isotope geochemistry sr nd pb and petrogenesis of leucite bearing volcanic rocks from colli albani volcano roman magmatic province central italy inferences on volcano evolution and magma genesis the colli albani composite volcano is made up of strongly silica undersaturated leucite bearing rocks magmas were erupted during three main periods but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs the most alkali rich magmas restricted to the caldera forming period pre caldera are extremely enriched in incompatible trace elements and display more radiogenic sr 87sr 86sr 0 71057 0 71067 with slightly less radiogenic pb with respect to those of the post caldera period post caldera volcanic activity was concentrated in three different volcanic environments external to the caldera along the caldera edge and within the caldera the post caldera magmas produced melilite to leucitite bearing plagioclase free leucitites in contrast to the pre caldera lavas they are characterised by lower incompatible trace element abundances and less radiogenic sr 87sr 86sr 0 71006 0 71039 magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre caldera period the multiple caldera collapses dissected and partially obliterated the early magma chamber during the post caldera stage magmas were channelled through several pathways and multiple shallow level magma reservoirs were established a lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab derived component is suggested as the mantle source of colli albani parental magmas two different parental magmas are recognised for the pre and post caldera stages the differences may be related to the interplay between smaller degrees of melting for the pre caldera magmas and more carbonate rich recycled subducted lithologies in the post caldera magmas

a noncognate relationship between megacrysts and host basalts from the tuoyun basin chinese tian shan abstract abundant kaersutite and alkali feldspar megacrysts occur together with mantle derived and lower crustal xenoliths including kaersutite hornblendite and syenite in the early cretaceous alkaline basalts of the tuoyun basin in the westernmost chinese tian shan particularly several kaersutite hornblendite cumulate xenoliths have the assemblage of kaersutite alkali feldspar titanian mica titanomagnetite clinopyroxene in which kaersutite occurs as an early stage cumulus phase crystallized from a parental magma and alkali feldspar occurs as a late stage intercumulus phase from the evolved magma between accumulating kaersutite grains the megacrystic and xenolithic kaersutite has much higher mg values 0 70 0 96 than the host basalt 0 47 0 60 the kaersutite and alkali feldspar megacrysts have similar initial ratios 0 7032 0 7033 and 0 7035 0 7038 respectively significantly different from their host basalts 0 7047 0 7054 xenolithic petrography and megacrystic sr isotope geochemis

mafic and felsic magma interaction in granites the hercynian karkonosze pluton sudetes bohemian massif the hercynian post collisional karkonosze pluton contains several lithologies equigranular and porphyritic granites hybrid quartz diorites and granodiorites microgranular magmatic enclaves and composite and lamprophyre dykes field relationships mineralogy and majorand trace element geochemistry show that 1 the equigranular granite is differentiated and evolved by small degrees of fractional crystallization and that it is free of contamination by mafic magma 2 all other components are affected by mixing the end members of the mixing process were a porphyritic granite and a mafic lamprophyre the degree of mixing varied widely depending on both place and time all of the processes involved are assessed quantitatively with the following conclusions most of the pluton was affected by mixing implying that huge volumes 475 km of mafic magma were available this mafic magma probably supplied the additional heat necessary to initiate crustal melting part of this heat could have also been released as latent heat of crystallization only a very small part of the karkonosze granite escaped interaction with mafic magma specifically the equigranular granite and a subordinate part of the porphyritic granite minerals from these facies are compositionally homogeneous and or normally zoned which together with geochemical modelling indicates that they evolved by small degrees of fractional crystallization 520 accessory minerals played an important role during magmatic differentiation and thus the fractional crystallization history is better recorded by trace rather than by major elements the interactions between mafic and felsic magmas reflect their viscosity contrast with increasing viscosity contrast the magmatic relationships change from homogeneous hybrid quartz diorites granodiorites to rounded magmatic enclaves to composite dykes and finally to dykes with chilled margins these relationships indicate that injection of mafic magma into the granite took place over the whole crystallization history consequently a long lived mafic source coexisted together with the granite magma mafic magmas were derived either directly from the mantle or via one or more crustal storage reservoirs compatible element abundances e g ni show that the mafic magmas that interacted with the granite were progressively poorer in ni in the order hybrid quartz dioritescgranodioritescenclavesccomposite dykes this indicates that the felsic and mafic magmas evolved independently which in the case of the karkonosze granite favours a deep seated magma chamber rather than a continuous flux from mantle two magma sources mantle and crust coexisted and melted almost contemporaneously the two reservoirs evolved independently by fractional crystallization however mafic magma was continuously being intruded into the crystallizing granite with more or less complete mixing several lines of evidence e g magmatic flux structures incorporation of granite feldspars into mafic magma feldspar zoning with fluctuating trace element patterns reflecting rapid changes in magma composition indicate that during its emplacement and crystallization the granite body was affected by strong internal movements these would favour more complete and efficient mixing the systematic spatial temporal association of lamprophyres with crustal magmas is interpreted as indicating that their mantle source is a fertile peridotite possibly enriched metasomatized by earlier subduction processes

petrology and geochemistry of potassic and ultrapotassic volcanism in central italy petrogenesis and inferences on the evolution of the mantle sources major trace element sr isotopic and mineral chemical data are reported for mafic volcanic rocks mg value 65 from the northern central sector of the potassic volcanic belt of central italy the rocks investigated range from potassic series ks and high k series hks to lamproitic lmp and kamafugitic kam through a transitional series trans thus covering the entire compositional spectrum of potassic and ultrapotassic magmas kam rocks are strongly silica undersaturated and compared with the other rock series have low sio2 al2o3 na2o sc and v and high cao k na na k al ks and hks have high al2o3 cao and variable enrichment in k2o and incompatible elements lmp rocks are saturated in silica and have high sio2 k2o k2o na2 mgo ni and cr and low al2o3 cao na2o sc and v trans rocks display intermediate compositional characteristics between lmp and ks all the rocks under study have fractionated hygromagmaphile element patterns with high lil hfs element values and negative anomalies of ti ta nb and ba negative sr anomalies are observed in the lmp and trans rocks lil elements show overall positive correlations with k2o whereas different trends of sr and hfse vs k2o are defined by lmp trans and ks hks kam 87sr 86sr range from about 0 710 to 0 716 ks hks and kam rocks have similar 87sr 86sr values clustering around 0 710 lmp and trans rocks have the highest 87sr 86sr values geochemical and isotopic data reported for the most primitive italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of italian potassic magmatism simple mass balance calculations exclude however an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of central italy volcanics underwent contamination with fluids and or melts released by upper crustal material previously brought into the mantle by subduction processes different trends of incompatible elements vs k2o observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of lmp rocks fluids or melts rich in ca sr and with high lile hfse value and sr isotopic composition around 0 710 are the most likely contaminant of the source region of ks hks and kam volcanics variations in cao na2o and ferromagnesian element abundances and ratios suggest that in some zones the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism

how late are k feldspar megacrysts in granites abstract various petrologists have suggested that k feldspar megacrysts grow in granites that are extensively crystallized even at subsolidus conditions however experimental evidence indicates that though k feldspar nucleates relatively late in the crystallization history abundant liquid is available for development of large crystals a great deal of evidence involving many different factors favours a magmatic phenocrystic origin for k feldspar megacrysts in granites namely simple twinning oscillatory zoning euhedral plagioclase inclusions and concentric crystallographically controlled arrangements of inclusions in addition abundant evidence has been presented of 1 mechanical accumulation of k feldspar megacrysts in granites 2 alignment of megacrysts and megacryst concentrations in magmatic flow foliations 3 involvement of megacrysts in zones of magma mixing in granite plutons and 4 occurrence of megacrysts in some volcanic rocks implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains

petrology and isotope geochemistry of san vincenzo rhyolites tuscany italy two groups of rhyolites have been recognized at san vincenzo tuscany italy group a rhyolites are characterized by plagioclase quartz biotite sanidine and cordierite mineral assemblages they show constant mgo and variable cao and na2o contents initial87sr 86sr ratios in group a samples range between 0 71950 and 0 72535 whereas the nd isotopic compositions are relatively constant 0 51215 0 51222 group b rhyolites are characterized by orthopyroxene and clinopyroxene as additional minerals and show textural mineralogical and chemical evidence of interaction with more mafic magmas the sr and nd isotopic ratios range between 0 71283 0 71542 and 0 51224 0 51227 respectively magmatic inclusions of variable size 1 mm to 10 cm were found in groups b rhyolites these inclusions consist mainly of diopsidic clinopyroxene and minor olivine and biotite they are latitic in composition and represent blobs of hybrid intermediate magmas entrained in the rhyolitic melts these magmatic inclusions have relatively high sr contents 996 1529 ppm and sr and nd isotope ratios of 0 70807 0 70830 and 0 51245 0 51252 respectively 87sr 87sr data on minerals separated from both group a and b rhyolites and magmatic inclusions reveal strong isotopic disequilibria due to the presence of both restitic and newly crystallized phases in group a rhyolites and due to interaction of rhyolites with a mantle de rived magma in group b rhyolites isotopic data on whole rocks and minerals allow us to interpret the group a rhyolites as representative of different degrees of melting of an isotopically fairly homogeneous pelitic source conversely group b rhyolites underwent interactions with a mantle derived magma the crustal source as inferred from isotopic systematics would be characterized by87sr 86sr and143nd 144nd ratios close to 0 7194 and 0 51216 respectively the sub crustal magma would have sr isotopic composition close to 0 7077 and a143nd 144nd ratio greater than or equal to 0 51252 these isotopic features are different from those reported for the parental magmas postulated for vulsini and alban hills in the nearby roman magmatic province and are similar to those of the vesuvius and ischia magmas

