osseous skeletal material and fish scales in marine sediments under the oxygen minimum zone off northern and central chile abstract the significance of whale falls for the study of the biogeography evolution and biodiversity of deep sea biota has been recently recognized by international programs since large carcasses are known to give rise to biogenic chemosynthetic ecosystems however the plain accumulation of smaller bone material in the shallower settings of the continental shelf and upper slope under the hypoxic conditions of the oxygen minimum zone omz has received much less attention here we describe new findings of skeletal material and fish scales in marine sediments under the omz off northern and central chile which combined with previous reports for the study area lead us to suggest the existence of a band in the benthos of accumulation of bones and scales extending at least twenty degrees in latitude 18 38 s future studies should focus on the characterization of biotic communities living upon these resources in order to elucidate their peculiarities and importance in the eastern south pacific

crustal shortening in the palmyride fold belt syria and implications for movement along the dead sea fault system an edited version of this paper was published in tectonics by the american geophysical union agu copyright 1990 agu see also http www agu org journals tc http atlas geo cornell edu syria chaimov tectonics 1990 html

high salinity fluid inclusions formed from recycled seawater in deeply subducted alpine serpentinite abstract the origin of high pressure brines has been investigated in the erro tobbio peridotite western alps a mantle slice that was exposed to the seafloor of the mesozoic ligurian piedmontese tethys and was later involved in alpine subduction hydrothermal alteration by seawater derived fluids led to replacement of the mantle assemblage by cl bearing serpentine 0 35 wt cl brucite 0 2 wt cl and alkali bearing phyllosilicates 0 2 wt cl 0 2 0 55 wt na2o 1 5 wt k2o relics of these hydrous phases occur in olivine titanian clinohumite antigorite assemblages formed at 2 5 gpa and 550 600 c during partial devolatilization and veining of the hydrothermally altered peridotite the high pressure phases lack chlorine and alkalis and are coeval with fluid inclusions trapped in the syn eclogitic veins the inclusions are salt saturated and contain up to 50 wt cl na k mg and fe high fluid chlorinity was probably achieved during rehydration of relict mantle minerals and deposition of hydrous phases in the veins the data presented suggest that the seafloor hydrothermal signature was inherited by the eclogitic fluid due to partitioning of chlorine and alkalis into the fluid phase the presence of salty brines in eclogitized hydrous peridotites can indicate deep recycling of seawater derived fluids hydrous ultramafic systems can therefore act as large scale carriers of seawater into the mantle

effects of hydrothermal alteration on the compositions of chromian spinels chromite spinels in hydrothermally altered rocks from fracture zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the josephine ophiolite california display a wide variety of compositions alteration of the spinel may not be visible in thin section the primary composition changes accompanying hydrothermal alteration are increase in cr cr al and or fe2 fe2 mg in general altered spinel grains associated with hornblende and chlorite show an increase in cr cr al from core to rim altered spinel grains associated with serpentine show an increase in fe2 fe2 mg from core to rim but may not show an increase in cr cr al the compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende and from reaction of hornblende to form chlorite these observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes further the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent

ultramafic rocks of a fracture zone ophiolite north cascades washington abstract the ingalls complex was deformed in a late jurassic oceanic fracture zone an unusually diverse group of ultramafic tectonites comprise three units in this ophiolite unit 1 consists mostly of poorly to moderately foliated harzburgite and dunite characterized by porphyroclastic textures irregular shaped and tabular dunite bodies probably represent intrusive bodies or residues of partial melting voluminous unit 2 consists mostly of poorly to strongly foliated iherzolite and clinopyroxene bearing harzburgite plagioclase peridotite is present locally olivine and enstatite generally define equigranular mosaics or weakly porphyroclastic textures clinopyroxene however in some samples displays only weak deformation compositional zoning simple growth twins and interstitial commonly poikilitic texture clinopyroxene and plagioclase in these samples probably formed from a melt after recrystallization of olivine and enstatite indicating that these iherzolites are impregnated peridotites other iherzolites and clinopyroxene bearing harzburgites may represent weakly depleted mantle pods of metagabbroic gneiss within unit 2 probably are small intrusions that were deformed as they cooled unit 3 represents a major high temperature 700 900 c shear zone that separates units 1 and 2 and consists of strongly foliated commonly mylonitic iherzolites and hornblende peridotites the latter are the most strongly foliated ultramafites and olivine in them records stresses as high as 275 mpa the abundance of hornblende implies a genetic relationship between mylonitization and the hydration and metasomatism necessary to form such rocks from iherzolites mineral chemistry and geothermometry are typical of mantle tectonites in many ophiolites and oceanic fracture zones there is a particularly strong similarity between the spinels in the ingalls complex and the spinels from the owen and vema fracture zones hornblende in unit 3 ranges from edenite to edenitic hornblende calculated temperatures from cpx opx pairs in unit 2 range from 950 to 1000 c these data are best explained by horizontal and vertical displacements in oceanic fracture zones which may juxtapose lithosphere formed at different structural levels and with different petrologic histories unit 1 represents a block of upper mantle which probably experienced convective upwelling and partial melting beneath a spreading ridge near its intersection with a fracture zone during convective upwelling at least parts of the upper mantle represented by unit 2 were impregnated by a melt the impregnated iherzolite may be accounted for by the edge effect at a fracture zone or reduced melt production at a fracture zone due to ribbon spreading the mylonite zone of unit 3 reworks iherzolites and harzburgites which were originally part of the block represented by unit 2 and probably records deformation in the active segment of the fracture zone these observations document the complexities that may occur in ultramafic rocks within oceanic fracture zones they also suggest that impregnation metasomatism and high stresses are important in these zones

mesozoic and cenozoic deformation inferred from seismic stratigraphy in the southwestern intracontinental palmyride fold thrust belt syria this paper was published in the geological society of america bulletin the geological society of america retains the copyright to this paper geological society of america p o box 9140 boulder co 80301 9140 usa see also http www geosociety org http atlas geo cornell edu syria chaimov gsa bull 1992 html

the pacific decadal oscillation and changes in anchovy populations in the northwest pacific the pacific decadal oscillation pdo has been identified as an important driver for fluctuation of fish populations on the eastern pacific ocean however the relationship between changes in fish population and climate oscillations on a decadal time scale in the northwest pacific is still unclear due to the lack of reliable long term time series data in the present study a time series of engraulis japonicus japanese anchovy populations was reconstructed using the density of sedimentary fish scales in the yellow sea basin e japonicus populations and the pdo index showed similar patterns on a decadal time scale our results confirm that climate is a major driver of ecological changes on a decadal time scale and indicate that suitable sea water temperature might be the main forcing of anchovy migration this work also demonstrates the potential of predicting changes in fish population based on climate records

