Australian Plate Research Articles

Analysis of oxide content in sand and rock found in public mining of west sumatra province using XRF test

Indonesia is regionally located on two large plates, which are the Pacific plate in the north and the Australian plate in the south. Due to the geological activity of these two plates, it results in a complex tectonic pattern supporting the formation of mineralization. Therefore, Indonesia is considered as a country rich in various minerals and oxide sources. The purpose of this study is as a preliminary study to analyze the element of atom / oxide contained in rocks and sand found in public mining of West Sumatra Province. The initial identification done is to perform X-ray fluorescence test (XRF) on rock samples taken from Jorong Bukit Harapan Darmasraya Regency and Manggani, 50 Kota Regency. The sand samples are taken from Kupitan area Sijunjung Regency, Pinti Kayu Gadang Muara Labuh and jorong pulai Sitiung Darmasraya regency. XRF test results for rock and sand samples from these five areas indicate the presence of six dominant oxides with large percentage i.e. Al2O3, SiO2, P2O5, CaO, TiO2, Fe2O3 oxides. The content of SiO2, Al2O3, Fe2O3, CaO, TiO2, and P2O5 foundon rock samples is quite high 53.01-57.77%, 29.982-32.191%; 5.113-10.302%; 2.119-2.367%; 0.9021.809%, and 0.685-0.968% respectively. Meanwhile, the sand samples indicate the content of SiO2, Al2O3, Fe2O3, CaO, TiO2, and P2O5 15.103-52.652%; 5.379-17.621%; 9.22-58.593%; 1.54-9.22%; 0.702-12.238% and 1.261-2.545% respectively.

Aftershocks of the 2012 Off-Coast of Sumatra Earthquake Sequence

Aftershocks of the 2012 Off-Coast of Sumatra Earthquake Sequence exhibit a complex and diffuse spatial distribution. The first-order complexity in aftershock distribution is clear and well beyond the influence of typical earthquake location uncertainty. The sequence included rupture of multiple fault segments, spatially separated. We use surface-wave based relative centroid locations to examine whether, at the small scale, the distribution of the aftershocks was influenced by location errors. Surface-wave based relative location has delineated precise oceanic transform fault earthquake locations in multiple regions. However, the relocated aftershocks off the coast of Sumatra seldom align along simple linear trends that are compatible with the corresponding fault strikes as estimated for the GCMT catalog. The relocation of roughly 60 moderate-earthquake epicentroids suggests that the faulting involved in the 2012 earthquake aftershock sequence included strain release along many short fault segments. Statistical analysis and temporal variations of aftershocks show a typical decay of the aftershocks but a relatively low number of aftershocks, as is common for intraplate oceanic earthquakes. Coulomb stress calculations indicate that most of the moderate-magnitude aftershocks are compatible with stress changes predicted by the large-event slip models. The patterns in the aftershocks suggest that the formation of the boundary and eventual localization of deformation between the Indian and Australian plate is a complicated process.

The Timing and Style of Oblique Deformation Within New Zealand's Kaikōura Ranges and Marlborough Fault System Based on Low‐Temperature Thermochronology

AbstractThe ~150‐km‐wide dextral Marlborough Fault System and adjacent Kaikōura Mountains accommodate oblique convergence between the Pacific and Australian plates at the NE end of the South Island, New Zealand. Low‐temperature thermochronology from this region places new limits on the timing and style of Marlborough faulting and mountain building. We sampled rocks for apatite and zircon (U‐Th/He) and apatite fission track dating from a range of elevations spanning ~2 km within the Kaikōura Ranges, which stand high above the active Marlborough dextral faults. The data reveal Miocene cooling localized to hanging wall rocks, first along the Clarence Fault in the Inland Kaikōura Range, then along the Jordan Thrust in the Seaward Kaikōura Range, followed by widespread, rapid cooling reflected in all samples across the study area starting at ~5 Ma. Our results suggest that topographic relief in this region predates the onset of dextral faulting and that portions of the Marlborough Faults were once thrust faults that coincided with the early development of the transpressive plate boundary. We relate Pliocene to present rapid exhumation across the field site, including at low‐elevation sample sites in Marlborough Fault foot walls, to seaward translation and overthrusting of crust atop the downgoing slab by dextral Marlborough Fault motion. Our results show that spatial and temporal patterns in exhumation reflect a complex and evolving deformation field in the Marlborough Fault System over the past ~25 million years of Kaikōura orogeny.

