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

the bucobello 322 ka fossil bearing volcaniclastic flow deposit in the eastern vulsini volcanic district central italy mechanism of emplacement and insights on human activity during mis 9 abstract we present a multidisciplinary study of a fossiliferous site located in the vulsini volcanic district on the western side of the tiber river valley north of rome highlighting the peculiar geologic factors that contributed to the origin and preservation of an outstanding archaeological record testifying of the early human frequentation in this region mighty explosive eruptions since at least 500 ka affected the investigated area eventually culminating in the formation of the huge bolsena caldera tectonic deformation accompanying volcanic activity caused large fault displacements shaping the ground surface and contributing to route the path and possibly to trigger the catastrophic emplacement of volcaniclastic flows a sedimentary trap originated by fault scarp cutting through a streambed was likely the cause for the large accumulation of bones and stone artifacts ripped up and carried by a volcaniclastic flow at 322 ka the analysis of the fossil assemblage reveals both gnawing traces by carnivores and cut marks from the percussion tools employed by humans to butch the carcasses however the occurrence of retouched and unretouched blanks within the lithic assemblage also testifies for provenance from a wider area of human activity which included hunting and scavenging probably at a nearby butchering site

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

nature of mantle source contributions and the role of contamination and in situ crystallisation in the petrogenesis of proterozoic mafic dykes and flood basalts labrador proterozoic tholeiitic dyke swarms share many compositional features with and pose similar petrogenetic problems to phanerozoic continental flood basalts but there are few extrusive equivalents of such swarms the mesoproterozoic 1 27 ga harp dyke swarm in labrador is one where possible extrusive equivalents exist in the seal lake group but are slightly displaced in space and time and can probably be related by models of progressive crustal extension here we try to evaluate the roles of crystal differentiation in situ crystallisation crustal assimilation and the relative contributions of asthenosphere and lithosphere derived melts in the petrogenesis of the mafic magmas modelling of the major and trace element variations both within individual dykes and between dykes and within the lava sequence does not suggest an important role for continental crust involvement while in situ crystallisation processes could account for some of the compositional variations the most successful models invoke mixing or contamination of asthenospheric magmas with by veined material in the lower lithosphere upper asthenosphere which carries the continental characteristics the results imply an important role for hydrous phases such as phlogopite and hornblende in the sub lithosphere mantle much of the low mgo character of mafic dykes may result from significant removal of mafic phases during in situ crystallisation within the lithosphere

roman comagmatic province central italy evidence for subduction related magma genesis geochemical data on mafic volcanics show that important affinities exist between the roman and the calc alkaline rocks from the aeolian arc south tyrrhenian sea these affinities together with the close association of calc alkaline and k rich volcanics in the aeolian arc and in the naples area the continuity in the variation of abundances of incompatible elements from calc alkaline to potassic suites and the similarity in terms of major element geochemistry support a genetic relationship of the roman magmatism and the subduction processes that affected the apennines in tertiary time and are still active under the aeolian arc in the genetic model presented here both calc alkaline and k rich magmas were generated within a mantle heterogenously enriched in lil elements composition of the mantle was modified by addition of material probably sediments dragged down by the undergoing slab the geochemical and petrological differences displayed by the calc alkaline and k rich volcanics are accounted for by the different conditions of melting as well as by chemical and isotopic heterogeneities of the source 26 references 3 figures 1 table

petrology and mineralogy of wollastonite and melilite bearing paralavas from the central apennines italy small outcrops of wollastonite and melilite bearing pyrometamorphic rocks paralavas are found along the apennine chain in central italy at the localities of colle fabbri and ricetto these rocks have coarse to fine grained crystalline spotted and glassy textures the colle fabbri rocks have abundant and ubiquitous wollastonite with plagioclase clinopyroxene melilite is found only in the most ca rich and silica poor samples garnet perovskite quartz leucite silica rich glassy mesostasis and ocelli filled by calcite are present locally the ricetto rock is made up of wollastonite and melilite with minor clinopyroxene set in a glassy matrix with a few crystals of restitic quartz these rocks have variable contents of sio2 43 to 64 wt and cao 37 to 3 7 wt the latter decreases with increasing mgo al2o3 fe2o3 tot tio2 k2o sio2 and most trace elements excluding sr peculiar parageneses e g coexisting melilite and anorthite in the most silica poor samples abundance of wollastonite mineral compositions gehlenite rich melilite al ti and fe3 rich clinopyroxene al ti rich but fe poor garnet and major and trace element geochemistry suggest that the colle fabbri and ricetto rocks are not ultimately mantle derived but are the result of melting devolatilization and recrystallization of marly sediments 50 60 to 5 10 calcite with clay minerals quartz likely due to coal fires the 87sr 86sr and 143nd 144nd range from 0 70772 to 0 71190 and from 0 51223 to 0 51219 respectively again suggesting sedimentary protoliths of a mixed nature substantial chemical and isotopic differences between these samples and those from the roman magmatic province are highlighted

volcanology history and myths of the lake albano maar colli albani volcano italy abstract the polygenetic albano maar is the most recent centre of the colli albani volcano located just few kilometres to the south east of roma presently the maar hosts a 167 5 m deep crater lake the deepest in europe the maar is to be considered quiescent as phreatic activity is documented throughout the holocene this paper illustrates the close relationships between the activity of the maar and the history of settlement in the roman region as recorded in the geology archaeology history and legends of the area severe fluctuations of the groundwater table and catastrophic overflows of the lake albano from the maar rim had occurred prior to and after the early prehistoric settlements dated in the maar area at the eneolithic times ca iii millennium b c repeated lahars occurred along the northwestern slope of the maar filling in the paleodrainage network and forming a vast plain paleohydraulic analyses on fluvial and lahar deposits originated from the holocene phreatic activity of the albano maar indicate sediment water flows in excess of hundreds of cubic metres per second absolute age determinations of the paleosoil underlying one of the most recent deposits of the lahar succession at 5800 100 yr b p 14 c cal are in perfect agreement with the age of the overlying eneolithic age settlements the last catastrophic overflow is described in the roman literature as a consequence of the anger of poseidon against the romans in 398 b c for their war against the etruscans in 394 b c the romans decided to prevent the repetition of such events by the excavation through the maar crater wall of a 1 5 km long drain tunnel which is still operational keeping the lake 70 m below the lowest point of the maar rim this tunnel drain may be regarded as the first prevention device for volcanic hazard in history and shows an unprecedented development of the engineering technology under the pressure of hazard perception the surprising and still largely unknown results of this study are very important to redefine the hazard of the roman region

time dependent sr and nd isotope variations during the evolution of the ultrapotassic sabatini volcanic district roman province central italy the sabatini volcanic district svd active between 0 8 and 0 07 ma is a volcanic field in the roman province central italy located along the tyrrhenian margin of the italian peninsula in this volcanic region high k magmas originated from a metasomatised phlogopite bearing peridotite mantle recording subduction related fluids and or melting processes here we investigate magma evolution during the six main eruptive phases of the svd by means of chemical and isotopic sr and nd analyses specifically we analyzed clinopyroxene crystals from juvenile pumice and scoria clasts and lavas from 40 major svd eruptive units chronologically well constrained by 40ar 39ar dating 87sr 86sr and 144nd 143nd ratios in svd clinopyroxene range 0 7095 0 7115 and 0 51210 0 51214 respectively the mean sr and nd isotope compositions of each eruptive phases show a gradual long term decrease over the entire svd eruptive history however when considering the distinct temporal windows of the individual eruptive phases a significant variability of the sr nd isotope ratios emerges thus highlighting a more complex time dependent geochemical trend for the erupted magmas with respect to a previously described trend at the nearby colli albani volcanic district 0 6 0 04 ma geochemical features of clinopyroxene in lavas and juvenile pyroclasts suggest that magma differentiation occurred in an open system due to assimilation of siliciclastic sedimentary rocks moreover a critical review of the available geochemical data in light of 40ar 39ar ages allows the recognition of the svd as the source of widespread tephra markers recorded in the central mediterranean area by previous works

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

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

crystal chemistry of clinopyroxenes from potassic and ultrapotassic rocks in central italy implications on their genesis the clinopyroxenes mentioned have been investigated by single crystal x ray diffraction combined with electron microprobe analysis the aim of this study was to characterize the crystal chemical variations of clinopyroxenes in order to delineate the intracrystalline constraints which are characteristic of specific magmatic environments clinopyroxenes cpx crystallized from peralkaline ultrapotassic melt with kamafugitic and lamproitic affinities are characterized by high si contents which are insensitive to variations in silica abundance and silica saturation of the melt the high si occupancy in clinopyroxenes from kamafugitic magma is coupled to large m1 i e mg and fe2 and m2 high ca occupancy sites whereas in clinopyroxenes from magmas with lamproitic affinity high si content is combined with large m1 but small m2 sites clinopyroxenes from romantype alkaline potassic and ultrapostassic rocks are characterized by an expanded tetrahedron high iva1 content and small m1 site which is combined with small m2 polyhedron in clinopyroxenes from the potassic rocks and large m2 site in those from the ultrapotassic rocks

post collisional polycyclic plutonism from the zagros hinterland the shaivar dagh plutonic complex alborz belt iran the petrological and geochronological study of the cenozoic shaivar dagh composite intrusion in the alborz mountain belt nw iran reveals important clues to decipher complex relations between magmatic and tectonic processes in the central sectors of the tethyan alpine himalayan orogenic belt this pluton is formed by intrusion at different times of two main magmatic cycles the older cycle 1 is formed by calc alkaline silicic rocks which range in composition from diorites to granodiorites and biotite granites with abundant mafic microgranular enclaves the younger cycle cycle 2 is formed by k rich monzodiorite and monzonite of marked shoshonitic affinity the latter form the larger volumes of the exposed plutonic rocks in the studied complex zircon geochronology laser ablation icp ms analyses gives a concordia age of 30 8 2 1 ma for the calc alkaline rocks cycle 1 and a range from 23 3 0 5 to 25 1 0 9 ma for the shoshonitic association cycle 2 major and trace element relations strongly support distinct origins for each magmatic cycle rocks of cycle 1 have all the characteristic features of active continental margins shoshonitic rocks cycle 2 define two continuous fractionation trends one departing from a k rich basaltic composition and the other from an intermediate k rich composition a metasomatized mantle origin for the two shoshonitic series of cycle 2 is proposed on the basis of comparisons with experimental data the origin of the calc alkaline series is more controversial but it can be attributed to processes in the suprasubduction mantle wedge related to the incorporation of subducted melanges in the form of silicic cold plumes a time sequence can be established for the processes responsible of the generation of the two magmatic cycles first a calc alkaline cycle typical of active continental margins and second a k rich cycle formed by monzonites and monzodiorites this sequence precludes the younger potassic magmas as precursors of the older calc alkaline series by contrast the older calc alkaline magmas may represent the metasomatic agents that modified the mantle wedge during the last stages of subduction and cooked a fertile mantle region for late potassic magmatism after continental collision

a novel multidisciplinary bio and geo chronological approach for age determination of palaeolithic bone artifacts in volcanic settings an example from eastern sabatini latium italy in this study we provide combined biochronologic and chronostratigraphic constraints to the fluvial lacustrine succession cropping out near the village of rignano flaminio 35 km north of rome where two bone instruments have been recovered along with several vertebrate fossil remains the presence of bone tools is characteristic of the latium region whereas it is rare in the rest of italy but very few sites in which such artifacts occur have precise geochronological constraints in the investigated site the presence of cervus elaphus eostephanoceros among other taxa indicates a time interval limited to marine isotopic stage mis 13 and mis 11 the occurrence of the tufo rosso a scorie nere pyroclastic flow deposit dated 449 2 ka at the base of the sedimentary deposits hosting the faunal assemblage allows us at restricting the interval to mis 11 moreover applying a recently validated conceptual model accounting for an aggradational mechanism linked with sea level rise during glacial termination for the sedimentary successions of the tiber river and its tributaries in a relatively wider area around rome we further constrain the age to 430 405 ka following this approach we present a review of the archaeological sites of latium yielding bone instruments remarking that only other four sites have been recently provided with geochronological constraints through the application of the multidisciplinary methodology applied here

the alban hills and monti sabatini volcanic products used in ancient roman masonry italy an integrated stratigraphic archaeological environmental and geochemical approach abstract the rocks of alban hills and monti sabatini volcanoes central italy and their associated epiclastic deposits have been extensively used as building material in ancient rome from about viiith century bce to ivth century ce however the identification of the source areas of these rocks is difficult due to the lack of an integrated stratigraphic and geochemical analysis of the relationships between the two volcanic districts and to the alteration affecting the primary products as consequence of weathering and pedogenetic processes here a comprehensive upgraded stratigraphic and geochronological review of the two volcanic districts corroborated by new geochronological data for several eruptive units and altered deposits is presented coupled to a complete geochemical background achieved by means of newly determined major and trace element analyses for all the main eruptive units a study of the alteration processes of the primary products is also presented and the age of the main weathering and pedogenetic phases associated to quaternary climatic changes are also investigated the results are integrated with those from literature in order to construct discriminant diagrams based on selected trace elements and allow us to characterize the primary and altered volcanic deposits in the rome area distinguish products of different volcanic districts discuss the effects of different weathering processes on the mobility of some elements and provide a reference frame for the provenance of the volcanic materials employed in ancient roman masonry the interdisciplinary data set and results presented here provide groundwork for volcanological climate pedological and archaeological provenance studies

the geochemistry of potassic lavas from vulsini central italy and implications for mantle enrichment processes beneath the roman region major and trace element and 143nd 144nd 0 51209 0 51216 and 87sr 86sr 0 70879 0 71105 isotope analyses are presented on a representative group of lavas from the vulsini district of the roman magmatic province three distinct series are identified the high k and low k series are similar to those described from other italian volcanoes while the third is represented by a group of relative ly undifferentiated leucite basanites which are thought to be near primary mantle melts major and trace element variations within the high k series are consistent with fractional crystallisation from a parental magma similar to the most magnesian leucitites crustal contamination resulted in an increase in 87sr 86sr with increasing fractionation but it was superimposed on magmas which had already inherited a range of incompatible element and isotope ratios from enrichment processes in the sub continental mantle these are reviewed using the available results from vulsini roccamonfina and ernici transition element abundances and ta yb ratios indicate that the pre enrichment mantle was similar to that of e type morb and that these elements were not mobilised by the enrichment process mixing calculations suggest that three components were involved in the enrichment process mantle comparable with the source of morb and two other components rich in trace elements one the low k component had high sr nd th ta and ba nb and no europium anomaly while the second had lower sr nd a negative europium anomaly and very high th ta it was also characterised by low nb ba and high rb ba ratios similar to those reported from phlogopite rich peridotite xenoliths the trace element enrichment processes are therefore thought to have occurred in the mantle wedge above a subduction zone with the trace element characteristics of the high k end member reflecting the subduction of sediments and the stabilisation of mantle phlogopite

petrology of final stage latera lavas vulsini mts mineralogical geochemical and sr isotopic data and their bearing on the genesis of some potassic magmas in central italy a detailed investigation on the final stage latera lavas has shown the presence of three groups of magma having different petrochemical affinities 1 typical high potassium series hks magmas represented only by evolved rocks group a 2 hks like volcanics with slightly lower k2o na2o ratios and lower k2o and incompatible trace element contents than the typical hks of the roman magmatic province group b 3 potassic series ks with higher k2o na2o ratios and higher sio2 mgo cr ni rb th and lree contents and lower ba and sr contents than the typical roman ks group c compared to the hks volcanics the latter group of volcanics have higher th contents and rb ba and ce sr ratios and lower lree sr rb and ba contents and lower lile hfse and lree hfse ratios it has been also shown that the group c lavas display a general composition similar to that of radicofani volcanics suggesting a transitional character between the typical roman type ks rocks and the tuscan lamproites crystal fractionation was mainly responsible for the petrological variations observed within the two hks groups which are believed to derive from two distinct parental magmas probably a leucite tephrite liquid group a and a leucite basanite liquid group b limited and variable crustal assimilation processes were associated with crystal fractionation in the evolution of the group b magmas on the other hand the group c magmas underwent virtually no fractionation during their ascent to surface thus their composition can be considered almost primary different degrees of partial melting at high p and high xco2 conditions of a metasomatized phlogopite bearing peridotitic mantle source are suggested to explain the genesis of the group a and b primary magmas on the other hand low p and low xco2 conditions during the partial melting of a phlogopite bearing mantle source slightly depleted in clinopyroxene are suggested for the genesis of the group c magmas moreover the different incompatible element contents and ratios between the hks group a and b and ks group c rocks studied should reflect primary characteristics of the mantle sources

eocene melting of precambrian lithospheric mantle analcime bearing volcanic rocks from the challis kamloops belt of south central british columbia abstract potassic silica undersaturated mafic volcanic rocks form a minor portion of the predominantly calc alkaline eocene challis kamloops volcanic belt which extends from the northwestern united states into central british columbia canada their major occurrence is in the penticton group in south central british columbia where they reach a thickness of up to 500 m and form the northwestern edge of the montana alkaline province these analcime bearing rocks 53 52 ma old are typically rhomb porphyries of ternary feldspar an28ab52or20 additional phenocryst phases include clinopyroxene analcime phlogopite and rare olivine the rocks are characterized by high total alkalis particularly k2o 4 5 wt as well as by a distinct enrichment of large ion lithophile elements versus heavy rare earth elements and high field strength elements they have unusual isotopic compositions compared to most other rocks of the challis kamloops belt particularly high negative nd values and elevated but relatively uniform initial 87sr 86sr ratios 0 7065 the potassic silica undersaturated rocks overlie precambrian crust and lithosphere and were at least in part derived from ancient metasomatized subcontinental mantle lithosphere which was modified in a precambrian subduction setting the alkaline rocks of the challis kamloops belt are related to a slab window environment in particular they were formed above the southern edge of the kula plate adjacent to the kula farallon slab window whereas the montana alkaline province situated well to the southeast was formed directly above the kula farallon slab window upwelling of the hotter asthenospheric mantle may have been the thermal trigger necessary to induce melting of fertile and metasomatized lithospheric mantle

