stable organic carbon isotope stratigraphy across oceanic anoxic event 2 of demerara rise western tropical atlantic ocean drilling program odp leg 207 recovered expanded sections of organic carbon rich laminated shales on demerara rise western tropical atlantic high resolution organic carbon isotope and total organic carbon toc records are presented which span the cenomanian turonian boundary interval ctbi including the oceanic anoxic event oae 2 from four sites oriented along a nw striking depth transect these records represent the first high resolution carbon isotope records across oae 2 from the south american margin of the tropical atlantic due to the scarcity of age significant fossils the main purpose of this study was to develop a detailed carbon isotope stratigraphy in order to correlate the ctbi across the depth transect and to tie this to biostratigraphically well defined sections in the western interior basin pueblo usa boreal shelf seas eastbourne england and western tethys oued mellegue tunisia all four sections studied document a 6 increase of 13corg values at the base of the ctbi which is followed by an interval of elevated 13corg values and a subsequent decrease our results supply an important stratigraphic base for subsequent paleoceanographic studies on late cenomanian to early turonian sediments from demerara rise and elsewhere

dependence of volcanic systems on tectonic stress conditions as revealed by features of volcanoes near izu peninsula japan abstract five volcanoes asama fuji izu tobu izu oshima and miyakejima which are aligned along the same volcanic chain in central japan are subjected to different degrees to the stress conditions associated with the continental collision and subduction along wedge shaped trenches near izu peninsula at a great distance from the collision boundary asama is characterized by an axially symmetric edifice with a unique summit crater for magma effusion and miyakejima has a similar symmetric structure accompanied by radial eruptive fissures at the opposite extreme izu tobu which is the closest to the collision boundary consists of many small monogenetic volcanoes that lack a central vent in intermediate locations fuji and izu oshima exhibit elongated volcanic edifices with both summit vents and parallel fissures on their flanks for magma effusion to understand this systematic trend of volcanic features growth of volcanic systems is analyzed based on magma transport in cylindrical conduits and planar fissures available in individual stress conditions it is assumed in this analysis that fissures are produced with extensional stresses or high magma pressures enough to overcome compressive stresses and that cylindrical conduits that have arisen from localization of fissures can be persistently used for repeated magma supply the analysis predicts that volcanoes are classified into the following three types that represent their growth processes in different stress conditions 1 a polygenetic volcano having an axially symmetric edifice grows with unique magma supply through the central conduit under compressive or neutral stresses 2 a polygenetic volcano having an elongated edifice grows with a summit crater and eruptive fissures parallel to the elongation under weak extensions and 3 a group of small monogenetic volcanoes is constructed along many parallel fissures under strong extensions this classification is examined for the five volcanoes and some other volcanoes in the world the alternate occurrences of summit and flank eruptions observed at some polygenetic volcanoes are interpreted to be controlled by the summit height magma densities and stress conditions that influence the pressure of a common magma source

dyke intrusion model for the 1989 seismovolcanic activity off ito central japan in the last 10 years extensive earthquake swarms have occurred intermittently in the region east of izu peninsula central japan in july 1989 an active swarm again took place off ito city and among all past activities it was nearest to land and shallowest this activity eventually became a weak submarine eruption the first of its kind in this region associated with this event a borehole tiltmeter at 92 m depth installed several kilometers from the source area detected distinct continuous tilt change with the following features 1 tilt of 20 rad was observed within 1 week preceding the eruption 2 tilt change showed a good correlation to swarm activity 3 no obvious coeruption tilt change was observed on the basis of the tilt record and swarm distribution we constructed a dislocation model to interpret the seismovolcanic activity the model consists of two tensile faults each of which corresponds to magma intrusions in may and july and a right lateral reverse fault representing the largest earthquake m5 5 at 1109 lt on july 9 this model can simulate not only the above tilt data but also the record of a nearby dilatometer the results from daily laser distance measurements and daily global positioning system monitoring as well as results from other conventional distance surveys and leveling surveys in the surrounding region from this model we conclude that the intersection of the shear fault with the tensile fault caused magma to come up into soft sedimentary layers at the seabottom creating a lava dome later an instability brought about a magma phreatic explosion which did not generate any substantial crustal deformations at deeper levels

