intercalibration of 40ar39ar dating standards a number of standards used for k ar and 40ar39ar dating have been intercalibrated multiple splits 15 40 mg each of mmhb 1 sb 3 biotite lp 6 biotite 40 60 ga1550 biotite fish canyon tuff 3 biotite taylor creek rhyolite sanidine bern 4 muscovite bern 4 biotite and pennsylvania state university orthoclase 1a were irradiated in capsules fused and analyzed in replicate analyses most of these standards proved to be homogeneous in 40ar 39ark ratio age k ca and 36ar contents mmhb 1 is inhomogeneous in age at the 15 mg level indicating it is unsuitable for use as an interlaboratory standard using material taken straight from the bottle the orthoclase sample is also inhomogeneous at the 30 mg level quoted relative to an age of 162 9 ma for the sb 3 biotite standard total fusion ages are lp 6 biotite 40 60 128 1 ma ga1550 biotite 97 8 ma fish canyon tuff 3 biotite 27 95 ma taylor creek rhyolite sanidine 28 0 ma bern 4 muscovite 18 51 ma bern 4 biotite 17 21 ma these ages are in good agreement with the absolute k ar ages of these minerals different preparations of biotite and sanidine standards from a welded tuff such as the fish canyon tuff may not be of identical ages tests on submilligram splits reveals that sb 3 biotite ga1550 biotite fish canyon tuff 3 biotite and taylor creek rhyolite sanidine are suitable for use as monitors in laser work the sanidine specimen appears to be the most suitable for use as the primary monitor for 40ar39ar dating

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

a mechanistic study of nonlinear solute transport in a groundwater surface water system under steady state and transient hydraulic conditions two laboratory experiments were conducted to investigate the effects of tides and buoyancy on beach hydraulics in the presence of a seaward groundwater flow due to an elevated regional water table in the first experiment case 1 the difference in concentration between the salt water at sea and the water of the regional aquifer was small 2 4 g l 1 such that it did not engender density gradients the salt acts as a tracer in this case in the second experiment case 2 the difference was 32 0 g l 1 which creates a significant density gradient this case corresponds to the presence of fresh groundwater in the subsurface of the coasts of the continental united states the experiments were numerically simulated by the marine unsaturated marun model a numerical model for density and viscosity dependent flows in two dimensional variably saturated media the long term experimental and numerical results showed that the seawater plume entered the beach from the sea and occupied most of the intertidal zone the maximum depth of the seawater plume was near the midsection of the intertidal zone and it decreased near the low and high tide lines when viewed in the context of case 2 these results indicate an inverted salinity distribution in beaches subjected to tides with salt water from sea overtopping the freshwater lens for both cases water from the regional aquifer moved seaward beneath the seawater in the intertidal zone and pinched out near the low tide mark we also noted that beach hydraulics are highly two dimensional with water entering the beach at a near vertical angle and leaving it at a near horizontal angle which casts doubts on analyses of beach hydraulics based on the dupuit assumption findings from this work have direct implications within the practice of bioremediation of oil spills on beaches we found that applying dissolved nutrients on the beach surface at low tide is superior to applying them in a trench landward of the beach this is because the residence time of the nutrient plume in the bioremediation zone of the beach in the prior situation is longer than that in the latter

evolution of feldspars at the amphibolite granulite facies transition in augen gneisses sw norway geochemistry and sr isotopes the sveconorwegian augen orthogneisses of rogaland vest agder sw norway were emplaced as amphibole and biotite bearing granodiorites at 1040 ma concordant rb sr and zircon u pb ages they underwent prograde metamorphism which increased from lower amphibolite facies in the eastern zone to granulite facies in the western zone close to the rogaland anorthosite complex k feldspar megacrysts initially crystallised as phenocrysts and were chemically equilibrated during metamorphism as shown by the flat ba concentration profiles and the increase of the anorthite content from an1 1 in the amphibolitefacies to an2 6 in the granulite facies this increase of the an content suggests an increase in metamorphic temperature the ree content of the megacrysts is related to the associated accessory minerals which depend upon the metamorphic grade sphene allanite apatite zircon and rarely thorite in amphibolite facies and apatite zircon monazite thorite in lower amphibolite and granulite facies amphibole and biotite inclusions in megacrysts were also equilibrated during metamorphism groundmass k feldspar and plagioclase experienced late metamorphic changes during uplift an internal rb sr mineral isochron plagioclase apatite k feldspar defines an age of 870 ma which represents the closure of the rb sr isotopic system in minerals of the augen gneisses this age also represents a k feldspar cooling age in regionally distributed augen gneiss samples the k feldspar cooling age appears to be similar to or slightly older than the biotite cooling age

maximum warning times for imminent volcanic eruptions accelerations in seismicity are important precursors to eruptions at volcanoes reawakening after extended repose intervals these have previously been quantified for subduction zone settings in terms of the linkage of crustal faults by shearing introducing a damage mechanics criterion for the weakening of rock between major fractures the model is here modified for failure in tension consistent with conditions in crust surrounding a pressurized magma reservoir the results indicate that final accelerations develop over similar to 2 3 weeks at tensile strains of 4 5 3 2 x10 3 since a week or more is required to identify an accelerating trend seismic forecasts of eruptions after long repose are unlikely to be reliable more than days in advance improvements will require the integration of additional precursors or extension of the model to earlier stages of fracture growth in stressed crust

isotopic constraints on the timing of crustal accretion of the bamble sector norway as evidenced by coronitic gabbros abstract this paper presents the first sm nd data for coronitic gabbros hyperites from the high grade proterozoic bamble sector norway sm nd whole rock isochron ages of the vestre dale gabbro 1 11 0 14 ga the jomasknutene gabbro 1 77 0 19 ga and the flosta gabbro 1 64 0 23 ga indicate that contrary to earlier ideas intrusion of these gabbros is not exclusively bound to the sveconorwegian orogeny 1 2 0 9 ga some of the gabbros were already emplaced at the onset of or during the gothian orogeny 1 75 1 5 ga initial nd values of about 5 5 of jomasknutene and flosta gabbros provide clear evidence of a depleted mantle reservoir beneath this part of the southwest scandinavian domain this highly positive value differs from the nd isotope evolution curve for the southwest scandinavian mantle as postulated by mearns et al 1986 which assumes that depletion of the mantle beneath this part of scandinavia started at c 1 74 ga however the initial nd value of the vestre dale gabbro plots close to this curve whereas 143nd 144nd ratios of the mantle sources of the tromoy and arendal gabbros evolved with approximately chondritic 144sm 144nd ratios their nd 1 1 ga values range from 5 1 0 3 to 6 0 0 3 gothian metasomatism of a depleted mantle source by lile and lree bearing fluids provides a mechanism to obtain low nd isotope ratios in magmas represented by the vestre dale gabbro examples of low nd isotope magmas have also been found in the telemark sector and in southern sweden the marked depletion in nb indicates that the metasomatic fluids were possibly related to gothian subduction

a geochemical and geophysical reappraisal to the significance of the recent unrest at campi flegrei caldera southern italy volcanic unrest at calderas involve complex interaction between magma hydrothermal fluids and crustal stress and strain campi flegrei caldera cfc located in the naples italy area and characterised by the highest volcanic risk on earth for the extreme urbanisation undergoes unrest phenomena involving several meters of uplift and intense shallow micro seismicity since several decades despite unrest episodes display in the last decade only moderate ground deformation and seismicity current interpretations of geochemical data point to a highly pressurized hydrothermal system we show that at cfc the usual assumption of vapour liquid coexistence in the fumarole plumes leads to largely overestimated hydrothermal pressures and accordingly interpretations of elevated unrest by relaxing unconstrained geochemical assumptions we infer an alternative model yielding better agreement between geophysical and geochemical observations the model reconciles discrepancies between what observed 1 for two decades since the 1982 84 large unrest when shallow magma was supplying heat and fluids to the hydrothermal system and 2 in the last decade compared to the 1980 s unrest the post 2005 phenomena are characterized by much lower aquifers overpressure and magmatic involvement as indicated by geophysical data and despite large changes in geochemical indicators our interpretation points out a model in which shallow sills intruded during 1969 1984 have completely cooled so that fumarole emissions are affected now by deeper co2 richer magmatic gases producing the modest heating and overpressure of the hydrothermal system our results have important implications on the short term eruption hazard assessment and on the best strategies for monitoring and interpreting geochemical data this article is protected by copyright all rights reserved

the volcanic and geothermally active campi flegrei caldera an integrated multidisciplinary image of its buried structure the campi flegrei caldera in southern italy is one of the greatest geohazard areas on earth evidence of an active magmatic and geothermal system is provided by ongoing ground uplift with volcano tectonic and long period lp seismicity the persistent degassing of 1500 tonnes of co2 per day the presence of hot fumaroles at temperatures of 90 150 c brine rich aquifers with total dissolved solids up to 33 g l 1 and high thermal gradients in the crust with temperatures reaching 420 c at 3 050 m b s l since the 1940s more than 100 exploratory boreholes have been drilled in the area to depths of 80 3 100 m by the azienda geologica italiana petroli agip and the societa anonima forze endogene napoletane safen to date however no systematic reanalysis of the drilling data has been carried out and the buried volcanic structure has not been updated using the most recent scientific results and previous findings by integrating unpublished data from the agip and safen reports with published information from geological volcanological petrological petrophysical and geophysical studies this paper presents an improved picture of the campi flegrei caldera that will be useful for volcanic hazard assessment and mitigation in the naples area and for future research planning the results suggest that intra caldera activity has been influenced by how the magmatic system at depths greater than about 4 km has determined the transfer of magma volatiles and heat to the overlying geothermal system and ultimately to the surface in particular intriguing is that the most volcanically active central eastern sector of the caldera which is subject to intense bradyseismic ground movement and gas emission coincides with a structurally delimited subsurface rock volume characterized by an uprising of the 100 c isotherm a deep water supply to the shallower aquifer the early disappearance of secondary calcite lp seismicity and high seismic s wave attenuation in this area we also document evidence of repeated injection at depths of c 1 5 3 0 km of isolated and small volume batches of magma where occurred their crystallization and degassing shallow intrusions and degassing of magma are thus identified as two of the key processes that drive unrest in campi flegrei

the chemistry of quartz in granitic pegmatites of southern norway petrogenetic and economic implications trace element concentrations in quartz from 188 granitic pegmatites in the froland and evje iveland pegmatite fields southern norway have been determined to establish exploration targets for high purity quartz and to gain a better understanding of the genesis of pegmatites hosting these deposits both pegmatite fields were formed during the sveconorwegian grenvillian orogeny 1145 900 ma at the western margin of the fennoscandian shield in situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry la icp ms spot size 75 m to assess levels of lattice bound impurities rather than mineral and fluid inclusions that are relatively easily removed during high purity quartz processing quartz in the froland pegmatites has relatively pure and homogeneous compositions containing 46 24 gg 1 al 8 3 gg 1 ti 1 4 0 8 gg 1 ge and 11 7 gg 1 li the ti in quartz geothermobarometer gives an average pegmatite crystallization temperature of 537 39 c temperature estimates are highest along the northwestern margin of the pegmatite field 550 c whereas the most differentiated pegmatites occur toward the northeast the area of greatest economic potential for high purity quartz lies just north of the central part of the field where individual pegmatites contain 1 million metric tons mt quartz with low average trace element contents of 67 11 gg 1 from mineral chemical criteria and a range of other geologic factors we propose that pegmatite melts in the froland field were generated by fluid present crustal melting at about 1060 ma in zones of localized high strain deformation during progressive thrusting along the porsgrunn kristiansand fault zone quartz in the evje iveland pegmatites has more variable compositions with 69 57 gg 1 al 19 11 gg 1 ti 2 3 1 8 gg 1 ge and 7 5 gg 1 li from its ti content it crystallized at temperatures of 613 70 c the regional spatial distribution of ti in quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with amazonite cleavelandite replacement zones which show crystallization temperatures down to 442 c quartz from the evje iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents heterogeneous chemistry and low volume the evje iveland pegmatites show no apparent genetic link to a granite intrusion instead they probably formed as a result of partial melting at the depth of their amphibolite country rocks at around 910 ma this is related to a regional low pressure high temperature metamorphic event at about 930 to 920 ma

