geochemical and geochronological evidence for early triassic calc alkaline magmatism in the menderes massif western turkey pan african basement rocks and a paleozoic cover series which were intruded by the protoliths of leucocratic orthogneisses have been recognized in the menderes massif located in the western part of the alpine orogenic belt of turkey this geochemical and geochronological study focuses on the evolution of the menderes massif at the end of paleozoic time geochemical data suggest that the crustally derived leucocratic orthogneisses have chemical composition typical of calc alkaline and s type granite zircon grains which are euhedral with typical igneous morphologies were dated by the 207pb 206pb evaporation method single zircon dating of three samples yielded mean 207pb 206pb ages of 246 5 241 5 and 235 6 ma these ages are interpreted as the time of protolith emplacement in triassic geological and geochronological data suggest that leucocratic granites were emplaced in a period following a metamorphic event related to the closure of the paleo tethys the leucocratic granites were metamorphosed during the alpine orogenesis and transformed into orthogneisses the similar triassic magmatic event at 233 2 ma was also occurred using single zircon evaporation method from granitic gneisses which rest upon the migmatites with tectonic contacts in naxos cycladic complex this indicates that the menderes massif and cycladic complex had a common pre early triassic magmatic evolution

crystal fractionation of adakitic magmas in the crust mantle transition zone petrology geochemistry and u pb zircon chronology of the seme adakites eastern pontides ne turkey abstract plutonic and porphyritic intrusions of adakitic rocks are widely distributed in the southern part of the eastern pontides orogenic belt in turkey ranging in age from late paleocene to early eocene these intrusions provide critical information to evaluate the early cenozoic geodynamic evolution of the eastern mediterranean region here we report the results from our field petrologic geochemical and zircon u pb geochronological studies on adakitic intrusions in the seme area from the southern part of eastern pontides belt the seme granitoid daldibi dacite and aslanca dacite porphyry from this region carry abundant plagioclcase amphibole and biotite phenocrysts and have geochemical affinities typical of adakites including high sio2 58 48 75 6 wt al2o3 15 78 18 28 wt na2o 3 94 5 08 wt sr 506 1413 ppm and la 12 6 52 9 ppm moderate k2o 1 77 2 76 wt and low y 4 7 14 2 ppm and yb 0 28 1 29 ppm the early eocene intrusions in the seme area have compositional similarities with high slica adakites and their geochemical features suggest the involvement of slab derived melts the zircons separated from these rocks show euhedral crystal shapes with oscillatory cores typical of crystallization from magmas as also confirmed by their high th u ratios 0 78 to 1 15 u pb analyses of zircons from the quartz diorite yielded a weighted mean 206pb 238u age of 53 16 0 45 ma zircon grains from the aslanca dacite porphyry occurring as a late phase within the seme body show u pb isotopic ages of 53 and 52 ma concordant with u pb ages of zircons from quartz diorite based on major trace and rare earth element data we present a model suggesting crystal fractionation and or differentation processes of subduction related adakitic magmas stored in the crust mantle transition zone and their transfer into shallow depths of the overriding continental lithosphere

detecting the near surface redox front in crystalline bedrock using fracture mineral distribution geochemistry and u series disequilibrium oxidizing conditions normally prevail in surface waters and near surface groundwaters but there is usually a change to reducing conditions in groundwater at greater depth dissolved o2 originally present is consumed through biogenic and inorganic reactions along the flow paths fracture minerals participate in these reactions and the fracture mineralogy and geochemistry can be used to trace the redox front an important task in the safety assessment of a potential repository for the disposal of nuclear waste in crystalline bedrock at an approximate depth of 500 m in sweden is to demonstrate that reducing conditions can be maintained for a long period of time oxygen may damage the cu canisters that host nuclear waste additionally in the event of a canister failure oxidizing conditions may increase the mobility of some radionuclides the present study of the near surface redox front is based on mineralogical redox sensitive minerals geochemical redox sensitive elements and u series disequilibrium investigations of mineral coatings along open fractures the fractures have been sampled along drill cores from closely spaced 100 m deep boreholes which were drilled during the site investigation work in the laxemar area south eastern sweden carried out by the swedish nuclear fuel and waste management co skb the distribution of the redox sensitive minerals pyrite and goethite in open fractures shows that the redox front switch from mainly goethite to mainly pyrite in the fractures generally occurs at about 15 20 m depth calcite leaching by recharging water is indicated in the upper 20 30 m and positive ce anomalies suggest oxidation of ce down to 20 m depth the u series radionuclides show disequilibrium in most of the samples indicating mobility of u during the last 1 ma in the upper 20 m u is mainly removed due to oxidation or has experienced complex removal and or deposition at depths of 35 55 m both deposition and removal of u are indicated below 55 m recent deposition of u is generally indicated which suggests removal of u near surface oxidation and deposition of u below the redox front scattered goethite occurrences below the general redox front down to ca 80 m and signs of u removal at 35 55 m mostly correlate with sections of high transmissivity and or high fracture frequencies this shows that highly transmissive fractures are generally required to allow oxygenated groundwaters at depth greater than ca 30 m removal of u oxidation below 55 m within the last 300 ka is not observed although penetration of glacial waters to great depths has been confirmed in the study area their potential o2 load seems to have been reduced near the surface

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

generation of the early cenozoic adakitic volcanism by partial melting of mafic lower crust eastern turkey implications for crustal thickening to delamination abstract early cenozoic 48 50 ma adakitic volcanic rocks from the eastern pontides ne turkey consist of calc alkaline and high k calc alkaline andesite and dacite with sio2 contents ranging from 56 01 to 65 44 wt this is the first time that early eocene volcanism and adakites have been reported from the region the rocks are composed of plagioclase amphibole quartz and mg rich biotite they have high and low mg values ranging from 55 to 62 and 13 to 42 respectively high mg rocks have higher ni and co contents than low mg samples the rocks exhibit enrichments in large ion lithophile elements including the light rare earth elements depletions in nb ta and ti and have high la yb and sr y ratios their relative high isr 0 70474 0 70640 and low end 50 ma values 2 3 to 0 8 are inconsistent with an origin as partial melts of a subducted oceanic slab combined major and trace element and sr nd isotope data suggest that the adakitic magmas are related to the unique tectonic setting of this region where a transition from a collision to an extension stage has created thickening and delamination of the pontide mafic lower crust at 50 ma the high mg adakitic magmas resulted from partial melting of the delaminated eclogitic mafic lower crust that sank into the relatively hot subcrustal mantle and its subsequent interaction with the mantle peridotite during upward transport leaving garnet as the residual phase elevates the mgo content and mg of the magmas whereas low mg magmas formed by the melting of newly exposed lower crustal rocks caused by asthenospheric upwelling which supplies heat flux to the lower crust the data also suggest that the mafic lower continental crust beneath the region was thickened between the late cretaceous and the late paleocene and delaminated during late paleocene to early eocene time which coincides with the initial stage of crustal thinning caused by crustal extensional events in the eastern pontides and rules out the possibility of an extensional regime before 50 ma in the region during the late mesozoic to early cenozoic