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

seawater basalt reaction and the origin of greenstones and related ore deposits massive sulfide deposits of copper zinc and iron and associated stringer deposits multicomponent equilibrium calculations of the reaction of seawater with tholeiitic basalt at 300 degrees c followed by calculation of the effects of cooling the resultant solution to 25 degrees c and mixing it with seawater the calculated mineralogy and zoning patterns resemble many natural ore assemblages observed in deposits of the kuroko type east pacific rise west shasta district according to the calculations silica should be abundant in the massive sulfide deposits modified journal abstract

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

a holocene record of marine fish remains from the northeastern pacific abstract ocean drilling program leg 169s retrieved a complete holocene sequence from saanich inlet british columbia canada fish and diatom remains were extracted from sediments at site 1034 very small fish bones teeth and scales were ubiquitous except in the lowermost glaciomarine clays scales degraded with depth in the identifiable fraction pacific herring were the most abundant with pacific hake and cartilaginous fish yielding significant fractions fish remains appear just before 12 000 bp but greatest diversity does not occur until about 6500 bp a smoothed abundance curve highlights two periods of maximal abundance at about 1500 and 6500 bp abundances in the last 1000 years are lower than the rest of the record a correlation with abundances of seven phytoplankton taxa is significant diatoms explain about a third of the variance this study demonstrates the use of fish and diatoms from the same paleosedimentary matrix to examine millennia scale correlations between primary and tertiary production

seismic reflection structure of intracratonic palmyride fold thrust belt and surrounding arabian platform syria copyright 1990 aapg reprinted by permission of the aapg whose permission is required for further use see also http aapgbull geoscienceworld org http atlas geo cornell edu syria mcbride aapg 1990 html

rare gases water and carbon in kaersutites abstract kaersutites from kakanui new zealand and from three localities in the southwestern united states have been analyzed for rare gases water and carbon to investigate the volatile signature of the sub continental mantle this study does not confirm the high 3 he 4 he and 21 ne 22 ne ratios reported by saito et al 1 for the kakanui kaersutite instead a 3 he 4 he ratio of 6 r a and atmospheric 21 ne 22 ne ratios were measured which are consistent with our current knowledge of the earth s mantle a low 40 ar 36 ar of 320 and more than 10 8 cm 3 g of 36 ar confirms the argon results of saito et al and indicates that significant quantities of 36 ar reside in this portion of the mantle kaersutites from the southwestern united states arizona have a heterogeneous helium isotope signature ranging from 8 8 r a at san carlos to 0 46 at hoover dam all d h ratios for the water in kaersutites 56 to 78 represent typical mantle values with no apparent correlation with 3 he 4 he the correlation of increasing carbon content 140 400 ppm with increasing 13 c 24 5 to 16 7 may reflect differences in the proportions of oxidized and reduced carbon in these samples

bouguer gravity trends and crustal structure of the palmyride mountain belt and surrounding northern arabian platform in syria copyright 1990 geological society of america see also http dx doi org 10 1130 2f0091 7613 281990 29018 3c1235 3abgtacs 3e2 3 co 3b2 http atlas geo cornell edu syria best 1990 html

behavior of li and its isotopes during serpentinization of oceanic peridotites analyses of li and li isotopes in serpentinized peridotites have been performed using thermo ionisation mass spectrometry tims and secondary ion mass spectrometry sims techniques on samples collected from the southwest indian ridge swir in the bulk samples li concentrations range from 0 6 to 8 2 ppm while whole rock 6li values range from 2 9 to 14 in situ analyses display a greater range in both li concentration 0 1 19 5 ppm and li isotopic composition 27 to 19 with the serpentinized portions having higher li concentrations than the associated relict phases these variations may reflect changes in li partitioning and isotopic fractionation between serpentine and fluid with temperature and water rock ratio they may also be explained by changes in the composition of the serpentinizing fluid over the course of serpentinization as the serpentine forms by interaction with a circulating fluid it preferentially removes 6li causing the li in the fluid to become isotopically heavier the isotopic composition of the initial hydrothermal fluid is dominated by basalt derived li which easily overwhelms the very low li content originally present in seawater as this fluid circulates through ultramafic rocks it induces the formation of serpentine that incorporates this mantle derived li hence li in serpentine is mainly derived from oceanic crust rather than from seawater and serpentinization involves li recycling within this crust consequently li isotopes are good tracers of the hydrothermal contribution in serpentinizing fluid these results imply that serpentinized peridotites are probably only a minor sink of oceanic li

crustal structure of central syria the intracontinental palmyride mountain belt an edited version of this paper was published in tectonophysics by elsevier science copyright 1992 elsevier science see also http dx doi org 10 1016 0040 1951 92 90395 m http atlas geo cornell edu syria al saad et al 1992 html

sr isotopic constraints on hydrothermal alteration of ultramafic rocks in two oceanic fracture zones from the south atlantic ocean ultramafic rocks from the islas orcadas and shaka fracture zones have been progressively hydrated starting at temperatures greater than 700 c and continuing to less than 250 c the hydration is manifest as a sequence of alteration minerals including in order of decreasing temperature amphibole talc talc plus secondary olivine chlorite secondary clinopyroxene prehnite and serpentine early high temperature minerals display lower87sr 86sr ratios and higher k rb and sr than later lower temperature minerals one explanation for the change in87sr 86sr ratios is that early high temperature reactions are the result of hydration by fluids characterized by a relatively strong basaltic geochemical signature and the later lower temperature alteration is the result of hydration by fluids characterized by a relatively weaker basaltic signature and relatively stronger seawater signature

late holocene paleofish populations in effingham inlet british columbia canada abstract paleontological studies of fish remains in laminated sediments provide a proxy relationship between fish populations and ocean climate this study examines climate variability from approximately 500 y b p to 4000 y b p as recorded in fish remain abundances primarily scales collected from laminated sediments within effingham inlet on the west coast of vancouver island british columbia the study also discusses technical issues involving fish remains from laminated sediments including sampling resolution sediment volume identification of remains and appropriate abundance considerations the dominant species in the assemblage include northern anchovy and pacific herring with lesser percentage abundances from rockfish hake elasmobranches and surfperch the data indicate that northern anchovy experienced a shift in scale deposition abundance at approximately 2800 y b p with not only a greater total abundance but also a greater consistency of deposition with time pacific herring underwent cyclical deposition that changed little through time statistical analysis reveals that none of these species is directly responding to climatic signals as indicated in the lithological and palynological record but that this could have been partially due to the sampling resolution of the piston core analysis indicates a lack of correlation between the two dominant species as might be expected on the basis of their opposing lifestyle strategies with respect to sea surface temperatures with appropriate sampling strategies paleohistorical fish remains from laminated sediments reflect changes in population structure and behaviour for some species illustrate basic secondary trophic information and provide potential clues to basin scale oceanographic climatological variability

