the emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and ph front here we argue that life emerged on earth from a redox and ph front at c 4 2 ga this front occurred where hot c 150 c extremely reduced alkaline bisulphide bearing submarine seepage waters interfaced with the acid warm c 90 c iron bearing hadean ocean the low ph of the ocean was imparted by the ten bars of co 2 considered to dominate the hadean atmosphere hydrosphere disequilibrium between the two solutions was maintained by the spontaneous precipitation of a colloidal fes membrane iron monosulphide bubbles comprising this membrane were inflated by the hydrothermal solution upon sulphide mounds at the seepage sites our hypothesis is that the fes membrane laced with nickel acted as a semipermeable catalytic boundary between the two fluids encouraging synthesis of organic anions by hydrogenation and carboxylation of hydrothermal organic primers the ocean provided carbonate phosphate iron nickel and protons the hydrothermal solution was the source of ammonia acetate hs h 2 and tungsten as well as minor concentrations of organic sulphides and perhaps cyanide and acetaldehyde the mean redox potential eh across the membrane with the energy to drive synthesis would have approximated to 300 millivolts the generation of organic anions would have led to an increase in osmotic pressure within the fes bubbles thus osmotic pressure could take over from hydraulic pressure as the driving force for distension budding and reproduction of the bubbles condensation of the organic molecules to polymers particularly organic sulphides was driven by pyrophosphate hydrolysis regeneration of pyrophosphate from the monophosphate in the membrane was facilitated by protons contributed from the hadean ocean this was the first use by a metabolizing system of protonmotive force driven by natural aph which also would have amounted to c 300 millivolts protonmotive force is the universal energy transduction mechanism of life taken together with the redox potential across the membrane the total electrochemical and chemical energy available for protometabolism amounted to a continuous supply at more than half a volt the role of the iron sulphide membrane in keeping the two solutions separated was appropriated by the newly synthesized organic sulphide polymers this organic take over of the membrane material led to the miniaturization of the metabolizing system information systems to govern replication could have developed penecontemporaneously in this same milieu but iron sulphur and phosphate inorganic components of earliest life continued to be involved in metabolism

world s largest known precambrian fossil black smoker chimneys and associated microbial vent communities north china implications for early life abstract black smoker chimneys and biological vent communities have been identified at many sites on the deep seafloor particularly along oceanic spreading centers we report the largest and oldest known microbe rich sub meter sized black smoker chimneys and mounds from a 1 43 billion year old sulfide deposit in a continental graben in northern china these chimneys are especially well preserved with characteristic morphology internal textures and internal cylindrical mineralogical zonation four main types of chimneys are distinguished on textural and mineralogical criteria exhibiting either zn fe sulfide or pb zn fe sulfide internal cylindrical mineralogical zones the chimneys mark vent sites in submarine grabens indicating focused flow venting processes the fossil chimneys have mineralogical and geological evolutionary features similar to their counterparts on the modern seafloor and other submarine hydrothermal vents black smoker vent fluids and seafloor tectonism played important roles for formation of the massive sulfide deposits in the mesoproterozoic we also report the first known remarkably diverse assemblage of fossil microbialites from around and inside precambrian vent chimneys demonstrating that proterozoic life flourished around submarine hot vents and deep within the chimney vent passages filamentous spherical rod and coccus shaped fossil microbes are preserved preferentially on sulfide precipitates based on the depth and setting of the fossil biota the organisms that produced the microbialites were likely sulfate reducing chemosynthetic and thermophyllic microbes textural and mineralogical evidence shows that biomineralization processes enhanced chimney growth and sulfide precipitation close association of microorganisms with sulfide chimneys in modern deep sea hydrothermal vents and younger ophiolites has sparked speculation about whether life may have originated at similar vents however little is known about fossil equivalents of vent microfossils and black smoker chimneys from earth s early evolution the fossilized microorganisms from the gaobanhe black smoker chimney sulfide deposits include thread like filaments with branching and twisted forms and preserved organic carbon representing fossilized remnants of microbial mats metabolized at high temperatures characteristic of venting fluids the preservation of fossil microorganisms provides evidence that microbial populations were closely associated with black smoker chimneys in earth s early history the microbial population clearly constitutes the site for mediating mineral formation these ancient microbial fossils lead to a much better understanding of early life on the deep seafloor the discovery of the mesoproterozoic microfossils within black smoker hydrothermal chimneys indicates that hydrothermal activity around sea floor vents supported dense microbial communities and supports speculation that vent sites may have hosted the origin of life

