deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

a multichannel seismic study of lithospheric flexure across the hawaiian emperor seamount chain existing models assume that the thickened crust beneath seamounts is the result of a surface volcanic load flexing an elastic plate new results suggest that flexed oceanic crust beneath the hawaiian emperor seamount chain is underlain by a 4 km thick deep crustal body we intepret the body as a deep crustal sill complex associated with the tholeiitic stage of volcano building along the chain

petrology of gabbroic xenoliths from mauna kea volcano hawaii gabbroic xenoliths from the hawaiite summit cone of mauna kea volcano hawaii are up to 15 cm in size and form two groups olivine pl cpx gabbros and opaque oxide pl cpx gabbros both types have members that are laminated and probably cumulate in origin and each type has interstitial glass of hawaiitic mugearitic composition olivine gabbros have mgo 12 25 wt feo 4 12 and tio2 0 5 1 whereas opaque oxide gabbros have mgo about 6 wt feo 12 18 and tio2 5 7 due to 11 27 vol fe ti oxides cli nopyroxene and plagioclase compositions in both gabbro types fs7 14 wo41 47 al2o3 3 4 an52 89 or0 5 3 indicate that these xenoliths are products of hawaiian magmatism and not n type mid ocean ridge basalts these phases plus olivine compositions fo71 84 paragenesis and mixing models using representative mauna kea basaltic rocks indicate that the gabbros are crystalline products from mafic alkalic parent basalt e g 8 wt mgo modeling shows that residual liquid after 25 30 crystallization of ol pl cpx the xenoliths may be basalt hawaiite of the hamakua volcanics on mauna kea alternatively 60 crystallization of ol pl cpx mt il feasibly produced liquid represented by the hawaiite of laupahoehoe volcanics interstitial glass may represent liquid after more than 60 crystallization crystallization depth was shallow if daughter magmas were hamakua but was at least at 8 kbar pressure if laupahoehoe hawaiites were produced due to absence of liquidus cpx in laupahoehoe rocks laupahoehoe hawaiite transported the xenoliths to the surface

accretionary process of the tertiary setogawa and mikasa groups southwest japan the middle eocene to lower miocene setogawa group consists of pelagic hemipelagic and terrigenous sediments with volcanic intercalations the sediments were deposited in and below the lower bathyal zone the setogawa group is a wedge shaped volcano sedimentary pile deformed by reverse faults and asymmetric folds at the landward edge and constitutes a subduction complex the reverse faulting and asymmetric folding took place abruptly accompanied by tilting uplifting and gravity sliding of strata and dewatering and consolidation of sediments this was followed by the lower miocene mikasa group which consists of in ascending order debris flow deposits terrigenous and volcano terrigenous sediments the basal debris flow deposits were mostly derived from the upper part of the setogawa group they buried the structural depressions formed by the reverse faulting and asymmetric folding and eroded the underlying strata over the short timespan included in the stichocorys delmontensis zone the mikasa g

selected geochemical factors influencing diagenesis of eocene carbonate rocks peninsular florida u s a abstract the geochemical significance of three selected ions mg2 na and sr2 supports a model of dolomitization by brackish groundwater this groundwater zone contains sufficient quantities of mg2 to facilitate dolomitization mg ca ratios 1 rising and falling of sea level and fluctuations of the phreatic zone related to climatic variations account for the thickness of the dolomite layers and the chemical distributions within these layers sodium concentrations in the calcite are 70 185 ppm indicating formation in brackish water dolomite has sodium concentrations between 50 1400 ppm suggesting formation in waters of similar salinity strontium in calcite ranges from 320 600 ppm suggesting diagenesis in slightly saline waters in an open system dolomite contains 241 ppm sr2 on the average and calcite has 418 ppm sr2 the sr2 concentrations of the dolomite are characteristic of diagenesis in water less saline than sea water average strontium concentrations in the dolomite occur in two distinct groups 260 ppm for dolomite with 39 43 mole mgco3 and 195 ppm for the dolomite with 44 50 mole mgco3 the difference in the sr2 concentrations of the two dolomite groups indicates the higher mole mgco3 dolomite recrystallized in a less saline environment than the lower mole mgco3 dolomite these different environments are attributed to a relatively more saline coastal environment and a less saline inland environment the more nearly stoichiometric dolomite 44 50 mole mgco3 has less scatter when mole mgco3 is plotted against sr2 and na this suggests a greater approach to equilibrium with the dolomitizing fluid than the lower mole mgco3 39 43 dolomite the more saline environment has higher mg ca ratios and promotes more calcium rich dolomite during diagenesis because of the inhibition from competing foreign ions and because it is thermodynamically a more favorable environment which causes more rapid crystallization the less saline waters allow recrystallization to proceed more slowly producing better ordering in the dolomites textural preservation and development of subhedral to euhedral rhombic crystals

