Arm Of Sulawesi Research Articles

History of the Celebes Sea Basin based on its stratigraphic and sedimentological record

The stratigraphic and sedimentary history of the Celebes Sea Basin provides the basis for a tectonic model for its evolution which is consistent with new regional plate reconstructions. Cores drilled on Leg 124 of the Ocean Drilling Program (sites 767 and 770) form a stratigraphic record from the basement to the sea floor in just under 800 metres of sedimentary succession. The basement itself is basalt with a strong MORB affinity. Radiolaria in pelagic mudstones at the base of the succession indicate a late middle Eocene age. A very condensed pelagic sequence (90 m in 20 Ma) suggests a setting which was distal from sources of terrigenous clastics and volcaniclastics and below the CCD. These characteristics are similar to the West Philippine Sea Basin (drilled on DSDP Legs 31 and 59), which also has oceanic basement, dated at 44–42 Ma, and Paleogene pelagic strata. These data are therefore consistent with any plate reconstruction model which has these two basins forming as part of the same ocean basin. During the Miocene quartz-rich sandy turbidites were deposited in the Celebes Sea Basin. This influx of terrigenous clastics occurred for a brief period in middle to late Miocene times (c. 10 Ma). The nearest large continental landmass which could have acted as the source of this mature siliciclastic detritus was the island of Borneo, and the onset of this clastic supply may be related to uplift caused by collision events on the island. Cessation of terrigenous clastic supply to the basin centre occurred as southward subduction of the underlying oceanic crust beneath the northern arm of Sulawesi began. It is speculated that the development of a trench along the southern margin of the basin acted as a trap for detritus coming from Borneo, diverting material from the basin centre.

GPS compared to long-term geologic motion of the north arm of Sulawesi

Geodetic data acquired in the north arm of Sulawesi are compared with geologic and palaeomagnetic data from north Sulawesi and the Celebes Sea. The objective of this study is to assess whether the long-term motion deduced from palaeomagnetic and geological studies is coherent with the extrapolation of the current motions measured by GPS. Palaeomagnetic data that have been collected in the north arm of Sulawesi indicate that since 5 Ma about 20 to 25° of semi-rigid rotation occurred about a pole located north of Manado. This suggests 200 to 250 km of left-lateral displacement along the Palu–Koro fault with a displacement rate of 4 cm/year. A rather similar displacement on the Palu fault is derived using the distribution of the asymmetric magnetic anomalies of the Celebes seafloor. The distribution implies that 200 to 250 km of oceanic crust was subducted at the north Sulawesi trench. Another marker for the rotation is derived from the opening of the Gulf of Tomini and the NW migration of the calc-alkaline subduction-related volcanism. The far-field observation by GPS of 4 cm/year of left-lateral strike-slip motion over 17 months and the 5 year average of 3.4±0.3 cm/year on a transect across the Palu fault fit well with the geological observations that indicate a motion of 4 to 5 cm/year of the north arm. We therefore conclude that the current rates deduced from GPS measurements approximate the long-term rates and may hence be extrapolated over a few million years.

BRINGING HOME THE BACON: A SPATIAL MODEL OF WILD PIG HUNTING IN SULAWESI, INDONESIA

A spatial model is developed for the hunting of two endemic wild pig species, the babirusa and the Sulawesi wild pig, in the northern arm of Sulawesi, Indonesia. The spatial component of the model allows the influences of distance from the end market, road condition, and the distribution of vegetation types to be included into the model. These are all key determinants of the effects of hunting pressure on populations of these species. The model shows that under current economic conditions at equilibrium, the babirusa will be reduced to very small numbers in remote parts of the region, while the Sulawesi wild pig will be less badly affected. Under the conditions pertaining in the 1950s, before major road-building, the two species were much more widespread. The model is used to investigate the effects of various law-enforcement policies on hunting. It is shown that the best way to reduce hunting pressure on the babirusa is to enforce fines for the selling of babirusa meat in the end market. The model is also sensitive to changes in hunters’ opportunity costs, showing that if economic conditions in the region improved, the hunting rate would decrease substantially. This is a new application for coupled map lattice models, and one with great potential for the analysis of the population dynamics of other exploited species.