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

uranium and barium cycling in a salt wedge subterranean estuary the influence of tidal pumping abstract the contribution of submarine groundwater discharge sgd to oceanic metal budgets is only beginning to be explored here we demonstrate that biogeochemical processes in a northern florida subterranean estuary ste significantly alter u and ba concentrations entering the coastal ocean via sgd tidal pumping controlled the distribution of dissolved metals in shallow beach groundwater hourly observations of intertidal groundwaters revealed high u and low ba concentrations at high tide as a result of seawater infiltration into the coastal aquifer during ebb tide u decreased and ba increased due to freshwater dilution and more importantly biogeochemical reactions that removed u and added ba to solution u removal was apparently a result of precipitation following the reduction of u vi to u iv a significant correlation between ba and dissolved organic carbon doc in shallow beach groundwaters implied a common source likely the mineralization of marine particulate organic matter driven into the beach face by tidal pumping in deeper groundwaters where the labile organic matter had been depleted ba correlated with mn we estimate that net sgd fluxes were 163 and 1660 mol m 1 d 1 for u and ba respectively or 1 and 8 mol m 2 d 1 if a 200 m wide seepage area is considered our results support the emerging concept that subterranean estuaries are natural biogeochemical reactors where metal concentrations are altered relative to conservative mixing between terrestrial and marine endmembers these deviations from conservative mixing significantly influence sgd derived trace metal fluxes

water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in western australia abstract volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in western australia the filtered volumes were large 19 m 3 m 1 day 1 and 73 m 3 m 1 day 1 on two clean beaches but only 0 4 m 3 m 1 per tidal cycle on a beach covered in kelp and seagrass wrack the mean residence times of this water in the interstitial system and its percolation paths were both short 1 7 h and 2 5 m respectively water input was greater across a beach cusp horn than across a cusp embayment most input occurred in the upper swash zone where the water table was less than 20 cm deep tidal variations in input volumes were evident even with tide ranges of only 20 cm the inshore zone off these beaches filters on average 0 07 m 3 m 2 day 1 at an average depth of 5 5 m under 0 4 m waves of 6 5 s duration the importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore lagoon ecosystem is estimated and discused

age and cooling history of the kiglapait intrusion from an study abstract 40 ar 39 ar age spectra of hornblende biotite and feldspars from the kiglapait layered intrusion labrador give closure ages that define the subsolidus cooling history of the intrusion and its surroundings biotites give very good plateaus but u shaped age spectra are typical for hornblende antiperthite and plagioclase and a spectrum of multi plateau segments is found in mesoperthites isochron studies reveal an age range from 1298 14 ma for hornblende to 1217 28 ma for plagioclase multiple linear arrays or clusters appear on the isochron diagrams of perthitic feldspars indicating the effect of excess argon for antiperthite this excess argon resides mainly in the plagioclase domains based on its inverse correlation with k ca with the highest closure temperature the hornblende age is very close to the published sm nd rockmineral isochron age of 1305 22 ma and gives a good approximation to the crystallization age calculated closure temperatures of different feldspars combined with published values for hornblende and biotite show that this intrusion cooled rapidly down to an ambient temperature of about 240 c in the first 20 ma after its crystallization then underwent extremely slow cooling for a long time combining these results with the published pre intrusion ambient temperature of about 350 c a regional slow cooling is revealed and this implies a late uplift of the region during and after the kiglapait magmatism

the sveconorwegian orogeny reamalgamation of the fragmented southwestern margin of fennoscandia abstract the sveconorwegian orogeny encompasses magmatic metamorphic and deformational events between ca 1140 and 920 ma at the southwestern margin of fennoscandia in recent years the tectonic setting of this nearly 200 myr long evolution has been debated with some workers arguing for collision with an unknown continent off the present day southwest coast of norway and others advocating accretionary processes inboard of an active margin recently it has been suggested that orogeny may have been gravity driven by delamination and foundering of heavy subcontinental lithospheric mantle in an intraplate setting in some ways similar to proposed sagduction processes in the archaean resolving the tectonic setting of the sveconorwegian orogen has implications for correlation with other orogens and rodinia supercontinent reconstructions and for assessments of the evolution of plate tectonics on earth from the archaean to the present here we present new mapping and geochronological data from the bamble and telemark lithotectonic units in the central and western sveconorwegian orogen the former representing a critical region separating western parts of the orogen that underwent long lived high to ultrahigh temperature metamorphism and magmatism from parts closer to the orogenic foreland that underwent episodic high pressure events the data show that the units constituting the sveconorwegian orogen most likely formed at the southwestern margin of fennoscandia between ca 1800 and 1480 ma followed by fragmentation during widespread extension between ca 1340 and 1100 ma marked by bimodal magmatism and sedimentation a summary of sveconorwegian magmatic metamorphic and depositional events in the different units shows disparate histories prior to their assembly with adjacent units the most likely interpretation of this record seems to be that episodic sveconorwegian metamorphic and deformational events in the central and eastern parts of the orogen represent accretion and assembly of these units this process most likely took place behind an active margin to the southwest that sustained mafic underplating in the proximal back arc resulting in high to ultrahigh temperature metamorphism in the western parts in this interpretation all features of the sveconorwegian orogen are readily explained by modern style plate tectonic processes and hypotheses involving some form of vertical intraplate tectonics are not supported

tectonothermal evolution of high alumina rocks within the protogine zone southern sweden the protogine zone comprises a system of anastomosing deformation zones which approximately parallel the eastern boundary of the sveconorwegian 1200 900 ma province in south west sweden ages of granulite facies metamorphism in the sveconorwegian province require exhumation from c 30 to 35 km crustal depths after 920 880 ma 40ar 39 ar cooling ages are presented for muscovite from high alumina rocks formed by hydrothermal leaching associated with the protogine zone growth of fabric defining minerals was associated with a ductile deformational event muscovite from these rocks cooled below argon retention temperatures c 375 25 c at c 965 955 ma muscovite from granofels in zones of intense alteration indicates that temperatures 375 25 c were maintained until c 940 ma textural relations of al2sio5 polymorphs and chloritoid suggest that dated fabrics formed during exhumation the process of exhumation brittle overprint on ductile structures and hydrothermal activity along faults within the protogine zone tentatively are interpreted as the peripheral effects of initial neoproterozoic exhumation of the granulite region of south western sweden muscovite in phyllonites associated with the sveconorwegian thrust system cooled below argon retention temperatures at c 927 ma exhumation associated with this cooling could have been related to extension and onset of brittle ductile deformation superimposed on sveconorwegian contraction

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

step filling and development of a three layer magma chamber the neapolitan yellow tuff case history abstract the neapolitan yellow tuff the product of the largest known trachytic phreatoplinian eruption gives a good opportunity to investigate the filling mechanisms and internal dynamics of a trachytic magma chamber a detailed study of the geochemical mineralogical and isotopical features of the deposit was carried out to investigate the behaviour of the magma chamber before the eruption the collected data show three distinct compositional groups separated by gaps single depositional units contain glass shards formed contemporaneously although each of these shards is homogeneous they display the same compositional variations and gaps detected in pumice clasts this feature is taken as an evidence for interpreting the detected compositional gaps as real gaps in the chamber therefore the chamber was filled by three distinct magma bodies separated by compositional gaps the uppermost magma was alkali trachyte and highly homogeneous likely a consequence of vigorous convection the intermediate magma was trachyte with a slight and continuous compositional variation likely resulting from less intense convection the lowermost magma was compositionally zoned from alkali trachyte to latite downward this compositional zonation was most likely acquired during uprise from a deeper reservoir the three magmas entered the chamber sequentially from the uppermost to the lowermost the latter entered the chamber short before the beginning of the eruption its input was interpreted as a possible triggering factor for the eruption the results of this study strongly support a step filling mechanism for the neapolitan yellow tuff magma chamber and allow definition of the temporal succession of input of magma batches furthermore they also suggest that the magma bodies did not mix although at least the uppermost two coexisted inside the chamber for a time long enough to allow internal homogeneization by convection