tectonic evolution of northeastern siberia and adjacent regions abstract previous models for the tectonic evolution of northeastern siberia have proposed the existence of a kolyma plate composed of the kolyma and omolon massifs of presumed precambrian age lithologic similarities between the siberian platform and the cherskiy mountains and the presence of oceanic and island arc type deposits in the kolyma indigirka interfluve suggest that no such plate exists the eastern margin of the siberian plate is suggested to lie along a line between the ulakhan sis range the alazeya uplift and the arga tas range the cherskiy mountains and the verkhoyansk fold belt are parts of the siberian plate the paleozoic deposits of the omolon massif are unlike those found in the cherskiys or siberia paleomagnetic data from the omolon massif are discordant from data from siberia it is suggested that the omolon massif represents a microplate which accreted onto siberia in the jurassic ophiolites in central chukotka are of the same emplacement age as in the western brooks range and may have been emplaced at the initiation of the rotation of arctic alaska geometric and limited stratigraphic data suggest that the east siberian sea may be floored by oceanic crust left by an incomplete closure between arctic alaska siberia and omolon the tectonic position of the prikolymsk massif remains ambiguous

ascending freshwater mesohaline mixing a new scenario for dolomitization abstract the process of mixing zone dolomitization has received enough criticism in recent years to suggest that it no longer be considered viable for making large amounts of dolomite this study proposes an alternative model that still requires fluid mixing in this model ascending flow of freshwater mixes with evaporated seawater leading to extensive dolomitization the new model is constrained by data from upper miocene strata of southeast spain where dolomite yields fluid inclusion tm ice data that range from 0 2 to 2 3 c indicating precipitation from fluids of 4 to 43 ppt seawater salt equivalent thus confirming fluid mixing the 13c and 18o of the dolomite ranges from 4 5 to 3 0 vpdb and 0 9 to 6 0 vpdb respectively and displays positive covariance although such positive covariation may represent fluid mixing the mixing of two dolomites during sampling or an originally homogeneous dolomite that has been partially altered recrystallized fluid inclusion data and cathodoluminescence petrography disprove the mixture during sampling and partial alteration hypotheses modeling of the most positive dolomite 18o values indicates an evaporated seawater endmember of 43 ppt salinity identical to that of the most saline fluid inclusions because paleotopography is preserved in the study area the spatial variation in dolomite geochemistry can be mapped to evaluate if it is consistent with the hydrogeology of a typical mixing zone model or an alternative the data reveal that both downdip and updip areas were influenced by high salinity and low salinity fluid endmembers and that stratigraphically lower units have more depleted 13c and 18o than upper units these results are consistent with a model of upward flow of freshwater that provides the mechanism of mixing of freshwater and evaporated seawater upward flow and degassing of co2 from loss of pressure contributed to nearly platform wide dolomitization in this succession and may have analogs in other ancient successions

geochemistry of axial seamount lavas magmatic relationship between the cobb hotspot and the juan de fuca ridge axial seamount located along the central portion of the juan de fuca ridge axis and at the eastern end of the cobb eickelberg seamount chain is the current center of the cobb hotspot the axial seamount lavas are transitional between n type and e type mid ocean ridge basalt morb characteristics that they share with lavas along the rest of the juan de fuca ridge there are however subtle but distinct differences between the seamount lavas and those of the adjoining ridge segments these include higher na2o cao and sr at a given mgo content and lower silica saturation in the seamount lavas as compared with the ridge lavas lava chemistry and bathymetry indicate that axial seamount is a discrete volcanic unit with a more productive shallow magmatic plumbing system separate from the adjacent ridge segments these high magma supply rates have sustained a continuously replenished steady state magma reservoir that has erupted remarkably homogeneous lavas over a long time period despite this classic association of spreading center and hotspot volcanic activity there is no evidence in the lavas for geochemical or isotopic enrichment typical of hotspot or mantle plume activity the differences in composition between the axial seamount lavas and the juan de fuca ridge lavas are attributed to melting processes rather than to any fundamental differences in their mantle source compositions the higher magma production rates higher sr and lower silica saturation in the seamount lavas relative to the ridge lavas are thought to be a consequence of melt initiation at greater depths the melting column producing the seamount lavas is thought to be initiated in the stability field of spinel peridotite whereas the ridge lavas are produced from a melting column initiated at shallower levels possibly within or close to the stability field of plagioclase peridotite implicit in this interpretation is the conclusion that the juan de fuca ridge lavas and by analogy most morb are generated at shallow mantle levels mostly within the stability field of plagioclase peridotite this interpretation also requires that for the upwelling mantle to intersect the solidus at different depths the mantle supplying axial seamount must be hotter than the rest of the juan de fuca ridge axial seamount therefore reflects a thermal anomaly in the mantle rather than a geochemically enriched ocean island basalt type mantle plume

the role and impact of freshwater seawater mixing zones in the maturation of regional dolomite bodies within the proto floridan aquifer usa palaeogene dolostones from the sub surface of florida are ideal for the study of dolomite maturation because they record the early stages of a secondary dolomite overprint without destruction by later diagenetic overprints two distinct dolomite textures occur in the dolostones of the upper eocene ocala and lower oligocene suwannee limestones in west central florida a porous and permeable sucrosic dolomite and a less porous and relatively impermeable indurated non sucrosic dolomite in both textures the initial matrix dolomite is dully luminescent whereas the secondary overprint is dominantly luminescent cement in the suwannee and only neomorphic luminescent dolomite in the ocala the abundance of luminescent dolomite ranges from 2 to 38 which translates to 1 6 km3 of material in the suwannee and 13 5 km3 in the ocala extrapolated trace element contents sr and na and 18o values for the matrix and luminescent end members indicate a marine origin for the matrix dolomite in both units and a freshwater seawater mixing zone origin for the secondary luminescent dolomites the 18o values indicate that a saline middle mixing zone environment overprinted the suwannee but a more dilute mixing zone affected the ocala fluid fluid mixing models constrained by modern floridan aquifer hydrochemistry and extrapolated 87sr 86sr values of the luminescent phases indicate that the mixing zones operated during the late miocene to pliocene in the ocala and affected the suwannee in the pliocene the luminescent suwannee mixing zone cement reduced porosity up to threefold and permeability up to 100 fold which converted many sucrosic dolomites to indurated dolomites by contrast the neomorphic luminescent ocala dolomite did not have an appreciable impact on the maturations although freshwater seawater mixing zones were not the sites of the initial dolomitization the mixing zone environment did dramatically overprint and mature the regionally widespread dolomites of the ocala and suwannee limestones this maturation occurred shortly after formation of the proto floridan aquifer the timing suggests the matrix dolomites were ripe for alteration and that the only prerequisite for mixing zone dolomite is pre existing dolomite substrates to reduce kinetic barriers in contrast to recent claims the results of this study demonstrate that mixing zones can be effective in forming regionally significant amounts of secondary dolomite and influencing the petrophysical maturation of dolomite bodies

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

the combined use of 87sr 86sr and carbon and water isotopes to study the hydrochemical interaction between groundwater and lakewater in mantled karst abstract the hydrochemical interaction between groundwater and lakewater influences the composition of water that percolates downward from the surficial aquifer system through the underlying intermediate confining unit and recharges the upper floridan aquifer along highlands in florida the 87sr 86sr ratio along with the stable isotopes d 18o and 13c were used as tracers to study the interaction between groundwater lakewater and aquifer minerals near lake barco a seepage lake in the mantled karst terrane of northern florida upgradient from the lake the 87sr 86sr ratio of groundwater decreases with depth mean values of 0 71004 0 70890 and 0 70852 for water from the surficial aquifer system intermediate confining unit and upper floridan aquifer respectively resulting from the interaction of dilute oxygenated recharge water with aquifer minerals that are less radiogenic with depth the concentrations of sr2 generally increase with depth and higher concentrations of sr2 in water from the upper floridan aquifer 20 35 g l relative to water from the surficial aquifer system and the intermediate confining unit result from the dissolution of sr bearing calcite and dolomite in the eocene limestone dissolution of calcite 13c 1 6permil is also indicated by an enriched 13cdic 8 8 to 11 4 in water from the upper floridan aquifer relative to the overlying hydrogeologic units 13cdic groundwater downgradient from lake barco was enriched in18o and d relative to groundwater upgradient from the lake indicating mixing of lakewater leakage and groundwater downgradient from the lake the 87sr 86sr ratio of groundwater and aquifer material become less radiogenic and the sr2 concentrations generally increase with depth however sr2 concentrations are substantially less than in upgradient groundwaters at similar depths the lower sr2 concentrations result from the influence of anoxic lakewater leakage on the mobility of sr2 from clays based on results from mass balance modeling it is probable that cation exchange plays the dominant role in controlling the 87sr 86sr ratio of groundwater both upgradient and downgradient from lake barco even though groundwater from the three distinct hydrogeologic units displays considerable variability in sr concentration and isotopic composition the dominant processes associated with the mixing of lakewater leakage with groundwater as well as the effects of mineral water interaction can be ascertained by integrating the use of stable and radiogenic isotopic measurements of groundwater lakewater and aquifer minerals

permeability loss with depth in the cenozoic carbonate platform of west central florida relationships between matrix permeability and depth in shallow buried 500 m cenozoic limestones of florida were investigated using more than 12 000 minipermeameter measurements on 1210 m of slim hole core these data are considered representative of the matrix permeability reduction that accompanies early burial of shallow water subtidal to peritidal nonreefal carbonates of sta ble cratonic margins platforms shelves and ramps measured matrix permeabilities range from less than 4 0 to 6450 md for both limestones and dolostones although the median permeability of limestones 88 md exceeds that for dolostones 15 md sucrosic dolostones which have high intercrystalline po rosities have median matrix permeabilities of 1000 md non sucrosic dolostones which are much less porous have median matrix permeabilities of only 13 md neither population of dolostones exhibits a permeability with depth trend low permeability limestones consist of mudstones wackestones tidal laminites pedogenetically altered limestone lime mud rich breccia and well cemented grain supported rocks these low permeability limestones all exhibit median matrix permeabilities less than 35 md and none exhibit permeability with depth trends in contrast high mud packstones low mud packstones very low mud packstones and grainstones exhibit larger median matrix permeabilities 69 129 181 and 418 md respectively and a systematic reduction with depth in their mean and maximum permeabilities least squares exponential regressions indicate that burial depth explains 22 31 of the permeability variance in these grain supported rocks the balance of the variability within each textural class is attributed to variation in facies grain types grain sizes sorting etc and the amount of early preburial cementation in the absence of permeability enhancement by deep subsurface diagenesis or fracturing extrapolation of the permeability with depth trends suggests that the limestones that have the best reservoir potential in the deeper subsurface are grain supported limestones that have higher than begin page 1254 average matrix permeabilities in the near surface realm petrographic analyses and consideration of diagenetic histories suggest that matrix permeability of the dolostones and low permeability limestones was determined by early near surface dolomitization and cementation respectively and has yet to be affected by burial processes petrographic observations also suggest that the depth signal in grain supported limestones results from mechanical compaction and the onset of grain to grain pressure solution extrapolation of the matrix permeability data indicates that permeability loss with burial occurs faster than the documented burial related porosity loss for the same group of rocks this indicates that limestone permeability is more sensitive to burial compaction than limestone porosity thus preservation of reservoir quality rock during burial is more dependent on permeability preservation than on porosity preservation

k ar dating of some infra ophiolitic metamorphic soles from the eastern mediterranean new evidence for oceanic thrustings before obduction abstract k ar dating on separated minerals from the infra peridotitic metamorphic soles outcropping beneath various eastern mediterranean ophiolite complexes pindos nappe in greece lycian antalya beysehir hoyran mersin and pozanti karsanti nappes in the taurides belt turkey baer bassit nappe in syria shows that the main metamorphic recrystallization of those rocks occurred 25 30 m y prior to the tectonic emplacement of the ophiolite complexes onto a continental platform these data support the hypothesis of an early slicing of the oceanic crust before its obduction advocated recently by several authors

magma supply and storage at kilauea volcano hawaii 1956 1983 abstract shallow crustal magma reservoirs beneath the summit of kilauea volcano and within its rift zones are linked in such a way that the magma supply to each can be estimated from the rate of ground deformation at the volcano s summit our model builds on the well documented pattern of summit inflation as magma accumulates in a shallow summit reservoir followed by deflation as magma is discharged to the surface or into the rift zones magma supply to the summit reservoir is thus proportional to summit uplift and supply to the rift zones is proportional to summit subsidence the average proportionality constant is 0 33 10 6 m 3 rad this model yields minimum supply estimates because it does not account for magma which escapes detection by moving passively through the summit reservoir or directly into the rift zones calculations suggest that magma was supplied to kilauea during july 1956 april 1983 at a minimum average rate of 7 2 10 6 m3 month roughly 35 of the net supply was extruded the rest remains stored within the volcano s east rift zone 55 and southwest rift zone 10 periods of relatively rapid supply were associated with the large kapoho eruption in 1960 and the sustained mauna ulu eruptions in 1969 1971 and 1972 1974 bursts of harmonic tremor from the mantle beneath kilauea were also unusually energetic during 1968 1975 suggesting a close link between kilauea s deep magma supply region and shallow storage reservoirs it remains unclear whether pulses in magma supply from depth give rise to corresponding increases in shallow supply or if instead unloading of a delicately balanced magma transport system during large eruptions or intrusions triggers more rapid ascent from a relatively constant mantle source

double seismic zones and stresses of intermediate depth earthquakes data from japanese local seismograph networks suggest that the stresses in double seismic zones are in plate compression for the upper zone and in plate tension for the lower zone the stresses do not necessarily appear to be down dip it may therefore be possible to identify other double seismic zones on the basis of data which indicate that events with differing orientations of in plate stresses occur in a given segment of slab a global survey of published focal mechanisms for intermediate depth earthquakes suggests that the stress in the slab is controlled at least in part by the age of the slab and the rate of convergence old and slow slabs are under in plate tensile stresses and the amount of in plate compression in the slab increases with increasing convergence rate or decreasing slab age young and fast slabs are an exception to this trend all such slabs are down dip tensile since these slabs all subduct under continents they may be bent by continental loading double seismic zones are not a feature common to all subduction zones and are only observed in slabs which are not dominated by tensile or compressive stresses unbending of the lithosphere and upper mantle phase changes are unlikely to be the causes of the major features of double zones although they may contribute to producing some of their characteristics sagging or thermal effects possibly aided by asthenospheric relative motion may produce the local deviatoric stresses that cause double zones

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 1 lithostratigraphic units and volcanostructural implications abstract the sinking of a deep drill hole 3003 5 m for geothermal exploration in the eastern part of the piton de la fournaise volcano on reunion island has revealed the underlying lithostratigraphy six principal sequences have been distinguished a 0 440 m subaerial basaltic flows b 440 556 m a transitional series characterized by an alternation of subaerial basalts and submarine deposits vitric basalt and hyaloclastic breccia c 556 616 m submarine basalts lavas and hyaloclastites d 616 890 m subaerial basalts e 890 1010 m submarine basaltic deposits with abundant argillized hyaloclastites f 1010 3003 5 m a layered intrusive complex comprising 1010 1129 m sheets of gabbro injected into the lavas and hyaloclastites 1129 1920 m a zoned intrusion of olivine gabbro and dolerite 1920 3003 5 m stratified cumulate gabbro wehrlite dunite the occurrence of the first submarine deposits at 440 m 268 m below present sea level and the intercalation with them of subaerial basalts down to 890 m 728 m below present sea level tend to support a hypothesis of sliding into the sea during subsidence of the eastern flank of the fournaise massif the intrusive complex intersected from 1010 m down is regarded as a former shallow magma chamber a large positive gravimetric anomaly 40 50 mgal centered over grand brule and attributed to the intrusive complex indicates that its roof forms an ellipse 3 20 km elongated n s stratigraphic and morphological structural evidence on land and on the sea floor and the results of the mineralogical study of this very large magma chamber suggest that it belongs to an ancient edifice proto fournaise whose activity preceded the construction of the present fournaise and ended at about 0 6 ma on land the evidence for this earlier edifice is to be found in the zeolitised basalts and differentiated lavas hawaiites forming the basement to the phase 1 lava flows certain subsidence structures on the present fournaise are interpreted as resulting from settling of the proto fournaise volcano the destabilization of the east flank grand brule area of the currently active volcano and the location of the ne and se rift zones could be attributed to the same phenomenon

mineralogical changes along the freshwater saltwater interface of a modern aquifer abstract occurrence of dolomite is related to the distribution of geological and hydrochemical parameters in cores and wells penetrating the floridan aquifer along portions of the west coast of peninsular florida trace element analyses of the cores indicate correlations between strontium and sodium concentrations and the particular carbonate phase chloride sulfate and conductivity values indicate the position and extent of the freshwater saltwater interface thick sequences of carbonate rocks in western peninsular florida have been dolomitized in the freshwater saltwater mixing zone of the coastal aquifer correlations between the occurrence of dolomite and specific stratigraphic formations suggest that dolomitization was rock selective evidence of continuous formation of dolomite indicates that the process is actively occurring

focal mechanisms and locations of earthquakes in the vicinity of the 1975 kalapana earthquake aftershock zone 1970 1979 implications for tectonics of the south flank of kilauea volcano island of hawaii the november 29 1975 kalapana earthquake of magnitude 7 1 on the south flank of kilauea volcano hawaii represents a major rift tectonic event it is generally understood that the earthquake resulted from movement on a nearly horizontal fault plane with the crustal block south of kilauea s east rift zone moving south southeastward up to several meters well recorded earthquakes on the south flank of kilauea from 1970 to 1979 were analyzed and focal mechanisms determined to obtain a better understanding of the details of south flank tectonics included are a large number of earthquakes from the aftershock sequence of the 1975 earthquake hypocenters are distributed in a subplanar zone that dips 2 to 3 to the west at a depth of about 8 9 km depth we interpret this pattern to coincide with a portion of the slip plane of the kalapana earthquake and to be consistent with the notion of the slip plane occurring in a weak layer at the top of the old oceanic crust focal mechanisms are remarkably constant throughout this time period both before and after the 1975 event and closely agree with the mainshock mechanism p axis azimuths and slip vectors for the low angle fault planes are normal to the middle and lower east rift zones of kilauea there is suggestion of a change in the orientation of p axes from shallower to steeper plunge at the time of the kalapana earthquake such a change is consistent with a general reduction in the horizontal compressional stress normal to the rift zone at the time of the large earthquake no other evidence of precursory reorientation of the stress field was found and the precise predictability of this event remains in doubt however a general model of the tectonics of the volcanic rift system is now available that satisfies a number of geological and geophysical observations

the origin of tectonic stress in the lithosphere abstract the sources of lithospheric stress and their distinctive features are briefly reviewed it is suggested that there are two main categories of lithospheric stress renewable stress which persists despite continuing stress relaxation and non renewable stress which can be dissipated by relief of the initial strain the two most important types of renewable stress arise from plate boundary forces and from isostatically compensated loads non renewable stress systems include bending stresses membrane stresses and thermal stresses an important phenomenon generating large stresses at shallow depth is stress amplification caused by lower lithospheric creep this applies to renewable stresses but not to the non renewable type it is suggested that only renewable stresses contribute significantly to tectonic activity however bending and thermal stresses are locally important in subducting lithosphere

diverse basalt types from loihi seamount hawaii loihi seamount is the southeasternmost active volcano in the hawaiian emperor volcanic chain the seamount is considered representative of the early phase of hawaiian volcanism because of its youth small size and location near the melting anomaly seventeen dredge stations recovered transitional basalt alkalic basalt and basanite in addition to the expected tholeiitic basalt four flows of alkalic basalt contain common small dunite xenoliths the recovered samples have thin palagonite rinds and almost no manganese on the glassy surfaces we estimate that the lavas are less than about 4 000 yr old and many are less than 1 000 yr old loihi seamount is apparently in a transitional growth phase between the early eruption of alkalic lavas and the commonly observed subaerial tholeiitic eruptive phase previously thought to dominate hawaiian volcanism from inception until the postcaldera collapse alkalic stage

fluctuations in surface height of active lava lakes during 1972 1974 mauna ulu eruption kilauea volcano hawaii an active lava lake is one that forms directly on top of a magma column as opposed to an inactive one formed by passive ponding of lava within a preexisting crater two active lava lakes operating within summit craters of newly constructed volcanic shields at mauna ulu and alae were the longest lived of any observed in a hawaiian rift zone to date small scale fluctuations a few to 20 m in the height of lake surfaces are typically associated with degassing gas piston activity larger fluctuations as great as 200 m reflect major changes in eruptive activity measurements of surface height fluctuations of mauna ulu lake show gross positive correlation with variation in summit tilt which in turn reflects the inflation deflation state of kilauea s summit magma reservoir a more tenuous conclusion is that a sympathetic variation possibly exists between surface heights of the mauna ulu and alae lakes collectively these observations 1 require the existence of a fully engorged connected open and hydraulically efficient magma conduit system linking the summit reservoir with the lava lakes 2 provide additional evidence for the postulated regime of quasi steady state magma transfer that characterized much of the eruption 3 imply that fluctuations in lake surface reflect variation in magma supply rate to the reservoir and or outflow rate from the mauna ulu alae vents and 4 suggest undetected episodes of magma intrusion or storage in kilauea s east rift zone during 1973

flexure and seismicity beneath the south flank of kilauea volcano and tectonic implications we present a refined model for the tectonic behavior of kilauea volcano s south flank including flexure calculations and microearthquake data supportive of the model in our model the south flank moves seaward over the downwardly flexed ocean crust in a manner analogous to an accretionary prism in a subduction zone the flank is driven seaward by the gravitational stresses inherent in its shape this driving force is augmented by high density material in kilauea s rift zones elastic flexure calculations predict a configuration for the downwardly flexed crust which agrees with previous seismic refraction and gravity modeling this configuration in turn is consistent with the hypothesis that many earthquakes occur along the volcanic pile ocean crust interface focal mechanisms for these events predominantly indicate southeastward directed overthrusting we also propose a relationship between rift zone intrusion and south flank displacement including a suggestion that the decollement configuration controls the relative activity of kilauea s east and southwest rift zones

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 3 mineral chemistry of the cumulate rocks abstract dunites at the base of the grand brule intrusive body are deformed cumulates with olivine fo 84 5 fo 87 3 containing exsolution lamellae of spinel discrete grains of chrome spinel enriched in titanium with a high fe 3 fe 2 ratio and interstitial chrome diopside a complex assemblage of silicate inclusions pargasite orthopyroxene nepheline albite jadeite has been found in these spinels the mineral composition of wehrlite and gabbro overlaps that of dunite with olivine fo 76 9 fo 85 6 chrome spinel with up to 25 wt fe 2 o 3 chrome diopside and plagiocalse an 53 4 an 80 6 these cumulates are interpreted as the result of fractional crystallization in a frequently replenished magma chamber however this chamber does not seem to be related to the present piton de la fournaise structure and is interpreted as part of an older proto fournaise volcanic edifice peridotitic and gabbroic nodules found in lavas from the piton de la fournaise and piton des neiges volcanoes are probably derived from similar bodies

geology and petrogenesis of lavas from san cristobal island galapagos archipelago volcanism became emergent on san cristobal island 2 3 m y b p in the eruption of floods of alkaline basalt volcanism then coalesced in a central shield volcano which erupted continually until 0 6 m y b p at 0 9 m y b p activity began to jump to the northeast and the style of volcanism changed to fissure fed eruptions that have continued almost to historical time three distinct magma series occur on san cristobal an alkaline series a series of morb like tholeiites and a series of incompatible element enriched tholeiites that are typical of oceanic islands each series is represented by very primitive basalts that have been little modified since segregation from their sources each series also has more evolved lavas which range from low mg basalts to hawaiites and icelandites these evolved lavas are the result of simple fractional crystallization of magmas which produces major and compatible element compositions similar to those of observed primitive lavas the isotope and trace element data suggest that the different series are generated by different degrees of partial melting and mixing of both a depleted and an enriched source the first source is thought to be the depleted asthenosphere which generates the morb9s of the galapagos spreading center and the enriched source is the mantle plume associated with the galapagos hotspot

three hawaiian calderas an origin through loading by shallow intrusions the calderas of kilauea and mauna loa are highly dynamic structures and in the 200 year historic period have varied in volume by a factor of 2 and gained or lost 1 km3 per century the deeply eroded caldera of the extinct koolau volcano in oahu is wider than active hawaiian calderas and its lavas have a strong centripetal dip and funnel structure not evident at kilauea or mauna loa the differences can be attributed to the different erosion depths and the time integrated subsidence profile of kilauea is also a stepped funnel having its apex at halemaumau koolau caldera is the focus of an extraordinarily intense dike complex and an intriguing feature is the great diminution in dike concentration into the caldera it is thought that dike injection in any part of the complex generally continued until it reached 50 to 65 in outer parts of the caldera the complex was maintained at or rebuilt to this value despite subsidence in the center of the caldera where the positive bouguer anomaly is centered subsidence evidently greatly outpaced the capacity of dike injections to rebuild the complex assuming the same dike injection rate as kilauea and mauna loa yields a volumetric subsidence rate in koolau caldera exceeding 1 km3 per century hawaiian calderas are much more dynamic than calderas of silicic volcanoes shaped by frequent small events instead of a few great ones the temporal and volumetric correspondence of historical subsidence events with eruptions is poor and this and the high subsidence rates argue for a caldera forming mechanism that consumes the subsided rocks it is suggested that subsidence is caused by the great localized excess load of intrusive rocks carrying the center of the volcano into the thermally weakened lithosphere above the hawaiian hot spot it is envisaged that under steady state conditions the magma chamber rises as the injection of intrusions causes the level of neutral buoyancy at which the chamber is located to ascend and keeps pace with subsidence

replenishment rates of crustal magma and their bearing on potential sources of thermal energy abstract a general model of magma intrusion into the crust is developed which is based on a viscous dissipation forced convection flow process driven by gravitational buoyancy forces although some of the points in this general model have been studied before it is possible with the present model to go further and calculate magma volumetric intrusion rates from fundamental properties and parameters equations for forced convection in a conduit with viscous dissipation are combined with results for the temperature dependence of magma viscosity the volumetric intrusion rate is shown to be not a function of viscosity as might be expected but rather a function primarily of the rate of change of viscosity with temperature the model predictions for intrusion rate correlate well with field results for several sites where data exist for both intrusion or extrusion rate and for the temperature dependent behavior of magma viscosity the model predicts magma chamber replenishment rates equivalent to thermal energy rates on the order 10 gw gigawatts for a single active magma site assuming active magma sites on a 50 km spacing along volcanic lineaments leads to an estimate of a renewable magma intrusion rate into the crust of the western u s on the order of 2 tw terawatts

analysis of surface deformation data kilauea volcano hawaii october 1966 to september 1970 a least squares inversion technique has been applied to surface displacement measurements made at kilauea volcano hawaii in an attempt to locate centers of intrusive activity utilizing analytic expressions for the displacement field arising from dilatational sources in an elastic half space this technique allows for the simultaneous inversion of level tilt and horizontal distance measurements in terms of the location and volume of the intrusive body a variety of simple elastic model geometries representing possible shapes for intrusive bodies in the summit region of kilauea were examined none of the model geometries considered significantly improved the quality of the model fit to the available data over that obtained by a point source model calculations based on elastic models to consecutive level surveys were compared to available tilt data and horizontal distance measurements these comparisons indicate occasional departures from ideal elastic behavior the departure of measured tilt patterns from calculated tilt values may be the result of earthquake activity or episodic block movements superimposed on larger elastic displacements the departure of measured and calculated horizontal measurements reveals a gradual north south extensional strain across the summit caldera of kilauea in addition to the elastic uplift and subsidence patterns determined from level surveys a minimum estimate for the magma supply rate to kilauea is provided by the elastic models to the level data the average rate for the period from october 1966 to september 1970 was 0 07 km3 per year

magma reservoir subsidence mechanics theoretical summary and application to kilauea volcano hawaii an analytic model has been developed for the prediction of the three dimensional deformation field generated by the withdrawal of magma from a sill like storage compartment during an intrusion or eruption cycle the model is based on the work of berry and sales 1961 1962 and predicts the vertical displacement components over the areal plane model parameters are the depth of burial h the intrusion half width a the intrusion half length b the thickness of the magmatic interior at the moment of melt withdrawal tm and the planform aspect ratio a b the products of the model include areal deformation maps systematic variation in model parameters within the context of kilauea volcano hawaii have revealed that circular and elliptical deformation patterns result from the collapse of draining rectilinear intrusions at depth moreover the geometric parameters of a storage compartment may interact in complex ways to produce similar deformation patterns the model has been applied to kilauea volcano for three periods of pronounced summit subsidence 1 1921 1927 bracketing the steamblast eruptive phases of 1924 2 june 1972 to december 1972 and 3 december 1972 to may 1973 application of the model requires the simultaneous optimization of five predicted deformation features with respect to field measurements and the derivative deformation maps 1 the vertical displacement maxima 2 the vertical displacement gradients over the areal plane 3 the lateral extent of the deformation field 4 the aspect ratio of the subsidence pattern and 5 the strike of the major axis of the deformation field the constrained geometries and volumes of the inferred collapsed storage cavities for each period are 1 1921 1927 depth 3 km a 1500 m b 4500 m tm 20 m v 540 106 m3 2 june 1972 to december 1972 depth 3 3 km a 600 m b 2000 m tm 1 m v 4 8 106 m3 and 3 december 1972 to may 1973 depth 2 2 km a 500 m b 1612 m tm 1 m v 3 2 106 m3 for 2 and 3 calculated magmatic thicknesses tm happen to be in the range 3 48 0 15 m of measurements for sill like bodies in deeply dissected hawaiian shield volcanoes the fits obtained between calculated and observed deformation patterns allow quantification of the location overall dimensions orientation and volume of the discrete still molten interior of sill like compartments from which magma is tapped during eruption or intrusion

a single force model for the 1975 kalapana hawaii earthquake a single force mechanism is investigated as the source of long period seismic radiation from the 1975 kalapana hawaii earthquake m s 7 1 the observed love wave radiation pattern determined from the spectra of world wide standard seismograph network and high gain long period records at 100 s is two lobed with azimuth consistent with a near horizontal single force acting opposite strike 330 to the observed displacement direction of the earthquake this pattern is inconsistent with the expected double couple pattern assuming a form of the force time history of a one cycle sinusoid the total duration of the event estimated from rayleigh waves at two international deployment of accelerometers stations is approximately 180 s the peak amplitude f o of the time function is 1 10 15 n from amplitudes of love and rayleigh waves the interpretation is that the bulk of the seismic radiation was produced by large scale slumping of a large area of the south flank of kilauea volcano the single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass using the mass estimated from the tsunami generation area 10 15 10 16 kg the peak acceleration of the slide block 0 1 1 m s 2 inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane the slump model for the kalapana earthquake is also more qualitatively consistent with the large horizontal deformation 8 m on land and tsunami associated with the earthquake which are difficult to explain with the conventional double couple source model the single force source has been used previously to model the long period seismic waves from the landslide accompanying the eruption of mount st helens volcano and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation

incipient magma chamber formation as a result of repetitive intrusions an analytical solution for periodic magma intrusions in conduits was developed to study the onset of shallow magma chamber formation the solution is based on determining when a repetitive series of intrusions can cause the wall rock of a conduit to reach its melt temperature the results show that magma chamber formation in conduits is a strong function of the volume rate of intrusion and that magma chamber formation is likely when the intrusion rate exceeds 10 3 km3 yr which agrees with observations by other investigators once this critical value of intrusion rate is reached magma chambers are likely to begin forming after only a few intrusive pulses less than ten results for both cylindrical conduits and dikes show cylindrical conduits are more favourable for the formation of shallow magma chambers

gravity induced stresses near topography of small slope topographic modification of gravity induced near surface stresses results in significant departures from a lithostatic state a perturbation scheme provides approximate analytical solutions for plane strain of an elastic half space with an irregularly shaped free surface of small characteristic slope e the leading order effect of the topography is equivalent to that of a distributed normal load on a plane boundary and the correction at order e is due to a distributed shear traction on a plane boundary in the near surface region these two effects contribute at the same order to departures from the lithostatic stress field the contribution of the shearing has been neglected in most previous analyses we present explicit solutions for several particular geometries a symmetric ridge or valley an adjacent ridge and valley a shelf and a sharp crested ridge notable features include 1 for a sufficiently steep ridge the horizontal normal stress is compressive at the crest and decreases possibly becoming tensile with depth 2 large horizontal tension is induced in a valley bottom at greater depth these effects vanish and the stresses approach lithostatic similar analysis is applied to a half space under a far field tectonic compression or tension the result shows that the leading order effect of topography is equivalent to a distributed shear traction on a plane surface regional horizontal compression can be significantly reduced or even change to tension in the neighborhood of a topographic high

correlation between regional and global seismic activity abstract the regional seismic activity in sweden is significantly correlated to the global seismic activity this result suggests that the regional swedish activity is linked to the global activity by intraplate tectonics rather than being caused exclusively by regional effects such as the land uplift after the last glaciation

geochemical and geological evidence bearing on the origin of the bay of islands and coastal complex ophiolites of western newfoundland abstract suggestions that ophiolitic rocks of the bay of islands complex boic and coastal complex cc of southwestern newfoundland were formed at a seafloor spreading center are supported by 1 1 whole rock trace and major element data from diabases and basalts 2 2 spinel mineral chemistry from ultramafic rocks 3 3 the internal geology of the ophiolite terranes and 4 4 regional geologic and tectonic constraints in the western newfoundland appalachians diabase and basalt samples from the boic and the northern cc massifs are tholeiitic and geochemically indistinguishable from present day mid ocean ridge basalts morbs many diabases from the lewis hills massif the southernmost part of the cc are also identical to morbs but there is also an unusual suite of diabases from the lewis hills that is unlike any other suite yet reported from a variety of tectonic settings including island arcs ocean islands or spreading centers this suite is interpreted to have been produced by unusual magma generation processes in the deep structural levels of an oceanic ridge ridge transform fault approximately 90 of spinels from ultramafic rocks in the boic and cc have cr cr al ratios that are less that 0 60 comparable to those values reported from ultramafic rocks of the present day ocean basins these geochemical constraints in combination with previously described geological relationships within the ophiolite terranes and regional tectonic relationships in the western newfoundland appalachians suggest that the boic and cc ophiolites formed within a main ocean basin i e the early paleozoic iapetus ocean along a seafloor spreading center and ridge ridge transform fault respectively there is little evidence to suggest formation in either an island arc or back arc basin tectonic setting as such the boic and cc ophiolites are probably well suited for detailed petrologic structural and geophysical studies to determine the processes involved in the generation and evolution of contemporary oceanic crust and upper mantle

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 2 secondary minerals abstract the grand brule borehole intersects a thick pile of basaltic lavas down to 1010 m and a basic ultrabasic intrusive complex from 1010 to 3003 50 m the lavas are in general unaltered except in two fractured zones where hydrothermal fluids circulated at temperatures not exceeding 350 c the main secondary minerals there are pyroxene feldspar epidote actinolite and chlorite the entire thickness of the intrusive body intersected contains secondary minerals representing three stages of cooling 1 1 a late magmatic episode 600 900 c characterized by biotite kaersutite edenite and pargasite 2 2 a hydrothermal episode t 3 3 a phase of serpentinization t 350 c it is very likely that the two later events occurred simultaneously with physical and chemical interference

late cenozoic prograding wedges on the nw european continental margin their formation and relationship to tectonics and climate abstract during late pliocene to pleistocene times prominent prograding wedges were deposited along the continental margin of nw europe resulting in seaward shelf break migration of up to 150 km much of the sediment accumulation occurred marginal to the former mid to high latitude ice sheets the geographical distribution and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late pliocene to pleistocene climate deterioration and onset of major northern hemisphere glaciations the onset of wedge growth on the nw uk and irish margins was initiated at about 4 ma in response to tectonic tilting of the margin in that region however glacially derived sediments here comprise a significant proportion of the wedges especially since 0 44 ma for the faroe margin no detailed chronology is available however it may be inferred that onset of glacigenic wedge growth here did not post date that observed on the nw uk and irish margins offshore norway wedge growth has largely occurred since ca 2 7 ma in response to northern hemisphere glaciations also recording a major change in sediments transport routes at 0 8 1 1 ma reflecting larger fennoscandian ice sheets presently it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase in response to uplift in this area in the western barents sea an early phase of wedge growth was glacio fluvial in character off western spitsbergen the development was similar to that of the barents sea although the glacigenic wedge growth phase may have started somewhat earlier the wedges commonly display gently inclined seaward prograding clinoforms and transparent to chaotic internal acoustic facies sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that to various extents have been affected by bottom current action the clinoforms of these wedges vary in geometry from oblique to sigmoidal and they also show varying degrees of aggradation throughout their development the resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply sedimentary processes and accommodation space the latter being a function of tectonic movements and or loading induced subsidence as well as eustatic sea level fluctuations