characterization of granitoid and gneissic weathering profiles of the mucone river basin calabria southern italy the paper deals with the development of a multidisciplinary research on weathering profiles of granitoid and gneissic rocks related to tectonic and landscape evolution of the western sila grande massif calabria southern italy field scale observations and petrographical and mineralogical features are used to characterize in detail the weathering processes the weathering profiles of the granitoid cut slopes are generally simple showing a progressive weathering increase toward the top of the slopes whereas the weathering profiles of the gneissic cut slopes are generally complex with irregularities in the spatial distribution of weathered horizons the microfabric and petrographic analyses show that gneissic samples classes v vi of weathering grade are characterized by higher percentage of altered minerals and microfracture and void rather than granitoid samples classes v vi of weathering grade the main mineralogical changes concern the partial transformation of biotite and the partial destruction of feldspars mainly plagioclases associated with the neoformation of secondary minerals clay minerals and fe oxides and with a substitution of the original rock fabric neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage referred as physical changes coupled with chemical variations the final results of weathering process are a soil like material characterized by sand gravel grain size fraction for the granitoid rocks and by both silt clay and sand silt grain size fraction for the gneissic rocks this generally produces a greater value of the sgi sand generation index for granitoids and explains the great productivity in sandy deposits of this lithology

weathering and morphogenesis in a mediterranean climate calabria italy abstract deeply weathered plutonic rocks occur widely in the sila massif calabria southern italy three representative weathering profiles developed on the hilltops indicate that sand represents more than 50 by weight throughout most of the weathering profile and silt and clay size fractions are also well represented filling the interstices among corestones both sand and finer fractions of grus and soil horizons are thought to be derived from a combination of granular disintegration and chemical decomposition developed on relatively flat terrains of the sila massif these slopes are now experiencing transport limited morphodynamics under a montane modified mediterranean climate the depth of the weathered layers that have suffered little erosional truncation typically exceed 15 m and may reach 50 60 m or more major isolated or grouped exfoliation boulders are the most common minor landform feature developed on the sila massif granite boulders have developed as a result of spheroidal weathering and by removal of the sandy textured granite the schmidt hammer sh test on boulders and corestones suggests three distinctive degree of weathering from moderately to completely weathered rock and that biotite content is the major controlling factor of the granite mechanical behaviour understanding of the dynamics of this weathering system is crucial to the interpretation of the complex suite of variables that control landscape evolution of granitoid terrains

pleistocene glacial relief of the central part of mt prokletije albanian alps abstract the central and highest area of mt prokletije albanian alps is situated in northern albania and eastern montenegro at 42 30 n the highest peak is maja e jezerces 2694 m detailed geomorphological mapping was used to reconstruct the positions of former glaciers the longest ropojana glacier had a length of 12 5 km and surface of 20 km 2 others include valbona glacier 9 5 km 10 5 km 2 grbaja glacier 5 km 6 7 km 2 and bogicevica glacier 6 km 6 9 km 2 three series of moraines can be distinguished the lowest at an average altitude of 990 m average ela 1750 m the middle series at 1350 m ela 1942 m and the highest at 1900 m ela 2123 m as no advanced dating methods have yet been used to provide a numerical chronological framework for these features hypotheses are made based on the comparison with the advanced studies of other similar mountains in the mediterranean region the moraines of the first stage lowest series correspond to one of pre lgm glaciations middle or even early wurmian the second stage moraines probably correspond to lgm and the third stage could be attributed to younger dryas the mapping included a number of inactive and active rock glaciers as well as three small active glaciers surface 5 ha and less at 1980 2100 m altitude in the area close to maja e jezerces

orbicular oxides in carbonatitic kimberlites a renewed interest in mineral spheres that exhibit oscillatory layering is assured with the spectacular discovery of hematite beads in meridiani planum mars the martian blueberries are variously interpreted as sedimentary concretions impact spherules or accretionary lapilli we draw attention to a possible alternative that the spheres of oxides are of igneous origin in carbonate rich upper mantle systems two spherical oxide assemblages from cabonatitic kimberlites in the central namibia formerly south west africa volcanic field show similarities and contrasts to orbicular structures in carbonatites from uganda south africa germany finland and russia structures have rapakivi appearances that bear upon the controversial issue of a relation between kimberlites and carbonatites the first example is from a carbonatitic kimberlite adjacent to the mukorob kimberlite sesu stricto oblate spheroidal nuggets 2 1 5 0 5 cm have olivine now serpentine calcite cores with concentrically layered bands of ilmenite calcite and pedestals of ilmenite ilm 55 geik 40 hem 5 with intergranular calcite the spheres are matrix supported in massive ferroan calcite serpentine with minor apatite f 1 5 wt and barite the matrix contains xenocrystic mg al chromite 55 wt cr 2 o 3 mantled by ilmenite ilm 51 geik 43 hem 6 but the dominant groundmass oxide mineral is mg al ti mat magnetite the second example is from the carbonatite facies of the hatzium kimberlite and is also in a dike mat magnetite pellets 2 3 cm have alternating wide 1 mm and thin 0 25 mm bands of magnetite nucleated on a complex mixture of calcite feo 0 1 wt and serpentine 4 wt feo 0 5 1 wt al 2 o 3 the matrix assemblage of serpentine calcite mat magnetite has mineral compositions similar to the spheroids but is distinguished by abundant ba phlogopite and lesser apatite f 2 wt phlogopite is strongly zoned in patches and bands is kink banded and contains inclusions of mat magnetite calcite the assemblage is typical of phoscorites also known as camaforites in other carbonatites but the ilmenite spheroids appear to be restricted to mukorob our interpretation is that both types result from the nucleation of immiscible liquids a high density and high viscosity ore carbonate silicate component in a low viscosity phosphoric carbonatite melt on olivine or olivine magnetite assisted by frothing and slow degassing on decompression and dike intrusion

late cenozoic history of the eastern llanos of venezuela geomorphology and stratigraphy of the mesa formation abstract the study area corresponds to the mapire river basin in the southern part of the state of anzoategui and constitutes a region of low relief covered by the pleistocene mesa formation this formation consists of horizontally bedded alluvial sediments represented by light gray coarse to fine grained quartz sand with cross bedding marked by ochre red and pink alteration and to a minor extent by marsh deposits represented by laminated and spotted shale the typical topography consists of mesas north of the left margin of the orinoco river the musinacio and mapire mesas to the north of the mesas there is a topography of low hills covered by blocks of ferruginous crusts a typical tropical savanna climate exists in the region with a strong dry season which lasts 4 6 months followed by a rainy season with excess humidity the dominant erosional process is scarp retreat due to the action of the savanna climate on the lithology of the partly unconsolidated sediments it has formed deep canyons in the headwaters and is magnified by tectonic uplift and the lowering of the regional base level however some topographic forms have been preserved due to the hardening of the sands by iron oxides preliminary thermoluminescence dating of sand from two stratigraphic sections confirms the pleistocene age of the mesa formation 0 5 1 ma bp previously suggested by its stratigraphic position and geomorphological interpretation

late pleistocene holocene landscape evolution in fossa bradanica basilicata southern italy abstract studies in the middle basento river basin supported by reliable chronological data tephra layers and a number of absolute datings have allowed the reconstruction of late pleistocene holocene geomorphological evolution of the middle to low fossa bradanica area basilicata southern italy the original upper pleistocene hillslope has been dissected by deep gullies leaving relict slope pediments holocene filling of the basento river valley and gullies occurred as a succession of downcut and fill episodes a first phase of accumulation occurred in the late neolithic which was followed by a downcutting between 4500 and 3700 cal yr bp a second deposition phase took place in the greek roman period between 2800 and 1620 cal yr bp which was interrupted at around 2500 cal yr bp another downcutting phase took place between 1620 and 1500 cal yr bp followed by a deposition phase between 1440 and 1000 cal yr bp after 1000 cal yr bp a deep downcutting took place evidence collected with this study coupled with climate data recorded in other italian and european locations suggests that filling and downcutting episodes in fossa bradanica were predominantly climate driven anthropogenic impact only intensified or weakened these processes

minero petrographical features of weathering profiles in calabria southern italy abstract the paper reports interdisciplinary research of weathering profile stages on gneiss with regard to tectonic and landscape evolutions of the western sila grande massif southern italy the outcropping rocks consist of medium to coarse grained biotite garnet and sillimanite gneiss bgs g and medium to coarse grained biotite muscovite migmatitic gneiss m g the bgs g rocks are fractured and weathered with either massive or foliated texture whereas the m g rocks are intensely weathered and fractured with a massive texture and frequent pegmatite veins petrographical and mineralogical variations show that both gneissic rocks bgs g and m g samples underwent weathering processes characterized by a progressive chemical attack on the labile minerals with generation of neoformed minerals and substitution of the original rock fabric the weathering processes produced phyllosilicates and fe oxides neoformed clay minerals and ferruginous products replaced feldspars and biotite during the most advanced weathering stage microfractures and morphological variations occur on the original rock and thereby affect the surrounding landscape processes the weathering profile mineralogy and rock textures viewed in the context of landscape evolution provide useful insights into the widespread slope movement phenomena in the sila grande massif gneiss

geometry kinematics and deformation rates along the active normal fault system in the southern apennines implications for fault growth throw rates throws and kinematic data have been collected from a localised system of active normal faults in the southern apennines italy to assess how its growth history differs from that for a distributed fault system in the central apennines both show evidence for fault interaction in that 1 faults located centrally along strike have higher throws and throw rates than distal faults and 2 cumulative throw and throw rate profiles summed across strike show central maxima with values decreasing to zero at fault system tips however although throw rates increased through time in the central apennines we are unable to resolve such changes if they exist for the southern apennines specifically throw rates derived from offsets of 18 ka geomorphic surfaces are consistent with total throws in the southern apennines when extrapolated back through time but overestimate total throws in the central apennines by a factor of 2 4 suggesting an increase in throw rate through time for the latter we discuss why some fault systems appear to have throw rates that are constant through time whilst others accelerate during growth interaction

cr spinel compositions in serpentinites and their implications for the petrotectonic history of the zagros suture zone kurdistan region iraq accessory chrome spinels are scattered throughout the serpentinite masses in two allochthonous thrust sheets belonging to the penjween walash sub zone of the northwestern zagros suture zone in kurdistan based on field evidence the serpentinites are divided into two groups 1 highly sheared serpentinites 110 80 ma which occupy the lower contact of the ophiolitic massifs of the upper allochthonous sheet albian cenomanian age and 2 ophiolitic melange serpentinites of mixed ages 150 and 200 ma occurring along thrust faults on the base of the volcano sedimentary segment 42 32 ma of the lower allochthonous sheet the cr spinels of both groups show a wide range of ycr cr cr al atomic ratio from 0 37 to 1 0 while the xmg mg mg fe2 atomic ratio ranges from 0 0 to 0 75 based on the cr spinel compositions of the entire dataset and in conjunction with back scattered electron imaging from core to rim three spinel stages have been recognized the residual mantle stage a cr rich stage and a third stage showing a very narrow magnetite rim these three stages are represented by primary cr spinel pre serpentinization metamorphosed spinel and syn or post serpentinization spinel respectively the chemical characteristics of primary first stage cr spinels of both serpentinite groups indicate a tectonic affinity within a fore arc setting of peridotite protoliths the second stage indicates that cr spinels have undergone subsolidus re equilibration as a result of solid solid reaction during pre serpentinization cooling of the host rock here the primary cr spinel compositions have been partly or completely obscured by metamorphism during the third stage the cr spinels have undergone solid fluid re equilibration during syn or post serpentinization processes both the second and third stages point to diachronous metamorphic paths resulting from continuous tectonic evolution influenced by either slow or fast uplift of mantle protoliths in the fast metamorphic paths the primary chrome spinels are flanked by a very narrow magnetite rim the presence of two groups of distally separated serpentinites with different emplacement ages and fore arc tectonic affinity could indicate that the closure of the tethys ocean culminated in two fortuitous subduction processes

late cretaceous miocene sedimentary development of the arabian continental margin in se turkey adiyaman region implications for regional palaeogeography and the closure history of southern neotethys abstract the middle cretaceous late miocene sedimentary successions that are exposed on the arabian continental margin near adiyaman provide valuable insights into sedimentary tectonic and climatic processes that affected the southern neotethys and its continental margins deposition in the region began with aptian early campanian shelf carbonates followed by deepening during the mid campanian lithoclastic bioclastic turbidites accumulated along the downfaulted northern margin of the arabian platform during the campanian a flexurally controlled foredeep developed in advance of the emplacement of mesozoic allochthonous continental margin and oceanic rocks during the latest campanian early maastrichtian e g supra subduction zone kocali ophiolite alluvial detritus was shed from the emplaced allochthon in non marine to shallow marine deltaic settings during latest campanian early maastrichtian a marine transgression resulted in the establishment of a shallow marine shelf during the mid maastrichtian during the latest maastrichtian the platform submerged initiating deeper water hemipelagic sedimentation uplift took place during the palaeocene resulting in sediment instability slumping and formation of high density subaqueous gravity flows in response to regional faulting and tilting some areas in the north and the southwest emerged during the early middle eocene generating alluvial fans in a warm humid climate that favoured oxidation and reddening the likely control of the tectonic instability was far field compression related to the latest stages of subduction of the southern neotethys or the initial stages of collision of the arabian and tauride continents an oligocene hiatus is likely to reflect the formation of a collision related forebulge followed by flexural subsidence to form an early miocene foreland basin this was finally over ridden by the northerly active continental margin of the southern neotethys during early mid miocene regional suture tightening mid late miocene and related non marine coarse clastic sedimentation was followed by westward tectonic escape of the anatolian microplate towards the aegean region during plio quaternary time

record of cenozoic sedimentation from the amanos mountains southern turkey implications for the inception and evolution of the arabia eurasia continental collision abstract the sedimentary succession of the southern amanos mountains bordering the eastern margin of the karasu rift in south central turkey provides a record of environmental change from the eocene lutetian to the upper miocene tortonian that charts the final evolution of the northern margin of the arabian plate prior to and during continental collision eocene shallow marine carbonates hacidagi formation are interpreted as the youngest unit of the arabian passive margin succession deposited on a northwards facing carbonate ramp subsequent deformation and uplift took place during the oligocene represented by folding of the eocene and older strata this is interpreted to be the result of initial continental collision between arabia and eurasia unconformably overlying the eocene limestone are lower miocene conglomerates sandstones and palaeosols up to 150 m thick kici formation these were deposited in a range of marginal marine settings consisting of alluvial fan fan delta facies flood plain as well as basinal facies subsequently during the middle miocene local patch reefs developed in restricted areas kepez formation followed by upper miocene sediments gokdere formation composed of relatively deep water hemipelagic marl with clastic interbeds which represent a transgression during this period the upper miocene becomes sandier upwards this records the regression from the relatively deep water facies to coastal sediments water depth gradually became shallower until during pliocene time the area became continental in nature by the quaternary rifting had resulted in the development of the karasu rift with active alluvial fans along the margins and braided rivers depositing coarse conglomerates in the axial zone these conglomerates are interbedded with basaltic lava flows that resulted from the region extension across the area this research shows that initial continental collision occurred in this area after the lutetian 40 4 ma and before the aquitanian 23 03 ma supporting the hypothesis that the southern neotethys ocean closed during the late eocene to oligocene this was a time of climatic change including the onset of southern hemisphere glaciation in which the closure of the southern neotethys may have had played an important role

rapakivi texture an indication of the crystallization of hydrosilicates ii rapakivi granites have puzzled all who have seriously studied them typical rapakivi texture is a mixture of variously mantled non mantled or partly mantled concentrically zoned plastically distorted fragmented reaggregated large and small ovoids commonly they are potash feldspar often mantled by and having a variable content of plagioclase some display remarkable sphericity in form composition zoning sequence and crystallization pattern each ovoid reflects an individual development up to five concentric internal plagioclase rims have been observed and some ovoids may be isolated in autoliths and wall rocks anomalies and contradictions arise from any assumption of genesis from a cooling melt the recorded objective data imply that the magma from which rapakivi textures develop had similar diffusive and rheological properties to those of a partly dewatered macromolecular paste or a mixture of gelatinous hydrosilicates as indicated by deep oil wells this system is found at somewhat elevated temperatures at considerable depths within accumulated sediments in addition to the very specific diffusive and rheological properties of such partly dewatered sediments the system has as its major components normal solvated macromolecules of mixed clays silica gels and hydrous ferromagnesian minerals which are characterised by distinctive particle sizes and geometric shapes platelets spheres and rods respectively thixotropic liquefaction and intrusion of such concentrated gelatinous magma or sediment paste introduces relative movement between the component macromolecules whereby they can reduce surface energy by interaction to assume a close packed condition and aggregate during laminar flow into macro accretions comprised essentially of their respective particle shapes syneresis of these precursor accretions desorbs ions including the small montmorillonite particles behaving as a colloidal electrolyte these diffuse from the illitic cores to form a montmorillonite rich rim which it is suggested crystallizes together with the illitic cores to form mantled or polymantled feldspar ovoids crystallization of the rapakivi massif is associated with strong temperature rise stemming from exothermic crystallization of the close packed metastable colloids this follows the development of the characteristic texture the rounded and rimmed precursor accretions are formed during earlier lower temperature episodes of thixotropic liquefaction which are isothermal the fluidity is an earlier event there is high temperature dependent on the rate of water loss but no molten stage forty six typical features of rapakivi texture are described and illustrated each of which is directly attributable to specific interactions in an alternately dynamic and static colloidal system individual correlation between each observed distinctive feature of the rapakivi texture and the well documented physico chemical process is complete for sediment derived granites therefore the rapakivi texture can confidently be assumed to be an indication of the crystallization of their sedimentary hydrosilicate precursors

the geochemistry of the gercus red bed formation of northeast iraq abstract the major minor and trace element sr cr zn ni and co contents in 28 rock samples of red marl and carbonate representing the middle eocene gercus red bed formation of northeast iraq are presented the chemical data show a unique composition of both the red marl and carbonate which reflects the unusual mineralogy of these rocks examination of the averaged marl and carbonate and interelement correlation coefficients shows that four factors have largely contributed to the chemistry and distribution of elements in the rocks these factors are dolomite fe oxide and hydroxide non dolomite minerals and source rock p and sr are largely contained in dolomite mn is almost equally partitioned between dolomite and other detrital minerals na is present as independent phase and associated with clay minerals zn seems to be totally associated with clay minerals the fe oxides and hydroxides of the marl red pigment contains 26 and 22 of the total ni and co content respectively cr and ti are found to be relatively enriched in the red marl the ultrabasic nature of the non dolomite source rock is established the behaviour of ni and co in the strongly oxidising environment associated with red bed deposition is discussed

fossil cryogenic features in paleosols of southern italy characteristics and paleoclimatic significance the work presents the results of a study of two paleosols located at 1350 m a s l on the sila massif in southern italy the purpose of this research is to examine paleoenvironmental conditions during the last glaciation based mainly on soil morphological micromorphological and sedimentological data these two paleosols contain climatically sensitive cryogenic features including a sand wedge an ice wedge cast silt veins silt lenses reticulate silt veins and matrix lenses these features are interpreted to indicate that during the last glacial maximum this area in southern italy experienced conditions characterized by very low temperature little snow cover and great aridity

graphic logging for interpreting process generated stratigraphic sequences and aquifer reservoir potential with analog shelf to shoreface examples from the atlantic coastal plain province u s a abstract this paper demonstrates a process based method of graphic logging and stratigraphic interpretation that is based on a new texturally based classification of clastic sediment which is independent from composition cementation and geologic environment the method integrates facies analysis with sequence stratigraphy because it requires identifying surfaces compiling vertical changes in texture and attributes between surfaces and uses these parameters to identify facies units and interpret continuously deposited intervals four clastic shelf to shoreface successions from the atlantic coastal plain province cretaceous to holocene in age with established chronostratigraphic and sequence stratigraphic frameworks provide examples of the application of this method for each graphic logs standardized for texture show the facies and bounding surfaces that define the thickness and hierarchy of event strata e g sequences beds bedsets parasequences parasequence sets these are directly compared with gamma ray log response patterns and the distribution of factors that impact potential permeability shelf to shoreface successions were chosen because these facies exhibit the greatest diversity in composition siliciclastic carbonate and glauco phosphatics but in spite of this exhibit comparable and predictable graphic and gamma ray response patterns if systematically logged using this method for the process response model examined texture i e principal grain size controls the amplitude width of the graphic log its shape is constant and independent from composition the pattern in the correlated gamma ray log parallels the log of principal grain size except that an inverse response is associated with coarser lags the amplitude of the gamma log is controlled by composition a proxy for permeability developed from standardized textural fields is applied to two of the examples to shows how aquifer or reservoir potential is systematically tied to stratigraphic and sedimentologic parameters

weathering of gneiss in calabria southern italy abstract the effects of weathering in a mediterranean climate on the mineralogy and microfabric of paleozoic gneiss of the sila massif calabria southern italy have been studied field observations show highly weathered rock forms a residual soil micromorphological and mineralogical properties of bedrock and saprolite show that the weathering process is characterized by at least two major stages having two distinct rock microfabrics in the first stage the morphological features of the original rock are preserved and weathering is manifested mainly by microfracturing and large portions of the rock remain unaltered the second stage of weathering involves further development of microcracks and progressive chemical attack on the minerals this latter stage occurs along both compositional and microstructural discontinuities with etch pitting of feldspar and neoformation of clay minerals and ferruginous products replacing feldspar biotite and iron bearing garnet the determination of quantitative petrographic indices provides a measure of the various stages of weathering

the interplay of geomorphic processes and soil development in an upland environment calabria south italy abstract five representative soil profiles outcropping in the area around the cecita lake calabria south italy were characterised by field work chemical and mineralogical analyses optical and scanning electron microscopy interactions among weathering pedogenesis and geomorphic processes are emphasised in an attempt to link the results obtained at different scales of observation the important role of topography in controlling soil development or removal by erosive processes is discussed in relation to the natural geomorphological context and the effects of human pressure both present day and relict features were recognised in the studied soils and discussed in terms of environmental conditions and climatic changes the chemical composition of volcanoclastic components identified in some soil horizons with andosol like field appearance coupled with pedogenetic features contributed useful chronological constraints for the reconstruction of late quaternary geomorphic events

origin of mantle rapakivi feldspars experimental evidence of a dissolution and diffusion controlled mechanism experiments designed to simulate the dissolution of alkali feldspar during magma mixing produced plagioclase mantles that are texturally and compositionally similar to those in some hybrid volcanic rocks in hydrous dacite melt 69 sio2 at 0 8 gpa 850 c orthoclase or93 and sanidine or30 partially dissolved and were mantled by sodic plagioclase an25 30 although plagioclase nucleated epitaxially as a thin shell on the alkali feldspar surface near the time of initial resorption plagioclase subsequently grew inward mostly in the form of parallel blades toaard the receding dissolution surface orthoclase dissolved at a rate approximately proportional to the square root of run duration indicating diffusional control plagioclase grew inward within a static boundary zone of melt that formed between the original crystal dacite interface and the dissolution surface during orthoclase dissolution this boundary zone rapidly and simultancously gained na by diffusion from dacite and lost k by diffusion into dacite ca diffused more slowly into this zone from which non feldspar species were mostly excluded plagioclase was stable where sufficient ca had diffused in that the boundary zone melt intersected the plagioclase saturation liquidus plagioclase subsequently grew toward the receding dissolution surface as the ca compositional gradient and hence the site of plagioclase saturation stepped inward crystallization of plagioclase in the form of parallel blades allowed continued diffusive exchange of melt components between the dissolution surface and the host melt bladed growth also served to maintain at blade tips proximity of plagioclase to the dissolution surface thereby apparently preserving locally a thin zone of low variance melt in natural systems mantling of alkali feldspar by plagioclase will occur in a similar manner when a p t or x are changed to induce alkali feldspar dissolution b sufficient ca is available in the host melt to drive by diffusion boundary zone melt compositions to plagioclase saturation and c temperatures are low enough to stabilize sodic plagioclase and to maintain a coherent boundary zone these reqjirements are satisfied in volcanic systems when alkali feldspar is juxtaposed during mixing with hybrid melts of dacitic composition mantled feldspars in some intrusive systems i e rapakivi granites may form by a similar dissolution and diffusion controlled mechanism textural evidence of a similar origin may be obscurred in intrusive rocks however by products of late stage magmatic and subsolidus processes

orbicules an indication of the crystallisation of hydrosilicates i abstract observations relative to orbicular granites support later rimming layers built up on a previously formed nucleus plasticity and a soft stage during the development of the orbicule initial fluidity and a repeated fluidity of the inter orbicular matrix after or during orbicule formation diffusion of material to add onto and build up individually in each orbicule the successive rhythmic shells continuous growth of the orbicules even after some disruption and crystallisation of the orbicular material later than the formation of the orbicular structure to be consistent with these observations the magma in which orbicules develop must have the diffusive and rheological properties of a concentrated macromolecular paste or gel of mixed hydrosilicates the way in which all available water dissolves in such rock forming magmas at elevated temperature is by reaction with the silicates to form disordered solvated precrystalline hydrolysates such as silica gel clay and hydrous ferromagnesian minerals such an intrusive mass has the appropriate diffusive and thixotropic properties for 1 the formation of accretions aggregated nuclei 2 the overgrowth of concretions rhythmic rimming structures and 3 the repeated isothermal reliquifaction of the interorbicular matrix the orbicules and matrix have subsequently crystallised and further heated by exothermic dehydration reactions where the rate of reaction is governed by the rate at which water escapes from the system crystallisation is not by cooling through a melting point twenty eight characteristic features of orbicules are described and illustrated which fully accord with twelve properties and phenomena attributable only to particle interactions in an alternately dynamic and static colloidal system such an extraordinarily high correlation between the unique properties of the envisaged system and the resultant distinctive complex orbicular structures leaves little room for any alternative interpretation therefore orbicules can be confidently assumed to be an indication of the crystallisation of precursor hydrosilicates

lateglacial and early holocene pollen stratigraphy of the northern apennines italy a contribution to the north atlantic seaboard programme of igcp 253 termination of the pleistocene abstract pollen diagrams supported by 25 radiocarbon dates are presented for four sites in the ligurian emilian apennines northern italy which collectively span the late weichselian lateglacial and holocene coleopteran evidence is available for the lateglacial and early holocene sediments from one of the sites collectively the data provide a an internally consistent series of local pollen assemblages zones such that regional pollen assemblage zones are defined b a detailed chronology of vegetation changes in the region c an impression of environmental changes during the lateglacial holocene transition of particular note is the clear evidence for a marked younger dryas event which together with evidence from other parts of southern europe indicates that the climatic severity of this event did not diminish southwards on the european continent also of significance is the pollen and coleopteran evidence for mixed woodland in the region during the lateglacial interstadial which is not in keeping with previous reconstructions

petrogenesis of orbicular ijolites from the prairie lake complex marathon ontario textural evidence from rare processes of carbonatitic magmatism abstract a unique occurrence of orbicular ijolite is hosted in a matrix of contemporaneous holocrystalline ijolite at the 1 1 ga prairie lake carbonatite complex marathon ontario canada and is the only known occurrence of this textural type in a rock of ijolitic composition this mineralogical and petrological study of this orbicular ijolite highlights many of the differences from other rare occurrences of orbicular rocks described from carbonatites granites diorites and lamprophyres the orbicules occur along distinct densely packed bands in equigranular nepheline rich ijolite and range up to 6 cm in diameter macroscopically the orbicules show variability in the mineralogy of their cores detailed imaging of the cores shows evidence of quench textures radial outward zoning is common near the cores with concentric banding occurring toward the margins of the orbicules the mineralogy of the orbicules consists of nepheline diopside calcite apatite andradite melanite garnet titanite fe rich phlogopite titaniferous magnetite perovskite with secondary natrolite calcite and cancrinite the mineralogy of the host ijolite is similar to that of the orbicules mineral compositions from the orbicular ijolite and the host ijolite are similar within the orbicules anhedral minerals are found occurring in a matrix of garnet throughout the distinct concentric bands the textures within the concentric bands of the orbicules are best described as annealing recrystallization textures the rims of the orbicules form interlocking crystals with the host ijolite resulting in near indistinguishable boundaries the orbicules are interpreted to represent interaction of a partially crystallized quenched ijolitic melt which was in contact with a second pulse of consanguineous ijolite magma immersion in the latter resulted in sub solidus diffusion and annealing recrystallization orbicular textures were produced from previously formed quenched ijolite which was recrystallized producing the monominerallic concentric layers sequentially from the margins toward the center of the orbicule this proposed model for the formation of orbicular ijolite from prairie lake highlights the complexities of these rock types and supports previous models of magma mixing during the later stages of carbonatite emplacement and crystallization

petrology and geochemistry of the orbicular granitoid of caldera northern chile models and hypotheses on the formation of radial orbicular textures abstract the orbicular granitoid of caldera located at the northern part of the chilean coastal range is a spectacular example of radial textures in orbicular structures the orbicular body crops out as a 375 m 2 tabular to lensoidal intrusive sheet emplaced in the lower jurassic relincho pluton the orbicular structures are 3 7 cm in diameter ellipsoids hosted in a porphyritic matrix the orbicules are comprised by a qtz dioritic core 3 5 cm in diameter composed by pl hbl qtz bt kfs with equiaxial textures and a gabbroic shell 2 3 cm in diameter characterized by feathery and radiate textures with a plagioclase hornblende paragenesis the radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core the radial shell called here inner shell is in contact with the granodioritic equiaxial interorbicular matrix through a 2 3 mm wide poikilitic band around the orbicule outer shell the outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine grained rounded plagioclase and magnetite the oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule i e orthogonal to the radial inner shell the coarse grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and k feldspar megacrysts this work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole rock geochemical study of the different parts of the orbicular granitoid together with thermobarometric and crystallographic data and theoretical modeling of the crystallization and element partitioning processes we propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively superheating volatile exsolution undercooling geochemical fractionation and columnar and equiaxial crystallization according to the obtained results the formation of the orbicular granitoid of caldera may have initiated 1 during the generation of a magmatic fracture in the crystallization front of the relincho pluton where the water released by the host crystal mush was dissolved in the new batch of dioritic magma 2 the high influx of water rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls 3 volatile exsolution promoted crystallization under undercooling conditions 4 undercooling and nucleation around the core cold germs involved the physical and geochemical fractionation between two sub systems a gabbroic sub system that comprises the solid paragenesis with a residual water rich liquid and a granodioritic sub system 5 the orbicules including core and inner shell behaved as viscous bodies crystals residual liquid floating in the granodioritic magma 6 higher undercooling rates occurred at the starting stage close to the liquidus promoting columnar crystallization around the cores and formation of the shells conversely in the granodioritic matrix sub system equiaxial crystallization was promoted by low relative crystallization rates 7 the rest of the crystallization process evolved later in the outer shell and the matrix as suggested by the poikilitic textures observed in both sides of the orbicule contact and under conditions close to the solidus of both sub systems shell and matrix the water rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma generating the pegmatitic domains with large kfs megacrysts

textural evolution of the rapakivi granites south greenland sr o and h isotopic investigations the development of rapakivi texture in feldspars from the ketilidian granitoids of south greenland has been investigated using sr o and h isotopes a low temperature signature is found in the sr and o data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the k feldspar ovoids an origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar this mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of k feldspar to microcline rapakivi granites with both white and dark green feldspar occur in south greenland but show no major isotopic differences although the dark alkali feldspars contain significantly more fluid equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution

standardizing texture and facies codes for a process based classification of clastic sediment and rock abstract proposed here is a universally applicable texturally based classification of clastic sediment that is independent from composition cementation and geologic environment is closely allied to process sedimentology and applies to all compartments in the source to sink system the classification is contingent on defining the term clastic so that it is independent from composition or origin and includes any particles or grains that are subject to erosion transportation and deposition modifications to folk s 1980 texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this the revised ternary diagrams include additional textural fields that better define poorly sorted and coarse grained deposits so that all end members gravel sand and mud size fractions are included in textural codes revised textural fields or classes are based on a strict adherence to volumetric estimates of percentages of gravel sand and mud size grain populations which by definition must sum to 100 the new classification ensures that descriptors are applied consistently to all end members in the ternary diagram gravel sand and mud according to several rules and that none of the end members are ignored these modifications provide bases for standardizing vertical displays of texture in graphic logs lithofacies codes and their derivatives hydrofacies hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential folk s 1980 ternary diagram for fine grained clastic sediments sand silt and clay size fractions is also revised to preserve consistency with the revised diagram for gravel sand and mud standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences such as mixed carbonate siliciclastic ramp settings and the extreme ends of depositional systems

the genesis of the gaborone rapakivi granite complex in southern africa the gaborone granite is a mushroom shaped intrusion with a surface area of over 5000 km 2 the intrusion is layered consisting of a central core of rapakivi granite thamaga granite surrounded by successive shells of an equigranular leucocratic granite kgale granite a porphyritic granophyre or microgranite ntlhantlhe microgranite and an outermost zone of massive felsite kanye volcanics the whole lithological sequence is deduced to have been derived from a single highly viscous magma body emplaced into the crust at a high level the genesis is proposed as follows the outer felsites represent quenched primary magma with the underlying porphyritic granophyres having formed during a subsequent tranquil period after emplacement the rapakivi granite core was also of early crystallization above the floor but with significant textural characters impressed during updoming in the late crystallization stage residual liquid rich in sio 2 k 2 o and volatiles migrated upwards to form the kgale granite the gaborone granite was emplaced in the kaapvaal craton at about 2400 ma and its morphology was controlled by pre existing structures in the crust the country rock consists of archaean gneisses lobatse volcanic group supracrustals and locally transvaal supergroup strata chemically the gaborone granite is identical to other early proterozoic non orogenic granites of the kaapvaal craton it is also similar in many respects to the fennoscandian rapakivi granites

origin of red color in the gercus formation eocene northeastern iraq abstract the gercus formation eocene in northeastern iraq consists of a fluvial sequence of associated red and drab beds deposited under an arid to semi arid climate occurrence of pigment on grain contacts in the sandstones and the uniform distribution of pigment in the marls and siltstones indicate that part of the pigment is of predepositional or syndepositional origin most probably detrital ferric hydroxides that coated the grains alteration and corrosion of iron oxides and ferromagnesian minerals intensified pigment around some opaque grains and decreased heavy mineral content compared to the recent river sediments in the area point to intrastratal alteration and the diagenetic origin of part of the pigment iron contents indicate that leaching of ferric iron with an average of 1 41 fe from the drab marl and siltstone beds and 0 74 fe from the drab sandstone beds washed out the pigment or its precursor from these beds

the distribution of fe mn ni cr and co between the acid soluble and fe oxides and hydroxides and matrix fractions of the gercus red beds of northeast iraq abstract twenty samples of the gercus middle eocene red marl and carbonate of northeast iraq have been analysed for their mn cr ni co and fe content in the hcl soluble and free fe oxide and hydroxide phases the greater bulk of hcl soluble mn is associated with carbonate minerals only trace amounts up to 120 ppm of mn are associated with free fe oxides and hydroxides hcl soluble cr ni and co varies between 12 and 67 68 and 529 and 14 and 41 ppm respectively these constitute 4 5 26 and 36 9 respectively of their total content in the samples good positive correlation was found between free fe oxides and hydroxides and the associated cr ni co and mn content cr ni and co was found to be enriched in the free fe oxides and hydroxides relative to their total content in the main matrix enrichment factors are in the order co 5 0 ni 3 5 cr 2 4 this together with the similar partition order of these elements in the hcl soluble phase is in agreement with the relative mobility of these elements during the weathering transportation and deposition regime of the sediments

a new mechanism of granite emplacement intrusion in active extensional shear zones one of the principal ways in which continental crust grows is by the incorporation from deeper within the earth of large volumes of granitic magma a space problem exists1 as to how these magmas are accommodated in the crust traditionally two main emplacement mechanisms have been emphasized forceful intrusion whereby buoyancy driven magmas physically push the crust aside creating granitic diapirs and balloons and passive emplacement characterized by replacive mechanisms such as cauldron subsidence and stoping although more recent work2 3 has demonstrated that space for granites may be created within bends and offsets of large transcurrent faults the simple view of either forceful or passive still fails to account for the intrusive mechanisms of many granites here we report the discovery of a new igneous intrusion mechanism in the superbly exposed proterozoic continental crust of south greenland we have observed that rapakivi granite was intruded as large scale sheets along ductile extensional shear zones that were active during emplacement in such a process the space problem seems to be simply resolved

a new correlation of the glacial moraines in the southern apennines italy abstract analysis of late pleistocene moraines in the southern apennines in southern italy suggests a possible correlation with the sequence in other italian regions but correlations with other parts of europe remain uncertain the lowest moraines consisting of complex loops recognized on the highest peaks in the southern apennines are attributable to the maximum of the last main glaciation with the subsequent rise in the snow line the glaciers retreated to new limits marked by two further stadial moraines the oldest and older dryas respectively which according to federici 1979 can be referred to the first and second apenninic stages the highest moraine loop which is present only on the pollino group may date from the lisens stage of the younger dryas

last glacial maximum glaciers in the northern apennines reflect primarily the influence of southerly storm tracks in the western mediterranean abstract during the local last glacial maximum llgm the northern apennines hosted more than 100 valley and mountain glaciers covering collectively more than 260 km2 cosmogenic 10be exposure ages obtained for the first time along the apenninic range constrain the age of the llgm to pre date ca 21 ka the estimated volumes of these late pleistocene glaciers exceeded 9 1 km3 w e their reconstructed equilibrium line altitudes elas range from ca 1200 m a s l for northerly facing compound basin valley glaciers to ca 1620 m a s l for southerly facing mountain glaciers reconstructed elas in the western sector of the northern apennines were among the lowest recorded for the whole of the italian peninsula including the alps and also when compared with other mountain chains in the surrounding mediterranean basin these probably reflect exceptionally high accumulation rates fed by storm tracks in the western mediterranean which in turn has implications for the atmospheric circulation pattern that prevailed in the region at the time