slip distribution from the 1 april 2007 solomon islands earthquake a unique image of near trench rupture 1 we estimate the slip distribution from the mw 8 1 solomon islands earthquake in 2007 from two post seismic surveys measuring uplifted coral and submerged coastal features the occurrence of islands extremely proximal to the trench and nucleation of rupture allowed for the collection of unprecedented coseismic deformation dataset along a large megathrust earthquake using data from the two surveys along the southeastern half of the slip zone within five weeks of the event we model the elastic dislocation to identify the optimal 29 and alternate 20 dip and distribution of thrust along the southern rupture the vertical deformation which includes both coseismic and early postseismic deformation has highly variable and large slip within 25 km of the trench and straddling ranongga island the shallow focus of slip in the near trench area may explain the locally high tsunami run up on portions of simbo island however the aseismic contribution of afterslip remains unknown

subduction zone dynamics in the sw pacific plate boundary region constrained from high precision pb isotope data this study presents high precision pb isotope data obtained by mc icp ms for lavas from the solomon island arc that covers ca 1000 km of the sw pacific plate boundary following a reversal of subduction polarity the presence of the old subducted pacific oceanic crust and the presently subducting indian australian plate beneath the entire island arc is confirmed by geophysical and geochemical evidence new high precision pb isotope data now permit to distinguish more clearly between indian and pacific type subduction components in this complex plate tectonic constellation the values range from 206pb 204pb 18 345 to 18 845 207pb 204pb 15 498 to 15 545 and 208pb 204pb 38 120 to 38 372 indicating the absence of pelagic sediments in the sub arc mantle these data reveal a predominance of subduction components derived from ancient subduction of the pacific plate in contrast lavas with indian type pb isotope signatures are confined to the central new georgia group of the solomon islands where the young woodlark ridge spreading centre is currently subducting all other solomon arc segments with a lower geothermal gradient have apparently not yet been overprinted by younger subduction components over the past 6 myrs moreover trace element and pb isotope data for woodlark ridge basalts show that subduction components from the fossil pacific slab have locally modified the source of woodlark basin lavas altogether our study highlights the potential of high resolution pb isotope measurements to distinguish between indian and pacific type subduction components along the sw pacific plate boundary

molybdenum behavior during early diagenesis insights from mo isotopes 1 we present molybdenum isotope and concentration data from 14 sites in the eastern pacific from the central california to the peru margin the environments studied have been chosen to represent a broad range in oxidation reduction redox potential which provide a framework for the behavior of this redox sensitive element manganese rich hemipelagic sediments from the eastern tropical pacific have a mean characteristic mo isotope signature 98 95mo 0 49 0 04 two times the standard deviation of the mean 2 sdom with n 14 that reflects fractionation between ocean water and authigenic mo associated with mn oxides authigenic fe mo s deposits from reducing continental margin settings also have a characteristic mo isotopic signature 98 95mo 1 64 0 04 2 sdom with n 136 both of these values are in contrast to highly sulfidic 11 m h2saq restricted basin environments which contain mo isotope values analytically indistinguishable from seawater in terms of the mo isotope composition the modern oceanic mo sink is dominated by continental margin type environments where 98 95mo 1 6 and mn rich sediments where 98 95mo approximately 0 5 with a minor contribution from euxinic settings where h2saq 11 m

incipient subduction of the ontong java plateau along the north solomon trench abstract the ontong java plateau ojp in the western central pacific is the largest and thickest oceanic plateau and one of a few oceanic plateaus converging on an island arc solomon island arc sia to better understand the evolution of the north solomon trench nst active oblique convergence between the ojp and sia and late neogene development of malaita accretionary prism map we present 850 km of multichannel seismic reflection data integrated with 7832 km 2 of izanagi side scan sonar coverage we have focussed the study at the transition area between the well defined northwestern end of the north solomon trench and a diffusely deformed area where the trench is actively propagating in a northwestward direction the deeper structure beneath the survey area is discussed by phinney et al oceanic plateau accretion in the malaita accretionary prism inferred from multi channel seismic reflection data this issue using deeper penetration multichannel seismic reflection lines the serial cross sections provided by multichannel seismic profiling combined with the izanagi backscattering imagery provides a time series evolution for the development of the north solomon trench the main evolutionary stages include 1 the incipient trench in the northern area marked by a diffuse zone of deformation above a broad arch in the crust deeper penetration profiles by phinney et al show the bulge is related to a deeper decollement fault that is propagating upward and seaward through the crust 2 the formation of a continuous thrust front in the central area deeper penetration profiles by phinney et al show this thrust front is surface expression of the same decollement present at depth to the north the boundary between the surface trace of the thrust and the diffuse area of deformation in the northern area is inferred as a vertical high angle tear fault with left lateral offset 3 the formation of a deep elongate trench which controls gravitationally related slumping and sedimentation around the steep edges of the trench fill basin the areas to the southeast are those that have undergone convergence for the longest period of time and therefore show better developed trench structures and a reduced width of the map areas to the northwest have undergone convergence for a shorter period of time and show less developed trench structures and a wide area of the map