microchemical and sr isotopic investigation of zoned k feldspar megacrysts insights into the petrogenesis of a granitic system and disequilibrium crystal growth k feldspar megacrysts kfm are used to investigate the magmatic evolution of the 7ma monte capanne mc monzogranite elba italy dissolution and regrowth of kfm during magma mixing or mingling events produce indented resorption surfaces associated with high ba contents diffusion calculations demonstrate that kfm chemical zoning is primary core to rim variations in ba rb sr li and p support magma mixing i e high ba and p and low rb sr at rims but more complex variations require other mechanisms in particular we show that disequilibrium growth related to variations in diffusion rates in the melt may have occurred as a result of thermal disturbance following influx of mafic magma in the magma chamber initial 87 sr 86 sr ratios isr obtained by microdrilling decrease from core to rim inner core analyses define a mixing trend extending towards a high isr rb sr melt component whereas the outer cores and rims display a more restricted range of isr but a larger range of rb sr lower isr at the rim of one megacryst suggests mixing with high k calc alkaline mantle derived volcanics of similar age on capraia trace element and isotopic profiles suggest 1 early megacryst growth in magmas contaminated by crust and refreshed by high isr silicic melts as seen in the inner cores and 2 later recharge with mafic magmas as seen in the outer cores followed by 3 crystal fractionation with possible interaction with hydrothermal fluids as seen in the rim the model is compatible with the field occurrence of mafic enclaves and xenoliths

a reappraisal of seismicity recorded during the 1996 gjalp eruption iceland in light of the 2014 2015 barðarbunga holuhraun lateral dike intrusion this study performs a reanalysis of the seismicity recorded during the 1996 gjalp eruption that occurred at nw vatnajokull iceland the seismicity was recorded by the temporary hotspot network consisting of 30 three component broadband stations in total 301 events were identified between 29 september and 12 october and their phases were manually picked a velocity model was estimated from p phase travel times by using velest events were first located using the algorithm nonlinloc in order to obtain absolute locations precise relative locations were obtained with hypodd by utilizing catalog and cross correlation differential travel times results show that events clustered first along the sw rim of the bar arbunga caldera and later along the gjalp fissure with most hypocentral depths located between 3 and 8 km waveforms of the 10 largest events that followed the bar arbunga earthquake were inverted in order to obtain moment tensors for all events we found that the deviatoric moment tensor fits the data better than pure double couple or full moment tensor solutions events along the bar arbunga caldera exhibited reverse focal mechanisms while those at the gjalp fissure exhibited mostly strike slip faulting seismic velocity variations calculated using ambient noise interferometry point to the possibility that a small subglacial eruption occurred at bar arbunga before the main earthquake this removed melt from the magma chamber causing its roof to collapse and also resulted in the lateral migration of magma towards the gjalp fissure the 2014 2015 bar arbunga holuhraun eruption shares common characteristics with the 1996 gjalp eruption although the size of the latter was much smaller

crystallization paths of leucite bearing lavas examples from italy the salic phases found in leucite basanites trachytes and phonolites may be used to portray crystallization in the system naalsio 4 kalsio 4 caal 2si 2o 8 sio 2 the phonolite pentahedron only two lavas have been found that contain the assemblage leucite nepheline plagioclase sanidine and liquid a natural pseudo invariant assemblage at 900 c 100 equivalent to the isobaric invariant point of the four component system the diversity of phases in this group of lavas illustrates the role of halogens in controlling their crystallization paths thus the presence of f in the leucite basanites has stabilized magnesian biotite and suppressed sanidine as has been found in other basanitic lavas brown and carmichael 1969 the presence of cl in these same lavas has induced the crystallization of sodalite which takes the place of nepheline in the groundmass however in the leucite trachytes biotite has suppressed olivine and coexists with sanidine and leucite the presence of s may produce hauyne at the expense of nepheline and in general sulphate minerals which include apatite have the role in lavas of low silica activity that pyrrhotite plays in liquids of high silica activity both pyroxenes and titaniferous magnetites in this suite of lavas are very aluminous groundmass crystals of pyroxene may have one fifth of si replaced by al other phases which occur occasionally are melanite garnet and a potassium rich hastingsite but neither ilmenite nor a sulphide mineral has been found phenocryst equilibration temperatures derived from olivine and sr rich plagioclase are generally in the range from 1 050 c to 1 150 c the high content of incompatible elements e g k ba rb f sr p in these lavas suggests that they represent a small liquid fraction from a mantle source which possibly contains phlogopite

seismic heterogeneity of mt etna structure and activity a dense seismic array maintained temporarily for 7 weeks provides an approach to deducing the 3 d heterogeneity of the structure of the upper crust beneath mt etna volcano from the inversion of p and s wave arrivals of local earthquakes independent data from a different source array geometry using waves generated by distant shots at sea confirm a main lateral variation a high velocity body underlies part of the volcano its contrast with the surrounding thick sedimentary pile and its location extending from the present summit to the southeast suggests that it may have been built by the development and migration of past eruptive centres followed by caldera collapse local low velocity anomalies near its sharp western edge may be associated with presently active features

surface wave tomography and seismic source studies at campi flegrei italy abstract we analyse a set of events recorded in march 1984 during a period of intense seismicity of the last bradyseismic crisis to determine shallow velocity models and seismic source moment tensors in the campi flegrei region the velocity models of the crust are obtained by surface wave tomography two inland negative anomalies of group velocity resulting in our tomographic maps well agree with previous independent measurements whereas a third anomaly located in the pozzuoli gulf and not evidenced by previous studies is in correspondence with the caldera position the inversion of the dispersion curves allows us to extend the already available velocity models within the uppermost 2 km of the crust the obtained models are employed to study seismic source features by the moment tensor analysis preliminary synthetic tests are performed in order to minimise artefacts in the moment tensor solutions possibly due to numerical noise to station distribution or to the structural modelling approximation most of the investigated earthquakes are deviatoric mechanisms and the increase of the isotropic component is observed in connection with the change of the seismicity rate in the investigated temporal window

geochemistry of tuscan archipelago granitoids central italy the role of hybridization processes in their genesis this paper reports major trace and rare earth element data for selected samples from the elba giglio and monte cristo plutons which lie in the tuscan archipelago italy on the basis of field and petrologic constraints all the rocks can be divided into five facies and range in composition from granodioritic to alkali granitic with a strong predominance of monzogranites tuscan archipelago granitoids are clearly collision related rocks and they straddle the i and s types of chappell and white however mineralogical and chemical characteristics indicate that the more basic rocks are broadly i type while the high silica rocks are s type genetic models that relate these magmas through the segregation of their major and accessory mineral phases are inconsistent with major trace and ree element abundant data geological petrographical and geochemical constraints show that the microgranular mafic enclaves found within the rocks are blobs of mafic high temperature magma chilled within a cooler m

paleoproterozoic potassic ultrapotassic magmatism morro do afonso syenite pluton bahia brazil abstract the morro do afonso syenitic pluton masp is a small bimodal suite of lamprophyric and syenitic rocks located in the serrinha nucleus sao francisco craton northeastern brazil the unit consists predominantly of alkali feldspar syenite with numerous mafic xenoliths and dykes that are predominantly lamprophyric the syenite shows geochemical and isotopic features typical of the roman potassic magmas i e low tio2 up to1 2 low k2o al2o3 0 33 0 49 strong enrichment in lile and high lile hfse ratios fractionation mainly of clinopyroxene and amphibole explains the transition from lamprophyre to syenite magma mixing is required to explain the most evolved compositions masp syenites have paleoproterozoic crystallization ages 2 11 ga the nd isotope composition of mafic and felsic phases are similar e n d mafic 2 36 to 2 61 and e n d felsic 2 47 and they have archaean model ages tdm 2 56 2 58 ga that match the age of an inherited zircon grain ca 2 6 ga masp is similar to many other post orogenic syenitic plutons distributed over a wide area of sao francisco craton sfc which are closely comparable in age and also typically associated with ultrapotassic lamprophyre the present results suggest that a major proportion of the potassic ultrapotassic syenitic rocks of the sfc were emplaced in a narrow time interval from 2111 to 2080 ma limiting the time of metamorphism peak of the transamazonian orogeny to at least 2 1 ga these plutons show some evidence of having interactions with older felsic crustal rocks and are interpreted to be derived from partial melting of lithospheric mantle that was enriched by subduction

geochemical and b sr nd isotopic evidence for mingling and mixing processes in the magmatic system that fed the astroni volcano 4 1 3 8 ka within the campi flegrei caldera southern italy abstract the astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes within the campi flegrei caldera southern italy 4 1 3 8 ka bp whole rock geochemical and b sr nd isotopic investigations were carried out on representative samples of all seven eruptions the products vary from tephriphonolites to phonolites and from latites to trachytes they show textural mineralogical and isotopic evidence of disequilibrium including distinct clinopyroxene populations rounded and or resorbed plagioclase and alkali feldspar and reverse zoned phenocrysts of all these mineral phases the sr nd and b isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution suggesting open system processes in addition to fractional crystallisation moreover significant sr isotopic disequilibrium between the phenocrysts and glass has been documented for one sample the chemostratigraphy of the products indicates that astroni eruptions 1 through 5 were fed by magmas of trachytic to phonolitic composition that were less enriched in radiogenic sr and 11b up section this variability has been interpreted as the result of mingling between at least two distinct magmatic end members one more evolved and the other less evolved another heterogeneous batch of magma resulting from almost complete mixing between the same two end members was drained during eruptions 6 and 7 the more evolved end member characterised by 87sr 86sr 0 7075 143nd 144nd 0 51247 and 11b 8 was very similar to the magma that fed the final phases of the agnano monte spina eruption which occurred a few centuries earlier in the astroni vent area the less evolved end member had 87sr 86sr 0 70726 143nd 144nd 0 51251 and 11b 10 and was likely derived by fractional crystallisation of a mantle derived magma an abrupt decrease in both the sr isotope ratio and the th content detected at the transition between unit 4 and 5 suggests that another magma with a 87sr 86sr ratio intermediate between those of the two identified end members may have been involved in astroni activity the more evolved end member is interpreted as a residue of the agnano monte spina eruption that was invaded by either the intermediate or the less evolved magmatic end member promoting mingling and triggering astroni activity this study of astroni provides insights for both short and long term volcanic hazard assessment as the astroni volcano is the best example of a very close sequence of eruptions from the same vent area in the campi flegrei caldera

