geochemical fingerprint of insoluble material in soil on different limestone formations abstract in the karst region near divaca slovenia soils are developed on the limestone of three geological formations se ana lipica and liburnian in each formation six soil profiles were dug limestone insoluble residua was obtained and in liburnian formation interbedded material and material filling fractures and cavities was sampled all soils have silty clay and silty clayey loam texture ph levels in the range 4 5 7 0 high organic matter content and saturation with basic cations over 50 however soils on the se ana formation are deeper and more evolved and besides as rendzic phaeozem classify also as eutric cambisol their insoluble residuum is richest in mineral part the profiles on the lipica formation are a rendzic phaeozem and the shallowest soils on the liburnian formation are either a rendzic phaeozem or a rendzic leptosol additionally the soils formed over the lipica formation are characterised by a greater portion of the small rock fragments

the lost paleosols masked evidence for emergence and soil formation on the kimmeridgian jura platform nw switzerland abstract lagoonal carbonates of kimmeridgian age in nw switzerland formed in a tropical epeiric sea and exhibit indicators of subaerial emergence such as tidal biolaminites desiccation cracks flat pebble conglomerates and fenestral structures additionally 30 dinosaur tracksites from at least six stratigraphic intervals indicate repeated formation of land bridges between the platform and adjacent massifs populations of herbivorous and carnivorous dinosaurs necessitate substantial vegetation and consequently a soil cover but no striking evidence of paleosols have been found within the track bearing sequences however two stratigraphic levels exposed in nine outcrops exhibit distinctive hardgrounds that experienced early meteoric diagenesis during times of emergence initial induration began with the precipitation of thin micritic meniscus cements contemporaneously meteoric waters completely dissolved all aragonite leaving large voids iron hydroxides were precipitated in the uppermost 7 10 cm where they impregnated the porous micrite and constituted a separate cement generation which caused a penetrative dark red staining these aspects are suggestive of the formation of mediterranean type red soils on the emerged platform during transgression the soil was eroded and wave cut hardgrounds were superimposed on the hardgrounds formed during regression erosion is evidenced by micro karst truncated gastrochaenolites isp borings and the physical removal of steinkerns the eroded material including floral remains provided surplus nutrients leading to eutrophication this food rich environment supported the mass occurrence of gastropods in the nerineoid limestones and oysters nanogyra sp in the virgula marls

integrating the uranium series and elemental diffusion geochronometers in mixed magmas from volcan quizapu central chile magma mixing is a ubiquitous process in silicic magmatic systems we present pre and post mixing time scales for a single magma mixing event associated with the 1846 1847 eruption of volcan quizapu we compare and contrast 226 ra 230 th crystal residence ages between the mixed lavas of the 1846 1847 effusive eruption and the largely homogeneous plinian dacite eruption of 1932 both eruptions are dominated by the same dacite magma whereas the ear lier eruption contains evidence for a single episode of mafic recharge and mixing the use of uranium series mineral separate dating on a mixed magma requires deconvolution of different crystal populations we present a four component mixing model for the crystal separates to obtain dacite derived plagioclase model ages as well as andesite derived recharge plagioclase ages plagioclase model ages average 3 6 ka for dacite derived plagioclase from the mixed 1846 1847 eruption 1 4 kyr older than average plagioclase model ages of the 1932 eruption suggesting that magma mixing and reheating led to some resorption of young crystal rims in the 1846 1847 magmatic episode and or that some growth of plagioclase rims occurred during the repose time of 86 years the andesite derived plagioclase residence ages are younger than the corresponding dacite derived plagioclase residence ages but they are still of the order of thousands of years in addition we use mg diffu sion in plagioclase to constrain time scales of magma mixing we show that the 1846 1847 eruption was triggered by large volume mafic recharge magma that mixed and mingled with the resident dacite within probably days to weeks of the ensuing eruption

red mediterranean soils in jordan new insights in their origin genesis and role as environmental archives it is disputed whether terrae rossae form mainly out of the bedrock residue from allochthonous material like aerosols or by isovolumetric replacement furthermore whether they are mainly relic soils or are still forming is subject to debate these questions were addressed by comparing the geochemistry of several limestone and basalt based red mediterranean soils with lithosols on sandstone and limestone in jordan the bedrock residue was included at all test sites paleosols and initial soils on the limestone regolith of historic ruins delivered insights into the possible time frame of soil development a major reduction of elements in the soils compared to bedrock could be observed for cao in carbonaceous sio2 in arenaceous and fe2o3 and mgo in basaltic rocks all terrae rossae however are characterised by a significant increase of sio2 al2o3 tio2 fe2o3 k2o and a range of mainly metallic minor elements that cannot be derived from the bedrock a reasonable explanation could be input via aeolian transfer of minerals with clay minerals as the major carrier plus quartz this input probably originates in egypt and sudan and has remained largely unchanged over long periods growing aridity during the holocene has apparently increased the share of silt while clay deposition and soil development has been reduced at some sites metasomatic processes have contributed to soil development and might help to explain the depth of some profiles however formation of red soils during the holocene seems very limited and the red mediterranean soils may represent remains of a paleolandscape

