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

origin of high mountains in the continents the southern sierra nevada active and passive seismic experiments show that the southern sierra despite standing 1 8 to 2 8 kilometers above its surroundings is underlain by crust of similar seismic thickness about 30 to 40 kilometers thermobarometry of xenolith suites and magnetotelluric profiles indicate that the upper mantle is eclogitic to depths of 60 kilometers beneath the western and central parts of the range but little subcrustal lithosphere is present beneath the eastern high sierra and adjacent basin and range these and other data imply the crust of both the high sierra and basin and range thinned by a factor of 2 since 20 million years ago at odds with purported late cenozoic regional uplift of some 2 kilometers

the ultrapotassic rocks from southeastern spain the ultrapotassic rocks of orenditic affinity from southeastern spain have variable sio2 and mgo contents high k2o p2o5 ni cr ba ce th zr values and high k2ona2o nimgo ratios on the contrary tio2 nb y are moderate and feot cao v sc are low the parent magmas possibly generated from a phlogopite bearing mantle source enriched in many incompatible elements by metasomatic processes and probably they were characterized by very co2 co2 h2o ratio the low tip ratio and the moderate tio2 and nb contents in spite of the high alkaline element contents of the magmas suggest that titanium and niobium were retained in the source of the metasomatic fluids the low na contents may depend in part on the loss of this element via naf separation during the latest stage of crystallization crustal contamination cannot be excluded

messinian lago mare deposits near the strait of gibraltar malaga basin s spain a new stratigraphic unit named lm unit located at the base of the pliocene marine succession in the eastern sector of the malaga basin has been distinguished this unit is composed of two fining upward sequences bounded by a discontinuity related to synsedimentary tectonic activity both sequences are made up of basal alluvial deposits overlain by subaquatic deposits the lower sequence contains rich mollusc faunas characterized by bivalves lymnocardiinae and dreissenidae of paratethyan origin and non marine gastropods typical of oligo low mesohaline shallow waters and low diversified ostracod faunas of paratethyan origin loxocorniculina djafarovi tyrrhenocythere pontica euxinocythere maeotocythere praebaquana and amnicythere propinqua typical of low mesohaline waters alternances of monospecific ostracod assemblages made of cyprideis agrigentina or oligotypic assemblages made of c agrigentina and loxoconcha spp and richer assemblages made of l djafarovi accompanied by several amnicythere spp and camptocypria sp 1 characterize the upper sequence pointing to more unstable environment affected by salinity and depth changes some samples collected from this upper sequence yielded rare planktonic and benthic foraminifera which could suggest the sporadic establishment of quasi normal marine conditions in the westernmost mediterranean during the deposition of this sequence the palaeontological data and the palaeomagnetic results obtained in both the lm unit and the overlying pliocene marine sediments restrict the age of the former to the post evaporitic late messinian the age and the environmental conditions correlate these deposits with the lago mare event occurring throughout the mediterranean before the quick and widespread marine flooding of the mediterranean at the beginning of the pliocene

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

three dimensional crustal structure of the southern sierra nevada from seismic fan profiles and gravity modeling traveltime data from the 1993 southern sierra nevada continental dynamics seismic refraction experiment reveal low crustal velocities in the southern sierra nevada and basin and range province of california 6 0 to 6 6 km s as well as low upper mantle velocities 7 6 to 7 8 km s the crust thickens from southeast to northwest along the axis of the sierra nevada from 27 km in the mojave desert to 43 km near fresno california a crustal welt is present beneath the sierra nevada but the deepest moho is found under the western slopes not beneath the highest topography a density model directly derived from the crustal velocity model but with constant mantle density satisfies the pronounced negative bouguer anomaly associated with the sierra nevada but shows large discrepancies of 50 mgal in the great valley and in the basin and range province matching the observed gravity with anomalies in the crust alone is not possible with geologically reasonable densities we require a contribution from the upper mantle either by lateral density variations or by a thinning of the lithosphere under the sierra nevada and the basin and range province such a model is consistent with the interpretation that the uplift of the present sierra nevada is caused and dynamically supported by asthenospheric upwelling or lithospheric thinning under the basin and range province and eastern sierra nevada

post collisional tertiary quaternary mafic alkalic magmatism in the carpathian pannonian region a review mafic alkalic volcanism was widespread in the carpathian pannonian region cpr between 11 and 0 2 ma it followed the miocene continental collision of the alcapa and tisia blocks with the european plate as subduction related calc alkaline magmatism was waning several groups of mafic alkalic rocks from different regions within the cpr have been distinguished on the basis of ages and or trace element compositions their trace element and sr nd pb isotope systematics are consistent with derivation from complex mantle source regions which included both depleted asthenosphere and metasomatized lithosphere the mixing of dmm himu emii mantle components within asthenosphere derived magmas indicates variable contamination of the shallow asthenosphere and or thermal boundary layer of the lithosphere by a himu like component prior to and following the introduction of subduction components various mantle sources have been identified lower lithospheric mantle modified by several ancient asthenospheric enrichments source a young asthenospheric plumes with oib like trace element signatures that are either isotopically enriched source b or variably depleted source c old upper asthenosphere heterogeneously contaminated by dm himuemii emi components and slightly influenced by miocene subduction related enrichment source d old upper asthenosphere heterogeneously contaminated by dm himu emii components and significantly influenced by miocene subduction related enrichment source e melt generation was initiated either by i finger like young asthenospheric plumes rising to and heating up the base of the lithosphere below the alcapa block or ii decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs the tisia block d 2004 published by elsevier b v

tectonomagmatic characteristics of the back arc portion of the calama olacapato el toro fault zone central andes 1 post 20 ma magmatism in the central andes is either localized in the magmatic arc or distributed east of it on the altiplano puna plateau here there is a distinct concentration of magmatic centers on nw se trending lineaments such as the calama olacapato el toro cot that extends into the eastern cordillera to the east of the puna understanding the possible genetic relationship between prominent structures and magmatic centers on these lineaments is important to elucidate the tectonomagmatic evolution of the central andes we investigated the back arc area of the cot using remote sensing geological structural and petrochemical data our study demonstrates that this portion of the cot consists of nw se striking faults formed under overall left lateral transtension that decreases in activity toward the cot termini deformation on the cot occurred during and after activity of prominent n s striking transpressive fault systems and is coeval with magmatism which is focused on the central cot the most evolved magmatic rocks with an upper crustal imprint are exposed on the central cot whereas more primitive mantle derived mafic to moderately evolved magmatic rocks are found toward the cot termini this points to a genetic relationship between upper crustal deformation and magmatic activity that led to enhanced magma storage in the central cot cot magmas may result either from slab steepening or episodic delamination of the asthenospheric mantle

petrogenesis of calc alkaline shoshonitic and associated ultrapotassic oligocene volcanic rocks from the northwestern alps italy along the western alps there is geological evidence of late alpine oligocene magmatic activity which clearly postdates the lepontine eocene early oligocene metamorphism and related deformation of the alpine nappe pile this magmatic activity was notably delayed in relation to the most important convergent processes and may be related to buoyancy of lithosphere tensional tectonics and thermal updoming subsequent to the collision between the eurasian and african plates the geochemical features of the rocks and the geophysical characteristics of the alpine chain suggest that a shoshonitic and calcalkaline melts may have been generated by partial melting of metasomatized peridotitic material and subsequent fractional crystallization and crustal contamination silicic andesites and latites however could have been also derived from metasomatized eclogite or deep continental crust material b the ultrapotassic lamprophyres with high k p lree th zr u and high 87sr 86sr ratios were generated by partial melting of strongly metasomatized mantle the varied sr isotopic ratios may partially also reflect additional radiogenic component from the continental crust following magma segregation from the source

