backthrusting in accretionary wedges backthrusting of the rear of the accretionary wedge arcward over the rocks of the forearc basin is a common aspect of accretionary tectonics an older assumption that backstops of accretionary wedges dip back toward the arc and that accreted material is emplaced below such backstops is contradicted by observations from many active forearcs that indicate 1 backthrusting is common 2 forearc basins are nearly ubiquitous associates of accretionary wedges and 3 forearc basement where imaged appears to diverge from the sedimentary package dipping under the wedge while the overlying sediments are often lifted up against it backthrusting may be favored where relief is high between the crest of the wedge and the surface of the forearc basin because the relief must be supported by shear stress along the backthrust we find ratios of lt lb averaging 2 64 0 8 where lt is the horizontal distance from the crest of the wedge to the front of the toe and lb is the distance from the crest of the wedge to the surface projection of the backthrust this ratio is predicted to increase with total convergence and with sedimentation because the toe undergoes higher deformation rates than the backthrust and sedimentation in the trench favors outbuilding of the toe whereas sedimentation in the forearc basin tends to cancel the gravitational component of the driving stress for the backthrust

a late cretaceous and cenozoic reconstruction of the southwest pacific region tectonics controlled by subduction and slab rollback processes abstract a cenozoic tectonic reconstruction is presented for the southwest pacific region located east of australia the reconstruction is constrained by large geological and geophysical datasets and recalculated rotation parameters for pacific australia and lord howe rise pacific relative plate motion the reconstruction is based on a conceptual tectonic model in which the large scale structures of the region are manifestations of slab rollback and backarc extension processes the current paradigm proclaims that the southwestern pacific plate boundary was a west dipping subduction boundary only since the middle eocene the new reconstruction provides kinematic evidence that this configuration was already established in the late cretaceous and early paleogene from 82 to 52 ma subduction was primarily accomplished by east and northeast directed rollback of the pacific slab accommodating opening of the new caledonia south loyalty coral sea and pocklington backarc basins and partly accommodating spreading in the tasman sea the total amount of east directed rollback of the pacific slab that took place from 82 ma to 52 ma is estimated to be at least 1200 km a large percentage of this rollback accommodated opening of the south loyalty basin a north south trending backarc basin it is estimated from kinematic and geological constraints that the east west width of the basin was at least 750 km the south loyalty and pocklington backarc basins were subducted in the eocene to earliest miocene along the newly formed new caledonia and pocklington subduction zones this culminated in southwestward and southward obduction of ophiolites in new caledonia northland and new guinea in the latest eocene to earliest miocene it is suggested that the formation of these new subduction zones was triggered by a change in pacific australia relative motion at 50 ma two additional phases of eastward rollback of the pacific slab followed one during opening of the south fiji basin and norfolk basin in the oligocene to early miocene up to 650 km of rollback and one during opening of the lau basin in the latest miocene to present up to 400 km of rollback two new subduction zones formed in the miocene the south dipping trobriand subduction zone along which the solomon sea backarc basin subducted and the north dipping new britain san cristobal new hebrides subduction zone along which the solomon sea backarc basin subducted in the west and the north loyalty south fiji backarc basin and remnants of the south loyalty santa cruz backarc basin subducted in the east clockwise rollback of the new hebrides section resulted in formation of the north fiji basin the reconstruction provides explanations for the formation of new subduction zones and for the initiation and termination of opening of the marginal basins by either initiation of subduction of buoyant lithosphere a change in plate kinematics or slab mantle interaction

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

volcanic spreading at kilauea 1976 1996 the rift system traversing about 80 km of the subaerial surface of kilauea volcano has extended continuously since the m 7 2 flank earthquake of november 1975 widening across the summit has amounted to more than 250 cm decelerating after 1975 from about 25 to 4 cm yr 1 since 1983 concurrently the summit has subsided more than 200 cm even as the adjacent south flank has risen more than 50 cm the axes of the upper zones about 10 km from the summit subsided before 1983 at average rates of 9 and 4 cm yr 1 respectively and at rates of 4 and 3 cm yr 1 since the middle southwest rift zone is also subsiding and at the other end of kilauea s subaerial rift system subsidence along the lower east rift zone has averaged 1 2 cm yr 1 deformation of kilauea s south flank has been continuous although subject as well to displacements caused by major rift zone seismic swarms whereas horizontal strains across the subaerial south flank seem to have been generally compressive after 1975 they have been extensional since about 1980 or 1981 interrupted only by the east rift zone dike intrusion of 1983 because the magnitudes of these contractions and extensions are much less than the extension across the rift system the subaerial south flank is apparently sliding seaward on its basal decollement more than it is accumulating horizontal strains within the overlying volcanic pile kilauea suffers from gravitational spreading made even more unstable by accumulation of magma along the rift system at depths in excess of about 4 5 km in the presence hot rock incapable of withstanding deviatoric stresses this seismicly quiescent zone decouples the south flank from the rest of hawaii s volcanic edifice the rift zones at lesser depths exhibit a more brittle and therefore sporadic extensional behavior judging from the modern extension record of the summit which both predates the m 7 2 earthquake of 1975 and has outlived its 10 year period of aftershocks kilauea will continue to spread along its rift system as its south flank slips seaward to accommodate the accretion of magma and its relatively dense olivine rich differentiate

alternating seismic uplift and subsidence in the late holocene at madang papua new guinea evidence from raised reefs well preserved mid late holocene coral reefs are exposed in low coastal cliffs in the vicinity of the madang lagoon on the north coast of papua new guinea results from u th and 14 c dating of corals surveying and field mapping indicate several major changes in relative sea level over this period specifically there is evidence for a relative sea level fall of 4 5 m about 3000 calendar years b p followed by relative sea level rises of 1 5 m about 2400 calendar years b p and 0 5 m about 1200 calendar years b p and a subsequent relative sea level fall of 3 m some time in the past 1000 years since regional eustatic sea levels are believed to have been dropping gradually over this time frame these observed changes in relative sea level are interpreted as reflecting alternating tectonic uplift and subsidence furthermore the detailed structure and age relationships of the coral deposits indicate that both uplift and subsidence occurred rapidly most probably as coseismic events with vertical displacements of 0 5 to 4 5 m these events may be related to rupture on nw se trending reverse faults which have been mapped in the nearby adelbert range and possibly on ne trending cross faults which have been inferred from seismicity this interpretation implies a much greater degree of tectonic instability and potential seismic hazard in the region than previously recognized although the inferred coseismic vertical displacements are shown to be consistent with present day local seismicity in a broader context the study illustrates how detailed analysis of vertical changes in coral reef structure and assemblages may be used as a sensitive indicator of changing relative sea level capable of resolving century timescale events and reversals

tectonic evolution and copper gold metallogenesis of the papua new guinea and solomon islands region papua new guinea and the solomon islands are in one of the most prospective regions for intrusion related mineral deposits however because of the tectonic complexity of the region and the lack of comprehensive regional geological datasets the link between mineralization and the regional scale geodynamic framework has not been understood here we present a new model for the metallogenesis of the region based on a synthesis of recent studies on the petrogenesis of magmatic arcs and the history of subduction zones throughout the region combined with the spatio temporal distribution of intrusion related mineral deposits and six new deposit ages convergence at the pacific australia plate boundary was accommodated from at least 45 ma by subduction at the melanesian trench with related melanesian arc magmatism the arrival of the ontong java plateau at the trench at ca 26 ma resulted in cessation of subduction immediately followed by formation of cu au porphyry epithermal deposits at 24 20 ma throughout the melanesian arc late oligocene to early miocene tectonic reorganization led to initiation of subduction at the pocklington trough and onset of magmatism in the maramuni arc the arrival of the australian continent at the pocklington trough by 12 ma resulted in continental collision and ore deposit formation from 12 to 6 ma this is represented by cu au porphyry deposits in the new guinea orogen and epithermal au systems in the papuan peninsula from 6 ma crustal delamination in papua new guinea related to the prior pocklington trough subduction resulted in adiabatic mantle melting with emplacement of diverse cu and au porphyry and epithermal deposits within the papuan fold and thrust belt and papuan peninsula from 6 ma to the present day subduction at the new britain and san cristobal trenches from ca 10 ma resulted in an escalation in tectonic complexity and the onset of microplate tectonics in eastern papua new guinea and the solomon islands this is reflected in the formation of diverse and discrete geodynamic settings for mineralization within the recent to modern arc setting primarily related to upper plate shortening and extension and the spatial relationship to structures within the subducting slab

