viscosity of microlite bearing rhyolitic obsidians an experimental study to investigate the influence of microlites on lava flow rheology the viscosity of natural microlite bearing rhyolitic obsidians of calc alkaline and peralkaline compositions containing 0 1 0 4 wt water was measured at volcanologically relevant temperatures 650 950 c stresses 103 105 pa and strain rates 10 5 to 10 7 s 1 the glass transition temperatures t g were determined from scanning calorimetric measurements on the melts for a range of cooling heating rates based on the equivalence of enthalpic calorimetric and shear viscosity relaxation we calculated the viscosity of the melt in crystal bearing samples from the t g data the difference between the calculated viscosity of the melt phase and the measured viscosity for the crystal bearing samples is interpreted to be the physical effect of microlites on the measured viscosity the effect of 45 vol crystals for both of these samples a connectivity factor is apparent with for the latter a close packing framework of crystals which is interpreted to influence the apparent viscosity

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

the proterozoic of eastern bolivia and its relationship to the andean mobile belt abstract the previously unmapped bolivian sector of the central brazil shield 220 000 km in area has been studied during an anglo bolivian technical co operation programme the metamorphic basement comprises the lomas maneches granulitic complex the chiquitania gneissic complex and the san ignacio schist supergroup which crops out as metasedimentary belts rb sr dates on some of the granulites suggest a protolith age of 2000 ma but the outcrop pattern of the metamorphic rocks as a whole is due to the 1300 ma san ignacio orogeny which was accompanied by widespread granite emplacement and metamorphism up to granulite facies the sunsas cycle began with the deposition of the supracrustal sunsas vibosi group and closed with the development of the sunsas and aguapei mobile belts at 1000 ma the upper proterozoic brasiliano cycle is represented by a bifurcating sedimentary basin in the se of the area with a closing tectonic event of 520 ma correlation is suggested with units in the central brazil shield the bolivian belts are extrapolated east into brazil and their limits indicated to the west the belts show trends parallel to the phanerozoic andean chain and they reflect the major deflection in the chain the arica elbow furthermore when the belts are traced towards the andes their ages broadly correspond to those of the sub andean precambrian basement this leads to the proposal of an enlarged andean orogenic belt system 1000 km wide comprising a 1300 ma old proto andean orogen which has controlled the trends of subsequent mobile belts

prevalence of growth twins among anhedral plagioclase microlites crystal textures of volcanic rocks record the processes involved in magma storage and eruptive ascent syn eruptive crystallization in which groundmass crystals form and grow according to environmental factors such as thermodynamic undercooling strongly influences the texture of erupted magma this stage is difficult to isolate for study in natural rocks but well suited for laboratory experiments because the chemical compositions and crystallization timescales of eruptive processes can be emulated this study examines the incipient stages of plagioclase crystallization in hydrous rhyodacite magma undergoing decompression driven degassing experimental samples in which crystal growth at both near equilibrium and far from equilibrium conditions were examined using electron backscatter diffraction ebsd analysis to ascertain crystallographic lattice orientations of individual crystals the crystal orientation investigation affirms a common assumption invoked in textural studies of crystal number density contiguous crystals with parallel faces are crystallographically continuous whereas contiguous crystals with non parallel faces have unrelated crystal lattice orientations and as such represent separate crystals in the highly undercooled sample twinning is identified in 87 of the crystals examined in the near equilibrium sample 38 of the crystals are twinned we find that the observed twinning is unlikely to be the result of deformation transformation or synneusis but rather a result of growth defects introduced during the incipient stages of crystallization we suggest internal structural defects twins control macroscopic morphological defects embayments swallowtails and melt inclusions as a result of the high energy of the twin plane boundary formation of twins during the incipient stages of plagioclase crystallization is the single most important factor contributing to anhedral morphologies of feldspar microlites growing during magma decompression and plays a role in the development of some plagioclase hosted melt inclusions

morphological and morphometric approach to the study of the structural arrangement of northeastern abruzzo central italy abstract the morphotectonic research at the dipartimento di scienze della terra of the universita di roma la sapienza aims to define the role of tectonics and neotectonics in the morphological evolution of central italy in this context the relationships between morphology and tectonics have been investigated in an area of northern abruzzo extending from the apennine chain to the adriatic sea morphological and morphometric analyses carried out show that the geomorphological evolution of the study area was strongly affected by tectonics especially recently the most recent extensional tectonics intersect the previous compressive structures overthrust reverse faults folds strike slip faults determining the structural arrangement characterized by uplifted and downthrown blocks morphological analysis shows that extentional tectonics occurred with the following alignments nw se nnw sse ne sw ene wsw n s and e w the spatial variability of amplitude of relief values corroborated the observations obtained from previous analyses in particular the existence of different blocks differentially uplifted along the alignments mentioned above finally data obtained through the statistical analysis of preferred stream orientations confirm the previous considerations showing that the same tectonic directions markedly influenced the drainage network development streams of lower order preferentially follow the n s and e w directions which suggests that these tectonic trends were active until very recent times at least up to the late pleistocene the results obtained testify both to the effectiveness of the methodological approach and the likelihood of the proposed morphotectonic arrangement of the study area

d h ratios and h2o contents record degassing and rehydration history of rhyolitic magma and pyroclasts abstract volcanic eruptions of rhyolitic magma often show shifts from powerful vulcanian to plinian explosive episodes to a more gentle effusion of viscous lava forming obsidian flows another prevailing characteristic of these eruptions is the presence of pyroclastic obsidians intermingled with the explosive tephra this dense juvenile product is similar to the tephra and obsidian flow in composition but is generally less degassed than its flow counterpart the formation mechanism s of pyroclastic obsidians and the information they can provide concerning the extent to which magma degassing modulates the eruptive style of rhyolitic eruptions are currently subject to active research porous tephra and pyroclastic and flow obsidians from the 1060ce glass mountain rhyolitic eruption at medicine lake volcano california were analyzed for their porosity water content h2o and hydrogen isotopic composition d h2o in porous pyroclasts is correlated negatively with d and positively with indicating that the samples were affected by post eruptive rehydration numerical modeling suggests that this rehydration occurred at an average rate of 10 23 5 0 5 m2 s 1 during the 960 years since the eruption causing some pyroclasts to gain up to 1 wt of meteoric water pyroclastic and flow obsidians were not affected by rehydration due to their very low porosity comparison between modeled d h2o relationships in degassing magma and values measured in the glass mountain samples supports the idea that rhyolitic magma degasses in closed system until its porosity reaches a value of about 65 5 beyond which degassing occurs in open system until quench during the explosive phase rapidly ascending magma fragments soon after it becomes permeable creating porous lapilli and ash that continue to degas in open system within an expanding gas phase as suggested by recent studies some ash may aggregate and sinter on the conduit sides at different depths above the fragmentation level partly equilibrating with the continuously fluxing heavier magmatic vapor explaining the wide range of h2o contents and high variability in d measured in the pyroclastic obsidians using only h2o and d it is impossible to rule out the possibility that pyroclastic obsidians may also form by permeable foam collapse either syn explosively near the conduit sides below the fragmentation level or during more effusive periods interspersed in the explosive phase during the final effusive phase of the eruption slowly ascending magma degasses in open system until it reaches the surface creating flows with low h2o and d this study shows that h2o measured in highly porous pyroclasts of a few hundred years or more cannot be used to infer syn eruptive magma degassing pathways unless careful assessment of post eruptive rehydration is first carried out if their mechanism of formation can be better understood detailed analysis of the variations in texture and volatile content of pyroclastic obsidians throughout the explosive phase may help decipher the reasons why rhyolitic eruptions commonly shift from explosive to effusive phases

mineralogy of the lake zone thor lake rare metals deposit n w t canada the proterozoic ca 2 1 ga blatchford lake suite hosts significant concentrations of rare metals at the core of a peralkaline granite syenite pluton after emplacement of the grace lake granite and the thor lake syenite within it bodies of nepheline syenite ijolite and urtite were intruded beneath the present day lake zone this is the largest of five zones of mineralization and lies close to the apex of the thor lake syenite a region which was then subjected to albitization microclinization and finally rare metal mineralization the underlying silica undersaturated rocks contain clots of rare metal bearing minerals including cerianite ce britholite ce thorite and calcium catapleiite interstitial to nepheline and aegirine the lake zone itself contains major quantities of zr in zircon nb in ferrocolumbite pyrochlore group minerals aeschynite group minerals and fergusonite y and ce in allanite ce monazite ce and bastnasite group minerals lesser amounts of ta y heavy

rhyolite magma degassing an experimental study of melt vesiculation the vesiculation of a peralkaline rhyolite melt initially containing 0 14 wt h2o has been investigated at temperatures above the rheological glass transition tg 530 c by a in situ optical observation of individual bubble growth or dissolution and b dilatometric measurements of the volume expansion due to vesiculation the activation energy of the timescale for bubble growth equals the activation energy of viscous flow at relatively low temperatures 650 790 c but decreases and tends towards the value for water diffusion at high temperatures 790 925 c the time dependence of volume expansion follows the avrami equation

small catchments evolution on clayey hilly landscapes in central apennines and northern sicily italy since the late pleistocene abstract the study aims to define a possible evolutionary geomorphological model of small catchments i e

