special collection on the june 1993 volcanic eruption on the coaxial segment juan de fuca ridge the mid ocean ridge system is the primary site of oceanic crustal accretion and a major source of chemical thermal flux from the earth s interior to the hydrosphere although geological mapping geophysical exploration and hydrographie chemical surveys have provided important insights into accretionary processes until recently there has been no method of monitoring the dynamics of these systems over long periods and large areas insights into spreading center dynamics have depended on serendipitous discoveries of evidence of activity based on water column anomalies baker et al 1987 bathymetric differences fox et al 1992 or direct field observations haymon et al 1993 in situ instrumentation has been used to monitor dynamics at a few selected sites for long periods but these instruments are generally unable to telemeter data in real time

states of paleostress north and south of the periadriatic fault comparison of the drau range and the friuli southalpine wedge this study focuses on the analysis of structures and kinematics of a n s profile along the axis of maximum shortening of the european eastern alps the area includes the southern austroalpine unit in the north and the southalpine unit which is a part of the adriatic indenter the stratigraphically different units are separated by the periadriatic fault the major strike slip fault within the alps in order to assess the kinematics of these units mainly fault slip data from north and south of the periadriatic fault were analyzed we distinguish a succession of five main kinematic groups in both units 1 n s compression 2 nw se compression 3 ne sw compression 3 changes gradually from subvertical to subhorizontal 4 n s compression and 5 nw se compression our study reveals that the deformation sequence on either sides of the paf is similar the mean orientations of the principal stress axes however show small but consistent differences the subhorizontal axes north of the periadriatic fault plunge northward in the south southward a counterclockwise ccw rotation of the southern part in respect to the north is evident and in line with the well known counterclockwise rotation of the adriatic indenter as well as dextral displacement of the n fanning stress field along the periadriatic fault opposing plunge directions are interpreted as a primary feature of the internal stress field within an orogenic wedge further increased during ongoing compression

intra oceanic subduction related hydrothermal venting kermadec volcanic arc new zealand intra oceanic volcanic arcs mark the boundaries between converging lithospheric plates where subduction produces volcanic and tectonic activity that ensures a steady supply of magmatic heat and hydrothermal fluids to the seafloor here we report on the first broad and systematic survey of hydrothermal emissions generated along a submarine arc front more than half seven of 13 of the volcanoes surveyed along 260 km of the southern kermadec arc ne of new zealand are hydrothermally active our results indicate that volcanic arcs represent a previously unheeded but potentially extensive source of shallow 2 km water depth vent fields expelling fluids of a unique and heterogeneous composition into the oceans

continuous sampling of hydrothermal fluids from loihi seamount after the 1996 event for at least 9 years prior to july 1996 hydrothermal fluids flowed from pele s vents on loihi seamount hawaii in july august 1996 a tectonic volcanic event occurred that destroyed pele s vents creating a pit crater pele s pit and several sites with hydrothermal venting in october 1996 we deployed two new continuous water samplers osmosamplers at two of these hydrothermal sites and collected fluids using traditional sampling techniques to monitor the evolution of crustal and hydrothermal conditions after the event the samplers were recovered in september 1997 and additional discrete vent fluid samples were collected the osmosampler located along the south rift at naha vents captured a change in composition from a low chlorinity high k fluid relative to bottom seawater to a high chlorinity low k fluid these changes are consistent with the fluid cooling during ascent and being derived from several different sources which include high 330 c and low 330 c into which magmatic volatiles were added during the deployment thermal and fluid fluxes decreased at naha the transport of heat and chemicals was decoupled the chemical and thermal evolution of hydrothermal fluids after the event on loihi is consistent with previous models based on events that have occurred along mid ocean ridges the event at loihi clearly had an effect on the local hydrography however the integrated effect of chemical fluxes to global budgets from similar events is uncertain chemical fluxes from similar events may have a global impact if ratios of chemical e g co2 fe mn mg sulfate and k to thermal anomalies greatly exceed or are in the opposite direction to fluxes from mid ocean ridge hydrothermal systems

a decade of exploring a submarine intraplate volcano hydrothermal manganese and iron at lō ihi volcano hawai i 1 decadal time series observations of hydrothermal fluid emissions from l ihi volcano were initiated in 1992 using a combination of submersible and shipboard sampling strategies magmatic tectonic processes associated with a spectacular seismic event in july august 1996 led to the collapse of pele s vents 31 c near the volcano summit into a new pit crater pele s pit inundated by high temperature tmax 198 c focused and lower temperature 30 to 200 fold 1 5 months postcollapse and during the following year decreased a further twofold to threefold at pele s pit and 30 fold at east pit while a steady concentration of 400 nmol l tdfe prevailed throughout the remaining years of this study at pele s pit a gradual and threefold decrease in the concentration of dmn to about 15 nmol l was observed high temperature fluids 128 198 c 1997 1999 90 c 2001 venting simultaneously from different orifices within pele s pit had distinguishable fe mn ratios that can be attributed to different subseafloor origins fe mn ratios characteristic of fluids moderated by high temperature water rock reaction had low values in 1997 1998 1 6 0 7 increasing to about 7 in 1999 fluids moderated by magmatic degassing of co2 had much higher fe mn ratios increasing from 24 15 in 1997 1998 to 50 in 1999 and 63 87 in 2001 fe mn values of dispersing plumes at l ihi reflect an admixture of these sources and a relative fe abundance that is consistently high compared to mid ocean ridge systems the pulsed injection of mn and fe into the surrounding ocean associated with the 1996 tectonic magmatic event at l ihi was massive our decadal observations confirm that mn and fe are useful markers of the magnitude and evolution of the effects of magmatic perturbation on hydrothermal systems influenced by chronic magmatic degassing

analogue modelling of reverse fault reactivation in strike slip and transpressive regimes application to the giudicarie fault system italian eastern alps abstract sandbox analogue models were used to study the reactivation of a reverse fault in strike slip and transpressive regimes for comparison with the evolution of the giudicarie fault system in the central eastern alps the giudicarie system is interpreted as resulting from late miocene sinistral transpressive reactivation of an older late oligocene reverse fault the old reverse fault was reproduced as a pre cut dilatant surface obtained by pulling a stiff metal wire through the model sand layer the position of the pre existing fault with respect to the base plate fault accommodating the strike slip and transpressive faulting phase controlled the extent and geometry of reactivation the clearest reactivation in a pure strike slip regime was achieved in experiments where the basal strike slip fault was immediately below the pre existing fault plane this strong reactivation involved lateral extrusion and lateral stepping of secondary faults from the basal fault to the pre existing reverse fault in the case of transpression the most spectacular reactivation was achieved for a convergence angle of 10 strongly asymmetric structures developed on either side of the pre cut dilatant zone the analogue experiments reproduced very closely the structural features of the giudicarie fault system supporting a model involving a twofold tectonic evolution for the giudicarie fault system with later reactivation in sinistral transpression of an older reverse fault

seabeam depth changes associated with recent lava flows coaxial segment juan de fuca ridge evidence for multiple eruptions between 1981 1993 after a swarm of earthquakes was detected on the coaxial segment of the juan de fuca ridge in june july 1993 the area was resurveyed with seabeam multibeam sonar to search for depth changes associated with a submarine volcanic eruption quantitative comparison of the 1993 seabeam survey with surveys in 1981 82 and 1991 shows one area of seafloor depth change up to 29 m between 1991 93 exactly where a pristine lava flow was discovered in addition two other depth anomalies up to 37 m and 20 m are identified between 1981 91 evidence that other recent eruptions have occurred along this spreading ridge segment

the quantum event of oceanic crustal accretion impacts of diking at mid ocean ridges seafloor diking eruptive events represent the irreducible quantum events of upper oceanic crustal accretion they record events by which a large portion of the oceanic crust has formed through geological history since 1993 the u s navy s real time sound surveillance system has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast pacific these diking eruptive events trigger a sequence of related rapidly evolving physical chemical and biological processes magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms some of which thrive in high temperature anaerobic environments many of the organisms identified from these systems are archaea if microorganisms can thrive in the water saturated pores and cracks within deep volcanically active portions of our planet other hydrothermally active planets may harbor similar life forms

hydrological response to a seafloor spreading episode on the juan de fuca ridge seafloor hydrothermal systems are known to respond to seismic and magmatic activity along mid ocean ridges often resulting in locally positive changes in hydrothermal discharge rate temperature and microbial activity and shifts in composition occurring at the time of earthquake swarms and axial crustal dike injections1 2 3 4 5 6 7 8 9 10 corresponding regional effects have also been observed11 here we present observations of a hydrological response to seafloor spreading activity which resulted in a negative formation fluid pressure transient during and after an earthquake swarm in the sediment sealed igneous crust of the middle valley rift of the northernmost juan de fuca ridge the observations were made with a borehole seal and hydrologic observatory originally established in 1991 to study the steady state pressure and temperature conditions in this hydrothermally active area12 13 the magnitude of the co seismic response is consistent with the elastic strain that would be expected from the associated earthquakes but the prolonged negative pressure transient after the swarm is surprising and suggests net co seismic dilatation of the upper permeable igneous crust the rift valley was visited four weeks after the onset of the seismic activity but no signature of increased hydrothermal activity was detected in the water column it appears that water not magma filled the void left by this spreading episode

the schneeberg normal fault zone normal faulting associated with cretaceous se directed extrusion in the eastern alps italy austria abstract the cretaceous eo alpine collisional event in the european eastern alps is generally accepted to induce w nw directed thrusting both in basement and in sedimentary cover units this study presents the first evidence of eo alpine w nw directed normal kinematics along the schneeberg normal fault zone which separates eo alpine high pressure rocks in a footwall position from pre alpine basement rocks in a hanging wall position new garnet sm nd data indicate that exhumation of the high pressure rocks along the normal fault zone started around 95 ma ago and continued up to low greenschist brittle conditions at 76 ma as indicated by a rb sr age from a low temperature mylonite the occurrence of pre alpine basement rocks both in the hanging wall and the footwall of eo alpine high pressure rocks suggests exhumation by extrusion processes despite the displacement or removal of parts of the lower portion of the high pressure unit by tertiary strike slip faults eo alpine top to ese thrusting as expected for the structurally lower part of an extruding wedge was found at and below the base of the eo alpine high pressure rocks a rb sr age of 77 ma from a greenschist facies mylonite in this thrust shear zone shows the contemporaneity of deformation at the base and the top of the wedge the tectonic transport direction within the extruding wedge was e se opposite to the w nw direction so far reported for the eo alpine event in the eastern alps the contemporaneity of opposite tectonic transport directions during continental subduction may be explained by a double vergent wedge model with a narrow zone of ductile flow where the high pressure rocks were exhumed

