the palos verdes anticlinorium along the los angeles california coast implications for underlying thrust faulting 1 the palos verdes anticlinorium pva is a 70 km wide nw trending pliocene quaternary transpressional high that separates the onshore los angeles basin from the offshore san pedro basin the pva southwest limb underlies a 70 km long sw facing seafloor escarpment this escarpment is separated into two segments by a 6 km right step it overlies two levels of ne dipping low angle thrust faults these faults project beneath los angeles toward known sw verging blind thrust faults and may be the same regional faults these conclusions are based on a detailed geometric representation constructed from a regional analysis of 5000 km of multichannel seismic reflection profiles logs and paleontology from 19 wells published seafloor geology and multibeam bathymetric data patterns of sedimentation and erosion indicate that folding of pva initiated during pliocene time and propagated southward with folding of part of the southern pva occurring during the quaternary structural relief continues to grow with regional long term rock uplift of the pva crest and ongoing subsidence in the adjacent basins the low angle ne dipping faults beneath the pva must be late quaternary active in order to maintain hanging wall rock uplift above subsiding footwalls structural geometry requires that the underlying faults have slipped at 1 1 1 6 mm yr over quaternary time

18o exchange between steam and carbon dioxide in volcanic and hydrothermal gases implications for the source of water abstract the oxygen isotopic compositions of h 2 o and co 2 from 31 fumaroles from different volcanoes vesuvio campi flegrei vulcano and etna in italy soufriere of guadeloupe in lesser antilles prove that 18 o exchange between co 2 and steam is fast enough in natural gas phases to allow rapid isotopic reequilibration within a wide temperature range 100 1000 c the isotopic composition of h 2 o discharged by volcanic hydrothermal fumaroles is affected by isotopic reequilibration along with cooling of the gas phase and this secondary process must be taken into account when interpreting the origin of the water from isotopic data the use of corrected 18 o values computed considering the overall oxygen isotopic composition of the h 2 o co 2 system is therefore compulsory to overcome interpretative biases as an example we apply this method to 100 600 c fumaroles at vulcano crater whose isotopic composition is reinterpreted considering the effects of 18 o exchange between co 2 and h 2 o in contrast to most previous interpretations the corrected isotopic values for h 2 o clearly show that the vulcano system is fed by a two component mixture of magmatic water with a typical andesitic composition and either 18 o shifted seawater or magmatic steam partly condensed within the volcanic ground with minor contribution of local meteoric water the possible additional effects of isotopic reequilibration involving other o and h bearing gas species in volcanic fluids such as so 2 h 2 s hcl hf and h 2 have been also considered the influence of so 2 upon the isotopic composition of h 2 o is subordinate with respect to that of co 2 whereas significant shifts in deuterium composition are expected from hydrogen isotopic exchanges in the h 2 o h 2 s hcl hf h 2 gas system

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

isotopic identification of gases of a deep origin in french thermomineral waters within the subsurface convective system which constitutes the thermomineral waters of which the meteoric origin is proved by the oxygen deuterium couple the associated gases free or dissolved may represent the only juvenile component in this cycle the juvenile origin of the gases can be clearly established through ascertaining the isotopic composition of certain elements argon nitrogen carbon and helium the study of these gases associated with thermomineral waters has been undertaken systematically since 1976 one of the first objectives of these investigations has been the determination of the carbon isotopic compositions of the carbon dioxide bicarbonate system for 50 thermomineral springs in various geological settings the massif central pyrenees and vosges mountainous regions france on the basis of isotopic compositions three sources of primordial or initial carbon have been put forward which correspond to characteristic figures for the carbon compositions expressed in 13c values the exogenous carbon domain 13cco2 from 10 to 25 13chco 3 from 18 to 2 the endogenous magmatic carbon domain 13cco2 from 10 to 2 13chco 3 from 2 to 6 and the endogenous sedimentary carbon domain 13cco2 from 2 to 2 and 13chco 3 6 in the case of springs with exogenous carbon of which a part is atmospheric nitrogen isotopes confirm that origin in the cases of springs with magmatic or mantle carbon argon isotopes indicate also a deep origin

hydroclimatic and geothermal controls on the salinity of mbaka lakes sw tanzania limnological and paleolimnological implications summary the hydroclimatic and geothermal controls on the salinity of small tropical crater lakes masoko katubwi kyambangunguru ilamba and kingiri aligned with the mbaka fault line north of lake malawi are investigated by water stable isotopes which are used to trace evaporative processes as to establish lake water balances and by chloride concentrations allowing to identify the main salinity sources this region shows positive excess in the exchanges between atmosphere and lake surfaces p e 0 with the exception of lake ilamba the lakes are closed surface basins and their levels are relatively stable as catchment inflows cannot be neglected groundwater outflows have to compensate for this excess the isotopic budgets show that these lakes constitute a series of windows on the local shallow aquifer in addition the estimated losses by evaporation cannot solely account for the lake salinity observed as the most saline lake differs from not the most evaporated lake salinity is then investigated from chloride concentrations and seems to be controlled by inflows which results from the mixing between i fresh and ii hydrothermal ground waters the contrasts in lake salinity almost one order of magnitude are first related to the hydrothermal contribution which increases with the proximity of the mbaka fault second due to positive exchange with the atmosphere the lake salinity appears systematically diluted in regard to the respective inflows this dilution effect increases as the fraction of total inputs lost by evaporation or the lake water residence time increases this current hydrological study shows that local wetter conditions are not inconsistent with higher lake salinity and allows to conciliate the questioned and apparent contradictory lake masoko wetter and salty paleoenvironmental and paleoclimatic records for the last glacial maximum and younger dryas time intervals further in a general manner this work addresses the case of lake submitted to wet environment and highlights the potential contribution of hydrothermal water on lakes salinization occurring in active regions such as the east african rift system

thermal maturity of carboniferous to eocene sediments of the alpine dinaric transition zone slovenia abstract the alpine dinaric transition zone in slovenia comprises the fold and thrust belt of the southern alps south karawanken range julian alps slovenian basin and the dinarides the slovenian basin located between the julian and dinaric carbonate platforms evolved during middle triassic time and remained in a deep marine setting till the late cretaceous the thermal history of carboniferous to eocene rocks in that area was investigated using vitrinite reflectance vr data apatite fission track analysis and numeric 1d basin modeling the study shows that maturity patterns are mainly controlled by the thickness of upper cretaceous to eocene flysch deposits filling the accommodation space therefore the thermal overprint reaches a maximum 4 rr in triassic to cretaceous sediments of the slovenian basin and decreases towards the north and south minor sedimentary burial of the adriatic carbonate platform and the julian alps results in a lower thermal overprint 2 cooling of paleozoic and mesozoic sediments below 110 c occurred between late eocene and early oligocene times in different parts of the study area nappe stacking due to early dinaric and late cenozoic alpine compressional tectonics did not influence the thermal maturity of the sediments

geology and hydrogeochemistry of the jungapeo co2 rich thermal springs state of michoacan mexico abstract we present the first geothermal assessment of the jungapeo co2 rich mineral springs which are located in the eastern part of michoacan state central mexico at the southern limit of the trans mexican volcanic belt all but one of the 10 springs occur at the lower contact of the distal olivine bearing basaltic andesite lavas of the tuxpan shield a 0 49 to 0 60 ma old cluster of monogenetic scoria cones and lava flows the tuxpan shield has a maximum radius of 6 km and was constructed on top of a folded and faulted cretaceous basement consisting largely of marine limestones marls and shales the mineral waters are characterized by moderate temperatures 28 to 32 c mild acidity ph from 5 5 to 6 5 relatively high discharge rates effervescence of co2 gas clarity at emergence and abundant subsequent precipitation of hydrous iron silica oxides and carbonates around pool margins and issuing streamlets chemical and isotopic deuterium oxygen and tritium analyses of water and gas samples obtained during the period 1991 1997 indicate that the springs are largely composed of meteoric water from a local source with relatively short residence times water ages of 7 to 25 years spring waters are chemically characterized by moderate sio2 ca mg nearly equal to na k high hco3 moderate to low cl low f and so4 high b moderate li while br and as are low in contrast fe mn is exceptionally high thus the jungapeo waters cannot be regarded as high temperature geothermal fluids instead they resemble soda spring waters similar to other low to medium temperature soda waters in the world gas samples are extremely rich in co2 with no detectable geothermal h2s or h2 and very low contents of ch4 and nh3 indicating the gases are not derived from a high temperature resource carbon 13 analyses of co2 show a narrow range 6 7 and 7 2 that falls within the range for morb co2 thus most co2 seems to originate from the mantle but some co2 could originate from thermal degradation of organic remains in underlying cretaceous rocks 3 4he ratios range from about 2 to 3 rc ra indicating that a small mantle magmatic he component is present in the gases in conclusion the mineral waters are the surface expression of a low temperature geothermal system of limited size that originates from the combined effects of a high regional heat flow and possibly the remnant heat released from subjacent basaltic andesite magma bodies that constitute the root zone of the tuxpan shield

convergence rates across a displacement transfer zone in the western transverse ranges ventura basin california three cross sections are balanced and retrodeformed to the top of the pleistocene saugus formation and to a horizon close to the base of the jaramillo subchron to yield crustal shortening and shortening rates for the western transverse ranges of california the cross sections compare the shortening that occurs along a transfer zone in which displacement is transferred eastward from a surface reverse fault red mountain fault to a blind thrust and from that to a combination of both a surface reverse fault san cayetano fault and the blind thrust using an age of 250 50 ka for the top of the saugus formation based on amino acid racemization of fossil mollusks crustal shortening rates appear to have abruptly accelerated through time from 3 4 3 to 5 4 mm yr between 250 and 975 ka to 20 6 to 28 1 mm yr since 250 50 ka using an age of 500 ka for the top of the saugus formation based on paleomagnetic stratigraphy there is little increase in deformation rates through time ranging from 5 5 to 8 6 mm yr between 975 500 ka and from 10 3 to 14 1 mm yr since 500 ka more crustal convergence rates determined by global positioning system surveys taken over 4 6 years indicate a shortening rate of 7 10 mm yr across the basin this is consistent with the slower rates of deformation calculated using an age of 500 ka for the top of the saugus formation less

interpreting the geologic map expression of contractional fault related fold terminations lateral oblique ramps versus displacement gradients abstract fault related folds in contractional settings do not extend indefinitely but rather commonly terminate as plunging anticlines near the tips of the genetically related fault geologists often attribute the formation of such terminations to loss of slip on the underlying fault i e a displacement gradient to changes in fault geometry in which the fault laterally changes stratigraphic position along strike i e a lateral oblique ramp or to some combination of these mechanisms discerning between these formative mechanisms solely through the interpretation of the geologic map expression of the termination can be difficult because of the subjective nature of the criteria used e g lateral oblique ramps often are interpreted at terminations where folds plunge at steep angles where hanging wall cutoff lines trend at high angles to fault strike where stratigraphic contacts trend at high angles to fault strike etc we created pseudo three dimensional model terminations of individual fault related folds using both displacement gradients and lateral oblique ramps to determine if unique characteristics in their map expressions exist we show that map patterns of folds produced by a displacement gradient along a thrust fault of constant geometry are similar to map patterns of folds produced by constant slip on a thrust fault with a lateral oblique ramp specifically our modeling results suggest that 1 simple fault bend folds that plunge less than 20 and simple fault propagation folds that plunge less than 50 at their terminations can be created by both displacement gradients and lateral oblique ramps angles greater than these values suggest that a lateral oblique ramp may be involved in forming the termination 2 hanging wall cutoff lines at terminations that trend at angles less than about 35 to fault strike for simple fault bend and fault propagation folds also may be produced by both displacement gradients and lateral oblique ramps higher angles likely indicate the presence of a lateral oblique ramp at the termination 3 the angle at which stratigraphic contacts trend to the fault strike cannot be used to uniquely identify displacement gradients or lateral oblique ramps for simple fault related folds 4 stratigraphic separation diagrams can indicate the presence of ramps in the thrust sheet but do not uniquely differentiate between frontal ramps with displacement gradients and lateral oblique ramps and 5 actual changes in fault orientation after topographic influences have been taken into account by definition indicate a lateral oblique ramp in reality most natural fault related fold terminations probably share components of both displacement gradients and lateral oblique ramps with each structure possessing contributions from each mechanism

origine des substances dissoutes dans les eaux des sources thermales et des forages de la region asal ghoubbet republique de djibouti abstract from a chemical and sr isotopic study of hot fluids from the asal area republic of djibouti we conclude that the fluids result from basalt seawater interaction associated with variable evaporation some spring waters result from a mixing between geothermal water and seawater or asal lake water in contrast with previous studies dissolution from evaporitic rocks appears unimportant the negative boron anomaly in the fluids from the boreholes suggests the presence of a vapour dominated subsystem in the asal geothermal field

measuring vertical tectonic motion at the intersection of the santa cruz catalina ridge and northern channel islands platform california continental borderland using submerged paleoshorelines we used submerged paleoshorelines as strain markers to investigate holocene and late pleistocene vertical tectonic movement at the intersection of the offshore santa cruz catalina ridge with the southern boundary of the western transverse ranges within the california continental borderland past submerged shoreline positions were identified using high resolution multibeam bathymetry side scan sonar submersible observations and the presence of intertidal and subtidal invertebrate fossils numerous accelerator mass spectrometry ams 14 c ages of shells from these paleoshorelines were found to be between 27 000 yr radiocarbon rc and 11 500 yr before present indicative of shoreline colonization during and following the last glacial maximum lgm establishing these paleoshorelines as a usable datum for measuring vertical change since this time removal of the nontectonic component of vertical change using an ice volume equivalent eustatic sea level compilation indicates between 20 and 45 m of uplift of the eastern part of the northern channel islands block since the lgm lowstand resulting in an uplift rate of 1 50 0 59 mm yr over the last 23 k y this rate closely matches uplift predicted by published slip rates for the channel islands thrust which underlies the northern channel islands platform results from post lgm shoreline features on pilgrim banks are somewhat more ambiguous submarine paleoshoreline uplift together with the extensive upper crustal fold thrust style of deformation illustrates the transpressional interaction of the borderland and the western transverse ranges blocks where the santa cruz catalina ridge and northern channel islands intersect

hydrothermal activity in the northern tanganyika rift east africa abstract hydrothermal fluids from sub lacustrine and sub aerial sites were sampled in the north tanganyika rift during the 1991 tanganydro expedition two types of hydrothermal end member fluids a na hco 3 type and a na cl type have been identified within the sample set the na hco 3 hydrothermal fluids are emitted at the level of the sub lacustrine pemba and sub aerial kabezi and mashuzi sites which are located in the northernmost bujumbura sub basin the na cl hydrothermal fluid vents at the level of the sub lacustrine cape banza field on the southeastern edge of the ubwari ridge the two types of hydrothermal fluids display isotopic and chemical evidence of interaction with magmatic volatiles the magmatic effects are strongest in the fluid discharging on the pemba hydrothermal field where abundant co 2 bubbling accompanies fluid emission the 13 c values of the co 2 gas sampled at pemba and at cape banza indicate a magmatic origin the pemba fluid shows the highest alkalinity and boron content and the lowest ph of the hydrothermal end member fluids and it has equilibrated at depth at the highest temperature 214 7 c in addition the sulfide mineralizations associated with the pemba hydrothermal vents are enriched in as and tl which similarly to b can be transported as volatiles in magmatic fluids the northern tanganyika na hco 3 fluids are similar to the na hco 3 fluid of the geothermal system of lake bogoria in the eastern branch of the east african rift and they can be compared with the na hco 3 hydrothermal water that is inferred to flow into lake kivu the cape banza na cl fluids may derive from the mixing between meteoric water and a deep seated basement brine similar to the ones found in old continental shields such as the canadian shield the high equilibrium temperatures and the geochemistry of the north tanganyika rift hydrothermal fluids suggest that degassing magmatic bodies are present at depth in the area these magmatic bodies may be either the southern expression of the south kivu magmatism or a more recent activity not yet expressed as surface volcanism the hydrothermal sites are located along major active rift bounding faults which can be associated with deep and strong seismicity as in the case of the pemba field such deep fractures may have favoured the uprise of the magmatic bodies that are the source of heat and volatiles to the hydrothermal systems the circulation of hydrothermal fluids within the tanganyika lacustrine sedimentary pile could play an important role in the maturation of the organic matter enclosed in the lake sediments and the subsequent oil generation and migration

hydrogeochemistry of thermal and mineralized waters in the diyadin agri area eastern turkey abstract the diyadin geothermal area located in the eastern part of anatolia turkey where there has been recent volcanic activity is favorable for the formation of geothermal systems indeed the diyadin geothermal system is located in an active geodynamic zone where strike slip faults and tensional cracks have developed due to n s regional compression the area is characterized by closely spaced thermal and mineralized springs with temperatures in the range 30 64 c and flowrates 0 5 10 l s thermal spring waters are mainly of ca na hco 3 and ca mg so 4 types with high salinity while cold groundwater is mostly of ca na mg hco 3 type with lower salinity high contents of some minor elements in thermal waters such as f b li rb sr and cs probably derive from enhanced water rock interaction thermal water samples collected from diyadin are far from chemical equilibrium as the waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters the temperatures of the deep geothermal reservoirs are estimated to be between 92 and 156 c in diyadin field based on quartz geothermometry while slightly lower estimates are obtained using chalcedony geothermometers the isotopic composition of thermal water 18 o 2 h 3 h indicates their deep circulating meteoric origin the waters are likely to have originated from the percolation of rainwater along fractures and faults to the deep hot reservoir subsequent heating by conduction due to the presence of an intrusive cupola associated with the tendurek volcano is followed by the ascent of deep waters to the surface along faults and fractures that act as hydrothermal conduits modeling of the geothermal fluids indicates that the fluid is oversaturated with calcite aragonite and dolomite which matches travertine precipitation in the discharge area likewise the fluid is oversaturated with respect to quartz and chalcedony indicating the possibility of siliceous precipitation near the discharge areas a conceptual hydro geochemical model of the diyadin thermal waters based on the isotope and chemical analytical results has been constructed

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

geochemistry and habitat of the oils in italy all varieties of liquid petroleum ranging from condensates 50 degrees api to immature sulfur rich heavy oils as low as 5 degrees api have been found in italy however nonbiodegraded heavy oils account for about 70 percent of the total original oil in place geochemical analyses indicate that 11 oil groups are present in the italian basins and two main types of source rocks have been identified triassic carbonates and tertiary shales about 95 percent of the oils were originated from middle and upper triassic carbonates containing type ii kerogen about 1 percent 4total organic carbon toc and 500 mg hydrocarbon g toc only a relatively minor amount of oil was generated by tertiary shales containing type iii kerogen with toc generally less than 1 percent timing of generation and migration and bulk properties of oils were controlled by geodynamic histories of the three main italian geologic settings 1 apennine and southern alp thrust belts 2 foredeep depression bordering the thrust belts and 3 foreland nondeformed african continental margin within the apennine thrust belts deep burial during the neogene resulted in the generation of substantially lighter oils not only from deeply buried triassic but sometimes also from tertiary source rocks in the late neogene foredeep depocenters located in the central adriatic and southern sicily high subsidence up to 1000 m m y a low geothermal gradient 22 degrees c km and compressional tectonics caused the generation of immature heavy oils generally at depths below 5000 m nd temperatures greater than 100 degrees c rapid burial and higher geothermal gradients 32 degrees c km which occurred since the jurassic resulted in the generation of light oils from the late cretaceous to the oligocene in the southern sector of adriatic foreland

fluid geochemistry of natural manifestations from the southern poroto rungwe hydrothermal system tanzania preliminary conceptual model abstract the south poroto rungwe geothermal field in the northern part of the malawi rift tanzania divides in two main areas the relatively high altitude northern area around the main ngozi rungwe tukuyu and kyejo volcanoes is characterised by cold and gas rich springs in contrast hot springs occur in the southern and low altitude area between the kyela and livingstone faults the isotopic signature of the almost stagnant cold springs of the northern district is clearly influenced by h2o co2 g exchange as evidenced from negative oxygen shifts in the order of few deltas permil in contrast the isotopic signature of waters discharged from the hot springs of the southern district is markedly less affected by the h2o co2 g interaction this evidence is interpreted as an effect of the large permanent outflow of these springs which supports the hypothesis of a regional scale recharge of the major thermal springs measurements of carbon isotope variations of the dissolved inorganic carbon of waters and co2 g from the northern and southern springs support a model of co2 g driven reactivity all over the investigated area our combined chemical and isotopic results show that the composition of hot springs is consistent with a mixing between i cold surface fresh sfw and ii deep hot mineralised dhmw water indicating that the deep originated fluids also supply most of the aqueous species dissolved in the surface waters used as local potable water based on geothermometric approaches the temperature of the deep hydrothermal system has been estimated to be higher than 110 c up to 185 c in agreement with the geological and thermal setting of the malawi rift basin geochemical data point to i a major upflow zone of geothermal fluids mixed with shallow meteoric waters in the southern part of the province and ii gas absorption phenomena in the small perched aquifers of the northern volcanic highlands

hydrochemistry and isotopic composition of na hco3 rich groundwaters from the ballimore region central new south wales australia abstract groundwaters flowing under artesian pressure from the ballimore region central new south wales australia contain up to 95 na hco3 carbon dioxide effervesces from these groundwaters as they discharge from boreholes these groundwaters flow from a confined aquifer situated within fractured permian to jurassic sediments regional geological data and k ar dating of outcropping volcanic units indicate that magmatism occurred in this area between 12 and 14 ma ago radiometric and magnetic data supports the interpreted presence of intrusive bodies x ray fluorescence xrf data shows that the miocene magmatic units are sodium rich with the available samples being classified as either syenitic or trachytic hydrochemical and isotopic data indicate that these groundwaters are of meteoric origin and that this system is open with respect to co2 there is an external source of co2 feeding this groundwater system causing dic total alk the salinity of the na hco3 rich groundwaters range from 3000 to 8000 mg l and co2 aq concentrations are up to 1558 mg l log pco2 of 0 6 the ph of these samples range from 6 1 to 6 9 supporting the conclusion that the h2co3 hco3 couple control ph buffering the carbon 13 values 13c pdb of 5 to 3 indicate that the carbon source for these groundwaters is of inorganic origin it is inferred that this carbon source has a primary 13c similar to that typically quoted for mantle derived carbon 5 9 varying degrees of completeness of equilibrium isotopic fractionation resulting from the hydration dissociation of co2 into the groundwater forming hco3 co2 h2co3 hco3 leads to the observed range of carbon 13 data oxygen 18 18o smow and deuterium d smow isotopic data show a shift to the left of the meteoric water line supporting an interpretation of co2 exsolution gas exchange and fractionation resulting from incongruent silicate weathering reactions dissolved inorganic carbon carbon 13 and regional geological data suggest that the most plausible explanation for the high concentration of co2 in these effervescent sodium bicarbonate rich groundwaters is the mantle with this gas initially being delivered to the fractured strata by magmatic activity

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

geochemistry and habitat of natural gases in italy abstract systematic chemical and isotopic analyses were carried out on natural gases from 92 fields which represent more than 90 of the original gas reserves of italy a quantitative assessment of the various genetic gas types indicates that most of the gaseous hydrocarbons 80 were generated through bacterial activity and or diagenetic processes while only a minor amount 20 was produced by thermal degradation of organic matter the formation of the gas accumulations was geologically controlled by the neogene tectonic phases and by the sedimentary events associated with the growth of the apennines and southern alps in fact about 80 of italian natural gas reserves have been found in the apennine foredeep while the remaining part is equally distributed in the folded belt and in the foreland furthermore the influence exerted by tectono sedimentary characteristics is emphasized by the fact that thermal degradation of organic matter was the only process responsible for most of the gas generated in the apennine folded belt 97 thermogenic gases on the other hand the high rates of subsidence turbiditic sedimentation and very early compressional tectonics in the foredeep favored processes leading to the accumulation of very large quantities of biogenic gas 82 moreover geochemical and geological data as well as mathematical modelling demonstrate that migration and accumulation of italian natural gases mainly occurred later than 5 my ago and in some cases these phenomena are still active in fact in the multipay zone gas fields of the northern adriatic a kind of steady equilibrium is reached between loss of gas through the thin cap rocks often less than 1 m and continous replenishment from the bacterial fermentation and or low temperature thermochemical reactions

petroleum potential of the adriatic offshore croatia the adriatic offshore of croatia extends from the istrian peninsula in the northwest to the dubrovnik offshore area to the southeast and from the croatian coast line to the offshore boundary with italy geochemical prospecting comprised analyses of permian through pliocene quaternary sediments integrated results of geochemical analyses indicate the presence of source rocks in triassic ladinian carnian and lower to upper cretaceous units triassic source rock sequences within the thin limestone streaks from the lithologically mixed sabkha facies are evidenced in the southeastern portion of the adriatic carbonate platform complex algal bacterial organic matter of the predominantly marine origin is in the early stage of thermal maturation properties of analysed bitumen and oil samples imply a direct relationship with the associated source rocks cretaceous source rock sequences with good generating potential were determined in the central part of the adratic offshore layers of micritic limestone and bituminous laminated limestone contain mixtures of oil prone types i and ii high sulfur kerogen all the maturity parameters indicate immature to marginally mature stage of thermal transformation resulting from extremely low geothermal gradients in the area coupled with the observed burial history in addition to oil biogenic gases with a predominance of inorganic compounds co2 and h2s were recovered from the cretaceous carbonates the results of oil and gas analyses define the depositional environment during source rock accumulation and the subsequent thermal conditions it can be concluded that the biogenic gas accumulations in the pliocene quaternary sandstones in the northern adriatic area are the most prospective accumulations in the area

late cenozoic tectonic evolution of the los angeles basin and inner california borderland a model for core complex like crustal extension we propose that the los angeles basin inner california borderland lab ib and the southern borderland off baja california formed by large magnitude crustal extension beginning in latest oligocene earliest miocene time and that these regions represent major late cenozoic rifts the southern borderland is analogous to the gulf of california rift but the onset of rifting in this region may have preceded the opening of the gulf by as much as 15 to 20 m y the lab ib rift is more complex than the southern borderland because it formed in the wake of the rotating western transverse ranges wtr a large crustal block that has undergone more than 90 of neogene clockwise rotation total extension in both rifted regions is estimated to be in excess of 200 km or comparable to the magnitude of late cenozoic crustal extension now estimated for the basin and range province also like the basin and range the crustal floors of the basins in these highly extended domains are characterized by metamorphic core complexes and detachment faults voluminous miocene volcanic rocks and hanging wall fragments of pre rift strata and basement rocks stranded atop detachments during extension in support of this model we synthesize a wide variety of existing geologic data and present interpretations of new geophysical data seismic reflection profiles these profiles image features that we infer are detachment faults and overlying remnants of fragmented and rifted hanging wall rocks we also suggest that a similar but slightly earlier onset of crustal extension affected the santa maria basin and adjacent regions in central california and that the southern margin of this santa maria basin rift was overridden during neogene clockwise rotation of the wtr

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

map restoration of folded and faulted late cenozoic strata across the oak ridge fault onshore and offshore ventura basin california the ventura basin lies within the east west trending active fold and thrust belt of the western transverse ranges california this basin has been the site of significant earthquakes on structures within it and bordering it the purpose of our study is to identify the main structures in the basin and its borders and to quantify their rate of deformation our study includes the onshore and offshore ventura basin the arcuate basin bounding oak ridge reverse fault and the oxnard shelf to the south shortening fault slip and crustal block motions were studied using a three dimensional map restoration technique structure contour maps on the 6 ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program unfold and then fitting the unfolded surfaces across faults comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line average post 5 ma shortening rates estimated from our restoration are slower than both post 1 ma rates and present rates determined by global positioning systems most shortening due to folding in the onshore basin is post 1 ma although slip on the oak ridge fault has occurred both before and after 1 ma displacement due to faulting and folding includes left lateral strike slip motion on the northeast southwest coastal segment of the oak ridge fault and associated clockwise rotation of the adjacent ventura basin the oxnard shelf is bordered to the south by mountains and islands that have been previously interpreted as folds above thrust fault ramps this onshore offshore block moves as one continuous thrust sheet similarly beyond the well studied onshore fault a kinematically continuous offshore oak ridge mid channel left oblique fault system is interpreted to continue at least an additional 100 km westward beneath the santa barbara channel

palinspastic restoration of the anniston transverse zone in the appalachian thrust belt alabama abstract transverse zones are cross strike alignments of cross strike linking structures lateral ramps transverse faults and displacement transfer zones in foreland thrust belts cross strike links constitute one component of a three dimensional system of fault surfaces connecting strike parallel structures frontal ramps and detachment flats both geometrically and kinematically three dimensional palinspastic restoration provides the basis to consider causes of cross strike alignments of cross strike links into transverse zones as well as the role of transverse zones in kinematic history the anniston transverse zone in the appalachian thrust belt in alabama southeastern united states exemplifies the types and distribution of cross strike links within a transverse zone palinspastic reconstruction of the anniston transverse zone relies on matching hanging wall footwall pairs of frontal and lateral ramps for geometric balance in three dimensions in palinspastic map and cross section views cross strike links within the anniston transverse zone are systematically distributed across strike from hinterland to foreland as domains of lateral ramps transverse faults and displacement transfer zones in response to variations in depth to basement beneath the thrust belt and variations in thickness of decollement host weak rocks contrasting structural profiles characterize the thrust belt on opposite sides of the anniston transverse zone as a result of abrupt along strike changes at the cross strike alignment of cross strike links the anniston transverse zone is aligned with a northwest striking basement fault that offsets the boundary faults of the birmingham basement graben suggesting kinematic partitioning within the advancing thrust sheets at a stress concentrator the northwest striking basement fault separates domains of contrasting structural profiles of basement fault systems differing elevations of top of basement and differing thicknesses of the regional decollement host weak layer in the lower part of the sedimentary succession above basement rocks

the north tanganyika hydrothermal fields east african rift system their tectonic control and relationship to volcanism and rift segmentation the two branches of the east african rift system include numerous hydrothermal fields which are closely related to the present fault motion and to volcanic and seismic activity in this study structural data from pemba and cape banza hydrothermal fields western branch north tanganyika zaire are discussed in terms of neotectonic phenomena different types of records such as fieldwork onshore and underwater and landsat and spot imagery are used to explain structural controls on active and fossil hydrothermal systems and their significance the pemba site is located at the intersection of 000 020 trending normal faults belonging to the uvira border fault system and a 120 130 trending transtensional fault zone and is an area of high seismicity with events of relatively large magnitude ms 6 5 the cape banza site occurs at the northern end of the ubawari peninsula horst it is bounded by two fault systems trending 015 and is characterized seismically by events of small magnitude ms 4 the hydrothermal area itself is tectonically controlled by structures striking 170 180 and 080 the analysis of both hydrothermal areas demonstrates the rejuvenation of older proterozoic structures during recent rift faulting and the location of the hydrothermal activity at the junctions of submeridian and transverse faults the fault motion is compatible with a regional direction of extension of 090 110 the cape banza and pemba hydrothermal fields may testify to magma chambers existing below the junctions of the faults they appear to form at structural nodes and may represent a future volcanic province together with the four surface volcanic provinces existing along the western branch they possibly indicate an incipient rift segmentation related to valley valley or transverse fault valley junctions contrasting with the spacing of the volcanoes measured in the eastern branch these spacings appear to express the different elastic thicknesses between the eastern and western branches of the east african rift system perhaps related to a difference in stage of evolution of the two branches

the influence of oxygen isotope exchange between co2 and h2o in natural co2 rich spring waters implications for geothermometry abstract oxygen isotope ratio 18o value deviations from the meteoric water line with no significant change in the hydrogen isotope 2h composition have been reported in naturally occurring co2 rich waters from around the world here we review the effects of oxygen isotope exchange with co2 high temperature equilibration with bedrock minerals and mineral dissolution and precipitation reactions on the co2 rich water isotopic composition we present two case studies from daylesford australia and pah tempe utah usa mineral springs where we use a numerical geochemical modelling approach to resolve the influence of low temperature water rock interactions and co2 equilibration to the oxygen isotope ranges observed in the mineral waters in both cases we find that mineral dissolution precipitation reactions are unlikely to have a significant effect on the groundwater isotopic compositions and that the observed 18o values in natural co2 springs can be simply explained by equilibrium fractionation between water and free phase co2 traditionally the interaction of co2 and water in a natural co2 rich groundwater setting has only been associated with water 18o depletion and this is the first study to consider 18o enrichment we establish that in a natural setting co2 and water equilibration can result in water 18o depletion or enrichment and that the change in the oxygen isotope composition ultimately depends on the initial co2 and water 18o values our new conceptual model therefore provides a mechanism to explain water 18o enrichment at ambient temperatures this finding is critical for the use of 18o in groundwater geothermometry and for the interpretation of natural water circulation depths we argue that in some cases natural waters previously interpreted as geothermal based on their oxygen isotope composition may actually have acquired their isotopic signature through interaction with co2 at ambient temperatures

upper crustal structure and neogene tectonic development of the california continental borderland multichannel seismic reflection data sonobuoy seismic refraction data and regional geology are used to define the upper crustal structure of the southern california continental borderland and to delineate the characteristics of the main lithotectonic belts of the region the catalina schist belt is separated on its west side from the gently deformed nicolas forearc belt by faults that have steep west dips and pronounced normal separations on its east side the schist belt is bounded by a large detachment fault that dips gently to the east beneath the west edge of the peninsular ranges belt at the coastline near oceanside the catalina schist was uplifted from middle crustal depths and exposed during a major event of extensional tectonism that started in early miocene time in conjunction with about 10 of clockwise rotation of the western transverse ranges belt part of the uplift of the catalina schist could have occurred on the detachment fault but it is thought to have mostly occurred on the steep faults that bound the west edge of the schist belt a large amount of uplift is required and it probably involved strong footwall flexural deformation in the wake of the translating and rotating western transverse ranges and nicolas forearc belts extension accompanied by probable large amounts of right slip continued in the borderland region during and after middle miocene time the later stage of extension was accompanied by rapid clockwise rotation of the western transverse ranges of at least 90 most of the borderland including the belt of schist that was uplifted in early miocene time was further deformed into numerous basins and ridges during this stage of oblique extension the primary driving force for the deformation is thought to have been derived from the rapid northwest motion of the pacific plate after it had become coupled to the farallon plate system which had previously been subducted beneath the borderland

lake bogoria hot springs kenya geochemical features and geothermal implications abstract many boiling springs and fumaroles are present along the shores of lake bogoria which is a closed basin alkaline saline lake typical of african rifts two different geothermal waters both of na hco3 type have been recognized the first discharged by the boiling springs located along the western shores of the lake comes from a shallow steam heated thermal aquifer its temperature is close to 100 c as indicated by chalcedony solubility while the chloride content of these waters is slightly higher than 200 mg l 1 the second recognizable in the southernmost boiling springs is representative of a deeper and hotter geothermal reservoir the occurrence of mixing and boiling processes complicates the interpretation of geochemical data nevertheless a chloride content of about 660 mg l 1 an equilibrium temperature close to 170 c and a high carbon dioxide partial pressure at least 10 20 bar have been estimated for the deep geothermal reservoir

holocene explosive eruptions in the rungwe volcanic province tanzania abstract the holocene explosive eruptive record of rungwe and ngozi volcanoes of the rungwe volcanic province in tanzania was reconstructed based on detailed stratigraphic field evidence combined with whole rock major and trace element analyses of tephra samples this reconstruction is supported by 25 new radiocarbon dates on palaeosols that provide additional constraints on the holocene tephro chronostratigraphy we show evidence of two catastrophic ngozi eruptions and five rungwe pumice fallout deposits and also identify several more intercalated poorly preserved pumice and ash deposits the ngozi eruptions probably played a role in shaping the present day caldera the rungwe record includes a ca 2 2 km3 deposit of a plinian style eruption dated at ca 4 ka a sub plinian one at ca 2 ka and at least three additional smaller scale fallout deposits the rungwe explosive eruptive record shows that the volcano has been frequently active in its late holocene past this study highlights the need for volcanic monitoring in the region and presents herewith the first basis of future volcanic hazard assessment

stable isotope geochemistry of cold co2 bearing mineral spring waters daylesford victoria australia sources of gas and water and links with waning volcanism abstract mineral springs in the victorian central highlands australia have high co 2 contents and naturally effervesce 13 c values of co 2 gas and dissolved inorganic carbon are 10 6 to 7 0 and 5 9 to 0 1 respectively with a net 13 c of 8 to 3 the carbon in these waters was derived from a mantle source associated with local pliocene to recent basaltic newer volcanic province rocks previously reported 3 he 4 he 1 2 3 1 relative to air and high he ne ratios are also consistent with the presence of magmatic volatiles silica contents imply that the waters were never heated above 130 c and that the system is not hydrothermal the occurrence of carbonated mineral springs in a relatively small region of the newer volcanics province where volcanic activity ceased several thousands of years ago may be due to the presence of late intrusions combined with deep circulation of water through deeply weathered and fractured ordovician basement a region of low seismic velocity under the daylesford area potentially images those intrusions most spring waters have 18 o and 2 h values of 8 to 6 and 45 to 35 respectively and lie to the left of the local and global meteoric water lines the anomalously low 18 o values results from co 2 exsolution at low temperatures which strongly partitions 18 o into the gas the lack of waters lying to the right of the local meteoric water line also implies that water rock interaction at elevated temperatures did not occur the 2 h values are lower than contemporary meteoric water suggesting that the waters may have recharged under colder climate conditions several thousand years ago the local ordovician rocks are gold bearing the present spring system is cold and would not efficiently transport au however volcanic is waning and the spring systems at the time of volcanism may have been hotter and able to redistribute au

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

geochemical and isotope characterization of geothermal spring waters in sri lanka evidence for steeper than expected geothermal gradients summary seven geothermal springs from the precambrian high grade metamorphic terrain of sri lanka were investigated to assess their formation processes and to determine reservoir temperatures based on their chemical compositions silica based geothermometric calculations for the marangala and nelumwewa springs showed the highest average reservoir temperatures of 122 c and 121 c respectively samples of low temperature

paleomagnetism and neogene tectonics of the northern channel islands california geologic observations and previous paleomagnetic studies have suggested that the western transverse ranges arrived at their anomalous east west orientation by clockwise tectonic rotation a paleomagnetic study of the northern channel islands was undertaken in order to test the extent of rotated areas and to develop constraints on tectonic models concerning the formation of the southern california borderland the islands of anacapa santa cruz santa rosa and san miguel form an east west trending chain and are considered part of the transverse range physiographic province oligocene through miocene volcanic and intrusive rocks occur on these islands and were sampled for this paleomagnetic study eocene sandstones were sampled on san miguel island and eocene sandstones and miocene siltstones were sampled on santa cruz island paleomagnetic results from igneous units are characterized by declinations deflected clockwise by 69 to 81 from expected directions and inclinations which are too shallow by 10 to 25 normal and reversely magnetized units yield antipodal mean directions the mean result is concordant to the directions obtained from individual units which passed fold and baked contact tests these results suggest that the northern channel islands have been tectonically rotated into place since early miocene time as the outer borderland area translated northwestward within a large shear zone between the pacific and north american plates the data from the northern channel islands when averaged with the data from the santa monica mountains yield a result of i 36 1 5 1 d 72 6 6 3 for the southern part of the western transverse ranges 52 units 405 samples the shallow paleomagnetic inclinations suggest a northward latitude translation of 14 0 3 7 or 3 9 for the western transverse ranges however most plate tectonic reconstructions suggest only 4 3 of northward translation the discrepancy may be due to initial dips of the volcanic flows which would cause an artificial shallowing of inclination when the structural dip of the units was corrected to an assumed original horizontal other causes for the shallow inclinations could be the effects of an offset dipole field or nondipole field components or motions of small tectonic plates between the north american and pacific plates as the farallan plate broke up and was subducted

a balanced cross section of the 1994 northridge earthquake southern california the northridge earthquake of 17 january 19941 was the latest in a series of very damaging thrust fault generated earthquakes to strike california following the san fernando2 1971 coalinga3 1983 and whittier narrows4 5 1987 events like the last two of these the northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic hazard methods6 7 balanced cross sections8 9 which flatten and remove the crustal deformation can be used to identify and quantify the seismic hazard posed by thrust faults here we present a balanced cross section through the northridge portion of the transverse ranges fold and thrust belt10 which shows that the earthquake occurred on what we call the pico thrust a cross section of this sort constructed before the earthquake would have revealed the fault although it would not have predicted the earthquake cross sectional modelling of the pico thrust yields an average slip rate of 1 4 1 7 mm yr 1 and a recurrence interval of northridge sized mw 6 7 earthquakes every 1 500 1 800 years we show that the pico thrust is the back thrust to the 170 km elysian park thrust3 4 which underlies some of the most densely urbanized portions of the los angeles basin

thermal springs fumaroles and gas vents of continental yemen their relation with active tectonics regional hydrology and the country s geothermal potential abstract most thermal springs of continental yemen about 65 emergences at 48 sampling sites and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free gas phase whatever the emergence all the water discharges have an isotopic signature of meteoric origin springs seeping out from high altitudes in the central volcanic plateau show a prevalent na hco3 composition clearly affected by an anomalous flux of deep co2 deriving from active hydrothermal systems located in the jurassic amran group limestone sequence and or the cretaceous tawilah group likely underlying the 2000 3000 m thick volcanic suite at lower elevations co2 also affects the composition of some springs emerging at the borders of the central volcanic plateau although mixing to a limited extent with organic co2 infiltrating together with the meteoric recharge waters cannot be ruled out all the co2 rich gas samples have a 13c co2 signature that falls in the range of mantle co2 3 presently the thermal springs of yemen are prevalently used for spas and or bathing nevertheless liquid and gas geothermometry and geological considerations suggest that there are at least three areas al lisi al makhaya and damt inside the yemen volcanic plateau around dhamar that may be promising prospects for the future development of geothermal energy in yemen alternatively they could be used as a source of energy for small to medium scale agriculture and or industrial purposes moreover most of the thermal water discharges have the chemical characteristics of potable waters and in an arid country like yemen they have to be considered as long term water supply resources if the country should face water shortages

hydrogeochemistry of the simav geothermal field western anatolia turkey thermal waters hosted by menderes metamorphic rocks emerge along fault lineaments in the simav geothermal area thermal springs and drilled wells are located in the eynal citgol and nasa locations which are part of the simav geothermal field studies were carried out to obtain the main chemical and physical characteristics of thermal waters these waters are used for heating of residences and greenhouses and for balneological purposes bottom temperatures of the drilled wells reach 163 c with total dissolved solids around 2225 mg kg surface temperatures of thermal springs vary between 51 c and 90 c all the thermal waters belong to na hco3 so4 facies the cold groundwaters are ca mg hco3 type dissolution of host rock and ion exchange reactions in the reservoir of the geothermal system shift the ca mg hco3 type cold groundwaters to the na hco3 so4 type thermal waters thermal waters are oversaturated at discharge temperatures for aragonite calcite quartz chalcedony magnesite and dolomite minerals giving rise to a carbonate rich scale gypsum and anhydrite minerals are undersaturated with all of the thermal waters boiling during ascent of the thermal fluids produces steam and liquid waters resulting in an increase of the concentrations of the constituents in discharge waters steam fraction y of the thermal waters of which temperatures are above 100 c is between 0 075 and 0 119 reservoir ph is much lower than ph measured in the liquid phase separated at atmospheric conditions since the latter experienced heavy loss of acid gases mainly co2 assessment of the various empirical chemical geothermometers and geochemical modelling suggest that reservoir temperatures vary between 175 c and 200 c

neotectonics of the offshore oak ridge fault near ventura southern california the oak ridge fault is a large offset south dipping reverse fault that forms the south boundary of the ventura basin in southern california previous research indicates that the oak ridge fault south of the town of ventura has been inactive since 200 400 ka ago and that the fault tip is buried by 1 km of quaternary sediment however very high resolution and medium resolution seismic reflection data presented here show a south dipping fault on strike with the oak ridge fault that is truncated at 80 m depth by an unconformity that is probably at the base of late pleistocene and holocene sediment furthermore if vertically aligned features in seismic reflection data are eroded remnants of fault scarps then a subsidiary fault within the oak ridge system deforms the shallowest imaged sediment layers we propose that this subsidiary fault has mainly left slip offset these observations of holocene slip on the oak ridge fault system suggest that revision of the earthquake hazard for the densely populated santa clara river valley and the oxnard coastal plain may be needed

microplate capture rotation of the western transverse ranges and initiation of the san andreas transform as a low angle fault system tectonic rotation of the western transverse ranges block is explained by capture of the partially subducted monterey microplate by the pacific plate at about anomaly 6 time ca 20 ma as pacific monterey spreading slowed and eventually ceased the slip vector along the gently northeast dipping subduction interface beneath the california margin changed from slightly oblique subduction to transtensional dextral transform motion this change in slip vector and a shift of pacific plate motion eastward along the already subducted monterey plate interface imply that the san andreas transform began as a system of low angle faults that locally subjected the overriding continental margin to distributed basal shear and crustal extension this basal shear produced the rotated western transverse ranges this model helps explain the timing of initial rotation and basin formation the sudden appearance of widely distributed transform motion well inland of the margin in early miocene time why the western transverse ranges uniquely rotated as a large coherent crustal block and several fundamental structural characteristics of central and southern california the model also provides major constraints on the amount of pacific north america strike slip motion the position through time of offshore oceanic plates relative to onshore geology and a general explanation for what may happen as a spreading ridge approaches a trench and the subduction zone evolves into a transform system

kinematics of thrust sheets within transverse zones a structural and paleomagnetic investigation in the appalachian thrust belt of georgia and alabama deformation styles of orogenic belts change along strike across transverse zones tzs hence the kinematics of tzs is indispensable for three dimensional restoration of thrust belts we investigate the causes of deviation in strike of fold axes and fault surfaces in two tzs of the southern appalachians using structural cross sections and paleomagnetism in the rising fawn tz of georgia hanging wall lateral ramp folds yield paleomagnetic rotations and variation in magnitude of thrust translation plunge of folds differential slip and rotations are associated with lateral ramp geometry and along strike variation in the rheology and thickness of units that host lower and upper detachment levels in alabama the internal geometry strike and paleomagnetic rotations of the helena thrust sheet change across the anniston tz these differences resulted from movement of the helena thrust sheet over different footwall blocks and sub decollement basement graben structures and from differential slip along an oblique ramp rotations of thrust sheets within tzs occur where a thrust sheet was translated over 1 an oblique lateral ramp with contrasting rock strengths at lower and upper detachment levels 2 a transverse basement fault that separates contrasting basement structural domains and 3 intersections between frontal ramps and transverse structures because of the local causes of rotations in lateral structures paleomagnetic and structural analyses of tzs are necessary for understanding the kinematics and restoration of both single thrust sheets and large scale curves in thrust belts

geochemical characterization of organic facies in the dugi otok basin the adriatic sea yugoslavia sediments in the dugi otok basin are predominantly of upper and lower cretaceous age to characterize the organic facies we used geochemical analyses of core samples from different wells and a few outcrop samples geochemical data indicate that the carbonate sequences of the lower cretaceous represent a good source rock section with a high potential for petroleum the source rocks consist both of dark grey uniform micritic limestones and highly bituminous laminated limestones they are associated with oil stains and bitumen impregnations the organic matter is predominantly of marine origin algal sapropelic with a minor input of terrestrial components the extract contents of the samples are anomalously high but contain variable amounts of hydrocarbons and low saturated aromatic hydrocarbon ratios the maturation stage is immature to marginally mature as characterized by a high proportion of resins and asphaltenes with high sulphur content an even predominance of n alkanes a high ratio of acyclic isoprenoids to n alkanes pr ph 1 and a tmax around 430 c the organic facies in the dugi otok basin varies as it is possible to find both organic rich and oxidized organic lean sediments differences in organic facies have been caused by many changes in the depositional environment with tectonic processes contributing to the heterogeneity of the organic facies

diagnosing non meteorically induced variations in the chemistry of saline springs of the vrancea seismic area romania a monitoring operation conducted over more than seven years has been addressing chemical fluctuations displayed by several cool low discharge springs located close to the highly seismic vrancea area romania those outflows compositions proved to be strongly controlled by binary essentially isochemical mixing between a deep origin brine and meteoric freshwater by taking advantage of this particular setting there have been constructed diagrams aimed at investigating how the groundwater discharges na k mg geothermometric parameters fluctuated as a function of the chloride content taken to be an estimator of the freshwater induced dilution we made use of the reciprocal algebraic relationships existing between the equations describing the na k mg geothermometric parameters na k temperature and k mg temperature on the one hand and the so called maturity index mi on the other in an accordingly derived plot of mi against the logarithm of the chloride concentration a series of data points being quite uniformly off set from the mi dilution curve constructed for an apparently regular period suggested that episodically all concerned springwaters were simultaneously subject to some similar changes in the controlling geochemical processes one such modification intervened 3 4 months before the occurrence of the strongest earthquake m text w 5 8 of the hydrochemical monitoring period the consequently derived interpretation was that then the numerical values of certain geothermometric coefficients were likely altered such a process could be consistent with changes in the alkali feldspars solubility relationships possibly in response to episodic al si complexing which might develop within a hypothesised still active exhumation channel

late quaternary activity and seismic potential of the santa monica fault system los angeles california the santa monica fault is a 40 km long oblique left lateral reverse fault that extends through the densely urbanized northwestern los angeles california area and offshore parallel to the malibu coast the fault exhibits near surface strain partitioning in paleoseismologic trenches and has undergone at least six surface ruptures during the past 50 k y although events may be missing from the older part of the record and the ages of older events are based on poorly constrained soil age estimates at least two and probably three events occurred after the well dated burial of a prominent paleosol ca 16 17 ka the resulting 7 8 k y latest pleistocene holocene average recurrence interval for events large enough to cause surface rupture is much longer than the 1 9 3 3 k y maximum interval we calculate for hypothetical m w 6 9 7 0 earthquakes generated by rupture of the entire santa monica fault the pronounced disparity between the measured and calculated average recurrence intervals suggests that the santa monica fault undergoes infrequent and therefore probably very large earthquakes m w 7 0 if such large earthquakes have occurred we speculate that they may have been generated by simultaneous rupture of the santa monica fault with other faults in the transverse ranges southern boundary fault system such as the hollywood or anacapa dume faults the most recent definite santa monica fault surface rupture occurred between ca 10 and 17 ka although a more recent event probably occurred between ca 1 and 3 ka

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

listric thrusts in the western transverse ranges california some of the main faults accommodating current shortening in the western transverse ranges are probably listric because 1 they are associated with progressive tilting and 2 they may be preexisting normal faults that accommodated miocene extension these faults have been reactivated in the pliocene quaternary transpressive regime we propose a listric thrust model where slip is proportional to backlimb dip this model requires relatively little fault slip to account for progressive tilting and for wide in the dip direction and gently dipping backlimbs in contrast widely applied fault bend fold and fault propagation fold models relate fault slip to limb width alone and typically predict more shortening by the blind thrusts that can be accounted for by folding in the cover above them we trace the southernmost structural high in the transverse ranges from the santa monica mountains through the southern santa barbara channel the north dipping backlimb of this anticline is 20 30 km wide and 220 km long its presence suggests a very large north dipping thrust that could generate very large earthquakes the slip rate for this fault however is substantially lower for a listric thrust model than for a single step ramp flat model

restraining segments and reactivation of the santa monica dume malibu coast fault system offshore los angeles california 1 a regional west striking system of surface and blind faults transects northern metropolitan los angeles separating the santa monica mountains from two deep sedimentary basins the surface faults include the santa monica dume and malibu coast faults the three dimensional 3 d geometries of these faults and deformed dated strata were examined in order to determine how oblique shortening is accommodated how structural relief grows along a mountain front and how block translation is related to block rotation industry seismic reflection well and outcrop data were used to construct digital structure contour maps of several of these faults and three stratigraphic horizons that intersect them these maps swath bathymetry digital elevation models and seismicity were incorporated into a 3 d digital database modeling included new approaches to determining strike slip displacement by separate analyses of shortening and structural relief in a restraining double bend stratigraphic thicknesses indicate miocene extension across the santa monica and dume faults which have been reactivated as a single or linked moderately dipping arcuate fault that accommodates one coherent block motion via left lateral and left reverse displacement modeling indicates 5 km 8 1 km of left lateral displacement on part of the santa monica dume fault and 11 of clockwise rotation of the santa monica mountains during the last 4 1 m y modern displacement rates modeled from gps data are similar to our modeled post 4 ma rates of westward escape and clockwise rotation of the santa monica mountains

sycamore knoll a wave planed pop up structure in a sinistral oblique thrust system southern california continental borderland at the boundary between the western transverse ranges province and inner continental borderland of southern california strain is partitioned across the sinistral oblique anacapa dume fault system sycamore knoll a pop up structure 20 km west of point dume in the hanging wall of the north dipping anacapa dume fault stands out as an anomalous bathymetric high along the southern california coast we synthesize new and existing geophysical datasets including multibeam bathymetry backscatter and single multichannel seismic to understand the morphology and tectonic implications of sycamore knoll we identify a complete eustatic low stand submerged marine terrace package encircling sycamore knoll platform that corresponds to the last glacial maximum lgm the marine terrace deposits and wave planed surface of sycamore knoll require a late quaternary uplift rate of 0 55 0 5 0 3 mm yr relative to sea level by combining our uplift rate with previous estimates of basin subsidence and a revised structural model of the anacapa dume fault we determine a maximum slip rate in latest quaternary time of 1 50 0 5 0 3 mm yr and hence a post lgm rate of convergence across the anacapa dume fault of 0 60 0 2 0 1 mm yr

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

environmental control of carbon isotope variations in pennsylvania black shale sequences midcontinent u s a abstract a reversal of the conventional carbon isotope relationship terrestrial lighter than marine organic matter has been documented for two pennsylvanian desmoinesian cyclothemic sequence cores from the midcontinent craton of the central united states deep water organic rich phosphatic black shales contain a significant proportion of algal derived marine organic matter as indicated by organic petrography rock eval hydrogen index and c 27 c 29 sterane ratios and display the lightest 13c values max 27 80 for kerogen while shallower water more oxic facies e g fossiliferous shales and limestones contain dominantly terrestrial organic matter and have heavier 13ckerogen values to 22 87 for a stratigraphically adjacent coal 13c values for extract fractions were relatively homogeneous for the organic rich black shales with the lightest fraction often the aromatics being only 1 or less more negative than the kerogen differences between extract fractions and kerogens were much greater for oxic facies and coals e g saturates nearly 5 lighter than the kerogen a proposed depositional model for the black shales calls upon a large influx of nutrients and humic detritus to the marine environment from the laterally adjacent extremely widespread pennsylvanian peat swamps which were rapidly submerged by transgression of the epicontinental seas in this setting marine organisms drew upon a co2 reservoir which was in a state of disequilibrium with the atmosphere being affected by isotopically light recycled co2 derived from the decomposition of peaty material in the water column and possibly from the anoxic diagenesis of organic matter in the sediments

variations of geothermometry and chemical isotopic compositions of hot spring fluids in the rehai geothermal field southwestern china abstract geothermal variations origins of carbon bearing components and reservoir temperatures in the rehai geothermal field rgf of tengchong volcanic area yunnan province southwestern china are discussed on the basis of carbon isotope compositions combined with helium isotope ratios and geothermal data from 1973 to 2000 13 c values of co 2 ch 4 hco 3 co 3 and travertine in the hot springs range from 7 6 to 1 18 56 9 to 19 48 6 7 to 4 2 6 4 to 4 2 and 27 1 to 0 6 respectively the carbon dioxide probably has a mantle magma origin but ch 4 and he have multiple origins hco 3 and co 3 in rgf thermal fluids are predominantly derived from igneous carbon dioxide but other ions originate from rocks through which the fluids circulate the 13 c values of co 2 hco 3 aq and co 3 aq illustrate that isotopic equilibriums between co 2 and hco 3 aq and co 3 aq and between dic and travertine were not achieved and no carbon isotope fractionation between hco 3 aq and co 3 aq of the hot springs in rgf was found using various geothermometers temperatures of the geothermal reservoirs are estimated in a wide range from 69 c to 450 c that fluctuated from time to time the best estimate of subsurface reservoir temperature may be 250 300 c contributions of mantle fluids and shallow crust fluids in rehai geothermal field varied with time which resulted in variations of chemical and isotopic compositions and reservoir temperatures

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

degassing regime of hekla volcano 2012 2013 hekla is a frequently active volcano with an infamously short pre eruptive warning period our project contributes to the ongoing work on improving hekla s monitoring and early warning systems in 2012 we began monitoring gas release at hekla the dataset comprises semi permanent near real time measurements with a multigas system quantification of diffuse gas flux and direct samples analysed for composition and isotopes 13c d and 18o in addition we used reaction path modelling to derive information on the origin and reaction pathways of the gas emissions hekla s quiescent gas composition was co2 dominated 0 8 mol fraction and the 13c signature was consistent with published values for icelandic magmas the gas is poor in h2o and s compared to hydrothermal manifestations and syn eruptive emissions from other active volcanic systems in iceland the total co2 flux from hekla central volcano diffuse soil emissions is at least 44 t d 1 thereof 14 t d 1 are sourced from a small area at the volcano s summit there was no detectable gas flux at other craters even though some of them had higher ground temperatures and had erupted more recently our measurements are consistent with a magma reservoir at depth coupled with a shallow dike beneath the summit in the current quiescent state the composition of the exsolved gas is substantially modified along its pathway to the surface through cooling and interaction with wall rock and groundwater the modification involves both significant h2o condensation and scrubbing of s bearing species leading to a co2 dominated gas emitted at the summit we conclude that a compositional shift towards more s and h2o rich gas compositions if measured in the future by the permanent multigas station should be viewed as sign of imminent volcanic unrest on hekla

geomorphic indicators of active fold growth south mountain oak ridge anticline ventura basin southern california south mountain oak ridge near ventura california is an asymmetric anticlinal uplift forming at the present time above the active buried oak ridge reverse fault shortening along the oak ridge fault accumulated largely in quaternary time and is responsible for the growth and present topography of the westernmost 15 km of the ridge during the past 0 5 m y tectonic geomorphic analysis using several indices of active tectonics provides information concerning fold growth stream gradient indices are relatively high in the northern eroded fold scarp of the ridge a pattern consistent with the existence of active rapid slip on the oak ridge fault mountain front sinuosity along the northern slope of the anticlinal ridge roughly decreases from 2 to 1 toward the westernmost 10 km of observed surface folding valley floor width to valley height ratios along the northern flank of the ridge generally decrease westward from 1 5 to 0 5 values of the hypsometric integral along the northern flank increase significantly from 0 35 to 0 4 maximum 0 55 from east to west drainage density varies from 4 to 6 km km2 along both flanks of the south mountain oak ridge anticline entrenchment of streams into the southern backlimb of the fold along the westernmost 9 km of the structure decreases from 20 m to 1 m from east to west apparent backlimb rotation as measured by dip of strata along the westernmost 7 km of the fold decreases from east to west from 35 to 20 fold growth of the south mountain oak ridge anticline occurred during the past 0 5 ma following deposition of the saugus formation lateral and vertical fold growth were likely produced by westward decrease in fault slip along the buried oak ridge fault

late quaternary slip rate on the oak ridge fault transverse ranges california implications for seismic risk abstract the slip rate on the oak ridge fault at south mountain in the densely populated lower santa clara valley california is estimated as 6 15 to 12 3 mm yr since the end of saugus deposition at 0 4 to 0 2 ma slightly lower slip rate estimates result from a different projection of the top of the saugus in the hanging wall block of the fault an assumed displacement of 3 m per event gives an average recurrence interval of 250 to 500 yr with the major uncertainty being the age of the top of the saugus displacement of 2460 m of the top of the saugus at south mountain includes piercing point displacement and distributed displacement from drag folds near the fault both are the near surface expression of faulting at potential mainshock depths beneath well control slip rates for the nearby san cayetano and red mountain faults are not well constrained because post miocene strata are absent in their hanging wall blocks but available evidence suggests that their slip rates are about the same as that for the oak ridge fault earthquake return times measured in hundreds of years have been shown by others for the 1971 san fernando fault and a small fault near the red mountain fault and comparable return times are suggested for a normal fault in the hanging wall block of the oak ridge fault a trench on the harmon alluvial fan near the ventura county government center revealed evidence of cracks filled with sediments from below suggesting liquefaction during an earthquake the lower santa clara valley has not had a large damaging earthquake in 200 years of record keeping but one is expected there in the near future the december 21 1812 earthquake may have occurred on the offshore continuation of the oak ridge or red mountain fault

the isotopic and chemical composition of co2 rich thermal waters in the mont dore region massif central france chemical and isotope compositions of fluid samples collected between 1974 and 1986 from 52 springs or shallow boreholes located in the mont dore region massif central france were examined some springs and wells were sampled several times during this period the fluids emerge from quaternary volcanic rocks or paleozoic granite at temperatures between 4 and 62 c and the origin of the h2o is meteoric the waters can be classified into three groups bicarbonate fluids mixed bicarbonate chloride fluids with a mineralization up to 8 g l and acid sulfate fluids only two fluids contain sufficient cl to be considered as mature waters previous work has demonstrated that they all contain partly mantle derived co2 gas and that the co2 rich gas phase and bicarbonate chloride waters are separated at substantial depth mineralized fluids circulate at depth and undergo several processes such as cooling or dilution with recent freshwater during their ascent to the surface therefore the co2 rich gas phase can be partly dissolved in the freshwater or in deep fluids after their dilution this process leads to the dissolution of surrounding rocks such dissolution is discussed on the basis of major element concentrations na k ca mg as well as the sr 87 86 isotope ratio dissolution of s bearing minerals has also been demonstrated the presence of the co2 rich gas phase also leads to isotope exchange between co2 and h2o some mineralized fluids are less affected by these processes than others in which case they display the chemical and isotopic characteristics of the original deep fluids it was shown that the applicability of geothermometer calculations for these waters is hampered by several processes that modify the chemical composition however some geothermometers can be used for estimating the temperature of the deep fluids using the chemical composition of the less modified fluids they indicate that fluids emerging from volcanic rocks in the dordogne valley reach temperatures of around 100 130 c at depth while the temperature of the fluid that issues from the granite at saint nectaire is 160 175 c at depth

mantle derived volatiles in continental crust the massif central of france co2 rich gases and groundwaters from springs and boreholes originating within the basement of the massif central have variable3he 4he ratios with correspondingr ra values ranging from 0 8 to 5 5 and 0 3 to 2 8 respectively indicating the presence of a significant component of mantle helium molar concentrations of rare gases in the co2 rich gases are approximately 5 orders of magnitude greater than in the waters and suggest that a near surface henry s law fractionation has occurred between exsolving co2 and water 13c values of the co2 rich gases are in the range 4 2 to 6 1 i e in that range normally attributed to mantle carbon but which could also represent an average crustal composition and therefore do not discriminate between mantle and crustal sources c 3he ratios show 4 orders of magnitude variation from 1 4 1012 to 5 108 and compared to a mantlec 3he ratio of 109 indicate that either a complex fractionation has occurred between mantle helium and mantle co2 or more likely that mantle rare gases have been diluted by large quantities of co2 with an average crustal carbon isotope composition the regional distribution of3he and c does not show any obvious relationship to age or proximity of volcanic centres or major faults suggesting that mantle derived c and he components decoupled from their silicate melt sources at some depth the results from this area of active fluid circulation suggest that c isotope data derived from metamorphic terrains should be interpreted with great caution but that input of some mantle derived carbon is expected to accompany crustal extension

isotopic and geochemical identification of main groundwater supply sources to an alluvial aquifer the allier river valley france summary hydrodynamic hydrochemical and isotopic investigations were carried out on 18 points including boreholes piezometers and surface waters from february 2011 to august 2012 to assess groundwater quality in the unconfined shallow alluvial aquifer of the allier river one of the main tributary of the loire river the study area located near the city of clermont ferrand france plays an important socio economic role as the alluvial aquifer is the major source of drinking water for about 100 000 inhabitants the objective of the project aims at understanding the functioning of alluvial aquifers that occupy a pre eminent position in the hydrogeologic landscape both for their economic role production of drinking water and agricultural development and for their ecological role moreover this study also targets at determining the factors and processes controlling shallow groundwater quality and origin the water circulates from the south with a natural alimentation from the hills in the non pumped part of the alluvial aquifer in the pumping zone this general behaviour is altered by the pumping that makes the water from the allier river enter the system in a large proportion four end members have been identified for the recharge of the alluvial groundwater rainfall allier river surrounding hills aquifer and the southern non pumped part of the alluvial system results indicate that despite the global ca hco 3 water type of the groundwater spatial variations of physico chemical parameters do exist in the study area ionic concentrations increase from the allier river towards east due either to the increase in the residence time or a mixing with groundwater coming from the aquifer s borders stable isotopes of the water molecule show the same results boreholes close to the river bank are recharged by the allier river depleted values while boreholes far from the river exhibit isotopic contents close to the values of hills spring or to the southern part of the alluvial aquifer both recharged by local precipitation one borehole b65 does not follow this scheme of functioning and presents values attesting of a probable sealing of the allier river banks based on these results the contribution of each end member has been calculated and the functioning of the alluvial system determined

oak ridge fault ventura fold belt and the sisar decollement ventura basin california abstract the rootless ventura avenue san miguelito and rincon anticlines ventura fold belt in pliocene pleistocene turbidites are related to south dipping reverse faults rising from a decollement in underlying miocene shale to the east sulphur mountain anticlinorium comprises the upper plate of a south dipping set of thrusts sisar big canyon lion that merge downward into a decollement in mudstone of the rincon formation named here the sisar decollement shortening of the miocene and younger sequence is 3 km greater than that of the underlying competent vaqueros sespe and marine eocene sequence in the ventura fold belt and 7 km greater farther east at sulphur mountain cross section balancing requires that this difference be taken up by the paleogene sequence at the oak ridge fault to the south convergence is ne to nne based on earthquake focal mechanisms and piercing point offset of the south mountain seaknoll by the oak ridge fault a ne trending line connecting the west end of oak ridge and the east end of the sisar fault separates an eastern domain where late quaternary displacement is taken up entirely on the oak ridge fault and a western domain where displacement is transferred to the sisar decollement and its overlying rootless folds this implies that 1 the oak ridge fault near the coast presents as much seismic risk as it does farther east despite negligible shallow post 0 2 ma movement 2 ground rupture hazard is high for the sisar fault set in the upper ojai valley and 3 the decollement could fail on a low angle thrust at depth and produce an earthquake analogous to the 1987 whittier narrows event in los angeles

the escarot gas seep french massif central co 2 discharge from a quiescent volcanic system characterization and quantification of gas emissions abstract natural co2 emissions from the volcanic rocks of the french massif central are poorly constrained it is of interest better to assess the emission of such non anthropogenic gases that may significantly contribute to the global carbon budget we quantified the co2 emissions to the atmosphere in a small area 0 052 km2 located in the massif central close to lake pavin the most recent volcanic edifice in metropolitan france the specific character of this area known as the escarot mofette was earlier studied for soil gas concentrations only in june 2017 we used the accumulation chamber method for measuring co2 flux and related o2 depletion in the gases emitted at the soil atmosphere interface resulting in 176 data acquisitions over four days in addition 44 soil gas concentration measurements were made at selected locations co2 emission rates are estimated at 8100 1800 tons year of deep seated co2 and at 660 440 tons year of biologically produced co2 the uncertainty on these evaluations comes from the high frequency variability of co2 efflux in the more emissive areas and from the occurrence of heavy precipitation events though unexpected these events were used for quantifying the decreases in co2 efflux which were as high as 500 over a few hours or even days in some locations however repeat acquisitions performed under more favourable weather conditions showed errors of commonly accepted amplitude 15 the area showed several degassing centres aligned along a nnw sse direction that correlates well with known geological structures proving the ability of soil gas methods to map hidden faults the whole area is characterized by strong co2 enrichment and related o2 depletion but it is nonetheless possible to detect areas influenced by the rise of deep seated gases and a few peripheral areas where biological processes dominate co2 up to 10 vol this study of gas emissions in a non urban area also provides complementary information that is of use when extrapolated to similar structures in urban areas where the occurrence of such gas releases and its potential hazard may be more difficult to assess

use of hydrochemistry and isotopes for improving the knowledge of groundwater flow in a semiconfined aquifer system of the eastern slavonia croatia abstract knowledge of groundwater flow and accordingly groundwater residence time is immensely important for the sustainable management of groundwater resources this requires a good conceptual model of the aquifer system in this paper a conceptual model based on the interpretations of hydrogeological and hydrochemical data as well as measurements of environmental tracers 18 o 2 h 3 h was formulated for a semiconfined aquifer system in eastern slavonia in croatia the aquifer system is composed of quaternary gravel and sand and silty clayey interlayers and is covered with low permeability deposits measurements of water levels and environmental tracers in the study area clarified the groundwater flow evolution from the recharge area to the discharge area the content of stable isotopes confirmed that the groundwater originates from precipitation the tritium content and geochemical processes such as cation exchange silicate weathering suggested a relatively long residence time of groundwater in the part of the aquifer system that is further from the sava river the same is confirmed by the results of calculated particle tracking pathlines

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

recent deformation along the offshore malibu coast dume and related faults west of point dume southern california offshore faults west of point dume southern california are part of an important regional fault system that extends for about 200 km from near the city of los angeles westward along the south flank of the santa monica mountains and through the northern channel islands this boundary fault system separates the western transverse ranges on the north from the california continental borderland on the south previous research showed that the fault system includes many active fault strands consequently the entire system is considered a serious potential earthquake hazard to nearby los angeles we present an integrated analysis of multichannel seismic and high resolution seismic reflection data and multibeam bathymetric information to focus on the central part of the fault system that lies west of point dume we show that some of the main offshore faults have cumulative displacements of 3 5 km and many faults are currently active because they deform the seafloor or very shallow sediment layers the main offshore fault is the dume fault a large north dipping reverse fault in the eastern part of the study area this fault offsets the seafloor showing holocene displacement onshore the malibu coast fault dips steeply north is active and shows left oblique slip the probable offshore extension of this fault is a large fault that dips steeply in its upper part but flattens at depth high resolution seismic data show that this fault deforms shallow sediment making up the hueneme fan complex indicating holocene activity a structure near sycamore knoll strikes transversely to the main faults and could be important to the analysis of the regional earthquake hazard because the structure might form a boundary between earthquake rupture segments

the origin of reservoir fluids in the geothermal field of los azufres mexico isotopical and hydrological indications abstract the calculation of hydrological balance resulted in a potential average annual infiltration rate of 446 206 mm m 2 for the los azufres geothermal area which corresponds to a total of 82 10 6 m 3 per a due to the highly fractured and faulted structure of the volcanic formations a considerable potential for the infiltration of recent meteoric water into deeper sections of the volcanic formations can be assumed isotopic data indicate the minor importance of recent meteoric water for the recharge of the geothermal reservoir very negative 13 c values can be explained by the input of organic c from the surface but the lack of 14 c in the deep fluids reflects a pre historic age for the infiltration event of fossil meteoric water the dilution of the meteoric water by 14 c free co 2 gas from a shallow magma chamber complicates the exact age determination of the infiltration event which probably occurred during the late pleistocene or early holocene glacial period strong water rock interaction processes such as sericitization chloritization caused the primary brine composition to be camouflaged a preliminary hydrological model of the reservoir can be postulated as follows the fossil hydrodynamic system was characterized by the infiltration of meteoric water and mixing with andesitic and or magmatic water strong water rock interaction processes in the main part of the production zone prove the existence of former active fluid circulation systems due to changes in pressure and temperature the rising fluids get separated into liquid and vapour phases at a depth of 1500 m after cooling the main portions of both phases remain within the convective reservoir cycle isotope analyses of hot spring waters indicate the direct communication of the reservoir with the surface at some local outcrops a recent reactivation of the hydrodynamic system is caused by the geothermal production as indicated by the detection of lateral communication between some production and reinjection wells

an anomalous thermal water from hofsstadir western iceland evidence for past co2 flushing abstract the geothermal field at hofsstadir northern snaefellsnes peninsula iceland produces low temperature geothermal water with about 5 4 salinity the fluid temperature is 87 c near the reservoir temperature of 90 c as assessed from mineral solution equilibrium conditions the stable isotopic ratios 2h and 18o show that the water is significantly lighter than present day precipitation anywhere on the snaefellsnes peninsula it is offset from the meteoric water line towards isotopically depleted 18o values most likely due to co2 g h2o exchange at earlier times during evolution of the system such a concentration of stable isotopes is unique for icelandic groundwaters and has not been encountered anywhere else in iceland the water may either have its origin far north of the bay of breidafjor ur in the highland of the western fjordlands or dating back to a pre holocene age when local precipitation was considerably lighter due to the cold climate at that time the water is highly concentrated in ca in comparison with seawater and also compared to that of geothermal saline water elsewhere which indicates intensive and prolonged water rock interaction the 14c concentration is low about 7 4 pmc percent modern c compared to the cold local groundwater of about 74 6 pmc 13c for the thermal and cold waters is 4 9 and 2 3 respectively the geothermal water is used for heating the small town of stykkisholmur through a central heat exchanger plant due to the high salinity of the water the outbuilding of a health resort has been planned and the water has been used successfully for the treatment of psoriasis and is claimed to have beneficial effects in bathing therapy for rheumatism as well as for drinking cures

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

hydrothermal hydrocarbon gases 2 application in the east african rift system hydrocarbon gases are ubiquitous in the hydrothermal systems of the east african rift system ears though often found at very low concentrations in the volcanic eastern branch as compared to the sedimentary western branch study of the chemical and isotopic compositions of these hydrocarbons from sites in kenya ethiopia djibouti and uganda reveals considerable homogeneity over hundreds of km of the various rift units consideration of c and he isotopic evidence points to a predominantly crustal thermogenic origin for the hydrocarbons there being no evidence of mantle inputs in either the morb or hotspot sectors of the ears temperature information from geothermal wells has been utilised to investigate the relationship between reservoir temperatures and ratios of ch4 to c2h6 the general c1 c2 geothermometric relationship proposed in part 1 of this study holds reasonably well and is shown to give results equal to or better than the inorganic gas geothermometers presently in use both in the wellfields and undeveloped high enthalpy geothermal areas results from low enthalpy hot spring systems are less well correlated with apparent deep temperatures but consistent with data from similar systems elsewhere in the world

seismicity of tanzania distribution in time space magnitude and strain release abstract the seismicity of tanzania is examined from an earthquake catalogue the record of the seismic history of tanzania is found to be neither complete nor homogeneous a steady flow of earthquake data has only been available since 1954 for the period 1954 1988 the frequency magnitude analyses indicate that the events of magnitude 4 5 are reasonably reported and the recurrence relations exhibit consistent high b values for the three cases examined the cumulative annual seismic energy curve gives an average annual energy accumulation amounting to 2 7 10 12 j up to 1964 and an average annual energy accumulation of 3 9 10 12 j for the events of 1985 the spatial distribution of epicentres confirms the high correlation of seismic activity with the major rift tectonics and other zones of well known tectonic features however a number of events scatter in zones of less defined tectonism energy mapping revealed these pockets of high seismic activity

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

geochemical study of potential source rocks and crude oils in the anadarko basin oklahoma paleozoic source rocks and crude oils from the anadarko basin oklahoma have been characterized by means of a variety of organic geochemical techniques the potential source rocks investigated include the viola group sylvan shale lower mississippian limestone chester group springer formation and morrow group the woodford shale which is an important source rock in the basin and has been discussed extensively in the literature was used as a laboratory standard in this study the crude oils examined in this study were obtained from reservoir formations of various ages from throughout the basin the source rock screening analysis indicates that the lower and middle subfacies of the viola especially from the southeastern part of the basin have substantial oil generation potential the sylvan is not a source rock although the black shales in the springer and morrow have substantial oil and especially gas generation potential the results of this study support the proposal for multiple sources of oil and gas generation in the anadarko basin selected source rock and oil samples were characterized in more detail and the distributions and concentrations both relative and absolute concentrations of biomarkers in different source rocks and oils were determined the biomarker characteristics were combined with other geochemical and geological data to interpret the sources depositional environments diagenesis and catagenesis processes migration and weathering oil source rock correlations were made between source rocks and a number of crude oils based on quantitative and qualitative biomarker distributions petrographic descriptions and graptolite reflectance measurements were used to evaluate copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received november 1 1995 revised manuscript received april 8 1996 final acceptance september 13 1996 2arco international oil and gas company 2300 w plano parkway plano texas 75057 3school of geology and geophysics university of oklahoma norman oklahoma 73019

oxygen isotope geochemistry of geothermal wairakite abstract oxygen and hydrogen isotopic compositions of wairakite were determined for drillcore samples from exploration wells in the active geothermal systems in japan takigami and kirishima and in new zealand wairakei and ngatamariki and for samples from some extinct japanese hydrothermal systems the 18 o values range from 0 4 to 7 8 for wairakite from the active systems whereas they are generally higher ranging from 8 0 to 14 1 for the mineral from the extinct systems indicative of retrograde re equilibration with local meteoric water at low temperatures the d values of channel water are lower than those of hydrothermal fluids or local meteoric water the d h fractionation between channel water and external water becomes more negative as temperature lowers the monomineralic oxygen isotopic temperatures based on the framework oxygen channel water fractionation of wairakite are in good agreement with the measured present day downhole temperatures and or calculated geochemical temperatures for the takigami and wairakei geothermal fluids at takigami wairakite and associated calcite are found to be in oxygen isotopic equilibrium at the measured fluid temperature of around 220 c the kirishima geothermal system is thought to be in a waning stage of geothermal activity as recorded by fluid inclusion temperatures the wairakite isotopic temperatures are consistent with the above thermal history reflecting precipitation of wairakite from the most recent relatively cool water the disequilibrium oxygen isotopic relationship between some calcite wairakite pairs for the kirishima geothermal system suggests that the two minerals were precipitated from the waters with different 18 o values at different stages in the evolution of the system consistent with paragenetic relations of the minerals in core samples oxygen isotopic composition of wairakite can be used as a new single mineral isotopic geothermometer for active geothermal systems and be applied to elucidate their thermal evolution

tectonic controls on rift basin morphology evolution of the northern malawi nyasa rift radiometric k ar and ar 40 ar 39 age determinations of volcanic and volcaniclastic rocks combined with structural gravity and seismic reflection data are used to constrain the age of sedimentary strata contained within the seismically and volcanically active northern malawi nyasa rift and to characterize changes in basin and flank morphologies with time faulting and volcanism within the tukuyu karonga basin began at approximately 8 6 ma when sediments were deposited in abroad initially asymmetric lake basin bounded on its northeastern side by a border fault system with minor topographic relief extensions primarily by a slip along the border fault and subsequent regional isostatic compensation led to the development of a 5 km deep basin bounded by broad uplifted flanks along the low relief basin margin opposite border fault younger stratigraphic sequences commonly onlap older wedge shaped sequences although their internal geometry is often progradational intrabasinal faulting flankuplift and basaltic and felsic volcanism from centers at the northern end of the basin became more important at about 2 5 ma when cross rift transfer faults developed to link the tukuyu karonga basin to the rukwa basin local uplift and volcanic construction at the northern end of the basin led to a southeastward shift in the basin s depocenter sequence boundaries are commonly erosional along this low relief hanging wall margin and conformable in the deep lake basin the geometry of stratigraphic sequences and the distribution of the erosion indicate that horizontal and vertical crustal movements both across and along the length of the rift basin led to changes in levels of the lake irrespective of paleoclimatic fluctuations

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism