an overview of experimental models to understand a complex volcanic instability application to mount etna italy abstract volcanic edifices are often unable to support their own load triggering the instability of their flanks many analogue models have been aimed especially in the last decade at understanding the processes leading to volcano flank instability general behaviors were defined and the experimental results were compared to nature however available data at well studied unstable volcanoes may allow a deeper understanding of the specific processes leading to instability providing insights also at the local scale etna italy constitutes a suitable example for such a possibility because of its well monitored flank instability for which different triggering factors have been proposed in the last two decades among these factors recent insar data highlight the role played by magmatic intrusions and a weak basement under a differential unbuttressing at the volcano base this study considers original and recently published experimental data to test these factors possibly responsible for flank instability with the final aim to better understand and summarize the conditions leading to flank instability at etna in particular we simulate the following processes a the long term activity of a lithospheric boundary as the malta escarpment separating the ionian oceanic lithosphere from the continental sicilian lithosphere below the most unstable east flank of the volcano b spreading due to a weak basement with different boundary conditions c the pressurization of a magmatic reservoir as that active during the 1994 2001 inflation period d dike emplacement as observed during the major 2001 and 2002 2003 eruptions the experimental results suggest that 1 the long term activity of a lithospheric tectonic boundary may create a topographic slope which provides a differential buttressing at the volcano base a preparing factor to drive longer term 10 5 years instability on the east flank of the volcano 2 volcano spreading 4 years has limited effect on flank instability at etna 3 magmatic intrusions 1 years both in the form of mogi like sources or dikes provide the most important conditions to trigger flank instability on the shorter term

the influence of melting and melt drainage on crustal rheology during orogenesis partial melting significantly weakens crustal rocks by introducing a low viscosity liquid phase however near concomitant melt drainage can remove this weak phase potentially reversing the rheological effects such that the strength of a specific lithology depends on when the prograde pressure temperature path intersects a melting reaction how much melt is produced and how long this melt is retained before it is lost phase equilibria and mixed rheology modeling of typical metapelite and metagreywacke compositions indicate that these rocks undergo continuous but pulsed melt production during prograde metamorphism depending on whether melt removal is continuous or episodic and assuming geological strain rates the lithologies can retain a very low strength less than 1 mpa or transiently strengthen to 5 mpa following melt loss lithologies undergoing episodic melt loss can therefore cycle between being relatively weak and relatively strong components within a composite crustal section melt production retention and weakening in the middle to lower crust as a whole is more sustained during heating and melt production consistent with geodynamic inferences of weak melt bearing lower crust however the long term consequence of melting and melt loss is a 50 400 increase in the strength of residual lithologies the strengthening is more pronounced in metapelite than metagreywacke and is achieved through a combination of dehydration and the removal of the weak mica framework coupled to increased proportions of strong feldspars and garnet despite prolonged weakness melting and melt loss therefore ultimately result in a dry and elastic lower crust

temperature dependent rheology of bouncing putties used as rock analogs abstract experimental investigations have been carried out at the hans ramberg tectonic laboratory to determine the temperature dependent rheology of two bouncing or silicone putties commonly used for tectonic modelling namely rhodorsil gomme silbion and dow corning dilatant compound no 3179 using a capillary viscometer rheologic data are summarized in plots of stress pa versus shear strain rate s 1 rhodorsil gomme is generally newtonian and hence shows constant viscosity irrespective of strain rate and temperature its viscosity decreases by three orders of magnitude from 105 pa s to 102 pa s over the investigated temperature range 23 90 c by contrast dow corning dc3179 exhibits different flow regimes at different stress temperature combinations and the flow stress shows strong strain rate dependence within the same temperature range below 60 c dc3179 deforms above its yield strength with variable stress exponent of n 1 in the strain rate range 10 2 to 10 4 s 1 above 10 2 s 1 the power law exponent n of this material exhibits newtonian flow n 1 previous work has shown this behaviour of dc3179 at room temperature to be similar to that of a bingham plastic above 60 c this material deforms as a newtonian fluid and softens with increasing strain rate the viscosity of dc3179 spans three orders of magnitude from 106 pa s to 103 pa s for the same temperature range both materials show large variations of viscosity suggesting that they are thermally unstable i e they have large activation energies we applied the steady state creep equation a exp q rt n to characterize the flow behaviour of the silicone putties where the universal gas constant r 8 31 j k 1 mole 1 q is an activation energy for creep and a and n are constants the stress exponent n and the activation energy q for rhodorsil gomme remains nearly constant q 42 2 kj mole but for dc3179 the activation energy varies with temperature and stress at the investigated temperature range 23 90 c whereas the steady state creep equation can be used to characterize the flow behaviour of rhodorsil gomme it does not provide a good fit to the experimental data for dc3179 the activation energy for dc3179 varies with temperature and stress however for a restricted temperature range 60 90 c its activation energy q 82 3 kj mole also remains nearly constant as was also mentioned by previous investigators rhodorsil gomme is a suitable newtonian analogue for rock flow in nature dc3179 seems to be appropriate both as a newtonian and non newtonian rock analogue depending on temperature strain rate and power law exponent the implications of the test results to salt flow in nature are assessed

failure of volcano slopes magmatic intrusions can initiate and sustain massive and catastrophic volcano collapse their role is twofold involving both driving and resisting forces first flank stability is diminished by magmastatic and magma overpressures and steepened slopes that accompany intrusion second excess pore pressures in potential failure zones can be generated as a result of intrusion related mechanical or thermal straining of the rock fluid medium pressurized retrograde boiling in high level magma chambers or hydrothermal fluid circulation also earthquakes may aid collapse through inertial forces and shaking induced pore pressure generation these excess pore pressures reduce the sliding resistance as shown for wedge shaped slide blocks for selected cases the destabilizing influence of mechanically induced pore pressures is maximized as the intruded width or corresponding overpressure of the intrusion is increased the destabilizing influence of thermally induced pore pressures is conditioned by the seve

thermal modelling of very long lived 140 myr high thermal gradient metamorphism as a result of radiogenic heating in the reynolds range central australia abstract the reynolds range in the paleo mesoproterozoic aileron province of central australia exposes a differentially exhumed metamorphic rock system varying from greenschist to granulite facies calculated p t pseudosections indicate that peak metamorphic conditions in greenschist facies areas reached temperatures of 480 c and pressures of 3 2 5 kbar peak conditions at amphibolite facies are constrained to 500 620 c and 1 3 3 8 kbar p t modelling of two petrologically different granulite facies samples indicate that peak conditions in the exhumed granulite facies rocks reached 780 920 c and 3 5 5 4 kbar corresponding to high apparent thermal gradients of 152 218 c kbar in the amphibolite facies rocks in situ la icp ms u pb monazite geochronology records ages that range between 1680 and 1550 ma in contrast in the granulite facies rocks monazite records ages of ca 1560 ma the terrane contains significantly elevated rates of crustal heat production compared to global norms and when incorporated into lithospheric thermal models with reasonable boundary conditions and average thermal properties can plausibly account for the long lasting metamorphic conditions the thermal modelling shows that the long lasting 100 myr record of monazite u pb ages supported by previous studies reflects a continuous duration of elevated crustal temperatures an interpretation consistent with texturally simple mineral assemblages that lack any evidence for polymetamorphism in high crustal heat production terranes high thermal gradients and high temperatures will persist until exhumation removes the upper crust this physical reality provides a basis for the existence of arbitrarily long lived metamorphic systems even under high thermal gradients that are generally considered to be thermally anomalous however such thermal anomalism is not remarkable as there is abundant evidence for elevated rates of crustal heat production in the reynolds range and worldwide in terranes where accessory minerals record large continuous ranges of age robust volumetric measurements of crustal heat production rates are a necessary step in evaluating the potential thermal significance of such geochronological records failure to document rates of crustal heat generation invalidates many interpretations for drivers of metamorphism

volcanic spreading at kilauea 1976 1996 the rift system traversing about 80 km of the subaerial surface of kilauea volcano has extended continuously since the m 7 2 flank earthquake of november 1975 widening across the summit has amounted to more than 250 cm decelerating after 1975 from about 25 to 4 cm yr 1 since 1983 concurrently the summit has subsided more than 200 cm even as the adjacent south flank has risen more than 50 cm the axes of the upper zones about 10 km from the summit subsided before 1983 at average rates of 9 and 4 cm yr 1 respectively and at rates of 4 and 3 cm yr 1 since the middle southwest rift zone is also subsiding and at the other end of kilauea s subaerial rift system subsidence along the lower east rift zone has averaged 1 2 cm yr 1 deformation of kilauea s south flank has been continuous although subject as well to displacements caused by major rift zone seismic swarms whereas horizontal strains across the subaerial south flank seem to have been generally compressive after 1975 they have been extensional since about 1980 or 1981 interrupted only by the east rift zone dike intrusion of 1983 because the magnitudes of these contractions and extensions are much less than the extension across the rift system the subaerial south flank is apparently sliding seaward on its basal decollement more than it is accumulating horizontal strains within the overlying volcanic pile kilauea suffers from gravitational spreading made even more unstable by accumulation of magma along the rift system at depths in excess of about 4 5 km in the presence hot rock incapable of withstanding deviatoric stresses this seismicly quiescent zone decouples the south flank from the rest of hawaii s volcanic edifice the rift zones at lesser depths exhibit a more brittle and therefore sporadic extensional behavior judging from the modern extension record of the summit which both predates the m 7 2 earthquake of 1975 and has outlived its 10 year period of aftershocks kilauea will continue to spread along its rift system as its south flank slips seaward to accommodate the accretion of magma and its relatively dense olivine rich differentiate