stabilization of volcanic flanks by dike intrusion an example from kilauea dike propagation and dilation increases the compression of adjacent rocks on volcanoes especially oceanic shields dikes are accordingly thought to be structurally destabilizing as compression is incremented volcanic flanks are driven outward or downslope and thus increase their susceptibility to destructive earthquakes and giant landslides we show however that the 2 m thick dike emplaced along the east rift zone of kilauea in 1983 actually stabilized that volcano s flank specifically production of flank earthquakes dropped more than twofold after 1983 as maximum downslope motion slowed to 6 cm year 1 from approximately 40 cm year 1 during 1980 1982 as much as 65 cm of deflationary subsidence above kilauea s summit and upper rift zones accompanied the dike intrusion according to recent estimates this deflation corresponds to a reduction in magma reservoir pressure of approximately 4 mpa probably about as much as the driving pressure of the 1983 dike the volume of the dike approximately 0 10 0 15 km3 is orders of magnitude less than the estimated 200 to 250 km3 volume of kilauea s reservoir of magma and nearby hot mushy rock thus deflation of that reservoir reduces the compressional load on the flank over a much larger area than intrusion of the dike adds to it particularly at the dominant depth of seismicity 8 9 km a coulomb block model for flank motion during intervals between major earthquakes requires the low angle fault beneath kilauea s flank to exhibit slip weakening conducive to earthquake instability accordingly the triggering mechanism of destructive earthquakes several of which have struck hawaii during the past 150 years need not require stresses accumulated by dike intrusions

structural evolution of a modern arc continent collision in papua new guinea the finisterre mountains and western solomon sea of northern papua new guinea are the site of an active oblique arc continent collision comparison of structures along the length of the collision zone provides a history of its structural evolution here we compare the results of structural mapping in the finisterre mountains where collision is in an advanced state with side scan sonar images and potential field data from the western solomon sea which illuminate the structure of the juvenile collision zone an accretionary wedge complex composed of a southwestward younging stack of imbricate thrust sheets developed along a westward extension of the modern new britain trench prior to collision this accretionary wedge crops out in the finisterre mountains as the erap structural complex consequences of collision were doubling of the crustal thickness to 50 52 km rapid up lift of the finisterre terrane and initiation of a major out of sequence thrust that displaced the finisterre volcanics over younger sediments of the accretionary wedge this out of sequence thrust is mapped in the finisterre mountains as the wongat thrust and it is recognized in the western solomon sea on side scan sonar images a second generation out of sequence thrust formed after substantial uplift had subaerially exposed the collision zone this thrust crosscuts the wongat thrust forming a window of accretionary wedge sediments bounded to both the ne and sw by finisterre volcanics this younger out of sequence thrust is the gain thrust of the finisterre mountains at least 15 km of crustal shortening has occurred across the wongat thrust at 146 30 e longitude and the gain thrust has accommodated up to 7 4 km of shortening in the same area it is probable that the well lithified finisterre volcanics serve as the backstop for the accretionary wedge collision complex that is forming in the collision zone of the western solomon sea potential field models indicate that this backstop is arcward dipping thrusting of the back stop material over the accretionary wedge as we observe along the wongat thrust is expected for wedges with arcward dipping backstops a series of ne sw trending cross faults perpendicular to the dominant structural trend exist in the collision zone these faults have components of left lateral strike slip and se down dip slip motion it is likely that the finisterre terrane is being segmented along these faults with the segmentation caused by differential resistance to convergence between the downgoing continental crust of the collision zone and the oceanic crust of the subduction zone to the east the origin of the faults is uncertain previous authors believed that they formed during paleogene volcanic activity in the finisterre terrane the colinearity of several of these cross faults with major mapped faults on the downgoing plate raises the possibility that the finisterre range cross faults are upper plate manifestations of lower plate structures and as such reveal strong interplate coupling in the collision zone

large scale duplexes within the new britain accretionary wedge a possible example of accreted ophiolitic slivers a multichannel seismic line acquired in the western solomon sea images reflectors within the new britain accretionary wedge which we interpret as accreted duplexes of the downgoing oceanic plate the seaward edge of the largest duplex is located just 6 km from the toe of the accretionary wedge suggesting recent incorporation into the wedge these data therefore provide an excellent opportunity to determine the dynamics of oceanic basement accretion the oceanic basement is represented by a high amplitude low frequency reflector that can be traced up to 40 km arcward of the toe of the accretionary wedge on several seismic lines in this survey another prominent reflector similar in character to the basement reflector lies approximately one second higher in at least one seismic section this reflector is likely to be the top of a basement duplex structures imaged above the basement duplex define a preduplex accretionary wedge whereas those at the toe indicate a new episode of postduplex accretion we have tested this interpretation using both magnetic modeling and interval velocity analysis magnetic models of the wedge that include basement duplexes provide a good match to the observed magnetic data and provide limits on the size and interval velocities of the slivers interval velocities between the two strong reflectors calculated using stacking velocities and constrained through magnetic modeling exceed 5000 m s and are consistent with our interpretation of ophiolitic slivers within the accretionary wedge

deep structure of an arc continent collision earthquake relocation and inversion for upper mantle p and s wave velocities beneath papua new guinea we examine mechanisms of lithospheric growth and modes accommodating subcrustal convergence following the cessation of subduction by analyzing the seismicity and upper mantle velocities in the new guinea arc continent collision earthquakes in the papua new guinea png region from 1967 to 1984 have been relocated in a joint inversion with seismic velocities using p and s wave arrival times recorded by seismographs in png a total of 957 well recorded earthquakes were chosen for use in three dimensional velocity inversions from an initial catalog of 12 960 events based on the stability of initial hypocenter relocations constant velocity blocks were defined as irregular polyhedra to give fine detail in heavily sampled areas without introducing a large number of poorly controlled parameters and to exploit a priori knowledge of the geometry of velocity anomalies spherical geometry was used to accurately calculate long ray paths up to 1500 km in length most of the 700 best located hypocenters from the png data set are in the upper mantle beneath the finisterre huon fh ranges the newly accreted island arc terrane beneath the papuan peninsula and in the new britain seismic zone an oceanic subduction system these hypocenters show a well defined seismic zone dipping vertically or steeply to the north beneath the northern fh ranges from 125 to 250 km depth continuous along strike with the new britain seismic zone to the east which shows earthquakes to 600 km depth the steeply dipping intermediate depth seismicity flattens near 100 km depth beneath the fh ranges and forms a subhorizontal seismic zone beneath the fh ranges by contrast seismicity continues upward to the surface beneath new britain where the arc has not yet collided with new guinea the 100 km deep flat zone does not continue south of the fh ranges but appears to be truncated below the eastern and southern boundaries of the island arc terrane and no clear evidence for a south dipping seismic zone could be found the relationship of the flat part of the slab 100 km beneath the fh ranges and surface faulting is difficult to discern the apparent surface suture bounding the south side of the fh ranges is 100 km directly above the southern termination of intermediate depth seismicity nowhere in png could clear evidence for arc polarity reversal be found from seismicity all of the well located subcrustal earthquakes beneath the papuan peninsula lie in a narrow horizontal line between 125 and 175 km depth that follows the center of the peninsula and are distinctly separated from the fh seismic zone to the north these events do not require a southward subducting plate beneath the papuan peninsula an alternate and reasonable explanation for these events is that they are a result of unstable thickening of the lithosphere information on lateral heterogeneity in the mantle is limited because large variations in crustal velocities dominate the observed pattern of travel time residuals allowing for only crustal heterogeneity reduces travel time residual variances by 40 from a simple one dimensional structure while allowing for additional mantle heterogeneity results in 10 further reduction for the various parameterization s attempted here inversions with several different block geometries show low velocities at 35 to 171 km km depth beneath the bismarck sea back arc basin and high velocities just south of the intermediate depth fh seismic zone the pattern of lateral heterogeneity supports the inference from seismicity of north dipping slabs beneath both northeast new guinea and new britain

interactions between a transform fault and arc volcanism in the bismarck sea papua new guinea 1 we present a new interpretation of the geological evolution of the western branch of the bismarck sea seismic lineation bssl region offshore the northwestern coast of papua new guinea from mapping and interpretation of bathymetry and backscatter data acquired aboard r v kilo moana in 2004 at present the schouten islands parallel the papua new guinea coast but this distribution results from the left lateral displacement of some of these volcanic islands by the bismarck sea seismic lineation the trend of the islands and seamounts was initially aligned n s and then displaced by the bssl wei island lies on a large submarine edifice that may have formed as part of a leaky transform subsequent to forming wei island was bisected and its pieces were displaced 45 km using this distance together with the strike slip rate for the bismarck sea seismic lineation predicted from the north bismarck plate south bismarck plate pole the division occurred approximately 385 000 years ago

a classification of thrust fronts variations in structural style at thrust fronts are examined to determine whether they represent different stages of typical thrust sheet development or unique events as orogenic stresses declined thrust fronts are classified as buried or emergent in which either the sole thrust died out in the subsurface or emerged to the synorogenic surface buried thrust fronts are subdivided into two types type 1 fronts end in broad zones of low strain type 2 fronts end in zones of high strain emergent thrust fronts may display significant horizontal displacement strongly emergent or limited displacements of about 1 km weakly emergent tip stick thrust fronts exhibit high strains and out of sequence thrusting different types of thrust fronts are linked by transitional tip li e anticlines and strike slip zones most thrust front types represent different stages of typical thrust sheet development but those in type 1 display atypical development unique to thrust fronts

