tectonic history of sumba island indonesia since the late cretaceous and its rapid escape into the forearc in the miocene abstract the island of sumba lies within the sunda banda forearc and contains volcanic plutonic and volcaniclastic rocks that record a history of arc volcanism extending from late cretaceous 80 ma or earlier to oligocene 31 ma time during the late cretaceous sumba formed part of a great indonesian volcanic arc system near southeastern eurasia between late cretaceous and early miocene time sumba remained part of that arc system which ceased to be volcanically active by 31 ma during the late miocene 18 ma sumba as part of the relict arc system was situated near the present site of alor and wetar at 16 ma sumba was torn from the relict arc and began to move at a velocity of 50 mm yr in a west south westerly direction volcanism along the modern banda arc soon followed by 7 ma sumba finally came to rest after having moved 450 km into the forearc we interpret the rapid motion of sumba into the forearc as a discrete block to have been a response to the collision between australia and indonesia in the area of timor the savu basin possibly originated as an arc crestal rift which then opened behind sumba as the latter moved westward over the past 16 my more than 3 km of sediment have been deposited in the savu basin by erosion from the surrounding islands sumba stopped moving to the west south west at 7 ma after reaching approximately its present location since then the island has ceased to be a discrete tectonic fragment and has behaved as an integral part of the forearc during the past 7 my compressional tectonics within the forearc has led to elevation of the rocks exposed on sumba by as much as 4 km

thermal history of australian passive margin cover sequences accreted to timor during late neogene arc continent collision indonesia abstract paleotemperature indicators and apatite fission track analysis of australian continental margin cover sequences accreted to the active banda arc continent collision indicate little to no heating during rapid late neogene uplift and exhumation thermal maturation patterns of vitrinite reflectance conodont alteration and illite crystallinity show that peak paleotemperatures ppt increase with stratigraphic and structural burial the highest ppt is found in the northern hinterland of the accretionary wedge which was beneath progressively thicker parts of the upper plate towards the north major discontinuities in the pattern of ppt are associated with the position of major thrust ramps such as those forming the ramelau kekneno arch rka ppt for upper triassic to neogene strata south of the rka are 60 80 c which are similar to and in many cases lower than correlative and age equivalent units drilled on the nw australian shelf permian to lower triassic sedimentary strata thrust over younger units within and north of the rka have ppt of 100 220 c thrust sheets accreted beneath the upper plate have ppt approximately 90 c higher than those frontally accreted metamorphism of the northernmost units of these sequences yield ppt of 300 c thrust stacking yields an inverted thermal profile of ppt decreasing discontinuously downward and to the south towards the foreland the timing of ppt is constrained by apatite fission track ages from mostly triassic continental margin cover sequences ages of upper triassic units are primarily coeval with deposition and show little evidence of thermal annealing whereas those of lower triassic units are almost completely annealed and range from 1 8 0 5 19 2 9 7 ma the clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a triassic stratigraphic interval in the slope and rise of the nw australian continental margin the position of this zone on the present shelf is higher in the stratigraphic column due to the greater thickness of post breakup shelf facies units thrust stacking of rise slope and shelf units produces an inverted vertical profile of increasing apatite fission track age with depth lack of any long confined track lengths in apatite from all of the units requires rapid and recent exhumation of the thrust stack which is coincident with rapid phases of pliocene pleistocene exhumation documented throughout timor these data preclude pre late miocene tectonic burial or pre pliocene exhumation of the nw australian continental margin

effective elastic thickness of the northern australian continental lithosphere subducting beneath the banda orogen indonesia inelastic failure at the start of continental subduction abstract pliocene recent continent island arc collision of the northern australian continental lithosphere across the banda orogen from roti to the kai plateau 121 137 e longitude has formed an underfilled foreland basin within the timor tanimbar aru trough continental collision on northern australian lithosphere is most advanced near central timor island in terms of shortening and absorbing the forearc basin savu basin within the accretionary prism australian continental lithosphere north of area around central timor island is believed to be detached from the oceanic lithosphere effective elastic thickness eet of the northern australian continental lithosphere from roti to the kai plateau are derived using an elastic half beam model modeled deflection is matched to the seafloor bathymetry and the marine complete 3d bouguer gravity anomalies the eet varies from 27 to 75 km across the northern australian continental lithosphere from roti to kai plateau when the thickness of the elastic half beam is kept constant the highest eet values lies near central timor from the shelf to beneath the banda orogen the eet of the northern australian continental lithosphere is reduced from 90 to 30 km when the thickness of the elastic half beam is allowed to vary down dip elastic half beam modeling approximates the banda orogen as a triangular load and hidden subsurface loads as end point loads wider triangular loads modeling the load contribution from banda orogen need higher values of eet such an observation highlights the role of high eet in thin skinned collisional tectonics by promoting the support of wider accretionary prisms by parts of foreland basins with higher eet variations in eet may result from inelastic yielding in the northern australian continental lithosphere oroclinal bending of the australian continental lithosphere in the east from tanimbar to the kai plateau may create additional yielding and further decrease the eet change in eet occurred at the start of continental subduction in the late miocene early pliocene boundary due to change in curvature of the northern australian lithosphere near the shelf slope both in map and cross sectional view evidence for the inelastic yielding of the northern australian continental lithosphere near the present day shelf slope at the continental subduction is found in 1 the maximum change of eet near shelf slope in laterally variable eet calculations and 2 in the almost cessation of normal faulting in late miocene early pliocene seen on seismic reflection data from northern australian continental shelf slope elastic half beam models across central timor do not require end point loads and may imply that there are no slab pull forces from the oceanic lithosphere that are acting on the leading edge of the subducted northern australian continental lithosphere