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

absolute accumulation and isotope fractionation of si and fe during dolomite weathering and terra rossa formation abstract the behavior of silicon si and iron fe and their isotope fractionation during carbonate weathering and terra rossa formation are unclear here we focus on a 4 05 m thick terra rossa profile developed on dolomite in the yunnan guizhou plateau china we measured the mineral and geochemical composition magnetic susceptibility and si and fe isotopic composition of the terra rossa ferromanganese concretions fmcs and the dolomite and its insoluble residues the results indicate that there is absolute accumulation of si and fe during dolomite weathering and terra rossa formation due to the extraneous input of dissolved si and fe this means that the insoluble residues of dolomite are not the only source for terra rossa formation in addition we suggest that the high frequency dependent magnetic susceptibility fd and rubification of the terra rossa are the result of the oxidation of extraneous dissolved fe and the neoformation of finely dispersed fe oxides overall the terra rossa is characterized by the enrichment of light si and fe isotopes compared with insoluble dolomite residues and bulk dolomite the extraneous input of dissolved fe is characterized by a light isotopic signature whereas the si isotopic signature of the extraneous source is unclear due to modification by late desilicification si isotope fractionation in the terra rossa is mainly controlled by chemical weathering and associated mobilization and redistribution of si the 30 si values of terra rossa decrease with increasing weathering intensity while the re precipitation of mobilized si leads to the significant enrichment of isotopically heavy si in the basal terra rossa the 30 si values of terra rossa are not significantly affected by the adsorption of the fe and al oxyhydr oxides by contrast the major process that fractionates fe isotopes in the dolomite terra rossa weathering system is unclear in the terra rossa profile the 56 fe values of the fmcs are significantly lower than those of the surrounding terra rossa matrix these low 56 fe signatures of the fmcs reflect the preferential translocation of the light fe isotope while the fmcs may be able to record the low 56 fe characteristics of pore water

implications of pre eruptive magmatic histories of zircons for u pb geochronology of silicic extrusions zircons in silicic magmas begin to crystallize 10 s to 100 s of thousands of years ka prior to their eruption u pb and u th dating for zircons from 32 young extrusions indicate a range of mean pre eruption ages from 33 to 247 ka with a median of 92 ka explosive large volume widespread eruptions show a narrower range and a younger median of 70 ka these results indicate that the difference between initial zircon growth and eruption age measured by other e g 40ar 39ar techniques is in excess of the achievable analytical uncertainty for eruptions 30 million years ma and likely for eruptions of up to 300 ma protracted pre eruption zircon growth is well established by an increasing number of studies on magma process time scales but this source of eruption age bias has been largely ignored in chronostratigraphic applications of high precision u pb data until intrinsic properties of zircons or their host deposits enable a priori estimates of pre eruption age bias it is prudent to expand the uncertainties attending all u pb zircon ages interpreted as deposition ages in e g chronostratigraphic studies by 0 200 ka

provenance and formation of the red palaeosol and lithified terra rossa like infillings on the island of susak a high resolution and chronological approach abstract red palaeosol rp covering the carbonate basement exposed at the bottom of the loess section and lithified terra rossa like materials situated in cavities ltr1 and karstified fissures ltr2 in cretaceous limestones were investigated by means of high resolution approach to give a systematic and deeper palaeopedological insight into reddish materials and the exposed red palaeosols on the island of susak both selected geochemical indicators of weathering al si na k al and fed fet and provenance la ce as well as detailed mineralogical analysis clearly showed differences among ltr1 ltr2 and rp respectively ltr1 and ltr2 represent erosional remains of different soils that existed on the surface of the limestone bedrock prior to the formation of the rp ltr2 has the highest ztr zircon tourmaline rutile index index and contains bauxite minerals gibbsite and boehmite clays kaolinite and mixed layer clay minerals and haematite ltr2 bears characteristics of reworked bauxitic materials mixed with other soils that existed on the surface of the carbonate basement those materials might have been mixed and transported until they were captured in the karstified fissure and subsequently interlocked with calcite veins and lithified this might have happened from the eocene age on our attempt to resolve the age of ltr2 formation more precisely using palaeomagnetic investigations did not give unambiguous results because the extremely viscous behaviour of the ltr2 samples hinders the acquisition of a stable remanent magnetisation if we exclude the secondary calcite ltr1 bears typical mineralogical and geochemical characteristics e g fed fet ratio similar to those of istrian terra rossa insoluble residues of cretaceous limestone might have been the main parent materials for the ltr1 formation while the most likely additional fluxes influencing terra rossa formation on the island of susak were aeolian dust and flysch the erosion remains ended in limestone cavities and were mixed with cm to dm sized angular and subangular limestone clasts and subsequently interlocked with calcite veins and lithified the investigated rp profile comprised the following mineral horizons bwb1 bwb2 bwb3 r the rp formed in a lithologically uniform material that dominantly presents a mixture of loess and partly remains of older soils e g rounded clay coatings not related to macrovoids that existed on the surface of the cretaceous limestone fed fet ratio in rp reflects a low degree of weathering of fe containing primary silicates therefore we can conclude that the rp does not fit a rather limited variation of selected fe oxide characteristics typical for terra rossa the investigated rp was classified independently of the overlying material the full name of the palaeosol that we classified is as follows hypereutric chromic cambisol episiltic endoloamic since no reversal of the emf was recorded in the rp we concluded that the rp formed during the brunhes epoch luminescence dating was applied to establish the age of the rp based on the acquired data we assume that the rp very likely formed during the penultimate interglacial ois7

