Sorong Fault Zone Research Articles

The Tamrau Block of NW New Guinea records late Miocene–Pliocene collision at the northern tip of the Australian Plate

The Tamrau Block is a geological terrane located in the Bird’s Head Peninsula of NW New Guinea. Relatively little is known about this terrane and how it relates to other parts of western New Guinea. The geological history and provenance of this terrane is difficult to resolve because it is found at the boundary between the Australian, Philippine Sea, Caroline, and Pacific plates. This segment of the plate boundary records episodes of deformation, magmatism, and exhumation associated with the interaction of these three tectonic plates. For instance, the southern edge of the Tamrau Block is bounded by a major strike-slip fault zone (the Sorong Fault Zone), previous studies imply that the terrane may have been translated some distance along this fault zone during the Cenozoic. We seek to understand the geological history and provenance of the Tamrau Block. To do this, we report new field observations made during a three-month field campaign in a poorly exposed region, together with new petrographic and geochronology data. U–Pb detrital zircon age spectra were obtained from five sedimentary and metamorphic sequences and the results were combined with existing biostratigraphic age data to reassess the stratigraphy and tectonic history of the region. The oldest rocks in the Tamrau Block (the Tamrau Formation) represent Jurassic–Cretaceous passive margin sediments. These were deformed and metamorphosed in at least three distinct events – the first phase of which involved amphibolite facies conditions (and produced the first reported instance of metamorphic kyanite from the Bird’s Head), possibly in the Oligo–Miocene. These Jurassic–Cretaceous rocks are unconformably overlain by the Ajai Limestone. Both units are cross-cut and overlain by intrusives and eruptives of the middle Miocene Moon Volcanics. The heat associated with these intrusives baked the Tamrau Formation and the overlying Ajai Limestone, resulting in andalusite growth in the Tamrau Formation and hornfelsing of the limestones. Deposition of the overlying Koor Formation occurred from the middle–late Miocene, and was partially contemporaneous with volcanism. An episode of crustal shortening occurred after the deposition of the Koor Formation with the development of asymmetric folds and steeply-inclined reverse faults. This is marked by a late Miocene–Pliocene break in deposition between the Koor Formation and undeformed Opmorai Formation (∼10.5–4.5 Ma) and records the collision of part of an oceanic island arc (Tosem Block) to the Tamrau Block, an event also recognised in other parts of New Guinea. A comparison of the U–Pb detrital zircon age spectra from sedimentary rocks within the Tamrau Block and those reported in other studies indicate that there is no relationship between the rocks of the Tamrau and Kemum blocks (which are in faulted contact). Instead, the U–Pb detrital age data share similarities with rocks from the Lengguru Fold and Thrust Belt and Weyland Overthrust in the south-east. We therefore propose that the Tamrau Block was transported westwards ∼300 km to its current position along the Sorong Fault Zone after the late Miocene–Pliocene collision between the Tosem Block and the northern margin of the Australian Plate.

Indication Strike Slip Movement a Part of Sorong Fault Zone in Yapen Island, Papua, Indonesia

Indication Strike Slip Movement a Part of Sorong Fault Zone in Yapen Island, Papua, Indonesia

Late Cenozoic geodynamic evolution of eastern Indonesia

This paper presents an internally and globally consistent model of plate evolution in eastern Indonesia from Middle Miocene to Present time. It is centered on the Banda Sea region located in the triple junction area between the Pacific–Philippine, Australia and South–East Asia plates. The geological and geophysical data available from Indonesia were until recently insufficient to define a unique plate tectonic model. In this paper, the new data taken into account clearly restrict the possible interpretations. Owing to a great number of geological, geophysical and geochemical studies, the major plate boundaries (the Sunda–Banda subduction zone to the south, the Tarera–Aiduna Fault zone and the Seram Thrust to the east, and the Sorong Fault zone and Molucca Sea collision zone to the north) are now clearly identified. The age of the major tectonic structures is also better known. Geodetic measurements well constrain the Present time plate kinematics. We also consider the deformation history within eastern Indonesia, where numerous short-lived microplates and their related microcontinents successively accreted to the Asiatic margin. Moreover, magnetic anomalies identification of the North and South Banda Sea basins allows a precise kinematic reconstruction of the back-arc opening. We used the Plates software to test the coherency of our model, presented as a series of 4 plate reconstruction maps from 13 Ma to the present. Finally, the origin of oceanic domains restored by our reconstruction is discussed.