Magmatic evolution of Sulawesi (Indonesia): constraints on the Cenozoic geodynamic history of the Sundaland active margin

Tertiary and Quaternary magmatic rocks from West Sulawesi record the complex history of part of the Sundaland margin where subduction and collision have been and are still active. The present study, based on petrographic data, major- and trace-element chemistry and 40K 40Ar dating aims to document the age and chemical characteristics of the magmatic formations from West Sulawesi and to determine the corresponding constraints on the geodynamic evolution of the Sundaland border. The West Sulawesi magmatic province includes the South Arm of Sulawesi (Ujung Pandang area), the western part of Central Sulawesi with the Toraja and Palu areas, and finally, the North Arm, extending from Palu to Manado, which includes the Tolitoli and Manado areas. Paleocene magmatic activity seems to be restricted to an episode of calc-alkaline magmatism in the Ujung Pandang area (61-59 Ma). The major Eocene (50-40 Ma) magmatic event is tholeiitic and is documented in all areas except in Ujung Pandang. It led to the emplacement of tholeiitic pillow-lavas and basaltic dykes of back-arc basin (BAB) affinity. These rocks are potential equivalents to the Celebes Sea basaltic basement. From Oligocene to Miocene, magmatic eruptions produced successively island-arc tholeiitic (IAT) and calc-alkaline (CA) rock series. The youngest IAT activity occurred around 18 Ma in the central part (Palu area) and around 14 Ma in the North Arm (Tolitoli area) while CA magmas were emplaced in the North Arm at ca. 18 Ma (Tolitoli and Manado areas). Typical calc-alkaline activity resumed only in the North Arm (Tolitoli and Manado areas) during the Late Miocene (9 Ma) and is still active in the Manado region. In other areas (Palu, Toraja and Ujung Pandang areas) an important and widespread magmatic event occurred between 13 and 10 Ma and emplaced K-rich magmas, either silica-undersaturated alkali-potassic basalts (AK), ultrapotassic basanites (UK) or shoshonites (SH). K-rich activity continued in the south until the Pleistocene (0.77 Ma) with alkali-potassic, ultrapotassic and shoshonitic magmas. In Central Sulawesi (Toraja and Palu areas) the most recent magmatic event occurred between 6.5 and 0.6 Ma. The corresponding products are granitic rocks and widely distributed rhyolitic pyroclastic flow deposits. All these rocks are acidic in character (SiO 2 > 60%), with trace-element and isotopic signatures (SrNdPb) typical of a strong continental imprint. The most striking tectonic implication of this magmatic evolution is that West Sulawesi can no longer be considered as a typical magmatic arc as previously assumed. With the exception of the Manado area beneath which subduction is still active, calc-alkaline and island-arc tholeiitic lavas and plutonics are volumetrically minor with respect to K-rich magmas. Their occurrence through time is also fairly restricted, mostly to the period between 30 and 15 Ma. Another important feature is the occurrence of island-arc tholeiitic and calc-alkaline magmas crosscutting an older terrane of BAB affinity, the Tinombo Formation (Manado, Tolitoli and Palu areas). As this formation is being regarded as an equivalent to the Celebes Sea floor, the most likely explanation for this feature is the hypothesis of tectonic erosion linked to the NW-dipping subduction beneath the North Arm. The Late Miocene high-K magmatic activity in Central and South Sulawesi reflects the prevalence of a post-collisional tectonic regime following the docking of microcontinents of Australian origin to Central Sulawesi during Neogene times. The incompatible element-enriched character of these high-K rocks might reflect their derivation from a mantle source enriched through metasomatism related to a previous subduction event. Such a model cannot account for the Plio-Pleistocene CAK magmatism of Central Sulawesi, the acidic composition of which does not support a derivation from an ultrabasic source. The trace-element patterns of the CAK rocks are very similar to those of the high-grade metamorphics of Central Sulawesi, suggesting that the latter might represent their possible source. Such an anatectic model implies a collisional to post-collisional tectonic regime limited to Central Sulawesi, while a post-subduction regime prevailed in the south.

Palaeomagnetism of the Balantak ophiolite, Sulawesi

Palaeomagnetic data from the East Arm of Sulawesi provide constraints on the Cretaceous and subsequent history of a fragment of the tectonic mosaic of a complex region close to the junction between SE Asia, the Indo-Australian plate and the western Pacific microplates. Primary thermoremanence has been demonstrated in samples from 23 sites in a tilted Cretaceous-Palaeogene lava sequence in the Balantak ophiolite at Batusimpang on the eastern tip of the East Arm of Sulawesi. Its direction ( D = 60.5°, I = −32.1°, α 95 = 5.5°) indicates formation at 17 ± 4°S and ∼ 60° of subsequent clockwise rotation. The primany mode of remanence is deduced from NRM/TRM comparisons; low-temperature cycling and other rock magnetic tests point to SD magnetite as the principal remanence carrier. Supporting evidence for the palaeolatitude and northward movement of the East Arm is derived from other lavas at Binsil, and from the Boba Cherts, but lack of tectonic control limits the interpretation. The contrast between these results and the subequatorial origin of contemporary rocks on nearly Halmahera is consistent with subduction of Indian Ocean lithosphere beneath the Sunda margin in the late Mesozoic and early Tertiary. Large differences in declination of remanence in the E Sulawesi rocks indicate large clockwise and anticlockwise rotations of tectonic blocks only tens of kilometres across.

New paleomagnetic constraints on the Cenozoic tectonic evolution of the North Arm of Sulawesi, Indonesia

Extensive paleomagnetic sampling (34 sites) was carried out in Cenozoic formations of the North Arm of Sulawesi (between 120 and 124°E). Consistent results obtained between 120 and 122°E suggest the existence of a unique post-Miocene clockwise rotation of about 20–25° of the western part of the North Arm. This rotation probably occurred during the northward drift of the North Arm along the Palu-Matano sinistral transcurrent fault. Between 122.5 and 124°E, both clockwise and counterclockwise rotations with various amplitudes (from ±6° to 85°) are encountered, and these very likely correspond to individual microblock rotations due to pervasive deformation along shear zones. This result is consistent with the complex fault system of the Gorontalo and Kotamobagu shear zones that have been recognized on radar imagery and by SPOT image analyses.

Geological setting and styles of mineralization, north arm of Sulawesi, Indonesia