active tectonics in central italy constraints from surface wave tomography and source moment tensor inversion abstract we investigate the lithosphere asthenosphere structure and active tectonics of central italy with emphasis on the umbria marche area by means of surface wave tomography and seismic moment tensor inversion the data include a large number of short period local and regional group velocity measurements sampling the umbria marche apennines and the adria margin respectively incorporation of published phase velocity measurements sampling italy and surroundings results from deep seismic soundings which go through the umbria marche area the local group velocity maps covering the area reactivated by the 1997 1998 umbria marche earthquake sequence suggest an intimate relationship between the lateral earth structure variations and the distribution of the active fault systems and related sedimentary basins the upper crustal models reveal the importance of inherited compressional tectonics on the recent extensional deformation and associated seismic activity source inversion studies of the main events of the 1997 earthquake sequence show the dominance of normal faulting mechanisms whereas selected aftershocks between the fault segments at the step over reveal that the prevailing deformation is of strike slip faulting type at the regional scale the crust exhibits clear layering and varies in thickness from about 25 km below the tuscan metamorphic complex tmc to about 30 km below the val tiberina extensional thick sedimentary basin and reaches about 35 km below the umbria marche geological domain umd the lithospheric mantle lid is thin about 30 km below tmc while it is about 70 km thick below umd a lithospheric root about 120 km wide between the tmc and umd reaches a depth of at least 130 km a low velocity zone defined mantle wedge vs less than 4 2 km s in the uppermost mantle overlying the high velocity lid is detached this wedge is about 20 km thick and decouples the underlying lid from the crust the retrieved crust and upper mantle structure beneath central italy is in agreement with bouguer anomaly and heat flow data and supports a delamination process the high velocity upper mantle underlying the mantle wedge is inferred to be subcrustal lithospheric material delaminated from the overlying crust

medium pressure crystallization of a monchiquitic magma evidence from megacrysts of drever s block ubekendt ejland west greenland abstract megacrysts and polymineralic fragments of extraordinary diversity from a tertiary monchiquitic dyke of ubekendt ejland comprise three groups 1 cr diopside fassaitic diopside olivine fo90 5 81 5 cr al spinels ii fassaitic salite ferrisalite k ti pargasite ferropargasite apatite al ti magnetite iii scapolite hyalophane potassium feldspar nepheline analcime by comparison with mineralogy and phase relations in the host rock and experimental data from alkaline rocks the megacrysts are related to a sequence of crystallization from primitive monchiquitic to potassic phonolitic magmas rich in h2o and co2 at 5 11 kb group i megacrysts formed at temperatures of 1300 1150 c and group ii between 1150 800 c and f o 2 9 bar at the latter temperature high pco2 may have stabilized the scapolite in the more evolved liquid and k feldspar and nepheline began to crystallize at ca 800 c possibly together with the ferrisalite

the dynamics of the 2001 etna eruption as seen by full moment tensor analysis summary the mt etna eruption of july 2001 was announced by severe seismic activity and by the opening of a 7 km long zone of densely distributed fractures the large amount of data collected gave a unique opportunity to study the magma migration process and to infer the position and geometry of the uprising dyke results from multidisciplinary approaches suggest that the observed phenomenology was the result of the rapid intrusion of a vertical dyke oriented roughly n s and located a few km south of the summit region to add new constraints to the dynamics of the eruption process in this study we determine the full seismic moment tensors of 61 earthquakes selected among those occurring between july 12 and july 18 md 2 2 located in a depth ranging from 1 km above sea level a s l to 3 km below sea level b s l at the beginning of the seismic swarm the dominant component of the seismic source tensor is double couple percentage around 65 per cent on average statistical significant at 95 per cent confidence level and in the following hours the non double couple components increase at the expenses of the double couple such observations are related well with the system of fractures formed just before the eruption whereas the increasing non double couple components can be explained as the response of the confining rocks to the rising magma and degassing processes the type of focal mechanisms retrieved are predominantly of normal fault type 44 per cent strike slip 30 per cent and thrust mechanisms 9 per cent and outline a scenario that concurs with the stress regime induced by a dyke injection the space time analysis of seismic source locations and source moment tensors 1 confirms the evidence of a vertical dyke emplacement that fed the 2001 lateral eruption and 2 adds new insights to support the hypothesis of the injection of a second aborted dyke 2 km se from the fractures zone

carbonate assimilation at merapi volcano java indonesia insights from crystal isotope stratigraphy recent basaltic andesite lavas from merapi volcano contain abundant complexly zoned plagioclase phenocrysts analysed here for their petrographic textures major element composition and sr isotope composition anorthite an content in individual crystals can vary by as much as 55 mol an

crystal recycling in the steady state system of the active stromboli volcano a 2 5 ka story inferred from in situ sr isotope and trace element data in situ sr isotope data by microdrilling coupled with major and trace element analyses have been performed on plagioclase and clinopyroxene from seven samples collected during the 2002 2003 eruptive crisis at stromboli volcano aeolian islands italy on 28 december 2002 the persistent moderate explosive activity was broken by an effusive event lasting about 7 months a more violent explosion paroxysm occurred on 5 april 2003 two magma types were erupted namely a volatile poor and highly porphyritic magma hp magma poured out as scoria or lava and a volatile rich phenocryst poor magma lp magma found as pumice lp magma differs from the hp magma also for its slightly less evolved chemistry the groundmass composition and the lower sr isotope ratios micro sr isotope data show the presence of zoned minerals in strong isotope disequilibrium as previously found in products erupted in 1984 1985 and 1996 ad with 87sr 86sr values generally decreasing from cores to rims of minerals only some outer rims testify for equilibrium with the host groundmass the internal mineral zones with high sr isotope ratios 0 70665 0 70618 are interpreted as antecrysts crystallised during the previous activity and recycled in the present day system since the opening shoshonitic activity of the recent period which occurred at about 2 5 ka ago this result has implications for the dynamics of the present day plumbing system of stromboli at intermediate pressure about 2 3 km depth and allows us to propose a model whereby an hp magma reservoir is directly interconnected at the bottom with a cumulate crystal much reservoir efficient mixing between residing hp and input lp magmas can occur in this reservoir due to more similar rheological characteristics of the two magmas than in the conduit where crystallisation is enhanced by degassing antecrysts and possibly melts re enter in the hp magma reservoir both from the bottom recycled by ascending lp magmas crossing the crystal mush and from the top recycled by descending degassed and dense hp magma residual of the periodic strombolian explosions at the surface the isotope variation measured in the groundmasses allows calculating the proportion of the lp magma entering the shallow hp magma reservoir at 20 from this proportion we estimate that the total volume of lp magma input during 2002 2003 closely matches the magma volume erupted in the effusive event suggesting a steady state system at broadly constant volume the comparison with estimates of the lp magma volume ejected by the paroxysm indicates that the lp magma amount directly reaching the surface during the 5 april paroxysm is minimal with respect to that entering the system

inter and intracrystalline isotopic disequilibria techniques and applications in the last 20 years we have seen a significant expansion of techniques related to geochemical and isotopic microsampling of materials in the earth sciences from constraining pre eruptive histories of flood basalt magmas to identifying the natal rivers of origin of anadromous fishes these techniques have had significant impacts in a wide variety of scientific fields nowhere has the impact been greater than in identifying the sources processes and timing of processes involved in igneous magmatic systems both technique refinements and the development of new technologies have aided in advancing microsampling applications thus allowing for a better understanding of the sources and mechanisms responsible for changing geochemical and isotopic signatures in natural systems in this chapter we focus on the techniques and technologies associated with radiogenic isotope microsampling and review applications of these techniques as utilized in scientific investigations isotope microsamping is a logical extension of earlier studies that evaluated individual components of magmas and magma systems including melts and minerals from the use of petrographic microscopes and the later introduction of the electron microprobe the focus on internal chemical variations in melts and minerals is critical to assessing the petrogenetic histories of igneous rocks even today these technologies are used to ensure that further trace element and isotopic analyses are undertaken in a textural and major element context for trace elements and isotopes early studies e g cortini and van calsteren 1985 confirmed variations in the melt and mineral components of many igneous rocks but focused on mineral or glass separates potential information associated with isotopic variations retained by individual crystals or internal variations within individual crystals was lost later studies such as geist et al 1988 focused on isotope variations within single megacrysts to constrain mixing scenarios between basaltic andesitic and rhyolitic magmas and davidson et al 1990 used

the evolution of latera caldera central italy in the light of subsurface data subsurface geothermal exploration has considerably added to our knowledge of the latera volcanic complex a syenitic body is located about 2 km below the present day surface k ar data point a 0 9 ma age the primary magma was a silica saturated trachyte undersaturated hauyne bearing products are found near the carbonatic wall rocks and have been interpreted as reaction products subsurface data from deep drilling and geophysical surveys suggest that the latera caldera resulted from three main successive collapse phases i formation of an old caldera now buried related to the eruption of ignimbrites from the syenitic magma chamber ii sinking of the eastern sector as a consequence of the formation of the nearby bolsena caldera 0 3 ma iii multistage formation of the present latera caldera 0 16 ma