Palaeomagnetic data from a Mesozoic Philippine Sea Plate ophiolite on Obi Island, Eastern Indonesia

Palaeomagnetic data are presented from part of the Halmahera ophiolite exposed on Obi Island, eastern Indonesia. Until the late Neogene, Obi formed part of the southern Philippine Sea Plate; it is now isolated from that plate and is located between fault strands in the left-lateral Sorong Fault Zone. Two areas were sampled: the first area comprised two sites from a microgabbro and a third site in a thin intruding dyke, and the second area yielded one site from a sheeted dyke suite. The mean in situ direction for the two areas is D=216.1°, I=23.3° , where the angular separation is 34.7°. Rotating the mean directions back to the palaeo-vertical clusters the vectors, so that D=219.4°, I=12.1°, where the angular separation is 20.1°. This clustering, together with other lines of palaeomagnetic evidence, suggests that the magnetisation is primary. The ophiolite is Mesozoic, and most likely formed in the Jurassic. This information, together with recently published palaeomagnetic data from nearby Upper Cretaceous Philippine Sea Plate formations, suggest that the oldest parts of the Philippine Sea Plate were situated close to the equator in the western Pacific in the middle Mesozoic.

Tertiary evolution of the Eastern Indonesia Collision Complex

Eastern Indonesia is the zone of interaction between three converging megaplates: Eurasia, the Pacific and Indo-Australia. The geological basis for interpretations of the Tertiary tectonic evolution of Eastern Indonesia is reviewed, and a series of plate tectonic reconstructions for this region at 5 million year intervals covering the last 35 million years is presented. The oldest reconstruction predates the onset of regional collisional deformation. At this time a simple plate configuration is interpreted, consisting of the northward-moving Australian continent approaching an approximately E–W oriented, southward-facing subduction zone extending from the southern margin of the Eurasian continent eastwards into the Pacific oceanic domain. Beginning at about 30 Ma the Australian continental margin commenced collision with the subduction zone along its entire palinspastically-restored northern margin, from Sulawesi in the west to Papua New Guinea in the east. From this time until ca 24 Ma, the Australian continent indented the former arc trend, with the northward convergence of Australia absorbed at the palaeo-northern boundary of the Philippine Sea Plate (the present-day Palau-Kyushu Ridge). At ca 24 Ma the present-day pattern of oblique convergence between the northern margin of Australia and the Philippine Sea Plate began to develop. At about this time a large portion of the Palaeogene colliding volcanic arc (the future eastern Philippines) began to detach from the northern continental margin by left-lateral strike slip. From ca 18 Ma oblique southward-directed subduction commenced at the Maramuni Arc in northern New Guinea. At ca 12 Ma the Sorong Fault Zone strike-slip system developed, effectively separating the Philippines from the Indonesian tectonic domain. The Sorong Fault Zone became inactive at ca 6 Ma, since which time the tectonics of eastern Indonesia has been dominated by the anticlockwise rotation of the Bird’s Head structural block by some 30–40°. Contemporaneously with post-18 Ma tectonism, the Banda Arc subduction–collision system developed off the northwestern margin of the Australian continent. Convergence between Indo-Australia and Eurasia was accommodated initially by northward subduction of the Indian Ocean, and subsequently, since ca 8 Ma, by the development of a second phase of arc-continent collision around the former passive continental margin of NW Australia.