thorium distribution in the crust outcrop and grain scale perspectives abstract the spatial distribution of heat producing elements k u and th in the continental crust has long term implications for the thermal and physical evolution of orogens heat producing elements in particular th are most abundant in metasedimentary rock types as such these rock types have a significant control on the spatial distribution of heat production in the crust the major host of the heat producing element thorium in pelitic metasedimentary rocks is the ree th phosphate monazite we present in field gamma ray spectrometry in field grs data integrated with grain scale electron probe microanalysis data to reveal grain to terrane scale links in thorium distribution in field grs data shows that thorium is not depleted in granulite facies residual rocks that have lost melt with respect to their subsolidus counterparts concurrently the bulk thorium budget of monazite is approximately uniform within samples and if anything increases with increasing metamorphic grade monazite average grain size increases with metamorphic grade and prograde cores are largely preserved in granulite facies samples thorium is preserved in residual metasediments after melting and melt loss implying that even when melting and melt extraction is efficient it does not strip th from granulite facies rocks

a sequence of partial melting reactions at mt stafford central australia metasedimentary gneisses show a rapid change in grade in a 10 km wide low p high t regional aureole at mt stafford in the arunta block central australia migmatite occurs in all but the lowermost of five metamorphic zones which grade from greenschist zone 1 through amphibolite zones 2 3 to granulite facies zones 4 5 the sequence of partial melting reactions inferred for metapelitic rocks is dependant upon protolith temperature and fluid conditions the metapelite solidus in zone 2 reflects vapour present melting at p 3 kbar and t 640 c melting having initially been controlled by the congruent breakdown of the assemblage crd kfs bt qtz at slightly higher temperature andalusite in leucosome formed via the reaction kfs qtz bt h2oand melt and melt having been stabilized by the presence of boron sillimanite coaxially replaces andalusite in the high grade portion of zone 2 in zone 3 large aluminosilicate aggregates in leucosome are armoured by spl crd grt symplectites garnet partially pseudomorphs biotite cordierite or spinel in high grade portions of zone 3 zone 4 grt crd opx bearing metapsammite assemblages and garnet bearing leucosome reflect t 800 c and p 2 2 0 9 kbar in the model kfmash system the principal vapour absent melting step reflected significant modal changes related to the breakdown of the as bt tie line and the establishment of the spl crd tie line the bulk rock geochemistry of migmatite samples straddle the spl crd tie line the aluminous bulk rock composition of the common bedded migmatite restricted its potential to witness garnet forming and orthopyroxene forming reactions minor textural and modal changes in and above zone 3 reflecting biotite destablization in biotite poor assemblages

cordierite as a sensor of fluid conditions in high grade metamorphism and crustal anatexis cordierite h2o and co2 volatile saturation surfaces derived from recent experimental studies are presented for p t conditions relevant to high grade metamorphism and used to evaluate fluid conditions attending partial melting and granulite formation the volatile saturation surfaces and saturation isopleths for both h2o and co2 in cordierite are strongly pressure dependent in contrast the uptake of h2o by cordierite in equilibrium with melts formed through biotite dehydration melting controlled by the distribution of h2o between granitic melt and cordierite dw dw wt h2o melt wt h2o crd is mainly temperature dependent dw 2 5 6 0 for the h2o contents 0 4 1 6 wt percentage typical of cordierite formed through biotite dehydration melting at 3 7 kbar and 725 900 c this range in dw causes a 15 30 relative decrease in the total wt of melt produced from pelites cordierite in s type granites are h2o rich 1 3 1 9 wt and close to or saturated in total volatiles signifying equilibration with crystallizing melts that achieved saturation in h2o in contrast the lower h2o contents 0 6 1 2 wt percentage preserved in cordierite from many granulite and contact migmatite terranes are consistent with fluid absent conditions during anatexis in several cases including the cooma migmatites and broken hill granulites the cordierite volatile compositions yield ah2o values 0 15 0 4 and melt h2o contents 2 2 4 4 wt compatible with model dehydration melting reactions in contrast h2o leakage is indicated for cordierite from prydz bay antarctica that preserve h2o contents 0 5 0 3 wt which are significantly less than those required 1 0 0 8 wt for equilibrium with melt at conditions of 6 kbar and 860 c the co2 contents of cordierite in migmatites range from negligible 0 1 wt to high 0 5 1 0 wt and bear no simple relationship to preserved cordierite h2o contents and ah2o in most cases the cordierite volatile contents yield total calculated fluid activities ah2o aco2 that are significantly less than those required for fluid saturation at the p t conditions of their formation whether this reflects fluid absence dilution of h2o and co2 by other components or leakage of h2o from cordierite is an issue that must be evaluated on a case by case basis

the control of overburden thickness on resurgent domes insights from analogue models abstract resurgent doming consists of the uplift usually accompanied by volcanic activity of part of a collapse caldera analogue models were used to investigate the architecture of resurgent domes dry sand simulates the brittle crust uprising silicone located at the base of the sand pack simulates magma the deformation pattern depends mainly upon 1 the ratio aspect ratio between the thickness of the sand overburden and the width of the silicone intrusion 2 the duration of experiment for aspect ratios 1 two concentric domes develop the first formed outer dome is bordered by inward dipping reverse ring faults while the inner dome by outward dipping normal ring faults the layers inside the dome are uniformly dipping for aspect ratios 0 4 the dome shows a crestal depression surrounded by radial fractures followed by an apical extrusion of silicone the internal structure of the dome is made up of domed layers independently from the aspect ratio the duration of the experiment enhances silicone extrusion a consistent structure is observed in most resurgent domes in nature the comparison between experiments and nature suggests that two distinct resurgence modes occur mainly depending on the aspect ratio thickness width of the crust overlying the magma chamber aspect ratios 1 develop a resurgent block with uniformly dipping layers and peripheral volcanic activity ischia and pantelleria type aspect ratios 0 4 develop a resurgent dome with a crestal depression domed layers within and peripheral and internal volcanic activity valles and long valley type

hybrid collapse mechanism at piton de la fournaise volcano reunion island indian ocean 1 recent studies have shown that hydrothermal alteration in the core of volcanoes may weaken the edifice and trigger sector collapse lopez and williams 1993 day 1996 voight and elsworth 1997 van wyk de vries et al 2000 reid et al 2001 alteration of volcanic products must take place over long periods of times before collapse can occur so this process is considered to be less frequent than volcanic failure generated by magmatic intrusion and flank spreading however acceleration of this slow process may occur along one direction as a result of a weak lateral confinement following outward gravitational sliding of a flank of the volcano we present here evidence that the enclos fouque depression of piton de la fournaise volcano results from such a hybrid mechanism seaward sliding of the grand brule trough on top of an ancient hypovolcanic complex led to a lateral unconfined boundary along which collapse of the altered core of the edifice took place the result is a caldera like structure breached on the grand brule slide scaled experiments to simulate this process of pseudocaldera formation reveal tectonic features remarkably similar to those encountered in the field and demonstrate the mechanical consistency of the model similar processes may have played a role in the evolution of other volcanoes

tungurahua volcano ecuador structure eruptive history and hazards abstract tungurahua one of ecuador s most active volcanoes is made up of three volcanic edifices tungurahua i was a 14 km wide andesitic stratocone which experienced at least one sector collapse followed by the extrusion of a dacite lava series tungurahua ii mainly composed of acid andesite lava flows younger than 14 000 years bp was partly destroyed by the last collapse event 2955 90 years ago which left a large amphitheater and produced a 8 km3 debris deposit the avalanche collided with the high ridge immediately to the west of the cone and was diverted to the northwest and southwest for 15 km a large lahar formed during this event which was followed in turn by dacite extrusion southwestward the damming of the chambo valley by the avalanche deposit resulted in a 10 km long lake which was subsequently breached generating another catastrophic debris flow the eruptive activity of the present volcano tungurahua iii has rebuilt the cone to about 50 of its pre collapse size by the emission of 3 km3 of volcanic products two periods of construction are recognized in tungurahua s iii history from 2300 to 1400 years bp high rates of lava extrusion and pyroclastic flows occurred during this period the magma composition did not evolve significantly remaining essentially basic andesite during the last 1300 years eruptive episodes take place roughly once per century and generally begin with lapilli fall and pyroclastic flow activity of varied composition andesite dacite and end with more basic andesite lava flows or crater plugs this pattern is observed in the three historic eruptions of 1773 1886 and 1916 1918 given good age control and volumetric considerations tungurahua iii growth s rate is estimated at 1 5 106 m3 year over the last 2300 years although an infrequent event a sector collapse and associated lahars constitute a strong hazard of this volcano given the 3000 m relief and steep slopes of the present cone a future collapse even of small volume could cover an area similar to that affected by the 3000 year old avalanche the more frequent eruptive episodes of each century characterized by pyroclastic flows lavas lahars as well as tephra falls directly threaten 25 000 people and the agoyan hydroelectric dam located at the foot of the volcano

composite ground deformation pattern forerunning the 2004 2005 mount etna eruption 1 after the end of the 2002 2003 eruption mount etna activity was characterized only by gentle degassing at the summit craters and some earthquake swarms suddenly an eruption started on 7 september 2004 in complete absence of summit crater volcanic activity seismicity or seismic tremor and ground deformation this is the first time that magma poured out passively without preeruptive and coeruptive volcanic and or geophysical phenomena the primary key to understanding this event is represented by the ground deformation pattern recorded through gps measurements during the year before the eruption the ground deformation shows inflation superimposed by a predominant eastward movement of the eastern sector at a rate never observed before in a noneruptive period the images from satellite radar interferometry confirmed this pattern the deformation field clearly shows that the maximum tension in the eastern sector of the volcano caused the opening of the eruptive fracture which favored the silent pouring out of already resident magma

dynamic dyke propagation deduced from tilt variations preceding the march 9 1998 eruption of the piton de la fournaise volcano during the hour preceding the march 9 1998 eruption of the piton de la fournaise volcano the deformation network of the observatory recorded some large deformations in the summit area a broadband seismic station of the geoscope global network rer is located about 8 km away from the summit of the volcano signals from that station may be interpreted as tilt changes the combination of the above two kinds of signals allows by using a tensile fault model to constrain the geometry as well as some characteristics volume propagation velocity of the dyke that intruded the summit area during the hour preceding the beginning of eruptive activity

storage and mobility of nitrogen in the continental crust evidence from partially melted metasedimentary rocks mt stafford australia abstract the mt stafford region central australia provides well exposed metasedimentary rocks whose protoliths were deposited at ca 1 84 1 81 ga and that were metamorphosed at greenschist to granulite facies pressure temperature conditions at 1 8 ga the higher grade rocks show evidence of low pressure partial melting 2 4 kbars over a temperature range of 650 to 850 c these exposures afford evaluation of the extent to which n is retained through devolatilization and partial melting reactions experienced in the shallow to mid continental crust in the mt stafford metapelitic metapsammitic suite whole rock 15 n air values of the lowest grade greenschist facies rocks zone 1 range from 2 3 to 6 2 mean 3 6 1 1 5 n 7 and values for the highest grade granulite facies rocks zone 4 range from 2 1 to 8 5 mean 5 2 1 2 1 n 20 six of the twenty samples at the highest grade have values higher than those of the greenschist rocks regarded as likely protoliths all but a few of the zone 4 rocks have n concentrations lower than the mean n concentration for the lowest grade rocks ranges of 107 346 ppm mean 254 ppm for zone 1 rocks and 43 361 ppm mean 185 ppm for zone 4 rocks for the higher grade rocks which experienced multiple partial melting reactions varying retention of n as nh 4 in k feldspar or as n 2 in cordierite may indicate that n is held in peritectic products of partial melting rather than in the melt although assessments of element loss in the mt stafford suite are greatly complicated by the large degree of protolith related heterogeneity some elements do show modest decline in concentration with increasing grade consistent with their loss during devolatilization and partial melting nitrogen appears most similar in behavior to rb the lile most similar in ionic radius to nh 4 but of these two elements n shows somewhat greater evidence for whole rock loss k 2 o shows only very subtle hints of whole rock loss in some samples and cs shows considerably greater loss relative to n and rb resulting for example in increases in rb cs at the higher grades increased whole rock ba rb for some higher grade samples relative to that for lower grade equivalents likely reflects the formation of a major ba reservoir in k feldspar at the expense of biotite resulting in no obvious whole rock ba loss with rb liberated from biotite breakdown partitioning into the melts that at least partly left the system reduced whole rock b concentrations at the higher grades resulted from the breakdown of tourmaline during the melting reactions these varying degrees of reduction in whole rock n rb cs and b and possibly k 2 o concentration are accompanied by decreased concentrations in h 2 o as indicated by loi li and u the loss of u resulting in increased th u in the highest grade rocks apparent differential loss of these elements based on the whole rock data could reflect the amounts of melt produced and the extents to which the melts were removed at the scales sampled by the hand specimens that were analyzed six of the twenty zone 4 samples showing greater shift in 15 n to values of 7 4 to 8 4 tend to be among the samples showing the largest changes in other major and trace element concentrations and ratios believed to reflect melt removal e g k 2 o cs tio 2 b al 2 o 3 th u and ratios among rb sr ba and cs the metasedimentary rocks at mount stafford also contain 217 to 1186 ppm c likely as reduced c graphite but at the higher grades probably also as co 2 in the channels of cordierite at greenschist grade whole rock 13 c v pdb values are relatively uniform with organic compositions mean 25 1 1 1 6 n 7 but at the highest grade zone 4 values are as high as 17 7 mean 22 2 1 2 3 n 8 overall c and n apparently largely of organic origin show surprising retention in rocks having experienced peak temperatures of 800 c demonstrating their compatibility in mineral phases in fluid and melt residues for n as nh 4 in k feldspar and as n 2 in cordierite for c as graphite and as co 2 in cordierite these data have implications for deep earth n cycling bearing on the size of the n reservoir in the mid continental crust and thus long term storage of n previously residing in the atmosphere and biosphere and for the use of the 15 n of upper crustal intrusive rocks as a tracer of their deep crustal sources

formation of diatexite migmatite and granite magma during anatexis of semi pelitic metasedimentary rocks an example from st malo france petrological and geochemical variations are used to investigate the introduction formation of granite magma from diatexite migmatites derived from partial melting experiments show that protoliths of pelite metasedimentary rocks of pelitic to greywacke composition at st and greywacke composition yield up to 40 vol malo france anatexis occurred at relatively low temperatures granite melt over the temperature range 650 900 c and pressures 800 c 4 7 kbar principally through muscovite typical of anatexis of the continental crust conrad et dehydration melting biotite remained stable and serves as a tracer al 1988 vielzeuf holloway 1988 patino douce for the solid fraction during melt segregation the degree of partial johnston 1991 vielzeuf montel 1994 patino douce melting calculated from modal mineralogy and reaction stoichiometry harris 1998 therefore to make a granite magma was 40 vol there is a continuous variation in texture the melt fraction must be segregated from a solid fraction mineralogy and chemical composition in the diatexite migmatites of much greater volume and then collected together mesocratic diatexite formed when metasedimentary rocks melted the type of melt residuum separation process depends sufficiently to undergo bulk flow or magma flow but did not on the melt fraction present experience significant melt residuum separation mesocratic diatexite melt residuum separation at low degrees of partial that underwent melt segregation during flow generated 1 memelting f and consequently low melt fraction mf lanocratic diatexites at the places where the melt fraction was has been documented from metatexite migmatites in removed leaving behind a biotite and plagioclase residuum enriched these rocks melt segregation produced centimetre scale in tio2 feot mgo cao sc ni cr v zr hf th u and leucosomes distributed in a host composed of layers that ree and 2 a complementary leucocratic diatexite enriched in have melted and others that have not e g henkes sio2 k2o and rb where the melt fraction accumulated leucocratic johannes 1981 gupta johannes 1982 dougan 1983 diatexite still contained 5 15 vol residual biotite mg number sawyer 1987 tait harley 1988 barbey et al 1990 40 44 and 10 20 vol residual plagioclase an22 anatectic brown 1994 leucosomes represent small volumes of granite magma developed from the leucodiatexite first by further felsic magma formed when melt was squeezed out of the melt residuum separation then through fractional crystallization deforming matrix mclellan 1988 sawyer 1991 1994 most biotite in the anatectic granite is magmatic mg number brown 1994 brown et al 1995 and collected in low18 22 pressure sinks such as shear bands and inter boudin

