structure and evolution of the east sierran thrust system east central california 1 a belt of arc parallel northeast vergent contractional deformation the east sierran thrust system ests crops out for 150 km along the east side of the sierran continental margin arc the ests is nowhere wider than 20 km and it accommodated an estimated minimum of 9 3 km of horizontal shortening remarkably it experienced repeated episodes of broadly coaxial and coaxial planar contractional deformation beginning prior to 188 ma and continuing past 140 ma we postulate that the ests resulted primarily from episodic underthrusting of the back arc lithosphere beneath the east edge of the sierran arc facilitated by a buttressing effect of the arc as a result of this process rocks along the east flank of the batholith including the ests were episodically shortened against the arc buttress the ests experienced significant deformation during the nevadan orogeny indicating that contractional to transpressive deformation affiliated with this event affected the eastern wall rocks of the arc as well as its western wall rocks index terms 8102 tectonophysics continental contractional orogenic belts 9609 information related to geologic time mesozoic 8015 structural geology local crustal structure 9350 information related to geographic region north america keywords eastern california mesozoic structure cordilleran thrust system citation dunne g c and j d walker 2004 structure and evolution of the east sierran thrust system east central california tectonics 23 tc4012 doi 10 1029 2002tc001478

leachate analyses of volcanic ashes from stromboli volcano a proxy for the volcanic gas plume composition 1 many volcanoes show a change in chemical composition of the gas phase prior to periods of eruptive activity fine grained tephra erupted from active vents and transported through volcanic plumes can adsorb and therefore rapidly scavenge volatile elements such as sulfur halogens and metal species in the form of soluble salts adhering to ash surfaces analysis of such water soluble surface materials is a suitable supplement for remote monitoring of volcanic gases at inaccessible volcanoes in this work ash samples of the 2004 to 2009 eruptive activity of stromboli volcano were sampled leached and analyzed for major and trace elements data analysis and interpretation was focused on determining the relationship between chemical composition of water soluble components adhering to volcanic ash and the volcano s activity state first results show significant temporal variations in ash leachate compositions reflecting changes in the eruptive style of the volcano in particular we reveal that ash leachates s f and mg na ratios showed marked increases prior to a large scale explosion on 15 march 2007

atmospheric chemistry of a 33 34 hour old volcanic cloud from hekla volcano iceland insights from direct sampling and the application of chemical box modeling 1 on 28 february 2000 a volcanic cloud from hekla volcano iceland was serendipitously sampled by a dc 8 research aircraft during the sage iii ozone loss and validation experiment solve i it was encountered at night at 10 4 km above sea level in the lower stratosphere and 33 34 hours after emission the cloud is readily identified by abundant so2 1 ppmv hcl 70 ppbv hf 60 ppbv and particles which may have included fine silicate ash we compare observed and modeled cloud compositions to understand its chemical evolution abundances of sulfur and halogen species indicate some oxidation of sulfur gases but limited scavenging and removal of halides chemical modeling suggests that cloud concentrations of water vapor and nitric acid promoted polar stratospheric cloud psc formation at 201 203 k yielding ice nitric acid trihydrate nat sulfuric acid tetrahydrate sat and liquid ternary solution h2so4 h2o hno3 sts particles we show that these volcanically induced pscs especially the ice and nat particles activated volcanogenic halogens in the cloud producing 2 ppbv clox this would have destroyed ozone during an earlier period of daylight consistent with the very low levels of ozone observed this combination of volcanogenic pscs and chlorine destroyed ozone at much faster rates than other pscs that arctic winter elevated levels of hno3 and noy in the cloud can be explained by atmospheric nitrogen fixation in the eruption column due to high temperatures and or volcanic lightning however observed elevated levels of hox remain unexplained given that the cloud was sampled at night

rainwater and ash leachate analysis as proxies for plume chemistry at soufriere hills volcano montserrat chloride and sulphate concentrations in rainwater and water soluble leachates from volcanic ash samples track the compositions of gas emissions at the soufriere hills volcano montserrat from 1996 to 2001 there are both systematic spatial and temporal variations in the chloride sulphate ratio expressed as the equivalent hcl so2 mass ratio in rainwater and ash leachates temporal variations reflect changes in eruption rate and eruptive style mass ratios of hcl so2 in ash leachates correspond closely with those obtained by open path fourier transform infrared op ftir spectroscopy and reflect changes in volatile emissions throughout the eruption both leachate and op ftir spectroscopic analyses show mass ratios of hcl so2 1 during dome growth and hcl so2 1 during non eruptive periods the hcl so2 mass ratios in rainwater samples from 1996 and 1997 show temporal variations that correlate with changes in extrusion rate the hcl so2 ratios in plume affected rainwater and ash leachates from june and july 2001 correlate positively with increasing rockfall energy and with increasing eruption rate prior to a dome collapse event the hcl so2 mass ratios in water soluble ash leachates and rainwater samples collected at the same time and from the same sites are linearly correlated with rainwater hcl so2 ratios systematically two to three times higher than ash leachate ratios spatial patterns of rainwater ph and hcl so2 in rainwater and ash leachates are principally influenced by the proximity of the sampling sites to the active dome and to the typical pattern of dispersion of the plume by tropospheric winds these results demonstrate that rainwater chemistry and ash leachate analysis provides a useful indicator of volcanic activity and represents a valuable supplement to volcano surveillance efforts

emplacement of the santa rita flat pluton as a pluton scale saddle reef regional mapping indicates that the middle jurassic santa rita flat pluton exposed in the inyo range of eastern california is situated within the core of a south plunging synform defined by bedding in the surrounding metasedimentary wall rocks which dip beneath the pluton however bedding in rocks preserved above the pluton defines a south plunging antiform anisotropy of magnetic susceptibility analysis revealed that magnetic foliation within the pluton also defines a south plunging antiform and the accompanying magnetic lineation plunges subparallel to the axis of this antiform our data indicate that the pluton was initially intruded as a sill in the hinge zone of the enveloping synform subsequent vertical inflation of the sill resulted in upward doming of the overlying roof and formation of the antiform now observed at the current erosion level in the pluton and preserved roof rocks emplacement of the pluton at 164 1 5 ma u pb zircon age overlaps in time with regional thrust faulting and folding ca 185 148 ma recognized in the southern inyo range we speculate that space for initial emplacement of the pluton was produced during folding by layer parallel slip and hinge zone dilation producing a saddle reef like structure

paleogeographic and tectonic implications of the geology of the tiefort mountains northern mojave desert california geologic mapping petrologic and structural analyses and u pb dating in the tiefort mountains northern mojave desert california provide data on paleozoic paleogeography and mesozoic intra arc tectonics metasedimentary rocks consist primarily of quartzose schists and gneisses that are provisionally correlated with late precambrian cordilleran passive margin facies recognition of precambrian augen gneiss and metasedimentary rocks with craton margin protoliths suggests that the craton miogeocline boundary is in or near the tiefort mountains the presence of eugeoclinal rocks in ranges to the west implies truncation or telescoping of the miogeocline in this area the metasedimentary units are intruded by middle jurassic granite and diorite orthogneisses dated by u pb as ca 164 and ca 160 ma deformed rocks record amphibolite facies metamorphism and mylonitization during middle to late jurassic southeast vergent ductile shear pervasively annealed microstructures indicate that recrystallization outlasted deformation at south tiefort mountain the mylonitic fabric is deformed by northwest trending folds and crosscut by a swarm of mafic and felsic dikes dated as 148 14 ma at tiefort mountain synkinematic biotite granite gneiss is dated as ca 105 ma and mylonitic fabrics are folded about north trending axes the presence of the cretaceous orthogneiss suggests that two deformational events jurassic and cretaceous in age may have affected part of the study area dikes dated as ca 82 ma that crosscut all fabrics are interpreted to be part of a regional intrusive event the timing and vergence of shear zones at south tiefort mountain are similar to contractional shear zones in adjacent areas forming a belt of contractional deformation from the central mojave desert to the east sierran thrust system this deformation may be related to a period of late middle to late jurassic sinistral oblique subduction

exhumation of the inyo mountains california implications for the timing of extension along the western boundary of the basin and range province and distribution of dextral fault slip rates across the eastern california shear zone 1 new geologic mapping tectonic geomorphologic 10be terrestrial cosmogenic nuclide and u th he zircon and apatite thermochronometric data provide the first numerical constraints on late cretaceous to late quaternary exhumation of the inyo mountains and vertical slip and horizontal extension rates across the eastern inyo fault zone california the east dipping eastern inyo fault zone bounds the eastern flank of the inyo mountains a prominent geomorphic feature within the western basin and range province and eastern california shear zone u th he zircon and apatite thermochronometry yield age patterns across the range that are interpreted as indicating 1 two episodes of moderate to rapid exhumation associated with laramide deformation during the late cretaceous early tertiary 2 development of a slowly eroding surface during a prolonged period from early eocene to middle miocene 3 rapid cooling exhumation and initiation of normal slip along the eastern inyo fault zone accommodated by westward tilting of the inyo mountains block at 15 6 ma and 4 rapid cooling exhumation and renewed normal slip along the eastern inyo fault zone at 2 8 ma fault slip continues today as indicated by fault scarps that cut late pleistocene alluvial fan surfaces the second episode of normal slip at 2 8 ma also signals onset of dextral slip along the hunter mountain fault yielding a pliocene dextral slip rate of 3 3 1 0 mm a where a is years summing this dextral slip rate with estimated dextral slip rates along the owens valley death valley and stateline faults yields a net geologic dextral slip rate across the eastern california shear zone of 9 3 2 2 1 4 to 9 8 1 4 1 0 mm a

major ion bulk deposition around an active volcano mt etna italy bulk atmospheric deposition of major cations na k ca mg and anions cl f so4 were measured at 15 sites around an active volcano mount etna from 2001 to 2003 their composition indicates several natural sources among which deposition of plume derived volcanogenic gas compounds is prevalent for f cl and s plume derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano ph in the 2 45 5 57 range cation species have complex origin including deposition of plume volcanogenic ash and aerosols and soil dust wind re suspension of either volcanic or carbonate sedimentary rocks

tectonic implications of a petrographic and geochemical characterization of the lower to middle jurassic sailor canyon formation northern sierra nevada california the lower to middle jurassic sailor canyon formation in the northern sierra nevada of california consists of basinal volcaniclastic and tuffaceous sedimentary rocks petrographic and geochemical data from the formation provide an opportunity to assess a proposed 400 km of pre late cretaceous dextral strike slip displacement on the cryptic mojave snow lake fault a corollary to the proposed displacement is that triassic jurassic volcanic complexes exposed in eastern california were the source for sailor canyon formation sediments however geochemical data derived from volcanic rocks from this area are unlike those of the volcanic provenance characterized for the sailor canyon formation comparisons of geochemical data suggest that contemporaneous volcanic centers exposed in western nevada north of 38 n may be better candidates for the source of the volcanic material in the sailor canyon formation this interpretation implies that dextral strike slip displacement on the mojave snow lake fault may be less than 200 km a value that agrees with some interpretations of mesozoic intrabatholithic displacements in the sierra nevada

oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission volcanic sulfate aerosol is emitted from the vents of many active volcanoes but its origin has not yet been explained we report the first measurements of the isotopic compositions of near vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systematics of the aerosol and magma at masaya volcano nicaragua to draw preliminary conclusions about the production mechanism of near source volcanic sulfate the sulfate aerosol does not display a significant mass independent oxygen or sulfur isotopic signature which suggests that primary volcanic aerosol does not contribute to the larger mass independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores the oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the 18o value of the sulfate aerosol is 8 the sulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean 34s value of 7 7 0 8 similar to that of the magma 6 6 0 2 the low 17o value the 18o value of the magma 6 6 0 3 and the high 18o value of atmospheric oxygen 23 5 suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate instead the isotopic systematics of aerosol and magma are consistent with sulfate production either by high temperature equilibration of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of so4 2 from the magma

extensional arc setting and ages of middle jurassic eolianites cowhole mountains eastern mojave desert block california mesozoic strata in the cowhole mountains eastern mojave block california include 200 800 m of eolian quartz arenite aztec sandstone overlain by more than 575 m of silicic ignimbrites lava flows and minor sedimentary rocks cowhole volcanics u pb zircon geochronologic data on a crystal rich dacite lava flow in the aztec sandstone indicate that the sandstone is middle jurassic and is therefore age equivalent to backarc eolianites of the temple cap and carmel formations not the lower jurassic navajo formation as previously assumed our u pb zircon data on two ignimbrites of the cowhole volcanics indicate that they are the same age within error as the lava flow in the aztec sandstone at 170 3 ma new structural and stratigraphic data together with published data indicate syndepositional normal faulting and deposition of landslide blocks throughout deposition of this section these results are consistent with our previous volcanologic studies in middle jurassic rocks of southern arizona southeastern california and the central mojave block which document ignimbrite eruptions from calderas contemporaneous with deposition of craton derived eolian sands in extensional or transtensional intra arc basins busby c j schermer e r and mattinson j m 2002 extensional arc setting and ages of middle jurassic eolianites cowhole mountains eastern mojave desert block california in glazner a f walker j d and bartley j m eds geologic evolution of the mojave desert and southwestern basin and range boulder colorado geological society of america memoir 195 p 79 9

atmospheric dispersion environmental effects and potential health hazard associated with the low altitude gas plume of masaya volcano nicaragua masaya volcano 560 m a s l nicaragua re sumed its degassing activity in mid 1993 with the con tinuous emission of so 2 at rates increasing from 600 metric tons t day 1 7 0 kg s 1 in 1995 to 1800 t day 1 21 0 kg s 1 in 1999 the low altitude gas plume is typically blown westward by the prevailing wind across the masaya caldera and las sierras high lands which are at a higher elevation than the gas vent in this study the areal distribution of atmospheric so 2 concentrations was monitored within 44 km of the vent with a network of passive samplers measured so 2 air concentrations ranged from 2 to 90 ppbv in 1998 and from 2 to 230 ppbv in 1999 the data suggest that the volcanic emissions influenced air quality across a 1 250 km2 area downwind local topography exerts a strong control on plume dispersal and hilltops are particularly prone to fumigation and thus to high ambient so 2 lev els in a zone 22 km2 in size located within 15 km of the source the response of vegetation to sustained exposure to high atmospheric dose of volcanic so 2 and hf result ed in a strong reduction in the number of plant communi ties a transition zone of somewhat indefinite boundary surrounds the devastated zones and exhibits vegetation damage in the form of leaf injury in addition to the envi ronmental impacts of the volcanic emissions both short and long term public health hazards may exist in areas most exposed to the plume the harmful effects of the volcanic emissions on cultivated vegetation could be di minished by using windbreaks made of gas tolerant trees and shrubs such as eugenia jambos brosimum utile and clusia rosea the current gas crisis at masaya volcano provides an unique opportunity for investigating the at mospheric environmental and medical impacts of volca nic gases and aerosols

depletion rates of sulfur dioxide in tropospheric volcanic plumes the tropospheric sulfur cycle has been closely studied from the standpoint of anthropogenic emissions but less so with respect to volcanic sources we document here evidence for wide variation in lifetimes of volcanic so2 in the troposphere at one extreme our observations of the plume associated with the lavadome eruption of soufriere hills volcano montserrat suggest loss of gaseous so2 at rates exceeding 10 3 s 1 while this efficent so2 depletion reflects unusual environmental factors published measurements for mount etna s plume approach these rapid rates in such cases source strengths of so2 must significantly exceed apparent fluxes measured several kilometres downwind this implies that meteorological and geographic factors as well as volcanic degassing rates should be considered in the interpretation of fluxes of so2 measured beyond source vents with ramifications for volcano monitoring and eruption prediction furthermore since most calculations of global volcanic fluxes of sulfur and other species to the troposphere are based on extrapolation of so2 flux data they may underestimate true source strengths finally we consider that fast sulfur chemistry may also prevail in convecting eruption columns resulting in partial tropospheric scrubbing of sulfur from stratosphere bound plumes

