landform regolith mapping in the west african context abstract in this paper we present an integrated landform regolith mapping protocol chart for west africa developed using a case from central burkina faso the chart accounts for i the specificities of the ubiquitous duricrust capped remnants of the regional paleolandsurfaces particularly the residual or detrital character of the fe duricrusts and ii the diversity of the remaining non duricrusted portions of the landscape with an emphasis on the pitfalls encountered in determining the in situ or transported character of the regolith the paper also provides field identification criteria and illustrations of the typical west african landform regolith associations the landform regolith mapping chart is integrated into a prospectivity chart which is used to define exploration guides i defining sampling strategies ii interpreting potential geochemical anomalies and iii targeting lateral extensions of known bedrock mineralizations the mapping protocol further allows for the definition of a class of landform regolith association propitious to supergene mineral concentrations the mapping protocol is shown to be transposable to wetter contexts and more generally to other tropical shield provinces

relief inversion in the geomorphological evolution of sub saharan west africa abstract the geomorphology of much of sub saharan west africa is dominated by the presence of plateaux and plains with ferruginous and locally aluminous bauxitic duricrusts the plateaux occur at different elevations and have been correlated as two or more palaeosurfaces across much of the region the duricrusts have generally been considered to be residual formed by conformable erosion and chemical wasting of immediately underlying bedrock this concept has been central to interpretations as diverse as the formation and evolution of the landscape and the development of geochemical exploration models recent regolith landform mapping field observations and experience from mineral exploration in southern mali and burkina faso however demonstrate that the duricrusts are mainly ferricretes i e fe oxide cemented sediments these observations require a re interpretation of the geomorphological evolution of the region during the cenozoic the landscape has evolved by several cycles of weathering and erosion deposition triggered by climatic tectonic or other environmental changes it is proposed that an initial bauxitic lateritic regolith was partly eroded following uplift and or a change to a more arid climate and that the detritus rather than being removed was deposited on slopes and valleys during a subsequent humid period of lateritic weathering fe oxide cementation of this detritus formed ferricrete dehydration and hardening of the ferricrete after further uplift or aridity increased its resistance to erosion resulting in relief inversion with the detritus in turn being deposited downslope this too has been weathered and cemented to form a younger ferricrete the occurrence of ferricrete landforms in adjacent countries noted by field observation and inferred from satellite imagery demonstrates that relief inversion is a very widespread and important phenomenon in southern mali burkina faso and adjacent countries in semi arid west africa

introduction to the special issue challenges for mineral exploration in the 21st century targeting mineral deposits under cover abstract the global demand for mineral resources has dramatically increased in the last 50 years the challenge to keep pace with this demand is the driving force for innovation and also drives mineral exploration in regions where mineral deposits are under cover and therefore not exposed or near surface for which novel techniques are required to locate these mineral deposits hidden beneath this often hundreds of meters thick cover material generalizing regions under cover can be globally divided into three end member types 1 regions with intensely weathered cover in tropical or dry desert and semi arid climatic domains based on koppen geiger s climate classification 2 regions covered by sedimentary sequences that can span from the proterozoic to the cenozoic and glacial sediments and 3 regions under water seawater freshwater or ice this special issue aims to contribute to the debate in the field of mineral exploration in regions that are dominated by and present the complexity of cover by presenting different case studies and technology approaches to detect the distal footprint of mineral systems and deposits at depth

postapocalyptic greenhouse paleoclimate revealed by earliest triassic paleosols in the sydney basin australia the permian triassic boundary in the sydney basin of australia is coincident with a pronounced decrease in 13 c isotopic values of organic carbon the last coals anywhere in the world for all of the early triassic ca 6 m y time and extirpation of the glossopteris flora at the top of the illawarra and newcastle coal measures coal bearing paleosols of the latest permian represent extensive swamplands of the seasonally deciduous glossopteris flora in a humid cold temperate lowland southwest of an andean style volcanic arc stone rolls large ribs of floor rock up into the coal within some of the uppermost coals of the permian coal measures can be interpreted as string bogs of a kind now found in cold climates at latitudes of 68 70 which is compatible with a paleomagnetically estimated paleolatitude of 65 85 s for the sydney basin paleolatitude was not much different for earliest triassic time but paleosols of that age include inceptisols and entisols showing substantial chemical and textural weathering more like soils now forming at latitudes of 40 58 than those within polar circles this anomalous high latitude warmth set in at the permian triassic boundary sedimentation rates increased at the boundary marked by geochemically unusual acidification of clay and a dramatic carbon isotopic excursion these changes in environments and ecosystems can be explained by soil erosion following deforestation implied by the plant extinctions and abundant fungal remains at the permian triassic boundary evidence from paleosols can now be added to that from paleontological and isotopic studies showing that disruption of the carbon cycle at the permian triassic boundary resulted in a co 2 or ch 4 post apocalyptic greenhouse paleoclimate

behavior of gold in the lateritic equatorial environment weathering and surface dispersion of residual gold particles at dondo mobi gabon abstract a supergene gold dispersion halo has developed at dondo mobi southern gabon from the weathering of an auriferous lisvenite under equatorial humid rain forest conditions morphological and chemical studies were performed on gold particles extracted from both fresh and weathered rocks from different parts of the dispersion halo the results demonstrate that the gold particles are residual and are subjected to increasing weathering upward through the profile from the protore to the surface in the central part of the halo and at the surface both laterally upslope and downslope weathering continues downward into the formerly barren saprolites which were derived from proterozoic schist and archean gneiss rim of the halo thus the au content progressively decreases as does the ag content of gold particles with distance from the center of the ore body gold particles subjected to increased weathering are smaller with more rounded shapes and surfaces pitted by dissolution the dispersion pattern is controlled by au dissolution and translocation of residual gold particles these processes involve an autochthonous evolution in the central part of the halo and a para autochthonous evolution at the rim of the halo at dondo mobi chloride and humic substances are the only ligands present in significant concentrations that are capable of complexing au thermodynamic calculations demonstrate that under such acidic conditions ph ranges from 4 to 6 gold stability increases with increasing silver content the dominant au complexes formed have been calculated to be an aurous hydroxichloride complex and an organometallic complex both of which are stable at surficial conditions thus both chemical and translocation processes control the mobility of au and gold particles in equatorial lateritic weathering profiles

introduction to special issue on geologic remote sensing abstract herein we provide an overview of science and technology involved in remote sensing and outlines some practical constraints in applications to geological problems we further summarize diagnostic spectral features of important geological material that can be detected using satellite and air borne remote sensing finally the papers contained in the special issue are briefly introduced