instability of a lithospheric step beneath western north island new zealand lithospheres of different thicknesses are often juxtaposed by movement on a continental transform boundary such a boundary with a step change in densities may trigger a gravitational instability as lateral pressure gradients are created where normal mantle lithosphere terminates against less dense asthenospheric mantle here we show for plausible values of the lithospheric viscosity a mechanism by which the thicker mantle lithosphere will drip off into the lower density asthenosphere as the mantle deforms it also progressively thickens and then thins the overlying crust creating a topographic wave that migrates in concert with the removal of mantle lithosphere within western north island new zealand geophysical data define a sharp lithospheric step across the taranaki ruapehu line and geological observations provide a history of uplift and subsidence that has propagated southward in the past 12 m y the rate of observed north to south migration of the wave 30 mm yr its wavelength 250 km and amplitude 1 km are compatible with it being caused by progressive removal of mantle lithosphere if the viscosity of the uppermost lithospheric mantle is 5 10 20 pa s providing one of the clearest examples yet of this fundamental geological process

1 8 1 5 ga links between the north and south australian cratons and the early middle proterozoic configuration of australia abstract the archaean and early middle proterozoic 1 8 1 5 ga terranes of the north australian craton and the south australian craton are separated by 400 km of ca 1 33 1 10 ga orogenic belts and phanerozoic sediments however there is a diverse range of geological phenomena that correlate between the component terranes of the two cratons and provide evidence for a shared tectonic evolution between approximately 1 8 and 1 5 ga in order to honour these correlations we propose a reconstruction in which the south australian craton is rotated 52 counterclockwise about a pole located at 136 e and 25 s present day coordinates relative to its current position this reconstruction aligns the ca 1 8 1 6 ga orogenic belts preserved in the arunta inlier and the gawler craton and the ca 1 6 1 5 ga orogenic belts preserved in the mount isa block and the curnamona province before 1 5 ga the south australian craton was not a separate entity but part of a greater proto australian continent which was characterised by accretion along a southward migrating convergent margin ca 1 8 1 6 ga followed by convergence along the eastern margin ca 1 6 1 5 ga after 1 5 ga the south australian craton broke away from the north australian craton only to be reattached in its current position during the ca 1 33 1 10 ga albany fraser and musgrave orogenies

climate changes in northeastern brazil from deglacial to meghalayan periods and related environmental impacts abstract changes in insolation driven by precession and obliquity are considered the major driver of tropical precipitation on orbital time scales and responsible for vegetation and physical landscape changes during the late holocene over tropical south america here we investigate the environmental changes in the karst region of chapada do apodi northeastern brazil neb using a multi proxy approach including carbon 13c oxygen 18o and strontium 87sr 86sr isotopic analyses on speleothems from different caves carbonate bedrock and clastic cave deposits this approach reveals that the balance between soil formation and erosion and their alternating impact on vegetation and precipitation changes occurred in response to variations in the position and intensity of the intertropical convergence zone itcz over the region the high 13c and 18o and low 87sr 86sr values at 4 200 yrs bp indicate a massive episode of soil erosion resulting in the exposure of carbonate bedrocks over a large area of the karst terrain this event marks the beginning of the meghalayan chronozone characterized as the aridification of this region decline in soil production drying out of underground drainages and increased dominance of dry adapted flora species characteristic of a more open vegetation caatinga we investigated if the holocene climatic changes affected human occupation in the neb and found that the overall demographic course is virtually identical to the well established curve characterized by population deflation during middle holocene

origin of bermuda s clay rich quaternary paleosols and their paleoclimatic significance red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the quaternary carbonate formations of the bermuda oceanic island system these paleosols provide a basis for reconstructing quaternary atmospheric circulation patterns in the northwestern atlantic geochemical analyses were performed on representative paleosol samples to identify their parent dust source fine grained fractions were analyzed by energy dispersive x ray fluorescence to determine trace element zr y la ti and nb concentrations and to derive geochemical signatures based on immobile element ratios these ratios were compared with geochemical signatures determined for three possible sources of airborne dust 1 great plains loess 2 mississippi river valley loess and 3 saharan dust the zr y and zr la ratios provided the clearest distinction between the hypothesized dust sources the low ratios in the paleosol b horizons most closely resemble saharan dust in the 2 m size class fraction contributions from the two north american loessial source areas could not be clearly detected thus bermuda paleosols have a predominantly saharan aerosolic dust signature saharan dust deposition on bermuda during successive quaternary glacial periods is consistent with patterns of general circulation models which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30on despite lower than present sea surface temperatures in the north atlantic