tectonics of the new guinea area new guinea is a very large island 2500 km long by 600 km wide whose southern half geologically forms the northern part of the australian con tinent the long fold and thrust mountain range rising to heights above 4000 m that extends along the spine of central new guinea is the result of collisions of this northern margin of australia with island arcs during the northward drift of australia by some 3000 km during the last 37 m y the mountainous and hilly part of northern new guinea exposes igneous and metamorphic rocks milsom 1985 representing accreted parts of these collided arcs which are overlain by younger episutural or successor basins figure 1 the complex system of island arcs that sweep around the eastern side of australia and continue around northern australia new guinea linking the southwestern pacific region with eastern indonesia and the indian ocean essentially result from interactions between the wnw moving pacific plate and the nne moving india australia plate figure 2 the cenozoic fold and thrust mountain belts which characterize the aus tralian continental margin in new caledonia new guinea and eastern indonesia record the collisions figure 1 during the last 40 m y most occurred during the last 25 m y some in the last 3 m y associated with the continental margin and island arcs marginal to this continent over a strike length of 15 000 km

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

neogene basin history and paleomagnetism of a rifted and inverted forearc region on and offshore sumba eastern indonesia the island of sumba is located in the arc trench gap at the junction of the sunda and banda arcs to elucidate its enigmatic forearc position stratigraphic and paleomagnetic data were collected along three transects in central and east sumba sumba represents the emerged part of a terrane of se asian origin results of stratigraphic and paleomagnetic investigations on central and east sumba are presented and discussed in order to identify patterns of horizontal and vertical crustal movements a synthetic seismogram of the onshore record enables correlation with the offshore neogene e of sumba in order to interpret the data in a regional context the neogene basin history of sumba started when overall subsidence took place around the transition from early to middle miocene on east sumba above a basal condensed interval up to 600 m of middle late miocene volcaniclastic submarine fan deposits occur the sediments reflect island arc volcanism and are interpreted as parts of a prograding submarine fan system on a north dipping paleoslope fed by a volcanic source to the south of sumba biostratigraphic data indicate a high volcanic supply during the middle miocene and early middle tortonian a waning supply during the late tortonian and renewed supply during the messinian these patterns probably reflect variation in volcanic activity during the messinian calcilutites and foraminiferal chalks became dominant and deposition of these pelagic sediments continued into the early pliocene using the pattern of magnetic polarity changes in a selected interval the position of the mioceneepliocene boundary is better constrained seismic studies in the offshore area e of sumba van der werff 1995a b indicate the presence of an extensive tract of n prograding turbidites on sumba ridge savu basin the proposed correlation with the onshore record suggests lateral continuity from the island into the offshore area where the volcaniclastic submarine fan system presumably had its largest development subsidence proceeded so fast i m ka on east sumba that before the beginning of the late miocene sediments were deposited below the ccd this pattern suggests that the sumba region underwent strong crustal attenuation due to rifting as this was coupled with the arrival of volcaniclastics we envisage intra arc rifting coupled with the growth of a short lived volcanic arc further south its initiation at the transition of middle late miocene suggests interaction with the then approaching banda arc subduction system the paleomagnetic data indicate that during this process sumba was at a paleolatitude of 12 south and underwent a counter clockw ise rotation of 5 the reappearance of planktonic foraminiferal assemblages during the latest miocene and their present elevation above sea level suggest an average rate of post miocene uplift of 0 7 mm a emergence of sumba probably did not take place before 3 ma this inverted motion of the sumba terrane is probably coupled with the change to the present tectonic situation in which volcanic activity was resumed in the present inner arc after a non volcanic interval during the spreading stage 1 1997 elsevier science ltd

ostracods as tsunami tracers in holocene sequences this review analyses the ostracod record in holocene tsunami deposits using an overview of the 2004 indian ocean tsunami impact on its recent populations and the associated tsunamigenic deposits together with results from numerous investigations of other holocene sequences different features such as the variability of the local assemblages population density species diversity age population structure e g percentages of adults and juvenile stages or taphonomical signatures suggest that these microorganisms may be included amongst the most promising tracers of these high energy events in marshes lakes lagoons or shallow marine areas