new chronological and geochemical constraints on the genesis and geological evolution of ponza and palmarola volcanic islands tyrrhenian sea italy abstract a new geochronological and geochemical study of the volcanic rocks of the ponza and palmarola islands pontine archipelago has been carried out this archipelago is located along the boundary between the italian continental shelf and the opening tyrrhenian basin it is a key area to study volcanism related to the opening of the tyrrhenian sea ponza is the oldest felsic magmatic manifestation in the central tyrrhenian area previous studies suggested that ponza volcanic activity began before 5 ma twenty five new k ar ages constrain the volcanic activity rhyolitic hyaloclastites and dykes to the last 4 2 ma with two episodes of quiescence between 3 7 and 3 2 ma and between 2 9 and 1 0 ma a new volcanic episode dated at 3 2 2 9 ma has been identified on the central and southern ponza with emplacement of pyroclastic units at 1 0 ma a trachytic episode ended the volcanic activity the near island of palmarola exhibits rhyolitic hyaloclastites and domes dated between 1 6 and 1 5 ma indicating that the island was entirely built during the early pleistocene in a short span of time of ca 120 ka although only 6 8 km apart the two islands display significantly different geochemical signatures ponza rhyolites show major and trace element compositions representative of orogenic magmas of subduction collision zones high k calc alkaline and metaluminous rhyolites agpaitic index ai and alumina saturation index asi 3 and nb ta negative anomalies in palmarola the orogenic character is also present but much less marked than in ponza rhyolites have a peralkaline character ai 1 lower lile hfse th ta 11 15 low lree hfse ratios la nb 1 2 close to those of anorogenic lavas and the nb ta negative anomalies are almost absent y nb ratios indicate different magmatic sources one similar to island arc or active continental margin basalts for ponza rhyolites and the others probably involving an oib type component for palmarola rhyolites and ponza trachytes palmarola volcanics represent a transitional magmatism although a preserved collisional geochemical imprint they show geochemical features approaching those of anorogenic lavas erupted in a within plate context the change of magmatism evidenced in this study can be related to the tectonic evolution of the area indeed hf ta and rb contents suggest that the oldest pliocene rhyolites of ponza would emplace in a syn to late collisional setting while the younger pleistocene rhyolites of palmarola would be emplaced in a post collisional setting in which the orogenic character th ta decreases and mantle influence nb ta increases geochemical modeling strongly suggests that the palmarola rhyolites represent the waning stages of a subduction related magmatism the k ar datings allow us to estimate precisely the transition of magmatism to last less than 1 3 ma the transitional magmas may be the result of the upwelling of asthenospheric mantle inducing melting of a metasomatized lithospheric mantle and the mixing between these two sources this upwelling could occur during the extension of the tyrrhenian basin caused by the slab retreat and steepening or during a process of slab break off starting in the pliocene

carbon isotope record of the p t boundary and the lower triassic in the southern alps evidence for rapid changes in storage of organic carbon abstract the carbonate carbon isotope record of lower triassic shelf sediments was investigated in the pufels and l om picol uomo sections of the western central dolomites to derive a complete record from the permian triassic transition to the uppermost lower triassic from the western tethys the carbon isotope record shows the well studied decrease at the permian triassic boundary ptb followed by an increase to about 1 5 at the dienerian smithian boundary the 13c values increase to a pronounced 6 maximum a steady rapid drop until the upper smithian below 2 follows this 13c peak at the smithian spathian transition a steep rise to positive values is documented the positive carbon isotope peak is interpreted to reflect an interval of enhanced burial of organic carbon whereas the isotopic minima provide evidence of periods of oxidation of organic matter and or release of isotopically light carbon this may be ascribed to quickly changing environmental conditions which have already been postulated by paleontologists due to the delayed biotic recovery from the permian triassic extinction event because of the short time interval these positive isotope excursions represent their generation by burial of organic carbon in periods of high productivity and or anoxia appears plausible concurrent carbon isotopic excursions are reported from iran pakistan and oman as well as from southern china which indicate an at least tethys wide event if the excursion proves to be of global significance dark shale deposited in the pelagic panthalassa ocean may have acted as sink for organic carbon supporting the hypothesis of a periodically stratified ocean in the lower triassic

the deep seismicity of the tyrrhenian sea summary l he study reappraises the deep seismicity of the tyrrhenian sea careful examination of the quality of reported hypocentres shows that the earthquakes define a zone dipping nw about 200 km along strike 50 km thick and reaching a depth of about 500 km the zone is slightly concave to the nw at a depth of 300 km but contrary to many previous reports is not tightly concave nor are there significant spatial gaps in the seismicity which is effectively continuous with depth seismicity is however concentrated in the depth interval 250 300 km where the dip of the seismic zone changes from 70 above 250 km to a more gentle dip of 45 at greater depths seven fault plane solutions are available for the largest earthquakes in this depth interval all of them consistent with a p axis down the dip of the seismic zone and all of them requiring movement on faults out of the plane of the subducting slab two deep earthquakes near naples lie well outside the main zone of activity for one of which a fault plane solution is available that has ap axis not aligned with the dip of the seismic zone the tightly concave slabgeometry favoured by other reports is supported mainly by the location of these events near naples which we think may represent deformation in a separate probably shallower dipping piece of subducted lithosphere the lack of shallow seismicity and particularly of thrust faulting earthquakes at the surface projection of the benioff zone suggests that active subduction has ceased estimates of the convergence rate responsible for subduction in the last 10 myr far exceed the present convergence rate of africa and eurasia suggesting that the subduction was related instead to the stretching and thinning of the crust in the tyrrhenian sea

mineralogy and geochemistry of the weathering of the disseminated nickel sulfide deposit at mt keith western australia mineralogical and chemical studies have been made of the weathering profile developed from serpentinized dunite containing disseminated ni fe sulfides sulfide oxidation proceeds with the replacement of pyrrhotite by marcasite followed by the replacement of pentlandite by violarite then the replacement of violarite by millerite and finally by the decomposition of the sulfides this sequence is interpreted in terms of local electrochemical reactions and is contrasted with supergene sulfide alteration of massive or matrix sulfides nickel mn co zn and cu are enriched in this part of the profile termed the supergene zone the serpentine host rock is bleached and some mg is lost with increased weathering the serpentine becomes progressively replaced by clay minerals and substantial amounts of quartz and dolomite are deposited geochemically this zone termed the quartz dolomite zone is marked by sharp decreases in s and mg and by generally increasing si fe ni cu mn co zn al ti v as and ba overlying this zone is the ferruginous zone characterized by the dominance of goethite the common presence of clay minerals and the absence of serpentine manganese oxide minerals containing ni co and cu are precipitated in the lower part of this zone creating a local enrichment of these elements in the upper part of the ferruginous zone these elements are depleted aluminum cr ti v zr and as increase toward the top of this zone apparently owing to the introduction of these components from outside the serpentinite body toward the top of this same zone original rock textures are destroyed and concretionary pisolites develop the overlying hardpan clay zone is developed from transported detritus the mt keith weathering profile is broadly similar to profiles developed on other serpentinized dunites in western australia and particular differences can be explained by differences in their primary mineralogy and geomorphological setting there does not appear to be a simple relationship between the ni contents of the primary zones and those of derived surficial materials

spinifex biogeochemical expressions of buried gold mineralisation the great mineral exploration penetrator of transported regolith a major challenge for mineral explorers is to efficiently detect mineralisation beneath the weathered cover that extends across the landscape determination of the elemental composition of plants biogeochemical exploration can aid in the detection of buried ore deposits due to their root penetration through the weathered cover at the coyote prospect in western australia a range of plant species were sampled traversing a buried au orebody here it is shown that the soft spinifex triodia pungens accumulated important pathfinder elements related to the mineralisation which produced a multi element surficial expression of the underlying ore deposit spinifex grasses are one of the most widespread grasses over the australian continent and have vertical root systems that can extend for many 10s of metres through sedimentary cover and interact with buried mineral deposits and alteration zones in the underlying substrate spinifex biogeochemistry therefore has potential to be a low cost low environmental impact sampling medium for mineral exploration programs across large parts of arid australia the examination of similar grasses from other semi arid and arid regions from around the world therefore also warrants further investigation