distribution and sources of bulk organic matter om on a tropical intertidal mud bank in french guiana from elemental and isotopic proxies the mobile french guiana coast is a shoreface region downdrift of the amazon river where enormous quantities of inorganic and organic materials are exchanged with the atlantic ocean the rapid accumulation of these materials forms highly unstable shore attached mud banks which can be temporally emerged and then rapidly colonized and stabilized by microphytobenthos and opportunistic mangroves i e avicennia germinans mud banks are preferential sites for the accumulation and significant remineralization of organic matter om due to intense erosion deposition cycles and potential biological colonization the distribution and sources of bulk sedimentary om were characterized by elemental and isotopic analyses of four sediment cores together with samples from three potential om sources mangrove plants suspended particulate matter spm and microphytobenthos all collected from the landward face of the macouria mud bank french guiana total organic carbon toc and nitrogen tn concentrations in the sediment cores showed that om sources were characterized by spatio temporal variations in this mud bank the relative contributions of mangrove plants spm and microphytobenthos were estimated using a three end member mixing model based on tn toc atomic ratios and 13c values sedimentary om is mostly controlled by spm associated with variable amounts of om derived from mangrove plants and microphytobenthos these variations could be explained by topography and bed elevation which decrease submersion time and increase desiccation higher contributions of microphytobenthos are associated with black om rich laminae identified in sedimentary cores and linked to temporal emersion phases of the mud bank which favor the growth of benthic microalgae this result is confirmed by the calculation of the average sediment accumulation rate around 36 7 14 8 cm yr 1 taking into account the emersion of the study site every spring tide a fortnightly cycle this value is within the range of the previous results from other mud banks in french guiana but is more than ten times greater than values generally obtained in other coastal contexts

the northern giudicarie and the meran mauls fault alps northern italy in the light of new paleomagnetic and geochronological data from boudinaged eo oligocene tonalites this study concentrates on small intrusions along two important faults of the giudicarie fault system the northern giudicarie and the meran mauls fault summarised under the term tonalitic lamellae magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the ne sw striking northern part of the giudicarie fault system the meran mauls fault overprinted by younger thrusting the regional stressfield was oriented approximately nnw sse during tertiary times the distinctive change in deformation along the meran mauls fault from dextral strike slip to top se thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation based on the assumption of a preliminary straight periadriatic lineament bent by the nnw wards advancement of the southalpine indenter the tonalitic lamellae may be interpreted as lenses sheared off from the adamello batholith during indentation new u pb data on zircon show that some of the lamellae are of oligocene rupelian others of late eocene priabonian age an amphibole gabbro lens occurring on the meran mauls fault provides a middle eocene bartonian age among the major periadriatic plutons only the southern units of the adamello batholith also intruded in the eocene that suggests a strong correlation between the tonalitic lamellae and the adamello batholith the analyses of the remanent magnetisation and the curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures this indicates slow cooling of the investigated intrusions along the giudicarie fault system down to approximately 300 c which is in contrast to the fast cooling determined for the adamello intrusion units currently at the surface the new zircon fission track data also show later cooling of the tonalites along the giudicarie fault system when compared with the adamello batholith in the south and the mauls lamellae in the north indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the adamello and the mauls region this may be due to important top se thrusting and transpressive faulting in the footwall of the northern giudicarie fault and the meran mauls fault

temporal and spatial variability of hydrothermal manganese and iron at cleft segment juan de fuca ridge a unique data set for hydrothermal mn and fe was collected at cleft segment on the juan de fuca ridge between 1983 and 1991 the data set includes observations of focused and diffuse venting fluids and neutrally buoyant plumes formed by chronic and episodic venting manganese heat and iron heat ratios for plumes from the north end of the cleft segment were combined with independently determined estimates of plume heat flux to yield annually averaged chronic venting fluxes for mn of 0 36 0 17 mol s 1 and for fe of 0 61 0 34 mol s 1 over 6 years of plume measurements at north cleft segment observed episodic hydrothermal discharge accounted for 15 of the total vented mn and 35 of vented fe the chronic fluxes for mn and fe at a second venting center located at the south end of the cleft segment were estimated to be approximately equal to the fluxes at north cleft segment chronic plumes at north cleft segment are mixtures of focused and diffuse discharge that contribute heat mn and fe in variable proportions similar examination of south cleft segment data strongly suggests the presence of an as yet unobserved venting source relatively depleted in mn and fe but contributing substantially to the overall heat temporal and spatial variations in the concentrations of mn and fe and in mn heat and fe heat ratios for focused seafloor vents were difficult to resolve within complex chronic plumes manganese heat and iron heat ratios of megaplumes suggest they may have derived from reservoirs of diffuse fluids while smaller event plumes may have formed by different processes and have properties similar to chronic plumes the accurate assessment of segment scale hydrothermal fluxes of mn and fe requires coordinated measurements of representative seafloor sources and the neutrally buoyant plume that integrates all seafloor discharge

rethinking the origins of the red chert at la desirade french west indies la desirade in the lesser antilles contains one of the rare fragments of jurassic oceanic crust known on caribbean islands others in the northeastern caribbean occur on puerto rico and hispaniola these fragments each include radiolarian bearing chert that has been linked to an origin in the pacific ocean of these a fragment in sierra bermeja puerto rico is clearly of pacific origin as it contains lower jurassic radiolarians that predate the opening between north and south america red ribbon chert at el aguacate dominican republic is essentially identical to widespread radiolarites found in accreted material of the pacific basin and from pacific ocean odp site 801 extensive sampling in the atlantic basin has produced no jurassic radiolarites thus based on age the older of the sierra bermeja outcrops and lithology el aguacate two of these fragments are definitely of pacific origin re evaluation of the chert pillow lava sequence on la desirade in light of recent discoveries at spreading ridges has resulted in a revised interpretation of their probable origin a wide range of features of these cherts indicate pelagic and hydrothermal sedimentation at an upper jurassic spreading ridge one that almost assuredly existed in the eastern pacific realm these features include the types of chert found on the island lack of argillaceous partings small outcrop size discontinuous chert bodies presence of limestone squeeze ups into pillow lavas and indications of hydrothermal activity including epidotization of basalt migrating outward from pillow margins with chert rinds that record pelagic and hydrothermal sedimentation at an upper jurassic spreading ridge one that almost assuredly existed in the extreme eastern pacific realm

the western end of the eoalpine high pressure belt texel unit south tyrol italy eclogites in the texel unit eastern alps south tyrol italy represent the westernmost outcrops of the e w striking eoalpine high pressure belt ehb east of the tauern window the ehb forms part of a cretaceous intracontinental south dipping subduction collision zone however the same nappe stack displays a northwest dip at its western end this prominent change in dip direction gave rise to discussions on the general setting of the eoalpine collision based on our own observations and literature data we present a new tectonic model for the western end of the ehb due to the special situation of this area at the tip of the southalpine indenter originally south east dipping structures became overturned and former thrusts appear as normal faults e g schneeberg fault zone while former normal faults presently display thrust geometries e g jaufen fault thus we explain the current configuration with a coherent eoalpine subduction direction

an 40ar 39ar laser probe study of pseudotachylites in charnockite gneisses from the cauvery shear zone system south india the age of pseudotachylite formation in the crustal scale cauvery shear zone system of the precambrian southern granulite terrain south india has been analyzed by laser probe ar 40 ar 39 dating laser spot analyses from a pseudotachylite from the salem attur shear zone have yielded ages ranging from 1214 to 904 ma some evidence for the presence of excess ar is indicated by the scatter of ages from this locality the host gneiss preserves palaeoproterozoic rb sr whole rock biotite ages 2350 11 to 2241 11 ma a mylonite in the koorg shear ca 200 km to the north yielded an age of 895 17 ma the consistency of the age distribution from spot analyses precludes the presence of significant excess ar despite published evidence for the growth of high grade minerals within some components of the cauvery shear zone during the pan african event 700 550 ma the pseudotachylites in this study provide no evidence for pan african formation instead they document the first evidence for mesoproterozoic tectonism in the cauvery shear zone system thus prompting a review of the correlation between the cauvery shear zone system and the large scale shear zones located elsewhere in eastern gondwana c 2006 international association for gondwana research published by elsevier b v all rights reserved

thermochronological record of thrusting and strike slip faulting along the giudicarie fault system alps northern italy the giudicarie fault system represents the central approximately ne sw trending segment of the periadriatic fault system based on new fission track data the near surface evolution of the units bordering the giudicarie fault system gfs is analysed new and published zircon fission track zft data are compiled in an age contour map of the area and depict some first order features of cooling and exhumation pattern out of the three main permian plutons located in the footwall of the gfs the northern brixen pluton and southernmost kreuzberg pluton yielded zft ages of about 100 ma while the intermediate ifinger pluton cooled through the zircon partial annealing zone only in the miocene the ifinger granodiorite overthrusts the southalpine basement and the permian rocks of the athesian volcanic district along the nw dipping brittle naif fault across this thrust an important age jump from miocene to permian zft ages is observed suggesting that the deformation has jumped towards the southeast thus deactivating the related segment of the gfs the most eye catching feature of the age contour map is the corridor of young miocene zft ages from small tonalitic intrusions along the northern giudicarie fault this corridor connects early miocene 17 23 ma zft ages of the ne adamello with the middle late miocene 19 9 ma zft ages of the meran mauls basement and the western tauern window and provides evidence for a polyphase deformation along the gfs a three step evolution model is proposed for the gfs a shearing of the northern rim of the adamello batholith along the dextral strike slip periadriatic fault system b bending of the central part of the fault to a ne direction together with the adjacent intrusive rocks c dissection of the bend part meran mauls fault by the sinistral transpressive northern giudicarie fault and exhumation of small tonalitic bodies along this structure highlights different exhumation history for permian intrusions along the giudicarie fault system very consistent zft ages of 15 ma for the entire meran mauls basement corridor of miocene zircon fission track ages along the giudicarie fault system evidence for a polyphase deformation along the giudicarie fault system