pito and orongo fracture zones the northern and southern boundaries of the easter microplate southeast pacific abstract the easter rapanui microplate is a case example of a large dual spreading center system in a region where the fastest seafloor spreading on earth is occurring today recent theoretical models of the tectonic evolution of dual spreading center systems have explored the effects of shear and rigid rotation on the boundaries and internal structure of microplates but the models must be critically constrained by improved relative motion and structural fabric data sets during the january 1987 rapanui expedition on the n o jean charcot we conducted a sea beam magnetics gravity survey of a portion of the microplate boundaries the method that was used was to fully map selected portions of the boundaries in order to establish precise structural relationships the northern terminus of the east rift or eastern boundary of the microplate is expressed as a series of parallel nw se trending valleys including what appears to be with 5890 m depth the deepest active rift axis mapped in the pacific today pito rift the northern end of the pito rift merges with an e w to 083 narrow band of linear faults interpreted to be a transform fault between the nazca and easter rapanui plates the northern triple junction between the easter rapanui nazca and pacific plates is a rff type with the two transform faults colinear along an approximately e w direction the southwestern boundary of the easter rapanui microplate is marked by a series of en echelon offsets outlined by depressions which merge into an approximately e w zone where shear must be predominant the southern triple junction is a rrf junction with an overlapping ridge system the structural data acquired during the survey provide strong constraints for kinematic models of the microplate the structural data need to be combined with crustal age determinations in order to derive a model for the evolution of the microplate

reflection mapping across the convergent margin of western canada summary five marine multichannel seismic reflection profiles totalling 520 km were recorded across the western canada convergent margin where the juan de fuca plate is subducting beneath north america the data extend the results of lithoprobe on vancouver island the primary objectives are definition of the offshore accretionary structures and clarification of the convergent interaction between the two plates the main features of this preliminary interpretation are 1 the subduction deformation front is complex with evidence of sediments being accreted and subducted 2 the top of the oceanic crust and the mono are imaged below the deep water sedimentary basin 3 the top of the subducting plate is clearly imaged below the shelf 4 beneath the inner shelf one band of high reflectivity underlain by a zone of lesser reflectivity lies above the plate 5 alternative interpretations place the present zone of decoupling at the base of the reflective band or the top of the plate 6 the san juan and leech river faults that bound small accreted terranes are imaged as thrusts that merge at depth

great earthquakes on canada s west coast a review this article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geological survey of canada contribution 20090196 the first lithoprobe transect in 1984 across vancouver island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes

evidence of bacterial activity from micrometer scale layer analyses of black smoker sulfide structures pito seamount site easter microplate abstract we report the observation of an external layer less than 20 m thick attached to hydrothermal chimney fragments of black smokers collected from the pito seamount site on the easter microplate scanning electron microscope observations revealed bacterial imprints located on and within the layer which was associated with underlying layers of thin jarosite deposits and iron sulfides displaying corrosion features x ray electron microprobe drift and hplc measurements were used to determine the precise chemical composition and nature of compounds in the layer the external layer was composed mainly of a combination of hydrated ferric sulfate ferrous sulfate iron oxi hydroxide and elemental sulfur species a jarosite like mineral was found deeper in the layer we suggest that this layer may not be the result of an abiotic thermochemical precipitation but instead was formed chemically by bacterial processes these processes were 1 elemental sulfur oxidation which represents major energetic exchanges within the external layer and 2 bioleaching processes inducing iron oxidation originally elemental sulfur probably resulted from thermochemical precipitation the results of this study give new insight on the possible role and impact of related acidophilic microorganisms living in hot vent environments of the deep sea