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

40ar 39ar geochronology across the mylonite zone and the southwester granulite province in the sveconorwegian orogen of s sweden abstract the crustal segment between the mylonite zone mz and the protogine zone in southern sweden the southwestern granulite province sgp is characterized by numerous occurrences of granulite and upper amphibolite facies rocks including migmatitic gneisses mafic granulites garnet amphibolites and charnockites the southwest part of the mylonite zone north of varberg marks a tectonic upper boundary of the sgp a 40 ar 39 ar study was initiated across the mylonite zone and within the sgp in order to constrain and compare the ages obtained from within the sgp with those obtained north of and within the mylonite zone 23 homblendes and one muscovite have been analyzed the results of these analyses indicate the following 1 hornblendes from within and near the mz yield 40 ar 39 ar hornblende ages of 915 ma these ages are interpreted to date the dynamic crystallization or cooling below 500 c of the deformation associated with the mz 2 away from the mz there is a distribution of ages between those which yield younger sveconorwegian ages of 931 934 ma and those which yield older sveconorwegian ages generally between 960 and 1007 ma the younger age may be associated with orogenic uplift while the older one may be associated with an earlier sveconorwegian crustal thickening event 3 the one muscovite age of 904 ma would indicate a late cooling rate of at least 6 15 c ma cooling rates of this magnitude may suggest that the final uplift of the sveconorwegian orogen was related to large scale crustal extension

eruptive versus non eruptive behaviour of large calderas the example of campi flegrei caldera southern italy caldera eruptions are among the most hazardous of natural phenomena many calderas around the world are active and are characterised by recurrent uplift and subsidence periods due to the dynamics of their magma reservoirs these periods of unrest are in some cases accompanied by eruptions at campi flegrei caldera cfc which is an area characterised by very high volcanic risk the recurrence of this behaviour has stimulated the study of the rock rheology around the magma chamber in order to estimate the likelihood of an eruption this study considers different scenarios of shallow crustal behaviour taking into account the earlier models of cfc ground deformation and caldera eruptions and including recent geophysical investigations of the area a semi quantitative evaluation of the different factors that lead to magma storage or to its eruption such as magma chamber size wall rock viscosity temperature and regional tectonic strain rate is reported here for elastic and viscoelastic conditions considering the large magmatic sources of the cfc ignimbrite eruptions 400 2 000 km3 and a wall rock viscosity between 1018 and 1020 pa s the conditions for eruptive failure are difficult to attain smaller source dimensions a few cubic kilometres promote the condition for fracture eruption rather than for the flow of wall rock we also analyse the influence of the regional extensional stress regime on magma storage and eruptions and the thermal stress as a possible source of caldera uplift the present study also emphasises the difficulty of distinguishing eruption and non eruption scenarios at cfc since an unambiguous model that accounts for the rock rheology magma source dimensions and locations and regional stress field influences is still lacking

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

hornblende 40ar 39ar geochronology across terrane boundaries in the sveconorwegian province of s norway abstract hornblende incremental heating 40 ar 39 ar data were obtained from augen gneiss and amphibolite of the sveconorwegian province of s norway in the rogaland vest agder and telemark terranes four pyroxene rich samples located close 10 km to the anorthosite charnockite rogaland igneous complex define an age group at 916 12 14 ma and six samples distributed in the two terranes yield another group at 871 8 10 ma the first age group is close to the reported zircon u pb intrusion age of the igneous complex 931 2 ma and the regional titanite u pb age 918 2 ma whereas the second group overlaps reported regional mineral rb sr ages 895 853 ma as well as biotite k ar ages 878 853 ma in the first group the comparatively dry parageneses of low p thermal metamorphism m2 associated with the intrusion of the igneous complex are well developed and hornblende 40 ar 39 ar ages probably record a drop in temperature shortly after this phase in other hornblende biotite rich samples with presumably a higher fluid content the hornblende ages are probably a response to hornblende fluid interaction during a late sveconorwegian metamorphic or hydrothermal event a ca 220 m y diachronism in hornblende 40 ar 39 ar ages is documented between s telemark ca 870 ma and bamble ca 1090 ma differential uplift between these terranes was mostly accommodated by shearing along the kristiansand porsgrunn shear zone the final stage of extension along this zone occurred after intrusion of the herefoss post kinematic granite at 926 8 ma on the contrary the southern part of the rogaland vest agder and telemark terranes share a common cooling evolution as mineral ages are similar on both sides of the mandal ustaoset line the tectonic zone between them the succession within 20 m y of a voluminous pulse of post tectonic magmatism at 0 93 ga a phase of high t low p metamorphism at 0 93 0 92 ga and fast cooling at a regional scale ca 0 92 ga suggests that the southern parts of rogaland vest agder and telemark were affected by an event of post thickening extension collapse at that time this event is not recorded in bamble

ground movements and sea level changes in urban areas 5000 years of geological and archaeological record from naples southern italy abstract the occasion offered by the construction of a new branch of naples subway and the related geotechnical and archaeological investigations allowed recognition that the city shoreline underwent remarkable changes during the late holocene highstand when coastal evolution was influenced by vertical ground movements in particular for three investigation sites the density and quality of data were such to permit for the first time the reconstruction of graphs of relative sea level change rslc which compared with curves of the coeval eustatic changes in the tyrrhenian sea were transformed into data about the late holocene history of local tectonics by averaging the data collected in all the different sites the obtained curve of the tectonics suggests that the coastal strip of naples underwent a subsidence rate of 1 3 mm a from about 5000 bp to the xii century ad followed by a 1 m uplift during the last eight centuries mean rate of 1 0 mm a the subsidence trend is consistent with the regional tectonics even if the mean rate was less that in other portions of the bay of naples graben probably because the study area lies among the parallel synthetic faults forming the nw margin of that depression magnaghi sebeto fault zone and not on the proper hanging wall block the prevailing subsiding trend was probably interrupted by minor episodes of uplift not only in the last eight centuries but also during the 3rd millennium bc likely in connection with periods in which the volcano tectonic phenomena of the phlegrean fields district superimposed on the descending movements caused by the msfz the three investigation sites share substantially the same tectonic behaviour in the long term but the details of their rslc records show also discrepancies in some centuries if not due to errors in dating and or in estimating palaeo elevations such discrepancies could be ascribed to episodes of fragmentary tectonic behaviour due probably to occasional reactivation of some e w trending minor lines of the magnaghi sebeto fault zone

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

argon composition of metamorphic fluids implications for 40ar 39ar geochronology the concentration and isotopic composition of argon trapped in fluid inclusions within a mylonitic amphibolite were determined by combining electron microprobe sup 40 ar sup 39 ar laser microprobe and fluid inclusion analyses on the same samples in our study fluid in inclusions formed during ductile deformation was probably derived locally from the paleozoic caledonian sequences whereas brines emplaced in cross cutting fractures were derived from proterozoic footwall rocks several kilometers from the mylonite by utilizing sup 38 ar sub cl to correct for open quotes excess sup 40 ar close quotes we estimate a 370 ma closure age for the amphibole which is distinctly younger than the 440 480 ma plateau ages indicated by step heating spectra the open quotes excess sup 40 ar close quotes responsible for the anomalous plateaus probably resulted from diffusive re equilibration of the amphibole with the fluids present during ductile deformation of the mylonite the significantly younger cooling age determined by our method is concordant with ages determined from more recent geochronological studies in the region these ages indicate that the western gneiss terrain in our study area records deformation and cooling associated with siluro devonian tectonothermal metamorphism rather than an earlier caledonian tectonism as proposed in previous sup 40 ar sup 39 ar investigators 46 refs 8 figs

analytical models of deformation and residual gravity changes due to a mogi source in a viscoelastic medium abstract the popular mogi model describing deformation due to a small pressurized spherical cavity embedded in a homogeneous elastic half space is shortly reviewed similarities and differences with other isotropic deformation models are discussed and the interpretation of the different volume changes accompanying source inflation is provided the model is then generalized to viscoelastic rheology the overpressure needed within the source to reproduce the large deformation sometimes observed in volcanic regions is found to be strongly dependent on rheological parameters so that reasonably low values may be obtained if the relaxation time of the medium surrounding the source is short months instead of the extremely high values inferred from the elastic theory if the inflation of the source is due to the input of new magma from remote distance the resulting residual gravity change g may be easily computed thanks to the spherical geometry of the source and the density of the newly emplaced material may be inferred from the ratio of g w between the gravity change and the uplift this ratio is independent of the overpressure and the radius of the source which are generally ill defined parameters and is slightly dependent on the relaxation time in the transient phase explicit solutions are shown for a step like overpressure history and for a constant magma supply rate a more realistic model is also proposed in which the viscoelastic properties are restricted to a small spherical volume around the source surrounded by an elastic medium even if an accurate interpretation of deformation and gravity changes in volcanic areas generally requires taking into account topography elastic layering and the triaxial geometry of the inflation source values computed according to the generalized mogi model are compared with observations made during the 1982 84 uplift episode at campi flegrei caldera italy for the sake of illustration

redistribution of rare earth elements thorium and uranium over accessory minerals in the course of amphibolite to granulite facies metamorphism the role of apatite and monazite in orthogneisses from southwestern norway the amphibolite to granulite facies transition has been studied in a high k calc alkaline hornblende biotite k feldspar megacrystic augen gneiss series from the rogaland vest agder rog va sector of the sveconorwegian province southwest norway hornblende begins to break down mainly to clinopyroxene at the cpx in isograd and biotite mainly to orthopyroxene at the opx in isograd abbreviations for minerals following kretz 1983 the magmatic accessory mineral association comprises titanite and allanite which begin to break down before the cpx in isograd titanite is preserved as relict inclusions in other minerals at higher grade monazite and thorite formed in the breakdown of allanite monazite abundance reaches a maximum between the cpx in and opx in isograds the middle and heavy rare earth element m hrees except eu content of apatite steeply increases with increasing metamorphic grade and is directly correlated to the decrease of the modal abundances of titanite hornblende and biotite the u contents of apatite are low and do not increase with metamorphic grade the light rare earth elements lrees and th content of apatite are not correlated to the breakdown of allanite around the cpx in isograd but increase around the opx in isograd a simplified equation is proposed for monazite crystallisation in the vicinity of the cpx in isograd that accounts for the allanite titanite and hornblende breakdowns and the m hree substitution in apatite 3 m hree 2o3in hornblende and litanite 3 lree 2in allaniteo3 2ca5 po4 3apatite f oh 6sio2quartz 6 lree pmonaziteo4 2ca2 m hree 3 sio4 3 f oh lessingite in apatite 6caoin plagioclase at the opx in isograd the increase of lrees and th content of apatite results either from the breakdown of some monazite 3 lree po4monazite 3sio2quartz 4caoin plagioclase f2 h2o fluid ca5 po4 3 f oh apatiteca2 lree 3 sio4 3 f oh less ingite in apatite or the breakdown of the remaining allanite 3 lree 2o3in allanite 6sio2quartz 4caoin plagioclase f2 h2o fluid 2ca2 lree 3 sio4 3 f oh lessingite in apatite the release of fluorine from the breakdown of biotite at the opx in isograd may increase apatite stability relatively to monazite in the granulite facies when compared to amphibolite facies the granulite facies augen gneisses do not show any u or th depletion this means that changes in the accessory mineral associations and the simultaneous breakdown of hydrous minerals at the amphibolite granulite facies transition do not inevitably result in depleted granulite facies rocks but rather to an isochemical element redistribution the coexistence of small amounts of metamorphic monazite and of relict inclusions of titanite in upper amphibolite facies augen gneisses suggests that high k calc alkaline orthogneisses are a suitable material to date with the u pb method prograde path of amphibolite facies regional metamorphism on monazite and the cooling path on titanite