hybridization of a shallow i type granitoid pluton and its host migmatite by magma chamber wall collapse the tokuwa pluton central japan the miocene tokuwa pluton of i type granitoid affinity was emplaced discordantly into a cretaceous to paleogene accretionary complex and induced a contact aureole in which various thermally metamorphosed rocks were developed including hornfels metatexite diatexite and cordierite bearing tonalite crd tonalite of s type granite affinity the thermally metamorphosed rocks show low pressure reaction textures culminating in partial melting peak p t conditions of 3 kbar at 7808c are estimated on the basis of the twq thermobarometer for the garnet bearing rocks the rocks in the contact aureole exhibit a gradual transition from hornfels through metatexite and diatexite to crd tonalite the sr isotopic composition at the time of tokuwa pluton emplacement at 12 ma decreases systematically from metatexite 0 7100 0 7112 through diatexite 0 7078 0 7094 to crd tonalite 0 7067 0 7068 this trend is interpreted in terms of mixing between the tokuwa magma and the aureole migmatites the field relationships geochemical data and isotopic data collectively suggest that the emplacement of the tokuwa pluton triggered partial melting of the surrounding metasedimentary rocks subsequent hybridization of the tokuwa magma with the metatexite in variable proportions produced the crd tonalite and diatexite the hybridization was caused by invasion of the tokuwa magma into the migmatite zone accompanied by gravitational collapse of the previously crystallized wall of the magma chamber the data presented demonstrate that even a relatively low temperature shallow i type granitoid pluton can induce contact anatexis and hybrid s type granitoid formation at the intrusive contact

structural architecture of the colima volcanic complex 1 the colima volcanic complex cvc is currently the most active mexican volcano and is located in the western sector of the trans mexican volcanic belt inside the active colima rift a regional n s striking extensional structure the colima rift is filled by a 1 km thick sequence of quaternary lacustrine sediments alluvium and colluvium mostly underling the about 3000 m thick volcanic pile of the cvc in this work we present the results of a detailed morphostructural and field study of quaternary faults and fractures in the cvc and the surrounding area including the regional structures of the colima rift we also present a geometrical modeling of the faults inside the volcano and a numerical model of the gravity induced stress and strain fields of the cvc the study attempts to characterize the geometry kinematics and dynamics of the deformation features of the cvc and relate it with the volcano structure the geology of the substratum and the geodynamic setting of the region our model considers that the observed deformation of the cvc and the surroundings results from the interplay between the active n s trending regional extensional tectonics and the southward spreading of the volcano over its basement forming an e w oriented volcanotectonic graben the interaction between regional tectonics and previously unrecognized volcanic spreading can control magma migration and flank instability in an area where eruptions and sector failures represent a potential high risk for more than 500 000 people

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

large scale melt depletion in granulite terranes an example from the archean ashuanipi subprovince of quebec this study uses field petrographic and geochemical methods to estimate how much granitic melt was formed and extracted from a granulite facies terrane and to determine what the grain and outcrop scale melt flow paths were during the melt segregation process the ashuanipi subprovince located in the north eastern superior province of quebec is a large 90 000 km2 metasedimentary terrane in which 85 of the metasediments are of metagreywacke composition that was metamorphosed at mid crustal conditions 820 900 c and 6 7 kbar in a late archean dextral transpressive orogen decrease in modal biotite and quartz as orthopyroxene and plagioclase contents increase together with preserved former melt textures indicate that anatexis was by the biotite dehydration reaction biotite quartz plagioclase melt orthopyroxene oxides using melt orthopyroxene ratios for this reaction derived from experimental studies the modal orthopyroxene contents indicate that the metagreywacke rocks underwent an average of 31 vol partial melting the metagreywackes are enriched in mgo cao and feot and depleted in sio2 k2o rb cs and u have lower rb sr higher rb cs and th u ratios and positive eu anomalies compared to their likely protolith these compositions are modelled by the extraction of between 20 and 40 wt granitic melt from typical archean low grade metagreywackes a simple mass balance indicates that about 640 000 km3 of granitic melt was extracted from the depleted granulites the distribution of relict melt at thin section and outcrop scales indicates that in layers without leucosomes melt extraction occurred by a pervasive grain boundary porous flow from the site of melting across the layers and into bedding planes between adjacent layers in other rocks pervasive grain boundary flow of melt occurred along the layers for a few to tens of centimetres followed by channelled flow of melt in a network of short interconnected and structurally controlled conduits visible as the net like array of leucosomes in some outcrops the leucosomes contain very little residual material 5 biotite orthopyroxene indicating that the melt fraction was well separated from the residuum left in situ as melt depleted granulite only 1 3 vol percentage melt remained in the melt depleted granulites hence the extraction of melt generated by biotite dehydration melting in these granulites was virtually complete under conditions of natural melting and strain rates in a contractional orogen

faulting on the western flank of mt etna and magma intrusions in the shallow crust surface deformations on the western flank of mt etna volcano spanning 1980 2004 have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the s se rift and faulting sensitivity during this period an accurate analysis of strain parameters computed by inversion of sw electro optical distance data suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly ne sw buried fault crossing the area covered

volcano tectonic activity along structures of the unstable ne flank of mt etna italy and their possible origin abstract we describe the prehistoric historic activity of the main and minor volcano tectonic structures of the northeastern flank of mt etna giving new data which provide a clearer view of how destabilized volcanoes react to magma pressure and gravity forces data are mostly based on new lithostratigraphic surveys and on offset measurements of late pleistocene holocene deposits and historic man made features the north east rift ne rift is a volcanic rift that has guided mostly explosive but also secondary effusive activity since the end of the pleistocene monogenetic cones and explosive craters are strongly elongated and aligned along 66 main surface fractures and several others hidden but inferred from sinkhole alignments the opening direction is locally oblique with a left lateral component in the north eastern segment of the rift at the ne tip of the rift the movements are relieved by the normal left lateral pernicana fault pf an 11 km long structure comprising e w fault segments connected by right stepping en echelon faults our study demonstrates that the very high slip rates at a centennial scale of these structures are well constrained and similar ne rift 0 6 1 8 cm a pf 0 5 2 2 cm a and have been also recognized in the latest pleistocene holocene 2 7 cm a the e w fiumefreddo fault ff has normal left lateral kinematics and a historic slip rate of 0 1 cm a ripa della naca faults strike ne and are covered by unfaulted

source model for the 2001 flank eruption of mt etna volcano 1 using interferometric synthetic aperture radar insar we constrain the deformation sources for the july august 2001 flank eruption of mt etna volcano italy insar data from ascending and descending passes of the ers2 satellite reveal a pattern of deformation that cannot be explained by a dike intrusion alone in addition to a vertical dike beneath the south rift zone the spatially large 10 km scale 15 20 cm in range negative range displacement lobes across the western descending data and eastern ascending data flanks require a nearly symmetric set of shallowly dipping normal faults to each side of the central dike complexity in the observed insar surface displacements constrains an additional dike intrusion beneath its ne flank long term deformation of etna s eastern and southern flanks is well established through field and insar observations therefore the relative symmetry of motion beneath both the western and eastern flanks during the 2001 eruption is surprising our model of symmetric flank motion suggests that on the short time scales of a large dike intrusion volcanoes can deform differently from their long term deformation

structural assessment of mount etna volcano from permanent scatterers analysis a study of the deformation pattern of mount etna volcano based on the results from the permanent scatterers ps technique is reported ground motion data provided by the interferometric synthetic aperture radar insar ps technique from 1995 to 2000 are compared and validated by gps data an analysis of the ascending and descending line of sight los components of ground velocities has yielded detailed ground deformation maps and cross sections this analysis allows detection and constraint of discontinuities in the surface velocity field los velocities have then been combined to calculate the vertical and horizontal e w ground velocities a wide inflation of the edifice has been detected on the western and northern flanks over an area of about 350 km2 a seaward motion of the eastern and southern flanks has also been measured ps data allows the geometry and kinematics of the several blocks composing the unstable flanks to be defined even in the highly urbanized areas and their displacement rates have been measured with millimeter precision this analysis reveals the extension of some features beyond their field evidences and defines new important features the results of this work depict a new comprehensive kinematic model of the volcano highlighting the gravitational reorganization of the unbuttressed volcanic pile on its slippery clay basement on the southern flank but an additional drag force due to a strong subsidence of the continental margin facing the etna volcano is necessary to explain the ps velocity field observed on the eastern flank

time dependent deformation of the eastern flank of mt etna after slip or viscoelastic relaxation abstract major results of post intrusive gps monitoring of the 5 months encompassing and following the onset of 2002 03 mt etna eruption are presented and discussed here the overall ground deformation pattern is characterized by a time dependent relaxation function we evaluated two different parametrizations of relaxation functions each one linked to a different relaxation process i viscoelastic relaxation and ii after slip mechanism the former indicated that the process occurred within a weak layer characterized by viscosity values ranging between 7 1 1014 pa s and 1 3 1015 pa s the latter evidenced that frictional processes occurred beneath a layer of velocity strengthening having a thickness with values ranging between 0 4 km and 1 7 km either model may explain the observed time dependent deformation both from the statistical point of view and the comparison with geologic and seismic information although we are unable to favour one model rather than the other these results indicate that the mechanism responsible for the observed post intrusive deformation occurs within a sliding zone located inside the clayey sedimentary basement