Correlation of the Salawati and Tomori Basins, eastern Indonesia: a constraint on left-lateral displacements of the Sorong fault zone

Abstract The Salawati Basin of western New Guinea and the Tomori Basin of eastern Sulawesi, Indonesia, are two sedimentary basins located either side of the main fault strands in the Sorong fault zone strike-slip system. It is suggested that prior to displacement on the Sorong system the two formed a single sedimentary basin. Movement on the Sorong system occurred largely during the latest Miocene-Quaternary, contemporaneous with deposition of a clastic sedimentary succession. An older basinal sequence, essentially Miocene in age, is composed predominantly of carbonate sediments, and this may have formed part of the foreland basin sequence related to the east Sulawesi orogenic belt. Correlation of the Salawati and Tomori Basins implies a left-lateral displacement of about 900 km on part of the Sorong fault zone.

Evolution of the boundary between the Philippine Sea Plate and Australia: palaeomagnetic evidence from eastern Indonesia

The boundary between the Philippine Sea and Australian plates is the left-lateral Sorong Fault system of eastern Indonesia. Until recently, modelling this boundary for the period before about 5 Ma was difficult; the Tertiary motion of the Philippine Sea Plate was uncertain and palaeomagnetic data from areas adjacent to the fault were lacking. Recent geological and palaeomagnetic studies of the area north of the Sorong Fault have elucidated the Tertiary motion history of the Philippine Sea Plate, providing a reference for examining movements within the fault system. We report new palaeomagnetic data from within the Sorong Fault Zone, from the islands of Taliabu and Obi. Taliabu is part of the Sula Platform and is considered to be derived from Australia. Pelagic limestones from the Upper Cretaceous Tanamu Formation of Taliabu yielded a direction of D = 329.1°, I = −34.9° implying counter-clockwise rotation and a formation latitude of 19 ± 5°S. Sula and Misool are postulated to be part of a single microcontinent which had a different Late Cretaceous-mid-Tertiary movement history from Australia. The Sula Platform was transported to its present position by movement along the Sorong Fault system in the Late Miocene. Obi includes rocks of Philippine Sea and Australian origin; all the new sites are in rocks of Philippine Sea Plate origin. Since the Early Neogene the Philippine Sea Plate, which includes all islands north of the Sorong Fault, has rotated 40° clockwise and moved 10–15° northwards. Philippine Sea Plate rocks within the Sorong Fault Zone record similar latitude shifts, but different rotations. In north Obi, the Upper Oligocene Anggai River Formation and the Middle Miocene Woi Formation record ∼ 60° and ∼ 30° counter-clockwise rotations, respectively. The sense of rotation is consistent with motion within a left-lateral fault system, with the Philippine Sea and Australian plates providing the shear couple. In contrast, the Woi Formation in southeast Obi records 15–20° clockwise rotation; this area is separated from the zone of counter-clockwise movement in north Obi by a strand of the Sorong Fault. Arc volcaniclastic rocks from the Upper Cretaceous Leleobasso Formation of northwest Obi have a primary magnetisation with a mean direction of D = 357.1°, I = −21.9°. These rocks formed at ∼ 11°N or ∼ 11°S, depending on the interpreted rotation history, and indicate a Pacific rather than Indian Ocean origin. A volcanic arc at the southern edge of the Philippine Sea Plate collided with eastern New Guinea at ∼ 25 Ma. The Philippine Sea-Australia plate boundary then changed from subduction to strike-slip, as the Philippine Sea Plate began its Neogene rotation, initiating the Sorong Fault system. We suggest that many of the arc fragments in the New Guinea orogenic belt originated in the southern Philippine Sea Plate arc which has subsequently been dismembered by strike-slip faulting.