new insights into thermal history from single grain 40ar 39ar analysis of biotite single grains of biotite extracted from two hand samples of two granitoid rocks from the red lake greenstone belt of northwestern ontario were examined using a high sensitivity 40ar 39ar laser dating system for variations in age for small grains a striking correlation is seen between the ages and the grain sizes as measured by the cylindrical radii with smaller samples yielding younger ages this effect saturates at a radius of about 225 m above which the integrated age is independent of grain size by combining this grain size effect with biotite diffusion parameters taken from the literature continuous cooling curves were derived for the region these curves suggest the region cooled at a rate of about 0 3 c myr between 2635 and 2570 ma with its ability to define a grain size effect the laser probe mass spectrometer system provides new insight into thermal history

evaluation of electrical resistivity tomography ert for mapping the soil rock interface in karstic environments rocky desertification is a significant threat in the karst regions of southwest china studies of soil distribution can contribute to protecting and recovering the fragile karst ecosystem that is prevalent in this region with an underlying aim of being able to assess soil stocks in karstic environments this study evaluates the use of electrical resistivity tomography ert for delineating the soil rock interface using a synthetic model that recognizes the three dimensional nature of the subsurface experiments are performed to assess the impact of measurement errors and measurement configuration on recovery of the interface the inverted results show that the accuracy of the delineation of the soil rock interface decreases with the increase of measurement error and dipole spacing the results also show the importance of reliable estimation of measurement errors field based applications of ert at five exposed profiles in southwest china are also reported for the field data three dimensional modelling was necessary to account for the exposed face the field experiments show that ert can be effective at delineating the interface between soil and bedrock but resolution can be limited due to the scale of features or lack of contrast between soil and bedrock the method shows great promise as a means of assessing in a non invasive manner the soil bedrock interface and perhaps more significantly quantifying estimates of total soil stocks as we seek to quantify the vulnerability or resilience of this important landscape to anthropogenic and natural stresses

replacement of base metal sulfides by actinolite epidote calcite and magnetite in the ug2 and merensky reef of the bushveld complex south africa interaction of base metal sulfides pyrrhotite pentlandite and chalcopyrite with aqueous fluids in the ug2 chromitite layer and the merensky reef in the western bushveld complex has produced four common replacements 1 replacement of sulfides and orthopyroxene by actinolite or tremolite 2 replacement of sulfides and plagioclase by epidote 3 replacement of sulfides by calcite and 4 replacement of sulfides by magnetite the first three replacements are directly related to the presence of sulfides in the rocks and occur at the grain scale silicate minerals that are not in direct contact with sulfides are usually not affected the replacement of sulfides by magnetite accompanies regional serpentinization superimposed on the union section platinum group minerals including ru pt and pd sulfides pt and pd tellurides and pd arsenides occur in replacement aureoles around sulfide aggregates as well as within the aggregates suggesting that the platinum group minerals are more resistant to hydrothermal alteration than the associated base metal sulfides redistribution of chalcopyrite at least at the millimeter scale variable losses of s and ni and perhaps decoupling of pt and pd at the centimeter scale took place during secondary hydrothermal alteration these effects should be considered before models of primary mineralization processes can be meaningfully applied

soils in the karst landscape of bodoquena plateau in cerrado region of brazil abstract the aim of this study was to evaluate chemical physical mineralogical and micromorphological characteristics of soils in a toposequence formed from carbonate rich material in the karst landscape of bodoquena plateau in brazilian cerrado region in the state of mato grosso do sul as a support for soil classification and pedogenesis the hypothesis was that the limestone and slope shape and position influenced the soil attributes and the genesis also that the parent material and weather conditions of the region could result in an excess accumulation of calcium carbonate in the soils with consequent formation of calcic horizons soil profiles were sampled along a toposequence at the river terrace p1 plain p2 footslope p3 lower backslope p4 middle backslope p5 and shoulder p6 positions the profiles showed a large variation of attributes accordingly to the parent material and landscape position that influenced the degree of weathering and pedogenesis intensity noticeably the sum of bases and cation exchange capacity with maximum values of 30 9 cmolc kg 1 and 32 5 cmolc kg 1 respectively ph in water varying between 6 6 and 9 1 and dominance of quartz in the sand mineralogy with calcite and illite in the clay fraction followed by kaolinite also soils showed a high content of caco3 and micromorphology features such as coatings of pores by acicular calcite the soil classification corroborates the lesser development of the profiles where p1 p4 and p6 were classified as entisols p2 and p3 as alfisols and p5 as molisols

quantum magmatism magmatic compositional gaps generated by melt crystal dynamics compositional gaps are common in volcanic series worldwide the pervasive generation of compositional gaps influences the mechanical and thermal properties of the crust and holds clues on how our planet differentiates we have explored potential mechanisms to generate these gaps using numerical simulations coupling crystallization kinetics and multiphase fluid dynamics of magma reservoirs we show that gaps are inherent to crystal fractionation for all compositions as crystal liquid separation takes place most efficiently within a crystallinity window of 50 70 vol crystals the probability of melt extraction from a crystal residue in a cooling magma chamber is highest in this crystallinity window due to 1 enhanced melt segregation in the absence of chamber wide convection 2 buffering by latent heat of crystallization and 3 diminished chamber wall thermal gradients this mechanical control of igneous distillation is likely to have played a dominant role in the formation of the compositionally layered earth9s crust by allowing multiple and overlapping intrusive episodes of relatively discrete or quantized composition that become more silicic upward

trace and rare earth elements constraints on the sources of the yunfeng paleo karstic bauxite deposit in the xiuwen qingzhen area guizhou china abstract a number of carboniferous paleo karstic bauxite deposits occur in the xiuwen qingzhen area central guizhou province which constitute an important part of the central guizhou southern chongqing bauxite belt in southwestern china these deposits consist of lenticular and stratiform orebodies hosted in the lower carboniferous jiujialu formation which lies unconformably above carbonate rocks mainly dolomite of the middle and upper cambrian loushanguan group shilengshui formation and lower cambrian qingxudong formation although it is generally agreed that the bauxite resulted from weathering of cambrian rocks below the unconformity it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits in this study we examined the mineralogy and major trace and rare earth elements geochemistry of bauxite and bauxitic clays from the yunfeng deposit in the xiuwen qingzhen area and compared them to previously published data of a paleo weathering profile consisting of loushanguan dolomite underlying the sub carboniferous unconformity and the black rock sequence of the lower cambrian niutitang formation in order to evaluate the sources of the bauxite the bauxite ores are composed of diaspore as the main ore mineral along with small amounts of pyrite arsenopyrite galena stibnite xenotime and uranium bearing minerals and are characterized by high contents of uranium and phosphorus chondrite normalized ree patterns and various bivariant diagrams commonly used to study the provenance of bauxite including eu eu vs tio2 al2o3 eu eu vs sm nd tio2 vs al2o3 tio2 th th vs ta th vs nb and nb vs ta suggest that the loushanguan dolomite and the niutitang black rock sequence are both potential source rocks however a comparison in u and th contents between the paleo weathering profile of the loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores instead the black rock sequence may have contributed most of the ore forming materials which are mainly transported from source regions where the niutitang formation was exposed weathered and eroded therefore the yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin

warakurna large igneous province a new mesoproterozoic large igneous province in west central australia coeval mafic igneous rocks emplaced rapidly over 1 5 3 10 6 km 2 in western and central australia represent the erosional rem nants of a late mesoproterozoic large igneous province named here the warakurna large igneous province shrimp u pb dating of rocks separated by as much as 1500 km indicates that the main episode of magmatism occurred between 1078 and ca 1070 ma the warakurna large igneous province includes layered mafic ultramafic intrusions and mafic to felsic volcanic rocks and dikes in central australia a 1000 km long mafic sill province in western australia and several swarms of mafic dikes the large areal ex tent and short duration imply emplacement above a mantle plume head despite their wide separation the mafic rocks have similar mid oceanic ridge basalt normalized trace element patterns and rare earth element characteristics west directed paleocurrents westward radiating dike swarms and the occurrence of high mg rocks indicate that the center of the plume head was located be neath central australia other late mesoproterozoic large igneous provinces in the laurentia and kalahari cratons appear to be significantly older than the warakurna large igneous province in australia and thus are unlikely to be related to the same mantle plume head

behaviour of rare earth elements and yttrium in ferromanganese concretions gibbsite spots and the surrounding terra rossa over dolomite during chemical weathering abstract the behaviour of rare earth elements rees and yttrium y during chemical weathering processes has been investigated on a 4 05 m thick terra rossa profile over dolomite on the yunnan guizhou plateau china in this profile ferromanganese concretions and gibbsite spots coexist in the terra rossa solum analyses of rees y zr f s and toc as well as mineralogical studies were conducted on a suite of ferromanganese concretions gibbsite spots terra rossas dolomites and insoluble residues from the underlying dolomite these analyses helped us to understand the mobilization redistribution and fractionation of rees and y during chemical weathering the rees and y are mobilized and redistributed during the terra rossa formation rees except for ce are removed from the upper and middle profiles transferred downwards and then precipitated in the base profile resulting in remarkable enrichment in the terra rossa near the weathering front the significant increase of ph near the weathering front was responsible for ree excluding ce and y enrichment in the base profile y is quite mobile during extreme chemical weathering and most of it was carried away from the profile because of very efficient oxidative fractionation of ce a significant positive ce anomaly in terra rossa was found in the middle of the profile whereas the terra rossa near the weathering front exhibited notably negative ce anomalies moreover the presence of cerianite and its content in the ferromanganese concretions can explain the markedly positive ce anomaly and the variation of ce ce values with depth in profile these ce anomalies are characteristic of the geochemical environment especially the redox condition studies of ree distribution in the ferromanganese concretions gibbsite spots and surrounding terra rossa revealed that significant ree fractionation occurred rees and y were preferentially concentrated in the ferromanganese concretions rather than in the gibbsite spots the water rock interaction resulted in m type tetrad effects in some of the ferromanganese concretions gibbsite spots and terra rossa samples in addition the tetrad effect in terrestrial weathering processes likely played an important role in the fractionation of rees and y such as y ho sm nd and the eu anomaly change