the 1989 1990 activity of etna magma mingling and ascent of h2oclsrich basaltic magma evidence from melt inclusions abstract the melt inclusions in olivine phenocrysts from basaltic tephra erupted by etna volcano during the 1989 1990 eruptive period were investigated for major elements cl and s by electron microprobe fluorine by pigme particule induced gamma ray emission and h 2 o by sims the results indicate the ascent of basaltic magmas with different k 2 o concentrations possibly related to different feeding dykes lk basaltic melt inclusions rich in cl s and h 2 o are trapped in olivine fo 84 from the 1990 tephra and represent the early crystallization stage their composition in major elements is quite similar to those of most of the historic and even pre etnean alkali basalts but significantly lower in k 2 o compared with the 1989 1990 lavas only scarce hk basaltic melt inclusions were observed in the outer rim fo 79 6 of reversely zoned olivine phenocrysts and correspond to late crystallization stage at low pressure high sulfur concentration s 0 3 wt is a general characteristic of the etnean basaltic magmas with h 2 o s ratio as high as 7 the volatile abundances of the etna primitive basalts were computed at 1 45 wt for h 2 o 0 17 wt for cl and 0 047 wt for f with a high cl f ratio close to 3 6 the 1989 lava samples with cl at 660 90 ppm and f at 770 30 ppm have suffered a significant cl loss the possible behaviour of the volatile phase as co 2 h 2 o even cl is discussed with h 2 o and chlorine late degassing and an active role of h 2 o during the lava fountaining activity

structure and dynamics of the laacher see magma chamber eifel germany from major and trace element zoning in sanidine a cathodoluminescence and electron microprobe study microtextures and zoning patterns in sanidine phenocrysts from the phonolitic laacher see tephra germany were investigated in order to constrain processes occurring in the magma chamber before eruption the laacher see tephra unit is chemically zoned and has been inferred to represent the product of eruption of an inverted layered magma chamber samples from various levels in the deposit were investigated we used a combination of textural studies optical microscopy and back scattered electron bse imaging electron microprobe emp analysis of major minor and trace elements ca na k al si ba sr fe and ti and element mapping the samples studied contain two feldspar phases and the ternary composition of the sanidine thus constrains the temperature of crystallization whereas its trace element content reflects the melt composition the large diversity in textures found in the sanidine crystals can be classified into three types composite c type pseudooscillatory po type and resorbed patchy r type trace elementpoor lamellar composite alkali feldspars c type are found in samples inferred to represent the top and the middle part of the magma chamber they grew as composite crystals from the melt at temperatures as low as 650 c in a highly differentiated and volatilerich boundary layer at the magma chamber roof or wall pseudooscillatory zoning with resorption surfaces po type is found in sanidinesfromsamplesinferredtorepresentthemiddlepartandthebase of the magma chamber repeated large an variations 1 4 mol reflect temperature variations of 100 300 ca ssociated with changes in water content variations of minor and trace elements ba sr and ti in sanidine decoupled from the pseudo oscillations of the major elements reflect chemical changes in the melt and are damped by chemicaldiffusioninthemelt bothmajorandminorelementvariations inpo typecrystalsareinterpretedastheprogressiveinfluenceofamore mafic hotter melt this may be partly explained by the settling of crystals through the thermal and chemical gradient existing in the magma chamber however the additional role of magma recharge may be required to explain the large temperature variations resorbed patchy zoned crystals r type found mainly in samples corresponding to the middle part of the magma chamber reflect early growth in a differentiated boundary layer followed by resorption and overgrowthinthemainmagmabody manyofthelaacherseesanidine crystals did not crystallize for the most part in the melt in which they were erupted in the presence of preserved major and trace element zonation in the magma this observation indicates crystal dispersion within a layered magma chamber without large scale mixing and overturn

wollastonite anorthite gehlenite and fassaite bearing rocks igneous petrological oddity or paralavas we briefly review the petrological and geochemical features and physical characteristics of the colle fabbri and ricetto rocks to discuss their possible paramagmatic origin i e derived from complete melting after devolatilization of marly protoliths without any orthomagmatic ultimately mantle derived chemical or thermal input contrary to the various comments that have been made the overall mineralogical petrological and geochemical data provided in the literature well agree with this finding

dense surface seismic data confirm non double couple source mechanisms induced by hydraulic fracturing we have determined source mechanisms for nine high quality microseismic events induced during hydraulic fracturing of the montney shale in canada seismic data were recorded using a dense regularly spaced grid of sensors at the surface the design and geometry of the survey are such that the recorded p wave amplitudes essentially map the upper focal hemisphere allowing the source mechanism to be interpreted directly from the data given the inherent difficulties of computing reliable moment tensors mts from high frequency microseismic data the surface amplitude and polarity maps provide important additional confirmation of the source mechanisms this is especially critical when interpreting non shear source processes which are notoriously susceptible to artifacts due to incomplete or inaccurate source modeling we have found that most of the nine events contain significant non double couple dc components as evident in the surface amplitude data and the resulting mt models furthermore we found that source models that are constrained to be purely shear do not explain the data for most events thus even though non dc components of mts can often be attributed to modeling artifacts we argue that they are required by the data in some cases and can be reliably computed and confidently interpreted under favorable conditions

an evolving magma chamber within extending lithosphere an integrated geochemical isotopic and zircon u pb geochronological study of the gushan granite eastern north china craton the gushan granite located in the jiaobei terrane of the eastern north china craton carries mafic micro granular enclaves mmes and zoned k feldspar phenocrysts and is a typical example of magma gener ation and evolution in an extensional setting here we present whole rock major and trace element geochemistry sr nd isotopes and zircon u pb and hf isotope data on the granite and its enclaves the granite was emplaced at 120 ma it is high in sio2 k 2 o n a 2o lile and lree but low in mgo and hfse the granite are also marked by high initial 87 sr 86 sr 0 7103 and low end t 18 5 to 18 9 and zircon ehf t 16 6 to 22 0 values these features indicate that the host granite was mainly derived from ancient north china craton lower crust field petrographic and compositional studies indicate that mmes are products of mafic felsic magma interactions in the generation of the granite in the relatively late magmatic history available data suggest that enriched lithospheric mantle was a suitable candidate for the mafic magma end member involved in the magma interaction process internal sr nd isotopic variations within k feldspar phenocrysts are also evaluated to decipher the magmatic history in spite of a protracted cooling history and evidence of subsolidus alteration the k feldspar phenocrysts preserve marked primary sr nd isotopic variations initial 87 sr 86 sr ratios increase from the cores 0 7100 0 7102 to rims 0 7105 0 7110 whereas end t values show decrease from the cores 17 7 to 20 5 to rims 21 1 to 27 0 the overall isotopic profiles across the k feldspar phenocrysts are consistent with a continuous magma contamination process highly negative nd isotopic values of some k feldspar rims suggest that the precambrian basement rocks in the upper crust are potential candidates for the contam inant these results indicate that isotopic heterogeneity could be preserved within single crystal from much older slower cooled plutonic rocks and those isotopically zoned minerals are effective recorders of open magma system based on petrographic geochemical and isotopic studies we envisage multiple magmatic pulses mafic felsic magma interaction and continuous assimilation during the formation of the gushan granite a model involving lithospheric thinning and mantle crust interaction in an exten sional setting is proposed to account for the generation of the gushan granite and its enclaves

resolution of non double couple components in the seismic moment tensor using regional networks i a synthetic case study summary we perform a detailed synthetic study on the resolution of non double couple non dc com ponents in the seismic moment tensors from short period data observed at regional networks designed typically for monitoring aftershock sequences of large earthquakes in addition we test two different inversion approaches a linear full moment tensor inversion and a non linear moment tensor inversion constrained to a shear tensile source model the inversions are applied to synthetic first motion p and s wave amplitudes which mimic seismic observa tions of aftershocks of the 1999 mw 7 4 izmit earthquake in northwestern turkey adopting a shear tensile source model to analyse the resolution capability for the obtained non dc components inverted we contaminate synthetic amplitudes with random noise and incorporate realistic uncertainties in the velocity model as well as in the hypocentre locations we find that the constrained moment tensor inversion yields significantly smaller errors in the non dc components than the full moment tensor inversion in particular the errors in the compensated linear vector dipole clvd component are reduced if the constrained inversion is applied furthermore we show that including the s wave amplitudes in addition to p wave amplitudes into the inversion helps to obtain reliable non dc components for the studied station config urations the resolution remains limited due to the lack of stations with epicentral distances less than 15km assuming realistic noise in waveform data and uncertainties in the velocity model the errors in the non dc components are as high as 15 percent for the isotropic and clvd components respectively thus being non negligible in most applications however the orientation of p and t axes is well determined even when errors in the modelling procedure are high

the origin of k feldspar megacrysts hosted in alkaline potassic rocks from central italy a track for low pressure processes in mafic magmas abstract in situ sr isotope and microchemical studies were used to determine the provenance of k feldspar megacrysts hosted in mafic alkaline potassic ultrapotassic rocks and in differentiated rocks from two nearby volcanic apparatus in central italy at monte cimino volcanic complex mafic leucite free ultrapotassic megacryst bearing rocks of olivine latitic composition are associated with evolved latite and trachyte here latites and trachytes straddle the sub alkaline field age corrected 87sr 86sr values sri of the analysed cimino olivine latites vary from 0 71330 and 0 71578 and strongly increase at constant mg value latite and trachyte have lower sri than olivine latites ranging between 0 71331 and 0 71361 sri of k feldspar megacrysts from olivine latites are between 0 71352 and 0 71397 but core and rim 87sr 86sr ratios within individual megacryst are indistinguishable in all the mafic rocks the megacrysts are not in isotopic equilibrium with the hosts k feldspar megacrysts from both the latite and trachyte have similar sr isotope compositions sri 0 71357 0 71401 to those in the olivine latites however sri of megacryst in the trachyte vary significantly from core to rim sri from 0 71401 to 0 71383 as with the olivine latites the k feldspar megacrysts are not in isotopic equilibrium with bulk rock compositions of the latite or trachyte at vico volcano megacryst bearing rocks are mafic leucite free potassic rocks mafic leucite bearing ultrapotassic rocks and old trachytic rocks the mafic leucite bearing and leucite free rocks are a tephri phonolite and an olivine latite respectively a megacryst in vico trachyte is isotopically homogeneous sri core 0 71129 rim 0 71128 and in equilibrium with the host rock sri bulk rock 0 71125 sri of megacryst from tephri phonolite is clearly not in isotopic equilibrium with its host sri bulk rock 0 71158 and it increases from core sri 0 71063 to rim sri 0 71077 a megacryst in vico olivine latite is isotopically homogeneous sri core 0 71066 rim 0 71065 but not in equilibrium with the host rock sri bulk rock 0 71013 the sr isotope microdrilling technique reveals that cimino megacrysts were crystallised in a cimino trachytic magma and were subsequently incorporated by mixing mingling processes in the latitic and olivine latitic melts a model invoking the presence of a mafic sub alkaline magma which was mixed with the olivine latite is proposed to justify the lack of simple geochemical mixing relation between cimino trachytes and olivine latites this magmatological model is able to explain the geochemical characteristics of cimino olivine latites otherwise ascribed to mantle heterogeneity the similarity of core sri of megacrysts hosted in vico tephri phonolite and olivine latite suggests that the k feldspar megacrysts are co genetic isotopic equilibrium between megacryst and vico host trachyte indicates that the trachyte is the parent of this megacryst on the contrary the megacrysts hosted in tephri phonolite and olivine latite do not derive from the old trachytic magma because no diffusion process may explain the core to rim sr isotope increase of the xenocryst hosted in the tephri phonolite the megacrysts hosted in the vico mafic rocks might derive from a trachytic melt similar in composition to the old vico trachytes