a spheroidal weathering model coupling porewater chemistry to soil thicknesses during steady state denudation abstract spheroidal weathering a common mechanism that initiates the transformation of bedrock to saprolite creates concentric fractures demarcating relatively unaltered corestones and progressively more altered rindlets in the spheroidally weathering rio blanco quartz diorite puerto rico diffusion of oxygen into corestones initiates oxidation of ferrous minerals and precipitation of ferric oxides a positive v of reaction results in the build up of elastic strain energy in the rock formation of each fracture is postulated to occur when the strain energy in a layer equals the fracture surface energy the rate of spheroidal weathering is thus a function of the concentration of reactants the reaction rate the rate of transport and the mechanical properties of the rock substitution of reasonable values for the parameters involved in the model produces results consistent with the observed thickness of rindlets in the rio icacos bedrock 2 3 cm and a time interval between fractures 200 300 a based on an assumption of steady state denudation at the measured rate of 0 01 cm a averaged over times longer than this interval the rate of advance of the bedrock saprolite interface during spheroidal weathering the weathering advance rate is constant with time assuming that the oxygen concentration at the bedrock saprolite interface varies with the thickness of soil saprolite yields predictive equations for how weathering advance rate and steady state saprolite soil thickness depend upon atmospheric oxygen levels and upon denudation rate the denudation and weathering advance rates at steady state are therefore related through a condition on the concentration of porewater oxygen at the base of the saprolite in our model for spheroidal weathering of the rio blanco quartz diorite fractures occur every 250 yr ferric oxide is fully depleted over a four rindlet set in 1000 yr and saprolitization is completed in 5000 yr in the zone containing 20 rindlets spheroidal weathering thus allows weathering to keep up with the high rate of denudation by enhancing access of bedrock to reactants by fracturing coupling of denudation and weathering advance rates can also occur for the case that weathering occurs without spheroidal fractures but for the same kinetics and transport parameters the maximum rate of saprolitization achieved would be far smaller than the rate of denudation for the rio blanco system the spheroidal weathering model provides a quantitative picture of how physical and chemical processes can be coupled explicitly during bedrock alteration to soil to explain weathering advance rates that are constant in time

the anarak jandaq and posht e badam metamorphic complexes in central iran new geological data relationships and tectonic implications abstract the anarak jandaq and posht e badam metamorphic complexes occupy the nw part of the central east iranian microcontinent and are juxtaposed with the great kavir block and sanandaj sirjan zone our recent findings redefine the origin of these complexes so far attributed to the precambrian early paleozoic orogenic episodes and now directly related to the tectonic evolution of the paleo tethys ocean this tectonic evolution was initiated by late ordovician early devonian rifting events and terminated in the triassic by the eocimmerian collision event due to the docking of the cimmerian blocks with the asiatic turan block the variscan accretionary complex is a new name we proposed for the most widely distributed metamorphic rocks connected to the anarak and jandaq complexes this accretionary complex exposed from sw of jandaq to the anarak and kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal sea ophiolitic remnants including gabbro basalts with a supra subduction geochemical signature new 40ar 39ar ages are obtained as 333 320 ma for the metamorphism of this sequence under greenschist to amphibolite facies moreover the limy intercalations in the volcano sedimentary part of this complex in godar e siah yielded upper devonian tournaisian conodonts the northeastern part of this complex in the jandaq area was intruded by 215 15 ma arc to collisional granite and pegmatites dated by id tims and its metamorphic rocks are characterized by some 40ar 39ar radiometric ages of 163 156 ma the variscan accretionary complex was northwardly accreted to the airekan granitic terrane dated at 549 15 ma later from the late carboniferous to triassic huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the anarak and kabudan this new period of accretion is supported by the 280 230 ma 40ar 39ar ages for the anarak mild high pressure metamorphic rocks and a 262 ma u pb age for the trondhjemite rhyolite association of that area the triassic bayazeh flysch filled the foreland basin during the final closure of the paleo tethys ocean and was partly deposited and or thrusted onto the cimmerian yazd block the paleo tethys magmatic arc products have been well preserved in the late devonian carboniferous godar e siah intra arc deposits and the triassic nakhlak fore arc succession on the passive margin of the cimmerian block in the yazd region the nearly continuous upper paleozoic platform type deposition was totally interrupted during the middle to late triassic local erosion down to lower paleozoic levels may be related to flexural bulge erosion the platform was finally unconformably covered by liassic continental molassic deposits of the shemshak one of the extensional periods related to neo tethyan back arc rifting in late cretaceous time finally separated parts of the eocimmerian collisional domain from the eurasian turan domain the opening and closing of this new ocean characterized by the nain and sabzevar ophiolitic melanges finally transported the anarak jandaq composite terrane to central iran accompanied by large scale rotation of the central east iranian microcontinent ceim due to many similarities between the posht e badam metamorphic complex and the anarak jandaq composite terrane the former could be part of the latter if it was transported further south during tertiary time

the arkot dag melange in arac area central turkey evidence of its origin within the geodynamic evolution of the intra pontide suture zone abstract in northern turkey the intra pontide suture zone is represented by an east west trending belt of deformed and or metamorphic units located at the boundary between the istanbul zonguldak terrane to the north and the sakarya terrane to the south these units can be regarded as issued from the intra pontide domain whose geodynamic history is still a matter of debate along the akpinar arac bayramoren geotraverse located in central turkey an ophiolite bearing melange known as the arkot dag melange is well exposed along the intra pontide suture zone the arkot dag melange plays a key role in the interpretation of the geodynamic history of the intra pontide domain and can be described as a late santonian chaotic sedimentary deposit consisting of an up to 1000 m thick succession of slide blocks of different sizes and lithologies enclosed in a sedimentary matrix consisting of shales coarse grained arenites pebbly mudstones and pebbly sandstones the slide blocks from a few meters to hectometers in size are represented by metamorphic rocks mainly micaschists and gneisses by ophiolites peridotites gabbros iat and babb basalts and cherts and by sedimentary rocks cherts neritic and pelagic limestone marly limestone and ophiolite bearing turbidites the youngest age among the slide blocks has been provided by the ophiolite bearing turbidites where a late coniacian nannofossil assemblage has been found the cherts have provided a wide range of ages from the middle triassic to late cretaceous whereas the fossils found in the limestone indicate late jurassic to early cretaceous ages the matrix of the arkot dag melange even if unaffected by metamorphism shows deformations represented by multiple meters thick cataclastic shear zones at the boundaries of the melange slices or inside of them according to its features the source area of the arkot dag melange was most likely a continental and oceanic thrust sheet emplaced in the late cretaceous onto a continental margin the data collected from the different slide blocks suggest that the intra pontide domain was characterised by an oceanic basin opened at the latest in the early jurassic the opening of the intra pontide oceanic basin was followed by the development of a subduction zone with a subsequent opening of suprasubduction oceanic basin in the middle jurassic early cretaceous the convergence in this suprasubduction oceanic basin started at the early late cretaceous boundary by an obduction process whereas its final closure can be regarded as late paleocene in age

investigating the complex interface where bedrock transforms to regolith abstract the interface where bedrock transforms to regolith is not planar but rather has a roughness that varies with the scale of observation the complexity of this surface is manifested in both element depth and fragment size depth distributions and may sometimes be related to the longitudinal profiles of watershed streams the fractal nature of the bedrock regolith interface means that the interface has a thickness which is 20 m in two ridgetop examples from pennsylvania and puerto rico such weathering thicknesses modeled as a function of one dimensional fluid flow are affected by the balance between rates of weathering and erosion one dimensional models are consistent with weathering advance rates that vary with equilibrium solubility and porefluid velocities and not reaction kinetics however fluid flow is not strictly downward and one dimensional permeability of regolith changes as particle size and bulk density changes with depth thus both downward and lateral flow occurs especially at reaction fronts where reactions change permeability the rate of weathering advance is therefore affected by the 3 dimensional distribution of reaction zones that affect permeability across the watershed quantitative models of such phenomena over a range of spatial and temporal scales are needed