formation of lateral patterns in rock properties by dolomitization evidence from a miocene reaction front bonaire netherlands antilles abstract petrophysical and geochemical properties of dolomites may exhibit a nested set of lateral patterns typically at the scales of a few meters to 20 m this study assesses whether those lateral patterns are inherited from the limestone precursor or formed during dolomitization sampling was done across a preserved limestone to dolomite reaction front in grainstones of the miocene seroe domi formation bonaire netherlands antilles post dolomitization diagenetic overprinting in the two rock types is absent or minimal two 65 m lateral transects were drilled at 30 cm spacing in two separate beds porosity permeability and geochemical 18o 13c mn sr and na analyses were performed on all 287 recovered samples and 287 thin sections were point counted for petrographic attributes variography shows that dolomite abundance and porosity contain three scales of lateral variability much of the signal is random sample to sample noise as 65 of the total spatial variance occurs at 30 cm spacing however porosity and dolomite abundance also exhibit a short scale correlation length of 3 7 m and a long range oscillatory pattern hole effect at 16 m both of which are also periodic trace elements mn sr and permeability exhibit short range correlation to 5 8 m but no long range pattern mole mg and 13c show increasing variance with distance and all other dolomite attributes exhibit no spatial patterns no limestone attributes show evidence for any short range or long range oscillatory patterns this indicates that the lateral patterns in dolomite abundance porosity permeability sr and mn contents were not inherited from the limestone precursor dolomitization is interpreted to be the cause of the observed spatial patterns as that is the only geologic process that has affected the dolomite but not the limestone on the other side of the front geochemical self organization during the dolomitization process is suggested to be the mechanism by which the spatial patterns in the dolomites emerge a model for that self organizing process is proposed that involves positive feedbacks between precipitation dissolution textural properties reaction rates carbon transport and the evolving flow field relative to mississippian permian and eocene dolomites that have been studied previously the seroe domi dolomites have similar porosity variance at 30 cm spacing and hole effects with slightly greater wavelengths and much larger magnitudes any differences are interpreted to be related to diagenetic history the older dolomites have been affected by burial diagenesis and or weathering which would likely increase sample to sample variability therefore increasing short scale randomness decreasing the magnitude of hole effects and shortening wavelengths of hole effects the lateral patterning formed by dolomitization may thus not be as strongly expressed in ancient dolomites that have complex burial histories

constraints and deception in the isotopic record the crustal evolution of the west musgrave province central australia abstract the hf and nd isotopic evolution of the musgrave province central australia is used to constrain the timing of crust formation and lithospheric organisation of proterozoic australia the dataset from this region challenges two widely held tenets of hf and nd isotope systematics namely that crust formation events can only be identified as periods when crystallisation ages correspond to model ages and that linear hf evolution arrays away from depleted mantle along crustal lu hf or sm nd slopes reflect reworking of the same source hf isotopes in musgrave province zircon crystals indicate two major crust formation events at c 1900 ma and at 1600 1550 ma although no juvenile rocks or crystals are known from c 1900 ma radiogenic addition into the crust at this time is required to account for consistent nd and hf evolution patterns which show no indication of an initially heterogeneous source oxygen isotopes in zircon grains confirm that much of the c 1900 ma hf isotopic signal is not compromised by mixtures furthermore the correspondence between mantle extraction and the commencement of reworking of archean material supports new crust generation at c 1900 ma and a coupling between lower and upper crustal processes the c 1900 ma timing of juvenile addition is dissimilar to that in the albany fraser and arunta orogens and may reflect continental arc development on the margin of a southern continent the general hf isotopic evolution trend of the musgrave province apparently reflects reworking from a dominant c 1900 ma source with some additional unradiogenic and radiogenic input through time however in the 1220 1050 ma interval this apparent isotopic evolution contrasts with geological observations that indicate input of voluminous mantle derived material intracontinental rifts and other regions with sustained very high temperature crustal recycling processes generate magmatic provinces with extreme hfse enrichment this can have a profound influence on isotopic evolution trends suppressing typical juvenile addition patterns isotopic mixture modelling indicates that a significant volume of mantle derived material can be accommodated within hfse enriched magmas without diverging isotopic signatures from apparent reworking trends in the musgrave province the crust had become so hfse enriched during the prolonged musgrave orogeny 1220 1150 ma that it was insensitive to mantle input which is estimated to have been as much as 85 during this event