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

deformation and eruptions at mt etna italy a lesson from 15 years of observations this work was partly funded by ingv and the italian dpc and was supported by asi the preview project and crdc amra dpc ingv flank project providing the funds for the publication fees

insights into fluid circulation across the pernicana fault mt etna italy and implications for flank instability article i nfo we conducted geophysical geochemical measurements on a 2k m n s profile cutting across the pernicana fault one of the most active tectonic features on the ne flank of mt etna the profile passes from the unstable e flank of the volcano to the south to the stable n flank and significant fluctuations in electrical resistivity self potential and soil gas emissions co2 rn and th are found the detailed multidisciplinary analysis reveals a complex interplay between the structural setting uprising hydrothermal fluids meteoric fluids percolating downwards ground permeability and surface topography in particular the recovered fluid circulation model highlights that the southern sector is heavily fractured and faulted allowing the formation of convective hydrothermal cells although the existence of a hydrothermal system in a volcanic area does not surprise these results have great implications in terms of flank dynamics at mt etna indeed the hydrothermal activity interacting with the pernicana fault activity could enhance the flank instability our approach should be further extended along the full extent of the boundary between the stable and unstable sectors of etna for a better evaluation of the geohazard in this active tectonic area

formation and evolution of granite magmas during crustal reworking the significance of diatexites taylor mclennan 1985 the physical processes ina continuous section through reworked archaean crust records the volved particularly how granite magma is formed remain generation of granitic magma and its subsequent development in the controversial miller et al 1988 white chappell opatica subprovince in the canadian shield there the transition 1990 a partially melted source can form a granitic from palaeosome to granite was a closed system process through magma only if large volumes of melt are separated from intermediate stages of patch migmatite and diatexite the average most of their residuum understanding this process is degree of partial melting was less than 30 but the melt crucial to determining how crustal recycling and differfraction was redistributed within individual diatexite layers during entiation occurs for example melt residuum separation deformation regions that lost melt became residual diatexites could be a nearly perfect single stage process at the enriched in tio2 feot mgo cao sc cr co sr rare earth site of partial melting as described for leucosomes in elements ree and high field strength elements hsfe melt metatexite migmatites wickham 1987a sawyer 1991 accumulated to create diatexite magmas enriched in large ion 1994 brown et al 1995 alternatively the separation lithophile elements lile but contaminated with residuum macould be an imperfect multi stage process that yields a terial such diatexite magmas are parental to granites found at magma with a large residual component as is observed higher crustal levels in the terrane flow of the diatexite magma in in diatexite migmatites bea 1991 greenfield et al response to deformation separated some of its residuum into schlieren 1996 sawyer 1996 the metatexite model necessarily parautochthonous plutons were created where ascending granitic produces leucocratic residuum free granites such as magma locally ponded below impermeable layers and structures those described by le fort 1981 and montel et al magma left the anatectic region in dykes and lost its remaining residuum as it crystallized consequently the allochthonous granite 1991 and maximizes the geochemical signature of magmas that rose through 20 km of crust to feed the highest level crustal differentiation in contrast the diatexite model plutons in this region are highly fractionated and essentially free of can produce residuum rich granites and so reduce the residuum geochemical effect of crustal differentiation as chappell 1996 noted how anatectic magmas formed in the deeper crust evolve to the granitic magmas emplaced in the upper crust is also poorly known because few crustal sections

malta escarpment fault zone offshore eastern sicily pliocene quaternary tectonic evolution based on new multichannel seismic data 1 the malta escarpment represents the dominant morphological feature offshore eastern sicily linking the deep ionian basin to the east with the hyblean carbonate platform to the west interpretation of purposely acquired multichannel seismic data allows division of the malta escarpment into two portions characterized by different tectonic structures along the segment south of siracusa the malta escarpment is not affected by recent faulting and appears as a steep surface that flattens out toward the ionian basin a recent deformation characterized by a broad area of uplift occurs 20 30 km east from the slope along a nnw sse trend the segment of the malta escarpment extending north of siracusa on the other hand is characterized by the presence of nnw sse east dipping recent extensional faults and related sedimentary basins the observed structural features support the occurrence of a lithospheric tear between the ionian oceanic basin and the hyblean plateau

temperature and bulk composition control on the growth of monazite and zircon during low pressure anatexis mount stafford central australia the formation age and trace element composition of zircon and monazite were investigated across the prograde low pressure metamorphic sequence at mount stafford central australia three pairs of inter layered metapelites and metapsammites were sampled in migmatites from amphibolite facies t 600 c to granulite facies conditions t 800 c sensitive high resolution ion microprobe u pb dating on metamorphic zircon rims and on monazite indicates that granulite facies metamorphism occurred between 1795 and 1805ma the intrusion of an associated granite was coeval with metamorphism at 1802 3ma and is unlikely to be the heat source for the prograde metamorphism metamorphic growth of zircon started at t 750 c well above the pelite solidus zircon is more abundant in the metapelites which experienced higher degrees of partial melting compared with the associated metapsammites in contrast monazite growth initiated under sub solidus prograde conditions at granulite facies conditions two distinct metamorphic domains were observed in monazite textural observations petrology and the trace element composition of monazite and garnet provide evidence that the first metamorphic monazite domain grew prior to garnet during prograde conditions and the second in equilibrium with garnet and zircon close to the metamorphic peak ages from sub solidus prograde and peak metamorphic monazite and zircon are not distinguishable within error indicating that heating took place in less than 20 myr

flank instability structure of mt etna inferred by a magnetotelluric survey this paper presents a magnetotelluric mt survey of the unstable eastern flank of mt etna we take thirty soundings along two profiles oriented in the n s and nw se directions and from these data recover two 2d resistivity models of the subsurface both models reveal three major layers in a resistive conductive resistive sequence the deepest extending to 14 km bsl the shallow layer corresponds to the volcanic cover and the intermediate conductive layer corresponds to underlying sediments segmented by faults these two electrical units are cut by e w striking faults the third layer basement is interpreted as mainly pertinent to the apennine maghrebian chain associated with sw ne striking regional faults the detailed shapes of the resistivity profiles clearly show that the ne rift is shallow rooted 0 1 km bsl thus presumably fed by lateral dikes from the central volcano conduit the nw se profile suggests by a series of listric faults reaching up to 3 km bsl then becoming almost horizontal toward the se the resistive basement dramatically dips from 3 km to 10 km bsl in correspondence with the timpe fault system several high conductivity zones close to the main faults suggest the presence of hydrothermal activity and fluid circulation that could enhance flank instability our results provide new findings about the geometry of the unstable etna flank and its relation to faults and subsurface structures

the effect of volcanic constructs on rift fault patterns volcanoes in rift situations often show distinctive hour glass fault patterns with increased fault throw as the volcano is approached we present analogue models that show that this is caused by an interaction of the regional stress field with that set up by the volcano mass for faults to be reorientated there must be a ductile layer below the volcano this can be hot crust at mid ocean ridges continental rifts or weak sedimentary strata increased volcano size or mass and lower brittle ductile ratios lead to increased fault curvature whereas an increased regional extension rate decreases the effect volcanoes on one side of a rift may capture it forming the axis of a new rift with curved or en echelon zones on either side by concentrating extension magma is more easily erupted so volcanoes may erupt more magma of less evolved composition a positive feedback between increased extension and magma eruption rate will lead to rift narrowing which can favor the formation of oceanic crust

in situ migmatite and hybrid diatexite at mt stafford central australia metasedimentary gneisses show a rapid change in grade within a 10 km wide low p high t regional aureole at mt stafford arunta block central australia migmatites occur in all but the lowermost of five metamorphic zones which are characterized by 1 muscovite quartz schist 2 andalusite cordierite k feldspar granofels with small melt segregations 3 spinel sillimanite cordierite k feldspar migmatite 4 garnet orthopyroxene cordierite migmatite and minor diatexite and 5 biotite cordierite plagioclase diatexite that shows a transition to granite a subsolidus unit comprising interbedded sandstone and siltstone is equivalent to bedded migmatite the main rock type in zones 2 4 mesoscopic textures and migmatite classification of this unit vary with grade in zone 2 metatexite is developed in siltstone layers that are separated by quartz rich unmelted metapsammite layers melt segregation was less efficient in zones 3 and 4 where the dominant migmatite layering is a modified bedding high proportions of melt were present in zone 4 in which schlieren migmatite is transitional between bedded migmatite and metapelite sourced diatexite the preservation of sedimentary structures and coexistence of melt reactants and products in zone 4 metapelite imply that melting proceeded insitu without substantial migration of melt zone 5 biotite cordierite plagioclase diatexite carries rafts of bedded migmatite with strongly resorbed edges as well as large k feldspar and quartz augen this unit of comparatively ca rich migmatites is inferred to have been formed by the mixing of locally derived and injected granitic melt

one two and three phase viscosity treatments for basaltic lava flows 1 lava flows comprise three phase mixtures of melt crystals and bubbles while existing one phase treatments allow melt phase viscosity to be assessed on the basis of composition water content and or temperature two phase treatments constrain the effects of crystallinity or vesicularity on mixture viscosity however three phase treatments allowing for the effects of coexisting crystallinity and vesicularity are not well understood we investigate existing one and two phase treatments using lava flow case studies from mauna loa hawaii and mount etna italy and compare these with a three phase treatment that has not been applied previously to basaltic mixtures at etna melt viscosities of 425 30 pa s are expected for well degassed 0 1 w h2o and 135 10 pa s for less well degassed 0 4 wt h2o melt at 1080 c application of a three phase model yields mixture viscosities 45 crystals 25 35 vesicles in the range 5600 12 500 pa s this compares with a measured value for etnean lava of 9400 1500 pa s at mauna loa the three phase treatment provides a fit with the full range of field measured viscosities giving three phase mixture viscosities upon eruption of 110 140 pa s 5 crystals no bubble effect due to sheared vesicles to 850 1400 pa s 25 30 crystals 40 60 spherical vesicles the ability of the three phase treatment to characterize the full range of melt crystal bubble mixture viscosities in both settings indicates the potential of this method in characterizing basaltic lava mixture viscosity