shallow seismicity of arc continent collision near lae papua new guinea abstract in northeastern new guinea the narrow ramu markham valley rmv separates island arc rocks to the north from those of continental origin to the south and appears to be the western onland extension of the new britain trench to explore the tectonic processes at the leading edge of the island arc during collision we operated a portable seismic network for six weeks near the city of lae at the eastern end of the rmv we observed a narrow near vertical belt of seismicity between 10 and 30 km depth that we call the lae seismic zone lsz starting at the rmv in the southwest and trending northeasterly cutting across surface geologic structure the truncation of the lsz along a steep plane by the ramu markham fault zone rmfz and earthquake first motions suggest that the earthquakes occur in the hanging wall of a steep n dipping fault that crops out at the rmfz we also consider that the lsz is within the lower plate of a gently dipping thrust below 20 km depth the microearthquake zone is truncated by a gently ne dipping plane coinciding in depth and dip with nodal planes of recent large mb 5 6 and 6 0 thrust earthquakes we suggest that the huon peninsula is being emplaced onto the australian plate along a gently 25 dipping thrust fault that is 20 km deep beneath lae the rmfz may be a steeply dipping thrust fault that connects with this gently n dipping thrust but accommodates little convergence at present the lsz trends nearly perpendicular to an anticlinal range which appears to be sheared in a left lateral sense p wave first motions for earthquakes in the lsz with steep 70 to 90 dip nodal planes that strike parallel to the lsz suggest a component of south side up displacement also hence the crustal block south of the lsz may be rising relative to the huon peninsula and the rapid quaternary uplift rates estimated for the lae coastal region may be higher than the uplift rate of the huon peninsula as a whole we suggest that the lsz reveals a tear of small offset in the huon terrane but may be similar to a structure that produced a magnitude 7 earthquake near madang in 1970

cenozoic tectonics of new guinea major hydrocarbon discoveries have been made in eastern and westernmost new guinea and there is great potential for additional discoveries although the island is a type locality for arc continent collision during the cenozoic the age number and plate kinematics of the events that formed the island are vigorously argued the northern part of the island is underlain by rocks with oceanic island arc affinities and the southern part is underlain by the australian continental crust based on regional sedimentation patterns it is argued herein that the cenozoic tectonic history of the island involves two distinct collisional orogenic events the first cenozoic event the peninsular orogeny of oligocene age 35 30 ma was restricted to easternmost new guinea emergent uplifts that shed abundant detritus resulted from the subduction of the northeastern corner of the australian continent beneath part of the inner melanesian arc this collision uplifted the papuan ophiolite and formed the associated mountainous uplift that was the primary source of siliciclastic sediments that largely filled the aure trough between the oligocene and miocene the paleogeography of the region was similar to present day new caledonia the continental crust under central and western new guinea remained a passive margin the second event the central range orogeny began in the latest middle miocene when the bulldozing of australian passive margin strata first created emergent uplifts above a north dipping subduction zone beneath the western part of the outer melanesian arc the cessation of carbonate shelf sedimentation and widespread initiation of siliciclastic sedimentation on top of the australian continental basement is dated at about 12 ma this collision emplaced the irian ophiolite and created the present mountainous topography forming the spine of the island

subduction versus accretion of intra oceanic volcanic arcs insight from thermo mechanical analogue experiments we perform thermo mechanical laboratory experiments designed to explore the behaviour of the volcanic arc during intra oceanic arc continent collision following oceanic subduction and subsequent back arc opening the overriding oceanic lithosphere is made of two layers representing the oceanic crust and the lithospheric mantle this lithosphere carries a volcanic arc and is thinned and weakened beneath both the arc and the back arc basin the subducting plate contains three parts one layer oceanic and two layer crust and mantle continental lithosphere with a continental margin between them when the continental margin reaches the trench and starts subducting the overriding plate undergoes growing horizontal compression and finally fails in the vicinity of the back arc spreading centre which is the weakest part of this plate the failure can result in subduction of the whole arc plate comprised between the trench and the back arc spreading centre during subduction of the arc plate the mantle part of this plate subducts completely while the behaviour of the arc crust depends on its thickness and strength which is a function of composition and temperature we tested four cases with different arc crust thicknesses and composition rheology with total lithosphere thickness in the arc being constant three types of tectonic evolution have been obtained complete arc subduction complete arc accretion and partial arc subduction accretion the result is largely controlled by the crustal thickness of the arc a thin arc thickness equivalent to v16 km in nature made of the same strong material as the oceanic crust subducts completely without leaving any trace at the surface on the contrary a thick arc equivalent to v26 km in nature made of the same material is scraped off and accreted to the overriding plate the lower crust of such an arc is hotter therefore its strength at moho depth and coupling between crust and mantle are small in addition the thick arc has a high isostatic relief and hence a greater mechanical resistance to subduction therefore the arc is scraped off if the arc is made of a weaker continental like material or contains a weak layer low friction interface it is completely or partially scraped off even if it is small when there is no back arc opening before collision no thin and weak lithosphere in the rear of the arc the overriding plate fails in the arc area which may result in a complete fore arc block subduction with the volcanic arc remaining at the surface the obtained models are compared with mountain belts with nearly no trace of arc activity oman with accreted arc kohistan and with small remnants of subducted arc southern tibet 2003 elsevier science b v all rights reserved

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

double sided onshore offshore seismic imaging of a plate boundary super gathers across south island new zealand abstract onshore offshore seismic refraction profiling allows for the determination of crustal and mantle structures in the transition between continental and oceanic environments islands and narrow landmasses have the unique geometry of allowing for double sided onshore offshore experiments that favor the construction of composite super gathers using the acquisition of onshore offshore and ocean bottom seismometer receiver gathers land explosion shot gathers and near vertical incidence multichannel seismic mcs profiling a number of sites at plate boundaries are amenable to the application of double sided onshore offshore imaging including the indo australian pacific transform boundary on south island new zealand by comparing the ratio of island width to mantle refraction pn maximum crossover distance using nondimensional distances we provide an indicator of raypath coverage for crustal illumination islands or narrow land masses whose widths are less than twice their maximum crossover distance are candidates for double sided onshore offshore experiments the sight south island geophysical investigation experiment in new zealand is located where the width of south island is sufficiently narrow with respect to its crustal thickness that a double sided onshore offshore experiment allows for complete crustal imaging of the associated plate boundary

tectonics of the new guinea region the new guinea region evolved within the obliquely and rapidly converging australian and pacific plate boundary zone it is arguably one of the most tectonically complex regions of the world and its geodynamic evolution involved microplate formation and rotation lithospheric rupture to form ocean basins arc continent collision subduction polarity reversal collisional orogenesis ophiolite obduction and exhumation of ultra high pressure metamorphic rocks we describe the major onshore and offshore tectonic and geologic components including plate boundaries seismicity faults and magmatism and we integrate these with emerging ideas about mantle dynamics to evaluate the cenozoic tectonic evolution of new guinea future research opportunities to resolve the mantle structure beneath new guinea will enable mantle dynamics to be linked to lithospheric and surface processes virtually all plate tectonic and mantle processes have been active in the new guinea region throughout the cenozoic and as such

convergent margin extension associated with arc continent collision the finsch deep papua new guinea the finsch deep is an asymmetric rhomboidal basin with a maximum depth of 5400 m situated to the north of the solomon sea triple junction papua new guinea anomalous slip vector azimuths regional plate velocities earthquake hypocenters and bathymetric depth relative to surrounding terranes all indicate that the finsch deep is not a passive feature developed behind the subduction front our interpretation of all available data including seismological studies detailed bathymetry side scan character and seismic sections suggests that the finsch deep has developed due to n s extension in the transition zone from continental collision west of the solomon sea triple junction to oceanic subduction to the east the key mechanisms thought to drive convergent margin extension within the new guinea collision are slab pull and oblique subduction researchers studying other convergent margins have recognized underplating and tectonic erosion as driving mechanisms for extension though we have no evidence to either support or discount their presence within the new guinea collision

stratigraphic constraints on the development and timing of arc continent collision in northern papua new guinea abstract the finisterre mountains of northern papua new guinea are the site of an active southeast propagating collision between the finisterre terrane and the australian continental margin the clastic sedimentary sequence on the southern flank of the range records the history of the collision the age of initial collision can be deduced from the second of two provenance shifts that occur in the sequence as revealed by a study of 69 dated sandstones the first shift at about 16 18 ma was from volcanolithic sediments to mixed provenance sediments rich in quartz and metasedimentary lithic fragments these latter sediments were probably derived from the orogenic belt active along the australian continental margin at that time at 3 0 3 7 ma the volcanic source was rejuvenated initial collis on at this time uplifted the finisterre terrane causing the provenance shift here we break the stratigraphic sequence into three units the sarawaget beds the erap structural complex and the leron formation the sarawaget beds are middle eocene to early miocene volcanolithic sandstones that were deposited as clastic aprons un the flanks of the finisterre volcanic are volcanic activity ceased in the early miocene the erap complex is divided into two clastic subunits the sukurum and nariawang units and one basaltic subunit the gorambampan unit the sukurum unit consists of turbidites deposited south of the extinct finisterre arc from the latest early miocene through the early pliocene much of the sediment in the unit was derived from low to medium grade metasedimentary units on the active northern margin of the australian continent renewed subduction i the late miocene or pliocene occurred along the new britain trench just south of the remnant finisterre arc closing an eastward widening small ocean basin the sukurum unit probably represents an accretionary prism that formed at this subduction zone scattered seamounts that were scraped off the downgoing plate are preserved as the gorambampan unit initial collision of the finisterre terrane with the continental margin at 3 0 3 7 ma uplifted the paleogene volcanic rocks which were rapidly eroded and deposited as the volcanolithic turbidites of the nariawang unit southeastward propagation of the collision tip caused incorporation of the nariawang unit into the accretionary wedge rapid uplift raised the terrane foreland above sea level sometime after 1 3 mo the fluvial lacustrine and marginal marine deposits of the leron formation accumulated in a terrane foreland basin that developed south of the collision zone further propagation of the thrust front toward the foreland incorporated the leron formation into the fold and thrust belt rapid uplift of the finisterre range and voluminous volcanolithic sedimentation continue to the present in the finisterre range arc continent collision is marked by a provenance shift from metasedimentary and quartzose detritus to volcanic detritus in another modern arc continent collision on taiwan collision has caused a shift from volcanic to metasedimentary detritus we attribute this discrepancy to the presence of the finisterre terrane an extinct arc in the forearc region of the finisterre arc continent collision and the absence of a similar terrane in the forearc area on taiwan the very different evolution of sandstone provenance in the active taiwan and finisterre collision zones shows that local factors can profoundly influence the provenance histories of collision zones no one model of sediment provenance evolution can characterize all collision zones whether modern or ncient