The north arm of Sulawesi consists of a Neogene island arc (North Sulawesi Arc) built upon Paleogene volcanic-sedimentary basement and underlain by oceanic crust, which is followed to the west by an arcuate, highly deformed terrane (neck of Sulawesi) characterized by metamorphic rocks and felsic granitoids belonging to the Sundaland continental margin. These two terranes have been contiguous during the Tertiary. The evolution of the North Sulawesi Arc is divided into two stages separated by collision of the north arm with the Sula Platform microcontinent in mid-Miocene time. During the Early Miocene a calc-alkaline andesitic arc developed in relation to west-directed subduction. Arc-continent collision resulted in back-arc thrusting, clockwise rotation of the north arm, and inception of subduction along the North Sulawesi Trench. Post-collisional magmatism in the North Sulawesi Arc produced felsic to mafic volcanic suites that are thought to be related primarily to rifting of the former arc rather than directly to subduction. In the neck of Sulawesi,LILE and LREE-element enriched, potassic granites (Dondo suite) of continental affinity (Sr 87/Sr 86 0.71) were generated. The north arm of Sulawesi is comparatively well mineralized. Porphyry CuAu and porphyry Mo mineralization is approximately 2–4 Ma old based on preliminary KAr dating and geological relationships. The former developed in an oceanic terrane following collision-related arc reversal, whereas the latter developed in a continental terrane that underwent lower crustal melting during extension following the same collision. Porphyry CuAu mineralization in the North Sulawesi Arc is associatedwith clusters of small hornblende diorite or quartz diorite stocks, but the specific volcanic environment above these intrusions and their magmatic affinity remain unknown. Mineralization related to porphyry CuAu districts includes CuAu skarn, polymetallic vein and high sulphidation epithermal Au (+enargite). Porphyry Mo mineralization in the neck of Sulawesi is related to small stocks or roof apophyses of the Dondo batholith. Cogenetic granites are exposed over 5000 km 2 and are intruded in an arcuate belt, more than 400 km long, parallel to the Sula Platform collision zone. Unimodal felsic volcanics of Plio-Pleistocene age, which occur locally along the inner side of the north arm and further to the south, are probably the extrusive equivalents of the Dondo granites. Epithermal Au mineralization (typically quartz-calcite veins ± adularia) is associated mainly with the Early Miocene andesitic arc but there are important exceptions, and in general the age of mineralization is poorly known. A district-wide correlation between epithermal Au mineralization and porphyry CuAu mineralization is not apparent. The most important epithermal Au district (Kotamobagu) is inferred to be associated with a long-lived volcanic center represented by the Moat caldera. Epithermal gold systems in the North Sulawesi Arc are generally eroded deeply, typically with chlorite-epidote wallrock alteration, and little is known about their associated volcanic environment. In addition to high sulphidation Au mineralization related to porphyry systems, other styles and settings of Au mineralization in the north arm are exemplified by the Gunung Pani rhyolitic dome, the Patung diatreme breccia, the Mesel jasperiod, hosted partly by carbonate rocks, and sedimentary replacement Au-base metal mineralization at Doup. Diversity of mineralization in the north arm is further illustrated by VMS mineralization in volcanic basement to the Neogene arc, and by metamorphogenic quartz vein Au mineralization in the neck of Sulawesi.

The Mindanao collision zone: a soft collision event within a continuous Neogene strike-slip setting

Two volcanic belts are presently juxtaposed on Mindanao Island in the southern Philippines. Southward, the collision is still active in the Molucca Sea which is commonly regarded as a region of doubly verging subduction, plunging eastward below the Halmahera arc and westward below the Sangihe arc. In the Molluca Sea, tectonic features related to the incipient collision appear only in the very thick sediments of the basin, and the morphology of the parallel Halmahera, Talaud and Sangihe ridges is closely controlled by recent N-S strike-slip faults. Among these faults, the Philippine Fault is a neotectonic feature crosscutting the Agusan-Davao Basin which seals tectonic events not younger than Eocene. In addition, the Central Cordillera shows strong similarities with the Pacific Cordillera for both stratigraphy and tectonic evolution, and several indications favour a Eurasian margin affinity for the Daguma Range (Southern and Eastern Kudarat Plateau that may be part of the Sangihe arc, as inferred for the Zamboanga Peninsula and the Northern Arm of Sulawesi. Thus the island of Mindanao can be divided into two composite terranes, the western one (northward extension of the Sangihe arc) being restricted to the Kudarat Plateau and the Zamboanga Peninsula. The apparent continuation of the Sangihe arc into the Central Cordillera of Mindanao is thus the result of post collision tectonics. The portion of the suture where the collision is completed curves westward north of the southern peninsula and extends beneath the sediments of the Cotabato Basin or the volcanic plateaus of the Lanao-Misamis-Bukidnon Highlands. In the northern part, the contact is linear and suggests, together with the absence of compressional deformation, a docking of the eastern oceanic terrane (Philippine Mobile Belt-Halmahera arc) against the western continental terrane (Zamboanga-Daguma) in a strike-slip environment. Prior to Early Pliocene, the eastern and the western terranes were subject to different tectonic regimes with direction of extension perpendicular to the present one. From Late Pliocene to present, both terranes are affected by NNE and E-W compression.