viscosity of the dome of mount st helens abstract a sample of dacite from the dome of mt st helens has been studied experimentally and found to have a viscosity that declines from about 10 15 at 800 c to 10 3 poise at 1500 c its yield strength declines from about 2 10 6 dynes cm 2 at 800 c to less than the precision of our measurements 10 4 dynes cm 2 above 1050 c the geometrical form of the dome is approximately consistent with these properties if the internal temperature of the dome is between 900 and 1000 c the melting behavior of the crystalline dacite has been determined between 1000 and 1225 c data on the composition of the liquid fraction and sizes and proportion of crystals have been used to derive a set of equations for predicting the effective viscosity of crystal bearing magmas below their liquidus temperatures although of the bulk composition of the magma has changed little the increasing crystallinity and viscosity appear to have influenced eruptive behavior of the volcano during its most recent periods of activity

morphostructural elements of central eastern abruzzi contributions to the study of the role of tectonics on the morphogenesis of the apennine chain abstract the relief features of the apennine chain have been developed in a complex geomorphological and geological evolution from neogene to quaternary in order to define regional geomorphological characteristics of the central and eastern part of the abruzzi region central italy between the fucino plane and the adriatic coast a schematic map of morphostructural elements structural landforms and erosional landforms was constructed the results point out the clear coherence of present landforms with the tectonic framework in the abruzzi area in the chain area exhumed thrust ridges and faulted homocline ridges are present generally nw se nnw sse n s separated by tectonic valleys fault line valleys tectonic basins and tectonic karstic basins partially filled up with continental deposits in the piedmont periadriatic area the most important morphological elements are represented by homocline relief gently ne dipping mesa relief dip stream valleys sw ne and alluvial plains the latter grade eastwards towards the coastal plain

textural constraints on effusive silicic volcanism beyond the permeable foam model transitions between explosive and effusive phases of silicic volcanic eruptions have been related either to stratification of volatiles in the source magma body or to the loss of volatiles through the permeable host rock of the conduit one way to distinguish between these two models is to map and analyze the vesicular and glassy textures found in silicic lava flows in this paper we present textural observations and isotopic evidence from active and recent silicic lava flows which show that at least some vesiculation occurs during surface advance of extrusions after magma has reached the earth s surface this view is in contrast to the widely promoted permeable foam model which states that all volatiles escape during ascent of the magma and that all dense glassy material in lava flows forms from the collapse of pumiceous lava i e that silicic lavas emerge as highly inflated foam flows such interpretations which claim that silicic lavas are completely degassed upon extrusion and that all degassing must take place on the time scale of the eruption neglect several important pieces of evidence including the presence of obsidian in extremely small domes and of vesicular zones in the interiors of silicic flows the copious loss of volatiles through eruption plumes between eruptive phases and direct observations of surface vesiculation during growth of the mount st helens lava dome the permeable foam model also implies the unlikely requirement that explosive to effusive transitions be associated with an increase in eruption rate we present a more comprehensive model for the emplacement of silicic extrusions that allows for early gas loss during ascent as well as late stage vesiculation we then discuss how the redistribution of volatiles during surface flow can increase explosive hazards from silicic lavas days weeks or months after the lava emerges from the vent

sequence response to syndepositional regional uplift insights from high resolution sequence stratigraphy of late early pleistocene strata periadriatic basin central italy abstract this paper deals with the depositional sequences that occur within the uppermost part of the plio pleistocene periadriatic basin fill in the southern marche region central italy the succession is an early pleistocene easterly dipping clastic wedge showing an overall shallowing trend from slope clays to shallow marine and non marine deposits comprising two major sequences namely qmb and qmc analysis has provided new insights into i the nature of sedimentary facies and facies associations occurring within the upper part of qmb and qmc ii the gradual contact within qmb between regressive littoral deposits rld and underlying deep marine blue clays iii the composite origin of the emilian surface which is a widespread erosional unconformity separating qmb from qmc iv the cyclothemic pattern of qmc composed of downstepping small scale depositional sequences v the role played by synsedimentary uplift on the stacking pattern of small scale sequences and their internal architecture up to three small scale depositional sequences have been recognised within qmc qmc1 qmc2 and qmc3 they are up to 50 m thick and defined by previously unrecorded lower rank regionally extensive surfaces facies organization indicates that as a rule in ascending stratigraphic order each small scale sequence may includes a distinctive basal unconformity surface that can be traced from incised valleys to associated interfluves an incised valley fill a transgressive surface of marine erosion a transgressive systems tract a highstand systems tract a regressive surface of marine erosion and an attached falling stage systems tract in proximal positions the small scale sequences are dominated by transgressive and highstand systems tracts with incised valley fills and falling stage systems tracts absent or volumetrically much less significant in relatively basinward locations where the regressive surfaces of marine erosion converge with the lower sequence boundary the falling stage systems tract may represent the entire depositional sequence high frequency sequences display a distinctive stacking pattern and form a tectonically induced forced regressive sequence set underlain by a composite tectonically enhanced regressive surface of marine erosion formed by the lateral connection of lower rank sequence boundaries

geomorphic expression of active tectonics in a rapidly deforming forearc sila massif calabria southern italy we examine the tectonic geomorphology of la sila calabria southern italy a high standing 1500 m plateau surrounded by crustal extension with map dem and field data these data are used to constrain a simple geodynamic model that describes short wavelength deformation of the plateau rim topographic metrics including drainage patterns river longitudinal profiles and swath profiles are consistent with field stratigraphic relationships collectively suggesting that local tectonic deformation is embedded within a broader regional uplift that has increased the mean elevation of the sila plateau during the quaternary the concavity steepness and length gradient index of modeled river longitudinal profiles proved to be the most useful metrics for recording the effects of locally active faults a previously unrecognized horst on the northeastern portion of the plateau was identified with these data nevertheless the core of the sila plateau remains relatively undeformed with respect to its flanks which are characterized by steep fault bounded escarpments active extension has dropped base level for and unloaded the plateau rim causing deep fluvial incision and associated flexural uplift of the footwall this footwall uplift helps maintain a separate external and nearly radial drainage away from the plateau along its flanks and a nearly closed drainage for the plateau interior a drainage divide roughly correlates with the plateau rim inhibiting the process of drainage integration through the sila interior and subsequent landscape dissection as a result geomorphic processes driving erosion of the sila upland are lagging behind the tectonic processes that have driven rock uplift leading to an overall increase in mean surface elevation these results underscore the importance of the lag times a landscape may endure in transforming from one tectonic and base level condition to another we conclude that the calabrian forearc has a similar geomorphic evolution as the more northern apennines consistent with the emerging view that growth of apennine topography has been recent quaternary rapid and possibly decoupled from rock deformation in the orogenic wedge

geomorphology of soft clastic rock coasts in the mid western adriatic sea abruzzo italy abstract we present the first detailed overall study on the rock coasts in the central adriatic sea abruzzo italy which is one of the few cases of a coast with clastic soft rocks in the entire mediterranean area the coast is composed of cliffs with small beaches coastal slopes with or without a contiguous coastal plain and intervening low lying coasts it is developed on the eastern seaward side of a wide plateau and mesa landscape shaped on an early middle pleistocene clay sand sandstone conglomerate marine sequence covered by late pleistocene holocene continental deposits the study focuses on the overall coast and on eight specific sites combining i dem 2 m cell lidar derived analysis and geological geomorphological surveys of the emerged and submerged areas for the cliff coastal slope characterization ii the results of u th 14c sediment dating and archaeological and palaeontological attributions for constraining the coastal evolution and iii aerial photo time series 1954 2013 time span analysis for the recent cliff retreat assessment the overall features of the cliffs and coastal slopes were defined in terms of their morphology lithology tectonic setting landforms and geomorphological processes whereas the analysis of late pleistocene holocene continental deposits and landform distribution defined and constrained the evolution of the coastal system this enabled us to define eight different types of coastal cliffs slopes meaningful for clastic soft rock coasts the coastal types were defined in terms of i lithology 15 cliffs on marine sandstone 15 cliffs on marine conglomerate 3 cliffs on continental deposits 43 coastal slopes on clay sand sandstone conglomerate sequences ii morphostructural setting i e clay sandstone conglomerate interface elevation and iii of state of activity 3 8 active cliffs 13 8 inactive cliffs 15 9 palaeocliffs 43 of inactive and locally reactivated landslides on coastal slopes variable retreat rates were also defined from retreat measurements over a 60 year time span ranging from 0 15 m yr to 1 m yr and were found to be induced by episodic and localized cliff recession processes and connected to combined wave cut and gravity induced slope processes the assessment of coastal and gravity induced geomorphological processes combined with the analysis and dating of the continental deposits allowed us to define the late pleistocene to present evolution and timing and the evolutionary mechanisms of the main coastal types of soft rock coasts they are connected to wave cut and gravity induced erosion cycles on cliffs and to large rotational ancient landsliding with local recent reactivations on coastal slopes for the different coastal types the expected hazard conditions were outlined