The character and significance of basement rocks of the southern Molucca Sea region

Pre-Neogene basement rocks in the southern Molucca Sea region include ophiolitic rocks, arc volcanic rocks and continental rocks. The ophiolitic complexes are associated with arc and forearc igneous and sedimentary rocks. They are interpreted as the oldest parts of the Philippine Sea Plate with equivalents in the ridges and plateaux of the northern Philippine Sea. In the Molucca Sea region igneous components include rocks with a “supra-subduction zone” character, bonintic volcanic rocks and basic volcanic rocks with a “within-plate” character; “MORB-type” rocks are rare or absent. The ophiolitic rocks are overlain by Upper Cretaceous and Eocene sedimentary and volcanic rocks. Plutonic rocks of island arc origin which intrude the ophiolites yield Late Cretaceous radiometric ages and amphibolites with ophiolitic protoliths yield Eocene ages. The “supra-subduction zone” ophiolites are speculated to have originated during a mid-Cretaceous plate reorganization event. For the Late Cretaceous and Eocene the present-day Marianas arc and forearc provides an attractive model. Volcanic rocks from the basement of Morotai, western Halmahera and much of Bacan. These also have an island arc character and are probably of Late Cretaceous-Paleogene age. Both the arc volcanic rocks and the ophiolitic complexes are overlain by shallow water Eocene limestones and an Oligocene rift sequence including basaltic pillow lavas and volcaniclastic turbidites. The distribution of the Eocene-Oligocene sequences indicate pre-Mid/Late Eocene amalgamation of the ophiolitic and arc terranes. Mid Eocene-Oligocene extension appears to be synchronous with opening of the central West Philippine Basin. Continental crust probably arrived in this region in the Late Paleogene-Early Neogene, either due to collision of the Australian margin with Pacific arc-ophiolite terranes or by terrane movement along the Sorong Fault Zone.

Evolution of the Sorong Fault Zone, Northeast Indonesia

The Sorong fault zone (SFZ) of northeast Indonesia is a broad zone of inferred left-lateral shear at the triple junction of the Indo-Australian, Eurasian, and Pacific plates. It is widely believed that fragments of the northern Australian continental margin in New Guinea are being detached and translated westward in this shear zone until they collide with the eastern margin of Eurasia (Sundaland) in the region of Sulawesi Island. However, the details of terrane translation, amalgamation, and docking remain poorly documented. In particular, the timing of events is very poorly constrained, with estimates for the commencement of the SFZ ranging from early Miocene or older to Pleistocene. Recent investigations of the SFZ and the adjacent regions of Sulawesi and Irian Jaya (Indonesian New Guinea), including new fieldwork in several of the SFZ island-terranes (Waigeo, Halmahera, Bacon, Obi, and Sula), suggest a less mobilist interpretation of the region than previous reconstructions. In general, the closest interisland geological correlations are between the geographically closest islands. This would seem to favor rather conservative reconstructions, and a new interpretation of the region based on this tenet is proposed. Although arc-continent collision commented in New Guinea during the mid-Oligocene and only slightly later in Sulaswesi, themore » SFZ did not begin to develop in its present form before the late Miocene.« less

The southern termination of the Philippine Trench

Recent studies of the southern end of the Philippine Trench using GLORIA sidescan sonar and single channel seismic data and geological studies on the island of Halmahera suggest that the trench is in the process of propagating south and that some of the ESE-WNW convergence is transferred via a broad NE-SW zone of dextral strike-slip across northern Halmahera into the Molucca Sea Collision Zone. NE-SW ridges and lineaments on the seafloor can be traced into major faults and structural trends on land. The bathymetric expression of the Philippine Trench is lost where it meets an oceanic plateau on the Philippine Sea Plate. This elevated and probably thickened plateau appears to have inhibited any further propagation of the trench southwards. To the north of the plateau there is a well-developed accretionary prism, but to the south deformation of sediments on the seafloor is less intense. A prominent ridge, with sediments passively banked up against it marks the southern limit of deformation associated with the Philippine Trench. To the south lies the eastern Halmahera-Waigeo Ophiolite Terrane, an area of shallow water and islands underlain by ophiolitic basement between Halmahera and the Sorong Fault Zone. There are no bathymetric or structural features to indicate any form of active link between the Philippine Trench and the Sorong Fault through or along the northern side of this ophiolite terrane. There is no earthquake evidence for any form of fault linking the Philippine Trench to either the Palau Trench or the Sorong Fault, but there are numerous earthquake epicentres reported between the southern end of the trench and the Molucca Sea. The island of Halmahera is considered to lie in a diffuse boundary zone at the margin of the Philippine Sea Plate. Continued collision of the opposing arcs in the Molucca Sea will ultimately prevent further E-W convergence between Halmahera and Sulawesi. It is predicted that either the Philippine Trench will propagate south along its present line to meet the Sorong Fault or that another trench will develop further to the east. In either case the arc and ophiolite terrane of Halmahera might then be accreted onto the Eurasian margin.