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

global tectonic significance of the solomon islands and ontong java plateau convergent zone abstract oceanic plateaus areas of anomalously thick oceanic crust cover about 3 of the earth s seafloor and are thought to mark the surface location of mantle plume heads hotspot tracks represent continuing magmatism associated with the remaining plume conduit or tail it is presently controversial whether voluminous and mafic oceanic plateau lithosphere is eventually accreted at subduction zones and therefore 1 influences the eventual composition of continental crust and 2 is responsible for significantly higher rates of continental growth than growth only by accretion of island arcs the ontong java plateau ojp of the southwestern pacific ocean is the largest and thickest oceanic plateau on earth and the largest plateau currently converging on an island arc solomon islands for this reason this convergent zone is a key area for understanding the fate of large and thick plateaus on reaching subduction zones this volume consists of a series of four papers that summarize the results of joint us japan marine geophysical studies in 1995 and 1998 of the solomon islands ontong java plateau convergent zone marine geophysical data include single and multi channel seismic reflection ocean bottom seismometer obs refraction gravity magnetic sidescan sonar and earthquake studies objectives of this introductory paper include 1 review of the significance of oceanic plateaus as potential contributors to continental crust 2 review of the current theories on the fate of oceanic plateaus at subduction zones 3 establish the present day and neogene tectonic setting of the solomon islands ontong java plateau convergent zone 4 discuss the controversial sequence and timing of tectonic events surrounding ontong java plateau solomon arc convergence 5 present a series of tectonic reconstructions for the period 20 ma early miocene to the present day in support of our proposed timing of major tectonic events affecting the ontong java plateau solomon islands convergent zone and 6 compare the structural and deformational pattern observed in the solomon islands to ancient oceanic plateaus preserved in precambrian and phanerozoic orogenic belts our main conclusion of this study is that 80 of the crustal thickness of the ontong java plateau is subducted beneath the solomon island arc only the uppermost basaltic and sedimentary part of the crust 7 km is preserved on the overriding plate by subduction accretion processes this observation is consistent with the observed imbricate structural style of plateaus and seamount chains preserved in both precambrian and phanerozoic orogenic belts

characteristics on fault coupling along the solomon megathrust based on gps observations from 2011 to 2014 the solomon megathrust along the western solomon arc generated two megathrust earthquakes in the past decade mw 8 1 in 2007 and mw 7 1 in 2010 to investigate the interseismic deformation and inferred coupling on the megathrust we deployed the first continuous gps network in the western solomon islands our 2011 2014 gps data and the back slip inversion model show coupling ratio as high as 73 along the southeastern 2007 rupture segment but only 10 on average along the segment of 2010 event based on the spatial distribution of coseismic slip aftershock clusters derived coupling pattern and paleo geodetic records we discovered the former as a semi permanent asperity and the latter as a potential megathrust barrier we propose that a characteristic earthquake of magnitude not less than mw 8 will recur in an interval of 100 or more years by either single or doublet earthquake