proximal and remote spectroscopic characterisation of regolith in the albany fraser orogen western australia abstract vast parts of the australian continent are prospective for precious and base metal mineralisation but exploration is hindered by extensive cover of often deeply reaching regolith new operational exploration methods are required that can help to characterise the cover and provide information about bedrock signatures this paper shows how mineral mapping information from a combination of satellite multispectral advanced spaceborne thermal emission and reflection radiometer aster imagery and drill core hyperspectral profiling data hylogging can be used to unravel the regolith stratigraphy and to describe regional variations of regolith landforms delivering important information for mineral exploration the case study is located in the neale tenements in the northeastern albany fraser orogen western australia which is prospective for tropicana style gold mineralisation by interpretation of indicator minerals from hyperspectral drill hole logging data the regolith stratigraphy atop a metamorphic basement comprising saprock ferrugineous saprolite kaolinitic saprolite silcrete and transported cover is recorded in cm detail important mineralogical parameters extracted from the hyperspectral subsurface data and validated by xrd and ftir are 1 the abundance and type of iron oxides 2 the abundance and crystallinity of kaolinite 3 the abundance and composition of primary minerals such as white mica and 4 the abundance of quartz the hylogging data served as ground control points for mineral mapping information provided by csiro s aster geoscience products which are a collection of mineral maps that highlight variations in the abundance type or chemistry of selected mineral groups key aster geoscience products for regolith characterisation were the ferric oxide and aloh abundance and composition images the comparison of the surface with the subsurface data suggests three major different regolith landforms including erosional depositional and relict areas which were used to generate a map showing transported versus relict and erosional areas erosional domains were mapped out in great detail providing important information for exploration in saprolite dominated areas furthermore source areas of transported material could be identified which may help to understand the distribution of geochemical signatures collected during for example geochemical soil sampling projects

the development and behaviour of low angle normal faults during cenozoic asymmetric extension in the northern apennines italy abstract movements on low angle normal faults lanf are not predicted by traditional anderson byerlee frictional fault mechanics our investigations centre on three normal fault systems active at distinct times during the regional extension of the northern apennines with each showing different degrees of crustal exhumation these are from e to w the altotiberina fault system umbria the radicofani fault system tuscan mainland and the zuccale fault system isle of elba regional extension has been a continuous process since middle miocene migrating progressively from west to east with deformation accommodated by a set of e to ne dipping lanf and more steeply sw dipping antithetic structures the lanf acted as regional detachments accommodating a majority of the extension in the northern apennines with individual faults exhibiting several kilometres of displacement regionally the stress field has been characterised by a vertical 1 and a ne sw tuscan mainland and umbria to e w elba trending 3 where exposed at the surface the main lanf detachments possess a well developed fault core of foliated fault rocks in which fluids have played a key role in weakening due to reaction softening and the onset of stress induced solution precipitation mechanisms we speculate that the e dipping normal faults initiated with relatively low angles of dip due to differential drag generated by mantle flow following slab retreat and roll back beneath the apennine chain

birth of a volcanic passive margin in cambrian time rift paleogeography of the ossa morena zone sw spain abstract mapping at 1 10000 scale of both north n and south s flanks of the variscan monesterio antiform in the ossa morena zone southern spain in association with detailed petrographic and major element analyses of magmatic rocks has revealed the building of a passive but volcanically active oceanic margin in cambrian time this margin was located in northern gondwana and represents the beginning of an extensional tectonic regime that concluded with the opening of the rheic ocean at time of eruption middle cambrian the n flank was located on the northern coastline of a marine basin in the process of passive rifting the vents mainly located in its western part were subaerial continental and or shallow marine on the s flank eruptions and deposits were shallow marine occurring as lava flows and pillows interstratified within shallow marine sediments on both flanks intrusives were emplaced after the extrusives lateral thickness variations of the sedimentary deposits testify to the building during four distinct periods of a rifted passive margin with a shifting locus of volcanic activity over time the composition of magmas was bimodal the mafic magmas are silica saturated alkaline to sub alkaline and somewhat ti rich perhaps originating from partial melting of a subcontinental mantle that was less metasomatized with time the youngest magmatism with an affinity close to that of morb likely had an asthenospheric source the alkaline felsic products are diverse and may have originated from a very heterogeneous continental crust in each set partial melting relationships prevail suggesting that the melts rose along open fractures as soon as they formed in the context of lithospheric thinning it is possible that mantle and crustal melting was triggered by decoupling between rheologically different materials

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

the lithosphere asthenosphere system in the calabrian arc and surrounding seas southern italy a fairly detailed structural model of the lithosphere asthenosphere system thickness s and p wave velocities of the crust and of the uppermost mantle layers has been defined in the calabrian arc region southern tyrrhenian sea calabria and the northwestern part of the ionian sea in southern italy using seismic data from literature as a priori constraints of the nonlinear inversion of surface wave data

supergene gold in silcrete as a vector to the scuddles volcanic massive sulfides western australia this study reports data on the first occurrence of economic supergene au in a near surface silcrete horizon over the scuddles volcanic massive sulfide vms deposit in the golden grove district western australia a deep weathering profile was developed on dacite rhyodacite siltstone and breccia that host primary cu zn and pb sulfides with au ag ore from the base the weathering profile at scuddles is subdivided into five main zones 1 supergene sulfide enrichment zone 2 supergene oxide enrichment zone 3 ferruginous saprolite 4 leached zone of kaolinitic saprolite and silcrete and 5 lateritic zone of mottled clays ferruginous duricrust and gravels silcrete at scuddles hosts supergene au deposit that formed in two generations the first is intimately associated with ag halides during supergene enrichment of the primary vms and the second is associated with kaolinite in dissolution cavities inside ag halides during lateritic weathering these two au generations imply more than one mechanism of au remobilization and formation multiple fluid pathways and superimposed episodes of weathering under variable timing and climatic conditions gold grains are pure nanocrystalline up to 10 nm and clustered together forming microcrystalline aggregates a few au grains are residual in silcrete with ag sb rich cores and ag poor rims possibly formed during dealloying of ag and sb chemically au in silcrete is associated with a multi element concentration of ag i br cl sb sn bi hg mo w te and ge gold and ag in the supergene weathering profile were mobilized to silcrete as a halide complex under acidic and saline conditions generated during the oxidation of massive sulfides at depth the precipitation of au ag halides in the silcrete may have taken place in response to a rise in ph gold was likely remobilized with kaolinite from the surface lateritic zone facilitated by decays of plant roots and bioturbation the clustered spongy cube octahedral platy six sided dendritic and reniform like morphologies of au in cavities inside ag halides may indicate biogenic related processes in its precipitation recognizing au ag rich silcrete over the buried vms at scuddles highlights the significance of the silcrete in finding buried vms particularly if the gossan is absent

accidental gas emission from shallow pressurized aquifers at alban hills volcano rome italy geochemical evidence of magmatic degassing abstract recent studies suggested that alban hills rome is a quiescent and not an extinct volcano as it produced holocene eruptions and several lahars until roman times by water overflow from the albano crater lake alban hills are presently characterized by high p co2 in groundwaters and by several cold gas emissions usually in sites where excavations removed the superficial impervious cover gas consists mostly of co 2 with minor h 2 s and the diffuse co 2 soil flux is locally very high accidental gas blowouts occurred during shallow well drillings tens to hundreds m depth in zones with no surface gas manifestations indicate the presence of gas pressurized aquifers confined underneath impermeable layers within both the volcanic rock pile and the underlying pleistocene loose sediments degassing mostly occurs in correspondence of bordering faults of buried horsts cut in the mesozoic carbonate basement hosting the main aquifer carbon isotopic composition 13 c co2 suggests that co 2 is at least partly originated by thermal decarbonation of these limestones 3 he 4 he isotopic ratio of the gas up to 1 9 ra is the same or even slightly higher than that of olivine and clinopyroxene fluid inclusions of the alban hills volcanic products indicating a possible magmatic source for the gas low r ra values compared to morb and island arc magmas are characteristic of the potassic roman comagmatic province and reflect a deep involvement of crustal material in the magma genesis the lack of high temperature fumaroles can be explained by an efficient meteoric cold water penetration and circulation in the volcano permeable terrains