Geology of a Miocene collision complex, Buton, eastern Indonesia

The island of Buton in eastern Indonesia is part of a Neogene collision zone that encompasses much of the eastern margin of Sulawesi. Miocene collision of microcontinents with a west-dipping subduction zone emplaced the Tukang Besi platform (TBP) against Buton, and the Sula platform (SP) against the East Arm of Sulawesi, and thrust large ophiolite sheets eastward over the imbricated margins of the platforms. Reconnaissance observations of the resulting collision complex in Buton (Wolio Complex) indicate that imbricate west-dipping thrust sheets and overturned folds are the predominant structural element, although later steep faults offset the imbricate stack and largely control present map patterns. The Wolio Complex consists of the sedimentary Turumbia sequence, peridotite, and two distinct groups of metamorphic rocks. The Turumbia sequence makes up most of the eastern part of the Wolio Complex and consists mostly of deep-water limestone ranging in age from Late Triassic through late Eocene or Oligocene. It is interpreted as a deep-water facies of the western TBP margin. Ophiolitic rocks are represented in present outcrop only by massive peridotite in the western part of the Wolio Complex, but the compositions of clasts in conglomerates overlying the Wolio Complex indicate that a full ophiolite succession was exposed to erosion during the collision. Metabasite and metachert ranging in grade from greenschist to amphibolite facies are found locally in fault contact with peridotite and are interpreted as the remnants of a metamorphic sole developed at the base of the ophiolite. Pelitic phyllite and quartzite in northeastern Buton probably represent a slice of the continental basement of the TBP, for similar rocks have been dredged from the northeast margin of the TBP and also form the pre-Mesozoic basement of the SP. The middle to upper Miocene Tondo Formation in Buton consists of clastic strata derived from uplift and erosion of the Wolio Complex, placing an upper limit on the age of TBP collision. We infer a middle Miocene time of collision, with oblique convergence continuing into late Miocene time. In contrast, sparse biostratigraphic data place the age of the SP-East Arm collision in the late Miocene. Separate microcontinents may have collided successively with different parts of the Buton-Sulawesi convergent margin, or a single large microcontinent may have been fragmented during oblique collision.

Late Cenozoic sedimentary and tectonic history of south Buton, Indonesia

A description and interpretation are given of the Upper Cenozoic sedimentary record of south Buton. Various sections and outcrops were studied and sampled for their microfossil content, to provide age and paleobathymetrical data. Together with information from the literature, these data from the base for a geohistory analysis to evaluate the vertical motions. Deposition started some 11 Ma ago, after the main deformation of the island, which was related to the collision of a microplate carrying Buton, with the southeast arm of Sulawesi. Coarse and fine terrigenous debris accumulated in a rapidly subsiding foreland basin; subsidence may have exceeded 100 cm/ka. When the rate of subsidence decreased a late Miocene-early Pliocene period of quiet pelagic sedimentation followed. From the late Pliocene onwards (around 3.5 Ma bp) an overall uplift took place, with rates between 30–120 cm/ka. This drastic change is explained by the collision of Buton with a submerged microcontinent that presently forms the Tukang Besi platform, situated southeast of Buton, which interaction resulted in wrench type tectonics and a clockwise rotation of over 60° for south Buton.

Tectonic development of East Indonesia

The outer non-volcanic arc in eastern indonesia appears to have been formed as a marginal part of the Australian continent in the southern hemisphere before Upper Jurassic. Timor and Sumba did not reach their present positions until Mid Miocene or later. The major tectonic event in Timor and Seram occured during Mid Pliocene and has been correlated with the collision between the margin of the Australian continent and the subduction zone of the volcanic arc. Data from trace elements, particularly Sr and Nd isotopes, suggest that the continental crust was subducted beneath the island arc. At the end of the Pliocene, the subduction zone shifted from the northern part of Timor to the Timor trough. A paper in 1975 proposed the Sumba fracture within the Indonesian Island Arc and a further paper in 1980 modified this proposal. These interpretations of eastern Indonesia have claimed that a continuous arc system extends from east of the Sumba fracture through Tanimbar and then swings north. The present report, however, describes a tectonic fracture at Pantar Strait. The evidence for this Pantar Strait fracture is discussed and it is interpreted as being initially a wrench fault at about 3 Ma. Paleomagnetic data indicate that northern arm of Sulawesi has rotated clockwise more than 90°. In the Miocene, Seram and the northern arm of Sulawesi collided with the western edge of the present Sula island, which was then just beginning to move westward along left-lateral transform faults after the Lower Miocene continent-arc collision in New Guinea. As a result of this later collision, the northern arm of Sulawesi and Seram became detached from the trench-transform junction and moved continuously in northwest and southwest direction along inferred transform faults. The volcanic arcs along both sides of the Molucca Sea increase in K from south to north without corresponding changes in Sr-isotope composition. These changes are interpreted as resulting from decreasing degress of partial melting northward because of arc-arc collisions. These tectonic movement are also related to the back-arc spreading of the Banda Sea and the Celebes Sea.