Review on the Tectonic Terranes Associated with Metallogenic Zones in Southeast Asia

The paper presents an overview of the relationships between the interior structures of tectonic terranes and the distribution of tectonic-metallogenic zones in Southeast Asia. Episodic tectonic activities occurred in this archipelagic area, generating metallogenic belts in multi-terranes. Since the Late Paleozoic, opening and closure of the Paleotethys and Neotethys led to multiple suture zones between different blocks, mainly between the Indochina terrane, the Nambung terrane, the Sibumasu terrane and the West Myanmar terrane. During the Mesozoic to Cenozoic, the formation of accreted terranes and their related islands was caused by subduction and collision processes between the Pacific and Australian plates toward the Eurasian Continent, forming Sundaland and its affiliated islands, the Philippines and its subsidiary islands, the Papua New Guinea terrane and its related islands and the Sunda epicontinental arc system. Within the margin of terranes resulted in the structural transfer zones, their secondary tectonic units can be divided into island arc belts, back-arc basins, suture zones, marginal fold belts and orogenic belts. The metallogenic assemblages are mainly distributed within these structural zones of the terranes. According to the relationship between these tectonic units and the distribution of mineral resources, the tectonic-metallogenic belts can be divided into 24 metallogenic belts in Southeast Asia. They are characterized by a diversity and frequency of metallogenic material combination which is likely to reflect the complexity of the material distribution during mineralization processes, mostly by the structural transformation during the dissociation-convergence process between multiple terranes. Therefore, the formation of ore deposits was not only restricted by the evolution (opening and closure) of Paleo-and Neotethys, but may also be controlled by the interaction of the terranes with different tectonic attributes which provided multiple sources of metallogenic material.

Magma production along the Lord Howe Seamount Chain, northern Zealandia

AbstractOne of the world’s most notable intraplate volcanic regions lies on the eastern Australian plate and includes two age-progressive trails offshore (Tasmantid and Lord Howe seamount chains) and the world’s longest continental hotspot trail (Cosgrove Track). While most studies agree that these chains formed by the rapid northward motion of the Australian plate over a slowly moving mantle source, the volcanic output along these trails, their plate–mantle interactions and the source of the magmatism remain unconstrained. A geophysical mapping and dredging campaign on the RV Southern Surveyor (ss2012_v06) confirmed the prolongation of the Lord Howe Seamount Chain to the South Rennell Trough, ∼200 km further north than previously sampled. Radiometric dating of these new samples at 27–28 Ma, together with previously published results from the southern part of the chain, indicate straightforward northward motion of the Australian plate over a quasi-stationary hotspot as predicted by Indo-Atlantic and Pacific hotspot models. A peak in Lord Howe Seamount Chain magmatism in late Oligocene time, also seen in the Tasmantid and Cosgrove trails, matches a 27–23 Ma slowdown of Australian plate motion. The average magma flux of the Lord Howe hotspot is estimated at 0.4 m3 s−1, similar to rates of crustal production at the South Rennell Trough prior to cessation of spreading in middle Oligocene time, supporting a potential genetic relationship to this spreading system. In addition, plate tectonic modelling suggests that the seamounts and plateaus in the Coral Sea may host the earliest evidence of plume activity in the area.