Late Palaeogene–Quaternary geology of Halmahera, Eastern Indonesia: initiation of a volcanic island arc

The Late Palaeogene–Quaternary stratigraphy of Halmahera is described, and new formation names are proposed, based on recent field investigations of the NE and central part of the island. This stratigraphic information provides new insights into the Neogene history of Halmahera and the development of the present island arc. The Late Palaeogene and younger rocks rest unconformably on an ophiolitic Basement Complex which formed part of a Late Cretaceous–Early Tertiary fore-arc. After volcanic arc activity ceased in the Eocene the former fore-arc terrane was uplifted and deeply eroded in the Late Palaeogene. Some of the Late Palaeogene–Early Miocene river valleys are currently being re-excavated by the present rivers. Slow subsidence began in the mid–late Oligocene and by the end of the Miocene all eastern Halmahera was the site of shallow-water carbonate deposition. There is no evidence for arc volcanism in central Halmahera at this time and the reported Oligo-Miocene volcanism in nearby regions is interpreted as volcanism related to the Sorong Fault system. The Miocene shallow water region subsided rapidly in the Early Pliocene and the sedimentary basin formed was filled with marls succeeded by siliciclastic turbidites, with increasing amounts of calc-alkaline volcanic debris from a Pliocene volcanic arc built on the western arms of Halmahera, probably on the eroded Early Tertiary arc. This phase of rapid subsidence in the Pliocene back-arc region resulted from the initiation of subduction of the Molucca Sea lithosphere eastwards beneath Halmahera. Differential subsidence on NW–SE and NE–SW sets of faults in the region immediately behind the active arc led to the formation of deep sediment-filled basins adjacent to the eastern arms. A major deformation event in the Pleistocene resulted in folding and local thrusting at the junction between eastern and western Halmahera and volcanism ceased in the Pliocene arc. The third Halmahera arc, the Quaternary arc, currently active in the northern part of the islands, began activity within the last 1 Ma and is built upon the deformed and partly eroded Pliocene arc. The Pleistocene deformation event and shift in position of the arc are interpreted as the result of the interaction of the eastward-dipping Molucca Sea plate with adjacent plates, either with a fragment of the Australian continent in the Sorong Fault zone and/or with the Philippine Sea plate beneath northern Halmahera.

Northern New Guinea Wrench Fault System: A Manifestation of Late Cenozoic Interactions Between Australian and Pacific Plates: ABSTRACT

Cenozoic plate interactions between the Australian and Pacific plates have yielded a variety of convergent tectonic styles. Two major products of this convergence are the Sorong fault zone of Irian Jaya and the Ramu-Markham fault zone of Papua. The Sorong fault system has been documented to extend westward more than 500 mi (800 km) from Teluk Sarera to Kep Banggai as a left-lateral strike-slip fault. The Ramu-Markham fault system is of disputed displacement and has been previously interpreted to extend from over 310 mi (500 km) just east of the Sepik River into the Huon Gulf. A consideration of Australian-Pacific Cenozoic plate kinematics, Holocene vectors, earthquake focal mechanisms, photogeologic lineation analyses, and the assimilation of other pertinent geologic data suggests that the Ramu-Markham fault zone is an extension of the Sorong fault system and that together they represent significant left-lateral strike-slip motion in rigid crustal basement. This motion has produced large scale en echelon surface expressed faults and folds in detached overlying Neogene sediments. Furthermore, this wrench fault system has led to the transcompressional development and deformation of the Meervlakt, Piore, Sepik, and Ramu basins of northern New Guinea. An understanding of the tectonic evolution of these basins is tantamount to an assessment of their evolving hy rocarbon potential. End_of_Article - Last_Page 980------------

