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

variations in the nd isotopic composition of foraminifera from atlantic ocean sediments 143nd 144nd ratios have been measured in recent core top foraminifera from 25 sites throughout the atlantic ocean the average nd 0 value from this study agrees well with previous estimates of the average nd isotopic composition of the atlantic based on analyses of ferromanganese deposits and seawater samples however the larger data base and the nature of the samples have allowed us to identify distinct provenances of nd isotopes in the atlantic

dynamic modelling of stress accumulation in central italy we develop a viscoelastic dynamic model to calculate the stress distribution in central italy induced by different geodynamic processes likely active in the region africa eurasia convergence adriatic underthrusting subduction and asthenospheric upwelling underneath tuscany model results are compared with the hypocentral distribution of earthquakes and with the orientation of p and t axes available for the region the first order characteristics of the seismotectonic observations in central italy are subcrustal seismicity the pair extension compression in tuscany and in the outer apennines and the flexural behaviour evident in long wavelength orientation of t axes these features are reproduced by the combination of two processes underthrusting of the adriatic plate under the apennines and asthenospheric upwelling underneath tuscany the comparison with available data does not give insights about slab pull as an ongoing process

the role of continental margins in the final stages of arc formation constraints from teleseismic tomography of the gibraltar and calabrian arc western mediterranean abstract the deep seismicity and lateral distribution of seismic velocity in the central western mediterranean point to the existence under the alboran and tyrrhenian seas of two lithospheric slabs reaching the mantle transition zone gibraltar and calabrian narrow arcs correspond to the slabs similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll back mechanism in which the two arcs are symmetrical end members we present a new 3 d tomographic model at mantle scale for the calabrian arc and compare it with a recently published model for the gibraltar arc by monna et al 2013a the two models calculated with inversion of teleseismic phase arrivals have a scale and parametrization that allow for a direct comparison the inclusion in both inversions of ocean bottom seismometer broadband data improves the resolution of the areas underlying the seafloor networks this additional information is used to resolve the deep structure and constrain the reconstruction of the central western mediterranean geodynamic evolution the gibraltar tomography model suggests that the slab is separated from the atlantic oceanic domain by a portion of african continental margin whereas the calabrian model displays a continuous oceanic slab that is connected via a narrow passage 350 km to the ionian basin oceanic domain starting from the comparison of the two models we propose the following interpretation within the mediterranean geodynamic regime dominated by slab rollback the geometry of the african continental margin located on the lower plate represents a critical control on the evolution of subduction as buoyant continental lithosphere entered the subduction zones slab pull caused tears in the subducted lithosphere this tectonic response which occurred in the final stages of arc evolution and was strongly controlled by the paleogeography of the subducted plates explains the observed differences between the gibraltar and calabrian arcs

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

heterogeneous brittle ductile deformation at shallow crustal levels under high thermal conditions the case of a synkinematic contact aureole in the inner northern apennines southeastern elba island italy abstract we present an example of interaction between magmatism and tectonics at shallow crustal levels in the late miocene the metamorphic units of the eastern elba island northern apennines were intruded at very shallow crustal levels by a large pluton 60 km 2 with the development of an hectometre sized contact aureole defined by growth of low pressure high temperature mineral assemblages p max max 650 c structural data show that the contact aureole is associated with a km sized antiform of the foliation and by several metre to decametre thick high strain domains consisting of strongly foliated rocks containing synkinematic ht lp mineral assemblages and ductile shear zones of variable thickness these shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration associated with the thermal peak of contact metamorphism to subgrain rotation and bulging recrystallization the latter mostly associated with the cataclastic overprint these transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation deformation accompanied the development and cooling of the contact aureole which recorded the switch from high temperature ductile to low temperature brittle conditions the geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks

origin of the acidic volcanics of the tolfa district tuscan province central italy an elemental and sr isotopic study volcanic rocks from the southern part of the tuscan province the tolfa district range in composition from dacites to rhyolites they have relatively high contents of many incompatible elements and their 87sr 86sr ratios vary between 0 7129 and 0 7148 28 analyses with one analysis of 0 7112 the four major eruption centres of the district can be distinguished geochemically it is shown that the variation of major and trace elements within each area can be explained by fractional crystallization without significant crustal assimilation the geochemical patterns of the incompatible elements of the investigated volcanics have a close similarity to the alkaline undersaturated volcanics from the nearby roman province the geochemical and isotopic similarity between the tolfa volcanics and those of the roman province suggests a common origin for these components of the magmas it is suggested that while the origin of the lil element enrichment of the roman province magmas is a mantle which was metasomatised by fluids or melts derived from upper crustal material of sedimentary origin recycled into the mantle by subduction the tolfa volcanics were derived directly from the subducted material by melting

crustal structure of northern latium central italy from receiver functions analysis new evidences of a post collisional back arc margin evolution abstract the crustal velocity structure in a region of central apennines of italy at the hinge between the highly stretched portion of the monte argentario promontory and the magmatic province of the tolfa domes complex northern latium is discussed in this study s wave velocities at depth have been constrained by the modeling of p wave receiver functions rf from both temporary and permanent broadband seismic stations the computer 3d vs models show a thin crust 19 25 km made of a shallow and thin sedimentary cover a very high velocity and anisotropic layer related to a metamorphic basement and a low vs anisotropic layer in the middle lower crust above a shallow moho discontinuity modeled at about 20 km depth the volcano tectonic evolution of this portion of tyrrhenian back arc margin has been strongly influenced by its peculiar crustal architecture the low vs layer acted as a shear zone in the middle lower crust during the tyrrhenian extension also helping the development of plio quaternary magmatism our findings potentially give new constraints on the evolution of the area and to the general comprehension of back arc development in collisional regions

new data and hypothesis on the development of the tyrrhenian basin abstract among those basins which developed during the neogene and quaternary at the rear of the perimenditerranean mountain chains the tyrrhenian basin is the most recently formed comparing the available geological and geophysical data the tyrrhenian domain and its neighbourhoods can be divided into more or less homogeneous sectors namely northern and southern tyrrhenian apenninic chain maghrebides chain apulian and iblean african foreland ionian foreland for each sector the different phenomena involved and the crustal characteristics are discussed the evolution of the domain has been explained by the application of a crustal stretching model developed for continental margins this approach predicts the formation of basinal areas as a result of the europe africa collisional movements within a plastic rigid deformation model taking into account the mass redistribution after collision the model explains both the distension developed within the collisional system and the penecontemporaneous development of compressive and distensive phases as a consequence of the intraplate stresses horizontal shearings affecting the whole lithosphere at different levels occur with delaminations asthenosphere uprising and gradual collapse in the upper crust e w trending and strike slip dextral faults played a primary role in the evolution of the tyrrhenian basin inducing the largest tearings at the end of the major transcurrent systems such an evolution is complicated by the migrating motion of the shear zone from n to s and by the penecontemporaneous stop in the extension from the northern towards the southern domains of outstanding importance is the shear zone which borders the southern tyrrhenian enabling the opening of the basin and allowing the development of the major group of en echelon sub basins with a nw se trend

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

the tyrrhenian apennines system structural setting and seismotectogenesis abstract the available geological geophysical and seismological data of the tyrrhenian apennines system are briefly reviewed and synthesized in a number of sketch maps integrating and comparing these data a large scale simple shear kinematic model is proposed for the tyrrhenian apennines system that is here interpreted as an oblique asymmetric passive continental margin developed during the progressive counterclockwise rotation of the adriatic foreland from the late miocene to the present in the frame of this working hypothesis the thinning and stretching of the tyrrhenian crust were accommodated by progressive eastward motion of extensional allochthonous slices bounded by low angle west dipping oblique shear zones rotating above a common detachment that penetrates into the mantle lithosphere at any given time the most external eastward moving slice is bounded by a transtensional shear zone at the top and by a transpressional one at the bottom the displacement within the hanging wall of the transtensional shear zone is accommodated by high angle normal faults and en echelon grabens the displacement within the hanging wall of the transpressional shear zone is instead accommodated by co axial en echelon sets of folds thrusts and high angle strike slip faults thus the development of the late miocene pliocene pleistocene contractional strain field of the apennines of italy might not be a consequence of complex subduction processes but subordinate to the deformation processes that lead to the progressive opening of the tyrrhenian sea the seismicity of the crustal apennines of italy is analyzed in the frame of the above history of progressive deformation and a seismotectogenetic model is outlined

styles and regimes of orogenic thickening in the peloritani mountains sicily italy new constraints on the tectono metamorphic evolution of the apennine belt the peloritani mountains constitute the sicilian portion of the calabria peloritani arc italy a tectono metamorphic edifice recording the history of the subduction exhumation cycle during tertiary convergence between the african and european plates here we describe the kinematic and the petrological characteristics of the major shear zones bounding the lowermost continental derived metamorphic units cropping out in the eastern portion of the peloritani mountains both meso and micro scale shear sense criteria indicate a top to the sse tectonic transport during a general evolution from ductile to brittle deformation conditions quantitative thermobarometry on texturally equilibrated phengite chlorite pairs crystallized along the shear bands indicates pressure of 6 8 kbar at temperatures of 360 440 c for the structurally highest units and 3 4 kbar at 380 440 c for the lowest ones this documents an overall inverse type nappe arrangement within the tectonic edifice and a transition from an alpine 13 18 c km 1 to a barrovian type 28 36 c km 1 geothermal gradient during the progress of the alpine orogenic metamorphism in the peloritani mountains the integration of these results allows the peloritani mountains to be considered as a constituent element of the apennine orogenic domain formed during the progressive space time transition from oceanic to continental subduction at the active convergent margin

evidence for low temperature ultrapotassic siliceous fluids in subduction zone environments from experiments in the system k2omgoal2o3sio2h2o kmash experiments in the system k2o mgo al2o3 sio2 h2o kmash were undertaken with the piston cylinder apparatus to study the reactions 1 1 phengite quartz k mg rich siliceous fluid feldspar phologopite h2o 2 2 phengite talc k mg rich siliceous fluid phlogopite quartz coesite h2o at temperatures between 400 and 700 c the ultrapotassic fluid appearing at pressures above 15 kbar on the low temperature sides of the corresponding reaction curves which show positive dp dt slopes is probably supercritical the p t positions of the reactions are compatible with kmash mineral reactions studied previously and with melting investigations in the kmash system undertaken at temperatures higher than 700 c it is possible that natural rocks chiefly k rich metasediments subducted as minor portions of the oceanic crust could give rise to low temperature ultrapotassic fluids mainly at temperatures between 300 to 600 c and pressures between 15 and 30 kbar the ascending k rich fluids would penetrate the overlying mantle to metasomatize it after termination of the subduction process heating of this mantle material previously cooled by the subducted lithosphere could lead to the formation of high temperature k rich magmas

common trace element characteristics of crustal and mantle derived k rich magmas at mt amiata central italy rare earth and other trace element data are reported for k rich mafic inclusions and siliceous lavas from mt amiata southern tuscany italy which form an almost complete mixing series as a result of magmachamber replenishment despite a wide range of sio2 contents 48 67 wt most of the rocks are equally enriched in light ree 200 300 and heavy ree 10 15 relative to chondritic values whereas intermediate ree are slightly less abundant in the lavas compared with the inclusions eu shows negative anomalies eueu 0 49 0 70 that are most pronounced in the lavas the compatible elements cr v sc and co are found to behave like sr ba and most major elements as they show a distinct inverse correlation with sio2 while cs follows na and li and markedly increases with sio2 however k and a number of other predominantly incompatible elements viz rb zr la ce yb lu nb y hf th and u display surprisingly little or no variation and all of the rocks have unusually high concentrations of many of these elements based on arguments that mixing in the magma chamber was not accompanied by significant selective enrichment of certain elements these chemical characteristics are attributed to the end members which can be identified as a silica saturated tuscan type magma and a primitive silica undersaturated roman type magma of the high k series it is tentatively suggested that the different sources in the lower crust and upper mantle from which the end member magmas are thought to originate were metasomatized by the same fluids prior to melting

mechanisms of crustal deformation thirty sixthwilliam smith lecture the energy source for crustal deformation is isotopic heating and secular cooling of the mantle in a true solid heat would be lost to the surface by conduction however solid state creep processes allow the earth s solid mantle to exhibit a fluid behaviour thus thermal convection can convert heating into directed motion variations in temperature lead to variations in densitythrough thermal expansion and contraction although the resultant body forces are vertical horizontal variations in temperature lead to horizontal body forces at an ocean ridge the variations in the thickness of the lithosphere lead to the elevation of the ridge the result is a substantial horizontal ridge push force this force along with the trench pull force on the descending lithosphere is the primary force driving plate tectonics lithospheric thinning must occur beneath continental rifts and plateau uplifts i suggest that lithospheric thinning is caused by the diapiric penetration of hot asthenospheric rock to the crust mantle boundary this penetration may also cause lithospheric stoping and plateau uplifts lithospheric thinning leads to large tensional stresses above the zone of thinning these forces are generally much larger than the compressional forces generated by crustal thinning the forces generated by lithospheric thinning are quite large and may be responsible for the propagation of continental rifts in island arcs and andean type orogenic belts both lithospheric thinning and crustal thickening result in large tensional forces probably the most complex zone of crustal deformation is the continental collision variations in types of continental collisions are discussed

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

crustal evolution of the hercynian belt of western europe evidence from lower crustal granulitic xenoliths french massif central abstract granulite facies lower crustal xenoliths scavenged by the tertiary basaltic pipes of bournac and roche pointue massif central france have been analysed for major and trace elements and radiogenic sr nd isotope ratios they display wide variations in major elements rare earth elements and isotopes 87 sr 86 sr 0 7041 0 7216 nd 11 9 to 1 5 which tend to correlate with the three different rock types encountered basic and acidic meta igneous and metasediments the basic liquids are of calc alkaline affinity and cumulates are abundant there is a gap in silica content between the basic and acid meta igneous xenoliths the isotopic compositions suggest mixing of old pre existing continental crust represented by the metasediments and mantle derived basic melts which represent juvenile addition to the crust during the hercynian orogeny the basic meta igneous rocks have been contaminated during their emplacement into the crust whereas the surrounding metasediments have suffered partial fusion and contamination by the same liquid producing the hercynian granitoids which have nd and sr initial ratios identical to those of the lower crustal xenoliths the residue from melting may be represented by the acid meta igneous rocks some of which have positive eu anomalies these results indicate that an important basaltic underplating event occurred during the evolution of hercynian orogenic belt although the exact timing of the underplating requires further constraint

subduction related intermediate depth and deep seismicity in italy insights from thermal and rheological modelling geological data suggest that after a period of oceanic lithosphere subduction about 170 km of continental lithosphere were subducted under the northern apennines since about 23 myear at rates of ca 1 cm year whereas more than 700 km of mesozoic oceanic lithosphere ionian lithosphere have been subducted under the calabrian arc at rates of about 3 cm year however a well developed wadati benioff zone can be only recognised below the calabrian arc down to depths of 450 500 km whereas intermediate depth seismicity reaches maximum depths of about 90 km under the northern apennines we model the thermal state of these two subduction zones and apply temperature dependent non linear rheological laws to evaluate the down dip extent of brittle regions in the two subduction zones we show that differences in subduction rate and in slab composition continental vs oceanic produce a far deeper down to 290 380 km brittle field in the colder calabrian slab than in the warmer northern apenninic slab 70 120 km thus explaining differences in the maximum depth of seismicity in both regions concerning deep earthquakes in the calabrian subduction zone models predict that metastable olivine persists down to depths of 430 km this could possibly explain the maximum depth of earthquakes in the area the small extent of the metastable olivine wedge produces a small density anomaly that cannot explain the pervasive down dip compression observed in the ionian slab 2004 elsevier b v all rights reserved

