multiple sources of quaternary tephra layers in the mariana trough abstract tephra layers in quaternary sediments stolper and newman 1994 model of binary mixing of source components with one endmember being the nmorb source of stolper and newman 1994 and the other one being a compositionally variable slab derived h2o rich component similar to the h2o component of stolper and newman 1994 this interpretation implies that the variation in k2o content in the arc derived glasses about a factor of 3 at 60 wt sio2 reflects a magmatic diversity that is inherent to the central mariana arc and is not necessarily reflective of temporal changes of the composition of arc magma sources

estimation of spatio temporal recharge of aquifers in mountainous karst terrains application to sierra de las nieves spain summary we describe a method for estimating the daily spatially distributed recharge of aquifers in mountainous karst terrains using a water balance water recharge into an aquifer is a highly variable process over both time and space many methods have been developed to assess aquifer recharge although most have been applied to detrital aquifers many karst aquifers especially in mediterranean areas occur in mountainous environments where rainfall and evapotranspiration can vary considerably over space and time and where there are usually few rainfall and temperature monitoring stations we have used an advanced geostatistical method to estimate daily rainfall and temperature the method involves kriging with an external drift using a climatological semi variogram model inferred by modified maximum likelihood the depth of the soil epikarst layer is estimated from remote sensing and terrain analysis data together with field observations and electrical resistivity tomography because of the karst nature of the mountainous terrain concentrated infiltration is allowed for in some places the parameters are calibrated against the cumulative discharge of various springs the method is illustrated by a case study of the sierra de las nieves aquifer in the mountainous karst region of southern spain

fractal analysis of mingled mixed magmas an example from the upper pollara eruption salina island southern tyrrhenian sea italy abstract upper pollara eruption products 13 ka salina island italy include both homogeneous and heterogeneous pumices resulting from mixing mingling processes between an hk andesite and a high sio2 rhyolite representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling mixing structures image analysis techniques are applied and eight grey color ranges classes are extracted from high resolution scans of pumice class 1 lighter colors and class 8 darker colors show end member glass compositions i e hk andesite and high sio2 rhyolite respectively these two classes show spot to cluster like morphological structures intermediate classes show an hk dacitic to rhyolitic composition and a banding to fold like morphology fractal analysis by box counting of the boundary pattern of eight grey classified images is performed over a length scale of 0 028 1 8 cm fractal dimension d is between 1 01 and 1 84 coupled fractal analysis and geochemical data reveal that d increases as the degree of magma interaction homogenization increases this feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection we conclude that the increase of d observed in the upper pollara samples reflects the transition from fractal mixing to homogenization end member magmas hk andesite and high sio2 rhyolite represent isolated mixing regions while homogenized magmas represent active mixing regions in the analyzed pumices isolated and active mixing regions coexist at scales between 10 4 and 10 2 m morphological and compositional features of the upper pollara pumices result from turbulence

alteration and geochemical patterns in the 3 7 3 8 ga isua greenstone belt west greenland abstract volcanic rocks of the 3 7 3 8 ga isua greenstone belt have undergone heterogeneous poly phase post magmatic alteration resulting in mobilisation of many elements including lree and th in contrast nb ta ti zr y and hree were relatively immobile during alteration processes the degree of element mobility appears to have been controlled by chemical composition primary volcanic structures carbonate and silica enrichment and proximity to ultramafic units and shear zones on the basis of the geochemical characteristics of the least altered samples two distinct associations have been recognised in structurally separated lithotectonic sequences these magmatic associations are a low hfse association tio2 0 20 0 40 wt zr 12 30 ppm nb 0 13 0 80 ppm y 6 14 ppm in the central arc sequence resembling tertiary boninites and a high hfse association tio2 0 50 1 14 wt zr 34 77 ppm nb 1 2 2 7 ppm y 11 28 ppm in the outer and inner arc sequences comparable to phanerozoic island arc basaltic to picritic volcanic rocks these two geochemically distinct sequences were likely to have been juxtaposed as a consequence of phanerozoic style plate tectonic processes operating in the early earth the isua volcanic rocks are characterised by sub chondritic nb ta 10 16 ratios post magmatic alteration can be ruled out as the cause of these low ratios rather these ratios reflect a compositional characteristic of the paleoarchean mantle source s the sub chondritic nb ta ratios may have resulted from either preferential sink of nb into the core as a weakly siderophile element or preferential retention of nb in the subducted oceanic crust during subduction zone petrogenetic processes alternatively the building blocks of the earth were not composed of ci like chondritic material

contribution of structural analysis to understanding the geodynamic evolution of the calabrian arc southern italy abstract a marked curvature of crustal structures characterizes the calabrian arc in southern italy the overall deformation of the arc seems mostly controlled by the sangineto shear zone to the north and by the mt kumeta alcantara shear zone to the south which both separate different crustal sectors other important fault systems cut the iblean foreland scicli ragusa fault zone and many others dissect the crystalline units of central calabria neotectonic structural analyses have been carried out in order to recognize the character of the plio pleistocene tectonic phases and their bearing on the present configuration of the arc after the middle miocene extensional phase an early middle pliocene compressional phase is detectable in many parts of the arc right and left lateral displacements respectively characterize the mt kumeta alcantara and sangineto shear zones and right lateral movements are also detectable within the scicli ragusa fault system finally the pleistocene tensional regime seems to have been controlled mainly by uplift the structural and neotectonic data allow us to propose a model of the recent evolution of the arc which was bent mainly as a result of opposed wrench faulting along the sangineto and mt kumeta alcantara shear zones

lateral spreading phenomena and weathering processes from the tropea area calabria southern italy this paper describes the lateral spreading landslides the weathering processes and the hydrogeological risk patterns of the nw sector of monte poro calabria southern italy based on the development of a multidisciplinary research the tectonic uplift of the area combined with the litho structural features of the sedimentary deposits overlying the intensely weathered granitoid complex produces important gravitational phenomena characterized by lateral spreading kinematics the contact between deposits with a different behaviour together with the high slope energy related to the tectonic uplift processes is the main cause of widespread fracturing and disjoint of the lithologies associated with lateral spreading phenomena these phenomena are also testified by the various trenches and cracks characterized by a parallel orientation relatively to the main fluvial incisions measures of these deformations were obtained with a quantitative result by the use of interferometric stacking methods the experimental results confirm this morphological scenario characterized by strain values ranging between 20 and 25 mm year relatively to the landslides detected geomorphological analysis of the drainage basins in the study area indicates a juvenile stage of the stream networks this pattern is consistent with the high rate of tectonic uplift of the area hence the continuous rejuvenation of the stream networks and their low level of hierarchy these conditions of geomorphic equilibrium of the stream networks the widespread occurrence of geological instability in continuous evolution are the main causes of high hydrogeological risk conditions for this coastal area

long term behaviour of the late quaternary normal faults in the straits of messina area calabrian arc structural and morphological constraints abstract the calabrian arc is located in the peri tyrrhenian orogenic belt of southern italy and is characterised by intense post collision dynamics this consists of rapid regional uplifting combined with active normal faulting affecting the tyrrhenian side of calabria and the ionian coast of sicily the siculo calabrian rift zone the effects of the two combined processes are well exposed in the straits of messina area that represent a major transfer zone located between two opposing sets of normal faults characterising the southern calabria and the northeastern sicily branches of the rift in the straits of messina region the distribution and elevation of the upper quaternary marine terraces suggest a southward propagation of the normal fault belt from calabria to sicily it occurred at about 125 ka after a long period of tectonic quiescence and was triggered by huge elastic releases in southern calabria the long term behaviour recorded on the distinct fault segments of the rift is to relate to the presence of a crustal barrier that influenced both the geometry and the fault propagation along the rift zone

thermal tl and optical stimulated luminescence osl techniques for dating quaternary colluvial volcaniclastic sediments an example from the crati basin northern calabria abstract within the colluvial clastic deposits of the crati basin near the village of tarsia a decimetre to metre thick volcaniclastic stratum outcrops interbedded within poorly structured sandy pelitic deposits the volcaniclastic stratum is structureless powdery pinkish grey or yellowish brown slightly pedogenized towards the top and characterized at the base by centimetre sized clasts of crystalline rocks the depositional and textural features suggest a primary fall out of volcanic ash during a period when the climate favoured modification of the landscape and re mobilization of the ash as mud flows with the first rainy episode this area was subjected to strong uplift 0 7 mm yr and climatic effects of the last glacial maximum and the preservation of this volcaniclastic stratum represents an unusual and exceptional event the volcanic ash representing the principal component of the deposit is composed of shards and pumices of phonolithic composition with millimetre sized phenocrysts of sanidine the non volcanic component consists of quartz clasts and to a much lesser extent feldspars and fragments of metamorphic rocks thermal tl and optical stimulated luminescence osl techniques were used to date the potassium feldspar crystals of volcanic origin and the quartz crystals from the non volcanic component the stratum contains sediments of different origins the feldspar fraction was subjected to high temperatures at the moment of volcanic emission zeroing the internal luminescence clock the quartz fraction was exposed to light probably only at the moment of sedimentation with the possibility of only partial bleaching of luminescence signal osl ages are chronologically undistinguishable between the quartz and feldspar fractions the quartz and feldspar fraction ages obtained by osl are respectively 28 3 ka and 27 2 ka tl measurements reveal an age of 41 3 ka for the quartz fraction and 33 3 ka for the feldspar fraction the age and chemical and mineralogical composition of the volcanic fraction indicate the source for the large explosive eruptions occurred in the campanian area ischia flegrei southern italy between 42 and 25 ka