Adaptive Neural Fuzzy Inference System and Automatic Clustering for Earthquake Prediction in Indonesia

Earthquake is a type of natural disaster. The Indonesian archipelago located in the world's three mega plates; they are Australian plate, Eurasian plate, and Pacific plate. Therefore, it is possible for applied of earthquake risk of mitigation. One of them is to provide information about earthquake occurrences. This information used for spatiotemporal analysis of earthquakes. This paper presented Spatial Analysis of Magnitude Distribution for Earthquake Prediction using adaptive neural fuzzy inference system (ANFIS) based on automatic clustering in Indonesia. This system has three main sections: (1) Data preprocessing, (2) Automatic Clustering, (3) Adaptive Neural Fuzzy Inference System. For experimental study, earthquake data obtained Indonesian Agency for Meteorological, Climatological, and Geophysics (BMKG) and the United States Geological Survey’s (USGS), the year 2010-2017 in the location of Indonesia. Automatic clustering process produces The optimal number of cluster, that is 7 clusters. Each cluster will be analyzed based on earthquake distribution. Its calculate the b value of earthquake to get the seven seismicity indicators. Then, implementation for ANFIS uses 100 training epochs, Number of membership function (MFs) is 2, MFs type input is gaussian membership function (gaussmf). The ANFIS result showed that the system can predict the non-occurrence of aftershocks with the average performance of 70%.

Sunda and Sumatra Block Motion in ITRF2008

The Southeast Asia region is mostly surrounded by active subduction zones in which the Australian plate, the Indian plate, and the Philippine Sea plate submerges beneath the continental plates and blocks. The Sunda block covers the large part of the Southeast Asia region, which comprises of Indochina, the South China Sea, the northeastern part of Sumatra, Borneo, the northern part of Java, and the shallow seas in between. We collect the GPS data in the whole Southeast Asia region for the period from 1994 to 2016, and process the original carrier phase data of GPS using GAMIT/GLOBK 10.6 to obtain the velocity field in the International Terrestrial Reference Frame, ITRF2008. The velocity field thus obtained is utilized to update the Euler rotation parameters of the Sunda block in ITRF2008, and model the long-term slip rates between the adjacent plate and blocks. In this study, we model the Sunda block and the Sumatra block together with the Australian plate by using TDEFNODE. The estimated Euler pole parameters of the Sumatra and Sunda blocks are estimated as their locations at (37.4°S, 106.8°E) and (46.2°N, 89.4°W), respectively, and their angular velocities of 0.371°/Myr clockwise, and 0.327°/Myr counter clockwise, respectively. These parameters result in the slip rate of the Sumatra fault with magnitude of ~9 mm/yr.

A Quiet but Deep Trouble in Tonga Subduction Zone

The Tonga subduction zone marks the convergent plate boundary between the Pacific and Australian plates, and it produces more large-magnitude deep earthquakes (depth >300 km) than anywhere else in the world. Deep earthquakes constitute less than 1% of the total earthquakes (M > 6) of the world and among them, ~66% are hosted by the Tonga subduction zone alone. On 19 August 2018, it produced globally the second largest deep earthquake (Mw 8.2, depth ~580 km) in the instrumentally recorded history of earthquakes. The 24 May 2013 Okhotsk earthquake with Mw 8.3 still holds the record for being the largest magnitude deep earthquake.

Tectonic and oceanographic process interactions archived in Late Cretaceous to Present deep‐marine stratigraphy on the Exmouth Plateau, offshore NW Australia