reprint of introduction to special issue on geologic remote sensing abstract herein we provide an overview of science and technology involved in remote sensing and outlines some practical constraints in applications to geological problems we further summarize diagnostic spectral features of important geological material that can be detected using satellite and air borne remote sensing finally the papers contained in the special issue are briefly introduced

spatial variations of p residuals and deep structure of the european lithosphere spatial variations of these normalized residuals as large as 2 s were derived from events in different focal regions an average residual at each station was calculated from 23 selected groups compiled from 181 events evenly distributed as to their azimuths and distances the 3 d inversion of the residuals yielded very much the same picture of the relatively high and low velocity provinces for the upper layer of the mantle as compared with the map of average residuals the map of average residuals mainly reflects variations in the thickness of the lithosphere and its thermal state regions of low velocities include the pannonian basin and central carpathians the northern apennines and the po plain as well as the rhine graben the rhenish massif and the north german polish platform high velocities are observed in the south western margin of the east european platform and in three well defined zones situated in the inner part of the western alps in the eastern part of the austrian alps and in the eastern carpathians besides the effects of inhomogeneities also anisotropic effects are anticipated from the spatial diagrams of the residuals which show a similar pattern within large tectonic provinces r

petrology and geochemistry of volcanic rocks from the island of panarea implications for mantle evolution beneath the aeolian island arc southern tyrrhenian sea abstract major trace element and radiogenic isotope sr nd pb data are reported for a suite of rocks from the panarea volcano a large structure that is largely hidden below sea level and outcrops only as a group of small islands between lipari vulcano and stromboli in the eastern aeolian arc the exposed rocks mostly consist of high potassium calc alkaline hkca andesites dacites and some rhyolites shoshonitic basalts have been collected from submarine centres mafic calc alkaline ca rocks occur as thin layers of late erupted strombolian scoriae major and trace element data are scattered but define generally linear trends on inter element diagrams sr isotope ratios do not display significant increase with evolution although rough positive trends of 87sr 86sr versus sio2 and rb sr can be recognised within some units the mafic rocks display varying enrichment in potassium from ca to shoshonitic compositions and are characterised by variable abundances of incompatible trace elements which increase with potassium there is an increase of 87sr 86sr ratios and a decrease of 143nd 144nd and 206pb 204pb ratios from ca to hkca and shoshonitic mafic rocks the scattered and incomplete nature of the outcrops make it difficult to constrain magmatic evolution at panarea geochemical and isotopic data suggest that afc and mixing were important evolutionary processes however geochemical modelling does not support the possibility that the first order compositional variations observed in the mafic rocks are the result of these processes and suggests a genesis in a heterogeneous mantle source recent studies have highlighted strong differences in terms of incompatible trace element ratios and isotopic signatures between the western central and the eastern aeolian arc rocks from the western islands alicudi filicudi salina vulcano have typical magmatic arc geochemical signatures and relatively unradiogenic sr isotope compositions by contrast the eastern island of stromboli has a more radiogenic sr isotope signature and shows trace element abundances and ratios that are intermediate between arc and intraplate compositions panarea mafic rocks have geochemical and isotopic signatures that are intermediate between those observed in the two sectors of the arc the late erupted ca scoriae of panarea have trace element and isotopic compositions similar to those of the mafic rocks from the western islands of filicudi and alicudi whereas the hkca and shoshonitic mafic rocks have isotopic and trace element signatures that are closer to those of stromboli this reflects the particular position of panarea which is sited midway between the western central arc and stromboli according to some recent views subduction of the ionian sea plate is actively occurring beneath the eastern aeolian arc with rollback of the subduction zone toward the southeast the tindari letoianni malta escarpment fault zone is considered to be the boundary between the active subducting plate in the east and the african plate and western aeolian arc in the west it is suggested that the rollback of the ionian plate generated inflow of mantle material from below the western arc into the mantle wedge above the subducting ionian slab this situation generated a hybrid mantle beneath panarea which resulted in a mixture of western type and resident eastern arc mantle materials the latter had a composition akin to the source of stromboli magmas early hkca and shoshonitic magmatism tapped such a hybrid source whereas the younger ca activity has been derived from melting of unmodified western type mantle material the late eruption of ca rocks with a composition similar to western arc can be explained by assuming that a continuing inflow process had increased the amount of western type mantle with time thus favouring the late appearance of ca magmas this hypothesis accounts for the overall decrease of potassium with time which is the opposite of the trend observed in other aeolian islands

rheology of the northern apennines lateral variations of lithospheric strength abstract a thermorheological wsw ene profile along the northern apennines is presented the variations in rheology are estimated using two different models the conventional model in which only frictional sliding and power law creep are taken into account and a new model in which in addition to the previous two mechanisms a high pressure brittle fracture mechanism is included upper and lower bounds for the rheology are considered a hard case where the lower crust is mafic granulite and the lithospheric mantle is dry peridotite and a soft case where the lower crust is felsic granulite and the lithospheric mantle is wet peridotite important differences in lithospheric rheological structure are inferred between the western and the eastern sectors of the chain in the former a creme brulee structure generally applies in the latter a jelly sandwich structure applies these rheological models therefore are not alternative but end members of a continuous spectrum of rheological behaviours

west african lateritic pediments landform regolith evolution processes and mineral exploration pitfalls this paper is a contribution to the understanding of surface dynamics of tropical shields over geological timescales emphasis is put on the fundamental and applied implications of regolith production and dispersion processes through the formation dissection and preservation of landforms it is based on the case study of sub saharan west africa which recorded neogene 24 3 ma stepwise dissection of its topography through the emplacement of three lateritic pediment systems which still occupy most of its surface pediments are erosional transportation slopes having been weathered and duricrusted pediment regolith associations therefore depend on the parent rock transport dynamics and preservation of the material having transited on their surface as well as on the intensity of their weathering duricrusting iron oxy hydroxide cemented clastic sediments detrital ferricretes and unconsolidated clastic sediments are the dominant outcropping material and as such represent a challenge for mineral exploration that relies on surface geochemical sampling to detect metal concentration in the bedrock landform regolith mapping beyond the scale of modern interfluves combined with paleolandscape reconstitution are relevant to provide exploration guides for i interpreting geochemical anomalies on pediments ii tracing their potential source when they have been transported on pediments and iii targeting suspected ore bodies concealed beneath pediment s past and present latitudinal climatic zonation of pedimentation and weathering patterns suggests a gradation of pedimentation process across the intertropical zone and explains why pediments may have been overlooked in equatorial environments with implications for mineral exploration successive pediment systems adapted to uneven knickzone bearing river networks producing a spatially consistent and reduced 80 m stepping pattern of pediments independent from elevation or distance to base level pediments pediplains are therefore not proxies of uplift and their preservation over geological timescales typifies regions submitted to 10 m my erosion rates the identification and study of lateritic pediments bear important implications on shield sediment routing systems and a better access to the bedrock and its resources which may still be underestimated in the tropics

seismic anisotropy beneath the northern apennines italy and its tectonic implications we examined shear wave splitting in sks and s phases from 22 teleseisms at 10 temporary stations on a transect across the northern apenninic arc the array near 43 n spans from corsica island across the tyrrhenian region and the apenninic belt to the adriatic coast we applied particle motion covariance matrix decomposition and cross correlation methods to estimate the polarization direction of the fast split shear wave and the delay time between split phases t most of the analyzed shear waves show clear evidence of splitting the in the adriatic foreland and in the apennines are approximately parallel to the strike of the mountain belt nw se the largest t correspond to the highest elevations suggesting that anisotropy is related to the compressional tectonics which built the apennines and that this tectonic compression involved at least the entire lithosphere in the tyrrhenian area we observe oriented about e w suggesting a reorientation of the mantle fabric due to astenospheric flow responsible for the e w post orogenic extension observed at the surface