geologic investigations in the cayman trough evidence for thin oceanic crust along the mid cayman rise the mid cayman rise is a 110 km long accreting plate boundary 2cm yr full rate characterized by a deep rift valley eighteen transponder navigated dives were made by the submersible alvin along the rift valley walls in two areas on opposite sides of the rift valley the relief of the walls is produced by a large number of inward facing small throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m from these escarpments 142 samples were collected and gabbroic rocks 116 samples characterized by a wide range of compositions and a complex metamorphic history predominate in number over other rock types basalt serpentinized ultramafic we interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the mid cayman rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt this carapace is und

a post glacial isotope record of primary production and accumulation in the organic sediments of saanich inlet odp leg 169s changes in palaeoproduction in saanich inlet british columbia were examined from sediments using total organic carbon contents and stable carbon isotope ratios sediments were obtained from holes 1033b and 1034b of ocean drilling program leg 169s these cores contain two distinct zones 1 carbon poor corg 0 5 wt glaciomarine muds from the upper pleistocene and 2 carbon rich corg1 3 wt well laminated sediments from the holocene a slight monotonic rise in corg and 13corg throughout the holocene suggests that primary production in the inlet has been steadily increasing some influence of changes in local land vegetation is also evident sharp decreases in corg and 13corg in the early holocene probably represent material deposited from a major flood differences in organic 13corg between light and dark laminae are related to seasonal variations in species composition temperature and nutrient conditions

existence of interplane earthquakes and neutral stress boundary between the upper and lower planes of the double seismic zone beneath tohoku and hokkaido northeastern japan abstract using data from the recently constructed nationwide dense seismic network we determined the hypocenters and focal mechanisms of many intermediate depth intraslab earthquakes within the pacific slab beneath northeastern japan the results show that in addition to the upper and lower planes of the double seismic zone a considerable number of intraslab earthquakes also occur between the two planes this interplane earthquake activity is not homogeneously distributed in space being high beneath eastern hokkaido and the fore arc regions of southeast and central tohoku the focal mechanisms of the interplane earthquakes tend to be of the down dip compressional type dc in tohoku and the hokkaido corner but down dip tensional type de in eastern hokkaido upper plane earthquakes are characterized by dc type stress while lower plane earthquakes are de type in both tohoku and eastern hokkaido the existence of interplane earthquakes enables estimation of the position of the neutral plane between the upper plane dc stress and the lower plane de stress we did so by applying stress tensor inversions to focal mechanism data obtained in the present study and japan meteorological agency jma data the results show that the neutral plane is located about 22 km beneath the upper plate interface beneath tohoku but only about 10 km beneath the upper surface beneath eastern hokkaido this difference in the location of the neutral plane may be due to the difference in buoyancy force exerted by the less dense metastable olivine wedge that is a result of the oblique plate subduction beneath hokkaido comparison of large intraslab earthquakes beneath the two regions shows that their aftershock areas are limited by the neutral plane suggesting that large earthquake ruptures are confined to either the dc or de stress field and do not go beyond the neutral plane

the use of sedimentary fish remains for interpretation of long term fish population fluctuations abstract the varved marine sediments of saanich inlet british columbia retain a detailed record of fish remains we examine methods to process and interpret sedimentary fish remains and explore sources of bias in transfer and preservation through time in high resolution box cores spanning the last 130 years scales outnumber vertebrae a consistent record across replicates is recognizable once outliers are removed pacific herring and hake remains make up over 90 of the identifiable remains cores from odp leg 169s covered the entire holocene scale recovery is poor so the record is based on fragmented bones bones associated with the backbone gill arches and fins yield the best taxonomic information in both core sets low frequency signals are resolved using a five sample running mean because the data series in the short cores are autocorrelated spectral analysis is the best approach to identify high frequency signals that explain much variance in the scale data high cross spectral coherencies confirm a basin wide signal in scale deposition the herring scale deposition data are compared to recent fishery biomass estimates and confirm similarities in timing of low frequency trends and signals experiments with herring in large tanks explore the transfer of scales from fish to the ocean floor shedding and predation are found to provide a regular rain of scales to the sediments overall the sedimentary fish remains record in basins with good preservation shows promise as a means to identify generalized long term fish histories through the holocene as well as a more specific pacific herring and hake story over the last century

chemical transfer between mantle xenoliths and basic magmas evidence from oceanic magma chambers the trinity ophiolite northern california abstract the trinity ophiolite consists of small magma chambers inside a large mantle body xenoliths of mantle peridotite occur both in gabbroic cumulates along the walls and in the matrices of ultrabasic breccias on the floors of the magma chambers field relationships and petrographic data suggest that these fragments of original mantle peridotite were modified by contact with basic magmas by modal metasomatism quantitative elemental mass transfers determined from the composition volume and density variations of reacting minerals demonstrate both closed and open system conditions for the major si al ti na ca fe and mg and trace elements cr ni in the open system material gains and losses provide information on the composition of the fluid taking part in the metasomatic reaction during a first stage of metasomatism the mantle xenoliths were affected by high temperature reactions at 600 to 925 c they resulted from the interaction between solid mantle lherzolites and basic melts the reactions are 1 1 those forming orthopyroxene magnetite simplectite 2 2 those forming plagioclase magnetite corona 3 3 clinopyroxene spinel i pargasitic hornblende spinel ii chemical interactions between the upper mantle and oceanic magma chambers occurred as soon as the basic magmas had ascended through the upper mantle the chemically modified magmas within oceanic magma chambers were depleted in ti fe and na this could partly explain regional variations of the chemical compositions of primary magmas produced beneath slow spreading ridges the breakdown of olivine to orthopyroxene and magnetite participates in the control of the partition of magnetic fe ti oxides between oceanic crust and mantle during the second stage the serpentinization of olivine and the production of talc were superimposed on the products of the first stage these reactions require large amounts of h2o the hydrothermal fluid was probably seawater it circulated in the brecciated area along the walls and floors of the magma chambers located at shallow depths such structural discontinuities thus played the role of penetration channels favoring seawater circulation in the oceanic crust all the chemical reactions examined suggest a significant open system element transfer by infiltrating melts or circulating fluids the results of this study suggest that caution is required in the interpretation of mineralogical and chemical information provided by mantle xenoliths carried to the surface by ascending magmas