a fluvial record of long term steady state uplift and erosion across the cascadia forearc high western washington state six late quaternary river terraces preserved along the clearwater river in northwestern washington state provide a 140 ka record of long term incision and uplift across the western side of the cascadia forearc high terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio fluvial deposits and the global eustatic curve the terraces overlie flat bedrock surfaces called straths which represent uplifted segments of the river channel bedrock incision is measured by the height of a strath relative to the adjacent modern river channel the straths along the clearwater show an upstream increase in bedrock incision ranging from 0 at the coast to a maximum of 110 m in the headwaters the incision at any point along the profile increases systematically with strath age the calculated incision rates range from 10 ky the clearwater river valley has maintained a steady state profile defined by a long term balance in the rates of incision and rock uplift upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range these results are consistent with other evidence indicating a long term steady state balance between the accretionary influx and the erosional outflux for this part of the cascadia subduction wedge since 14 ma these results help show how terrace deposits form in tectonically active landscapes the dominantly fluvial clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages in turn the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well the fluvial system shows strong forcing by the glacial climate cycle even so the river appears to have returned to the same valley profile during each cycle of strath cutting thus bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle 100 ky but appears to be relatively steady when averaged over longer time scales a simple kinematic model is used to examine how uplift of the cl our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating if accretion occurred entirely at the front of the wedge the present west coast should be moving to the northeast at 3 m ky relative to a fixed puget sound this prediction is in good agreement with offset of a 122 ka sea cliff preserved at the southwest side of the clearwater valley profile in this case the long term margin perpendicular shortening would account for 20 to 35 percent of the geodetically measured northeast southwest shortening across the olympic mountains

a comparison of volcanic eruption processes on earth moon mars io and venus the silicate planets and satellites display a wide range of physical chemical and atmospheric characteristics which may influence the nature of volcanism a major geological process common to the evolution of the surfaces of these bodies consideration of the process of magma ascent and eruption from first principles allows predictions to be made concerning volcanic eruption styles and expected landforms and deposits on each planetary body examination of actual land forms and deposits in light of these predictions leads to a better understanding of the nature of volcanic eruption processes and outlines outstanding problems

a model for calculating the viscosity of natural iron bearing silicate melts over a wide range of temperatures pressures oxygen fugacites and compositions a new general model that takes into account the pressure and redox state effect is presented to calculate melt viscosities of natural fe bearing melts this new model is applicable to melts that span a wide range of temperatures from 733 to 1873 k pressures 0 001 15 kbar h2o content from 0 to 12 3 wt and compositions from ultramafic mafic to silicic melts the accuracy of the model is calculated to be 0 23 log units of viscosity which is within or close to experimental uncertainty the transport properties including glass transition temperature and melt fragility can also be calculated from this model a spreadsheet to calculate the viscosity is provided in an electronic supplement

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

physical volcanology and eruption dynamics of peralkaline agglutinates from pantelleria peralkaline rhyolitic lava like lobes showing direct evidence for a spatter fed origin are associated with eruptive centres that document a transition from explosive to effusive fountain fed activity owing to the preservation of spatter clasts clast dimensions can be used to model the eruptive dynamics of these deposits we conducted an integrated field experimental and theoretical study of the cala di tramontana centre pantelleria italy with the aim to better understand its eruptive behaviour this centre is composed of four units and a close association of fall lapilli tack welded agglutinate and spatter fed lava like lobes these units were fed initially from a fissure vent and later from a circular vent for the last erupted lobe field evidence indicates that fall out accumulated rapidly coalescing into a 10 m thick deposit that flowed downslope and became lava like high eruption rates and high heat flows are interpreted to promote welding of spatter proximal to the vent overburden pressures and thermal insulation from the accumulating spatter caused complete homogenisation of spatter within the interior of the flow laboratory vesiculation experiments show that peralkaline obsidian can vesiculate at temperatures as low as 620 c over a 4 hour period and indicate that airborne agglutinate can deform and weld rapidly within minutes of landing we measured viscosity on a natural pantellerian sample using the parallel plate method over a temperature range of 560 600 c viscosities of 1010 1011 pa s and an activation energy of 311 kj mol were obtained based on undeformed clast sizes and densities eruption dynamics modelling indicates that gas eruption velocities ranged from 90 to 130 m s 1 erupted mass fluxes were 200 kg s 1 m 1 and 2 104 kg s 1 from the fissure and localised circular vents respectively magmatic viscosities of between 105 and 107 pa s for t 750 850 c precluded intermittent strombolian activity due to gas bubble coalescence in addition the amount of magmatic water available to drive the eruption fountains ranged from 0 4 to 0 6 wt significantly less than the estimated 1 5 wt of exsolved volatiles implying that significant passive degassing occurred

morphology of fluvial networks on titan evidence for structural control abstract although titan s surface shows clear evidence of erosional modification such as fluvial incision evidence for tectonism has been less apparent on earth fluvial networks with strongly preferred orientations are often associated with structural features such as faults or joints that influence flow or erodibility we delineated and classified the morphologies of fluvial drainages on titan and discovered evidence of structural control fluvial networks were delineated both on synthetic aperture radar sar images covering 40 of titan from the cassini titan radar mapper up through t71 and on visible light images of the huygens landing site collected by the descent imager spectral radiometer disr the delineated networks were assigned to one of three morphologic classes dendritic parallel or rectangular using a quantitative terrestrial drainage pattern classification algorithm modified for use with titan data we validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations and confirmed that only a small fraction of the networks are falsely identified as structurally controlled as a second validation we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular application of this modified algorithm to our titan networks results in a classification of rectangular for one half of the sar and disr networks a review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages based on the similar brittle response of rock and cryogenic ice to stress we infer that structures formed under tension are the most likely cause of the rectangular titan networks delineated here the distribution of these rectangular networks suggests that tensional stresses on titan may have been widespread

morphotectonic approach to the drainage analysis in the north marche region central italy abstract the umbro marchean apennines form an arcuate nw se fold and thrust belt of ne convexity the orogen developed from the early miocene and shortened the more than 5 km thick meso cenozoic stratigraphic succession by about 30 the internal part of the mountain chain is however overprinted by sw dipping extensional normal faults that bound the plio pleistocene continental basins nevertheless the distribution of river terraces all along the main river valleys clearly indicates that middle upper pleistocene and holocene vertical uplift dominated over local anticlinal uplift for the entire studied area the drainage network of the marche region in the external part of the umbro marchean apennines has an overall sub parallel pattern oriented mainly sw ne and transversely breaches the main calcareous anticlinal ridges before reaching the adriatic coast emergence and drainage initiation may have begun as early as the messinian cave systems formed during the erosion history and document former stream levels the breaching of the high amplitude anticlinal ridges was controlled mainly by joint systems and locally by nne ssw striking faults in turn both superimposition and stream piracy phenomena could have played a significant control in the drainage network development and in places complex mechanisms involving antecedence cannot be ruled out for streams bypassing anticlinal ridges

evaluation of a relaxation geospeedometer for volcanic glasses abstract the cooling of silicate melts influences the character of volcanic processes primarily through the effect of temperature on melt viscosity but also through the derivative thermal properties expansivity and heat capacity if the cooling rates of volcanic facies can be established then the undoubtedly complex processes of erupting cooling and degassing magmas can be more readily understood the frozen structure of every glass volcanic or synthetic is influenced by the previous cooling history moreover the relaxation of the glass structure back to equilibrium during reheating across the glass transition is also dependent on the quenched in structure and thus can be used to determine the cooling rate history in this study differential scanning calorimetry dsc measurements have been used to determine the enthalpic relaxation of four volcanic glasses each glass has been heated at known heating rates in the calorimeter to temperatures above the glass transition interval the first heating of the glass involves the relaxation of the structure frozen in during the volcanic cooling subsequent controlled heating and cooling in the calorimeter enables the determination of a set of kinetic parameters which can be used to model the heat capacity curves by modeling the transient values of heat capacity across the glass transition interval the relaxation of enthalpy and the volcanic cooling rate across the glass transition interval can be obtained from our study we can demonstrate four different cooling rates for volcanic glasses over a range of three orders of magnitude from 4 c min 1 to 2 c day 1 we propose that the enthalpic relaxation of silicate melts can be applied as a geospeedometer to the study of volcanic rocks from a variety of occurrences

structural constraints on palaeomagnetic rotations south of the arica bend northern chile implications for the bolivian orocline abstract palaeomagnetic data from the central andean fore arc appears to support the bolivian orocline model with clockwise rotations to the south and counter clockwise rotations to the north of the arica bend respectively however counter clockwise rotations in northernmost chile extend south of the arica deflection consistent with mesozoic rotations in southern peru this suggests that the bolivian orocline model needs to be redefined we present a palaeomagnetic study of 140 specimens from 15 sites sampled in middle jurassic sediments and volcanics of the camaraca formation and in the upper jurassic lower cretaceous cuya dykes of northernmost chile 19 2dgs 70 3 w the calculated pole 81 4 s 354 7 e 95 6 7 when compared with the upper jurassic pole for cratonic south america 89 0 s 217 1 e 95 4 6 suggests that the sampled area has undergone a small counter clockwise rotation of approximately 10 the change from counter clockwise to clockwise rotations occurs between 19 s and 23 s and may correspond to a known bend in the peru chile trench these rotations were probably the result of in situ block rotation in response to shear this shear is the result of stresses in the subducted lithosphere with sinistral shear to the north counter clockwise rotations and relatively larger dextral shear to the south clockwise rotations of the bend in the trench respectively the amount of shear is reduced in the area of the bend due to contortion of the subducting slab these stresses resulted due to the shape of the andean margin rather than as a result of oroclinal bending the arica bend is interpreted as an ancient feature which may have evolved from a hot spot generated triple junction rift system the velasco alkaline province of eastern bolivia possibly formed the failed arm of this triple junction