water table outcropping on macro tidal beaches a simulation model abstract during the fall of the tide the coastal water table within a beach may become decoupled from the ocean resulting in the formation of a seepage face where water outcrops on the inter tidal profile a simulation model called seep is developed to simulate the point of decoupling and the subsequent motion of the seepage face as it continues to fall across the inter tidal profile the model is based entirely on the dynamics of an isolated water particle on the seepage face i e the pressure distribution within the beach is ignored sensitivity analysis of the seep model to beach face slope and permeability characteristics suggests that small variations to these parameters can result in significantly differing rates of exit point motion and hence seepage face extent to test the predictive capability of the seep model results are presented from a field investigation of exit point dynamics on a macro tidal beach north queensland australia the simulation model is found to accurately reproduce the observed seepage face motion at this field site in addition a re analysis of seepage face extent reported in nielsen 1990 from a protected micro tidal environment shows similarly strong agreement between the reported and modelled exit point elevation

rapid cooling and exhumation in the western part of the mesoproterozoic albany fraser orogen western australia abstract the albany fraser orogen of southwestern australia is an understudied orogenic belt which is interpreted to record the mesoproterozoic suturing of the yilgarn craton of western australia to the mawson craton of east antarctica during rodinia assembly previous u pb geochronology has dated peak amphibolite to granulite facies metamorphism in the orogen at ca 1180 ma here we report the first 40ar 39ar thermochronology of hornblende biotite and muscovite grains from a 360 km transect across the western albany fraser orogen and uncover a record of strikingly fast syn orogenic cooling and exhumation to the north muscovites from the northern foreland record cooling at ca 1159 ma in the central and southern domains of the orogen the biranup and nornalup zones hornblende yields ca 1169 ma cooling ages and biotite yields ca 1172 1144 ma cooling ages the new cooling ages imply that the three domains were exhumed rapidly following peak metamorphism at ca 1180 ma attained a similar structural level by ca 1159 ma and have experienced a uniform exhumation history since that time to constrain mineral closure temperatures and post peak metamorphic cooling rates we conducted a monte carlo simulation which fully propagates uncertainty and minimises error correlations modelling of cooling from hornblende to biotite closure temperatures ca 585 c and 365 c respectively in the nornalup and biranup zones yields fast cooling rates of 33 9 17 c ma and 22 5 7 c ma respectively these fast cooling rates imply rapid exhumation in an active tectonic setting undergoing peak metamorphism although the structural evolution of the albany fraser orogen remains poorly constrained the transpressional tectonic activity associated with deformation in the western part of the albany fraser orogen may have been an active driver of this fast exhumation this is distinctly different from exhumation models for granulite facies domains in other mesoproterozoic orogens which typically experience post orogenic slow 1 5 c ma cooling driven by mechanisms such as orogenic collapse and erosion we consider that the observed differences reflect the interpreted syn tectonic transpressional exhumation history of the albany fraser orogen which is an underrepresented tectonic regime in the mesoproterozoic cooling record

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

the thermal significance of potassium feldspar k ar ages inferred from age spectrum results 40ar39ar age spectrum analyses of three microcline separates from the separation point batholith northwest nelson new zealand which cooled slowly 5 c ma 1 through the temperature zone of partial radiogenic 40ar accumulation are characterized by a linear age increase over the first 65 percent of gas release with the lowest ages 80 ma corresponding to the time that the samples cooled below about 100 c the last 35 percent of 39ar released from the microclines yields plateau ages 103 99 and 93 ma which reflect the different bulk mineral ages and correspond to cooling temperatures between about 130 to 160 c theoretical calculations confirm the likelihood of diffusion gradients in feldspars cooling at rates 5 c ma 1 diffusion parameters calculated from the 39ar release yield an activation energy e 28 8 1 9 kcal mol 1 and a frequency factor grain size parameter d0l2 5 6 3 9 14sec 1 this arrhenius relationship corresponds to a closure temperature of 132 13 c which is very similar to the independently estimated temperature from the observed diffusion compensation correlation this d0l2 implies an average diffusion half width of about 3 m similar to the half width of the perthite lamellae in the feldspars the range in microcline k ar ages from the separation point batholith is the result of relatively small temperature differences within the pluton during cooling comparison of the diffusion laws determined for microcline with those for anorthoclases and other homogeneous k feldspars e 40 to 52 kcal mol 1 reveals that ar diffusion is more highly temperature dependent in the disordered structural state than in the ordered structural state previously published u shaped age spectra are probably the result of the superimposition of excess 40ar upon diffusion profiles of the kind described here

radon 222 budget in catalina harbor california 2 flow dynamics and residence time in a tidal beach we measured the flux of water through a beach at the head of catalina harbor california by monitoring the water table in a transect of wells perpendicular to the shoreline during a 24 h period the volume of sediments filled and drained the tidal wedge was 7 4 m 3 m shoreline 1 and the flux of water pumped across the beach face was 1 0 0 3 m 3 d 1 m shoreline 1 222 rn concentrations measured in four wells were used to calculate the minimum age of water in the beach radon samples collected below the tidal wedge were not in equilibrium with the production rate suggesting vertical mixing across the base of the tidal wedge the age of water ranged from up to 8 0 d landward of the high water mark to less than 2 0 d in the littoral zone this latter age agreed with an independent estimate of 1 7 0 5 d on the basis of a mass balance for radon at the head of the harbor however a mass balance for water in the tidal wedge was significantly greater 3 0 0 5 d the difference was most likely due to evasion of radon from wet unsaturated sediments water draining out of the beach was a mixture of water that infiltrated the beach on the previous high tide and older water from either below or the back of the tidal wedge

tidal water table fluctuations in a sandy ocean beach tidal water table fluctuations observed for 27 days in a gently sloped ocean beach are predicted well by numerical models based on the boussinesq equation driven with the observed 10 min averaged shoreline ocean beach intersection motion diurnal and semidiurnal water table fluctuations are almost completely damped 100 m landward of the mean shoreline location on this fine grained sand beach but fluctuations at spring neap periods 14 days are attenuated less comparison of the observations with the predictions suggests that the asymmetries in the water table level time series measured in this study result from nonlinearity owing to the large relative to the wavelength horizontal shoreline excursions rather than from nonlinearity owing to finite amplitude water table fluctuations cross shore variations of the aquifer depth are predicted to have a small effect on the landward decay rate of the water table fluctuations the seepage face width is predicted accurately and depends on the nonplanar beach profile in general the development of a seepage face is predicted to have little effect on the water table level landward of the intertidal region

coastal groundwater dynamics off santa barbara california combining geochemical tracers electromagnetic seepmeters and electrical resistivity this paper presents repeat field measurements of 222 rn and 223 224 226 228 ra electromagnetic seepage meter derived advective fluxes and multi electrode stationary and continuous marine resistivity surveys collected between november 2005 and april 2007 to study coastal groundwater dynamics within a marine beach in santa barbara california the study provides insight into magnitude and dynamics of submarine groundwater discharge sgd and associated nutrient loadings into near shore coastal waters where the predominant sgd drivers can be both spatially and temporally separated rn 222 and 223 224 226 228 ra were utilized to quantify the total and saline contribution respectively of sgd the two short lived 224 223 ra isotopes provided an estimate of apparent near shore water mass age as well as an estimate of the ra derived eddy diffusion coefficient kh 224 ra 2 86 0 7 m 2 s 1 223 ra 1 32 0 5 m 2 s 1 because 222 rn t 3 8 day and 224 ra t

contiguous laurentia and baltica before the grenvillian sveconorwegian orogeny close geochronological correspondence of mesoproterozoic extension related magmatism and comparable tectonic and geochronological evolution of the grenville and svecononvegian orogens suggests that the laurentian and baltic shields could have been joined during the mesoproterozoic and did not separate until after the grenvillian sveconorwegian orogeny the combined grenville svecononvegian orogen is here interpreted to have formed during the collision of coherent laurentia baltica with an unknown craton which is in contrast to earlier explanations that favour a late mesoproterozoic rotation between laurentia and baltica followed by collision of these two cratons with each other

petrology and geothermobarometry of granulite facies metapelites from the hisoy torungen area south norway new data on the sveconorvegian p t t path of the bamble sector the high grade rocks metapelite quartzite metagabbro of the hisoy torungen area represent the south westernmost exposures of granulites in the proterozoic bamble sector south norway the area is isoclinally folded and a metamorphic p t t path through four successive stages m1 m4 is recognized petrological evidence for a prograde metamorphic event m1 is obtained from relict staurolite chlorite albite staurolite hercynite ilmenite cordierite sillimanite fine grained felsic material quartz and hercynite biotite sillimanite within metapelitic garnet the phase relations are consistent with a pressure of 3 6 0 5 kbar and temperatures up to 750 850 c m1 is connected to the thermal effect of the gabbroic intrusions prior to the main m2 sveconorwegian granulite facies metamorphism the main m2 granulite facies mineral assemblages quartz plagioclase k feldspar garnet biotite sillimanite are best preserved in the several metre wide al rich metapelites which represent conditions of 5 9 9 1 kbar and 790 884 c these p t conditions are consistent with a temperature increase of 80 100 c relative to the adjacent amphibolite facies terranes no accompanying pressure variations are recorded up to 1 mm wide fine grained felsic veinlets appear in several units and represent remnants of a former melt formed by the reaction bt sil qtzgrt lq this dehydration reaction together with the absence of large scale migmatites in the area suggests a very reduced water activity in the rocks and xh2o 0 25 in the c o h fluid system was calculated for a metapelitic unit a low but variable water activity can best explain the presence or absence of fine grained felsic material representing a former melt in the different granulitic metapelites the strongly peraluminous composition of the felsic veinlets is due to the reaction grt former melt silcrd bt qtz h2o which has given poorly crystalline cordierite aggregates intergrown with well crystalline biotite the cordierite and biotite producing reaction constrains a steep first stage retrograde relative to m2 uplift path decimetre to metre wide strongly banded metapelites quartz plagioclase biotite garnet sillimanite inter layered with quartzites are retrograded to m3 amphibolite facies assemblages a p t estimate of 1 7 5 6 kbar 516 581 c is obtained from geothermobarometry based on rim rim analyses of garnet biotite plagioclase sillimanite quartz assemblages and can be related to the isoclinal folding of the rocks m4 greenschist facies conditions are most extensively developed in millimetre wide chlorite rich calcite bearing veins cutting the foliation