rapid regolith formation over volcanic bedrock and implications for landscape evolution abstract the ability to quantify how fast weathering profiles develop is crucial to assessing soil resource depletion and quantifying how landscapes evolve over millennia uranium series isotopes can be used to determine the age of the weathering front throughout a profile and to infer estimates of regolith production rates because the abundance of u series isotopes in a weathering profile is a function of chemical weathering and time this technique is applied to a weathering profile in puerto rico developed over a volcaniclastic bedrock u series isotope compositions are modelled revealing that it takes 40 60 kyr to develop an 18 m thick profile this is used to estimate an average regolith production rate of 334 46 mm kyr this value is higher by a factor of up to 30 when compared to production rates estimated for weathering profiles developed over granitic or shale lithologies this quantitatively underpins the lithological control on rates of regolith production in a neighbouring watershed but over a granitic bedrock production rates are only 30 40 mm kyr moreover by comparing these results to a compilation of soil erosion rates it is clear that landscapes are controlled by the balance or imbalance between regolith production and erosion soil mantled landscapes are the result of a relative balance between production and erosion whereas in cratonic areas thicker weathering profiles are generated because erosion fails to match regolith production rates

shallow seismic reflection mapping of the overburden bedrock interface with the engineering seismograph some simple techniques where unconsolidated overburden exceeds 20 m in thickness the reflection method may be efficiently used with a 12 channel engineering seismograph to map topography on the overburden bedrock interface as well as possible structure within the overburden the two techniques we suggest are the simplest forms of reflection profiling which can be applied with a minimum amount of equipment which we suggest is a 12 channel enhancement seismograph a 12 geophone array and a hammer source these techniques require good transmission characteristics of the overburden as well as a sharp velocity discontinuity at the overburden bedrock interface for data processing and display a microcomputer is essential

overview of tectonic settings related to the rifting and opening of mesozoic ocean basins in the eastern tethys oman himalayas and eastern mediterranean regions

late palaeozoic marginal basin and subduction accretion the palaeotethyan kure complex central pontides northern turkey the kure complex located in the central pontides of northern turkey is a c 20 km thick pile of thrust imbricated deep sea sediments intercalated with a dismembered ophiolite the ophiolitic rocks include serpentinized harzburgite massive gabbro cumulate and isotropic sheeted dykes and basic volcanic rocks the extrusive rocks are mainly pillow lavas sheet flows and lava breccias geochemical evidence of immobile major and trace elements and pyroxene chemistry indicate mid ocean ridge mor and volcanic arc basalt vab compositions and suggest that the kure ophiolite was generated above a subduction zone chrome spine1 analysis also supports this interpretation in some thrust sheets the extrusives are depositionally overlain by hemi pelagic shales passing up into terrigenous turbidites and shales which are up to several hundred metres thick in intact successions cyprus type massive sulphides interpreted as precipitates from black smokers are located along the lava sediment contact individual intact sediment units up to several kilometres thick within the kure complex are separated by narrow up to 10 m wide zones of intense shearing layer parallel extension and melange formation asymmetrical folds reverse faults thrusts and duplex structures throughout the kure complex indicate mainly northwards emplacement the kure complex is thought to have opened in the late palaeozoic as a marginal basin above a northward dipping palaeotethyan subduction zone located along the southern margin of eurasia the kure marginal basin later closed in response to inferred southward subduction leading to development of an accretionary prism prior to late jurassic time the kure complex is unlikely to represent the main palaeotethyan suture as has been suggested in some earlier tectonic reconstructions regional comparisons with dobrogea crimea and caucasus suggest the kure basin opened then closed along a south eurasia active margin

probing deep weathering in the shale hills critical zone observatory pennsylvania usa the hypothesis of nested chemical reaction fronts in the subsurface weathering is both an acid base and a redox reaction in which rocks are titrated by meteoric carbon dioxide co2 and oxygen o2 in general the depths of these weathering reactions are unknown to determine such depths cuttings of rose hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the susquehanna shale hills observatory ssho pyrite concentrations are insignificant to depths of 23 m under the ridge and 8 9 m under the valley likewise carbonate concentrations are insignificant to 22 and 2 m respectively in addition a 5 6 m thick fractured layer directly beneath the land surface shows evidence for loss of illite chlorite and feldspar under the valley secondary carbonates may have precipited the limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale however carbonate depletion coincides with the winter water table observed at 20 m ridge and 2 m depth valley it would be fortuitous if carbonate containing strata are found under ridge and valley only beneath the water table furthermore pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature we propose that deep transport of o2 initiates weathering at ssho and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity according to this hypothesis the mineral distributions at ssho are nested reaction fronts that overprint protolith stratigraphy the fronts are hypothesized to lie subparallel to the land surface because o2 diffuses to the water table and causes oxidative dissolution of pyrite pyrite derived sulfuric acid h2so4 plus co2 also dissolve carbonates above the water table to understand how reaction fronts record long term coupling between erosion and weathering will require intensive mapping of the subsurface copyright 2013 john wiley sons ltd

geophysical and remote sensing based approach to model regolith thickness in a data sparse environment abstract mapping regolith thickness to bedrock is important for environmental modeling in general and for seismic hazard assessment in particular however regolith thickness is often ignored in such studies because of its presumed difficulty of mapping in many terrains to overcome this limitation we developed a generic remote sensing and geophysics based approach to model regolith thickness for areas with limited possibility of direct field observations the approach was tested in a seismically active and depositional landscape in northern pakistan regolith thickness was sampled at exposed bedrock outcrops along the river bed and scarps at unexposed sites the regolith bedrock interface was identified through electrical resistivity survey thus providing an indirect measurement of regolith thickness a geomorphic classification of landforms and topographic attributes were derived from a remote sensing based aster digital elevation model and spot 5 satellite imagery landform was the most important predictor adjusted r2 72 1 showing the importance of geomorphic interpretation a multivariate linear model based on landform elevation and distance to stream was able to predict the regolith thickness adjusted r2 91 7 including field observed abrupt changes at landform boundaries

investigation of in situ weathering of quartz diorite bedrock in the rio icacos basin luquillo experimental forest puerto rico abstract the rio icacos basin in puerto rico is the site of the highest measured chemical solute fluxes for a catchment on granodiorite this is partly attributable to high annual rainfall 4300 mm high average temperature 23 c and moderate relief the bulk of these fluxes is contributed by dissolution of plagioclase and amphiboles in zones of partially weathered rock 0 5 1 5 m thick underlying saprolite these zones are characterized by systems of onion skin rindlets each 3 10 cm thick in which porosity development is dominated by weathering of plagioclase to kaolinite fe bearing aluminosilicate minerals hornblende augite and biotite persist in the weathered rock after plagioclase has weathered to completion but hornblende and augite disappear between the porous rindlet systems and saprolite a new watershed scale solute mass balance corroborates earlier studies and yields an overall reaction stoichiometry that closely resembles complete weathering of the rock except quartz and biotite to kaolinite and fe3 oxides our findings indicate that steady state assumptions are reasonable and useful in studying weathering at this site estimated steady state sediment yields based on net solute fluxes and average bedrock composition of 3 24 10 9 to 3 60 10 9 kg m 2 s 1 are smaller than measured values indicating that sediment generation is currently accelerated with respect to steady state however sediment generation has recently been closer to steady state since weathering within the rindlet systems occurs on multiple fronts moving upward and downward two new steady state conceptual models are developed to account for 1 multiple parallel weathering fronts and 2 differential rates of advance of weathering fronts due to porosity development based on these models in situ weathering rates for plagioclase at two sample locations of 2 7 10 15 and 5 0 10 15 mol na g 1 s 1 are calculated values comparable to bet surface area normalized rates of 2 7 10 16 to 5 0 10 15 mol na m 2 s 1

palaeozoic early tertiary tethyan evolution of melanges rift and passive margin units in the karaburun peninsula western turkey and chios island greece