a submarine slide scar and channel filled with slide blocks and megarippled globigerina sands of possible contourite origin from the pliocene of sumba indonesia abstract early pliocene deep water sequences estimated depositional depth 1 2 km near kambatatana sumba island include a slide scar which evolved into a channel the channel measures over 120 m in width and 20 m in depth after an initial phase of sliding overall quiescene is marked by a burrowed surface the overlying fill consists of intimately associated current and slide deposits the former are characterized by climbing megaripples with set heights of 0 3 1 2 m indicating suspension rich currents these megaripples mainly consist of foraminiferal and washed out from pliocene pelagic chalks and marls mixed with some shallow water benthos the slide blocks display the lithology of the underlying pliocene sediment and vary in size from a few cm to 15 m some blocks underwent deformation during sliding whereas others retained their original shape comparison with data from analogous modern settings suggests that the channel was located at the transition between a relatively steep and more gentle submarine slope syntectonic deformation related to gradual uplift of sumba probably induced locally steeper slopes on the distal part of a sediment starved miocene turbidite fan which originally was inclined at an angle of around 2 the general slope during the pliocene is estimated to have been less 1 1 30 the origin of the megarippled foraminiferal sand units is uncertain but they may have been supplied by contour currents presently shaping parts of the seafloor morphology in this region

collisional melange development geologic associations of active melange forming processes with exhumed melange facies in the western banda orogen indonesia analysis of block assemblages matrix clay mineral composition and microfauna and offshore seismic reflection profiles reveal that the bobonaro melange in the timor region is sourced from mud rich australian continental margin sequences that are remobilized during accretion and form various facies depending on the structural conditions of emplacement melange facies include broken formation matrix rich mud injections and classic mixed block in clay facies each of these are distinguished by varying degrees of remobilization mixing and dispersion at different structural positions across the orogenic wedge the most important structural control is whether melange was generated beneath or in front of upper plate banda forearc basement banda terrane at the present collisional deformation front in the timor trough seismic reflection profiles show that melange forms mostly by stratal detachment and fluid assisted remobilization above a basal decollement propagating laterally along overpressured jurassic to cretaceous clay rich sequences of the distal australian continental margin the broken clay rich material injects upward through faults to form intrusive bodies at the base of slope cover sediment to form mud ridges at the surface similar patterns of stratal disruption are exposed onshore in the pliocene kolbano fold and thrust wedge of southern timor which is structurally contiguous with the timor trough deformation front melange in the kolbano mountains is mostly broken formation and matrix rich injections of mud from jurassic and cretaceous units deformation mechanisms include intense layer parallel extension associated with emplacement by mud diapirs that rise from near the decollement upward to the surface along fault conduits in the hinterland of the orogenic wedge east timor and northern west timor melange is dominantly of mixed block in clay facies with large blocks derived from roof thrust sheets of intermixed banda terrane and maubisse formation units at the structural base of these thrust sheets is the sonnebait disruption zone sdz which formed the initial suture between the banda terrane and structurally underthrust australian continental margin sequences during the late miocene to early pliocene the thickest accumulations of mixed block in clay melange in the timor region are found at the southern edge outlet of the sdz near the central and viqueque synorogenic basins the extent of block dispersion and mixing in the sdz is indicative of intense shear strains perhaps induced by an oversupply of accretable material when the suture zone was clogged by underthrusting of the australian continental margin

plate tectonics and island arcs the plate tectonic concepts that developed rapidly in the late l960s made possible the understanding of island arcs before that time mobilistic concepts evolved slowly hindered particularly in the united states by an obstructionist geoscience establishment the volcanic belts of island arcs form about 100 km above subducting plates convergent plate boundaries evolve complexly with time and at any one time vary greatly along their lengths seismicity defines positions but not trajectories of descending slabs which sink more steeply than they dip and are overridden by advancing upper plates subduction occurs beneath only one side at a time of an internally rigid plate and the common regime in an overriding plate behind a surficial accretionary wedge is extensional except where a collision is underway back arc basin lithosphere is built behind or by migrating island arcs which lengthen and increase their curvatures a collision can involve two active arcs in which case intervening lithosphere sinks beneath both of them or an active margin and a passive one either type of collision generally is followed by the breaking through of new subduction beneath the composite mass of light crust from a new trench on the outside of the aggregate conversely a new subduction system commonly is a by product of collision a strip of back arc basin crust is in many cases left attached to the aggregate in front of the new trench and becomes the basement for a fore arc basin the leading edge of which is raised as melange is stuffed under it sedimentation in trenches is predominantly longitudinal and can be from distant sources accretionary wedges are dynamic being thickened at both toes and bottoms by tectonic accretion and thinned by gravitational forward flow melange is largely a product of tectonic imbrication and flowage driven by these conflicting processes not of submarine sliding high pressure metamorphic rocks form beneath overriding plates not within wedges in front of them arc magmas incorporate much material from the lithosphere through which they rise and vary correspondingly with the evolving composition of that lithosphere arc crust is inflated into geanticlines by intrusive rocks and thermal expansion submarine island arc volcanic rocks are widely spilitized with na enrichment and ca depletion by hydrothermal reaction with sea water the lower crust of mature island arcs consists of granulite facies rocks of mafic intermediate and felsic intermediate compositions the mohorovicic discontinuity may be primarily a constructional boundary representing the shallow limit off crystallization of voluminous rocks of ultramafic composition or plagioclase free mineralogy

