deep structures of the palawan and sulu sea and their implications for opening of the south china sea abstract compared to the northern south china sea continental margin the deep structures and tectonic evolution of the palawan and sulu sea and ambient regions are not well understood so far however this part of the southern continental margin and adjacent areas embed critical information on the opening of the south china sea scs in this paper we carry out geophysical investigations using regional magnetic gravity and reflection seismic data analytical signal amplitudes asa of magnetic anomalies are calculated to depict the boundaries of different tectonic units curie point depths are estimated from magnetic anomalies using a windowed wavenumber domain algorithm application of the parker oldenburg algorithm to bouguer gravity anomalies yields a 3d moho topography the palawan continental block pcb is defined by quiet magnetic anomalies low asa moderate depths to the top and bottom of the magnetic layer and its northern boundary is further constrained by reflection seismic data and moho interpretation the pcb is found to be a favorable area for hydrocarbon exploration however the continent ocean transition zone between the pcb and the scs is characterized by hyper extended continental crust intruded with magmatic bodies the nw sulu sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the proto south china sea pscs is further constrained with additional age constraints from inverted moho and curie point depths we confirm that the spreading of the se sulu sea started in the early oligocene late eocene due to the subduction of the pscs and terminated in the middle miocene by the obduction of the nw sulu sea onto the pcb

sediment budgeting a case study in the katiorin drainage basin kenya the primary objective of this study was to compute a detailed budget for a small semiarid tropical drainage basin in kenya results indicated that transfer of sediments inputs from primary source areas was minor in comparison to changes in storage the major sediment source area within the katiorin drainage basin was the colluvial hillslope zone the net change in storage within this zone was approximately 2100 mg yr 1 surface wash and rilling were the dominant transport processes responsible for the remobilization of colluvial sediments sediment storage within the in channel reservoir increased by 60 mg yr 1 which was minor when compared to the total store of sediment in this reservoir during 1986 the channel network stored only a small fraction 3 per cent of the sediment delivered from the hillslope subsystem therefore the in channel reservoir had limited influence on sediment conveyance to the basin outlet these data indicate that a static equilibrium condition cannot be assumed within the katiorin drainage basin such an assumption would result in erosion estimates of approximately 5 5 mm yr 1 for the entire basin based on a sediment output of 7430 mg km 2 yr 1 and a measured bulk density of 1 35 mg m 3 however this masked the actual rates of 1 2 to 7 1 mm yr 1 in subbasin primary source areas and rates of 0 6 to 17 mm yr 1 for colluvial material in the various subbasins the extreme accelerated erosion rates resulted from minimal ground vegetation steep slopes soil crust formation an erodible substrate and a well integrated drainage network for rapid conveyance of sediments from the hillslope subsystem to the basin outlet

3d seismic investigation of the structural and stratigraphic characteristics of the pagasa wedge southwest palawan basin philippines and their tectonic implications abstract the pagasa wedge is a poorly imaged deepwater orogenic wedge that has been variously interpreted as representing an accretionary prism a former accretionary prism modified by thrusting onto a thinned continental margin and a gravity driven fold thrust belt this study using 2d and 3d seismic data together with well information indicates that at least the external part of the wedge is dominantly composed of mass transport complexes capped by syn kinematic sediments that have thrusts and normal faults superimposed upon them drilling shows that despite stratigraphic repetition of eocene middle miocene units there is stratigraphic omission of oligocene and early miocene units this absence suggests that mass transport processes have introduced the eocene section into the wedge rather than tectonic thrusting the accretionary prism stage oligocene of the central palawan ophiolite history appears to be marked by predominantly north vergent deformation the deep regional unconformity 17 ma likely indicates the approximate time when obduction ceased in palawan the pagasa wedge is a late stage product of the convergence history that was active in its final phase sometime above the top of the nido limestone 16 ma and the base of the tabon limestone in the aboabo a1x well 9 ma the top of the wedge is traditionally associated with the middle miocene unconformity mmu however the presence of multiple unconformities diachronous formation tops local tectonic unconformities and regional diachronous events e g migrating forebulges all suggest simply giving a single age or assigning a single unconformity such as the mmu as defining the top of the pagasa wedge is inappropriate the overall ne sw trend of the wedge and the dominant nw transport of structures within the wedge diverge from the more northerly transport direction determined from outcrops in palawan and also from the nido limestone in the sw part of the pagasa wedge possibly this nw transport direction is more related to gravity driven structures responding to uplift of ne sw dangerous grounds margin during the middle miocene related to slab breakoff than it is to thrusting rooted in a plate boundary the final modification of the wedge occurred when the effects of compression deformation on the wedge had largely ended but gravity processes in particular mass transport and normal faulting still operated

lower crustal erosion induced by mantle diapiric upwelling constraints from sedimentary basin formation followed by voluminous basalt volcanism in northwest kyushu japan abstract a sequence of geological events beginning with basement subsidence to form a shallow water sedimentary basin and subsequent voluminous basalt volcanism and uplift of land has been observed in the back arc region of northwestern kyushu japan the basin consists of a succession of marine and non marine sediments with a total thickness of 1000 1500 m which range in age from 43 to 10 ma the basalt volcanism commenced at 10 ma and continued until 1 ma uplift started at around 30 ma and continued after the cessation of the basalt volcanism these geological phenomena may be explained by the convective coupling between the ductile lower crust and upper mantle induced by mantle diapiric upwelling thus surface subsidence leading to sedimentary basin formation is attributed to lower crustal erosion by mantle diapiric upwelling for an earth model with lower crustal and upper mantle viscosities of 10 19 10 20 pa s 5 km of lower crust can be eroded 10 20 myr after the start of convective coupling between the ductile lower crust and upper mantle compatible with the period estimated by observations in this process the melt due to adiabatic mantle diapiric upwelling accumulates beneath the lower crust the accumulation of low density melt in the space originally occupied by mantle material causes crustal uplift when the stress state became extensional as inferred from the extension of okinawa trough during the middle to late miocene 1 the melt filling the eroded lower crustal area may have reached the surface leading to voluminous basalt volcanism

thermal structure beneath tohoku northeast japan combined with geophysical observations and petrological considerations we have studied the thermal models of the tohoku northeast japan subduction zone the temperature of the deeper part of the mantle wedge is constrained by the petrological requirements that demand a high temperature region 1400 c beneath the volcanic zone to satisfy this condition namely to explain the arc volcanism in the tohoku subduction zone a high temperature upper mantle beneath the japan sea possibly 1400 c at the depth shallower than 100 km is required heat flow distribution which constrains the temperature structure at shallower depth shows that low heat flow values ranging from 20 to 50 mw m2 are distributed between the trench and aseismic front and consistently high heat flow values 80 120 mw m2 prevail in the area landward of the volcanic front including the japan sea recent heat flow measurements indicate that the transition from low to high heat flow occurs between the aseismic front and volcanic front this heat flow distribution restricts the form of the flow in the mantle wedge and shear stress acting at the plate boundary a rigid non moving triangular region bounded by the subducting slab and the vertical plane beneath the aseismic front is necessary to explain the low heat flow zone between the trench and aseismic front shear stress of about 500 to 1000 bar is supposed to act at the interface between the subducting slab and rigid triangular mantle we also suggest that to explain the peak of heat flow near the volcanic front 120 mw m2 magma migration rate of about 0 05 cm3 cm 2 year 1 is necessary a comparison of the thermal structure of the tohoku subduction zone with that of the central south america which was preliminary calculated by the similar scheme shows that the temperature in the mantle wedge of the central south america is probably lower than that of the tohoku subduction zone this difference may result in that of the nature of volcanic rocks

finite element modeling of lower crustal flow a model for crustal thickness variations small scale convection beneath continental lithosphere is likely to initiate viscous flow in the ductile lower crust positive lithospheric bending will develop above upwelling mantle flow leading to a lateral squeezing out of crustal material from elevated areas which results in significant crustal thickness variations in its final stage this process was studied with a finite element approach for viscous material for a number of different viscosity contrasts between lower crust and lithospheric mantle significant moho undulations of the order of at least 5 km within a time period of about 50 m y can only be reached if the lower crustal viscosity is less than 1021 pa s or if the lithospheric mantle viscosity is less than 1024 pa s the maximum topography is a function of the viscosity contrast and is generally of the order of a few hundreds of meters with a relaxation time between 5 and 103 m y strongly dependent on the crustal viscosity in conclusion this process might be important to explain crustal thinning and thickening of the order of about 10 km in areas of enhanced thermal gradient