discriminating secondary from magmatic water in rhyolitic matrix glass of volcanic pyroclasts using thermogravimetric analysis abstract pyroclasts from explosive eruptions such as the 1060 ce explosive glass mountain eruption of medicine lake volcano california contain large amounts of water this may be the consequence of diffusive rehydration of the volcanic glass by meteoric secondary water after the eruption discriminating between magmatic and secondary water in the matrix glass of pyroclasts is important because the degassing of magmatic water affects the intensity of volcanic eruptions such discrimination has remained a challenging problem especially because some aspects of water diffusion in silicate glasses at low temperatures and atmospheric pressure remain poorly constrained we used thermogravimetry to analyze the loss of water from natural volcanic glasses and glasses that were hydrated in the laboratory at magmatic temperatures and pressures numerical modeling of diffusive water loss during thermogravimetric analyses accounted for the interconversion of molecular water h 2 o m and hydroxyls groups oh and indicates that glass mountain pumices contain 0 2 0 5 wt primary water but gained 1 2 wt of meteoric water by diffusive rehydration during the past 950 years these results confirm that the majority of magmatic water is lost from the magma during explosive eruptions furthermore the integration of thermogravimetric analysis and numerical modeling facilitates discrimination between the magmatic and secondary water content of volcanic glasses

extensional basins in the tectonically bimodal central apennines fold thrust belt italy response to corner flow above a subducting slab in retrograde motion the apennines fold thrust belt has developed over the past 20 m y in response to southeastward retrograde migration of the adriatic trench in a region of ongoing subduction but little plate convergence the orogenic belt is characterized by a gently sloping southwestern flank in a state of regional extensional collapse and a steeply sloping northeastern flank in regional contraction in any given area in the central apennines the chronologies of thrusting and subsequent extension provide an estimate of the time required for attainment of high elevation 2 5 3 0 km the time between initial extension and eruption of local ultramafic lavas provides an estimate of the time required to collapse by regional crustal thinning these estimates suggest that the northeastern contractional flank of the range is rising at least twice as fast as the southwestern flank is collapsing we propose that the bimodal state of stress in the apennines is maintained by corner flow in the mantle wedge beneath the crest of the range

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

a rheological investigation of vesicular rhyolite abstract the rheology of vesiculating rhyolitic systems exerts a strong control on the transport of silicic magmas in the subvolcanic to volcanic environments we present here an investigation of vesiculating and vesiculated rhyolites using dilatometric methods this study examines the effect of vesicle content on the viscosity of a natural supercooled rhyolitic liquid with 0 70 vesicles the experimental samples of rhyolitic glass are derived from fusion of a natural obsidian from little glass butte oregon crystal free rhyolite glasses of varying porosity were prepared by fusing obsidian powder in a pt crucible differing porosities were obtained by varying the temperature 1300 1650 c and duration 0 5 6 h of the fusions cylindrical samples of the resulting vesiculated rhyolites were cored from the crucible using diamond tools and their ends were ground flat and parallel for dilatometry the porosity of each sample was determined from archimedean buoyancy density determinations and comparison with bubble free rhyolite 2 331 g cm 3 porosity 1 p p o the density of foamed samples was determined using their mass volume and regular geometry viscosities were determined in the parallel plate mode at stresses of 5 10 3 to 10 5 pa the viscosimeter was calibrated using nbs 711 glass the bubble contents were microscopically investigated using a video reflected light system and image analysis software distribution functions of the size orientation aspect ratio and surface porosity were obtained the viscosity of rhyolite decreases with increasing bubble content a general relationship of the form 0 1 c describes the effect of porosity in volume fraction on the viscosity where c is a dimensionless constant 22 4 2 9 and log 10 0 10 94 0 04 pa s at 850 c

shear thickening dilatancy in crystal rich flows abstract rheological models of molten rock are mostly based on behaviours in which viscosity is constant with respect to strain rate e g newtonian bingham plastic or viscosity decreases with increasing strain rate pseudo plastic or shear thinning rheological models in which viscosity increases with increasing strain rate shear thickening or dilatant models have rarely been used yet such behaviour is common in particulate systems whereas magmas with low crystal content may be appropriately modelled by the former behaviours greater crystal content may lead to particle interactions resulting in shear thickening behaviour the effect is illustrated using a powdered rhyolitic rock mixed with water which exhibits extreme shear thickening behaviour caused by particles moving apart as they move past each other the expansion of the grain fabric during flow is opposed by the applied loads such that dilatancy is invariably associated with shear thickening rheology crystal rich lava may exhibit shear thickening dilatancy a proposition supported by observations of glass rich microscopic shear zones disrupting crystal fabrics plutonic crystal mush may also exhibit shear thickening dilatancy which can explain synplutonic intrusion involving brittle fracture followed by ductile disruption in general strain rate is an important contributor to the transition from ductile to brittle behaviour in crystal rich igneous rocks

the equivalence of enthalpy and shear stress relaxation in rhyolitic obsidians and quantification of the liquid glass transition in volcanic processes abstract the relaxation of enthalpy and shear stress has been investigated for six silicic volcanic obsidians calc alkaline rhyolitic obsidians from ben lomond dome new zealand erevan dry fountain armenia and little glass butte usa peralkaline obsidians from mayor island new zealand and eburru kenya and a macusanite obsidian from se peru the temperature dependences of enthalpy and shear stress relaxation are obtained from the dependence of the calorimetric heat capacity peak temperature on heating rate and the dependence of shear viscosity on temperature respectively both processes enthalpy relaxation and shear stress relaxation can be approximated to be arrhenian in the investigated temperature ranges relevant to volcanological processes activation energies derived for enthalpy and shear stress relaxation for each sample are equal this equality permits the calculation of viscosity at the glass transition as a function of cooling rate of a volcanic melt the relationship between viscosity at the glass transition and the cooling rate is given by log10 s at tg k log10 q where s the shear viscosity at the glass transition q is the cooling rate in c s 1 and k is a constant the six melt compositions investigated here exhibit a value of k 10 49 0 31 for the modeling of volcanic processes this equation allows the prediction of the viscosity at the glass transition temperature for a given value of cooling rate taken together with the maxwell relation an effective relaxation time can be obtained for the cooling rate prediction of the glass transition temperature permits the allotment of temperature ranges for the liquid and glassy segments of the cooling history of the volcanic melt and thus for the correct assignment of glassy and liquid values of the derivative thermodynamic properties such as expansivity and heat capacity in thermodynamic modeling of late stage volcanic processes

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

a tectonostratigraphic synthesis of the sub andean basins inferences on the position of south american intraplate accommodation zones and their control on south atlantic opening it has been shown in the accompanying paper that the sub andean foreland can be subdivided longitudinally into a number of tectonostratigraphic domains to test the hypothesis that changes in palaeo depositional setting rely on the presence of a series of transverse zones of structural accommodation data have been digitally compiled from across the south american continent spatial and temporal geological relationships have been analysed and evaluated as a means of identifying the position of tectonostratigraphic domain boundaries structural accommodation zones and patterns of subsidence and intraplate deformation the results suggest that individually these structural accommodation zones represent a composite of deep crustal fractures which on a regional scale interlink to form a transcontinental belt or zone that can accommodate intraplate deformation during episodes of plate reorganization their strong spatial relationship with mesozoic intraplate alkaline igneous activity suggests that they exerted an important control on lithospheric melt siting during gondwana breakup these localized zones of high heat flow have important implications for source rock maturity in the interior phanerozoic intracratonic basins of south america on the south atlantic margin the majority of these crustal lineaments correlate with failed arms of triple junction rifts and define the boundaries to tectonostratigraphic domains recognized along the south atlantic rift system

sulfuric acid speleogenesis in the majella massif abruzzo central apennines italy abstract many active and inactive hypogene sulfuric acid cave systems are known along the apennines italy the cavallone bove cave system is located in the external part of the central apennine chain in the majella massif and opens at 1470 m asl along the taranta gorge south of chieti the presence in these caves of peculiar geomorphological features such as feeders rising channels megacusps cupolas and replacement pockets offers evidence of rising acidic fluids the secondary mineral deposits including meter size white gypsum deposits alunite jarosite black layers of iron manganese oxides and hydroxides along with a rare association of authigenic rutile ilmenite minerals indicate a sulfuric acid origin stable isotope analyses of sulfates further confirm a sulfuric acid speleogenetic sas origin of these minerals and in general of the whole cave system with h2s coming from the bacterial sulfate reduction of deep seated triassic evaporites interacting with hydrocarbons alunite dating demonstrates this water table sas cave to have been active at least until 1 52 0 28 ma all the evidence suggests that cavallone bove is an ancient sulfuric acid karst system that was uplifted