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

the pb sr nd isotope geochemistry of some recent circum mediterranean granites pb sr and nd isotopic compositions have been analyzed in recent granites from northern africa northern italy and greece lead isotope compositions of k feldspars are rather homogeneous and cluster close to the modern lead of stacey and kramers 1975 but with slightly higher207pb 204pb and208pb 204pb ratios the cyclades samples however have higher206pb 204pb ratios addition of mantle derived lead was probably very limited which supports a quasi closed system evolution of this element in the continental crust the sr nd data fall in the enriched part of the143nd 144nd vs 87sr 86sr diagram and define a smooth hyperbolic mixing curve over a wide area straddling different orogens most granites may be accounted for by a binary mixture between a recycled crustal component and a depleted mantle like component no correlation is observed between either pb and sr or nd isotopic ratios or any isotopic ratio and major element contents quantitative modelling suggests that two cases fit the sr and nd characteristics of these granites they both require anatexis of the crust on a scale large enough to average the isotopic properties of heterogeneous terranes in the first case the mantle derived component may be represented by differentiated island arc type magmas and the granites result from mixing these magmas with anatectic melts in the second case mantle derived igneous rocks such as obducted ophiolites are part of the crustal source and their variable involvement in the anatectic process causes isotopic variations

groundwater ages and reaction rates during seawater circulation in the dead sea aquifer the dead sea system provides a unique opportunity to study flow velocities and reaction rates during seawater circulation in the aquifer we present here a novel application of calculating groundwater age and velocity along the flow path of the hypersaline water from the dead sea into the aquifer using the buildup rate of 228 ra in this water the calculated circulation velocities are 1 10 m y which is in agreement with estimates based on the na cl ratios in this water 1 5 4 m y the latter is unique to the dead sea aquifer system where the na cl ratio has been decreasing during the past 50 years due to the precipitation of halite in the lake the velocity estimates facilitated the calculation of the rates of water rock interactions in the dead sea aquifer

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

age and temperature constraints on metamorphism and exhumation of the syn orogenic metamorphic complexes of northern apennines italy abstract the apennine range is a young convergent orogen that formed over a retreating subduction zone syn orogenic metamorphic rocks are exposed in the mid tuscan ridge tuscan coast and tuscan archipelago and provide information about processes of continental subduction and exhumation associated with accretion and retreat apatite and zircon fission track analyses were applied to some of these syn orogenic metamorphic rocks the new low temperature thermochronological data helped to constrain the timing of the metamorphic peak and the age and modality of exhumation of these rocks that were structurally buried at 20 to 40 km depth during the main tectonogenic phase of the northern appenine belt in the giglio and elba islands and in the monti dell uccellina along the coast minimum ages of partially reset zircon samples yielded a first time constraint on the late oligocene age of the metamorphic peak the ca 27 ma obtained at the monti dell uccellina is coeval to that found in the alpi apuane located at the northern termination of the mid tuscan ridge the data from the tuscan archipelago point to a slightly older age in the monti pisani south of the alpi apuane and in the argentario promontary along the coast south of the monti dell uccellina completely reset zircon samples but composed by different populations were behaving as multiple thermochronometers and confirm the already proposed isothermal nature of the exhumation occurred after the metamorphic peak zircon p1 peak indicated that at 13 10 ma rocks were already at shallow crustal levels

the southern tyrrhenian subduction zone deep geometry magmatism and plio pleistocene evolution abstract we report on a high resolution vp vp vs and qp model of the southern tyrrhenian subduction zone obtained by the inversion of p and s wave arrival times and t values from intraslab seismicity the arcuate shape of the southern apennines calabrian arc sicilian maghrebides is perfectly mirrored by two rather continuous low and high vp bands lying beneath the belt system at ca 25 and 100 km respectively between 100 and 300 km two independent high vp slabs lie beneath the neapolitan region and the southern tyrrhenian sea separated by unperturbed mantle we suggest that the ca 150 km wide slab window beneath the southern apennines opened after a tear occurring within a composite subduction system formed by the apulian continental lithosphere and the ionian oceanic slab the abrupt slab rupture induced ultrafast southeastward retreat of the ionian slab and the 19 cm yr spreading of the back arc oceanic marsili basin between ca 2 1 and 1 6 ma ago the 25 km low vp zone beneath the arc denotes continental upper crustal rocks below the chain its striking continuity requires a unique orogenic wedge at 25 km depth below the southern apennines the calabrian arc and the sicilian maghrebides the alternative explanation would imply the ubiquitous occurrence of autochthonous lower plate rocks at 25 km depth i e a puzzling autochthonous continental calabria the ionian slab beneath calabria shows high vp high qp and low vp vs anomalies typical of old oceanic lithosphere intermediate depth seismicity is concentrated within its thin oceanic crust suggesting the occurrence of vigorous metamorphism the slab dehydration promotes the melting of the overlying mantle as testified by high vp vs and low qp anomalies between the slab and the aeolian magmatic arc

tectonic control on laccolith emplacement in the northern apennines fold thrust belt the gavorrano intrusion southern tuscany italy

pb isotopic zoning of k feldspar megacrysts determined by laser ablation multi collector icp ms insights into granite petrogenesis this study investigates pb isotopic zoning in magmatic k feldspar megacrysts from the monte capanne pluton elba italy using laser ablation multi collector icpms the studied crystals provide an ideal opportunity to use in situ techniques to assess the extent of open system processes and better characterize the components involved in the genesis of complex magma systems earlier investigations of the pluton identified the importance of magma mixing between mantle and crustal derived magmas the investigated k feldspar megacrysts exhibit strong zoning in 207pb 206pb and 208pb 206pb correlated with lead elemental variations we interpret these variations as reflecting growth zoning as opposed to secondary diffusive exchange despite a great variety of zoning patterns we were able to correlate different events of megacryst growth reflecting crystallization in a dynamic magma system our two step model includes 1 growth of a granitic magma chamber by addition of low 208pb 206pb magma to a high 208pb 206pb magma contaminated with crustal material i e the megacryst cores and 2 recharge by mantle derived magma i e the megacryst rims we interpret the thorogenic nature of the megacryst rims to reflect the mantle derived component involved in the mixing process taking account of other data from the tuscan magmatic province the mantle source is inferred to have been metasomatized by continental material during subduction tims sr isotopic data from microdrilled cores in one megacryst provides general support for the model but show that the two isotopic systems are decoupled

a new holocene relative sea level curve for the south shetland islands antarctica abstract precise relative sea level rsl data are important for inferring regional ice sheet histories as well as helping to validate numerical models of ice sheet evolution and glacial isostatic adjustment here we develop a new rsl curve for fildes peninsula south shetland islands ssis a sub antarctic archipelago peripheral to the northern antarctic peninsula ice sheet by integrating sedimentary evidence from isolation basins with geomorphological evidence from raised beaches this combined approach yields not only a holocene rsl curve but also the spatial pattern of how rsl change varied across the archipelago the curve shows a mid holocene rsl highstand on fildes peninsula at 15 5 m above mean sea level between 8000 and 7000 cal a bp subsequently rsl gradually fell as a consequence of isostatic uplift in response to regional deglaciation we propose that isostatic uplift occurred at a non steady rate with a temporary pause in ice retreat ca 7200 cal a bp leading to a short lived rsl rise of 1 m and forming a second peak to the mid holocene highstand two independent approaches were taken to constrain the long term tectonic uplift rate of the ssis at 0 22 0 48 m ka placing the tectonic contribution to the reconstructed rsl highstand between 1 4 and 2 9 m finally we make comparisons to predictions from three global sea level models

geochemical and isotopic sr pb evidence of crust mantle interaction in acidic melts the tolfa cerveteri manziana volcanic complex central italy a case history abstract the tolfa cerveteri manziana volcanic complex tvc 3 5 ma located about 100 km north of rome represents the southernmost outcrop of the tuscan magmatic province the overlapping of tuscan acidic and roman alkaline volcanic rocks in the area makes it suitable for the study of the interaction between crustal and mantle derived melts major trace element rb sr ba y nb zr pb u and th rare earth element and sr and pb isotopic data on lavas quartz latites rhyolites and high silica rhyolites magmatic enclaves and metasediments from the basement allow the following conclusions to be drawn 1 a the tvc volcanic rocks are derived from the anatexis of a metasedimentary source having a composition similar to that of the metasediments present in the basement beneath the m amiata geothermal region at depths ranging from 1 4 to 3 2 km 2 b the anatectic magma during its differentiation by fractional crystallization interacted with two mafic magmas with differing sr and pb isotopic compositions and variable degrees of enrichment in incompatible elements the most differentiated rocks high silica rhyolites are the most highly contaminated 3 c the inferred mafic contaminants appear to be derived from a heterogeneous metasomatized mantle with isotopic and geochemical characteristics similar to those of the mantle which presently underlies the roman and campanian regions

boninitic and low ti subduction related lavas from intraoceanic arc backarc systems and low ti ophiolites a reappraisal of their petrogenesis and original tectonic setting a comprehensive review of boninitic and other low ti subduction related lavas from modern intraoceanic arc backarc systems and of low ti ophiolites shows a complete compositional range from boninite to island arc basalts transitional low ti types distinguishable from the main magma types are well represented and defined here as 1 transitional boninites mainly from low ti ophiolites and 2 low ti island arc basalts major compatible and incompatible elements are clearly decoupled in all these low ti subduction related magmas in general their petrogenesis reflects a high degree of hydrous but not necessarily water saturated melting at pressures lower than 15 20 kbar of severely depleted mantle sources enriched in lile and h2o which are residual after the earlier extraction of basalt s as the residues after the extraction of low ti subduction related magmas very likely have a dunitic clinopyroxenefree harzburgitic composition it is proposed that the cao al2o3 ratios of the primary melts reflect those of their mantle sources particularly for the boninites and transitional boninites in this model the source of boninites sensu stricto would show a variable degree of depletion from clinopyroxene bearing to clinopyroxene free harzburgite whereas those of transitional boninites low ti island arc basalts would have clinopyroxene bearing harzburgite clinopyroxene poor lherzolite compositions the metasomatizing components involved in the genesis of low ti island arc basalts have a very close affinity with those involved with the sources of normal island arc tholeiites the common eruptive setting indicates that these low ti lavas represent extreme magma types of an otherwise normal island arc tectonomagmatic regime the petrogenesis of tertiary boninites and transitional boninites and the comparable magma types of the low ti ophiolites require at least these components 1 a variably depleted mantle source probably a subarc mantle residual after island arc basalt extraction 2 a hydrous fluid probably derived from dehydration of the subducted altered oceanic crust which carries most of sr ba k and rb in the subarc source and 3 a lree zr and nb enriched component with a low 143nd 144nd ratio probably derived from an ocean island type source it is proposed that this third component also carried significant amounts of rb and k which totally obliterated the ba spike typical of island arc tholeiites iats and produced the distinctive rb spike typical of the boninite transitional boninite magmas this component is hypothetically identified in liquids produced by partial melting of small scale large magnitude k richerite phlogopite bearing heterogeneities within the hot rising asthenospheric diapirs required in the model of crawford et al 1981 for the genesis boninite transitional boninite magmas geochemical thermal and geological constraints are best explained in a model which restricts the genesis of boninite transitional boninite magmas to the early stages of intraoceanic interarc spreading and to important rifting phases of the arc and or early interarc basin structures connected with hot rising asthenospheric mantle diapirs

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

the interplay between global tectonic processes and the seismic cycle in the umbria marche seismogenic region summary for the central apennines peninsular italy a series of tectonic mechanisms are reproduced by means of finite element models in order to study the effects of active tectonics on the seismic cycle in the umbria marche seismogenic zone continental extension and rift push effects induced by small scale convection are modelled within 2 d viscoelastic models of the crust lithosphere system in vertical cross sections perpendicular to the strike of the major tectonic structures under study namely the apennines and the colfiorito fault zone where the 1997 seismic sequence took place with the aim of constraining the active tectonic mechanisms at the regional scale and the behaviour of the fault in the seismogenic zone at the local scale modelled baseline rate of change are compared with newly acquired gps data retrieved from the two permanent gps receivers of camerino came and elba elba deliberately installed along the modelled transect these receivers are located at both edges of the continental extension in the front of the apennines close to the adriatic plate in the east and in the rear of the chain in the tyrrhenian domain the deformation pattern inferred from seismicity and from the geodetic data is consistent with small scale convection in the tyrrhenian domain which reproduces extension in the rear of the apennines and compression in the front of the chain a convective mechanism associated with backarc opening and doming of the asthenosphere provides an extensional rate along a baseline connecting two sites in the front of the chain camerino and in its rear elba comparable to the observed baseline rate of change the viscosity of the lower crust plays a fundamental role in determining the style of stress in the crust lithosphere system once constrained by means of the extensional baseline rate inferred from gps the modelled slip across the colfiorito fault and the modelled earthquake recurrence time are consistent with the 1997 normal fault event and with palaeoseismicity respectively

mine waste dumps and heavy metal pollution in abandoned mining district of boccheggiano southern tuscany italy mining activity in the boccheggiano fontalcinaldo area southern tuscany dates back at least to the 16th century ad and lasted up to very recent times copper rich hydrothermal veins massive pyrite deposits and their gossans were exploited two mine waste dumps fontalcinaldo fontebona one flotation tailings impoundment gabellino and one roasting smelting waste dump merse ribudelli in the study area were selected to ascertain the environmental effects of such protracted mining activity primary waste mineralogy is mainly characterized by pyrite gypsum quartz carbonates chlorites and micas secondary oxidation mineralogy includes fe and cu sulfates and hydroxy sulfates cu carbonates fe and al oxyhydroxides and other phases neogenic cassiterite at fontalcinaldo probable calkinsite ce la 2 co3 3 4h2o at fontebona mine waste samples show extremely variable contents of toxic elements cu pb zn bi cd as with average values in the order of hundreds to thousands of parts per million except for bi and cd in some samples the abundance of proper minerals of these metals cannot account for the entire metal load conceivably either solid solution substitutions or adsorption processes contribute to the intake of released metals into newly formed minerals release and transport of pollutants was affected to variable degrees by acid neutralization processes the highest metal and acid concentrations occur close to the investigated wastes and rapidly decrease moving downstream some hundreds of meters or less with the partial exception for mn and fe other than dilution effects this phenomenon may be ascribed to metal adsorption and precipitation of solid phases

are crustal thickness variations in old mountain belts like the appalachians a consequence of lithospheric delamination comparison of moho geometry and reflection character of active collision zones like the alps with those of fossil collision zones like the appalachians lends support for the view that lithospheric delamination is both a common and fundamentally important component of collisional orogeny in particular the relative crustal thinning commonly observed beneath the internides of old collisional orogens is an expected consequence of delamination neither precollisional crustal thickness variations nor an unrelated postcollision extensional event is required to produce this feature acceptance of the delamination hypothesis in turn fundamentally alters one s view of the tectonic evolution of old collisional orogens in the case of the appalachians delamination has direct implications for the interpretation of alleghanian granites the direction of subduction leading to final closure between laurentia and gondwana and the thermal state of the lithosphere at the onset of atlantic rifting a corollary of the delamination hypothesis is that lateral reflectivity variations cannot be used to define paleogeographic terranes in the deep crust of old orogens conversely the observation that delamination leaves a distinctive geophysical imprint on the crust itself provides an important additional clue for deciphering the tectonic evolution of such regions

steady propagation of delamination events delamination of the lithospheric thermal boundary from overlying continental crust propagates laterally from the line of initiation accelerating as the sinking slab of detached lithosphere grows longer this propagation has been numerically modeled with steady state equations in a moving reference frame by matching an interior finite element solution to flexible boundary conditions which represent the mechanical and thermal response of the surroundings the form of the solution depends on the shear coupling of intruding asthenosphere to the top of the sinking slab across a thin layer of crustal material without coupling the tip of the intrusion cools and stiffens to form a wedge dividing the crust cold mode with coupling the intrusion is forced to convect and remains ductile hot mode the cold mode can propagate at all velocities the hot mode has a lower limiting velocity of 1 2 cm year but offers less resistance at higher speeds resistance to delamination includes a constant term from the buoyant crustal downwarp plus a velocity proportional term representing viscous deformation however the proportionality constant of the latter term is only weakly dependent on crust and lithosphere viscosities matching this resistance to loading lines of 100 to 800 km slabs sinking in a mantle of 1022 p velocities of 0 3 8 0 cm year are obtained changes in viscosity affect this rate but cold mode delamination is unstoppable except at continental margins or by failure in the sinking slab the surface expression of delamination is a leading outer rise followed by a submarine trough with a large negative free air anomaly which finally evolves into a 1 km plateau if crustal viscosity and velocity are both low however there is a montonic crustal uplift with no trough thus the present lack of linear supracontinental oceans does not preclude delamination at up to 4 cm year driven by slabs up to 400 km in length

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

upper mantle properties of the tuscan tyrrhenian area a framework for its recent tectonic evolution abstract within the alpine mediterranean deformational system several interesting features in the physical properties of the upper mantle have been recognized through the regional analysis of surface wave dispersion a large upper mantle anomaly uma here called the tuscan uma has been identified in the area northeast of corsica which includes part of the northern tyrrhenian sea and part of the north central apennines this anomalous upper mantle area together with the upper mantle characteristics of the tyrrhenian sea located further to the south provides a natural framework for comprehensive interpretation of the large data set of geological and geophysical observations such as land and marine geology volcanism gravity magnetic data seismic data and seismology deep temperatures and surface heat flow

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

tomographic images of the upper mantle below central europe and the mediterranean results from delay time tomography of the european mediterranean upper mantle are discussed and where possible interpreted in terms of geodynamic processes slab like positive velocity anomalies of which the locations correlate well with deeper seismicity are found beneath spain the tyrrhenian basin and the aegean these structures are interpreted as images of subducted slabs large aseismic regions with positive velocity anomalies are found beneath the western mediterranean italy the alps dinarides the pannonian basin northern greece and the aegean these anomalies can also be linked to subducted lithosphere from the anomaly patterns it is deduced that subduction occurred below the western mediterranean and along both sides of the adriatic micro plate beneath the dinarides and northern greece the velocity structures suggest detachment of the slab from the surface

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

odp leg 107 in the tyrrhenian sea insights into passive margin and back arc basin evolution leg 107 of the ocean drilling program drilled a west northwest east southeast transect of seven sites across the tyrrhenian sea the youngest of the sub basins of the mediterranean sea sites 654 653 652 and 656 document the rifting and subsidence of the sardinia passive continental margin on the upper margin site 654 we cored a classic transgressive sequence subaerial conglomerates overlain by oyster bearing sands overlain by marine marl comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are tortonian late miocene to messinian latest miocene in age whereas synrift sediments on the lower margin are messinian to pliocene in age during the messinian desiccation of the mediterranean sites 654 and 653 now on the upper sardinian margin apparently occupied a basinal setting where they received nannoplankton bearing clays interbedded with laminated gypsum sites 656 and 652 now on the lower sardinia margin were apparently higher standing during the desiccation event their messinian facies are subaerial and lacustrine respectively we infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a rolling back subduction zone or in terms of extension of continental crust by shear along a deep detachment fault sites 655 651 and 650 were drilled into two small basalt floored basins of the central and eastern tyrrhenian emplacement of basaltic crust in the central tyrrhenian vavilov basin apparently began more than a million years before emplacement of basaltic crust in the eastern tyrrhenian marsili basin this observation is compatible with previous suggestions that the tyrrhenian has grown southeastward in response to rollback of the down going slab that currently dips northwestward under the toe of italy at the easternmost site high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2 500 m it has apparently subsequently subsided to its present depth of 4 100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid ocean ridge