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

internal differentiation of the archean continental crust fluid controlled partial melting of granulites and ttg amphibolite associations in central finland fault bound blocks of granulite and enderbite occur within upper amphibolite facies migmatitic tonalitic trondhjemitic granodioritic ttg gneisses of the iisalmi block of central finland these units record reworking and partial melting of different levels of the archean crust during a major tectonothermal event at 2 6 2 7 ga anhydrous mineral assemblages and tonalitic melts in the granulites formed as a result of hydrous phase breakdown melting reactions involving amphibole at peak metamorphic conditions of 8 11 kbar and 750 900 c a nominally fluid absent melting regime in the granulites is supported by the presence of carbonic fluid inclusions the geochemical signature of light rare earth element lree depleted mafic granulites can be modelled by 10 30 wt partial melting of an amphibolite source rock leaving a garnet bearing residue the degree of melting in intermediate granulites is inferred to be less than 10 wt and was restricted by the availability of quartz pressure temperature estimates for the ttg gneisses are significantly lower than for the granulites at 660 770 c and 5 6 kbar based on the p t conditions melting of the ttg gneisses is inferred to have occurred at the wet solidus in the presence of an h 2 o rich fluid a hydrous mineralogy abundant aqueous fluid inclusions and the absence of carbonic inclusions in the gneisses are in accordance with a water fluxed melting regime low ree contents and strong positive eu anomalies in most leucosomes irrespective of the host rock composition suggest that the leucosomes are not melt compositions but represent plagioclase quartz assemblages that crystallized early from felsic melts furthermore similar plagioclase compositions in leucosomes and adjacent mesosomes are not a migmatite paradox as both record equilibration with the same melt phase percolating along grain boundaries

the low pressure partial melting behaviour of natural boron bearing metapelites from the mt stafford area central australia this study has examined the 300 mpa partial melting behaviour of four metapelites collected from the highest grade rocks occurring below the anatectic zone of the mt stafford area arunta inlier central australia in this area metasediments are interpreted to have undergone partial melting within the andalusite stability field possibly as a result of a lowering of the metapelite solidus by the presence of boron in the rocks two of the samples were two mica metapelites mts70 and mts71 these both contained significant quantities of tourmaline and were thus boron enriched the other two samples are biotite metapelites one of these rocks contains only a trace of tourmaline mts8 and the other is tourmaline free mts7 despite expectations that muscovite in the two mica samples would break down via a subsolidus reaction muscovite was stable to above 750 c due to the incorporation of ti phengitic and possibly f components into its structure between 750 and 800 c muscovite melted out completely via a coupled muscovite biotite fluid absent incongruent reaction tourmaline was partially consumed in this reaction with the elbaitic component being preferentially consumed in the most mica rich sample this reaction produced 60 melt at 800 c in the biotite metapelites biotite melting began at a temperature below 800 c and was accompanied by very modest melt production at this low temperature in contrast to the two mica metapelites the main pulse of melt production in these samples occurred at a temperature between 850 and 950 c in both these samples biotite melt coexisted over a temperature range in excess of 150 c and in mts8 biotite was still in the run products at 950 c the very refractory nature of these evolved biotite compositions is most likely a consequence of both the presence of a ti buffering phase in the assemblage ilmenite and the essentially plagioclase free nature of the starting compositions under the fluid absent conditions of this study tourmaline is clearly a reactant in the partial melting process but does not appear to shift the fluid absent incongruent melting reactions markedly in the tourmaline rich two mica metapelites tourmaline only disappears from the run products at a temperature above 850 c where it coexisted with a substantial melt proportion this appears to coincide with the point of maximum boron concentration in the melts

petrological and geochemical variations of a turbidite like metasedimentary sequence over the metatexite to diatexite transition within the pampean orogen argentina large masses of turbidite systems have been metamorphosed in orogenic systems during earth s history under granulite facies conditions the transformation of turbidite sedimentary successions into metasedimentary sequences drives intracrustal differentiation by anatexis and melt residuum separation we report on a migmatite terrane developing from turbidite successions that were buried into the deep crust during the neoproterozoic to early cambrian pampean orogeny in central argentina at the exposed middle crustal paleodepths migmatites occur on the regional scale but lithological zones are characterized by 1 bedded migmatites 2 metatexite and 3 diatexite bedded migmatites are the low temperature part of the migmatite terrane where the alternating metapelite and metagreywacke layers are traceable among migmatites of different protoliths the temperature 790 c was sufficient high for melting the metapelite but not for melting the metagreywacke the majority of the migmatite terrane consists of stromatic metatexites in which the limit among different progenitors is either faint or erased by migmatization metatexite zone acts as melt transfer in the migmatite terrane in the stromatic migmatites the major oxide composition of leucosomes and tabular bodies of leucogranite resembles those of the glasses of experimental petrology however leucosomes and leucogranites are crystallized melts that have low zr th and lree contents and positive eu anomalies resulting from accessory mineral retention in melting residues the transformation of metatexite into diatexite is gradational over tens of metres and related to an accumulated melt fraction that dismembers the stromatic fabric the most abundant diatexite is mesocratic and has little or lacks k feldspar a subordinate proportion of diatexites is leucocratic contains k feldspar phenocrysts and shows igneous like textures leucogranites and leucocratic diatexites are the potential carriers of an anatectic melt rich component from granulite facies migmatite sequences toward shallow crustal levels turbidite successions are fertile protoliths that undergo widespread melting under low granulite facies temperature 850 c and the development of large diatexite massifs makes them suitable sources of granitic magmatism

petrogenesis of metatexite and diatexite migmatites determined using zircon u pb age trace element and hf isotope data higo metamorphic terrane central kyushu japan metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite facies zones of the higo low p high t metamorphic terrane here we report data from an outcrop in the highest grade part of the granulite facies zone in which diatexite occurs as a 3 m thick layer between 2 m thick layers of stromatic structured metatexite within pelitic gneiss the migmatites and gneiss contain the same peak mineral assemblage of biotite plagioclase quartz garnet k feldspar with retrograde chlorite muscovite and some accessory minerals of ilmenite rutile titanite apatite zircon monazite pyrite zinc sulphide calcite calculated metamorphic p t conditions are 800 900 c and 9 12 kbar zircon in the diatexite forms elongate euhedral crystals with oscillatory zoning but no core rim structure zircon from the gneiss and metatexite forms euhedral subhedral grains comprising inherited cores overgrown by thin rims the overgrowth rims in the metatexite have lower th u ratios than zircon in the diatexite and yield a 206pb 238u age of 116 0 1 6 ma which is older than the 110 1 0 6 ma 206pb 238u age derived from zircon in the diatexite zircon from the diatexite has variable ree contents with convex upward patterns and flat normalized hree whereas the overgrowth rims in the metatexite and gneiss have steep hree enriched patterns however both types have similar positive ce and negative eu anomalies 176hf 177hf ratios in the overgrowth rims from the metatexite are more variable and generally lower than values from zircon in the diatexite based on u pb ages trace element and hf isotope data the zircon rims in the metatexite are interpreted to have crystallized from a locally derived melt following partial dissolution of inherited protolith zircon during anatexis whereas the zircon in the diatexite is interpreted to have crystallized from a melt that included an externally derived component by integrating zircon and petrographic data for the migmatites and pelitic gneiss the metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source whereas the diatexite migmatite included an externally derived juvenile component the cretaceous high temperature metamorphism of the higo metamorphic terrane is interpreted to reflect emplacement of mantle derived basalts under a volcanic arc along the eastern margin of the eurasian continent and advection of heat via hybrid silicic melts from the lower crust post peak crystallization of anatectic melts in a high t region at mid crustal depths occurred in the interval c 116 110 ma as indicated by the difference in zircon ages from the metatexite and diatexite migmatites