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

long river profiles tectonism and eustasy a guide to interpreting fluvial terraces along three rivers at the mendocino triple junction northern california strath cut and fill terraces have formed in response to tectonic and eustatic processes detailed surveying and radiometric dating at multiple sites indicate that lower reaches of the rivers are dominated by the effects of oscillating sea level primarily aggradation and formation of fill terraces during sea level high stands alternating with deep incision during low stands a eustasy driven deposi tional wedge extends tens of kilometers upstream on all rivers tapering to zero thickness this distance is greater than expected from studies of the effects of check dams on much smaller streams elsewhere due in part to the large size of these rivers however the change in gradient is nearly identical to other base level rise studies the depositional gradient is about half that of the original channel middle to upper reaches of each fiver are dominated by the effects of long term uplift primarily lateral and vertical erosion and formation of steep unpaired strath terraces exposed only upstream of the depositional wedge vertical incision at a rate similar to that of uplift has occurred even during the present sea level high stand along rivers with highest uplift rates strath terraces have steeper gradients than the modem channel bed and do not merge with marine terraces at the river mouth consequently they cannot be used to determine altitudes of sea level high stands strath formation is a continuous process of response to long term uplift and its occurrence varies spatially along a river depending on stream power and hence position upstream strath terraces are found only along certain parts of a coastal stream upstream of the aggradational effects of oscillating sea level and far enough downstream that stream power is in excess of that needed to transport the prevailing sediment load for a given size fiver the greater the uplift rate the greater the rate of vertical incision and consequently the less the like lihood of strath terrace formation and preservation

the uplift of the adriatic flank of the apennines since the middle pleistocene new insights from the tronto river basin and the acquasanta terme travertine central italy abstract the apennines chain is an active neogene fold and thrust belt resulting from the westward subduction of the adriatic microplate starting from the end of the early pleistocene the chain was affected by an increase in regional uplift recent gps data resolved uplift rates of 1 2 mm yr for the whole apennines whereas in the adriatic flank several studies estimated rates between 0 3 and 0 5 mm yr over the last 1 myr a number of works investigated the evolution of the drainage systems along the periadriatic margin of the apennines providing long term incision rates studies from the northern part of this sector reported uplift rates varying from 0 2 to 1 1 mm yr whereas only few studies concentrated on the central sector of the adriatic flank of the apennines focusing mainly on the evolution of the lower reach of major rivers this work aims to quantify the long term rock uplift and incision rates of the eastern portion of the central apennines through the analysis of the tronto river basin because of its geologic and geomorphological configurations this basin is an ideal test site to investigate the influence of tectonics and climate on the recent topographic evolution of the central apennines the basin extends with a roughly wsw ene direction from the inner sector of the chain to the adriatic coast crossing several tectonic structures such as the amatrice extensional basin and the acquasanta and montagna dei fiori anticlines in particular in the acquasanta terme area the right flank of the tronto river valley is characterized by fluvial and travertine deposits organized and exposed in several levels in this work we investigated the hydrography river longitudinal profiles and topography swath profile slope and local relief of the tronto river basin coupling these data with field observations and geochronological analysis on the continental sediments fluvial deposits and travertines outcropping in the acquasanta terme area to better characterize the nature of travertines we performed geochemical characterization of three travertine forming thermal springs obtaining their physico chemical parameters the percentage of dissolved gases and the isotopes content finally we applied a knickpoint celerity model to chronologically constrain the geomorphological evolution of the whole drainage system the results show the occurrence of a continuous tectonic uplift 0 5 mm yr across the study area since middle pleistocene the uplift together with climate fluctuations drove the incision 0 6 mm yr of the landscape and the delineation of the present drainage network these data are consistent with previous estimates of uplift and incision rates in adjacent areas and provide new constraints on the quaternary evolution of the central apennines this study highlights how the coupling of field surveys with morphometric and topographic analyses of a drainage system is crucial to understand and quantify the influence of tectonic and climate changes in shaping the landscape

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

temperature dependent thermal expansivities of silicate melts the system anorthite diopside abstract the temperature dependent thermal expansivities of melts along the join anorthite diopside have been determined on glassy and liquid samples using a combination of calorimetry dilatometry and pt double bob archimedean densitometry supercooled liquid volumes and molar thermal expansivities were determined using scanning calorimetric and dilatometric measurements of properties in the glass region and their behavior at the glass transition the extraction of low temperature liquid molar expansivities from dilatometry calorimetry is based on an assumed equivalence of the relaxation of volume and enthalpy at the glass transition using a method developed and tested by webb et al 1992 this method corrects for transient effects at the glass transition which can lead to serious overestimates of liquid thermal expansivity from peak values superliquidus volumes were determined using double pt bob archimedean densitometry at temperatures up to 1650 c the resulting data for liquid volumes near glass transition temperatures 810 920 c and at superliquidus temperatures 1400 1650 c are combined to yield thermal expansivities over the entire supercooled and stable liquid range the molar expansivities are in general temperature dependent the temperature dependence of thermal expansivity increases from anorthite to diopside composition the thermal expansivity of anorthite is essentially temperature independent whereas that of diopside decreases by 50 between 800 and 1500 c with the consequence that the thermal expansivities of the liquids in the anorthite diopside system converge at high temperature

geomorphological evidence for anti apennine faults in the umbro marchean apennines and in the peri adriatic basin italy abstract the apennines are a relatively recent mountain chain which has been affected by uplift movements since the upper pliocene in fact the remnants of an erosional surface reduced close to base level is preserved at the top of the relief there is no general agreement on the geodynamic stress field and mechanisms which are creating the chain however it is largely accepted that uplift occurred together with the activation on the western side of the chain of extensive faults oriented in the apennine direction nw se which have been linked to the opening of the tyrrhenian sea a great debate is going on about the presence and significance of anti apennine faults ne sw which have been observed by some authors but completely denied by others the main evidence is represented by 1 block faulting of the remnants of the erosional surface along the marchean ridge more elevated relief delimiting relatively depressed areas was created in correspondence with the sibillini mts and mt s vicino similar evidence has been found in the umbro marchean ridge locally more than 1500 metres of displacement have been observed between more and less uplifted remnants 2 block faulting of fan deltas and related beaches of sicilian to crotonian age with more elevated sediments preserved between the tronto and tenna rivers and between the musone and esino rivers maximum displacement along a transect parallel to the coast is 200 metres 3 fault scarps affecting the middle pleistocene river terraces as observed along the esino the tronto the chienti and the tenna river valleys maximum displacements are in the order of 50 metres 4 faulting of horizontal karst galleries and reorientation of the cave network as in the frasassi gorge maximum displacements are about 100 metres 5 captures and alignments in the drainage network of the main river courses 6 large scale gravitational movements as in the ancona landslide and along the chienti and esino rivers their activation occurred in most cases after the lower pleistocene and although their displacements may be of relatively limited extent dispite their recent activity they played a major role in the modelling of the landscape these faults display transtensive extensional and trascurrent movements apart from the controversial geodynamic significance of these faults from a geomorphological point of view they must be considered transverse elements of the stress field from blocks more or less uplifted along the apennine chain the importance and timing of activity of these faults in the quaternary geomorphological evolution of the umbria marchean apennines is demonstrated using evidence usually underestimated by structural geologists which can contribute to a debate based on a multidisciplinary approach

river patterns and their meaning abstract rivers are largely responsible for shaping the earth s continental landscapes river patterns the spatial arrangements of channels in the landscape are determined by slope and structure at site and sector scale channel morphology varies spatially and in time but river patterns and drainage texture or the frequency of stream lines per unit area together determine the intricacy or otherwise of topography most river patterns evolve through natural selection slope induces the formation of such patterns as parallel radial and distributary while structure produces straight angular trellis and annular arrangements once established patterns tend to persist nevertheless at many sites the usual patterns have been disturbed and patterns that are anomalous in terms of slope and structure have been produced by diversion tectonism volcanism glaciation mass movements and human activities by antecedence superimposition inheritance or underprinting by the persistence of deeply eroding rivers which encounter alien structures and by climatic change river patterns provide clues to underlying structure and to the chronology of events they have also proved significant in the search for minerals

influence of pre eruptive degassing and crystallization on the juvenile products of laterally directed volcanic explosions abstract strikingly similar examples of edifice collapse and directed blast are the 18 may 1980 eruption of mount st helens msh washington usa and the 30 march 1956 eruption of bezymianny volcano bz kamchatka russia in these cases flank failures led to near instantaneous decompression and fragmentation of intra edifice cryptodome magma which produced catastrophic laterally directed blasts in both instances the blast products consisted of juvenile material with bimodal density vesicularity distributions low and high density modes at 1900 and 2400 kg m 3 for bz 1600 and 2300 kg m 3 for msh although the proportion of high density material is greater at bz blast materials also exhibit striking variety in groundmass crystallinity 90 vol despite having fairly uniform pheno crystallinities suggesting that degassing driven groundmass crystallization occurred to varying extents within cryptodome magma at both volcanoes new bulk rock h2o and d measurements confirm that progressive open system outgassing occurred prior to both blasts the correlations between crystallinity clast density and bulk h2o contents suggest that syn blast magma expansion was modulated both by non uniform volatile distribution within the cryptodome and rheological controls associated with non uniform crystal content spatial heterogeneities in volatiles and crystallinity within a given cryptodome are attributed to distance from the wallrock margin which probably correlates with timing of magma injection the greater proportion of high density material at bz is speculatively related to lower blast energy compared with msh

coupled conduit and atmospheric dispersal dynamics of the ad 79 plinian eruption of vesuvius abstract the ad 79 eruption of vesuvius is certainly one of the most investigated explosive eruptions in the world this makes it particularly suitable for the application of numerical models since we can be quite confident about input data and the model predictions can be compared with field based reconstruction of the eruption dynamics magma ascent along the volcanic conduit and the dispersal of pyroclasts in the atmosphere were simulated the conduit and atmospheric domain were coupled through the flow conditions computed at the conduit exit we simulated two different peak phases of the eruption which correspond to the emplacement of the white and gray magma types that produced plinian fallout deposits with interlayered pyroclastic flow units during the gray phase the input data independently constrained and representative of each of the two eruptive phases consist of liquid magma composition crystal and water content mass flow rate and pressure temperature depth of the magma at the conduit entrance a parametric study was performed on the less constrained variables such as microlite content of magma pressure at the conduit entrance and particle size representative of the eruptive mixture numerical results are substantially consistent with the reconstructed eruptive dynamics in particular the white eruption phase is found to lead to a fully buoyant eruption plume in all cases investigated whereas the gray phase shows a more transitional character i e the simultaneous production of a buoyant convective plume and pyroclastic surges with a significant influence of the microlite content of magma in determining the partition of pyroclast mass between convective plumes and pyroclastic flows

