epithermal mineralization and ore controls of the shasta au ag deposit toodoggone district british columbia canada the shasta gold silver deposit british columbia canada is an adularia sericite type epithermal deposit in which deposition of precious metals coincided with the transition of quartz to calcite dominant gangue mineralization is associated with stockwork breccia zones in potassically altered dacitic lapilli tuffs and flows and consists of pyrite sphalerite chalcopyrite galena acanthite electrum and native silver pre and post ore veins consist solely of quartz and calcite respectively fluid inclusion microthermometry indicates that ore minerals were deposited between 280 and 225 c from a relatively dilute hydrothermal fluid 1 5 wt nacl equivalent abundant vapor rich inclusions in ore stage calcite are consistent with boiling oxygen and hydrogen isotopic data 18ofluid 1 5 to 4 1 dfluid 148 to 171 suggest that the fluid had a meteoric origin but was 18o enriched by interaction with volcanic wallrocks initial 280 c fluid ph and log f o2 conditions are estimated at 5 3 to 6 0 and 32 5 to 33 bar respectively during ore deposition the fluid became more alkaline and oxidizing ore deposition at shasta is attributed to localization of meteoric hydrothermal fluids by extensional faults mineralization was controlled by boiling in response to hydraulic brecciation calcite and base metal sulfides precipitated due to the increase in ph that accompanied boiling and the associated decrease in h2s concentration led to precipitation of gold and silver

formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

tectono sedimentary characteristics of late miocene quaternary extensional basins of the northern apennines italy abstract extensional and compressional regimes exist at the same time in adjacent parts of the northern apennines italy and the former regime succeeded the latter at the same place as the thrust mountain front moved eastward since miocene times numerous extensional basins have developed west of the present mountain divide the westernmost ones formed over attenuated continental crust since late miocene and have been subjected to several subsidence and uplift events with rates of subsidence generally faster than rates of sedimentation they contain continental deposits overlain by gypsum bearing upper miocene marine sequences and siliciclastic marine pliocene deposits these basins were affected by shallow magmatism and are still experiencing high geothermal gradient and late to post magmatic activities such as in the renowned thermal region of larderello to the east closer to the present mountain divide the extensional basins formed later from pliocene to quaternary contain continental fluvial and lacustrine deposits and have not experienced near surface magmatic activities the sedimentary fill architecture of the apennine extensional basins is similar to that of other european american and african extensional or transtensional systems for instance a common characteristic is the prevalence of large alluvial fan deposits at the hanging wall shoulder of half grabens coarser smaller alluvial fans at the footwall shoulder and some fluvial deposits introduced longitudinally unlike the african rifts though the sedimentary facies distribution of extensional basins which developed in active orogenic zones such as in the apennines may be strongly affected by uplifting steep mountain slopes and can have large thick coarse alluvial fans also on the footwall side of the half grabens

products of subglacial volcanic eruptions under different ice thicknesses two examples from antarctica late cenozoic subglacially erupted volcanic sequences are scattered throughout the antarctic peninsula two of the best preserved examples at mount pinafore alexander island c 5 5 6 ma and brown bluff graham land c 1 ma are complete enough to be regarded as sequence holotypes for this uncommonly preserved eruptive depositional setting despite a common glacial association the sedimentary lithofacies in the two outcrops suggest flowing and ponded water conditions respectively indicating significant differences in the depositional palaeoenvironments the original ice thicknesses exerted a major control on the lithofacies which resulted from each eruptive phase at mount pinafore the lithofacies were confined within a steep sided valley during successive eruptions beneath thin 100 150 m wet based ice the much thicker succession at brown bluff is a tindar tuya edifice which formed within a small basin probably 15 km across confined by ice 400 m thick

ternary feldspar thermometry in granulites from the oaxacan complex mexico coexisting feldspars from across 2 000 km2 of the granulite facies oaxacan complex southern mexico exhibit variable amounts of solid solution from nearly binary ab an and ab or to substantially ternary ab an or reintegrated analyses of 21 coarsely exsolved perthite af plagioclase pl pairs yield af or30 63 ab30 56an2 15 and pl or1 2ab70 84an11 28 these data have been used to test existing two feldspar geothermometers for this extended composition range

geological structure of a long living geothermal system larderello italy we have examined the data of 600 geothermal wells and re interpreted approximately 500 km seismic profiles through the field of larderello italy we conclude that the two main seismic reflectors present below the geothermal area host two different fluids 1 superheated steam in the upper h horizon reached by drillholes and 2 supercritical fluid in the deeper k horizon reached by few unproductive or damaged wells the superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at larderello whereas the supercritical fluid represents a potential unconventional deep seated resource still to be assessed the high temperatures existing in correspondence of the k horizon suggest that the silica rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks unless occasional fluid overpressure and abrupt high strain rates occur

restricted rifting and its coexistence with compressional structures results from the crop 3 traverse northern apennines italy a geological interpretation of the deep seismic reflection line crop 3 italian program crosta profonda deep crust profile no 3 which crosscuts the northern apennines from the tyhrrenian to the adriatic coast is presented the profile images the lithosphere up to 15 s twt and highlights several peculiarities a the lower crust is bedded by discontinuous sub parallel reflective markers which terminate at 7 s beneath the western side of the profile b in the same area a notable reflection is recognizable at 10 s and is interpreted as the top of the asthenosphere c east plunging shear zones are recognizable throughout the crust by contrast the adriatic outer side of this line shows a reflections deepening westward from 13 to 15 s twt related to the base of the crust 33 38 km depth b the absence of thick bedding of reflective markers within the lower crust and c tectonic structures affecting the basement which are different from those which deform the cover of the northern apennines geological interpretation is based on the eastward migration of ductile shear zones which have been recognized on the seismic line the bending of the outer zone crust is considered to be a consequence of the rifting process with the application of pushing forces against the adriatic lithosphere which cannot escape toward east

crustal structures in the geothermal areas of southern tuscany italy insights from the crop 18 deep seismic reflection lines abstract two deep seismic reflection lines named crop 18a and 18b and roughly nnw sse oriented were acquired to investigate the crust between the larderello and the mt amiata geothermal areas both located in southern tuscany since the early middle miocene southern tuscany has been affected by extensional tectonics and since the pliocene by widespread magmatism presently extension is demonstrated by ne dipping normal faults and brittle shear zones which affect the crust down to the brittle ductile transition in the larderello area these shear zones are seismically evidenced by ne dipping weak reflections and by the loss of the k horizon reflectivity a regional mid crustal high amplitude reflector located at the top of the brittle ductile transition the crop 18a and 18b lines were reprocessed down to 10 s twt down to the crust mantle boundary their reflectivity results are closely related to the direction of the survey a clear decrease in reflectivity occurs when the survey plane intersects the crustal shear zones along strike nevertheless both lines display segments with low reflectivity and homogeneous acoustic impedance which indicate intrusive magmatic bodies at different crustal levels a wide partially crystallised granitoid may be sited at about 7 8 km depth underneath the larderello geothermal field in the lower part of the crust the crop 18a and 18b transects show group of bright reflections mainly related to the occurrence of pressurised fluids and or lithological differences the base of the crust is located at about 20 km depth

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

ridge forming ice bounded lava flows at mount rainier washington large 0 3 4 km3 andesite and dacite lava flows at mount rainier washington sit atop or are perched along the sides of high ridges separating deep valleys early researchers proposed that these ridge forming lavas flowed into paleovalleys and displaced rivers to their margins entrenchment of the rivers then left the lavas atop ridges on the basis of exceptional flow thickness ice contact features and eruption age measurements we propose that the lavas flowed beside and between valley glaciers that filled the adjacent valleys in the pleistocene when the glaciers retreated the flows were left high on the adjacent ridges these lavas were never situated at valley floors and do not represent products of reversed topography instead ridge forming and perched lava flows at mount rainier and at many other high stratovolcanoes illustrate the ability of ice to dam deflect and confine flowing lava

disruption of drift glacier and origin of floods during the 1989 1990 eruptions of redoubt volcano alaska abstract melting of snow and glacier ice during the 1989 1990 eruption of redoubt volcano caused winter flooding of the drift river drift glacier was beheaded when 113 to 121 10 6 m 3 of perennial snow and ice were mechanically entrained in hot rock avalanches and pyroclastic flows initiated by the four largest eruptions between 14 december 1989 and 14 march 1990 the disruption of drift glacier was dominated by mechanical disaggregation and entrainment of snow and glacier ice hot rock avalanches debris flows and pyroclastic flows incised deep canyons in the glacier ice thereby maintaining a large ice surface area available for scour by subsequent flows downvalley flow rheologies were transformed by the melting of snow and ice entrained along the upper and middle reaches of the glacier and by seasonal snowpack incorporated from the surface of the lower glacier and from the river valley the seasonal snowpack in the drift river valley contributed to lahars and floods a cumulative volume equivalent to about 35 10 6 m 3 of water which amounts to nearly 30 of the cumulative flow volume 22 km downstream from the volcano the absence of high water marks in depressions and of ice collapse features in the glacier indicated that no large quantities of meltwater that could potentially generate lahars were stored on or under the glacier the water that generated the lahars that swept drift river valley was produced from the proximal eruption induced volcaniclastic flows by melting of snow and ice

late miocene valley confined subglacial volcanism in northern alexander island antarctic peninsula isolated late miocene volcanogenic sequences in northern alexander island antarctic peninsula form an unusual cogenetic association of volcaniclastic sandy gravelly lithofacies including tillites and volcanic lava hyalocalstite lithofacies using simple lithofacies analysis and theoretical considerations of hydrodynamic effects of subglacial eruptions valley confined volcanic activity beneth thin wet based ice is suggested the alexander island successions are complete enough to be regarded as model sequences for this uncommonly recorded type of eruptive depositional activity the sedimentary lithofacies represent resedimented tuffs and meltout or flow tills which were probably deposited in subglacial ice tunnels eroded or enlarged by volcanically heated meltwater the volcanic lithofacies formed by the interaction of hot magma with the ice tunnel walls generating abundant meltwater and water saturatedsediments resulting in the formation of heterogeneous masses of lava and hyaloclastite there is no obvious sequence organisation in the sedimentary sections this is probably due to a complex interplay of eruption related and environmental hydrodynamic factors affecting the relative proportions of water and entrained sediment

subglacial and ice contact volcanism at the oraefajokull stratovolcano iceland eruptions of oraefajokull have produced mafic and silicic magmas and have taken place in both glacial and interglacial periods the geology of the volcano records the differing response of magmas of contrasting composition to interaction with ice of variable thickness and gives insight into the development of a long lived ice covered stratovolcano vatnafjall a ridge on the southeast flank of oraefajokull is the first area of the volcano to have been mapped in detail and the geological map is presented here alongside descriptions of each erupted unit the oldest units comprise pillow lavas hyaloclastite and jointed lava flows that were formed during subglacial basaltic eruptions involving abundant meltwater the products of a subsequent explosive initially phreatomagmatic subglacial rhyolite eruption were confined by ice to form a tephra pile over 200 m thick that was intruded by dense rhyolite magma towards the end of the eruption confinement by ice caused a later trachydacite lava flow to form buttresses and a steep pillar whilst some of the meltwater produced infiltrated the lava to generate red and black glassy breccias and cause localised steam explosions it is likely that much of it drained down the steep topography the most recently erupted units are subaerial basaltic lava flows the oldest of which were erupted during an interglacial period and have subsequently been partially eroded and scoured by advancing ice ice has been important in shaping the edifice by confining eruptive products to form constructional features and by later eroding parts of them to form deep valleys reconstructions of volcano ice interaction allowed the local thickness of the glacier at the time of each eruption to be estimated and demonstrates that the upper surface of the ice has varied in elevation by over 700 m

swift snowmelt and floods lahars caused by great pyroclastic surge at mount st helens volcano washington 18 may 1980 the initial explosions at mount st helens washington on the moring of 18 may 1980 developed into a huge pyroclastic surge that generated catastrophic floods off the east and west flanks of the volcano near source surge deposits on the east and west were lithic sorted lacking in accretionary lapilli and vesiculated ash not plastered against upright obstacles and hot enough to char wood all attributes of dry pyroclastic surge material deposited at the surge base on steep slopes near the volcano transformed into high concentration lithic pyroclastic flows whose deposits contain charred wood and other features indicating that these flows were hot and dry stratigraphy shows that even the tail of the surge had passed the east and west volcano flanks before the geomorphically distinct floods lahars arrived this field evidence undermines hypotheses that the turbulent surge was itself wet and that its heavy components segregated out to transform directly into lahars nor is there evidence that meters thick snow slab avalanches intimately mixed with the surge to form the floods the floods must have instead originated by swift snowmelt at the base of a hot and relatively dry turbulent surge impacting hot pyroclasts probably transferred downslope momentum to the snow surface and churned snow grains into the surge base melting snow and accumulating hot surge debris may have moved initially as thousands of small thin slushflows as these flows removed the surface snow and pyroclasts newly uncovered snow was partly melted by the turbulent surge base this and accumulating hot surge debris in turn began flowing a self sustaining process feeding the initial flows the flows thus grew swiftly over tens of seconds and united downslope into great slushy ejecta laden sheetfloods gravity accelerated the floods to more than 100 km h as they swept down and off the volcano flanks while the snow component melted to form great debris rich floods lahars channeled into valleys

quantification of extraterrestrial lava flow effusion rates through laboratory simulations we have used carefully controlled laboratory simulations to develop a model which relates lava flow morphology to effusion rate and rheology through comparisons with measured and estimated eruption rates on earth this approach allows us to constrain eruptive styles and compositions of extraterrestrial lava flows by applying this model to lava flows on the moon mars and venus we have determined that all the common flow morphologies domes folds and levees on these planets could have been produced by basalt like or andesite like lavas through either continuous or episodic emplacement the presence of more evolved magma compositions on other planets is not required to explain any of the observed lava flow morphologies

geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy abstract serri g innocenti f and manetti p 1993 geochemical and petrological evidence of the subduction of delaminated adriatic continental lithosphere in the genesis of the neogene quaternary magmatism of central italy in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 117 147 the neogene quaternary magmatism of the northern apenninic arc took place in four phases separated in space and time which become progressively younger from west to east phase i 14 ma phase ii 7 3 6 0 ma phase iii 5 1 2 2 ma phase iv 1 3 0 1 ma this magmatism is the result of the activation of three physically separate sources 1 the adriatic continental crust extracted from the mantle in the late proterozoic 2 a strongly refractory recently k enriched harzburgitic mantle located in the mechanical boundary layer mbl of the lithosphere and 3 a recently metasomatized cpx rich mantle compositionally variable from iherzolite to wehrlite clinopyroxenite interpreted as an ephemerally k enriched asthenosphere the adriatic continental crust is the dominant source of the acid plutonic and volcanic rocks of the tuscan region the acid magmatism is mostly found inside an ellipsoidal area about 150 300 km centred on giglio island here defined as the tuscan crustal dome within this area mantle derived magmas unaffected by important crustal contamination processes and mixing with crustal anatectic melts have so far not been found pure crustal magmas are rare but are represented for example by some of the san vincenzo and roccastrada rhyolites virtually all the tuscan acid centres show evidence of mixing with potassic mantle derived magmas major and trace elements as well as 87 sr 86 sr and 143 nd 144 nd data on primitive rocks mg 65 reveal two groups of mantle derived magmas these define two distinct mantle enrichment trends both essentially due to the additions of k rich components which metasomatized separate compositionally diverse upper mantle sectors in both cases the most remarkable mineralogical effect of these enrichment processes is the production of variable amount of phlogopite through reaction between fluids and or melts with the mantle the rocks of group i ol hy and q normative lamproites ultrapotassic high mg latites ultrapotassic shoshonites and shoshonites saturated trend are considered to be derived by partial melting at low pressure 87 sr 86 sr 0 717 ce sr 0 3 and k 2 o na 2 o 6 7 and low ratios of 143 nd 144 nd 0 5121 0 5120 and ba la 87 sr 86 sr 0 712 and k 2 o na 2 o 8 9 values and low 143 nd 144 nd ba la 0 10 ratios these constraints do not allow to exclude a complete identity between the k rich components which metasomatized the mantle sources of the saturated and undersaturated trend magmas the geochemical and isotopic features of the components that metasomatized the mantle sources of the northern apenninic arc magmatism can be explained by a geodynamic process which causes a large amount of crustal materials to be incorporated within the upper mantle we propose that the delamination and subduction of the adriatic continental lithosphere related to the still ongoing northern apennine continental collision provide a viable mechanism to explain the genesis and eastward discontinuous migration of the magmatism in central italy the subduction of delaminated lithospheric mantle with lower crustal slivers would have exposed uppermost mantle adriatic mbl and crustal units previously imbricated in the apennine chain to the heating advected by the upwelling of a recently and ephemerally k enriched asthenospheric mantle wedge and by the underplating of magmas derived from it we consider that the diapiric uprising of a hot crustally contaminated asthenosphere occurs in the wake left above the sinking of the adriatic delaminated subducting continental lithosphere the delamination subduction process of the adriatic lithosphere has probably started in the early middle miocene but earlier than 15 14 ma ago as indicated by the age and petrologic characteristics of the first magmatic episode sisco lamproite of the northern apennine orogenesis

crustal models of the geothermal areas of southern tuscany italy abstract geological and geophysical data gathered in the geothermal areas of southern tuscany located in the inner part of the northern apennines indicate the presence of granite intrusions the most relevant data are 1 regional asthenospheric ascent to a depth of 40 50 km 2 granitic dykes as old as 3 8 2 9 ma and a widespread contact aureole found in several deep geothermal wells 3 very high heat flow values interpreted as the result of convective circulation of hot fluids above shallow magmatic bodies 4 the presence of low density bodies inferred from low gravity values often correlated with positive heat flow anomalies 5 the occurrence of a highly reflective horizon named k in a depth range of 3 12 km in the geothermal areas as shown by seismic reflection data 6 a 30 40 km wide low velocity body below the k horizon whose existence is supported by local earthquake tomography and teleseismic studies 7 the presence of a conductive body which correlates well with the anomalous tomographic and teleseismic body as revealed by magnetotelluric surveys the goal of the paper is to test different alternative crustal models by using these data the models are 1 granite intrusion 2 geopressurized fluids below impervious layers 3 contact metamorphic aureole 4 mylonite layers at the upper lower crust transition and 5 some combination of the four the occurrence of shallow intrusive bodies still partially molten and associated with saline brines is considered the most tenable model

geology fluid inclusions and geochemistry of the zhazixi sb w deposit hunan south china abstract the zhazixi sb w deposit in the xuefeng uplift south china exhibits a unique metal association of w and sb where the w orebodies are hosted by interlayer fractures and the sb orebodies are contained within nw trending faults this study proposes that the w and sb mineralization took place in two separate periods the mineral paragenesis of the w mineralization reveals a mass of quartz scheelite and minor calcite the mineral assemblage of the sb mineralization developed after w mineralization and consists of predominantly quartz and stibnite and small amounts of native sb berthierite chalcostibnite pyrite and chalcopyrite fluid inclusions in quartz and coexisting scheelite are dominated by two phase liquid rich aqueous inclusions at room temperature microthermometric studies suggest that ore forming fluids for w mineralization are characterized by moderate temperatures 170 270 c low salinity 3 7 wt nacl equiv low density 0 75 0 95 g cm 3 and moderate to high pressure 57 2 99 7 mpa and these fluids experienced a cooling and dilution evolution during w mineralization ore forming fluids for sb mineralization are epithermal types with low temperatures 150 230 c low salinity 4 6 wt nacl equiv moderate density 0 82 0 94 g cm 3 and high pressure 42 2 122 5 mpa and these fluids display an evident decline in homogenization temperature during sb mineralization laser raman analyses of the vapor phase indicate that the ore forming fluids for both w and sb mineralization contain a small amount of co 2 the ore forming fluids for sb mineralization are identified as predominantly originating from the continental crust as suggested by the low 3 he values 0 009 10 12 cc stp g and 3 he 4 he ratios 0 002 0 056 ra as well as high 36 ar values 1 93 10 9 cc stp g and 40 ar 36 ar ratios 909 5 2279 7 the source of s is identified to be the neoproterozoic wuqiangxi formation as traced by the 34 s v cdt values of stibnite 3 1 9 4 the 208 pb 204 pb 37 643 40 222 207 pb 204 pb 15 456 15 681 and 206 pb 204 pb 17 093 20 042 ratios suggest a mixture of lower crustal and supracrustal pb sources it is thus concluded that the ore genesis of the zhazixi sb w deposit is related to the intracontinental orogeny during the early mesozoic fluid mixing is considered to be the critical mechanism involved in w mineralization whereas a fluid cooling process is responsible for sb mineralization furthermore the absence of au is attributed to the low a s content in sb mineralizing fluids

multiple hydro fracturing by boron rich fluids in the late miocene contact aureole of eastern elba island tuscany italy in eastern elba island tuscany italy a shallow crustal level felsic tourmaline bearing dyke sill swarm of late miocene age is associated with abundant tourmaline quartz hydrothermal veins and metasomatic masses development of these veins and masses in the host rocks demonstrates multiple hydro fracturing by magmatic boron rich saline fluid tourmalines in felsic dykes are schorl whereas in veins and metasomatic masses tourmaline composition ranges from schorl dravite through dravite to uvite this compositional shift is evidence for an increasing contribution to the magmatic boron rich fluids by a mg ca ti rich external component represented by biotite rich and amphibolite host rocks this system can be envisaged as an exposed proxy of the high temperature hydrothermal system presently active in the deepest part of the larderello travale geothermal field tuscany