seafloor bioalteration of sulfide minerals results from in situ incubation studies we present results of incubation studies conducted at low temperatures 4 c in the vicinity of a seafloor hydrothermal vent system we reacted fe s cu and zn bearing minerals including pyrite marcasite chalcopyrite sphalerite elemental sulfur and a portion of a natural chimney sulfide structure for 2 months at the main endeavour segment of the juan de fuca ridge in the pacific ocean our study utilizes fluorescent in situ hybridizations fish scanning and transmission electron microscopy sem tem and light microscopic analysis the surfaces of these minerals are solely colonized by bacteria and not by archaea colonization densities vary over an order of magnitude with the following sequence elemental sulfur chimney sulfide marcasite pyrite sphalerite chalcopyrite and correspond well with the abiotic oxidation kinetics of these materials excepting elemental sulfur which is both the least reactive to oxidizing species and the most heavily colonized colonization densities also correspond with apparent degree of reaction dissolution pitting accumulation of secondary alteration products heavy accumulations of secondary fe oxides on fe bearing minerals most notably on the chimney sulfide form in situ as the result of mineral dissolution and the activity of neutrophilic fe oxidizing bacteria results suggest that mineral oxidizing bacteria play a prominent role in weathering of seafloor sulfide deposits and that microbial utilization of mineral substrates contributes to biomass production in seafloor hydrothermal environments

local thickening of the cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle seismic reflection profiles from three different surveys of the cascadia forearc are interpreted using p wave velocities and relocated hypocentres which were both derived from the first arrival travel time inversion of wide angle seismic data and local earthquakes the subduction decollement which is characterized beneath the continental shelf by a reflection of 0 5 s duration can be traced landward into a large duplex structure in the lower forearc crust near southern vancouver island beneath vancouver island the roof thrust of the duplex is revealed by a 5 12 km thick zone identified previously as the e reflectors and the floor thrust is defined by a short duration reflection from a b2 km thick interface at the top of the subducting plate we show that another zone of reflectors exists east of vancouver island that is approximately 8 km thick and identified as the d reflectors these overlie the e reflectors together the two zones define the landward part of the duplex the combined zones reach depths as great as 50 km the duplex structure extends for more than 120 km perpendicular to the margin has an along strike extent of 80 km and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity where velocities are less than 7000 m s 1 we suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion the absence of seismicity from within the e reflectors implies that they are significantly weaker than the overlying crust and the reflectors may be a zone of active ductile shear in contrast seismicity in parts of the d reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex merging of the d and e reflectors at 42 46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km we suggest that pervasive reflectivity in the upper mantle elsewhere beneath puget sound and the strait of georgia arises from similar shear zones

seismic reflection images of the crust of the northern part of the chugach terrane alaska results of a survey for the trans alaska crustal transect tact deep crustal seismic reflection data show strong reflections from the middle and lower crust of the convergent continental margin near the eastern end of the aleutian trench these data were collected across the border ranges fault system a major suture zone that separates the peninsular and chugach tectonostratigraphic terranes the chugach terrane consists of metamorphosed strongly deformed flysch subduction melange as well as blueschist and greenschist facies rocks even so highly reflective rocks lie at great depth within or beneath this terrane the shallow part of the seismic section 0 5 s reveals only a few reflections which undulate and interweave indicating that some of them originate outside of the plane of the seismic section other undulating events could reveal early cenozoic granitic plutons or antiformal stacks of rock imbricated along thrust faults in contrast to this shallow reflection pattern three reflection bands contain most of the events on the middle part of the seismic section 5 12 s or 12 34 km we interpret divergent reflections within the uppermost band 5 5 5 s as gently north dipping thrust faults and subparallel reflections truncated at the boundaries of the upper and middle bands may image a metamorphic foliation or thrust faults if the truncated reflections represent thrust faults then the reflection geometry suggests that subparallel roof and floor thrust faults bound imbricated rocks forming duplex structures the upper and middle bands are separated by an area on the seismic section that reveals few reflections this area correlates approximately in depth with a high velocity 7 5 km s layer evident in refraction models the poorly reflective high velocity unit might be volcanic rocks like those exposed in the structurally lowest part of the chugach terrane if so then the bottom of the poorly reflective rocks indicates the base of the chugach terrane rocks that cause the upper and middle reflection bands and the intervening poorly reflective volcanic rocks may form a midcrustal shear zone that is about 10 km thick the deepest band of subparallel reflections 30 35 km correlates closely in depth with the top of the wadati benioff zone associated with the underthrusting pacific plate the reflections probably stem from the decollement that separates lithospheric plates within the subduction zone this reflection band increases abruptly in thickness possibly indicating local underplating of subducted sediment no events from the oceanic moho have been recognized neither the border ranges fault system the suture between the chugach and peninsular terranes nor deep crustal layers of the peninsular terrane are evident in these seismic reflection data