titanium in quartz thermometry on synkinematic quartz veins in a retrograde crustal scale normal fault zone abstract previous studies have suggested that estimation of deformation temperatures in quartz mylonites by titanium in quartz geothermometry is only possible at temperatures 500 c above which efficient ti exchange is achieved via grain boundary migration recrystallization based on quartz mylonite samples collected across the simplon fault zone sfz we demonstrate that deformation temperatures of dynamic recrystallization can be obtained down to 350 c a prerequisite for such temperature estimates at the low temperature end of ductile deformation of quartz is the formation of synkinematic quartz veins and their immediate overprint either by subgrain rotation sgr or bulging recrystallization blg it is the slow growth of the synkinematically precipitating vein quartz that allows for equilibration of ti in the vein quartz this ti concentration may only slightly be modified during sgr hence ti in qtz thermometry provides a close approach to the vein formation temperature ti concentrations are partially reset during blg and resulting temperatures are thus maximum temperatures of quartz recrystallization importantly undeformed vein quartz always yield vein formation temperatures investigation of the dynamic recrystallization processes overprinting synkinematic quartz veins thus allows for a critical independent evaluation of the ti in quartz temperatures obtained for the sfz there is a decrease in recrystallized grain sizes towards the fault plane and a change in the dominant recrystallization process associated with a narrowing of the shear zone as indicated by the ti in quartz temperature estimates this strain localization correlates with cooling from 560 c in the oldest microstructures at the periphery of the shear zone down to 350 c in the youngest microstructures of the footwall near the hanging wall contact a great benefit of the approach presented here is that intermediate to low temperature plastic deformation in quartz can now also be assessed such novel temperature constraints on quartz crystallization are essential for better constraining deformation and rheology in the upper earth s crust

polyphase seismic faulting in the ivrea zone italian alps revealed by 40ar 39ar dating of pseudotachylytes terra nova 23 162 170 2011 abstract most fault related pseudotachylytes in the val sesia area ivrea zone nw italian alps occur in two areas near the canavese line in the kinzigite formation paragneisses and in an elongate belt in the mafic complex gabbros away from the canavese line 40ar 39ar dating indicates that pseudotachylytes from the kinzigite formation were formed in the late eocene likely during the early stages of the collision between the nw corner of the adriatic indenter and the european margin pseudotachylytes from the mafic complex were formed under a transpressive strain regime as suggested by kinematic indicators and yield early cretaceous albian 40ar 39ar ages their formation is possibly related to shortening during the inception of the tectonic inversion of the adriatic passive margin

exploring the ar isotope record of an early miocene pseudotachylyte in an early oligocene intrusion rieserferner pluton eastern alps abstract we investigate the influence of unmelted clasts on the 40ar 39ar age record of a miocene pseudotachylyte within the early oligocene riesenferner pluton eastern alps this case study is ideal to investigate the effect of inherited ar retained in survivor clasts because although seismic faulting was only slightly younger 39ar laser analyses of low k microlitic domains free of discernable clasts yield slightly but significantly older ages than those from the high k matrix results suggest that older ages up to 4 on average from low k domains are due to contamination by plagioclase clasts and suggest an age of 17 12 0 22 ma for coseismic slip this age dates the last stage of activity of the giudicarie fault during tectonic indentation of the dolomites block of the southern alps against the nappe stack of the eastern alps

a method for quantitatively estimating diffuse and discrete hydrothermal discharge submarine hydrothermal fluids discharge as undiluted high temperature jets and as diffuse highly diluted low temperature percolation estimates of the relative contribution of each discharge type which are important for the accurate determination of local and global hydrothermal budgets are difficult to obtain directly in this paper we describe a new method of using measurements of hydrothermal tracers such as fe mn fe heat and mn heat in high temperature fluids low temperature fluids and the neutrally buoyant plume to deduce the relative contribution of each discharge type we sampled vent fluids from the north cleft vent field on the juan de fuca ridge in 1988 1989 and 1991 and plume samples every year from 1986 to 1991 the tracers were on average 3 to 90 times greater in high temperature than in low temperature fluids with plume values intermediate a mixing model calculates that high temperature fluids contribute only 3 of the fluid mass flux but 90 of the hydrothermal fe and 60 of the hydrothermal mn to the overlying plume three years of extensive camera ctd sled tows through the vent field show that diffuse venting is restricted to a narrow fissure zone extending for 18 km along the axial strike linear plume theory applied to the temperature plumes detected when the sled crossed this zone yields a maximum likelihood estimate for the diffuse heat flux of8 9 104 w m for a total flux of 534 mw considering that diffuse venting is active along only one third of the fissure system for mean low and high temperature discharge of 25 c and 319 c respectively the discrete heat flux must be 266 mw to satisfy the mass flux partitioning if the north cleft vent field is globally representative the assumption that high temperature discharge dominates the mass flux in axial vent fields leads to an overestimation of the flux of many non conservative hydrothermal species by about an order of magnitude

kinematic analysis and analogue modelling of the passeier and jaufen faults implications for crustal indentation in the eastern alps crustal deformation in front of an indenter is often affected by the indenter s geometry rheology and motion path in this context the kinematics of the jaufen and passeier faults have been studied by carrying out paleostress analysis in combination with crustal scale analogue modelling to infer 1 their relationship during indentation of the adriatic plate and 2 their sensitivity in terms of fault kinematics to the geometry and motion path of adria the field study reveals mylonites along the jaufen fault which formed under lower greenschist facies conditions and is associated with top to the west northwest shear with a northern block down component in addition a brittle reactivation of the jaufen shear zone under nnw sse to nw se compressional and ene wsw tensional stress conditions was deduced from paleostress analysis the inferred shortening direction is consistent with fission track ages portraying neogene exhumation of the meran mauls basement south of the fault along the passeier fault deformation was only brittle to semi ductile and paleostress tensors record that the fault was subjected to e w extension along its northern segment varying into nw se compression and sinistral transpression along its southern segment in the performed analogue experiments a rigid triangular shaped indenter was pushed into a sand pile resulting in the formation of a passeier like fault sprouting from the indenter s tip these kinds of north trending tip faults formed in all experiments with shortening directions towards the nw n or ne consequently we argue that the formation of the passeier fault strongly corresponds to the outline of the adriatic indenter and was only little affected by the indenter s motion path due to induced strain partitioning in front of the different indenter segments the associated fault kinematics along the passeier fault including both e w extension and nnw to nw shortening however is most consistent with a northward advancing adriatic indenter

buoyancy driven plumes in rotating stratified cross flows plume dependence on rotation turbulent mixing and cross flow strength a three dimensional time dependent convection model is used to describe circulation and property fields in rotating stratified and moving fluids near a point source of heat the study context and consequently model scales are those of chronically discharging hydrothermal vent fields found at submarine ridge crests hydrothermal plumes having distinctive thermal and chemical anomalies have been observed to rise several hundreds of meters above the deep sea floor before being advected away by background cross flows typically of magnitude 1 4 cm s 1 the model is used to study effects of rotation and indicate differences in plumes with respect to variation of subgrid scale turbulence intensity and cross flow strength counterrotating vorticity couplets in all three coordinate directions develop in the lower plume stem at startup and follow the plume to the level of neutral buoyancy for a nonrotational case 0 patterns resemble those previously found for jets injected into homogenous cross flow ambient fluid entrainment into the convecting column is primarily from the upstream side but deflection of background flow around both sides of the rising column is the root of the relative vorticity z couplet in the lower plume turbulence intensity within the buoyant region of the plume and or globally controls smoothness and temporal variability of distal nonbuoyant plume distributions allowing or preventing oscillations of potential temperature for example at background buoyancy frequency n over the range of turbulent mixing studied rise height of plumes did not change appreciably but breadth of plumes counterintuitively increased for decreasing turbulent mixing strength increasing cross flow strength u0 bends model plumes such that rise height u0 0 4 for the two largest values of cross flow for which r the ratio of maximum vertical velocity to u0 took values of 2 8 and 1 0 plumes showed evidence of bifurcation

the remarkable longevity of submarine plumes implications for the hydrothermal input of iron to the deep ocean the longevity of submarine plumes generated at sea floor hydrothermal systems constrains the hydrothermal input of chemical species into the deep ocean decades of observations of episodic event plumes suggest that a key process governing the dynamics of an hydrothermal cloud spreading out laterally from a buoyant rising plume is the production of internal layering here we use analog experiments on turbulent hot particle laden plumes and clouds to show that this layering occurs where particle diffusive convection driven by the differential diffusion of heat and small mineral precipitates gives rise to a large scale double diffusive instability where hydrothermal clouds are enriched in fine minerals this particle diffusive convection can extend the longevity of an event plume to 2 yr after its emplacement the very long residence time imposed by diffusive convective effects enables complete dissolution of fine sulfide and sulfate minerals we develop a new theoretical model that includes both sedimentation and dissolution processes to quantify the potential amount of iron produced by the dissolution of iron sulfide minerals settling through the cloud by diffusive convection a key prediction is that the concentration of dissolved iron in hydrothermal clouds can reach up to 19 3 nm19 3 nm which represents about 5 of the global hydrothermal discharge if these results are representative of all hydrothermal vent fields hydrothermal systems could provide 75 of the global budget of dissolved iron in the deep ocean regionally this flux is expected to scale in magnitude with mid ocean ridge heat flow consistent with observations and global ocean models