soils in the mediterranean region what makes them different mediterranean climates are characterized by winter rains with some months of excess rainfall over evatranspiration warm and dry summer months with moisutre deficits drying out soils and their annual vegetation xeric moisture regime they are found on western parts of all continents between the cooler temperature zone and the hot dry desert zone the largest mediterranean region surrounding the mediterranean sea extends over 4 300 000 km2 and exhibits a wide variety of soils and geo ecosystems characteristics landscape attributes are the high proportion of mountains with sleep slopes significant additions of saharan desert dust to practically all soils of the region and a large proportion of limestone and other calcareous rocks as soil parent materials characteristics soil behavior features are moderate weathering with pervection leaching lessivage of mostly 2 1 clays into b horizons xeralfs luvisols hematite induced reddening of the clays due to summer dehydration of free iron oxyhydroxides carbonate dissolution and reprecipitation with prevalence of calcic horizons xerolls calcisols in semiarid regions and development of vertisols mostly in lowlands where deep layers of swelling cracking clays have sedimented shallows soils on nearly bare slopes mostly a result of erosion subsequent to deforestation are frequent leptosols cambiosols inceptisols entisols red or brown mediterranean soils are no longer used as a separate classification group in modern well defined soil property controlled taxonomies soil taxonomy fao system but were partially replaced by duchaufour s term fersiallitic soils in some classification systems terra rossa continues to be used in some classification for hard limestone derived red soils mostly shallow the effects of man s past and current interference with the lanscape are pervasive in most regions and predictions for possible future effects on the soils and ecosystems due to greenhouse gas induced warming and rainfall change are partly negative partly still too uncertain

rare earth and alkali elements in stalagmites as markers of mediterranean environmental changes during termination i abstract speleothems represent a key source of information on climate variations in continental environments as they enable high temporal resolution reconstructions the stalagmite salam3 presented in this study comes from the salamandre cave se france gard region its growth period determined by 230th 234u chronology and mod age extrapolation falls between 10 91 1 00 kyr bp and 13 43 0 25 kyr bp which corresponds to the transition between the last glacial period and the holocene this period is essential for the understanding of past and future climate variations in this study trace elements were measured along the growth axis of this stalagmite and results were compared with the elementary composition of bedrock and soil above the cave three periods were identified with high li rb cs th and rare earth element ree concentrations between 13 43 0 25 and 13 11 0 27 between 12 70 0 34 and 12 30 0 15 kyr and between 11 31 0 86 and 11 15 0 87 kyr our results suggest that the alkali metals alkalis studied are either associated in the detrital phase with the clay and particle fraction correlation with th or with the organic matter and colloids as complexed ligands correlation with mn to attribute the origin of ree measured within the stalagmite we compared their pattern with those of soil and bedrock and two sources were deduced i periods with an enrichment in light ree and no cerium anomaly corresponding to mobilization from soil during weathering episodes such as the bolling allerod period ii from bedrock during a longer residence time of water in the epikarst such as during the younger dryas and the holocene thus as illustrated in this study combined analysis of ree and alkalis can provide key information on soil weathering linked to climate environmental change

magma accumulation rates and thermal histories of plutons of the sierra nevada batholith ca zircon u pb geochronology results indicate that the john muir intrusive suite of the central sierra nevada batholith california was assembled over a period of at least 12 ma between 96 and 84 ma bulk mineral thermochronology u pb zircon and titanite 40ar 39ar hornblende and biotite of rocks from multiple plutons comprising the muir suite indicates rapid cooling through titanite and hornblende closure following intrusion and subsequent slow cooling through biotite closure assembly of intrusive suites in the sierra nevada and elsewhere over millions of years favors growth by incremental intrusion estimated long term pluton assembly rates for the john muir intrusive suite are on the order of 0 001 km3 a 1 which is inconsistent with the rapid magma fluxes that are necessary to form large volume magma chambers capable of producing caldera forming eruptions if large shallow crustal magma chambers do not typically develop during assembly of large zoned intrusive suites it is doubtful that the intrusive suites represent cumulates left behind following caldera forming eruptions

episodic growth and homogenization of plutonic roots in arc volcanoes from combined u th and u th he zircon dating abstract tracing the fate of unerupted magma is challenging because plutonic roots of young volcanoes are largely inaccessible here we develop the use of zircon age spectra to determine crystal provenance and source rocks for volcanic products in analogy to detrital crystals in sediments u th zircon crystallization ages for the soufriere volcanic complex saint lucia lesser antilles frequently predate their eruption as determined from combined u th and u th he zircon dating the oldest dated eruptions are 273 15 ka and 264 8 ka 1 uncertainty for morne bonin dacite and bellevue pumice deposit respectively the most recent eruptions formed morphologically pristine domes in the center of the qualibou depression belfond 13 6 0 4 ka terre blanche 15 3 0 4 ka u th u pb zircon crystallization ages determined for crystal rims and interiors range between near eruption ages to 600 ka older xenocrysts are absent zircon crystallization age distributions are complex yet systematic crystal rim ages in the most recently erupted volcanic rocks match those of co erupted plutonic inclusions whereas crystal interiors are equivalent to the cumulative distribution of zircon ages from older eruptions this is evidence that silicic lava domes and pyroclastic flows share a common source that is located underneath the qualibou depression where the intrusive roots of this long lived arc volcanic system became homogenized through thermal and mechanical reprocessing of individual batches of unerupted magma from earlier volcanic episodes within timescales of

