extrinsic controls on the evolution of hawaiian ocean island volcanoes 1 extrinsic parameters that affect the evolution of magmatic systems within and beneath ocean island volcanoes include physical variables such as confining pressure which controls magma degassing and temperature of the underlying lithosphere and crust which controls magma crystallization during ascent other extrinsic parameters are environmental variables coupled to the hydrosphere and atmosphere such as hydrothermal circulation systems and even rainfall all these extrinsic factors interact with intrinsic parameters such as magma supply rates or composition to modulate the evolution of magma chambers and the petrologic processes that take place within them

relicts of the early cretaceous seamounts in the central western yarlung zangbo suture zone southern tibet abstract despite more than 30 years studies in the yarlung zangbo suture zone yzsz southern tibet is still a region of discovery and the geological evolution of the neo tethys here remains controversial in this paper we present the new field observation petrography zircon u pb dating and geochemistry of the zhongba mafic rocks in the western segment of the yzsz zircon u pb analyses from a diabase using sims secondary ion mass spectrometry yielded a concordant age of 125 7 0 9 ma all the zhongba mafic rocks exhibit lree enrichment lan ybn 4 7 15 8 without eu anomalies eu 0 97 1 01 their primitive mantle normalized trace element patterns are similar to those of the average oib and hawaii alkaline basalts as well as other oib type rocks already reported in the central western yzsz these observations lead us to suggest the existence of a series of seamounts within the neo tethys during the early cretaceous these oib type rocks could be originated from 1 hotspot mantle 2 near ridge seamounts by melting induced mixing of two distinct mantle sources 3 late stage magmatism fed by melts that originated from an asthenospheric window due to slab delamination combining literature data from the entire yzsz which include studies of the morb and iab type rocks and mantle peridotites we prefer the third explanation that the oib type rocks represent a late stage magmatic activity above an intra oceanic supra subduction zone within the neo tethys

volcanic morphology of west mata volcano ne lau basin based on high resolution bathymetry and depth changes high resolution 1 5 m mapping from the autonomous underwater vehicle auv d allan b of west mata volcano in the northern lau basin is used to identify the processes that construct and modify the volcano the surface consists largely of volcaniclastic debris that forms smooth slopes to the nw and se with smaller lava flows forming gently sloping plateaus concentrated along the ene and wsw rift zones and more elongate flows radiating from the summit two active volcanic vents prometheus and hades are located 50 and 150 m wsw of the 1159 m summit respectively and are slightly nw of the ridgeline so the most abundant clastic deposits are emplaced on the nw flank this eruptive activity and the location of vents appears to have been persistent for more than a decade based on comparison of ship based bathymetric surveys in 1996 and 2008 2010 which show positive depth changes up to 96 m on the summit and north flank of the volcano the widespread distribution of clastic deposits downslope from the rift zones as well as from the current vents suggests that pyroclastic activity occurs at least as deep as 2200 m the similar morphology of additional nearby volcanoes suggests that they too have abundant pyroclastic deposits

single crystal 40ar 39ar dating of the olorgesailie formation southern kenya rift single crystal laser fusion sup 40 ar sup 39 ar analyses and several conventional bulk fusion sup 40 k sup 40 ar dates have been used to determine the age of volcaniclastic strata within the olorgesailie formation and of associated volcanic and sedimentary units of the southern kenya rift in the principal exposures along the southern edge of the legemunge plain the formation spans the interval from approximately 500 to 1 000 ka deposition continued to the east along the ol keju nyiro river where a tuff near the top of the formation has been dated at 215 ka in these exposures the formation is unconformably overlain by sediments dated at 49 ka a possible source for the olorgesailie tephra the ol doinyo nyokie volcanic complex contains as ash flow dated at approximately 1 ma extending the known age range of this complex to encompass that of virtually the entire olorgesailie formation in the legemunge plain these geologic examples illustrate the importance of the single crystal sup 40 ar sup 39 ar dating technique whereby contaminant altered or otherwise aberrant grains can be identified and eliminated from the determination of eruptive ages for reworked or altered pyroclastic deposits the authors have presented a computer modeling procedure based on an inverse isochron analysis thatmore promotes a more objective approach to trimming sup 40 ar sup 39 ar isotope data sets of this type less

age and petrology of alkalic postshield and rejuvenated stage lava from kauai hawaii at the top of the waimea canyon basalt on the island of kauai rare flows of alkalic postshield stage hawaiite and mugearite overlie tholeiitic flows of the shield stage these postshield stage flows are 3 92 ma and provide a younger limit for the age of the tholeiitic shield stage the younger koloa volcanics consist of widespread alkalic rejuvenated stage flows and vents of alkalic basalt basanite nephelinite and nepheline melilitite that erupted between 3 65 and 0 52 ma all the flows older than 1 7 ma occur in the west northwestern half of the island and all the flows younger than 1 5 ma occur in the east southeastern half the lithologies have no spatial or chronological pattern the flows of the koloa volcanics are near primary magmas generated by variable small degrees of partial melting of a compositionally heterogeneous garnet bearing source that has about two thirds the concentration of p2o5 rare earth elements and sr of the source of the honolulu volcanics on the island of oahu the same lithology in the koloa and honolulu volcanics is generated by similar degrees of partial melting of distinct source compositions the lavas of the koloa volcanics can be generated by as little as 3 percent to as much as 17 percent partial melting for nepheline melilitite through alkalic basalt respectively phases that remain in the residue of the honolulu volcanics such as rutile and phlogopite are exhausted during formation of the koloa volcanics at all but the smallest degrees of partial melting the mantle source for kauai lava becomes systematically more depleted in 87sr 86sr as the volcano evolves from the tholeiitic shield stage to the alkalic postshield stage to the alkalic rejuvenated stage at the same time the lavas become systematically more enriched in incompatible trace elements on a shorter timescale the lavas of the koloa volcanics display the same compositional trends but at a lower rate of change the source characteristics of the koloa volcanics considered along with those of the honolulu volcanics support a mixing model in which the source of rejuvenated stage lava represents large percent melts of a plume source mixed with small amounts of small percent melts of a heterogeneous mid ocean ridge source

major effusive eruptions and recent lava fountains balance between expected and erupted magma volumes at etna volcano 1 over the last four decades etna has shown a high output rate through numerous eruptions the volcano has displayed two eruptive behaviors the first is characterized by effusive eruptions that efficiently drained the storage system and emitted large volumes of magma the second behavior is related to lava fountains erupting small magma batches which are normally with high frequency and have been considered as precursors of major effusive eruptions in this paper we present an updated estimation of emitted volumes from etna eruptions which include the 38 lava fountain episodes that occurred from january 2011 to april 2013 these recent explosive episodes have been frequent discharging significant magma volumes observing the steady trend of magma output over time we present insights on expected erupted volumes we highlight that the january 2011 to april 2013 lava fountains efficiently drained the intermediate shallow storage system and favored a balance between the incoming and outgoing magma

mauna loa s submarine western flank landsliding deep volcanic spreading and hydrothermal alteration four new remotely operated vehicle dives carried out by monterey bay aquarium research institute mbari reveal a heterogeneous distribution of lithologies and compositions along a transect across the submarine west flank of mauna loa from the outer scarp of the frontal bench to the upper flank the frontal bench is composed predominantly of volcaniclastic sediments ranging from very fine grained monomictic hyaloclastites to coarse grained compositionally mixed volcaniclastic breccias the predominance of subaerially derived clasts suggests accumulations of landslide deposits probably emplaced along a regional shear plane preserved in cataclastic breccias with local foliations and grain trails repeated packages of inversely graded strata are interpreted to reflect thrust imbrication of the resulting volcaniclastic apron during volcanic spreading of mauna loa s western flank similar to that now documented along k lauea s south flank many of the rocks from the bench show evidence for alteration ranging from low grade burial diagenesis to higher grade hydrothermal alteration including phases never before observed in submarine hawaiian rocks including epidote talc sphene and corrensite alteration is concentrated in deformed zones denoting pathways for fluid flow into or out of the volcanic edifice formed at depth the altered rocks were subsequently transported along low angle thrust faults into the bench and exposed along high angle fractures and faults the upper submarine flanks are draped by subaerially erupted submarine emplaced pillow lavas and interbedded hyaloclastites generated by shoreline crossing lava flows basalt glasses indicate mauna loa origin but imply earlier compositions than present day lavas consistent with ar ar ages suggesting eruption 0 28 0 10 ma late stage detachment of a nearshore slump produced the lika 2 debris avalanche that broke through the frontal bench perhaps portending the evolution of the active hilina slump now present on k lauea volcano s south flank

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

human impact in a tourist karstic cave aracena spain human intrusion on the cave of marvels southwestern spain has produced a series of effects on the water fall in the level of the pools due to pumping from nearby wells the air increased temperature and co2 concentration as well as decreased relative humidity and the rock in addition plant colonization favored by the lighting system has irreversibly altered numerous speleothems the processes of degradation are especially intense in the sectors with less air volume and limited ventilation the analysis of the cave deposits by scanning electron microscopy and thin section analysis revealed that floral pollution constitutes one of the most aggressive agents against the calcite and aragonite precipitates being responsible for biochemical and biophysical degradation of the first order

the nature and rate of weathering by lichens on lava flows on lanzarote abstract samples of lichen covered and bare lava surfaces from lanzarote dating from the 1730 1736 eruption have been analysed using scanning electron microscopy sem energy dispersive spectroscopy eds and x ray diffraction xrd to investigate the relative roles of biological and inorganic weathering processes lichens here grow preferentially on n and ne facing surfaces and create a range of nanomorphological features as a consequence of their weathering activities the fruticose lichen stereocaulon vesuvianum and a mixture of crustose lichen species are found to be particularly effective agents of weathering comparison of the thickness of the weathering rind on bare and lichen covered samples mean thickness 15 7 and 253 9 m respectively shows a significant difference at the 99 confidence level following previous studies in hawaii by jackson and keller am j sci 269 1970 466 these results are used to suggest that lichens on lanzarote lava flows cause a 16 times increase in weathering rates over those found on bare surfaces comparison of these results with those from similar lava flows in hawaii indicates that under the wetter climate of hawaii both biological and inorganic rates are over double those found in lanzarote

the continuing story of etna s new southeast crater 2012 2014 evolution and volume calculations based on field surveys and aerophotogrammetry abstract during the years 2013 2014 the new southeast crater nsec at the summit of mount etna produced frequent episodes of lava fountaining paroxysms and its cone continued to grow at unprecedented rates many of the episodes were of rather brief duration and violently explosive producing mostly pyroclastic material and minor volumes of lava other episodes especially those since mid december 2013 were characterized by violent strombolian activity without producing sustained lava fountains and significant amounts of tephra but emitting more voluminous lava flows one episode of intense strombolian and effusive activity that was possibly fed from the nsec conduit occurred from vents located approximately 1 km north of the crater on the east flank of the northeast crater in july august 2014 the evolution of the nsec cone between 2012 and 2014 was documented by repeated gps surveys carried out both from a distance and on the cone itself by the acquisition of comparison photographs and by two aerophotogrammetric surveys from these surveys the highest point of the nsec results to have grown from 190 m may 2012 to 215 m october 2014 above the pre cone surface reaching an elevation of 3290 m and its volume more than doubled to 50 0 6 5 10 6 m 3 representing the 40 of the total bulk volume of the volcanic products including pyroclastic fallout erupted in 2011 2014 which is 147 2 10 6 m 3 101 3 10 6 m 3 dense rock equivalent the whole of the 2011 2014 nsec activity marks an unusually high frequency of rather explosive tephra rich eruptive episodes compared to etna s activity in past decades and centuries although the average magma production rate in this interval is close to the supposed long term output rate of the volcano the latest eruptive episodes show a tendency of the nsec coalescing with the old southeast crater cone which therefore represents a miniature example of a growing compound volcano at the summit of etna

the influence of light attenuation on the biogeomorphology of a marine karst cave a case study of puerto princesa underground river palawan the philippines karst caves are unique biogeomorphological systems cave walls offer habitat for microorganisms which in turn have a geomorphological role via their involvement in rock weathering erosion and mineralisation the attenuation of light with distance into caves is known to affect ecology but the implications of this for biogeomorphological processes and forms have seldom been examined here we describe a semi quantitative microscopy study comparing the extent structure and thickness of biocover and depth of endolithic penetration for samples of rock from the puerto princesa underground river system in palawan the philippines which is a natural unesco world heritage site organic growth at the entrance of the cave was abundant 100 occurrence and complex dominated by phototrophic organisms green microalgae diatoms cyanobacteria mosses and lichens thickness of this layer was 0 28 0 18 mm with active endolith penetration into the limestone mean depth 0 13 0 03 mm in contrast phototrophs were rare 50 m into the cave and biofilm cover was significantly thinner 0 01 0 01 mm p 0 000 and spatially patchy 33 occurrence endolithic penetration here was also shallower 0 01 mm p 0 000 and non uniform biofilm was found 250 m into the cave but with a complete absence of phototrophs and no evidence of endolithic bioerosion we attribute these findings to light induced stress gradients showing that the influence of light on phototroph abundance has knock on consequences for the development of limestone morphological features in marine caves this includes notches which were most well developed at the sheltered cave entrance of our study site and for which variability in formation rates between locations is currently poorly understood

biomechanical and biochemical weathering of lichen encrusted granite textural controls on organic mineral interactions and deposition of silica rich layers the crustose lichen rhizocarpon geographicum weathers the lower devonian shap granite by both biomechanical and biochemical means biomechanical weathering is mediated by fungal hyphae that penetrate into the rock via intergranular boundaries at 0 002 0 003 mm year 1 once inside the granite hyphae exploit intragranular pores along cleavage and fracture planes in biotite alkali and plagioclase feldspar grains of biotite exposed at the lichen granite interface have been fragmented by biomechanical action in 122 years after an extended period of biomechanical weathering of 10 kyr outcrop surfaces sub mm sized fragments of biotite and plagioclase feldspar abound in lower parts of the lichen s thallus grains of biomechanically weathered biotite show the clearest evidence for biochemical weathering typically k and fe are leached from the biotite but other cations may also be removed leaving a silica dominated relic the silica rich remains of biotite and possibly also feldspar have been redistributed along the lichen granite interface forming a silica rich layer this silica rich material also cements fractures and pores beneath the interface alkali feldspars from outcrop surfaces have been weathered chemically as indicated by etch pits on cleavage surfaces and fractures but it is not obvious that lichen was involved in the dissolution the etch pits were probably formed during earlier phases of non biochemical weathering that widened intergranular and intragranular pores facilitating subsequent access of fungal hyphae into the granite despite evidence for biomechanical and biochemical weathering it is unlikely that colonisation of granite surfaces by r geographicum at shap significantly enhances their weathering rate relative to bare rock surfaces the lichen may actually retard weathering by protecting the surface from frost action binding fragmented mineral grains and depositing protective silica rich layers

effect of lichen colonization on chemical weathering of hornblende granite as estimated by aqueous elemental flux abstract it has long been suspected that lichens increase the rate of physical and chemical weathering of rock surfaces thus playing a role in biogeochemical cycles however the relative weathering flux of elements from lichen colonized rock versus bare rock has been minimally studied previous attempts to quantify the effect of lichen cover on weathering have focused disproportionately on evidence from altered weathering rinds on basalt here in a field experiment on hornblende granite in new jersey usa we measured the cumulative waterborne net efflux of five elements over 31 days and six rain events from multiple constructed miniature watersheds consisting of either lichen covered or exposed bare rock on average lichen covered watersheds showed approximately double the silicon flux and three times the calcium and magnesium flux compared to bare rock additionally efflux of these elements was higher in lichen covered watersheds across all six rain events this suggests that lichens do indeed promote increased chemical weathering compared to bare rock thus likely increasing sequestration of atmospheric co 2 under equal conditions of atmospheric pco 2 temperature and rainfall it was also observed that lichen covered watersheds showed a 50 reduction in iron flux and had a greater ratio of calcium and magnesium to silicon flux compared to bare rock watersheds the possible causes of these patterns are discussed

rock weathering by the lichenlecidea auriculata in an arctic alpine environment scanning electron microscopy reveals that lecidea auriculata penetrates rock surfaces detaching incorporating and expelling flakes of rock measurements on an age sequence of moraine ridges illustrate changes in the extent and intensity of weathering over time a minimum rate of surface lowering 0 0012 mm a 1 is 25 to 50 times faster than weathering due to other processes in the same area the spatial pattern of weathering is influenced by the narrow ecological range of the species surface rocks on dry exposed sites are probably weathering much more rapidly than those in adjacent damp hollows and beneath snowpatches

lidar surveys reveal eruptive volumes and rates at etna 2007 2010 the quantification of eruptive activity represents one major challenge in volcanology digital comparison of lidar based elevation models of etna italy was made to quantify the volumes of volcanics emitted in 2007 2010 during this period etna produced several summit paroxysms followed by a flank eruption we integrated the total volume difference resulting from the subtraction of the 2007 and 2010 digital elevation models with volumes of eruptive products based on field and aerial surveys to attribute volumes with hitherto unrealized precision to poorly constrained eruptions the total erupted volume of 2007 2010 is 86 106 m3 most 74 106 m3 of which is made up by the lava flows of the 2008 2009 flank eruption the survey also reveals the high lava volume 5 73 106 m3 and average eruption rate 400 m3 s 1 of the 10 may 2008 paroxysm whose flow front stopped 6 2 km from the vent not far from the town of zafferana etnea

weathering and particle entrapment at the rock lichen interface in italian volcanic environments abstract the present work investigated the biogeophysical and biogeochemical weathering associated to the growth of epilithic lichens on recent lava flows from mt etna sicily and mt vesuvius campania the chosen lichen species were the crustose lecidea fuscoatra the foliose xanthoparmelia conspersa and the fruticose stereocaulon vesuvianum an integrated approach based on the study of both disturbed and undisturbed samples of lichenized rock was applied in order to allow for the complexity of the rock lichen interface environment in terms of micromorphological mineralogical and chemical properties to this aim a number of rock blocks colonised by intact thalli of different lichen species were collected in order to have at least 10 thalli for each species in each environment xrd and xrf analyses coupled to microscopic om submicroscopic sem and microanalytical eds observations were the used techniques in both study environments the chemical mineralogical and micromorphological properties of the incoherent materials found at the rock lichen interface suggested that they mostly consist of rock fragments eroded from the surroundings and accumulated in cavities and fissures of the rough lava flows according to the thallus morphology the lichens colonising the lava preserve the interface materials from further wind and water erosion provide such materials with organic matter and moisture and entrap allochthonous quartz sea salts iron oxides and clay minerals calcium oxalate production by l fuscoatra and x conspersa al enrichment around s vesuvianum hyphae and iron accumulation at the interface constitute evidence of lichen interaction with the underlying sediments larger differences between rock and interface materials occur at vesuvius vs etna site in line with the young age of the lavas recent lichen colonisation only results in a physical reorganisation and slight chemical modification of the materials accumulated at the rock lichen interface whose abundance should not be considered an indicator of bioweathering in volcanic environments the ability of lichens to retain a considerable amount of unconsolidated material

microscale biopitting by the endolithic lichen verrucaria baldensis and its proposed role in mesoscale solution basin development on limestone data are reported demonstrating the potential role of microscale morphologies induced by endolithic lichen communities specifically verrucaria baldensis in the initiation and development of mesoscale solution basin formation on limestone in the burren county clare a biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonization and growth associated perithecial biopitting followed by biopit coalescence to form biotroughs their subsequent enlargement and eventual incipient solution basin formation this model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input the complexity of interactions at the lichen rock interface are identified with emphasis on the spatial and temporal variability of these underlining the point that as with macrotopographies at the landscape scale rock surface microtopographies also reflect historical weathering legacies copyright 2011 john wiley sons ltd

coeval biochemical and biophysical weathering processes on quaternary sandstone terraces south of rabat temara northwest morocco despite numerous investigations on substrate inhabiting microflora especially lichens very little is known about the colonization of coastal escarpments by lithobiontic micro organisms inland of a retreating coastline in africa reported herein are the results of a combined field observation and microscopy study focusing on the connection between microrelief of the substrate colonies of lithobiontic micro organisms in particular the lichen xanthoria parietina and microstructures of putative bacterial origin the occurrence of weathering pits in which the early stages of the biotic development occurs and the subsequent disintegration of the rock indicate that lichens mosses and fungi act synergistically by alternating chemical and mechanical weathering penetration of grains by expansion and contraction of the hyphae depletes the rock matrix and contributes to the mechanical breakdown of the rock calcite rhombs on the weathered surfaces of the calcite cemented sandstones are severely etched with well developed rhomb shaped etch pits spiky calcite holes or has one or more of the faces removed and their cores exposed and leached nanofilaments c 100 700 nm and nanomicrobial fruiting bodies c 250 nm emanating from micropores appear to be common on affected crystalline structures weddellite present immediately below the thallus is a strong indicator of biomineralization quartz responds differently to chemical weathering by producing peeling structures and microbrecciation features the dissolution of these crystals appears to be a surface reaction controlled process mediated by microbial microfilaments and nanofilaments a model is proposed firstly indicating early stage biochemical weathering followed by biophysical weathering disintegration of the rock outcrops in due to a complex interplay of several events probably beginning at the nanoscale with penetration of sites on crystal faces copyright 2006 john wiley sons ltd

an updated global review of solutional weathering processes and forms in quartz sandstones and quartzites abstract quartz is considered one of the less soluble minerals of the earth s crust and thus hardly affected by chemical weathering despite this for more than forty years it is clear that the formation of caves and peculiar solutional weathering dominated landforms in quartz rich lithologies is common and shares several similarities to the well known karstic ones in carbonate rocks in the last thirty years great strides have been made in furthering our knowledge of the distribution of these forms around the world and the geochemical processes involved these studies have clearly shown that solutional weathering is a fundamental process acting through intergranular dissolution of quartz increasing the rock porosity and decreasing the rock strength to erosion this process has been described in the concepts of arenization and phantomization and the widespread evidences of the fundamental role of quartz solution in landform genesis has even developed to the extent of several geomorphologists reassessing the definition of the term karst and its application to these peculiar lithologies nonetheless the process is complicated by several factors related both to environmental conditions water chemistry and availability as well as to the compositional and textural characters of the lithology presence of clays iron hydroxides carbonate cement etc all these aspects have to be taken carefully in consideration in order to understand if solution is a dominant or accessory process in the landscape evolution in this review the state of knowledge on the relevant chemical processes weathering mechanisms and speleogenesisk involved in the surface and underground karstification and clear examples of quartz solution and solutional landforms from different world locations are outlined and discussed

a quantitative scanning electron microscope study of evidence for lichen weathering of limestone mendip hills somerset many saxicolous lichens may cause physical and chemical weathering of limestone substrates but their geomorphological importance has not been fully determined a simple method of producing quantitative descriptions of lichen material and petrographic evidence of weathering using the sem has been developed and tested on samples from the mendip hills england the technique reveals a variable and often sparse distribution of lichen material and associated weathering effects below a thin clearly defined lichen thallus

ecological perspectives on rock surface weathering towards a conceptual model a wide range of information is now available on the ecology of rock surface microorganisms including bacteria fungi and algae and lichens and their role in weathering in particular locations external environmental conditions as well as rock characteristics determine the type of rock surface community and thus the style of biological weathering a simple preliminary conceptual model can be drawn which relates biological weathering activity to an environmental stress gradient and which is applicable at a range of scales further research needs carrying out to test and extend this model in order to make some progress towards the important goal of assessing the overall importance of biological weathering to geomorphology

a note on the role of the lichen collema auriforma in solution basin development on a carboniferous limestone substrate a study carried out on carboniferous limestone in the north and west of ireland supports the idea that rock substrate is removed by the direct mechanical action of lichens an experiment in which the lichen collema auriforma was subjected to a number of wetting drying cycles showed using scanning electron microscopy that contraction of the lichen thallus during the drying phase plucked rock fragments from the substrate surface this process could contribute to the formation of karstic features including solution basins

unspiked k ar dating of the honolulu rejuvenated and ko olau shield volcanism on o ahu hawai i many mantle plume volcanoes undergo rejuvenated volcanism after a period of construction and erosion of their shield the cause of this renewed volcanism has been enigmatic and various models have been proposed however the lack of geochronological data has hindered evaluation of these models unspiked k ar ages on groundmass in 41 samples from 32 vents of honolulu volcanics and eight samples of underlying kodolau volcanics were determined in order to reveal the temporal distribution of rejuvenated vents and the length of the hiatus between the end of shield and start of rejuvenated volcanism the new geochronological results show that kodolau shield volcanism ended at 2 1 ma and that rejuvenated volcanism started at 0 8 ma resulting in a 1 3 million year hiatus in volcanic activity two distinct pulses were found for honolulu volcanism at 0 80 0 35 and 0 1 ma during the first pulse the eruption frequency increased with time and there was no spatial pattern in vent distribution although three vents along a nne ssw trend produced similar compositions and may have been coeval volcanism apparently waned from 0 35 0 12 ma with only one eruption the second pulse occurred along two rifts that trend n s and ne sw although the ages for the 10 dated flows are indistinguishable at around 0 1 ma lavas from the two rifts have distinct compositions weakly alkalic vs melilite nephelinite the first more widely distributed pulse of volcanism is probably related to secondary melting downstream from the hawaiian plume stem which may be related to lithospheric thinning the second pulse focused along two rifts may be related to decompressional melting as the shield passed over the flexural arch d 2005 elsevier b v all rights reserved

weathering processes on the rock surface in natural outcrops the case of an ancient marble quarry belevi turkey weathering and mineralogical processes observed in a marble quarry in turkey are compared with similar processes occurring on monument surfaces patina formations microstromatolitic microlaminated monolayered as well as destructive processes mainly biopitting and bioerosion are associated with microbial colonisation of the rock surfaces and one influenced by microclimatic conditions patina stratification is independent of substrate rock but is affected by the position and orientation of rock surfaces the different layers formed by mineralisation processes may reflect the seasonality of climatic events and the consequent colonisation bio deteriorative processes take place mainly when the climatic conditions cause the organisms to live below the surface

the weathering effects of the lichen lecidea aff sarcogynoides koerb on magaliesberg quartzite the effect of the weathering processes generated by lecidea aff sarcogynoides koerb on the substrate was studied by means of a scanning electron microscope the elements present in the substrate magaliesberg quartzite and in the lichen thallus were determined by x ray fluorescence spectrometry for the purpose of comparison the elements present were mostly similar although a few were present in the thallus which were not observed in the quartzite it is possible that those elements present in the lichen thallus which were not present in the substrate may have been extracted from the atmosphere the occurrence of small hollows weathering pits in which the early stages of plant development occurs and the disintegration of the rock indicate that lecidea aff sarcogynoides koerb contributes to the chemical weathering processes by chelation and mechanically by the penetration and expansion of hyphae a model is proposed in which a possible mechanism for these weathering processes is suggested

a submarine perspective of the honolulu volcanics oahu lavas and volcaniclastic deposits were observed and collected from 4 submarine cones that are part of the honolulu volcanics on oahu hawaii the locations of these and a few additional but unsampled vents demonstrate that nearly all the vents are located on or very close to the shoreline of oahu with the most distal vent just 12 km offshore the clastic samples and outcrops range from coarse breccias to cross bedded ash deposits and show that explosive volcanism at depths between about 350 and 590 m depth played a part in forming these volcanic cones the eruptive styles appear to be dominantly effusive to strombolian at greater depths but apparently include violent phreatomagmatic explosive activity at the shallower sites along the submarine southwest extension of the koko rift the compositions of the recovered samples are broadly similar to the strongly alkalic subaerial honolulu volcanics lavas but the submarine lavas erupted further from the koolau caldera have slightly more radiogenic sr isotopic ratios and trace element patterns that are distinct from either the subaerial honolulu volcanics or the submarine north arch lavas these patterns are characterized by moderate to strong positive sr and p anomalies and moderate to strong negative cs rb u th zr and hf anomalies most samples have strong negative k and moderate negative ti anomalies as do all subaerial honolulu volcanics and north arch samples but one group of samples from the koko rift lack this chemical signature the data are consistent with more garnet in the source region for the off shore samples than for either the on shore honolulu volcanics lavas new ar ar ages show that eruptions at the submarine vents and diamond head occurred between about 0 5 ma and 0 1 ma with the youngest ages from the koko rift these ages are in general agreement with most published ages for the formation and suggest that some much younger ages reported previously from the koko rift are probably erroneously young d 2005 elsevier b v all rights reserved

techniques for measuring rock weathering application to a dated fan segment sequence in southern tunisia there are a number of techniques for estimating the amount of weathering a clast has undergone these usually have the objective of establishing an ordinal chronology of geomorphological surfaces or investigation of site specific conditions affecting weathering rates three such techniques are applied to a dated sequence of alluvial fan segments in southern tunisia two of these techniques depend on measuring surface roughness the micro roughness meter and a displacement approach and one uses the structural weakening of the rock fabric schmidt hammer the micro roughness meter enables calculation of standard deviation of surface height variation root mean square roughness and surface autocorrelation function of these techniques schmidt hammer rebound values standard deviation root mean square roughness and the displacement technique show systematic changes on the three fan segments which are statistically significant at the 0 05 level however the amount of variance in all datasets is very large indicating the need for caution in application of these techniques for relative dating 1998 john wiley sons ltd

the role of intragranular microtextures and microstructures in chemical and mechanical weathering direct comparisons of experimentally and naturally weathered alkali feldspars abstract electron microscopic observations of alkali feldspars from soils show that intragranular microtextures such as exsolution lamellae and microstructures primarily dislocations are both highly significant determinants of the weathering behaviour of these minerals in particular strained structure around intersecting edge dislocations in the plane of exsolution lamellae 6 01 dissolves at a rate which is orders of magnitude greater than unstrained feldspar producing a mesh of intersecting etch tubes extending 5 10 3 cm into the crystal as a result dissolution at dislocations is the major source of solutes during initial stages of chemical weathering in the field with progressive chemical weathering the most highly reactive feldspar is consumed by growth and coalescence of etch tubes but outer parts of the grain are physically weakened leading to mechanical flaking that increases available surface area and exposes further reactive sites in contrast previous dissolution experiments and microscopy of reacted surfaces have shown little or no correlation between dissolution rate and dislocation density and few visible signs of dissolution at particularly reactive sites to resolve the apparent discrepancy between field and laboratory behaviour we have carried out flow through dissolution experiments using ph 2 hcl at 25 c on three alkali feldspars with carefully characterized intragranular microtextures and microstructures these alkali feldspars were 1 eifel sanidine an alkali feldspar that has no microtextures at the tem scale and a low dislocation density 2 3 108 cm 2 and 3 naturally weathered alkali feldspars also from the shap granite which have the same microtextures as unweathered shap granite alkali feldspars but because they have been weathered have a lower density of dissolution reactive dislocations exposed on grain surfaces

evidence that three seamounts off southern california were ancient islands abstract many seamounts world wide exhibit features that suggest they were once islands rodriguez and san juan seamounts and northeast bank within 250 km of the continental margin of the western us were explored with the rov tiburon and found to have guyot morphology beach deposits and erosional features degassed volcanic lavas and pyroclasts and cooling and alteration patterns unusual for submarine erupted lavas these features are evaluated as evidence that the volcanoes stood above sea level the summit of rodriguez seamount is a smooth gently domed platform rough hills stand above the platform and consist of dense degassed a a flows erupted subaerially bedded sandstones and rounded cobbles interpreted to be beach deposits occur near the top of a major break in slope at about 700 m depth the summit of northeast bank is also a smooth gently domed platform beach deposits were observed just below the pronounced break in slope at about 500 m the summit of san juan seamount is a northeast southwest trending series of rough ridges rather than a dome however subaerially exposed a a like lava flows were found above 700 m oxidized olivine degassed volcanic glass and secondary phosphatization of the lavas are found both shallower and deeper than the breaks in slope and their presence may not be robust indicators of subaerial exposure rodriguez stood at least 70 m above sea level and formed a small island 6 8 km 2 in area prior to subsiding at least 700 m northeast bank was a large island perhaps 200 m above sea level and 90 km 2 in area the summit ridge of san juan emerged as a line of eight small islands with a total area of about 2 8 km 2 and the tallest island rose at least 140 m above sea level the subsidence of northeast bank within the california borderland rodriguez seamount on the continental slope and san juan seamount on the adjacent ocean crust occurred since they formed 7 to 11 million years ago the minimum subsidence is consistent with cooling and contraction of the underlying lithosphere

limestone weathering in contemporary arid environments a case study from southern tunisia weathering features are described from a meteorologically arid area in southern tunisia active weathering is concentrated in topographic lows pits and pans that concentrate available moisture and are associated with endolithic and epilithic algae responsible for algal boring plucking and etching of the limestone substrate deposits of gypsum have concentrated through evaporation within hollows and occur as isolated patches of tabular crystals indicating an additional weathering agent characteristic of arid environments the active development of a complex microkarst and associated salt weathering are combining to destroy linear karstic features such as rillenkarren widespread case hardening and in places patches of iron and manganese rich rock varnishes the complexity of active and inherited weathering features belies the perceived simplicity and lack of weathering opportunities associated with aridity instead it focuses on the need to consider the nature of microclimatic conditions at the rock air interface especially when seeking to define desert weathering environments it also highlights the difficulties of interpreting polygenetic landforms and the importance of microscale studies for identifying the impact of contemporary climatic conditions

promotion of chemical weathering by higher plants field observations on hawaiian basalts abstract an electron microprobe and petrographic microscope were used to study the biota rock interface beneath higher plant communities and lichens as well as unvegetated surfaces on hawaiian basalt flows ranging from a few years to several thousand years in age and currently receiving moderate to extremely high annual rainfall we find dramatic order of magnitude minimum acceleration of weathering rates beneath vascular plants on the youngest flows relative to adjacent non or primitively vegetated controls notably rocks colonized by the common fruticose lichen stereocaulon uulcani bulk dissolution of plagioclase accounts for most of the weathering observed beneath higher plants on these young basalts analysis of older flows under mature forests reveals that chemical weathering beneath vascular plant communities continues unabated for thousands of years after initial colonization moreover such weathering is not limited to exterior basalt surfaces but is commonly found adjacent to joints and vesicles within the rock where it is often associated with fine sub 2 mm diameter plant roots plagioclase dissolution was also observed on lichen encrusted and unvegetated flows a few hundred to thousands of years in age but it was typically much less advanced than beneath higher plants and rarely extended more than several millimeters from exterior rock surfaces chemical denudation rates on older flows with higher plants are at minimum ten times greater than those with only lichens or microbiota in the environments studied if s uulcani and associated microflora resemble the terrestrial precursors to vascular plant communities then the results of studies such as this have implications for the history of atmospheric co 2 and the earth s climate

freshwater biodissolution rates of limestone in the temperate climate of the dinaric karst in slovenia abstract dissolution rates in two freshwater karst systems were determined by using tablets of dense micrite biopelmicrite cretaceous limestone submerged limestone tablets in riverbeds were subjected to a natural gradient from complete darkness to direct sunlight higher light rates significantly p

limestone weathering in eastern australia part 2 surface micromorphology study results from long term microerosion meter mem studies indicate that microenvironments are characterized by different erosion rates a complementary study carried out on the same sites examines the microscale morphology in each environment optical and scanning electron microscopy were used to identify a range of features thought to reflect different processes under subaerial conditions micromorphology is dominated by biological weathering features owing to the presence of microflora sites permanently covered by soil or stream water have only dissolution etch features though stream sites may exhibit microfractures sites with periodic exposure exhibit both dissolution and biological etch features the natural environment is more accurately reflected by allowing some microflora colonization of mem sites rather than preventing colonization by artificial means

two hourly surface change on supra tidal rock marengo victoria australia a traversing micro erosion meter was used to measure rock surface micro topography over 40 cm2 on a supra tidal cliff face from early morning to late evening in late spring from 06 00 hours to 22 00 hours the relative heights of 188 coordinates were obtained using the meter at 2 hour intervals resulting in a data set of 1607 readings monitoring shows that rock surfaces are dynamic entities with significant rise and fall relative to the first measurement at shorter timescales than previously reported the maximum positive rise between readings was 0 261 mm and lowering was 0 126 mm the pattern of change did not relate as expected to environmental variables such as temperature or insolation rather the surface showed greater surface change in the early morning and late afternoon it is hypothesized that this pattern relates to the expansion and contraction of lichen thalli as moisture is absorbed during higher humidity in the morning and late afternoon the implications of these results for weathering studies are considered copyright 2006 john wiley sons ltd

the spectrum of persistent volcanic flank instability a review and proposed framework based on kīlauea piton de la fournaise and etna abstract persistent motion of the south flank of k lauea volcano hawai i has been known for several decades but has only recently been identified at other large basaltic volcanoes namely piton de la fournaise la reunion and etna sicily thanks to the advent of space geodetic techniques nevertheless understanding of long term flank instability is based largely on the example of k lauea despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens for example the rate of flank motion at k lauea is several times that of etna and piton de la fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes gravitational spreading also appears to be the dominant driving force at k lauea given the long term steady motion of the volcano s south flank regardless of eruptive intrusive activity whereas magmatic activity plays a larger role in flank deformation at etna and piton de la fournaise k lauea and etna however are both characterized by heavily faulted flanks while piton de la fournaise shows little evidence for flank faulting a helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity which encompasses both magma supply and edifice size and on the other hand by the structural setting of the volcano especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones a volcano s size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank and possibly the level of faulting of that flank while the volcano s structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a type example especially given that the example is usually k lauea which defines an extreme end of the spectrum and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide

geochemistry of kauai volcanics and a mixing model for the origin of hawaiian alkali basalts a comprehensive model is developed to explain the major trace element and strontium and neodymium isotopic characteristics of alkali basalts from hawaii the model is similar to that of chen and frey 1983 in that it requires mixing of a small melt fraction of morb source material with another component to generate the alkalic suite of a particular hawaiian volcano it differs from the chen and frey model in that the other end member must be different from primitive mantle if it is to be consistent with both trace element and isotopic data alkali basalts and tholeiites from kauai analyzed in this study show a nearly complete transition in sr and nd isotopes there is a relatively well constrained array on a nd sr isotope correlation plot that can be explained by two component mixing of kauai tholeiite magma and a small amount of melt of east pacific rise source rock after corrections are made for fractional crystallization involving primarily clinopyroxene and olivine the sr and ba concentrations of kauai lavas plot along mixing curves defined by the above sources providing positive tests of the mixing hypothesis implications of this model are 1 the main source of hawaiian shield building tholeiites is a mixture of subducted crust primitive mantle and depleted asthenosphere that has been homogenized prior to melting 2 early alkalic volcanism as at loihi seamount will be characterized by greater isotopic heterogeneity than will late stage alkali basalt production and 3 there are two fundamentally distinct types of alkalic lavas erupted towards the end of magmatism at a given hawaiian volcano one represents smaller degrees of melting of the same source that generated shield building tholeiites kohala type the other derives from the mixed source discussed in this paper haleakala kauai type

late devonian oib alkaline gabbro in the yarlung zangbo suture zone remnants of the paleo tethys article i nfo the yarlung zangbo suture zone yzsz is believed to be composed of material largely derived from the destruction of the neo tethys that occurred from early mesozoic to early cenozoic we report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a melange zone of the western yzsz single zircon u pb analyses from one representative gabbro sample by sims secondary ion mass spectrometry yielded a combined crystallization age of about 363 7 1 7 ma 1 in situ hf isotopic analyses yielded ehf t values of 2 6 to 5 5 suggesting an enriched mantle source all of the gabbro samples show typical ocean island basalt oib affinity with little or no continental crust contamination they also display strong geochemical similarities with the hawaii basalts and the xigaze seamount basalts suggestive of their intra oceanic setting these observations in combination with the early carboniferous layered gabbros reported at luobusa indicate that these rocks could represent remnants of the paleo tethys we propose that a branch ocean separating the western qiangtang terrane and the lhasa terrane from the gondwana continent might have been present during the late devonian and the early carboniferous providing new constrains on the configuration of paleo tethys in tibetan plateau during early late paleozoic