dissolved and particulate trace metals in hydrothermal plumes at the mid atlantic ridge seawater samples from the non buoyant plume have been collected at the tag 26 n and snakepit 23 n hydrothermal sites on the mid atlantic ridge mar and analysed for dissolved 0 4 m trace metals up to 50 of vent fluid fe is present in the 0 4 m fraction in the non buoyant plume increases in particulate concentrations of cd are accompanied by a reduction in dissolved cd to levels below ambient seawater we show that dissolved cd is scavenged from seawater in the buoyant section of the plume while cd re dissolves from the particles in the non buoyant plume up to 43 of hydrothermally injected cu is found in the 0 4 m fraction in the non buoyant plume

timing of alpine fault gouges k ar ages from clay rich fault gouges in the european alps are consistent internally with established field constraints and with fission track ages demonstrating the applicability of this method for direct dating of brittle deformation illite grown by retrograde hydration of granitic and or high grade metamorphic protoliths is the major k bearing mineral in the fractions that have been separated 0 1 to 6 10 m the ages obtained are bracketed by apatite and zircon fission ages from adjacent localities this together with the interpreted cooling curve for one well constrained sample from the simplon fault indicates that illite grew or the k ar isotopic system in illite closed at temperatures in the range 120 150 c consistent with the stability of illite alone rather than illite smectite average ages obtained for fractions finer than 2 m were 1 5 2 2 6 ma 2 for 11 analyses from the detachment and footwall of the simplon fault 2 8 8 0 6 ma for four analyses from the centovalli fault at trontano 3 19 9 2 6 ma for two analyses from a major riedel fault related to the periadriatic fault offsetting the tertiary bergell tonalite at gesero 4 21 5 5 5 ma for two analyses from a zone parallel to the periadriatic fault in the adjacent southern alps in val morobbia and 5 14 5 3 9 ma for two analyses from a gouge zone on the northern rim of the tertiary mauls tonalite in the eastern alps the ages from the simplon centovalli and periadriatic faults are not identical and do not lend support to models linking these three faults as a single coeval structure

chemical plumes from low temperature hydrothermal venting on the eastern flank of the juan de fuca ridge we report evidence for chemical anomalies in the water column from low temperature ridge flank hydrothermal venting during cruises in 1992 and 1994 samples were taken from the water column for trace metals nutrients dissolved gases and particles near each of three basaltic outcrops overlying 3 5 m y old crust on the eastern flank of the juan de fuca ridge in cascadia basin the water column above one of these outcrops baby bare which rises about 70 m above a flat turbidite plain was the most thoroughly sampled thermal chemical mn fe 3he ch4 and o2 and particulate anomalies in the water column confirm the existence of 1 early diagenesis of organic matter in seafloor sediment which produces a flux of dissolved metals and nutrients to bottom seawater 2 hydrothermal emissions which are both focused spring like and diffuse and 3 resuspension of sediment by turbulent flow of tidal currents about a topographical high on the basis of data from the water column and thermal and chemical pore water data from 46 piston and gravity sediment cores near and on baby bare flankflux 90 and 92 we constrain the composition of seawater in basement and thus the composition of spring like water given this composition no measurable dissolved silica or phosphate hydrothermal anomalies are expected in the water column

k ar dating of synkinematic clay gouges from neoalpine faults of the central western and eastern alps abstract with ongoing alpine convergence and deformation during exhumation there is a general progression from ductile to brittle behaviour on the periadriatic fault and kinematically related faults farther north e g the simplon rhone fault and a diffuse discontinuous zone of generally dextral strike slip movement on the southern boundary of the aar massif k ar dating of fine grained illite from clay fault gouges provides a reliable method for establishing the maximum age of this transition to brittle faulting and for short lived faults the approximate time of faulting itself the new results establish that brittle faulting on the northeastern segment of the canavese fault i e the part of the periadriatic fault southwest of lago maggiore occurred around 20 ma with south side up kinematics a k ar age of ca 17 ma for the crosscutting giudicarie fault in the eastern alps is effectively identical with an already published pseudotachylyte age and places a lower limit on major and continuous strike slip movements of the periadriatic fault the age of brittle faulting farther north on the southern border of the aar massif is from 13 6 0 3 to 8 3 1 1 ma consistent with the younger cooling and exhumation in this area the dominantly dextral brittle faulting becoming younger to the north reflects the continued indentation and anticlockwise rotation of adria as alpine units become exhumed and progressively welded to the southern block in contrast to the eastern alps there is no field evidence for westward lateral extrusion of alpine units relative to adria and the european foreland

40ar 39ar dating of penninic front tectonic displacement w alps during the lower oligocene 31 34 ma direct absolute dating of the penninic frontal thrust tectonic motion is achieved using the 40 ar 39 ar technique in the pelvoux crystalline massif western alps the dated phengites were formed syn kinematically in shear zones they underline the brittle ductile stretching lineation pressure shadow fibres and slickensides consistent with underthrusting of the european continental slab below the propagating penninic thrust chlorite phengite thermobarometry yields 10 15 km and t 280 c while 40 ar 39 ar phengite ages mainly range between 34 and 30 ma with one younger age at 27 ma this early oligocene age range matches a major tectonic rearrangement of the alpine chain preservation of prograde 40 ar 39 ar ages is ascribed to passive exhumation of the pelvoux shear zone network sandwiched between more external thrusts and the penninic front reactivated as an e dipping detachment fault partial resetting in the low temperature part of argon spectra below 24 ma is ascribed to brittle deformation and alteration of phengites

the oligocene alps domal unroofing and drainage development during early orogenic growth abstract the source of huge volumes of quartzofeldspathic detritus feeding oligo miocene foredeep turbidites of the apennines has long remained an unsolved geological enigma in this article we reinterpret the available sandstone petrography fission track stratigraphic and geomorphological evidence to demonstrate that the adriatic foredeep was dominantly sourced by a himalayan type tectonic aneurysm growing in the central alps since the late oligocene the lepontine dome the lepontine dome is the envelope of distinct subdomes that formed stepwise from east to west during northwestward indentation of adria beneath the axial alps focused erosion of domal culminations cut by antecedent drainage started suddenly in the late oligocene with unroofing of recently emplaced plutons and young amphibolite facies gneisses exhumation was tectonically driven and possibly accelerated by positive feedback between erosion and uplift of hot weak rocks from depth the huge volumes of resulting detritus gonfolite macigno clastic wedge were transported southward for hundreds of kilometers along the rapidly subsiding foredeep formed since middle eocene times in front of the alpine retrobelt and nascent apennine forebelt such massive sediment influx following 15 2 myr of starved foredeep sedimentation testifies to rapid formation of mountain relief in the central alps synchronous to dextral activity along the insubric fault the lepontine dome remains today as the only deeply dissected region in the alps where medium grade metamorphic rocks of the axial belt are extensively exposed the relationships between geological structures and drainage patterns still mirror those formed originally at oligocene times river headwaters have not been significantly displaced since then and their thalwegs constrain finite lateral displacement relative to the southalpine retrowedge to a maximum of 10 20 km our reconstruction has wide implications not only for a better understanding of the tertiary evolution of the alps apennines orogenic couple but also for general relationships among tectonic activity relief formation drainage development erosion distribution and long distance sediment transfer during continental collision and orogenic growth

lateral extrusion in the eastern alps revisited refining the model by thermochronological sedimentary and seismic data 1 this study comprises a reassessment of the classical model of lateral extrusion in the eastern alps by using recently published geochronological data sedimentary ages from intramontane basins ages and distribution of magmatic rocks and information from seismic profiles extrusion related faulting continuously propagated from the western toward the central eastern part of the eastern alps during oligocene to middle miocene times this is confined by oblique convergence between the adriatic and european plates during middle miocene times extrusion became not only lateral in terms of parallel to the trend of the eastern alps but was characterized by a displacement vector at a high angle to the strike of the orogen this resulted in the exhumation of the schladming and pohorje blocks that were exhumed within extensional bridges at the northern and southern terminations of the pols lavanttal fault system respectively from middle miocene to recent times extrusion was controlled by overall extension between the dinaric and carpathian subduction zones the influence of north directed compression triggered by the northward moving adriatic plate diminished and the influence of the retreating carpathian subduction zone increased this gave rise to miocene volcanism that is exclusively found east of the dinaric subduction zone we therefore consider that lateral extrusion in the eastern alps can be subdivided into distinct tectonic phases with less pronounced eastward extension related displacement between late oligocene and middle miocene times as soon as the eastern alps passed the dinaric subduction zone the entire domain became highly extensive

zircon petrochronology and 40ar 39ar thermochronology of the adamello intrusive suite n italy monitoring the growth and decay of an incrementally assembled magmatic system the adamello intrusive suite is a composite batholith in northern italy with an estimated 2000 km3 volume assembled incrementally over a time span of 10 to 12 million years the history of crysta

interactions between serpentinite devolatilization metasomatism and strike slip strain localization during deep crustal shearing in the eastern alps the greiner shear zone in the tauern window eastern alps changes from a zone of distributed dominantly sinistral shear in supracrustal rocks to a series of narrow gully forming dextral splays where it enters basement gneisses within these splays granodiorite is transformed into quartz poor biotite and or chlorite schists reflecting hydration removal of si ca and na and concentration of fe mg and al stable isotope analyses show a prominent increase in d and a decrease in 18o from granodiorite into the shear zones these changes indicate significant channelized flow of an externally derived low 18o high d fluid through the shear zones the shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the greiner zone and the stable isotope data support alteration via serpentinite derived fluid monazite in schist from one shear zone yields spot dates of 29 20 ma indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the alpine orogeny c 30 ma we suggest that alpine metamorphism of serpentinites released large amounts of high d low 18o si undersaturated fe mg saturated fluids that became channelized along prior zones of weakness in the granodiorite infiltration of this fluid facilitated growth of chlorite and biotite which in turn localized later dextral strain in the narrow splays via cleavage parallel slip this dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the eastern alps this study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis

modes of orogen parallel stretching and extensional exhumation in response to microplate indentation and roll back subduction tauern window eastern alps the tauern window exposes a paleogene nappe stack consisting of highly metamorphosed oceanic alpine tethys and continental distal european margin thrust sheets in the eastern part of this window this nappe stack eastern tauern subdome etd is bounded by a neogene system of shear the katschberg shear zone system kszs that accommodated orogen parallel stretching orogen normal shortening and exhumation with respect to the structurally overlying austroalpine units adriatic margin the kszs comprises a 5 km thick belt of retrograde mylonite the central segment of which is a southeast dipping low angle extensional shear zone with a brittle overprint katschberg normal fault knf at the northern and southern ends of this central segment the kszs loses its brittle overprint and swings around both corners of the etd to become subvertical dextral and sinistral strike slip faults the latter represent stretching faults whose displacements decrease westward to near zero the kinematic continuity of top east to top southeast ductile shearing along the central low angle extensional part of the kszs with strike slip shearing along its steep ends combined with maximum tectonic omission of nappes of the etd in the footwall of the knf indicates that north south shortening orogen parallel stretching and normal faulting were coeval stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the kszs to have begun at 23 21 ma leading to rapid cooling between 21 and 16 ma this exhumation involved a combination of tectonic unroofing by extensional shearing upright folding and erosional denudation the contribution of tectonic unroofing is greatest along the central segment of the kszs and decreases westward to the central part of the tauern window the kszs formed in response to the indentation of wedge shaped blocks of semi rigid austroalpine basement located in front of the south alpine indenter that was part of the adriatic microplate northward motion of this indenter along the sinistral giudicarie belt offsets the periadriatic fault and triggered rapid exhumation of orogenic crust within the entire tauern window exhumation involved strike slip and normal faulting that accommodated about 100 km of orogen parallel extension and was contemporaneous with about 30 km of orogen perpendicular north south shortening of the etd extension of the pannonian basin related to roll back subduction in the carpathians began at 20 ma but did not affect the eastern alps before about 17 ma the effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the tauern window area therefore we propose that roll back subduction temporarily enhanced rather than triggered exhumation and orogen parallel motion in the eastern alps lateral extrusion and orogen parallel extension in the eastern alps have continued from 12 to 10 ma to the present and are driven by northward push of adria

nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions abstract in the neves area the pre alpine intrusive protolith of the zentralgneise unit tauern window eastern alps is well preserved in a kilometric scale low strain domain without pervasive alpine deformation it is compositionally heterogeneous consisting predominantly of granodiorites with lesser leucocratic granites and different generations of lamprophyres and aplites the intrusive rocks are crosscut by fractures that were locally infiltrated by fluids and surrounded by alteration haloes incipient alpine amphibolite facies ductile deformation is strongly localized on these precursor fractures and on lithological planar heterogeneities resulting in the development of several different types of shear zones fractures without alteration haloes initially accommodate slip entirely on the fracture itself with increasing deformation a foliation is progressively developed in the adjacent host rock eventually producing a single heterogeneous ductile shear zone with the typical sigmoidal foliation pattern strong layers aplite dykes and bleached alteration haloes developed to either side of precursor fractures localize shear on their boundaries to produce characteristic paired shear zones shearing is more evenly distributed within weak layers lamprophyres and quartz veins with a marked discontinuity in shear strain against the adjacent little deformed granodiorite shear zone development was accompanied by the formation of new fractures and quartz rich veins in the host rock which in turn also localized shear magmatic contacts fractures and quartz veins are mostly steeply dipping and effectively span the complete range of strike orientations the kinematics of the overprinting strike slip shear zones was determined by the orientation of the initial discontinuities relative to the local principal compressive stress axis 1 here oriented ca 345 discontinuities of almost all orientations show shear reactivation even in the case of very low resolved shear stress indicating an overall viscous response of the system without a specific yield stress the geometry and kinematics of the shear zone network suggest that the overall deformation in low strain domains was close to coaxial during deformation along the shear zone network compatibility was maintained by fracturing with the development of new quartz veins and by distributed ductile deformation of the host rock especially within contractional domains of the shear network and at shear zone intersections deformation never propagates into the undeformed homogeneous granodiorite as discrete ductile shear zones but is limited by the original extent of the precursor discontinuities shear zone development in intact rock is always preceded by fracturing which localizes subsequent shear reactivation

acoustic detection of a seafloor spreading episode on the juan de fuca ridge using military hydrophone arrays until recently no practical method has been available to continuously monitor seismicity of seafloor spreading centers the availability of the u s navy s sound surveillance system sosus for environmental research has allowed the continuous monitoring of low level seismicity of the juan de fuca ridge in the northeast pacific on june 22 1993 noaa installed a prototype system at u s naval facility whidbey island to allow real time acoustic monitoring of the juan de fuca ridge using sosus on june 26 2145 gmt a burst of low level seismic activity with accompanying harmonic tremor was observed and subsequently located near 46 15 n 129 53 w on the spreading axis of the juan de fuca ridge over the following 2 days the activity migrated to the nne along the spreading axis with the final locus of activity near 46 31 5 n 129 35 w the nature of the seismicity was interpreted to represent a lateral dike injection with the possibility of eruption on the seafloor based on this interpretation a response effort was initiated by u s and canadian research vessels and both warm water plumes and fresh lavas were subsequently identified at the site

structure of the lithosphere beneath the eastern alps southern sector of the transalp transect abstract the interpretation of the seismic vibroseis and explosive transalp profiles has examined the upper crustal structures according to the near surface geological evidences and reconstructions which were extrapolated to depth only the southern sector of the transalp transect has been discussed in details but its relationship with the whole explored chain has been considered as well the seismic images indicate that pre collision and deep collision structures of the alps are not easily recognizable conversely good records of the neo alpine to present architecture were provided by the seismic sections two general interpretation models crocodile and extrusion have been sketched by the transalp working group 2002 both illustrate the continental collision producing strong mechanical interaction of the facing european and african margins as documented by giant lithosphere wedging processes arguments consistent with the extrusion model and with the indentation of adriatic southalpine lithosphere underneath the tauern window tw are according to the previous dss reconstructions the bouguer anomalies and the receiver functions seismological data the european moho descends regularly attaining a zone south of the periadriatic lineament pl the moho boundary and its geometry appear to be rather convincing from images of the seismic profile the tauern window intense uplift and exhumation is coherent with the strong compression regime which acted at depth thus originating the upward and lateral displacement of the mobile and ductile penninic masses according to the extrusion model the indentation of the penninic mobile masses within the colder and more rigid adriatic crust cannot be easily sustained wedging of the adriatic stiffened lower crust under high stresses and into the weaker penninic domain can be a more suitable hypothesis furthermore the intrusion of the european penninic crustal wedge underneath the dolomites upper crust is not supported by any significant uplifting of the dolomites the total average uplift of the dolomites during the neogene appears to be 6 7 times smaller than that recognized in the tw markedly the northward dip of the pl reaching a depth of approximately 20 km is proposed in our interpretation finally the adriatic upper crustal evolution points to the late post collision change in the tectonic grow up of the eastern alps orogenic chain the tectonic accretion of the northern frontal zone of the eastern and central alps was interrupted from the late miocene serravallian tortonian onward as documented by the molasse basin evolution on the contrary the structural nucleation along the s vergent tectonic belt of the eastern southern alps montello friuli thrust belt severely continued during the messinian and the plio pleistocene this structural evolution can be considered to be consistent with the deep under thrusting and wedge indentation of the adriatic lithosphere underneath the southern side of the eastern alps thrust and fold belt similarly the significance of the magmatic activity for the construction of the southern alps crust and for its mechanical and geological differentiation which qualified the evolution of the thrust and fold belt is highlighted starting with the permian triassic magmatism and progressing with the paleogene occurrences along the periadriatic lineament and in the venetian magmatic province lessini euganei hills

the pejo fault system an example of multiple tectonic activity in the italian eastern alps the pejo fault in the italian eastern alps is a major sinistral transtensional fault it marks the boundary between basement units displaying contrasting thermal histories with alpine i e mesozoic cenozoic cooling ages preserved in the footwall juxtaposed against variscan i e carboniferous permian age in the hanging wall structural investigations together with fission track analysis confirm a late cretaceous age for the pejo fault which excludes any direct kinematic contribution of the pejo fault to the late oligocene neogene evolution of the central eastern segment of the periadriatic fault however our results establish the importance of a major early oligocene north south to north northwest south southeast shortening phase in the central eastern alps which resulted in the development of new reverse shear zones in the reactivation of the pejo fault with a reverse motion and in regionally important folding the pejo mylonites are folded on a kilometer scale around an east northeast trending axis field observations and fission track analysis suggest a post oligocene age for the folding phase apatite fission track data in the pejo valley area reveal the base of a fossil apatite partial annealing zone exhumed to the surface this finding argues for 4 km of exhumation since the miocene which was related to a major pulse of exhumation that began at ca 15 ma this study suggests that the simple distinction between largely pre alpine fabrics of variscan age in the hanging wall of the pejo fault tonale nappe and alpine fabrics cretaceous in the footwall campo ortler nappe is not universally valid alpine overprinting is confined to the mylonitic shear zone itself deeper into the footwall pre alpine structures are still well preserved earlier maps and interpretations based on a clear distinction between tonale and campo should be viewed with caution

late oligocene neogene evolution of europe adria collision new structural and geochronological evidence from the giudicarie fault system italian eastern alps the giudicarie fault system giudicarie sensu stricto meran mauls passeier thurnstein and jaufen faults represents a sharp break in the generally e w strike direction of the orogen scale periadriatic fault system and is a key element for understanding the late oligocene neogene evolution of the alpine chain the kinematics timing and magnitude of movements on the giudicarie fault system are presented here on the basis of a detailed structural study of the component fault segments combined with zircon and apatite fission track analysis from closely spaced samples two main tectonic phases are established 1 back thrusting of the austroalpine units over the southern alps around 32 ma recorded by basement and limestone mylonites along the giudicarie and meran mauls faults with transport directions toward 100 110 and 2 later sinistral transpressive displacement characterized by structures at the ductile brittle transition which overprinted the top to e ese thrust related mylonites but also partitioned into a major system of transcurrent faults in the southalpine domain it was during this later event that the periadriatic fault attained its present day geometry however the amount of sinistral displacement along the giudicarie system was only 15 20 km the magnitude is established here from the 15 km sinistral offset of the jaufen mylonites across the passeier brittle fault and the 20 km long gap in the otherwise continuous distribution of oligocene tonalitic lamellae along the giudicarie fault a direct structural connection is also established between the brenner and the jaufen faults this constrains the timing of the second phase since it must postdate the main exhumation phase of the tauern window at 20 18 ma the results of this study argue against an originally straight periadriatic fault the giudicarie fault formed a restraining bend in this part of the periadriatic fault system since at least the late miocene and probably since the late oligocene