geochemistry and tectonic development of cenozoic magmatism in the carpathian pannonian region this review considers the magmatic processes in the carpathian pannonian region cpr from early miocene to recent times as well as the contemporaneous magmatism at its southern boundary in the dinaride and balkans regions this geodynamic system was controlled by the cretaceous to neogene subduction and collision of africa with eurasia especially by adria that generated the alps to the north the dinaride hellenide belt to the east and caused extrusion collision and inversion tectonics in the cpr this long lived subduction system supplied the mantle lithosphere with various subduction components the cpr contains magmatic rocks of highly diverse compositions calc alkaline k alkalic ultrapotassic and na alkalic all generated in response to complex post collisional tectonic processes these processes formed extensional basins in response to an interplay of compression and extension within two microplates alcapa and tisza dacia competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism mainly as a result of extension and differences in the rheological properties and composition of the lithosphere extension led to disintegration of the microplates that finally developed into two basin systems the pannonian and transylvanian basins the southern border of the cpr is edged by the adria microplate via sava and vardar zones that acted as regional transcurrent tectonic areas during miocene recent times major trace element and isotopic data of post early miocene magmatic rocks from the cpr suggest that subduction components were preserved in the lithospheric mantle after the cretaceous miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere changes in the composition of the mantle through time support geodynamic scenarios of post collision and extension processes linked to the evolution of the main blocks and their boundary relations weak lithospheric blocks i e alcapa and western tisza generated the pannonian basin and the adjacent styrian transdanubian and z rand basins which show high rates of vertical movement accompanied by a range of magmatic compositions strong lithospheric blocks i e dacia were only marginally deformed where strike slip faulting was associated with magmatism and extension at the boundary of adria and tisza dacia strike slip tectonics and core complex extension were associated with small volume miocene magmatism in narrow extensional sedimentary basins or granitoids in core complex detachment systems along older suture zones sava and vardar accommodating the extension in the pannonian basin and afterward pliocene quaternary inversion magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

on the origin of the strait of gibraltar most interpretations of the early pliocene opening of the strait of gibraltar involve a tectonic process however no tectonic structure of this age has been unequivocally documented that could account for such a hypothesis on the other hand the sea level drop of the mediterranean during the messinian salinity crisis has dramatically enhanced continental erosion and in particular regressive fluvial erosion we show that such erosional process inevitably developed in the gibraltar area we finally propose that regressive fluvial erosion was at the origin of the opening of the strait of gibraltar

evidence for deep melting of hydrous metasomatized mantle pliocene high potassium magmas from the sierra nevadas 1 phase equilibrium experiments have been conducted on a primitive pliocene olivine leucitite wc 1 from the central sierra nevada california the near liquidus phase relations were determined from 1 2 to 3 4 gpa and at temperatures from 1350 to 1460 c in a piston cylinder apparatus the composition with 2 h 2 o is multiply saturated with olivine and clinopyroxene at approximately 3 1 gpa and 1460 c and with 6 water in the coexisting melt phlogopite is stable these results indicate that the magma was derived from a hydrous source at greater than 100 km depth xenoliths carried by other young pliocene lavas in the vicinity of wc 1 have yielded temperatures of equilibrium from 700 to 900 c with one outlier at 1060 c these xenoliths are consistent with the hypothesis that the lower lithosphere under the sierra nevada delaminated just prior to the pliocene and fluid metasomatized mantle melted to produce the high potassium pliocene lavas we suggest that subduction derived fluids drive a reaction that consumes garnet orthopyroxene to create clinopyroxene phlogopite and that the high potassium sierran magmas are created by melting phlogopite clinopyroxene metasomatized peridotite

strontium isotopes as tracers of groundwater induced floods the somme case study france major ions trace elements and o h and sr isotopes have been determined for surface water and groundwater in the somme catchment northern france the present study using a coupled hydrological and geochemical stable and sr isotopes approach focuses on the interactions between ground and surface water stable water isotopes 18o 2h show that all waters have a purely local origin from precipitation without significant evaporation or water rock interaction as all points plot close to the general meteoric water line water chemistry in the different catchments shows large variations in major element contents plotting na vs cl contents and mg2 no3 k so42 sr2 concentrations reveals a slight variations in groundwater composition b agricultural input into surface waters and c some similarities between ground and surface waters suggesting the former to be responsible for the chemical signature of the dissolved river load strontium isotope ratios measured in groundwater range from 0 70769 to 0 70808 clearly higher than that of chalk matrix water 0 707337 variations of sr isotope signatures in groundwater from the chalk aquifer are significant and help identifying different groundwater bodies the different signatures in groundwater are better explained by matrix heterogeneity which can present lateral facies variations than by a strong anthropogenic influence the sr isotope compositional range in surface waters is very wide varying from 0 70775 to 0 70816 and defining a trend towards a more radiogenic sr isotope signature with high sr contents and high mg sr ratios the relationship between 87sr 86sr and the mg sr ratios allows different end members to be defined the rivers are influenced by anthropogenic disturbance even during flood periods and river water has geochemical characteristics very similar to those of groundwater indicating a strong influence from groundwater feeding the rivers

potassium rich volcanic rocks of the muriah complex java indonesia products of multiple magma sources abstract the extinct pleistocene volcano muriah situated behind the main pleistocene recent sunda magmatic arc in north central java has erupted at least two contrasted groups of lavas one group forms a well defined compositional series anhydrous series from leucite basanite to tephritic phonolite with olivine and tschermakitic clinopyroxene the main phenocrysts the other group the hydrous series includes compositionally variable tephrites and high k andesites with common plagioclase biotite and amphibole lavas of the anhydrous series are much richer in lil trace elements than the most potassic lavas of neighbouring active volcanoes but relative hfs element enrichment is less pronounced ree patterns have almost constant slopes from la 250 600 times chondrites to yb 5 10 times chondrites while those of lavas of active centres are less light enriched and show flattening in the heavy ree anhydrous series initial 87sr 86sr ratios 0 7043 0 7046 are lower than those of active centres 0 7047 0 7053 hydrous series lavas are intermediate in all these geochemical characteristics the most mafic a series leucite basanite with mg mg fe 2 0 69 140 ppm ni and 620 ppm cr was probably derived from the primary magma for the series by fractionation of only 5 wt olivine its ree pattern suggests derivation from a garnet bearing source experiments on this basanite with up to 10 olivine and 20 orthopyroxene added and in the presence of h2o and h2o co2 mixtures have shown that for all but very high magma water contents the olivine and garnet liquidus fields are widely separated by fields of phlogopite and clinopyroxene there is no liquidus field of orthopyroxene hence if magma production involved an equilibrium melting process alone the most probable sources are of garnet bearing phlogopite clinopyroxenite type alternatively this magma may represent the end product of interaction between a low k basanite magma from a garnet lherzolite source in the asthenosphere and a phlogopite bearing lherzolite zone in the lower lithosphere its production was probably related to crustal doming and extension superimposed on the dominant subduction regime hydrous series magmas may have resulted from mixing between anhydrous series magmas and high k calc alkaline basaltic to andesitic magmas more directly related to subduction processes

improved modelling of the messinian salinity crisis and conceptual implications abstract this paper presents the last developments of a simple oceanographic modelling of the water and salt budgets of the mediterranean sea during the late miocene salinity crisis the messinian mediterranean is treated as analogous to the present one i e divided into two main basins separated by a sill at shallow or intermediate depth when the supply of marine water from the atlantic is progressively reduced both basins undergo a rise in salinity until saturation is reached this is when the true evaporitic sedimentation begins before the level drawdown the partition of the mediterranean into two mains basins causes a shift in the evaporitic sedimentation from the distal eastern basin to the proximal western basin so that the evaporitic deposits are not fully contemporaneous in the western and the eastern basin the drawdown is limited by the equilibrium of the evaporation and chemical activity of the brines at the surface against the surface area and evaporation attempts at adjusting the model both to an accurate stratigraphic frame and to a rough budget of the evaporites shows that the upper evaporites and brackish water lago mare series must have been deposited as secondary deposits after the closure of the atlantic passages was completed the present evaporitic potentialities of the mediterranean sea remains quite as strong as during the miocene so that climatic change cannot be inferred from the msc itself

revisiting the time scale and size of the zanclean flood of the mediterranean 5 33ma from cfd simulations abstract the incision zanclean channel which crosses the strait of gibraltar and the alboran sea has been interpreted as the geological fingerprint of a cataclysmic stream of water which flowed from the atlantic into a desiccated mediterranean about 5 33mabp the mathematical support for this theory is provided by a simple conceptual model for hydrodynamics and erosion that regardless of the initial conditions leads to scenarios of catastrophic flooding with water flows exceeding tens or hundreds of sv which fill 90 of the mediterranean in few months or few years this paper revisits the incision model and carries out new numerical simulations of the zanclean flood of the mediterranean with a two dimensional non linear depth averaged hydrodynamic model the numerical output allows solving the equation for time this way it is possible to estimate the final incision and the involved time scales under different modelled scenarios when lateral erosion is reformulated in terms of the causal processes instead of a questionable scaling law initial conditions become relevant those involving narrow connecting channels can be discarded a flooding scenario with an excavated channel of a few hundred meter depth can be achieved with the initial conditions of a wide sill covered by a water lamina the threshold stress to initialize erosion must be surpassed in the very early stages of the flooding which requires a catastrophic start up tectonics may have played a major role in it through strike slip faulting