origin of strongly reversed rims on plagioclase in cumulates abstract narrow reversed rims on plagioclase are ubiquitous in troctolites and olivine gabbros of the kiglapait intrusion and may be a common feature of all such cumulates the rims occur at plag plag plag ol and less strongly at plag aug grain boundaries they are optically obvious at an and can reach an 32 mol or more in parallel k na drops sharply although ubiquitous from sample to sample the reversed rims are only locally present at grain boundaries even for the same pair of crystals in contact they are prominent in linear networks suggesting the last trace of intercumulus liquid a subsolidus origin is ruled out by the absence of reactants at plag plag and plag ol boundaries and by the local rather than pervasive development of rims the rims are required to grow from intercumulus liquid in which the partition of an component between crystals and liquid increases with the trapped augite component of the liquid calculations from published experimental data show that an 30 can easily be achieved by such a process it is also probable that the trapped liquid is part of an an rich boundary layer generated by solute rejection during adcumulus growth the ability of the rims to sustain steep k na gradients despite a long subsolidus cooling history proves that the k na exchange rate is vanishingly small over a geologic time scale in an rich feldspar suggesting that at low k content the potassium is site bound to the tetrahedral al si distribution reversed rims therefore provide important information on diffusion limits as well as on the late stage solidification history of plagioclase rich cumulates moreover they demonstrate that plagioclase geothermometry cannot be divorced from effects of liquid composition and structure as monitored for example by augite content

terrestrial originated submarine groundwater discharge through deep multilayered aquifer systems beneath the seafloor a large quantity of submarine groundwater discharge sgd of about 1000 m3 day 1 m 1 of the 600 km long shoreline of south atlantic bight has been estimated by moore global biogeochemical cycles 2010b 24 gb4005 doi 10 1029 2009gb003747 however there is great uncertainty in estimating the percentage of net land originated groundwater recharge of sgd moreover most previous studies considered the homogeneous case for the coastal superficial aquifers here we investigated the terrestrial originated sgd through a multilayered submarine aquifer system which comprises two confined aquifers and two semi permeable layers the inland recharge includes a constant part representing the annual average and a periodical part representing its seasonal variation an analytical solution was derived and used to analyse the distributions of the terrestrial originated sgd from the multilayered aquifers along the winyah bay transect south atlantic bight it is found that the width of the zone of sgd from the upper aquifer ranges from 0 8 to 8 0 km depending on the leakance of the seabed semi permeable layer a head of the upper aquifer at a coastline 1 0 m higher than the mean sea level will cause a sgd of 1 82 18 3 m3 day 1 m 1 from that aquifer as the seabed semi permeable layer s leakance varies from 0 001 to 0 1 day 1 providing considerable possibility for considerable land originated sgd seasonal terrestrial originated sgd variations predicted by the analytical model provide consistent explanation of the seasonal variation of 226ra observed by moore journal of geophysics 2007 112 c10013 doi 10 1029 2007jc004199 the contribution of the lower aquifer to sgd is only 1 2 12 of that of the upper aquifer copyright 2014 john wiley sons ltd

linking growth episodes of zircon and metamorphic textures to zircon chemistry an example from the ultrahigh temperature granulites of rogaland sw norway in situ u th pb analyses by ion microprobe on zircon in intact textural relationships are combined with backscatter and cathodoluminescence imaging and trace element analyses to provide evidence for growth episodes of zircon this approach helps a to unravel the polymetamorphic history of aluminous migmatitic and granitoid gneisses of the regional contact aureole around the rogaland anorthosite norite intrusive complex and b to constrain the age of m 2 ultrahigh temperature uht metamorphism and the subsequent retrograde m 3 event all samples yield magmatic inherited zircon of c 1035 ma some an additional group at c 1050 ma this suggests that loss of pb by volume diffusion in non metamict zircon is not an important factor even under extreme crustal conditions furthermore the identical inheritance patterns in aluminous garnet cordierite osumilite bearing migmatites and orthogneisses indicate a metasomatic igneous instead of a sedimentary protolith for the migmatite results for the m 1 metamorphic event at c 1000 ma bp are consistent in all samples including those from outside the orthopyroxene in isograd the latter do not show evidence for zircon growth during the m 2 metamorphic episode zircon intergrown with or included within m 2 metamorphic minerals magnetite spinel orthopyroxene give an age of 927 7 ma 2 n 20 the youngest observed results are found in zircon outside m 2 minerals some overgrown by m 3 mineral assemblages late garnet coronas garnet quartz and orthopyroxene garnet symplectites and yield a slightly younger pooled age of 908 9 ma 2 n 6 these textures are relative time markers for the crystallization of zircon overgrowths during discrete stages of the uht event these youngest age groups are consistent with the emplacement age of the rogaland intrusive complex and the last magmatic activity tellnes dyke intrusion respectively this is direct and conclusive evidence for uht metamorphism in the regional aureole being caused by the intrusions and corrects earlier notions that the events are not linked trace element behaviour of zircon tb u and y content has been tracked through time in the samples and shows variations both within and between samples this heterogeneous behaviour at all scales appears to be common in metamorphic rocks and precludes the use of rules of thumb in the interpretation of zircon chemistry but chemical tracers are useful for recognition of zircon growth or recrystallization during metamorphism

rb and sr diffusion in alkali feldspars with implications for cooling histories of rocks volume diffusion of sr and rb have been measured in orthoclase feldspar as well as sr diffusion in albite using isotope exchange hydrothermal solutions and analysis by ion microprobe for water pressures of 1000 bars the kinetics of diffusion parallel to the c axis are given by the arrhenius relations strontium transport in the or is isotropic to within a factor of four the measurements use a new procedure in which only the elements in question are present in the starting fluid cooling rates of igneous rocks can now be determined from closure temperatures material balance and the rb sr dating method based on the departures of the mineral data from the whole rock isochron for cooling rates less than approximately 100 c my

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

significance of the 1982 2014 campi flegrei seismicity preexisting structures hydrothermal processes and hazard assessment we find that the double difference relocated seismicity which occurred over the last 30 years at campi flegrei was triggered by the uprising of fluids preferentially concentrated along onshore and offshore nw striking preexisting caldera faults focal volumes of the 2005 2014 seismicity do not overlap that of the 1982 1984 period when a major uplift of 1 8 m occurred in the central sector of the caldera this indicates a transition from an elastic to a plastic behavior due to fluid saturation and heating of the rocks in the hydrothermal reservoir the 2012 2014 deeper earthquakes are located in a low vp vs zone at the western boundary of the hydrothermal reservoir where a volume increase from a magmatic body at 3 5 km depth has been recognized the progressive rheological change from elastic to plastic in the upper 4 km of the crust implies that a slow upward migration of magma may not necessarily be preceded by earthquakes or swarms

genesis of intermediate igneous rocks at the end of the sveconorwegian grenvillian orogeny s norway and their contribution to intracrustal differentiation abundant ferroan metaluminous granitoids 970 950 ma emplaced at the end of the sveconorwegian collisional orogeny 1130 900 ma are dominated by intermediate to silicic compositions with rare mafic facies both 73 fractional crystallization of an amphibole bearing gabbroic cumulate substracted from the parent mafic composition and 30 non modal batch melting of an amphibolitic source equivalent in composition to the mafic facies produce a monzodioritic liquid with appropriate trace element composition a better fit is obtained for the partial melting process both processes could have occurred simultaneously to produce mafic cumulates and restites as there is no evidence for large volumes of dense mafic rocks in the sveconorwegian upper crust these dense mafic rocks were probably produced in the lower crust formation of these granitoids thus contributed to the vertical stratification of the proterozoic continental crust and also to the transfer of water from the lower crust to the surface

incremental heating of hornblende in vacuo implications for 40ar 39ar geochronology and the interpretation of thermal histories increasing evidence of the incompatibility between the geologic thermal histories deduced from the sup 40 ar sup 39 ar incremental heating technique and those derived form other methods have necessitated a careful evaluation of the assumptions inherent in the former approach sup 40 ar sup 39 ar age spectra are frequently used to infer the spatial distribution of ar in hydrous minerals and as such require that the mineral remains stable while heated in vacuo aliquots of mmhb 1 and inter laboratory hornblende standard used for k ar and sup 40 ar sup 39 ar dating were heated in vacuo at temperatures of 500 700 930 and 1 050c for 30 min up to 700c no physical changes in the hornblende were observed with the scanning electron microscope although x ray diffraction data indicate that it had dehydroxylated to oxyhornblende at this temperature the onset of the structural decomposition of the oxyhornblende as revealed by backscattered and secondary electron images occurs at approximately 930c and is directly correlated with the initial release of 6 of its radiogenic ar sup 40 ar the breakdown of the oxyhornblende by the internal nucleation of incongruent melt is almost 93 complete by 1 050c the reaction products being titano magnetite melt a pyribole phase and internal voids because ar is released simultaneously frommore these products and is subsequently homogenized in vacuo this breakdown can yield plateau age spectra regardless of any original ar spatial gradients in the mineral consequently independent evidence may be required to establish whether a plateau date from hornblende is truly a geologically significant age less

science at the policy interface volcano monitoring technologies and volcanic hazard management this paper discusses results from a survey of volcanologists carried out on the volcano listserv during late 2008 and early 2009 in particular it examines the status of volcano monitoring technologies and their relative perceived value at persistently and potentially active volcanoes it also examines the role of different types of knowledge in hazard assessment on active volcanoes as reported by scientists engaged in this area and interviewees with experience from the current eruption on montserrat conclusions are drawn about the current state of monitoring and the likely future research directions and also about the roles of expertise and experience in risk assessment on active volcanoes while local knowledge is important it must be balanced with fresh ideas and expertise in a combination of disciplines to produce an advisory context that is conducive to high level scientific discussion

the bay of naples southern italy constraints on the volcanic structures inferred from a dense seismic survey 1 the bays of naples and pozzuoli host volcanic areas that have been active within recent history in addition the vicinities areas around the vesuvius volcano and the campi flegrei caldera are extremely densely inhabited over the past decade this situation has prompted several active seismic experiments focused on the vesuvius volcano more recently the serapis active seismic survey covered the entire bay of naples with particular attention to pozzuoli bay the processed serapis p wave travel time collection extended with a previously acquired data set has allowed the computation of the most comprehensive three dimensional p wave velocity distribution for the bay of naples which includes a small scale high resolution model of the campi flegrei caldera the joint interpretation of the velocity distribution together with both the available gravity measurements and models and the geothermal drilling information has allowed us to locate and map lithological units at depths we propose a model of the campi flegrei caldera in relation to the underlying mesozoic limestone unit in this model no magma chamber exists in the upper 6 km beneath the bay of naples the feeding system of the campi flegrei caldera is directly controlled by the tectonic structures affecting the limestone unit beneath the bay of naples two ne sw normal faults run beneath the vesuvius volcano and campi flegrei which are related to the pre pleistocene apenninic tectonics