recycling of crystal mush derived melts and short magma residence times revealed by u series disequilibria at stromboli volcano abstract the presence of crystal mushes in the feeding system of active volcanoes is generally revealed by antecrysts representing the crystalline portion of old magmas recycled in the juvenile material but very little is known about the fate of interstitial liquid hosted within the crystal rich mush i e antemelt u series disequilibria measured in magmas erupted in the past 18 years at stromboli volcano provide the first geochemical evidence of the involvement of antemelt and help constraining the timescales of the processes occurring in the plumbing system of the volcano despite almost constant major and trace element composition significant variations in isotope ratios are observed 230 th 232 th decreases with time whilst 238 u 232 th 226 ra 230 th and 87 sr 86 sr are different in the two types of magma erupted magma with low phenocryst content lp is erupted as pumices during paroxysm and is thought to belong to a deep reservoir highly porphyritic magma hp is erupted during the normal strombolian activity as scoria and during the effusive events as lavas and it is considered to derive from the former one within a shallow reservoir through degassing driven crystallisation mixing and incorporation of antecrysts the distinct 238 u 232 th of lp and hp magma requires the involvement of a component with high 87 sr 86 sr and 238 u 232 th deriving from older magmas erupted earlier in the volcano history up to 2 5 ka the incompatibility of u and th in major mineral phases limits the possible effect of antecrysts hence requiring the involvement of a u and th rich antemelt the decrease of 226 ra excess from lp to hp magmas provides further and independent evidence for the involvement of a few thousands years old antemelt the variation with time of 230 th 232 th within lp and hp magmas is exploited to constrain the residence time of magmas in the deep and shallow reservoir of the volcano to 55 yrs inferred reservoir volume 0 5 km 3 and 2 10 yrs inferred reservoir volume 0 02 0 09 km 3 respectively our results show the occurrence of magmatic processes operating at different timescale within the feeding system of a so called steady state volcano such as stromboli we show that while most of the magma is erupted within few years a portion of it made of both crystals antecrysts and residual liquid antemelt can be stored in the plumbing system for thousands of years to be eventually rejuvenated and mixed back into the shallow reservoir the presence of antemelts may also affect the eruptive mechanism by promoting heat transfer in locked crystal mushes hence favouring their remobilisation

magma mixing recharge and eruption histories recorded in plagioclase phenocrysts from el chichon volcano mexico operative throughout the 200 ky history of the el chichon magma consistent core to rim decreases of sr sr ratios and coincident system increases in sr concentrations in plagioclase phenocrysts of varying size 1 cm to 2 mm are reported from samples of the 1982 and pre 1982 200 ka eruptions of el chichon volcano maximum sr sr ratios of 0 7054 significantly higher than the wholerock isotopic ratios 0 7040 0 7045 are found in the cores

waveform inversion for point source moment tensor retrieval with variable hypocentral depth and structural model summary in the inversion scheme of high frequency seismograms recorded by a local network we have developed the unconstrained moment tensor description to study weak events which are believed to reflect small scale complexities of the tectonic structure in order to allow the source mechanism to change with time each moment tensor component has its own time history in the inversion the measure of the similarity between the synthetic seismograms and the observed records is obtained by minimizing the norm l2 of their difference the initial synthetic seismograms are constructed by summing a set of time dependent functions named base functions these base functions are computed by normal mode summation for a discrete set of source depths and for two structural models considered to represent acceptable extremes for the region under study in the course of the inversion using a linear interpolation new base functions are computed for intermediate values of the starting depths and structures thereafter new synthetic seismograms are computed and compared with the observed records until the convergence is reached within some pre assigned threshold for the norm l2 the method has been tested by treating as observed records synthetic seismograms both displacement and velocity generated for instantaneous and finite duration sources the observed records have been computed for two structures one belonging to the structural range within which the base functions were computed the other lying outside this range random noise has been superimposed on the records when inverting synthetic records computed for a structure contained within the range of interpolation for the base functions the full moment tensor is retrieved satisfactorily provided that the noise level does not exceed about 20 per cent for records computed for a structure lying outside this range a spurious volumetric part of the moment tensor appears however if the volumetric part of the moment tensor is removed the source time function can be reconstructed satisfactorily and the source mechanism can be determined from the deviatoric part of the moment tensor the procedure has been applied to vertical component seismograms recorded in the friuli ne italy area for the ml 2 9 event of 1987 december 27 the retrieved source mechanism is in agreement with the distribution of the few first arrival polarities available and the source time function indicates a possible multiple rupture process

further testing of the bedding plane slip model for hydraulic fracture opening using moment tensor inversions abstractmoment tensors are calculated by using the p wave first motion peak amplitudes of 59 microseismic events with high signal to noise ratio these events are from a surface microseismic data set gathered during hydraulic fracture stimulation of the marcellus gas shale in washington county pennsylvania usa the majority of these 59 events have a horizontal nodal plane a few degrees characteristic of a dip slip horizontal slip moment tensor if the horizontal nodal plane is an auxiliary the vertical nodal plane has a pure dip slip motion which is inconsistent with the opening motion for vertical hydraulic fractures that enables proppant loading this points to slip on horizontal nodal planes with the auxiliary vertical nodal planes aligned with the local maximum horizontal stress orientation as indicated by drilling induced fractures in nearby vertical wells these 59 microseismic events are caused by slip on horizontal mechanical discontinuities such as bedding planes during the opening of ver

an analcime mugearite megacryst association from north eastern new south wales implications for high pressure amphibole dominated fractionation of alkaline magmas an analcime rich mugearite near spring mount in north eastern new south wales contains dominant kaersutite lesser anorthoclase and rare ti rich mica megacrysts and also rare group i peridotite xenoliths and granitoid inclusions mineralogical experimental and sr and nd isotopic data are interpreted to indicate that the megacrysts are cognate with their host and that megacryst precipitation occurred at pressures in the vicinity of 1 gpa isotopic and other data indicate minimal crystal contamination of the melt the generation of this evolved lava 100 mg mg fe2 m 55 differentiation index di 52 56 by high pressure amphiboledominated fractionation of a mantle derived hydrous alkali basaltic parent m 70 is inconsistent with observed megacryst abundances 3 and absence of group ii cumulates and with the magnitude of the crystal extracts 45 crystals indicated by crystal fractionation models these data suggest the mugearite is not a high pressure differentiate of a hypothetical primary parental magma m 70 alternatively its composition might approximate that of a primary magma derived from a relatively fe rich amphibole lherzolite mantle source

zircon u pb and k feldspar megacryst rb sr isotopic ages and sr hf isotopic composition of the mesozoic heyu pluton eastern qingling orogen china abstract mesozoic granitoids are ubiquitous in china and have attracted the interests of many geologists not only because of their mineralization potential but also because they carry information on source material emplacement mechanisms and crustal architecture most of the plutons were created by multi stage magma emplacement and offer particular challenge for unraveling the emplacement and cooling history a multi isotope approach combined with single grain dating analyses provides a means to understand magma geneses even in complex magmatic settings this study presents rb sr isotope data for k feldspar megacrysts and u pb ages and hf isotopic composition for zircons from the composite heyu pluton exposed in eastern qinling orogen central china zircon u pb concordia ages of 150 and 140 ma and single k feldspar rb sr isochron ages between 133 and 121 ma were obtained from early and late magmatic stages respectively consistent with slow cooling or isotopic re equilibration of the rb sr k feldspar system the distinct k feldspar morphology of early and late intrusive phases is controlled largely by the emplacement depth likely to be associated with a gravity driven sinking model corresponding zircon e hf t values are 21 8 to 18 0 and 17 2 to 10 3 for early and late intrusive phases respectively indicating different magma sources

seismic tomography of etna volcano abstract a 3 d velocity model beneath etna volcano has been obtained through inversion of p wave arrivals of local earthquakes about 300 seismic events distributed around this volcano from surface up to a depth of 20 km have been used to infer the p wave velocity structure high p wave velocity bodies have been found in the upper portion of the volcanic edifice in a region where positive values of bouguer anomalies have previously been found low velocity bodies are identified at depths lower than 10 km and may be related to magmatic reservoirs the spatial pattern of these deeper velocity anomalies appears to be correlated at surface with the distribution of spatter cones in the nw quadrant a high velocity anomaly is correlated to the presence of a deeper seismicity the distribution of relocated hypocenters is not homogeneous but shows some features apparently related to the presence of magmatic bodies

microseismicity tectonics and seismic potential in the western himalayan segment nw himalaya india abstract the tectonics and seismic potential of the western himalayan segment 30 33 n 76 80 e of the nw himalayan india region have been determined in this study 423 earthquakes were located in the nw himalaya between 2004 and 2013 using more than 4495 p and 4453 s differential travel times to determine the moment tensors for 8 mw 4 0 of these earthquakes using their broadband regional waveforms the geometry of the main himalayan thrust mht plane which varies along the strike of the himalaya in flat and ramp segments with a dip ranging between 2 5 to 4 to 19 below the himalayan frontal thrust hft in the south to the south tibetan detachment std in the north has also been deduced in this study two crustal ramps were reported in this study with a depth variance below the main central thrust mct and to the south tibetan detachment std between 12 to 22 km and 28 to 40 km depth respectively the estimated earthquake potential prevailing in the western himalayan seismic gap lying between the epicentral zone of the 1905 kangra earthquake and the 1975 kinnaur earthquake reveals that the total amount of energy released since the last great event is only a fraction 3 5 of the accommodated energy i e 1 1e 28 dyne cm yr this suggests that if an earthquake hits this nw himalayan segment in the future its magnitude might be around mw 8 0

diffusion of sediment on the lee of dune like bedforms theoretical and numerical analysis theoretical and empirical analyses of flow structure sediment transport and sediment size characteristics at the crest of dune like bedforms indicate that it is possible to describe at least semi quantitatively the diffusion and deposition of sediment on the leeside of such structures a numerical program based on this analysis simulates the grain size distribution and deposition rate on the leeside of dunes for specified flow conditions and bed material evaluation of flow and sediment variables through the numerical simulation program shows that flow velocity flow depth and sediment size have a strong influence on the deposition rate and texture of leeside sediment before avalanching sorting of the bed material in particular appears to exert a strong control on both the grain size and the deposition rate gradients

behaviour of trace elements during magmatic processes in the crust application to acidic volcanic rocks of tuscany italy abstract plio quaternary acidic rock suites from three volcanic centres of tuscany italy san vincenzo roccastrada and monte amiata are composed predominantly of rhyolitic and rhyodacitic ignimbrites the rocks are characterized by distinct enrichments particularly of k and rb and display considerable compositional differences among the various volcanic centres the volcanic rocks of roccastrada and most of s vincenzo were probably generated by partial melting of metapelitic rocks from the paleozoic basement of tuscany leaving a residue composed of biotite cordierite and quartz and sometimes plagioclase or garnet the enrichment of k and related elements can be attributed to selective contamination by fluids the other volcanic rocks including trachytes of mt amiata have also been affected by interaction with an upper mantle component probably k rich basaltic rocks a similar petrogenetic model can be applied to the granodiorite pluton of mt capanne elba which belongs to the same magmatic cycle since the variation trends observed in the tuscany volcanic rocks are similar to those reported from many acidic plutons it appears that crustal anatexis accompanied by interaction with upper mantle components has frequently played an important role in the genesis of the granitic rocks

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

sr isotope disequilibrium during differentiation of the bandelier tuff constraints on the crystallization of a large rhyolitic magma chamber the 1 61 ma otowi member of the bandelier tuff jemez mountains volcanic field new mexico is a caldera forming high silica rhyolitic ignimbrite with a precursor fallout deposit the otowi member has high rb sr ratios the 87 rb 86 sr ratios from sanidines and glasses range from 14 to 570 most sanidines from glomerocrysts in the ignimbrite have 87 sr 86 sr i 0 7052 0 7056 whereas the ratios from glasses from glomerocrysts range from 0 7052 to 0 7079 quartz phenocrysts containing glass inclusions from both the initial fallout and the ignimbrite are markedly more radiogenic at 87 sr 86 sr i 0 7105 0 7113 despite having much lower rb sr ratios than glomerocryst glasses these relations require that the inclusion glasses are more contaminated with proterozoic country rock than are glomerocryst glasses textural isotopic and trace element data support a model in which crystals grow in a boundary layer with the most inclusion rich quartz grains closest to the magma country rock contact phenocrysts and glomerocrysts represent fragments from different zones of the chamber9s crystalline carapace disseminated throughout the magma prior to eruption an important implication of these results is that glass inclusions do not necessarily represent precursor magma compositions hence extrapolation of measured volatile contents of inclusion glasses to the entire volume of an erupted magma should be approached with caution

petrogenesis of the ultrapotassic lincoln syenite maine late silurian early devonian melting of a source region modified by subduction driven metasomatism the late silurian early devonian 418 1 ma lincoln syenite exposed discontinuously over a distance of 75 kilometers in south central and mid coastal maine represents one of the most unusual igneous rocks in the appalachian orogen detailed field and petrographic study reveals that most of the exposed syenites have been variably affected by post magmatic recrystallization however a small proportion of the syenites in south central maine preserve original igneous minerals and textures and allow for an unobstructed study of the igneous petrogenesis the syenites are characterized by large dark colored alkali feldspar megacrysts set in a finer grained matrix dominated by alkali feldspar clinopyroxene orthopyroxene biotite oxides the rocks are intermediate in terms of sio2 content 55 59 wt yet are ultrapotassic 6 7 wt k2o and relatively primitive in terms of their mgo mg 67 cr 400 ppm and ni 150 ppm concentrations additionally the rocks exhibit large ion lithophile element enrichment relative to the high field strength elements along with elevated concentrations of light rare earth elements 200 300 chondritic abundances the syenites show limited radiogenic isotopic variability with relatively high initial 87sr 86sr values 0 707 to 0 710 relatively low initial end values 4 8 to 6 7 and initial pb isotopic compositions characteristic of igneous rocks in central maine for example 207pb 204pb 15 577 to 15 639 the geochemical characteristics of these rocks are most consistent with a model involving the partial melting of a mantle wedge previously metasomatized by subduction derived fluids crystallization of this magma was influenced by the presence of significant amounts of water that suppressed plagioclase feldspar crystallization facilitated the crystallization of mg rich biotite and ultimately resulted in the nucleation and growth of the alkali feldspar megacrysts correlation with the geochemically similar parks pond pluton in eastern maine extends the distribution of late silurian early devonian ultrapotassic magmatism in maine to an orogen parallel distance of over 150 km comparisons with rocks of similar composition in known tectonic environments suggest the lincoln syenite and by association the parks pond pluton formed as a result of lithospheric extension superimposed on a sub continental lithospheric mantle source region previously modified by subduction driven metasomatism the timing and structural position of this ultrapotassic magmatism is consistent with a geodynamic model involving slab break off or the convective removal of lithospheric mantle delamination in association with acadian convergence both processes facilitate a brief period of crustal extension and decompression melting of source rocks previously modified by subduction related processes

stability of fault plane solutions for the major n italy seismic events in 2012 abstract we propose a critical analysis of the moment tensor solutions of the major seismic events that affected northern italy in 2012 inverting full waveforms at regional distance using the non linear method named inpar we investigate period dependent resolution that affects in particular the solutions of shallow events this is mainly due to the poor resolution of mzx and mzy components of the seismic tensor when inverting signals whose wavelengths significantly exceed the source depth as a consequence instability affects both source depth and fault plane solution retrieval and spurious large compensated linear vector dipole components arise the inversion performed at cutoff periods shorter than 20 s reveals in many cases different details of the rupture process which are supported by independent geodynamical arguments thus we conclude that inversion of full waveforms at cutoff period as short as possible should be preferred

intra grain sr isotope evidence for crystal recycling and multiple magma reservoirs in the recent activity of stromboli volcano southern italy over the last several hundred years stromboli has been characterized by steady state strombolian activity the volcanic products are dominated by degassed and highly porphyritic hp magma black scoria bombs lapilli and lava flows of basaltic shoshonitic composition periodically about one to three events per year more energetic explosive eruptions also eject light coloured volatile rich pumices with low phenocryst content lp magma that have more mafic compositions than the hp magma an in situ major and trace element and sr isotope microanalysis study is presented on four samples chosen to characterize the different modes of activity at stromboli a lava flow 1985 1986 effusive event a scoria bomb from the normal present day activity of stromboli april 1984 and a scoria and coeval pumice sample from a recent more explosive eruption september 1996 plagioclase an

an experimental study of subaquaeous slipface deposition abstract a flume study indicates that grainflow on slipfaces accounts for most cross strata formed in unidirectional shallow water flows the slipfaces studied were on small megaripples and delta like steps 0 06 0 28 m high during intermittent avalanching at relatively low flow velocities periods between avalanches were marked by grainfall onto the slipface the intensity of which was greatest near the brink of the slipface and increased with current velocity nearly all grainfall deposits however were incorporated into subsequent grainflows grain flow cross strata were made up of relatively distinct layers at least near the base of the slipface continuous avalanching at high flow velocity was marked by a steady stream of grains forming more poorly defined cross strata although the fundamental cause of grain flow is the gradual buildup of sediment on the upper slipface to the angle of initial yield four other processes were recognized as promoting avalanching 1 migration of superimposed bedforms to the brink 2 generation of turbulent pulses upstream of the brink 3 lee eddy impingement on the lower slipface and 4 extension of the lee eddy above the brink the lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow regression analyses showed that the slipface advance per avalanche sa is strongly correlated with the slipface height h expressed approximately by sa 0 060h in addition sa is a direct function of the rate of slipface advance vb the relationship among sa h and vb can be expressed as sa h 0 0385 1 0 134 min cm vb 1 cross strata dip angles between 28 and 34 show no systematic relation to h and vb but dip angles greater than 34 occurred only when both h and vb were small and dip angles less than 28 occurred only when both h and vb were large

phase relations and fractionation sequences in potassic magma series modelled in the system camgsi 2 o 6 kalsio 4 mg 2 sio 4 sio 2 f 2 o 1 at 1 bar to 18 kbar liquidus phase relations in the system diopside kalsilite forsterite quartz with 3 wt f were examined at 1 bar and the locations of important invariant points were determined at 18 kbar at all pressures within this range a large liquidus field for fluorphlogopite phl exists and has a large influence on both melting and fractionation processes one eutectic point was found to the silica rich side of the plane lc fo di at di1ks30fo2qz67 where a melt coexists with san qz phl and di at 840 c and 1 bar another eutectic point must exist in the silica poor part of the system because the phase topology determines that thermal barriers must exist at this point a feldspathoid either lc or ks must coexist with fo phl and a ca bearing phase such as di the exact location and phase assemblage were not determined but the equilibrium melt must have a composition rich in di 29 wt and extremely poor in qz 8 wt the composition of the first eutectic moves towards lower sio2 contents with increasing pressure di3ks40fo1qz56 at 18 kbar whereas the second does not exist at 18 kbar due to the disappearance of lc as a stable liquidus phase liquids which coexist with mafic minerals such as en fo phl and di are important for the genesis of potassium rich mafic rocks by partial melting in the mantle and for the early stages of fractional crystallisation the equilibrium melt at the invariant point fo en phl di l at 1125 c is very poor in fo and di components at atmospheric pressure di5ks37fo5qz53 whereas at 18 kbar the melt contains large amounts of fo and di di19ks31 fo28qz21 and has a composition close to that of natural lamproites kamafugites do not correspond to melts in this system under any of the studied conditions and appear to require co2 in the source fractionation processes from primitive potassic basanite melts are controlled principally by the size and not the mere presence of the liquidus phase field for phlogopite at high pressures where the phl field is large olivine is eliminated early from the fractionating assemblage and cpx phl fractionation may lead to relatively silica rich rock differentiates such as trachytes at low pressures extensive olivine and restricted phl crystallisation prevents silica enrichment in the melt resulting in phonolitic differentiates later crystallisation of alkali feldspar accentuates the trends laid down in the early stages of fractionation

determination and uncertainty of moment tensors for microearthquakes at okmok volcano alaska summary efforts to determine general moment tensors mts for microearthquakes in volcanic areas are often hampered by small seismic networks which can lead to poorly constrained hypocentres and inadequate modelling of seismic velocity heterogeneity in addition noisy seismic signals can make it difficult to identify phase arrivals correctly for small magnitude events however small volcanic earthquakes can have source mechanisms that deviate from brittle double couple shear failure due to magmatic and or hydrothermal processes thus determining reliable mts in such conditions is a challenging but potentially rewarding pursuit we pursued such a goal at okmok volcano alaska which erupted recently in 1997 and in 2008 the alaska volcano observatory operates a seismic network of 12 stations at okmok and routinely catalogues recorded seismicity using these data we have determined general mts for seven microearthquakes recorded between 2004 and 2007 by inverting peak amplitude measurements of p and s phases we computed green s functions using precisely relocated hypocentres and a 3 d velocity model we thoroughly assessed the quality of the solutions by computing formal uncertainty estimates conducting a variety of synthetic and sensitivity tests and by comparing the mts to solutions obtained using alternative methods the results show that mts are sensitive to station distribution and errors in the data velocity model and hypocentral parameters although each of the seven mts contains a significant non shear component we judge several of the solutions to be unreliable however several reliable mts are obtained for a group of previously identified repeating events and are interpreted as compensated linear vector dipole events

geologic volcanologic and tectonic setting of the vico cimino area italy abstract although the cimino and vico volcanic complexes are located close to each other in a structural low they belong to two different provinces cimino is connected to the tuscan roman anatectic magmatic province and vico to the roman campanian potassic alkaline province barberi et al 1971 marinelli 1975 the two volcanic centers lie on a basement formed by clays and sands of a miocene pliocene aged sedimentary cycle the mount cimino complex forms a central volcano composed of a series of rhyodacitic domes it was emplaced along a nw se trending fracture zone which can be followed for about 16 km cimino volcano was active from 1 4 m y to 0 95 m y ago eruption of rhyodacitic ignimbrites were preceded and followed by the emplacement of domes of the same composition fluid lavas of latitic and olivine latitic composition were emitted from the central volcano during the final phase of activity vico is a central volcano mainly composed of lava with a composite summit caldera it was emplaced along a ne sw trending fracture system the vico stratovolcano is formed by lavas of various compositions including phonolitic tephrites tephritic phonolites and slightly undersaturated trachytes the construction of the stratovolcano the most ancient exposed products of which have an age of 0 4 m y was followed by the eruption of four pyroclastic flows totalling several cubic kilometers which are dated at 0 3 0 15 m y the collapse of the caldera is most likely connected to the eruption of these pyroclastic flows the ring fractures of the caldera are associated with the emplacement of a pyroclastic unit most of which erupted along the inner northeast and north rim of the caldera post caldera activity is characterized by the emission of tephritic phonolitic and tephritic products that form the intra caldera stratovolcano named mount venere the vico cimino area northern latium located between the apennine chain and the tyrrhenian sea lies along the circum tyrrhenian belt that extends from northern tuscany to campania this zone has experienced post orogenic tensional movements since the middle miocene the teconic evolution of the tyrrhenian basin is closely associated with acid anatectic and potassic alkaline volcanism along the tyrrhenian margin of the apennines the age composition and geographic position of the volcanoes are controlled by different magnitudes of tensional tectonics and crustal thinning processes of the western margin of the apennine chain

monitoring volcanic and geothermal areas by full seismic moment tensor inversion are non double couple components always artefacts of modelling non double couple mechanisms ndc in volcanic environments are good indicators of local modifications of stress induced by dike injection high fluid pressure movements or by thermal cooling nevertheless the possible biasing effects of wave propagation in structurally complicated regions the presence of noise or a not appropriate station coverage can make the identification of ndc as true source phenomena uncertain in this paper we illustrate possible sources of fake ndc and we demonstrate that by the error analysis that we apply it is possible to discriminate spurious artifacts and physically meaningful solutions tests with synthetic seismograms and the analysis of observed ones in volcanic and geothermal areas are thoroughly discussed

the relationship between potassic and calc alkaline post orogenic magmatism at vico volcano central italy abstract post orogenic magmatism in italy took place during the plio pleistocene alkaline ultrapotassic magmas and sub alkaline magmas were erupted from closely spaced volcanoes throughout the central part of italy therefore central italy is one of the best site to study the relationship between calc alkaline and alkaline magmatism in complex tectonic regimes activity at vico volcano developed in three periods between 0 419 ma and 0 095 ma vico products overlie leucite free volcanic rocks of monte cimino volcano that have a variable affinity from high potassium calc alkaline to ultrapotassic most of the vico rocks are leucite bearing roman type ultrapotassic however during the first period leucite free silicic rocks are interbedded with leucite bearing products the early erupted vico magmas are isotopically distinct from the youngest magmas age corrected sr sr i 0 71110 0 71149 and nd nd i 0 51210 0 51211 isotope ratios fall within the gap between roman type including younger vico and monte cimino rocks some leucite free vico rocks contain orthopyroxene crystals and al contents in clinopyroxenes are lower than those in clinopyroxenes from roman type rocks these characteristics are however also found in monte cimino rocks at the beginning of the first period leucite free latites to trachytes and rhyolites with high sr i 0 71127 0 71149 were erupted trachytes and leucite bearing latites with lower sr i 0 71110 0 71138 were erupted later the younger trachytes have higher rb and lre element contents than older leucite free rocks with similar sio 2 contents furthermore the onset of leucite crystallization is marked by a change in 87 sr 86 sr and sio 2 sr isotope ratios and their time related variations as well as the presence of two different trends in some trace element variation diagrams define two distinct modes of magma differentiation magmas evolved along a stratigraphically lower trend at the beginning of the activity whereas they evolved differently along a stratigraphically upper trend later in the volcanic history modelling of geochemical and sr isotope variations indicates that along the lower trend fractional crystallisation was the main evolutionary process whereas along the upper trend mixing between a leucite free magma and a leucite bearing magma occurred during crystallisation the sr isotope compositions of rocks from the early stage of activity at vico suggest mixing between magmas having different petrological affinities a leucite bearing roman type magma and a high potassium calc alkaline magma

uth fractionation by fluids in k rich magma genesis the vico volcano central italy abstract the 230th 238u disequilibrium method has been applied to the potassic volcanic series of vico latium central italy the 3 main events of the recent volcanic activity have been dated using whole rock isochrons the lava flows of the main cone were erupted between 260 and 180 ky pyroclastic flows are dated around 90 ky and the final effusive activity mte venere around 60 ky these results are in good agreement with previous k ar ages the intense th u fractionation th u varying from 3 2 to 11 is apparently not related to processes of partial melting and crystal fractionation the th u fractionation is the most intense in basic terms of the first episode and is due to the percolation of a deep hydrothermal fluid which impoverishes u in different batches of primary magmas more limited th u fractionations in highly differentiated magma are due to u accompanied by sb and alkalies enrichments in the shallow magma chambers a time integrated model is proposed for the evolution of the 230th 232th ratio in the mantle source of vico it shows that th u and th ta fractionations are probably related to the bulk k u and th enrichment of the mantle of the roman province around 300 ky ago a metasomatic enrichment by a silicate melt is proposed to explain the anomalously high th u and th ta fractionations

a kinematic model for the structure of lee side deposits a kinematic model for the structure of the lee side deposit of a dune like bedform gilbert type delta or similar step is developed based on the assumptions that initial deposition is entirely by grainfall that the rate of deposition decreases as a power function of distance downflow from the brink of the slipface and that the resulting steepening of the slipface is periodically interrupted by avalanching the parameters used in the model are 1 the deposition rate at a given distance from the brink 2 the exponent in the equation relating the deposition rate to distance from the brink 3 the bedform migration rate 4 the bedform height 5 the avalanche speed 6 the angle of initial yield and 7 the residual angle after avalanching from these parameters can be calculated structural characteristics such as the proportions of bottomset and foreset deposits the proportions of avalanche and grainfall deposits in the foreset deposit and the spacing of avalanche grainfall couplets the model correctly predicts the trends of changing avalanche activity and changing structural character with changes in flow character grain size and bedform height in both air and water moreover the model correctly predicts certain consistent structural differences between aeolian and subaqueous lee side deposits quantitative evaluation of the model requires more accurate data on the values of the input parameters than are presently available