rapid magmatic processes accompany arc continent collision the western bismarck arc papua new guinea new u th ra major and trace element and sr nd pb isotope data are presented for young lavas from the new britain and western bismarck arcs in papua new guinea new britain is an oceanic arc whereas the latter is the site of an arc continent collision building on a recent study of the manus basin contrasts between the two arcs are used to evaluate the processes and timescales of magma generation accompanying arc continent collision and possible slab detachment all three suites share many attributes characteristic of arc lavas that can be ascribed to the addition of a regionally uniform subduction component derived from the subducting altered oceanic crust and sediment followed by dynamic melting of the modified mantle however the western bismarck arc lavas diverge from the pb isotope mixing array formed by the new britain and the manus basin lavas toward elevated 208pb 204pb we interpret this to reflect a second and subsequent addition of sediment melt at crustal depth during collision 238u and 226ra excesses are preserved in all of the lavas and are greatest in the western bismarck arc high mg andesites with high sr y ratios in the westernmost arc are attributed to recent shallow mantle flux melting at the slab edge data for two historical rhyolites are also presented although these rhyolites formed in quite different tectonic settings and display different geochemical and isotopic compositions both formed from mafic parents within millennia

active arc continent collision earthquakes gravity anomalies and fault kinematics in the huon finisterre collision zone papua new guinea the huon finisterre island arc terrane is actively colliding with the north edge of the australian continent the collision provides a rare opportunity to study continental accretion while it occurs we examine the geometry and kinematics of the collision by comparing earthquake source parameters to surface fault geometries and plate motions and we constrain the forces active in the collision by comparing topographic loads to gravity anomalies waveform inversion is used to constrain focal mechanisms for 21 shallow earthquakes that occurred between 1966 and 1992 seismic moment 1017 to 3 1020 n m twelve earthquakes show thrust faulting at 22 37 km depth the largest thrust events are on the north side of the huon peninsula and are consistent with slip on the ramu markham thrust fault zone the northeast dipping thrust fault system that bounds the huon finisterre terrane thus much of the terrane s crust but little of its mantle is presently being added to the australian continent the large thrust earthquakes also reveal a plausible mechanism for the uplift of pleistocene coral terraces on the north side of the huon peninsula bouguer gravity anomalies are too negative to allow simple regional compensation of topography and require large additional downward forces to depress the lower plate beneath the huon peninsula with such forces plate configurations are found that are consistent with observed gravity and basin geometry other earthquakes give evidence of deformation above and below the ramu markham thrust system four thrust events 22 27 km depth directly below the ramu markham fault outcrop are too deep to be part of a planar ramu markham thrust system and may connect to the north dipping highlands thrust system farther south two large strike slip faulting earthquakes and their aftershocks in 1970 and 1987 show faulting within the upper plate of the thrust system the inferred fault planes show slip vectors parallel to those on nearby thrust faults and may represent small offsets in the overriding plate these faults along with small normal faulting earthquakes beneath the huon finisterre ranges and a 25 along strike rotation of slip vectors demonstrate the presence of along strike extension of the accreting terrane and along strike compression of the lower plate

u pb geochronology of archean metasedimentary rocks in the pontiac and abitibi subprovinces quebec constraints on timing provenance and regional tectonics abstract u pb isotopic ages of single detrital zircons have been obtained from metasandstones in the northern part of the pontiac subprovince and from the cadillac kewagama and lac caste groups within the southern abitibi subprovince youngest detrital zircon ages from these sequences are 2685 2686 2687 and 2693 ma respectively the lac fourniere pluton which intrudes pontiac group metasedimentary rocks is dated at 2682 1 ma a similar age was previously measured from a pluton that cuts the kewagama group these data bracket deposition of greywacke in the pontiac and abitibi subprovinces to 2685 3 ma in contrast the youngest zircon found in a volcaniclastic unit interbedded with timiskaming group metawacke is 2673 2 ma while the age of a pluton that intrudes the timiskaming is 2672 1 ma thus the timiskaming group is distinctly younger than the other metasedimentary rocks the normalized probability distributions of detrital zircon ages from the pontiac and the abitibi metasedimentary rocks as well as of dated igneous rocks from the southern abitibi subprovince all show that their major zircon populations formed in the age range 2685 2710 ma the distributions for the abitibi metaturbidites and dated igneous rocks are very similar suggesting that metasedimentary rocks in the abitibi belt were mostly derived from the surrounding granite greenstone terrain the largest peak of the pontiac distribution is a few million years younger than that from the abitibi metasedimentary rocks but there is a correlation between major peaks and both groups show similar age ranges for older pre abitibi components 2750 2850 and 3020 3030 ma deposition of the ca 2685 ma sediments was virtually syn deformational based on previous field geochemical and isotopic studies as well as the detrital zircon age data the pontiac group may represent a foreland basin that may have developed from an accretionary prism the source of much of the sediment may have been an uplifted extinct continental arc to the north the arc was mostly eroded into the sediment basin and perhaps tectonically overridden by a southward advancing nappe complex comprised of its back arc basin now partly preserved in the southern volcanic zone of the abitibi subprovince metaturbidites exposed between metavolcanic assemblages within the greenstone belt may represent overturned unconformities at the structural base of the greenstones these were brought up by high angle faults which also localized deposition of non marine timiskaming type sediments it is tentatively suggested that pontiac type metasedimentary rocks extend most of the way beneath the abitibi subprovince the oldest part of the basin emerging as the quetico group in the western superior province

volcano collapse and tsunami generation in the bismarck volcanic arc papua new guinea during a cruise on the r v kilo moana in 2004 we mapped 12 debris avalanches from volcanoes in the bismarck volcanic arc estimated their sizes and computed the size of potential tsunami run up in major local population centers from these features we used the towed side scan instrument hawaii mr1 the hull mounted em120 system for swath bathymetry and backscatter intensity a shallow penetration chirp system several bottom camera tows and selected cores we calibrate our computations with the known tsunami run up of the ritter collapse even the small collapses may have had significant run up on near by coastlines had any of the collapses we have identified occurred in modern times each would affect a presently populated region of the coastline to a moderate or significant degree

late miocene to recent formation of the aure moresby fold thrust belt and foreland basin as a consequence of woodlark microplate rotation papua new guinea the aure moresby fold thrust belt and aure moresby foreland basin are located in the eastern gulf of papua gop papua new guinea png and formed during late miocene recent as the result of large scale counterclockwise rotation of the 355 000 km2 woodlark microplate to document the structure stratigraphy and age of convergent deformation along the poorly studied western edge of the rotating woodlark microplate we integrate results of 2 538 km of previously unpublished 2 d seismic reflection data with onshore geologic and gps studies from previous workers the late miocene aure moresby fold thrust belt is a 400 km long northwest trending fold belt exposed onshore in papua new guinea that plunges to the southeast where continuous folds and northeast dipping thrusts can be imaged in the subsurface for more than 250 km the arcuate trend of the aure moresby fold thrust belt along the southwestern coast and offshore areas of the papuan peninsula parallels the shape of the adjacent offshore aure moresby foreland basin and the strike of the transpressional segment of the left lateral owen stanley fault zone osfz passing along the center of the papuan peninsula as the osfz becomes more transtensional east of 148 e folds of the aure moresby fold thrust belt along southern coast of the peninsula become less prominent and the adjacent aure moresby foreland basin transitions into an undeformed cenozoic passive margin setting these observations of convergent an left lateral deformation along the aure moresby fold thrust belt are consistent with 1 counterclockwise rotation of the woodlark microplate known from regional gps studies 2 coeval opening of the woodlark basin along its southern edge in the late miocene and 3 rapid subduction at the new britain trench along its northern edge the kinematics of the rotating woodlark microplate are driven by slab pull forces acting on the actively subducting northern edge of the microplate