a seismotectonic picture of the inner southern western alps based on the analysis of anomalously deep earthquakes abstract the anomalously deep seismicity beneath the western po plain is here analyzed to shed light on the complex and still poorly understood tectonic configuration of the internal side of the western alps area the original dataset including 590 earthquakes deeper than 20 km recorded during the last 25 years has been accurately relocated with hypodd using both catalog and cross correlation differential times we found that the distribution of seismic events faithfully mirrors the presence of two distinct tectonic domains axial belt domains 1 and 2 originally belonging to the paleogene alpine wedge and now anomalously juxtaposed beneath the sedimentary infill of the western po plain shallow low magnitude earthquakes 8 km and accommodated in correspondence of the fault could be linked to its neogene activity coeval with the northward translation of the retreating adriatic slab

geochronological constraints on the evolution of the periadriatic fault system alps fault rocks from various segments of the periadriatic fault system paf alps have been directly dated using texturally controlled rb sr microsampling dating applied to mylonites and both stepwise heating and laser ablation 40ar 39ar dating applied to pseudotachylytes the new fault ages place better constraints on tectonic models proposed for the paf particularly in its central sector along the north giudicarie fault oligocene e se directed thrusting 29 32 ma is currently best explained as accommodation across a cogenetic restraining bend within the oligocene dextral tonale pustertal fault system in this case the limited jump in metamorphic grade observed across the north giudicarie fault restricts the dextral displacement along the kinematically linked tonale fault to 30 km dextral displacement between the tonale and pustertal faults cannot be transferred via the peio fault because of both late cretaceous fault ages 74 67 ma and sinistral transtensive fault kinematics in combination with other pseudotachylyte ages 62 58 ma widespread late cretaceous paleocene extension is established within the austroalpine unit coeval with sedimentation of gosau group sediments early miocene pseudotachylyte ages 22 16 ma from the tonale pustertal jaufen and passeier faults argue for a period of enhanced fault activity contemporaneous with lateral extrusion of the eastern alps this event coincides with exhumation of the penninic units and contemporaneous sedimentation within fault bound basins

composition and sedimentation of hydrothermal plume particles from north cleft segment juan de fuca ridge in 1990 and 1991 particles from buoyant and neutrally buoyant hydrothermal plumes above hydrothermal vents at the north cleft segment of the juan de fuca ridge were sampled to study their changing composition and fluxes away from the vent field in the rising buoyant plume 75 of the p v cr and as scavenging from seawater by hydrothermal precipitates occurs in the first 50 m above the vent cu and zn are most enriched in buoyant plume particles collected from the first few meters above the vent however the degree of enrichment decreases very rapidly with increased height above the vents due to sedimentation of the more dense cu and zn rich sulfide phases using the plume data coupled with the results of our analysis of sediment trap samples we estimated that more than 99 and 99 9 respectively of the total hydrothermal fe and mn produced at the vent field are transported beyond the vent field and dispersed in the open ocean

observations of manganese and iron at the coaxial seafloor eruption site juan de fuca ridge magmatic injection during june july 1993 on the coaxial segment of the juan de fuca ridge resulted in an axial lava eruption an overlying chronic style hydrothermal plume and at least three megaplume like event plumes a comprehensive view of mn and fe liberated as hydrothermal discharge during this volcano hydrothermal event was obtained as part of a rapid field response that included continuous in situ measurements of mn and fe distribution maps for mn fe and temperature anomaly within the chronic and event plumes reveal significant thermochemical diversity that we ascribe to variable extraction efficiencies for heat and metals by source fluids and to plume age differences the mn heat data suggest that diffuse fluids could be the primary source of the chronic plume at northern coaxial segment but make only a minor contribution to event plumes measurements of ephemeral fe ii were used to estimate that the event plumes were 2 4 and 6 8 days old when first sampled corresponding to formation times during peak seismic activity the inventories of mn and fe within the three coaxial event plumes were similar to values previously reported for megaplumes

dating the longevity of ductile shear zones insight from 40ar 39ar in situ analyses we attempt to improve temporal constraints on the longevity and the termination of ductile shear zones by performing texturally controlled in situ 40ar 39ar analyses of pre kinematic muscovite biotite and k feldspars of syn kinematic phengite and k feldspar and of post kinematic phengite within the same samples of sinistral shear zones from the western tauern window eastern alps additionally two samples were dated by the rb sr method microsampling relative sequences of mineral formation based on microstructural cross cutting relationships were confirmed by in situ 40ar 39ar analyses showing that syn kinematic minerals are in general younger than pre kinematic minerals and older or of equal age than the post kinematic minerals of the same sample from the rim to the core of the western tauern window syn kinematic phengite and k feldspar reveal a set of formation ages varying between 33 and 15 ma for the northernmost and peripheral shear zone ahorn shear zone between 24 and 12 ma for the intermediate shear zone network tuxer shear zones and between 20 and 7 ma for the southernmost and central shear zone greiner shear zone the age variation of syn kinematic phengite and k feldspar analyses is larger than the analytical error of each age obtained in addition isochron calculations of the syn kinematic minerals reveal atmospheric like 40ar 36ar intercepts therefore the obtained age values of the syn kinematic minerals are interpreted as formation ages which date increments of a long lasting deformation period the time range of deformation of each shear zone system is bracketed by the oldest and youngest formation ages of syn kinematic phengite and k feldspar post kinematic phengite laths show the youngest formation ages and overlap with the youngest syn kinematic formation ages this relationship indicates that post kinematic growth occurred immediately after syn kinematic mineral formation at the end of ductile sinistral shear hence the termination of deformation is dated by the ages of these post kinematic phengite blasts pre kinematic minerals are characterized by break down and exsolution reactions and their age values are heterogeneous and often affected by the presence of extraneous ar these age values are usually older than but sometimes overlapping with ages of the syn kinematic minerals using the temporal constraints obtained by the ages of pre syn and post kinematic minerals we could assess partly overlapping time intervals of syn kinematic mineral formation of 19 myr 33 15 ma in the ahorn shear zone 13 myr 24 12 ma in the tuxer shear zones and 14 myr 20 7 ma in the greiner shear zone this indicates successive localization and propagation of ductile shear zones in the western tauern window from lower metamorphic sites at the rim towards higher metamorphic sites in the center

unique event plumes from a 2008 eruption on the northeast lau spreading center the creation of ocean crust by lava eruptions is a fundamental earth process involving immediate and immense transfers of heat and chemicals from crust to ocean this transfer creates event plumes megaplumes massive ellipsoidal eddies with distinctive and consistent chemical signatures here we report the discovery of unique event plumes associated with a 2008 eruption on the northeast lau spreading center instead of a large plume hundreds of meters thick we detected at least eight individual plumes each 50 m thick and apparently only 1 3 km in diameter yet still rising 200 1000 m above the eruption site low and uniform 3he heat 0 041 10 17 mol j and dissolved mn heat 0 04 nmol j ratios in water samples were diagnostic of event plumes high h2 concentrations up to 9123 nm and basalt shards confirmed extensive interactions between molten lava and event plume source fluids remote vehicle observations in 2009 mapped a new small 1 5 5 8 106 m3 lava flow our results suggest that event plumes are more variable and thus perhaps more common than previously recognized small event plumes may be preferentially associated with small or sheet flow eruptions and massive event plumes with slowly extruding pillow mounds 25 75 m thick despite this correlation and high h2 concentrations existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes the creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation

dating fault generated pseudotachylytes comparison of 40ar 39ar stepwise heating laser ablation and rb sr microsampling analyses three different geochronological techniques stepwise heating laser ablation 40ar 39ar rb sr microsampling have been evaluated for dating fault generated pseudotachylytes sampled along the periadriatic fault system paf of the alps because pseudotachylytes are whole rock systems composed of melt clast and alteration phases chemical control from both ar isotopes cl k ca k ratios and empa analyses is crucial for their discrimination when applied to stepwise heating 40ar 39ar analyses this approach yields accurate melt related ages even for complex age spectra the spatial resolution of laser ablation 40ar 39ar analyses is capable of contrasting melt clast and alteration phases in situ provided the clasts are not too fine grained the latter of which results in integrated mixed ages without geological information elevated cl k and ca k ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40ar due to incomplete isotopic resetting during frictional melting rb sr microsampling dating did not furnish geologically meaningful ages on the basis of isotopic disequilibria among pseudotachylyte matrix phases and independent rb sr microsampling dating of cogenetic ultra mylonites the concordant 40ar 39ar pseudotachylyte ages are interpreted as formation ages the investigated pseudotachylytes altogether reveal a cretaceous to miocene history for the entire paf consistent with independent geological evidence individual faults however consistently reveal narrower intervals of enhanced activity lasting a few million years electronic supplementary material to this paper can be obtained by using the springer link server at http dx doi org 10 1008 s00410 002 0381 6

helium heat and the generation of hydrothermal event plumes at mid ocean ridges hydrothermal event plumes are unique water column features observed over mid ocean ridges presumably generated by the sudden release of large volumes of hot buoyant fluid although the specifics of event plume generation are unknown event plumes have been attributed to the rapid emptying of a hydrothermal reservoir or to rapid heat extraction from a recently emplaced dike or seafloor lava flows the chemical and thermal signatures of event plumes as compared to the underlying steady state plumes offer important clues to the generation of event plumes event plumes have low 3he heat ratios of 0 4 10 17 mol j 1 similar to vent fluids from mature hydrothermal systems in contrast the steady state plumes found beneath the event plumes have elevated and variable 3he heat ratios of 2 to 5 10 17 mol j 1 fluids collected directly over fresh lava flows have even higher 3he heat ratios of 2 to 8 10 17 mol j 1 up to 30 times the event plume values these disparate 3he heat ratios place strong constraints on models of event plume generation especially models which rely on heat extraction from seafloor eruptions published by elsevier science b v

detection of an unusually large hydrothermal event plume above the slow spreading carlsberg ridge nw indian ocean about 90 of earth s volcanism occurs along the global mid ocean ridge system here sporadic volcanic and tectonic activity is thought to cause cataclysmic release of hydrothermal fluids forming event plumes each plume often contains as much hydrothermal effluent and heat as chronic hydrothermal venting from a typical vent site discharges during a year to date only a few event plumes have been detected and only above intermediate rate spreading ridges in the pacific here we report the first evidence for an unusually large event plume that originated from the slow spreading 3 cm yr full rate carlsberg ridge in the nw indian ocean at 70 km long up to 4540 km3 in volume and with up to 24 1016 j of excess heat this event plume was substantially larger than previous ones and demonstrates that dispersion of hydrothermal heat and biological products from slow spreading ridges may be more significant and effective than hitherto imagined

detection and response to volcanic hydrothermal events on the mid ocean ridge the mid ocean ridge is by far the most continuous volcanic system on the planet but since it lies beneath more than 2 km of seawater a thorough study of its thermal and chemical interaction with the ocean remains very difficult until 1990 the end of the period covered by the last iugg report literally all of our understanding of the dynamics of magmatic accretion on the mid ocean ridge was based on inferences from 1 geochemical geophysical and morphologic studies of long sections of the ridge using a variety of instruments mounted on ships hulls or towed on long cables near the seafloor and 2 submersible based mapping and sampling of small sections of the ridge particularly hydrothermally active ones these types of studies have continued to flourish parmentier 1995 humprhis 1995 but the past 4 years have also seen the first near real time observations of accretion events on two pacific spreading centers and the development of technology and techniques that can monitor the occurrence and extent of such events over a selected portion of the ridge system these monitoring capabilities allow interdisciplinary studies of seafloor hydrothermal systems so that the thermal and chemical effects of hydrothermal venting on the oceans can be assessed

in situ observations of dissolved iron and manganese in hydrothermal vent plumes juan de fuca ridge in situ measurements of dissolved manganese and total dissolved iron were conducted in hydrothermal plumes over the juan de fuca ridge using a submersible chemical analyzer scanner the scanner was deployed as part of a ctd transmissometer rosette instrument package on both tow yos and vertical casts during the vents leg i cruise in 1989 dissolved manganese and total dissolved iron concentrations along with temperature and light attenuation anomalies were determined over the ridge crest every 5 s discrete samples for laboratory analyses of dissolved iron ii total dissolved iron ii iii and manganese were also collected metal to heat ratios me q measured in situ were extremely variable in one steady state plume while an event plume had constant me q uniform values of mn q in the event plume demonstrate that mn behaves conservatively in the near field plume variability in the mn q ratios in a steady state plume indicated the presence of at least two hydrothermal sources with distinct me q values a simple mixing model shows that the contribution of mn from high me q sources with a composition characteristic of black smoker vents varies between 1 and 99 within the core of the steady state plume with an average value of 55 on average over 50 of the excess heat within the plume originates from low me q ratio sources with a composition characteristic of low temperature diffuse flow vent fluids less than 4 of the volume of hydrothermal fluids in the plume originates from black smokers the fe ii concentrations were used to provide an estimate of plume age on a transect across the ridge axis plume ages were about 2 5 days on axis and 12 days off axis these plume ages were modeled to provide estimates of plume transport and horizontal diffusion and show excellent agreement with ages determined using 222rn

post eruption succession of macrofaunal communities at diffuse flow hydrothermal vents on axial volcano juan de fuca ridge northeast pacific abstract hydrothermal vents harbor dense aggregations of invertebrate fauna supported by chemosynthesis severe tectonic events and volcanic eruptions frequently destroy vent communities and initiate primary succession at new vents on ridge crest submarine lava flows an eruption on axial volcano 1500 m depth a seamount on the juan de fuca ridge jdfr in the northeast pacific ocean occurred in january 1998 which created new substratum and vents this study examines the development of the macrofaunal vent assemblages associated with tubeworms ridgeia piscesae at eight diffuse flow vents over the following 3 years biological collections by suction of lava surfaces also characterized pre tubeworm assemblages coupled fluid sampling showed an overall decrease in temperature sulphide and sulphide to heat ratios over 3 years as well as large spatial variability across the new vents we examined collections of pre eruption diffuse flow vent assemblages at axial volcano to compare the stages of new community development to mature vents mature vent assemblages are characterized by two major community types dominated by limpets lepetodrilus fucensis and alvinellid polychaetes paralvinella pandorae and or p palmiformis the following post eruption succession patterns emerged first r piscesae tubeworms took up to 3 years to establish aggregations at the new vents and the majority of pre tubeworm assemblages were dominated by grazing polychaetes second species colonized quickly and by 30 months after habitat creation 60 of axial s species pool had arrived at the new vents abundance at mature vents predicted colonization success with some notable exceptions third shifts in species dominance occurred rapidly and by year 3 new vent assemblages resembled mature pre eruption communities in general tubeworm assemblages were dominated by alvinellid polychaetes p pandorae and p palmiformis in the first 2 years post eruption with limpets l fucensis becoming more numerous in year 3 fourth successional trajectories corresponded to four habitat variables the timing of r piscease recruitment vent age maximum vent fluid sulphide to heat ratios and maximum vent fluid temperatures the two mature community types dominance by limpets or alvinellid polychaetes seem to relate in part to vent differences in fluid properties with limpets more prevalent than alvinellids at diffuse vents with lower maximum sulphide to heat ratios and temperatures we present a general model of post eruption succession for juan de fuca ridge diffuse flow vents the model incorporates potential abiotic and biotic drivers of community development and identifies six successional stages a pre tubeworm assemblage four tubeworm assemblage states determined by the relative dominance of alvinellid polychaetes and the limpet and a final senescent stage when venting wanes future eruptions will allow for this model to be tested through direct observation and experimentation

chemical reaction rates and entrainment within the endeavour ridge hydrothermal plume the aging of the hydrothermal plume over the endeavour segment of the juan de fuca ridge was estimated by measuring the222rn3he ratio in the plume as it dispersed despite uncertainties in the source function of hydrothermal input it wa determined that the relative sequence of removal from the plume ish2 c 222rn ch4 mn where c is a measure of particle concentration and the mean life of222rn is 5 5 days h2 is removed from the plume within hours of input while mn is not removed within the two week timescale of the radon helium clock entrainment of bottom water within the buoyant plume may introduce additional chemical signatures into the spreading effluent layer over that which would be introduced by hydrothermal discharge alone this is particularly significant for those chemical species which are not greatly enriched in the vent fluids relative to bottom water concentration and which display a nutrient like profile in the deep ocean thus we found that significant fractions of the si and226ra anomalies in the plume were not of hydrothermal origin but were derived from entrained bottom water which has a higher concentration of these elements than ambient water at plume height

the control of precursor brittle fracture and fluid rock interaction on the development of single and paired ductile shear zones abstract ductile shear zones can occur as relatively isolated single structures as arrays or as characteristic paired zones in continuous glaciated exposures of metagranodiorites from the tauern window eastern alps the control of initial dilatant brittle fracture and associated fluid rock interaction on the geometry of subsequent ductile shear zones can be unequivocally established shearing occurred under amphibolite facies conditions fractures in weakly deformed metagranodiorites are often less than 1 mm thick but extend for tens of metres many are healed joints without shear offset others show minor mm cm discrete dextral offset such brittle faults commonly display a low angle en echelon arrangement with displacement transferred between discrete fracture segments by ductile compressive bridges the geometry of more strongly reactivated zones depends on the degree and heterogeneity of fluid rock interaction which is related to fluid infiltration and veining along the primary fractures with little fluid rock interaction reactivation produces single heterogeneous ductile shear zones centred on and immediately flanking the pre existing fracture with increased fluid rock interaction a bleached halo is developed symmetrically to either side of a central epidote quartz garnet calcite vein ductile shear zones commonly flank this bleached zone to develop a characteristic paired pattern strain is partitioned localizing in the central fracture vein and the flanking shear zones paired zones may anastomose in accordance with changes in the width of the central bleached zone but are always symmetrically spaced with regard to the central fracture vein with increasing deformation the ductile shear zones broaden into the adjacent metagranodiorite but not into the bleached zone which remains preserved as a low strain region paired shear zones can also develop to either side of aplite dykes examples of characteristic paired shear zones usually with a clear central vein are found in many areas ranging from greenschist to eclogite facies suggesting that the mechanism of their formation is quite general

evidence for iron and sulfur enrichments in hydrothermal plumes at axial volcano following the january february 1998 eruption in response to 12 days of seismic activity at axial volcano juan de fuca ridge in january february 1998 the nsf noaa sponsored axial response team conducted three response cruises in february august and august september to map and sample hydrothermal plumes over the region vertical profiles of particulate fe and s over the eruption site show high concentrations from about 1400 m to the bottom chemical and scanning electron microscope analysis of the february plume samples revealed anhydrite fe ferrihydrites elemental sulfur and angular glassy basalt shards up to 190 m in the longest dimension many of these shards had halite coatings which is consistent with subseafloor basalt seawater reactions at temperatures 450 c at 1500 m depth in august and september cruises the basalt shards were no longer present in the hydrothermal plumes instead the plumes were predominantly composed of fe ferrihydrites elemental sulfur and sulfur filaments a unique feature of this data set is the high concentrations of elemental sulfur in the lower 60 m of the water column the sulfur results are suggestive of a significant enrichment of the bacterial biomass in the water column over the eruption site with time within the axial caldera approximately 10 20 of the total sulfur is present as sulfur filaments these post eruption particle compositional changes have strong similarities to the results from the 1993 coaxial eruption on the juan de fuca ridge

transition from orogen perpendicular to orogen parallel exhumation and cooling during crustal indentation key constraints from 147sm 144nd and 87rb 87sr geochronology tauern window alps abstract the core of the alpine orogen in the eastern alps tauern window experienced a change from orogen normal shortening and post nappe doming to predominantly orogen parallel extension and tectonic unroofing during late oligocene to miocene northward indentation of the adriatic microplate a new 147 sm 144 nd isochron age of 25 7 0 9 ma on a garnet bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the tauern window indicates that high temperatures related to post nappe barrovian type metamorphism overlapped in time with the onset of doming new 87 rb 87 sr biotite ages from this same complex combined with previously published 87 rb 87 sr white mica ages suggest that doming and exhumation began no later than 28 ma immediately in front of indenting austroalpine crustal blocks then migrated laterally to the ese during rapid exhumation and orogen parallel stretching beginning at about 23 ma rapid cooling ended at approximately 17 ma in the footwall of the katschberg normal fault which delimits the eastern margin of the tauern window a similar pattern of migrating doming orogen parallel extension and cooling is recognized in the western part of the tauern window where rapid exhumation began at about 20 ma some 2 3 ma later than in the eastern part this difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the tauern window are attributed to fragmentation of the aforementioned austroalpine blocks along the leading edge of the main adriatic indenter southern alps as this indenter advanced to the north

in situ sr isotope analysis of mantle carbonates constraints on the evolution and sources of metasomatic carbon bearing fluids in a paleo collisional setting abstract carbonate bearing wedge peridotites attest the mobilization of carbon c by slab fluids melts circulating in a subduction setting in general coh fluids are thought to derive from the dehydration partial melting of the crustal portions of slabs especially during the exhumation of crust mantle melanges along continental subduction channels in this study we combined textural observations with in situ sr isotope analyses of mantle carbonates occurring in different microstructural sites to test whether the fluids responsible for the carbonation of a mantle wedge are derived from the subducted continental crust or not we focus on the ulten zone peridotites eastern italian alps associated with high grade felsic rocks where carbonates occur mainly as dolomite and minor magnesite and calcite in situ laser mc icp ms analysis of peridotites representing different episodes of a complex metasomatic history indicates that sr isotopic variations can be linked to the different microstructural positions of carbonates the c metasomatism of the uz peridotites is proposed to have occurred in two stages the first stage is the hp carbonation at peak eclogite facies conditions with formation of interstitial matrix dolomite in textural equilibrium with hornblende to pargasite amphibole and cl apatite this dolomite exhibits relatively unradiogenic 87sr 86sr present day values of 0 70487 0 00010 requiring different sources with respect to the associated migmatites and the overhanging mantle wedge carbonation continued during exhumation with local injection of c rich fluids forming a dolomite vein in association with tremolite and chlorite the dolomite vein shows a wide range of 87sr 86sr 0 7036 0 7083 reflecting both the primary composition of carbonates and the consequent interaction with crustal fluids as expected in a crust mantle melange the second stage is c remobilization by dolomite dissolution and precipitation of brucite intergrowths with calcite during the final exhumation this remobilization event has resulted in a similar sr composition to the precursor dolomite the mantle wedge is therefore capable of storing carbonates which have been shown to represent a complex metasomatic evolution from eclogite facies conditions to very shallow structural levels therefore fluids released from subducting slabs of continental lithosphere might be responsible for the crystallization of metasomatic minerals such as amphibole phlogopite and zircon in the overlying ultramafic rocks conversely the role of these metasomatic fluids on the carbonation of mantle wedge is likely overestimated the combination of geochemical isotopic and textural evidence suggests that dolomite inclusions and interstitial dolomite are derived in large part from a distinct source of c bearing fluids that could be related to depleted mantle wedge sources and or trondhjemitic igneous activity in contrast at the end of exhumation residual coh fluids released by the associated stromatic gneisses and orthogneisses resulted in late stage dolomite veins having the highest sr isotope values in the ulten zone peridotites

jura alps and the boundary of the adria subplate abstract the thin skinned jura fold thrust belt is the frontal part of a thick skinned late miocene alpine nappe important late miocene structures in the alps that help define this nappe are the external massifs in the north the orobic thrusts and the piemontese southern alps in the south the giudicarie brenner line in the east and more vaguely the south end of the belledonne massif in the west a bottom boundary compatible with the data is the brittle ductile transition bdt this jura nappe is separated from the latest oligocene early miocene helvetic nappe system most obviously by the late miocene orobic giudicarie brenner fault complex in contrast the distinctive boundary of the early miocene thick skinned helvetic nappe was the iorio tonale line it in the south merging into the piemontese southern alps at what may be termed the locarno singularity the point of minimum width of the thick skinned alps the northern boundary passed through the gotthard and montblanc massifs motion along the southern boundary was dextrally transpressive associated with complex strain partitioning patterns one part of these patterns is the confusing entity comprising the piemontese southern alps and the lepontine dome the slivers composing the piemontese southern alps are dragged dextrally by the iorio tonale strike slip at the locarno singularity and thereby exhibit an important characteristic trait of exotic terranes crustal slivers dragged along strike slip faults the lepontine dome around the locarno singularity on the north side of the iorio tonale line displays the characteristics of a backstop in thrust systems as modeled in sandbox experiments the special boundary functioning as a backstop compatible with the transpressive kinematics was the ivrea body a strong mafic ultramafic granulitic complex which in the early miocene migrated dextrally along the iorio tonale line forcing detachment to descend into the hot middle crust and producing an upsurge of the hot masses in the late miocene jura phase this particular impediment had moved to the west enabling decollement at the brittle ductile transition to propagate across the insubric line into the lombardic domain large scale strain partitioning manifestations resemble those of the equally dextrally transpressive southern boundary of the caribbean plate in spite of a difference in scales the foremost of these manifestations are regional right slip faults slicing through a broad band of contraction accompanied by collapse basins

spectra and magnitudes of t waves from the 1993 earthquake swarm on the juan de fuca ridge a swarm of earthquakes on the crest of the juan de fuca ridge was detected in june and july 1993 by a network of hydrophones the activity migrated 60 km along the crest suggesting a lateral dike injection and the possibility of a volcanic eruption subsequent geologic and oceanographic investigations confirmed that an eruption had taken place examination of the individual acoustic arrivals shows changes in the character of the signal that are consistent with an injection of magma a reduction in the rise time of the wave packet and a proportional increase in high frequency energy was observed and is interpreted to result from a shoaling of the earthquake source region second the source magnitudes were largest at the onset of the swarm and became smaller over time also consistent with shoaling of the dike the appearance of the t wave arrivals changed significantly 5 days after the beginning of the swarm potentially indicating the onset of a surface eruption

reply to comment by m r palmer and g g j ernst on helium heat and the generation of hydrothermal event plumes at mid ocean ridges by j e lupton e t baker and g j massoth

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

k ar and ar ar dating the aim of this chapter is to present the k ar and ar ar dating techniques in the context of noble gas studies since there are already several recent texts on k ar and ar ar dating dickin 1995 mcdougall and harrison 1999 the focus of this section will be aspects of argon transport and storage in the crust which affect k ar and ar ar dating including ar loss from minerals by diffusion and ar gain by minerals or excess argon the k ar dating technique was one of the earliest isotope dating techniques developed soon after the discovery of radioactive potassium and provided an important adjunct to u pb and u he dating techniques the ease of measurement and ideal half life 1250 million years see table 2 below for dating geological events has made this the most popular of isotopic dating techniques aldrich and nier 1948 first demonstrated that 40ar was the product of the decay of 40k and soon after k ar ages were being measured in several laboratories most often using an absolute method such as a mcleod gauge to measure argon concentrations the first published k ar results by such a technique were those of smits and gentner 1950 who analyzed sylvite from the buggingen oligocene evaporite deposits obtaining an age of 20 million years mass spectrometers which simultaneously measured very small amounts of gas and the isotope ratios necessary to make corrections for atmospheric contamination quickly replaced manometric techniques crucially the use of static vacuum techniques pioneered by john reynolds at the university of california berkeley meant that mass spectrometers were sufficiently sensitive to analyse the small amounts of gas released from common rocks and minerals although the earliest mass spectrometers were built in house the introduction of the commercially available ms10 farrar et al 1964 a small 180 metal mass spectrometer built for

crustal structure of the eastern alps along the transalp profile from wide angle seismic tomography abstract the objective of the transalp project is an investigation of the eastern alps with regard to their deep structure and dynamic evolution the core of the project is a 340 km long seismic profile at 12 e between munich and venice this paper deals with the p wave velocity distribution as derived from active source travel time tomography our database consists of vibroseis and explosion seismic travel times recorded at up to 100 seismological stations distributed in a 30 km wide corridor along the profile in order to derive a velocity and reflector model we simultaneously inverted refractions and reflections using a derivative of a damped least squares approach for local earthquake tomography 8000 travel time picks from dense vibroseis recordings provide the basis for high resolution in the upper crust explosion seismic wide angle reflection travel times constrain both deeper crustal velocities and structure of the crust mantle boundary with low resolution in the resulting model the adriatic crust shows significantly higher p wave velocities than the european crust the european moho is dipping south at an angle of 7 the adriatic moho dips north with a gentle inclination at shallower depths this geometry suggests s directed subduction azimuthal variations of the first break velocities as well as observations of shear wave splitting reveal strong anisotropy in the tauern window we explain this finding by foliations and laminations generated by lateral extrusion based on the p wave model we also localized almost 100 local earthquakes recorded during the 2 month acquisition campaign in 1999 seismicity patterns in the north seem related to the inn valley shear zone and to thrusting of austroalpine units over european basement the alignment of deep seismicity in the trento vicenza region with the top of the adriatic lower crust corroborates the suggestion of a deep thrust fault in the southern alps