deformed symmetrical volcanoes analog modeling of volcanic cones traversed by strike slip faulting was conducted and the cones were analyzed for deformation characteristics the study shows that symmetrical volcanoes that have undergone basal strike slip offset may be deformed internally without manifesting any change in their conical shape volcanoes deformed by strike slip faulting may already have well developed fractures in their interior yet still appear as a symmetrical cone exhibiting concentric contours when viewed on a topographic map moreover slight changes in the basal shape of the cone induced by strike slip movement can be restored by the relatively faster resurfacing and reshaping processes from the deposition of younger eruptive products these findings pose a subtle but significant point in the assessment of volcanic landslide hazards not all perfect cones are undisturbed the detection of concealed deformation is important because fractures induce further instability in volcanoes and act as slip planes during volcano collapse events there are many examples of symmetrical volcanoes in nature the faultless appearance of such perfect cones can be misleading which requires careful attention in hazards assessment

contrasted tectonic styles for the paleoproterozoic evolution of the north china craton evidence for a 2 1 ga thermal and tectonic event in the fuping massif structural analysis along with 40ar 39ar and u pb datings in the fuping massif provide new insight into the evolution of the eastern part of the trans north china belt north china craton from 2 7 ga to 1 8 ga d1 is responsible for the development of a dome and basin structure coeval with crustal melting giving rise to migmatite and nanying gneissic granites at 2 1 ga this dome and basin architecture resulted from the interference between a n s compression of a weak ductile crust and gravity driven vertical flow in a high thermal regime the next events involved flat lying ductile thrusting d2 and normal faulting d3 dated at around 1880 ma and 1830 ma respectively the d2 and d3 events belong to the trans north china orogeny that results in the final amalgamation of the north china craton the d1 deformation is considered as evidence for an earlier orogen developed around 2 1 ga prior to the trans north china orogeny the change in the deformation style between the 2 1 ga and 1 8 ga could be viewed as a consequence of the cooling of the continental crust in the north china craton

extension induced by volcanic loading in regional strike slip zones volcanoes and strike slip pull apart structures are commonly found together we use theoretical predictions and analogue modeling to evaluate the effect of volcanic loading in strike slip zones and the converse effect of regional strike slip faults on volcano structure theoretical predictions indicate that regional stress is reoriented by volcano loading to cause extension analogue models indicate that volcanoes in strike slip zones develop extensional pull apart structures a graben typically forms normal to the minimum regional stress axis 3 at a cone cones emplaced onto preexisting faults increase that fault9s tensional component if the substratum is weak enough to permit volcano spreading thrusts form normal to the maximum stress axis 1 a feedback situation can arise i e loading related extension allows more magma influx more eruption and thus increased loading this process can create large volcano tectonic depressions volcano structures may also be used as indicators of regional strike slip movements

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

crustal structure of the ionian margin of sicily etna volcano in the frame of regional evolution abstract crustal imaging could be achieved on normal incidence reflection profiles offshore eastern sicily by using industrial grade reflection seismic with improved marine sources thick recent sediments a reflective pile including the mesozoic deposits a transparent upper crust and a band of low frequency reflections attributed to the lower crust are imaged in the seismic sections the structure of the crust and its thickness show features inherited from the mesozoic evolution as a passive margin by which ionian basin crust was formed around the hyblean continental promontory of africa to constitute the southern plate in the later convergence with europe the seismic images are also marked by the lithospheric deformation due to the neogene overriding of the northern part of this paleomargin by the calabro peloritan block of european continental crust this transpressive motion may have been guided along the northern part of this paleomargin where the seismic profiles evidence a hinge line between the northward upslope of the moho of that old passive margin and its downslope to the present slab under the tyrrhenian sea etna volcano is located at the intersection of this mantle upwarp by a zone of active sea bottom normal faults which cut across the formerly constructed compressional belt the onset of its volcanic activity is roughly coeval with that of the cessation of interplate thrusting and could hence be related to a change of the coupling of the ionian slab this slab is now probably disconnected from the overriding plate and rolled back in front of the expanding hot tyrrhenian asthenospheric dome with the mobilisation of a viscous mantle material at depth an active lithospheric fault is here imaged which cuts over more than 100 km into the ionian basin the fault runs from the tyrrhenian margin in the sse direction of etna updip of the southwestern lateral edge of this slab leaving north eastward the extruded calabrian block and on its south westward edge the uplifted crust and mantle structures of etna along it the crust including the mesozoic and deeper layers has sagged vertically in the segment in front of the slab with a finite throw across the fault increasing from the basin towards etna

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

tectonic control on the eruptive dynamics at mt etna volcano sicily during the 2001 and 2002 2003 eruptions abstract the eruptive events of the july august 2001 and october 2002 january 2003 at mt etna provide new insights for reconstructing the complex geometry of the feeding system and their relationship to regional tectonics the 2001 eruption took place mainly on the upper southern sector of the volcano the eruption was preceded by a large earthquake swarm for a few days before its onset and accompanied by ground deformation and fracturing the development of surface cracking along with the seismic pattern has allowed us to recognize three distinct eruptive systems the sw ne nnw sse and n s systems which have been simultaneously active such eruptive systems are only the upper portions of a complex feeding system that was fed at the same time by two distinct magmas the sw ne and nnw sse systems connected with the se crater conduit were fed by magma coming from depth whereas the n s system served instead as an ascending pathway for an amphibole bearing magma residing in a shallow reservoir the eruptive activity started again on october 2002 on the ne rift zone where about 20 eruptive vents were aligned between 2500 and 1900 m a s l and on the southern flank from the central crater to the montagnola the onset of eruptive activity was accompanied by a seismic swarm as in the 2001 eruptive event two independent feeding systems formed characterized by distinct magmas the sw ne system controlled the feeding of the northeast rift and was accommodated by left lateral displacement along the wnw ese trending pernicana fault the n s system fed the eruptions on the southern flank moreover the associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano and offshore these two last eruptions indicate that at mt etna the ascent of magma as well as the accommodation of deformation is strongly dominated by local extensional structures that are connected to a regional tectonic regime

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

evidence for dike emplacement beneath iliamna volcano alaska in 1996 two earthquake swarms comprising 88 and 2833 locatable events occurred beneath iliamna volcano alaska in may and august of 1996 swarm earthquakes ranged in magnitude from 0 9 to 3 3 increases in so2 and co2 emissions detected during the fall of 1996 were coincident with the second swarm no other physical changes were observed in or around the volcano during this time period no eruption occurred and seismicity and measured gas emissions have remained at background levels since mid 1997 earthquake hypocenters recorded during the swarms form a cluster in a previously aseismic volume of crust located to the south of iliamna s summit at a depth of 1 to 4 km below sea level this cluster is elongated to the nnw sse parallel to the trend of the summit and southern vents at iliamna and to the regional axis of maximum compressive stress determined through inversion of fault plane solutions for regional earthquakes fault plane solutions calculated for 24 swarm earthquakes located at the top of the new cluster suggest a heterogeneous stress field acting during the second swarm characterized by normal faulting and strike slip faulting with p axes parallel to the axis of regional maximum compressive stress the increase in earthquake rates the appearance of a new seismic volume and the elevated gas emissions at iliamna volcano indicate that new magma intruded beneath the volcano in 1996 the elongation of the 1996 1997 earthquake cluster parallel to the direction of regional maximum compressive stress and the accelerated occurrence of both normal and strike slip faulting in a small volume of crust at the top of the new seismic volume may be explained by the emplacement and inflation of a subvertical planar dike beneath the summit of iliamna and its southern satellite vents

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

roles for fluid and or melt advection in forming high p mafic migmatites fiordland new zealand a series of striking migmatitic structures occur in rectilinear networks through western fiordland new zealand involving for the most part narrow anorthositic dykes that cut hornblende bearing orthogneiss adjacent to the dykes host rocks show patchy spatially restricted recrystallization and dehydration on a decimetre scale to garnet granulite although there is general agreement that the migration of silicate melt has formed at least parts of the structures there is disagreement on the role of silicate melt in dehydrating the host rock a variety of causal processes have been inferred including metasomatism due to the ingress of a carbonic mantle derived fluid hornblende breakdown leading to water release and limited partial melting of host rocks and dehydration induced by volatile scavenging by a migrating silicate melt variability in dyke assemblage together with the correlation between dehydration structures and host rock silica content are inconsistent with macroscopic metasomatism and best match open system behaviour involving volatile scavenging by a migrating trondhjemitic liquid