sequestration mechanisms and anthropogenic inputs of rhenium in sediments from eastern canada lakes abstract the concentrations of re as well as those of several other geochemical variables were measured in dated sediment cores and in porewater samples from four lacustrine basins in eastern canada one perennially oxic located 40 km from quebec city and three seasonally anoxic located within 25 km of non ferrous metal smelters the drainage basins of these lakes are uninhabited and have not been affected by human activity or wildfires all of the depth profiles of dissolved re indicate higher re concentrations in the water overlying the sediment than in the porewater diffusion of re across the sediment water interface a progressive decrease in porewater re concentrations to reach minimum values of 0 5 pm within a 10 cm sediment depth interval modeling of these re porewater profiles with a one dimensional transport reaction equation indicates that re is removed from porewater within this depth interval based on thermodynamic predictions of re speciation and of saturation states and on comparison of these predictions with sulfide porewater profiles we infer that re is removed from porewater by precipitation of rheniite res2 s the rate constant for the formation of res2 s in sediments is estimated from the modeling exercise to be 0 51 0 64 10 21 mol cm 3 s 1 accumulation of sedimentary re shows a strong authigenic component as in anoxic marine sediments sharp increases in solid phase re during the last century are attributed to atmospheric deposition of anthropogenic re deriving from coal burning and nearby smelter emissions

oligocene to recent tectonic history of the central solomon intra arc basin as determined from marine seismic reflection data and compilation of onland geology systematic analysis of a grid of 3450 km of multichannel seismic reflection lines from the solomon islands constrains the late tertiary sedimentary and tectonic history of the solomon island arc and its convergent interaction with the cretaceous ontong java oceanic plateau ojp the ojp the largest oceanic plateau on earth subducted beneath the northern edge of the solomon arc in the late neogene but the timing and consequences of this obliquely convergent event and its role in the subduction polarity reversal process remain poorly constrained the central solomon intra arc basin csb which developed in oligocene to recent time above the solomon arc provides a valuable record of the tectonic environment prior to and accompanying the ojp convergent event and the subsequent arc polarity reversal recognition of regionally extensive stratigraphic sequences whose ages can be inferred from marine sedimentary sections exposed onland in the solomon islands indicate four distinct tectonic phases affecting the solomon island arc phase 1 late oligocene late miocene rifting of the northeast facing solomon island arc produced basal normal fault controlled asymmetrical sequences of the csb the proto north solomon trench was probably much closer to the csb and is inferred to coincide with the trace of the present day kia kaipito korigole kkk fault zone this protracted period of intra arc extension shows no evidence for interruption by an early miocene period of convergent soft docking of the ontong java plateau as proposed by previous workers phase 2 late miocene pliocene oblique convergence of the ontong java plateau at the proto north solomon trench kkk fault zone and folding of the csb and formation of the malaita accretionary prism map the highly oblique and diachronous convergence between the ontong java plateau and the solomon arc terminates intra arc extension first in the southeast russell subbasin of the csb during the late miocene and later during the pliocene in the northwest shortland subbasin of the csb folds in the csb form by inversion of normal faults formed during phase 1 phinney et al sequence stratigraphy structural style and age of deformation of the malaita accretionary prism solomon arc ontong java plateau convergent zone show a coeval pattern of southeast to northwest younging in folding and faulting of the map phase 3 late pliocene early pleistocene arc polarity reversal and subduction initiation at the san cristobal trench effects of this event in the csb include the formation of a chain of volcanoes above the subducting australia plate at the san cristobal trench the formation of the broad synclinal structure of the csb with evidence for truncation at the uplifted flanks and widespread occurrence of slides and seismites deposits formed by seismic shaking phase 4 pleistocene to recent continued shortening and synclinal subsidence of the csb continued australia pacific oblique plate convergence has led to deepening of the submarine elongate basin axis of the synclinal csb and uplift of the dual chain of the islands on its flanks

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

effect of storms during drought on post wildfire recovery of channel sediment dynamics and habitat in the southern california chaparral usa author s florsheim joan l chin anne kinoshita alicia m nourbakhshbeidokhti samira abstract current global warming projections suggest a possible increase in wildfire and drought augmenting the need to understand how drought following wildfire affects the recovery of stream channels in relation to sediment dynamics we investigated post wildfire geomorphic responses caused by storms during a prolonged drought following the 2013 springs fire in southern california usa using multi temporal terrestrial laser scanning and detailed field measurements after the fire a dry season dry ravel sediment pulse contributed sand and small gravel to hillslope channel margins in big sycamore creek and its tributaries a small storm in wy 2014 generated sufficient flow to mobilize a portion of the sediment derived from the dry ravel pulse and deposited the fine sediment in the channel totaling 0 60 m3 m of volume per unit length of channel the sediment deposit buried step pool habitat structure and reduced roughness by over 90 these changes altered sediment transport characteristics of the bed material present before and after the storm the ratio of available to critical shear stress t o t c increased by five times storms during wy 2015 contributed additional fine sediment from tributaries and lower hillslopes and hyperconcentrated flow transported and deposited additional sediment in the channel together these sources delivered sediment on the order of six times that in 2014 further increasing t o t c these storms during multi year drought following wildfire transformed channel dynamics the increased sediment transport capacity persisted during the drought period characterized by the longer residence time of relatively fine grained post fire channel sedimentation this contrasts with wetter years when post fire sediment is transported from the fluvial system during the same season as the post fire sediment pulse results of this short term study highlight the complex and substantial effects of multi year drought on geomorphic responses following wildfire these responses influence pool habitat that is critical to longer term post wildfire riparian ecosystem recovery