lithospheric extension near lake mead nevada a model for ductile flow in the lower crust small variations in gravity anomalies and topographic elevation observed in areas that have undergone highly variable amounts of upper crustal thinning can be satisfactorily explained by ductile flow of lower crustal material under the proper conditions in this study we examine the boundary between the unextended colorado plateau and a strongly extended domain in the basin and range province in the lake mead nevada region bouguer gravity and topography data suggest that both present and preextensional variations in crustal thickness between the unextended and extended regions are small analytic channel flow models show that viscosities required for ductile flow in a lower crustal channel to reduce discontinuities in crustal thickness associated with variable amounts of extension are highly dependent on the channel thickness and on the length scale of flow required finite element modeling of newtonian flow and power law creep shows that flow over the length scale of the eastern basin and range 500 km or more corresponding to upper crustal extension by a factor of 1 4 3 over 10 m y requires effective viscosities less than 10 18 10 20 pa s for ductile channels 10 25 km thick flow over shorter length scales 150 km may be accommodated with effective viscosities as high as 10 21 pa s modeling suggests that these effective viscosities may be sustained by lower crustal material deforming at laboratory derived power law creep rates the longer scale flow may require elevated crustal temperatures more than 700 c depending on the composition and material properties assumed under the boundary conditions assumed in this study the linear viscous flow models yield a satisfactory approximation to deformation by power law creep this work suggests that flow in the lower crust may be a viable mechanism for producing small variations in total crustal thickness between strongly extended and less extended regions and thereby explaining the relative uniformity in gravity and topography between such regions

factors affecting natural rates of slope development summary two locations in southwestern australia 120 km apart are comparable in terms of soils natural vegetation lithology and to a lesser extent topography but not in terms of climate the low rainfall area 400 mm has erosion rates an order of magnitude greater than the higher rainfall location 1400 mm however data from unbounded hillslope erosion plots in other parts of australia do not yield such a clear relationship neither are slope erosion rates related to differences in vegetation lithology or slope angle differences in denudation rates obtained from stream sediment data in australia and worldwide support a climatic interpretation but the comparability between these data and those obtained from hillslope plots is unclear it is suggested that this comparison may provide a fruitful area for further research

viscoelastic versus viscous deformation and the advection of pre stress summary the heaviside response of an incompressible viscous half space is compared to that of a viscoelastic half space that may or may not be compressible elastically it will be shown that the difference between viscous and viscoelastic response is detectable from uplift data provided that the age of the data goes back far enough it is also possible to resolve using the post glacial rebound data whether the viscous model or the viscoelastic model is preferred provided that the ice model is better constrained moreover the rate of solid fluid transition is wavenumber k dependent and the transition is not as rapid nor as small as was previously predicted finally the advection of pre stress is shown to be required in viscoelastic deformation problems of the earth and that it is responsible for viscoelastic gravitational relaxation

shear wave velocity structure of reed bank southern continental margin of the south china sea abstract the shear wave velocity structure of a wide angle seismic profile obs973 2 across reed bank in the southern continental margin of the south china sea scs is simulated by 2 d ray tracing method based on its previous p wave model this profile is 369 km long and consists of fifteen three component ocean bottom seismometers obs the main results are as follows 1 the model consists of seven layers and the shear wave velocity increases from 0 7 km s at the top of sediment layer to 4 0 km s in the lower crust 2 the moho depth decreases from 20 22 km at the reed bank to 9 11 km at the deep oceanic basin with the shear wave velocity of 4 2 km s below the moho 3 the v p v s ratio decreases with depth through the sedimentary layers attributed to increased compaction and consolidation of the rocks 4 in the continental upper crust at model distance 90 170 km s wave velocity 2 5 3 2 km s is relatively low and v p v s ratio 1 75 1 82 is relatively high compared with the other parts of the crust corresponding to the lower p wave velocity in the previous p wave model and normal faults revealed by mcs data indicating that a strong regional extensional movement had occurred during the formation process of the scs at the reed bank area 5 the s wave structures indicate that reed bank crust has different rock compositions from that in the east section of the northern margin denying the presence of conjugate relationship of reed bank with dongsha islands according to p wave models and other data we inferred that reed bank and macclesfield were separated from the same continental crust during the rifting and break up process

intraplate stresses and dynamical aspects of rifted basins abstract intraplate stresses play a important role during the syn and post rift evolution of sedimentary basins deviations from long term thermal patterns of post rift subsidence as well as the development of unconformities within rifted basins reflect to a large extent the temporal fluctuations of the regional stress fields in the lithosphere it appears that incorporation of intraplate stresses in dynamical models for basin development together with a quantification of the role of petrological changes in the crust lithosphere system can explain some of the observed shortcomings of thermal models of post rift basin subsidence late neogene accelerations in tectonic subsidence in the deeper parts of rifted basins in the northern atlantic and mediterranean regions could reflect a change in the level of intraplate stress over large areas of the globe non thermal contributions to the subsidence record affect estimates of crustal extension and consequently influence the depth at which hydrocarbon source rocks enter the maturity window stress induced changes in basement topography have also important consequences for the budget of fluid flow in the deeper parts of the sediment fill of the rifted basins as well as on the dynamics of diapirism

development patterns and controlling factors of tertiary carbonate buildups insights from high resolution 3d seismic and well data in the malampaya gas field offshore palawan philippines abstract the comprehensive subsurface database of the malampaya buildup late eocene to early miocene offshore nw palawan provides a rare insight into the development of south east asian cenozoic carbonate systems and their controlling factors the newly acquired high resolution three dimensional seismic survey combined with facies and well log analysis allowed a better understanding of the internal architecture of a carbonate platform whose development was largely controlled by tectonic deformation the malampaya carbonate system was initiated in the late eocene as an attached shelf influenced by significant clastic input the late eocene early oligocene shelf was subject to syn depositional extensional tectonics eastward tilting and block faulting that favoured the development of small size buildups on structural highs after a stage of eastward reef progradation an aggrading carbonate shelf frequently affected by subaerial exposure developed from the earliest late oligocene to the early miocene during this period recurrent reactivation of highs along the western and northeastern buildup margins determined the asymmetric morphology and internal architecture of the carbonate system the final demise of the carbonate buildup occurred in the late early miocene it resulted from an increase in subsidence rate and or a sharp increase in nutrient input additional parameters like eustacy oceanographic conditions and the type of carbonate producers played a subordinate role in the buildup development and ultimate demise

seismic evidence for the influence of fluids on the 2005 west off fukuoka prefecture earthquake in southwest japan abstract high resolution 3 d seismic velocity vp and vs and poisson s ratio structures in the epicentral area of the 2005 west off fukuoka prefecture earthquake were determined by inverting a large number of high quality p and s wave arrival times and sp depth phase data to better understand the genesis of the main shock and its aftershock sequence the hypocenters of the earthquakes used in this study were relocated with a combined method which enables to accurately relocate the earthquakes occurred outside the seismic network by using sp depth phase data together with double difference travel time data this new approach of earthquake location can be applied to other offshore regions of subduction zones where few seismic stations exist while numerous suboceanic earthquakes occur strong crustal velocity heterogeneities were revealed in the hypocentral area which might reflect the existence of fluids geometrical irregularities of the fault zone and geothermal anomalies in the region the main shock hypocenter was located near a distinct zone characterized by low velocity high poisson s ratio and high conductivity anomalies being considered to be associated with the existence of fluids in and around the source area such fluids might have reduced the seismic velocity of the crustal materials around the main shock hypocenter and weakened the mechanic strength of the fractured rock matrix in the source area and thus triggered the 2005 west off fukuoka prefecture earthquake

back arc extension in the okinawa trough the okinawa trough lying to the east of china is a back arc basin formed by extension within continental lithosphere behind the ryukyu trench arc system middle to late miocene uplift associated with normal faulting of the initially adjacent ryukyu nonvolcanic arc and the taiwan sinzi folded belt corresponds to the first rifting phase the timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern okinawa trough the rifting occurred after a major early miocene change in the motion of the philippine plate with respect to eurasia and ceased during the pliocene a second rifting phase started about 2 m y ago at the plio pleistocene boundary and has continued until the present time it has proceeded to a more advanced stage in the middle and southern okinawa trough than it has farther north detailed bathymetric sea beam seismic reflection and magnetics data collected during the pop 1 cruise of the r v jean charcot reveal the principal features of the extensional processes the back arc spreading phase started very recently in the southern and middle okinawa trough as exemplified by several en echelon and in some cases overlapping active central graben oriented n70 e n80 e some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies transform faults between these en echelon active rifts are not obvious we suggest that the major part of the southern okinawa trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern okinawa trough the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough the system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of okinawa island whereas active volcanoes in the ryukyu arc occur only north of okinawa island we refer to this transition between active arc and back arc volcanism as the volcanic arc rift migration phenomenon vamp globally back arc volcanism propagated from the southern okinawa trough to the okinawa vamp area rifting continues to occur in the northern okinawa trough but is not yet accompanied by associated volcanism the okinawa vamp area is characterized by a series of parallel basaltic ridges oriented n75 e with associated linear magnetic anomalies characteristic of dyke intrusions we suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending n75 e and that this zone presently ends at the southern extremity of the active volcanic chain the initial phase of formation of back arc basin oceanic crust is non steady state and is characterized by the lack of a developed fracture zone pattern the termination of the vamp area in the direction of the volcanic zone of the arc is consistent with the suggestion of molnar and atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs apparently back arc extension initially occurred within the continental lithosphere located westward of the ryukyu arc along its whole length but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward this migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc it is this transfer of volcanism that we call the vamp process thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc this interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence since the plate motion in the phillippine sea is oblique to the trench at least in the southern part of the okinawa trough we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc the motion of the ryukyu platelet with respect to eurasia is consequently an extensional strike slip motion trending roughly parallel to the okinawa trough

