subduction zones as a 77–96. consequence of lateral compositional buoyancy contrast within the lithos- Setiabudi, B.T. Campbell, I.H. & Palin, M.J. 2001. Age of calc-alkaline phere: A petrological perspective. Journal of Petrology, 44, 851–866. magmatism associated with the Kelian gold deposit, Indonesia: an example Page, B.N.G. Bennett, J.D. Cameron, N.R. Bridge, D.M. Jeffrey, D.H. Keats, of zircon U-Pb dating by excimer ablation ICP-MS. In: A Hydrothermal W. & Thaib, J. 1979. A review of the main structural and magmatic Odyssey, New Developments in Metalliferous Hydrothermal Systems features of northern Sumatra. Journal of the Geological Society, London, 136, Research 569–579. Conference, 17–19 May James Cook University, Townsville, Australia, Parkinson, C.D. Miyazaki, K. Wakita, K. Barber, A.J. & Carswell, D.A. 1998. 185–186. An overview and tectonic synthesis of the pre-Tertiary very-high-pressure Sewell, R.J. Campbell, S.D.G. Fletcher, C.J.N. Lai, K.W. & Kirk, P.A. 2000. metamorphic and associated rocks of Java, Sulawesi and The Pre-Quaternary Geology of Hong Kong. Hong Kong Geological Survey, Kalimantan, Indonesia. Island Arc, 7, 184–200. Geological Memoir. Patmosukismo, S. & Yahya, I. 1974. The basement configuration of the Shaw, R.D. 1997. Some implications of Eurasian and Indo-Australian plate northwest Java area. In: Indonesian Petroleum Association, Proceedings 3rd Annual collision on the petroleum potential of Tertiary, intracratonic basins of Convention, 129–152. Southeast Asia. In: Howes, J.V.C. & Noble, R.A. (eds) Proceedings of Petronas. 1999. The Petroleum Geology and Resources of Malaysia. Petronas, Kuala the International Conference on Petroleum Systems of SE Asia & Australia, May Lumpur. 21–23 Jakarta, Indonesia. Indonesian Petroleum Association, Jakarta, Pieters, P.E. & Sanyoto, P. 1993. Geology of the Pontianak/Nangataman Sheet area, Indonesia, 63–80. Kalimantan 1:250,000. Geological Research and Development Centre, Siebert, L. & Simkin, T. 2002. Volcanoes of the World: an Illustrated Catalog of Bandung, Indonesia. Holocene Volcanoes and their Eruptions. Smithsonian Institution, Global Pieters, P.E. Abidin, H.Z. & Sudana, D. 1993. Geology of the Long Pahangai Volcanism Program Digital Information Series, GVP-3. World Wide Web sheet area, Kalimantan. Geological Survey of Indonesia, Directorate Address: http://www.volcano.si.edu/world/ of Mineral Resources, Geological Research and Development Centre, Bandung, Sikumbang, N. 1986. Geology and tectonics of Pre-Tertiary rocks in the Meratus Quadrangle 1716, 1:250,000. Mountains, South-East Kalimantan, Indonesia. PhD thesis, University of Polachan, S. Pradidtan, S. Tongtaow, C. Janmaha, S. Intarawijitr, K. & London. Sangsuwan, C. 1991. Development of Cenozoic basins in Thailand. Marine Sikumbang, N. 1990. The geology and tectonics of the Meratus Mountains, and Petroleum Geology, 8, 84–97. South Kalimantan, Indonesia. Geologi Indonesia, 13, 1–31. Prouteau, G. Maury, R.C. Sajona, F.G. Pubellier, M. Cotten, J. & Bellon, H. Simons, W.J.F. Socquet, A. & Vigny, C. et al. 2007. A decade of GPS in 2001. Le magmatisme post-collisionnel du Nord-Ouest de Bornéo, produit Southeast Asia: Resolving Sundaland motion and boundaries. Journal of de la fusion d’un fragment de croûte océanique ancré dans le manteau Geophysical Research, 112, B06420, DOI: 10.1029/2005JB003868. supérieur. Bulletin de la Société Géologique de France, 172, 319–332. Smyth, H. Hall, R. Hamilton, J.P. & Kinny, P. 2005. East Java: Cenozoic Pubellier, M. Rangin, C. Le Pichon, X. & DOTSEA working group. 