the role of the subcutaneous zone in karst hydrology abstract the subcutaneous zone is the upper weathered layer of rock beneath the soil but above the permanently saturated phreatic zone it is of particular hydrological importance in karst because of its high secondary permeability arising from the considerable chemical solution in this zone however corrosional enlargement of fissures diminishes with depth thus permeability decreases in the same direction with the result that percolation is inhibited except down widened master joints and faults storage of water consequently occurs in this zone particularly after storms the upper surface of this suspended saturated layer in the subcutaneous zone is defined by a perched water table which slopes towards points of rapid vertical percolation the potential induces lateral water movement converging on the most permeable areas such as beneath dolines leakage from the subcutaneous store sustains slow percolation in the vadose zone cross correlation of rainfall with percolation rates in caves in new mexico u s a and new zealand reveal response lags of 2 14 weeks with no apparent relationship to depth below the surface other percolation sites show no correlation with rainfall interpreted as being a consequence of considerable friction in tight fissure networks the recognition of storage and rapid as well as very slow percolation from the subcutaneous zone requires re interpretation of the components of hydrographs from karst springs and of some conceptual models of karst aquifers the importance of subcutaneous storage in sustaining baseflow discharge at some sites must be recognised as must the contribution of subcutaneous water to flood hydrographs methods of estimating the volumes of subcutaneous and phreatic components of karst spring flood hydrographs are presented the paper concludes with a discussion of the significance of subcutaneous hydrologic processes for an understanding of karst geomorphology the desirability of explaining karst landform evolution in terms of hydrologic processes is stressed

the riddle of volcaniclastic sedimentation in ancient deep water basins a discussion abstract sedimentary records of deep water basins are useful tools for understanding how volcanism shapes distal environments furthermore these basins represent uncontaminated places where catastrophic eruptions are clearly preserved for these reasons the study of the depositional records of deep sea realms becomes of primary importance to better understand the temporal incidence and the consequences of catastrophic events that may occur on earth however their inaccessible underwater conditions limit the possibility of deep investigations thus ancient analogues represent the best way to integrate direct observations with detailed sedimentological and petrographic analyses this work introduces concepts derived from the study of three sedimentary sequences that form the oligocene foreland and foredeep deep sea basins of the proto alpine belt each succession is characterized by its volcaniclastic detritus and two of them were deposited during volcanic activity we compare their sedimentological and volcanological characteristics highlighting the main features derived from a volcanically controlled sedimentation we emphasize 1 the importance of stratigraphy and petrography in the identification of criteria to recognize volcanism phases in ancient distal deep water sequences 2 the propensity of volcanism to produce detritus during its life rather than after its death and 3 the fundamental role of pyroclastic density currents in delivering particles from source areas to depositional basins these three points suggest that a deep knowledge of ancient sedimentary records integrates our knowledge on the interaction existing between volcanoes and surrounding environments with a hazard assessment perspective

field and geochemical characteristics of the mesoarchean 3075ma ivisaartoq greenstone belt southern west greenland evidence for seafloor hydrothermal alteration in supra subduction oceanic crust the mesoarchean ca 3075ma ivisaartoq greenstone belt in southern west greenland includes variably deformed and metamorphosed pillow basalts ultramafic flows picrites serpentinized ultramafic rocks gabbros sulphide rich siliceous layers and minor siliciclastic sedimentary rocks primary magmatic features such as concentric cooling cracks and drainage cavities in pillows volcanic breccia ocelli interpreted as liquid immiscibility textures in pillows and gabbros magmatic layering in gabbros and clinopyroxene cumulates in ultramafic flows are well preserved in low strain domains the belt underwent at least two stages of calc silicate metasomatic alteration and polyphase deformation between 2963 and 3075ma the stage i metasomatic assemblage is composed predominantly of epidote now mostly diopside quartz plagioclase hornblende scapolite and occurs mainly in pillow cores pillow interstitials and along pillow basalt gabbro contacts the origin of this metasomatic assemblage is attributed to seafloor hydrothermal alteration on the basis of the common presence of epidote inclusions in diopside and the local occurrence of epidote rich aggregates the stage i metasomatic assemblage is interpreted as relict epidosite the stage ii metasomatic assemblage occurs as concordant discontinuous layered calc silicate bodies to discordant calc silicate veins commonly associated with shear zones the stage ii metasomatic assemblage consists mainly of diopside garnet amphibole plagioclase quartz vesuvianite scapolite epidote titanite calcite scheelite given that the second stage of metasomatism is closely associated with shear zones and replaced rocks with an early metamorphic fabric its origin is attributed to regional dynamothermal metamorphism the least altered pillow basalts picrites gabbros and diorites are characterized by lree enriched near flat hree and hfse especially nb depleted trace element patterns indicating a subduction zone geochemical signature ultramafic pillows and cumulates display large positive initial end values of 1 3 to 5 0 consistent with a strongly depleted mantle source given the geological similarities between the ivisaartoq greenstone belt and phanerozoic forearc ophiolites we suggest that the ivisaartoq greenstone belt represents mesoarchean supra subduction zone oceanic crust 2006 international association for gondwana research published by elsevier b v all rights reserved

geostatistical approaches for incorporating elevation into the spatial interpolation of rainfall this paper presents three multivariate geostatistical algorithms for incorporating a digital elevation model into the spatial prediction of rainfall simple kriging with varying local means kriging with an external drift and colocated cokriging the techniques are illustrated using annual and monthly rainfall observations measured at 36 climatic stations in a 5000 km 2 region of portugal cross validation is used to compare the prediction performances of the three geostatistical interpolation algorithms with the straightforward linear regression of rainfall against elevation and three univariate techniques the thiessen polygon inverse square distance and ordinary kriging larger prediction errors are obtained for the two algorithms inverse square distance thiessen polygon that ignore both the elevation and rainfall records at surrounding stations the three multivariate geostatistical algorithms outperform other interpolators in particular the linear regression which stresses the importance of accounting for spatially dependent rainfall observations in addition to the colocated elevation last ordinary kriging yields more accurate predictions than linear regression when the correlation between rainfall and elevation is moderate less than 0 75 in the case study q 2000 elsevier science b v all rights reserved

a 125 kyr long geological record of seismic source repeatability the messina straits southern italy and the 1908 earthquake ms7 2 the occurrence of characteristic earthquakes along segments of major active belts has been described as early as the beginning of the century the large 1908 messina straits blind normal faulting earthquake provides an opportunity to investigate the repetition of characteristic earthquakes and the persistency of the main features of the fault zone over a time scale in the order of 100 kyr we have compared seismological and geodetic descriptions of the 1908 rupture process with long term crustal deformation recorded at different stratigraphic levels by marine terraces marine sedimentary units and landscape features the wealth of elevated coastal features in and around a region affected by large normal faulting earthquakes indicates that coseismic strain is superimposed on much faster uplift on a regional scale we investigated in detail the pattern of deformation of the 125 kyr old lowest emergent terrace and found that it mimics the pattern of elevation changes observed following the earthquake this suggests 1 that the 1908 earthquake is characteristic 2 that its segment boundaries have been stationary during the past 125 kyr and 3 that even the locations of the regions of largest coseismic release do not change through many seismic cycles based on a comparison between observed heights of the 125 kyr terrace and 1908 displacements we estimated an average repeat time of 1000 yr for a 1908 type earthquake we also investigated the height position age and state of deformation of older terraces and found 1 that uplift of the region started about 1 ma and has since continued rather uniformly at 0 9 1 4 mm yr 1 2 that during this time the straits have narrowed at a rate of 10 20 mm yr 1 and 3 that all the main geomorphic features of the messina straits result from the interaction of fast regional uplift 1908 type coseismic subsidence and global sea level fluctuations

mobilization of ree during crustal aging in the troodos ophiolite cyprus ree data for secondary minerals from low and high temperature alteration environments in the troodos ophiolite have been determined using a combined mass spectrometry neutron activation technique smectite and analcime ree mimic fresh rock profiles and have concentrations ranging from 1 5 times chondritic values celadonite is depleted in lree and total ree relative to the rocks groundmass replacing chlorite and epidote are similar to or enriched in ree relative to fresh rocks in contrast fault related chlorite and void filling epidote are lree enriched with large positive eu anomalies and yield comparable ree profiles to those of hydrothermal fluids venting at mid ocean ridges the zeolites clinoptilolite and laumontite are also lree enriched with ree contents significantly lower than rock values carbonate is enriched in hree relative to lree and concentrations vary from 0 2 to 18 times chondritic values ree data for these minerals indicate that seawater ree contents are modified by seawater rock interaction in volcanic sequences and sheeted dykes in oceanic crust during axial hydrothermal alternation and subsequent crustal aging the absolute and relative abundances of ree in seawater derived solutions evolve in response to the precipitation of secondary minerals and the prevailing water rock ratios rocks altered at low temperatures will show no change or a decrease in ree content the lree hree ratio will reflect the proportion of smectite celadonite and carbonate in the groundmass assemblage in contrast rocks altered at high temperatures will show no change or an increase in ree the lree hree ratio will reflect the proportion of void filling and groundmass replacing chlorite and epidote in the rock

mantle degassing on a near shore volcano se tyrrhenian sea the presence of a seamount like structure located a few nautical miles offshore the capo vaticano promontory western calabria s italy was revealed by combined geophysical and geochemical investigation the edifice covers 55 km2 with a top located at a depth of about 70 m below sea level and consists mainly of a nw trending structure orthogonally interrupted by minor ridges the largest of which is affected by extensional faults the top of the edifice hosts active vents injected fluids that have been investigated for dissolved volatiles gas analyses revealed high co2 and ch4 contents several orders of magnitude above the atmospheric type values expected for shallow coastal marine waters and a noteworthy enrichment in mantle derived 3he which is an unambiguous indicator of the mantle origin of the fluids our results combined with available data from the literature suggest that the edifice is a tectonically controlled volcanic system which presence near the calabria region changes the role played by faults in the frame of the subduction process

geomorphic constraints on uplift history in the aspromonte massif southern italy abstract the landscape morphology of the aspromonte massif southern italy shows hanging low relief surfaces that correlate with uplifted landsurfaces which are preserved all around the massif the drainage network has deeply incised the high standing low relief landscapes seen here as being the remnants of phases of relief smoothing prior to strong uplift that has affected the area since the middle pleistocene gis aided estimation of the rock volumes eroded since the late early pleistocene indicate high variability in denudation rates between the gently rolling landscapes and the river valleys in this framework longitudinal river profiles are examined for 42 river channels to constrain multiple non equilibrium conditions and to reconstruct the long term uplift history of the massif most profiles consist of three four segments separated by knickpoints and suggest a complex incision pattern longitudinal profiles reveal two upper low gradient channel segments a zone of steep channels further down the low relief landsurface margin and a very steep lower channel segment particularly in the western quadrant upper channel segments correspond to the relict landscape rlandscape a high standing landsurface on top of the massif and the hanging landscape hlandscape a landsurface surrounding the rlandscape respectively steeper middle and lower segments are the result of two phase river incision that is linked to changes in regional uplift rates and subordinately to rock strength properties indeed analysis of river longitudinal profiles could indicate initially relatively slow aspromonte uplift during the early pleistocene and then pulses of rapid uplift during the middle late pleistocene multi segment river longitudinal profiles are therefore evidence of the transient landscapes of aspromonte in response to pulsed massif uplift

sedimentological and petrographic evolution of a fluvio lacustrine environment during the onset of volcanism volcanically induced forcing of sedimentation and environmental responses

the monte guardia eruption lipari aeolian islands an example of a reversely zoned magma mixing sequence the monte guardia rhyolitic eruption 22 ka lipari aeolian islands italy produced a sequence of pyroclastic deposits followed by the emplacement of lava domes the total volume of dense magma erupted was nearly 0 5 km3 the juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence mafic magmatic enclaves streaky pumices mineral disequilibria and heterogeneous glass composition petrographic mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre eruptive chemico physical magmatic conditions the results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member a denser mixed magma was first erupted followed by a larger volume of an unmixed lighter rhyolitic one this compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber the monte guardia rhyolitic magma stored below 200 mpa was volatile rich and fluid saturated or very close to this despite its relatively low explosivity in contrast to previous interpretations there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input the entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence 1 the occurrence of thermal instabilities in a density stratified salic to mafic magma chamber and 2 the intrusion of rising rhyolite into a shallower mafic sill dike

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

epidote group minerals in low medium pressure metamorphic terranes epidote group minerals are common in metamorphosed mafic to intermediate igneous rocks quartzofeldspathic sediments and calc alumina silicate marl rocks of higher grade zeolite to medium grade amphibolite facies of low medium pressure contact and regional metamorphic terranes i e pressure and temperature conditions below the calcite to aragonite transition within any one rock epidote composition in terms of fe3 fe3 al can be variable but in general is limited by whole rock composition such that epidote group minerals in metabasite lithologies are more fe rich than those in marls that tend to be more al rich and typically include zoisite because of their wide range of p t stability epidote group minerals of variable composition may form in a single rock during several stages of metamorphic re equilibration slow rates of intra crystalline fe3 al exchange especially at low temperatures preserve complex zonation patterns in individual grains that can serve as a tape recorder providing evidence for continuous or discontinuous prograde and retrograde reactions and the p t fluid redox conditions of metamorphism thus relic lower grade epidote typically fe rich often form cores over which new typically less fe rich higher grade epidote rims form in such a case the boundary between the two generations of epidote may be sharp or gradational depending on the temperature history of the rock and fe3 al diffusivity often compositional differences are blurred across the boundary in addition to zoning is the spread of individual epidote grain compositions within a rock even on a thin section scale this is related to variation in the composition of coexisting phases or reactants e g quartz ca al silicates such as plagioclase margarite lawsonite mafic silicates such as chlorite pumpellyite amphiboles other ca fe3 silicates such as prehnite andraditic garnet carbonates fe oxides relict volcanic glass which serve as compositional micro domains in which epidote may form

discovery of epidosites in a modern oceanic setting the tonga forearc the first suite of oceanic epidosites has been recovered from the tonga forearc epidosites are metal depleted rocks composed of subequal proportions of epidote and quartz that lack any original igneous texture epidosites have been interpreted to form in upflow zones at the base of ore forming oceanic hydrothermal systems that vent as black smokers on the sea floor tongan epidosites metasomatically replaced basaltic and plagiogranite protoliths and formed under similar conditions to epidosites hosted in many ophiolites interpreted to have formed in a suprasubduction zone setting the similarities shared by the tongan and suprasubduction zone ophiolite epidosites along with the absence of epidosites in collections from modern mid ocean ridges suggest that tectonic setting plays a role in their formation

validating the kagis black box gis based model in a mediterranean karst aquifer case of study of mela aquifer se spain this research was funded by the spanish ministry of science and innovation projects cgl2013 48802 c3 3 r and cgl2015 69773 c2 1 p and by the university of alicante projects gre15 19 and gre17 12

karst massif susceptibility from rock matrix fracture and conduit porosities a case study of the sierra de las nieves malaga spain the potential contamination of a karst massif from surface sources can be evaluated and represented in a susceptibility map in the case of a carbonate aquifer the susceptibility assessment must take into account their very complex and heterogeneous nature the complexity originates in the presence of three types of porosity matrix rock fracture and conduit porosity this paper presents a method for karst susceptibility mapping by estimating the three porosity types and evaluates their integration in a single susceptibility index matrix rock porosity is measured in the laboratory from samples collected in the field and is well correlated with lithology fracture porosity is estimated from fracture mapping and field measurements of secondary fracture porosity geostatistical methods are used to obtain continuous fields of rock matrix porosity and fracture porosity conduit porosity is calculated from a power model fitted to speleological cave mapping data however because of the scarcity and sampling bias of conduit data probabilistic models are conjectured a fourth porosity factor evaluated is the detritic filling of karst depressions the integration of the different porosities in a single susceptibility factor gives a quantitative map that is reclassified to provide a qualitative easy to interpret susceptibility index map of the karst system porosity estimation may also be of interest in recharge estimation and mathematical modelling of flow and transport in karst systems the case study used to illustrate this approach is the sierra de las nieves karstified rock mass a high relief mediterranean karst in the province of malaga in southern spain

liquid immiscibility in the archean greenstone belt of piumhi minais gerais brazil abstract liquid immiscibility has been used for explaining several modern situations either in effusive or in intrusive rocks liquid immiscibility is also proposed for explaining the variolitic structures in the archean rocks of the abitibi greenstone belt ontario the volcanic sequence of the lower portion of the greenstone belt of piumhi minas gerais brazil shows the occurrence of variolitic structure that may have been formed by liquid immiscibility this possibility is supported by the following points a the contact between varioles and matrix is very sharp b spinifex texture occurs both in the varioles and in the matrix and the single crystal may cross the varioles c the varioles and the matrix show contrasting compositions the latter has the composition of a basaltic komatiite and the former varies form that of an alkali basalt to andesite and d a test by a thermodynamic model from literature shows that although with some doubt the free energy of the possible parent liquid is higher than that of the two unmixed liquids