geoid and topography associated with sublithospheric convection negligible contribution from deep currents abstract the sources of geoid and topography anomalies in a convecting upper mantle with realistic temperature and pressure dependent viscosity are studied the results differ from those obtained in previous studies with layered depth dependent viscosity for a newtonian viscosity the topography and the geoid anomalies coming from below the low viscosity zone i e deeper than 250 km amount to 30 m and 10 cm respectively while they are reduced to 10 m and 10 cm for a non newtonian viscosity it represents at most 6 of the complete signal and affects very little the geoid over topography ratio the weakness of the contribution from the lower part of the cell is due to both small kernels and small lateral temperature variations at depth yet a linear regression of the complete geoid signal versus topography yields an apparent compensation depth shallower than the base of the lithosphere the damping of the vertical stress through a lithosphere with a depth dependent viscosity implies a departure from isostasy and is the cause of the shallow apparent compensation depths found in our model

geomorphic considerations for erosion prediction current soil erosion prediction technology addresses processes of rainsplash overland flow sediment transport and rill erosion in small watersheds the effects of factors determining sediment yield from larger scale drainage basins in which sediment movement is controlled by the combined small scale processes and a complex set of channel and other basin scale sediment delivery processes such as soil creep bioturbation and accelerated erosion due to denudation of vegetation have been poorly evaluated general suggestions are provided for the development of erosion prediction technology at the geomorphic or drainage basin scale based on the separation of sediment yield data for channel and geomorphic processes from those of field scale soil loss an emerging technology must consider 1 the effects on sediment yield of climate geology and soils topography biotic interactions with other soil processes and land use practices 2 all processes of sediment delivery to a channel system and 3 the general tendency in most drainage basins for progressively greater sediment storage in the downstream direction

a sediment budget for a small semiarid watershed in southeastern arizona usa article i nfo article history a sediment budget was developed for a 43 7 ha and a nested 3 7 ha semiarid shrub dominated watershed based on hydrologic geomorphic erosion and sediment data collected from 1963 through 2006 on the usda ars walnut gulch experimental watershed in the southwestern us sediment budgets based on such extensive and intensive field campaigns over several decades are rare the sediment budget was bal anced with a high degree of confidence because the study watershed is controlled by an earth dam at the out let although the channel network is well developed and incising in the steeper reaches of the watershed hillslopes are the dominant source of sediment contributing 85 of the overall total sediment yield erosion and sediment redistribution were driven by highly variable rainfall and runoff during july august and september sediment transfers are influenced by channel abstractions and the presence of the outlet dam which created conditions for deposition in the pond approach reach although earth dams are ubiquitous throughout the southwestern us and they can provide a measure of outlet sediment yield these outlet mea surements may be insufficient to interpret temporal and spatial variability in watershed sediment dynamics identification of dominant processes and sediment sources is critical for determining management actions that will improve rangeland conditions published by elsevier b v

floodplain evolution in a small tectonically active basin of northern california sediment cores were collected along oodplains in the navarro river basin of coastal northern california to examine the controls on oodplain evolution in a tectonically active setting sedimentary strata were subsampled for organic content bulk density and grain size measurements organic samples were analysed for 14c age which yielded net averaged sedimentation rates for all cores overbank deposition rates decreased at all study sites through time and declined in the downstream direction the ability of intermediary order streams to store sediment in oodplains decreased the ability of highest order streams to record sediment pulse events the effects of anthropogenic disturbance primarily logging on long term overbank deposition rates were minimal climatic variability by affecting sediment loading in the channel network is the principal control on oodplain evolution through the holocene a hypothetical model is proposed to explain overbank deposition rates in the navarro basin which may be extrapolated to the northern coastal california region during the late pleistocene and holocene the complexities observed in sediment storage and routing in this study imply that caution should be made when extrapolating sediment yield measurements obtained at river mouths or coastal shelves to geomorphic events within small tectonically active basins

mantle upwelling revealed by genetic algorithm inversion of the magnetovariational anomaly around kyushu island japan 1 the spatial extent of an outstanding mantle upwelling in the west of kyushu island japan has been estimated by a genetic algorithm inversion here we show how the mantle upwelling manifests in modeling of observed anomalies of temporal geomagnetic variations i e magnetovariational anomalies around southwest japan observed ratios of the vertical to horizontal geomagnetic components at short periods are known as indicators of subsurface electrical contrasts however they are also sensitive to the presence of oceans and continents because of much more conductive seawater than land rocks to circumvent the difficulty we used three dimensional nonuniform thin sheet approximation to subtract out the conductive as well as inductive effects of the ocean on the magnetovariational anomalies the observed anomalies were then inverted by a genetic algorithm inversion for conductance the product of electrical conductivity and thickness with the known bathymetry as a priori information the derived conductance model has particular sensitivity to the northeastern portion of spatial extent of the mantle upwelling probably centered at the east china sea the upwelling may result in horizontal flows of the uppermost mantle which induce the horizontal stress field that can trigger hazardous shallow intraplate earthquakes of large magnitude such as the earthquake off the west coast of fukuoka prefecture that occurred on 20 march 2005 the northeastern rim of the mantle upwelling thus revealed can also be related to an unidentified boundary between the amurian plate and the eurasia plate

characteristics and evolution of cenozoic sediments in the liyue basin se south china sea the liyue basin in southeastern south china sea is considered to be a cenozoic basin superimposed on the mesozoic erathem the present account is based on comprehensive analysis of seismic profiles dragnet and core samples cenozoic deposits in the basin are characterized by a sequence of marine detrital and carbonate rocks there are two regional unconformities t 70 and t 40 corresponding to the commencement and termination of sea floor spreading in the south china sea in the late oligocene and late early miocene respectively the cenozoic sedimentary evolution of the basin recorded different sedimentary responses to sea floor spreading in the south china sea and reflected differences in the basin structure paleogeographic pattern and sedimentary characteristics before 30 ma late oligocene and after 30 ma the evolution of sea floor spreading changes in sea level and sediment sources controlled the cenozoic sedimentary infill c 2012 elsevier ltd all rights reserved

morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region abstract flows in ephemeral channels in semiarid areas are only occasional and channel changes are episodic but the flash floods can be devastating and have major geomorphological impacts data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels for this purpose nine reaches of river channel in three catchments in se spain the nogalte torrealvilla and salada have been sites for measurement of flows and their effects over the period 1997 2012 the sites encompass a range of channel size channel morphology substrate vegetation and position within the catchments a major difference is between schist and marl bedrock areas peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events over the 16 year period an average of 0 5 flow events per year has been recorded at the schist sites and an average of one per year at the marl sites but occurrence has been highly variable from year to year threshold daily rainfall for channel flow is mostly 15 20 mm but higher rainfalls do not always produce flow one to two major floods have occurred in each of the catchments in the period including the extreme flood event of september 2012 in the nogalte catchment measured morphological changes have occurred between 2 and 10 times at the monitored sites the same size flow can have differing effects depending on the state of the system low flow can mobilise sediment without producing much morphological change the long term trajectory of the reaches and the sediment substrate has a major influence on response to events channel change is governed by threshold values of hydraulic conditions the measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in management

lower crustal flow in an extensional setting constraints from the halloran hills region eastern mojave desert california postextensional uplift and tilting of quaternary lake sediments in the halloran hills eastern mojave desert california suggest that regional scale flow within the lower crust is occurring in response to tectonic loads created during upper crustal extension in late miocene time the concept that significant flow within the lower crust may occur for millions of years after the cessation of extension indicates that topographic gradients can be modified by regional scale flow within the lower crust and that direct constraints on lower crustal flow can be obtained by quantitative analysis of rates of postextensional surface tilting an analytic solution developed in this paper combines viscous flow in the lower crust flexural bending within the midcrust and isostasy into an invertible linear differential equation that describes the topographic response to upper crustal extension assuming that there was no topographic relief across the halloran hills region prior to extension inversion of modern topographic data indicates that crustal thinning above the halloran hills detachment increases westward with a listric geometry and that little crustal thinning has occurred east of the western flank of clark mountain in good agreement with the known geometry of the fault and the location of its breakaway zone incorporation of quaternary tilting data indicates that the modern viscosity beneath the halloran hills assuming a 10 km lower crustal channel is a maximum of 1019 pa s and that the viscosity of the lower crust has decreased by at least 1 to 2 orders of magnitude since 8 ma this corresponds to a temperature increase of at least 75 to 100 c at the moho in our opinion the most likely source of this temperature increase is a regional scale thermal event within the underlying mantle and diffusion of heat upward into the lower crust if correct these results have important implications for the way in which crustal extension is linked to mantle heating within the basin and range province