deformation and metamorphism of the aileu formation north coast east timor and its tectonic significance abstract the large block of metamorphic rocks along the north coast of east timor is of special interest as it occurs at the boundary between continental and oceanic crust in an island arc continent collision zone a detailed study of the structure and metamorphic history of 400 km2 of this formation showed it has a complex history of penetrative deformation but the structure is coherent pelites psammites and limestones interlayered with dolerites and amphibolites have been metamorphosed in a medium pressure environment they now form a metamorphic province zoned from low greenschist facies in the southwest to upper amphibolite facies in the east the earliest recognised deformation phase predated the metamorphism and produced a widespread layer parallel schistosity but no recognisable folds the second deformation phase post dated the metamorphic maximum and micropetrological evidence indicates a gradual cooling during this event this deformation produced tight folds with an axial plane schistosity and transposed the earlier structures the progressively weaker third and fourth phases developed crenulation cleavages and related folds under greenschist facies conditions open fifth phase macroscopic folds were probably synchronous with strike slip faulting parallel to the north coast later dip slip faulting juxtaposed the aileu formation with permian and mesozoic sediments of very low metamorphic grade reconnaissance k ar radiometric dating using hornblende and biotite showed the prograde metamorphic maximum occurred before 11 ma ago and implies that the second and strongest deformation phase occurred in the late miocene this young age establishes the relationship of the deformation events to the collision between australia and the inner banda arc the proposed models for the structure of timor must be modified to fit the deformation history of the aileu formation if timor is essentially autochthonous the aileu formation was probably deposited in a palaeozoic graben and the metamorphic maximum may have occurred in the jurassic the overthrusting models must be modified in the light of the close correlation in time between penetrative deformation and emplacement of the proposed thrust sheets the analogy proposed between timor and normal convergent margins is not supported but it may be possible to draw analogies with the molucca sea

the wetar back arc thrust belt eastern indonesia the effect of accretion against an irregularly shaped arc the 350 km long east west trending wetar back arc thrust belt in eastern indonesia is a result of the collision of australia with the indonesian island arc along the northwest margin of wetar island a short 50 km section of the thrust belt trends northeast coincident with the offset of the indonesian arc by the newly discovered left lateral wetar atauro fault which runs along the shelf region and trends northeast the wetar atauro fault may be viewed as a large scale lateral ramp or wrench fault separating the eastern wetar thrust belt from the western wetar thrust belt the interaction of strike slip faulting and back arc thrust faulting creates several arc blocks whose geometry strongly affects the structure of the deformed wedge of sediment accreting in the wetar back arc thrust belt the varying orientations of the arc backstop make the wetar back arc thrust belt a perfect laboratory for the study of oblique convergence along most of its length the wetar thrust belt parallels the arc slope however along the northeast trending offset in the thrust belt seamarc ii side scan sonar plus seismic reflection data show that the trend of the thrust belt is not parallel to the trend of the arc slope rather it is intermediate between the trend of the arc slope and the perpendicular to the expected convergence direction the side scan images allow us to map the geometry of four main thrust faults the wetar liran atauro and alor faults the wetar liran and atauro faults trend northeast parallel to the thrust front and do not have an en echelon relationship the westernmost fault in the survey area the alor fault trends almost east west the orientation of the wetar atauro fault is consistent with a maximum principal stress within the arc oriented between 8 and 23 west of north depending on the internal coefficient of friction this agrees well with the p axes of nearby earthquake focal mechanisms which trend consistently west of north suggesting that the regional principal tectonic compression is oriented west of north because the thrust belt is oblique to the arc slope we infer the structural directions are influenced by both the arc backstop and by the regional tectonic stress the tectonic compression due to arc continent collision in this region may be modified by the arc geometry in several ways 1 the stress necessary to support the arc topography may be significant close to the arc 2 the change in thickness of the elastic part of the lithosphere may cause a concentration of tectonic stress and 3 the difference in material properties between the relatively rigid arc bulldozer and the weak basin sedimentary fill may be an important factor in producing a thrust belt that conforms roughly to the shape of the arc the structure of the wetar back arc thrust zone demonstrates that the development of small rigid blocks within a major collision zone may produce complex structural patterns and local directions of shortening that are highly oblique to the main direction of plate convergence

tectonic collision processes after plate rupture abstract rupture of a continental plate subducted below a forearc produces a fold and thrust mountain belt with fast overthrusting of nappes post rupture plate unflexing leading to reflexure provides a mechanism for foreland basin formation application to the australia banda arc collision accounts for the origin of the timor trough its imbrication and contemporaneous extension in outer arc as well as reversal of subduction direction after the emplacement of nappes

ocean trench blocked and obliterated by banda forearc collision with australian proximal continental slope abstract the bathymetry and abrupt changes in earthquake seismicity around the eastern end of the java trench suggest it is now blocked south east of sumba by the australian jurassic rifted continental margin forming the largely submarine roti savu ridge plate reconstructions have demonstrated that from at least 45 ma the java trench continued far to the east of sumba from about 12 ma the eastern part of the java trench called banda trench continued as the active plate boundary located between what was to become timor island then part of the australian proximal continental slope and the banda volcanic arc this banda trench began to be obliterated by continental margin arc collision between about 3 5 and 2 ma the present position of the defunct banda trench can be located by use of plate reconstructions earthquake seismology deep reflection seismology dsdp 262 results and geological mapping as being buried under the para autochthon below the foothills of southern timor locating the former trench guides the location of the apparently missing large southern part of the banda forearc that was carried over the australian continental margin during the final stage of the period of subduction of that continental margin that lasted from about 12 ma to about 3 5 ma tectonic collision is defined and distinguished from subduction and rollback collision in the southern part of the banda arc was initiated when the overriding forearc basement of the upper plate reached the proximal part of the australian continental slope of the lower plate and subduction stopped collision is characterised by fold and thrust deformation associated with the development of structurally high decollements this collision deformed the basement and cover of the forearc accretionary prism of the upper plate with part of the unsubducted australian cover rock sequences from the lower plate together with parts of the forearc basement they now form the exposed banda orogen the conversion of the northern flank of the timor trough from being the distal part of the banda forearc accretionary prism carried over the australian continental margin into a foreland basin was initiated by the cessation of subduction and simultaneous onset of collisional tectonics this reinterpretation of the locked eastern end of the java trench proposes that from its termination south of sumba to at least as far east as timor and probably far beyond the java banda trench and forearc overrode the subducting australian proximal continental slope locally to within 60 km of the shelf break part of the proximal forearc s accretionary prism together with part of the proximal continental slope cover sequence were detached and thrust northwards over the java banda trench and forearc by up to 80 km along the southwards dipping savu thrust and wetar suture these reinterpretations explain the present absence of any discernible subduction ocean trench in the southern banda arc and the narrowness of the forearc reduced to 30 km at atauro north of east timor

plate rupture by hydraulic fracture resulting in overthrusting lithospheric plates bending into subduction zones may become ruptured by hydraulic fracturing initiated by the injection of mobilized sediments thick poorly indurated water laden sediments of the proximal continental rise are the most obvious potential source for the large volume of material required for this process rupture of the descending plate may result in the subducted oceanic part of the lithosphere becoming detached and sinking independently while the more buoyant continental part rises by isostatic rebound we show here that applying this model to eastern indonesia provides an explanation for the banda arc geometry the apparent absence of a normal forearc and for the position of the thrust sheets relative to the benioff zone1 we also report that it can account for the short phase of deformation of the australian continental margin preceding its uplift of 3 km ref 1

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

rates of neogene and quaternary tectonic movements in the southern banda arc based on micropalaeontology it is generally considered that the outer banda arc islands are composed in part of strongly deformed sediments that accumulated at the north australian continental margin the onset and completion of folding nappe emplacement imbrication and uplift that produced the islands of the outer banda arc have been dated by means of planktonic foraminifera the dating of the onset of uplift of timor from a deep submarine position at the end of the neogene nappe emplacement to mountains now reaching nearly 3 km high indicates the rate of post collision uplift to have been initially 3 mm yr then it slowed to about 1 5mm yr where the australian continental margin meets the eastern end of the present java trench there are indications that the australian margin has overridden the trench in the timor region by 240 km micropalaeontological dating of the neogene collision between the australian continental slope proximal rise and the trench provides constraints for checking the overriding hypothesis by calculating rates of convergence derived from plate motions 7 5cm yr against the rates based on the tectonic model 7 4cm yr after nappe emplacement possibly faster than 6 25 cm yr shortening of the continental crust appears to have migrated towards the australian continent so that the shelf itself has become involved in the imbrication with shortening of the cover rocks between the nappes and the present shelf edge amounting to about 40 km during the last 2 ma