Collision, rotation, and the initiation of subduction in the evolution of Sulawesi, Indonesia

The island of Sulawesi, Indonesia, has been shaped and deformed as a result of collision with the Sula platform, a sliver of continental material from the northern margin of Australia‐New Guinea. The collision has resulted in rotation of the north volcanic arm of Sulawesi and the development of the accretionary wedge of the North Sulawesi trench. The North Sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west. Early stages of thrusting produce a steep frontal slope (8°–16°), indicative of relatively high basal shear stress, whereas the more advanced (western) zone of thrusting produces a gentle (2°) slope, consistent with low basal shear stress. Reported paleomagnetic data suggest post late Eocene counter‐clockwise rotation of the North Arm, and the offshore geophysics are explained by a pivot of the North Arm with respect to the Celebes basin about the eastern end of the arc. Convergence between the north Banda basin and Southeast Sulawesi is documented by the presence of the Tolo thrust. Its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30–40 km in the central part. The northern end transforms to the leftlateral Matano fault, with a reported offset of 20 km. The southern end of the thrust projects toward the deformed rocks of Buton, but the structural relations there are not clear. The Matano fault zone appears to connect westward with the Palu fault, which forms the western transform of the North Sulawesi trench. The Palu‐Matano fault system acts as a trench‐trench transform between the North Sulawesi trench and the Tolo thrust, and this system is described by the same rotation pole as that for the Sulawesi North Arm.

Reconnaissance microearthquake survey of Sulawesi, Indonesia

Several hundred earthquakes were recorded during the operation of a two‐week five‐station portable seismograph network on Sulawesi, Indonesia. Forty one of these events were locatable and half of these occurred beneath the eastern Gorontalo Basin in a north dipping zone which extends from the Batui Thrust on the East Arm of Sulawesi to about 100 km depth beneath the Gorontalo Basin. The Batui Thrust is the site of thrusting of the Banggai Islands continental fragment beneath the East Arm ophiolite and oceanic crust of the Gorontalo Basin. The observation of a zone of earthquakes dipping to the north from this thrust zone suggests that the leading edge of the Banggai Island block was subducted to at least 100 km depth. The eastern Gorontalo Basin earthquake zone may connect with a deep seismic zone beneath the Celebes Basin. Beneath the western Gorontalo Basin, a very narrow zone of earthquakes dips to the south, probably within lithosphere of the Celebes Basin subducted at the North Sulawesi Trench. Three shallow earthquakes occurred near Lake Matano in central Sulawesi, possibly on the Matano Fault, and their composite focal plane solution suggests east‐west extension. The occurrence of only one earthquake on the Palu Fault and the lack of short S‐P times at a station operated on the fault indicate that this feature was very quiet during the survey period.

Paleomagnetic evidence for clockwise rotation of the northern arm of Sulawesi, Indonesia

Paleomagnetic results from the northern arm of Sulawesi show that the arm has been subjected to a clockwise rotation of more than 90° and that its rotational motion began no later than the middle Miocene. The mean direction showing a normal polarity at the Eocene to the early Miocene is D = 98.0° and I = 6.9°. A declination value of D = 50.1° obtained from Miocene rocks indicates a transition stage of the rotational motion. The datum from Plio-Pleistocene volcanics is D = −4.6° and I = −9.3°. This suggests that the rotational motion terminated before the initiation of volcanic activity during the Plio-Pleistocene.