high temperature alteration of abyssal ultramafics from the islas orcadas fracture zone south atlantic ultramafic rocks dredged from the islas orcadas fracture zone along the sw indian ocean ridge 6 e and 54 s show evidence of progressive hydration beginning at temperatures greater than 600 c and perhaps as high as 900 c and continuing to less than 50 c there are two principal types of alteration present in the ultramafic rocks both of which are the result of hydration reactions the first type of alteration involves hydration of original clinopyroxene orthopyroxene and olivine to amphibole talc secondary olivine and serpentine the second is a vein type of alteration and results in the formation of veins of amphibole chlorite talc and serpentine the alteration appears to be episodic the sequence of events suggested by the petrography is 1 clinopyroxene altering to amphibole 2 orthopyroxene altering to talc or talc olivine 3 supersolvus hornblende veining 4 coexisting actinolite hornblende veining 5 chlorite chlorite actinolite or chlorite secondary clinopyroxene veining 6 talc veining 7 serpentine veining and 8 pervasive serpentinization the alteration fluid is most likely seawater it is suggested that the high temperature alterations may reflect seawater circulation into the upper mantle

a review of the tectonics of the northern middle east region the structure of the northern part of the arabian platform is reviewed in the light of hitherto unpublished exploration data and the presently accepted kinematic model of plate motion in the region the palmyra and sinjar zones share a common history of development involving two stages of rifting one in the triassic jurassic and the other during late cretaceous to early tertiary times deformation of the palmyra zone during the mio pliocene is attributed to north south compression on the eastern block of the dead sea transcurrent system which occurred after continental collision in the north in southeast turkey the asymmetry of the palmyra zone is believed to result from northward underthrusting along the southern boundary facilitated by the presence of shallow triassic evaporites an important nw se cross plate shear zone has been identified which can be traced for 600 km and which controls the course of the river euphrates over long distances in syria and iraq transcurrent motion along this zone resulted in the formation of narrow grabens during the late cretaceous which were compressed during the mio pliocene to a large extent present day structures in the region result from compressional reactivation of old lineaments within the arabian plate by the transcurrent motion of the dead sea fault zone and subsequent continental collision

cumulate gabbros from the southwest indian ridge 54 s 7 16 e implications for magmatic processes at a slow spreading ridge a diverse volcanic and plutonic rock suite was recovered from the center of the 80 km long ridge segment of the southwest indian ridge 54 s 7 16 e between the islas orcadas and shaka fracture zones the cumulus nature of the gabbroic rocks in the suite is indicated by phase modal and cryptic layering igneous lamination and low incompatible element abundances we present a mass balance model for calculating the proportions and compositions of cumulus phases and crystallized intercumulus liquid from bulk rock major element compositions the model is based on the ability to define a compositional array of basaltic liquids and on the assumption that cumulus minerals are initially in equilibrium with trapped liquid calculated proportions of trapped liquid range from 3 15 values that are characteristic of adcumulates to mesocumulates models of postcumulus crystallization indicate significant enrichments of incompatible elements and buffering of compatible elements in residual trapped liquids thus explaining the high tio2 contents observed in magnesian clinopyroxenes cumulus phase assemblages and compositions suggest solidification in shallow level magma chambers but disequilibrium plagioclase compositions suggest some crystallization at greater depth furthermore basalt compositions projected onto the olivine clinopyroxenequartz pseudoternary suggest magma generation over a range of pressures from less than 10 to greater than 20 kb as well as polybaric fractional crystallization we suggest that the southwest indian ridge is characterized by low magma supply with small batches of melt that either ascend directly to the surface having undergone limited polybaric crystallization or are trapped in shallow crustal magma chambers where they evolve and solidify to form cumulate gabbros the adcumulus nature of the gabbros investigated here suggests slow cooling rates typical of large intrusions implying relatively large but ephemeral magma chambers below segments of the southwest indian ridge

metamorphic history of serpentinite mylonites from the happo ultramafic complex central japan serpentinite mylonites from the happo ultramafic complex show evidence of two stages of mylonitization at different temperature conditions peridotite mylonites exhibit two types of olivine porphyroclasts and neoblasts produced at the earlier stage the olivine neoblasts have a stretching lineation with a fabric suggesting plastic deformation along 0 1 0 0 0 1 in addition to the olivine fabric the stable association of olivine orthopyroxene and tremolite in the peridotites that survived later serpentinization and the si and na contents of tremolite suggest that the earlier mylonitization took place at temperatures between 700 and 800 c later mylonitization was associated with high temperature serpentinization to form serpentinite mylonites in contrast to a common type of serpentinite in orogenic belts the serpentinite mylonites are cohesively foliated rich in olivine and diopside and poor in antigorite the diopside has low al cr and na contents typical of a retrograde origin and the olivine has a homogeneous composition except in areas subjected to contact metamorphism at a later stage modal composition and mineral chemistry suggest that the serpentinite mylonites were formed by a hydration reaction of tremolite and olivine to produce diopside and antigorite under stable conditions of olivine at temperatures between 400 and 600 c later stage mylonitization has preferentially been superimposed on the earlier stage mylonite zone with a common direction of foliation the difference in temperature between the two mylonitization stages suggests that the shear zone was episodically active during the emplacement of the happo complex conditions of relatively high temperature for serpentinization at a convergent plate boundary and high permeability caused by the early mylonitization favoured the formation of the serpentinite mylonites

anchovy population and ocean climatic fluctuations in the humboldt current system during the last 700 years and their implications a marine sedimentary record collected from 87 m water depth in a coastal environment of the humboldt current system mejillones bay 23 s northern chile was used to reconstruct the past 700 years of ocean climatic conditions and to study the influence of any changes on anchovy population dynamics we analyzed quartz organic carbon total nitrogen alkenones and fish scales four stratigraphic units in the sediment column correspond with fluctuations in these and other proxies low scale deposition rate sdr values from 1330 to 1420 suggest a low abundance of anchovy in this coastal environment three subsequent cycles of ca 170 years each showed an increase and decrease of anchovy populations which is in agreement with changes in the wind regime sea surface temperature and primary productivity since ca 1840 marked fluctuations of sdr have been observed probably as a consequence of the onset of a different oceanographic regime characterized by intensified southern winds and upwelling colder surface waters higher primary productivity and enhanced la nina like interdecadal variability an increase of the anchovy population was observed until halfway through the 20th century followed by a decrease even though water temperature decreased and primary productivity increased this situation is likely the consequence of the increased fishery activity that developed in this zone during the last 60 years after analyzing the results obtained for anchovy sdr we can determine that there is a relation between the abundance of this species and phases of the pacific decadal oscillation pdo in which an increase in the sdr coincides with a pdo cold phase while a decline coincides with a warm phase fast fourier transformation analysis applied to the time series obtained from the mejillones sediment core and to the north atlantic oscillation nao the pdo and the solar irradiance index time series shows three different decadal cycles 80 100 years 61 75 years and 45 48 years approximately furthermore the results of this study suggest that both the pdo and the nao and the biogeochemical markers of mejillones exhibit periodicities that fall within the 80 to 100 year gleissberg solar cycle indicating that global solar radiation plays a key role in the local ocean climatic processes and confirming teleconnection linkages between widely separated regions

a holocene record of diatom and silicoflagellate microfossils in sediments of saanich inlet odp leg 169s odp leg 169s laminated sediment cores provided a unique opportunity to examine changes in the siliceous phytoplankton community of saanich inlet these laminated sediments are rich in diatom and silicoflagellate remains as a result of the inlet s high production and excellent preservation our results suggest that species composition and abundance of diatoms and silicoflagellates in the inlet have changed very little since the inlet s formation carbon and opal data indicate an increase in primary productivity with time which is not apparent in the fossil data however the discrepancy between data sets may be due to changes in grazer activity which could have reduced the number of identifiable fossils individual species were useful for identifying changes in the inlet some planktonic diatoms suggest that nutrient supply was highest in the early mid holocene increases in the abundance of a partially benthic diatom paralia sulcata follow variations in sea level and availability of benthic habitat in the inlet a large peak of the silicoflagellate dictyocha fibula corresponds to a catastrophic flood event in the early holocene which probably washed terrestrial material and low salinity water from the british columbia mainland into saanich inlet fossil data were also analyzed to infer past changes in the environment using a weighted averaging calibration and regression technique these data suggest that only minor variations in sea surface temperature have occurred

a new high resolution radiocarbon bayesian age model of the holocene and late pleistocene from core md02 2494 and others effingham inlet british columbia canada with an application to the paleoseismic event chronology of the cascadia subduction zone annually laminated sediments from the anoxic inner basin of effingham inlet pacific coast of vancouver island british columbia canada yield a high resolution 42 m paleoenvironmental record from the present to about 14 ka 14c bp 17 ka cal bp a new age model based on 68 radiocarbon dates from twigs and small plant material from the 40 m core md02 2494 and 2 m freeze cores from the surface is anchored by the mazama ash and varve counting a poisson process sedimentation model is used applying a new method to determine the poisson k value giving a realistic age model compatible with the multi proxy core data twenty one seismites which are lithofacies in the effingham cores that may be representative of seismically triggered mass wasting events are identified and dated precisely then compared with the chronology of the deep sea turbidite record farther south in the cascadia subduction zone csz to determine if regional sediment disturbances can be identified with 16 proposed correlations

tectonics of slow spreading mid ocean ridges and consequences of a variable depth to the brittle ductile transition geophysical evidence especially microearthquakes that extend into the upper mantle beneath the inner floor of the mid atlantic and gorda ridges indicates that the axial magma chamber episodically freezes beneath slow spreading ridges freezing of the axial magma chamber will result in a variable thermal structure that has important tectonic consequences most importantly large near axis faults will intersect as the brittle ductile transition deepens causing some of the faults to become locked the topographic effect of fault locking will be a variation in the width of the inner floor from narrow 10 km when a magma chamber is absent the deep microearthquakes also imply that faults at slow spreading ridges extend into the upper mantle the nature of these faults at depth is unknown but the following hypotheses are presented 1 the faults may be planar and pass downward into aseismic ductile shear zones and 2 the faults may sole into a flat detachment fault defining a sharp boundary between brittle faulting and homogeneous ductile flow such low angle normal faults are common in continental extensional domains large scale tilting 50 70 is probably common at slow spreading ridges and implies either listric faulting or rotation of planar faults and fault blocks similar to toppling dominoes calculations of temperatures at the brittle ductile transition are made assuming olivine and diabase rheologies for the mantle and crust respectively the temperature is approximately 800 c when the transition is at 8 km depth and approximately 600 when the transition is at 2 km depth the strength of the lithosphere varies dramatically with the rise and fall of the brittle ductile transition as magma chambers form and subsequently freeze strong lateral temperature gradients will be present when a magma chamber is formed resulting in localization of faulting within thin weak crust above the chamber when the magma chamber freezes lateral temperature gradients will be small and the strength of the lithosphere will be similar over a wide area this results in active faulting occurring over a width of as much as 60 km some ophiolites possibly provide insights to the tectonic processes at slow spreading ridges the entire crustal section of the josephine ophiolite was tilted by approximately 50 prior to deposition of overlying pelagic sediments this tilting probably took place by faulting suggesting that oceanic faults extended into the upper mantle possible oceanic faults have been identified in the josephine ophiolite but their oceanic origin cannot be established beyond doubt

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

compositional heterogeneities in upper mantle peridotites from the zambales range ophiolite luzon philippines abstract the zambales range of western luzon philippines is formed largely of mafic and ultramafic rocks that constitute a classic ophiolite assemblage we recognize two distinct blocks acoje and coto on the basis of mineralogy chemistry and the thickness of crustal sections we interpret these ophiolite units as remnants of crust and mantle from supra subduction zone settings the coto block from a backarc basin and the acoje block from a nascent island arc hawkins and evans 1983 evans 1983 we present data to contrast the peridotite sections of the two different blocks and discuss their origin both peridotite units are primarily harzburgite with minor dunite in both units there are large concentrations of chromite that form ore deposits there are subtle changes in lithology and mineralogy in each unit that are correlated with depth below the crustal section dunite orthopyroxene poor harzburgite and chromite increase in abundance upward toward the geological moho and the base of cumulate ultramafic rocks of the lower crustal section the upward changes in lithology are matched by changes in modal abundance and composition of the minerals that document increasing upward depletion of the peridotite units in basaltic components mineral show an increase in mg and cr and a decrease in fe ca and al these changes are best developed in the uppermost 1000 m of each peridotite unit we attribute these compositional changes mainly to different extents of partial melting to a lesser extent the changes reflect local exchange between mafic melts in transit to the surface and depleted mantle and exchanges during metamorphic recrystallization the crustal rocks of the coto block resemble rocks from backarc basins the uppermost levels of the peridotite comprise rocks similar to many abyssal peridotites the acoje block crustal rocks are best explained as remnants of a nascent island arc the upper mantle peridotite from acoje is more depleted than that from coto having higher mg mg fe in silicates higher cr cr al in chromites a greater proportion of dunite and less clinopyroxene in the harzburgite the more extensive depletion of the acoje block island arc peridotite probably is due to the multiple melting events that were imposed on these rocks during their evolution in first generation of ocean crust and then later the generation of island arc crust

palynological records of red tide producing species in canada past trends and implications for the future abstract increases in red tides and other harmful algal blooms habs during the past 50 yr on both the atlantic and pacific coasts of canada suggest that global scale factors such as climate change and increased international shipping trade are the driving forces because the historical record is too short to understand the long term dynamics of habs the holocene history of harmful phytoplankton species was examined using ultra high resolution studies annual to decadal scale of dinoflagellate cysts as a proxy for red tide production paleoecological transfer functions were then applied to the cyst assemblage data to determine correlations with changes in sea surface temperature and salinity pacific records were obtained from varved marine sediments in saanich inlet british columbia and in the santa barbara basin off california comparison of annual cyst production and historical plankton data provides cyst theca ratios from which the magnitude of past bloom size can be evaluated the 10 500 yr pacific record clearly shows that the largest blooms correspond to cysts of protoceratium reticulatum and gonyaulax spinifera during the early holocene sporadic blooms of potentially toxic alexandrium spp lingulodinium polyedrum and gymnodinium spp also occurred from ca 7000 to 5000 yr bp and more frequently from ca 2000 to 3000 yr bp individual holocene blooms were up to 10 times larger than in the historical record but they almost always occurred sequentially without overlap of red tide species in pre historical times the bloom cycles started and stopped abruptly in 10 yr or less and they persisted for about 100 1000 yr in contrast the variability and near concurrence of species blooms in the modern past 60 yr record is unmatched in the past and suggests disequilibrium of the natural ecosystem structure atlantic records from la have and emerald basins on the scotian shelf are less precise because bioturbation limits time resolution to ca 25 yr however cyst abundances of cf alexandrium protoceratium reticulatum gonyaulax spinifera and lingulodinium polyedrum were also an order of magnitude larger in the early holocene where they correspond to a summer sea surface warming of 2 5 c lesser peaks also appear during the past 2000 yr where they apparently correspond to a slight increase in winter temperature there is no evidence of much lower salinity that would support stronger stratification the similarity of pre industrial age cyst records of red tide histories in the oceanographically different pacific and atlantic regions of canada indicates that climate change including surface temperature and storminess is the main driving force stimulating blooms this implies that habs will reoccur regardless of efforts to limit spreading however reduced pollution may decrease the hab diversity thereby stabilizing the population dynamics and increasing the predictability of bloom occurrences

high temperature hydrothermal alteration of ultrmafic cumulates from the base of the sheeted dikes in the josephine ophiolite nw california ultramafic cumulate pods occur locally just below the base of the sheeted dike complex in the josephine ophiolite in north western california these ultramafic rocks occur with metagabbros and both are extensively intruded by mafic dikes the ultramafic cumulates contain evidence of high temperature hydrothermal alteration early alteration possibly above 900 c which continued to progressively lower temperatures 350 c this hydrothermal alteration has been partially obscured by later low grade regional metamorphism petrographic evidence for the hydrothermal alteration includes 1 hydration of primary clinopyroxene to hornblende 2 supersolvus secondary hornblende 3 subsolvus coexisting hornblende actinolite and actinolite chlorite 4 alteration of hornblende to chlorite 5 alteration of orthopyroxene and olivine to serpentine and 6 serpentine veining the composition of the altering fluid appears to change with temperature

description and interpretation of the composition of fluid and alteration mineralogy in the geothermal system at svartsengi iceland abstract the bulk composition and mineralogy of hydrothermally altered tholeiite along with the composition and speciation of fluid have been determined for a well defined alteration zone at 240 c and 110 bars at svartsengi iceland mass balances between the geothermal fluid and altered tholeiite relative to a seawater fresh water mixture and unaltered tholeiite indicate the overall reaction per 1000 cm 3 is 1325 gm plagioclase 1228 gm pyroxene 215 gm oxide minerals break down to form 685 gm chlorite 636 gm albite 441 gm quartz 249 gm epidote 266 gm calcite 201 gm oxide minerals 15 gm pyrite requiring an influx of 123 gm co 2 10 gm h 2 s and 4 gm na 2 o and a release of 57 gm sio 2 35 gm feo 21 gm cao 8 gm mgo and 4 gm k 2 o principal reactions deduced from textural evidence include na ca exchange in plagioclase precipitation of quartz calcite and anhydrite and formation of chlorite and epidote by reactions between groundmass minerals and fluid thermodynamic analyses of authigenic minerals and downhole fluid indicate that the fluid maintains a state close to equilibrium with the secondary mineral phases chlorite epidote albite quartz calcite prehnite anhydrite pyrite and magnetite whereas remnant primary labradorite and augite are out of equilibrium with the fluid water rock ratios for the system are determined under a variety of assumptions however the open nature of the system makes comparisons with experimental and theoretical closed system studies ambiguous

constraints on arabian plate motion and extensional history of the red sea analysis of the geologic and geophysical data from the western and northern margin of the arabian plate combined with data from the red sea gulf of aden leads to an interpretation of arabian plate motion that supports an episodic extensional history in the red sea and gulf of aden phase 1 extension began in medial to late eocene and was caused by the nw propagation of the reoriented central indian ridge spreading center it stretched and thinned continental crust along numerous wrench and normal faults that reactivated preexisting structures first phase extension stopped when the arabian plate terminally sutured to eurasia in the medial miocene and halted northward movement of arabia relative to africa the combined african arabian plates moved north more slowly constricting and thickening continental crust in the bitlis zagros sutures while the red sea remained technically quiescent and accumulated salt by the early pliocene continued northward movement was accommodated by lateral extrusion of large continental wedges north of the bitlis zagros sutures this allowed arabia to move northward faster than africa and reopen the red sea where phase 2 extension was expressed by seafloor spreading extension within the red sea gulf of aden rift system has been controlled by the interactions and effects of two factors 1 convergent processes between the north margin of the arabian plate and the eurasian plate to the north and 2 northwest propagation of extension associated with the medial eocene reorganization of the central indian spreading center

overview of late quaternary stratigraphy in saanich inlet british columbia results of ocean drilling program leg 169s abstract continuous coring in saanich inlet ocean drilling program odp leg 169s british columbia canada yielded a detailed record of late quaternary climate oceanography marine productivity and terrestrial vegetation two sites 1033 and 1034 were drilled to maximum depths of 105 and 118 m recovering sediments ranging in age from 13 300 to less than 300 14 c yr earliest sediments consist of dense largely massive gray glaciomarine muds with dropstones and sand and silt laminae deposited during the waning stages of glaciation deposition of organic rich olive gray sediments began in the fjord about 12 000 14 c yr ago under well oxygenated conditions as reflected by the presence of bioturbation and a diverse infaunal bivalve community at about 10 500 14 c yr a massive gray unit 40 50 cm thick was emplaced in a very short span of time the unit is marked by a sharp lower contact a gradational upper contact and an abundance of reworked tertiary microfossils it has been interpreted as resulting from massive flood events caused by the collapse of glacial dams in the fraser valley of mainland british columbia progressively greater anoxia in bottom waters of saanich inlet began about 7000 14 c yr ago this is reflected in the preservation of varved sediments consisting of diatomaceous spring summer laminae and terrigenous winter laminae correlation of the sediments was based on marked lithologic changes the presence of massive intervals reflecting localized sediment gravity flow events the mazama ash occasional thin gray laminae indicative of abnormal flood events in nearby watersheds varve counts between marker horizons and 71 accelerator mass spectrometry ams radiocarbon dates

abyssal peridotite mylonites implications for grain size sensitive flow and strain localization in the oceanic lithosphere abstract microstructures preserved in abyssal peridotites dredged from the oceans record several different physical regimes of deformation fabrics associated with deformation processes at slow spreading mid ocean ridges form two major classes of abyssal peridotites based on detailed microstructural observations the most abundant class are medium to coarse grained tectonites with microstructures that reflect deformation processes during mantle upwelling and emplacement to the base of the lithosphere these tectonites give geothermometric temperatures of 755 c or higher interpreted to represent lower temperature limits for diffusive exchange in coarse grained abyssal peridotites during cooling this conclusion is consistent with flow laws for olivine at these temperatures the second class of abyssal peridotites previously largely undescribed for the mid ocean ridge environment include fine grained mylonites associated with faulting and shear zones that develop during extension and cooling of the oceanic lithosphere when the brittle plastic transition extends into mantle rocks these mylonites give temperatures of 600 c which we suggest represent a lower temperature limit for plastic deformation reduced grain size in mylonites allows for diffusive exchange to continue to these low temperatures relict augen in the mylonitic samples preserve equilibration temperatures similar to those exhibited by the coarse grained tectonites based on flow laws for olivine we suggest that deformation in some fine grained mylonites occurred by diffusion creep down to 600 c rheological data for olivine indicate that dislocation creep is not likely to occur at this temperature we conclude that a reduction in grain size by cataclasis or dynamic recrystallization resulted in a transition in deformation mechanisms from dislocation to diffusion creep during uplift and or cooling the observation of these fine grained mylonites indicates that shear zones that extend into the upper mantle will be weaker than expected if deformation was accommodated by brittle processes or dislocation creep weak faults may promote the development of long lived detachments in the upper mantle this inference supports mid ocean ridge tectonic models that suggest that ultramafic rocks exposed at the inside corners of ridge axis discontinuities are exhumed along long lived detachment faults

continental margin evolution of the northern arabian platform in syria copyright aapg 1993 reprinted by permission of the aapg whose permission is required for further use see also http atlas geo cornell edu syria best 1993 html

the distribution of carboniferous permian siliciclastic rocks in the greater arabian basin correlative sequences of sandstones silt stones claystones and thin argillaceous carbonate beds of late carboniferous early permian age occupy a distinct stratigraphic position over the entire greater arabian basin these rocks are bracketed by a regional unconformity below and a conformable succession of permian carbonates above them the basal contact is marked by a pronounced angular unconformity which separates this carboniferous permian succession from underlying much older rocks the carboniferous permian rocks crop out in thin bands and scattered small exposures in the basin but they are commonly encountered in the subsurface the age assignment for these rocks is based on both fossil plants and palynomorphs as well as on stratigraphie position these rocks are represented by the unayzah formation of arabia and the gulf region the amanus formation of syria the hazro formation of southeast turkey the ga9ara formation of iraq the faraghan formation of southwest iran the asfar formation of north oman the gharif and khlata formations haushi group of south oman and the akbarah formation of north yemen sandstones of these carboniferous permian sequences are important hydrocarbon exploration targets as significant quantities of hydrocarbons are currently produced from reservoirs of these rocks in several oilfields in the basin

spectrophotometer analysis of holocene sediments from an anoxic fjord saanich inlet british columbia canada abstract a borehole core through the holocene sediments of saanich inlet british columbia canada was analyzed using high resolution spectrophotometry to determine whether spectral signal variations can be used as environmental climatic proxies the effects of post drilling oxidation and water loss on the core sample were assessed by comparing spectral measurements taken onboard the research ship immediately after the core was opened with shore based measurements taken one year later for saanich inlet sediments the shore based measurements provided more reliable indications of the degree of basin anoxia our spectral analyses allowed us to identify all the major features of the saanich inlet sediment sequence mazama ash and fraser river drainage stratigraphic markers oxygenation state of the basin by using the first derivative value at 675 nm as a proxy for changes in organic matter content and the colorimetric parameter b as an indicator of diatom content we were able to recognize changes in terrestrially derived organic matter om and diatom concentrations in the sediment we suggest that these variations are due to changes in upwelling intensity and fluctuations in sea level during the holocene our results confirm the potential value of spectrophotometry in identifying sediment composition and in reconstructing paleoenvironments

stratigraphy and structure of eastern syria across the euphrates depression abstract a n s crustal scale geotransect across the northern arabian platform in eastern syria reveals an alternating series of basement uplifts and basins separated by predominantly transpressional fault zones above an effectively uniform crust four major tectonic provinces are crossed along a 325 100 km corridor that extends from the iraqi border in the south to the turkish border in the north the rutbah uplift the euphrates depression the abd el aziz structural zone and the qamichli uplift these features are the manifestations of reactivated pre cenozoic structures that responded to forces acting along nearby arabian plate boundaries particularly cenozoic convergence and collision along the margins of the northern arabian platform i e the bitlis suture and the east anatolian fault in southern turkey and the zagros suture in iran and iraq the database for this study consists of 3000 km of industry seismic reflection data 28 exploratory wells and geologic and bouguer gravity maps the deep crustal structure and in part the basement geometry along this transect are inferred from two dimensional modeling of bouguer gravity whereas the shallow about 8 km structure is constrained primarily by well and seismic data features of the geotransect reveal 1 1 a relatively uniform crustal column approximately 37 km thick with only minor crustal thinning beneath the euphrates crustal thinning may be slightly more pronounced beneath the euphrates about 35 km to the southeast of the transect where the bouguer gravity anomaly is slightly higher 2 2 along the euphrates depression ongoing subsidence which began during the late cretaceous resulted in the deposition of at least 3 km of late cretaceous and cenozoic rocks the structural complexity of the paleozoic and most of the mesozoic sedimentary sections along the transect contrasts markedly with a relatively simple flat lying cenozoic section along most of the transect a notable exception is the abd el aziz uplift where cenozoic rocks are strongly deformed 3 3 while euphrates subsidence continued throughout the cenozoic the inversion of the e w trending abd el aziz structure into a fault bounded tilted block began in the miocene perhaps as a response to the last episode of intense miocene collision along the nearby bitlis and zagros suture zones

upper crustal velocity structure and basement morphology beneath the intracontinental palmyride fold thrust belt and north arabian platform in syria an edited version of this paper was published in geophysical journal international by blackwell publishing copyright 1993 blackwell publishing see also http www blackwellpublishing com journal asp ref 0956 540xs http atlas geo cornell edu syria seber gji 1993 htm

prograde phase relations in the state 2 14 well metasandstones salton sea geothermal field california seventy five core samples of medium to fine grained metasandstones from the state 2 14 borehole were studied petrologically and mineralogically to evaluate compositional variations of geothermal minerals and prograde metamorphic reactions three distinct metamorphic zones are defined based on the appearance of index minerals with increasing grade they are 1 chlorite calcite chl cc zone at depths between 610 and 2480 m 2 biotite bt zone between 2480 and 3000 m and 3 clinopyroxene cpx zone between 3000 and 3180 m all of the studied metasandstones at depths greater than 906 m contain epidote ep and quartz qtz with or without albite ab characteristic assemblages ep qtz ab are 1 chl cc k feldspar ksp phengitic muscovite for the chl cc zone 2 bt chl ksp anhydrite anh and bt act chl for the bt zone and 3 diopsidesalite act bt oligoclase actinolitic hornblende for the cpx zone epidote exhibits a compositional variation ranging from 0 11 to 0 42 xfe fe fe al many amphibole grains of the clinopyroxene zone show patchy or lamellar intergrowths of both actinolite and actinolitic hornblende on a scale less than a few tens of micrometers these amphiboles show distinct compositional discontinuities such as in al2o3 contents 2 7 4 8 wt and fe fe mg ratios 0 41 0 55 the cpx zone samples thus mark the transition from the greenschist to amphibolite facies other important secondary phases include rutile or anatase depths 940 m peristerite 1235 m and mn salite 2484 m the observed assemblages and compositions of minerals are chemographically interpreted utilizing an epidote projection in the simple system al2o3 k2o mgo cao sio2 h2o co2 reactions for the appearance of index minerals are elucidated in a qualitative t xco2 diagram the results indicate that l the compositions of chl and bt are highly variable depending on the bulk composition however chl in the chl cc zone becomes enriched in mg with increasing depth 2 bt forms by a discontinuous reaction ksp chl cc bt ep qtz h2o co2 hence the first appearance of bt is greatly affected by the fluid composition 3 the hydrothermal fluid in equilibrium with the analyzed assemblages is very low in xco2 0 03 and 4 the absence of wairakite and prehnite is attributed to the high fo2 values of the salton sea geothermal system

a crustal structure study of jordan derived from seismic refraction data abstract the interpretation of a deep seismic refraction study in jordan performed in may 1984 shows that much of the country is underlain by continental crust 32 35 km thick and normal mantle with a velocity of 8 0 8 2 km s in the aqaba region southwest and central jordan east of wadi araba the crustal thickness is of the order of 32 35 km while in the amman region it is not less than 35 km in southeast jordan the crust thickens to at least 37 km in what is probably the transition to the arabian shield type of crust the boundaries between the upper and lower crust at about 20 km depth and the lower crust and uppermost mantle are probably transition zones the upper crystalline crust has velocities of 5 8 6 5 km s while the lower crust has velocities greater than or around 6 65 km s while the crystalline basement is exposed in southwest jordan and is at a depth of 2 2 5 km north of amman it is at a depth of not less than 5 km in central jordan a comparison of the crustal type and structure of jordan and the adjacent dead sea rift with that of the black forest and the rhine valley yields a striking resemblance the situation of the jordan dead sea rift is explained in terms of the continental crust of arabia rifting in preference to the thin oceanic crust of the mediterranean sea

fish scales in sediments from off callao central peru abstract we study fish scales as a proxy of fish abundance and preservation biases together with phosphorus from fish remains p fish in a sediment core retrieved off callao peru 12 1 s 77 42 w water depth 179 m core length 52 cm we interpret our results as a function of changing redox conditions based on ratios of redox sensitive trace elements cu al mo al ni al zn al v al terrigenous indicators fe in clays ti al and biogenic proxies caco 3 biogenic opal total nitrogen organic carbon barite ba the core covers roughly 700 years of deposition based on 210 pb activities extrapolated downcore and 14 c dating at selected intervals our fish scale record is dominated by anchovy engraulis ringens scales followed by hake merluccius gayii scales the core presented an abrupt lithological change at 17 cm corresponding to the early 19th century above that depth it was laminated and was more organic rich 10 15 organic carbon than below where the core was partly laminated and less organic rich fish p total ratios were also observed within the upper 17 cm of the core the behavior of biogenic proxies and redox sensitive trace elements was similar more reduced conditions corresponded to higher contents of caco 3 c org total nitrogen and fish scales suggesting that these proxies might convey an important preservation signal

the role of reacting solution and temperature on compositional evolution during harzburgite alteration constraints from the mesoarchean nuasahi massif eastern india abstract we investigate the microtextural chemical features of partially serpentinized harzburgites from the lower ultramafic unit of the mesoarchean nuasahi massif eastern india in order to understand the role of reacting fluid composition and temperature on the phase evolution across replacement interfaces during progressive alteration two distinct types of pseudomorphic replacement textures are identified type 1 replacement texture was developed after primary orthopyroxene and is composed of talc olivine lizardite tremolite magnetite primary olivine was replaced by mesh textured mg rich lizardite magnetite at the center of the olivine grains and successive layers of relatively fe rich lizardite magnesite and calcite toward olivine rims defining type 2 replacement texture the nuasahi harzburgite was initially out of equilibrium with respect to h 2 o co 2 bearing reacting solution and the secondary compositions have mainly evolved in the cao mgo feo sio 2 al 2 o 3 h 2 o co 2 system as a result of fluid rock interaction the alteration process across orthopyroxene interfaces has started at relatively higher temperature conditions 400 h 2 o c o 2 aq ratio in the solution across replacement interfaces the fe 2 mg 1 chemical exchange potential of the equilibrating system plays an important role in dictating the fe mg ratio of the secondary compositions and the molar proportions of magnetite the precipitation of tremolite and calcite in some isolated areas reflects a variation in ca activity in the reacting fluid the precipitation of carbonates may also be associated with an increase in ph in the interfacial solution the pattern in phase evolution across type 1 interfaces suggests a greater extent of diffusion of solutes toward inner interfaces relative to the rim center during progressive alteration of the nuasahi harzburgite possibly due to an increase in permeability in replaced phases with increasing magnitude of diffusion toward type 1 inner reacting interfaces the widespread presence of arrested replacement features suggests an alteration event under low fluid rock ratio and or sluggish reaction kinetics with decreasing temperature

nature of serpentinization of ultramafic rocks from hero fracture zone antarctic constraints from stable isotopes abstract serpentinites from the hero fracture zone drake passage antarctica contain serpentine amphibole talc chlorite and magnetite as well as relict olivine pyroxene and spinel from a spinel peridotite precursor two episodes of serpentinization are recognized the first event produced lizardite and antigorite whereas the second produced only lizardite the initial and subsequent serpentinization events occurred at about 178 283 c and 170 298 c respectively calculated water rock ratios of the serpentinization events are less than 5 for the initial event and greater than 5 for the subsequent event a model involving deep seawater infiltration in the fracture zone followed by serpentinization of mantle peridotite and buoyancy driven uplift controlled by relatively small scale faults and not by a large scale detachment fault is invoked to explain the emplacement of serpentinite on the surface