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

variable rates of late quaternary surface uplift along the banda arc australian plate collision zone eastern indonesia radiometrically dated emergent coral terraces from southeastern indonesia provide estimates of differential vertical strain in the banda arc continent collision complex at semau island two samples from the lowest emergent reef 5 7 m yield 230th dates that correspond to the 5a c 83 ka sea level highstand and a low surface uplift rate of 0 2 0 3 m per 1000 years at rote island samples from the lowest emergent reef c 1 2m on both north and south sides of the island yield late holocene ages and an average short term uplift rate of c l 1 5m per 1000 years similarity of ages from different samples on the north coast of rote suggests possible coseismic emergence survey data from nine emergent reefs and marine notches up to 170m in altitude on the south side of rote indicate that uplift rates may have been c l 1 5m per 1000 years for c l20000 130000 years combined with previous studies these results indicate that late quaternary surface uplift rates vary an order of magnitude along the strike of the banda orogen vertical displacement rates are greatest in young parts of the orogen where the shelf slope break recently has been underthrust beneath the orogenic wedge as at rote and in older parts of the orogen where retroarc thrust faulting occurs as at alor island this paper presents new 230th ages and associated surface uplift rates for emergent coral reefs on two islands near west timor in southeastern indonesia fig 1 on rote island no previous work has been done on emergent corals on semau island only one coral sample has yielded a previous age estimate jouannic et a 1988 both islands are located in an important zone of transition from subduction to collision along the plate boundary between the indian australian and eurasian plates whereas the transition from subduction to collision is poorly preserved in most other collision zones it is well preserved in the timor region many lines of evidence indicate that both horizontal and vertical rates of deformation are greater in this area than elsewhere in the orogen this paper also compiles all previous estimates of surface uplift rates from coral dating on islands throughout southeastern indonesia we use this compilation to consider regional variability in vertical strain rates in relation to recent models of tectonic processes in the banda arc australian continental margin collision zone cenozoic deformation in the banda arcaustralian continental plate collision zone the indonesian region contains an active subduction zone accretionary arc volcanic island arc and emergent collision zone in western indonesia oceanic crust of the indian australian plate is subducting northward beneath the eurasian plate along the java trench forming the sunda volcanic arc and accretionary wedge which includes the volcanic islands of sumatra and java fig 1 in eastern indonesia where oceanic crust has been subducted completely underthrusting of buoyant australian continenta1lithosphere since about 3 ma changes the java trench into a collisional foredeep and the locally inactive banda arc into an arc continent collision zone along the timor trough hamilton 1979 bowin eta 1980 silver eta 1983 breen eta 1986 karig eta 1987 underthrusting of the mature australian continental margin significantly increases the influx of accretionary material and the frictional resistance to slip along the plate boundary harris 1991 collisional strain merritts d eby r harris r edwards r l chang h 1998 variable rates of late quaternary surface uplift along the banda arc australian plate collision zone eastern indonesia in stewart i s vitafinzi c eds coastal tectonics geological society london special publications 146 213 224 214 d merritts et al explanation of symbols thrust fault teeth on upper plate

mesozoic and late tertiary submarine fan sequences and their tectonic significance sumba indonesia abstract the indonesian island of sumba occupies a critical zone which separates a normal subduction complex java trench system from a continent island arc collision zone banda arc sumba is considered by some authors to be a microcontinental fragment although in this context its pre fragmentation origin is uncertain detailed studies of the stratigraphy of sumba however throw light on the origin and subsequent geological history of the island and surrounding areas on available evidence the oldest outcropping rocks are of cretaceous age and locally contain a tropical tethyan marine fauna they comprise dark coloured sometimes carbonaceous and often volcanogenic mudstones sandstones gravels and diamictites pervasively intruded by andesitic and dacitic dykes and locally intruded by granodiorite plutons these sediments are siliclastic and appear to have had a continental provenance the cretaceous rocks in many areas compromise part of a major submarine fan complex which at least in south central sumba prograded towards the southwest and south shallow marine and non marine paleogene sediments and volcanic agglomerates lie unconformably above the uplifted tilted and eroded cretaceous strata these are overlain in turn by the widely outcropping miocene sumba formation an oceanic sequence with island arc affinities accessible outcrops of the sumba formation comprise platform carbonates with abundant reef developments in west sumba and a major submarine fan pelagic chalk complex in east sumba the fan complex which extends beneath the southern savu sea north of sumba is dominated by large scale slumps olistostromes and thin and thick bedded turbidites turbidite sands and gravels invariably are volcaniclastic containing components derived from a typical inner volcanic arc complex paleocurrent indicators are difficult to find in the sumba formation thus it is uncertain at this stage whether the volcaniclastic turbidites were derived from the present volcanic arc or from an undetermined source which may since have subsided the portion of the fan complex which underlies east sumba however has undergone vertical uplift since its emplacement of between one and several kilometres uplift is actively in progress at present possibly due to underthrusting by northward moving australian continental crust in this context the island of sumba comprises an uplifted north tilted and subaerially exposed part of the forearc basin of the indonesian arc this uplift can be related to initial stages of continental collision

the sumba enigma is sumba a diapiric fore arc nappe in process of formation abstract the anomalous updomed morphological expression of sumba island its enigmatic lack of strong neogene deformation and the northward morphological indentation of southern sumbawa and flores require explanation the stratigraphy of sumba may be correlated with the cretaceous to miocene part of the timor allochthon the sedimentary and eruptive rock succession in sumba shows remarkable similarities with the allochthonous palelo wiluba and cablac deposits of timor in both islands the cretaceous parts of these sequences are regarded as characteristic of fore arc deposits built on thin continental crust the timor nappe is interpreted as a 5 km thick tectonic flake of the banda fore arc thrust onto the australian continental margin in the mid pliocene collision the postulated sumba nappe has not yet been thrust onto the australian margin which in the sumba region has not yet converged as close to the arc as in the timor area the postulated sumba nappe is interpreted as a diapiric elongated dome of the sunda fore arc that is being squeezed by the converging margin of australia against the volcanic islands of sumbawa and flores the absence of indications on the seismic reflection profiles for the presence of the thrust fault of the sumba nappe may perhaps be explained by the thrusts being nearly horizontal within flat lying strata the savu thrust is correlated with the probably older pre late pliocene wetar suture as a major southward dipping lithospheric rupture east of 124 e this suture does not seem to have moved much since the mid pliocene collision that emplaced the nappes on timor however microearthquake data suggest some activity is continuing

the paris concept an experimental demonstration of sea surface altimetry using gps reflected signals this paper presents the passive reflectometry and interferometry system paris concept and how it originated in the european space agency esa noordwijk the netherlands in 1993 as a novel method to perform mesoscale ocean altimetry the paris concept uses signals of opportunity such as the signals from the global navigation satellite systems gnss which are reflected off the ocean surface to perform mesoscale ocean altimetry essentially the relative delay between the direct and the reflected signals received from a low earth orbit satellite provides information about sea surface height the paper describes an original experiment on sea surface altimetry using gps reflected signals the objective of the experiment was to demonstrate the potential of the paris concept this experiment is the first one ever published on performing sea surface height estimations using reflected navigation signals in a controlled environment the key result of the experiment is the demonstration of a root mean squared rms height accuracy within 5 s of 1 of the used code chip 3 m for c a code direct extrapolation of this experimental result to the 10 times higher chip rate p code signal allows us to predict a height error of 30 cm in 5 s provided adequate models are used to take into account systematic effects the paper ends presenting the potential of the paris concept for long term ocean altimetric observations in view of the current trends of the gnss systems

subducted slabs beneath the eastern indonesia tonga region insights from tomography tomographic images of mantle structure beneath the region north and northeast of australia show a number of anomalously fast regions these are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems several strong anomalies are related to current subduction the inferred slab lengths and positions are consistent with neogene subduction beneath the new britain and halmahera arcs and at the tonga and the new hebrides trenches where there has been rapid rollback of subduction hinges since about 10 ma there are several deeper flat lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by australia since 25ma beneath the bird s head and arafura sea is an anomaly interpreted to be due to north dipping subduction beneath the philippines halmahera arc between 45and 25ma a very large anomaly extending from the papuan peninsula to the new hebrides and from the solomon islands to the east australian margin is interpreted to be the remnant of south dipping subduction beneath the melanesian arc between 45and 25ma this interpretation implies that a flat lying slab can survive for many tens of millions of years at the bottom of the upper mantle in the lower mantle there is a huge anomaly beneath the gulf of carpentaria and east papua new guinea this is located above the position where the tectonic model interprets a change in polarity of subduction from north dipping to south dipping between 45and 25ma we suggest this deep anomaly may be a slab subducted beneath eastern australian during the cretaceous or subducted north of australia during the cenozoic before 45ma the tomography also supports the tectonic interpretation which suggests little neogene subduction beneath western new guinea since no slab is imaged south of the new guinea trench however one subduction zone in the tectonic model and many others that associated with the trobriand trough east of papua new guinea and the miocene maramuni arc is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations 4 2002 elsevier science b v all rights reserved

oligocene and miocene carbonate platform development in the browse basin australian northwest shelf abstract extensive 2d and 3d seismic reflection data calibrated by wells provide new insights into the lateral extent morphology internal architecture and age of carbonate platforms in the subsurface of the browse basin australian northwest shelf nws the oldest carbonate build ups are interpreted as a giant bryozoan build up complex of oligocene age 34 03 27 8 ma in the late burdigalian tropical reef growth began and numerous reef rimmed carbonate platforms progressively coalesced into an extensive barrier reef from the mid langhian to the early tortonian the browse basin contained an elongate along margin barrier reef system over 500 km long this barrier reef possibly extended in the southwest into the northern carnarvon basin after the early tortonian reefs on top or landward of this major barrier reef system were smaller and less connected this significant reduction in area covered by reef rimmed platforms likely resulted from cooling following the mid miocene climate optimum and relatively high subsidence rates the reef rimmed carbonate platforms that formed between the late burdigalian and the early tortonian are very similar throughout the browse basin platform development after the early tortonian was regionally diverse high subsidence rates in the northern browse basin are interpreted to have promoted the development of thick aggrading platforms lower subsidence in the south led to thinner more widespread platforms recurrently shifting location in response to eustatic change the final phase of reef decline around 6 ma coincides with an increase in current driven drift sedimentation current related winnowing of sediments from the lagoons and slopes of the remaining carbonate platforms likely contributed to their final drowning