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

crustal extension in the northern apennines the transition from compression to extension in the alpi apuane core complex an interpretation of northern apennine geology is presented which relates the temporal and spatial occurrence of both compressional and extensional deformation features in terms of the changing dynamic evolution within an accretionary wedge after a model proposed by platt 1986 followed by the initiation and development of continental rifting during cretaceous to eocene time an accretionary wedge formed as remnant tethyan oceanic crust subducted beneath the rotating corsica sardinia microplate microplate collision during the oligocene was characterized by the rapid imbrication of buoyant continental crust of the italian continental margin the record of which is preserved within the duplex structure geometry of the alpi apuane region the overthickened wedge geometry returned to a more stable configuration by developing extensional features during the miocene both listric normal faults at upper crustal levels and shear zones indicating evidence of distributed ductile extensional strain at mid crustal levels are recorded it is proposed that large scale regional extension with associated volcanism beginning in the messinian was represented by the intrusion of asthenospheric material from the subducted plate into the already attenuated accretionary complex further rifting perhaps aided by subduction and back arc processes in the southern apennines led to the formation of the tyrrhenian sea as an oceanic basin both the apennines and north american core complexes record evidence of crustal thickening followed by crustal thinning and finally of continental rifting this suggests that the similar histories of these regions with vastly different plate tectonic settings may both be explained by processes linked to the changing internal dynamics of accretionary wedges

deformation pattern in the central mediterranean and behavior of the african adriatic promontory abstract the adriatic platform has been described in the literature both as an africa promontory moving in close connection with the main continent and as an independent microplate this evident incongruity is mainly due to the wide spectrum of kinematic hypotheses proposed on the basis of paleomagnetic data and to the fact that the adriatic africa transition is not marked by any clear decoupling fracture or by any interruption of lithological facies along the marginal belts apennines maghrebides and dinarides hellenides in this work it is argued that the counterclockwise rotation of the adriatic plate driven by africa pushing beneath the calabrian arc and southern tyrrhenian may coherently account for all major plio quatemary events in the central mediterranean

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

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

evidence for mantle metasomatism an oxygen and strontium isotope study of the vulsinian district central italy this paper presents new o and sr isotope data for lavas from the northern part of the roman perpotassic province the samples comprise the tephritic leucititic to leucite phonolitic lavas and the saturated lavas from the vulsinian district the olivine leucite melilitite of san venanzo and the kalsilite diopside melilitite of cupaello previous oxygen isotope work on the lavas of the vulsinian district suggested crustal contamination of normal mantle derived magmas the new data cover the ranges previously found o and sr isotope ratios of evolved lavas of the undersaturated suite indicate assimilation in variable amounts of up to ca 10 of continental crustal material the saturated lavas probably assimilated large amounts up to ca 50 of crust lavas chemically identified as corresponding to little modified mantle derived liquids are high in both87sr 86sr and 18o 0 7103 0 7107 7 8 to 9 4 vulsini 0 7104 12 3 san venanzo and 0 7112 14 4 cupaello these high values are interpreted to have been inherited from a metasomatized parental mantle hydrous fluids enriched in large ion lithophile elements and high in 18o and87sr 86sr are thought to have mixed with mantle of normal 18o and87sr 86sr the fluids probably origi dehydration of continent derived sediments which were subducted beneath a mantle wedge in the continent continent collision of the corsica sardinia block and the adriatic italian plate this hypothesis is supported by pb and nd isotopic evidence and is probably valid for the entire roman province

magma emplacement in a thrust ramp anticline the gavorrano granite northern apennines italy 1 magma emplacement in the upper crust is often associated with crustal extension whereby space for intrusions is made by dilation along transtensive and strike slip faults the lenticular shape of several intrusions indicates that a further mechanism for magma intrusion is laccolith emplacement with roof uplift of the overburden additionally melts exploit rheological discontinuities e g sedimentary layering during their ascent we present an emplacement model for intrusion of the shallow level gavorrano granite northern apennine italy which is located at the core of an open anticline the shape of the intrusion and structural features of the host rocks are indicative of a synkinematic emplacement in a growing thrust anticline space was provided by the opening of dilatation zones at the core of anticline as a consequence of different amounts of translation between hanging wall and footwall units which were separated by evaporitic rocks these evaporitic units acted as major decollement layers analog models provide results in good agreement with the structural setting of the anticline and emphasize the possibility that melts filled the dilatation zone with the decollement layers further facilitating intrusion

crustal structure and moho depth profile crossing the central apennines italy along the n42 parallel 1 we present results from a teleseismic receiver function study of the crustal structure in the central apennines italy data from 15 stations deployed in a linear transect running along the n42 parallel were used for the analysis a total number of 364 receiver functions were analyzed the crustal structure has been investigated using the neighborhood algorithm inversion scheme proposed by sambridge 1999a obtaining crustal thicknesses bulk crustal vp vs ratio and velocity depth models in each inversion the degree of constraint of the different parameters has been appraised by the bayesian inference algorithm by sambridge 1999b the study region is characterized by crustal complexities and intense tectonic activity recent volcanism orogenesis active extensional processes and these complexities are reflected in the receiver functions however the relatively close spacing among the seismometers about 20 km helped us in the reconstruction of the crustal structure and moho geometry along the transect crossing the apennines from west to east the moho depth varies by more than 20 km going from a relatively shallow depth around 20 km on the tyrrhenian side deepening down to about 45 km depth beneath the external front of the apenninic orogen and rising up again to about 30 km depth in correspondence of the adriatic foreland despite the strong variability of the crustal thickness the average crustal vs values show little variation along the transect fluctuating around 3 km s the average vp values obtained from the vs and vp vs are generally lower than 6 km s