seamount formation and associated caldera complex and hydrothermal mineralization in ancient oceanic crust troodos ophiolite cyprus abstract the inter graben zone between the solea and mitsero grabens in the northern part of the troodos ophiolite cyprus displays igneous tectonic and physiographic features that are characteristic of seamount volcanism at modern oceanic spreading centers in this zone the 200 m high alestos hill volcanic edifice consisting of pillow lavas with preserved lava tubes and cone sheet intrusions is interpreted to have developed as a seamount fed by a late stage off axis shallow level gabbroic pluton that was intrusive into young oceanic crust concentric cone sheet intrusions and associated faults and shear zones in and around the alestos hill seamount collectively form a seafloor caldera complex which probably formed during the extrusion of lavas and subsequent cauldron subsidence over the gabbroic pluton the ene trending elongated massive sulfide ore deposit formation in the alestos memi area represents a focused upflow zone for hydrothermal fluids driven by the same off axis gabbroic intrusion responsible for formation of the alestos hill seamount the ene trending and up to 150 m wide alestos memi fault zone dissects the elongated ore body in a dextral sense and might have provided a high permeability conduit in the upper crust for upwelling hydrothermal flow at the time of magmatism the geometry of this fault zone and its kinematic relations with a n s striking alestos forest normal fault in the west are suggestive of its transfer fault origin reminiscent of mineralized transfer faults found at the mid atlantic ridge the active tag hydrothermal mound with massive sulfide deposits that is located on a small volcanic dome 3 km off axis and along a transfer fault in the trans atlantic geotraverse tag area at 26 n provides a modern analogue for the alestos hill seamount and associated faulting and mineralization in the ancient oceanic crust of the troodos ophiolite these findings indicate that off axis magmatism played a major role in crustal accretion hydrothermal alteration and ore mineralization during the late stage evolution of the troodos ophiolite

some aspects of the recent tectonics in the strait of messina italy abstract during pliocene and pleistocene times the strait of messina was subjected to extensional tectonism which was contemporaneous with marine sedimentary processes various tectonic sedimentary features created by this combination of processes are reviewed depocentres synsedimentary truncations and the association of sedimentary dykes related to extensional fissuring and hydraulic fracturing these features are regarded as characteristic accompaniments to extensional block faulting the recent structural evolution of the strait of messina margins provides an illustration of high magnitude vertical movements occurring within a short time interval the subsidence phase is related to fault movements which generate important fault scarps and sedimentary dykes phases of upheaval in contrast correspond to a general uplift of the margins unrelated to the local fault movements

dome growth rates eruption frequency and assessment of volcanic hazard insights from new u th dating of the panarea and basiluzzo dome lavas and pyroclastics aeolian islands italy abstract new geochronological data are presented and discussed together with field data in order to reconstruct the geo volcanological evolution of panarea island attention is focused on the discrepancies between geochronological data compared with field evidence field data provide evidence that the panarea dome was continuously built up without a significant break in volcanic activity continuous extrusion of new magma allowed the dome to emerge subaerially subaerial effusive activity followed with the alternation of exogenous and endogenous phases of growth that led to the formation of radial and tangential lava lobes and plugs the younger volcanic products are represented by a thick succession of pyroclastic products discontinuously outcropping all over the island dated here for the first time samples were dated through the u th disequilibrium method which is also able to provide information on the geological processes at the origin of u th fractionation the chronology of the volcanic events at panarea suggests that the volcanic activity developed through two main phases effusive activity mainly characterized the first phase of the dome growth while during the second phase explosive activity prevailed the second phase occurred from 31 7 to 20 2 ka assessing the age of the first phase is more difficult the age of 155 12 ka which is in the same time span obtained from k ar or ar ar methods is not consistent with field evidence furthermore although the alignment of the points on the isochron is very good the initial value of the 230th 232th ratio is very low and does not have a clear meaning our data strongly suggest that the age of 155 12 ka is not realistic two alternative scenarios are proposed implying a revision of the geological and geochronological evolution of the island together with the significance of the marine terraces on panarea

tectonic and volcanic evolution of panarea aeolian islands italy abstract based on new geophysical volcanological structural and radiometric data a morphological structural reconstruction of the submarine part of the panarea volcanic edifice is provided and a model for the evolution of the entire complex is proposed panarea is a small part of a much larger submarine edifice whose overall shape is one of a truncated cone with an eastern protrusion the base of the cone is about 1500 m below sea level it has a diameter of about 23 km and an area of 460 km2 several lobes are present on the steep eastern slopes of the cone and the wide submarine top is of a morphology which is more complex than previously thought the evolution of the panarea volcanic complex occurred in three stages 1 1 development of a central volcano in the western sector of the complex the island of panarea represents the top of this volcano 2 2 eastward shifting of volcanic activity producing development of the lobed eastern sector of the complex 3 3 extensive caldera collapse of the central part of the complex and emplacement within the collapsed area of domes and lava bodies of various affinities some of which are basaltic ne sw oriented structures seem to have had a fundamental role during the development of the panarea volcanic complex these structures have been active until recent times and are of regional significance indeed the evolution of nearby stromboli has been controlled by the ne sw trending structures panarea and stromboli also display similar magnetic anomaly trends geochemical affinities and temporal relationships in volcanism

icp ms a powerful tool for high precision trace element analysis in earth sciences evidence from analysis of selected u s g s reference samples abstract inductively coupled plasma mass spectrometry icp ms is a powerful analytical technique with considerable application to geochemistry in this paper we demonstrate the power of icp ms as a tool in petrogenetic studies data for 28 elements in seven u s g s basalt and andesite reference samples agv 1 bcr 1 bhvo 1 bir 1 dnc 1 w 1 and w 2 are presented accuracy and precision standard deviation for 26 of these elements is either excellent a detailed description of the icp ms technique we have developed is given a simple hf hno 3 dissolution in screwtop teflon bombs was used for sample preparation icp ms instrumental sensitivity was measured by external solutions with surrogate calibration for 4 elements matrix correction was made by use of standard addition naturally occurring internal standards rb y ce and pb were used to correct for instrumental drift between sample and spiked sample measurements we report data for the elements li cs rb sr ba zr hf nb ta y sc u th pb and all 14 of the ree in addition the procedure acquired data for be mo w tl and bi many elements in this array are crucial for the evaluation of petrogenetic models and source tracing herein lies the real power of icp ms one technique one dissolution small sample size good limits of detection good to excellent accuracy and good precision for many geochemically important elements

widespread syn eruptive volcaniclastic deposits in the pleistocenic basins of south western calabria abstract since late tortonian depositional sequences developed along the southern calabrian forearc inside the half graben depressions of the mesima gioia tauro and reggio calabria basins in these basins volcaniclastic sedimentation took place during lower to middle pleistocene volcaniclastic deposits consist of isolated pumice swarms ash layers and thick successions of lapilli and ash in this paper we describe and discuss the depositional characteristics of these volcanogenic sediments and the morphology mineralogy and chemistry of pumices shards lithics and crystal fragments these deposits all have the characteristics of a proximal tephra fall deposit from a plinian plume which has been reworked in a shore environment in the mesima basin the deposits reach 6 m in thickness and in the gioia tauro plain 21 m of pumiceous sediments have been cored in a drill hole the compositional homogeneity of fragments and the absence of non volcanic detritus as well as of soil or organic matter suggest that the deposits were quickly reworked after their primary emplacements all the tephra deposits exhibit calc alkaline affinity and dacitic to rhyolitic composition the mineralogical assemblage including orthopyroxene as phenocryst indicates provenance from magmatic arc volcanism icp ms and la icp ms analyses of crystals and glass point to a common origin probably from a single eruption this makes these volcaniclastic layers a very useful tool for stratighaphic reconstructions at a regional scale the geological setting of the deposits their petrological and geochemical signature and the occurrence of large size clasts suggest a provenance from explosive eruptions preceding the emplacement of the 50 ka dacitic lava dome of the island of panarea aeolian archipelago however a provenance from a different calc alkaline volcanic system cannot be excluded these deposits can therefore represent the only evidence of a large explosive eruption in the southern tyrrhenian sea whose very proximal equivalent is not preserved

boninite like volcanic rocks in the 3 7 3 8 ga isua greenstone belt west greenland geochemical evidence for intra oceanic subduction zone processes in the early earth abstract the 3 7 3 8 ga isua greenstone belt of southwest greenland is characterized by variably metamorphosed metasomatised and deformed lithotectonic successions of volcanic and sedimentary rocks the voluminous mafic volcanic rocks are composed primarily of pillow basalts intercalated with ultramafic units the sedimentary rocks consist mainly of banded iron formation cherts conglomerates and siliciclastic turbidites the least altered metavolcanic amphibolites the garbenschiefer unit from the central tectonic domain of the isua greenstone belt are characterized by high mg number 0 60 0 80 mgo 7 18 wt al2o3 14 20 wt ni 60 645 ppm and cr 60 1920 ppm contents but low tio2 0 20 0 40 wt zr 12 30 ppm y 6 14 ppm and rare earth element ree concentrations these compositional features collectively represent a coherent mafic to ultramafic suite chondrite normalized ree patterns are concave upward on the primitive mantle normalized extended trace element diagrams they are characterized by relative depletion of nb but with an enrichment of zr relative to neighboring rees alteration deformation and crustal contamination can be ruled out as the cause of the distinct and coherent composition the average initial end value of these metavolcanic rocks is 2 collectively these geochemical characteristics are comparable to those of phanerozoic boninites given the observation that in the tertiary boninites are exclusively associated with intra oceanic subduction environments e g izu bonin mariana subduction system this suggests that intra oceanic subduction zone like geodynamic processes were operating as early as 3 7 3 8 ga

boninites from the neoarchaean gadwal greenstone belt eastern dharwar craton india implications for archaean subduction processes abstract boninites are rare in archaean arcs all over the world whilst there are some reports from the phanerozoic convergent margins in this paper boninites are reported for the first time from an archaean greenstone belt of india which have not been reported from any other indian greenstone belt as yet the greenstone belts of western dharwar craton are characterized by high mg basalts and komatiites whereas in the greenstone belts of eastern dharwar craton boninites represent the high mg lavas these boninites are characterized by 1 high mgo 12 24 wt 2 enriched in transition elements such as ni 423 1184 ppm cr 943 2765 ppm 3 low tio2 0 22 0 36 wt 4 high al2o3 tio2 ratio 29 50 5 gd ybn less than one 6 slight enrichment in lree depletion in mree compared to lree and hree resulting in u shaped ree patterns 7 negative nb ta zr hf ti and v anomalies despite the depletion in mree these characteristics differentiate them from deep mantle plume related magmas these boninites are compositionally similar to those found in modern and fossil island arcs from intraoceanic subduction settings and provide evidence to propose that two stage melting of the archaean mantle wedge generated this type of high mg magma the other high mg type magma komatiitic suite found in the greenstone belts of western dharwar craton has an enriched deep mantle plume source and its dry melting whereas boninites are generated by wet melting of the refractory depleted mantle wedge under high temperature and fluid pressure generated by dehydration of the slab the geological setting hfse and ree data show that possibly the 2 7 ga peak of geological activity had transitional characteristics between those of paleoarchaean and phanerozoic high thermal and fluid flux is inferred to generate these mg enriched and mree hfse lfse depleted suite this discovery of boninites from gadwal greenstone belt indicate that even in archaean subduction of small young and hot oceanic plates produced magmatic assemblage resembling to those of some of the cenozoic subduction complexes

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr

archean metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 2 mobility of trace elements and petrogenetic constraints qualitative evaluation of altered mafic pillows from the rouyn noranda district of the abitibi metavolcanic belt reveals that for low grade metamorphism the high field strength elements hfs zr y ti and the rare earth elements ree are immobile however where alteration is extreme the ree elements are leached and redeposited by carbonate rich and k rich metasomatic fluids whilst zr y and zr ti remain unchanged rubidium ba and to a lesser extent sr are mobile at all levels of alteration however provided certain filters are applied the original geochemical values of the lavas for the alkaline elements the hfs elements and the ree can be defined the geochemical variations thus identified for the volcanic series of the rouyn noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma

a buried volcano in the calabrian arc italy revealed by high resolution aeromagnetic data 1 aeromagnetic data collected between the aeolian volcanoes southern tyrrhenian sea and the calabrian arc italy highlight a wnw ese elongated positive magnetic anomaly centered on the capo vaticano morphological ridge tyrrhenian coast of calabria characterized by an apical subcircular flat surface results of forward and inverse modeling of the magnetic data show a 20 km long and 3 5 km wide magnetized body that extends from sea floor to about 3 km below sea level the magnetic properties of this body are consistent with those of the medium to highly evolved volcanic rocks of the aeolian arc i e dacites and rhyolites in the calabria mainland widespread dacitic to rhyolitic pumices with calc alkaline affinity of pleistocene age 1 0 7 ma are exposed the tephra falls are related to explosive activity and show a decreasing thickness from the capo vaticano area southeastward the presence of lithics indicates a provenance from a source located not far from capo vaticano the combined interpretation of the magnetic and available geological data reveal that 1 the capo vaticano wnw ese elongated positive magnetic anomaly is due to the occurrence of a wnw ese elongated sill 2 such a sill represents the remnant of the plumbing system of a pleistocene volcano that erupted explosively producing the pumice tephra exposed in calabria and 3 the volcanism is consistent with the aeolian products in terms of age magnetic signature and geochemical affinity of the erupted products the results indicate that such volcanism developed along seismically active faults transversal to the general trend of the aeolian arc and calabria block in an area where uplift is maximized 4 mm yr such uplift could also be responsible for fragmentation of the upper crust and formation of transversal faults along which seismic activity and volcanism occur

karst groundwater resources in the countries of eastern mediterranean the example of lebanon the hydrogeological study of some karst systems in lebanon shows important storage capacity up to 27 billions m3 for zarka system the spring of orontes river their geological and morphological settings as well as their hydrodynamic function show structures developed below the level of present springs probably up to several hundreds meters at depth since miocene those carbonate formations were subject to a remarkable instability of their base levels variations of sea level of which the messinian salinity crisis is the major phase and effects of the alpine orogenesis combined with climate variations to develop complex multiphased karst systems karstification occurs frequently in the whole formation often deeply below sea level or underneath sediment filling of continental basins the surface karst landscape is often intensely eroded those multiple superimposed karst phases give the carbonate aquifers their large extension and storage capacity these karst aquifers show the typical easy restoration of storage they have the ability to bear large interannual recharge variations and support exploitation under high pumping rates however these aquifers have some disadvantages for sustainable management in some regions successful boreholes which allow high pumping rates also induce uncontrolled exploitation another consequence is natural seawater intrusion as well as the submarine discharge of fresh groundwater in coastal aquifers those carbonate aquifers are subject to important economical stress which jeopardizes their durability the systematic study and understanding of carbonate aquifers in eastern mediterranean is a preliminary condition to any integrated and sustainable management of water resources studies in progress in lebanon may serve as examples to the whole region

contrasting geochemical patterns in the 3 7 3 8 ga pillow basalt cores and rims isua greenstone belt southwest greenland implications for postmagmatic alteration processes abstract pillow basalts from the early archean 3 7 to 3 8 ga isua greenstone belt west greenland are characterized by well preserved rims and concentric core structures the pillow rims and cores have different mineral assemblages and chemical and isotopic compositions the rims have systematically higher contents of fe2o3 mgo mno k2o rb ba ga y and transition metals than the cores in contrast the cores possess higher concentrations of sio2 na2o p2o5 sr pb u nb and the light rare earth elements rees than the rims these compositional variations in the rims and cores are likely to reflect the mobility of these elements during posteruption alteration variations of many major and trace element concentrations between the rims and cores of the isua pillow basalts are comparable to those of modern pillow basalts undergoing seafloor hydrothermal alteration al2o3 tio2 th zr and the heavy rees display similar values in both rims and cores suggesting that these elements were relatively immobile during postemplacement alteration in addition the rims and cores have distinctive sm nd and rb sr isotopic compositions in that the rims are characterized by higher 143nd 144nd and 87sr 86sr ratios than the cores the pillow basalts yield 2569 170 ma and 1604 170 ma errorchron ages on 143nd 144nd vs 147sm 144nd and 87sr 86sr vs 87rb 86sr diagrams respectively the sm nd errorchron age may correspond within errors to a late archean tectonothermal metamorphic event recorded in the region the sm nd errorchron may have resulted from a combination of isotopic homogenization and preferential loss of nd relative to sm during late archean metamorphism although the rb sr errorchron age overlaps with the timing of an early to mid proterozoic tectonothermal metamorphic event recorded in the region because of a considerably large mean square of weighted deviates value and scatter in 86sr 87sr and 87rb 86sr ratios this age may not have a precise geological significance the 1 6 ga rb sr errorchron is likely to have resulted from the loss of radiogenic 87sr collectively the sm nd and rb sr data obtained from the 3 7 3 8 ga isua pillow basalt rims and cores are consistent with disturbances of the sm nd and rb sr systems by tectonothermal metamorphic events long after their eruption in contrast to the sm nd and rb sr systems the lu hf system appears to be largely undisturbed by metamorphism five core samples and three rim samples yield a 3935 350 ma age within error of the approximate age of eruption 3 7 to 3 8 ga two rim samples that have gained lu give an age of 1707 140 ma within error of the rb sr errorchron age initial 176hf 177hf ratios of the undisturbed samples at 3 75 ga lie within 1 e unit of the chondritic value suggesting no long term depletion in the mantle source of the basalts

metamorphism denudation and sea level in the archean and cooling of the earth abstract over long enough time scales an antagonistic balance acting between tectonics uplift and rifting and the sedimentary cycle erosion and deposition probably keeps continental surfaces close to sea level we argue that this balance constitutes the primary mechanism for keeping long term continental freeboard constant by regulating the continental thickness an important implication is that the long term uplift or down warp history of ancient continental segments provides direct information on secular changes in the isostasy of the adjacent ocean basins through time the amount of uplift can be estimated from the regional metamorphic grade the burial pressures at present exposure of ten undisturbed archean granite greenstone segments are estimated to be 1 5 0 5 kb from this we infer a maximum long term uplift and erosion of 5 2 km for stable continent since 3 0 ga implying a mean continental thickness of 46 km at the time of crustal stabilization for a constant mean ocean depth isostasy requires a palaeo oceanic crust 14 2 km thick in the middle archean alternatively if little continent existed then the oceans would have been shallower and the palaeo oceanic crust 21 2 km thick assuming plate spreading did occur in the archean potential temperatures in the shallow mantle at 3 ga were 90 30 c or 170 20 c for no continent hotter than those prevailing today these temperatures translate into time averaged cooling rates for the shallow mantle of 57 c ga 1 and are comparable to estimates of the present day cooling rate for the whole earth the low burial pressures are a strong argument against the existence of catastrophic mantle flush events in the geological past which have been predicted by some mantle convection models taken together these constraints suggest a plume related geological setting i e oceanic plateau like flood basalt for the initial stage of greenstone belt evolution

influence of rainfall quantity on the isotopic composition 18o and 2h of water in mountainous areas application for groundwater research in the yunquera nieves karst aquifers s spain abstract the isotopic composition 18 o and 2 h of rainwater and groundwater was determined in the yunquera nieves hydrogeological unit a karstic massif in s spain with complex orography and hydrogeology the aims were to identify 1 the source of the water 2 the main factors determining the isotopic content 3 the catchment area of the springs and 4 the aquifer behaviour the isotopic content of the sampled waters is of mixed atlantic mediterranean origin and is opposite to the quantity of rainwater distribution both in space and time spatially water is isotopically less depleted toward the eastern sector where rainwater quantity is lower which is locally affected by the orography thus it is possible to differentiate the catchment areas of the main springs aquifer recharge is produced by winter precipitation when rainfall water is isotopically more negative and evaporation is lower the decrease in rainfall quantity during the study period provoked an increase in 18 o and 2 h values both in rainwater and in groundwater the recorded variations of the isotopic content of the rainfall are rapidly evident in the spring waters which demonstrates a well developed karst network inside the carbonate aquifers and thus the existence of conduit flow systems

review on groundwater recharge in carbonate aquifers from sw mediterranean betic cordillera s spain this paper presents a review of groundwater recharge assessment in some 50 carbonate aquifers of the extreme sw mediterranean domain betic cordillera southern spain an area highly vulnerable to climate change the selected aquifers represent a broad range of meteorological and geological conditions and consequently results can be expanded eastward to other mediterranean aquifers the methods most commonly applied for recharge assessment over the past 20 years are aquifer water budget and soil water balance while these methods support the first steps in groundwater management in spain precision in quantification requires other methods to be incorporated they include chloride mass balance diverse lumped model codes and empirical methods such as aplis in eastern areas of the betic cordillera where semiarid conditions prevail lumped and distributed models for recharge assessment and calibration are based on the time series of water table data the mean annual rainfall recharge and coefficient infiltration as percentage of rainfall are respectively 648 262 mm year and 38 a high correlation was observed between annual rainfall and annual recharge in all the studied aquifers however the infiltration coefficient can vary substantially even with the same annual rainfall recharge this reflects significant differences in the degree of surface karstification and the development of the vegetal cover soil epikarst system in the carbonate aquifers of the betic cordillera the results of this work may serve to improve the assessment and management of renewable water resources in western mediterranean carbonate aquifers the findings are moreover useful for future comparisons involving recharge assessments under different scenarios of climate change and changes in land use

tephra layers along the southern tyrrhenian coast of italy links to the x 5 x 6 using volcanic glass geochemistry we present the geochemistry of glass fragments from three visible tephra layers outcropping in southern italy two tephra deposits les1 and les2 outcropping in the palinuro area cilento southern italy correspond stratigraphically to the cil1 and cil2 tephra units giaccio et al 2012 respectively in turn these are correlated with the x 5 ca 105 ka and x 6 ca 108 ka marine tephra markers on the basis of their major element glass compositions in order to reinforce these tephra correlations we examine both their major and trace element glass compositions les1 compositions were compared with other correlatives of the x 5 tephra layer pop3 sulmona basin tm 25 lago grande di monticchio lgdm cil1 palinuro from the central mediterranean our data validate a correlation of the palinuro tephra layer les1 to the x 5 correlatives the palinuro tephra deposit les2 has glass compositions which correspond precisely with correlatives of the x 6 marker tephra cil2 palinuro tm 27 lgdm i 9 ionian sea and prad 2812 prad1 2 adriatic sea a tephra in the valle del crati calabria appears to overlap in composition with the les2 tephra indicating a probable correlation with the x 6 marker these new data provide a detailed geochemical characterisation of two widespread marker horizons and are crucial for establishing precise correlations of sedimentary archives across the central mediterranean region

metal depleted root zones of the troodos ore forming hydrothermal systems cyprus the cupriferous pyrite deposits of cyprus were precipitated from hydrothermal solutions derived by interaction of contemporaneous seawater with hot mafic rock at the ancient troodos spreading centre here we identify the zones in which this interaction took place the zones occur in the lower part of the sheeted dyke complex and within them 30 50 of the rock is made up of epidosite an epidote quartz rock replacing the dykes as sheets and pipes the epidosites contain abundant fluid inclusions which give trapping temperatures of 350 400 c or even higher and contain water normally near seawater in salinity zones of epidosite are elongate parallel to the strike of the sheeted dykes and are up to 1 km wide the rocks throughout these zones are strongly depleted in cu and zn and the metals removed are sufficient to supply the ore deposits in fact several large ore deposits lie along strike from zones of epidosite all of these features support the identification of the epidosites as the hydrothermal reaction zones the location of the epidosite zones immediately above the gabbros of the plutonic complex supports the hypothesis that the heat to drive the ore forming systems came from the underlying magma as is also likely for modern black smoker springs

timing of late archaean terrane assembly crustal thickening and granite emplacement in the nuuk region southern west greenland abstract a breakthrough in understanding the structural and metamorphic evolution of archaean gneiss complexes occurred with the recognition that the nuuk region of southern west greenland comprised separate terranes assembled in the late archaean from northwest to southeast these are the akia 3220 2970 ma akulleq 3870 3600 and 2820 ma and tasiusarsuaq 2920 2860 ma terranes the minimum time of assembly is recorded by the first event common to all component terranes using shrimp u pb zircon geochronology the oldest events common to all terranes including emplacement of crustally derived granites contemporaneous metamorphism and anatexis have been dated at 2710 2725 ma in the akulleq terrane areas where in situ diatexite formed abundant granitoid sheets were intruded and common growth of metamorphic zircon mostly low th u in most lithologies occurred in the akia and tasiusarsuaq terranes there was only intrusion of a lesser number of 2720 ma granitoid sheets because metamorphic zircons of that age have not been found the 2720 ma event is interpreted as marking or shortly following terrane assembly when the diverse components of the akulleq terrane were tectonically juxtaposed with the other two this new documentation of metamorphic and associated igneous events within an accreting cratonic region is an illustration that the stabilisation of extensive areas of archaean gneisses can be due to accretionary tectonics long after the individual components were first formed

the origin of hydrothermal metalliferous sediments associated with the early mesozoic othris and pindos ophiolites mainland greece abstract metalliferous sediments and sulphides are associated with the jurassic othris and pindos ophiolites central and northern greece these ophiolites formed at an early mesozoic spreading ridge within a small pindos ocean basin created by rifting of the northern margin of gondwanaland ubiquitous terrigenous silt was derived from adjacent continental margins mainly the pelagonian microcontinent to the east in the othris area disseminated massive and vein sulphides occur within and above morb type pillow lavas and volcaniclastic sediments sulphide was precipitated in quartz veins within fault controlled stockworks episode with local epidosite is locally very abundant in extrusives immediately underlying thick si fe rich hydrothermal sediments massive sulphides were precipitated as small fault controlled bodies that are directly overlain by fe rich mudstones and fe rich cherts strongly depleted in mn mudstones relatively enriched in hydrothermal fe mn cu zn pb ree and ba were ponded into small fault controlled hollows around the fringes of the sulphide precipitating field elsewhere e g northern othris manganese rich layers in ribbon radiolarites are strongly enriched in mn and trace elements metal enriched deposits are also found within slices of mid ocean ridge type lavas associated with melange avdella melange structurally underlying the pindos ophiolite nw greece sulphides there are restricted to tiny massive deposits overlying pillow lava and sulphide veins within ophiolitic extrusives pillow lavas are overlain by volcanic talus breccias shed from submarine fault scarps overlying metalliferous mudstones are enriched in fe and other hydrothermal constituents probably derived from nearby sulphide precipitating zones and mixed with lithogenous sediments the metalliferous deposits preserve a variety of hydrothermal deposits within an early mesozoic small ocean basin the pindos sediments reflect mixing of ferruginous hydrothermal constituents with terrigenous sediment possibly during the earlier stages of basin opening the othris sulphide and ferruginous oxide sediments record evidence of a small high temperature hydrothermal field formed near the spreading axis when the ocean neared its maximum width manganese rich cherts in the northern othris area reflect widespread accumulation of hydrothermal constituents on the abyssal plain derived from axial high temperature hydrothermal fields and or related to low temperature off axis discharge

eustatic and tectonic control on late quaternary alluvial fans along the tyrrhenian sea coast of calabria south italy abstract the late quaternary evolution of the western coastal range northern calabria has been reconstructed by means of a multidisciplinary approach we have focused on the role of allocyclic mechanisms tectonics and base level change considered as factors influencing alluvial fan development in particular we identify no clear evidence for a major influence of climate age constraints were provided by a tephra layer and a paleosol coupled with geomorphological correlations middle pleistocene perched terraces and fan relicts hanging above fault scarps indicate that tectonics caused switches in fan dynamics between aggradational and erosional phases as tectonic activity declined during late middle pleistocene eustatically driven changes in base level possibly plus low rates of tectonic subsidence represent the main factor which controlled late pleistocene fan development the two major fan aggradation phases occurred during periods of climate amelioration prior to highstands whereas high sea levels ois 5 and 1 promoted channel incision into the fan surfaces this continued during periods of climate deterioration with a seaward progradation of alluvial deposition sea level rise is seen as creating accommodation space producing very open fans locally within mountain embayments the fans are characterised by a mushroom shape in plan view and by a retrograde stacking pattern of alluvial fan facies

contrasting styles of tectonism and magmatism in the late archaean crustal evolution of the northeastern part of the ivisârtoq region inner godthabsfjord southern west greenland abstract varieties of late archaean gneisses recognized on the basis of field petrographic and chemical data include multiphase tonalitic granitic gneisses with abundant enclaves of amphibolite granodioritic gneisses largely devoid of enclaves leucocratic schlieric gneisses with pods of amphibolite and hornblendite and grey granitic gneisses with locally abundant enclaves of amphibolite the bulk of the gneisses are correlated with the nuk gneisses c 3000 2900 ma of outer godthabsfjord most of the gneisses were emplaced during a period of horizontal tectonic interleaving of thick slices of amitsoq gneisses c 3700 ma and younger malene supracrustal rocks mainly amphibolites older than c 2900 ma interleaving took place on tectonic slides during regional horizontal heterogeneous simple shear movements flattening strains modified ameralik amphibolite dykes in the amitsoq gneisses and gave rise to s fabrics banding and schistosity in the malene rocks the s fabrics facilitating emplacement of voluminous nuk gneisses mainly as broadly concordant sheets potash feldspar blastesis and localized partial melting occurred in some of the earlier phases of nuk gneisses and possibly the amitsoq gneisses but the timing of these processes in relation to this period of emplacement is uncertain high temperatures appear to have been sustained into the second period of deformation when large mainly upright domes and synforms some cuspate were superimposed on the broadly horizontal pile of amitsoq gneisses malene rocks and nuk gneisses tectonic fabrics are dominated by mineral and ribbing lineations coaxial with folds of this second period magmatic emplacement of sheets of granitic gneisses and pegmatites continued many of the sheets being injected coplanar with the second phase parasitic folds pegmatites and schlieric gneisses were generated by syntectonic and younger feldspar blastesis and partial melting the close of late archaean magmatism is marked by the post tectonic qorqut granite and pegmatite complex c 2500 ma the horizontal tectonic movements emplacement of gneisses generation of domes and synforms and syntectonic injection of younger granitic gneisses appear to have taken place in the interval between c 3000 2600 ma ago similar relations between late archaean tectonism and magmatism have been recognized elsewhere in the archaean block of greenland but syntectonic injection of granitic gneisses and transformation of older gneisses to schlieric types appear to be more widespread in this part of the archaean block in ivis rtoq

high bromine contents and low clbr ratios in hydrothermally altered archaean komatiitic rocks west greenland abstract in archaean supracrustal rocks in west greenland komatiitic and tholeiitic rocks have undergone alteration by circulating hydrothermal solutions whereby the rocks were partly transformed into calc silicate assemblages the alteration which also formed extensive stratabound scheelite mineralizations took place partly at the sea floor and partly below the sea floor prior to metamorphism and deformation of the volcano sedimentary pile the altered komatiitic and tholeiitic rocks contain up to 418 ppm bromine and cl br ratios down to 1 6 compared with 60 1300 ppb bromine and cl br ratios of 430 in mid ocean ridge basalts cl and br was not detected by electron microprobe in any of the minerals found it is suggested that the volcano sedimentary pile was altered by hot brines which had attained high halogen contents by reaction with mafic and ultramafic rocks during brine rock interaction the cl br ratio of the brines decreased and the metal contents increased the metalliferous bromine enriched brines ascended towards the sea floor the bromine and some of the metals precipitated in the upper part of the volcano sedimentary pile and in the volcanic rocks at the sea floor high bromine contents and low cl br ratios may indicate presence of major orebodies

oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern oman and their relationship to the overlying massive sulphide deposits the extraordinarily well preserved and well exposed semail ophiolite of northern oman hosts several large plagiogranite intrusions in proximity to economic copper sulphide deposits of the lasail mining district a progression of isotopic chemical and mineralogical transformations observed within the plagiogranites and high level gabbros hlg and a comparison of these effects with those in the lowermost dykes of the immediately overlying sheeted dyke complex sdc tracks the evolution of hydrothermal fluids and the alteration of overlying dykes and pillow lavas during discharge of these fluids on the sea floor the largest hydrothermal alteration aureoles and the greatest extent of metamorphic veins and metasomatic replacement features are found adjacent to the largest high level plagiogranite bodies beneath and adjacent to the major ore bodies in northern oman the ubiquitous presence of metamorphic actinolitic hornblende sodic plagioclase epidote and titanite in metabasalts within the high temperature alteration zones points to the most likely mineralogical and structural controls on the development and evolution of the hydrothermal fluids depleted cu contents of the adjacent crustal rocks and cu enrichments above the plagiogranite intrusions demonstrate the redistribution of heavy metals adjacent to the complexes field relationships implicate the formation of both the epidosites and plagiogranites in the genesis of the ore deposits an important process inferred from the field and geochemical data is the assimilation of previously hydrothermally altered basaltic and gabbroic country rocks by stoping into the magma chambers developed near the sdc gabbro horizon in the ophiolite we suggest that this process of combined assimilation fractional crystallization together with replenishment and recharge by injection and quenching of basaltic magma pillows into these plagiogranite magma chambers i e rafc plays a major role in the development of these composite intrusions

the geology and tectonic evolution of the pietersburg greenstone belt south africa abstract the pietersburg greenstone belt occurs near the northern margin of the low grade granite greenstone terrain of the kaapvaal craton to the north lies the high grade granite greenstone terrain which constitutes the southern marginal zone of the limpopo belt the original relationship between the two terrains has been overprinted by the effects of the limpopo orogeny and are therefore not known a better understanding of the tectonic evolution of the pietersburg greenstone belt may help to clarify this relationship the rocks of the southwestern part of the pietersburg greenstone belt have been mapped in considerable detail the rocks can be subdivided into two sequences the first comprises a sequence of massive to pillowed metabasalts metagabbros and metaperidotites as well as bif fine grained mafic tuffs and sediments the sequence was subjected to extensive hydrothermal metamorphism at low pressures and variable temperatures in the greenschist to amphibolite facies this suggests an oceanic like environment the second sequence known as the uitkyk formation comprises a sequence of terrestrial clastics which overlie the first sequence with a profound unconformity sedimentology indicates that the uitkyk formation formed in a prograding alluvial fan or braided alluvial plain the uitkyk sediments were deformed and infiltrated by fluids that precipitated quartz tourmaline gold and siderite soon after deposition age relationships bedding cleavage relationships and younging directions indicate that both the sediments and simatic rocks were involved in a phase of thrust related deformation d2 that resulted in south over north stratigraphic repetition under generally low grade conditions of metamorphism post d2 granites date this thrusting at pre 2 69 ga d2 was probably diachronous and at surface the deformation was accompanied by syntectonic terrestrial sedimentation and placer gold deposition the tectonic environment was probably one of an intermontane accretionary or terrestrial foreland basin within this tectonic environment the basement and cover became tectonically stacked across evolving shear zones combined field and microstructural relationships within a major fault zone have revealed a complex history of progressive d2 deformation metamorphism mineralisation and associated sedimentary processes the zone represents a deformed syn sedimentary duplex that was carried piggy back above an allochthonous thrust sheet of simatic rocks at the deepest levels this fault and other shear zones were intruded by syntectonic granitoids this late archaean northward verging d2 thrust stack model for the greenstone belt with the syntectonic granites intruding the thrusts from beneath the greenstone belt is in good accord with the recent geophysical observations the age of cover sedimentation is older than 2 69 ga but younger than 2 98 ga in age this supports suggestions that these deposits are age equivalent of the upper gold bearing sediments of the witwatersrand basin and that the northwards thrusting in both basins may be of the same age and related to the same regional tectonic forces the simatic rocks of the pietersburg greenstone belt may have been part of a more extensive allochthonous simatic terrain which includes the similar greenstone remnants of the southern marginal zone of the limpopo belt such a terrain must have been disrupted and metamorphosed during the northward directed imbrication and tectonic burial recorded in the pietersburg belt prior to the climax of the limpopo orogeny the latter subsequently severely disrupted the pietersburg greenstone belt during ventersdorp times 2 6 2 7 ga

implications of melting for stabilisation of the lithosphere and heat loss in the archaean abstract the increased depth and volume of melting induced in a higher temperature archaean mantle controls the stability of the lithosphere heat loss rates and the thickness of the oceanic crust the relationship between density distributions in oceanic lithosphere and the depth of melting at spreading centres is investigated by calculating the mineral proportions and densities of residual mantle depleted by extraction of melt fractions the density changes related to compositional gradients are comparable to those produced by thermal effects for lithosphere formed from a mantle which is 200 c or more hotter than modern upper mantle if archaean continental crust formed initially above oceanic lithosphere the compositional density gradients may be sufficient to preserve a thick archaean continental lithosphere within which the archaean age diamonds are preserved the amount of heat advected by melts at mid ocean ridges today is small but heat advected by melting becomes proportionally more important as higher mantle temperatures lead to a greater volume of melt and as the rate of production of oceanic plates increases archaean tectonics could have been dominated by spreading rates 2 3 times greater than now and with mantle temperatures between ca 1600 c and 1800 c at the depth of the solidus mid ocean ridge melting would produce a relatively thick but light refractory lithosphere on which continents could form protected from copious volcanism and high mantle temperatures

heavy metal and sulfur transport during subcritical and supercritical hydrothermal alteration of basalt influence of fluid pressure and basalt composition and crystallinity crystalline basalt diabase and basalt glass have been reacted with a na ca k cl fluid of seawater ionic strength at 350 425 c 375 400 bars pressure and fluid rock mass ratios of 0 5 1 0 to assess the role of temperature basalt diabase chemistry and texture on heavy metal and sulfur mobility during hydrothermal alteration alteration of basalt diabase is characterized by cation fixation and hydrolysis reactions which show increased reaction progress with increasing temperature at constant pressure correspondingly ph in a series of 400 bar experiments ranges from 4 8 to 2 7 at 350 and 425 c respectively and is typically lower for alteration of a sio2 rich crystalline basalt than for other rock types due in part to relatively high sio2 concentrations in solution high sio2 concentrations stabilize hydrous na and ca rich alteration phases causing ph to decrease according to reactions such as 3 0 caal2si2o8 1 0 ca 2 0 h2o 2 0 ca2al3si3o12 oh 2 0 h phases experimentally produced include mixed layer chlorite smectite ca rich amphibole and clinozoisite clinozoisite was identified as a replacement product of plagioclase from diabase solution interaction experiments in direct response to h production dissolved fe mn and h2s concentrations increase dramatically for early stage reaction h2s typically exceeds fe and mn however at 425 c and after long term reaction at 400 c h2s is lost from solution apparently in response to pyrite replacement of oxide and silicate phases pyrrhotite formed at temperatures 375 c whereas magnetite was identified in all run products except from basalt glass alteration cu and zn concentrations in solution are not simple functions of ph these metals achieve greatest solubility in fluids from experiments at 375 400 c except when basalt glass is used as a reactant the relatively low concentrations of these species in solution during basalt glass reaction may be due to adsorption by fine grained alteration phases

sand waves echinocardium traces and their bathyal depositional setting monte torre palaeostrait plio pleistocene southern italy stacked cross sets up to 2 5 m thick produced by sand wave migration and meniscate trace fossils produced by echinocardium cordatum both considered in the literature as typical of shallow water marine depositional settings commonly occur in the bathyal plio pleistocene deposits of monte torre calabria southern italy the plio pleistocene sediments form two coarsening upward depositional sequences separated by an unconformity and by a palaeobathymetric gap of at least 300 m the lower sequence passes upwards from hemipelagic marls and thin bedded turbidites to thick bedded sandy turbidites then to sand wave deposits alternated with sandy turbidites and finally to base of slope megabreccias facies characteristics and relationships and the occurrence of deep sea faunal associations indicate deposition in the bathyal zone the facies of the upper sequence reflect a fan delta environment no deeper than a few tens of metres the depositional setting of the lower sequence where the sand wave deposits and meniscate trace fossils occur appears to have been a tectonically controlled seaway connecting the tyrrhenian and ionian seas this seaway became progressively narrower with time evolving into a strait the overall coarsening upward trend reflects the upward transition from a low to a high energy environment possibly caused by the tectonic narrowing of the seaway deposition and erosion from high concentration turbidity currents and from tidal bottom currents were important processes periods of tectonic activity producing first the uplift of the seaway margins and culminating with the uplift of the strait sequence itself are marked by scattered rockfall deposits the strait setting causing the development of powerful oxygenated bottom currents produced optimal conditions in the bathyal zone for the colonization of sandy bottoms by a single infaunal r selected species echinocardium sp

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

archean ocean floor metamorphism in the north pole area pilbara craton western australia abstract archean greenstones ca 3 49 3 46 ga in the north pole dome pilbara craton western australia have undergone prograde metamorphism from prehnite pumpellyite facies to greenschist amphibolite facies observations of 3000 thin sections shows that a metamorphic aureole was restricted to within a few kilometers of the contact with the 3459 ma north pole monzogranite three types of alteration were observed carbonate silicic and chlorite types the distribution of the three types of alteration suggests that secondary chemical migration of elements occurred in the whole area but that some samples were unaffected by this alteration the southern north pole area is outside of the contact metamorphic aureole and is composed of five units from north unit i to south unit v dipping south about 30 70 metamorphism of the north pole greenstones corresponds to the low pressure type which is broadly comparable to that inferred for ocean floor metamorphism prehnite pumpellyite pp transitional tr and greenschist gs facies prograde metamorphic zones occur from structural top to bottom within each of units metamorphic grade increases downward through the units and metamorphic isograds never cut unit boundaries

hydrothermal alteration in a modern suprasubduction zone the tonga forearc crust an extensive suite of hydrothermally altered basalts gabbros and plagiogranites was recovered from the trench facing slope of the tonga forearc the tectonic setting lithology and geochemistry of these samples make them a unique collection for comparison with suprasubduction zone ssz ophiolites petrography mineral chemistry and geothermometry are used to constrain the metamorphic evolution of ocean crust formed in a modern ssz setting seawater derived hydrothermal fluids first penetrated the lower crust along grain boundaries and microscopic fracture networks at temperatures 800 c as the plutonic sequence cooled amphibole progressively replaced the mafic phases followed by chlorite and epidote below 550 c basalts record peak alteration temperatures up to 773 c however most were altered at lower temperatures typical of mid ocean ridge mor volcanic sequences kelman 1998 epidosites formed by pervasive alteration of basalt and plagiogranite at greenschist facies conditions and at high water rock ratios pervasively altered gabbros and basalts display evidence of late cataclastic deformation and or contain veins that is likely related to a later tectonic event such as trench rollback the range of alteration temperatures and mineral assemblages in basalts and gabbros are similar to those described from both ssz ophiolites and mors however the degree of alteration in basalts and the presence of epidosites in the tonga collection are most similar to alteration characteristics in ssz ophiolites the initiation of high temperature brittle deformation in the absence of ductile deformation suggests that the tonga forearc crust was constructed in a magma rich environment similar to fast spreading mors