laser probe40ar39ar measurements of loss profiles within individual hornblende grains from the giants range granite northern minnesota usa abstract a nd glass laser has been used as a probe mapping natural argon diffusion in partially outgassed hornblende grains at a resolution of around 50 m the hornblendes are from the giants range granite 2700 ma minnesota taken approximately 2 km from the contact with the duluth gabbro complex 1100 ma the full range of ages can be discerned within individual hornblende grains using the laser extraction technique but more importantly diffusion profiles up to 500 m in length have been detected the profiles reflect large variations in domain size within single grains diffusive argon loss was controlled not only by lattice dominated volume diffusion but a network of fast diffusion paths now defined by biotite inclusions and also indirectly by mineral reactions associated with the contact metamorphism three natural argon loss profiles from subgrains of different sizes yield good fits to theoretical volume diffusion loss curves and a mean time integrated diffusion parameter d t dt of 7 1 0 9 10 5 cm 2 this parameter constrains the possible heat loss models for the duluth gabbro

formation of dykes feeder dykes and the intrusion of dykes from magma chambers the paper discussed the formation of dykes and applies the results to iceland it is postulated that dykes follow the pathway of least work and of least tensile strength and thereby intrude the subvertical joints in lava flows it is suggested that dykes form in magma pulses where each dyke is split in two by the next magma pulse and so on in iceland the estimated time between successive magma pulses is of the order of several hundred days statistical considerations indicate that in iceland the probability of seeing dykes end upwards is only 1 2 which agrees with observations it is concluded that many and probably the majority of dykes are non feeders this together with the low probability of finding the connection between feeder and lava flow explains the scarcity of observed feeder dykes it is concluded that overpressure in shallow magma chambers needed to drive magma through crustal fractures in iceland is usually smaller than the tensile strength of the host rock several mpa which thereby is the critical factor in dyke intrusion

asymmetric lithosphere as the cause of rifting and magmatism in the permo carboniferous oslo graben compared to other permo carboniferous rift basins of nw europe the oslo graben has two distinct characteristics first it initiated inside cold and stable precambrian lithosphere whereas most permo carboniferous basins developed in weaker phanerozoic lithosphere and second it is characterized by large volumes of magmatic rocks despite relatively little extension seismic reflection surveys show that the crust thickens from southern norway to southern sweden the most significant moho deepening occurring from the oslo region eastwards deep seismic studies also suggest that the base of the lithosphere deepens markedly eastwards from the oslo region such a long wavelength lithospberic geometry cannot be explained by the permian or post permian evolution of the area hence the oslo graben appears to have evolved at the transition between two lithospheric domains with contrasting thickness numerical thermo mechanical modelling is applied to test if this transitional position can influence the dynamics of rifting different models with varying lithosphere thickness contrast are considered model results show that a crust and lithosphere thickness contrast comparable to the oslo region can explain rifting and focusing of magmatism in a narrow zone with minor thinning of the crust models also account for the major characteristics of the oslo graben in terms of location and strain distributions in the crust the geological society of london 2004

sr and nd isotope systematics of polymetamorphic archean gneisses from southern west greenland and northern labrador sr and nd isotopic data for middle to late archean polymetamorphic felsic gneisses from localities in the nuuk area west greenland are compared and contrasted with new isotopic results for early archean amitsoq gneisses and with data for isotopically reworked kiyuktok gneisses from the saglek area labrador sr isotopic data for individual suites of felsic gneisses record the time integrated effect of variable rb sr fractionation during prograde and retrograde events as well as the effect of source inhomogeneity contrasting petrologic and sr nd isotopic characteristics are the result of differences in level of exposure caused partially by juxtaposition of terranes of different metamorphic character by movement on ductile shear zones and post shearing folding deformation sm nd systematics of felsic gneisses from nordafar ikerasakitsup akornga tinissaq and kangimut sammisoq qasigianguit define a geologically meaningless ca 3280 ma nd isochron which is the result of mixing of samples from unrela

tide induced seawater groundwater circulation in a multi layered coastal leaky aquifer system abstract mean groundwater levels of a multi layered coastal leaky aquifer system are considered the system consists of an unconfined aquifer a confined aquifer and a semi permeable layer between them both exact asymptotic solutions and approximate perturbation solutions are derived for multi sinusoidal component sea tide at inland places far from the coastline the perturbation solutions show a good agreement with the exact asymptotic solutions due to the watertable dependent transmissivity of the unconfined aquifer the mean groundwater levels of the aquifer system stand considerably above the mean sea level even in the absence of net inland recharge of groundwater and rainfall these lead to landward positive gradients of both the mean watertable and mean head in the region near the coastline which consequently results in a seawater groundwater cycle seawater is pumped into the unconfined aquifer by the sea tide and divided into two parts one part returns to the sea driven by the mean watertable gradient the rest part leaks into the confined aquifer through the semipermeable layer and returns to the sea through the confined aquifer driven by the mean head gradient the total discharge through the confined aquifer is significant for coastal leaky aquifer system with typical parameter values this seawater groundwater cycle has impacts on better understanding of submarine groundwater discharge and exchange of various chemicals such as nutrients and contaminants in coastal areas if the observed mean water levels in coastal areas are used for estimating the net inland recharge the enhancing processes of sea tide on the mean groundwater levels should be taken into account otherwise the net inland recharge will be overestimated

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

magnetic fabrics in the holum granite vest agder southernmost norway implications for the late evolution of the sveconorwegian grenvillian orogen of sw scandinavia abstract the holum granite vest agder southernmost norway has been considered to be the oldest 980 ma undeformed post tectonic pluton of a late sveconorwegian granitoid series that form two belts in southern norway and sw sweden an integrated structural study of this granite pluton based on a survey of its anisotropy of low field magnetic susceptibility ams complemented by microstructural observations optical microscopy and rock magnetism investigations including measurements of partial anhysteretic remanent magnetization and its anisotropy paarm is presented here the magnetic susceptibility and the ams of the holum granite are carried by large magnetite grains coaxiality between the magnetite controlled ams fabric and the rock fabric is verified which allows the use of the former as a proxy for the latter microstructural evidence of a deformation continuum in the granite from magmatic to solid state and homogeneity and continuity of the ams fabrics across the pluton demonstrate that the holum granite is not post tectonic but that it was emplaced in a tectonic strain field a model of emplacement and deformation during the last sveconorwegian regional folding phase evidenced in the country rocks of the pluton is proposed

on the effects of 3 d mechanical heterogeneities at campi flegrei caldera southern italy 1 campi flegrei caldera located near the highly populated city of naples southern italy is characterized by long term subsidence punctuated by fast uplift phases most of the interpretations of the ground deformation are still based on standard models that assume the lithosphere to behave as a homogeneous half space however several geophysical investigations show the presence of vertical and lateral heterogeneities especially in the shallow subsurface which might have an effect on the interpretation of the surface displacements our 3 d finite element models constrained by seismic tomography to take into account the realistic distribution of mechanical heterogeneities demonstrate that at campi flegrei the assessment of the source location is independent of the consideration of 3 d heterogeneities while the evaluation of its strength is overestimated thus we propose an approach that still allows use of standard homogeneous half space models but accounts for 3 d heterogeneity effects this procedure applied to the deformation field revealed by differential synthetic aperture radar interferometry dinsar over the past 16 years provides new insights for the understanding of the ground displacements observed at campi flegrei caldera this work provides an approach for a quantitative evaluation of the effects of mechanical heterogeneities on surface deformation analogous procedures can be also applied in other volcanic areas where similar to campi flegrei caldera a priori information on the mechanical heterogeneities distribution is available

apparent argon diffusive loss 40ar 39ar age spectra in amphiboles detailed investigations have been made of two amphibole samples where 40ar 39ar age spectra have been interpreted to show argon diffusive loss both samples display complex compositional zoning that reflects partial major and minor element chemical re equilibration during later thermal events that is associated with the loss of radiogenic 40ar the apparent diffusive loss age spectra in these samples are an artefact of this chemical re equilibration process one sample additionally shows the effect of potassium gain and contamination with a potassium rich phase biotite the resulting ages in this sample are geologically meaningless and the apparent fit to a theoretical diffusive loss curve is coincidental this study shows that volume diffusive loss of argon appears to operate at slower rates than argon loss by chemical re equilibration in amphiboles

a re examination of the influence of composition on argon retentivity in metamorphic calcic amphiboles abstract the effect of composition on argon retention in metamorphic hornblende has been re evaluated by the 40 ar 39 ar step heating method utilizing the same samples from a k ar study in which a relationship between hornblende composition and argon retention was inferred incremental heating of the hornblendes yields 40 ar 39 ar age plateaus or near plateaus between 1081 3 and 1112 3 ma these data support a simple cooling history through argon closure following high grade metamorphism consistent with recent geochronological studies of the bamble sector of norway no clear evidence of extraneous argon is preserved in the 40 ar 39 ar data nor is there any sign of a thermal disturbance following argon closure contrary to the k ar results the 40 ar 39 ar data show no relationship between hornblende cooling age and composition the results of this investigation together with those from other studies suggest that the composition of metamorphic hornblende is not an important factor in controlling its argon closure temperature published studies inferring a compositional dependence on the argon closure temperature in metamorphic hornblende are commonly based on analytical data from impure retrogressed altered recrystallized or microstructurally complex hornblendes which are not representative of the diffusive properties of a pure hornblende such mineralogical and structural complexities may form both above and below the closure temperature of hornblende which may give rise to variable hornblende ages from rocks that have experienced the same geologic history such complexities forming at high temperature may contribute to a modified or variable characteristic grain size s of diffusion resulting in a modified complex hornblende closure temperature these complexities may contribute to low apparent hornblende ages if formed below its true closure temperature in addition variable hornblende ages may be obtained if fine grained mineral intergrowths are present and undergo recoil related phenomena during irradiation geologically meaningful hornblende ages are possible only when proper care is taken in sample selection and characterization

emplacement of polygeneration pegmatites in relation to sveco norwegian contractional tectonics examples from southern norway abstract recent studies have demonstrated that there is a strong link between sites of concentrated magmatism and crustal deformation zones magmatism is often described as being syn kinematic where one or more increments of intrusion punctuate deformation with successive generations of injections being progressively deformed pegmatite formation in the mesoproterozoic of south norway has been considered as post kinematic in nature relative to sveconorwegian grenvillian deformation 1 13 ga to 0 85 ga during accretion of the sw margin of baltica this paper presents structural observations from mapping of some pegmatites in the bamble terrane of south norway demonstrating that the pegmatites are structurally related to sveconorwegian fold geometries associated with peak metamorphism at approximately 1 14 ga and are kinematically related to overthrust geometries associated with the initial overthrusting phase of the porsgrunn kristiansand fault when the bamble terrane docked with the underlying telemark terrane local fold geometries suggest a strain regime where the maximum contractional axis is sub horizontal and oriented nw se consistent with the regional kinematics the pegmatites display a systematic deformation pattern consistent with deformation in the isoclinal fold limbs pegmatites are also deformed into asymmetric antiformal folds above reverse shear structures and are also cut by these structures thus showing a thrust geometry the undeformed pegmatites are emplaced in sub horizontal fractures and suggests sub horizontal contractional axis related to overthrusting which is identical to the strain regime of the folding the evidence suggests that the pegmatites are syn tectonic and were injected into reverse shear related fractures deformation was progressive and incremental with longer periods of ductile deformation at low strain rate punctuated by shorter periods of fracturing and pegmatite injection at high strain rate this work therefore implies an intimate spatial and temporal relationship between deformation and magmatism during crustal accretion on the western margin of fennoscandia

diffusion controlled growth of pyroxene bearing margins on amphibolite bands in the granulite facies of rogaland southwestern norway implications for granulite formation in the rogaland granulites of southern norway thin anhydrous pyroxene bearing margins 5 10 mm are observed mainly in migmatitic banded gneisses at the contact between hornblende rich metabasites and charnockites according to field data the development of these margins post dates any deformation petrographic data show that they are zoned three different types have been recognized 1 metabasite plagioclase orthopyroxene plagioclase clinopyroxene gneiss 2 metabasite plagioclase orthopyroxene clinopyroxene plagioclase clinopyroxene gneiss 3 metabasite plagioclase orthopyroxene gneiss

generation of late cretaceous silicic rocks in se china age major element and numerical simulation constraints abstract rhyolite dominating bimodal volcanic suites rhyolite basalt mafic dikes and a type granites distribute from n zhejiang to s fujian over 800 km in the southeast coast magmatic belt scmb the late yanshanian ly orogenic belt in se china data of 40ar 39ar and k ar whole rock ages and la icpms u pb zircon ages indicate that rhyolitic volcanism 101 72 ma is contemporaneous with the a type granitic intrusions 100 90 ma and mafic dike injections 94 77 ma this time span is used to define the upper volcanic series in zhejiang fujian areas one striking feature of rhyolites in the scmb is that many are strongly peraluminous sp and others mostly restrict in fujian are peralkaline to mildly peraluminous p mp and chemically resemble a type granites the sp character is unique among well known large rhyolite provinces worldwide based on experimental works for a common thermal regime and inherited zircon age information we suggest that sp and p mp rhyolites represent low pressure melting of the felsic quartzofeldspathic granite metapelite and the accompanied granodioritic tonalitic and trondhjemitic member of the core complex assemblage respectively to account for the decreasing aluminosity they could have also been contaminated by young igneous rocks and ancient crust to a lesser degree during ascent to the surface plate subduction and lithosphere extension processes respectively are numerically simulated for the magma generation of these rhyolites using the mafic underplating model results suggest that the most effective controlling factor to generate sp and associated p mp a type magmas during 95 80 ma is thinning of the lithosphere thickness with a high exhumation rate under this circumstance the core complex assemblage can be uplifted to lower level of the crust and match the constraint of experimental works

radiogenic isotope systematics of the herefoss granite south norway an indicator of sveconorwegian grenvillian crustal evolution in the baltic shield abstract a new pb pb mineral isochron dates the crystallization of the herefoss granite south norway to 926 8 ma confirming earlier rb sr evidence of a late sveconorwegian grenvillian age initial sr and nd isotopic compositions recalculated to esr 926 ma 40 end 926 ma 3 2 to 0 8 indicate that the magma has originated from a mixture of two distinct source components 1 a crustal component which has resided in a moderately lile enriched reservoir f rb 7 to 8 238 u 204 pb 17 22 since 1 6 1 9 ga this crustal component is clearly distinct from the extremely lile enriched metasedimentary country rocks of the granite f rb 21 238 u 204 pb 24 2 a mantle derived component e nd 4 6 to 5 9 e sr 12 to 9 238 u 204 pb 7 96 younger than 1 5 ga the ranges of initial sr nd and pb composition observed in the intrusion indicate that the magma was isotopically heterogeneous at the time of emplacement and that the crustal contribution amounted to 35 55 by the end of the sveconorwegian orogeny the southwestern part of the baltic shield had acquired a compositionally layered structure where an uppermost zone of the crust with extreme lile enrichment was underlain by a heterogeneous layer consisting of rocks with normal upper crustal degree of lile enrichment and mafic intrusions younger than 1 5 ga there is no evidence of involvement of lile depleted deep continental crust source material in the petrogenesis of the herefoss granite rejuvenation of the lower crust by injection of mantle derived magmas underplating has been an important process in the evolution of the southwestern part of the baltic shield the absence of a young mantle derived component from 1 12 ga charnockitic intrusions in the bamble sector and from the 989 ma grimstad granite suggests that this process may have been contemporaneous with late sveconorwegian mafic magmatism in the rogaland vest agder sector further to the west

excess40ar in metamorphic rocks from broken hill new south wales implications for40ar 39ar age spectra and the thermal history of the region 40ar 39ar age spectrum analyses of samples from broken hill new south wales indicate that the region has experienced a complex thermal history following high grade metamorphism 1660 ma ago the terrain cooled slowly 3 c ma 1 until about 1570 ma ago when the temperature fell below about 500 c following granitoid emplacement 1500 ma ago the region remained relatively cold until affected by a thermal pulse 520 40ma ago causing temperatures to rise to 350 c in some places during this event accumulated40ar was released from minerals causing a significant ar partial pressure to develop laboratory ar solubility data combined with the40ar 39ar age spectra gives a local estimate of this partial pressure of 10 4atm the region finally cooled below 100 c about 280 ma ago 40ar 39ar age spectrum analyses of hornblende plagioclase and clinopyroxene containing excess40ar are characterized by saddle shaped age spectra detailed analysis of plagioclase samples reveals a complex diffusion behaviour which is controlled by exsolution structures this effect in conjunction with the presumed different lattice occupancy of excess40ar with respect to radiogenic40ar appears to be responsible for the saddle shaped age spectra

direct determination of total and fresh groundwater discharge and nutrient loads from a sandy beachface at low tide cape henlopen delaware total groundwater discharge from a sandy seepage site to the delaware bay at cape henlopen delaware was determined together with the associated nutrient loads by trapping the discharge from a length of the shoreline in a tidal pond at low tide and measuring the discharge of the trapped water through a weir at steady state salinity was used to parse the total groundwater discharge from the beachface at low tide into a recycled estuarine component and a new fresh groundwater component based on 16 measurements over 18 months average total discharge and average freshwater discharge at low tide were found to be 2 76 6 1 08 and 0 87 6 0 43 l min21 m21 of shoreline respectively the estuarine component of discharge varied with the maximum height of the immediately preceding high tide owing to the control of freshwater discharge by the average upland hydraulic gradient away from the beach individual measurements of freshwater discharge at low tide represent a good estimate of this discharge component over time scales of hours to days based on the nutrient concentrations in the discharge waters nutrient loads from the beach to the adjacent estuary at low tide were 148 6 79 7 5 6 5 1 and 197 6 101 mmol min21 m21 of shoreline for total dissolved n p and si respectively groundwater discharge and these nutrient fluxes contribute significantly to the unusually productive benthic communities that inhabit the seepage and nearby intertidal zones estuaries receive their primary inputs from fluvial discharges and exchange with the ocean but it is increasingly evident that atmospheric deposition and direct groundwater discharges from uplands also play a significant role in estuarine biogeochemical processes paerl 1997 burnett et al 2003 although groundwater discharge is thought to represent only a small fraction of the total freshwater discharge to estuaries and the ocean there is increasing evidence that nutrients and contaminants associated with this discharge may play a more significant ecological role than implied by the relatively small discharge valiela et al 1992 burnett et al 2003 shaw 2003 this is particularly true in coastal plain settings where nutrient and contaminant inputs to the groundwater from domestic industrial municipal and agricultural practices may be high the hydraulic conductivity of soils and aquifer sediments is large and the topographically driven groundwater flow to shallow upland streams is low submarine groundwater discharge in many settings appears to be associated with productive benthic communities johannes and hearn 1985 bussmann et al 1999 zipperle and reise 2005 and may influence sediment water exchange through the imposition of hydraulic gradients the modification of subbottom flow paths and the alteration of diagenetic reactions and rates moore

on the metamorphic history of an archaean granitoid greenstone terrane east pilbara western australia using the40ar 39ar age spectrum technique abstract age spectrum analyses of blue green hornblendes from amphibolites from the western shaw belt east pilbara western australia indicate an age of at least 3200 ma for early regional metamorphism ages on hornblende and muscovite from the narrow contact zone with the adjacent yule batholith probably date updoming of the granitoid gneiss terranes at 2950 ma hornblendes from within the shaw batholith and from a contact zone of a post tectonic granitoid yield ages of 2840 2900 ma indicating either prolonged high temperatures within the granitoid gneiss terranes or a separate thermal pulse associated with the intrusion of post tectonic granitoids the preservation of very old hornblendes in a narrow greenstone belt surrounded by massive granitoid gneiss domes indicates that remarkable contrasts in metamorphic geotherms existed over short distances during the late archaean suggesting that updoming occurred during a period of rapid tectonism

ground deformation at campi flegrei italy implications for hazard assessment campi flegrei caldera west of naples in southern italy has an exceptional documented record of ground deformation from roman times onwards systematic recording began in the nineteenth century for earlier dates information has been obtained from archaeological studies and from contemporary descriptions of the locations of buildings usually roman with respect to sea level especially important have been accounts related to the serapis a roman market place built in the second century bc and now incorporated within the modern town of pozzuoli the long term patterns of ground deformation have conventionally been investigated on the premise that campi flegrei naturally tends to a state of static equilibrium this study argues that instead the area naturally tends to a steady rate of subsidence at about 17 mm a 1 after this background rate has been removed the data indicate that a permanent uplift of some 33 m has occurred from roman times up until the present day 2005 at the time of writing attributable to the intrusion of 1 85 km3 of magma of which only 1 has been erupted uplift has occurred in three episodes the third of which is still in progress the behaviour can be interpreted in terms of the intermittent ascent of magma between a reservoir of c 102 103 km3 at depths of 8 15 km or greater to a much smaller shallower system at depths of about 3 4 km should the current pattern of deformation follow previous trends uplift is expected to continue for another 80 90 years during whieh time campi flegrei will be characterized by an elevated possibility of eruption the geological society of london

geochronology and thermochronology by the 40ar39ar method ian mcdougall and t mark harrison oxford university press 1988 212p u s 55 00 isbn 0 19 504302 2

rifting in heterogeneous lithosphere inferences from numerical modeling of the northern north sea and the oslo graben oslograbenevolvedinthecoldandstableprecambrian lithosphere of fennoscandia whereas the northern northsearifttookbirthinfreshlyreworkedcaledonian lithosphere huge volumes of magmatic rocks characterize the relatively narrow oslo graben in contrast little magmatism is documented for the wide northern north sea rift differences in timing between both rifts are inferred but still debated we present numerical thermomechanical models along a lithospheric e w section that involves both the oslo graben and the northern north sea area because the modeled section crosses the boundary between caledonian and proterozoic provinces thermal and compositional heterogeneities are considered as is suggested by various geophysical data sets we also consider lithospheric thickness heterogeneities in the precambrian lithosphere modeling results suggest that the northern north sea was on top of weak lithosphere very sensitive to far field stresses consequently we suggest that rifting in the northern north sea began as early as regional extension was effective i e late carboniferous early permian and does not postdate the oslo graben as it is commonly assumed rifting in the strong precambrian lithosphere is unexpected modeling results suggest thatapre existinglithosphericthicknesscontrastwithin the fennoscandian lithosphere favored rifting in the oslo graben index terms 8109 tectonophysics continental tectonics extensional 0905 8159 tectonophysics evolution of the earth rheology crust and lithosphere 8020 structural geology mechanics 9335 information related to geographic region europe 9614 information related to geologic time paleozoic keywords numerical modeling rifting rheology lithosphere oslo graben north sea citation pascal c and s a p l cloetingh rifting in heterogeneous lithosphere inferences from numerical modeling

the mealy dykes labrador petrology age and tectonic significance the mealy dykes constitute a major olivine diabase swarm in the mealy mountains grenville province labrador the dykes intrude anorthosites and monzonites of the mealy mountains complex and outcrop over an area of at least 4000 km2 the swarm strikes east northeast and may constitute the largest group of unmetamorphosed diabase dykes in the grenville province the mealy dykes are moderately iron rich olivine tholeiites typically nonporphyritic thick dykes have coarse grained interiors that show some fractionation but variations in bulk chemical composition are relatively modest olivine fo47 fo27 plagioclase cores an63 an47 rims an47 an30 and low ca augite are the principal silicate minerals coexisting magnetite and ilmenite suggest that solidus temperatures were about 980 c and that subsolidus oxide re equilibration continued to near 530 c or perhaps lower a whole rock rb sr errorchron age for the mealy dykes yielded 1380 54 ma sr1 0 7028 0 0002 which within precision estimates i

the present state of the magmatic system of the campi flegrei caldera based on a reconstruction of its behavior in the past 12 ka abstract new geochemical and sr isotope data have been acquired on samples representative of volcanic units erupted inside the resurgent campi flegrei caldera cfc over the past 12 ka these data integrated with previous published petrological and with newly acquired geochronological volcanological and geothermal data shed light on the nature and timing of the processes that controlled the evolution of the phlegraean magmatic system in the past 12 ka three isotopically and geochemically distinct magmatic components were erupted at the cfc as either homogeneous or mixed magma batches one component campanian ignimbrite component cic 87 sr 86 sr 0 70735 0 70740 is similar to the trachytic magma extruded during the first phase of the campanian ignimbrite ci eruption 37 ka a second component neapolitan yellow tuff component nytc 87 sr 86 sr 0 70750 0 70757 is similar to the latitic alkali trachytic magma batches extruded during the course of the neapolitan yellow tuff nyt eruption 12 ka a third component minopoli component mic 87 sr 86 sr 0 7086 is similar to the trachybasaltic magma of the minopoli 2 mi eruption 9 7 ka these components were erupted as either single batches of magma or mixed ci nyt or mi nyt batches of magma through vents located either along the structural boundary of the nyt caldera or inside the nyt caldera mainly on portions of the resurgent block under extensional stress the ci and nyt components represent residual portions of older large volume magma reservoirs which have fed eruptions since about 60 and 15 ka respectively the least evolved mi component was erupted only during the 12 9 5 ka and 8 6 8 2 ka epochs of activity through vents located on a ne sw regional fault system this component could represent a deeper reservoir tapped by the ne sw regional fault system reactivated after the nyt caldera collapse deeper mi and shallower ci and nyt magmatic systems interacted by mixing among batches of magma during their rise to surface overall the data suggest that the cfc magmatic system today is characterized by the presence of two larger independent reservoirs filled by residual portions of the ci and nyt magmas these generated many smaller shallower pockets of evolved magma that fed most of the eruptions that occurred in the cfc over the past 12 ka moreover a deeper reservoir mi tapped by the ne sw regional fault system provided batches of less evolved magma that mixed with magma present in the shallower pockets

genesis and evolution of unrest episodes at campi flegrei caldera the role of thermal fluid dynamical processes in the geothermal system we develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients the model simulates geothermal systems in calderas given the boundary conditions and the fluid dynamical properties of the medium the model allows computation in fluid dynamical stationary states of parameters characterizing the flow such as flow velocity and temperature and pressure distributions at depth the model is applied to investigate the effects of the local geothermal system on the unrest episodes at campi flegrei caldera using experimentally determined fluid dynamical parameters for the caldera rocks we show that changes of water flow in shallow aquifers under the effect of pressure and or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises in particular they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift they can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport on such grounds an integrated mechanic thermal fluid dynamical model was built allowing us to give a semiquantitative global explanation to the genesis and evolution of unrest phenomena results obtained here can be generalized to other similar calderas

argon retentivity and argon excess in amphiboles from the garbenschists of the western tauern window eastern alps 22 hornblende k ar ages and 10 39ar 40ar spectra were obtained for hornblende garbenschists from the western tauern window the post kinematic amphiboles were produced during the late alpine prograde metamorphism 6 10 kb and 500 570 c two nearly potassiumfree cummingtonites rimming hornblende yield k ar ages of 120 ma while the 20 tschermakitic hornblendes scatter between 17 and 37 ma the reason for this scatter is excess ar possibly incorporated into amphiboles during healing of fractures now traceable by trails of fluid inclusions excess ar is semiquantitatively corrected for by combining cogenetic hornblende and cummingtonite with k ar isochrons it can be quantified in 4 out of 10 hornblendes by 39ar 40ar stepwise heating experiments ages of 18 20 ma result for corrected hornblendes the retentivity of 40ar after correction for excess shows no correlation with chemistry within the narrow compositional range observed rather it shows intriguing correlations with irregularities in ca k spectra pointing to a microstructurally controlled mechanism for ar loss this observation leads to a critical evaluation of the closure temperature constant which apparently depends on an incompletely known number of mineralogical and environmental parameters in particular those 39ar 40ar release spectra which yield low temperature steps with younger ages than the plateaus are not interpretable in terms of a synchronous closure this gives evidence that loss of radiogenic isotopes proceeds by a more complex mechanism than simple volume diffusion through isotropic media

39ar 40ar ages from the yozgat batholith preliminary data on the timing of late cretaceous extension in the central anatolian crystalline complex turkey abstract isotopic dating of sheared and unsheared rocks can be important in understanding deformational processes in orogenic belts this study examines 40ar 39ar dating of granitoids and mylonitic rocks to constrain intrusive and deformational events within the northern part of the central anatolian crystalline complex cacc the kerkenez granitoid within this complex comprising primarily quartz monzonite and hornblende granite contains discrete ductile shear zones these zones are characterized by protomylonite and mylonite formations with metamorphism conditions that reach lower amphibolite facies mylonitic foliations and lineations and asymmetric kinematic indicators e g asymmetric porphyroclasts composite shear bands with top to the northwest shear senses considering the high closure temperatures 500 c for hornblende and 350 c for k feldspar both hornblende quartz monzonite and hornblende granite in the kerkenez granitoid may have cooled rapidly suggesting that hornblende quartz monz

40ar 39ar study of plagioclases from the rogaland anorthosite complex sw norway an attempt to understand argon ages in plutonic plagioclase abstract the combined use of stepwise heating and uv laser ablation 40 ar 39 ar techniques with microprobe analyses on plutonic plagioclase allows the investigation of complex argon release and retention the complexity arises from the multiphase nature of the samples comprising plagioclase k feldspar in antiperthite secondary sericite and various inclusions in which some of the components also exhibit variable ages fragments of plagioclase megacrysts and plagioclase separates from whole rock samples were selected from a well constrained series of anorthosite leuconorite intrusions of the rogaland igneous complex sw norway intruded at ca 930 ma all samples exhibit saddle like staircase shaped argon release spectra ages rise from around 400 600 to 750 900 ma though three samples exhibit excess argon released at high temperatures the most remarkable aspect of this data is however the apparently linear correlation of 40 ar 39 ar with ca k the stepwise heating data reveal late stage cooling ages considerably younger than the intrusive age and low temperature reheating of the rogaland igneous complex during caledonian overthrusting arrhenius plots for the stepwise heated samples show a linear trend of diffusion data at low temperatures followed by a systematic break around 900 1060 c single spot ages obtained using a uv laser show extreme age variations with heterogeneous excess argon contained in inclusions but no correlation of 40 ar 39 ar with ca k this lack of correlation indicates that the two component mixing model with two end members of distinct ages suggested by the stepwise heating data is an artefact resulting from a more complex mechanism of argon release the most apparent interpretation of this data is that both plagioclase and another potassium rich minor component probably k feldspar antiperthite yield variable but correlated ages because the excess argon is found exclusively in samples from marginal leuconorite bodies and never in the core of the megacrysts it is probably derived from the outgassing of the k rich country rock

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

tectonic stress and renewed uplift at campi flegrei caldera southern italy new insights from caldera drilling deep drilling is a key tool for the investigation of active volcanoes in the modern earth sciences as this provides the only means to obtain direct information on processes that occur at depth data acquired from drilling projects are fundamental to our understanding of volcano dynamics and for mitigation of the hazards they pose for millions of people who live close to active volcanoes we present here the first borehole measurement of the stress field in the crust of campi flegrei southern italy a large active caldera and one of the highest risk volcanoes worldwide measurements were performed to depths of 500 m during a pilot study for the campi flegrei deep drilling project these data indicate an extensional stress field with a minimum horizontal stress of ca 75 to 80 of the maximum horizontal stress which is approximately equal to the vertical stress the deviation from lithostatic conditions is consistent with a progressive increase in applied horizontal stress during episodes of unrest since at least 1969 as the stress field is evolving with time the outcome of renewed unrest cannot be assessed by analogy with previous episodes interpretations of future unrest must therefore accommodate the possibility that campi flegrei is approaching conditions that are more favourable to a volcanic eruption than has previously been the case such long term accumulation of stress is not expected to be unique to campi flegrei and so might provide a basis for improved forecasts of eruptions at large calderas elsewhere