occurrence and origin of andalusite in peraluminous felsic igneous rocks andalusite occurs as an accessory mineral in many types of peraluminous felsic igneous rocks including rhyolites aplites granites pegmatites and anatectic migmatites some published stability curves for and sil and the water saturated granite solidus permit a small stability field for andalusite in equilibrium with felsic melts we examine 108 samples of andalusite bearing felsic rocks from more than 40 localities world wide our purpose is to determine the origin of andalusite including the t p x controls on andalusite formation using eight textural and chemical criteria size compatibility with grain sizes of igneous minerals in the same rock shape ranging from euhedral to anhedral with no simple correlation with origin state of aggregation single grains or clusters of grains association with muscovite with or without rims of monocrystalline or polycrystalline muscovite inclusions rare mineral inclusions and melt inclusions chemical composition andalusite with little significant chemical variation except in iron content 008 171 wt feo compositional zoning concentric sector patchy oscillatory zoning cryptically reflect growth conditions compositions of coexisting phases biotites with high siderophyllite eastonite contents aliv 268 007 atoms per formula unit muscovites with 057 401 wt feo and 002 285 wt tio2 and apatites with 353 018 wt f coexisting muscovite biotite pairs have a wide range of f contents and fbt 1612fms 0015 most coexisting minerals have compositions consistent with equilibration at magmatic conditions the three principal genetic types of andalusite in felsic igneous rocks are type 1 metamorphic a prograde metamorphic in thermally metamorphosed peraluminous granites b retrograde metamorphic inversion from sillimanite of unspecified origin c xenocrystic derivation from local country rocks and d restitic derivation from source regions type 2 magmatic a peritectic water undersaturated t associated with leucosomes in migmatites b peritectic water undersaturated t as reaction rims on garnet or cordierite c cotectic water undersaturated t direct crystallization from a silicate melt and d pegmatitic watersaturated t associated with aplite pegmatite contacts or pegmatitic portion alone type 3 metasomatic water saturated magma absent spatially related to structural discontinuities in host replacement of feldspar and or biotite intergrowths with quartz the great majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin of the many possible controls on the formation of andalusite excess al2o3 water concentration and fluid evolution high be b li p high f high fe mn ti and kinetic considerations the two most important factors appear to be excess al2o3 and the effect of releasing water either to strip alkalis from the melt or to reduce alumina solubility in the melt of particular importance is the evidence for magmatic andalusite in granites showing no significant depression of the solidus suggesting that the and sil equilibrium must cross the granite solidus rather than lie below it magmatic andalusite however formed is susceptible to supra or sub solidus reaction to produce muscovite in many cases textural evidence of this reaction remains but in other cases muscovite may completely replace andalusite leaving little or no evidence of its former existence

use of vegetable oil and silica powder for scale modelling of magmatic intrusion in a deforming brittle crust in the upper crust intrusive bodies adopt different configurations depending on the tectonic setting this paper describes a new technique for analogue modelling of such intrusions specifically of low viscosity magma into a deforming brittle crust proper dynamic scaling is an important consideration if the crust has a coulomb failure envelope the model material should have a cohesion c of 40 pa to 7500 pa if the intruding magma is highly mobile the model fluid should have a viscosity of 4 10 9 pa s to 75 pa s for the model crust we have used crystalline silica powder si crystal siliceous microspheres si sphere of grain size 30 m and a mixture si mix of both materials the mechanical properties of these powders have been obtained by shear and tension shear tests si crystal powder is cohesive c 300 pa angle of internal friction 45 and represents competent rock si sphere powder is much less cohesive c 10 pa 25 and represents incompetent rock si mix has intermediate properties the model magma is a vegetable oil which solidifies at room temperature its viscosity when molten is 2 10 2 pa s at 50 c using these materials we have done some preliminary experiments to investigate the intrusion of low viscosity magma into sedimentary basins in non deformed settings intrusions were saucer shaped cone sheets in horizontal extension they were steep dykes finally in horizontal shortening intrusions were basal sills that branched into thrust faults

detachment depth revealed by rollover deformation an integrated approach at mount etna this work was partially funded by ingv and the dpc ingv project flank and partially by the asi srv project

petrogenesis of the puerto eden igneous and metamorphic complex magallanes chile late jurassic syn deformational anatexis of metapelites and granitoid magma genesis a suite of schists gneisses migmatites and biotite granitoids from the puerto eden igneous and metamorphic complex peimc and biotite hornblende granitoids of the south patagonian batholith southern chile has been studied for that purpose the chemistry of minerals and the bulk rock composition of major and trace elements including rb sr and sm nd isotopes were determined mineralogical observations and geothermobarometric calculations indicate high temperature and low pressure conditions ca 600 700 c and 3 to 4 5 kbar for an event of metamorphism and partial melting of metapelites in late jurassic times previously determined by shrimp u pb zircon ages structures in schists gneisses migmatites and mylonites indicate non coaxial deformation flow during and after peak metamorphic and anatectic conditions andalusite schists and sillimanite gneisses yield initial 87sr 86sr ratios of up to 0 7134 and end150 values as low as 7 6 contemporaneous biotite granitoids and a coarse grained orthogneiss have initial 87sr 86sr ratios between 0 7073 and 0 7089 and end150 values in the range 7 6 to 4 4 this indicates that metamorphic rocks do not represent the natural isotopic variation in the migmatite source thus a heterogeneous source with a least radiogenic component was involved in the production of the biotite granitoids the peimc is considered as a segment of an evolving kilometre sized and deep crustal shear zone in which partial melts were generated and segregated into a large reservoir of magmas forming composite plutons in late jurassic times a biotite hornblende granodiorite and a muscovite garnet leucogranite show initial 87sr 86sr ratios of 0 7048 and 0 7061 and end100 values of 2 6 and 1 8 respectively and are thus probably related to early cretaceous magmas not involved in the anatexis of the metasedimentary rocks

seismic anisotropy from sks splitting beneath northeastern tibet the northeastern boundary of the tibetan high plateau is marked by a 2 km topographic drop and a coincident rapid change in crustal thickness surface tectonics are dominated by the kunlun strike slip fault system and adjacent kunlun concealed thrust the main objective of the current study is to map lateral variations of seismic anisotropy parameters in this region along the linear indepth iv array in order to investigate the link between surface and internal deformation in the context of crust and mantle structure to achieve this aim we performed minimum transverse energy based sks splitting measurements using 23 stations of the indepth iv array deployed across the northeastern margin of tibet average fast polarization directions and splitting time delays are obtained by averaging stacked misfit surfaces of all analyzed events at each station the agreement of fast directions with the strikes of major active strike slip faults and strike slip focal mechanisms but not with fossil structures such as the jinsha suture implies that the anisotropy records lithospheric petrofabric formed by recent deformation within the lithosphere rather than representing frozen in anisotropy or shear within the asthenosphere due to absolute plate motion the distribution of large splitting delays throughout the northern plateau suggests that deformation is distributed rather than focused onto narrow shear zones associated with the kunlun strike slip faults the drop in splitting delays toward the qaidam is then a natural consequence of the much lower degree of deformation there

a syn eruptive ground deformation episode measured by gps during the 2001 eruption on the upper southern flank of mt etna ground deformation occurring on the southern flank of mt etna volcano during the july august 2001 eruption was monitored by gps measurements along an e w profile crossing the fissure system this profile was measured eight times during the eruption using the stop and go semi kinematic technique horizontal and vertical displacements between gps surveys are reported for each station the most significant event is a deformation episode occurring during the first week of the eruption between 25 27 july displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture data inversions for measured displacements were performed using the okada model the model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east dipping fault parallel to the 1989 fracture

small scale models of oceanic transform zones previous studies about oceanic transform zones reveal major morphological and structural differences that cannot be explained by simple factors such as spreading rates or offsets in order to determine how kinematic and mechanic parameters control the deformation pattern we perform small scale modeling using sand and silicone putty as analog material of brittle and ductile layers of oceanic lithosphere respectively the three dimensional depth geometry of these layers follows the thermal structure of the ridge transform system the structure of the deformed transform zone is very sensitive to input parameters specially to the offset the obliquity of the deformed zone with the extension direction i e spreading direction in a natural system depends on the offset and on the brittle layer thickness for greater thickness or a shorter offset the transform domain widens and the components of extension become significant for smaller lithosphere thickness or larger offset the transform domain becomes narrow with steeper walls and mainly undergoes strike slip deformation such variability in possible controls on the offset length may help explain the structure complexity observed within the oceanic transform zones a comparison with 28 natural systems indicates the same relationship of the offset with the angle between the principal transform displacement zone ptdz and spreading direction a relationship between offset and width is clearly established for mid atlantic ridge mar transforms as on analog models a similar relationship is observed for the east pacific rise epr transforms but with greater variabilty this difference is interpreted as resulting either from greater complexity of transform zones on epr than on mar making it difficult to estimate some parameters from different mechanical behaviors between slow and fast spreading systems or from higher rheological complexity of natural systems than out model

melt producing versus melt consuming reactions in pelitic xenoliths and migmatites abstract melt producing reactions have operated both in pelitic xenoliths and in pelitic migmatites but melt consuming reactions related to in situ melt crystallization are largely restricted to migmatites hence xenolith reaction textures may provide clues on the relative roles of both reaction types in migmatites a comparison of xenoliths and migmatites results in a catalogue of textural and chemical features some of which are argued to be diagnostic the results have implications for the identification of restite in igneous rocks and for the relative importance of prograde and retrograde processes in different domains of layered migmatites