2005. basins, volcanoes and ancient basement. In: Indonesian Petroleum Association, DOTSEA: Deep Offshore Tectonics of South East Asia. A synthesis of deep marine Proceedings 30th Annual Convention, 251–266. data in Southeast Asia. Mémoire de la Société Géologique de France. Smyth, H.R. Hamilton, P.J. Hall, R. & Kinny, P.D. 2007. The deep crust Pupilli, M. 1973. Geological evolution of South China Sea Area; tentative beneath island arcs: inherited zircons reveal a Gondwana continental reconstruction from borderland geology and well data. In: Indonesian fragment beneath East Java, Indonesia. Earth and Planetary Science Letters, Petroleum Association, Proceedings 2nd Annual Convention, 223–242. 258, 269–282. Putthapiban, P. 1984. Geochemistry and geochronology of Phuket granites, Phuket, Smyth, H.R. Hall, R. & Nichols, G.J. 2008. Early Cenozoic volcanic arc Thailand. PhD thesis, La Trobe University, Melbourne, Australia. history of East Java, Indonesia: the stratigraphic record of eruptions on a Putthapiban, P. 1992. The Cretaceous–Tertiary granite magmatism in the continental margin in a tropical setting. In: Draut, A.E. Clift, P.D. & Scholl, west coast of Peninsula Thailand and the Mergui Archipelago of D.W. (eds) Formation and Applications of the Sedimentary Record in Arc Collision Myanmar/Burma. In: Piancharoen, C. (ed.) Proceedings of a National Zones. Geological Society of America Special Publication, 436, DOI: 8 Conference on Geologic Resources of Thailand: Potential for Future Development, 10.1130/2007.2436(10). Supplementary Volume, 17–24 November Bangkok, Thailand, 75–88. Soeria-Atmadja, R. Maury, R.C. Bellon, H. Pringgoprawiro, H. Polvé, M. & Putthapiban, P. & Gray, C.M. 1983. Age and tin–tungsten mineralization of Priadi, B. 1994. Tertiary magmatic belts in Java. Journal of Southeast Asian the Phuket granites, Thailand. In: Geology and Mineral Resources of Thailand, Earth Sciences, 9, 13–17. 19–28 November, Bangkok, 1–10. Soeria-Atmadja, R. Suparka, S. Abdullah, C. Noeradi, D. & Zutanito. 1998. Rangin, C. Le Pichon, X. & Mazzotti, S. et al. 1999. Plate convergence Magmatism in Western Indonesia, the trapping of the Sumba Block and measured by GPS across the Sundaland/Philippine Sea plate deformed the gateways to the east of Sundaland. Journal of Asian Earth Sciences, 16, boundary: the Philippines and eastern Indonesia. Geophysical Journal Inter- 1–12. national, 139, 296–316. Sribudiyani, Muchsin, N. & Ryacudu, R. et al. 2003. The collision of the East Regenauer-Lieb, K. Yuen, D.A. & Branlund, J. 2001. The initiation of Java Microplate and its implication for hydrocarbon occurrences in the subduction: Criticality by addition of water? Science, 294, 578–580. East Java Basin. In: Indonesian Petroleum Association, Proceedings 29th Annual Replumaz, A. & Tapponnier, P. 2003. Reconstruction of the deformed Convention, 335–346. collision zone between India and Asia by backward motion of lithospheric Stern, R.J. 2004. Subduction initiation: spontaneous and induced. Earth and blocks. Journal of Geophysical Research, 108, 2285, DOI: 10.1029/ Planetary Science Letters, 226, 275–292. 2001JB000661. Suggate, S. & Hall, R. 2003. Predicting sediment yields from SE Asia: A GIS Replumaz, A. Karason, H. van der Hilst, R.D. Besse, J. & Tapponnier, P. approach. In: Indonesian Petroleum Association, Proceedings 29th Annual Conven- 2004. 4-D evolution of SE Asia’s mantle from geological reconstruc- tion, 289–304. tions and seismic tomography. Earth and Planetary Science Letters, 221, Sukamto, R. 1982. The geology of the Pangkajene and Western part of Watampone, 103–115. Sulawesi, 1:250,000. Geological Research and Development Centre, Ritsema, J. & van Heijst, H.-J. 2000. Seismic imaging of structural hetero- Bandung, Indonesia. geneity in the Earth’s mantle: Evidence for large-scale mantle flow. Science Sukamto, R. 1986. Tectonik Sulawesi Selatan dengan acuan khusus, ciri–ciri himpunan Progress, 83, 243–259. batuan daerah Bantimala. PhD thesis, Intitut Teknologi Bandung, Indonesia. 146 R. Hall

Supriatna, S. Mragono, U. Sutrisno, de Keyser, F. Langford, R.P. & Trail, D.S. Complex, NW Sulawesi, Indonesia. Journal of Asian Earth Sciences, 29, 1993. Geology of the Sanggau sheet area, Kalimantan, 1:250,000. Geological 751–777. Research and Development Centre, Bandung, Indonesia. Villeneuve, M. 2004. Radiogenic isotope geochronology. In: Gradstein, F.M. Tan, D.N.K. & Lamy, J.M. 1990. Tectonic evolution of the NW Sabah Ogg, J.G. & Smith, A.G. (eds) A Geological Timescale 2004. Cambridge continental margin since the late Eocene. Bulletin of the Geological Society of University Press, Cambridge, 87–95. Malaysia, 27, 241–260. Wakita, K. 2000. Cretaceous accretionary-collision complexes in central Tapponnier, P. Peltzer, G. & Armijo, R. 1986. On the mechanics of collision Indonesia. Journal of Asian Earth Sciences, 18, 739–749. between India and Asia. In: Coward, M. P. & Ries, A.C. (eds) Collision Wakita, K. Munasri & Widoyoko, B. 1994. Cretaceous radiolarians from the Tectonics. Geological Society, London, Special Publications, 19, 115–157. Luk–Ulo Melange Complex in the Karangsambung area, Central Java, Tate, R.B. 2001. The Geology of Borneo Island. Geological Society of Malaysia, Indonesia. Journal of Southeast Asian Earth Sciences, 9, 29–43. Kuala Lumpur, Malayasia. Wakita, K. Sopaheluwakan, J. Miyazaki, K. Zulkarnain, I. & Munasri. 1996. Thorkelson, D.J. 1996. Subduction of diverging plates and the principles of Tectonic Evolution of the Bantimala Complex, South Sulawesi, Indonesia. slab window formation. Tectonophysics, 255, 47–63. In: Hall, R. & Blundell, D.J. (eds) Tectonic Evolution of SE Asia. Geological Thorkelson, D.J. & Taylor, R.P. 1989. Cordilleran slab windows. Geology, 17, Society, London, Special Publications, 106, 353–364. 833–836. Wheeler, P. & White, N. 2002. Measuring dynamic topography: An analysis Thuy, N.T.B. Satir, M. Siebel, W. Venneman, T. & Long, T.V. 2004. of Southeast Asia. Tectonics, 21, DOI: 10.1029/2001TC900023. Geochemical and isotopic constraints on the petrogenesis of granitoids Whittaker, J.M. Müller, R.D. Sdrolias, M. & Heine, C. 2007. Sunda–Java from the Dalat zone, southern Vietnam. Journal of Asian Earth Sciences, 23, trench kinematics, slab window formation and overriding plate deforma- 467–482. tion since the Cretaceous. Earth and Planetary Science Letters, 255, 445–457. Tjia, H.D. 1992. Holocene sea-level changes in the Malay–Thai Peninsula, a Widiyantoro, S. & van der Hilst, R.V. 1997. Mantle structure beneath tectonically stable environment. Bulletin of the Geological Society of Malaysia, 31, Indonesia inferred from high-resolution tomographic imaging. Geophysical 157–176. Journal International, 130, 167–182. Tjia, H.D. 1996. Sea-level changes in the tectonically stable Malay–Thai Wikarno, R. Hardjono, T. & Graha, D.S. 1993. Distribution of radiometric ages in peninsula. Quaternary International, 31, 95–101. Indonesia, 1:5000000. Geological Research and Development Centre, Band- Toth, J. & Gurnis, M. 1998. Dynamics of subduction initiation at preexisting ung, Indonesia. fault zones. Journal of Geophysical Research, 103, 18 053–18 067. Williams, H.H. & Eubank, R.T. 1995. Hydrocarbon habitat in the rift graben Utoyo, H. 1997. Petrologi Batuan Volkanik dan Plutonik Formasi Palepat dan of the Central Sumatra Basin, Indonesia. In: Lambiase, J.J. (ed.) Hydrocarbon Formasi Silungkang Daerah Solok dan Muarabungo. Laporan Tahunan Habitat in Rift Basins. Geological Society, London, Special Publications, 80, Proyek Kajian dan Informasi Geologi Tematik Tahun Anggaran 1996/1997. 331–371. Puslitbang Geologi, Deartment Pertambangan dan Energi, Bandung, 1. Williams, H.H. Flower, M. & Eubank, R.T. 1995. Characteristics of selected van Bemmelen, R.W. 1949. The Geology of Indonesia. Government Printing Palaeogene and Cretaceous lacustrine source basins of Southeast Asia. In: Office, Nijhoff, The Hague. Lambiase, J.J. (ed.) Hydrocarbon Habitat in Rift Basins. Geological Society, van de Weerd, A. Armin, R.A. Mahadi, S. & Ware, P.L.B. 1987. Geologic London, Special Publications, 80, 241–282. setting of the Kerendan gas and condensate discovery, Tertiary sedimen- Williams, P.R. Johnston, C.R. Almond, R.A. & Simamora, W.H. 1988. Late tary geology and paleogeography of the northwestern part of the Kutei Cretaceous to Early Tertiary structural elements of West Kalimantan. Basin, Kalimantan, Indonesia. In: Indonesian Petroleum Association, Proceedings Tectonophysics, 148, 279–298. 16th Annual Convention, 317–338. Williams, P.R. Supriatna, S. Johnston, C.R. Almond, R.A. & Simamora, van der Voo, R. Spakman, W. & Bijwaard, H. 1999. Tethyan subducted slabs W.H. 1989. A Late Cretaceous to Early Tertiary accretionary complex in under India. Earth and Planetary Science Letters, 171, 7–20. West Kalimantan. Bulletin Geological Research and Development Centre, Bandung, van Hattum, M.W.A. Hall, R. Pickard, A.L. & Nichols, G.J. 2006. SE Asian Indonesia, 13, 9–29. sediments not from Asia: Provenance and geochronology of North Borneo Wilson, M.E.J. Bosence, D.W.J. & Limbong, A. 2000. Tertiary syntectonic sandstones. Geology, 34, 589–592. carbonate development in Indonesia. Sedimentology, 47, 395–419. van Leeuwen, T.M. 1981. The geology of southwest Sulawesi with special Yang, J.-H. Wu, F.-Y. Chung, S.-L. Lo, C.-H. Wilde, S.A. & Davis, G.A. 2007. reference to the Biru area. In: Barber, A.J. & Wiryosujono, S. (eds) The Rapid exhumation and cooling of the Liaonan metamorphic core complex: Geology and Tectonics of Eastern Indonesia. Geological Research and Develop- Inferences from 40Ar/39Ar thermochronology and implications for Late ment Centre, Bandung, Indonesia, Special Publication, 2, 277–304. Mesozoic extension in the eastern North China Craton. Bulletin of the van Leeuwen, T.M. & Muhardjo. 2005. Stratigraphy and tectonic setting of Geological Society of America, 119, 1405–1414. the Cretaceous and Paleogene volcanic-sedimentary successions in north- Yuwono, Y.S. 1987. Contribution a l’étude du volcanisme potassique de l’Indonesie. west Sulawesi, Indonesia: implications for the Cenozoic evolution Exemples du sud-ouest de Sulawesi et du volcan Muria (Java). PhD thesis, of Western and Northern Sulawesi. Journal of Asian Earth Sciences, 25, Université de Bretagne Occidentale. 481–511. Yuwono, Y.S. Priyomarsono, S. Maury, R.C. Rampnoux, J.P. Soeria-Atmadja, van Leeuwen, T.M. Allen, C.M. Kadarusman, A. Elburg, M. Palin, J.M. R. Bellon, H. & Chotin, P. 1988. Petrology of the Cretaceous magmatic Muhardjo & Suwijanto. 2007. Petrologic, isotopic, and radiometric age rocks from Meratus Range, Southeast Kalimantan. Journal of Southeast Asian constraints on the origin and tectonic history of the Malino Metamorphic Earth Sciences, 2, 15–22.

Received 12 November 2008; revised typescript accepted 5 February 2009.