quaternary geomorphological evolution of the tremiti islands puglia italy abstract the archipelago of the tremiti islands situated in the centre of the adriatic sea is considered nationally and internationally a very important geological laboratory in the area of connection between the central and southern apennines already rich in cenozoic stratigraphic structural and seismological data this study discusses structural geomorphologic data with particular attention to features useful to define the islands quaternary evolution the identification of the main morphogenic events is based on the study of landforms that are spatially and chronologically comparable with depositional erosional features of the quaternary continental succession analysis of geomorphology and quaternary continental deposits supported by radiometric dating allows reconstruction of the islands quaternary evolution and provides some contributions at a regional scale

new data on holocene relative sea level along the abruzzo coast central adriatic italy abstract a continuously cored borehole was used to analyse holocene relative sea level changes in the pescara coastal plain located along the central adriatic coast abruzzo central italy the core was retrieved from the uppermost 19 m deposits 600 m from the present day shoreline sedimentological and palaeontological analyses identified a transition from fluvial strata to brackish water lagoon and foreshore deposits five biological sea level markers were sampled and their ages constrained by ams 14 c dating span between 2 39 and 7 68 ka cal bp heights m above mean sea level of the collected samples have been corrected taking into consideration uncertainties of the vertical positioning with respect to palaeo sea level vertical tectonic displacements have been evaluated through the comparison of relative sea level data with the site specific predicted holocene sea level curve correlations with available morphotectonic and stratigraphic data also were used the results suggest negligible rates of vertical tectonic displacement during the holocene at least along a coastal strip of 40 km located between pescara and sangro river mouths abruzzo

interactions between mantle upwelling drainage evolution and active normal faulting an example from the central apennines italy summary in this paper we show that the processes that have shaped the quaternary surface development of the apennines in central italy are all consequences of a single subcrustal process the upwelling of the mantle the relationship between gravity and topography shows that mantle convection is responsible for a long wavelength 150 200 km topographic bulge over the central apennines and stratigraphic evidence suggests this bulge developed in the quaternary active normal faulting is localized at the crest of this bulge and produces internally draining fault bounded basins these basins have been progressively captured by the aggressive headward erosion of major streams that cut down to the sea on the flanks of the regional bulge the only surviving closed basins are those on the apennine watershed most distant from the marine base level where continued normal faulting is still able to provide local subsidence that defeats their capture by the regional drainage network understanding the competition between regional capture and local fault related subsidence of intermontane basins is crucial for recognizing potentially hazardous active faults in the landscape and also for interpreting the sediment supply to adjacent offshore regions central italy provides a good modern analogue for processes that are probably common in the geological record particularly on rifted margins and intracontinental rifts but may not have been fully appreciated

emplacement history of a low viscosity fountain fed pantelleritic lava flow abstract the strongly peralkaline 8 ka flow mayor island new zealand was emplaced as a low viscosity fountain fed lava flow the flow stratigraphy comprises from top to base a finely vesicular pumiceous carapace an upper obsidian layer central crystalline rhyolite a lower obsidian layer incorporating a crumble breccia above a fall lapilli unit rare relict clasts welded within the lowermost 0 5 m of the lower obsidian layer support a fountain fed origin for the 8 ka flow five physical parameters density porosity microlite size void and autoclast aspect ratios and water content were measured throughout the thickness of the lava flow and show that prolonged vesiculation occurred in the upper 33 of the flow thickness and that autoclast and pyroclast shapes and microlite lengths were influenced by the thermal conditions of the lava after eruption crystallisation of the flow interior commenced before the flow stopped moving compared with calc alkaline rhyolites the high flow temperature 950 c and peralkaline chemistry contributed to a less polymerised low viscosity melt log 6 4 pa s these data and structural observations of the 8 ka flow suggest that near complete homogenisation and remobilisation of spatter from a lava fountain occurred on the caldera rim producing a distally tapering lava sheet that also spilled back down the caldera wall towards the vent

textural evidence for dilatant shear thickening rheology of magma at high crystal concentrations investigation of the rheology of magmas at high crystal concentrations by experimental means has proved problematic an alternative approach is to study textures of igneous rocks that not only preserve evidence of the kinematics of magma flow such as flow direction but can also preserve evidence of rheology flow textures in multiply intruded trachyte dykes on fraser island eastern australia record evidence of dilatant flow during solidification this conclusion is reached by interpretation of microscopic ductile shear zones that disrupt the groundmass of aligned feldspar laths detailed three dimensional investigation demonstrates that the dihedral angle between conjugate micro shear zones is approximately 65 this conjugate angle is equivalent to that observed in dilatant granular materials such as sand dilatant behaviour is synonymous with shear thickening rheology indicating that the magma flow is time dependent and resists high flow rates some of the dykes contain autobrecciation fragments that may represent localities where the ductile flow rate threshold was exceeded newtonian or pseudoplastic shear thinning rheology of crystal poor magmas must progressively give way to shear thickening rheology during cooling and increasing crystal concentration

origin of the bolivian andean orocline a geologic study utilizing landsat and shuttle imaging radar abstract the origin of the major andean orocline in bolivia where the north trending southern andes abruptly change direction by 45 and continue northwestward into peru has been investigated by photogeologic techniques utilizing landsat imagery and shuttle imaging radar sir a in conjunction with published literature and maps the evidence suggests that this orocline might have been formed beginning in the miocene by the pacific coastal region being bent around the resistant brazilian shield as a result of the relative motions between the eastward moving coastal region and the westward moving south american continent the eastward motion of the coast was further increased about 10 m y b p when the opening of the east pacific rise increased the rate of eastward motion of the subducting nazca plate the brazilian shield with its deep roots provided greater resistance to this motion resulting in the decoupling of the andes along a wide left lateral strike slip fault zone extending east west from the altiplano through santa cruz and into the interior indicated left lateral motion across this fault decreases from 180 km on the east side of the andes to 50 or 60 km in the altiplano the difference being taken up in compressing the eastern cordillera and sub andean foredeep from an average width of 350 km in southern bolivia and argentina to an average width of 220 km in northern bolivia and peru the resistance of the shield may also have resulted in counter clockwise rotation of and lateral angular shear in the andes north of the break zone

progressive growth of the cerro bayo cryptodome chachahuen volcano argentina implications for viscous magma emplacement cryptodome and dome collapse is associated with volcanic hazards such as explosive eruptions pyroclastic flows and volcanic edifice collapse study of the growth and evolution of volcanic domes

an expanded model and application of the combined effect of crystal size distribution and crystal shape on the relative viscosity of magmas abstract this study examines the combined effect of crystal size distributions csd and crystal shape on the rheology of vesicle free magmatic suspensions and provides the first practical application of an empirical model to estimate the relative effect of crystal content and csd s on the viscosity of magma directly from textural image analysis of natural rock samples in the form of a user friendly texture rheology spreadsheet calculator we extend and apply established relationships between the maximum packing fraction m of a crystal bearing suspension and both its rheological properties and the polydispersity of a csd by using analogue rotational rheometric experiments with glass fibres and glass flakes in silicone oil acting as magma equivalent this study also provides new insights in the relationship between m and the aspect ratio rp of suspended particles

diverging drainage in the marche apennines central italy abstract in the marche apennines diverging drainage developed on the surface of mid pleistocene fanglomerates or at places on correlated erosional glacis in mountain areas diverging nets correspond with wide glacis shaped in severe cold climates at the end of the middle pleistocene glacis were formed by deposition of coalescing alluvial fans and concurrent shaping of smooth erosional surfaces along and near their margins in the coastal zone wide fans and related fluvial plains were constructed in crotonian times close to the mouth of trunk streams crossing a just emerged piedmont area both the control of the cone shaped topography on post aggradational flow patterns and the entrenching of primitive distributary channels are conceivable in developing the diverging drainage of the study area four case studies from areas differing both in age and in geological and structural settings attest to the recurrence of this drainage in composing together with other patterns the grain of larger nets moreover the diverging drainage of the coast area allows us to infer that superposition is an effective mechanism of net development on plio pleistocene terrains of the marche apennine piedmont at the time when they became emergent