volcanic mixed avalanches a distinct eruption triggered mass flow process at snow clad volcanoes a generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at mount st helens nevado del ruiz and redoubt volcano between 1982 and 1989 these mixed avalanches traveled as far as 14 km at velocities up to 27 m s involved as much as 10 7 m 3 of rock and ice and left unmelted deposits of single flow units as thick as 5 m during flow downslope heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures apparently giving these mixed avalanches mobilities equal to or greater than those of dry debris avalanches of similar volume the avalanches studied for this report began as snow avalanches triggered during explosive phases of the eruptions by ballistic bombardment of snow slopes by hot pyroclastic debris erosion by the avalanches incorporated additional snow fragments of glacier ice and other rock debris mixed avalanche deposits were massive very poorly sorted and ungraded to inversely graded prior to melting although rock debris composed as much as 70 wt of the frozen samples the bulk volumetric content of rock debris was only 9 to 36 snow and ice composed between 36 and 72 of the frozen samples with void space making up the remainder of the volume deformation and consolidation after melting of the ice content reduced the deposits to loose porous layers that were only a fraction of their original thickness and that later gave little hint of their origin after melting and desiccation the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record

enhanced co2 mineral sequestration by cyclic hydraulic fracturing and si rich fluid infiltration into serpentinites at malentrata tuscany italy abstract the magnesite deposits of malentrata tuscany italy were derived from serpentinite silicification carbonation of the ligurian ophiolite and represent a natural analogue of in situ co 2 mineral sequestration carbonation of magnesium silicate minerals e g serpentine olivine at temperatures below 200 c is an exothermal process involving incorporation of carbon dioxide into stable carbonates e g magnesite dolomite serpentinites at malentrata were transformed to a brownish friable rock characterized by the occurrence of opal chromian montmorillonite fe rich magnesite and minor iron sulfides and oxides widespread lenses of cohesive rocks occur within the altered serpentines resulting from the complete silicification of the protolith the pervasive alteration of serpentinite was accompanied by the formation of a network of magnesite and dolomite veinlets and large magnesite dolomite veins along major structures field observations petrography and mineral chemistry define the following crystallization sequence in the major veins i early microgranular fe poor magnesite ii comb textured fe rich magnesite and dolomite cementing the early brecciated magnesite vein infill and iii late quartz chalcedony and rare opal in the cavities the mineral assemblage observed both in veins and in host rock is indicative of low temperature hydrothermal alteration driven by si and co 2 rich fluids under relatively low ph conditions pervasive and cyclic hydraulic fracturing maintained a high structural permeability during the whole hydrothermal event creating conduits for the input and output fluids the concomitant presence of co 2 and silica in the fluid enhanced the congruent dissolution of serpentine and hampered immediate carbonate deposition the mg bearing solutions were focused out of the reactor zone and promoted massive carbonate veining along the main structural discontinuities this two steps reaction dissolution of serpentinite followed by carbonate precipitation outside the reacting volume seems to be very efficient and provide new insights on in situ and ex situ induced mineral carbonation and its industrial applications

solidifying bingham extrusions a model for the growth of silicic lava domes in a previous study of the effects of cooling and solidification on flows issuing onto a horizontal plane and spreading under gravity we considered the case of a viscous fluid that solidifies to form a thin surface crust with a finite yield strength in that case the coupling of solidification and viscous stresses in the flow led to a sequence of flow regimes or styles of flow and crustal deformation here we study the spreading from a small source of a plastic material having a yield strength before cooling in this case the fluid again begins to freeze as it spreads radially under gravity and forms a dome having a surface crust which is stronger than the extruded fluid if cooling is sufficiently rapid compared to gravity driven spreading the flow is found to be controlled by solidification the flow again takes on one of a number of flow regimes depending on the pace of solidification relative to the rate of lateral flow or extrusion rate however these flow regimes are quite different from those for the viscous extrusions implying that the internal yield stress has a strong influence on the behaviour styles of flow ranged from inflation of an axisymmetric dome to irregular extrusion of lateral lobes and vertical spines these qualitatively different regimes have much in common with the eruption styles of volcanic lava domes produced by effusion of extremely viscous silicic magmas which may possess a yield strength and the model provides information about the factors influencing the morphology and hazards of such volcanic flows

thermo mechanical model for incremental fracturing in cooling lava flows abstract this study presents an idealized quantitative model of stress development and incremental fracturing in cooling lavas it appears that columnar jointing forms in lavas by a process of incremental fracturing driven by thermal stresses the fractures progress inward from the cooling surfaces as time increases the cooling of a horizontal layer of lava has been modeled analytically for three cooling regimes conductive cooling with liquid magma present conductive cooling after total solidification and hydrothermal cooling horizontal thermal stresses develop and cause vertical fractures at the upper and lower surfaces of the lava as the lava cools layer after layer becomes elastic thermal stresses develop in these thin layers between previously fractured lava where it is assumed stresses have been released and the hot interior lava where temperatures exceed the elastic temperature limit stresses are analyzed by treating each unfractured elastic layer as a slab restrained in bending unrestrained from contraction the stress level at which incremental fracturing occurs extending previous fractures and the effect of stress and temperature conditions on fracture penetration are discussed our analysis yields values for the length of incremental fracture as a function of time and material strength for both a thin lava flow cooling conductively incremental fracture lengths increase with time and for a thicker lava flow in which hydrothermal convection is important incremental fracture lengths are constant with time our results are compared to observed striae widths measured from the base of basaltic lava columns striae represent successive incremental fractures the comparison shows agreement in magnitude and trend after some amount of cooling i e striae and incremental fracture lengths increase with time at an accelerating rate

subglacial volcanics on the control of magma chemistry on pillow dimensions abstract axial dimensions glass thicknesses and plunges of 822 icelandic pillows of olivine tholeiitic to andesitic compositions are presented the pillows formed during subglacial volcanic eruptions at water depths of a few hundred meters their average diameters are olivine tholeiite 40 cm tholeiite and basaltic andesite 15 cm and andesite 30 cm the olivine tholeiite pillows have highly vesicular glass rims and vesicular interiors whereas the tholeiite and basaltic andesite pillows are characterized by very low vesicularity throughout the andesite pillows have nonvesicular glass margins but commonly highly vesicular interiors the glass rims thicken linearly with increasing diameter both for the olivine tholeiite and the andesite pillows although the increment is much faster for the latter the small average diameter pillows of tholeiite and basaltic andesite are characterized by highly abundant and evenly dispersed euhedral grains of magnetite during formation the olivine tholeiite pillows can apparently expand relatively freely prior to the crust attaining sufficient strength to prevent further growth the non vesicular and relatively thick crust of tholeiite basaltic andesite and andesite pillows apparently obtains strength quickly to prevent further growth

transtensional shear zones controlling volcanic eruptions the middle pleistocene mt amiata volcano inner northern apennines italy terra nova 00 1 10 2010 abstract the mt amiata volcano is characterized by the sw ne alignment of the eruption centres as well as other italian pleistocene volcanoes we carried out a structural and kinematic analysis in a broad stripe comprehending the eruption centres and the substratum towards ne and sw the results point out that a transtensional left lateral brittle shear zone affects the pre neogene substratum the middle pleistocene volcanic rocks and the late pleistocene travertines this transtensional structure is active since the early pliocene it controlled the location of the eruption centres through pull apart structures thus providing the deep structural channels for the uprising of magma to the surface the mt amiata volcano represents a key study area to investigate the pleistocene to present relationships between tectonics and magmatism in the tyrrhenian area

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

epithermal precious metal deposits of italy an overview epithermal precious metal deposits have only quite recently been added to the metallogenic view of italy it was only in the late 1980s that two districts were recognized in sardinia and southern tuscany previously long known for a large variety of other commodities the sardinian epithermal precious metal district is associated with the oligocene miocene sardinian calc alkaline magmatic cycle the most relevant areas include the au deposit at furtei already in production and the osilo prospect where extensive exploration is under way the deposit at furtei contains at least six tonnes of gold metal the mineralogy of the deposit and of the alteration assemblages is typical of the acid sulfate high sulfidation class of volcanic hosted epithermal deposits fluids associated with alteration and mineralization have moderate temperatures 200 300 c and low salinities less than 6 wt nacl equivalent high temperature high salinity fluids similar to porphyry style systems also circulated at furtei at osilo a number of quartz veins containing up to several ppm au have been identified the alteration assemblage includes adularia and illite i e is typical of low sulfidation deposits fluid inclusion homogenization temperatures range from 198 to 270 c with salinities of less than 4 wt nacl equivalent

use of joint growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows abstract thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken lava flows are thus divided by vertical joints that by changes in joint spacing and form define horizontal intraflow layers known as tiers entablatures are tiers with joint spacings less than about 40 cm whereas colonnades have larger joint spacings we use structural and petrographic methods to infer heat transfer processes and to constrain environmental conditions that produce these contrasting tiers joint surface morphology indicates overall joint growth direction and thus identifies the level in a flow where the upper and lower crusts met rock texture provides information on relative cooling rates in the tiers of a flow lava flows without entablature have textures that develop by relatively slow cooling and two joint sets that usually meet near their middles which indicate mostly conductive cooling entablature bearing flows have two main joint sets that meet well below their middles and textures that indicate fast cooling of entablatures and slow cooling of colonnades entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades solidification times of entablature bearing flows constrained by lower joint set thicknesses are much less than those predicted by a purely conductive cooling model these results are best explained by a cooling model based on conductive heat transfer near a flow base and water steam convection in the upper part of an entablature bearing flow calculated solidification rates in the upper parts of such flows exceed that of the upper crust of kilauea iki lava lake where water steam convection is documented use of the solidification rates in an available model of water steam convection yields permeability values that agree with measured values for fractured crystalline rock we conclude therefore that an entablature forms when part of a flow cools very rapidly by water steam convection flooding of the flow top by surface drainage most likely induces the convection colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water

sb hg ore deposit distribution controlled by brittle structures the case of the selvena mining district monte amiata tuscany italy abstract this paper deals with the tectonic control on the hydrothermal system that gave rise to sb hg ore deposits in the monte amiata area that was one of the most relevant mining district for the exploitation of mercury in italy the study area selvena mining district is located in southern tuscany inner northern apennines one of the most important mineralized area in the western mediterranean region southern tuscany was severely affected by middle late miocene low angle normal faults later dissected by pliocene pleistocene faults coeval magmatism late miocene pleistocene and hydrothermal activity pliocene present the selvena mining district is located south of middle pleistocene monte amiata volcanic complex our structural and kinematic study is based on the integration among fieldwork borehole and mine data the results highlight two pleistocene holocene left lateral transtensional shear zones linked by normal faults defining a coeval pull apart structure here the sb hg mineralization transported by meteoric hydrothermal fluids mainly is particularly diffuse and concentrated in the cataclasites and in damage zones of the normal faults furthermore a widespread mineralization also occurs in the cataclasites of miocene low angle normal faults mine evidence suggests that ore bearing fluids percolated through structural conduits located along the fault planes and resulting parallel to the intermediate stress axis geological structures and ore deposit distribution are related to a single hydrothermal circuit with meteoric water channelled to depth through conduits parallel to the intermediate stress axis of the transcurrent shear zones then hydrothermal fluids mainly ascended through the almost vertical deformation zones located at the intersection between normal and strike slip faults thus hydrothermal fluids permeated also the middle late miocene cataclasites this study shed light on the relationships between geological structures and mineralization in southern tuscany and underlines the importance to investigate mine areas to understand hydrothermal fluids path

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

experimental simulation of basalt columns abstract basalt columns can be simulated by the desiccation of mixtures of starch and water this note presents photos of starch columns from laboratory experiments and summarizes results of an extended study muller g 1998 starch columns analog model for basalt columns j geophys res 103 15239 15253 basalt cooling and starch desiccation are diffusion processes causing contraction and cracks column related crack patterns in basalt and starch are largely similar differences in their spatial and time scales are due to the difference in the diffusion constants which is about two orders of magnitude starch experiments give a few new insights into basalt column formation

starch columns analog model for basalt columns desiccation of starch water mixtures produces tensile crack patterns which appear to be interesting but largely unknown study objects for fracture mechanics structural geology and volcanology this paper concentrates on columnar jointing and on columns in starch starch columns have polygonal cross sections and are very similar to basalt columns they are produced by lamp drying starch specimens with dimensions of several centimeters and have diameters in the millimeter range the columns develop behind a crack front which propagates from the surface into the interior the experiments supported by x ray tomograms show that polygonal regularity of the crack pattern is not present at the surface but develops during penetration this transition is steered by a minimum fracture energy principle the analogy between basalt cooling and starch desiccation is far reaching water concentration in starch is analogous to temperature in basalt both quantities obey diffusion equations water loss is equivalent to heat loss the resulting contraction stresses have similar dependences on depth and time and in both cases the material strength is exceeded the starch experiments show that column diameters are controlled by the depth gradient of water concentration at the crack front high low gradients are connected with thin thick columns by analogy a similar relation with the temperature gradient exists for basalt columns the normalized starch gradients are about 3 orders of magnitude larger than the normalized gradients in basalt this explains why starch columns are much thinner than basalt columns the gradients are so different because the crack front speeds differ by a factor of about 10 after 3 days the speed is about 10 mm d in starch but about 100 mm d in basalt peck 1978 the speed difference in turn results from the difference of the diffusion constants the hydraulic diffusivity of starch is 2 orders of magnitude lower than the thermal diffusivity of basalt

geochemistry and geochronology of the banxi sb deposit implications for fluid origin and the evolution of sb mineralization in central western hunan south china abstract central western hunan in south china hosts the largest antimony belt in the world with two types of sb deposits identified sb au woxi type and sb only xikuangshan type banxi is the most representative deposit in the region with vein type sb mineralization hosted in neoproterozoic clastic rocks stibnite developing in ores and arsenopyrite mainly occurring in altered country rocks trace element contents including rare earth elements ree and isotopic ratios s pb sr nd he and ar in stibnite and or arsenopyrite were analyzed to determine the timing of ore formation and to elucidate fluid origin and evolution processes most sulfides have high ree contents 45 103 ppm moderate fractionation between lree and hree lree hree 6 38 11 56 and slightly negative eu anomalies eu eu 0 53 0 72 the 34 s values are 3 88 5 81 for stibnite and 9 25 11 82 for arsenopyrite the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios range from 18 617 to 18 635 15 695 to 15 739 and 38 965 to 38 981 for stibnite and from 18 594 to 18 609 from 15 587 to 15 698 and from 38 893 to 38 926 for arsenopyrite the 87 rb 86 sr and 87 sr 86 sr ratios are 0 3016 3 538 and 0 711463 0 717591 respectively for stibnite and 0 2251 2 214 and 0 711244 0 711565 respectively for arsenopyrite the 147 sm 144 nd and 143 nd 144 nd ratios are 0 1174 0 9816 and 0 511942 0 512768 for stibnite with end t values t 130 ma ranging from 12 4 to 6 6 and two stage model ages t 2dm ranging from 1457 to 1932 ma the 40 ar 36 ar and r ra ratios where ra is the atmospheric 3 he 4 he ratio of 1 4 10 6 are 409 545 and 0 0088 0 0348 respectively for stibnite the rb sr and sm nd isotopic analyses of the sulfides yield isochron ages of 129 4 2 4 ma 2 mswd 1 3 and 130 4 1 9 ma 2 mswd 1 6 respectively the combined trace element and isotopic data set indicates that the ore forming fluids were a mixture of dominantly deep basement derived solute rich parent water and a small amount of dilute heated meteoric water the decreases in ree 34 s 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb 87 rb 86 sr 87 sr 86 sr 147 sm 144 nd and 143 nd 144 nd and increases in 40 ar 36 ar and 4 he contents in the stibnite from the earlier quartz stibnite mineralization stage stage ii through to the later stibnite mineralization stage stage iii indicate that the influx of meteoric water increased during sb mineralization the deep sourced relatively high temperature rock reacted fluid mixed with increasing amounts of more oxidized low temperature meteoric fluids causing the precipitation of arsenopyrite and stibnite sequentially at the banxi deposit a two period genetic model has been proposed for the world class sb mineralization in the central western hunan region the woxi type sb au deposits were derived from orogenic fluids generated from folding and shearing during the caledonian and indosinian orogeny whereas the xikuangshan type sb deposits were formed by mixing heated basement derived hydrothermal fluid circulating during the flare up of magmatism in south china with lower temperature meteoric water

conductive cooling of lava columnar joint diameter and stria width as functions of cooling rate and thermal gradient abstract much evidence exists that column diameter and stria width of columnar joints in lava flows vary inversely with cooling rate t t and thermal gradient t x at the point of fracture as the flow cools some evidence suggests that lava flows cool conductively a conductive cooling model yields cooling rate and thermal gradient through space and time for cooling igneous bodies both for extrusive and intrusive settings thermal gradient and cooling rate are then linked to stria width and column diameter with faster cooling leading to narrower columns and steeper gradients to narrower striae this model shows large regions within a body where the ratio of thermal gradient to cooling rate is nearly constant and predicts that the ratio of stria width to column diameter is also nearly constant this prediction is consistent with field observations both in this and other works the model also suggests that if conductive cooling dominates then joint spacing i e column diameter should increase inward from the margins of the body as should stria width

the crustal structure of the northern apennines central italy an insight by the crop03 seismic line in this paper the crop03 deep seismic reflection profile in the northern apennines is described and re considered in light of new geophysical data and interpretations made available in the last five years particularly from heat flow measurements aeromagnetics tomography active stress determination and passive seismology the crustal structure of the northern apennines is shown to be composed of two distinct domains to the west is the tyrrhenian domain and to the east is the adriatic domain these domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels in the tyrrhenian domain the upper oligocene lower miocene compressive structures are no longer recognizable because they are dissected by subsequent extensional tectonic features the seismic profile highlights the strong asymmetry of extensional deformation and the upper crust is affected by a set of six major east dipping low angle normal faults in the adriatic domain compressive tectonics have acted since the middle miocene and the pattern of shallow contractional structures is well preserved the geological interpretation of the seismic data supports a thick skinned style of deformation where the basement is involved in the major thrust sheets the good quality of seismic data also allows for determining the total shortening produced by the contractional structures in the central part of the profile at the border between the tyrrhenian and adriatic domains seismic data shows the presence of an intermediate sector the sector consists of a highly reflective window where the refraction data indicate a local doubling of the crust for about 30 km a scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the northern apennines since the upper oligocene

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

refinement of the evaluation of the role of co 2 in modifying estimates of the pressure of epithermal mineralization pressure is the most important of the intensive parameters for relating epithermal mineralization to the geologic setting this paper describes the limitations on pressure and therefore depth of mineralization that may reasonably be derived from simple observations of the behavior of fluid inclusions i e the existence of ice or co 2 clathrate on the liquidus the amount of expansion or contraction of the bubble as the host inclusion is crushed in oil on the microscope stage and the freezing and homogenization temperatures for the inclusion it is based on the reasonable model that mineralization occurs from a hydrostatically pressured nacl co 2 h 2 o fluid consistent with the probability that h 2 o and co 2 are the only gases contributing significantly to the total pressure the pressure of co 2 is of course a function of co 2 content but from 100 degrees to 300 degrees c it is a surprisingly minor function of either temperature or salinity the presence of the clathrate in freezing studies of fluid inclusions indicates pressures of co 2 that add at least 1 km to the probable depth of inclusion trapping compared to that estimated from co 2 free water thus undetected i e no clathrates on cooling co 2 in fluid inclusions can nonetheless contribute very significantly to the possible depth of epithermal mineralization on the other hand the observation that fluid inclusions crushed in oil have bubbles that do not expand i e 2 at 25 degrees c demonstrates co 2 contents that could add at most a few tens of meters to the depth of mineralization

interdigitated fluvial clastic deposits and calcareous tufa testifying an uplift of the catchment area an example from the pianizzoli area southern tuscany italy abstract calcareous tufa as well as other types of continental carbonates are largely sensitive to climate variations as a consequence the relationship between climate variations and tufa deposition is relatively well known and calcareous tufa deposits are often used as a reliable climatic proxy in many geological settings conversely the response of tufa to tectonics and uplifting processes is relatively poorly known due to their genetic independence from geothermally heated groundwater springs and associated tectonic controlled upwelling conduits in tectonically active settings the aim of this paper is to describe a peculiar stratigraphic succession where calcareous tufa deposits are closely associated and interbedded with coarse grained clastic deposits the study area is located in southern tuscany massa marittima where extensional tectonic processes responsible for the emplacement of magmatic bodies at shallow crustal levels have been active from pliocene to quaternary age and caused a diffuse uplift as well as local volcanic eruptions and hydrothermal fluid circulation the succession described in the paper recorded phases of calcareous tufa dominated deposition i e overall medium low hydrodynamic energetic settings repeatedly interbedded with coarse grained clastic fluvial sediments which testify an abrupt change in both the energy of the depositional environment and the sediment supply nevertheless during the phases dominated by clastic sedimentation tufa deposition was not inhibited as it would be expected for climate influenced settings suggesting that the observed stratigraphic settings were a consequence of a local uplift of the catchment area these findings indicate that calcareous tufa deposits could be a sensitive proxy to tectonics when they are associated with coarse grained clastic deposits in a geological setting where the origin of the clastic sediments cannot be explained by autocyclic or climate induced factors

the glaciovolcanic evolution of an andesitic edifice south crater tongariro volcano new zealand abstract unusual deposits mapped and logged in detail around the summit area of tongariro volcano tongariro volcanic centre new zealand indicate that the construction and evolution of a substantial portion of this andesitic stratovolcano was beneath a significant ice cap or summit glacier as the edifice was built under and through the overlying ice the style of volcanism evolved in a complex history of growth initially a 100 m thick widespread hyaloclastite deposit was emplaced within a subglacial eruption formed meltwater lake this was followed by several phases of effusive and explosive eruptions producing lava flows and primary volcaniclastic deposits emplaced along channels carved into the ice by heated meltwater the clastic deposits contain quenched bombs and structural features that indicate waterlain transport and emplacement and soft sediment deformation such accumulation of water on a steep sided edifice without evidence for a subaerial crater lake along with lava flow features indicating confinement suggest that a substantial summit glacier was responsible for the production and retention of water and the architecture of these deposits recent studies at nearby ruapehu volcano have provided good evidence for glaciovolcanic interactions during the last glacial period however until now little was known of the physical lava ice interactions in the centre during the last interglacial period and the earlier part of the last glacial period 110 64 ka these new data support a reinterpretation for the volcanic evolution of the older tongariro edifice and the emplacement mechanisms of primary volcaniclastic deposits they also help to constrain local ice thicknesses and extents at the times of eruption in addition this study contributes to a sparse global catalogue of glaciovolcanic deposits of andesitic composition particularly of primary volcaniclastics preserved at mid latitude stratovolcanoes the variety of deposit types indicates a volcano building and evolving with glaciation and is an outstanding example of the types of glaciovolcanic interaction that can occur at one volcano

lateral extrusion of a thermally weakened pluton overburden campiglia marittima tuscany the ascent and emplacement of magmas in the upper crust modify the local pre existing thermal and rheological settings such changes have important effects in producing anomalous structures mass extrusion rock fracturing and in some conditions hydrothermal mineralizations in the campiglia marittima area detailed field mapping led to the reconstruction of a local deformation history that overlaps chronologically and spatially with regional extension this local deformation was triggered at the miocene pliocene boundary by the intrusion of a monzogranitic pluton beneath a carbonate sedimentary sequence the emplacement of the pluton produced a perturbation in the rheological behaviour of the carbonate host rocks producing transient ductile conditions in the very shallow crust the carbonate rocks were thermally weakened and flowed laterally accumulating downslope of the pluton roof mainly toward the east as the thermal anomaly was decaying the brittle ductile boundary moved progressively back towards the pluton and large tension gash shaped volumes of fractured marble were generated these fractured volumes were exploited by rising hydrothermal fluids generating sigmoidal skarn bodies and ore shoots this work presents the campiglia marittima case study as a prime example of structural interference between regional extensional structures and local lateral mass extrusion in a transient ductile rheological regime triggered by pluton emplacement

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

modelling the evolution of columnar joints abstract cooling cracks developing from the margins of solidifying lava flows or intrusive dykes or sills often propagate inward and divide the rock into prismatic columns it has been shown that 1 the initial crack pattern that forms at the surface of the body is not as regular as the pseudo hexagonal pattern which evolves later 2 columnar structures develop by repeated step wise crack advances forming cm to dm transverse bands on the column faces 3 even within well developed colonnades the polygonal outlines continue to shift slightly from one crack advance to the next we propose that each new crack should propagate parallel to the highest thermal gradient ahead of the current crack tip when adjacent columns are of unequal size the local asymmetry of the isotherms drives the new crack toward the biggest and hottest column we present a geometrical model and algorithm that follows this rule and mimics the successive crack advances as the cooling front migrates into the lava sheet or dyke the model polygonal pattern obtained consists of convex irregular polygons with a variable number of sides but in which pentagons and hexagons predominate the algorithm successfully reproduces the rapid evolution from an initial immature crack pattern to a pseudo hexagonal mature one in which the average number of sides approaches six it predicts also the predominance of y type crack junctions the rapid evolution toward columns of approximately equal sizes and the persistent changes in length and diverging orientation of growth steps observed along the sides of columns the model polygonal patterns exhibit geometrical properties which are very similar to those observed in well developed columnar jointed flows such as the giant s causeway

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

highly extended terrains lateral segmentation of the substratum and basin development the middle late miocene radicondoli basin inner northern apennines italy 1 this paper deals with the evolution of sedimentary basins not delimited by normal faults with a substratum characterized by an upward concave shape and with infilling sediments synclinally deformed we describe the middle late miocene radicondoli basin representing an example of such bowl shaped basins its tectonic origin is controversial being related both to compression and extension these opposite interpretations bear significant consequences on the geodynamic context in which the inner northern apennines developed during the middle late miocene the results of our structural studies carried out in the substratum and infilling sediments indicate that the radicondoli basin is an example of a hanging wall basin developed in an extensional setting extensional tectonics determined the lateral segmentation of the substratum competent levels i e tuscan nappe and verrucano group and the consequent collapse of overlying less competent levels i e the ligurian units with the formation of a bowl shaped tectonic depression here the syntectonic sediments serravallian late messinian are deformed in a large syncline characterized by minor gravity driven folds with vergences toward the depocenter and traces of their axial planes parallel to the basin margins this paper highlights the role of the competence contrast during the postcollisional tectonic evolution and the influence of substratum lateral segmentation for the accommodation of syntectonic sediments

foliation relationships and structural facing vs vergence determinations in refolded low grade metamorphic rocks an example from the tuscan metamorphic basement northern apennines italy three tectonic foliations and their angular relation with bedding allow the determination of facing vs vergence and fold interference pattern in polyphase low grade metamorphic terrains composed of palaeozoic and triassic turbiditic rocks cropping out in the inner part of the northern apennines mt leoni area the d1 deformational event late oligocene early miocene is typified by southeast verging folds f1 and related tectonic foliation s1 with a hp lt mineralogical assemblage developed during the emplacement of the northern apennines tectonic units the d2 deformational event early middle miocene caused f2 east verging folds and related tectonic foliation s2 during greenschist facies metamorphism the d3 deformational event middle miocene formed f3 gentle upright folds with a foliation s3 developed only in the fold closures and never accompanied by blastesis foliation angular relationships as well as their intersections with the bedding allowed us to define the facing vergence and interference pattern of map scale folds where a penetrative s2 crenulation cleavage affected the metapelitic tops of turbiditic strata s1 structural facing could be misinterpreted at the outcrop scale simulating a northwest vergence of f1 folds this is due to a false dihedral angle between s0 and s1 occurring in the metapelites due to the rotation of s1 in the hinges of the overprinting crenulation cleavage domains s2 q 2005 elsevier ltd all rights reserved

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

tectonic control on hydrothermal circulation and fluid evolution in the pietratonda poggio peloso southern tuscany italy carbonate hosted sb mineralization abstract this paper deals with the development of an exhumed sb ore deposit associated with neogene quaternary magmatism of southern tuscany this epithermal mineralization represents a fossil hydrothermal system that was probably active during the volcanic activity that produced rhyolitic lava flows 2 3 ma presently exposed close to the study area roccastrada volcanic complex volcanism was coeval with strike oblique slip and normal faults that controlled the hydrothermal circulation faults were active until the pleistocene our study based on fluid inclusion and structural data demonstrates that fluids were channeled in damage zones of the pliocene quaternary strike oblique slip and normal faults and permeated within damage zones of middle late miocene extensional detachments consisting of fractured carbonate rock masses sandwiched between successions with very low permeability fluids produced a diffuse hydrothermal alteration both in the cataclasite and in carbonate damage zones where jasperoid strata bounds developed fluid inclusion investigation allowed tracing the evolution of the hydrothermal fluids that is interpreted in terms of a progressive cooling of the hydrothermal system such evolution could be related to large infiltration of shallow waters from the early mineralizing stage fluids at about 200 225 c salinity around 3 wt nacl equiv down to the later post ore stages characterized by more diluted fluids salinity of about 2 1 wt nacl equiv having lower temperatures t h around 155 c the latest hydrothermal activity in the area is indicated by fluid inclusions hosted in late calcite veins that are characterized by t h values of about 125 c this fossil hydrothermal system may provide a close analog to the active geothermal systems occurring in southern tuscany thus the results are useful for better understanding the relationships between brittle structures and fluids migration

migration of geothermal fluids in extensional terrains the ore deposits of the boccheggiano montieri area southern tuscany italy an integrated study based on fluid inclusion 18o composition and structural analyses was carried out on a pliocene fossil hydrothermal system located to the south of the present active larderello geothermal field in the boccheggiano montieri area the study area is typified by mineralized cataclastic levels related to late oligocene early miocene thrust surfaces and to the following two generations of normal faults of miocene and pliocene ages respectively within the damage zone of the pliocene boccheggiano fault the mineralization is mainly made up of quartz and pyrite quartz pb zn sulfides or quartz pb zn sulfides fluorite carbonates assemblages occur instead in the older cataclastic levels two generations of liquid rich fluid inclusions were recognized in quartz and fluorite the first one with homogenization temperatures ranging between 172 and 331 c and salinity between 0 0 and 8 8 wt naclequiv records the early stage of hydrothermal activity the second generation of fluid inclusions documents a later stage with homogenization temperature from 124 to 288 c and salinity from 0 2 to 1 9 wt naclequiv fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and or temperatures was a widespread process during the early stage and that fluid temperatures decreased moving from the boccheggiano fault toward the more distal and older cataclastic levels the 18o values of water in equilibrium with hydrothermal quartz which range from 5 7 to 0 1 are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in 18o through water rock interaction and or with magmatically derived fluids results indicate that the damage zone of the pliocene boccheggiano fault represented the main channel for the flow of meteoric water which was heated at depth then mixed with high salinity fluids and finally ascend to infiltrate along the older cataclastic levels our results based on fluid inclusions oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the boccheggiano fault and the older cataclasites which were thus hydraulically connected

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

surface morphology of columnar joints and its significance to mechanics and direction of joint growth columnar joints in basaltic lava flows display conspicuous bands oriented normal to column axes new observations show that each band contains a single plumose structure and thus represents an individual crack or joint segment formed during a discrete growth event analysis of plumose structure and intersections of cracks leads to a new kinematic model of columnar jointing and provides the first direct proof that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies columnar joints form by nucleation and growth of new cracks on the edges of older cracks each new crack begins at a point and propagates mostly normal to column axes and along the leading edge of a developing column face where thermal stress is concentrated inward propagation of cracks toward hotter regions is limited by a decrease of thermal stress and by the brittle ductile transition of lava outward and lateral propagation is limited by mechanical interaction with previous cracks and by low thermal stress in already fractured lava cracks often diverge slightly from the planes of previous cracks probably because of spatial and temporal changes in directions of local principal stresses mechanical interaction causes a diverging crack to overlap curve toward and usually intersect the previous crack behind its edge leaving a blind tip that points in the overall growth direction of the columnar joints this and other directional criteria are applied to determine joint growth patterns in several lava flows of the western united states in two tiered and multi tiered flows downward growing columnar joints usually meet upward growing joints well below the middle of the flows which indicates very rapid cooling of upper portions relative to lower portions this supports the idea that convection of water in columnar joints connected to the surface may be an important mechanism for cooling the upper portions of these flows whereas conduction is probably the dominant cooling mechanism at the bases

morphological features of miocene submarine coherent lavas from the green tuff basins examples from basaltic and andesitic rocks from the shimokita peninsula northern japan basaltic and andesitic volcanic rocks of miocene age exposed in the shimokita peninsula northern japan illustrate morphological features of typical submarine coherent lavas of the green tuff basins in japan they are pillow lobes with surface structures such as ropey wrinkles corrugations spreading cracks and tensional cracks and lava lobes composed of a lithic core and glassy border zone or rim with an in situ breccia zone grading outward into surrounding hyaloclastite in addition they include massive lavas with columnar joints and jointed dykes the submarine coherent lavas and dykes are commonly associated with hyaloclastic breccias such as pillow fragment breccia and angular fragment breccia the descriptions of the miocene volcanic rocks in the shimokita peninsula provide good criteria for recognition of submarine coherent lavas of basalt and andesite

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity

cooling rate variation in natural volcanic glasses from tenerife canary islands silicate melts form glasses in a variety of geological environments the relaxation equilibration of the frozen glass structure provides a means of investigating the quench rates of natural glasses and this cooling history provides an important constraint for models of melt dynamics phonolite glasses from the central volcanic edifice of tenerife canary islands indicate a range of five orders of magnitude cooling rate determined by modeling the relaxation of the structure dependent property enthalpy h across the glass transition the relaxation of enthalpy is determined by heat capacity c p h t measurement of natural glass samples by differential scanning calorimetry dsc upon heating the heat capacity curve in the vicinity of the glass transition has a geometry characteristic of the previous cooling rate a series of thermal treatments applied to each individual sample results in a set of sample specific parameters which are used to model the heat capacity curve of the naturally cooled glass the cooling rate is then derived the equivalence of shear and enthalpic relaxation enables the relaxation of enthalpy for these volcanic samples to be described by a general term for the evolution of fictive temperature quench rates for thirty one glasses are calculated to be within the range 10 c s 1 to 7 c per day the cooling rates quoted are linear approximations across the glass transition within different volcanic facies cooling rates depend on several factors the most rapidly cooled glasses occur where samples lose heat by radiation from the surface our analyses indicate that in certain environments a natural annealing process results in slow quench rates this is interpreted as either a slow initial cooling process or the reheating of a glass to an annealing temperature within the glass transition interval the latter results in relaxation to a lower temperature structure controls on these processes include the initial temperature and dissipation of thermal energy from the volcanic body our results are consistent with an influence of volatiles on quench rates in volcanic bombs where glass adjacent to vesicular layers is relatively rapidly quenched we interpret this as a rapid quench rate frozen into the glass resulting from a change in viscosity due to volatile degassing in lava flows the conduction of heat from the hot flow interior controls the cooling process and diminishes the effect of volatile exsolution relaxation geospeedometry can be applied to glass samples from a variety of geological environments where cooling rates cannot be measured directly such measurements provide a means of determining cooling rates for a variety of volcanic processes an independent calibration for existing temperature and time data and a means for testing cooling rate dependent models

kinematics and geometry of miocene low angle detachments and exhumation of the metamorphic units in the hinterland of the northern apennines italy abstract this paper deals with the lateral segmentation crustal boudinage and exhumation of the metamorphic units in the hinterland of the northern apennines during the late miocene extension the study area mt leoni area is part of the middle tuscan ridge a regional morpho tectonic feature in which the deepest tectonic units of the northern apennines are broadly exposed crustal seismic profiles and deep boreholes indicate that the middle tuscan ridge coincides with the outcropping part of a laterally discontinuous geological body mainly made up of hp lt and greenschist facies metamorphic units extensional detachments characterised by top to the east sense of shear and staircase geometry produced the lateral segmentation of the metamorphic units their activity can be ascribed to late tortonian late messinian times geometry and kinematics of the extensional detachments have been compared with the miocene extensional structures developed at shallow depths in the overthickened crust of the northern apennines allowing understanding of the extensional tectonic evolution which reorganised the hinterland northern apennines collisional belt