AbstractDeep‐marine deposits provide a valuable archive of process interactions between sediment gravity flows, pelagic sedimentation and thermohaline bottom‐currents. Stratigraphic successions can also record plate‐scale tectonic processes (e.g. continental breakup and shortening) that impact long‐term ocean circulation patterns, including changes in climate and biodiversity. One such setting is the Exmouth Plateau, offshore NW Australia, which has been a relatively stable, fine‐grained carbonate‐dominated continental margin from the Late Cretaceous to Present. We combine extensive 2D (~40,000 km) and 3D (3,627 km2) seismic reflection data with lithologic and biostratigraphic information from wells to reconstruct the tectonic and oceanographic evolution of this margin. We identified three large‐scale seismic units (SUs): (a) SU‐1 (Late Cretaceous)—500 m‐thick, and characterised by NE‐SW‐trending, slope‐normal elongate depocentres (c. 200 km long and 70 km wide), with erosional surfaces at their bases and tops, which are interpreted as the result of contour‐parallel bottom‐currents, coeval with the onset of opening of the Southern Ocean; (b) SU‐2 (Palaeocene—Late Miocene)—800 m‐thick and characterised by: (a) very large (amplitude, c. 40 m and wavelength, c. 3 km), SW‐migrating, NW‐SE‐trending sediment waves, (b) large (4 km‐wide, 100 m‐deep), NE‐trending scours that flank the sediment waves and (c) NW‐trending, 4 km‐wide and 80 m‐deep turbidite channel, infilled by NE‐dipping reflectors, which together may reflect an intensification of NE‐flowing bottom currents during a relative sea‐level fall following the establishment of circumpolar‐ocean current around Antarctica; and (c) SU‐3 (Late Miocene—Present)—1,000 m‐thick and is dominated by large (up to 100 km3) mass‐transport complexes (MTCs) derived from the continental margin (to the east) and the Exmouth Plateau Arch (to the west), and accumulated mainly in the adjacent Kangaroo Syncline. This change in depositional style may be linked to tectonically‐induced seabed tilting and folding caused by collision and subduction along the northern margin of the Australian plate. Hence, the stratigraphic record of the Exmouth Plateau provides a rich archive of plate‐scale regional geological events occurring along the distant southern (2,000 km away) and northern (1,500 km away) margins of the Australian plate.

The evolution of a Middle Miocene deep-water sedimentary system in northwestern New Zealand (Taranaki Basin): Depositional controls and mechanisms

Abstract Through the Oligocene and Miocene, New Zealand basins underwent widespread subsidence, related to the evolution of the convergent plate boundary between the Pacific and Australian plates. In Taranaki Basin on the western margin of the North Island, a deep water siliciclastic sedimentary system developed in response to basin subsidence and hinterland uplift. Basinward of the evolving shelf, basin floor sandstones and mudstones were deposited, some of which constitute important petroleum reservoirs and seals. Extensive 3D reflection seismic coverage has enabled us to map the character and distribution of basin floor sedimentary units and to develop a comprehensive sequence stratigraphic model. The stacking patterns of depositional sequences reflect an overall progradation of basin floor sedimentary facies and change in geometries through time, while associated elements such as fan lobes and channel systems increased in dimension. Structural change and southward progressing tectonic uplift most likely controlled increasing sediment input into the basin. In addition, an intensification of bottom current activity led to the development of sediment drifts, which we suggest was related to oceanographic changes at the end of the Middle Miocene Climatic Optimum. While turbidite depositional systems were dominant during lowstands, sediment reworking by shore parallel currents is interpreted to have been a dominant process during highstands. We document a change from sand-dominated to more mud-dominated deposits through the Middle Miocene and propose that this change in sediment character may be related to a higher degree of chemical weathering on land, possibly related to the northward migration and intensification of westerly winds.

Geophysical and geological characterisation of dredge locations from RV Southern Surveyor voyage ss2012_v06 (ECOSATI): hotspot activity in northern Zealandia

In October-November 2012 a geophysical mapping and dredging campaign in the eastern Coral Sea was conducted on the RV Southern Surveyor during voyage ss2012_v06 (ECOSATI). Part of this campaign was focussed in northernmost Zealandia where volcanic seamounts and uplifted portions of the Lord Howe Rise were targeted to determine the age and location of the northern portion of the Lord Howe Seamount Chain. Geophysical and geological analysis of the dredge sites from the southernmost South Rennell Trough and Chesterfield Plateau confirm the extension of the Lord Howe Seamount Chain ~200 km northward than previously identified, with an age-progression extending to ~27-28 Ma. These new samples, together with previously published samples from the youngest part of the chain, show consistency with both Indo-Atlantic and Pacific hotspots. The average magma flux rate of the Lord Howe hotspot is estimated at 0.4 m3/s, which is similar to the rates of crustal production at the South Rennell Trough, A peak in magmatism along the trail in the late Oligocene may be related to a slowdown in the motion of the Australian plate sometime between 27-23 Ma. The results of the geophysical and geological sampling and estimates of magma flux from the Lord Howe Seamount Chain will assist in thermal history modelling in the sedimentary basins of northern Zealandia and will help provide a geological framework for frontier resource exploration in this region.