accretion of the franciscan complex attending jurassic cretaceous geotectonic development of northern and central california scattered igneous activity marks the triassic margin of california but an andean volcanic plutonic arc began to form in the sierra nevada white inyo range and klamath mountains at ca 170 ma during underflow of the oceanic lithosphere this calc alkaline belt supplied volcanogenic erosional debris to the mariposa galice proximal overlap sequence by ca 165 160 ma transpression also generated high pressure low temperature basaltic eclogites garnet blueschists and amphibolites along the middle and late jurassic convergent plate junction at ca 170 155 ma most of these returned surfaceward as tectonic blocks only during the mid cretaceous the high grade metamafic metamorphosed mafic blocks that formed during construction of the emergent arc and derived mariposa galice strata predate the onset of franciscan trench deposition near the end of jurassic time the klamath salient evidently migrated 200 km westward an earliest cretaceous westward stepout of the convergent junction apparently formed directly offshore from the klamath imbricate orogen but to the south preexisting oceanic crust capped lithosphere was trapped landward as the coast range ophiolite andean arc detritus began to accumulate on this ophiolitic basement within the great valley forearc and outboard franciscan oceanic trench at ca 145 140 ma because earliest cretaceous relatively continuous great valley strata were deposited on the stable north american plate protected from both surface and subcrustal erosion forearc terrigenous sedimentation also signaled coeval deposition in the outboard trench 10 25 m y after middle and late jurassic initiation of the continental margin calc alkaline arc voluminous sedimentation and the accretion of franciscan and san joaquin sections of great valley rocks took place during mid and late cretaceous time after a flare up in igneous arc activity at 125 120 ma the youngest sierran granites have ca 85 ma ages reflecting extinction of the magmagenic zone beneath northern and central california and presumably reflecting subhorizontal oceanic plate underflow attending the laramide orogeny feebly zeolitized upper cretaceous and lower tertiary franciscan coastal belt rocks derived from the now inactive arc underwent only low pressure burial metamorphism reflecting shallow offloading and or large scale transpression they were not appreciably subducted although coastal belt units are members of the franciscan lithotectonic assemblage their origin contrasts with the rest of the subduction complex

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

franciscan geologic history constrained by tectonic olistostromal high grade metamafic blocks in the iconic california mesozoic cenozoic accretionary complex figure 1 subduction generated a nw trending andean arc along the californian margin beginning at 175 ma coeval high pressure hp transformation of oceanic crust in an east dipping subduction zone probably accompanied plate convergence but recovered franciscan eclogite and garnet blueschist blocks chiefly possess younger recrystallization ages of 165 150 ma these jurassic hp metamafic rocks were sequestered in a low temperature environment well into cretaceous time fragments of actinolitic rinds partially surround many such high grade blocks only slightly younger than the hp metamorphism these rinds reflect metasomatic exchange between metabasalt and serpentinized harzburgite along the dynamic oceanic crust mantle hanging wall during storage of the mafic rocks at moderate depth high grade tectonic blocks later were brought toward the surface in circulating low density sheared mud matrix melange and or in buoyant serpentinite bodies most exotic hp metamafic blocks occur in melanges of the franciscan central belt reflecting tectonic insertion within the subduction zone not near surface additions to the clastic section however rare high grade clasts in feebly recrystallized franciscan conglomerates suggest erosion and sedimentary deposition for some hp blocks the addition of dense metabasaltic olistoliths to the mid and upper cretaceous section requires that these hp material were carried surfaceward first as tectonic fragments perhaps immersed in low density serpentinite or mud matrix melange then eroded and transported into the trench hp rocks are conspicuously lacking in coeval great valley strata whatever the origin of particular high grade rocks widespread post depositional shearing has largely obliterated their original natures but all dense metamafic blocks of jurassic recrystallization age must have been supplied to the cretaceous franciscan accretionary complex by entrainment in a low density circulating muddy matrix or serpentinite body the vast majority of exotic hp blocks resides in central belt melanges and appears to be tectonic rather than olistostromal in origin 1 pending yes

new evidence for cretaceous strike slip faulting in the united states cordillera and implications for terrane displacement deformation patterns and plutonism early to mid cretaceous dextral strike slip faulting involving up to 400 km displacement has been documented in the southern sierra nevada of california in western idaho the salmon river suture juxtaposes unrelated oceanic and continen tal rocks along a major near vertical shear zone that was active in the early to mid cretaceous these two structural zones have been treated as separate entities however new data indicate that they likely connect via a structural discontinuity in northwest nevada and southeast oregon herein called the western nevada shear zone wns current structures within the wns record dip slip contractional deformation however regional relations structural and stratigraphic indicate a mismatch in the early mesozoic geology of rocks across the wns that is best explained by dextral strike slip displacement of several 100 km these relations argue that an early strike slip structure along the wns was reactivated and obscured during later regional shortening deformation most likely related to the cretaceous sevier orogeny the wns is along strike and broadly coeval with the salmon river suture zone and strike slip boundaries in the sierra nevada we hypothesize that all these features are related elements of a major structural boundary in the western united states cordil lera this boundary is interpreted to have accommodated significant dextral strike slip displacement of outboard arc terranes of the cordillera in the early cretaceous followed by reactivation as a localized contractional zone in the mid cretaceous during the sevier orogeny cretaceous batholiths of the united states cordillera closely parallel the boundary which we suggest formed a major crustal flaw that localized and facilitated emplacement of arc magmas

oxygen isotopic study of late mesozoic cooling of the mount barcroft area central white mountains eastern california the middle jurassic barcroft mafic granodiorite and late cretaceous ternary minimum mcafee creek granite are important components of the igneous arc sited along the sw north american margin bulk rock analyses of 11 samples of the metaluminous i type barcroft comagmatic suite have an average 18o value of 7 4 0 6 all values 1 four barcroft specimens average end 3 6 1 8 87sr 86sr 0 707 0 001 the pluton consists of petrochemically gradational ca amphibole rich gabbro diorite granodiorite metadiorite and rare alaskite aplite for most of the pluton oxygen isotope exchange of quartz feldspar s biotite and ca amphibole accompanied local deuteric alteration eight specimens of slightly peraluminous granitic rocks of the muscovite bearing mcafee creek series have an average 18o of 8 6 0 5 four mcafee type samples average end 7 8 1 7 87sr 86sr 0 711 0 004 for both plutons bulk rock evidence of exchange with near surface water is lacking suggesting 5 10 km cooling depths barcroft minerals exhibit regular oxygen isotopic partitioning from high to low 18o in the sequence quartz plagioclase k feldspar amphibole biotite along the se margin of the pluton quartz and biotite in lower cambrian quartzites are higher in 18o and show slightly larger fractionations than igneous analogues exchange with fluids derived from these heated contact metamorphosed country rocks increased bulk 18o 16o ratios of barcroft border rocks and constituent plagioclase subsolidus tremolite actinolite especially of granitic dikes transecting the wall rocks oxygen isotope thermometry for seven barcroft pluton quartz amphibole and six quartz biotite pairs indicate apparent subsolidus temperatures averaging 519 49 c quartz plagioclase pairs from two barcroft granodiorites yield values of 519 and 515 c a quartz biotite pair from a quartzite adjacent to the barcroft pluton yields an apparent temperature of 511 c in agreement with estimates based on contact metamorphic parageneses except for its se margin barcroft pluton silicates evidently exchanged oxygen isotopes under local deuteric conditions compatible with ca amphibole thermobarometric analyses areal distributions for quartz plagioclase quartz amphibole and quartz biotite pairs reveal that putative annealing temperatures are lowest in ne trending axial portions of the barcroft body so it simply cooled inwards intrusion 70 million years later by the mcafee creek granite had no discernable effect on 18o values of barcroft minerals and bulk rocks

plinian airfall deposits of basaltic composition two widespread scoria fall deposits locally known as the fontana lapilli and san judas formation are demonstrated to have issued from masaya caldera complex nicaragua and to be the first documented plinian airfall deposit of basaltic composition data from maps of median grain size average maximum pyroclast diameter and average maximum diameter of lithic fragments provide conclusive evidence of the plinian nature of both deposits the volume within the 1 mm isopach of the fontana lapilli is 12 km3 3 4 km3 dense rock equivalent and within the san judas formation it is 1 2 km3 0 35 km3 dre theoretical eruption parameters calculated for the fontana lapilli and san judas formation respectively include muzzle velocity 170 m s and 150 m s column height 50 km and 18 km volume eruption rate 2 105 m3 s and 1 104 m3 s and duration 2 h and 10 h these are all similar to the calculated parameters for silicic plinian eruptions basaltic magmas are generally considered incapable of erupting in the manner characteristic of plinian eruptions recognition of them argues that factors other than high viscosity may be of fundamental importance

guadalupe pluton mariposa formation age relationships in the southern sierran foothills onset of mesozoic subduction in northern california we report a new 153 2 ma sims u pb date for zircons from the hypabyssal guadalupe pluton which crosscuts and contact metamorphoses upper crustal mariposa slates in the southern sierra a 950 m thick section of dark metashales lies below sandstones from which clastic zircons were analyzed at 152 2 ma assuming a compacted depositional rate of 120 m myr accumulation of mariposa volcanogenic sediments which overlie previously stranded middle jurassic and older ophiolite chert argillite belts in the sierran foothills began no later than 160 ma correlative oxfordian kimmeridgian strata of the galice formation occupy a similar position in the klamath mountains we speculate that the late jurassic was a time of transition from 1 a mid paleozoic middle jurassic interval of mainly but not exclusively strike slip and episodic docking of oceanic terranes 2 to transpressive plate underflow producing calcalkaline igneous arc rocks outboard blueschists at 170 150 ma whose erosion promoted accumulation of the mariposa galice overlap strata 3 continued transpressive underflow attending 200 km left lateral displacement of the klamath salient relative to the sierran arc at 150 140 ma and development of the apparent polar wander path cusps for north and south america and 4 then nearly orthogonal mid and late cretaceous convergence commencing at 125 120 ma during reversal in tangential motion of the pacific plate after 120 ma nearly head on subduction involving minor dextral transpression gave rise to voluminous continent building juvenile and recycled magmas of the sierran arc providing the erosional debris to the great valley fore arc and franciscan trench

geology of the inyo mountains volcanic complex implications for jurassic paleogeography of the sierran magmatic arc in eastern california an 3 1 km thick volcanic complex exposed in the southern inyo mountains east central california records jurassic subaerial depositional environments along the east flank of the sierran arc this complex which we name the inyo mountains volcanic complex is subdivided into lower middle and upper stratigraphic intervals the 200 580 m thick lower interval comprises predominantly epiclastic strata deposited on alluvial fans and adjacent river flood plains that were inclined northeast mafic lava flows and rare reworked tuff in this interval record the onset of jurassic volcanism in this part of the arc the 300 700 m thick middle interval is composed predominantly of intermediate to silicic lava flows and tuffs representing a major episode of volcanism ending at ca 169 ma that is contemporaneous with emplacement of numerous plutons in the region the 2260 m thick upper interval is composed of epiclastic strata with minor intercalations of volcanic rock most of this interval accumulated on low gradient flood plains that hosted evaporative lakes and that were episodically invaded by alluvial fan complexes three new u pb age determinations constrain the lower half of the upper interval to have been deposited during the interval from ca 169 ma to 150 ma the uppermost part of the complex remains undated but probably accumulated prior to 140 ma the inyo mountains volcanic complex is part of a belt of volcanic complexes that are the easternmost preserved jurassic complexes of the sierran arc these complexes share sufficient similarities to suggest that they represent a distinctive arc flank depositional province significantly different from that represented by coeval volcanic complexes preserved in roof pendants farther west closer to the magmatic axis of the arc similarities among arc flank complexes include predominantly to exclusively subaerial settings substantial 30 portions of epiclastic strata and existence at times of north to northeast inclined paleoslopes we infer on the basis of the varying types and amounts of volcanic rocks that whereas most complexes in the arc flank province were rarely if ever proximal to major eruptive centers complexes in two areas white mountains and eastern mojave desert were at times located in or adjacent to such centers these differences lead us to speculate that the east flank of the jurassic arc consisted of eastward projecting volcanic salients separated by arc recesses typified by the inyo mountains area in which epiclastic deposition was dominant

sulfur and halogen gases at masaya caldera complex nicaragua total flux and variations with time santiago crater of masaya caldera complex near managua nicaragua entered a phase of intense magmatic degassing in late 1979 the flux of so2 increased rapidly from a previous average of 380 t d 1 to approximately 1200 t d 1 in february 1980 we report on results of a study of the gas flux and geochemistry conducted as part of a broader interdisciplinary study of the volcano and its impact on the adjacent environment masaya is an unusual volcano because of its low shield like form consistent tholeiitic basaltic composition frequent activity and especially because of the approximately 25 year cycle of major non eruptive degassing crises we have used a combination of techniques involving remote sensing using a correlation spectrometer cospec of the flux of so2 and direct filter sampling of the ratios of the sulfur and halogen gases and aerosols to quantify the flux of all of these species the three stage filters successively trap aerosols halogen acid gases and sulfur dioxide and are analyzed by ion chromatography we have used the ratios of various species with the cospec measurements of the flux of so2 to calculate that the average flux of so2 is 1275 t d 1 hcl is 830 t d 1 hf is about 16 t d 1 and hbr is at most 1 t d 1 h2s and so4 are only minor sulfur species the flux of so2 and hcl represents the largest reported noneruptive sustained volcanic release of these species in the world masaya contributed 7 of the total so2 estimated to have been released by volcanoes worldwide in 1981 the flux of so2 has declined by about 9 each year since 1979 and can be modeled as a first order kinetic rate law with a decay constant of approximately 0 04 yr 1 approximately 2 2 106 tons of so2 has been released between september 1979 and september 1985 the ratio s cl has declined more rapidly than the flux of so2 reflecting the greater solubility of hcl than so2 in the magma the so2 flux at santiago varies more widely within a single day than observed at other degassing volcanoes and may be controlled at least in part by effects of the solid earth tide an area larger than 500 km2 has been severely impacted downwind of the volcano downwind ground level concentrations of so2 of 0 25 ppm are frequently encountered acid rain unusually chloride rich has a ph as low as 2 63 s cl ratios in the gas plume increase downwind probably as a result of the high solubility and dry deposition velocity of hcl preliminary analyses of primary concentrations of sulfur and chlorine in the magma of the present lava lake are used to calculate that at least 1 2 km3 has been completely degassed with respect to sulfur to provide the observed flux this implies that 10 km3 have been degassed by previous crises in the past century and further suggests a magma supply rate of approximately 0 1 km3 yr comparable with kilauea or etna volcanoes during historic time only two lava flows have been extruded implying an unusually low ratio of extrusion intrusion of only 0 0007

so2 loss rates in the plume emitted by soufriere hills volcano montserrat to improve interpretation of volcanic so2 flux data it is necessary to quantify and understand reactions involving so2 in volcanic plumes so2 is lost in volcanic plumes through a number of mechanisms here we report so2 measurements made with miniature ultraviolet spectrometers at soufriere hills volcano montserrat a low altitude volcano 1000 m above sea level whose plume entrains humid marine air in the planetary boundary layer traverses very near 2 km downwind from soufriere hills volcano significantly underestimate at source so2 emission rates on the order of 70 146 when not accounting for the decay rate similar so2 loss is likely to occur in plumes from other tropical low altitude volcanoes under conditions of high relative humidity 20 of active volcanoes worldwide these results suggest that the global volcanic so2 emission rate may be underestimated as the estimates are based on measurements taken downwind of volcanoes by which time significant loss of so2 may have taken place the loss rates calculated here could be used in conjunction with downwind so2 fluxes to estimate at source so2 emission rates from volcanoes with similar environmental conditions to those at soufriere hills volcano

trace elements in the particulate phase of the plume of masaya volcano nicaragua masaya volcano nicaragua has been passively degassing since 1993 this gas crisis provides a unique opportunity for investigating the degassing of magmatic volatiles here we studied the chemical composition of the volcanic particulate phase collected directly from the plume the objective was to gain new insights into the volatilities and emission rates of trace elements the results indicate enrichments in the aerosol phase of all analyzed trace elements including not only those known to be volatile such as cu and te but also elements considered as refractory such as rare earth elements rees and th rees were fractionated with a significant enrichment of light rare earth elements lrees over heavy rare earth elements hrees this pattern suggests degassing of lrees as chlorides in general the emission of most trace elements in volcanic plumes is governed by the primary degassing of chloride compounds however sem eds data and chemical analysis of aerosol filters allow us to state that trace elements can also be released as sulphate and chloro sulphate compounds the trace element emission rates at masaya are significant and place this volcano as a major gas emitter however for some elements like cu masaya s contribution to the global volcanic flux seems disproportionate probably pointing to the poor dataset available for other degassing volcanoes

contact metamorphism of the white mountain peak metavolcanic complex eastern california the nnw trending white inyo range represents the eastern continuation of the sierran volcanic plutonic arc along the central california nevada state line south of white mountain peak the ne trending steeply se dipping barcroft structural break transects the orogenic belt this high angle reverse fault downdropped deformed weakly recrystallized mid mesozoic mildly alkaline white mountain peak mafic and felsic metavolcanic flows interlayered volcanogenic metasedimentary strata and minor subvolcanic plugs against a folded neoproterozoic lower paleozoic quartzite and carbonate metasedimentary section on the south the middle jurassic barcroft granodioritic pluton later intruded the barcroft break the middle jurassic cottonwood and late cretaceous mcafee creek pellisier flat granitoids also invaded the superjacent section on the ne heating of the white mountain peak metavolcanic complex by the barcroft and nearby plutons caused a southeastward progressive increase in metamorphic grade producing neoblastic biotite epidote and hornblende in mafic volcanic rocks minor hypabyssal stocks and biotite epidote andalusite in felsic volcanic rocks volcaniclastic strata gradual increases in biotite ti and plagioclase an contents reflect this se metamorphic zonation utilizing hornblende actinolite muscovite celadonite and biotite solid solutions thermobarometry indicates lithostatic pressures of 2 3 kbar during recrystallization with temperatures ranging from a background value of 350 c far from the barcroft pluton to 500 c along the intrusive contact physical conditions were similar to those developed in the neoproterozoic lower paleozoic platform strata directly south of the barcroft granodiorite the region constitutes a typical example of the p t evolution of the late mesozoic californian crustal margin where episodic magma emplacement caused widespread contact metamorphism

timing of exhumation wheeler pass thrust sheet southern nevada and california late jurassic to middle cretaceous evolution of the southern sevier fold and thrust belt zircon u th he zhe thermochronologic data for 46 samples from the wheeler pass thrust sheet which carries thick passive margin strata and is discontinuously exposed across the southern part of the sevier fold and thrust belt record late jurassic cooling related to exhumation during early thrust slip and local middle cretaceous cooling related to footwall basement imbrication within the frontal part of the wheeler pass sheet exposed in the northwest spring mountains zhe ages decrease from ca 160 to 140 ma over a paleodepth interval of 6 to 9 km in devonian to lower cambrian strata interpreted to record exhumation and enhanced cooling above a frontal ramp followed by slow cooling a similar pattern of zhe ages occurs over a more limited paleodepth range exposed within the resting spring range to the south in the nopah range zhe ages of ca 140 ma in lower cambrian strata record early cooling followed by slow cooling until ca 100 ma zhe ages in underlying paleoproterozoic basement rocks decrease from ca 100 to 85 ma over a paleodepth interval of 9 to 12 km interpreted to record uplift exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the keystone thrust system late jurassic slip on the wheeler pass thrust overlapped with deformation along the nw trending east sierran thrust system early hinterland crustal thickening and growth of the sierra magmatic arc and may have been correlative with early deformation in the central nevada thrust belt slip on the wheeler pass thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the sevier belt probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

airborne i doas measurements at mt etna bro and oclo evolution in the plume abstract spatial distributions of bromine monoxide bro chlorine dioxide oclo and sulfur dioxide so 2 were determined in the volcanic emissions of mt etna on 8th and 9th of july 2011 by airborne imaging differential optical absorption spectroscopy ai doas slant column densities scds in units of molec cm 2 of up to 4 2 10 14 for bro 1 5 10 14 for oclo and 4 6 10 18 for so 2 were detected assuming so 2 to be a stable tracer to overcome dilution effects measurements of bro so 2 and oclo so 2 ratios from distances of 1 19 km to the summit crater region were used to investigate the evolution of bro and oclo within corresponding plume ages of 2 34 min along the centerline of the plume relatively constant bro so 2 ratios of 1 4 10 4 and 2 0 10 4 were detected on 8th and 9th of july 2011 respectively furthermore the bro so 2 ratio was investigated along several cross sections of the volcanic plume on both days significant increases by a factor of 2 3 in the bro so 2 ratio from the center to the edge of the plume were seen from simultaneous measurements of bro and oclo the mixing ratios of clo could be inferred to range from about 80 to 300 ppt in addition decreases in the bro so 2 ratio with time could be observed by measurements three to four hours before the culmination of a paroxysm at mt etna on 9th july 2011

petrochemistry of granitic rocks in the mount barcroft area implications for arc evolution central white mountains easternmost california the north northwest trending white inyo range locally defines the western edge of the great basin the northeast trending barcroft structural break lies astride the province boundary along this preintrusive high angle reverse fault middle mesozoic white mountain peak alkaline volcanic and intercalated volcaniclastic rocks on the north are separated from uppermost proterozoic lower cambrian miogeoclinal quartzite and carbonate strata on the south by the 165 1 ma shrimp rg sensitive high resolution ion microprobe reverse geometry u pb zircon barcroft pluton although locally faulted the subparallel southeast and northwest borders of the body display intrusive contacts finer grained comagmatic metadiorite occurs as early stage dikes in the wall rocks eastward the 100 ma mcafee creek granite intrudes the barcroft pluton tertiary diabase dikes crosscut the section the two granitic series reflecting local evolution of the mesozoic arc system are described in this paper 1 mafic granitoid rocks of the calc alkaline barcroft series including chemically intergradational granodiorite gabbro diorite metadiorite and rare alaskite aplite all rich in large ion lithophile elements liles and depleted in high field strength elements hfses and 2 granite of the felsic mcafee creek series which has even greater enrichment of liles and greater depletion in hfses than the barcroft pluton rocks rich in hornblende clinopyroxene and belonging to the ca rich metaluminous barcroft series exhibit a broad range of chemical and mineral compositions and represent products of both mixing between high and low silica members of the series to generate intermediate compositions and fractional crystallization to generate the most mafic cumulate rocks the younger more homogeneous k rich mcafee creek type muscovite granite possesses mildly peraluminous minimum melt compositions field evidence for magma mixing and isotopic data for the barcroft series e nd t 1 53 to 5 50 87 sr 86 sr i 0 7053 0 7063 and the mcafee creek granite e nd t 5 64 to 9 76 87 sr 86 sr i 0 7062 0 7116 require open system processes and involvement of preexisting crustal rocks in their genesis the barcroft series is one of several shallow level magma systems now recognized in the sierran arc that include significant amounts of reworked preexisting crustal material these magma series are distinct from those that represent demonstrably deeper levels of mesozoic magma systems and lack isotopic evidence for significant involvement of older crust despite these differences in magma sources and evolution both magma series evolved along indistinguishable petrologic and chemical trends igneous rocks in the white mountains record post paleozoic growth of this part of the californian margin 1 jurassic and younger subduction partial fusion of the overlying mantle wedge and or deep seated mafic crust ascent of mildly alkaline and later calc alkaline magmas attending andean style volcanic plutonic arc production with significant involvement of preexisting crustal rocks 2 late cretaceous thickening heating and crustal contamination followed by rise of peraluminous granite minimum melts and 3 neogene basin and range lithospheric transtension tapping of upper mantle diabasic melt and dike emplacement

degassing of halogens from basaltic volcanism insights from volcanic gas observations abstract the currently available data set of s cl f abundances in volcanic gas plumes and high temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints on the modes of halogen degassing from mafic silicate melts apart from large volcano to volcano variations reflecting remarkable differences in volatile abundances in the source magmas each of the explored volcanoes displays large changes of so2 hcl and so2 hf ratios with the style of volcanic activity with hcl hf staying fairly constant halogen abundances are low and so2 hcl and so2 hf are high when fresh volatile rich magmas sustain degassing as during explosive eruptions at the onset of eruptive cycles or shortly before paroxysmal events low so2 hcl and so2 hf ratios are instead characteristic of late stages of volcanic degassing typically being observed in the concluding stages of basaltic eruptions or during periods of reduced magma supply at persistently degassing volcanoes these observations are taken as evidence of halogens being less keen to enter the gas phase relative to s during degassing of basaltic magmas and quantitatively interpreted in light of a rayleigh type open system degassing model the model though simple quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide and allows prediction of vapour melt partitioning contrasts of factors 9 and 36 for the volatile couples s cl and s f respectively these predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of p t x conditions

a total volatile inventory for masaya volcano nicaragua nerc project magma dynamics at persistently degassing basaltic volcanoes a novel approach to linking volcanic gases and magmatic volatiles within a physical model ne f004222 1 and ne f005342 1

sweet chestnut castanea sativa leaves as a bio indicator of volcanic gas aerosol and ash deposition onto the flanks of mt etna in 2005 2007 sweet chestnut leaves castanea sativa collected from the flanks of mt etna volcano in 2005 2007 were analysed by inductively coupled plasma mass spectrometry to investigate the spatial and temporal variability of element concentrations the aim of this work was to determine whether these leaves are a bio indicator for volcanic gas aerosol and ash deposition and to gain new insights into the environmental effects of quiescent and eruptive volcanic plumes results show a positive correlation between sample variability in the concentration of elements in castanea sativa and enrichment factors of elements in the plume the spatial and temporal variability of chalcophilic elements as cd cu mo tl zn is consistent with prevailing winds transporting eruptive plumes to the south east of the summit resulting in enhanced plume deposition onto the flanks of the volcano similar spatial and temporal variability was found for the halide forming elements cs k rb and intermediate elements al co mn the spatial variability of chalcophilic intermediate and halide forming elements during quiescent periods was diminished relative to eruptive periods and could not be explained by plume deposition in contrast the concentrations of lithophilic elements ba ca mg sr did not show any clear spatial variability even during eruptive periods comparisons between enrichment factors for elements in castanea sativa and literature values for enrichment factors of the volcanic plume groundwater and lichen were made whilst castanea sativa offers insights into the spatial and temporal variability of deposition the species may not be a bio indicator for plume composition due to biological fractionation

volcanic plume monitoring at mount etna by diffusive passive sampling 1 this paper reports the use of diffusive tubes in determining hf hcl and so2 in the volcanic plume of mount etna in an attempt to highlight the potential of this method in studying volcanoes in a first application a network of 18 diffusive tubes was installed on etna s flanks aimed at evaluating the atmospheric dispersion of the volcanic plume on a local scale results showed a monotonic decrease in volatile air concentrations with distance from the craters hf from 0 15 to 0 003 mol m 3 hcl from 2 to 0 01 mol m 3 and so2 from 11 to 0 04 mol m 3 revealing the prevalently volcanic contribution matching of so2 hcl and hcl hf volatile ratios with contemporaneous measurements at the summit craters validated the use of diffusive tubes in tracing the chemical features of a volcanic plume from remote locations a first tentative assessment of dry deposition rates of volcanogenic acidic gases was also made yielding 2 5 74 t d 1 so2 0 6 17 t d 1 hcl and 0 02 0 6 t d 1 hf and revealing the potential environmental impact of gas emissions in a second experiment carried out during the recent october 2002 to february 2003 eruption of etna diffusive tubes provided a continuous record of the chemical composition of the eruptive plume from a safe distance of 1 km from the vents thus considerably decreasing the risks involved in sampling this highlighted a clear time decrease in so2 concentrations and so2 hcl ratios which was interpreted as due to progressive exhaustion of volatile degassing and eruption energy

comparison of analogue model and field station em responses on southern vancouver island abstract measurements of geomagnetic induction responses for a laboratory analogue model that includes a simulation of the subducting juan de fuca plate are compared with those obtained at three sites on vancouver island good agreement between model and field responses at the central vancouver island site is observed over the period range 3 60 min while at the east and west coastal sites good agreement is achieved only for periods greater than 20 min at shorter periods departures of the observed responses from those of the model are possibly the result of upper crust inhomogeneities not replicated in the simulation and the complex strait with its numerous small islands and its irregular coastlines inadequately simulated in the course model nevertheless the analogue model results are consistent with the premise of a juan de fuca plate underlain by the conductive asthenosphere subducting at a shallow depth beneath vancouver island