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

mechanical erosion and reheating of the lithosphere a numerical model for hotspot swells it is currently debated if either thermal erosion of the lithosphere or dynamical support is the source of topography and geoid anomalies the origin of tins controversy lies probably in the difficulty to model simultaneously these two effects for this purpose we have studied the time dependent behavior of two dimensional convection with a temperature and pressure dependent viscosity the use of a control volume method allows us to define a rigid zone simulating the mechanical lithosphere the interface between the lithosphere and the convective mantle is determined by a viscosity cutoff first some experiments model the rise of a plume below the lithosphere in order to observe the evolution of the uplift and thus to appreciate the various processes involved in the swell formation before the plume reaches the base of the thermal lithosphere an uplift a few hundred meters in amplitude develops which can only be ascribed to a pure dynamical support the major uplift occurs when the ductile part of the lithosphere the convective boundary layer is squeezed by the plume the reheating of the mechanical lithosphere takes place after this transient stage of dynamical erosion however this late process is very slow but can magnify the amplitude of the swell if the lithosphere stays long enough above the plume these results shed some light on the different mechanisms occurring during the swell formation but the configuration modeled does not correspond to the one expected for actual hotspot swells they feature plume rising up to the lithosphere while natural situations correspond to lithosphere drifting above preexisting plumes an experiment with a moving lithosphere was run and shows that thermal erosion does not affect significantly a moving lithosphere even for relatively slow drifting velocities few centimeters year indeed the thermal structure of the lithosphere is not modified above the 800 c isotherm except for a motionless plate in this case the resulting swell should be greater this could explain why azores crozet or cap verde swells are so high on the other hand the shape of a swell over a moving lithosphere is strikingly reminiscent of the hawaiian swell

tectonic stratigraphic division and blind fold structures in nansha waters south china sea extensive multiple channel reflection seismic data have been collected in the nansha spratley islands waters the southern margin of the south china sea stratigraphic correlation is shown with focus on a comprehensive geophysixcal survey line run front offshore nw sabah to offshore se vietnam according to the varying tectono stratigraphy from southeast to northwest five tectonic belts can be determined i e the palawan borneo nappe nansha trough nanwei liyue compressive belt zheng he extensional belt and the circum southwest subbasin belt in the palawan borneo nappe neogene quaternary deposits were highly upthrust northwestwards resulting in a series of moderately to tightly folded anticlines separated by open synclines the nansha trough was a narrow deep water belt filled with thick undisturbed neogene quaternary deposits the nanwei liyue compressive bell was dominated by strongly folded paleo anticlines overlain by an undeformed sedimentary cap with a pronounced hiatus of paleogene sediments the zheng he extensional belt consisted of a rugged topography and paleogene half grabens bounded by listic faults the major extensional faults were reactivated to cut through the overlying neogene quaternary deposits over the circum southwest subbasin belt neogene quaternary deposits draped on the largely subsided fault blocks related to the late oligocene mid miocene seafloor spreading based on the regional stratigraphic correlation the prominent paleo anticlines found within the nanwei liyue compressive belt are deduced to consist of mainly mesozoic marine sediments that were compressed in the late mesozoic era therefore the nansha microcontinent block is shown to be a collision complex assembled during late mesozoic era c 2004 elsevier ltd all rights reserved

response of the ha ha river to the flood of july 1996 in the saguenay region of quebec large scale avulsion in a glaciated valley modifications to valley form due to extreme flooding in the lower 34 km of the ha ha river were analyzed heavy regional precipitation in july 1996 triggered extreme runoff and the catastrophic drainage of ha ha lake producing discharges of 1100 m3 s 8 times the 100 year flood dominant valley modifications revealed by comparing preflood and postflood topographies derived photogrammetrically were related to two large scale avulsions in particular a deep retrogressive incision which bypassed the 30 m high perron falls exporting 6 106 m3 of glacial stratified drift from a 2 km section of valley and producing massive sedimentation in the reach downstream reconstructed maximum flow power values support the existence of a 300 w m2 threshold for major scouring of the alluvial valley bottom the evidence highlights the potential for massive scour and fill and reorganization of the long profile with potentially catastrophic effects on infrastructure during extreme floods in glaciated valley settings

lateritic duricrust and relief inversion in australia abstract ollier and galloway have suggested that australian ferricretes were formed in low lying positions in the landscape and are now exposed in high situations as a result of relief inversion however denudation rates reported here from a number of locations across australia are far too slow to permit this interpretation on the other hand evidence from two sites is presented in support of their suggestion that the formation of lateritic duricrusts is not necessarily genetically linked with deep weathering

thermal state of northwest kyushu mantle suggested by the petrochemistry of the tara dake basalts 1 temperatures of northwest kyushu mantle are estimated using petrochemical data of the relatively primitive tara dake basalts erupted at around 1 ma model primitive melt compositions estimated by the addition of equilibrated olivines to bulk compositions indicate that melting temperatures range from 1230 to 1300 c at around 1 gpa moderately high melting temperatures of the tara dake basalts indicate that mantle upwelling in nw kyushu is caused not by thermal plumes but by the convection at the boundary between the continent and the ocean

variability of sediment removal in a semiarid watershed field and documentary data from walnut gulch watershed an instrumented semiarid drainage basin of approximately 150 km 2 57 mi 2 in southeastern arizona show that 83 of the alluvium removed from the basin during a 15 year erosion episode beginning about 1930 was excavated from the highest order stream the amount of alluvium removed in the erosion episode would have been equal to a covering of about 4 cm 1 6 in over the entire basin the rate of sediment removal during the erosion episode was 18 times greater than the rate of present channel sediment transport production of sediment from slopes and channel throughput at present rates are approximately equal and refilling will not occur under present conditions the channel forms left by the massive evacuation of sediment impose controls on the spatial distribution of tractive force and total stream power that make renewed storage of sediment likely in only a few restricted locations modern instrumented records of a decade or more provide an inadequate perspective on long term sediment movement

tectonics and global change inferences from the late cenozoic subsidence and uplift patterns in the atlantic mediterranean region summary quantitative subsidence analysis for a number of rifted basins in the northern atlantic mediterranean region provides evidence for rapid phases of plioquaternary subsidence the observed acceleration in tectonic subsidence occurs after a phase of general quiescence in subsidence in these basins and deviates from predictions of stretching models the latter indicate a decay of subsidence with time after mesozoic tertiary basin formatioh and a slow tectonic subsidence in plio quaternary times a possible explanation for the observed patterns of anomalous subsidence could be an increase in the level of intraplate compression in the northern atlantic region intraplate stress changes in the plio quaternary are related to the dynamics of african eurasian collision processes and a reorganization of spreading directions in the atlantic possibly reflecting a plate reorganization of global nature it seems that the plio quaternary record reflects a period of increased levels of neotectonic activity interplaying with periods of de glaciation stress induced topography in the onshore parts of continental margins coupled with the stress induced subsidence in the offshore deeper parts of the basins could have contributed to recent phases of uplift in fennoscandia augmenting the uplift induced by glacial unloading estimates of ice thicknesses are directly inferred from the observed uplift ignoring other driving mechanisms whereas topography plays a crucial role in the dynamics of glaciation it is therefore important to quantdy the interplay of rapid tectonic uplift and subsidence phases with climatic effects during the plio quaternary

anomalous lower crustal structure and origin of magmatism in the southeastern margin of the south china sea abstract late cenozoic continental rifting and breakup separated the southern margin of the south china sea scs from the northern margin it remains unknown whether the high density velocity zones hvzs in the lower crust extend southwards from the northeastern margin of the scs to the conjugate southern margin we integrated two newly acquired and processed multichannel seismic reflection profiles with gravity and magnetic data across the liyue reed bank and north palawan basin to clarify the characteristics of crustal structure and their relationship to post rift magmatism our results show an asymmetric distribution of the hvzs in the conjugate margins the lower crust anomalous reflections are isolated and mostly restricted in the areas of the ocean continent transition oct and the distal sag in gravity modeling the crustal thickness decreases from 20 km in the proximal sag to a minimum of 6 km in the distal sag and these anomalous reflections spatially correspond to high density zones no more than 4 km in thickness the magmatic features are presented by igneous intrusions at the top of the basement that deform post rift strata in the early miocene these hvzs above which the crustal stretching factor is 3 3 5 8 support that an anomalously hot asthenospheric mantle persisted during lithospheric thinning resulting in magmatic underplating and density drop in the uppermost mantle during early breakup

the origin of sedimentary basins a status report from the task force of the international lithosphere program abstract better insights into the mechanisms of basin formation have a direct bearing on the predictive power of forward models for basin fill models that link flexure normal faulting and thrusting on a subbasin scale provide important constraints on the tectonic control of the sedimentary record enabling a quantitative comparsion with eustatic contributions to the basin architecture thus of special importance is the need to link processes with different spatial and temporal scales involved in the evolution of extensional and compressional basins by numerical modelling a new generation of basin modelling concepts and techniques is one of the main objectives of the task force origin of sedimentary basins of the international lithosphere program the focus of this work is on the quantification of the effects of the thermomechanical structure of the lithosphere and its interplay with regional and local stress changes other important developments include the step towards three dimensional modelling and the full integration of rapidly expanding fission track and other data sets to constrain vertical motions in basins as natural laboratories for the interactive testing and development of new basin modelling techniques a number of basins with high quality data from industry government and academia have been selected on the basis of specific testable problems

a mechanism for crustal thinning without lateral extension in some continental regions thin crust is found without observing significant indications of extensional tectonics we argue that in such regions upwelling mantle flows may give rise to sublithospheric loading stresses which may be able to squeeze out the ductile lower crust but leave the upper crust and sub crustal lithosphere essentially unstretched this model allows us to constrain the viscosity of the lower crust if the amount and time scale of crustal thinning is observed in any subsidence basin we applied our model to the pannonian basin hungary and found lower crustal viscosities between 1020 and 1021 pa s comparing this viscosity with laboratory data of crustal rocks results in lower crustal temperatures of about 600 to 800 c which are in good agreement with geothermal models our model might also help to understand the appearance of a very thick crust and lithosphere without any pronounced topography as it is found in fennoscandia

an integrated geophysical study on the mesozoic strata distribution and hydrocarbon potential in the south china sea abstract a series of drilling dredge and seismic investigations indicate that mesozoic sediments exist in the south china sea scs which shows a bright prospect for oil and gas exploration in order to study the distribution of mesozoic strata and their residual thicknesses in the scs we carried out an integrated geophysical study based mainly on gravity data gravity basement depth and distribution of residual mesozoic thickness in the scs were obtained using gravity inversion constrained with high precision drilling and seismic data in addition the fine deep crustal structures and distribution characteristics of mesozoic thicknesses of three typical profiles were obtained by gravity fitting inversion mesozoic strata in the scs are mainly distributed in the south and north continental margins and have been reformed by the later tectonic activities they extend in ne trending stripes are macro controlled by the deep and large ne trending faults and cut by the nw trending faults which were active in later times the offset in nw direction of mesozoic strata in nansha area of the southern margin are more obvious as compared to the north margin in the pearl river mouth basin and southwest taiwan basin of the north continental margin the mesozoic sediments are continuously distributed with a relatively large thickness in the nansha area of the south margin the mesozoic strata are discontinuous and their thicknesses vary considerably according to the characteristics of mesozoic thickness distribution and hydrocarbon potential analyses from drilling and other data dongsha uplift chaoshan depression southwest taiwan basin peikang uplift and liyue bank have large thickness of the mesozoic residual strata have good hydrocarbon genesis capability and complete source reservoir cap combinations show a bright prospect of mesozoic oil gas resources

reply to the comment on stratigraphic architecture of sedimentary basin induced by mantle diapiric upwelling and eustatic event by h mashima

the impact of eustatic sea level fluctuations temperature variations and nutrient level changes since the pliocene on tropical carbonate platform xisha islands south china sea abstract sedimentological paleontological and geochemical data from core xk 1 in the xisha islands south china sea allow a detailed documentation of the evolution of the reef bank system from the early pliocene to the late pleistocene and of the aeolianite deposits from the late pleistocene to the holocene a bank characterized by heterozoan carbonates occurred until 1 7 ma between 1 7 and 0 2 ma the system turned into a reef dominated by photozoan carbonates after 0 2 ma the aeolianite deposits composed of heterozoan skeletal grains occupied this area a pliocene to pleistocene decrease in the abundance of planktonic foraminifera and some benthic foraminifer species generally associated with deep water settings indicates a long term shallowing upwards trend resulting from the large scale eustatic sea level falls seven exposure horizons are recorded in core xk 1 due to high frequency sea level changes the thickness of the reef body in the individual cycles increased after the middle pleistocene transition this is interpreted as a consequence of the increase in duration of the short term sea level highstands the formation of heterozoan aeolianite deposits after 0 2 ma is probably caused by climate cooling related with the intensification of east asian winter monsoon the rapid increase in coral abundance at 1 7 ma correlates well with a sharp decline in nutrient level recorded by decreases in geochemical nutrient indexes values declines in bryozoan and red algae rhodolith abundance and decreases in the abundance of foraminifer species indicative of elevated nutrient level this correlation indicates that the carbonate factory turnovers were also affected by nutrient level fluctuations which could be linked to a paleoceanographic reorganization these results demonstrate that together with sea level fluctuations also paleoceanographic changes had a significant effect on the pliocene holocene tropical carbonate system

the petroleum potential of deep water northwestpalawan block gsec 66 abstract this paper presents the results of the evaluation of the petroleum potential of thedeep water acreage of philodrill gsec 66 or what the authors call the northwest malampaya block all the elements necessary for a major hydrocarbon accumulation are believed to be present in the block probable source rocks are the deep water nido limestone the pre nido early tertiary syn rift section and pre tertiary sediments potential reservoirs include the nido reefal buildups nido and pre nido detrital and or fractured carbonates early miocene galoc elastic equivalent turbidites and pre nido sediments the principal play types recognized in the area are the late oligocene to early miocene reefs and the erosional karsted carbonate highs after evaluation of available pre 1982 seismic data an acquisition program of 1625 km was undertaken eleven leads prospects were delineated in the area after the interpretation of this new seismic data two prospects were upgraded to drillable status the santa monica prospect and the ipil prospect the santa monica prospect is a well defined four way dip closure on the nido limestone with a vertical closure of over 1500 feet and an areal closure of over 20 500 acres the ipil prospect is a gently closed feature developed at the nido limestone platform level with an areal closure of over 11 600 acres and a vertical relief of 400 feet the technical merits of the delineated huge prospects combined with the very favorable deep water exploration terms of the philippines and their proximity to the soon to be developed malampaya camago field make this block a very promising area for further exploration work

north palawan block philippines its relation to asian mainland and role in evolution of south china sea the island of mindoro the northern part of palawan island and the reed bank area southwestern philippines together constitute a continental fragment the north palawan block lying within an island arc oceanic setting the permian to paleogene rocks of these areas indicate a geologic origin and history for the block contrasting with that of the rest of the philippine archipelago these rocks also suggest that the north palawan block once occupied a pre drift position contiguous with the south china mainland four prominent pre neogene regional unconformities are recognized both onshore and offshore the china mainland in taiwan and in the north palawan block the synchrony of these unconformities and the facies relation of the unconformity bounded sedimentary units strongly suggest a common pre neogene history for all these areas by contrast an important regional unconformity occurring at the top of the middle miocene throughout the palawan area is absent from the asian mainland extension in the south china sea basin since the mesozoic which has separated the north palawan block from the asian mainland has been approximately uniform from west to east however there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea floor spreading from the foregoing observations and using the most recent magnetic spreading anomaly data for the south china sea a suite of palinspastic reconstructions has been prepared which shows the evolution of the south china sea area from the late triassic to the pliocene the reconstructions illustrate 1 the convergent continental margin setting of the north palawan block during much of the jurassic and cretaceous 2 the late cretaceous inception of the philippine island arc system 3 the subsequent counter clockwise rotation of the arc system from the late eocene onward 4 the paleocene to middle miocene opening of the south china sea and 5 the early to middle miocene collision between the north palawan block and the palawan subduction system

architecture development and geological control of the xisha carbonate platforms northwestern south china sea newly acquired seismic data allow improved understanding of the architecture and evolution of isolated carbonate platforms on the continental slope of the northern south china sea the xisha carbonate platforms were initiated on a basement high the xisha uplift in the early miocene and have remained active up to the present their distribution is limited to pre existing localized fault bounded blocks within the xisha uplift so individual platforms were small in size at the beginning of the miocene however during the middle miocene the platform carbonate factories flourished across an extensive area with 55 900 km 2 the platforms began to backstep in response to a relative sea level rise in the late miocene platform edge reefs patch reefs pinnacle reefs atoll reefs and horseshoe reefs all developed on various platforms the distribution of platform carbonates shrank significantly during pliocene quaternary time to isolated carbonate platforms represented today by xuande atoll and yongle atoll tectonics and eustasy were the two main controls on platform development tectonics controlled both the initial topography for reef growth and the distribution of platforms including those that survived the drowning event associated with the late miocene rapid relative sea level rise eustasy controlled high frequency carbonate sequence development crown copyright c 2014 published by elsevier b v all rights reserved

depth of the decoupling plate interface and thermal structure under arcs subduction proceeds as thrust movements at the boundary between the subducting plate and the rigid overlying plate at depth below this mechanically decoupling plate interface the subducting plate couples with the overlying mantle and flow is induced in the mantle wedge this induced flow is the main factor that controls thermal structure under arcs depth of this decoupling to coupling transition at the plate interface is estimated from observed surface heat flow in the northeastern japan arc using a two dimensional numerical simulation of thermal structure the estimated depth is about 70 km the termination depth of thrust earthquakes agrees well with the depth of the coupling transition which indicates that these earthquakes occur at the decoupling plate interface the mechanism of this decoupling plate interface is discussed in this paper it is believed that water associated with the subducting oceanic crust reduces the frictional stress at the plate interface and thrust movement thus becomes possible petrological studies show that dehydration reaction in the subducting oceanic crust terminate at about 2 0 gpa and have little temperature dependence termination depths of thrust earthquakes estimated from seismic studies are nearly the same 60 80 km for various arcs this indicates that depth of the decoupling to coupling transition is controlled by the termination depth of dehydration reaction in the subducting oceanic crust across arc heat flow profiles observed in various subduction zones show similar features heat flow is very low in the forearc region and increases steeply at the volcanic front considering that the depth of the slab is about 100 km at the volcanic front for various arcs this heat flow feature is closely related to the depth of the slab thus it is concluded that thermal structure under arcs is mainly controlled by the depth of the pressure dependent dehydration reactions in the subducting oceanic crust

the tempo of geomorphological change evidence from southeastern australia a revised denudational chronology based on k ar dating of basalts for much of southeastern australia shows that many major topographic features are far older than was previously realized some upland surfaces originated in the mesozoic and others in the early tertiary in some areas the last major uplift and onset of canyon cutting occurred prior to the mid oligocene apart from the slow headward extension of canyons and localized high level stripping much of the region had taken on approximately its present day form by the mid miocene paradoxically however none of the mechanisms that have been proposed to explain the survival of paleoforms hold here these instances may well be typical of large parts of the interior of tectonic plates and a revision of widely held estimates of modal rates of denudation seems required

stratigraphic well correlations for 3 d static modeling of carbonate reservoirs the principles and purposes of stratigraphic well correlation in carbonate sedimentary systems are defined and discussed within the context of static reservoir modeling the challenge of well correlations is to relate the heterogeneities measured at core and well scales to the spatial heterogeneities at reservoir and flow unit scales the introduction of a priori knowledge in the process of stratigraphic well correlation is critical to support the stratigraphic rules and to establish a coherent geological and petrophysical concept the links between well correlation and geostatistics are discussed with regard to the stationarity hypothesis and property trend analysis we stress that wells are incomplete and biased samples of the geological reality which is not dependent unlike the dynamic reservoir behavior on the well numbers location and spacing stratigraphic rules are applied as a function of the well spacing relative to the geological reality a simple trigonometric method combining angle of base profile paleobathymetry and well spacing is introduced to check the validity of the well correlation in carbonate ramp like systems two models based respectively on outcrop and subsurface with seismic data are discussed in detail to show the combined influence of the data set sedimentary systems and diagenetic transformations on stratigraphic well correlations

the natural and human structuring of rivers and other geomorphological systems a tribute to william l graf this special issue honors the contributions of william l graf to geomorphology and river science a hallmark of will s work over the course of his career has been a focus on the natural and human structuring of river systems more broadly will has been an innovator and leader who has shaped the way in which geomorphologists conduct research through his work he has made fundamental contributions to basic fluvial theory to the understanding of human impacts on river systems and to policy relevant science he has demonstrated by example how to pursue policy relevant science and to participate in science based policy formulation his contributions to river science can be classified into several themes 1 the hydrology and geomorphology of suburban drainage systems 2 riparian vegetation and river systems 3 the spatial structure and dynamics of incised channels 4 the dynamics of dryland river systems 5 heavy metals in river systems 6 dams and dam removal and 7 water and public policy the papers in this special issue reflect many aspects of these themes and address topics related to 1 the understanding of rivers and other geomorphic systems in the midst of dynamic physical change 2 human influences on geomorphic processes 3 the intersection of geomorphology and public policy and 4 the fusion of geomorphic analysis and giscience

late pleistocene and holocene sea level change in the australian region and mantle rheology summary spatial and temporal variations in sea level are produced by the melting of the late pleistocene ice and by the earth s response to the redistribution in surface loads by examining different parts of the sea level curves of the past 20 000 yr from geographically widely distributed regions it becomes possible to constrain models of the melting history of the ice sheets and of the earth s rheology observations from sites away from the former arctic ice sheets such as the australian and south pacific region are particularly important for constraining the total meltwater volumes added into the oceans in the past 20 000 yr and the rates at which this occurred these observations indicate that the antarctic ice sheets provided a significant contribution to the sea level rise at a rate that was approximately synchronous with the melting of the laurentide ice sheet except for the interval 9000 6000 yr ago when it may have lagged behind minor melting of the antarctic ice sheet appears to have continued throughout the late holocene differential observations of the late holocene sea level change recorded at sites in the same region are particularly useful for estimating parameters describing the earth s non elastic response to surface loading the effective parameters used here are a lithospheric thickness an upper mantle viscosity and a lower mantle viscosity describing the response below 670 km depth with the observations used here it is not possible to separate the lithospheric thickness h from the upper mantle viscosity and the viscosity results are based on the assumption that 50 h 100 km neither do these observations provide a resolution of the depth dependence of viscosity in the upper mantle and the resulting estimates are effective parameters only differential sea levels along continental margins and along the shores of large gulfs and bays constrain the effective upper mantle viscosity to be about 1 2 1020 pa s 1 while differential values from islands of different sizes are suggestive of a somewhat lower value the lower mantle taken to be below 670 km depth viscosity is about two orders of magnitude greater than this the estimated ice and rheological models explain many of the holocene sea level observations throughout the australian and southern pacific region the tilting of continental margins as exemplified by observations of variable amplitudes of the holocene high stands and the variable times at which sea levels first reached their present level along the north queensland coast and great barrier reef is well represented by these models differential holocene sea levels observed along the narrow spencers gulf of south australia are also well explained by the models and in neither case is it necessary to invoke tectonic motions predicted late holocene sea levels at small to medium sized islands are characterized by small amplitude high stands that reached their maximum values about 4000 2000 yr ago consistent with observations from the society cook and tuamotu islands

south china continental margin signature for sandstones and granites from palawan philippines abstract we report results of heavy mineral analysis and u pb dating of detrital zircons from metasediments and cenozoic sandstones and u pb dating of zircons from cenozoic granites of the north palawan continental terrane npct and the south palawan terrane spt the npct metasediments are derived mainly from granitic and metamorphic rocks of continental character they contain zircons that indicate a maximum depositional age of late cretaceous and other age populations indicating a south china origin the sediments were deposited on the south china margin before rifting of the continental margin during opening of the south china sea miocene spt sandstones contain similar heavy mineral assemblages suggesting sources that included npct metasediments metamorphic basement rocks at the contact between the spt and the npct south china sea rift volcanic and or minor intrusive rocks and the palawan ophiolite complex the spt sandstones are very similar to lower miocene kudat formation sandstones of northern borneo suggesting a short lived episode of sediment transport from palawan to borneo in the early miocene following arc continent collision u pb dating of zircons shows that the central palawan granite is eocene 42 0 5 ma the capoas granite was intruded during a single pulse or as two separate pulses between 13 8 0 2 ma and 13 5 0 2 ma inherited zircon ages from the capoas granite imply melting of continental crust derived from the south china margin with a contribution from cenozoic rift related and arc material

vp and vs tomography of kyushu japan new insight into arc magmatism and forearc seismotectonics high resolution 3d tomographic images of the crust and upper mantle are determined under the entire arc region of kyushu by inverting a large number of arrival time data of p wave s wave and sp depth phases the hypocenters of the offshore earthquakes are accurately located by applying a combined method that makes use of sp depth phases and double difference of the p wave and s wave arrival times our tomographic results confirmed the major features delineated by previous studies and revealed some new features of structural heterogeneity related to arc magmatism beneath the kyushu arc high velocity anomalies correspond to the subducting philippine sea slab whilst low velocity zones in the mantle wedge are clearly imaged coinciding well with the velocity heterogeneities determined by previous studies strong low velocity anomalies are distributed extensively along the volcanic front and extend to the back arc side in the crust and upper mantle our present seismic images together with the previous results suggest that the fluids supplied by the dehydration processes of the descending philippine sea slab and the hot upwelling materials related to the opening of the okinawa trough might have contributed to the unzen volcanism under the forearc region of the kyushu subduction zone prominent low velocity anomalies are visible at depths of 10 40 km along the upper boundary of the subducting philippine sea slab and large interplate earthquakes are located around the low velocity zones which is similar to the features revealed in the northeast japan subduction zone the spatial distribution of large thrust earthquakes below the offshore region reflects the existence of weak coupled or decoupled portions on the interface of the subducting philippine sea slab

high strain rate zone in central honshu resulting from the viscosity heterogeneities in the crust and mantle abstract a linear zone with high strain rates along the backarc side of central honshu the so called niigata kobe tectonic zone has been revealed by the dense gps array geonet operated by the geographical survey institute of japan in order to explore the origin of this zone we examine rheological heterogeneities in the crust or mantle above a subducting slab which possibly contribute to the high strain rates we calculate velocity profiles at the surface of the upper plate due to loading and unloading of the subducting philippine sea plate using a 2 dimensional finite element method from the numerical experiments we find that the high strain rates can be reproduced by viscosity heterogeneities either in the crust or the mantle if viscosity heterogeneity in the crust is an origin the conditions to be satisfied are i an effective elastic thickness of 5 km for short term loading 10 2 10 3 yr ii a low viscosity 19 pa s in the lower crust beneath the zone with a normal viscosity 10 21 pa s in the ambient lower crust and iii a uniform viscosity of 10 19 pa s in the upper mantle on the other hand if viscosity heterogeneity in the mantle is an origin the conditions to be satisfied are i an effective elastic thickness of 30 km for short term loading ii a low viscosity 10 18 pa s at least down to a depth of 60 km in the zone and to a depth of 10 km further seaward below the moho depth and iii a viscosity of 10 20 pa s in the ambient mantle the crust heterogeneity model contradicts the 15 km cut off depth of intraplate seismicity and the 20 km effective elastic thickness previously inferred from gravity and topography in central honshu the fact that quaternary active faults and intraplate earthquakes are not particularly concentrated in the zone also favours the mantle viscosity heterogeneity model thus we prefer the mantle heterogeneity model we suggest that upward movement of water dehydrated from the subducting philippine sea and pacific plates partial melting of the mantle above the pacific plate and serpentinization in the wedge mantle above the philippine sea plate are possible origins of the low viscous upper mantle possible low viscosities in the upper mantle wedge presented in this study seem to provide important constraints for subduction processes of oceanic plates and strain accumulation processes in the upper plate