adakite like granitoid porphyries in the eastern pontides ne turkey potential parental melts and geodynamic implications abstract the tectonic setting of the eastern pontides during the late mesozoic to early cenozoic remains a subject of debate petrogenesis of adakite like granitoid porphyries plays a critical role in determining the nature of the lower continental crust and mantle dynamics during orogenic processes in the region here we describe for the first time the late paleocene to early eocene adakite like granitoid porphyries from the northern part of the eastern pontides although their counterparts in the southern part have recently been found the adakitic porphyries which emplaced into the subduction related turonian santonian volcanics from northern part of the region consist of i type calc alkaline quartz monzonite tonalite sio2 62 89 65 07 wt and high k calc alkaline granodiorite granite associations sio2 69 06 70 43 wt the former displays peraluminous to metaluminous signatures whereas the latter shows peraluminous geochemical character the granite granodiorite porphyries have high k2o 3 32 3 84 wt and low na2o 3 48 4 61 wt and mgo 0 91 1 04 wt relative to the quartz monzonite tonalite association k2o 1 50 1 92 wt na2o 4 08 6 45 wt mgo 1 44 2 07 wt ar ar geochronology studies on the amphibole separates reveal that the adakite like porphyries have a crystallization ages of 51 34 0 27 to 53 55 0 34 ma here we contend that these rocks were formed by partial fusion of a mafic lower continental crust in a collisional phase but not in a subduction setting all the samples exhibit the typical geochemical characteristics of adakite that is high sr 250 1141 ppm high sr y ratios 16 147 low y 6 8 14 8 ppm and low hree concentrations they are similar to adakites formed by slab melting associated with the subduction zone however the rocks exhibit heterogeneity in isotopic composition with isr ranging from 0 70554 to 0 70986 end 51 ma from 8 5 to 0 9 and nd model ages from 0 72 to 1 26 ga the samples are characterized by relatively high th th u and no significant eu anomalies implying that garnet was stable in their source during partial melting the compositional diversity between rock groups is probably related to partial melting of heterogeneous lower crustal source all of the features are inconsistent with a slab melting origin and slab related petrogenetic model but instead they favor an origin by melting of heterogeneous lower continental crust due to a thermal anomaly that was induced by the upwelling of the asthenosphere through a slab break off in a collisional setting these interpretations argue against the evidence for the presence of an early cenozoic arc setting in the eastern pontides instead the early cenozoic time in the region may be attributed to a geodynamic response to a post collisional uplift phase that occurred along the continent continent collision between the pontide and the anatolide tauride blocks

post collisional adakite like magmatism in the agvanis massif and implications for the evolution of the eocene magmatism in the eastern pontides ne turkey abstract in the anatolia the caucasus and northwest iran the eocene epoch is characterized by widespread basic to acidic magmatism whose temporal and spatial evolutions and origin are poorly understood in this paper we provide geochronological and geochemical data on a suite of early eocene intrusions from northeast turkey and discuss their origin within a regional tectonic framework post to late collisional moderate to small bodies of quartz diorite and leucogranodiorite as well as later dacite porphyries intrude permo triassic low grade metamorphic rocks in the southern part of the eastern pontides very close to the neo tethyan izmir ankara erzincan suture in places the intrusives display well developed subsolidus foliations indicating on going penetrative deformation during and shortly after emplacement different emplacement depths were inferred based on the contact metamorphic mineral assemblages al in hornblende barometry and igneous textures quartz diorite 14 16 km vs dacitic porphyries 7 km biotite and hornblende ar ar and zircon u pb data indicate that the compositionally and texturally different intrusives were emplaced at 51 ma ypresian three lines of evidence indicate that the early eocene represents a tectonically active time with high exhumation rates 0 6 cm a 1 i the quartz diorite and dacitic porphyries were emplaced at different crustal depths ii the emplacement ages of these texturally distinct intrusive rocks are geochronologically undistinguishable and iii intrusive rocks locally show a well developed foliation the intrusive rocks display high abundances of al 2 o 3 sr ba lrees and low abundances of y sc and hrees and are similar to high silica adakites from supra subduction zone settings the geochemical features imply a residual and or fractionating assemblage rich in hornblende garnet pyroxene and poor in plagioclase all rock types display similar sr nd isotopic characteristics with initial e nd and 87 sr 86 sr values ranging from 1 0 to 1 1 and from 0 70421 to 0 70494 respectively these three coeval rock groups quartz diorite leucogranodiorite and dacite porphyries were generated from a similar source by variable degrees of partial melting and fractionation these data together with those from the literature clearly reveal that the adakitic signature is common in paleocene to early eocene igneous rocks in northern turkey on both sides of the izmir ankara erzincan suture but disappears towards the middle eocene regional geological constraints indicate that the continental collision between the pontides and the anatolide tauride block occurred in the paleocene and that the middle eocene represents a period of major extension characterized by a marine transgression we therefore suggest that the early eocene adakitic magmatism in northern turkey resulted from the presence of a thickened continental crust following the continental collision along the neo tethyan izmir ankara erzincan suture whereas the voluminous middle eocene magmatism was related to extensional collapse of a thickened orogen

regolith mass balance inferred from combined mineralogical geochemical and geophysical studies mule hole gneissic watershed south india the aim of this study is to propose a method to assess the long term chemical weathering mass balance for a regolith developed on a heterogeneous silicate substratum at the small experimental watershed scale by adopting a combined approach of geophysics geochemistry and mineralogy we initiated in 2003 a study of the steep climatic gradient and associated geomorphologic features of the edge of the rifted continental passive margin of the karnataka plateau peninsular india in the transition sub humid zone of this climatic gradient we have studied the pristine forested small watershed of mule hole 4 3 km2 mainly developed on gneissic substratum mineralogical geochemical and geophysical investigations were carried out i in characteristic red soil profiles and ii in boreholes up to 60 m deep in order to take into account the effect of the weathering mantle roots in addition 12 electrical resistivity tomography profiles ert with an investigation depth of 30 m were generated at the watershed scale to spatially characterize the information gathered in boreholes and soil profiles the location of the ert profiles is based on a previous electromagnetic survey with an investigation depth of about 6 m the soil cover thickness was inferred from the electromagnetic survey combined with a geological pedological survey taking into account the parent rock heterogeneity the degree of weathering of each of the regolith samples has been defined using both the mineralogical composition and the geochemical indices loss on ignition weathering index of parker chemical index of alteration comparing these indices with electrical resistivity logs it has been found that a value of 400 ohm m delineates clearly the parent rocks and the weathered materials then the 12 inverted ert profiles were constrained with this value after verifying the uncertainty due to the inversion procedure synthetic models based on the field data were used for this purpose the estimated average regolith thickness at the watershed scale is 17 2 m including 15 2 m of saprolite and 2 m of soil cover finally using these estimations of the thicknesses the long term mass balance is calculated for the average gneiss derived saprolite and red soil in the saprolite the open system mass transport function indicates that all the major elements except ca are depleted the chlorite and biotite crystals the chief sources for mg 95 fe 84 mn 86 and k 57 biotite only are the first to undergo weathering and the oligoclase crystals are relatively intact within the saprolite with a loss of only 18 the ca accumulation can be attributed to the precipitation of caco3 from the percolating solution due to the current and or the paleoclimatic conditions overall the most important losses occur for si mg and na with 286 106 mol ha 62 of the total mass loss 67 106 mol ha 15 of the total mass loss and 39 106 mol ha 9 of the total mass loss respectively al fe and k account for 7 4 and 3 of the total mass loss respectively in the red soil profiles the open system mass transport functions point out that all major elements except mn are depleted most of the oligoclase crystals have broken down with a loss of 90 the most important losses occur for si na and mg with 55 106 mol ha 47 of the total mass loss 22 106 mol ha 19 of the total mass loss and 16 106 mol ha 14 of the total mass loss respectively ca al k and fe account for 8 6 4 and 2 of the total mass loss respectively overall these findings confirm the immaturity of the saprolite at the watershed scale the soil profiles are more evolved than saprolite but still contain primary minerals that can further undergo weathering and hence consume atmospheric co2

tectonic significance of the geochemistry and petrology of ophiolites in southeast anatolia turkey abstract the southeast anatolian ophiolites form discontinuous linear belts of oceanic fragments immediately north of the bitlis zagros suture which marks a continental collision zone between the arabian platform to the south and the taurides to the north the late cretaceous ophiolites in the southeast anatolia are represented by the kizildag in the hatay area the goksun and the berit to the north of kahramanmaras ispendere in the malatya area and komurhan guleman in the elazig area the goksun berit ispendere komurhan and guleman ophiolites were attached to the base of the tauride platform i e the malatya keban along its northern active margin and intruded by the i type calc alkaline granitoids of late cretaceous age in contrast the kizildag hatay ophiolite was thrust over the arabian passive margin in the south the cumulate rocks in the ophiolites are represented by dunite wehrlite lherzolite olivine clinopyroxenite olivine gabbronorite olivine gabbro gabbronorite and gabbro highly magnesian olivines fo88 to 74 and pyroxenes mg 95 to 60 as well as highly calcic plagioclases an95 to 68 from the cumulate rocks differ from oceanic equivalents which mainly formed from a mor basaltic melt the order of crystallization in mineral phases whole rock and mineral chemistry data from the cumulates suggest that the primary magma is compositionaly similar to that observed in modern island arc tholeiitic sequences the volcanic and subvolcanic rocks exhibit tholeiitic compositions chondrite normalized ree n morb normalized multi element patterns and tectonic discrimination diagrams suggest the existence of two main types of parental basic magmas in the crustal rocks of the se anatolian ophiolites these are i iat series that characterize the kizildag goksun ispendere komurhan and guleman ophiolites and ii low ti boninitic series known only in the kizildag ophiolite the geochemistry of the crustal rocks suggests that they formed in a suprasubduction zone tectonic setting including arc forearc environments in the southern neotethys these well preserved plutonic oceanic crustal remnants mainly exhibit an intact ophiolite pseudostratigraphy and are overlain by a volcanic sedimentary unit made up of alternations of basic to acidic extrusive rocks debris flows volcaniclastic sandstones and pelagic limestones interpreted as a tholeiitic ensimatic island arc assemblage built on the suprasubduction zone type crust the metamorphism of some of the ophiolites i e berit in the se anatolia might be related to later stages of intraoceanic subduction during the evolution of the southern neotethys

mesozoic adakitic rocks from the xuzhou suzhou area eastern china evidence for partial melting of delaminated lower continental crust abstract adakitic rocks in the xuzhou suzhou area eastern china consist of dioritic and monzodioritic porphyries and were dated at 131 132 ma by the shrimp u pb zircon method these rocks have high mgo content 1 47 5 73 high mg values 0 49 0 61 and high la yb and sr y ratios these features are similar to rocks derived from partial melting of a subducted oceanic slab however their high initial 87sr 86sr 0 7053 0 7075 and low end t values 4 43 to 13 14 are inconsistent with the origin from slab melting these rocks often contain garnet residual crystals and eclogite garnet clinopyroxenite and garnet amphibolite xenoliths petrographical characteristics and estimated p t conditions of these xenoliths indicate that they were once deeply subducted and subsequently underwent rapid exhumation in the early mesozoic garnet residual crystals from the porphyries show similar chemical compositions to garnets from garnet clinopyroxenite and garnet amphibolite xenoliths ages of the inherited zircons of the xenoliths and their host rocks likely indicate that sources for the adakitic magma and protoliths of the eclogite and garnet clinopyroxenite xenoliths in the study area were from precambrian basement of the north china craton the data also suggest that the lower continental crust in the eastern north china craton was thickened during the early mesozoic and delaminated in the early cretaceous the high mg adakitic magma resulted from partial melting of this delaminated lower continental crust and its subsequent interaction with the mantle during upward transport leaving garnet as the residual phase

vertical motions of the puerto rico trench and puerto rico and their cause 1 the puerto rico trench exhibits great water depth an extremely low gravity anomaly and a tilted carbonate platform between reconstructed elevations of 1300 m and 4000 m i argue that these features are manifestations of large vertical movements of a segment of the puerto rico trench its forearc and the island of puerto rico that took place 3 3 m y ago over a time period as short as 14 40 kyr i explain these vertical movements by a sudden increase in the slab s descent angle that caused the trench to subside and the island to rise the increased dip could have been caused by shearing or even by a complete tear of the descending north american slab although the exact nature of this deformation is unknown the rapid 14 40 kyr and uniform tilt along a 250 km long section of the trench is compatible with scales of mantle flow and plate bending the proposed shear zone or tear is inferred from seismic morphological and gravity observations to start at the trench at 64 5 w and trend southwestwardly toward eastern puerto rico the tensile stresses necessary to deform or tear the slab could have been generated by increased curvature of the trench following a counterclockwise rotation of the upper plate and by the subduction of a large seamount

seismic imaging of the shallow subsurface shear wave case histories obtaining high resolution images of the geology and hydrogeology of the subsurface in the depth range from ground level to 50 m is one of the major challenges of modern geophysics the methods which are commonly used such as compressional wave surveys and ground penetrating radar often suffer from adverse effects caused by the near surface conditions changes in water saturation and various sources of noise this paper demonstrates some of the advantages offered by the use of shear wave seismology and by the combination of shear and compressional wave seismic methods in shallow subsurface investigations multicomponent shallow seismic tests were carried out at four different sites to examine the effectiveness of different acquisition geometries under a variety of near surface geological conditions near surface conditions encountered at the sites included thick clays clay sand sequences overlying chalk mudstone overlying granodiorite bedrock and landfill material under all conditions shear wave data acquisition was found to have advantages over compressional wave acquisition for the investigation of the shallow subsurface shear head waves being unaffected by water saturation achieved penetration to greater depths at a site in crewkerne dorset where compressional head wave penetration was limited to the near surface layers better vertical resolution was achieved at shallow depths using shear wave reflection energy at a landfill site shear wave reflections from shallow interfaces were in some cases less affected by noise compared with the equivalent compressional wave reflections combinations of shear and compressional wave data recording allowed the measurement of a poisson s ratio log and gave indications of seismic anisotropy at two sites where dipping clay layers were present

geochemical characteristics of the adakite like dodurga pluton central pontides n turkey implications for middle triassic continental arc magmatism in southern black sea region the tracing of triassic arc magmatism is much debated for a long time along the sakarya composite terrane in turkey and the southern black sea region the dodurga pluton is located in the central pontides n turkey one of the most complicated regions around the black sea region and represents the first documented middle triassic continental arc in the region this pluton comprises of dacite porphyry and granodiorite and displays calc alkaline signatures which is in agreement with arc related and i type magmas the pm normalized multi element and cn normalized ree patterns are akin to volcanic arc granites and characterized by liles and lrees enrichments relative to hfses and hrees coupled with negative nb anomalies which confirm derivation in a subduction related tectonic setting moreover the major and trace element systematics of the samples including higher sr y ratios 22 93 101 36 and lower yb contents 0 31 1 30 ppm are consistent with those from adakitic melts compared to classical arc magmas therefore this pluton also represents the first middle triassic adakite like magmatic occurrence in turkey overall petrographic and geochemical signatures reported here indicate that the dodurga pluton might have been derived from a heterogeneous source mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin based on the tethyan evolution in the anatolian realm three geodynamic scenarios are possible for its formation and it could have been formed as a result of northward or southward subduction of the paleotethys ocean or northward subduction of the northern branch of neotethys ocean during the middle triassic

the tectonics of the strandja massif late variscan and mid mesozoic deformation and metamorphism in the northern aegean the strandja massif is a mid mesozoic orogenic belt in the balkans build on a late variscan basement of gneisses migmatites and granites new single zircon evaporation ages from the gneisses and granites indicate that the high grade metamorphism and plutonism is early permian in age 271 ma the late variscan basement was unconformably overlain by a continental to shallow marine sequence of early triassic mid jurassic age during the late jurassic early cretaceous oxfordian barremian the lower mesozoic cover and the basement were penetratively deformed and regionally metamorphosed in greenschist facies possibly due to a continental collision an rb sr biotite whole rock age from a metagranite dates the regional metamorphism as late jurassic 155 ma deformation involved north vergent thrust imbrication of the basement and the emplacement of allochthonous deep marine triassic series over the jurassic metasediments the metamorphic rocks of the strandja massif are unconformably overlain by the cenomanian shallow marine sandstones during the senonian the northern half of the strandja massif formed a basement to an intra arc basin and to a magmatic arc generated above the northward subducting tethyan oceanic lithosphere the srednogorie arc closed during the early tertiary through renewed northward thrusting of the strandja massif

soil layering and preferential flow impacts on seasonal changes of gpr signals in two contrasting soils abstract experimental evidence has shown that soil layering can significantly alter water movement through soil profiles especially in sloping landscapes detailed knowledge of soil layering and its position in the landscape is therefore necessary for determining dynamic subsurface flow in this study we used ground penetrating radar gpr in combination with high resolution real time soil water monitoring to investigate seasonal changes in gpr signals to identify soil horizon interfaces and their impacts on water flow in two contrasting soils the results showed that 1 in the deep rushtown soil located in a concave hillslope gpr reflections in the bw bc and bc c horizon interfaces became clearer as soil became wetter such increased contrast along interfaces was due to the presence of water associated with water restricting bc horizon and lateral flow from upslope area and 2 in the shallow weikert soil located in a planar hillslope gpr reflections in the soil bedrock interface and the weathered unweathered rock interface become intermittent as soil became wetter this scattering of gpr reflection was due to the non uniform distribution of water in fractured shale bedrock and possible tree root effects while wet condition permitted the enhanced detection of water distribution in both soil profiles optimal time for detecting soil layering was different for these two soils wet condition was more suited for detecting water restricting dense layer in the deep rushtown soil while dry season was optimal for identifying the soil bedrock interface in the shallow weikert soil overall this study demonstrates the value of repeated gpr surveys in different seasons to capture subsurface hydrologic processes and the impacts of soil layering and preferential water distribution on seasonal changes of gpr signals it also provides a useful reference for selecting optimal time for gpr survey in the field

germanium silicon as a flow path tracer application to the rio icacos watershed 1 we use dissolved silicon together with its geochemical twin germanium for the first time as a hydrologic tracer to study water delivery to the stream during storm events in the rio icacos watershed puerto rico ge and si were measured on base flow stormflow springwater and soil water samples compositions of all of these waters appear to reflect varying contributions from three components which we attribute to solutes released from bedrock weathering groundwater from short term soil water interaction quick soil water and longer term soil water interaction matrix soil water base flow stream waters have high si and moderate ge ge si ratio 0 29 mol mol consistent with a predominantly bedrock weathering source as indicated by their similarity with water sampled from springs emerging from the saprolite bedrock boundary on a hillslope landslide scar during storm events there is a shift toward more dilute compositions but higher ge si ratios similar to those measured on water samples from temporary depression storage and overland flow quick soil water geochemical mass balance shows that 80 90 of the stream chemistry can be explained by mixing groundwater with this quick soil water composition which we infer to reflect new water traveling as shallow throughflow stream water 18o values decrease to more negative values typical of precipitation supporting rapid delivery of rainwater to the stream channel during stormflow the third component with a ge rich composition characteristic of soil matrix water sampled by tension lysimeters is required to explain higher stream water ge si ratios measured during hydrograph recession we infer from this an additional slower and less dominant pathway for delivery of soil water to the stream channel

bivergent thrust wedges surrounding oceanic island arcs insight from observations and sandbox models of the northeastern caribbean plate at several localities around the world thrust belts have developed on both sides of oceanic island arcs e g java timor panama vanuatu and the northeastern caribbean in these localities the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt for example in the northeastern caribbean a north verging accretionary prism lies to the north of the eastern greater antilles arc hispaniola and puerto rico whereas a south verging thrust belt called the muertos thrust belt lies to the south researchers have attributed such bivergent geometry to several processes including reversal of subduction polarity subduction driven mantle fl ow stress transmission across the arc gravitational spreading of the arc and magmatic infl ation within the arc new observations of deformational features in the muertos thrust belt and of fault geometries produced in sandbox kinematic models along with examination of published studies of island arcs lead to the conclusion that the bivergence of thrusting in island arcs can develop without reversal of subduction polarity without subarc mantle fl ow and without magmatic infl ation we suggest that the eastern greater antilles arc and comparable arcs are simply crustalscale bivergent or doubly vergent thrust wedges formed during unidirectional subduction sandbox kinematic modeling suggests in addition that a broad retrowedge containing an imbricate fan of thrusts develops only where the arc behaves relatively rigidly in such cases the arc acts as a backstop that transmits compressive stress into the backarc region further modeling shows that when arcs behave as rigid blocks the strike slip component of oblique convergence is accommodated entirely within the prowedge and the arc the retrowedge hosts only dip slip faulting frontal thrusting the existence of large retrowedges and the distribution of faulting in an island arc may therefore be evidence that the arc is relatively rigid the rigidity of an island arc may arise from its mafi c composition and has implications for seismic hazard analysis

formation of the late palaeozoic early mesozoic karakaya complex and related ophiolites in nw turkey by palaeotethyan subduction accretion several pre jurassic tectonic units in nw turkey are crucial to the current debate regarding the timing and direction of subduction of palaeotethys a major ocean that separated eurasia and gondwana in late palaeozoic early mesozoic times the most critical unit is the karakaya complex a deformed low grade assemblage of oceanic origin which comprises a nw verging se dipping stack of tectonostratigraphic units here interpreted as a palaeotethyan accretionary complex the units display lithologies consistent with origins in seamount trench abyssal and rifted carbonate platform settings clastic basin sequences developed on top of the complex other relevant tectonostratigraphic units in the area include ultrabasic rocks of supra subduction zone affinity which tectonically overlie permian carbonate platform units with intervening metamorphic soles and melanges restored structural trends suggest the presence of a southward dipping palaeotethyan subduction zone bordering gondwana related units during the late permian triassic this was probably additional to more important regional northward subduction along the southern margin of eurasia from the eastern mediterranean to the himalayas

jurassic accretionary complex and ophiolite from northeast turkey no evidence for the cimmerian continental ribbon permian triassic and late cretaceous accretionary complexes ascribed to the consumption of two distinct oceans the paleo and neo tethys are exposed over extensive areas in the eastern mediterranean region however a separating continental ribbon the so called cimmeride continent between the paleo and neo tethys during early mesozoic time cannot be defined here we report a previously unknown early jurassic metamorphic oceanic accretionary complex and ophiolite from northeast turkey bounded by oceanic accretionary complexes of permian triassic and late cretaceous age to the north and the south respectively without a continental domain in between this special tectonic position and widespread coexistence of permian triassic and late cretaceous accretionary complexes alongside the izmir ankara erzincan suture imply that 1 the southern margin of laurasia in the eastern mediterranean region grew by episodic accretionary processes from late paleozoic to end mesozoic time without involvement of a cimmerian continental ribbon and 2 the paleo tethys and northern branch of the neo tethys were not distinct oceans in the eastern mediterranean region

chromite and pge geochemistry of the elekdag ophiolite kastamonu northern turkey implications for deep magmatic processes in a supra subduction zone setting abstract the geochemistry of chromium spinel and platinum group elements pge provides significant information about conditions in the mantle during the emplacement and genesis of ophiolitic complexes the elekdag ophiolite is a greenschist to amphibolite facies ophiolite that was emplaced onto the sakarya zone in the central part of the pontides of northern turkey nw se trending elekdag ophiolite hosts small scale chromitite occurrences in serpentinized harzburgite and dunite and have maximum resource of several thousands t cr2o3 the chromitites the elekdag ophiolite can be divided in to high cr and high al types the calculated melt composition of the high cr chromitites is 9 4 13 2 wt al2o3 0 2 0 4 wt tio2 with feo mgo ratios of 0 4 1 9 which are indicative of boninitic compositions however the high al chromitites have 14 7 17 3 wt al2o3 and 0 3 0 8 wt tio2 with feo mgo ratios of between 0 3 and 0 8 which are consistent with morb like tholeiitic affinities the total pge content of the chromitites range between 82 and 1466 ppb and the average pge content of the high cr and high al chromitites are 267 ppb and 195 ppb respectively the chromitites are characterized by low pd ir ratios of 0 02 0 20 that is characteristic of non fractionated chromitites the chondrite normalized pge pattern of the chromitites resemble those of mantle derived cr rich chromitites in ophiolites of the supra subduction zone ssz elsewhere mineral and bulk rock pge data for the elekdag chromitites indicate that high cr chromitites formed from cr rich and al and ti poor boninitic melts most probably in the fore arc setting in the deeper part of the mantle this was succeeded by the mineralization of high al chromitites from a differentiated boninitic melt at shallow depths close to the moho discontinuity

effects of a tectonically triggered wave of incision on riverine exports and soil mineralogy in the luquillo mountains of puerto rico we document the long term response of a tropical mountain stream to tectonics and show how this response exerts a first order spatial control on the delivery of weatherable minerals to forest soils in its catchment these minerals in turn affect nutrient availability and biogeochemical cycles the luquillo mountains is a rainforest covered isolated massif on puerto rico island instead of displaying typical concave up long profiles of most mountain streams the rivers draining the southern flank of these mountains display a systematic downstream increase in gradient using concentrations of in situ produced cosmogenic 10be in quartz from river sediments we find that the downstream steepening is due to the propagation of an erosion wave along the rivers from the coastal plain upstream toward the headwaters decreased 10be concentration along the steepened reaches knickpoint faces or knickzones results from faster denudation of the valley sides around the steepened reaches the upper portions of the steepened reaches knickpoint lips cluster in elevation around the altitude of a flat lying dissected surface traceable around the luquillo mountains inspection of similar platforms over other parts of puerto rico and in the surrounding seas suggests that the dissected surface is an uplifted shore platform formed in the early pliocene 4 my ago upstream of the knickpoints rivers possess alluvial reaches still graded to this uplifted platform they represent relict profiles of the rivers that once drained an island that was surrounded by the now uplifted platform we conclude that the knickpoints initiated when the platform started to rise above the caribbean sea the knickpoints then started propagating upstream defining the front of a slow moving wave of erosion 10be derived catchment scale denudation rates measured above and below the knickpoints indicate a 30 210 increase in denudation associated to the passage of the knickpoints mineralogical analysis of the soils show that soils upstream of the knickpoints overlie deeply depleted saprolite and only contain recalcitrant minerals whereas soils downstream of the knickpoints experience an input of fresh weatherable minerals this influx considerably increases nutrient availability porder et al 2015 in a forest where atmospheric inputs are otherwise the main source of nutrients mcdowell et al 1990 zarin and johnson 1995 pett ridge 2009

self organization in chemical lateritic weathering abstract ferruginous laterites consist of different superposed horizons characterized by their mineralogical and structural composition climatic changes are foremost among the parameters used to explain variations of mineralogy and structures however several types of structures can be explained as the spontaneous and autonomous change of the geochemical soil system without the intervention of external factors such as climate or tectonics two examples illustrate this self organization of lateritic horizons formation of a ferruginous nodular horizon and formation of a conglomeratic iron crust self organization results from reaction transfer feedbacks between permanently precipitated and dissolved minerals and continuously percolating solutions allowing the geochemical soil system to be in constant search of equilibrium

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

dehydration melting of a basaltic composition amphibolite at 1 5 and 2 0 gpa implications for the origin of adakites this study presents the results of dehydration melting experiments on a basaltic composition amphibolite under conditions appropriate to a hot slab geotherm 1 5 and 2 0 gpa and temperatures of 850 to 1150 c dehydration melting produces an omphacitic augite and garnet bearing residue coexisting with rhyolitic to andesitic composition melts at 1 5 gpa the amphibolite melts in two stages between 800 and 1025 c the 2 0 gpa data also define two melting stages at 2 0 gpa the first stage involves nearly modal melting of the original amphibolite minerals qtz pl amp to produce melt cpx grt during the second stage the eclogite restite melts non modally 0 86 cpx 0 14 grt 1 melt the experimental results were combined with data from the literature to generate a composite p t phase diagram for basaltic composition amphibolites over the 800 to 1100 c temperature range for pressures up to 2 0 gpa comparison of the major element compositions of the experimentally produced melts with compositions of presumed slab melts adakites shows that partial melting of amphibolite at conditions appropriate to a hot slab geotherm produces melts similar to andesitic and dacitic adakites except for significant mgo and cao depletions trace element modelling of amphibolite dehydration melting using the 2 0 gpa melting reactions produces ree abundances similar to those of adakites at 10 15 wt batch melting but the models do not reproduce the high sr y ratios characteristic of adakites taken together the major and trace element results are not consistent with the derivation of adakites by dehydration melting of the subducted slab with little or no interaction with the mantle wedge or crust if adakites are partial melts of the subducted slab they must undergo significant interaction with the mantle and or crust during which they acquire a number of their distinctive characteristics

tectonic evolution of the intra pontide suture zone in the armutlu peninsula nw turkey abstract the armutlu peninsula and adjacent areas in nw turkey play a critical role in tectonic reconstructions of the southern margin of eurasia in nw turkey this region includes an inferred intra pontide oceanic basin that rifted from eurasia in early mesozoic time and closed by late cretaceous time the armutlu peninsula is divisible into two metamorphic units the first the armutlu metamorphics comprises a precambrian high grade metamorphic basement unconformably overlain by a palaeozoic low grade mixed siliciclastic carbonate volcanogenic succession including bimodal volcanics of inferred extensional origin with a possibly inherited subduction signature the second unit the low grade iznik metamorphics is interpreted as a triassic rift infilled with terrigenous calcareous and volcanogenic lithologies including basalts of within plate type the triassic rift was unconformably overlain by a subsiding jurassic late cretaceous cenomanian passive margin including siliciclastic carbonate turbidites radiolarian cherts and manganese deposits the margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in turonian time geochemical evidence from meta basalt blocks within ophiolite derived melange suggests a supra subduction zone origin for the ophiolite the above major tectonic units of the armutlu peninsula were sealed by a maastrichtian unconformity comparative evidence comes from the separate almacik flake further east considering alternatives it is concluded that a mesozoic intra pontide oceanic basin separated eurasia from a sakarya microcontinent with a wider northern neotethys to the south lateral displacement of exotic terranes along the south eurasian continental margin probably also played a role e g during late cretaceous suturing in addition to overthrusting

temporal changes in suspended sediment transport in an atlantic catchment nw spain catchment scale suspended sediment ss transport studies in northwest spain are of special interest as little research at this scale has been done in this region however the role of sediments in the transfer of nutrients and contaminants to coastal areas in this region has been highlighted data were collected from the corbeira catchment during a 3 year period and the variability in ss load at different temporal scales within events variability monthly seasonal and annual was analyzed the statistical relationship between discharge and suspended sediment concentration ssc from samples obtained every 15 days as well as during runoff events in october 2004 to september 2007 showed a marked scatter of points hence the rating curve method does not seem appropriate to estimate ssc in this catchment the results also demonstrated that at the within events scale most of the ss peaks preceded the discharge peaks 70 of runoff events implying that zones nearby or well connected to the stream are the dominant sediment source areas in some cases rills and ephemeral gullies developed in cropland were the main source of sediment delivered to the stream furthermore a reduction in ssc was observed in sequences of events which can be mainly linked to a phenomenon of sediment exhaustion at the seasonal scale most of the total annual ss load was transported during the autumn months the period in which generally the largest number of events occurred while in the summer total annual ss load was very low 1 at the annual scale specific ss yield ssy ranged from 5 4 to 11 2 mg km 2 y 1 the variability in ssy was correlated with the number and magnitude of runoff events recorded yearly since runoff events dominated ss transport and yield for instance in the last hydrological year 2006 07 more than 80 of the ss load was exported in runoff events involving 10 of the time

early triassic potassic volcanism in the afyon zone of the anatolides turkey implications for the rifting of the neo tethys afyon zone which was derived from the anatolide tauride platform during closure of the neo tethys is made up of pre mesozoic basement and unconformably overlying triassic early tertiary cover series the afyon zone contains widespread metavolcanic rocks which are dominated by rhyolite dacite and trachyandesite they form a distinct volcanic succession which is separated from the underlying silurian lower carboniferous metacarbonates and meta siliciclastics by a regional unconformity trachyandesitic metavolcanics are made up of massive lava flows pyroclastics and epiclastics less frequently domes and dikes which were developed on a deeply eroded subaerial landmass u pb and pb pb zircon geochronology yielded lower triassic 250 ma ages which are interpreted as extrusion age of trachyandesitic volcanics based on the stratigraphic geochronological and geochemical data we suggest that these lower triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the gondwana which led to the development of the northern branch of the neo tethys

triassic limestone turbidites and serpentinite the cimmeride orogeny in the central pontides the basement of the central pontides and by implication that of crimea consists of pre permian low grade metaclastic rocks intruded by latest permian early carboniferous 305 290 ma granitoids further up in the stratigraphic sequence are triassic limestones which are now preserved as olistoliths in the deformed upper triassic turbidites new conodont and foraminifera data indicate an anisian to carnian middle to late triassic age for these hemi pelagic hallstatt type limestones the siliciclastic turbidites surrounding the triassic limestone contain the norian late triassic bivalve monotis salinaria the same species is also found in the tauric series in crimea the upper triassic flysch in the central pontides is locally underlain by basaltic pillow lavas and includes kilometre size tectonic slices of serpentinite both the flysch and the serpentinite are cut by an undeformed acidic intrusion with an ar ar biotite age of 162 4 ma callovian oxfordian this indicates that the serpentinite was emplaced into the turbidites before middle jurassic time most probably during latest triassic or early jurassic time and that the deformation of the triassic sequence pre dates the middle jurassic regional geological data from the circum black sea region including widespread upper triassic flysch upper triassic eclogites and blueschists of oceanic crustal affinity and apparent absence of a cimmerian continent between the cretaceous and triassic accretionary complexes indicate that the latest triassic cimmeride orogeny was accretionary rather than collisional and is probably related to the collision and accretion of an oceanic plateau to the southern active margin of laurasia

water saturated magmas in the panama canal region a precursor to adakite like magma generation amphibole while uncommon as a phenocryst in arc lavas is increasingly recognized as a key constituent in the petrogenesis of arc magmas fractional crystallization of water saturated arc magmas in the lower crust can yield substantial volumes of amphibole cumulates that depending on the pressure of crystallization may also contain garnet fractionation of this higher pressure assemblage has been invoked as a possible mechanism in the production of magmas that contain an adakitic signature this study examines newly dated late oligocene 25 37 0 13 ma hypabyssal amphibole rich andesites from cerro patacon in the panama canal region these andesites contain nodules of amphibole cumulates that are 4 6 cm in diameter and are almost entirely composed of 5 10 mm amphibole crystals dominantly ferri tschermakite geochemical variations optical and chemical zoning of the cerro patacon amphiboles are consistent with their evolution in a crystal mush environment that had at least one recharge event prior to entrainment in the host andesite amphiboles hosted within the cumulate nodules differ from those hosted in the cerro patacon andesite and contain consistently higher values of ti we suggest these nodules represent the early stages of fractionation from a water saturated magma cerro patacon andesites have ree concentrations that plot at the most depleted end of central american arc magmas and exhibit a distinctive depletion in the middle ree these geochemical and petrographic observations strongly support significant amphibole fractionation during formation of the cerro patacon andesite consistent with the petrographic evidence fractionation of water saturated magmas is a mechanism by which adakitic compositions may be produced and the cerro patacon andesites do exhibit adakite like geochemical characteristics e g elevated sr y 28 34 however the relatively elevated concentrations of y and hree indicate garnet was not stable in the fractionating assemblage during this early stage of arc development

triassic volcanism in the eastern fore caucasus evolution and geodynamic interpretation abstract the aim of this paper is to describe the triassic regional geodynamic framework of the eastern fore caucasus area from data on volcanics and related sedimentary deposits these deposits only known by drilling represent the lowermost horizons of a slightly deformed mesozoic and cenozoic cover and rest unconformably on folded mainly devonian to carboniferous series they are thought to be for the most part postcollisional the sedimentary record of early to middle triassic evolution allows visualisation of uplift events associated with continental basin formation preceding and following the opening of a deep passively subsiding marine basin tectonic instability indicated by tilted strata prevailed throughout the whole period the subsidence maximum corresponding with a total immersion below sea level occurred during the olenekian early triassic during middle triassic times the area was continuously uplifted and progressively emerged to become strictly continental with a fluvio lacustrine sedimentation during the late triassic two periods of intense volcanic activity occurred during early middle and late triassic times the former comprises 1 subaerial explosive eruptions of rhyolitic magma the vents of which are presumably located about 50 100 km southwest of the study area and 2 submarine effusive eruptions of basalts and rhyolites within an actively subsiding trough the numerous unconformities within the volcano sedimentary sequence testify to a tectonically active setting during the late triassic eruptions were subaerial mainly explosive nuees ardentes and rhyo dacitic basaltic and andesitic lava flows and domes were minor in both eruptive periods mafic magmas had a calc alkaline affinity and their diversity would have been the result of partial melting of a heterogeneous metasomatized subcontinental mantle several compositional gaps within the acidic group reflect melting of distinct components of the continental crust fractional crystallisation or even partial melting trends can be deciphered within mafic and rhyolitic groups the geodynamic background of early middle triassic volcanism was one of extension the precise nature of the extension is unclear but could include active rifting back arc extension or even transtension in a strike slip fault zone with their great contribution of felsic rocks about 90 the late triassic subaerial volcanics can trace an important crustal partial melting event they could belong to an overheated zone of an andean type volcanic belt

architecture of the deep critical zone in the rio icacos watershed luquillo critical zone observatory puerto rico inferred from drilling and ground penetrating radar gpr