early miocene lamproite from the colorado plateau tectonic province southeastern utah usa abstract newly discovered olivine phlogopite lamproite dikes intrude jurassic siliciclastic strata in the green river desert subregion of the western colorado plateau tectonic province in southeastern utah the dikes yield an age of 22 ma both from 40 ar 39 ar step heating of phlogopite and from isochron modeling of laser fused sanidine this age is similar to those of mica rich minettes and melanephelinites of the wasatch plateau about 125 km northwest and within the age range of the navajo potassic volcanic field about 150 km to the southeast the dikes intruded a pre existing northwest oriented fracture system containing previously introduced bitumen indicating that some regional lineaments of this trend are early miocene or older the dikes are highly lree enriched and display lamproite specific ree ratios and phlogopite and sanidine compositions incompatible element and radiogenic isotope nd sr pb ratios suggest that lithospheric source material modified by ancient subduction processes together with younger asthenospheric source components produced the melt timing of the intrusion coincides with the transition from early middle cenozoic calc alkaline plutonism to the dominantly mafic basin and range type volcanism of the late cenozoic while the lamproite occurrence indicates thermal input from the mantle model non uniqueness for both magma source depths and geophysical structure prevents quantitative comparison of early miocene with present day lithospheric thickness

sr and o isotope constraints on source and crustal contamination in the high k calc alkaline and shoshonitic neogene volcanic rocks of se spain the neogene volcanic province of se spain nvps is characterized by calc alkaline ca high k calc alkaline kca shoshonitic sh ultrapotassic up and alkaline basaltic ab volcanic series all these series except the ab have high lilerlree lilerhfse and brbe ratios and high but variable sr pb and o isotope compositions the kca and sh lavas contain metapelitic xenoliths whose mineralogical and chemical composition are typical of anatectic restites the geochemical characteristics of ca kca sh and up series suggest that they originated from the lithospheric mantle previously contaminated by fluids derived from pelagic sediments additionally the presence of restite xenoliths in the kca and sh lavas indicates some sort of interaction between the mantle derived magmas and the continental crust trace element and isotope modeling for the kca and sh lavas and the restites point towards the existence of two mixing stages during the first stage the lithospheric mantle was contaminated by 1 5 of fluids derived from pelagic sediments which produced

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

rayleigh wave phase velocities small scale convection and azimuthal anisotropy beneath southern california 1 we use rayleigh waves to invert for shear velocities in the upper mantle beneath southern california a one dimensional shear velocity model reveals a pronounced low velocity zone lvz from 90 to 210 km the pattern of velocity anomalies indicates that there is active small scale convection in the asthenosphere and that the dominant form of convection is three dimensional 3 d lithospheric drips and asthenospheric upwellings rather than 2 d sheets or slabs several of the features that we observe have been previously detected by body wave tomography these anomalies have been interpreted as delaminated lithosphere and consequent upwelling of the asthenosphere beneath the eastern edge of the southern sierra nevada and walker lane region sinking lithosphere beneath the southern central valley upwelling beneath the salton trough and downwelling beneath the transverse ranges our new observations provide better constraints on the lateral and vertical extent of these anomalies in addition we detect two previously undetected features a high velocity anomaly beneath the northern peninsular range and a low velocity anomaly beneath the northeastern mojave block we also estimate the azimuthal anisotropy from rayleigh wave data the strength is 1 7 at periods shorter than 100 s and decreases to below 1 at longer periods the fast direction is nearly e w the anisotropic layer is more than 300 km thick the e w fast directions in the lithosphere and sublithosphere mantle may be caused by distinct deformation mechanisms pure shear in the lithosphere due to n s tectonic shortening and simple shear in sublithosphere mantle due to mantle flow

minette lavas and associated leucitites from the western front of the mexican volcanic belt petrology chemistry and origin during the late pliocene k rich minette and leucitite lavas erupted in the western mexican volcanic belt near the town of los volcanes a region which is located much closer to the middle america trench than the main line of currently active andesite stratovolcanoes during this period the tectonic regime in western mexico was highly complex due to the simultaneous occurrence of active subduction of the young rivera plate and rifting caused by crustal extension most of these basic lavas contain phenocrysts of phlogopite augite and apatite along with microphenocrysts of leucite and fe ti oxide olivine is absent from all but two of the flows one an olivine leucitite and the other a felsic minette the phlogopite phenocrysts and high whole rock fe2o3 feo ratios which are characteristic of this suite record evidence of high magmatic water contents and oxygen fugacities all of these rock types are highly enriched in the large ion lithophile and light rare earth elements with sr 5100 ppm ba 4800 ppm and ce 330 ppm they are also mildly enriched in the high field strength elements e g zr 260 700 ppm and display the strong relative enrichment of the lile over the hfse that is characteristic of magmas erupted in convergent margins consideration of high pressure phase equilibria in the mg2sio4 camgsi2o6 kalsio4 sio2 system shows that the minettes from this region are not related through fractional crystallization to the more mgo rich olivinebearing minettes which have erupted in other parts of the western mexican volcanic belt during the quaternary this conclusion is consistent with both the trace element geochemistry of these lavas and with the results of fractional crystallization models instead the data suggests that these high k magmas were derived from a source region which consists predominantly of phlogopite clinopyroxene and apatite and which has formed through hydrous enrichment of the subarc mantle in response to subduction

computational fluid dynamics simulations of the zanclean catastrophic flood of the mediterranean 5 33 ma abstract numerical simulations of the mediterranean sea filling after the messinian salinity crisis have been carried out with a two dimensional non linear depth averaged hydrodynamic model it overcomes simplifications and gross estimates of previous 0 d models erosion of the seabed has been implemented in the model domain the highest erosion rates were found in the alboran island passage and in the eastern side of the strait of gibraltar regressive erosion at a final stage can account for the incision channel found in camarinal sill this last limits the inflow to some 90 sv when the cross section in the eastern side becomes higher water level in the mediterranean increases at a rate of a few meters per day detailed views of the induced circulation in the mediterranean sea have also been obtained

assessing the water balance of the upper rhine graben hydrosystem the upper rhine alluvial aquifer is an important transboundary water resource however as in many alluvial systems the aquifer inflows and outflows are not precisely known because of the difficulty of estimating the river infiltration flux and the boundary subsurface flow to provide a thorough representation of the aquifer system a coupled surface subsurface model was applied to the whole aquifer basin and several parameter sets were tested to investigate the uncertainty due to poorly known parameters e g aquifer transmissivity computed by an inverse model river bed characteristics twelve simulations were run and analyzed using standard statistical criteria and also a more advanced statistical method the karhunen loeve transform klt this analysis showed that although the model performed reasonably well some piezometric level underestimations persisted in the south of the basin an accurate representation of the aquifer behaviour would require river infiltration and the functioning of irrigation canals in the hardt area to be taken into account it also appeared that increasing the maximum river infiltration flow deteriorated the quality of the results river infiltration to the aquifer was estimated to represent about 80 of the aquifer inflows with a mean annual value around 115 16 5 m3 s thus with an uncertainty of 14 this quantity is larger than estimated in previous studies but is in agreement with some results obtained during low water periods this important conclusion highlights the vulnerability of the upper rhine graben aquifer to pollution from the rivers and to climate change since it is highly probable that the rivers regimes will be affected by reduced snow cover on the neighbouring mountain ranges

limestone assimilation and the origin of co2 emissions at the alban hills central italy constraints from experimental petrology abstract the alban hills volcanic region 20 km south of rome in the roman province emitted a large volume of potassic magmas 280 km 3 during the quaternary chemical interactions between ascending magmas and the 7000 8000 m thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys in this paper we characterize the effect of carbonate assimilation on phase relationships at 200 mpa and 1150 1050 c by experimental petrology calcite and dolomite addition promotes the crystallization of ca rich pyroxene and mg rich olivine respectively and addition of both carbonates results in the desilication of the melt furthermore carbonate assimilation liberates a large quantity of co 2 rich fluid a comparison of experimental versus natural mineral glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different alban hills eruptions a maximum of 15 wt assimilation is suggested by some melt inclusion and clinopyroxene compositions however most of the natural data indicate assimilation of between 3 and 12 wt carbonate current high co 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth we calculate that a magma intruding into the carbonate basement with a rate of 1 2 10 6 m 3 year estimated by geophysical studies and assimilating 3 12 wt of host rocks would release an amount of co 2 matching the current yearly emissions at the alban hills our results strongly suggest that current co 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate hosted reservoir at 5 6 km depth with important consequences for the present day volcanic hazard evaluation in this densely populated and historical area

application of the coupled model to the somme river basin summary hydrological modeling of the somme river basin situated in the north of france was made with special emphasis on the stream aquifer interaction due to immense groundwater storage in the chalk aquifer a damaging flood took place in the basin in spring 2001 to best represent the phenomena occurring in the basin the coupled model also known as modcou was selected to be applied to this particular basin the whole model structure consists of several components namely surface model groundwater model unsaturated zone model and the coupled model in order to run the surface model meteorological forcing land use and soil type data were acquired by using land use and soil type data production zones were obtained the surface model partitions the precipitation between surface runoff infiltration and actual evapotranspiration according to the parameters of production zones the unsaturated zone model computes the recharge of groundwater by using infiltration from the surface using a nash cascade model by using the groundwater model a steady state piezometric head distribution is obtained to serve as an initial condition to the coupled model the unsteady groundwater and surface flow simulations are carried out by the coupled model initially spatial information on the basin was extracted by using digital elevation model dem analysis after acquiring the necessary spatial data the surface and aquifer grids were generated by using nested grid generators which make refinement on the stream network and subcatchment boundaries in order to increase the accuracy of numerical solution a very detailed calibration was performed by following a step by step procedure in which the best fit in flow and piezometric head hydrographs was sought in the surface model concentration time and parameters of production zones are calibrated for coupled surface groundwater flows transmissivity specific yield and discharge coefficient and for flow in unsaturated zone storage constant were calibrated during the simulations intense and interrupted exfiltrations were observed over the basin two algorithms were developed in order to correct the issue caused by the coarse resolution of the dem 1 a fill algorithm was used to remove the sinks and obtain a smoother surface and 2 a correction procedure for river cell elevations is proposed to acquire continuous exfiltration along the stream network validation of the model was made using the discharges at two points on the somme namely hangest sur somme and peronne which had not been used in any stage of the modeling process and satisfactory results were obtained the groundwater behavior its effect on the surface flow and the flood of 2001 are satisfactorily represented

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

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

catastrophic flood of the mediterranean after the messinian salinity crisis around 5 6 million years ago the mediterranean sea became disconnected from the world s oceans and during the period that followed known as the messinian salinity crisis sea levels fell dramatically as the waters evaporated the water returned about 5 3 million years ago but the details about this the largest known flood in earth s history remain sketchy a study making use of boreholes seismic data and numerical modelling suggests that it was a catastrophic event though it started as a trickle that may have lasted several thousand years as much as 90 of the incoming water was transferred in less than two years such an abrupt flood may have involved peak rates of sea level rise of more than 10 metres a day 5 33 million years ago in an event known as the zanclean flood atlantic waters refilled a mostly desiccated mediterranean sea which had become disconnected from the world s oceans however the nature abruptness and evolution of this flood remain poorly constrained using borehole and seismic data and a model study it is now suggested that 90 per cent of the water was transferred in a short period of a few months to two years with peak rates of sea level rise in the mediterranean possibly reaching more than 10 metres per day the mediterranean sea became disconnected from the world s oceans and mostly desiccated by evaporation about 5 6 million years ago during the messinian salinity crisis1 2 3 the atlantic waters found a way through the present gibraltar strait and rapidly refilled the mediterranean 5 33 million years ago in an event known as the zanclean flood4 the nature abruptness and evolution of this flood remain poorly constrained4 5 6 borehole and seismic data show incisions over 250 m deep on both sides of the gibraltar strait that have previously been attributed to fluvial erosion during the desiccation4 7 here we show the continuity of this 200 km long channel across the strait and explain its morphology as the result of erosion by the flooding waters adopting an incision model validated in mountain rivers this model in turn allows us to estimate the duration of the flood although the available data are limited our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 108 m3 s 1 three orders of magnitude larger than the present amazon river and incision rates above 0 4 m per day although the flood started at low water discharges that may have lasted for up to several thousand years our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years this extremely abrupt flood may have involved peak rates of sea level rise in the mediterranean of more than ten metres per day

an absarokite from a phlogopite lherzolite source an absarokite sio2 47 72 wt k2o 3 41 wt occurs in the katamata volcano sw japan the rock carries phenocrysts of olivine phlogopite clinopyroxene and hornblende chemical compositions of bulk rock feo mgo 0 73 and minerals mg rich olivine and phlogopite cr rich chromite suggest that the absarokite is not differentiated melting experiments at high pressures on the katamata absarokite have been conducted the completely anhydrous absarokite melt coexists with olivine orthopyroxene and clinopyroxene at 1310 c and 1 0 gpa the melt with 3 29 wt of h2o also coexists with the above three phases at 1230 c and 1 4 gpa phlogopite appears at temperatures more than 80 c below the liquidus on the other hand the melt is not saturated with lherzolite minerals in the presence of 5 13 wt of h2o and crystallizes olivine and phlogopite as liquidus phases the stability limit of phlogopite is little affected at least by the present variation of h2o content in the absarokite melt it is suggested that the absarokite magma was segregated from the upper mantle at 1170 c and 1 7 gpa leaving a phlogopite lherzolite as a residual material on the basis of the above experimental results and the petrographical observation that olivine and phlogopite crystallize at an earlier stage of crystallization sequence than clinopyroxene the contribution of phlogopite at the stage of melting processes is also suggested by the geochemical characteristics that the absarokite is more enriched in rb k and ba and depleted in ca and na than a typical alkali olivine basalt from the same volcanic field

messinian salinity crisis regulated by competing tectonics and erosion at the gibraltar arc the persistent shallow connection between the atlantic ocean and the mediterranean sea that caused the messinian salinity crisis may have been sustained by a balance between tectonic uplift and erosion due to inflow about six million years ago a series of geological factors drastically reduced the exchange of water between the atlantic ocean to the mediterranean sea through what is now the strait of gibraltar the resulting widespread salt precipitation in the mediterranean linked to a decrease in sea level of about 1 5 kilometres due to evaporation is known as the messinian salinity crisis the exact mechanism that caused the crisis remains uncertain here daniel garcia castellanos and antonio villasenor propose a competition between the obstruction of the gibraltar arc seaway by tectonic uplift and its erosional deepening by water inflow controlled by the resulting changes in sea level difference across the gibraltar arc as a possible mechanism for the crisis the messinian salinity crisis1 2 5 96 to 5 33 million years ago was caused by reduced water inflow from the atlantic ocean to the mediterranean sea resulting in widespread salt precipitation and a decrease in mediterranean sea level of about 1 5 kilometres due to evaporation3 the reduced connectivity between the atlantic and the mediterranean at the time of the salinity crisis is thought to have resulted from tectonic uplift of the gibraltar arc seaway and global sea level changes both of which control the inflow of water required to compensate for the hydrological deficit of the mediterranean1 4 however the different timescales on which tectonic uplift and changes in sea level occur are difficult to reconcile with the long duration of the shallow connection between the mediterranean and the atlantic5 needed to explain the large amount of salt precipitated here we use numerical modelling to show that seaway erosion caused by the atlantic inflow could sustain such a shallow connection between the atlantic and the mediterranean by counteracting tectonic uplift the erosion and uplift rates required are consistent with previous mountain erosion studies with the present altitude of marine sediments in the gibraltar arc6 7 and with geodynamic models suggesting a lithospheric slab tear underneath the region8 9 10 the moderate mediterranean sea level drawdown during the early stages of the messinian salinity crisis3 5 can be explained by an uplift of a few millimetres per year counteracted by similar rates of erosion due to atlantic inflow our findings suggest that the competition between uplift and erosion can result in harmonic coupling between erosion and the mediterranean sea level providing an alternative mechanism for the cyclicity observed in early salt precipitation deposits and calling into question previous ideas regarding the timing of the events that occurred during the messinian salinity crisis1

the messinian guadalhorce corridor the last northern atlantic mediterranean gateway miocene tectonics with the last survi ving gateway occurring during the early messinian north west of malaga in the region of the guadalhorce river valley the guadalhorce gateway pro vided a significant control on messin ian pre evaporitic oceanic circulation in the mediterranean sea it acted as a major outflow channel of mediterra nean water into the atlantic and its closure induced water mass restriction and stratification in the western medi terranean immediately prior to the messinian salinity crisis abstract messinian marine deposits of the guadalhorce river valley in southern spain record evidence of the last northern gateway that existed between the mediterranean and the atlantic they comprise sandstones and conglomerates with unidirectional cross bed sets up to nearly 1 km long in their down sedimen tary dip direction these cross bed sets relate to extremely fast 1 0 1 5 m s 1 bottom currents flowing from the mediterra nean into the atlantic the guadalhorce gateway which had a maximum width of 5 km and a maximum water depth of 120 m was an important element controlling the messinian pre evaporitic oceanic circulation in the mediterranean sea as it acted as a major outflow channel its closure limited the exchange of water between the atlantic and the mediterranean to the rifian corridors of morocco inducing water mass restriction and stratification in the western mediterranean immediately prior to the messinian salinity crisis

tectonic significance of changes in post subduction pliocene quaternary magmatism in the south east part of the carpathian pannonian region the south eastern part of the carpathian pannonian region records the cessation of convergence between the european platform moesia and the tisza dacia microplate plio quaternary magmatic activity in this area in close proximity to the vrancea zone shows a shift from normal calc alkaline to much more diverse compositions adakite like calc alkaline k alkalic mafic na alkalic and ultrapotassic suggesting a significant change in geodynamic processes at approximately 3 ma we review the tectonic setting timing petrology and geochemistry of the post collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration the calc alkaline volcanism 5 3 3 9 ma marks the end of normal subduction related magmatism along the post collisional c limani gurghiu harghita volcanic chain in front of the european convergent plate margin at ca 3 ma in south harghita magma compositions changed to adakite like calc alkaline and continued until recent times 0 03 ma interrupted at 1 6 1 2 ma by generation of na and k alkalic magmas signifying changes in the source and melting mechanism we attribute the changes in magma composition in front of the moesian platform to two main geodynamic events 1 slab pull and steepening with opening of a tear window adakite like calc alkaline magmas and 2 renewed contraction associated with deep mantle processes such as slab steepening during post collisional times na and k alkalic magmas contemporaneous post collisional volcanism at the eastern edge of the pannonian basin at 2 6 1 3 ma was dominated by na alkalic and ultrapotassic magmas suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the adriatic indentation similar timing magma chamber processes and volume for k alkalic shoshonitic magmas in the south apuseni mountains 1 6 ma and south harghita area at a distance of ca 200 km imply a regional connection with the inversion tectonics

a quantitative analysis of the desiccation and re filling of the mediterranean during the messinian salinity crisis abstract notwithstanding the great deal of attention that the messinian evaporites of the mediterranean region have received from an observational point of view there is to date no consensus as to their mechanism of formation we aim to contribute to the investigation through a quantitative analysis of the processes of desiccation and re filling these processes are thought to have played a role in particular during the deposition of the upper part of the evaporite sequence we calculate the evolution of sea level and average salinity based on both the present day geometry and a paleogeographic reconstruction and assess the sensitivity to variations in the freshwater budget our results support previous inferences that desiccation and re filling are fast desiccation occurs on a time scale of 3 8 kyr re filling probably even faster equilibrium sea levels imply that most water has gone from the western basin while a significant water column remains in the eastern basin whether or not the eastern basin reaches the level of halite saturation depends critically on in particular the freshwater budget the fast rate of desiccation and re filling imply that temporal differences in the onset of salt precipitation between western and eastern basin and between marginal basins and basin centres are below the resolution of astronomical dating also when atlantic sea level periodically varied from below to above the level of the intervening sill the mediterranean basin will have responded with repeated desiccation and re filling fast re filling is found to require only a small connection to the atlantic ocean this in combination with the previous results suggests the mediterranean is unlikely to attain stable intermediate water levels

how did the messinian salinity crisis end the cause of the desiccation of the mediterranean sea during the messinian salinity crisis has been widely debated but its re flooding remains poorly investigated interpretations generally involve tectonic collapse of the strait of gibraltar or global sea level rise or even a combination of both the dramatic sea level fall in the mediterranean has induced deep fluvial incision all around the desiccated basin we investigate erosion dynamics related to this base level drop by using the numerical simulator eros we show that intense regressive erosion develops inevitably in the gibraltar area eventually inducing the piracy of the atlantic waters by an eastward flowing stream and the subsequent re flooding of the mediterranean

fully conservative coupling of hec ras with modflow to simulate stream aquifer interactions in a drainage basin this work describes the application of a methodology designed to improve the representation of water surface profiles along open drain channels within the framework of regional groundwater modelling the proposed methodology employs an iterative procedure that combines two public domain computational codes modflow and hec ras in spite of its known versatility modflow contains several limitations to reproduce elevation profiles of the free surface along open drain channels the drain module available within modflow simulates groundwater flow to open drain channels as a linear function of the difference between the hydraulic head in the aquifer and the hydraulic head in the drain where it considers a static representation of water surface profiles along drains the proposed methodology developed herein uses hec ras a one dimensional 1d computer code for open surface water calculations to iteratively estimate hydraulic profiles along drain channels in order to improve the aquifer drain interaction process the approach is first validated with a simple closed analytical solution where it is shown that a piccard iteration is enough to produce a numerically convergent and mass preserving solution the methodology is then applied to the groundwater surface water system of the choele choel island in the patagonian region of argentina smooth and realistic hydraulic profiles along drains are obtained while backwater effects are clearly represented

phase equilibria of phlogopite lamprophyres from western mexico biotite liquid equilibria and p t estimates for biotite bearing igneous rocks olivine and augite minette powders have been equilibrated from one bar to nearly 2 0 kbar water saturated and from 900 to 1300 c and then quenched rapidly at oxygen fugacities controlled between the nickel nickel oxide nno and hematite magnetite hm oxygen buffers the liquidus of both samples is suppressed 100 c at water saturated conditions and 1500 bar both lavas contained between 3 and 4 wt water at the stage of phenocryst precipitation the partitioning of ferric and ferrous iron between phlogopite and liquid has been determined on eight samples across 3 log f o2 units when these determinations are combined with previous studies fe2o3 feo total of mg rich biotite can be calculated knowing log fo2 t and xfe thermodynamic modelling of biotite liquid equilibria results in two expressions for calculating activity coefficients for annite and phlogopite in natural biotites based on the partitioning of bao and tio2 between biotite and liquid we have formulated a thermometer and barometer over the range of 400 c tio2 partitioning between phlogopite and liquid is a function of temperature 50 c and is insensitive to pressure and h2o and o2 activities bao partitioning between phlogopite and liquid is a function of both temperature and pressure 4 kbar the latter being most important applying the tio2 and bao partitioning expressions to lamprophyre and lamproite suites shows that mexican minettes equilibrated at low pressures 5 to 15 kbar 4 kbar and temperatures 1090 to 1160 c 50 c while australian lamproites equilibrated at higher p up to 30 kbar 4 kbar and t 1125 to 1400 c 50 c experimental glass compositions and phenocryst fractionation calculations together with the bao and tio2 based pressure calculations indicate that felsic minettes from the mexican suite of lavas can be generated by simple fractionation of a more mafic parent minette at mid to lower crustal pressures

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

lago mare and the messinian salinity crisis evidence from the alboran sea s spain this paper provides a new environmental sedimentological and stratigraphic context of the lago mare deposits from the north alboran region and clarifies their chronologic location with respect to the messinian salinity crisis we present new micropaleontological data dinoflagellate cysts calcareous nannoplankton planktonic foraminifers correlated with field observations and offshore seismic interpretations we show that the lago mare event known in three onshore localities rio mendelin near malaga zorreras near sorbas gafares near nijar follows the marine reflooding of the mediterranean basin which ended the messinian salinity crisis chronologically these lago mare deposits last from the latest messinian to the early zanclean in fact the first influx of paratethyan organisms is revealed by the dinoflagellate cyst record from near malaga within a gilbert type fan delta overlying the messinian erosional surface invading molluscs and or ostracods may have persisted in lagoonal coastal areas more or less affected by discontinuous marine influxes sorbas and nijar the malaga area is convenient for a paleogeographic and sedimentary reconstruction which shows the prevalent forcing of sea level changes during the time interval 5 600 5 332 ma at the difference of the usually solicited prevalent tectonics the studied lago mare event is the third episode resulting in such a paleobiological assemblage in the mediterranean region and corresponds to the final two way water exchange at high sea level between the mediterranean and the former paratethys it documents the onset of the modern marine circulation in the mediterranean after the reflooding ending the messinian salinity crisis

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

the role of fluorine and oxygen fugacity in the genesis of the ultrapotassic rocks the effects of h2o co2 ch4 and hf on partial melting of a model phlogopite harzburgite mantle are considered with regard to the production of ultrapotassic magmas fluorine has a polymerising effect in h2o poor conditions but in the presence of abundant h2o where hf rather than f is dominant the overall effect is depolymerisation methane also dissolves by forming oh groups and so has a depolymerising effect group i ultrapotassic rocks lamproites probably originate from primary magmas with sio2 contents ranging from around 40 wt to at least 52 wt this range can be explained by differing depths of origin from a similar source with a similar reduced h2o ch4 hf volatile mixture the formation of silica rich initial melts from a model phlogopite harzburgite is assisted by the presence of ch4 and hf dissociation of less than 0 1 wt h2o driven by h2 loss is sufficient to cause oxidation during emplacement to observed oxidation states silica poor ultrapotassic rocks could be produced at higher pressures in a reduced environment or in an oxidised environment with high co2 co2 h2o ratios

mantle heterogeneity beneath eastern california from magnetotelluric measurements 1 a 300 km long magnetotelluric profile across the great valley sierra nevada and california basin and range reveals minimum resistivity differences of 1 order of magnitude at depths from moho at 30 35 km to depths greater than 200 km horizontal wavelengths of 25 km are seen for these changes at depths shallower than 100 km and the isabella high seismic wave speed anomaly is present in the section between depths of 100 and 200 km as a minimum tenfold resistivity increase a transformation from electrical resistivity to temperature and melt fraction using a petrological model and laboratory measurements reveals that partial melt is relatively uncommon and confined primarily to depths between 30 and 100 km the remainder of the observed resistivity variation is attributed to lateral variations in temperature predicted melt fractions match those inferred from miocene quaternary xenoliths but modeled temperatures are 200 c higher than inferred from thermobarometric analyses of the xenoliths possible causes for this discrepancy include an incorrect starting material for the petrological model exotic conductive phases higher conductivity due to oxidation state and or iron content and diffusion of ions through the solid matrix i show that hydrogen diffusion or higher oxygen concentrations are plausible explanation for the higher model temperatures less than 200 ppm h 106 si in olivine would increase the conductivity of the matrix sufficiently to allow temperatures inferred from the resistivity section to match those from the xenoliths a possible source of the hydrogen would be fragments of sinking metasomatized mantle lithosphere that melted during cenozoic delamination

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

alpine polyphase tectono metamorphic evolution of the south carpathians a new overview abstract the main terrains involved in the cretaceous tertiary tectonism in the south carpathians segment of the european alpine orogen are the getic supragetic and danubian continental crust fragments separated by the severin oceanic crust floored basin during the early middle cretaceous times the danubian microplate acted initially as a foreland unit strongly involved in the south carpathians nappe stacking multistage folding thrusting events uplift erosion and extensional stages and the development of associated sedimentary basins characterize the south carpathians during cretaceous to tertiary convergence and collision events the main cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the south carpathians are mid cretaceous austrian phase and latest cretaceous laramide or getic phase in age the architecture of the south carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom the getic supragetic basement cover nappes the severin and arjana cover nappes and danubian basement cover nappes all tectonically overriding the moesian platform the severin nappe complex including obarsia and severin nappes with late jurassic early cretaceous ophiolites and turbidites is squeezed between the danubian and getic supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred mid to late cretaceous subduction collision followed by tectonic inversion processes early cretaceous thick skinned tectonics was replaced by thin skinned tectonics in late cretaceous thus the former middle cretaceous austrian nappe stack and its albian lower senonian cover got incorporated in the intra senonian laramide getic stacking of the getic supragetic severin arjana nappes onto the danubian nappe duplex the two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the banatitic magmas 84 73 ma the overthrusting of the entire south carpathian cretaceous nappe stack onto the fold thrust foredeep units and to the moesian platform took place in the late miocene intra sarmatian times and was followed by extensional events and sedimentary basin formation

the zanclean megaflood of the mediterranean searching for independent evidence abstract about six million years ago the mediterranean sea underwent a period of isolation from the ocean and widespread salt deposition known as the messinian salinity crisis msc allegedly leading to a kilometer scale level drawdown by evaporation one of the competing scenarios proposed for the termination of this environmental crisis 5 3 million years ago consists of a megaflooding event refilling the mediterranean sea through the strait of gibraltar the zanclean flood the main evidence supporting this hypothesis is a nearly 390 km long and several hundred meters deep erosion channel extending from the gulf of cadiz atlantic ocean to the algerian basin western mediterranean implying the excavation of ca 1000 km3 of miocene sediment and bedrock based on the understanding obtained from pleistocene onshore megaflooding events and using ad hoc hydrodynamic modeling here we explore two predictions of the zanclean outburst flood hypothesis 1 the formation of similar erosion features at sills communicating sub basins within the mediterranean sea specifically at the sicily sill and 2 the accumulation of the eroded materials as megaflood deposits in areas of low flow energy recent data show a 6 km wide amphitheater shaped canyon preserved at the malta escarpment that may represent the erosional expression of the zanclean flood after filling the western mediterranean and spilling into the eastern basin next to that canyon a 1600 km3 accumulation of chaotic seismically transparent sediment has been found in the ionian sea compatible in age and facies with megaflood deposits another candidate megaflood deposit has been identified in the alboran sea in the form of elongated sedimentary bodies that parallel the flooding channel and are seismically characterized by chaotic and discontinuous stratified reflections that we interpret as equivalent to gravel and boulder megabars described in terrestrial megaflood settings numerical model predictions show that sand deposits found at the miocene pliocene m p boundary in odp sites 974 and 975 south balearic and tyrrhenian seas are consistent with suspension transport from the strait of gibraltar during a flooding event at a peak water discharge of 108 m3 s 1

the miocene pliocene boundary and the messinian salinity crisis in the easternmost mediterranean insights from the hatay graben southern turkey accepted manuscript version published version at http dx doi org 10 1016 j sedgeo 2015 11 012 license in accordance with the journal s policy cc by nc nd

effects of digital elevation model resolution on derived stream network positions 1 this study examines the effect of digital elevation model dem resolution on the positional accuracy of derived hydrologic networks and quantitatively confirms that dem resolution should be greater than the average hillslope length when used for hydrologic modeling seven hundred kilometers of mapped stream networks are compared to stream networks derived from 17 dems with resolutions ranging from 30 m to 3 km comparison between predicted and mapped streams reveals that accuracy of predicted stream locations decays quickly beyond a dem resolution of 180 m a new application of gyasi agyei et al s 1995 dem resolution suitability test based on average slope and vertical resolution indicates an average hillslope length of between 150 and 180 m tarboton et al s 1991 method of determining average hillslope length based on slope and accumulation areas reconfirms the length to be 150 m and verifies the link between network accuracy and hillslope scale two algorithms are used to derive stream networks the d algorithm tarboton 1997 which allows for flow dispersion and the d8 algorithm o callaghan and mark 1984 which does not a comparison between the d8 and d algorithms shows that modeling flow dispersion is not necessary in steep terrain as both algorithms performed equally well however the d algorithm is found to be less susceptible to modeling erroneous hillside flow convergence making it preferable to the d8 algorithm when used by tarboton et al s 1991 method of determining the average hillslope lengths finally field observation indicates that predicted first and second order streams tend to exist when predicted however mapped streams have a higher positional accuracy

a modelling study on tsunami propagation in the caspian sea a numerical model that simulates the propagation of tsunamis produced by submarine earthquakes was applied to the caspian sea the model was first applied to the june 1990 rudbar earthquake and our results proved to be coherent with previous simulations it was also applied to the krasnovodsk earthquake 1895 which had not been simulated before and it was found that the coastal area was flooded by a tsunami as reported in literature nevertheless it was a rather local effect since the tsunami was generated in very shallow waters some worst case hypothetical earthquakes were simulated in the most seismically active regions of the caspian in general both the east and west coasts of the central caspian sea would be the most affected by these earthquake induced tsunamis with potential significant effects in some cases in cities such as baku

petrogenesis of isotopically unusual pliocene olivine leucitites from deep springs valley california high k mafic alkalic lavas 5 4 to 3 2 wt k2o from deep springs valley california define good correlations of increasing incompatible element e g sr zr ba lree and compatible element contents e g ni cr with increasing mgo strontium and nd isotope compositions are also correlated with mgo 87sr 86sr ratios decrease and nd values increase with decreasing mgo the sr and nd isotope compositions of these lavas are extreme compared to most other continental and oceanic rocks 87sr 86sr ratios range from 0 7121 to 0 7105 and nd values range from 16 9 to 15 4 lead isotope ratios are relatively constant 206pb 204pb 17 2 207pb 204pb 15 5 and 208pb 204pb 38 6 depleted mantle model ages calculated using sr and nd isotopes imply that the reservoir these lavas were derived from has been distinct from the depleted mantle reservoir since the early proterozoic the sr nd pb isotope variations of the deep springs valley lavas are unique because they do not plot along either the em i or em ii arrays for example most basalts that have low nd values and unradiogenic 206pb 204pb ratios have relatively low 87sr 86sr ratios the em i array whereas basalts with low nd values and high 87sr 86sr ratios have radiogenic 206pb 204pb ratios the em ii array high k lavas from deep springs valley have em ii like sr and nd isotope compositions but em i like pb isotope compositions a simple method for producing the range of isotopic and major and trace element variations in the deep springs valley lavas is by two component mixing between this unusual k rich mantle source and a more typical depleted mantle basalt we favor passage of morb like magmas that partially fused and were contaminated by potassic magmas derived from melting high k mantle veins that were stored in the lithospheric mantle the origin of the anomalously high 87sr 86sr and 208pb 204pb ratios and low nd values and 206pb 204pb ratios requires addition of an old component with high rb sr and th pb ratios but low sm nd and u pb ratios into the mantle source region from which these basalts were derived this old component may be sediments that were introduced into the mantle either during proterozoic subduction or by foundering of proterozoic age crust into the mantle at some time prior to eruption of the lavas

a high pressure experimental study on a magnesian rich leucite lamproite from the west kimberley area australia petrogenetic implications liquidus and subliquidus phase relations of a leucite lamproite wolgidite from the west kimberley area australia have been studied experimentally under the volatile conditions of 3 22 wt h2o x co 2 0 11 and 13 0 wt h2o x co 2 0 03 between 10 to 40 kbar under these conditions liquids are vapour undersaturated in experiments with 13 0 wt h2o olivine is the liquidus phase up to 24 kbar and orthopyroxene above 24 kbar phlogopite and rutile occur close to the liquidus above 16 kbar crystallization temperatures of clinopyroxenes are 50 120 c below the liquidus

experimental constraints on ultrapotassic magmatism from the bohemian massif durbachite series czech republic the equilibrium phase relations of a mafic durbachite 53 wt sio2 from the t ebic pluton representative of the variscan ultrapotassic magmatism of the bohemian massif 338 335 ma have been determined as a function of temperature 900 1 100 c pressure 100 200 mpa and h2o activity 1 1 6 1 wt h2o in the melt two oxygen fugacity ranges were investigated close to the ni nio nno buffer and 2 6 log unit above nno buffer nno 2 6 at 1 100 c olivine is the liquidus phase and co crystallized with phlogopite and augite at 1 000 c for the whole range of investigated pressure and water content in the melt at 900 c the mineral assemblage consists of augite and phlogopite whereas olivine is not stable the stability field of both alkali feldspar and plagioclase is restricted to low pressure 100 mpa at nearly water saturated conditions 3 4 wt h2o and t 900 c a comparison between experimental products and natural minerals indicates that mafic durbachites have a near liquidus assemblage of olivine augite ti rich phlogopite apatite and zircon followed by alkali feldspar and plagioclase similar to the mineral assemblage of minette magma natural amphibole diopside and orthopyroxene were not reproduced experimentally and probably result from sub solidus reactions whereas biotite re equilibrated at low temperature the crystallization sequence olivine followed by phlogopite and augite reproduces the sequence inferred in many mica lamprophyre rocks the similar fractionation trends observed for durbachites and minettes indicate that mafic durbachites are probably the plutonic equivalents of minettes and that k and mg rich magmas in the bohemian massif may have been generated from partial melting of a phlogopite clinopyroxene bearing metasomatized peridotite experimental melt compositions also suggest that felsic durbachites can be generated by simple fractionation of a more mafic parent and mixing with mantle derived components at mid crustal pressures

phase relations in the phlogopite apatite system at 20 kbar implications for the role of fluorine in mantle melting phase relations have been determined at 20 kb in the simple fe ti free systems hydroxyphlogopite hydroxyapatite and hydroxyfluorphlogopite hydroxyfluorapatite in order to determine distribution of fluorine between phlogopite apatite and melt under mantle conditions no excess h2o was present in the hydroxyphlogopite hydroxyapatite system and the f oh ratio was unity in the f bearing system both systems are pseudobinary and contain forsterite at phlogopite rich compositions in the f absent system the minimum melting occurs at 1225 c and phl85ap15 whereas in the f bearing system this temperature is 1260 c and phl66ap34 phlogopite in the f absent system has lower al than in the f bearing system with both showing si mg iv al vi al as the principal substitution increase in cao in forsterite increases with increasing apatite in the bulk composition and is more pronounced in the f absent system distribution of fluorine between phlogopite and liquid and apatite and liquid shows that d f phl glass ranges from 2 1 25 depending on temperature and bulk composition whereas the d f apat glass is about unity these results suggest that fluorine will tend to remain in the solid phases rather than the melt during partial melting in the mantle hence the enrichment of fluorine in ultrapotassic magmas and its role in their evolution are constrained

oldest lamproites from peninsular india track the onset of paleoproterozoic plume induced rifting and the birth of large igneous province abstract potassic and ultrapotassic magmatism from deep lithospheric sources in intra cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of large igneous provinces lips triggered by mantle plumes here we report for the first time precise zircon u pb age data from a suite of lamproites in the bastar craton of central india that mark the onset of paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major lip events during the precambrian evolution of the indian shield the lamproites from the nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile apatite and zircon the rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite geochemical features of the lamproites correlate with their counterparts in peninsular india and other similar suites elsewhere in the world related to rift settings and also indicate oib like magma source the associated syenite shows subduction related features possibly generated in a post collisional setting magmatic zircon grains with high th u ratios in the syenite from the nuapada lamproite form a coherent group with an upper intercept age of 2473 8 ma representing the timing of emplacement of the magma zircon grains in three lamproite samples yield four distinct age groups at ca 2 4 ga 2 2 ga 2 0 ga and 0 8 ga the 2 4 ga group corresponds to xenocrysts entrained from the syenite whereas the 2 2 ga group is considered to represent the timing of emplacement of the lamproites the ca 2 0 ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern bastar and the adjacent dharwar cratons a few young zircon grains in the syenite and lamproites show a range of early to middle neoproterozoic ages from 879 to 651 ma corresponding to younger thermal event s as also represented by granitic veins cutting across these rocks and extensive silicification zircon lu hf isotope data suggest magma derivation from a refertilized paleo mesoarchean sub continental lithospheric mantle or oib type sources the differences in hf isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale a combination of the features from geochemical and zircon hf isotope data is consistent with asthenosphere lithosphere interaction during the lamproite magma evolution the timing of lamproite emplacement in central india correlates with the global 2 2 ga record of lips we link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction accretion history prior to the neoarchean cratonization as well as the thermal blanket effect of the earth s oldest supercontinent pulsating plumes and continued rifting generated voluminous dyke swarms across the bastar and dharwar cratons forming part of a major global rifting and lip event

computational fluid dynamics simulations of the late pleistocene lake bonneville flood abstract at approximately 18 0 ka pluvial lake bonneville reached its maximum level at its northeastern extent it was impounded by alluvium of the marsh creek fan which breached at some point north of red rock pass idaho leading to one of the largest floods on earth about 5320 km3 of water was discharged into the snake river drainage and ultimately into the columbia river we use a 0d model and a 2d non linear depth averaged hydrodynamic model to aid understanding of outflow dynamics specifically evaluating controls on the amount of water exiting the lake bonneville basin exerted by the red rock pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the bonneville basin these models are based on field evidence of prominent lake levels hypsometry and terrain elevations corrected for post flood isostatic deformation of the lake basin as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood internal flow dynamics in the northern lake bonneville basin during the flood were affected by the narrow passages separating the cache valley from the main body of lake bonneville this constriction imposed a water level drop of up to 2 7 m at the time of peak flow conditions and likely reduced the peak discharge at the lake outlet by about 6 the modeled peak outlet flow is 0 85 106 m3 s 1 energy balance calculations give an estimate for the erodibility coefficient for the alluvial marsh creek divide of 0 005 m y 1 pa 1 5 at least two orders of magnitude greater than for the underlying bedrock at the outlet computing quasi steady state water flows water elevations water currents and shear stresses as a function of the water level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the bonneville flood about 18 days would have been required for the outflow to grow from 10 to 100 of its peak value at the time of peak flow about 10 of the lake volume would have already exited eroding about 1 km3 of alluvium from the outlet and the lake level would have dropped by about 10 6 m

timing of volcanism in the sierra nevada of california evidence for pliocene delamination of the batholithic root recent seismic experiments across the southern sierra nevada california show that the range lacks a thick crustal root xenolith studies indicate that delamination and loss of much of the lower crust may have occurred between 10 and 3 ma we estimate that delamination occurred ca 3 5 ma on the basis of a sudden pulse of mafic potassic magmatism within and just east of the sierra nevada from 4 to 3 ma this pulse interrupted the low level of volcanism that had prevailed regionally since 13 ma delamination could have promoted magmatism via decompression melting heating of the shallow lithosphere by upwelling asthenosphere and foundering of crustal rocks into the mantle and could have provided dynamic support to the range foundering of the lower crust may have occurred spontaneously owing to negative buoyancy or may have been triggered by extension between the sierra nevada and death valley

high ti amphibole as a petrogenetic indicator of magma chemistry evidence for mildly alkalic hybrid melts during evolution of variscan basic ultrabasic magmatism of central iberia central iberian variscan granite batholiths and anatectic complexes are punctuated by coeval stocks of hydrous high k calc alkaline ultrabasic to intermediate rock series despite their overall calc alkaline affinity the mafic ultramafic members contain high ti amphibole oikocrysts rimmed by lower ti amphibole cummingtonite and high ti amphibole replacing early phlogopite to understand the factors controlling the saturation of high ti amphibole in the parental magmas clinopyroxene melt phlogopite melt and amphibole melt relationships are reviewed this analysis reveals that for melts with intermediate compositions the affinity of tio2 for amphibole rises in alkalic magmas accordingly mildly alkalic trachytoid to subalkaline medium to high k andesite and dacite compositions are estimated for interstitial high ti amphibole saturated melts amphibole ce pb ratios reveal a mantle crust hybrid nature for interstitial melts with subalkaline trachytoid compositions the hydrous character of the variscan basic magmas favoured an overall magmatic evolutionary trend with a low rate of variation of na2o with respect to silica during amphibole crystallization

the fascination of a shallow water theory for the formation of megaflood scale dunes and antidunes abstract exceptional megaflood scale bedforms on earth are commonly associated with the catastrophic draining of glacial lakes in the late pleistocene the widest studied events have been the missoula and altai floods with 300 700 m flow depth 1 20 m bedform height and 10 300 m wavelength nowadays the saint venant equations have succeeded at simulating the catastrophic glacial lake drainage process numerically but we still lack a depth averaged morphodynamic theory able to predict the growth of dunes and antidunes the disparity of spatial scales in megafloods prevents the use of non depth averaged rotational flow equations motivating the present shallow water theory for the formation of megaflood scale bedforms we adopt a non equilibrium sediment transport equation rooted in einstein s pioneering work here we prove that the bed instability triggers to form dunes and antidunes simply by lagging the entrainment term for sediment mass conservation or the bottom shear stress with respect to the depth averaged flow velocity we formalise this result using a linear stability theory that captures the existence regions of dune and antidune in addition to the roll wave instability furthermore in the spirit of kennedy annu rev fluid mech vol 1 1969 pp 147 168 we derive a closed form solution of growth rate and wave speed of the bedform the nondimensional groups controlling the linear instabilities are the froude number r the shields parameter sh and the grain roughness relative to flow depth d subsequently we simulate the drainage of the largest missoula flood numerically to explain the formation of giant antidunes in the camas prairie montana us during the late stage of the megaflood also considered are large fields of gravel dunes in the kuray chuja lake basin altai mountains siberia the simulated hydraulic conditions over bedforms in both basins yield values of the nondimensional parameters that lie in the theoretical region of dunes and antidunes according to the proposed theory and in situ measurements in sandy rivers and flume experiments

mineral composition in cognate inclusions in late miocene early pliocene potassic lamprophyres with affinities to lamproites from the denizli region western anatolia turkey implications for uppermost mantle processes in a back arc setting abstract mineral assemblages of both cognate inclusions and host lamprophyres with lamproitic affinity in kocapinar district denizli western anatolia consist of phlogopitic mica diopsidic clinopyroxene k feldspar apatite opaque and carbonates calcite dolomite two distinct types of cognate inclusions have been defined in host lamprophyres clinopyroxene rich cci and clinopyroxene phlogopite rich cpci whole rock compositions of inclusions show a near primitive nature with high mgo 7 56 15 1 wt cr 195 2270 ppm ni 213 335 ppm contents and a potassic character k2o 2 0 2 8 wt na2o 0 4 2 2 wt data imply that the inclusions crystallized from magmas formed by melting of phlogopite bearing pyroxenites in a peridotitic mantle source however the presence of reverse zoning in clinopyroxenes with salitic fe rich green cores in host lamprophyres and cpci inclusions suggest that the denizli lavas represent mixtures of distinct probably ultrapotassic and alkali basaltic magmas estimated geobarometric constraints inferred from clinopyroxene compositions in cci and cpci inclusions indicate moderate pressures of pyroxene crystallization ranging between 1 7 and 2 2 gpa and corresponding to 53 70 km depths under low pressure magma fractionation results reveal that i the origin of denizli lamprophyres with transitional between arc type and intra plate type geochemical signatures is consistent with a shallow level mantle petrogenesis rather than a deep seated origin related to mantle convection ii the source was a highly refractory and metasomatized peridotitic mantle present at the base of the lower crust iii metasomatic agents that affected the mantle lithosphere beneath denizli region are distinct from those beneath other western anatolia orogenic centers and iv the transitional character of kocapinar denizli lamprophyric rocks were probably formed as a result of either underplating or contamination of asthenospheric magma at the base of the mantle lithosphere or assimilation of delaminated continental edge lithospheric mantle via ascending asthenosphere denizli lamprophyres are interpreted to have formed during the formation of a basin graben structure in the latest miocene early pliocene just after late miocene exhumation of menderes massif

structure and kinematics of the south iberian paleomargin and its relationship with the flysch trough units extensional tectonics within the gibraltar arc fold and thrust belt western betics abstract the superposition of structures observed in a selected area of the external zones of the betic orogen situated in the westernmost segment of the peri mediterranean mountain belt reveals an alternation of compressional and extensional events during the overall convergence of the african and eurasian plates that bound the system an early miocene compressional event produced the formation of the so called gibraltar arc fold and thrust belt formed by the units derived from the south iberian paleomargin and the flysch trough this wedge constitutes the footwall of the gibraltar thrust whose hanging wall corresponds to the alboran domain the outward migration of the compressional front w to nwward in the south iberian segment was followed by the outward migration of the extensional locus related to the middle miocene rifting that led to the alboran basin subsidence the tectonic inversion of the gibraltar thrust was accompanied by normal faulting of the innermost part of the paleomargin and the flysch trough units finally the alboran region underwent n s to nw se compression from late miocene onwards which caused the uplift of the gibraltar arc area

mantle earthquakes crustal structure and gravitational instability beneath western north island new zealand a cluster of 30 52 km deep earthquakes and a 7 10 km step in the moho beneath western north island new zealand are both interpreted as manifestations of active delamination of the continental lower crust and mantle lithosphere these phenomena occur in the back arc region beneath the east west oriented taranaki ruapehu tr line which strikes at a high angle to the present day plate boundary through new zealand across the line there is an abrupt change in crustal and mantle lid thickness and in upper mantle seismic attenuation q p 1 showing that the mantle lithosphere has been highly thinned on the north side we show from a receiver function profile that nearly all of the deep earthquakes reside in the uppermost mantle on the northern side of the tr line a sum of earthquake moment tensors suggests strike slip motion either parallel or orthogonal to the tr line resulting in northwest southeast oriented horizontal extension active normal faults oriented northwest southeast and north south are seen at the surface on each side of the tr line but the surface is uplifting here at 0 4 mm yr this requires the mantle lithosphere to be thinning at a higher rate than the overlying crust consistent with a delamination process

thermal and geochemical evolution of the mantle wedge in the northeast japan arc 1 contribution from experimental petrology melting phase relations at high pressures have been examined for four mg rich basalts from both the trench and the backarc sides of the miocene ne japan arc all these basalts crystallize olivine and orthopyroxene on the liquidus at pressures lower and higher than the point of multiple saturation with those two phases respectively the pressure of multiple saturation is rather constant for all samples 1 0 1 4 gpa suggesting that 1 there was no across arc variation in the depth of magma segregation in the miocene ne japan arc 2 the depth of magma segregation remains constant since 20 ma in the trench side of the volcanic arc whereas it has changed from 30 40 km to 60 km beneath the backarc side of the arc this temporal variation may be caused by increasing thickness of the lithosphere beneath the backarc region associated with cooling of the mantle wedge after the opening of the japan sea backarc basin in the early miocene