geological significance of seismic reflections and imaging of the reservoir architecture in the malampaya gas field philippines the integration of petrographic analyses of cores and thin sections petrophysical measurements and well logs demonstrates that variations in acoustic impedance in the malampaya buildup upper eocene to lower miocene offshore northwest palawan are related to vertical changes in porosity and pore type which are dominantly controlled by diagenetic processes the nido limestone was subdivided into 10 50 m 30 150 ft thick units characterized by specific diagenetic patterns and petrophysical properties diagenetic units the alternation between tight and porous diagenetic units is mainly controlled by meteoric diagenesis leaching and pedogenesis and by late burial cementation and leaching well to seismic ties show that the main seismic reflectors within the buildup interior reflect the boundaries between diagenetic units most of the negative amplitude reflectors are related to unconformities whereas positive amplitude reflectors have a more questionable chronostratigraphic value and may represent the bases of cemented lenses that can crosscut time lines comparison with other southeast asian tertiary buildups indicates different origins of seismic reflections related to distinct patterns of diagenetic evolution the identification of such seismodiagenetic units and of their controlling factors is of paramount importance for the architecture and the petrophysical characterization of carbonate reservoirs

electrical conductivity anomalies beneath the western sea of kyushu japan geomagnetic depth soundings have been made in the area covering kyushu island and its neigh boring islands in the western sea of kyushu to investi gate the back arc conductivity structure the in phase induction arrows derived from geomagnetic variations are found to point roughly southwestwards at most sites on kyushu island for the period range 300 7200 sec this is quite different from some other areas of japan the non uniform thin sheet model calculation indicates that the induction arrows in this area are strongly influ enced by the surrounding seas however the observed arrows have much more intense westward components than indicated by the model calculations this strongly suggests existence of highly conducting layers hcls beneath the east china sea and the existence of hcls in the upper mantle are confirmed by a two dimensional finite element modeling these hcls may be consid ered to be a part of mantle upwelling extended to east

magma evolution observed in the matsuura basalts in northwest kyushu japan an example of high pressure open system fractional crystallization in a refilled magma chamber near the crust mantle boundary abstract formation of an extensive shallow water sedimentary basin before the voluminous matsuura basalt volcanism in the back arc volcanic belt in northwest kyushu japan seems to indicate the lower crust erosion due to the upwelling of the mantle which results in the decompression melting of mantle to form basaltic magma the matsuura basalts 10 to 1 ma range in composition from low alkali tholeiitic basalt through alkali olivine basalt to basaltic andesite their compositions show a wide variation in mgo from 11 6 wt to 2 8 wt their chemical characteristics are 1 evolution across the alkali subalkali boundary 2 crescent form of the basalt distribution on a sio2 vs mgo diagram 3 enrichment in normative plagioclase component and a diminution in normative clinopyroxene component with the magma evolution 4 abrupt termination of this plagioclase enrichment trend at mgo 3 3 wt 5 marked enrichment in sio2 in aphyric basalts with mgo

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

middle to late cenozoic tectonic events in south and central palawan philippines and their implications to the evolution of the south eastern margin of south china sea evidence from onshore structural and offshore seismic data abstract using recently gathered onland structural and 2d 3d offshore seismic data in south and central palawan philippines this paper presents a new perspective in unraveling the cenozoic tectonic history of the southeastern margin of the south china sea south and central palawan are dominated by mesozoic ophiolites palawan ophiolite distinct from the primarily continental composition of the north these ophiolites are emplaced over syn rift eocene turbidites panas formation along thrust structures best preserved in the ophiolite turbidite contact as well as within the ophiolites thrusting is sealed by early miocene 20 ma sediments of the pagasa formation isugod formation onland constraining the younger limit of ophiolite emplacement at end late oligocene 23 ma the onset of ophiolite emplacement at end eocene is constrained by thrust related metamorphism of the eocene turbidites and post emplacement underthrusting of late oligocene early miocene nido limestone this carbonate underthrusting at end early miocene 16 ma is marked by the deformation of a seismic unit corresponding to the earliest members of the early middle miocene pagasa formation within this formation a tectonic wedge was built within middle miocene from 16 ma to 12 ma forming a thrust fold belt called the pagasa wedge wedge deformation is truncated by the regionally observed middle miocene unconformity mmu 12 ma a localized post kinematic extension affects thrust fold structures the mmu and late miocene to early pliocene carbonates e g tabon limestone this structural set up suggests a continuous convergent regime affecting the southeastern margin of the south china sea between end eocene to end middle miocene the ensuing structures including juxtaposed carbonates turbidites and shallow marine clastics within thrust fold belts have become ideal environments for hydrocarbon generation and accumulation best developed in the northwest borneo trough area the intensity of thrust fold deformation decreases towards the northeast into offshore southwest palawan

the continent ocean transition at the southeastern margin of the south china sea abstract the south china sea formed by magma poor or intermediate volcanic rifting in the paleogene we investigate the structure of the continent ocean transition cot at its southern margin off nw palawan between the continental blocks of reed bank and the islands of palawan and calamian several surveys recorded by the bgr from 1979 to 2008 established a comprehensive database of regional seismic lines accompanied with magnetic and gravity profiles we interpret two major rifted basins extending in the ne direction across the shelf and slope separated by a structural high of non volcanic origin the continent ocean transition is interpreted at the seaward limit of the continental crust when magnetic spreading anomalies terminate some 80 100 km farther north the area in between displays extensive volcanism as manifest by extrusions that occasionally reach and cut the seafloor by dykes and by presumed basaltic lava flows occurring after break up the cot is highly variable along the nw palawan slope one type shows a distinct outer ridge at the cot with a steep modern seafloor relief the other type is characterised by rotated fault blocks bounded by listric normal faults ramping down to a common detachment surface half grabens developed above a strongly eroded pre rift basement the seafloor relief is smooth across this other type of cot we suggest the pre rift lithospheric configuration had major influence on the formation of the cot besides transfer zones volcanic domains confined to the north of competent crustal blocks correlate with the style of the cot gravity modelling revealed an extremely thinned crust across the shelf we propose a depth dependent extension model with crust being decoupled from mantle lithosphere explaining the discrepancy of subsidence observed across the south china sea region

multi parameter imaging in the 2016 mw 7 0 kumamoto earthquake kyushu japan and its implications for fluids in seismogenesis abstract fluids associated with structural heterogeneities in a seismogenic layer play a crucial role in triggering earthquakes and controlling their rupture processes but the mechanism of fluid intrusion and the relationship with earthquake initiation are unclear this study presents new seismic evidence of an earthquake mostly triggered by fluid intrusion associated with magmatism in kyushu sw japan seismic imaging revealed two zones with slow seismic velocities beneath the unzen and aso volcanoes with high poisson s ratio extending into the rupture belt of the 2016 mw 7 0 kumamoto earthquake the following features particularly the high poisson s ratio anomalies suggest the presence of fluids in the source area ascending from nearby magmatism anomalous crack density and saturation rate imply that the fractures pores are not fully saturated with fluids in the crust of the beppu shimabara graben possibly providing a path for fluids to penetrate into the source area either through highly fracture damaged faults or via incompletely saturated pores cracks fluid penetrating into the hypocenter areas from deep magma increases the pore pressure and decreases the coulomb failure function we therefore speculate that a system such as this with high pore pressure and fluids in the host faults might lower the threshold for fault failure thus increasing the likelihood of failure of the mainshock fault the results of this study suggest that the presence of fractures pores within extensional rift zones around the world might be critical for fluid migration and contribute to the initiation development and migration of seismic activity

thermal contraction and flexure of intracratonal basins a three dimensional study of the michigan basin summary cooling of continental lithosphere by thermal conduction to the surface following a heating event imposes a load on the lithosphere and causes subsidence as the basement rocks contract accumulation of sediments in the resulting depression forms a sedimentary basin studies of the geometry of sedimentary basins with horizontal dimensions of a few hundred kilometres suggests the lithosphere responds to loads by regional flexure of a strong elastic or viscoelastic upper lithosphere two and three dimensional models for flexure of the lithosphere owing to thermal contraction are applied to the michigan basin 2 d flexural models are compatible with previously estimated rheological parameters for an elastic lithosphere an effective flexural rigidity of about 5 1029 dyne cm can explain observed gravity anomalies and structural contours across the michigan basin a viscoelastic lithosphere requires an effective flexural rigidity of about 1032 dyne cm for a viscosity of 1025 poise for a 3 d elastic or viscoelastic lithosphere effective flexural rigidity must be approximately an order of magnitude smaller 2 1028 and 1031 dyne cm respectively larger values leave an excessive remaining load at the centre of the basin which is not indicated by observed gravity anomalies the decrease in effective flexural rigidity is attributed to greater difficulty in equi dimensional bending of a 3 d plate the magnitude and spatial distribution of the computed thermal contraction load are consistent with the presumed mechanism as the thermal anomaly of the initial heating event was present mainly at great depths in the lithosphere the lack of geological evidence for an initial heating event prior to subsidence is not a fatal objection to the thermal contraction mechanism of subsidence a driving load presumably from subsurface processes including crustal stretching and emplacement of dense rocks into the crust is necessary to explain the net subsidence of the basin from the time before the heating event until the lithosphere beneath the basin cooled without this driving load the thermal expansion would produce uplift but the surface would subside only back to sea level after the lithosphere cooled theoretical gravity results indicate that the driving load is centred at a depth of approximately 15 km deviations in subsidence curves from exponentials associated with thermal contraction can be explained by changes in sediment supply spatial variations in sediment load caused by regional facies changes produce migration of the centre of maximum deposition water and basement depths are determined for sequential time intervals during basin development the predicted depositional environments are consistent with lithofacies maps of the middle devonian

seismic evidence for mesozoic strata in the northern nansha waters south china sea abstract according to previous studies mesozoic deposits have been unequivocally identified in the northeastern nansha waters southern margin of the south china sea scs thick lower structural layers in the north nansha waters have not clearly been identified as either mesozoic or cenozoic strata these strata are characterized by strong top erosion tilted layer or folded anticlines new long offset multi channel seismic data show refracted phases from the top of the lower structural layer in the northern nansha waters a major velocity leap approximately from 1 6 km s to 3 8 km s or 2 9 km s to 5 3 km s calculated from the refraction wave of seismic data is found across a prominent angular unconformity indicating a major sedimentary hiatus according to the stratigraphic characteristics and velocity range of the lower structural layer velocity leap at the top of lower structural layer and ubiquitous absence of upper cretaceous strata in the nansha waters the lower structural layer of the northern nansha waters are interpreted as mesozoic based on the similarities in stratigraphic characteristics of the lower structural layers between the northern and central nansha waters previous studies from gravity data and multi channel seismic data we propose that lower structural layers over central nansha waters may also mesozoic this further suggests that the intensity of upper crustal extension was moderate in nansha waters during the cenozoic which related to a combination of the cenozoic slab pull of the proto scs and lithosphere delamination over an ancient orogenic belt between the northern and southern continental margins of the scs which may weaken extension of upper crust over the nansha waters

roles of mantle diapir and ductile lower crust on island arc tectonics abstract in order to examine the relationships between surface geological phenomena in island arcs and lower crustal and upper mantle dynamics crustal and upper mantle responses induced by upper mantle density heterogeneities with magnitudes expected from the seismic tomography beneath the northeastern japan arc have been evaluated according to the rheological model with a low viscosity lower crust and low viscosity uppermost mantle low density lower crustal material above mantle diapiric upwelling is mechanically dragged along by asthenospheric shear stresses and then lower crustal material flows from the back arc corner to the fore arc corner the surface subsidence for this process is about 300 m on a geological time scale of 5 50 my and the formation of a sedimentary basin with about the same lateral scale as the mantle diapir can be expected in the area above the mantle diapir stage s the subducted slab in island arc will operate as a barrier to the lateral movement of lower crustal material accumulation of low density lower crustal material may occur at the edge of the overriding plate during this process at a critical stage of the pressure in the mantle wedge of fore arc region high temperature lower crustal material may then be exposed along the tectonic line stage e as the result of discharging lower crustal material along the tectonic line the pressure in the lower crust will be decreased and accelerated subsidence accompanied by volcanism is expected in the sedimentary basin cretaceous geological phenomena in southwest japan may be explained by this physical mechanism its linked surface crustal movement and the flow of lower crustal material a relatively slow deposition in the period of about 140 120 ma observed in the kanmon sedimentary basin may be interpreted as the geological representation of stage s from about 110 ma the kanmon sedimentary basin was supplied with a large quantity of volcanic sediments and simultaneously expanded and suddenly subsided at about the same time low pressure high temperature metamorphism and granitic activity ryoke belt occurred along the areas to the south of the kanmon group it may be possible to interpret these geological phenomena along the median tectonic line mtl as the surface geological events corresponding to stage e it is however stressed that the time and spatial scale for this coupling is determined by the rheological structure of the lower crust and upper mantle and by the scale of mantle diapir

deep structure of the northeastern japan arc and its relationship to seismic and volcanic activity evidence for possible deep seated magmatic activity beneath northeastern japan can be obtained from seismic observations tomographic inversions of p wave velocity data show low velocity zones distributed in the crust and upper mantle beneath active volcanoes in or around these zones anomalously low frequency micro earthquakes perhaps caused by magmatic activity are found at depths of 25 40 km distinct s wave reflectors corresponding to the upper surfaces of magma bodies are found at depths of 10 18 km large crustal earthquakes also occur around the low velocity zones these observations reveal the distribution of magma reservoirs at depths and elucidate its relation with shallow seismicity beneath volcanic arcs

sea level changes and carbonate platform evolution of the xisha islands south china sea since the early miocene abstract analyses of the biogeochemical branched and isoprenoid tetraether bit index and elemental geochemistry from well xk1 provide insight into the development of the xisha islands carbonate platform in the south china sea scs since the early miocene bit is the ratio of branched glycerol dialkyl glycerol tetraethers bgdgts to isoprenoid glycerol dialkyl glycerol tetraethers igdgts which are derived from meteoric and marine environments respectively bit serves as a novel proxy for tracking sea level changes the bit curve of well xk1 is characterized by low high low high alternating stages indicating the superposition of sea level changes on carbonate platform evolution in the scs following the rapid expansion of the scs in the early stages of the early miocene biogenic reefs began to form and bit oscillated intensely the scs started to regress after its initial expansion during the middle miocene at which time global sea level was also falling significantly the combination of both tectonic activity and eustatic variation has resulted in the deposition of strata with reef beach facies which are characterized by high bit values relative sea level reached its lowest point in the late stages of the middle miocene 11 6 ma subsequent sea level rise between the late miocene and pliocene induced a negative shift in bit and lagoonal facies formed under optimal warm marine conditions periodic exposure caused the reefs of the xisha islands to suffer from erosion during the pleistocene which is consistent with a second elevation in the bit index however modern trends show increasing regional water depths again major and trace element curves na si p b ga mo zn as well as the associated ratios na2o k2o na2o sio2 b ga ti sr zr sr al sr th u accurately record sea level variations several significant discontinuities correlate with sea level shifts and provide important details about the geomorphology sedimentation patterns and diagenesis types on the scs carbonate platform the agreement between organic and inorganic geochemical data demonstrates that our reconstructions of scs sea level changes and modes of carbonate platform development are robust our findings also demonstrate that carbonate evolution in the xisha islands was shaped by relative sea level changes implying that sea level fluctuations in the scs were controlled by global eustatic factors in addition to regional tectonic subsidence

tomographic low velocity anomalies in the uppermost mantle around the northeastern edge of okinawa trough the backarc of kyushu a simultaneous inversion for three dimensional velocity structure and hypocentral parameters is used to determine the tomographic images of the backarc of kyushu southwestern japan the data used in the imaging are the first arrival times of 2736 local earthquakes recorded at 305 stations in a wide region from western japan to eastern china additional data are provided by including arrival times of 357 teleseismic earthquakes we got the high resolution of the uppermost mantle images for p waves at least in the depth range to 150 km the latitude range of 30 34 n and the longitude range of 128 132 e results of inversion reveal a major zone of strong low velocity under west off kyushu island in the depth from 40 km to 100 km this feature may result from partially melting in relation to the upwelling of hot mantle around the northeastern edge of the extending okinawa trough

pb sr isotopic evidence for contribution of deep crustal fluid to the hishikari epithermal gold deposit southwestern japan abstract the gold bearing quartz adularia veins of the world class hishikari mine in southwestern japan occur in a geological regime where the rocks of the upper to middle crust are simple and their chemical and sr nd pb isotopic compositions are well studied detailed comparison of pb and sr isotopic data of the hishikari veins with those of all possible source materials demonstrates that metals in the veins were essentially derived from a mixture of magmatic fluid with a deep crustal fluid that originated near the boundary between the shimanto middle crust and the underlying subcontinental crustal materials we propose that the release of the deep crustal fluid was triggered by intrusion of the shishimano rhyodacite magma related to timing of the mineralization this fluid mixture carried metals to the brittle upper crust along fissures created by extensional stress forming the ore deposits although the deep crustal fluid has not been paid much attention it may be distributed over a large scale in the deep crust from the continent to the arc system and play an important role in the genesis of magmatic hydrothermal ore deposits and in the generation of flow induced deep tremor