Reconnaissance palaeomagnetic results from sulawesi, indonesia, and their bearing on palaeogeographic reconstructions

Magnetic remanence of Jurassic radiolarian chert from the southwest arm of Sulawesi (Celebes) yields a palaeomagnetic pole at 55°N,32°E, indicating rotation of about 35° anticlockwise since the late Mesozoic. This pole is close to those obtained from Cretaceous rocks of the Malay Peninsula and West Kalimantan and suggests that the three areas may have formed part of the same plate since the late Mesozoic, or at least that Sulawesi has not moved much relative to the other two areas. Measurements from Jurassic cherts from the southeast arm of Sulawesi show a magnetic inclination of 61° ; although too few samples were obtained for firm conclusions to be drawn, this does suggest that the cherts in the southeast arm were formed at higher latitudes and is compatible with the hypothesis that eastern Sulawesi was part of an Australian plate and was welded onto west Sulawesi in the Cainozoic. Measurements on tuffs, sills and lavas of late Cainozoic age on the flanks of the Lompobatang volcano mostly show directions near the existing field, four sites in a reversed sense, and one normal.

Gravity results and emplacement geometry of the Sulawesi ultramafic belt, Indonesia

Research Article| September 01, 1978 Gravity results and emplacement geometry of the Sulawesi ultramafic belt, Indonesia Eli A. Silver; Eli A. Silver 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Search for other works by this author on: GSW Google Scholar Yoko Joyodiwiryo; Yoko Joyodiwiryo 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Search for other works by this author on: GSW Google Scholar Robert McCaffrey Robert McCaffrey 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Search for other works by this author on: GSW Google Scholar Author and Article Information Eli A. Silver 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Yoko Joyodiwiryo 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Robert McCaffrey 1Earth Sciences Board and Center for Coastal Marine Studies, University of California, Santa Cruz, California 95065 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1978) 6 (9): 527–531. https://doi.org/10.1130/0091-7613(1978)6<527:GRAEGO>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Eli A. Silver, Yoko Joyodiwiryo, Robert McCaffrey; Gravity results and emplacement geometry of the Sulawesi ultramafic belt, Indonesia. Geology 1978;; 6 (9): 527–531. doi: https://doi.org/10.1130/0091-7613(1978)6<527:GRAEGO>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Preliminary results of gravity observations on the Southeast Arm of Sulawesi in eastern Indonesia provide evidence on the structure of the large ultramafic belt and associated melange units. Gravity highs at the schist-ultramafic contact indicate that the ultramafic rocks are very thick there, possibly dipping beneath the schist. The gravity effect of the ultramafic rocks decreases eastward away from the schist, and a gravity low over a large zone of limestone and melange requires a thick body of low density material, probably melange, to nearly surround the limestone blocks. The interpreted structure imposes constraints on models of emplacement of the ultramafic slab and is compatible with slicing off slivers of ocean crust and upper mantle in a subduction zone, but it is not compatible with obduction or with diapiric intrusion. Uplift of ultramafic rocks was aided initially by the presence of abundant low-density melange and, finally, by the collision of Sulawesi with the Banggai-Sula Islands. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Radiocarbon dates of elevated shorelines, Indonesia and Malaysia. Part 1

Four new radiocarbon dates of elevated strandlines in tectonically active areas of eastern Indonesia and East Malaysia indicate average rates of uplift that range between 4.5 and 9 mm annually during the past 24,000 yr. These values are at least three times higher than former estimates from eastern Indonesia. Another radiocarbon date from the south arm of Sulawesi—also tectonically mobile—indicates a rate of uplift of 1.4–2.5 mm per year which corresponds with earlier determinations. This particular case, however, suggests that the sample was probably located close to a north-south axis about which southern Sulawesi was tilted during the Quaternary. In the Langkawi islands, West Malaysia, one of the regionally ubiquitous shorelines at about 2 m above sea level was dated at 2590 ± 100 yr BP which corresponds with Fairbridge's (1961) Abrolhos Submergence.