passive seismology and deep structure in central italy in the last decade temporary teleseismic transects have become a powerful tool for investigating the crustal and upper mantle structure in order to gain a clearer picture of the lithosphere asthenosphere structure in peninsular italy between 1994 and 1996 we have deployed three teleseismic transects in northern central and southern apennines in the framework of the project geo modap european community contract ev5v ct94 0464 some hundreds of teleseisms were recorded at each deployment which lasted between 3 and 4 months although many analyses are still in progress the availability of this high quality data allowed us to refine tomographic images of the lithosphere asthenosphere structure with an improved resolution in the northern and central apennines and to study the deformation of the upper mantle looking at seismic anisotropy through shear wave splitting analysis also a study of the depth and geometry of the moho through the receiver function technique is in progress tomographic results from the northernmost 1994 and the central 1995 teleseismic experiments confirm that a high velocity anomaly hva does exist in the upper 200 250 km and is confined to the northern apenninic arc this hva already interpreted as a fragment of subducted lithosphere is better defined by the new temporary data compared to previous works based only on data from permanent stations no clear high velocity anomalies are detected in the upper 250 km below the central apennines suggesting either a slab window due to a detachment below southern peninsular italy or a thinner perhaps continental slab of adriatic lithosphere not detectable by standard tomography we found clear evidence of seismic anisotropy in the uppermost mantle related to the main tectonic processes which affected the studied regions either ne sw compressional deformation of the lithosphere beneath the mountain belt or arc parallel asthenospheric flow both giving nw se fast polarization direction and successive extensional deformation e w trending in the back arc basin of northern tyrrhenian and tuscany preliminary results of receiver function studies in the northern apennines show that the moho depth is well defined in the tyrrhenian and adriatic regions while its geometry underneath the mountain belt is not yet well constrained due to the observed high complexity

exploring uni element geochemical data under a compositional perspective abstract different features of geochemical information were studied by comparing spatial distribution of concentration values and compositional data values geochemical data are compositional and should be treated as such to avoid spurious correlations and misleading interpretations however geochemists are also interested to discuss in terms of elemental concentrations in this work the spatial distribution of fe mn ti co cr ni and v based on 3535 topsoil samples collected in campania region southern italy and analysed by icp ms after aqua regia digestion is studied unielement maps and coda based maps namely of ilr transformed data and of two subcompositions of 3 components have been produced and interpreted results show that the ilr maps often show different geochemical patterns from those provided by the maps based on raw concentrations namely for v fe and co this is not surprising as each studied ilr is a log ratio of an element against the others and account for the compositional variability nevertheless the geochemical patterns of both raw and ilr based maps relate mostly with the geolithological features of the region 1 ti ni cr log ratio variables are the best pathfinder in differentiating between volcanic relative enrichment in ti and non volcanic relative enrichment in ni and cr areas 2 soil alteration phenomena could locally enhance log ratios of ti due its high geochemical stability 3 the spatial analysis of ilr fe and ilr mn variables amplifies their relative degree of enrichment in correspondence of silici clastic formations suggesting that mn fe oxides of clay minerals mainly dominate the geochemical composition of the soils of the survey area 4 local enrichments of cr and ni at the main rivers mouths and in the metropolitan areas of naples and salerno possibly of anthropogenic origin are highlighted in the 3 part subcomposition analysis the developed exploration methodology of uni element geochemical data under a compositional perspective leads to deeper insight and the gain is a more accurate interpretation of processes controlling soils geochemical variability

origin of sulphur in the quaternary perpotassic melts of italy evidence from hauyne sulphur isotope data abstract hauyne na ca 4 8 alsio 4 6 so 4 s 1 2 is a rare mineral which occurs in ejecta and lavas of perpotassic volcanoes of the roman comagmatic region italy as a high temperature sulphur bearing phase it is a valuable indicator of the sulphur characteristics in the melt therefore sulphur isotope determinations were carried out for the first time on samples from some italian volcanoes on average 34 s values 1 1 to 10 8 are above the normal range 0 to 3 for igneous materials and can be classified into two groups phenocrysts in lavas avg 34 s 4 2 and metasomatic crystals in ejecta avg 34 s 8 3 such data are compatible with the hypothesis that hydrous fluids released from subducted sediments were responsible for the high volatile and lile supply to the mantle region where the magma generating process occurred

a geological assessment of airborne electromagnetics for mineral exploration through deeply weathered profiles in the southeast yilgarn cratonic margin western australia abstract mineral exploration in regolith dominated environments is challenging requiring the development of new technical tools and approaches when airborne electromagnetics aem is combined with information on stratigraphy mineralogy geochemistry drilling and landscape observations in a geological context it becomes a powerful approach to describe the architecture of the regolith cover this has significant implications for mineral exploration in any regolith dominated terrain rdt this research presents two case studies of aem data integrated in a geological context for mineral exploration in the yilgarn craton margin albany fraser orogen afo in one of the study sites presented study site 1 neale tenement the availability of aem data allowed for lateral and vertical extrapolation of the information contained in datasets at specific locations thereby creating a 2d architectural model for the regolith cover in addition it was determined 1 the total thickness of the regolith cover and its variability between 2 m and 65 m 2 that low conductivity transported overburden and silcrete units with a total thickness between 5 and 45 m is widely distributed capping the upper saprolite and 3 that the silcrete unit varies laterally from being completely cemented to permeable and that these permeable areas windows coincide vertically with mineralogical textural moisture salt content changes in the underlying saprolite resulting in increased conductivity this has been interpreted as resulting from more intense vertical weathering and consequently a higher vertical geochemical dispersion of the basement signature towards surface aem has been used to assist in identifying and describing the lateral continuity of these windows in areas with no direct field observations surface geochemical sampling above these permeable areas may deliver more reliable geochemical basement signatures in the second study site silver lake tenement the aem data was strongly influenced by the high conductivity of the hypersaline groundwater this had a significant effect on the aem response resulting in reduced depth penetration and reduced resolution of subtle conductivity contrasts between cover units despite this the aem data set combined with geological observations in the area was able to map the presence and extent of a buried palaeochannel network the most significant architectural sedimentary feature in the cover this interpretation allowed for a more efficient drilling campaign to be designed to sample the fresh basement rock suites in the area by avoiding drilling into palaeochannels integrated and constrained by the geological context the application of aem conductivity models by geologists is envisioned as one of the most promising tools within the exploration geologist toolbox to understand the architecture of the cover