gps and seismological constraints on active tectonics and arc continent collision in papua new guinea implications for mechanics of microplate rotations in a plate boundary zone 1 the island of new guinea is located within the deforming zone between the pacific and australian plates that converge obliquely at 110 mm yr new guinea has been fragmented into a complex array of microplates some of which rotate rapidly about nearby vertical axes we present velocities from a network of 38 global positioning system gps sites spanning much of the nation of papua new guinea png the gps derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in png we simultaneously invert gps velocities earthquake slip vectors on faults and transform orientations in the woodlark basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region the data are best explained by six distinct tectonic blocks the australian pacific south bismarck north bismarck and woodlark plates and a previously unrecognized new guinea highlands block significant portions of the ramu markham fault appear to be locked which has implications for seismic hazard determination in the markham valley region we also propose that rapid clockwise rotation of the south bismarck plate is controlled by edge forces initiated by the collision between the finisterre arc and the new guinea highlands

structure and evolution of the magnitogorsk forearc basin identifying upper crustal processes during arc continent collision in the southern urals the southern urals of russia contain a well preserved example of a paleozoic arc continent collision in which the intraoceanic magnitogorsk volcanic arc and its forearc basin sediments accreted to the east european craton during the devonian the magnitogorsk arc records the evolution from incipient intraoceanic subduction to a mature arc and by comparing its surface geological features with those in active arc continent collision settings it is possible to identify upper crustal processes that were active in the southern urals the arc edifice can be divided into western and eastern volcanic fronts that were active during different stages of arc evolution and for which two distinct phases of forearc basin development can be recognized the late lower to middle devonian aktau formation represents a remnant of the intraoceanic to collisional forearc basin to the irendyk volcanic front whereas the middle devonian to lower carboniferous ulutau koltubanian and zilair formations were deposited in a suture forearc basin to the east magnitogorsk volcanic front it was not until the late devonian that these two basins were joined structural mapping combined with reflection seismic profiling shows these basins to be affected by open nonlinear volcanic basement cored synsedimentary folds the karamalytash anticline appears to have the geometry of a growth fold that formed during deposition of sediments in the suture forearc basin the forearc region is affected by minor thrusting that involves the volcanic basement although it is not clear if these thrusts reactivate preexisting trench parallel faults synsedimentary deformation slumping and olistostrome development were common throughout the suture forearc basin history but were especially widespread during the late devonian when the full thickness of the continental crust is interpreted as having arrived at the subduction zone

geodynamic processes of taiwan arc continent collision and comparison with analogs in timor papua new guinea urals and corsica abstract the taiwan arc continent collision involves four geodynamic processes intra oceanic subduction initial arc continent collision advanced arc continent collision and arc collapse subduction these processes now occur simultaneously in 19 24 30 n but have operated sequentially southward since the late miocene although the geological and geophysical features appear to change progressively from north to south across the island they are distinct within individual tectonic regimes using the present scenario as a basis for comparison it is suggested that timor is at the initial arc continent collision stage while papua new guinea and urals proceeded to the advanced arc continent collision stage however corsica represents an even more advanced stage than in taiwan where a previously accreted arc has collapsed and been totally removed

post 8 ma reconstruction of papua new guinea and solomon islands microplate tectonics in a convergent plate boundary setting papua new guinea and the solomon islands are located in a complex tectonic setting between the converging ontong java plateau on the pacific plate and the australian continent here we present a late neogene to quaternary plate tectonic reconstruction for this region the reconstruction was performed using gplates software and is based on data derived from multiple geological datasets including seafloor magnetic isochrons 3d models of subducted slabs paleomagnetic data deformation patterns and the spatio temporal distribution of arc magmatism the reconstruction shows that since ca 6 ma the crustal elements that comprise papua new guinea and the solomon islands began interacting in advance of the impending collision between the ontong java plateau and australian continent leading to the inception of regional microplate tectonics and escalation in tectonic complexity the bismarck sea initially formed as a back arc basin behind the new britain arc but was later modified during arc continent collision following collision the west bismarck sea developed into a transpressional zone associated with subduction of the caroline plate and north bismarck microplate at the new guinea trench farther east seafloor spreading occurred in response to the clockwise rotation of the south bismarck microplate relative to the australian plate the solomon sea plate was subjected to anticlockwise rotation relative to papua new guinea primarily due to the west dipping subduction at the new britain trench which resulted in initiation of subduction at the trobriand trough and extension in the woodlark basin from ca 5 ma crustal shortening in the upper plate which now forms the solomon islands resulted from the resistance of the relatively hot and buoyant woodlark basin lithosphere to subduction at the san cristobal our reconstruction shows that tectonism at convergent plate boundaries could involve an intricate relationship between microplate rotations seafloor spreading and subduction segmentation over timescales considerably 10 ma by unraveling the tectonic evolution of this complex region we provide insights into the development of microplate tectonics at convergent margins in general and the possible diagnostic geological records that might be preserved in ancient orogenic systems

dynamic basis of volcanic spreading the established models of the structure and dynamics of a typical hawaiian volcano lead inevitably to a paradox finite element viscoelastic calculations using tecton melosh and raefsky 1980 1981 predict that a compressional stress field should characterize their upper flanks instead extension is observed the paradox is solved by postulating that volcanic evolution is determined by feedback processes related to growth and spreading of the volcanic edifice many examples of the process of spreading are documented in the geologic literature on volcanoes of a very broad size range and very different geologic settings the process is similar across many orders of magnitude in size the deformation of the substratum related to magma intrusion during lava dome building events is at the lower end of the scale the spreading of seafloor at oceanic ridges is at the higher end of the scale volcanoes may evolve from small constructs into huge shield volcanoes and perhaps into ocean plates key elements for volcanic spreading are 1 the existence of a weak basal layer and 2 a sufficiently high mass and magma influx to drive the process as the mass of a volcano grows it passes through five phases which may overlap repeat or be omitted building compressing thrusting intruding and spreading during the building phase the mass of a volcano does not significantly affect the stress field of the substratum primitive magmas are likely to be erupted as the mass increases the volcano subsides and becomes characterized by a compressional stress field which inhibits any further intrusion of magma into the volcanic edifice magma may differentiate in the crust allowing for large caldera forming eruptions to occur in the next phase thrusting begins on a decollement usually located at the foot of the edifice while the stress field on the upper slopes of the volcano remains compressional the stress at the base close to the center becomes extensional allowing the magma to intrude and differentiate at the base of the edifice a basal intrusive complex begins to grow explosive eruptions may be expected finally spreading of this complex creates an extensional stress field on the upper flanks of the volcano confining compression to the lower slopes of the edifice the extension allows primitive magma to erupt again at the summit the process of spreading seems to have a fundamental influence on the structural and magmatic evolution of volcanoes at every scale this process results from coupling and feedback between the gravitational and thermal fields thus studying this process may improve our understanding of the relation between structural dynamics and magma evolution and of the origin and evolution of volcanic seismicity and eruptions

seismotectonics of new guinea a model for arc reversal following arc continent collision the structure and evolution of the northern new guinea collision zone is deduced from international seismological center isc seismicity 1964 1985 new and previously published focal mechanisms and a reexamination of pertinent geological data a tectonic model for the new guinea margin is derived which illustrates the sequential stages in the collision and suturing of the bewani toricelli adelbert finisterre huon new britain arc to central new guinea followed by subduction polarity reversal in the west east of 149 e the solomon plate is being subducted both to the north and south bringing the new britain and trobriand forearcs toward collision west of 149 e the forearcs have collided and together they override a fold in the doubly subducted solomon plate lithosphere which has an axis that is parallel to the strike of the ramu markham suture and that plunges westward at an angle of 5 beneath the coast ranges of northern new guinea active volcanism off the north coast of new guinea is related to subduction of the solomon plate beneath the bismarck plate active volcanism of the papuan peninsula and quaternary volcanism of the new guinea highlands are related to slow subduction of the solomon plate beneath the indo australian plate along the trobriand trough and the trough s former extension to the west respectively from 144 148 e seismicity and focal mechanisms reveal that convergence between the sutured bismarck and indo australian plates is accommodated by thrusting within the finisterre and adelbert ranges and compression of the new guinea orogenic belt together with basement involved foreland folding and thrusting to the south the finisterre block overthrusts the new guinea orogenic belt whereas the adelbert block is sutured to new guinea and overthrusts the oceanic lithosphere of the bismarck sea along the new guinea trench west of 144 e seismicity defines a southward dipping wadati benioif zone and focal mechanisms indicate oblique subduction only this oldest westernmost portion of the collision has progressed past suturing to a full reversal in subduction polarity

seismic and geological controls on earthquake induced landslide size abstract landslide size controls the destructive power of landslides and is related to the frequency of occurrence with larger landslides being less frequent than smaller ones for this reason the analysis of landslide size is essential for landslide hazard assessment we analyse six earthquake induced landslide inventories with earthquake magnitude ranging between 6 6 and 7 9 mw papua new guinea 1993 chichi 1999 northridge 1994 niigata chuetsu 2004 iwate miyagi nairiku 2008 wenchuan 2008 for each inventory we developed magnitude frequency curves to analyse the size distribution of landslides as a function of ground motion distance from the seismic source both fault trace and epicentre local relief and lithology for three earthquakes we observed a clear relationship between the landslide size and ground motion with larger landslides associated with higher ground motion we investigate different possible causes for such observation and propose that the main mechanical reason is that stronger shaking induces higher stresses that may overcome the strength which increases with depth triggering larger landslides we also show that landslide size decreases with distance from the fault trace whereas this trend is not clear for distance from the epicentre local relief does not seem a first order control on landslide size for the earthquake induced landslides considered here some lithologies do influence landslide size but we were unable to identify a general behaviour for different lithologies