lithoprobe crustal reflection structure of the southern canadian cordillera 2 coast mountains transect the lithoprobe seismic reflection transect across the southern coast mountains of the canadian cordillera images fundamental crustal structures presumably related to collision of the intermontane and insular composite terranes and deep levels in the upper plate of the offshore cascadia subduction belt the eastern part of the coast mountains are characterized by east dipping upper crustal reflectors that project to exposed faults and east dipping lower crustal reflectors they are truncated by subhorizontal to west dipping middle and upper crustal reflectors these geometric relationships are interpreted to have formed during an early phase of primarily west directed contraction that created the east dipping structures of the upper and lower crust and a later phase of east directed shortening caused by wedging of the intermontane belt into the lower and middle crust of the tectonic stack subsequently the coast belt may have been displaced eastward on contractional faults that ascend from the lower crust beneath the intermontane belt and surface in the omineca and foreland belts extensional faults bounding the east flank of the coast mountains and west flank of the central nicola horst in the intermontane belt flatten into the middle and lower crust of the intervening region and geometrically outline crustal boudinage within the western coast mountains east dipping reflections spanning the middle crust to upper mantle are traced updip to vancouver island and the underlying cascadia subduction zone the c reflector on vancouver island is believed to separate wrangellia from underlying accreted terranes and is correlated to the mainland where it forms the upper boundary of a reflective lower crustal wedge that flattens into the moho if the moho is not a young feature then some accreted material appears to have wedged into the continental framework above the crust mantle boundary possibly causing shortening in the overlying crust and creating midcrustal ramps observed on the reflection data the structurally lower e reflections interpreted as shear zones originate at the subduction contact offshore and project landward into sub moho reflections within the upper plate on the mainland the region between the e reflector and the descending oceanic plate is interpreted to be subducted lower continental crust and mantle

the electrical conductivity distribution beneath vancouver island a region of active plate subduction magnetotelluric mt and geomagnetic depth sounding gds data were recorded at 25 locations across vancouver island canada over the subducting juan de fuca plate the gds data respond to a number of local conductive features at frequencies above 10 hz while at longer periods the in phase and quadrature induction arrows are colinear and are aligned approximately normal to the continental shelf with a maximum amplitude response near the southwest coast interpretation of the mt data show the presence of a conducting zone at depths greater than 20 km beneath vancouver island and correlating with a strong seismic reflector extensive testing with two dimensional models shows the mt and gds data are consistent with a proposed geoelectrical structure containing a conducting layer extending from the pacific ocean dipping beneath vancouver island and in electrical contact with the mainland conductive region the layer has a horizontal conductance of 200 s that may decrease to 100 s beneath the northeast side of vancouver island related geophysical studies suggest the conductive zone is above the actual thrust surface of the juan de fuca plate the conducting layer is most likely the result of cracks and pores filled with saline fluids which are supplied bymore water subducted with the oceanic crust and by dehydration reactions the presence of fluids has significant implications for thrust earthquakes and for metamorphic reactions that occur in subduction zones the conductance of the upper mantle between 90 and 390 km is best modeled at approximately 1 500 s less

thickness and composition of the bonanza arc crustal section vancouver island canada the composition and origin of continental crust is in part constrained by evidence preserved in exhumed arc crustal sections the bonanza arc on vancouver island canada is a jurassic aged arc crust section exhumed in the eocene we use al in hornblende geobarometry of felsic plutons in the bonanza arc to assess the depths of crystallization of its exposed arc crust plutons of the unfoliated island plutonic suite are emplaced as sheets at depths of 2 10 km within a stratigraphy of devonian to triassic supracrustal rocks the west coast complex is more generally strained and intrudes below the pre jurassic supracrustals at depths of 10 18 km previous work shows that rare ultramafic units within the west coast complex crystallized at depths of 14 26 km the bonanza arc crustal section has a present structural thickness of at least 15 km the average composition for each arc component volcanic and plutonics when apportioned into the crustal section derived by stratigraphy and hornblende barometry shows the bulk composition of the entire arc is basaltic andesite 56 sio 2 mg mg fe mg 50 not unlike some estimates for bulk continental crust although only vestiges of ultramafic rocks occur in the bonanza arc today a significant component 6 20 km of this rock type must have been present in the section for the bulk arc to have been a melt in equilibrium with mantle olivine and may have been lost by foundering or tectonic thinning

geochemistry and morphology of metalliferous sediments and oxyhydroxides from the endeavour segment juan de fuca ridge abstract we present first data on the geochemistry mineralogy and morphology of near vent sediments 35 and 200 m from active vent and ridge flank sediments approximately 3 km from the vent field as well as oxyhydroxide deposits from the endeavour segment juan de fuca ridge the purpose of the study was to understand better the origin and characteristic features of metalliferous sediments associated with base and precious metal massive sulfides in volcanic terrains hydrothermal components in sediments are fe si s rich and mn fe si rich phases sulfides and barite which were exclusively derived from plume fallout sulfides are only a minor constituent of near vent sediments 2 4 wt and were not detected in ridge flank sediments the study suggests that the distribution of hydrothermal phases and associated elements in near vent and ridge flank sediments is affected mainly by processes of agglomeration dissolution absorption and settling that take place within a plume and to a lesser extent post depositional processes rapid deposition of sulfides in the vicinity of the vents is reflected in a sharp drop of the cu concentrations in sediments with increasing distance from the vents besides sulfides important carriers of pb cu zn and co in near vent sediments are fe mn oxyhydroxides that occur together with silica as aggregates of gel like material and flaky particles and as coatings on filaments away from the vents trace metals are mostly in fe mn oxyhydroxides and authigenic fe rich montmorillonite oxyhydroxides at the main endeavour field are interpreted to have originated from oxidation of mound sulfides accompanied by precipitation of primary fe oxyhydroxide silica from low temperature fluids at the mothra field seafloor deposits and chimney crusts composed of fe oxyhydroxide mn silica are considered to be direct precipitates from hydrothermal fluids that have been less diluted with seawater oxyhydroxide deposits exhibit unique microtextures that resemble mineralized microorganisms and may indicate existence of diverse microbial communities

a quantitative approach to bedrock velocity resolution and precision the lithoprobe vancouver island experiment bedrock velocities obtained from the inversion of first break picks of multichannel seismic reflection data have been used to aid the interpretation of shallow reflectors the trade off between resolution and stability of inversion results has been examined models have been optimized by minimizing the variability of static corrections and a monte carlo method has been used to estimate their precision a velocity of 4 6 0 4 km s for the leech river complex lrc compares with velocities of 5 9 0 6 and 5 8 0 3 km s for the neighboring geological units velocity contrasts associated with the change in lithologies may therefore be a contributing factor for generating reflections from the faults that bound the lrc velocities of 5 5 0 4 and 4 6 0 6 km s on either side of the san juan fault suggest that an event identified on several shot gathers may be a reflection from a steeply dipping fault

carbonate mineralogy and faunal relationship in tropical shallow water marine sediments cape comorin india the carbonate mineralogy of recent sediments from the western and eastern continental shelves around cape comorin off the southern tip of india was determined by x ray diffraction analyses the results show that in the sediments where benthic foraminifera are the most abundant component as on the extreme western side and on a narrow strip between the depths of 40 and 50 m on the eastern side gulf of manaar the carbonate mineralogy is dominated by high magnesium calcite in sediments where molluscs exceed other components as on the eastern shelf between 10 and 40 m the most abundant mineral is aragonite low magnesium calcite does not appear to be related to depth or carbonate components

lithoprobe seismic reflection profiling across vancouver island results from reprocessing summary multichannel seismic reflection sections recorded across vancouver island have revealed two extensive zones of deep seismic reflections that dip gently to the northeast and a number of moderate northeasterly dipping reflections that can be traced to the surface where major faults are exposed based on an integrated interpretation of these data with information from gravity heat flow seismicity seismic refraction magnetotelluric and geological studies it is concluded that the lower zone of gently dipping reflections is due to underplated oceanic sediments and igneous rocks associated with the current subduction of the juan de fuca plate and that the upper zone represents a similar sequence of accreted rocks associated with an earlier episode of subduction the high densitylhigh velocity material between the two reflection zones is either an underplated slab of oceanic lithosphere or an imbricated package of mafic rocks reprocessing of data from two of the seismic lines has produced a remarkable image of the terrane bounding leech river fault with its dip undulating from 60 near the surface to 20 at 3 km depth and 38 at 6 km depth