understanding the collapse eruption link at stromboli italy a microanalytical study on the products of the recent secche di lazzaro phreatomagmatic activity abstract the secche di lazzaro sdl phreatomagmatic activity with the associated neostromboli sector collapse represents the most powerful activity of the last 6 ky at stromboli as revealed by its present day activity stromboli is one of the most eruptive volcanoes in italy and flank instability along its nw flank is a common process volcano instability is often dramatised by explosive eruptions thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself the possible role of pre eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies we studied the juvenile components scoria and pumice of the pyroclastic deposits from the sdl phreatomagmatic activity with the aim to understand the eruption collapse link the sdl pyroclastic sequence has been investigated in three different outcrops at secche di lazzaro sdl sw sequence at vallone del monaco sdl s and along the old path from stromboli village to the active craters sdl n juvenile components are ks shoshonites similar to the most evolved lavas erupted at the end of the neostromboli potassic period our study indicates that the sdl system is strongly heterogeneous and made up by at least two different sequences sdl n and sdl sw sdl s with different textural characteristics of the deposits and composition of the juvenile components mineral chemistry data show a variable presence of recycled crystals antecrysts possibly deriving from the previous neostromboli activity up to 13 ky ago whole rocks are characterised by small but significant differences between the sdl n and the southern samples pointing out the presence of compositionally different potassic magmas and the crystallization and recycling of slightly different mineral assemblages a clear isotope heterogeneity has been also found and explained by the presence of 10 minimum of less radiogenic antecrysts whereas crustal contamination would have only affected the higher sr radiogenic residual melt these data suggest that the sdl phreatomagmatic eruptions were fed by compositionally distinct potassic magmas which rested and evolved in two shallow magma conduits when the magma supply ceased in the waning phase of the neostromboli activity our results also rule out the occurrence of new arrivals of refreshing magmas in the sdl feeding system as well as other internal magma related causes as triggers for the sdl explosive eruptions accordingly external collapse related causes seem effectively more suitable for triggering the sdl phreatomagmatic eruptions by decompression of the magmatic systems we also suggest the sdl n and sdl sw sdl s sequences are generated by two respective explosive events separated in time and or space they can be respectively related to multiple failures of sciara del fuoco which successively depressurised the sdl n and the sdl sw sdl s magma conduits

upper mantle domains beneath central southern italy petrological geochemical and geophysical constraints the italian peninsula shows high complexity of the mantle crust system and of the plio quaternary magmatism the lithospheric thickness has remarkable lateral variations from about 110 km to about 30 km intermediate and deep focus earthquakes indicate the presence of a lithospheric slab under the aeolian calabrian area and at the southern end of campania much less extensive intermediate depth seismicity characterizes the roman tuscany region where the existence of a relic slab has been hypothesized the deep seismicity in the southern tyrrhenian sea is associated with active calcalkaline to shoshonitic volcanism in the aeolian arc alkaline potassic volcanism occurs in central italy and potassic lamproitic magmatism coexists with crustal anatectic and various types of hybrid rocks in the tuscany area the parallelism between changing magmatism and variation of the structure of the crust mantle system makes central southern italy a key place where petrological and geophysical data can be used to work out an integrated model of the structure and composition of the upper mantle beneath tuscany the upper mantle has been affected by intensive subduction related metasomatism this caused the formation of phlogopite rich veins that cut through residual spinel harzburgite and dunite these veins possibly partially molten may explain the unusually soft mechanical properties that are detected just below the moho in the roman province the upper mantle is formed by a relatively thin lid the mantle part of the lithosphere and by metasomatic fertile peridotite probably connected with the upraise of an asthenospheric mantle wedge above the apennines subduction zone geochemical data indicate that metasomatism though still related to subduction had different characteristics and age than in tuscany in the eastern sector of the aeolian arc and in the neapolitan area the upper mantle appears to be distinct from the roman and tuscany areas and is probably formed by fertile peridotite contaminated by the presently active subduction of the ionian sea floor the overall picture is that of a mosaic of various mantle domains that have undergone different evolutionary history in terms of both metasomatism and pre metasomatic events the coexistence side by side of these sectors is a key factor that has to be considered by models of the geodynamic evolution of the central mediterranean area

the development of regolith exploration geochemistry in the tropics and sub tropics abstract this essay traces the development of geochemical exploration from its early beginnings in the modern era during the 1930s concentrating especially in its application to deeply weathered terrain in the tropics and sub tropics following promising results obtained in temperate regions in north america and europe test orientation surveys were conducted to see whether similar procedures were applicable in the tropics where conventional geological prospecting was largely precluded due to the extensive cover of a deep lateritic regolith and consequent lack of outcrop after initial work in sierra leone and nigeria the emphasis transferred to east africa in the 1950s and 1960s aimed principally at cu exploration many of the basic principles for exploration in dominantly residual free draining terrain were quickly established in this period exploration in terrains with more complex weathering histories however raised a number of difficulties due to leaching and secondary concentrations of elements problems in selecting and identifying appropriate sample media and extensive transported overburden these were encountered especially in more arid regions in australia and africa during exploration for ni and au during the 1970s and 1980s this led to a change in approach placing weathering and geochemical dispersion in the context of regolith and landscape evolution a return to the early concept of landscape geochemistry the 3d expression of mineralization in the landscape is depicted as empirical conceptual models that account for both relict features and active processes and portray element associations dispersion mechanisms and host materials they also indicate suitable sample media sampling intervals and procedures for analysis and interpretation

geochemistry of the albano and nemi crater lakes in the volcanic district of alban hills rome italy abstract lake albano located 20 km to the se of rome is hosted within the most recent crater of the quiescent alban hills volcanic complex that produced hydromagmatic eruptions in holocene times stratigraphic archaeological and historical evidence indicates that the lake level underwent important variations in the bronze age before the iv century b c several lahars were generated by water overflows from the lake and in the iv century b c romans excavated a drainage tunnel the lake is located above a buried carbonate horst that contains a pressurized medium enthalpy geothermal reservoir from which fluids escape to the surface to produce many important gas manifestations of mostly co2 previous studies recognized the presence of gas emissions also from the crater bottom in 1997 the possibility of a nyos type event triggered by a lake rollover was considered very low because the co2 water concentration at depth was found to be far from saturation however considering the high population density nearby the italian civil protection department recommended that periodical monitoring be carried out to this scope we initiated in 2001 a systematic geochemical study of the lake thirteen vertical profiles have been repeatedly carried out in 2001 2006 especially in the deepest part of the lake 167 m in 2006 measuring t ph dissolved o2 and electrical conductivity water samples were collected from various depths and chemically and isotopically analysed two similar profiles have been measured also in the nearby nemi crater lake results indicate that in the 4 5 years of monitoring the pressure of gas dissolved in the lake albano deep waters remained much lower than the hydrostatic pressure a co2 soil survey carried out on the borders of the two lakes indicates the presence of some zones of anomalous degassing of likely magmatic origin a water overturn or a heavy mixing of deep and shallow waters likely occurred in winter 2003 2004 when cold rainfall cooled the surface water below 8 5 c such overturns cause only a limited gas exsolution from the lake when the deep water is brought to a few meters depth but can explain the observed decrease with time of dissolved co2 at depth and related water ph increase a gas hazard could occur in the case of a sudden injection through the lake bottom of a huge quantity of co2 rich fluids which might be caused by earthquake induced fracturing of the rock pile beneath the lake a limnic gas eruption might also occur should co2 concentration build up within the lake for a long time

mineral exploration in regolith dominated terrains global considerations and challenges abstract mineral exploration through transported cover is becoming one of the fundamental challenges for the exploration industry in this century the sharp increase in demand for commodities driven by a growing population and technology based society is coupled with the decrease in world class ore deposit discoveries in the last three decades this is setting the stage for an unprecedented scenario that is ensuring that the market supply for critical metals ni co au pge etc is satisfied this situation is becoming the driving force for a restructuring of mineral exploration paradigms new technologies and methodologies are being developed and as a consequence regions that were considered to be unfavourable for ore deposit exploration are now being reconsidered among these areas are vast regions of regolith dominated terrains rtd with basement rock suites buried under thick transported cover and or deeply weathered profiles this special issue presents several studies on mineral exploration in rtds in brazil china and australia and addresses some of the issues that hinder exploration in these problematic terrains in the hope of reaching a broad audience and encouraging researchers from a wide spectrum of disciplines to contribute to this exciting and inspiring exercise

petrogenesis of monte vulture volcano italy inferences from mineral chemistry major and trace element data the paper presents major and trace element data and mineral compositions for a series of foiditic tephritic to phonolitic rocks coming from monte vulture southern italy and investigates their origin evolution and relationship with the other centres of the roman province