arc segmentation and seismicity in the solomon islands arc sw pacific abstract this paper evaluates neotectonic segmentation in the solomon islands forearc and considers how it relates to regional tectonic evolution and the extent of ruptures of large megathrust earthquakes we first consider regional geomorphology and quaternary vertical displacements especially uplifted coral reef terraces then we consider geographic seismicity patterns aftershock areas and vertical displacements for large earthquakes focal mechanisms and along arc variations in seismic moment release to evaluate the relationship between neotectonically defined segments and seismicity notably one major limitation of using seismicity to evaluate arc segmentation is the matter of accurately defining earthquake rupture zones for example shoreline uplifts associated with the 1 april 2007 mw 8 1 western solomons earthquake indicate that the along arc extent of rupture was about 50 km smaller than the aftershock area thus if we had relied on aftershocks alone to identify the 2007 rupture zone as we do for most historical earthquakes we would have missed the rupture s relationship to a major morphologic feature in many cases the imprecision of defining rupture zones without surface deformation data may be largely responsible for the poor mismatches to neotectonic boundaries however when a precise paleoseismic vertical deformation history is absent aftershocks are often the best available tool for inferring rupture geometries altogether we identify 16 segments in the solomon islands these comprise three major tectonic regimes or supersegments that correspond respectively to the forearc areas of guadalcanal makira the new georgia island group and bougainville islands subduction of the young and relatively shallow and buoyant woodlark basin and spreading system distinguishes the central new georgia supersegment from the two neighboring supersegments the physiographic expression of the san cristobal trench is largely absent but bathymetric mapping of the surface trace of the interplate thrust zone defines it adequately the new georgia supersegment has smaller arc segments and more islands due to general late quaternary forearc uplift very close to the trench where vertical displacement rates tend to be faster prior to the 2007 earthquake it had much lower rates of seismic activity than the neighboring supersegments generally the mean along arc lateral extent of solomon arc segments is about 75 km somewhat smaller than the segments reported in some other island arcs such as japan 100 260 km but larger than those of the tonga 30 80 km and central new hebrides arcs 30 110 km these differences may be real but it may occur simply because the coral friendly tropical environment of the south pacific arcs numerous emerged forearc islands and high seismicity rates provide an unusually favorable situation for observing variations in vertical tectonic activity and thus for identifying segment boundaries over the past century seismic slip in the solomons as indicated by seismic moment release has corresponded to about half the plate convergence rate however there are notable variations along the arc even with the 2007 earthquake the long term moment release rate in the new georgia supersegment is relatively low and this may indicate that large earthquakes are imminent

model for the formation of large transtensional basins in zones of tectonic escape tectonic escape is strike slip dominated motion of colliding continental or arc crust in the direction of subductable oceanic crust i describe four examples of large transtensional basins in cenozoic zones of tectonic escape and propose that these basins formed along newly formed transtensional faults formed between the collided and escaping parts of the plate the reoriented direction of the escaping plate split along the new transtensional fault zone is determined by the presence of a free face or subductable oceanic crust continued subduction toward the free face is driven by the force of gravity acting on dense oceanic crust slab pull the four examples presented here show that a variety of transtensional deformational styles can be generated within this specific type of divergent tectonic setting these transtensional styles include pull apart basins at fault stepovers more asymmetrical rift like basins thought to be formed under conditions of fault normal extensional stresses and single or multiple short spreading ridges transtensional styles may be controlled more by the type and age of crust present than the angle of reorientation of the escaping plate

evidence for late eocene emplacement of the malaita terrane solomon islands implications for an even larger ontong java nui oceanic plateau 1 most tectonic models for the solomon islands arc invoke a miocene collision with the ontong java plateau ojp to halt cessation of pacific plate subduction initiate australian plate subduction and emplace the malaita terrane which shares the characteristic basement age and geochemistry of ojp existing paleomagnetic evidence however required the malaita terrane to have been fixed to the arc from at least the late eocene new sampling has yielded a paleomagnetic pole from aptian albian limestones and mudstones that falls between the apparent polar wander paths for the australian plate and ojp confirming the extended period of residence of the malaita terrane on the arc arc derived turbidities within late eocene through miocene limestones on malaita and santa isabel and related clasts in broadly contemporary sandstones and conglomerates on santa isabel also attest to early emplacement modeling the emplacement at 35 ma satisfies both the paleomagnetic data and the sediment provenance continuing the reconstruction to 125 ma leaves the malaita terrane far from ojp at the time of plateau formation ojp is now understood to have formed as part of a larger ontong java nui also comprising the hikurangi and manihiki plateaus separated by spreading during the cretaceous restoring the separation of the known elements and invoking an additional triple junction unites the now largely subducted malaita terrane with the rest of ontong java nui subduction of substantial areas of the ontong java nui plateau with little geological signal other than a reduction in arc volcanism is a corollary

blueschists eclogites and subduction zone tectonics insights from a review of late miocene blueschists and eclogites and related young high pressure metamorphic rocks abstract in this paper late miocene blueschist and eclogite belts including the world s youngest blueschist belt in timor tanimbar island chain eastern indonesia and the world s youngest coesite bearing eclogite papua new guinea together with selected cenozoic high pressure and ultrahigh pressure metamorphic rocks are reviewed from a synthesis of the geology metamorphism and chronology of these rocks the formation and exhumation process are evaluated and the significance on tectonics at convergent plate boundaries is discussed

what regulates rhenium deposition in euxinic basins abstract rhenium is greatly enriched in black shales and euxinic basin sediments relative to its crustal abundance the enrichment process is generally assumed to involve reduction of reo 4 the principal re species in seawater to an insoluble re iv oxide or sulfide in suboxic and anoxic environments the specific biotic or abiotic mechanism of reduction has so far defeated efforts to discover it here an alternative mechanism of fixing re in sediments is examined experimentally thiolation of reo 4 leading to particle reactive thioperrhenates re vii o n s 4 n or to re vii sulfide precipitates or coprecipitates using optical absorption methodology we obtain the first measurements of equilibrium constants for formation of reo 3 s and res 4 as well as a solubility constant for a colloidal re 2 s 7 polymer from these constants we conclude that most euxinic environments contain insufficient sulfide to stabilize thioperrhenates as major species similarly re 2 s 7 polymers are too soluble to form in near neutral ph waters although they might form in acidic mine waters or during supergene hypogene enrichment processes to explain remarkable similarities between mo and re vertical profiles in the black sea we propose that both elements become thiolated at surfaces of a fe mo s colloidal phase and consequently coprecipitate coprecipitation implies that the triggering mechanism for re removal from euxinic basins is neither reduction nor thiolation of reo 4 but instead saturation of sulfidic waters with the fe mo s phase coprecipitation favors removal of mo more than re from the aqueous phase explaining increasing aqueous phase re mo ratios as these elements are depleted from sulfidic waters the raleigh fractionation law describes the process well similar partition coefficients describe the evolution of re mo ratios quantitatively both in sulfidic black sea waters and in sulfidic hingham bay pore waters

collision of manihiki plateau fragments to accretional margins of northern andes and antarctic peninsula the manihiki plateau a large igneous province lip was emplaced in the early cretaceous as a single plateau together with the ontong java plateau and the hikurangi plateau additional to the present manihiki plateau fragments to its northeast and east have been formed plate kinematic reconstructions suggest the capturing of these fragments by the farallon plate and the phoenix plate respectively by tracing these fragments we report a paleocene collision of the northeastern manihiki plateau fragment with the northern south american craton the northern andes exhibit multiple terranes of lip origin we infer based on geophysical petrological and geochemical data that the pinon formation consists of crustal units of the former manihiki plateau an early cretaceous collision of the eastern manihiki plateau fragment is reconstructed for west antarctica the subduction of this fragment in the palmer land region can be associated with the so called palmer land event and a flattening of the subduction slab by reconstructing the dispersal of the fragments of the manihiki plateau we provide a deeper insight in the possible subduction scenarios and buildup of the accretional margins of the northern andes and the antarctic peninsula