reflections from midcrustal rocks within the mesozoic subduction complex near the eastern aleutian trench seismic reflection data collected in 1973 by western geophysical company show that highly reflective rocks make up the midcrust of the convergent margin adjacent to the eastern aleutian trench these rocks form an arch that strikes obliquely across the strongly expressed northeast southwest structural grain of exposed mesozoic rocks in an earlier report we proposed that the deep events mark the location of either the presently subducting plate or the top of underplated rocks however the short radius of curvature of this arch precludes the possibility that the deep events indicate the igneous oceanic crust instead the deep reflections could be from underplated rocks that have been arched by the imbrication or underplating of strata below the reflective rocks high amplitude water layer and interbed multiples prevent precise connection of shallow and deep geology for example the border ranges fault a suture between major tectonostratigraphic terranes is not revealed on any of our seismic sections we speculate however that one band of reflections that rises toward but does not reach the surface is from the eagle river thrust fault which separates late cretaceous melange from deformed turbidite sequences of the same age

integrated geophysical modelling of terranes and other structural features along the western canadian margin an integrated geophysical data set has been used to develop structural models across the continental margin west of vancouver island canada a modern accretionary complex underlies the continental slope and shelf and rests against and below the allochthonous crescent and pacific rim terranes these terranes in turn abut against the pre tertiary wrangellia terrane that constitutes most of the island gravity and magnetic anomaly data constrained by seismic reflection seismic refraction and other data were interpreted to determine the offshore positions of these terranes and related features iterative 2 5 dimensional forward models of anomaly profiles were stepped laterally along the margin to extend areal coverage over a 70 km wide swath oriented normal to the tectonic features an average model was then developed to represent this part of the margin the pacific rim terrane appears to be continuous and close to the coastline along the length of vancouver island consistent with emplacement by strike

paleogeographic evolution of the united states pacific northwest during paleogene time paleogeographic reconstructions for oregon and washington during paleogene time illustrate a major transition from a dominantly compressional prior to middle eocene time to an extensional tectonic regime this transition resulted in the development of three phases of paleogene basin evolution in the united states pacific northwest during the initial phase basins formed along the continental margin during collision of oceanic islands sediments in these basins were derived from nearby orogenic highlands the second phase of basin development began in middle eocene time and consisted of rapid subsidence of individual basins that formed within a broad forearc region nonmarine basins that formed during this phase were caused by extension possibly associated with transcurrent faulting rapid sedimentation in both marine and nonmarine basins during this time consisted dominantly of sandstone derived from cretaceous plutonic sources far to the east the final stage of basin development was the modification

evidence for underthrusting beneath the queen charlotte margin british columbia from teleseismic receiver function analysis summary the queen charlotte fault zone is the transpressive boundary between the north america and pacific plates along the northwestern margin of british columbia two models have been suggested for the accommodation of the 20 mm yr 1 of convergence along the fault boundary 1 underthrusting 2 internal crustal deformation strong evidence supporting an underthrusting model is provided by a detailed teleseismic receiver function analysis that defines the underthrusting slab forward and inverse modelling techniques were applied to receiver function data calculated at two permanent and four temporary seismic stations within the queen charlotte islands the modelling reveals a 10 km thick low velocity zone dipping eastward at 28 interpreted to be underthrusting oceanic crust the oceanic crust is located beneath a thin 28 km eastward thickening 10 continental crust

the vancouver island seismic project a co crust onshore offshore study of a convergent margin the seismic structure of the british columbia continental margin has been investigated using four reversed refraction profiles the profile across strike extended 350 km from the volcanic arc on the continent to the deep ocean of the juan de fuca plate the three profiles along strike were located on vancouver island on the continental shelf and in the deep ocean on the juan de fuca plate interpretation of the profile along vancouver island yields a well constrained model for the upper crust with velocity increasing from 5 3 km s at the surface to 6 4 km s at 2 km depth to 6 75 km s at 15 5 km depth where the velocity increases sharply to 7 km s the velocity structure of the deep crust and the crustal thickness are poorly constrained four possible velocity functions based on ambiguous first arrivals and or secondary phases interpreted as moho reflections are presented the preferred one includes a deep crustal low velocity zone with a crustal thickness of 37 km models with a constant 7 1 km

lithoprobe southern vancouver island seismic reflection sees through wrangellia to the juan de fuca plate multichannel seismic reflection profiles obtained on vancouver island show that above a zone of decoupling between the north american and juan de fuca plates wrangellia is underplated by two accreted terranes of probable oceanic origin both the zone of decoupling and wrangellia are disrupted by easterly dipping faults some of which are thrusts the crustal structure of wrangellia comprises paleozoic and mesozoic volcanic and sedimentary rocks disposed as roof pendants upon and large irregular masses within a ubiquitous jurassic plutonic and metamorphic complex

reflection signature of seismic and aseismic slip on the northern cascadia subduction interface at the northern cascadia margin the juan de fuca plate is underthrusting north america at about 45 mm yr 1 ref 1 resulting in the potential for destructive great earthquakes2 3 the downdip extent of coupling between the two plates is difficult to determine because the most recent such earthquake thought to have been in 1700 4 occurred before instrumental recording thermal and deformation studies5 indicate that off southern vancouver island the interplate interface is presently fully locked for a distance of 60 km downdip from the deformation front great thrust earthquakes on this section of the interface with magnitudes of up to 9 4 5 have been estimated to occur at an average interval of about 590 yr ref 3 further downdip there is a transition from fully locked behaviour to aseismic sliding where high temperatures allow ductile deformation with the deep aseismic zone exhibiting slow slip thrust events6 here we show that there is a change in the reflection character on seismic images from a thin sharp reflection where the subduction thrust is inferred to be locked to a broad reflection band at greater depth where aseismic slip is thought to be occurring this change in reflection character may provide a new technique to map the landward extent of rupture in great earthquakes and improve the characterization of seismic hazards in subduction zones

lithospheric structure in the southern canadian cordillera from a network of seismic refraction lines lithospheric velocity structure and its relationship to regional tectonics and development of the southern canadian cordillera are derived from a synthesis of interpretations from nine in line seismic refraction wide angle reflection profiles and broadside data recorded during the lithoprobe southern cordillera refraction experiment score and other refraction experiments across southern british columbia and one profile in northwestern washington consistency of the score two dimensional models at their intersection positions is achieved through application of a simultaneous inversion of all relevant traveltime data the cross sectional and map presentations demonstrate the strong degree of three dimensional heterogeneity within the crust and upper mantle a first order characteristic is the continuous increase in crustal velocities westward from the foreland belt to the insular belt the variations do not correlate with the morphogeological belts they do correspond with large scale geological and or

cocorp deep seismic reflection traverses of the u s cordillera summary cocorp seismic reflection traverses of the u s cordillera at 40 n and 48 5 n latitude reveal some fundamental similarities as well as significant differences in reflection patterns on both traverses autochthonous crust beneath thin skinned thrust belts of the eastern part of the cordillera is unreflective immediately to the west the cordilleran interior is very reflective above a flat prominent reflection moho mesozoic accreted terranes in the western part of the orogen are underlain on both traverses by very complex reflection patterns in constrast to more easily deciphered patterns beneath areas of cenozoic accretion the prominent reflection moho beneath the orogenic interior on both transects probably evolved through a combination of magmatic and deformational processes during cenozoic extension the main differences between the two traverses lie in the reflection patterns of the middle and lower crust in the cordilleran interior these differences are probably related to the way cenozoic extension was accommodated at depth laminated middle and lower crust above the reflection moho in the western basin and range 40 n may be related to magmatism ductile pure shear and large scale transposition during cenozoic extension by contrast beneath the eastern basin and range 40 n and the orogenic interior in the nw united states 48 5 n cenozoic extension was probably accommodated along dipping deformation zones throughout the crust