the crustal structure of the northern apennines central italy an insight by the crop03 seismic line in this paper the crop03 deep seismic reflection profile in the northern apennines is described and re considered in light of new geophysical data and interpretations made available in the last five years particularly from heat flow measurements aeromagnetics tomography active stress determination and passive seismology the crustal structure of the northern apennines is shown to be composed of two distinct domains to the west is the tyrrhenian domain and to the east is the adriatic domain these domains have distinctive geological and geophysical characteristics that exhibit distinct reflectivity patterns at all crustal levels in the tyrrhenian domain the upper oligocene lower miocene compressive structures are no longer recognizable because they are dissected by subsequent extensional tectonic features the seismic profile highlights the strong asymmetry of extensional deformation and the upper crust is affected by a set of six major east dipping low angle normal faults in the adriatic domain compressive tectonics have acted since the middle miocene and the pattern of shallow contractional structures is well preserved the geological interpretation of the seismic data supports a thick skinned style of deformation where the basement is involved in the major thrust sheets the good quality of seismic data also allows for determining the total shortening produced by the contractional structures in the central part of the profile at the border between the tyrrhenian and adriatic domains seismic data shows the presence of an intermediate sector the sector consists of a highly reflective window where the refraction data indicate a local doubling of the crust for about 30 km a scenario is presented that attempts to describe the geodynamics that drove the tectonic evolution of the northern apennines since the upper oligocene

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

the main characteristics of the lithosphere asthenosphere system in italy and surrounding regions we present a summary of the available information on rayleigh wave dispersion data for the italian area the dispersion curves can be grouped into two main families according to their shape one with an almost linear trend in the period range from 40 to 150 sec the other with a relatively flat portion in the period range from 40 to 80 sec the inversion of these data shows that there are strong lateral variation in the lithosphere system a very rapid transition in the lithospheric thickness from about 130 km to about 30 km as well as in the s wave velocity of the lithosphere and asthenosphere

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

beno gutenberg contribution to seismic hazard assessment and recent progress in the european mediterranean region abstract the fundamental work of beno gutenberg has inspired and guided an appreciable part of research in modern seismology both from the experimental and the theoretical point of view among the several topics of seismology that have benefited from the fundamental contribution of gutenberg we consider particularly relevant the description of the asthenospheric low velocity channel the definition of the surface waves magnitude and the gutenberg richter law since they are pivotal tools for seismic hazard assessment the quite revolutionary model for the lithosphere asthenosphere system in the european area predicts the existence of almost aseismic lithospheric roots these roots are located in correspondence of most of the orogenic belts and interrupt the asthenosphere low velocity channel that has been identified by beno gutenberg in 1948 the model of the european upper mantle proposed for the first time in 1979 and subsequently refined has stimulated a considerable amount of research which has nicely confirmed the major innovative features of the early model at present the subduction of the lithosphere at continent continent collisions supported not only by seismological data is a widely accepted concept within the community of earth scientists even if it contradicts one of the basic dogmas of the original formulation of plate tectonics the proposed model for the alpine apennines area supplies a new and unifying framework for the interpretation of the quaternary magmatism at present generally accepted by petrologists and geochemists the theoretical basis for the gutenberg s surface wave magnitude calibration function has been supplied by the use of complete synthetic seismograms and thus it has been possible to formulate the theoretical m s depth correction the introduction of the depth correction for m s enables the computation of surface wave magnitude for all earthquakes regardless of their focal depth this is especially important for the quantification of subcrustal historical earthquakes for which the seismic moment may be difficult to estimate from recordings of early mechanical seismographs the new m s calibrating function yield both distance and depth independent magnitude estimates the analysis of the global seismicity using the seismotectonic regionalization in subduction zones mid oceanic ridge zones island arcs shows that a single gutenberg richter gr relation is not universally applicable and that a multiscale seismicity model can reconcile two apparently conflicting paradigms the self organized criticality mechanism and the characteristic earthquake concept the multiscale representation has been applied to italy where the zones at the space scale of 400 500 km quite well reproduce the shapes of the regions used to apply the globally tested cn intermediate term earthquake prediction algorithm

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

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

sea level changes and buried islands in a complex coastal palaeolandscape in the south of western australia implications for greenfield mineral exploration abstract weathering intensity changes due to climatic variability across tectonically stable portions of continental crust can generate a thick and extensive weathered cover resulting in regolith dominated terrains rdts mineral exploration in rdts is challenging because of the lack of bedrock outcrop and the difficulty of linking surface regolith geochemistry to the geology at depth complex weathering obscures the expression of the basement geochemistry in the regolith and therefore the footprints of mineral systems are difficult to detect the southeast of the yilgarn craton and the albany fraser orogen afo in the south of western australia is an rdt that extends along the coastline and the eucla basin this study proposes a landscape evolution model of the afo driven by transgression regression sea level changes that resulted in the formation of numerous islands and development of estuarine zones this model contrasts with the river system dominated landscape evolution present in the yilgarn craton this difference has significant implications for mineral exploration and geochemical interpretation of the regolith in this region weathering profiles developed on inland and on island are thicker and more mature than those developed in sea inundated areas even if in the yilgarn craton local areas display reworking of weathering profiles and other complexities from permian non marine tertiary sediments and quaternary fluvial and aeolian sediments at a regional scale if vertical geochemical mobility of elements has occurred on inland and on island are more reliable for understanding geochemical anomaly basement relationships whereas the marine inundated areas require a more detailed investigation because of the role of marine reworking of weathering profiles and possible mixture of sediments from different provenances landscape changes from the topographically high dissected yilgarn environment with thick saprolite development and uneven basement topography to the nearly flat regions dominated by sand dunes and thin saprolite development at the coastline these regions are the result of the erosional and depositional effects of successive sea level transgression regression cycles within this framework the following four different regolith settings have been identified in a progressive change from yilgarn craton environments to the modern coastline 1 albany 2 kalgoorlie norseman 3 esperance and 4 neale mapping the palaeocoastlines islands and estuarine zones as well as the region of influence of marine limestones and sediments can significantly improve the understanding of how surface geochemistry relates to the landscape and how it links with the geology at depth and therefore how it may reflect the presence of mineral systems understanding the difference in the landscape evolution between the afo and yilgarn craton is essential to properly calibrate mineral exploration protocols in both regions

regional stress field in the area of stromboli italy insights into structural data and crustal tectonic earthquakes abstract crustal tectonic seismicity on stromboli is here discussed along with the regional tectonic and geodynamic context of the aeolian archipelago italy the aim of this paper is to contribute to the reduction of the crucial gap in information concerning the tectonic activity originating at the volcano stromboli in the last decade it is indeed well known that strombolian eruptions related to the persistent state of activity on this volcano allow a fast collection of seismic data which are mainly represented by explosion quakes and tremor however only some sporadic information concerns tectonic earthquakes due to their low occurrence rate a catalog of 150 crustal tectonic earthquakes recorded at stromboli from 1985 to 1996 is presented here the analyses of the seismograms were carried out on the basis of the records of the station str located in the southwestern part of the island the magnitude considered ranged from 1 5 to 3 7 hypocentral location indicates foci at less than 12 km although for the majority of the earthquakes which are not recorded at the seismic stations deployed on the other islands of the aeolian archipelago a shallower within a few kilometers depth can be hypothesized the strain release associated with the 150 tectonic earthquakes of our catalog was also evaluated the low levels of occurrence and seismic energy release reached throughout the ca twelve years analyzed here confirm the minor role played by processes of brittle failure of rocks this aspect of seismic activity is nevertheless important as it can provide a contribution to the knowledge of the dynamics of this volcano the focal mechanisms available integrated with data from the literature show the t axes oriented about ne sw and nw se these findings are consistent with the deformative and tectonic characteristics of this volcanic edifice and of the aeolian archipelago which shows the same two directions of extension this is in agreement with subduction which is very old or which passively evolves towards the final stages and is controlled by the transform activity of the aeolian tindari giardini fault system