occurrence of boron rich potassic melts in the vulsini volcanic district italy evidence from melt inclusions abstract boron was analyzed by nuclear microanalysis technique using the 11 b p 8 be reaction in potassic to highly potassic melts mg mg 2 mg 2 fe 2 0 70 trapped as melt inclusions in olivine fo 91 7 90 5 phenocrysts from the vulsini volcanic district northwestern roman province italy these data evidence unusual b concentrations from 60 to 100 ppm up to five times higher than any documented values in primitive subduction related magmas the melt inclusions display variable concentrations in b k sr and f with constant ratios between elements for a single volcanic event that strongly suggest variations of the extents of batch partial melting of a mantle source enriched in b k sr and f conversely b k and b cl ratios in potassic magmas mg 0 70 as exemplified by melt inclusions in olivine fo 90 are variable on the scale of the whole roman province these variations cannot be explained by either fractional crystallization or differing extents of the mantle source melting alone this is also supported by the range in th ta ratios 52 10 of the whole rock samples variability of the b k or b cl ratios cannot be related to a single stage metasomatism event the data indicate the possible occurrence of b rich contaminant and or high inputs of subducted derived components in the mantle wedge beneath the vulsini area within the peculiar geodynamic setting of the northern part of the apenninic arc in addition by determining boron concentrations using nuclear microanalysis involving the 11 b p 8 be nuclear reaction we have illustrated the sensitivity of the nuclear reactions in the analysis of the light elements

petrology and geochemistry of ultrapotassic rocks from the montefiascone volcanic complex central italy magmatic evolution and petrogenesis abstract the montefiascone volcanic complex belongs to the roman magmatic province of central italy the volcanic activity took place in an extensional post collisional setting during late pleistocene giving rise to lava flows and pyroclastic deposits the extrusive products consist of moderately to strongly undersaturated k rich lavas ranging in composition from trachybasalts through leucite basanites and leucititic tephrites to tephritic leucitites they show the typical geochemical and isotopic characters of the roman potassic magmas i e low tio2 low k2o al2o3 strong enrichment in lile high lile hfse ratios highly radiogenic 87 sr 86 sr ratios 0 71005 0 71112 and unradiogenic 143 nd 144 nd 0 51209 0 51229 corresponding to end 10 7 to 6 8 large chemical variations have been recognized within the montefiascone volcanics resulting both from the occurrence of different primary magmas and shallow level fractionation processes the differentiation mainly took place by means of closed system fractional crystallisation with local influence of crustal assimilation the leucite basanites represent primary mantle magmas which did not yield derivative products whereas the leucititic tephrites tephritic leucitites and trachybasalts comprise highly differentiated rocks strongly depleted in compatible elements and enriched in lile fractional crystallisation dominated respectively by clinopyroxene leucite and clinopyroxene plagioclase yielded the most evolved tephritic leucitites and trachybasalts in contrast assimilation of metamorphic basement rocks characterized by highly radiogenic 87 sr 86 sr is needed to explain the moderate increase of the 87 sr 86 sr ratio within the leucititic tephrites the geochemical and isotopic signatures shown by the montefiascone primary magmas require a clinopyroxene and phlogopite rich mantle source in particular partial melting of a veined lithospheric mantle can account for the occurrence of different primary magmas characterized by relatively constant sr and nd isotopic compositions depleted mantle nd model ages 1 1 1 5 ga suggest that the mantle enrichment may be a very old event unrelated to the subduction that preceded the roman magmatism this hypothesis is further supported by the strong similarity in age and isotopic composition between the montefiascone volcanics and the kamafugitic and carbonatitic rocks of the adjoining ultra alkaline umbria latium district

geochemistry of water and gas discharges from the mt amiata silicic complex and surrounding areas central italy abstract the mt amiata volcano in central italy is intimately related to the post orogenic magmatic activity which started in pliocene times major trace elements and isotopic composition of thermal and cold spring waters and gas manifestations indicate the occurrence of three main reservoir of the thermal and cold waters in the mt amiata region the deepest one is located in an extensive carbonate reservoir buried by thick sequences of low permeability allochthonous and neo autochthonous formations thermal spring waters discharging from this aquifer have a neutral ca so4 composition due to the presence of anhydrite layers at the base of the carbonate series and possibly to absorption of deep derived h2s with subsequent oxidation to so42 in a system where ph is buffered by the calcite anhydrite pair marini and chiodini 1994 isotopic signature of these springs and n2 rich composition of associated gas phases suggest a clear local meteoric origin of the feeding waters and atmospheric o2 may be responsible for the oxidation of h2s the two shallower aquifers have different chemical features one is ca hco3 in composition and located in several sedimentary formations above the mesozoic carbonates the other one has a na cl composition and is hosted in marine sediments filling many post orogenic nw se trending basins strontium ba f and br contents have been used to group waters associated with each aquifer although circulating to some extent in the same carbonate reservoir the deep geothermal fluids at latera and mt amiata and thermal springs discharging from their outcropping areas have different composition na cl and ca so4 type respectively considering the high permeability of the reservoir rock the meteoric origin of thermal springs and the two different composition of the thermal waters self sealed barriers must be present at the boundaries of the geothermal systems the complex hydrology of the reservoir rocks greatly affects the reliability of geothermometers in liquid phase which understimate the real temperatures of the discovered geothermal fields more reliable temperatures are envisaged by using gas composition based geothermometers bulk composition of the 67 gas samples studied seems to be the result of a continuous mixing between a n2 rich component of meteoric origin related to the ca so4 aquifer and a deep co2 rich component rising largely along the boundaries of the geothermal systems nitrogen rich gas samples have nearly atmospheric n2 ar 83 and 15 n 14 n 0 ratios whereas co2 rich samples show anomalously high 15n values up to 6 13 likely related to n2 from metamorphic schists lying below the carbonate formations on the basis of average 13 c 12 c isotopic ratio 13c around 0 co2 seems to originate mainly from thermometamorphic reactions in the carbonate reservoir and or in carbonate layers embedded in the underlying metamorphic basement distribution of 3 he 4 he isotopic ratios indicates a radiogenic origin of helium in a tectonic environment that in spite of the presence of many post orogenic basins and mantle derived magmatics can presently be considered in a compressive phase

the thermal structure of the mediterranean upper mantle a forward modelling approach we develop and present an approach for gaining insight into the thermal structure of the upper mantle in a tectonically active region as a starting point for the analysis we use regional geological reconstructions based on data from surface geology shallow seismics and paleomagnetism for these reconstructions we determine the necessarily associated upper mantle processes such as subduction we then forwardly model the thermal structure of upper mantle corresponding with the geological reconstruction used in this way we obtain an estimate of a very important characteristic the temperature distribution of the upper mantle that is independent from those estimates from the usual deep seismic methods if sufficient detailed information on the seismological structure of the region is available a quantitative test of our modelling results is possible via the temperature dependence of seismic velocities we apply our approach to the mediterranean area for which we will test the reconstruction published by dercourt et al 1986

dissolved potassium in the shallow groundwaters circulating in the volcanic rocks of central southern italy abstract the water rock interaction processes occurring in the low temperature shallow volcanic aquifers of central southern italy were simulated by means of the eq3 6 software package in reaction progress mode in the investigation both the roman magmatic province and monte amiata which belongs to the tuscan magmatic province were included the average k2o content of the volcanic rocks from the two areas is similar but the main k bearing phases are leucite in the roman magmatic province and sanidine at monte amiata computed concentrations of major dissolved components and sio2 are consistent with analytical data suggesting that the results of the eq3 6 runs are reliable simulations of the natural water rock interaction processes hence eq3 6 results can be used to investigate the transfer of k from rocks to water it turns out that the attainment of saturation with sanidine during early stages of rock dissolution limits k concentration in the monte amiata groundwaters to around an average of 2 9 1 3 mg l 1 1sd in the silica undersaturated roman magmatic province saturation with leucite is not attained during the evolution of groundwaters and consequently k concentration reaches comparatively high levels with an average of 24 6 27 1 mg l 1 1sd most of these unusually high k concentrations are due to natural weathering of silicates without any anthropogenic influence

the tectonic significance of italian magmatism an alternative view to the popular interpretation the tyrrhenian rift zone has been the site of widespread magmatism since late tortonian times a pronounced asymmetrical distribution reflecting the tectonic structure characterizes italian magmatism sodic basalts occur on the western tyrrhenian flank and transitional morb basalts occur in the tyrhenian sea the eastern flank however is characterized by k alkaline and hk to ultra alkaline e g carbonatites and melilitites rocks major trace elements and isotopic compositions allow two major magmatic lineages to be identified one relating to a non radiogenic basaltic end member and the other to a mantle end member enriched in ca with high lile hfse ratio and high sr isotopic ratios their mantle sources are located within the lithosphere thermal boundary layer tbl and the metasomatized phlogopite carbonate asthenosphere at the base of the tbl respectively the composition and spatial distribution of volcanism and relative mantle sources tend to map the geometry of the lithospheric mantle and to define a pronounced increase in depth from less than 60 km to about 100 km across the boundary between the thinned tyrrhenian lithosphere and the adriatic lithosphere a mechanism of intra continental passive rifting which drives mantle upwelling is sufficient to satisfy the petrological and geochemical constraints and the observed tectonic environment without requiring a subduction plane

long term risk in a recently active volcanic system evaluation of doses and indoor radiological risk in the quaternary vulsini volcanic district central italy abstract volcanic rocks in the vulsini volcanic district central italy contain high concentrations of 238u 232th and 40k due to subduction related metasomatic enrichment of incompatible elements in the mantle source coupled with magma differentiation within the upper crust due to their favorable mechanical properties they have been extensively used for construction since the etruscan age in the old buildings of the bolsena village one of the most populated ancient village in the area the major source of indoor radioactivity is 222rn a radioactive noble gas descendant of 238u direct 222rn indoor measurements have detected extremely high values in the old center due to the combined effect of building materials radon fluxes from the volcanic basement and low air exchange rates in these cases the evaluated risk of developing lung cancer within a 75 year lifetime reaches up to 40 for ever smokers simulations of standard rooms built with different tuffs and lavas collected from the vulsini volcanic district have also provided estimations of the effective doses and lifetime risk for radiogenic cancer other than by the method adopted for calculation the total evaluated risk for each volcanic rock depends on different parameters such as radionuclide content radon emanation power occupancy factor and air exchange rate occupancy factor and air exchange rate appear as the only controlling parameters able to mitigate the indoor radiological risk