Delineasi Zona Prospek Sistem Panasbumi Daerah ‘P’ Menggunakan Pemodelan Multi Dimensi Data Magnetotelurik Terintegrasi Data Geologi dan Geokimia

A study for delineating geothermal system of prospect area “P” has been done by using multi-dimensional modeling of magnetotelluric data. Physiographycally, geothermal prospect of “P” area is located at non-volcanic Banda inner arc hosted by Malihan Sekis rock complex with Perm-Trias age. The existance of geothermal system in this area is indicated by the presence of thermal manifestations in form of 6 chloride-bicarbonate hot springs with temperature in the the range of 37-67oC, and pH of 6-7. The development of geothermal system is most probably associated with strong tectonic activity caused by the collision between Seram island plate and Australian plate that ignite the occurence of intrussive body as heat source. In order to know the subsurface information of prospect area, magnetotelluric (MT) survey has been done. The processing of MT data was started from time-series data, continued by noise filtering, rotation of strike orientation and static shift correction to obtain better MT curve. The data were then being inversed by means of 1-Dimensional, 2-Dimensional and 3-Dimensional inversion methods. Reservoir temperature is estimated to be around 160-180 oC and classified as moderate temperature. The result of MT data inversions shows the presence of conductive layer ( 300 ?m) with updome shape appears underneath the manifestations occurence (MAP1, MAP2, MAP4, and MAP5), indicating that the heat source is located in northern part and elongate to souteast direction. The conceptual model of geothermal system was built based on integrated interpretation of geological, geochemical and geophysical data. The prospect area and recommendation of drilling location is estimated to be ± 3 km2 around upflow zone. Keywords: Prospect zone, geothermal system, magnetotelluric method, multi-dimension modeling

Kerusakan Kerusakan Bangunan Rumah Tinggal (Studi Kasus: Gempa Aceh 2 juli 2013)

Central Aceh Regency and Bener Meriah Regency of the Aceh Province is geologically located in the subduction of the Asian and Australian plate encounters, and is located at the end of Sumatra's fault / transform fault. This is what makes Aceh vulnerable to earthquake disaster. On July 2, 2013 a magnitude 6.1 earthquake shook the province of Aceh causing damage to buildings adjacent to the epicenter. Judging from the strength of the earthquake, this earthquake is one of the major earthquakes that hit Aceh. A research on the ratio of damaged house was conducted through a direct observation of spaciousness by taking samples of damaged houses for each category (collapsed, heavily damaged, moderately damaged, and lightly damaged) then an average is taken for each category of damage. The Result of research shows that the average ratio for collapsed houses are 96,25%, severe damage 70,08%, moderate damage 28,08% and light damage 3,87%, the average value of damage ratio is includes in the standard which established by Fema 1999. Keywords: Damage Ratio, Earthquakes, house damage category

Illumination of deformation by bending stresses and slab pull within the Southern Hikurangi Double Benioff Zone

ABSTRACTDouble Benioff Zones (DBZ) are ubiquitous in subduction systems worldwide, but the stress systems that give rise to them are not well known. We characterise stress orientations in the upper and lower bands of a DBZ in the dipping subducted Pacific plate beneath the southern Hikurangi margin, New Zealand. Stress orientations were calculated from focal mechanisms with 10 or more polarity picks, using a Bayesian stress inversion technique. The stress orientations in the upper band of seismicity are consistent with a down-dip extensional stress regime, whereas stress orientations within the lower band of seismicity are consistent with a down-dip compressional stress regime. This demonstrates that bending stresses are dominant within the Pacific plate beneath the southern North Island, possibly due to subduction beneath thickened mantle lithosphere of the Australian plate.

Lateral H2O variation in the Zealandia lithospheric mantle controls orogen width

Mantle xenoliths exhumed from beneath the South Island of New Zealand offer an opportunity to investigate the role of lithospheric mantle water in influencing deep lithosphere deformation and formation of the narrow Southern Alps mountain range during orogeny along the Australia–Pacific plate boundary. Fourier transform infrared spectrometry (FTIR) water measurements on clinopyroxene (cpx), orthopyroxene (opx) and olivine of peridotite xenoliths from seven localities across the Zealandia continent reveal a lateral variation of H2O within the Oligocene–Miocene lithospheric mantle. There is a “wet” domain beneath what is now the Southern Alps mountain range with average measured H2O concentrations of 610 ppm for cpx and 298 ppm for opx. In contrast, dominantly “dry” domains with average H2O concentrations of 110 ppm for cpx and 49 ppm for opx reside beneath East Otago, Chatham Island and Auckland Islands. Contrasting H2O concentrations within olivine (calculated to be 60 to 100 ppm for the wet domain versus <10 ppm for the dry domains) indicate a lateral gradient in mantle effective viscosity of up to one order of magnitude beneath the Southern Alps and the surrounding regions. The narrow width of the Southern Alps orogen, ∼80 km, contrasts with most of its broad counterparts worldwide, such as the North American Cordillera where the mantle was hydrated and weakened by the subduction of the Farallon plate. However, those developed orogens were often complicated by subsequent tectonic overprinting. Our findings show that the pre-existing rheologically weak zone of the mantle lithosphere, most likely resulting from hydration by the subduction of the oceanic lithosphere attached to the Australian plate beneath the South Island of New Zealand at ∼25 Ma, affects the continental deformation at or near the surface and controls the width of the developing Southern Alps orogen.

Early Cretaceous origin of the Woyla Arc (Sumatra, Indonesia) on the Australian plate

Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland – the Eurasian core of SE Asia – in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic ‘Ngalau Plate’ between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic–Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N–S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.

Tectonic plates parameters estimated in International Terrestrial Reference Frame ITRF2008 based on DORIS stations

This paper concerns an analysis of the accuracy of the estimated parameters Ω (Φ, Λ, ω) which define the tectonic plate motions. The study is based on the velocities of station positions in the IERS (International Earth Rotation and Reference Systems Service) which has published new realization of the International Terrestrial Reference System—ITRF2008 for Doppler Orbitography by Radiopositioning Integrated on Satellite DORIS technique. Eurasian, African, Australian, North American, Australian, Pacific, Antarctic and South American plates were used in the analysis. The influence of the number and localization of stations on the plate surface on the estimation accuracy of the tectonic plate motion parameters were discussed. The results were compared with the APKIM 2005 IGN model and our earlier estimation for the SLR technique. In general, a remarkable concurrent agreement between the present and the APKIM 2005 solutions was found.

SH wave structure of the crust and upper mantle in southeastern margin of the Tibetan Plateau from teleseismic Love wave tomography

The deep structure of southeastern Tibet is important for determining lateral plateau expansion mechanisms, such as movement of rigid crustal blocks along large strike-slip faults, continuous deformation or the eastward crustal channel flow. We invert for 3-D isotropic SH wave velocity model of the crust and upper mantle to the depth of 110 km from Love wave phase velocity data using a best fitting average model as the starting model. The 3-D SH velocity model presented here is the first SH wave velocity structure in the study area. In the model, the Tibetan Plateau is characterized by prominent slow SH wave velocity with channel-like geometry along strike-slip faults in the upper crust and as broad zones in the lower crust, indicating block-like and distributed deformation at different depth. Positive radial anisotropy (VSH > VSV) is suggested by a high SH wave and low SV wave anomaly at the depths of 70–110 km beneath the northern Indochina block. This positive radial anisotropy could result from the horizontal alignment of anisotropic minerals caused by lithospheric extensional deformation due to the slab rollback of the Australian plate beneath the Sumatra trench.