flexural behavior of the continental lithosphere in italy constraints imposed by gravity and deflection data a procedure is developed that systematically matches observations of plate flexure and gravity anomalies at simple convergent boundaries to the bestfitting two dimensional flexural geometry obtained by a thin elastic sheet of specified elastic strength the procedure allows analytical solution for three independent variables one of which is the initial preflexure elevation of the reference surface and two of which are related to the vertical forces and bending moments that act on the plate application to four profiles constructed across the apennine convergent system in italy shows that the observed depth of the basal pliocene surface which marks the base of the foredeep basin and the observed bouguer gravity anomalies can be fit by a two dimensional elastic plate model with an effective elastic thickness of about 20 km on three profiles and about 10 km on the fourth profile the initial elevation prior to flexure is determined to have been about 1000 m below sealevel on all profiles large bending moments and or vertical shear forces are required to act at the effective plate ends in order to maintain the observed deflection moments between 0 5 1017 and 3 1017 n and shear forces between 3 1012 and 3 1012 n m gravity modelling indicates that on the two northernmost profiles these terminal forces can not be supplied by a static mass at crustal depths and suggests that on all four profiles the terminal forces are supplied by anomalously dense material present at depths of 75 150 km beneath and west of the west coast of italy this dense material probably corresponds to westward subducted lithosphere of the adriatic plate extending from the northern apennines to the southern apennines and calabria this study suggests that in subduction systems like the apennines that are characterized by backarc extension forces acting on subducted lithosphere at depth can be expressed at the surface in the geometry of the foredeep basin that forms adjacent to the subduction zone

regional exploration for channel and playa uranium deposits in western australia using groundwater abstract shallow calcrete aquifers in the central north of the yilgarn craton in western australia are the host to numerous secondary carnotite u deposits sampling and analysis of approximately 1400 shallow aquifer groundwaters were conducted to test if u mineralisation of this type may be found using a 5 km sample spacing results show this can be achieved all the economic deposits and most of the minor deposits and occurrences are associated with groundwater that has carnotite kuo2vo4 approaching or exceeding saturated conditions soluble u concentrations alone identified the largest deposit yeelirrie and several smaller deposits but this parameter was not as successful as the mineral saturation indices palaeodrainage distribution and thickness of cover combined with surface drainage and catchment boundaries provided background information of u primary sources and for areas with the highest exploration potential for channel and playa u deposits granites in the se of the study area are less prospective with regard to secondary u deposits groundwater geochemistry in conjunction with palaeodrainage mapping may greatly improve exploration through cover where radiometric geophysics is not effective the study of regional shallow groundwater for u shows multiple benefits for mineral exploration the economy and potable water quality

the pianico tephra an early middle pleistocene record of intraplate volcanism in the mediterranean distal tephra are a valuable record of the volcano tectonic evolution of an area under study here we document the case of the early middle pleistocene rhyolitic tephra of pianico discovered in the southern italian alps the geochemical characteristics of pianico are unique among the distal tephra outcropping in italy and indicate an intraplate volcanism at the source the alkali composition and trace elements show a striking resemblance with the rhyolitic complex of the euganean hills located 170 km from pianico however these rhyolites are much older oligocene alternatively the source of this intraplate volcanic episode could be located in the southern tyrrhenian sea

eurid a regionalized 3 d seismological model of europe abstract this paper presents a 3 d regionalized model of the european crust and mantle velocity structure down to depths of approximately 300 km the model is entirely based upon the existing geological and geophysical literature and it incorporates topographic and bathymetric features the resulting model which we call eurid european i data set consists of approximately 6400 1 d vertical structures having an average separation of about 100 km eurid is compared quantitatively with eur s91 a recent s wave velocity tomographic model obtained from body and surface wave waveform inversion zielhuis a nolet g 1994 shear wave velocity variations in the upper mantle beneath central europe geophys j int 117 695 715 it is found that the s wave velocities in eurid and in eur s91 zielhuis and nolet 1994 do not differ by more than about 4 over most of the area to validate eurid surface wave dispersion analysis is performed along some selected paths the fundamental mode group velocity curves obtained using 1 d average models derived from eurid are found in good agreement with those determined from observations broadband waveform synthetics are also calculated along the same paths and compared with the observed time series overall we believe that eurid is representative of our current knowledge of the crust upper mantle structure beneath europe and it can be used to model realistically ground motion for periods above 10 s within structurally homogeneous regions the first digital version of this structure database is available for public use

regional setting structure and descriptive geology of the middle proterozoic syama gold deposit mali west africa the syama gold deposit lies in a birimian 2 0 2 2 ga greenstone belt in southern mali gold mineralization is hosted by a thin 0 5 2 0 km but regionally extensive sequence of basalt and andesite interbedded graywacke and argillite and andesitic lamprophyric intrusions this sequence is bounded on the east by andesitic conglomerate and graywacke and on the west by interbedded graywacke and argillite in the syama mine area this ore bearing sequence is structurally layered overturned and east vergent massive competent basalt and conglomerate bound the hanging wall and footwall respectively of the mineralized interval lateritic weathering developed an oxide orebody that overlies sulfide mineralization the oxide orebody extends to 35 to 40 m below the surface sulfide mineralization extends to a depth of at least 500 m mineable oxide reserves are 3 0 million tons with an average grade of 3 20 g ton geologic sulfide reserves from the top of sulfides to 320 m below the surface are 21 million tons with an average grade of 4 02 g ton the oxide deposit was expressed on the surface as a series of 3 to 15 m deep ancient mine workings which extended 800 m along the strike of the deposit and sparse outcrops of silicified rock oxide ore occurs as two deposits a surficial deposit consisting of ancient tailings and dump material which are 0 1 to 5 m thick and extend up to 200 m away from the ancient workings and an in situ lode or saprolite deposit which lies immediately below the ancient workings and extends downward into sulfide mineralization the sulfide deposit consists of lenticular bodies of intense ankerite quartz veinlet stockworks zones of sheeted ankerite quartz veinlets and breccia bodies pyrite is the principal gold bearing mineral and occurs disseminated in veinlet halos and breccia clasts green chloritic basalt is the preferred but nonexclusive host of the mineralization it is commonly bleached by ankerite albite and sericite alteration in the pyritic gold bearing zones silica na 2 o au co 2 s and c have been added to mineralized zones hosted by basalt fe 2 o 3 al 2 o 3 and trace metals have been removed andesitic lamprophyric intrusions and graywacke argillite layers also host disseminated pyrite mineralization faulted beds of graphitic graywacke argillite and zones of silicification bound most individual orebodies the volcanic rocks at syama were probably originally deposited in a narrow rift or graben in an intra arc setting gold mineralization overlapped with compressional deformation and intrusive activity the mineralized horizons at syama lie within a sequence of rocks which has been either stacked or attenuated by layer parallel reverse faults these faults coincide with abrupt regional and mine scale contrasts in rock competency intrusive rocks form a volumetrically significant part of the mineralized sequence and may have aided hydrothermal alteration as a source of heat both the graywacke argillite layers and the altered basalt and intrusions may have been a source for some of the elements and fluids responsible for the mineralization and alteration the mineralization at syama is similar to other middle proterozoic gold deposits in the birimian shield of west africa and to archean gold deposits hosted by mafic volcanic rocks in terms of tectonic setting wall rock alteration form of mineralization and associated structures

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits