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

collapse of the thickened variscan crust in the french massif central mont pilat extensional shear zone and st etienne late carboniferous basin abstract a large scale extensional shear zone is described from the mont pilat area in the northeastern part of the french massif central this shear zone is about 2 km thick and is characterized by well developed n dipping foliation and stretching lineations deformation occurred under conditions of retrograde metamorphism from high temperature conditions to greenschist facies it is superimposed on a composite foliation related to the earlier variscan 380 350 ma compressional events associated with southward emplacement of nappes and hp mt metamorphism regional n s lineations and shear criteria observed at a regional scale indicate a northward displacement of the hanging wall during extension large strains locally recorded in thick mylonitic zones suggest that displacement was substantial some tens of kilometres late superimposed extensional brittle deformation and pseudotachylites show that northward displacement on normal faults continued at a shallower depth a large granitic pluton granite du velay intruded late in the the variscan orogeny was associated with extension some small leucogranitic syntectonic melts were emplaced within the shear zone and are strongly deformed geochronological rb sr data on these leucogranite bodies give an age of 320 ma and 40 ar 39 ar dating of synkinematic biotites from gneissose rocks in the shear zone yields a plateau age of 313 ma these data show that extensional ductile deformation and magmatism were still active during the latest late carboniferous thus extension occurred immediately after the well known late palaeozoic collision type compressional tectonics which had significantly thickened the crust we propose that the extensional tectonism described here is due to the gravitational collapse of the initially thick variscan crust the stephanian intracontinental sedimentary basin of st etienne was formed along the hanging wall of the normal shear zone during the late stages of this post orogenic crustal extension

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

a k ar and 40 ar 39 ar study on white micas from the brixen quartzphyllite southern alps the brixen quartzphyllite basement of the southern alps italy consists of metasediments which had suffered progressive deformation and low grade metamorphism pmax 4 kbar tmax 375 25 c during the palaeozoic it has been excavated by pre permian erosion buried again beneath a pile of permo mesozoic to cainozoic sediments estimated tmax 150 c and is now exposed anew due to late alpine uplift and erosion the behavior of the k ar system of white micas is investigated taking advantage of the narrow constraints on their thermal history imposed by the geological stratigraphic reference systems

the geochemical evolution of clinopyroxene in the roman province a window on decarbonation from wall rocks to magma abstract we present results from magma carbonate interaction experiments designed to shed light on the geochemical evolution of clinopyroxene in the roman province central italy atmospheric pressure experiments were performed at 1140 1160 and 1180 c under nno mh and air oxygen buffering conditions the starting materials were a shoshonite and a phonotephrite doped with different amounts of cao and cao mgo whose stoichiometric proportions reproduced the assimilation by magmas of calcite and dolomite respectively the results show that clinopyroxenes spinels and residual glasses are ubiquitous phases in all run products calcite doped runs crystallize more clinopyroxene than dolomite doped runs at the same conditions this leads to the formation of strong desilicated cao rich melts showing compositions comparable to those of magmatic skarns during magma carbonate interaction the content of fe3 in clinopyroxene increases with increasing fo2 promoting the substitution of al for si in tetrahedral site local charge imbalances are also compensated by the incorporation of highly charged cations such as ti into the crystal lattice according to this cation substitution al ca fe3 ti rich clinopyroxenes of the skarn environment testify to continuous co2 fluxes produced by the thermal decomposition of carbonate wall rocks nevertheless the oxidative capacity of co2 progressively decreases from the skarn shells towards the interior of the magma chamber driving the crystallization of si fe2 mg rich clinopyroxenes

the marine atmospheric boundary layer during semaphore i mean vertical structure and non axisymmetry of turbulence this paper describes the vertical structure of the marine atmospheric boundary layer analysed using aircraft measurements in the azores region during semaphore structure des echanges mer atmosphere proprietes des heterogeneites oceaniques recherche experimentale the flights were performed in the middle of the solar day during near anticyclonic conditions with weak to moderate winds and weak surface sensible heat flux over a homogeneous oceanic area the boundary layer was characterized by a mixed layer driven by surface fluxes which was not coupled to the overlying broken stratocumulus layer this decoupling is demonstrated by the shape of the continuous profile of the dissipation rate of turbulent kinetic energy computed from the continuous slant profiles performed by the aircraft this method makes it possible to determine the thickness of the mixed layer which is a relevant scale for the parametrization of the profiles the turbulence field is analysed through the wavelength of the spectrum peak of the vertical velocity computed on 392 runs more or less parallel or perpendicular to the mean wind it demonstrates a stretching of the most energetic eddies along the mean wind the consequences of this non axisymmetric behaviour of the turbulent field on the flux estimates from aircraft data are discussed