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

significance of snowblow in the generation of loch lomond stadial younger dryas glaciers in the western pennines northern england geomorphological mapping has identified the former existence of five cirque glaciers that formed during the loch lomond stadial in the western pennines northern england landforms in mallerstang which previously have been interpreted as moraine ridges are shown to be better explained as large complex landslides reconstruction of these former glaciers has allowed the calculation of the former equilibrium line altitudes ela by a number of different methods values for the ela show a range across the area from 311 m to 608 m od but with low values 311 m and 428 m for the two western glaciers these are explained by the existence of large plateau areas adjacent to the former glaciers which contributed additional mass to the glaciers by snowblow on to the glacier surfaces delimitation of the potential snowblow area for each glacier shows that it has a distinct orientation with the western sector 225 315 being statistically significant with the ela indicating the importance of winds from this direction in determining the existence of these palaeoglaciers the significance of snowblow for the generation of small glaciers in marginal areas means that such local factors must be investigated before regional firn line trends are determined in former glaciated areas

phase relationships in the system kalsio 4 mg 2 sio 4 sio 2 h 2 o as a model for hybridization between hydrous siliceous melts and peridotite the system kalsio4 mg2sio4 sio2 h2o includes model representatives of 1 hydrous siliceous magma from subducted oceanic crust the eutectic liquid in kalsi3o8 sio2 h2o and 2 the overlying mantle peridotite the assemblage forsterite enstatite fo en in a series of partly schematic isobaric isothermal sections the products of hybridization between the model materials at pressures between 20 and 30 kbar have been determined the liquid dissolves peridotite components with little change in composition hybridization is not a simple mixing process because of the incongruent melting of peridotitic assemblages with phlogopite ph hybridization causes solidification of the liquid with products a sequence of three mineral assemblages ph ph quartz qz and ph en the products represent an absolute geochemical separation and local concentration of all potassium from the liquid hybridization is accompanied by h2o saturation of melts and evolution of aqueous fluid although there are significant differences between the melt composition and that of the magma rising from subducted oceanic slab and between fo en and the mantle rock extrapolation of the results suggests that the conclusions can probably be extended to mantle conditions with sodium in the melt and jadeitic clinopyroxene included in the hybrid products

origin of minette by mixing of lamproite and dacite magmas in veliki majdan serbia composite dykes consisting of leucominette and dacite as well as discrete dykes and flows of minette and lamproite composition occur in the veliki majdan area western serbia this area is part of the serbian tertiary magmatic province which consists of numerous small occurrences of ultrapotassic igneous rocks the composite dykes have leucominette margins up to 150cm thick enclosing a central part of dacite up to 100m in width between these two lithologies a decimetre sized transition zone may occur petrography mineral chemistry and bulk rock geochemistry including sr nd and pb isotopes provide evidence that the minettes and leucominettes formed by hybridization between a felsic magma similar in composition to dacite and a mantle derived lamproitic magma the leucominettes and minettes contain all phenocryst types biotite plagioclase quartz present in the dacites but in partly resorbed and reacted form the mica displays a great diversity of resorption textures as a result of partial dissolution incipient melting and phlogopitization suggesting superheating of the felsic melt during hybridization the mineral modes and mineral compositions of the leucominettes and minettes resemble those in the lamproites a model for the modification of lamproite melt towards minette is presented in which minette is formed by mixing of lamproite and530 felsic magma the lack of any significant correlation between pb isotopic ratios and some of the mixing indices sio2 zr zr nb 143 nd 144 ndi recognized in the hybridization model for the veliki majdan dykes may be a result of similarity of the pb isotopic signature in the two end members highly phlogopitized biotite xenocrysts in the minettes are ascribed to the retention of volatile components after magma mixing and crystallization of a new generation of phlogopite from the hybridized magma the magma mixing model explains the reverse zoning and resorption features of phlogopite macrocrysts commonly recognized in calcalkaline lamprophyres elsewhere therefore this mixing mechanism may be globally applicable for the origin of minettes associated with calcalkaline granitic plutonism in postorogenic settings

looking into a volcanic area an overview on the 350 m scientific drilling at colli albani rome italy abstract a 350 m deep borehole was drilled in the colli albani volcanic district central italy in order to understand the shallow crust structure beneath the volcanic complex characterize the rock physical properties especially through in situ measurements and afterward laboratory experiments assess the local present day stress field install a broad band seismometer at depth the borehole is located adjacent to the western rim of the tuscolano artemisio caldera where several phenomena of unrest recently occurred in 1989 90 a seismic swarm affected this area and a related uplift was recognized in addition high gas concentrations mainly co 2 and h 2 s in aquifers and soils caused illnesses and casualties among inhabitants and animals in the past we describe the investigations carried out at the drill site and the results achieved from data analysis wire line drilling produced a complete stratigraphic record of the quaternary volcanic units down to the plio pleistocene sedimentary sequence and geophysical logs allowed a characterization of the rock physical properties from a tectonic point of view data provided by dipmeter and borehole televiewer were used for investigations on the recent and present day stress field and the results are compared to those available in the literature in the volcanic units we recognized two main fracture systems sw and nw dipping several faults intersecting the borehole show planes with oblique striae indicating a prevalent strike slip component of the movement finally borehole breakout analysis defined an active stress field with a e w oriented minimum horizontal component at the end of the drilling a blow out occurred due to pressurized fluids trapped into the sandy unit drilled in the last few meters of the hole sampling these fluids gave an additional value to the borehole providing information about the deep volcanic circulation and its possible connection to a deep seated magma chamber the main results show water with a na hco 3 chemistry and the highest salinity ever recognised in the area electrical conductivity 10 12 ms cm stable o and h isotopes reveal a meteoric origin of water and the absence of tritium points out a long residence time in the aquifer emitted gas is co 2 dominated with n 2 as second most important component helium isotopic composition of the gas allows us to estimate a magmatic component ranging in the interval 40 50 one of the highest in the colli albani carbon isotopes of co 2 0 53 vs pdb suggest that it could derive partly from a magmatic source and partly by the thermal decarbonation of the carbonatic basement

mis 9 to mis 5 terraces along the tyrrhenian sea coast of latium central italy assessing interplay between sea level oscillations and tectonic activity abstract we present a review of the geomorphology of the tyrrhenian sea coast of central italy integrated by a novel structural geomorphological study coupled with statistical analysis of topographic culminations and comparison with a digital elevation model aimed at reconstructing a suite of paleo surfaces corresponding to remnant portions of marine terraces we performed geochronological sedimentological micromorphological and mineralogical investigations on the deposits forming the different paleo surfaces between civitavecchia and anzio towns in order to provide chronostratigraphical paleogeographical and paleoenvironmental constraints using the newly achieved dataset we correlate these paleo surfaces with the coastal terraces formed during past sea level highstands as recognized by previous studies and we refine their correlation with the marine isotope stage mis timescale in particular we have extended our geomorphological analyses landward in the area between the tiber river mouth and anzio in order to include the oldest paleo surface developed above the deposits of the last large explosive eruption at 365 4 ka in the colli albani volcanic district results of this study allow us to recognize a set of higher paleo surfaces at elevation ranging 108 thought 71 m a s l which we interpret as one tectonically displaced widespread coastal terrace originated during the mis 9 1 highstand we correlate the previously identified paleo surfaces of 66 62 m a s l and 56 52 m a s l with the equivalent coastal terraces developed during the sea level highstands of sub stages 7 5 and 7 3 7 1 moreover based on data from literature on relative elevation of maximum sea level during the highstands of mis 11 through mis 5 1 we assess the regional uplift and the concurrent tectonic displacements that have occurred since 900 ka in this area

syn depositional substrate deformation produced by the shear force of a pyroclastic density current an example from the pleistocene ignimbrite at monte cimino northern lazio italy substrate deformation by pyroclastic density currents is very sparsely described in the literature the rare occurrence of syn depositional substrate deformation suggests that special circumstances are required to transmit shear from the base of a pyroclastic density current into the deposited ignimbrite and the substrate one example of a substrate deformed by a pyroclastic density current is found at the base of the pleistocene ignimbrite at monte cimino central italy a series of reverse faults that offsets the basal contact were produced by the shear force of the pyroclastic current during deposition of the ignimbrite the faults formed on the vent facing side of a palaeo slope that strikes sub parallel to the flow direction of the pyroclastic current fault offsets suggest motion was parallel to the flow direction of the pyroclastic current rather than down slope we propose that these faults resulted from fluctuations in the shear force of the pyroclastic density current as it was channelled down a palaeovalley the lower flow boundary which separated the deposited ignimbrite and the substrate from the moving pyroclastic density current momentarily stepped down into the substrate so that the upper 0 5 m of the substrate and about 1 5 m of the deposited ignimbrite became incorporated into the current this momentary coupling of the current and the substrate induced reverse faulting in the substrate and the deposited portion of the ignimbrite deposition appears to have been ongoing during the formation of these faults as well as afterward following the formation of the faults the lower flow boundary seems to have been quickly re established above the faults approximately 1 5 m above the base of the ignimbrite allowing deposition to continue without further deformation of the substrate

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

a proposal for the kinematic modelling of w dipping subductions possible applications to the tyrrhenian apennines system in w dipping subduction zones there is a general eastward progression of the back arc basin accretionary wedge foredeep complex with the forward progression early stages of the complex are revealed by slices of upper crust and sedimentary cover abandoned to the west left floating above a new section of mantle a major shear zone should form at the new moho separating upper crust slices of earlier accretionary stages and the eastward flowing mantle the mantle wedging at the top of the subduction plane could be responsible for the uplift of the central parts of the belt the retreating of the subduction hinge is interpreted as due to the push generated by the eastward mantle flow detected in the hot spot reference frame the foredeep depth is mainly a function of the radius of curvature of the subduction hinge the frontal wedge is constructed from the stacking of the upper layers of the subducting plate and the syntectonic clastics that fill the foredeep which are progressively involved in thrusting and later by extension in order to preserve volume balance the lithosphere of the eastern plate before subduction has to be the same size as that which has been subducted due to the longer length of the arc with respect to the original length of the linear margin between the two converging plates laterally stretched subducted lithosphere is predicted at depth w dipping subductions usually have a short life probably due to their inherent capability to produce new lateral heterogeneities of the lithosphere the thin back arc which are a key factor in controlling and generating new subductions both e and w dipping this model is applied to the apennines tyrrhenian sea system

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

properties of the lithosphere in collisional belts in the mediterranean a review abstract a brief review of the lithosphere asthenosphere properties is given for the mediterranean area the strongest lateral heterogeneities are found in the proximity of tectonically active areas such as collisional belts high s wave velocities below about 70 km denote the presence of deep seated almost aseismic lithospheric roots under the western alps the north central apennines and the cordillera betica an alternative explanation of the data related to mechanisms of intermediate and deep focus earthquakes in the tyrrhenian sea and aegean sea is discussed in the frame of the dynamic subduction model proposed by freund et al 1980 which postulates that the slab is disrupted in blocks and pulled down gravitationally

petrological characterization of the mantle source of mediterranean lamproites indications from major and trace elements of phlogopite lamproites are among the most enigmatic mantle generated melts and are typically abundant in phlogopite we investigated the major and trace element chemistry of phlogopite crystals from mediterranean lamproite occurrences in spain serbia and turkey the most primitive lamproite samples were selected in order to evaluate the generation of the different phlogopite populations in their distinct mantle setting s phlogopite hosted in mediterranean lamproites can be grouped into different compositional arrays on the basis of their major element chemistry using al2o3 feot and tio2 concentrations contents of cr f and presumably ti allow discrimination of the macrocrysts into phlogopite phenocrysts which are liquidus and near liquidus phases and mantle xenocrysts further distinction among different populations of mantle derived phlogopite can be achieved considering trace element and isotopic ratios the latter also distinguish between crustal and asthenospheric imprints on the source of the lamproitic parental melt

petrology geochemistry and sr isotope characteristics of lavas from the area of commenda mts vulsini italy major trace element and sr isotope compositions are reported for a suite of lavas coming from the area of commenda in the se vulsinian district the analyzed samples have all low silica contents and variable but generally high cao mgo and feot based on k2o and k2o na2o ratio the rocks from commenda can be classified as belonging to the potassic series ks and the high potassium series hks the hks rocks appear to have derived by cristal liquid fractionation from the most mafic types with separation of olivine and clinopyroxene and then of clinopyroxene leucite the most primitive hks rocks have aphyric texture and high mg values cr and ni contents which are close or within the range of values of magmas formed by partial melting of periodititic mantle sources the ks rocks have lower incompatible element contents as the hks rocks with similar degree of evolution

alkaline syenites in eastern cathaysia south china link to permian triassic transtension two alkaline syenite plutons the tieshan and yangfang plutons have recently been recognized within ne trending fault zones in eastern cathaysia south china the rocks are very enriched in k2o 6 28 9 39 wt rare earth elements ree particularly light ree and large ion lithophile elements but are relatively low in high field strength elements isotopically they are characterized by high initial 87sr 86sr 0 7093 to 0 7123 and low nd t values 5 64 to 10 63 the geochemical data suggest that the alkaline syenites most likely formed via fractional crystallization of enriched mantle derived magmas sensitive high resolution ion microprobe zircon u pb dating indicates that these two intrusions have late permian 254 4 ma and early triassic 242 4 ma crystallization ages respectively our data suggest that a tectonic regime dominated by transtension probably existed from at least the latest permian into the triassic and was responsible for the formation of the tieshan and yangfang alkaline syenites when combined with previous paleomagnetic structural and sedimentology data we suggest that the transtension along the ne trending strike slip fault zones was related to oblique subduction of the pacific plate underneath south china

recent terrestrial and satellite observations to model deformations at colli albani volcano central italy the colli albani volcanic complex rome italy has been dominated by episodic eruptions commencing around 561 ka and ending with the most recent activity of the albano maar phase 70 ka earthquakes of moderate intensity gas emissions and significant ground deformations are the recent evidences of a residual activity former geodetic data from leveling surveys gps stations and insar observations tracked ongoing significant uplift of the order of few mm year near the colli albani western flank different uplift rates were detected by each technique in different time spans suggesting also the possibility of sporadic recharge of the hydrothermal system the renewed high precision leveling data from igmi survey carried out in 1997 1999 and the last leveling survey carried out in 2006 show that the uplift along the route is currently significant at an average rate of 3 mm year radar interferograms from alos satellite show uplift rate of 6 mm year southwest of the central sector of the leveling route we have undertaken a joint inversion of the various geodetic data vertical rates from leveling surveys gps site velocities and insar observations acquired by alos satellite using a nonlinear inversion technique to estimate the parameters of a point pressure source possibly capable of explaining the ongoing deformation at colli albani volcano

the problem of the moho in the alps abstract the tertiary alps are the product of continental collision and material balance estimates require the subduction of continental crust and the underlying moho the present moho in the alpine region consists of three parts that of the european plate me that of the adriatic african plate ma and a new moho m2 believed to have developed in the subducted continental crust by high pressure metamorphism at 40 60 km depth the fate of m2 however is uncertain some of it is apparently destroyed subsequently as some eclogite facies and even highest p coesite bearing rocks somehow find their way to the surface where they form exotic bodies from microscopic to nappe size on the other hand the continental moho exposed in the ivrea body tells a different story here continental granulite facies rocks are intruded by ultramafic and mafic masses this suggests an origin in an extensional environment possibly in subduction related gravitational collapse basins such successor basins succeed the basins of the original tethys that had been largely consumed by the late cretaceous they puncture the 1000 2000 km wide belt of africa europa collisional interaction e g the aegean the tyrrhenian and the pannonian basins although in some ways similar to the back arc basins of the pacific these mostly intracontinental basins differ in important aspects such as their small size in these basins asthenospheric upwelling replaces m2 by a new moho m3 and the eclogitic rocks underlying m2 by the ultramafic mafic intrusions of the ivrea type material balance considerations suggest that most of the eclogues remain part of the mantle for some time on the other hand recent deep reflection seismic surveys in several places indicate delamination of a part of the lower crust and the uppermost mantle with the formation of imbrications and duplexes some of which are wedged into the middle crust of the opposite plate they may be the first stage in the formation of granulite and eclogite nappes

tectonics dynamics and plio pleistocene magmatism in the central tyrrhenian sea insights from the submarine transitional basalts of the ventotene volcanic ridge pontine islands italy

orogens and slabs vs their direction of subduction abstract subduction zones appear primarily controlled by the polarity of their direction i e w directed or e to nne directed probably due to the westward drift of the lithosphere relative to the asthenosphere the decollement planes behave differently in the two end members in the w directed subduction zone the decollement of the plate to the east is warped and subducted whereas in the e to nne directed it is ramping upward at the surface there are w directed subduction zones that work also in absence of active convergence like the carpathians or the apennines w directed subduction zones have shorter life 30 40 ma than e or ne directed subduction zones even longer than 100 ma the different decollements in the two end members of subduction should control different ptt paths and therefore generate variable metamorphic assemblages in the associated accretionary wedges and orogens these asymmetries also determine different topographic and structural evolutions that are marked by low topography and a fast eastward migrating structural wave along w directed subduction zones whereas the topography and the structure are rapidly growing upward and expanding laterally along the opposite subduction zones the magmatic pair calc alkaline and alkaline tholeiitic volcanic products of the island arc and the back arc basin characterise the w directed subduction zones magmatic rocks associated with e or ne directed subduction zones have higher abundances of incompatible elements and mainly consist of calc alkaline shoshonitic suites with large volumes of batholithic intrusions and porphyry copper ore deposits the subduction zones surrounding the adriatic plate in the central mediterranean confirm the differences among subduction zones as primarily controlled by the geographic polarity of the main direction of the slab the western margin of the adriatic plate contemporaneously overridden and underthrust europe toward the west to generate respectively the alps and the apennines while the eastern margin subducted under the dinarides hellenides these belts confirm the characters of the end members of subduction zones as a function of their geographic polarity similarly to the pacific subduction zones

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

interaction between ultrapotassic magmas and carbonate rocks evidence from geochemical and isotopic sr nd o compositions of granular lithic clasts from the alban hills volcano central italy abstract magma carbonate rock interaction is investigated through a geochemical and sr nd o isotope study of granular lithic clasts ejecta from the alban hills ultrapotassic volcano central italy some samples group 1 basically represent intrusive equivalents of alban hills magmas a few samples group 2 are ultramafic have high mgo 30 to 40 wt and 18o and originated by accumulation of mafic phases that crystallised from ultrapotassic melts during assimilation of dolomitic rocks group 3 ejecta consist of dominant k feldspar and show major element compositions similar to phonolites which however are absent among the alban hills volcanics finally another group group 4 contains corroded k feldspars surrounded by a microgranular to porphyritic matrix made of igneous minerals k feldspar foids clinopyroxene phlogopite plus wollastonite garnet and some cuspidine group 4 ejecta are depleted in sio2 and enriched in cao with respect to group 3 the analysed ejecta have similar 143nd 144nd 0 51204 0 51217 as the alban hills lavas whereas 87sr 86sr 0 70900 0 71067 is similar to lower whole rocks 18o ranges from 7 0 to 13 2 reaching maximum values in ultramafic samples a positive correlation with cao is observed in single rock groups large ion lithophile element lile abundances and ree fractionation are generally high and extreme values of th u and lree are found in some group 3 and group 4 rocks mineralogical petrological and geochemical data reveal extensive interaction between magma and carbonate wall rocks involving both dolostones and limestones these processes had dramatic effects on magma compositions especially on phonolites which were transformed to foidites evidence of such a process is found in group 4 samples in which k feldspar is observed to react with a matrix that represents strongly undersaturated melts formed by interaction between silicate magma and carbonates trace element data also testify to a very important role for f co2 h2o s fluids during magma wall rock interaction fluid transfer was responsible for extreme enrichments in th u and lree especially observed in group 3 and group 4 rocks implications of these processes for potassic magma evolution in central italy are discussed

geophysical and petrological modelling of the structure and composition of the crust and upper mantle in complex geodynamic settings the tyrrhenian sea and surroundings abstract information on the physical and chemical properties of the lithosphere asthenosphere system las can be obtained by geophysical investigation and by studies of petrology geochemistry of magmatic rocks and entrained xenoliths integration of petrological and geophysical studies is particularly useful in geodynamically complex areas characterised by abundant and compositionally variable young magmatism such as in the tyrrhenian sea and surroundings a thin crust less than 10 km overlying a soft mantle where partial melting can reach about 10 is observed for magnaghi vavilov and marsili which belong to the central tyrrhenian sea backarc volcanism where subalkaline rocks dominate similar characteristics are seen for the uppermost crust of ischia a crust about 20 km thick is observed for the majority of the continental volcanoes including amiata vulsini roccamonfina phlegraean fields vesuvius vulture stromboli vulcano lipari etna and ustica a thicker crust is present at albani about 25 km and at cimino vico sabatini about 30 km the structure of the upper mantle in contrast shows striking differences among various volcanic provinces volcanoes of the roman region vulsini sabatini alban hills sit over an upper mantle characterised by vs mostly ranging from about 4 2 to 4 4 km s at the alban hills however slightly lower vs values of about 4 1 km s are detected between 60 and 120 km of depth this parallels the similar and rather homogeneous compositional features of the roman volcanoes whereas the lower vs values detected at the alban hills may reflect the occurrence of small amounts of melts within the mantle in agreement with the younger age of this volcano the axial zone of the apennines where ultrapotassic kamafugitic volcanoes are present has a mantle structure with high velocity lid vs 4 5 km s occurring at the base of a 40 km thick crust beneath the campanian volcanoes of vesuvius and phlegraean fields the mantle structure shows a rigid body dipping westward a feature that continues southward up to the eastern aeolian arc in contrast at ischia the upper mantle contains a shallow low velocity layer vs 3 5 4 0 km s just beneath a thin but complex crust the western aeolian arc and ustica sit over an upper mantle with vs 4 2 4 4 km s although a rigid layer vs 4 55 km s from about 80 to 150 km occurs beneath the western aeolian arc in sardinia no significant differences in the las structure are detected from north to south the petrological geochemical signatures of italian volcanoes show strong variations that allow us to distinguish several magmatic provinces these often coincide with mantle sectors identified by vs tomography for instance the roman volcanoes show remarkable similar petrological and geochemical characteristics mirroring similar structure of the las the structure and geochemical isotopic composition of the upper mantle change significantly when we move to the stromboli campanian volcanoes the geochemical signatures of ischia and procida volcanoes are similar to other campanian centres but sr pb isotopic ratios are lower marking a transition to the backarc mantle of the central tyrrhenian sea the structural variations from stromboli to the central vulcano and lipari and western aeolian arc are accompanied by strong variations of geochemical signatures such as a decrease of sr isotope ratios and an increase of nd pb isotope and lile hfse ratios the dominance of mafic subalkaline magmatism in the tyrrhenian sea basin denotes large degrees of partial melting well in agreement with the soft characteristics of the uppermost mantle in this area in contrast striking isotopic differences of plio quaternary volcanic rocks from southern to northern sardinia does not find a match in the las geophysical characteristics the combination of petrological and geophysical constraints allows us to propose a 3d schematic geodynamic model of the tyrrhenian basin and bordering volcanic areas including the subduction of the ionian adria lithosphere in the southern tyrrhenian sea and to place constraints on the geodynamic evolution of the whole region

comment on borgia a mazzoldi a brunori c a allocca c delcroix c micheli l vercellino a grieco g 2014 volcanic spreading forcing and feedback in geothermal reservoir development amiata volcano italia j volc geoth res 284 16 31 abstract borgia et al 2014 illustrated an active volcanic spreading model for the amiata volcanic area southern tuscany italy although at first glance the model may appear appealing this is not fully supported by the available data and the paper does not take into account their discussion accordingly the supposed negative consequences of the borgia et al 2014 model on both contamination of shallow water and geothermal exploitation can likely be regarded as speculative

an experimental and petrographic investigation of elephant moraine 79001 lithology a implications for its petrogenesis and the partitioning of chromium and vanadium in a martian basalt a composition approximating the lithology a groundmass ofthe elephant moraine eet 79001 martian basalt eg mcsween and jarosewich 1983 has been used to investigate the petrogenesis ofthe meteorite and the behavior ofcr and v at different oxygen fugacities crystallization experiments were carried out over a range of temperatures and oxygen fugacities of either iron wustite iw or iw 2 i e 1 5 log units below the quartz fayalite magnetite qfm buffer comparison oftrace element concentrations obtained by secondary ion mass spectrometry sims analysis in experimental silicates with those of natural silicates supports the fe ti oxide derived oxygen fugacity of qfm 1 8 0 3 for this basalt herd et al 2001 experimental distribution coefficients in conjunction with sims analyses of rims from the olivine and pyroxene xenocrysts in lithology a as well as analyses of lithology a groundmass pigeonite cores are used to calculate coexisting liquid concentrations of v and cr liquid compositions derived from pigeonite xenocryst rims and groundmass pigeonite cores are similar suggesting that the rims of orthopyroxene xenocrysts are overgrowths which have not previously been accounted for when reconstructing the groundmass composition this implies that the eg composition requires modification a similar exercise for the ferroan rims on olivine xenocrysts yields very different liquid compositions indicating that these rims are not overgrowths but are part of the xenocryst assemblage these results are shown to be consistent with the petrography of lithology a xenocrysts

relationships between ultrapotassic and carbonate rich volcanic rocks in central italy petrogenetic and geodynamic implications the pleistocene intra apennine volcanic iav centres occurring east of the potassium rich roman comagmatic province show variable petrological and geochemical composition some rocks have a strongly undersaturated ultrapotassic kamafugitic affinity with k2o na2o 8 20 whereas the rocks from the southern center of mt vulture are still strongly undersaturated in silica but are enriched in both na2o and k2o with k na around unity carbonate rich pyroclastic rocks believed to represent carbonatitic magmas are found in the iav centers kamafugites have high abundances of lile and high lile hfse ratios and their incompatible element patterns resemble closely those of ultrapotassic rocks from the adjoining roman province the vulture volcanics also display high contents of lile but their lile hfse ratios are intermediate between intraplate alkaline rocks and kamafugites the carbonate rich rocks exhibit an exotic mineralogy and high enrichments in lile which speaks for a carbonatitic affinity however they have similar incompatible element patterns but consistently lower abundances of almost all the elements than the associated silicate volcanics these data favour the hypothesis that the iav carbonate rocks may represent mixtures of silicate magmas and geochemically depleted carbonate material the sedimentary carbonates that crop out extensively along the apennine chain may be the source of barren carbonate material overall geochemical data of iav centres and of the rocks from the roman province display strong geochemical and isotopic evidence of being generated in an upper mantle that was modified by addition of upper crustal material brought down by subduction processes a possible exception is represented by mt vulture which however occurs east of the main axis of the apennines on the western margin of the foreland adria plate the occurrence of strongly undersaturated alkaline rocks requires magma generation at high pressures and xco2 this is in agreement with the hypothesis that subduction processes under the apennines occurred by consumption of poorly hydrated thinned or delaminated continental crust

evolution of the sardinia channel western mediterranean new constraints from a diving survey on cornacya seamount off se sardinia abstract sarcya 1 dive explored a previously unknown 12 my old submerged volcano labelled cornacya a well developed fracturation is characterised by the following directions n 170 to n s n 20 to n 40 n 90 to n 120 n 50 to n 70 which corresponds to the fracturation pattern of the sardinian margin the sampled lavas exhibit features of shoshonitic suites of intermediate composition and include amphibole and mica bearing lamprophyric xenoliths which are geochemically similar to ti poor lamproites mica compositions reflect chemical exchanges between the lamprophyre and its shoshonitic host rock suggesting their simultaneous emplacement nd compositions of the cornacya k rich suite indicate that continental crust was largely involved in the genesis of these rocks the spatial association of the lamprophyre with the shoshonitic rocks is geochemically similar to k rich and tio2 poor igneous suites emplaced in post collisional settings among shoshonitic rocks sample sar 1 01 has been dated at 12 6 0 3 my using the 40ar 39ar method with a laser microprobe on single grains the age of the cornacya shoshonitic suite is similar to that of the sisco lamprophyre from corsica which similarly is located on the western margin of the tyrrhenian sea thus the cornacya shoshonitic rocks and their lamprophyric xenolith and the sisco lamprophyre could represent post collisional suites emplaced during the lithospheric extension of the corsica sardinia block just after its rotation and before the tyrrhenian sea opening drilling on the sardinia margin odp leg 107 shows that the upper levels of the present day margin hole 654 suffered tectonic subsidence before the lower part hole 652 the structure of this lower part is interpreted as the result of an eastward migration of the extension during late miocene and early pliocene times data of cornacya volcano are in good agreement with this model and provide good chronological constraints for the beginning of the phenomenon

helium strontium isotope constraints on mantle evolution beneath the roman comagmatic province italy european social fund scottish universities carnegie trust for the universities of scotland

crystal chemistry of clinopyroxene from alkaline undersaturated rocks of the monte vulture volcano italy abstract the monte vulture is a late pleistocene stratovolcano composed of highly undersaturated alkaline potassic to ultrapotassic rocks belonging to the roman magmatic province these rocks are notably richer in na2o if compared to similar rocks of the roman province two distinct magmatic series have been recognized 1 feldspar bearing series ranging from basanite to phonolite and a volumetrically subordinate 2 feldspar free series consisting of melilitite melafoidite and hauynophyre the clinopyroxene compositions of the feldspar bearing series ranges from diopside to ferro salite hedenbergite and shows from basanite to phonotephrite increasing feotot al2o3 and tio2 and decreasing of mgo contents clinopyroxene in basanites and tephrites has generally high fe3 contents which is typical for clinopyroxene from the roman province clinopyroxene of the feldspar free series shows a more restricted variation in mgo and has often very high al2o3 feotot and tio2 contents in all the crystals examined the al3 content is high and is present mostly on the t site and for a minor part on the m1 site the m1 o2 distance shows a good correlation with the rm13 content clinopyroxene from basanites feldspar bearing series has the lowest rm13 and that from melilitite and hauynophyre feldspar free series the highest rm13 contents clinopyroxene crystals from feldspar free rocks have smaller m1 and larger t polyhedral volumes when compared to those in olivine melilitites and melilitites kamafugites from umbria but they show similar polyhedral volumes as clinopyroxene crystals from leucite bearing rocks although clinopyroxene from feldspar free rocks has small m1 volumes due to the high r3 contents m1 volumes of clinopyroxene from melilitites are larger than expected because of the higher fe3 al3 m1 values this larger m1 volume of clinopyroxene in melilitites causes a shortening of and a lengthening of the m2 o3 distance strong compositional and structural similarities between clinopyroxene of monte vulture and leucite bearing rocks of the roman province plagioclase bearing high potassium series hks indicate a common petrogenetic affinity on the other hand differences between clinopyroxene in feldspar free rocks from monte vulture and that in kamafugites i e olivine melilitites kalsilitites from central italy suggest significant magma dissimilarities between these two groups

the geochemistry and petrogenesis of the lavas of the vulsinian district roman province central italy the vulsinian lavas are dominated by a suite of undersaturated leucite bearing basic to intermediate compositions the remaining lavas are mainly oversaturated and have shoshonitic affinities one hundred and thirty five samples have been analysed for major elements and most for 20 trace elements twenty seven lavas have been analysed for ree they are all perpotassic for the undersaturated lavas k2o na2o 2 8 and have very high lil element concentrations e g rb 400 800 ppm th 25 150 ppm ree reecho c 200 lree hree cho c 20 even in the most basic rocks

petrogenesis of cretaceous shoshonitic rocks in the northern wuyi mountains south china a result of the roll back of a flat slab abstract potassic magmatism is commonly linked to post late orogenic environments such as foundering or convection thinning of continental lithosphere their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub continental lithospheric mantle here we report new shrimp zircon u pb ages whole rock geochemical results and sr nd and zircon hf isotope data from four potassic plutons the da an yingcheng zixi and honggong plutons in the northern wuyi mountains south china shrimp u pb zircon analyses indicate that these potassic rocks formed at 139 126 ma they are characterized by high sio 2 56 73 and k 2 o 3 8 6 7 with a k 2 o na 2 o ratio of 2 18 2 04 plotting within the field of high sio 2 shoshonites their i sr and end t values vary from 0 7077 to 0 7162 and 5 66 to 10 52 respectively the initial zircon ehf t values range from 2 3 to 13 1 corresponding to t dm modal ages between 707 and 1330 ma these geochemical and isotope characteristics indicate that these shoshonites derived from a subduction modified ancient subcontinental lithospheric mantle and then underwent significantly fractional crystallization of k feldspar plagioclase and accessory minerals such as apatite and fe ti oxides during magma ascent we interpret that asthenospheric mantle upwelling caused by eastward roll back of a flat slab triggered partial melting of the metasomatized lithospheric mantle to result in the early cretaceous shoshonitic magmatism in the northern wuyi mountains an integration of our new results with compiled data from the interior of the south china block reveals that the arc like geochemical signature is confined to the wuyi mountains region but becomes little or even invisible toward inland in south china this implies that the far field effects of the early mesozoic subduction only reached the wuyi mountains ca 500 km away from the trench consistent with flat or shallow subduction models

insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioclase phenocrysts plagioclase phenocrysts in dacites from the high k calc alkaline capraia volcano were investigated for major trace element and sr isotope variations in order to gain better insight into the proposed open system behaviour of the volcano repeated dissolution zones in plagioclases from the early erupted monte castello mc and later monte rucitello mr dacitic units are associated with a sharp increase in an content and variation in isotopic compositions 87sr 86sr 0 70872 0 71004 which argue for repeated magma mixing in particular petrographic and mineralogical evidence suggest that recharge with hot basaltic magma occurred repeatedly during the lifetime of the capraia volcanic system we attempted to correlate shared crystallization and resorption histories using chemical mol an fe and sr isotopic zoning in plagioclase in this correlation framework the observed mismatch between chemical and isotopic data in some phenocrysts is interpreted to reflect either growth of phenocrysts in a separate magma chamber or compositional zoning within a single magma chamber a minor role of crustal contamination is inferred instead the intra crystal variations in isotopic composition in plagioclase reflect the existence of distinct components that may have thoroughly mixed at the end of the mc plagioclase growth history the dominant radiogenic component is similar to lamproites occurring in tuscany recharge with this component occurred throughout the genesis of the mr dacites but was restricted to the early growth history of the mc dacites the mr plagioclases are inferred to have crystallized from separate more differentiated batches of magma that were likely to have evolved at the top of a zoned magma reservoir decrease in the an content after most dissolution zones in all phenocrysts and low temperature estimates from zircon saturation thermometry 800 c also emphasize the importance of crystal fractionation during the evolution of the volcano in agreement with the occurrence of a significant amount of rhyolitic material thus it is inferred that a rather large magma chamber may have existed during the first cycle of eruptive activity

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

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

phlogopite and tetra ferriphlogopite from brazilian carbonatite complexes petrogenetic constraints and implications for mineral chemistry systematics abstract the results of a mineral chemistry study of phlogopite and tetra ferriphlogopite in carbonatites and associated alkaline silicate rocks from the brazilian carbonatite complexes of jacupiranga tapira and catalao are presented a wide textural variety of mica is found ranging from primary magmatic crystals to late stage metasomatic phases primary micas from the carbonatites and from the associated plutonic silicate rocks follow distinct evolution paths with magma differentiation in all three complexes micas from the silicate rocks evolve from phlogopite towards annite although in jacupiranga they are more al rich among the micas crystallising from carbonatite liquids those from jacupiranga are typically al and mg rich while in tapira and catalao they are extremely al poor metasomatic micas bridge the gap between primary micas from silicate rocks and from carbonatites the complete phlogopite tetra ferriphlogopite series is reported from the catalao and tapira complexes this study shows that micas from carbonatite complexes may span a wide compositional range largely overlapping the fields of micas from several types of alkaline ultrapotassic rocks especially regarding ti and al contents the use of phlogopite composition and evolution to discriminate between different types of alkaline rocks should be undertaken with caution

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

melting and dynamic metasomatism of mixed harzburgite glimmerite mantle source implications for the genesis of orogenic potassic magmas abstract tectonically young orogenic settings are commonly the sites of post collisional silica rich ultrapotassic magmas with extreme k2o contents of up to 9 wt and k2o na2o 2 many experimental studies investigating the generation of these melts have concentrated on melting of homogenous phlogopite bearing peridotites whereas geochemical signatures indicate the involvement of at least two types of source rocks ultra depleted and k and trace elements enriched ones we report the results of melting experiments at 1 2 gpa of mixed glimmerite and harzburgite in which these rock types make up two halves each capsule melting begins in the glimmerite and its metasomatic effects on the harzburgite are apparent at 1100 c even before melt pools are visible the first melts are na rich seen in zoning of olivines and as growth of clinopyroxene in the harzburgite but change at higher degrees of melting to produce a typical lamproite like melt with k2o 10 wt a major advantage of this study is the preservation of distinct melts in different parts of the capsule which reflect a process of dynamic metasomatism within the harzburgite matrix the infiltrating melt derived from melting of the glimmerite changes consistently with the distance of travel through the harzburgite enabling quantification of the metasomatic effects as an increase in sio2 and k2o this results principally from assimilation of orthopyroxene which increases the ol opx ratio of the residual harzburgite the effects of quench olivine growth are recognizable and can be quantified due to a step change in composition at the glimmerite harzburgite border the large total surface area of olivine and small melt fraction mean that the amount of quench olivine is high within the harzburgite but negligible in the almost completely molten glimmerite melts of the glimmerite contain up to 8 10 wt k2o and 53 wt sio2 which increase to 55 56 wt after interaction with the harzburgite mediterranean lamproites resemble melts of glimmerite whereas melts that have interacted with harzburgite are more similar to less potassic but more sio2 rich shoshonites of the mediterranean region

k richterite olivine phlogopite diopside sanidine lamproites from the afyon volcanic province turkey middle miocene volcanic activity in the afyon volcanic province eastern part of western anatolia is characterized by multistage potassic and ultrapotassic alkaline volcanic successions the volcanism is generally related to the northward subduction of the african plate beneath the eurasian plate in afyon the middle miocene volcanic products consist of melilite leucitite tephriphonolite trachyte basaltic trachyandesite phonolite phonotephrite tephriphonolite and lamproite rocks near surface emplacement and relatively quiescent subaerial eruptions of lamproitic magma produced different emplacement forms such as dome plug shaped bodies and lava flows showing variation in volume and texture the mineralogical constituents of the lamproites are sanidine olivine 77 mg no 81 phlogopite 74 mg no 78 k richterite clinopyroxene 74 mg no 78 with accessory apatite calcite and opaque minerals afyon lamproites resemble mediterranean type si rich lamproites their compositional range is 50 52 wt sio2 4 8 wt mgo and they display a typical lamproitic affinity chondrite normalized ree patterns exhibit enrichment in lree relative to hree la yb cn 15 3 17 0 they show extreme enrichment in lile relative to primitive mantle values and troughs of nb and ti the lamproites give a range of high initial 87sr 86sr ratios and low 143nd 144nd ratios the geochemical and isotopic characteristics suggest that lamproitic magma is derived from highly metasomatized mantle the enrichment history may include metasomatic events related to subduction as in other active orogenic areas of the mediterranean

the origin of the potassic rock suite from batu tara volcano east sunda arc indonesia abstract atu tara is an active potassic volcano in the eastern sunda arc its leucite bearing rock suite can be subdivided into two groups one less evolved with th 20 ppm 87sr 86sr 18o and trace element systematics in the less evolved group suggests that existence of parental magmas with different mantle origins the mantle below batu tara is most likely heterogeneous and several source components are involved in magma genesis trace element and isotopic compositions of batu tara and adjacent volcanoes are consistent with the involvement of a subducted sedimentary crustal component as well as morb and oib mantle the latter with geochemical characteristics comparable to the mantle underlying muriah java melt extraction from this complex mixture is envisioned as a two stage process partial melts of the crust contaminated morb mantle mix in the mantle wedge with partial melts of oib domains different mixtures of these two melts provide the parental magmas that enter the volcanic plumbing system where crystallization hybridization and refilling processes occur the calcalkaline volcanoes in the arc segment show stronger signatures for a subducted crustal component than batu tara which displays a greater influence from the oib mantle source the potassium enrichment can therefore be attributed to contributions both from the enriched mantle and from subducted crustal material mantle type 18o values of the batu tara magmas indicate that the mantle wedge below potassic orogenic volcanoes is not necessarily strongly enriched in 18o

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

a synthesis and new perspective on the petrogenesis of kamafugites from west qinling china in a global context we discuss the overall characteristics of a recently recognized kamafugite province in west qinling china using field observations and geochemical data we discuss the petrogenesis of the kamafugites using new bulk rock major and trace element data and sr nd isotope compositions of representative samples together with the literature data in chinese and comparing them with type kamafugite suites from italy brazil and uganda all these four kamafugite suites show oib like rare earth element ree patterns but are much more enriched than oib in the progressively more incompatible elements the west qinling kamafugite samples resemble closely the ugandan and brazilian suites in having a negative anomaly of k p and ti and a positive nb ta anomaly yet the italian suite shows conspicuously a negative nb ta anomaly the four kamafugite suites have different 8nd t values and 87sr 86sr1 ratios implying their distinct sources and source histories we consider that the ideal sources for kamafugite magmas are most likely metasomatized sub continental lithosphere with components of ancient seafloor subducted calcareous terrigenous sediments the close association of kamafugite with carbonatite worldwide including the west qinling suite is consistent with both being derived from a single co2 rich silicate parental magma segregated during ascent as a result of decompression induced immiscibility in terms of both sources or source histories and processes our simple interpretation can effectively explain the petrogenesis of all the apparently different kamafugite suites suggests that the petrogenesis of kamafugites may actually be simple further effort should aim to test whether our interpretation is indeed valid globally c 2013 elsevier ltd all rights reserved

volcanological and petrological evolution of the eastern vulsini district central italy on the basis of recent field mapping data stratigraphic reconstruction and k ar datings a volcanological and petrological study of the bolsena and montefiascone volcanic zones eastern vulsini district has been carried out ten main eruptive phases with both effusive and explosive activity have been recognized these are characterized by a large range of magma compositions belonging to the leucitite basanite and shoshonite magmatic series within each series near primary magmas and slightly to strongly differentiated products are present although in different proportions the great majority of differentiated products mostly trachytic outcrops in the northern sectors of the eastern vulsini district bolsena volcanic zone where lavas or pyroclastics were erupted during moderate to large volume plinian type and ignimbrite forming explosive activity by contrast abundant rather undifferentiated magmas are more frequently found in the southern sectors of the eastern vulsini district montefiascone volcanic zone the structural setting of the sedimentary substratum as well as its lithological characteristics may have played an important role in producing this magma distribution the very shallow position a few hundred meters below the topographic surface of the top of the fracturated carbonate basement would have facilitated the uprising of abundant less evolved magmas in the montefiascone volcanic zone whereas relatively large magma bodies a few kilometer deep can only be inferred in the bolsena volcanic zone bolsena caldera where a front of overthrust sheets of the tuscan and umbrian sedimentology sequences is most probably present in this area source vents of explosive activity show a tendency to shift northeastward with time feeding systems were also differently oriented e w and wnw ese in the southern sectors and nw se and nnw sse in the northern sectors while a ns system was related to a late stage activity of the whole eastern vulsini district

genesis evolution and tectonic significance of k rich volcanics from the alban hills roman comagmatic region as inferred from trace element geochemistry trace element data are reported in 21 lava samples from the alban hills one of the most important volcanic complexes of the roman comagmatic region the samples consist mostly of tephritic leucitites with minor phonolitic tephrites and tephritic phonolites emplaced during two distinct phases of activity separated by a caldera collapse