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

sequence stratigraphy structural style and age of deformation of the malaita accretionary prism solomon arc ontong java plateau convergent zone possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau arc accretion and resulting collisional orogenesis deep penetration multi channel seismic reflection mcs data from the northern flank of the solomon islands reveal the sequence stratigraphy structural style and age of deformation of an accretionary prism formed during late neogene 5 0 ma convergence between the 33 km thick crust of the ontong java oceanic plateau and the 15 km thick solomon island arc correlation of mcs data with the satellite derived free air gravity field defines the tectonic boundaries and internal structure of the 800 km long 140 km wide accretionary prism we name this prism the malaita accretionary prism or map after malaita the largest and best studied island exposure of the accretionary prism in the solomon islands mcs data gravity data and stratigraphic correlations to islands and odp sites on the ontong java plateau ojp reveal that the offshore map is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the solomon the subducting ontong java plateau pacific plate and transferred to the solomon arc with the exception of an upper sequence of quaternary island derived terrigenous sediments the deformed stratigraphy of the map is identical to that of the incoming ontong java plateau in the north solomon trench

the energetic 2010 mw 7 1 solomon islands tsunami earthquake summary on 2010 january 3 a moment magnitude mw 7 1 earthquake struck the solomon islands very near the san cristobal trench causing extensive landslides and surprisingly large tsunami waves because of the unique proximity of islands to the trench 20 km and earthquake a post seismic survey successfully identified unexpected widespread coseismic subsidence towards the trench up to 80 cm with no discernable post seismic deformation approximately 1000 km from the earthquake ocean bottom pressure sensors measured 1 2 cm open ocean tsunami waves though spatially limited the local tsunami wave heights up to 7 m were comparable to the much larger adjacent 2007 mw 8 1 earthquake the seismically determined focal mechanism broad scale subsidence tsunami amplitude and open ocean wave heights are all explained by an extremely shallow low angle thrust adjacent to the impinging subduction of the two seamounts near the trench this event belongs to a potentially new class of shallow tsunami earthquakes that is not identified as deficient in radiated seismic energy

sequence stratigraphy structure and tectonic history of the southwestern ontong java plateau adjacent to the north solomon trench and solomon islands arc the ontong java plateau ojp is the largest and thickest oceanic plateau on earth and one of the few oceanic plateaus actively converging on an island arc we present velocity determinations and geologic interpretation of 2000 km of two dimensional multi channel seismic data from the southwestern ontong java plateau north solomon trench and northern solomon islands we recognize three megasequences ranging in age from early cretaceous to quaternary on the basis of distinct interval velocities and seismic stratigraphic facies megasequence oj1 is early cretaceous upper igneous crust of the ojp and correlates with basalt outcrops dated at 122 125 ma on the island of malaita the top of the overlying megasequence oj2 a late cretaceous mudstone unit had been identified by previous workers as the top of igneous basement seismic facies and correlation to distant deep sea drilling project ocean drilling program sites indicate that oj2 was deposited in a moderately low energy marine environment near a fluctuating carbonate compensation depth that resulted in multiple periods of dissolution oj2 thins south of the stewart arch onto the solomon islands where it is correlated with the kwaraae mudstone formation megasequence oj3 is late cretaceous through quaternary pelagic cover which caps the ontong java plateau it thickens into the north solomon trench and seismic facies suggest that oj3 was deposited in a low energy marine environment we use seismic facies analysis sediment thickness structural observations and quantitative plate reconstructions of the position of the ojp and solomon islands to propose a tectonic magmatic and sedimentary history of the southwestern ontong java plateau prior to 125 ma late jurassic and early cretaceous oceanic crust formed from 125 to 122 ma the first mantle plume formed igneous crust oj1 between 122 and 92 ma marine mudstone oj2 and kwaraae mudstone of malaita solomon islands was deposited on ontong java plateau at 92 ma a second mantle plume caused widespread volcanism on the plateau from 92 to 15 ma pelagic carbonate sediment oj3 was deposited at 15 ma the southern ontong java plateau was deformed by normal faults during its approach toward the north solomon trench finally from 4 to 0 ma the malaita accretionary prism formed during collision between a substantially thicker portion of the ontong java plateau and the solomon islands arc flexure of the ontong java plateau near the trench caused coeval normal faulting