moment tensor analysis of the central italy earthquake sequence of september october 1997 the larger earthquakes in the umbria marche central italy seismic sequence of september october 1997 are analyzed using long period seismograms from the mediterranean seismographic network mednet and additional data from the global seismographic network gsn we modify the harvard centroid moment tensor cmt algorithm to allow moment tensor inversion of long period waveforms primarily rayleigh and love waves for small earthquakes at local to regional distances 5 5 in the sequence moment tensors have previously been determined using teleseismic waveforms and standard methods of analysis our results agree well with those of earlier studies we determine additional moment tensors for the largest foreshock and 10 aftershocks with mw 4 2 the earthquakes are characterized by normal faulting mechanisms with a ne sw tension axis and the presumed fault plane dips towards the sw only one of the fourteen events studied has a different faulting geometry indicating instead right lateral strike slip faulting on a plane oriented approximately e w or left lateral faulting on a plane oriented n s the september 26 mainshock 09 40 ut accounts for only approximately 50 of the total moment release in the sequence

isotope and chemical microsampling constraints on the history of an s type rhyolite san vincenzo tuscany italy fine scale heterogeneities in strontium isotope ratios 40ar 39ar ages and chemical com sition have been determined for individual mineral grains and enclaves in the rhyolites of san vincenzo italy the rhyolites are peraluminous with phenocrysts of alkali feldspar piagioclase biotite and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry group b lavas are distinguished from group a in having higher mgo and cao contents as well as containing two pyroxenes and chilled latite enclaves the group b lavas show textural evidence for d sequilib um such as resorption and sieve zones in feldspars laser fusion 40ar 39ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4 38 0 04 ma though small amounts of excess argon are present in subhedral and cloudy crystals the groundmass in the group a sample has a higher initial r7sr 86sr 0 725 than that of the group b 0 7 13 the sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within grain zonation the feldspars and coarse grained biotites have initial 87sr 8 sr that are intermediate between those of the group a and b glasses with alkali feldspar generally having higher initial 87sr 86sr ratios than plagioclase chilled latite enclaves which are present in only the group b lavas have relatively low initial 8 sr 86sr ratios in the range 0 7082 0 7088 the mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and therefore cannot be the source of the strontium isotope dis equilibrium xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts clinopyroxene orthopyroxene clots orthopyroxene plagioclase clots and plagioclase with extensive sieve textures these grains all have relatively low initial 87sr 86sr ratios other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite spinel and sillimanite and alkali feldspars with excess 4 ar the strontium isotope di quilib um in phenocrysts of plagioclase alkali feldspar and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration a mode1 for the san vincenzo magma chamber is proposed in which the sr isotope evolution of the group b rhyolites is due to magma mixing of a crustal melt with latite magma containing unra diogenic strontium the variable initial strontium isotope compositions of group a phenocrysts may be due to assimilation or crystallization along the interface between mingled group a and b magmas

full moment tensor retrieval for two earthquake swarms at the alps dinarides junction summary we present the results of the analysis for the seismic source tensor of all events with m d 3 0 belonging to the moggio udinese swarm 1988 february eight events analysed and of the three events of the swarm that occurred between 1993 july 22 and 26 in the tricesimo area the latter sequence is particularly relevant for the assessment of seismic risk of friuli northeast italy since it is close to the densely populated area of udine we use a waveform inversion algorithm which allows us to retrieve the moment tensor rate functions mtrfs that can be factored into a moment tensor and a source time function stf from the orientation of the p axis and of the nodal planes we can hypothesize that the moggio udinese swarm p axis orientated globally between southeast northwest and east west reflects the influence of both the southeastern alpine and external dinaric stress field while in the tricesimo swarm in which the p axis orientations varies between southeast northwest and north south the southeastern alpine stress field seems to act on faults oriented southeast northwest belonging to the external dinaric system

magmatic interactions as recorded in plagioclase phenocrysts of chaos crags lassen volcanic center california the silicic lava domes of chaos crags in lassen volcanic national and mingling of this material into the silicic host these processes park contain a suite of variably quenched hybrid basaltic andesite are commonplace in some orogenic magma systems and may be magmatic inclusions the inclusions represent thorough mixing elucidated by isotopic microsampling and analysis of the plagioclases between rhyodacite and basalt recharge liquids accompanied by some crystallizing from them mechanical disaggregation of the inclusions resulting in crystals mixing into the rhyodacite host preserved by quenching on dome emplacement sr sr ratios 0 7037 0 7038 of the inclusions are distinctly lower than those of the host rhyodacite

an unusual occurrence of an exploitable k feldspar deposit hosted in the ordovician porphyroids southern sardinia geology mineralogy geochemical features and economic potential abstract an atypical potassium feldspar deposit of real economic potential has been found at arcu de su bentu southern sardinia italy the massive mineralization occurs in the middle ordovician porphyroids metavolcanic complex which consists of dominant metarhyolite and minor metarhyodacite lavas and or ignimbritic flows erupted in a sub aerial environment during variscan orogenesis the mineralized area was affected by low grade anchizone to greenschist facies metamorphism the deposit generally shows uniform macroscopic textural features over the entire outcrop the significant presence of k feldspar sanidine and quartz megacrystals the latter being generally smaller than the former mafic minerals do not occur in significant proportions although minor amounts of biotite and muscovite occur locally besides the uncommon lithological type the typical feature of this deposit is the unusual coarseness 10 to 20 cm in diameter of the potassium feldspar crystals the favourable geomorphological conditions of the area high k 2 o contents 6 to 8 wt high proportion of k feldspar in the mineralized rock 35 to 51 vol and large reserves estimated at 4 368 000 t in just one restricted part of the deposit are all favourable conditions for future economic exploitation in spite of this mineralogical and chemical impurities may adversely affect the possible use of k feldspar from arcu de su bentu in some conventional applications e g manufacture of high quality products such as ceramics to assess the real future economic development of the deposit market specific beneficiation is required although it is important to note that the bulk raw materials even if they have a lower market value could be still be targeted to specific industrial sectors e g red gres

geochemical characteristics of the south tuscany italy volcanic province constraints on lava petrogenesis abstract three suites of volcanic rocks from radicofani mts cimini and mt amiata south tuscany italy were analyzed for major and trace element contents and sr isotopic composition all samples are silica saturated hypersthene normative and some are peraluminous samples from radicofani and the less evolved mts cimini samples have high mg numbers 74 5 66 3 consistent with the fosteritic rich nature of their olivine phenocrysts and high bulk rock abundances of ferromagnesian trace elements all samples are highly enriched in light ree 150 315 chondrites compared to heavy ree 9 15 chondrites and have negative eu anomalies eu eu 0 92 0 44 87 sr 86 sr ratios are high and variable radicofani 0 7137 0 7150 mts cimini 0 7128 0 7138 mt amiata 0 7119 0 7131 a distinctive feature of the radicofani samples is that with decreasing age the rocks increase in k2o content but decrease in la ce these south tuscany rocks have geochemical characteristics of the calc alkaline and alkaline series namely in addition to the high k rb cs ba and lree contents they have high ratios of incompatible elements relative to the high field strength ions such as ti zr hf nb and hree when compared to an estimated primitive mantle composition in general the geochemical characteristics of south tuscany volcanics are consistent with mixing between crustal derived material and mantle derived magma the mantle derived component was unusually rich in radiogenic sr and incompatible elements and had geochemical features similar to basic lavas of the high k series in the roman province

evolution of silicic magma through assimilation and subsequent recharge evidence from sr isotopes in sanidine phenocrysts taylor creek rhyolite nm

deciphering textural and chemical zoning of k feldspar megacrysts from mt amiata volcano southern tuscany italy insights into the petrogenesis and abnormal crystal growth abstract this study reports the complex textural and chemical features of k feldspar megacrysts up to 5 cm long hosted in trachydacitic lava flows lava domes and coulees from mt amiata volcano tuscan magmatic province central italy backscattering and cathodoluminescence imaging coupled with core to rim major and trace elements patterns reveal complex zoning and resorption surfaces associated with sharp chemical variations e g sr and ba these zoning patterns originated by disequilibrium and re equilibration events related to the repeated influx of mafic magmas or convective motions in the trachydacitic magma reservoir multiple mafic magma refilling occurences are also supported by the field record of abundant microgranular magmatic enclaves in the studied products our results highlight that the abnormal dimension of the studied k feldspars originates by the interplay between petrological and kinetic processes involving i extensive dissolution ii heterogeneous nucleation iii alternation of spasmodic growth events in disequilibrium and near equilibrium crystallization the repeated influx of hotter magmas and reheating can determine the thermal condition to the growth of few large k feldspar megacrysts also the strong textural and chemical similarities observed in the k feldspar megacrysts from mt amiata volcanic rocks and mt capanne monzogranite elba island central italy support the hypothesis of a phenocrystic origin of intrusive k feldspar megacrysts

hengill triple junction sw iceland 1 tectonic structure and the spatial and temporal distribution of local earthquakes the hengill area is an unstable ridge ridge transform triple junction in sw iceland it contains the active central volcano hengill associated with the present accretionary zone and the extinct grensdalur central volcano associated with an accretionary zone that became inactive at about 0 7 m y when the locus of spreading migrated about 5 km w to the hengill zone the dominant tectonic trend of the area is n25 e parallel to the accretionary zones but transverse tectonic topographic features have also developed in the neighborhood of the two central volcanoes these result from local modification of the regional stress field associated with the spreading by radially symmetric stress fields associated with the volcanoes and the migration of volcanism a double high temperature geothermal system mirrors the double volcanic system the transform branch of the triple junction is represented by an ew striking zone of historic destructive earthquakes in the s of the area a seismological study was conducted with the aims of studying the tectonic structure and evaluating the passive seismic method as a geothermal prospecting tool the seismicity may be broadly divided into two groups first infrequent intense episodes of crustal movement occur that are associated with the release of tectonic stress along the plate boundary second continuous small magnitude activity occurs on a day to day basis this activity is mostly associated with the extinct grensdalur central volcano not the present plate boundary statistically significant temporal variations in b accompanied a swarm in the transform zone the continuous small magnitude activity may be geothermal in origin releasing thermal stress and not associated with plate boundary tectonics