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

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

rheology of arc dacite lavas experimental determination at low strain rates andesitic dacitic volcanoes exhibit a large variety of eruption styles including explosive eruptions endogenous and exogenous dome growth and kilometer long lava flows the rheology of these lavas can be investigated through field observations of flow and dome morphology but this approach integrates the properties of lava over a wide range of temperatures another approach is through laboratory experiments however previous studies have used higher shear stresses and strain rates than are appropriate to lava flows we measured the apparent viscosity of several lavas from santiaguito and bezymianny volcanoes by uniaxial compression between 1 109 and 1 315 k at low shear stress 0 085 to 0 42 mpa low strain rate between 1 1 10 8 and 1 9 10 5 s 1 and up to 43 7 total deformation the results show a strong variability of the apparent viscosity between different samples which can be ascribed to differences in initial porosity and crystallinity deformation occurs primarily by compaction with some cracking and or vesicle coalescence our experiments yield apparent viscosities more than 1 order of magnitude lower than predicted by models based on experiments at higher strain rates at lava flow conditions no evidence of a yield strength is observed and the apparent viscosity is best approached by a strain rate and temperature dependent power law equation the best fit for santiaguito lava for temperatures between 1 164 and 1 226 k and strain rates lower than 1 8 10 4 s 1 is log eta text app 0 738 9 24 times 10 3 t k 0 654 cdot log dot varepsilon where app is apparent viscosity and dot varepsilon is strain rate this equation also reproduced 45 data for a sample from bezymianny with a root mean square deviation of 0 19 log unit pa s applying the rheological model to lava flow conditions at santiaguito yields calculated apparent viscosities that are in reasonable agreement with field observations and suggests that internal shear heating may be significant ongoing heat source within these flows enabling highly viscous lava to travel long distances

the jebel hadid structure al kufrah basin se libya a possible impact structure and potential hydrocarbon trap abstract the jebel hadid structure that formed in the nubian sandstone of the southern al kufrah basin is a 4 7 km circular feature with a set of multiple concentric annular ridges the age of the structure is probably post early cretaceous to pre pliocene as the prevalent geological processes that usually account for the formation of circular structures magmatism diapirism sand volcanism karst dissolution glacial erosion can be widely excluded in this region we suggest that the jebel hadid structure might represent an eroded complex impact structure in particular the jebel hadid structure bears a strong morphological resemblance to the impact structure of tin bider in algeria general host rock properties may be compared to those at the upheaval dome impact structure usa numerous terrestrial impact structures are hosts to hydrocarbon reservoirs this investigation provides a first prospective approach based on remote sensing discussing the economic potential of a circular structure of suspected impact origin the still underexplored al kufrah basin is considered as a high potential area for future hydrocarbon exploration if we consider a possible impact origin of the jebel hadid structure this feature might provide local secondary pathways and traps for hydrocarbon migration accumulation in the nubian series and thus ought to be considered as a preferential site for oil and gas exploration

deformation of foamed rhyolites under internal and external stresses an experimental investigation the style of magma eruption depends strongly on the character of melt degassing and foaming depending on the kinetics of these processes the result can be either explosive or effusive volcanism in this study the kinetics of foaming due to the internal stresses of gas expansion of two types of obsidian have been investigated in time series experiments 2 min 24 h followed by quenching the samples the volumetric gas melt ratio has been estimated through the density measurements of foamed samples

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

groundmass crystallisation and cooling rates of lava like ignimbrites the grey s landing ignimbrite southern idaho usa constraining magmatic and eruptive processes is key to understanding how volcanoes operate however reconstructing eruptive and pre eruptive processes requires the ability to see through any post eruptive modification of the deposit the well preserved grey s landing ignimbrite from the central snake river plain provides an opportunity to systematically investigate the post eruptive processes occurring through a single deposit sheet despite overall compositional homogeneity in both bulk and glass compositions the grey s landing ignimbrite does preserve differences in the abundance of li in plagioclase crystals which are strongly associated with the host lithology li abundances in plagioclase from the quickly cooled upper and basal vitrophyres are typically low average 5 ppm n 262 while plagioclase from the microcrystalline interior of the deposit has higher li contents average 33 ppm n 773 given that no other trace elemental parameter in plagioclase varies we interpret the variability in li to reflect a post depositional process groundmass crystallisation of a rhyolite like grey s landing requires 50 crystallisation of sanidine and variable amounts of a silica rich phase quartz tridymite cristobalite and plagioclase to satisfy mass balance we suggest the low affinity of li for sanidine causes migration of groundmass li into plagioclase during crystallisation even within the microcrystalline interior of the deposit the morphology of the groundmass varies the more marginal finer grained regions are dominated by cristobalite as the sio2 rich phase while tridymite and quartz are additionally found in the more slowly cooled coarser grained portions of thick sections of the ignimbrite numerical models of cooling and crystallisation tested against field observations indicate that the groundmass crystallisation occurred relatively rapidly following emplacement a maximum of a few years where the ignimbrite is thickest these numerical models also illustrate that the time at which the potential for rheomorphism ceases either the ignimbrite is a solid glass or 50 crystalline is diachronous across the deposit

microlites and nanolites in rhyolitic glass microstructural and chemical characterization we used transmission electron microscopy tem and scanning electron microscopy sem to study magmatic crystals in the ben lomond rhyolite lava dome taupo volcanic center new zealand using tem and sem to investigate the size distributions of these crystals we identified three size populations microphenocrysts 1 2 m wide microlites 0 6 m wide and smaller crystals 0 6 m wide which we term nanolites the predominant mineral phases of the microlites and nanolites are augites pigeonites and hypersthenes the compositions and microstructures within these pyroxenes indicate disequilibrium crystallization at approximately 850 900 c and undercoolings as high as 300 c from equilibrium crystallization temperatures complex microstructures resulting from subsolidus reactions in augite and pigeonite are consistent with moderate cooling rates within the upper obsidian layer of the ben lomond rhyolite dome this study demonstrates the existence of sub micron magmatic crystals in a rhyolite and illustrates the potential of tem to provide unique information about the crystallization and cooling histories of glassy volcanic rocks

neogene paleomagnetism and oroclinal bending of the central andes of bolivia geophysical and tectonic evidence suggests that the principal vertical axis bending of the bolivian orocline is a late cenozoic event related to subduction and andean uplift to further test this hypothesis paleomagnetic data are presented from miocene basins within the altiplano and cordillera oriental of bolivia located in the presumed southern limb of the orocline to factor out potential vgp data samples were collected from sedimentary sections spanning at least 0 5 m y new paleomagnetic data are presented for two sites i e gerdas 21 s latitude 16 15 ma and quehua 20 s latitude 13 7 ma in conjunction with previously published paleomagnetic results from middle to late tertiary rocks from bolivia and peru spanning some 16 of latitude 6 22 s a consistent pattern of oroclinal development is as follows significant counterclockwise rotation about 15 20 in the northern limb negligible rotation in the axis at the latitude of the arica deflection and significant clockwise rotation about 15 20 in the southern limb although these paleomagnetic data could represent independent mesoscale 102 to 104 km2 block rotations the preferred interpretation is that they confirm the hypothesis that a significant portion about 30 40 of the oroclinal bending occurred during the late cenozoic using the unit mean paleomagnetic declinations in the well dated sections minimum rates of oroclinal bending during the late cenozoic are calculated to range from 0 6 m y to 1 7 m y the remaining 15 20 of observed curvature of the orocline probably resulted from an earlier phase of andean deformation or may represent the shape of the ancestral andes

modelling the impact of regional uplift and local tectonics on fluvial terrace preservation abstract a terrace formation model terrace combined with a longitudinal river profile model fluver was used to simulate fluvial terrace formation and preservation in the northwest iberian lower mino river basin under the influence of three tectonic conditions namely regional vertical uplift local basin subsidence and localised differential uplift the simulation results were compared against mapped terrace altitudes and deposit thicknesses the best results were achieved by combining all three tectonic factors indicating that specific terrace formation is a complex interplay of regional and local tectonics the best fit regional uplift rate of 0 10 m ka 1 over the past 600 ka is higher than the 0 08 m ka 1 previously estimated for a section farther to the west which can be attributed to an increase in tectonic uplift from the nw iberian atlantic margin toward the east local relative subsidence causes sediment accumulation in the local basin and less sedimentation in the fluvial terraces on the surrounding uplifting blocks different uplift rates on both sides of the valley caused preservation of unpaired terraces which are fill terraces on one side of the valley and strath terraces on the other side usually the formation of fill or strath terraces is considered to be only climate dependent our results indicate that local tectonics can be important in the terrace formation and preservation this suggests that terrace correlations in other river systems based on deposit thicknesses only might be over simplified

hyperquenched volcanic glass from loihi seamount hawaii abstract explosive submarine basaltic eruptions occurring in water depths of several kilometres commonly result in the formation of layered volcaniclastic deposits in order to quantify the cooling of such volcaniclastics we have identified and separated two types of glassy fragments from these deposits on loihi seamount 1 fine 30 80 m limu o pele bubble wall fragments and 2 coarser 0 8 1 2 mm dense angular fragments these pristine basaltic glasses have been subjected to differential scanning calorimetry dsc from room temperature up to temperatures above their glass transition heat capacity c p in j g 1 k 1 data reveal glassy and liquid regimes separated by clear hysteresis behaviour within the glass transition the transient c p in the glass transition interval exhibits a deep trough before the peak indicating very high cooling rates it is a classic feature of so called hyper quenching having been observed in dsc experiments on glasses produced using the splat quench d b dingwell p courtial d giordano and a r l nichols viscosity of peridotite liquid earth and planetary science letters 226 1 2 127 138 2004 and cascade fibre spinning y z yue j d christiansen and s l jensen determination of the fictive temperature for a hyperquenched glass chemical physics letters 357 1 2 20 24 2002 techniques the trough is deepest for the limu o pele fragments energy matching methods developed for the estimation of cooling rates for such glasses yield a rate of 10 5 31 k s 1 for the cooling of the fine sieve fraction of limu glass on the sea floor at loihi thus limu o pele volcaniclastics believed to be formed during mild submarine pyroclastic eruptions have experienced the fastest cooling of any natural volcanic glass measured to date such extreme cooling rates are likely to impact on many chemical and physical aspects of the stability of these glasses on the sea floor as well as their use as proxies for field variables of the earth s physical state and as monitors of the efficiency of chemical lithosphere hydrosphere exchange

textural history of recent basaltic andesites and plutonic inclusions from merapi volcano mt merapi in central java is one of the most active stratovolcanoes on earth and is underlain by a multistage plumbing system crystal size distribution analyses csd were carried out on recent merapi basaltic andesites and co eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales the basaltic andesites exhibit log linear kinked upwards csd curves for plagioclase and clinopyroxene that can be separated into two main textural populations large plagioclase phenocrysts 1 6 mm make up one population but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid crustal levels this population was subsequently influenced by crystal accumulation and the onset of crustal assimilation including the incorporation of high ca skarn derived xenocrysts textural re equilibration is required for these crystals to form a single population in csd a second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals 1 6 mm in size crustal assimilation is indicated by for example oxygen isotopes and based on the csd data crystallisation combined with contamination is likely semi continuous in these upper crustal storage chambers the csd data observed in the basaltic andesite samples are remarkably consistent and require a large volume steady state magmatic system beneath merapi in which late textural equilibration plays a significant role plagioclase csds of co eruptive magmatic and plutonic inclusions may contain a third crystal population 1 mm not found in the lavas this third population has probably formed from enhanced degassing of portions of basaltic andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic andesite mush inclusions a suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep merapi plumbing system as deduced from csd patterns and mineral assemblages

spatter stability constraining accumulation rates and temperature conditions with experimental bomb morphology we have developed the first experimental methodology to create a volcanic spatter pile using molten basalt this method permits reproduction of thermal conditions that yield the wide variety of spatter morphologies observed in nature the morphology of the clasts is most strongly controlled by the time the clast spends above the glass transition temperature which is in turn affected by the rate of accumulation and cooling of the deposit also spatter piles that remain hotter over longer durations experience increased fusion between clasts less void space between clasts and generally larger aspect ratios our experimental method successfully replicated natural microcrystal textures rheology and clast size work is still therefore required to achieve realistic vesicle distribution and deposit void space based on presented experimental work we estimate emplacement conditions of southern idaho spatter vents to have been 850 900 c with eruption temperatures closer to 1000 1100 c the rapid decrease from eruption temperature to effective emplacement temperature is the result of clast flight as well as equilibrating with the cooler surrounding material the morphology of the natural clasts matches experiments that have accumulation rates of 2 5 4 5 m h which also is consistent with the few measurements made at active eruptions finally we provide a constraint on the temperatures and accumulation rates that can lead to the construction of fused spatter features as well as provide the steps for future experiments to investigate other aspects such as compression impact and larger sizes of spatter formation by adapting our methodology

time dependent profiles of lava flows this work investigates the combined effects of a time dependent effusion rate and a spatially varying viscosity on the thickness profile of a flowing lava we formulate relatively simple governing equations as a primitive dynamical model for these two influences on lava flow morphology free boundary solutions for the profile of the flow and its extent are presented and analyzed for different boundary conditions at the source of the flow and several models for the spatial dependence of the viscosity the results presented here suggest that time dependence in the flow depth at the source and the form of the viscosity variation are significant influences on the morphology and dimensions of lava flows moreover this analysis implies that time dependent source conditions may contribute to the scatter in plots of eruption rate versus flow length and disparities between field and laboratory estimates of lava viscosity

rheology of melts from the colli albani volcanic district italy a case study in this study the first viscosity measurements in the glass transition range of melts from highly explosive large volume eruptions from the colli albani volcanic district cavd are presented the magmas are ultrapotassic rich in iron and cao and characterised by a low silica content 45 wt melt compositions range from tephri phonolitic to foiditic the colli albani eruptions appear anomalous since they produced a large volume of erupted material in spite of their silica undersaturated compositions the viscosity of the colli albani melt changes as the melt composition evolves from the original melt to a country rock contaminated melt to a crystal bearing melt with a permanent decrease in liquid viscosity conventional estimations of viscosities assume these magmas to have a low viscosity the presented data show that the melt viscosities are higher than expected taking into account further chemical or rheological features of a melt the investigated cavd melts are not that striking as assumed in comparison with other large volume eruptions consequently considering the alkaline earth to alkaline ratio together with the sio2 content could provide an alternative when comparing large volume eruptions

morphotectonic study of the lower sangro river valley abruzzi central italy abstract this work analyses the morphotectonic setting of the adriatic piedmont of central italy in order to outline the role of tectonics in the development of the fluvial landscape in this area particularly it focuses on the sangro river which flows in the southern abruzzi from the apennines through the piedmont to the adriatic coast the piedmont area developed in a marine environment from the pliocene to the early pleistocene resulting in the deposition of a clayey sandy sequence afterwards regional uplift processes with ne tilting led to the deposition of a regressive conglomeratic sequence as the area evolved into a continental environment this work is based on the qualitative and quantitative study of drainage patterns and on the analysis and correlation of selected morphological evidence of tectonics on fluvial terraces in order to define the role of tectonics in the geomorphological evolution of the lower sangro river valley the drainage network and its statistical azimuthal distributions are analysed the distribution and the transverse and longitudinal profiles of fluvial terraces are investigated and the morphological evidence for tectonics is then assessed river bends linear valleys beheaded and hanging valleys counterflow confluences of streams space and time correlation of these features allows us to highlight the effects of regional uplift tilting and local tectonics on drainage development following the emergence of the piedmont area middle pleistocene uplift and tilting determined a sw ne consequent and parallel drainage progressive incision shaped the sangro valley as a consequent valley local tectonics along nnw sse and wnw ese faults and fractures resulted in the incision of linear valleys beheading the previous sw ne drainage and controlled the development of a rectangular drainage network late middle pleistocene the drainage network was then rearranged by selective erosion processes maintaining a strong inheritance from of its middle pleistocene configuration

origin of rectangular and aligned lakes in the beni basin of bolivia abstract the origin of aligned rectangular shaped lakes in the beni basin of bolivia has been investigated utilizing landsat imagery shuttle imaging radar and the available scientific literature the lakes tend to line up in two preferred orientations northwest and northeast they occur in cenozoic sediments of the beni basin situated between the brazilian shield and the andean foredeep available evidence suggests that the shapes and orientations of the lakes are primarily controlled by a nearly orthogonal fracture pattern propagated upward from the underlying granitic brazilian shield basement these orientations and shapes may reflect a reactivated ancient global fracture pattern or may be the result of an e w greatest principal compressive stress 1 and subsequent downwarping and uplifting of the beni basin during the cenozoic andean orogeny the lakes themselves may occupy down dropped basement blocks induced in the gently upwarped basement while unusual these lakes are not unique this suggests that transmission of basement structure through overlying sediments may occur in other regions but that special conditions such as little or no lateral compression of the sediments the absence of high trees and vegetation stability of surface material from drifting and a high water table are necessary to preserve and enhance such surface features

the geochemical characteristics of granitoids in contrasting arcs and comments on magma sources geochemical variations in modern subduction related igneous suites with respect to arc maturity in time and space are illustrated using data for both volcanic suites basalt andesite and dacite and intrusive granitoid suites diorite tonalite granodiorite and granite from circum pacific arcs using trace element data we suggest that two groups of processes control the natural variation in the parental magmas of both suites a subduction zone enrichment of lithospheric mantle locally coupled with crustal assimilation allied with fractional crystallization afc in zones of thickened crust all of which yield magmas with enhanced concentrations of the large ion lithophile lil elements k rb th u lrees etc b with increasing distance from the active trench contributions from within plate sub continental lithosphere producing mantle derived magmas with enhanced levels of high field strength hfs elements among which nb ta hf and y are particularly distinctive thus even for the evolved granitoids of intrusive arc series ratios of hfs lil elements not significantly affected by crystal fractionation such as ta nb k rb la may throw some light on the origin of mafic intermediate precursor magmas in terms of these elements we suggest the following groupings for interpreting the tectonic associations of granitoid suites 1 primitive calcic arc granitoids with low lil and hfs element abundances 2 normal calc alkaline continental arc granitoids with enhanced lil element abundances and low hfs lil ratios 3 mature alkali calcic arc granitoids with high levels of lil and hfs elements and higher hfs lil ratios 4 back arc anorogenic alkaline granitoids with the highest levels of hfs elements

the geology and tectonic setting of the velasco alkaline province eastern bolivia the velasco alkaline province of mesozoic age is situated near to the bolivian brazilian border and is enclosed in precambrian gneisses of the brazilian shield it consists of an early volcanic suite and a series of 14 interfering circular ring and elliptical plutons and is associated with a silicified carbonatite complex the combined length of the province is nearly 80 km and it outcrops over an area of 440 km 2 the plutonic rock types range from foyaite to aegirine granite but each individual pluton may be classified as either over or under saturated the province was built up by a series of plutonic events which for the most part were aligned along a ne trending lineament normal faulting was active during the development of the province although the velasco alkaline province lies over 1500 km from the eastern continental margin it is deduced that it defines a plume generated triple point initiated at the same time as the break up of the south american africa plate

holocene millennial scale erosion and deposition processes in the middle reaches of inland drainage basins arid china in inland drainage basins many studies have been conducted regarding the geomorphologic evolution processes in the upper and lower reaches few of them have been done on the middle reaches which are the pivotal areas connecting the erosion effects of the upper reaches and the deposition processes in terminal areas in this study we presented a millennial scale study from middle reaches of the shiyang river and the shule river drainage basins during the holocene several sedimentary sections are selected to calculate millennial scale erosion and deposition rates results show that the middle reaches of the shiyang river and the shule river are characterized by deposition processes in the early and middle holocene but erosion processes prevailed during the late holocene at the same time the sedimentary facies grain size geochemical proxies and pollen proxies of the sediments from middle reaches of the two drainages were used to complement the erosion and deposition rates which are good for understanding the environment background during the geomorphologic evolution processes besides the main factor affecting the basin wide geomorphologic evolution is millennial scale climate change and the responses of the middle reaches to climate change are different from those of the upper and lower reaches