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

oceanic plateaus the fragmentation of continents and mountain building many anomalous rises in today s oceans may be submerged continental fragments detached from previous continents ancient island arcs or basaltic piles formed by hot spots and spreading centers these rises are embedded in their respective moving oceanic plates and are fated to be consumed at active margins where such rises are being consumed at present e g the nazca ridge they cause cessation of volcanism disruption of the downgoing slab and possible shifts in plate boundary configuration many past rises including numerous continental fragments have been recognized within mountain belts as allochthonous terranes they constitute a large portion of the orogenic belts in the north pacific from mexico through western north america alaska east siberia japan and in new zealand the orogenic deformation in these belts is possibly the result of the accretion of the allochthonous terranes many terranes have been accreted with substantial deformation also in the alpine chain well before major continent continent collisions it is suggested therefore that the accretion of fragments may be the common process of the deformation phase of mountain building subduction of normal oceanic crust may be insufficient for deformation whereas full continent continent collision may not be necessary the general validity of this conclusion depends critically on whether allochthonous terranes caused orogenic deformation in the andes or not most of the accreted fragments with continental affinities in the mesozoic cenozoic orogenic belts of the world can be traced back to the breakup of gondwana beginning with a pacifica domain in the permian through a larger india domain in the early mesozoic and continuing through the separation of the somalia plate in the near future the reasons for this 250 million year breakup process are not known but some kind of thermal process possible of mantle wide scale is implied

rhenium in the black sea comparison with molybdenum and uranium rhenium concentrations were measured in the black sea to determine the behavior of this redox sensitive element in an anoxic basin under reducing conditions re is removed from solution leading to its depletion from black sea deep waters compared with uranium water column re and mo profiles show evidence of removal from mid depths suggesting that these elements are scavenged either in the water column or slope sediments to a greater degree than u black sea surface waters are enriched in re reflecting re in rivers draining into the northern black sea that are enhanced up to 80 fold over other large world rivers this enrichment is most likely anthropogenic and may be due to coal burning in the region a simple two box model is used to demonstrate that re concentrations in the black sea are not in steady state with respect to current riverine inputs and authigenic fluxes riverine inputs of u and mo are not as significant perhaps reflecting the fractionation of re from the other elements during a high temperature combustion process re2o7 is volatile above 270 c

behavior of re and os during low temperature alteration results from himalayan soils and altered black shales re os analyses were performed on five soil profiles developed on silicate lithologies in the narayani drainage basin of the himalayas as well as on several altered black shales and associated alteration phases the results indicate that all of these samples have lost large amounts of re this re loss approached 100 in the black shale derived soils which also most probably lost substantial quantities of os the near constancy of os and re concentrations with depth indicates that this loss occurred quite early in the alteration process rather than progressively during the course of soil development a slight decrease in 187os 188os was observed toward the surface of the two black shale soil profiles possibly indicating a minor preferential mobility of radiogenic 187os for this lithology in the black shale derived saprolite and soils the loss of re and os was related to the loss of organic carbon the importance of this phase is underscored by the fact that organic material separated from a black shale sample accounted for nearly all of the os contained in the whole rock analysis of alteration phases from the surface of a weathered black shale showed that os liberated during alteration was partially reprecipitated in fe oxides with os isotopic compositions very similar to that of the original rock whereas re was removed with the fluid phase these results demonstrate the disproportionately large role that black shale weathering may play in determining the re and os contents of continental runoff and thus ultimately of seawater but they also emphasize the possible complexity of this process the data suggest that a large fraction of the os contained in black shales is released during chemical alteration which is apparently not the case for most other silicate rocks therefore the potential contribution of black shales to the dissolved os budget of runoff and river water may be even greater than that expected from the high os concentrations of these rocks the extent to which this os will affect the seawater os composition depends on how efficiently it is recaptured by secondary phases such as fe mn oxides in situ or during transport these results also underscore the high mobility of re with respect to os at every stage in the erosional process thus explaining the order of magnitude increase in re os ratio from the black shale source rocks to seawater

magnetic anomaly lineations from late jurassic to early cretaceous in the west central pacific ocean summary late jurassic to early cretaceous mesozoic magnetic anomaly lineations the phoenix magellan mid pacific mountains hawaiian and japanese lineation sets with fracture zones in the west central pacific ocean were identified more comprehensively than in any previous studies we fixed 2100 positions of identified magnetic anomalies based on magnetic data of 283 cruise tracks two remarkable fracture zones the phoenix and central pacific fracture zones were mapped and newly named our newly identified lineations from mlon to mo around the mid pacific mountains which belong to the hawaiian lineation set illustrated that the sea floor south of the mid pacific mountains has the same age as that of the north 132 118 ma our analysis of skewness parameters revealed that the older part of the phoenix set m17 m29 has skewness different from that of the younger part ml m14 implying an effect of magnetic overprints by the cretaceous volcanism it was confirmed that the spreading rate of the mesozoic pacific spreading system was the fastest in the world in the mesozoic a drastic change in spreading rates occurred simultaneously at the period between chrons m21 and m20 149 5 148 5 ma in all the mesozoic pacific spreading systems the event appears to be synchronous with events in other oceans such as the mesozoic atlantic and indian oceans

subduction zone recycling processes and the rock record of crustal suture zonesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent offshore observations at modern ocean margin subduction zones omszs reveal that bodies of accreted material are commonly volumetrically small or missing that crustal thinning and subsidence 3 5 km has occurred and that most trench axes lie close 5 30 km to the seaward tapering edge of coastal basement rock onshore mapping commonly documents missing or only narrow terranes of former forearc rock and the inboard migration of the arc magmatic front these observations are evidence that subduction is accompanied by the removal of sediment and crustal material from the submerged forearc by the kindred tectonic processes respectively of sediment subduction and subduction erosion subduction erosion truncates the margin migrates the trench inboard at 2 5 km ma onshore observations at ancient crust suturing subduction zones csszs imply that collisional suturing is accompanied by sediment subduction and truncation of both upper and lower plates during a protracted period of suturing 20 50 millio

theoretical modeling of rhenium isotope fractionation natural variations across a black shale weathering profile and potential as a paleoredox proxy we present the first data documenting environmental variations in the isotope composition of re and the first theoretical models of equilibrium re isotope fractionation factors variations of 187re at modern surface temperatures are predicted to be level for redox revii reiv and perrhenate thiolation reactions reviio4 reviioxs4 x reviis4 nuclear volume fractionations are calculated to be smaller than mass dependent effects values of 187re from new albany shale samples presented in this work and in a previous study show a range of 0 8 over a stratigraphic interval of 20 m the magnitude of variation is consistent with theoretical predictions and may provide evidence for changing 187re of seawater in the geologic past a 0 3 change in 187re across a 14 m horizontal black shale weathering profile is accompanied by a hundred fold decrease in re concentration and a 75 decrease in organic carbon associated with the transition from reducing to oxic weathering environment we attribute decreasing 187re to the loss of organically bound re component 187re 0 28 the re isotope composition of the complementary detrital silicate fraction varies from 0 59 to 1 5 depending on the choice of silicate re concentration

collision induced post plateau volcanism evidence from a seamount on ontong java plateau abstract many seamounts on the ontong java plateau ojp occur near the stewart arch a topographic high that extends parallel to the north solomon trench along the southern margins of the plateau despite the thick sediment cover several volcanic cones with strong acoustic reflection were discovered on the submarine flank of the nuugurigia seamount from such volcanic cones basalts were successfully sampled by dredging radiometric dating of basalts and ferromanganese encrustation indicate eruption age of 20 25 ma significantly younger than the 122 ma main ojp plateau and post plateau basalts the age range coincides with the collision of the ojp with the solomon arc the nuugurigia basalts geochemically differ from any other rocks sampled on the ojp so far they are alkali basalts with elevated sr low zr and hf and enriched mantle i emi like isotopic composition parental magmas of these alkali basalts may have formed by small degree melting of peridotitic mantle impregnated with recycled pyroxenite material having enriched geochemical composition in the ojp s mantle root we conclude that small volume alkali basalts from the enriched mantle root migrated through faults or fractures caused by the collision along the stewart arch to form the seamount our results suggest that the collision of the ojp with the solomon arc played an important role in the origin of similar post plateau seamounts along the stewart arch

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day