crustal structure beneath the strait of juan de fuca and southern vancouver island from seismic and gravity analyses 1 wide angle and vertical incidence seismic data from seismic hazards investigations in puget sound ships gravity modeling and seismicity are used to derive two dimensional crustal models beneath the strait of juan de fuca the eocene volcanic crescent siletz terrane is significantly thicker than previously recognized and extends from near the surface to depths of 22 km or greater for the northern strait a weak midcrustal reflector dipping east from 12 to 22 km depth is inferred from wide angle reflections a stronger deeper reflector dipping eastward from 23 to 36 km depth is associated with the top of reflector band e a zone of high reflectivity on coincident multichannel seismic mcs data interpreted as a shear zone a high velocity zone 7 60 0 2 km s 1 between these reflectors is interpreted as a localized slice of mantle accreted with the overlying crescent siletz terrane for the southern strait no deep high velocity layer is observed and the e band reflectivity is weaker than to the north a strong deep reflector interpreted as the oceanic moho dips eastward from 35 to 42 km seismicity within the subducting slab occurs mainly above the inferred oceanic moho gravity modeling constrained by the wide angle seismic models and seismicity is consistent with the inferred large thickness of crescent siletz and high density rocks 3030 kg m 3 in the lower crust

microorganisms in deep sea hydrothermal plumes the study of hydrothermal vents at oceanic spreading centres has led to a re evaluation of some basic tenets concerning energy flux through oceanic ecosystems and the sources and sinks for dissolved ions in sea water hydrothermal vents vary considerably from relatively low temperature 25 c fluid discharges to the spectacular high temperature 350 c black smokers1 3 the high temperature vents give rise to buoyant plumes which can be detected hundreds of kilometres away from ridge crests4 5 in the immediate vicinity of hydrothermal vents chemoautotrophic bacteria are present in vent fluids6 8 attached to rock surfaces9 10 and as endosymbionts in certain macro fauna11 deep sea hydrothermal plumes have not as yet been examined for the presence of bacteria we now report the presence of elevated bacterial biomass in a hydrothermal plume originating from the juan de fuca ridge and discuss the potential geochemical significance of these microorganisms

sulphide mineralisation in the deep sea hydrothermal vent polychaete alvinella pompejana implications for fossil preservation abstract hydrothermal vent fauna particularly vestimentiferan and polychaete worm tubes are occasionally preserved in the geological record the early stages of mineralisation are particularly important in defining whether or not preservation will occur and they are poorly understood tube samples of the polychaete worm alvinella pompejana collected from 13 n on the east pacific rise have been studied to identify the processes occurring during early pyrite marcasite mineralisation iron sulphide mineralisation is present within the walls of the organic dwelling tube and is induced by microbial fauna preserved within the tube micro layers various microorganisms were observed coating the inner tube surfaces together with 10 100 m sized fe and zn sulphide particles precipitated from vent fluids the microbes and particulate sulphides become entombed within the tube wall as further layers of organic material are secreted by the worm during tube building episodes this results in a laminated tube structure being formed composed of alternating layers of tube material and microbial sulphide rich interlayers the microbial sulphide layers provide a template for further mineralisation and replacement of the microbes with pyrite while degradation of the organic components occurs the iron monosulphides mackinawite and greigite have been identified as intermediatory phases that occur as precursor minerals during the formation of pyrite later marcasite mineralisation is observed to form over some of the pyritised organic layers once mineralisation has replaced most of the organic tube material the structure will then be preserved along with the host sulphide body these observations enhance our understanding of the mechanisms of fossil pyritisation in fine scaled organic structures throughout the geological record

models of convergent boundary tectonics implications for the interpretation of lithoprobe data physical models of convergent boundary processes can provide insights into compressional orogens such as those studied by lithoprobe we summarize the qualitative tectonic style of a series of mode

deep sea smokers windows to a subsurface biosphere since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from smoker vents on the east pacific rise the widely accepted upper temperature limit for life based on pure culture data has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees c many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees c we have postulated not only higher temperatures than these under deep sea hydrostatic pressures but also the existence of a biosphere subsurface to accessible seafloor vents new geochemical information from the endeavour segment of the juan de fuca ridge indicative of subsurface organic material caused us to re examine both the literature on hyperthermophilic microorganisms cultured from deep sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the endeavour segment here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of endeavour smoker fluids a case in keeping with rapidly evolving geophysical understanding of organic stability under deep sea hydrothermal conditions

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position