structure and emplacement of the nandurbar dhule mafic dyke swarm deccan traps and the tectonomagmatic evolution of flood basalts flood basalts such as the deccan traps of india represent huge typically fissure fed volcanic provinces we discuss the structural attributes and emplacement mechanics of a large linear tholeiitic dyke swarm exposed in the nandurbar dhule area of the deccan province the swarm contains 210 dykes of dolerite and basalt 1 km in length exposed over an area of 14 500 km2 the dykes intrude an exclusively basaltic lava pile largely composed of highly weathered and zeolitized compound pahoehoe flows the dykes range in length from 1 km to 79 km and in thickness from 3 to 62 m almost all dykes are vertical with the others nearly so they show a strong preferred orientation with a mean strike of n88 because they are not emplaced along faults or fractures they indicate the regional minimum horizontal compressive stress 3 to have been aligned n s during swarm emplacement the dykes have a negative power law length distribution but an irregular thickness distribution the latter is uncommon among the other dyke swarms described worldwide dyke length is not correlated with dyke width using the aspect ratios length thickness of several dykes we calculate magmatic overpressures required for dyke emplacement and depths to source magma chambers that are consistent with results of previous petrological and gravity modelling the anomalously high source depths calculated for a few dykes may be an artifact of underestimated aspect ratios due to incomplete along strike exposure however thermal erosion is a mechanism that can also explain this whereas several of the nandurbar dhule dykes may be vertically injected dykes from shallow magma chambers others particularly the long ones must have been formed by lateral injection from such chambers the larger dykes could well have fed substantial 1 000 km3 and quickly emplaced a few years flood basalt lava flows this work highlights some interesting and significant similarities and contrasts between the nandurbar dhule dyke swarm and regional tholeiitic dyke swarms in iceland sudan and elsewhere

relations between deformation and upper crustal magma emplacement in laboratory physical models abstract this paper presents analogue models for the emplacement of granitic magmas in upper crustal levels with different mechanical layering during shortening extension and strike slip deformation in particular we investigated how a weak layer embedded in the upper brittle crust can control the level of magma emplacement the adopted experimental setup was used to examine the control of soft rocks on the movement of magma through a deforming brittle crust model results indicate that the occurrence of a weak soft layer embedded in brittle stiff material has an impact on the level of magma emplacement the level of emplacement during both extension and shortening was systematically deeper for models with a soft layer than for purely brittle models during strike slip deformation the magma pierced the surface in both purely brittle and brittle ductile models

erosional response of south china to arc rifting and monsoonal strengthening a record from the south china sea abstract ocean drilling program sampling of the distal passive margin of south china at sites 1147 and 1148 has yielded clay rich hemipelagic sediments dating to 32 ma oligocene just prior to the onset of seafloor spreading in the south china sea the location of the drill sites offshore the pearl river suggests that this river or its predecessor may have been the source of the sediment in the basin which accounts for only 1 8 of the total neogene sediment in the asian marginal seas a mean erosion depth of 1 km over the current pearl river drainage basin is sufficient to account for the sediment volume on the margin two dimensional backstripping of across margin seismic profiles shows that sedimentation rates peaked during the middle miocene 11 16 ma and the pleistocene since 1 8 ma nd isotopic analysis of clays yielded nd values of 7 7 to 11 0 consistent with the south china block being the major source of sediment more positive nd values during and shortly after rifting compared to later sedimentation reflect preferential erosion at that time of more juvenile continental arc rocks exposed along the margin as the drainage basin developed and erosion shifted from within the rift to the continental interior nd values became more negative a rapid change in the clay mineralogy from smectite dominated to illite dominated at 15 5 ma synchronous with middle miocene rapid sedimentation mostly reflects a change to a wetter more erosive climate evidence that the elevation of the tibetan plateau and erosion in the western himalaya both peaked close to this time supports the suggestion that the asian monsoon became much more intense at that time much earlier than the 8 5 ma age commonly accepted

transient dike propagation and arrest near the level of neutral buoyancy abstract we present a finite difference perturbation method to investigate transient dike propagation from a magma chamber 1 2 km below the level of neutral buoyancy in oceanic crust and explore the role of density gradation in dike propagation arrest the dike is modeled as a magma filled blade crack and the host rock is assumed to be a linear elastic medium with graded mass density an integral equation approach is used to obtain the dike propagation velocity and stress intensity factor at the propagating dike tip the finite difference perturbation method is applicable generally to mafic dikes with v less than 50 pa m where is the magma viscosity and v the dike propagation velocity numerical results show that dike propagation velocity initially increases with dike length reaches a peak value when the dike tip reaches a position well above the level of neutral buoyancy and then rapidly decreases to zero after the dike propagates further into the region above the level of neutral buoyancy which indicates that density gradation is an effective mechanism for dike arrest the effects of host rock fracture toughness and magma chamber depth relative to the level of neutral buoyancy are also discussed

experiments on rift zone evolution in unstable volcanic edifices large ocean island volcanoes frequently develop productive rift zones located close to unstable flanks and sites of older major sector collapses flank deformation is often caused by slip along a decollement within or underneath the volcanic edifice we studied how such a stressed volcanic flank may bias the rift zone development the influence of basal lubrication and lateral flank creep on rift development and rift migration is still poorly constrained by field evidence here our analog experiments provide new insights we injected colored water into gelatin cones and found systematic orientations of hydro fractures dikes propagating through the cones at the base of the cone diverse friction conditions were simulated by variation of the basal creep conditions we modeled radial dike swarms collinear rift zones and three armed rift systems it is illustrated that a single outward creeping flank is sufficient to modify the entire rift architecture of a volcano the experiments highlight the general unsteadiness of dike swarms and that the distribution and alteration of weak substratum may become a major player in shaping a volcano s architecture

collision and fan shaped compressional stress pattern in the izu block at the northern edge of the philippine sea plate the izu block in central japan which is surrounded by the nankai suruga trough and the sagami trough is considered to be colliding with the eurasian eur plate at the northern edge of the philippine sea phs plate the stress state in the izu block is investigated from focal mechanism data mainly obtained by the seismic network of the national research institute for earth science and disaster prevention the predominant focal mechanisms in the central to eastern part of the izu block indicate strike slip faulting with p axes oriented n s to nw se and t axes oriented e w to ne sw whereas focal mechanisms in the western part are strike slip and reverse faulting with p axes oriented n s to ne sw indicating that the compressional axes remain horizontal throughout the region the compressional stress trajectories estimated from the p axes show a fan shaped pattern radiating from the northern edge of the izu block where the collision is considered to be occurring the fan shaped pattern of compressional stress trajectories is interpreted to be the result of the collision of the izu block with eur plate plane stress analysis by the finite element method supports this conclusion the stable distribution of the t axis directions in the central to eastern part is basically interpreted as resulting from the slab pull force by the subducting phs plate along the sagami trough furthermore this model can explain the seismic quiescence in the northern part of the suruga bay region

elastic thickness control of lateral dyke intrusion at mid ocean ridges abstract magmatic accretion at slow spreading mid ocean ridges exhibits specific features although magma supply is focused at the centre of second order segments melts are episodically distributed along the rift toward segment ends by lateral dyke intrusions it has been previously suggested that an along axis downward topographic slope away from the magma source is sufficient to explain lateral dyke propagation however this cannot account for the poor correlation between dyke opening and surface elevation in the 2005 2010 series of 14 dyke intrusions of afar ethiopia using mechanical arguments constrained by both geodetic and seismological observations we propose that the large dykes that initiate near the mid segment magma source are attracted toward segment ends as a result of a thickening of the elastic brittle lithosphere in the along rift direction this attraction arises from the difference of elastic resistance between the segment centre where the lithosphere is thermally weakened by long term focusing of melts and comparatively colder hence stronger segment ends the axial topographic gradient in magmatic rifts may be more likely explained as an incidental consequence of these variations of along axis elastic brittle thickness rather than the primary cause of lateral dyke injections

chemical and isotopic signature of bulk organic matter and hydrocarbon biomarkers within mid slope accretionary sediments of the northern cascadia margin gas hydrate system abstract the chemical and isotopic compositions of sedimentary organic matter som from two mid slope sites of the northern cascadia margin were investigated during integrated ocean drilling program iodp expedition 311 to elucidate the organic matter origins and identify potential microbial contributions to som gas hydrate is present at both locations iodp sites u1327 and u1328 with distinct patterns of near seafloor structural accumulations at the cold seep site u1328 and deeper stratigraphic accumulations at the slope basin site u1327 source characterization and evidence that some components of the organic matter have been diagenetically altered are determined from the concentrations and isotopic compositions of hydrocarbon biomarkers total organic carbon toc total nitrogen tn and total sulfur ts the carbon isotopic compositions of toc 13ctoc 26 to 22 and long chain n alkanes c27 c29 and c31 13c 34 to 29 suggest the organic matter at both sites is a mixture of 1 terrestrial plants that employ the c3 photosynthetic pathway and 2 marine algae in contrast the 15ntn values of the bulk sediment 4 to 8 are consistent with a predominantly marine source but these values most likely have been modified during microbial organic matter degradation the 13c values of archaeal biomarker pentamethylicosane pmi 46 4 and bacterial sourced hopenes diploptene and hop 21 ene 40 9 to 34 7 indicate a partial contribution from methane carbon or a chemoautotrophic pathway our multi isotope and biomarker based conclusions are consistent with previous studies based only on the elemental composition of bulk sediments that suggested a mixed marine terrestrial organic matter origin for these mid slope sites of the northern cascadia margin

eruption history conduit migration and steady discharge of magma for the past 50 000 yr at esan volcanic complex northern japan we have undertaken a detailed field petrological geochronological and modeling study of esan volcanic complex northern japan in order to establish its eruptive history over the past 50 000 yr the esan volcanic complex includes seven lava domes which are endogenous domes developed without basal edifices each dome was produced by intermediate to silicic magmas with 57 67 wt sio 2 that were erupted in magnitude 4 5 eruptions five explosively erupted pyroclastic units cover the aprons of these lava domes the spatial and temporal relationships of the domes and the pyroclastic units have been determined in order to constrain the eruptive sequence of the esan volcanic complex a simple elastic model assuming a hydraulic connection state was utilized to study variations in long term magma discharge at the esan volcanic complex which have been attributed to changes in magma storage conditions the stepwise change in magma discharge with time which is 4 2 5 3 10 4 m 3 yr is interpreted to reflect a change between magma chamber radius r c and magma depth h c caused by an upward migration of magma assuming a continuous input of magma from a deep source at a constant supply rate the magma storage system that existed during the early stage of the esan volcanic complex has been renewed which will result in a shorter recurrence interval between eruptions rather than a long period of dormancy 22 400 yr given this finding and the fact that the most recent eruption occurred 9000 yr ago there is currently a risk of a large eruption at the esan volcanic complex

crustal lineament control on mineralization in the anarak area of central iran abstract the anarak mining area in iran is identified as one of the best known examples of mineralization located at the intersection of two important crustal scale lineaments which are the e w striking great kavir fault and the nw se trending urumieh dokhtar magmatic belt the objective of this research is to investigate the role of the lineaments and their subsidiaries at anarak area in the genesis of mineral deposits lineaments are long lived features which control or affect ancient as well as young crustal sequences lineaments are also deep seated because they commonly control the emplacement of deep crustal or mantle derived magmas metallogenic areas of up to 1000 km 2 might be observed in areas where broad structural zones intersect because they can facilitate the localization of magmatic or hydrothermal centers the two lineaments that intersect in the anarak area were both very active during mineralization therefore it is likely that pull apart basins or other dilatational sites at the intersection point were not preserved for substantial lengths of time and single large magma conduits would have been divided into smaller conduits for magma penetration and hydrothermal circulation the presence of these small conduits in addition to a small magma input could produce conditions for the circulation of mainly meteoric waters in which the magmatism has acted as a heat source for the mineralization system this phenomenon has led to the generation of a metallogenic area with several similar small deposits within a circular area of radius 30 km centered at the intersection point the two most famous deposits in this area are talmessi and meskani in which mineralization had occurred in two separate stages first stage fissure filling copper sulfide mineralization associated with eocene magmatism veins veinlets and stockworks the second is an overprinting stage which occurred after a fairly long interval which involves the formation of ni co arsenides and u oxide minerals

spatiotemporal variation of organic geochemical properties since the mid miocene in the deep south china sea iodp expedition 349 abstract we performed an extensive survey of total organic carbon oc and stable oc composition of in the deep south china sea sediments from the international ocean discovery program iodp expedition 349 sites u1431 u1433 and ocean drilling program odp leg 184 site 1148 our results reveal dramatic spatial and temporal variations in organic geochemical characteristics among the three sites before 8 ma oc deposited at site u1431 may be predominantly terrigenous whereas oc deposited at sites u1433 and 1148 is mainly of marine origin after 8 ma oc accumulation at the three sites progressively increases mainly due to enhancement of marine primary productivity and input of terrestrial organic matter the three sites receive mainly marine oc whereas sites u1433 and 1148 receive relatively more terrestrial oc compared with site 1431 additionally methane concentrations vary from 20 to 100 000 ppmv at site u1433 and from 10 to 600 ppmv at site 1148 with higher geothermal gradients 78 and 84 c km respectively in contrast methane concentrations are 4000 km are primarily sourced from microbial production our findings suggest that the sources trajectories and fates of oc buried in the deep south china sea since the mid miocene are spatially and temporally variable controlled by sedimentological processes in the sub basins and regional tectonic evolution and long term paleoenvironmental changes

effect of local and regional stress fields on sheet emplacement in west iceland abstract at the tertiary reykjadalur central volcano in west iceland there is a remarkable change in strike dip thickness and percentage of sheets at a distance of about 9 km from the centre of the volcano at distances of less than 9 km the sheets strike in several main directions their average arithmetic mean dip is 45 and the average thickness 1 m locally the sheets make up nearly 90 of the rock but in 1 1 5 km long profiles they are 5 8 7 9 one third of the sheets are porphyritic containing as much as 50 of plagioclase phenocrysts within and in the vicinity of the central volcano there is thus a clear swarm of inclined cone sheets at distances greater than 9 km the sheets suddenly dip much more steeply average 81 become thicker average 3 15 m strike parallel to the nearby volcanic zones and have all the characteristics of regional dyke swarms in 2 5 10 5 km long profiles these dykes are only 0 83 1 84 of the rock one fourth of the dykes are porphyritic but the percentage of plagioclase phenocrysts is normally less than 10 we interpret this abrupt change from a local swarm of inclined sheets to swarms of regional dykes as reflecting changes in the stress field we propose that a local stress field controlled the strike dip and partly thickness of the sheets to a distance of 9 km from the centre of the volcano this local stress field which is also thought to have given rise to the collapse caldera associated with the volcano is attributed to a crustal magma chamber at a shallow depth below the volcano this crustal magma chamber is regarded as the source of most of the inclined sheets the regional stress fields associated with the volcanic zones is thought to have controlled dyke emplacement at greater distances from the volcano we suggest that many of the regional dykes were injected from a deep seated magma reservoir located at boundary between the crust and upper mantle

constraints on dike propagation from continuous gps measurements the january 1997 east rift zone eruption on kilauea volcano hawaii occurred within a network of continuous global positioning system gps receivers the gps measurements reveal the temporal history of deformation during dike intrusion beginning 8 hours prior to the onset of the eruption the dike volume as a function of time estimated from the gps data using elastic green s functions for a homogeneous half space shows that only two thirds of the final dike volume accumulated prior to the eruption and the rate of volume change decreased with time these observations are inconsistent with simple models of dike propagation which predict accelerating dike volume up to the time of the eruption and little or no change thereafter deflationary tilt changes at kilauea summit mirror the inferred dike volume history suggesting that the rate of dike propagation is limited by flow of magma into the dike a simple lumped parameter model of a coupled dike magma chamber system shows that the tendency for a dike to end in an eruption rather than intrusion is favored by high initial dike pressures compressional stress states large compressible magma reservoirs and highly conductive conduits linking the dike and source reservoirs comparison of model predictions to the observed dike volume history the ratio of erupted to intruded magma and the deflationary history of the summit magma chamber suggest that most of the magma supplied to the growing dike came from sources near to the eruption through highly conductive conduits interpretation is complicated by the presence of multiple source reservoirs magma vesiculation and cooling as well as spatial variations in dike normal stress reinflation of the summit magma chamber following the eruption was measured by gps and accompanied a rise in the level of the pu u o o lava lake for a spheroidal chamber these data imply a summit magma chamber volume of 20 km3 consistent with recent estimates from seismic tomography continuous deformation measurements can be used to image the spatiotemporal evolution of propagating dikes and to reveal quantitative information about the volcanic plumbing systems

september 2005 manda hararo dabbahu rifting event afar ethiopia constraints provided by geodetic data faults the volume of the 2005 dike 1 5 2 0 km 3 is not balanced by sufficient volume loss at dabbahu and gabho volcanoes 0 42 and 0 12 km 3 respectively taking into account the deflation of a suspected deep midsegment magma chamber simultaneously to dike intrusion produces a smoother opening distribution along the southern segment above the dike faults slipped by an average 3 m yielding an estimated geodetic moment of 3 5 10 19 nm one order of magnitude larger than the cumulative seismic moment released during the earthquake swarm between dabbahu and ado ale volcanic complexes significant opening occurred on the western side of the dike the anomalous location of the dike at this latitude offset to the east of the axial depression may explain this phenomenon a two stage intrusion scenario is proposed whereby rifting in the northern manda hararo rift was triggered by magma upwelling in the dabbahu area at the northern extremity of the magmatic segment although vigorous dike injection occurred during the september 2005 event the tectonic stress deficit since the previous rifting episode was not fully released leading to further intrusions in 2006 2009

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

slab dynamics in the transition zone abstract seismic images of horizontal slab segments in across or below the transition zone invoke scenarios in which slabs are laid down in the mantle through progressive trench retreat however observations of subduction characteristics do not exhibit a clear correlation between trench retreat and slab dip in the transition zone instead analysis of a range of subduction characteristics demonstrates that while transition zone slabs include slabs of many ages and subduction velocities with both retreating and advancing trench motion they also have several enigmatic characteristics such as faster sinking rates and a larger range in slab dip than slabs that extend to either shallower or deeper depths comparison of subduction characteristics with several analytical and numerical models of subduction dynamics suggests that many of the possible mechanisms for trapping slabs in the transition zone e g positive buoyancy sources viscous resistance slab weakening are only viable if the slab is already shallow dipping two scenarios for the formation of stagnant slabs are proposed 1 trench retreat prior to slabs entering the transition zone or caused by the negative buoyancy forces associated with the wadsleyite and ringwoodite phase transitions and 2 slow lateral migration of slabs in stable subduction zones

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

mechanics of two interacting magma driven fractures a numerical study to understand magma focusing from broad melting zones in the crust propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time dependent plane strain hydraulic fracturing model the source is assumed to generate a constant influx rate to feed the dike growth which is also aided by buoyancy effects in contrast to uncoupled model results the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights which might be produced either by previous magma intrusion or during nucleation the shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation with parameters given in dimensionless forms numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes in that dike interaction can produce a low stress field which is just above the tip of the shorter dike favorable to growth of the shorter dike the energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late time buoyancy viscosity propagation stage where considerable ascent occurs this growth behavior might provide the mechanism for simultaneous instead of sequential growth of various dikes in a single set

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

width change of a planar magma path implication for the evolution and style of volcanic eruptions abstract the width change of a planar path filled with magma is analyzed assuming that the process is controlled by laminar flow of an incompressible viscous magma between movable parallel walls of country rock the analysis shows that the width of a planar path changes at a rate is proportional to the effective opening pressure which is defined as the pressure of the penetrating magma plus the tensile stress component stretching the fluid interface when the opening pressure is a positive constant the fissure widens at an accelerating rate and finally diverges at a critical time constant which depends on the initial size of the fissure and the viscosity of magma as well as on the opening pressure in contrast the fissure gradually narrows under a negative opening pressure this result is applicable to a variety of magmatic processes first the orientation of a volcanic fissure or a dike is such that the tensile stress component is maximized because a fissure with this orientation becomes wider than those at other orientations as it has the minimum value of critical time constant second local irregularities in the geometrical and mechanical conditions of the magma sheet lead to significant variations in fissure width in the widening process this nonuniform increase in width is further exaggerated by mechanical and thermal erosion of the wall rock which makes the irregular surfaces irrecoverable in this manner a planar magma path tends to be split into isolated cylindrical conduits when the magma pressure is reduced and the fissure closes as a whole some actual fissure eruptions such as those at kilauea and izu oshima show evolutionary processes consistent with this prediction another application of the analysis is to explain how the style of a volcanic eruption is determined by the tectonics specifically extensional tectonics which gives a positive opening pressure for any magma pressure allows magma to ascend dispersively along various paths and produces a group of small monogenetic volcanoes in contrast contractional tectonics in which new fissures can be made only for a very high magma pressure concentrates magma into a restricted number of vents and leads to the growth of large polygenetic volcanoes

volcano morphology as an indicator of stress orientation in the java volcanic arc indonesia abstract stress fields in the earth s crust are important indicators leading to better understanding of geologic processes one way to acquire stress data is through morphometric analysis of volcanoes here we evaluate 141 quaternary age monogenetic and polygenetic volcanoes and volcanic fields in java indonesia using a 30 m srtm dem an 8 m demnas aerial photos published geological maps and landsat and google earth satellite imagery we analyze parameters that imply the geometry of the shallow magma plumbing system and ascent pathways crater ellipticity and elongation axis and the orientation of crater breaching bisectors the dominant trend of all of these parameters should indicate the direction of the maximum horizontal compressive stress hmax while the minimum horizontal stress hmin should be perpendicular to it the goal here is to estimate the principal stress axes at the time of dike emplacement to recognize any spatial variations in stress orientations and assess factors controlling the emplacement the resulting orientation of hmax in the western part of java is ne sw and the trend gradually rotates to nw se moving eastward abrupt changes in stress orientations and anomalies are also observed in the vicinity of prominent geologic structures highlighting the influence of preexisting structures on dike emplacement and eruption characteristics results of the morphometric analysis of volcanoes and volcanic fields conducted in this study help to estimate the past and present stress orientations in java and provide valuable understanding regarding the relationship between volcanic emplacement and crustal structures complementing other types of analysis

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

interaction of ascending magma with pre existing crustal fractures in monogenetic basaltic volcanism an experimental approach 1 magma transport through dikes is a major component of the development of monogenetic volcanic fields these volcanic fields are characterized by numerous volcanic centers each typically resulting from a single eruption therefore magma must be transported from source to surface at different places which raises the question of the relative importance of 1 the self propagation of magma through pristine rock and 2 the control exerted by pre existing fractures to address this issue we have carried out a series of analogue experiments to constrain the interaction of a propagating dike through a medium with pre existing fractures the experiments involved the injection of air into an elastic gelatin solid which was previously cut into its upper part to simulate pre existing fractures the volume of the dikes their distance from the fractures and the ambient stress field were systematically varied to assess their influence on potential dike fracture interactions the results show that distance and angle between dikes and fractures influence these interactions and the dike trajectory dike geometry and dynamics are also affected by both the presence of the fractures and the dike volume dikes propagating in between fractures tend to decelerate in nature interactions are expected for dikes and fractures separated by less than about 200m and dikes with a volume less than about 10 2 km 3 would experience a velocity decrease these results highlight the influence of pre existing fractures on the mechanics and dynamics of dikes these heterogeneities must be considered when studying the transport of magmas within the crust

comparison and implication of tex86 and u37k temperature records over the last 356kyr of odp site 1147 from the northern south china sea abstract proxy records from the south china sea scs have played an important role in understanding late quaternary scs environmental changes and the east asian monsoon eam variations but few long sea surface temperature sst records have been generated from the scs the recently established tex86 index provides an opportunity to generate long sst records especially for tropical oceans but the applicability and climatic interpretation of the tex86 index for the scs need further study we report and compare orbital scale resolution ca 5 3 kyr tex86 and u37k temperature records of the past 356 kyr for odp site 1147 from the northern scs both records display clear and similar glacial interglacial patterns the u37k sst fluctuated between 22 3 c and 28 3 c with a glacial interglacial difference of 4 5 c while the tex86 temperature fluctuated between 20 3 c and 25 4 c with a slightly smaller glacial interglacial difference of ca 4 c the tex86 temperature has been consistently lower than the u37k temperature over the past 356 kyr consistent with previous studies suggesting that the u37k index is a proxy for sst but the tex86 index is a proxy for subsurface temperature thus it is proposed that the temperature difference t between the u37k and tex86 records reflects mixed layer depth mld changes in the northern scs which fluctuated between 0 3 and 4 0 c with high values mostly during interglacials and lower values mostly during glacial stages mld changes in the northern scs are interpreted to be driven by eam changes with stronger winter monsoon resulting in a deeper mld and a smaller t thus the combination of u37k and tex86 records and their t can be used to reconstruct east asian winter monsoon variations as well as their influences on the hydrographic structure of the scs

tectonic evolution along the northernmost border of the philippine sea plate since about 1 ma abstract recent structural tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the philippine sea phs plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the phs plate and the northeast japan nej plate or the north american nam plate since about 1 ma the authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage a plate tectonic interpretation is proposed based upon the tectonic evolution with special reference to the mode of convergent motion in brief our interpretations are as follows the relative motion between the phs and the nej plates was not recognized geologically within the area studied from about 1 0 to 0 9 ma stage 1 suggesting either none or small influence from the coupling between the two plates during that period of time convergence between the phs and the nej plates was possibly in n s direction from 0 9 to 0 5 ma stage ii and probably north northwestward since 0 5 ma stages iii to v the mode of the convergent motion was that of buoyant subduction in stages ii and iii the mode changed gradually from buoyant subduction during stage iv to collision in stage v 0 07 ma to the present

rise and emplacement of magma during horizontal shortening of the brittle crust insights from experimental modeling 1 magmatic activity tends to concentrate at plate margins at divergent margins extensional tectonics provide steep conduits for magma to reach the surface at rapidly convergent margins such as the andes one might imagine that horizontal compression prevents the rise of magma nevertheless volcanoes are also common in order to study the mechanisms by which magma rises in a compressional context we resorted to laboratory experiments in which a brittle crust was shortened while magma was intruding our model materials were 1 cohesive fine grained silica powder representing brittle crust and 2 molten low viscosity vegetable oil representing magma in general horizontal shortening and injection were coeval but independent processes thrust faults accommodated the shortening while overpressured oil formed hydraulic fractures in those experiments where there was no shortening injection resulted in a saucer shaped intrusive body in the other experiments where there was shortening oil formed a basal sill before rising along thrust faults once in place the sill lubricated the base of the model so that arcuate thrusts formed at the leading edge of a plateau uplift of the plateau promoted further intrusion of oil at depth in general the pattern of deformation and intrusion depended on the kinematic ratio r between rates of shortening and injection the lengths of the basal sill and plateau increased with decreasing r on the basis of these results we have reexamined two natural examples of magmatic complexes which were emplaced in compressional tectonic settings tromen volcano in argentina and the boulder batholith of montana

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

magma chamber and eruptive processes at izu oshima volcano japan buoyancy control of magma migration underground magmatic processes are modeled for a sequence of eruptions that started on november 15 1986 at izu oshima volcano it is predicted from the seismic gap the seismic velocity structure the deformation center and the gravity minimum that there should be a magma chamber at a depth of about 4 km beneath the northwestern flank of the volcano the effusion of basalt that began at the summit crater established a well connected conduit system between the magma chamber and the summit crater the following eruption from new fissures a few days later produced more felsic and less homogeneous compositions basaltic andesite to andesite because of cooling and fractional crystallization of ascending magma subsequently four small eruptions were caused by gravitational sliding of sluggish semisolid magma into openings in and along the sides of the shallow conduit as magma was returning to the magma chamber systematic tilt changes due to transmission of pressure pulses from the summit crater to the magma chamber were observed during a small explosion on november 18 1987 and for many periods of episodic volcanic tremor the migration of magma is interpreted to have been driven by a buoyancy force associated with bubbles in the magma in this regard dominant ascent of magma beneath the summit crater and new fissures in november 1986 was triggered by vesiculation of volatiles in the magma and the subsequent return flow of magma resulted from the release of bubbles through degassing the observed response of volcanic processes following earthquake swarms northwest of the island is also explained by buoyancy controlled magma migration that could intensify the effect of small fluctuations in the crustal stress

self similar clustering distribution of structural features on ascraeus mons mars implications for magma chamber depth in platz t massironi m byrne p k hiesinger h eds 2015 volcanism and tectonism across the inner solar system geological society london special publications 401 203 218

effects of the crustal stress on the growth of dikes conditions of intrusion and extrusion of magma dike growth is analyzed on the basis of the fluid dynamical behavior of incompressible newtonian magma in a spatially uniform fissure of temporally variable width the length and width of the dike vary with the magma pressure at the dike entrance connected to the magma chamber and with the mean stress working normal to the dike walls the mean stress consists of the regional crustal stress and the mean elastic stress which is approximately evaluated using an analytic solution of the crack with a constant aperture the length and width of the dike are determined as a function of time by simple ordinary differential equations the dike can grow when the initial pressure of the entering magma is above the lithostatic pressure and high enough to suppress compression of the crustal stress the assumed size of the initial crack affects the growth only in the duration needed for an initial adjustment stage after this stage the width and length first grow exponentially and then the growth slows as magma is released from the chamber the growth in the later stage is classified into two types when the initial magma pressure is high enough the dike elongates unlimitedly while the width finally decreases this extrusive growth is likely to lead to eruptions the other intrusive growth in which the dike finally stops its growth with a finite length and width occurs when the crustal stress component normal to the fissure is of sufficiently strong extension buoyancy of magma is not very effective in the earlier growth stage but it shifts the marginal condition separating the extrusive and intrusive growths the extrusive and intrusive events that recently happened in izu oshima volcano and izu tobu volcano group japan are interpreted as the examples of these two growth types

seismicity during lateral dike propagation insights from new data in the recent manda hararo dabbahu rifting episode afar ethiopia seismicity released during lateral dike intrusions in the manda hararo dabbahu rift afar ethiopia provides indirect insight into the distribution and evolution of tensile stress along this magma assisted divergent plate boundary in this paper 5 dike intrusions among the 14 that form the 2005 present rifting episode are analyzed with local and regional seismic data during dike intrusions seismicity migrates over distances of 10 15 km at velocities of 0 5 3 0 km h away from a single reservoir in the center of the rift segment confirming the analogy with a slow spreading mid ocean ridge segment comparison with geodetic data shows that the reservoir is located 7 km down rift from the topographic summit of the axial depression dikes emplaced toward the north are observed to migrate faster and to be more voluminous than those migrating southward suggesting an asymmetry of tension in the brittle elastic lithosphere seismicity during dike injections is concentrated near the propagating crack front in contrast faults and fissures in the subsurface appear to slip or open aseismically coeval with the intrusions the seismic energy released during dike intrusions in the manda hararo rift appears to be primarily modulated by the local magnitude of differential tensile stress and marginally by the rate of stress change induced by the intrusion the low level of seismic energy accompanying dike intrusions despite their significant volumes is likely an indicator of an overall low level of tension in the lithosphere of this nascent plate boundary

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45

stress fields associated with the growth of a large shield volcano la palma canary islands 1 measurements of dyke orientations and fault slip data have been taken in 39 stations located in the northern part of the island of la palma canary archipelago these structures affect the materials belonging to the submarine growth stage and to the lower units of the subaerial shield volcano stage four sets of dykes have been distinguished groups i ii iii 1 and iii 2 the two younger dyke groups iii 1 and iii 2 with highly variable strikes are clearly related to the subaerial growth stage most of the measured faults are normal field relationships and the use of stress inversion methods allowed us to separate three different stress tensors tensor 2 is associated with the dykes of group iii 1 given the spatial distribution of the stations with faults of tensor 2 and dykes of its coeval group iii 1 it has been possible to obtain a map of trajectories of the maximum sh and minimum sh compressive stress axes in the horizontal comparison between this map and the results of theoretical models suggests that the stress field active during at least the early stages of growth of the shield volcano in la palma from near 1 7 myr to at least 1 2 myr ago includes a compressive radial volcanic component plus a regional tensile stress of a tectonic origin this second component might be the imprint in the atlantic oceanic lithosphere of the cenozoic convergence between the african and eurasian plates