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

active tectonics of the eastern sunda and banda arcs the tectonics of the eastern sunda and banda arcs of eastern indonesia are inferred from the centroid depths seismic moments and fault plane solutions of 63 large earthquakes that occurred between 1962 and 1984 source parameters are estimated by inverting long period teleseismic p and sh waves earthquakes show that the collision of the australian continent with the banda arc shortens the upper plate beneath the forearc and back arc basin over the broad area between the timor and seram troughs along the eastern end of the sunda arc and along the southern banda arc earthquakes reveal that the arc and forearc respond to collision by shortening in the direction of convergence by elongating in the direction perpendicular to convergence and by thrusting over the back arc basin shallow thrust and strike slip earthquakes beneath the banda basin the back arc basin demonstrate that deformation within the back arc accommodates some of the northward motion of the australian continent the rate of north south shortening of the entire upper plate at the longitude of timor calculated from the seismic moments of the earthquakes over the 22 year period is roughly 20 of the predicted convergence rate between australia and southeast asia strike slip faulting within the banda basin results also in eastward motion of the banda arc with respect to western indonesia and australia eastward extrusion of the banda arc results in thrusting at the aru trough earthquakes due to thrusting of the back arc basin beneath the volcanic arc are too shallow to corroborate that the arc s polarity has reversed although the wetar back arc thrust zone at present has a high seismic slip rate earthquakes and their mechanisms provide evidence that the lithosphere of the weber basin a 7500 m deep forearc basin rests on the subducting lithosphere without intervening asthenosphere so that the weber basin subsides in response to sinking of the subducting lithosphere closure of the banda basin is geometrically incompatible with the australian plate subducting simultaneously beneath both the timor and seram troughs instead the bird s head which subducts beneath seram is decoupled from the australian plate in western new guinea and probably moves west or southwest with respect to australia in the eastern indonesian example strike slip faulting plays a major role in the evolution of the collision zone and clearly demonstrates the complexity in three dimensions of continental accretion and mountain building by arc continent collision

the structural setting and tectonic significance of the lolotoi laclubar and aileu metamorphic massifs east timor abstract the lolotoi and laclubar metamorphic massifs of east timor form a part of the lolotoi metamorphic complex based on stratigraphic relationships with the australian affinity parautochthonous stratigraphic succession and structural arguments the lolotoi complex is interpreted as representing australian continental basement entrained into the timor arc continent collision complex by basement involved thrusting the lolotoi complex is not synonymous with the mutis complex defined from west timor which represents allochthonous metamorphic basement derived from the pre collisional banda forearc the aileu complex is a syn collisional metamorphic series with an inverted metamorphic gradient developed beneath overthrust allochthonous peridotite

back arc thrusting in the eastern sunda arc indonesia a consequence of arc continent collision the structure of the eastern sunda back arc region is dominated by two large north directed thrusts the wetar and flores thrusts and one or more minor thrusts which may represent early stages of subduction polarity reversal of the arc the relationships between thrusting and magmatic activity surface slopes cross arc faulting uplift forearc structure and collision by the australian continental margin provide constraints on the likely driving mechanisms of thrust formation driving mechanisms are considered in two broad categories one set of possible mechanisms originates within the upper plate and includes gravity sliding gravity spreading and magmatic intrusion the other set focuses on stress propagation between the upper and lower plates and for this arc system the major mechanism is that of continental collision while no one mechanism explains the range of observations we see in the back arc region all of these aspects play some role in the development of the thrusts we can eliminate upper plate mechanisms as primary driving forces because slope effects are similar in areas of both thrusting and nonthrusting in addition the wetar thrust shows a negative relation between thrusting and volcanism and side looking airborn radar images show no evidence of postvolcanic rifting that could accompany intrusion without volcanism collision between the arc and the australian continent provides the clearest driving mechanism but it does not explain the discontinuous nature or the particular location of the thrusts we suggest a sequence that appears to account for the data and to provide insight into the controversies often associated with other such thrust belts thrusting was initiated in those areas where the crust of the forearc region was thick a factor that facilitated stress propagation across the arc and where the crust of the back arc was thin which facilitated back arc thrusting thrusting concentrated at the base of the slope where the slope stress is maximum the early thrusting may have been helped also by thermal weakening of the crust due to volcanism as convergence proceeded volcanism waned then ceased in the eastern part of the arc the crust then strengthened and thrusting required higher stress to maintain and propagate this later stage should show higher seismic energy release which appears to be the case for the wetar thrust region displacement on the flores thrust appears to be matched by deflection of the volcanic arc we have estimated shortening in the back arc from interpretation of reflection profiles and for the flores thrust the value of approximately 30 km is consistent with that estimated for deflection of the arc compressional deformation continues west of the collision zone across the bali basin and into java it is reported in ne sumatra as well this deformation involves much less convergence than the eastern sunda thrusts and it may be related to magmatic processes to subduction of oceanic plateaus such as the roo rise or in the case of the bali basin to efficient lateral propagation of the flores thrust