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

mechanical role of backstops in the growth of forearcs we use numerical and laboratory modeling to analyze the mechanical role of backstops in the overriding plate at subduction zones a backstop is defined as a region within a forearc that has significantly greater shear strength than the sediment lying farther trenchward it can be thought of as the bulldozer behind an accretionary wedge we calculate the stress and displacement fields within forearcs for various backstop models using the finite element method and we simulate deformation over a backstop using a small scale laboratory model in this way we model the effects of the mechanical properties and geometry of a backstop on forearc structures we find that the growth of an outer arc high the development of an inner deformation belt with landward vergence and the seemingly paradoxical presence of an undeformed forearc basin within an otherwise highly deformed forearc can be explained by assuming the existence of a geometrically simple backstop with geologically reasonable contrasts in mechanical properties compared to the sediments just trenchward of it the structures produced in our numerical models are quite insensitive to the rheology boundary conditions and exact mesh geometry employed the general types of structures observed in the laboratory models depend only weakly upon the strength and the geometry of the backstop these results suggest that a detailed picture of an underlying backstop cannot be determined from surface information alone backstops in which the contact with the accretionary wedge dips arcward rather than trenchward however should produce only slightly different forearc structures with less development of both the outer arc high and the landward vergent inner deformation belt although natural forearcs are far more complex than our simple models they exhibit many of the same features indicating that relatively simple backstop mechanics may be a very important factor in the overall growth of forearcs

differential preservation in the geologic record of intraoceanic arc sedimentary and tectonic processes abstract records of ancient intraoceanic arc activity now preserved in continental suture zones are commonly used to reconstruct paleogeography and plate motion and to understand how continental crust is formed recycled and maintained through time however interpreting tectonic and sedimentary records from ancient terranes after arc continent collision is complicated by preferential preservation of evidence for some arc processes and loss of evidence for others in this synthesis we examine what is lost and what is preserved in the translation from modern processes to the ancient record of intraoceanic arcs composition of accreted arc terranes differs as a function of arc continent collision geometry forward facing collision can accrete an oceanic arc on to either a passive or an active continental margin with the arc facing the continent and colliding trench and forearc side first in a backward facing collision involving two subduction zones with similar polarity the arc collides backarc first with an active continental margin the preservation of evidence for contemporary sedimentary and tectonic arc processes in the geologic record depends greatly on how well the various parts of the arc survive collision and orogeny in each case preservation of arc terranes likely is biased towards those that were in a state of tectonic accretion for tens of millions of years before collision rather than tectonic erosion the prevalence of tectonic erosion in modern intraoceanic arcs implies that valuable records of arc processes are commonly destroyed even before the arc collides with a continent arc systems are most likely to undergo tectonic accretion shortly before forward facing collision with a continent and thus most forearc and accretionary prism material in ancient arc terranes likely is temporally biased toward the final stages of arc activity when sediment flux to the trench was greatest and tectonic accretion prevailed collision geometry and tectonic erosion vs accretion are important controls on the ultimate survival of material from the trench forearc arc massif intra arc basins and backarc basins and thus on how well an ancient arc terrane preserves evidence for tectonic processes such as subduction of aseismic ridges and seamounts oblique plate convergence and arc rifting forward facing collision involves substantial recycling melting and fractionation of continent derived material during and after collision and so produces melts rich in silica and incompatible trace elements as a result forward facing collision can drive the composition of accreted arc crust toward that of average continental crust

imaging the crustal magma sources beneath mauna loa and kilauea volcanoes hawaii three dimensional seismic p wave traveltime tomography is used to image the magma sources beneath mauna loa and kilauea volcanoes hawaii high velocity bodies 6 4 km s in the upper 9 km of the crust beneath the summits and rift zones of the volcanoes correlate with zones of high magnetic intensities and are interpreted as solidified gabbro ultramafic cumulates from which the surface volcanism is derived the proximity of these high velocity features to the rift zones is consistent with a ridge spreading model of the volcanic flank southeast of the hilina fault zone along the south flank of kilauea low velocity material

measurement of tectonic surface uplift rate in a young collisional mountain belt measurement of the rate of tectonically driven surface uplift is crucial to a complete understanding of mountain building dynamics the lack of a suitable rock record typically prevents determination of this quantity but the unusual geology of papua new guinea s finisterre mountains makes measurement of this rate possible the tectonic surface uplift rate at the finisterre range is 0 8 2 1 mmyr 1 approximately that expected to arise from crustal thickening

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

sedimentology of coarse grained alluvial fans in the markham valley papua new guinea abstract in alluvial sediment sequences recognition of a hierarchy of bounding surfaces and the shapes and associated lithofacies of the sediment bodies they define provide an appropriate framework for understanding associations among depositional forms the processes responsible for them and their controls on system development this methodology architectural element analysis integrates principles from geomorphology and sedimentology miall 1985 1988 it is used here to analyse the evolution of the modern umi fan and the alluvial fan part of the pleistocene leron formation in the markham valley papua new guinea a series of terraces has developed as the umi river has incised into its fan detailed stratigraphic analysis of the lowest terrace in exposures up to 25 m high and kilometres long reveals that the fan is dominated by sheetflood deposits with minimal preservation of either debris flow or hyperconcentrated flood flow sediments channel fill elements make up a larger proportion of exposures in the proximal fan than elsewhere while 95 of distal fan exposures are composed of sheetflood sequences these depositional features likely result from massive sediment dispersal associated with the rapidly uplifting upland terrain abundant sediment availability and flashy discharge regime channel fill units along with slope related deposits from debris and hyperconcentrated flood flows are only likely to be preserved in the trench backfilling phase following fan entrenchment reworking of deposits plays a dominant role in preservation of sheetflood deposits at the expense of slope related deposits an hierarchical framework of lithosomes is developed which characterizes various scales and bounding surfaces of depositional units which make up the umi fan cf miall 1988 decelles et al 1991 smaller elements observed in terrace exposures are described as first to fourth order lithosomes they reflect geomorphic processes which are evident in and adjacent to the modern umi river deposits which infill the trench are interpreted as a fifth order lithosome constrained by trench geometry proximal distal relationships are remarkably similar in the umi fan and leron formation fan sequences in both instances debris flow deposits are seldom observed the largest sixth and seventh order lithosomes which were deposited within a time frame of approximately one hundred thousand years are interpreted by analysis of the leron formation in relation to its tectonic setting the umi and pleistocene leron formation fans exemplify fan development in a post collisional molasse basin under a tropical monsoonal climate carbonate concretions observed in distal fan facies may provide a possible diagnostic feature of these tropical savanna fans

active low angle normal faulting in the woodlark extensional province papua new guinea a physical model 1 in eastern papua new guinea the seismicity geomorphology and results of seismic reflection profiling drilling and structural geological analysis reveal a zone of active low angle normal faulting the only clear known active example of this process worldwide this woodlark extensional province is 250 km long in the east west direction located within the continental crust to the south of the solomon sea ocean basin it adjoins the young oceanic spreading center farther east in the woodlark basin and since 4 ma has accommodated northward extension at rates of in excess of 10 mm yr 1 on low angle normal faults that are rooted to the north this geometry and the region s earlier history are assessed in the light of modern ideas for the mechanics of low angle normal faulting to derive a working hypothesis for the existence of this process in this region the extension in the woodlark extensional province and oceanic spreading in the woodlark basin are thus interpreted as consequences of the slab pull force due to northward subduction of the solomon sea floor which has caused the small solomon sea plate to separate from the australian plate it is suggested that this plate geometry developed by 6 5 ma following the ending of southward subduction of the solomon sea floor beneath what is now the woodlark extensional province the double thickness of lithosphere that formerly existed locally cooled the continental crust making it brittle to the moho following the end of this subduction the base of the continental lithosphere became progressively exposed to the asthenosphere causing dramatic heating of the overlying continental crust this resulted in transient thermal disequilibrium inducing transient horizontal lower crustal flow the shear tractions imparted on the base of the brittle layer by such flow combined with the stress components that develop after some of the lower crust has flowed from beneath a locality requiring it to be supported laterally rather than from below will rotate the principal axes of the stress tensor sufficiently to enable low angle normal faults to form and it is estimated that this sense of deformation was initiated around 4 ma the geometry of this study region means that this process will create north dipping low angle normal faults as are observed this scheme can also account for a great deal of other observational evidence including the available thermochronologic evidence and the observed vertical crustal motions to explain this instance of active low angle normal faulting thus requires knowledge of its relationship to earlier subduction and of effects of temperature dependent changes to continental crustal rheology in crust that was initially cold

collision propagation in papua new guinea and the solomon sea the mountain system in papua new guinea png is growing by accretion of australian margin strata to the front of the papuan fold and thrust belt in the south and by accretion of exotic terranes along its ne margin presently the finisterre terrane is being accreted along the ne margin of png and the collision point is migrating eastward within the solomon sea east of the collision point the new britain trench marks the tectonic front between the solomon sea and south bismarck sea plates whereas to the west the tectonic front lies in the southern part of the papuan fold and thrust belt present day sedimentary environments within the western solomon sea are inferred from interpretation of seismic reflection data similar facies are observed accreted to the front of the finisterre terrane in the markham valley the frontal leron formation is largely fluvial and shallow marine and the erap complex contains elements of turbidites and pelagic deposits there appears to be a smaller volume of coarse proximal marine strata accreted to the front of the finisterre terrane than is expected from interpretation of reflection profiles in the western solomon sea this difference may be attributed to a combination of submarine erosion in the markham canyon partial incorporation of these deposits into the erap complex and a difference in depositional rates and products carried to the solomon sea in the past relative to what is observed today based on plate motions alternative collision geometries and the youngest dates available for the erap complex we determine a rate of progression of the collision point of about 212 km m y during the past 1 m y

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

motion of kilauea volcano during sustained eruption from the puu oo and kupaianaha vents 1983 1991 kilauea erupted almost continuously from january 1983 through 1991 although the summit began subsiding during the rift zone dike intrusion that initiated this eruption remarkably steady ground surface motions began in late 1983 after a magnitude 6 6 earthquake beneath the slopes of nearby mauna loa volcano and continued until the onset of brief upper east rift zone earthquake swarms in late 1990 during these 7 years the summit and upper rift zones subsided up to 10 11 and 4 8 cm yr 1 respectively and summit baselines contracted up to 6 cm yr 1 baselines directed northward from the summit to stations on mauna loa extended at rates up to 7 cm yr 1 and a baseline from south of the summit to mauna loa extended 4 cm yr 1 much of this extension is inconsistent with deformation caused solely by summit magma reservoir collapse and more likely reflects rifting as the south flank of the volcano moved seaward from the summit and rift zones farther from the summit baselines crossing the south flank extended up to 2 cm yr 1 and a south flank tide gauge rose 2 cm yr 1 the lower east rift zone 40 50 km from the summit subsided about 2 cm yr 1 motion on kilauea then is broadly consistent with slip along low angle south flank faults generating subsidence that is focused at the summit and along the rift system behind the faulting and uplift along the coastal south flank ahead of it dislocation models that combine these elements show that much of kilauea s edifice migrated seaward producing ground surface motions along the south flank of up to about 6 cm yr 1 the magnitude 6 1 earthquake of 1989 punctuated these motions along the eastern south flank producing more than 25 cm of seaward displacement and 15 km east of the epicenter up to 24 cm of subsidence south of the lower east rift zone unlike the magnitude 7 2 south flank earthquake of 1975 the 1989 event was preceded neither by summit magma reservoir inflation nor by rift zone dike intrusions and accompanying compression of the south flank deformation was probably caused by the weight of the volcanic overburden and by ongoing dilation and slip within the rift system

grain size control of mineralogy and geochemistry in modern river sediment new guinea collision papua new guinea the new guinea collision includes diverse sediment source areas associated with arc continent collision to the west of the solomon sea triple junction and with subduction of oceanic crust to the southeast and northeast of the triple junction twenty seven sediment suites each comprising up to seven gravel sand and mud samples from the same locality were analysed to determine mineralogical and geochemical variation with changing grain size this paper deals primarily with the mineralogical variation compositional variation from coarse to fine grained fractions is generally 50 of each variable s abundance with many variables showing greater than 100 variation in contrast variation due to analytical error is generally less than 10 between year variation generally ranges from 15 to 25 and downstream variation is generally less than 50 petrographic results indicate that sediment composition is fundamentally dependent on grain size the principal control on sediment composition is mechanical weathering of rock fragments and compositional sorting of the constituent mineral phases while the gazzi dickinson method for point counting sediment reduces modal variability and in most cases provides robust provenance discrimination it is unsuitable for discerning faint source rock signatures often revealed by grain size dependent compositional variation only the upper plate magmatic arc provenance signature is evident from recalculated modal and geochemical data and that signature does not reflect the modern upper plate magmatic arc detailed petrographic analysis of grain types as opposed to recalculated modal or geochemical data is required to elucidate both upper and lower plate provenances and discriminate between ancient and contemporary arc provenances

paleomagnetism and tectonics of malaita solomon islands malaita in the solomon islands is the emergent expression of the pacific province a geologically distinct suspect terrane which is commonly held to be the margin of the ontong java plateau a thickened portion of pacific plate overthrust onto the rest of the solomon islands arc during a late miocene reversal of the polarity of the arc subduction of the australian plate replaced pacific plate subduction during this event and the solomon islands arc was transferred from the australian plate to the pacific plate a paleomagnetic survey of the eastern solomon islands included sampling in southern malaita magnetostratigraphic dating gives an age of 5 8 ma for the haruta calcisiltite hada calcisiltite facies change on malaita this facies change resulted from renewed volcanic activity following the initiation of australian plate subduction paleomagnetic poles from two pre pliocene units do not lie near the pacific apparent polar wander path apwp as the conventional model would suggest but rather fall on the australian apwp suggesting that the pacific province developed as a part of the australian plate correction for 6 5 ma of pacific australia relative motion produces an improved very close fit to the australian apwp consistent with the transfer of malaita along with the rest of the arc to the pacific plate at about that time magnetic paleolatitudes from a dsdp hole on the ontong java plateau which disagree with usually accepted pacific tertiary motion also fail to match the malaitan data the possibility that malaita could be a part of an ontong java sub plate somehow detached from the rest of the pacific plate can be discounted malaita and the rest of the pacific province arose in the fore arc of the originally north east facing arc collision of the ontong java plateau with the trench slowed subduction of the pacific plate and began subduction of the australian plate below the arc both subduction zones may have been active for a period beginning at about 10 ma and ending at about 3 ma until pacific plate subduction broke down and the pacific province was subsequently uplifted and deformed

drowned carbonate platforms in the huon gulf papua new guinea 1 the western huon gulf papua new guinea is an actively subsiding foreland basin dominated by drowned carbonate platforms we investigated these platforms using new high resolution multibeam side scan sonar and seismic data combined with submersible observations and previously published radiometric and sedimentary facies data the data reveal 14 distinct drowned carbonate platforms and numerous pinnacles banks that increase in age 20 450 kyr and depth 0 1 2 5 km ne toward the ramu markham trench superimposed on this overall downward flexing of the platforms toward the trench is a systematic tilting of the deep platforms 15 m km toward the nw and the shallow platforms 2 m km toward the se this may reflect the encroaching thrust load from the nw finisterre range and spatial variations in the flexural rigidity of the underlying basement the drowned platforms form a complex system of promontories and reentrants with abundant pinnacles and banks preserved at similar depths seaward of the main platforms this configuration closely mimics the present day huon coastline and its seaward islands fringed by modern coral reefs the platforms retain structural morphologic and sedimentary facies evidence of primary platform growth drowning and subsequent backstepping despite some lateral erosion of the platform margins 100 m slope defacement by mass wasting both platforms and pinnacles are composite features containing multiple terrace levels and notches corresponding to multiple phases of growth emergence and drowning in response to rapid climatic and sea level changes during the evolution of each structure on the basis of all observational and numerical modeling data we propose a chronology for the initiation growth and drowning of the 14 platforms over shorter timescales 100 kyr the rate and amplitude of eustatic sea level changes are critical in controlling initiation growth drowning or subaerial exposure subsequent reinitiation and final drowning of the platforms however continued tectonic subsidence and basement substrate morphology influence the overall backstepping geometry and subsequent tilting of the platforms over longer timescales 100 500 kyr

ramu basin papua new guinea a record of late miocene terrane collision the ramu basin lies along a plate boundary where the finisterre terrane is colliding with the indo australian plate estimates for the age of initial collision range from early miocene to middle pliocene two unsuccessful wells keram 1 and tsumba 1 drilled to basement and two dimensional seismic data show that folded and faulted early to middle miocene carbonates and clastics the wogamush sequence are overlain by relatively undeformed pliocene marine clastics the wewak sequence along a regional unconformity the pre pliocene section which is at the crux of resolving the age of initial collision has been correlated previously to the finisterre terrane clastics within that section derived from older terranes south of the basin imply an early miocene age for colli ion i propose that miocene sedimentary and volcanic rocks in the two wells are correlative with the wogamush beds of the maramuni arc the ramu basin can then be viewed as having a two stage evolution during the miocene the basin was part of the maramuni arc the polarity of which is unresolved a collisional successor basin developed in the late miocene as the finisterre terrane adelbert block collided with the arc thrust faults on the northeastern side of the basin truncated by a regional unconformity are interpreted to mark the suture of the adelbert block a northern earliest pliocene sediment source for the basal wewak sequence was probably the finisterre terrane but multiple source areas are inferred for the rest of that sequence middle pliocene inversion of the basin s n rtheastern flank characterized by reverse faulting and forced folding is attributed to plate boundary reorganization caused by rifting in the bismarck sea the ramu basin has numerous untested structures related to both collision and basin inversion folded miocene carbonates wogamush sequence pose a considerable risk regarding the presence of reservoir and the wewak sequence is dominated by volcanolithic arkoses with poor reservoir quality on the northeastern side of the basin where they are in structural closure gas prone source rocks are present but are largely immature reservoir and charge considerations place the ramu basin in the very high risk sector for exploration

suturing history of an allochthonous terrane at a modern plate boundary traced by flysch to molasse facies transitions abstract the southern boundary of the south bismarck plate in papua new guinea changes character from west to east as a consequence of oblique collision and suturing of the allochthonous finisterre terrane with the margin of the australian continent and plate plate rearrangements are occurring and a triple junction is migrating eastwards along the plate boundary characterization of modern sedimentary facies leads to the following correlations between facies and tectonic settings tectonic setting sector of plate boundary facies terrane already docked markham valley fluvial molasse terrane now docking huon gulf marine molasse terrane yet to dock western new britain trench conglomeratic flysch these relationships provide the basis for a tectonic depositional model showing the distribution and relationships between facies in time distance space along the plate boundary facies transitions are time transgressive and their trajectories provide a measure of the rate of triple junction migration rapid uplift of the southern margin of the south bismarck plate has exposed older sediments related to this history of terrane suturing their facies characterization provides support for the model but age control is insufficient for conclusive demonstration of its validity

rotations in the actively colliding finisterre arc terrane paleomagnetic constraints on plio pleistocene evolution of the south bismarck microplate northeastern papua new guinea abstract we report paleomagnetic results from 12 plio pleistocene localities in the actively colliding finisterre arc terrane of northeastern papua new guinea png calcareous hemipelagic cover rocks possess a stable syn collisional remagnetization indicating a clockwise rotation of the colliding terrane through about 40 in post miocene time a decrease in paleomagnetic declination anomalies as a function of along strike distance in the finisterre arc terrane analyzed by our preferred model of a linear remagnetization and a migrating euler pole suggests an average rotation rate of 8 ma 1 in good agreement with the instantaneous rate from global positioning system geodesy thus we propose that this rotation results from a coherent rigid body rotation of the finisterre terrane rather than from sequential docking of independently colliding blocks of the terrane moreover we conclude that these paleomagnetic declinations result mainly from south bismarck plate motion and not decoupled rotation of the crustal terrane independent of the underlying lithosphere we examine models of a syn collisional remagnetization with both fixed and migrating euler poles of south bismarck australia plate relative motion and suggest that the euler pole describing south bismarck plate motion has migrated southwestward to its present location on the collision suture in response to the propagating collision this plate kinematic model agrees with the variability in depth of the seismogenic slab beneath the collision zone our best fit model of pole migration describes south bismarck australia relative motion producing a highly oblique collision in its early stages with the finisterre arc terrane converging along a left lateral ramu markham suture gradually changing to the nearly orthogonal convergence observed today

comparison of two landslide susceptibility assessments in the champagne ardenne region france abstract the vineyards of the montagne de reims are mostly planted on steep south oriented cuesta fronts receiving a maximum of sun radiation due to the location of the vineyards on steep hillslopes the viticultural activity is threatened by slope failures this study attempts to better understand the spatial patterns of landslide susceptibility in the champagne ardenne region by comparing a heuristic qualitative and a statistical quantitative model in a 1120 km study area the heuristic landslide susceptibility model was adopted from the bureau de recherches geologiques et minieres the gegeaa reims university and the comite interprofessionnel du vin de champagne in this model expert knowledge of the region was used to assign weights to all slope classes and lithologies present in the area but the final susceptibility map was never evaluated with the location of mapped landslides for the statistical landslide susceptibility assessment logistic regression was applied to a dataset of 291 old holocene landslides the robustness of the logistic regression model was evaluated and roc curves were used for model calibration and validation with regard to the variables assumed to be important environmental factors controlling landslides the two models are in agreement they both indicate that present and future landslides are mainly controlled by slope gradient and lithology however the comparison of the two landslide susceptibility maps through 1 an evaluation with the location of mapped old landslides and through 2 a temporal validation with spatial data of recent 1960 1999 n 48 and very recent 2000 2008 n 46 landslides showed a better prediction capacity for the statistical model produced in this study compared to the heuristic model in total the statistically derived landslide susceptibility map succeeded in correctly classifying 81 0 of the old and 91 6 of the recent and very recent landslides on the susceptibility map derived from the heuristic model on the other hand only 54 6 of the old and 64 0 of the recent and very recent landslides were correctly classified as unstable hence the landslide susceptibility map obtained from logistic regression is a better tool for regional landslide susceptibility analysis in the study area of the montagne de reims the accurate classification of zones with very high and high susceptibility allows delineating zones where viticulturists should be informed and where implementation of precaution measures is needed to secure slope stability

climate sea level and tectonic controls on sediment discharge from the sepik river papua new guinea during the mid to late pleistocene abstract amongst the rivers draining the mountainous islands of the indonesian archipelago the sepik river of papua new guinea is the largest contributor of solute and particulate material to the world ocean sites u1484 and u1485 drilled during international ocean discovery program iodp expedition 363 provide a continuous 555 kyr long high resolution record of mainly siliciclastic slope sedimentation on the northern continental margin of png just offshore the mouth of the sepik river sedimentological analysis based on a combination of smear slide petrography particle size analysis high resolution physical properties track data and visual core description offers an unprecedented opportunity to investigate the evolution of this major tropical river throughout changing climate and sea level conditions during the mid to late pleistocene the sites u1484 and u1485 sediment records exhibit a dramatic lithologic change at 370 ka the oldest deposits are dominated by pelagic mud suggesting that the coarser grained terrigenous discharge from rivers draining the new guinea highlands including a proto sepik river was captured before reaching the ocean when the sepik river basin was an epicontinental sea the occurrence of coarser grained mass gravity mainly hybrid flows after 370 ka suggests that the epicontinental sea became a more restricted shallow water to nonmarine basin probably due to both basin infilling and the uplift of local coastal ranges during the last three glacial interglacial cycles 300 kyr this shallow inland basin was strongly affected by global variations in sea level during sea level lowstands the sepik river cut into older sediments and discharged further offshore onto the shallow continental margins promoting mass gravity flows pelagic mud deposition on the continental margin during the most extreme highstands following deglaciations suggests a return to shallow marine conditions in the sepik basin and repositioning of the river mouth further inland away from the shelf and from the location of the iodp sites this also indicates that variations in terrigenous fluxes during these extreme highstands were not solely controlled by the intensity of the hydrological cycle and that global sea level variations also influenced sediment deposition the sequence is interrupted by several massive grain flow deposits occurring diachronously at sites u1484 and u1485 and related to a period of intensified tectonic activity between 280 ka and 140 ka the sedimentologic characteristics of these mass gravity deposits and their lack of correlation between sites are interpreted as resulting from channelized flows along margin parallel fault controlled channels caused by local and regional failures of the continental margins including the area of the yalingi canyon 50 km north of the sites where large tsunamigenic events have also occurred in recent years time series analyses of magnetic susceptibility and natural gamma radiation proxies for sand and clay content respectively indicate that river discharge fluxes were modulated at orbital frequencies including obliquity scale cycles which suggests that precipitation and river discharge were not only linked to precessionally driven shifts in the mean position of the intertropical convergence zone but also to high latitude climate change

arc continent collisional orogenesis in the sw pacific and the nature source and correlation of emplaced ophiolitic nappe components abstract southwest pacific ophiolitic nappes emplaced upon the former margin of eastern australia provide a record of cyclical episodes of arc continent collisional orogenesis that occurred throughout the paleogene cenozoic nappes in papua new guinea new caledonia and northland new zealand consist of two key components 1 a basal and apparently older late cretaceous eocene metamorphosed normal to weakly enriched morb like basaltic ocean floor terrane and 2 an uppermost supra subduction zone ssz ophiolite that represents basement of the associated magmatic forearc a detailed comparison of geochemical characteristics of unequivocal ssz basalts with those considered as representative of the basaltic ocean floor terranes illustrates that formation of the majority of the latter is consistent with melting of a source transitional to normal n and enriched e morb these slight ree enriched or transitional t morb have generally been considered as the result of seafloor spreading in a back arc basin bab or basins to the east of australia in the late cretaceous paleocene 85 55 ma the enrichment recorded by the bab basalts is likely a result of upwelling plumes associated with initial fragmentation of eastern gondwana that left their signature on the mantle source consequently tapped by the bab basalts a subset of slightly more enriched basalts may owe their enrichment to source contamination minor assimilation of thinned gondwana derived continental crust associated lree depleted n mor basalts previously considered as part of the basaltic ocean floor terranes on the other hand are similar to ssz basalts of the northland and papuan ultramafic belt ophiolites refinement of existing tectonic models is hindered by ambiguities in the stratigraphic relationships of the underlying basaltic ocean floor terranes with the overlying ssz ophiolites a paucity of age data and uncertainties in the tectonomagmatic affinities of the underlying basalts nonetheless the geochemical characteristics displayed by lree depleted basalts of the basaltic ocean floor terranes suggest that these may instead represent younger magmatic forearc basement components subsequently overthrust by lower sections of a genetically related ophiolite whether these and for that matter the majority of basalts of the basaltic ocean floor terranes indeed represent complementary forearc crust to the ssz ophiolite as opposed to a slice of late cretaceous eocene bab floor backthrust beneath the ssz ophiolite upon emplacement will have to await the acquisition of corresponding radiometric age data