Tertiary Tectonic History of Salawati Area, Irian Jaya, Indonesia

The Salawati area constitutes the oil-producing western extremity of Irian Jaya, Indonesia. It lies in the complex area of interaction of three major crustal plates: the Pacific oceanic plate on the north, the Australian continental plate on the southeast, and the Asian continental plate on the southwest. Geometric, geomorphologic, geologic, and geophysical evidences strongly indicate that Salawati Island was attached to the Irian Jaya mainland during the time of Miocene-lower Pliocene reef development, and that it was separated in middle Pliocene to Pleistocene time, opening the Sele Strait rift zone. The island moved 17.5 km southwestward after an initial counterclockwise rotation of 13°. The rift zone is subsequent to the creation of the large left-lateral Sorong fault zone that is part of the transitional area separating the westward-moving Pacific plate from the relatively stable Australian plate. The motion was triggered during a widespread magmatic intrusion of the Sorong fault zone, when the basalt infiltrated a right-lateral fault system in the area of the present Sele Strait. Rifting along three parallel major left-lateral strike-slip faults can be traced from the Sele Strait to the southern part of Salawati Island. The amount of relative displacement increases from the southeast fault to the northwest fault. These faults later became the site of important down-to-the northwest, normal faulting to accommodate the subsidence resulting from the load of Pliocene-Pleistocene deposits derived from the high northern basaltic mountains. Pliocene-Pleistocene diastrophism thus has defined several zones of varied structural character: the Sele Strait, the Irian Jaya mainland, Salawati Island, and their respective surroundings. If Salawati Island is placed in its former Irian Jaya frame, and the northern compartment of the left-lateral Sorong fault zone is moved back east, the Miocene landscape appears to be characterized by a widespread carbonate development with reefs thriving at the edge of an early New Guinean landmass facing an open sea on the west. The original distribution of reefs is somewhat different from the present arrangement.

Oil-Bearing Reefs in Salwati Basin of Irian Jaya, Indonesia

Recent exploration activity in the Salawati basin, along the northwestern tip of Irian Jaya, Indonesia, has resulted in significant oil discoveries. Reservoir and trap are provided by highly porous and permeable Miocene reef rocks, which have yielded oil at rates of up to 32,000 bbl per day from individual wells. The Salawati basin is a structural-stratigraphic basin containing more than 15,000 ft (4,600 m) of marine Tertiary sedimentary deposits. The basin is bounded on the north by the Sorong fault zone which separates the Australian continental plate from the Pacific oceanic plate. Basin development was initiated in the Miocene when local downwarping and increased water depths resulted in the deposition of a basinal limestone and shale sequence in the area. Toward the east and south margins of the basin these sediments are replaced by shallow-water carbonate rocks which form a well-defined shelf and associated shelf margin. The productive reef belt is just basinward of the shelf and shelf-margin area. The reefs, which reach heights in excess of 1,600 ft (490 m), range in areal extent from 2 to 48 sq mi (5 to 124 sq km). Porosities within the reefal carbonate rocks are as much as 43 percent and average 20 to 30 percent. Late Pliocene-Pleistocene normal faults which cut many of the reefs, combined with postreef structural tilt, have modified considerably the original configuration of the reefs and the associated oil accumulations. The knowledge gained from the current exploration program concerning reef morphology, porosity variations, tectonic history, and other factors which control the oil accumulations should expedite future exploration efforts in the basin.