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

some constraints on geochemical features in the triassic mantle of the easternmost austroalpine southalpine domain evidence from the karawanken pluton carinthia austria

do smoothly curving spiral shaped inclusion trails signify porphyroblast rotation smoothly curving spiral shaped inclusion trails may form in porphyroblasts during the overprinting of near orthogonal foliations in schists that are relatively quartz rich and in general graphite poor the smooth curvature results from the combined effects of 1 the protection from progressive shearing provided by projecting crystal faces and 2 greater competency and generally wider zones of progressive shearing in these rock types than in ones that are less quartz rich and more graphtic therefore lack of truncations or abrupt changes in compositional zoning profiles and the presence of smoothly curving spiral shaped inclusion trails do not necessarily signify that the porphyroblast containing them rotated as it grew this has considerable significance for shear sense determinations in deformed and metamorphosed rocks

i type granitoids as indicators of a late paleozoic convergent ocean continent margin along the southern flank of the central european variscan orogen a belt of carboniferous to permian i type granitoid bodies is in the basement thrust sheets of the alps which correspond to the southern flank of the central european variscan orogen these predominantly granodioritic plutons contrast with a contemporaneous belt of s type granites which extends to the north of the alps in the moldanubian section of the variscan orogen the observed regional duality of variscan plutonism resembles the plutons along active circum pacific continental margins in that there are outer i type plutons and inner s type granitoid belts therefore central europe could have undergone a cordilleran type orogenic event in late paleozoic time involving northwestward subdcution of the paleo tethys ocean

geodynamic model for the palaeozoic crustal consolidation of western and central europe abstract the crystalline basement of western and central europe consists of a mosaic of crustal elements which were consolidated during pre grenvillian the grenvillian dalslandian morarian cadomian caledonian and hercynian orogenic cycles contemporaneous with the caledonian suturing of the precambrian laurentia greenland and fennosarmatian shields a number of gondwana derived cadomian micro cratons were accreted to the southern margin of laurasia following the late caledonian paroxysm the devonian and early carboniferous evolution of europe was dominated by continued northward subduction of the proto tethys plate at an arc trench system parallelling the southern margin of laurasia the accretion of additional gondwana derived continental fragments back arc rifting and a sinistral translation of major proportions between the laurentia greenland and the fennosarmatian sub plates the acadian and bretonian orogenies were of the pacific type the visean collision of gondwana with laurasia marked the onset of the himalayan type variscan orogeny during which collision related compressive stresses overpowered the devonian early carboniferous back arc rift systems and caused the development reactivation of a subduction zones the central armorican and saxothuringian successor basins became folded and destroyed during the latest visean whilst the variscan foredeep became scooped out in part by nappes involving the basement during the late westphalian major crustal shortening during the variscan diastrophism was accompanied by the anatectic remobilisation of subducted crustal and upper mantle material and a widespread syn and late orogenic magmatism the latest carboniferous early permian reorientation of the convergence direction between gondwana and laurasia induced the development of a complex wrench fault system transecting the variscan fold belt and an extensive post orogenic volcanism the hypotheses summarised here require confirmation by further palaeomagnetic and radiometric data and faunal analyses

cloudiness and marine boundary layer dynamics in the astex lagrangian experiments part i synoptic setting and vertical structure abstract a goal of the atlantic stratocumulus transition experiment astex southeast of the azores islands in the east central atlantic ocean during june 1992 was to examine the coupled evolution of cloud dynamical and thermodynamical vertical structure in a marine boundary layer mbl air mass as it advected from cold to warm water in the trade winds in two lagrangian observation periods during astex an unprecedentedly complete view of mbl and cloud evolution was achieved by nearly continuous aircraft coverage of such an air mass for 36 48 hours using three boundary layer aircraft supplemented by satellite ship and balloon observations during the first lagrangian period an accelerated stratocumulus to trade cumulus transition occurred in a clean marine air mass in the second lagrangian period a 200 hpa deep decoupled modified continental mbl persisted with almost no change in structure cumulus rising into intermittent stratocumulus were observed throughout the period the two contrasting a

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

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

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

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

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

importance of hercynian tectonics within the framework of the southern alps abstract the hercynian remnants present within the alpidic structural zones of the southern alps are reviewed the pattern of hercynian metamorphism is zonal from granulites in the western area to anchimetamorphic facies in the eastern one in the folded zone at the eastern margin a severe hercynian folding phase took place during the westphalian thrust sheets comprising sequences of different facies ranging in age from caradocian to early westphalian are sutured by late westphalian molasse deposits the assumption that the southern alps and the external dinarides remained outside the hercynian folding front is contradicted by field evidence

pre alpine and alpine evolution of the south alpine basement of the orobic alps new k ar age determinations on the gneisses and schists of the south alpine basement of the orobic alps and their separated minerals have been carried out to supplement and support the previous study ofbocchio et al 1981

relationships between chamber margin accumulates and pore liquids evidence from arrested in situ processes in ejecta latera caldera italy biotite and clinopyroxene rich mafic nodules occur together with syenite ejecta in ca 235 to 155 ka tuffs surrounding the latera caldera clinopyroxenites and leucite monzosyenites crystallized along the lower margins of a crustal magma system and record complex crystallization histories of potassic magmas that were parental to a range of lava and tuff compositions the mafic nodules have the mineral assemblage clinopyroxene biotite anorthite orthoclase leucite hauyne titanite apatite amphibole olivine phlogopite and comprise mesocumulate and orthocumulate layers that commonly alternate on the scale of several centimeters despite the apparently ultramafic nature of the early cumulate assemblage the common occurrence of intercumulate orthoclase leucite hauyne salitic clinopyroxene and vesicular glass indicates that interstitial liquids underwent late stage differentiation at relatively shallow depths but under highly variable conditions of volatile saturation many of the mafic nodules exhibit pronounced variations in the type and abundance of mineral reaction textures these range from unreacted assemblages to nodules in which cumulate megacrysts are surrounded by well developed symplectite halos the textural variability indicates strongly localized disequilibrium between cumulate frameworks and vapor saturated pore fluids and is attributed to convective fractionation of liquids through permeable crystal mush lithologic discontinuities exhibited by the xenolith suite and host magmas are best explained by variable communication between a compositionally stratified magma reservoir and its partly crystallized lower chamber margins periodic replenishment of this system by less evolved magmas subsequently promoted mixing and hybridization that are characteristic features of many latera lavas and tephra

the variscan structural and metamorphic evolution of the eastern southalpine basement the basement of the southern alps northern italy belongs to the southernmost part of the european variscan mountain belt in contrast to other areas of the alps the post variscan metamorphic and tectonic overprint is weak and therefore permits the unravelling of the variscan tectonometamorphic evolution of this region overprinting criteria and the mapping of the penetrative structural elements s2 and l2 allow three deformational events to be distinguished major variscan deformation d2 in the southern alps commenced in the carboniferous and lasted until the end of the late carboniferous tectonic movement during d2 was north directed and was accompanied and followed by greenschist facies metamorphism peak metamorphic conditions reached 450 550 c and 5 6 5 kbar in the brixen area and decreased in a southeasterly direction tectonic movement during d2 followed subduction of the plankogel terrane and collision of the noric terrane northernmost part of gondwana with laurasia and is interpreted to result from late orogenic extensional collapse of the variscan mountain chain extensional deformation caused exhumation of the basement rocks as evidenced by greenschist facies basement pebbles which show no substantial retrograde overprint in late carboniferous early permian conglomerates

trade wind rainfall atop mount waialeale kauai abstract very large coast to mountain rainfall gradients have been observed in the trade winds and winter monsoons since the surface moist layer is usually capped by a subsidence inversion near 2 km the rain is warm on the top of a mountainous island which is generally below the inversion such as kauai trade wind rainfall can be very great and the coast to top rainfall gradient very large autographic rainfall measurements at the top of mount waialeale 1598 m msl one of the wettest spots on the earth on kauai together with surface and upper air measurements made at lihue 20 km to the southeast and weather satellite images confirm and expand on earlier descriptions of the nature of mountain rainfall in the trade winds significant rain results from moderate or fresh trade winds being lifted up the eastern escarpment of waialeale but only when a band or area of cumulus extends upwind of the mountain small wind shear in the vertical and a sharp upper limit to the moist layer reduce entrainment

simulation of seasonal variation of marine boundary layer clouds over the eastern pacific with a regional climate model abstractthe seasonal cycle of marine boundary layer mbl clouds over the eastern pacific ocean is studied with the international pacific research center iprc regional atmospheric model iram the results show that the model is capable of simulating not only the overall seasonal cycle but also the spatial distribution cloud regime transition and vertical structure of mbl clouds over the eastern pacific although the modeled mbl cloud layer is generally too high in altitude over the open ocean when compared with available satellite observations the model simulated well the westward deepening and decoupling of the mbl the rise in cloud base and cloud top of the low cloud decks off the peru and california coasts and the cloud regime transition from stratocumulus near the coast to trade cumulus farther to the west in both the southeast and northeast pacific in particular the model reproduced major features of the seasonal variations in stratocumulus decks off the peru and california coasts includin

contrasting thermomechanical evolutions in the southalpine metamorphic basement of the orobic alps central alps italy in the southern alps a progressive metamorphic zonation with an increase in the geothermal gradient from ne to sw has been widely proposed however recent investigations have shown that the greenschist metamorphic imprint of the low grade zone corresponds to a metamorphic retrogression following amphibolite facies conditions on the other hand in the medium grade zone a later low pressure high temperature lpht metamorphic event has also been proposed in an attempt to resolve these different interpretations new petrological and partly new structural data have been obtained for two sectors of the orobic alps traditionally attributed to different metamorphic zones thermo barometric determinations supported by microstructural analysis indicate the following different pressure retrograde paths in each sector 1 in the val vedello basement wb rocks a first metamorphic imprint characterized by p 7 9 kbar and t 570 610 c was followed by a greenschist retrogression p 4 kbar and t 500 c 2 in the lario basement lb rocks the first detectable metamorphic stage characterized by mineral assemblages indicating p 7 9 kbar and t 550 630 c was followed by a lpht event synkinematic with f2 extensional deformation a greenschist retrogression marks the final uplift of these rocks reinterpretation of the available geochronological data indicates a diachronism for the two thermo mechanical evolutions in the light of these data we interpret the retrograde p t t path of the vvb rocks as a pre permian post thickening uplift and the retrograde p t t evolution of the lb rocks as a permo mesozoic uplift related to the extensional tectonic regime of the tethyan rifting

porphyroblast inclusion trails the key to orogenesis detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral shaped inclusion trails are common indicates that spiral shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates they formed instead by progressive growth by porphyroblasts over several sets of near orthogonal foliations that successively overprint one another the orientations of these near orthogonal foliations are alternately near vertical and near horizontal in all porphyroblasts examined this provides very strong evidence for lack of porphyroblast rotation the deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two stage cycle of 1 crustal shortening and thickening with the development of a near vertical foliation with a steep stretching lineation followed by 2 gravitational instability and collapse of this uplifted pile with the development of a near horizontal foliation gravitational spreading near coaxial vertical shortening and consequent thrusting on the orogen margins correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen this information combined with information about chemical zoning in porphyroblasts provides details about the structural metamorphic p t t paths the rocks have followed the ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical ductile tear transcurrent faults across which there is no component of bulk shortening or transpression

tectonics of the dolomites southern alps northern italy abstract in post variscan times the dolomites underwent a number of tectonic events which may be summarized as follows permian and triassic rifting phases broke the area into n s trending basins with different degrees of subsidence a middle triassic transpressive event then deformed the region along a n70 e axis generating flower structures within the basement volcano tectonic domal uplift and subsequent caldera formation occurred at the same time as the late ladinian magmatism early jurassic rifting also controlled the subsidence which increased eastward this long period of deformation was followed by a pre neogene late cretaceous palaeogene e w ene wsw compression which generated a w vergent belt possibly equivalent to the folded foreland of the dinaric chain a 70 km e w section of the dolomites indicates shortening of at least 10 km during the neogene the dolomites as far north as the insubric lineament were the innermost part of a s vergent thrust belt the basement of the dolomites was thrust southwards along the valsugana line onto the sedimentary cover of the venetian prealps for at least 10 km this caused a regional uplift of 3 5 km the valsugana line and its backthrusts on the northern side of the central dolomites generated a 60 km wide pop up in the form of a synclinorium within which the sedimentary cover adapted itself mainly by flexural slip often forming triangle zones the shortening linked to this folding is about 5 km with neogene thrusts faulting and folding pre existing thrust planes on the north eastern side of the dolomites neogene deformation is apparently more strictly controlled by the transpressive effects of the insubric lineament and shortening of the sedimentary cover may be greater than in the central dolomites minor deformation linked to the giudicarie belt is present in the western dolomites the present structure of the dolomites is thus the result of a number of tectonic events of different significance and different strike only a 3 dimensional restoration can unravel the true structure of the dolomites

mixed layer mode simulation of eastern north pacific stratocumulus abstract the cloud topped mixed layer theory developed by lilly 1968 is employed in a slightly generalized form to simulate stratocumulus in the eastern north pacific the radiation parameterization involves cloud top longwave cooling and mixed layer shortwave heating long wave emissivity and shortwave absorption are functions of cloud thickness the model is integrated along climatological trajectories which traverse the area bounded by 145 w 115 w 20 n and 40 n the results of the integration include fields of cloud top and cloud base height mixed layer thermodynamic structure and convective and radiative fluxes where it is possible to compare model generated fields with the observations of neiburger et al 1961 general agreement is found the model predicted location of the southern limit due to cloud top instability of stratocumulus clouds is in agreement with observations

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

conserved variable analysis of the convective boundary layer thermodynamic structure over the tropical oceans abstract an analysis of fgge dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial pacific deeper boundary layers show a double structure reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study

oblique crustal detachment in the variscan schwarzwald southwestern germany the schwarzwald is part of the central polymetamorphic crystalline belt of the variscan orogen moldanubian belt from north to south it consists of four terranes the metasedimentary zone of baden baden the polymetamorphic central schwarzwald gneiss complex the sedimentary metamorphic zone of badenweiler lenzkirch and the hotzenwald complex the largest of these terranes is the central schwarzwald gneiss complex csgc whose rocks record a history of protracted regional metamorphism and anatectic melt generation during variscan convergence between 350 and 325 ma the csgc became detached from a high temperature lower crustal substratum and was emplaced southeastward over paleozoic clastics volcanic rocks and crystalline slivers of the zone of badenweiler lenzkirch and the hotzenwald complex kinematic indicators suggest that these early convergent movements on retrograde shear zones and the concomitant crustal thickening were superseded by movements on divergent shear zones the ascent of voluminous granitic plutons from a mid crustal zone of melt generation into the upper crust was probably triggered by a change in the crustal kinematics from overall convergence to overall divergence at about 325 ma in detail this process was probably diachronous detachment of upper crust and large scale melt generation in the middle crust of the schwarzwald was probably facilitated by the tectonic stacking of water rich pelitic clastics and gneiss slivers with relatively even proportions of crystalline and pelitic materials

the iapetus model a plate tectonic concept for the variscan belt of europe abstract a plate tectonic model is presented explaining the evolution of the variscan belt of europe it regards the iapetus ocean and its branch the tornquist sea as the only ocean involved in the caledonian variscan and alleghenian mega orogen the iapetus and its marginal basins disappeared through oblique subduction and collision in the following sequence 1 1 northeastern iapetus including the tornquist sea caledonian orogeny 2 2 central iapetus acadian orogeny 3 3 adjacent marginal basins variscan orogeny and 4 4 southwestern iapetus alleghenian orogeny the area of the variscides was part of the continental margin of gondwana made up of ridges and ensialic basins no ocean lay within the variscan area during the palaeozoic although patches of oceanic crust probably existed in rift basins e g the lizard ophiolite after the silurian early devonian closure of northwestern and central iapetus the variscan area was surrounded by cratons on three sides in a manner similar to that around the modern mediterranean sea the subsequent variscan orogeny was essentially an ensialic thrusting and folding induced by a further approach of gondwana toward laurentia after the variscan collision gondwana rotated clockwise to the west by moving along a strike slip zone this rotation during the carboniferous opened the palaeo tethys in the east and caused the alleghenian collision in the west the middle ordovician to permian palaeogeography is presented on a series of maps modelling tectonic displacement and plate motions avalonia is interpreted as the ordovician volcanic island arc of gondwana separated from mainland gondwana by an oceanic gulf or a back arc basin the iberian arc may have originated by a continental escape of iberia from the center of collision into the oceanic gulf the variscan austro alpine and southern alpine units are today located near their earliest early carboniferous position

first permian early triassic zircon ages for tin bearing granites from the gemeric unit western carpathians slovakia connection to the post collisional extension of the variscan orogen and s type granite magmatism this study presents the first preliminary u pb zircon data on tin bearing s type granites from the gemeric unit of the western carpathians slovakia u pb single zircon dating controlled by cathodoluminescence suggests crystallization of the gemeric granites during permian to early triassic 303 241 ma time post crystallization low temperature metamorphic overprint is reflected by partial pb loss in zircons these gemeric granites are younger than the highly fractionated s type tin and rare element bearing leucogranites in the european variscides they may have resulted from partial melting triggered by increased heat flow from the mantle below the continental crust and most probably intruded during the post collisional extension and initial rifting of the variscan orogenic belt during alpine orogeny the gemeric granites were affected by a low temperature deformation and metamorphism

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

marine atmospheric boundary layer height over the eastern pacific data analysis and model evaluation the atmospheric boundary layer abl height h is a crucial parameter for the treatment of the abl in weather and climate models about 1000 soundings from 11 cruises between 1995 and 2001 over the eastern pacific have been analyzed to document the large meridional zonal seasonal and interannual variations of h in particular its latitudinal distribution in august has three minima near the equator in the intertropical convergence zone itcz and over the subtropical stratus stratocumulus region near the west coast of california and mexico the seasonal peak of h in the itcz zone between 5 68 and 11 28n occurs in the spring february or april while it occurs in august between the equator and 5 68n comparison of these data with the 10 yr monthly output of the community climate system model ccsm2 reveals that overall the model underestimates h particularly north of 208n in august and september directly applying the radiosonde data to the ccsm2 formulation for computing h shows that at the original vertical resolution with the lowest five layers below 2 1 km the ccsm2 formulation would significantly underestimate h in particular the correlation coefficient between the computed and observed h values is only 0 06 for cloudy cases if the model resolution were doubled below 2 1 km however the performance of the model formulation would be significantly improved with a correlation coefficient of 0 78 for cloudy cases

deformation partitioning during polyphase oblique convergence in the karawanken mountains southeastern alps abstract the karawanken mountains of southeastern austria straddle the insubric line a major fault zone that corresponds to the austroalpine south alpine border of the eastern alps they display polyphase structural patterns that resulted from deformation partitioning at shallow crustal levels following a poorly constrained late cretaceous deformation history paleogene contraction produced nw se trending fold thrust structures and possibly related sinistral cross faults miocene deformation produced both nw and se directed thrust faults and nw striking high angle dextral cross faults which merged with or displaced the w striking insubric line distributed dextral strike slip displacements of the order of 30 40 km and thrust displacement of 4 5 km along the northern karawanken front initiated subsidence of a small foreland basin north of the karawanken mountains recent regional deformation seems to be concentrated along cross cutting nnw striking dextral faults within a shifting system of seismogenic transfer faults that probably merge with the convergent south alpine thrust front to the west there are conspicuous parallels in the style of deformation along the karawanken mountains with that found along other seismogenic convergent strike slip faults such as those of southern california new zealand and anatolia

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

coupling of the radiative convective and surface fluxes over the equatorial pacific abstract an idealized energy balance model for a closed circulation is first presented to illustrate the coupling between the net tropospheric radiative cooling the surface fluxes and the mean subsidence away from the precipitation zones then a one dimensional diagnostic model and a radiation model with boundary layer clouds are combined to explore this coupling for a specific region using mean sounding data over the tropical pacific the radiatively driven subsidence rate at the top of the convective boundary layer is approximately 35 mb day 1 0 04 pa s 1 and is largely independent of boundary layer cloud fraction the sensitivity of the corresponding convective heat flux profiles to the mass divergence profile and cloud fraction within the boundary layer is explored reasonable assumptions give realistic surface sensible and latent heat fluxes for this region of approximately 10 and 130 w m 1 the paper illustrates the important background climatic control of the radiation field on the tropical surfa

observed lagrangian transition of stratocumulus into cumulus during astex mean state and turbulence structure aircraft measurements made during the first lagrangian of the atlantic stratocumulus transition experiment astex between 12 and 14 june 1992 are presented during this lagrangian experiment an air mass was followed that was advected southward by the mean wind five aircraft flights were undertaken to observe the transition of a stratocumulus cloud deck to thin and broken stratocumulus clouds penetrated by cumulus from below from the horizontal aircraft legs the boundary layer mean structure microphysics turbulence structure and entrainment were analyzed the vertical profiles of the vertical velocity skewness are shown to illustrate the transition of a cloudy boundary layer predominantly driven by longwave radiative cooling at the cloud top to one driven mainly by convection due to an unstable surface stratification and cumulus clouds during the last flight before the stratocumulus deck was observed to be broken and replaced by cumuli the total water flux the virtual potential temperature flux and the vertical velocity variance in the stratocumulus cloud layer were found significantly larger compared with the previous flights to analyze the cloud top stability the mean jumps of conserved variables across the inversion were determined from porpoising runs through the cloud top these jumps were compared with cloud top entrainment instability criteria discussed in the literature it is suggested that enhanced entrainment of dry air is a key mechanism in the stratocumulus cumulus transition

birth and evolution of the paleocarnic chain in the southern alps a review the present work is aimed at reviewing the state of the art of the studies centered on the pre collisional and collisional variscan evolution of the eastern southern alps the main focus is on the carnic alps a geologically spectacular and extremely complex area which has been a major subject of study for structural geologists stratigraphers and paleontologists for more than a century after decades of field studies aimed at unveiling the birth and evolution of this belt the tectonic and geodynamic interpretations proposed for almost a century by two different groups of authors remain substantially different german speaking authors over the decades have consistently proposed a scenario marked by a mature devonian passive margin which later on evolved into an active mississippian continental margin the following collisional phase resulted in an accretionary wedge that in its evolution might be compared to those generated by variscan events outside the alpine domain on the contrary italian authors have mainly put forward a pre collisional setting dominated by wrench fault tectonics followed by the formation of a large collisional thrust and fold belt arc shaped in plan view we illustrate the results accomplished so far and discuss the interpretations formulated by the two different research schools our review provides a chance to compare the different interpretations and at the same time prompts the need for new and targeted data collection in the area

the interactions among cyclone dynamics vertical thermodynamic structure and cloud radiative forcing in the north atlantic summertime storm track abstract this study investigates the changes in the vertical thermodynamic structure of the troposphere associated with the passage of cyclones and the corresponding influence on cloud radiative forcing crf the focus is the synoptic scale evolution of lower tropospheric sounding structure in the extratropical north atlantic during july 1985 89 the type and amount of low level cloud cover which has a strong impact on total crf in this region is sensitive to these variations composite profiles at ocean weather stations l and c are constructed for soundings with low level temperature inversions soundings with surface based inversions and soundings without inversions separately for conditions of large scale subsidence and ascent in addition collocated european centre for medium range weather forecasts analyzed fields and earth radiation budget experiment crf data are averaged for each composite sounding these composites correspond to distinct dynamical regimes associated with the movement of cycl

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

boundary layer depth entrainment and decoupling in the cloud capped subtropical and tropical marine boundary layer abstract estimates of marine boundary layer mbl depth and degree of decoupling for two regions of the subtropical and tropical east pacific are presented using satellite observations from the moderate resolution imaging spectroradiometer modis and the tropical rainfall measuring mission trmm microwave imager tmi these data are combined in a novel way with ncep reanalysis data and a mixing line parameterization to estimate the mean entrainment rate we over the two regions mean entrainment rates vary geographically and have maxima just downwind of the californian coast we 4 5 mm s 1 and also in the core of the equatorial east pacific cold tongue where mean we exceeds 6 mm s 1 entrainment exceeds subsidence by 30 or less in the subtropical stratocumulus regions north of the equatorial cold tongue entrainment greatly exceeds subsidence producing a rapid deepening of the mbl as air flows over a marked sst gradient shallow mbls zi 500 700 m are found to be well mixed in general the deco

porphyroblast inclusion trail orientation data eppure non son girate extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non coaxial ductile deformation of the matrix subsequent to their growth this has been demonstrated for all tectonic environments so far investigated the work also has provided new insights and data on metamorphic structural and tectonic processes including 1 the intimate control of deformation partitioning on metamorphic reactions 2 solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones and relative plate motion and 3 a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

the coastal boundary layer at the eastern margin of the southeast pacific 23 4 s 70 4 w cloudiness conditioned climatology abstract a basic climatological description of 29 years of surface and upper air observations at a coastal site 23 4 s 70 4 w in northern chile is presented the site is considered to be generally representative of the eastern coastal margin of the southeast pacific stratocumulus region which plays an important role in the global radiative balance the analysis focuses on two of the main elements affecting coastal weather in this region low level cloudiness and the state of the subsidence temperature inversion the objectives of the paper are 1 to present the basic climatological features of these elements and 2 to document the differences in the structure of this coastal boundary layer bl associated with the presence or absence of low level clouds low level clouds defined here as ceilings less than 1500 m agl occur at the site mostly in the night especially during austral winter and spring elevated subsidence inversions show a very large prevalence in the 1200 utc 0800 local time lt rad

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

extensional shearing deformation and kilometer scale a type folds in a cordilleran metamorphic core complex raft river mountains northwestern utah cordilleran metamorphic core complexes are characterized by ductile mylonitic deformation and regional stretching lineations in the raft river mountains a mylonitic zone and a late superimposed detachment fault separate precambrian crystalline and metasedi mentary basement rocks from an upper plate made of allochthonous paleozoic rocks which suffered a brittle extensive deformation we suggest that the mylonitic ductile deformation is the result of tertiary extensional tectonics strain analysis shows that 1 strain results from large scale progressive shearing deformation in a non coaxial regime 2 e w regional stretching lineations represent the direction of shearing and transport 3 shear criteria indicate an east directed movement 4 strain magnitude is increasing eastward 5 kilometer scale folds parallel to the lineations are interpreted as a type folds formed by eastward shearing of a previously northward dipping layering measurement of striated faults in the upper plate gives an e w direction of extension parallel to the lineations thus ductile and brittle deformations are closely related to the same regional scale extensional tectonics a model is proposed to explain the observed geometry and kinematics of the structures the mesozoic to paleocene cordilleran compressional tectonics induced an overthickening of the crust in the hinterland belt at the future emplacement of the complexes important uplift abnormal heating and granite emplacement occurred later during the collapse of the former belt the combined effects of thermal and gravitational instabilities during tertiary extensional tectonics enabled the development of a ductile shear zone localized at the precambrian basement paleozoic cover interface the brittle extension of the upper crust is displaced laterally along this flat shear zone and transformed farther east into the extended regions of the middle and lower crust

relation between mean boundary layer structure and cloudiness at the r v valdivia during astex abstract the relationship between boundary layer thermodynamic structure and cloud fields and their diurnal variation are explored using seven days of data from dw r v valdivia during the atlantic stratocumulus transition experiment cloudiness is at a maximum before dawn when the boundary layer bl has the thermodynamic structure of a partially mixed conditionally unstable stratocumulus layer which is close to mean saturation below the inversion cloudiness falls during the daytime and in the late afternoon the bl has two distinct layers a warmer drier cloud layer characteristic of trade cumulus above a more well mixed subcloud layer the observed mean profiles are consistent with an earlier suggestion that there is a cloud cover transition once the bl mixing line slope exceeds half that of the moist adiabat in contrast the bl structure in the ecmwf model for the same week has a much drier warmer more stable cloud layer than the observations

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

thermal modeling of extensional tectonics application to pressure temperature time histories of metamorphic rocks one and two dimensional finite difference models are used to generate theoretical pressure temperature time ptt paths for rocks uplifted from deep and intermediate crustal levels during extension via ductile stretching of the entire lithosphere pure shear and via movement of crustal blocks along rooted large scale low angle normal faults simple shear the temperature time paths of rocks uplifted by these pure shear and simple shear mechanisms have similar morphologies although rocks from pure shear settings reach their final depth at higher temperatures than do rocks uplifted by simple shear and experience a greater amount of posttectonic cooling the depth temperature paths of rocks uplifted from deep crustal levels 30 km depth via pure shear extension are often characterized by a period of nearly isothermal high dp dt uplift during the early stages of extension a modified pure shear extension model that includes enhanced heating in the lower lithosphere during extension generally produces ptt paths characterized by a more protracted period of nearly isothermal uplift in contrast simple shear uplift along low angle normal faults produces almost linear depth temperature paths with moderate dp dt and isothermal uplift is not observed for a given initial geotherm the single factor controlling the ptt paths of rocks unroofed below gently dipping normal faults that dip less than 30 is the rate at which unroofing takes place unroofing rate is defined as the rate of uplift relative to the surface and the syntectonic ptt paths are insensitive to fault dip or horizontal displacement rate current geothermometric and geobarometric techniques yield typical uncertainties in real pressure temperature and temperature time data of 1 kbar and 50 c thus it will be difficult to distinguish between these various extensional mechanisms on the basis of ptt data derived from a single sample or from a single structural level although use of data from samples collected from a broad range of structural levels may improve resolution ultimately the best prospect for distinguishing between simple shear and pure shear mechanisms through petrologic work lies in improving the precision of metamorphic pressure and temperature measurements to 0 5 kbar and 25 c

pressure temperature time evolution of the high pressure metamorphic complex of sifnos greece model studies of continental collision tectonics and pressure temperature time p t t predictions quantitatively demonstrate the key role of synsubduction uplift in the preservation of blueschist and eclogite facies metamorphic rocks rheological stratification of the subducting lithosphere allows development of detachment faults at the compositional boundary between the upper and lower crust material of supracrustal continental affinity is subducted to depths in excess of 50 km and then delaminated from the downgoing slab subduction continues while the detached domain is uplifted independently from the newly active hanging walls and footwalls two dimensional thermal calculations indicate that the nearby active subduction provides the cooling mechanism required to preserve blueschists and eclogites whereas the differential motions of the independently uplifted domains can explain the observed heterogeneity in p t t pathways with some domains displaying a greenschist overprint

the eruption pyroclastic flow behaviour and caldera in filling processes of the extremely large volume 1290 km3 intra to extra caldera permian ora ignimbrite formation southern alps italy abstract the permian ora formation 277 274 ma preserves the products of the ora caldera super eruption northern italy the stratigraphic architecture of the exceptionally well preserved intra caldera succession provides evidence for caldera collapse at the onset of the eruption a multiple discharge point fissure eruption style and progressive incremental caldera in filling by numerous pyroclastic flow pulses within the caldera the ignimbrites of the ora formation are voluminous 1290 km3 crystal rich 25 to 55 and ubiquitously welded the ora formation has been divided into four members a d which also define the principal eruption phases the eruption proceeded in four main stages 1 early caldera collapse and vent opening producing locally distributed basal co ignimbrite lithic breccia member a 2 vent clearing which produced the eutaxitic lithic rich ignimbrite and minor thin ground and ash cloud surge deposits member b 3 waxing and steady eruption which produced the dominant eutaxitic coarse crystal rich ignimbrite with local lithic rich and fine crystal rich ignimbrite and minor surge deposits member c and 4 waning eruption recorded by the eutaxitic fine crystal rich ignimbrite with local lithic rich ignimbrite deposits member d the incremental filling and late stage outpouring of pyroclastic material from the caldera is recorded by vertical and lateral lithofacies deposit variation and some correlation between stratigraphic sections these findings reveal a structure to the outwardly monotonous 1300 m thick intra caldera fill and thinner

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

multistage geochronological evolution of the velka fatra mountains a combined tims and ion microprobe study on zircons abstract new isotopic and geochronological data from the velka fatra mountains tatric unit of the central western carpathians are presented and discussed with a focus on the variscan orogeny and events during permian and early triassic times the investigated samples are meta to per aluminous granitoids and their trace element patterns indicate a volcanic arc origin this study presents u pb single zircon data measured on tims as well as on an ion microprobe sims the zircon age determinations were additionally constrained by cathodoluminescence cl most of the investigated granitoids yield variscan emplacement ages of about 310 ma however for the lubochna leucogranite a triassic crystallisation age at 231 17 ma was found the presence of such young slightly discordant zircon ages gives evidence for a so far unknown late permian early triassic magmatic event in the western carpathians

trade wind rainfall near the windward coast of hawaii a dynamically based mesoscale climatology of rainfall and other data are examined for typical trade wind conditions near hawaii relative distributions of rainfall are deduced from radar reflectivity data for a 4000 km 2 region over the windward island and the upstream ocean the cumulative rainfall data suggest three zones of forcing that are characteristic of 1 the regional ocean 2 upstream island induced divergence and 3 flow reversal near and over the island it is confirmed that most intense rainband amplifications occur over a mesoscale convergence line that separates the easterly trade winds from an island induced westerly flow this flow separation line resembles a classical gravity current when positioned over the windward island and near shore the domain scale cumulative rainfall is statistically associated with the strength of island blocking as defined by a froude number fr when fr is in the ordinary range 0 3 the island maximum is five times greater than the oceanic average when fr is elevated 0 3 the rainfall maximum increases to 10 times the oceanic average overall the windward island maximum is seven times the upstream oceanic average increased rainfall is more strongly correlated with increased wind speed than with a reduction in dry static stability both component variables of fr unlike rainfall amount the position of the island maximum is relatively insensitive to fr except in the hours surrounding sunrise in the upstream divergence zone 20 45 km offshore rainfall is double the oceanic background it is speculated that the cause is blocking related there are very strong diurnal variations in rainfall amount and distribution both over the island and the upstream ocean windward island rainfall is at a maximum in the hours surrounding midnight when breeze and blocking forcings are fully cooperative in the coastal region seemingly unrelated oceanic rainfall exhibits a strong nocturnal maximum the temporal phase of which may be influenced by wind speed a deep minimum in domain scale rainfall occurs near noon

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

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