RETRACTED: Early Cretaceous origin of the Woyla Arc (Sumatra, Indonesia) on the Australian plate

Abstract Key to understanding the plate kinematic evolution of the Neotethys oceanic domain that existed between the Gondwana-derived Indian and Australian continents in the south, and Eurasia in the north, is the reconstruction of oceanic plates that are now entirely lost to subduction. Relics of these oceanic plates exist in the form of ophiolites and island arcs accreted to the orogen that stretches from Tibet and the Himalayas to SE Asia that formed the southern margin of Sundaland. The intra-oceanic Woyla Arc thrusted over western Sundaland – the Eurasian core of SE Asia – in the mid-Cretaceous. The Woyla Arc was previously interpreted to have formed above a west-dipping subduction zone in the Early Cretaceous, synchronous with east-dipping subduction below Sundaland. The oceanic ‘Ngalau Plate’ between the Woyla Arc and Sundaland was lost to subduction. We present paleomagnetic results from Lower Cretaceous limestones and volcaniclastic rocks of the Woyla Arc, Middle Jurassic radiolarian cherts of the intervening Ngalau Plate, and Upper Jurassic–Lower Cretaceous detrital sediments of the Sundaland margin. Our results suggest that the Woyla Arc was formed around equatorial latitudes and only underwent an eastward longitudinal motion relative to Sundaland. This is consistent with a scenario where the Woyla Arc was formed on the edge of the Australian plate. We propose a reconstruction where the Ngalau Plate formed a triangular oceanic basin between the N–S trending Woyla Arc and the NW-SE trending Sundaland margin to account for the absence of accreted arc rocks in the Himalayas. As consequence of this triangular geometry, accretion of the Woyla Arc to the western Sundaland margin was diachronous, accommodated by a southward migrating triple junction. Continuing convergence of the Australia relative to Eurasia was accommodated by subduction polarity reversal behind the Woyla Arc, possibly recorded by Cretaceous ophiolites in the Indo-Burman Ranges and the Andaman-Nicobar Islands.

Source-to-sink constraints on tectonic and sedimentary evolution of the western Central Range and Cenderawasih Bay (Indonesia)

The island of New Guinea is the result of continent-arc collision that began building the island’s Central Range during the late Miocene. Recent studies have shown that rapid subduction, uplift and exhumation events took place in response to rapid, oblique convergence between the Pacific and the Australian plates. The tectonic and sedimentary evolution of Cenderawasih Bay, in the northwestern part of the New Guinea Island is still poorly understood: this bay links a major structural block, the Kepala Burung block, to the island’s Central Ranges. Previous studies have shown that Cenderawasih Bay contains a thick (>8 km) sequence of undated sediments. One hypothesis claims that the embayment resulted from a 3 Ma opening created by anticlockwise rotation of the Kepala Burung block with respect to the northern rim of the Australian plate. Alternatively, the current configuration of Cenderawasih Bay could have resulted from the southwest drift of a slice of volcanics and oceanic crust between 8 and 6 Ma. We test these hypotheses using (i) a geomorphologic analysis of the drainage network dynamics, (ii) a reassessment of available thermochronological data, and (iii) seismic lines interpretation. We suggest that sediments started to accumulate in Cenderawasih Bay and onshore in the Waipoga Basin in the late Miocene since the inception of growth of the Central Range, beginning at 12 Ma, resulting in sediment accumulation of up to 12,200 m. This evidence is more consistent with the second hypothesis, and the volume of sediment accumulated means it is unlikely that the embayment was the result of recent (2–3 Ma) rotation of structural blocks. At first order, we predict that infilling is mainly composed of siliciclastics sourced in the graphite-bearing Ruffaer Metamorphic Belt and its equivalent in the Weyland Overthrust. Ophiolites, volcanic arc rocks and diorites contribute minor proportions. From the unroofing paths in the Central Range we deduce two rates of solid phase accumulation (SPAR) since 12 Ma, the first one at a mean SPAR ranging between 0.12 and 0.25 mm/a with a maximum SPAR of 0.23–0.58 mm/a, and the second during the last 3 Ma, at a mean SPAR ranging between 0.93 and 1.62 mm/a and with a maximum SPAR between 2.13 and 3.17 mm/a, i.e., 6700–10,000 m of Plio-Pleistocene sediment accumulation. Local transtensional tectonics may explain these unusually high rates of sedimentation in an overall sinistral oblique convergence setting.