age and origin of terra rossa soils in the coonawarra area of south australia abstract the famous terra rossa soil in the coonawarra area south australia is dominated by locally derived aeolian detritus which probably accumulated over the last 120 130 ka four soil profiles and associated limestone and lunette deposits were investigated using the following methods mass balance geochemistry of bulk soil samples major and trace elements quantitative x ray diffraction xrd mineralogy strontium isotopes 87 86 as well as grain size analysis and cation exchange capacity these data show that the terra rossa soil from the coonawarra has a thick clayey b horizon which is geochemically homogeneous and dominated by smectite and kaolinite mass balance calculations show unrealistic weathering scenarios when plotted using silicate residuum from the underlying limestone as parent realistic weathering scenarios are produced with fine grained silicate material from local lunette deposits as parent strontium isotopes of silicate residuum from gambier limestone 0 78 contrast strongly with the clayey b horizon 0 726 strontium isotope ratios of silicate material from a local lunette 0 725 are similar to the b horizon soil values strontium isotope ratios from regional geological units indicate that the strontium signature in the lunette and soil b horizon is dominated by weathering products from the palaeozoic kanmantoo shales extensively exposed upwind to the west on kangaroo island and the fleurieu peninsula optical optically stimulated luminescence osl dating of 61 individual quartz grains single aliquot from three samples in the coonawarra soil profile one from the a horizon and two from the b horizon shows that most of the quartz sand grains have been buried for only a few thousand years many of the grains however have been buried for tens of thousands of years with three grains having exposure ages of between 105 and 109 ka the large population of young exposure dates represents quartz sands recently exposed in the a horizon and which have been translocated down to the b horizon the older exposure dates are interpreted as representing grains that were buried during or soon after the accumulation of wind blown silt and clay our current model concerning the timing and conditions of aeolian deposition of the coonawarra soil is that much of it accumulated during the relatively wet last interglacial period around 120 130 ka during that time span it is thought that the playa lunette systems in the low lying areas to the west were particularly active and generated a significant local dust flux

the burning heart the proterozoic geology and geological evolution of the west musgrave region central australia the musgrave province is one of the most geodynamically significant of australia s proterozoic orogenic belts lying at the intersection of the continent s three cratonic elements the west north and south australian cratons while remoteness and cultural sensitivity have slowed geological research into this region recent collaborative programs in western australia the west musgrave province have done much to address this this focus review provides a synthesis of this and previous work investigating the mesoproterozoic to neoproterozoic geological evolution of the province the musgrave province is a mesoproterozoic to neoproterozoic belt dominated by granites formed and deformed during several major events a cryptic juvenile basement is exposed mainly in the east musgrave province as c 1600 1550 ma orthogneiss and in the west musgrave province as isolated outcrops of granulite facies metagranites of the c 1575 ma warlawurru supersuite zircon hf isotopic data suggest an earlier major juvenile crust forming event at c 1950 1900 ma there is however no evidence that the province evolved over archean crust the c 1600 1550 ma period probably involved evolution within a primitive arc setting perhaps developed on c 1950 1900 ma oceanic or oceanic arc crust voluminous calc alkaline plutonism was accompanied by clastic and volcaniclastic basin formation during the 1345 1293 ma mount west orogeny this stage traced the evolution of a continental arc reflecting the final amalgamation of the combined north and west australian craton with the south australian craton the intervening c 1400 ma primitive crust the madura province on which the proto musgrave province had evolved was consumed during amalgamation the thickened crust resulting from this accretion was drastically thinned at the beginning of the c 1220 1150 ma musgrave orogeny as this central part of the new combined craton entered an extraordinary period of high heat flow characterised by c 100 m y of ultrahigh temperature metamorphism and high temperature anhydrous alkali calcic magmatism sourced from mash chambers developed at the base of the thinned crust the ridged cratonic architecture and a massive accumulation of high radiogenic heat producing granites within the mid crust perpetuated a thin crustal regime voluminous magmatism was again triggered during the c 1090 1040 ma giles event with the evolution of the magmatism dominated ngaanyatjarra rift this event was likely initiated through renewed movement along translithospheric faults that intersected the thermally perturbed musgrave province pinned at a cratonic junction mantle derived bimodal magmatism extended more or less continuously for 50 m y producing one of the world s largest layered mafic intrusions and supervolcano sized additions of juvenile felsic crust in the form of alkali calcic to alkali a type rhyolite deposits together the albany fraser orogen which developed over the southern margin of the west australian craton and the musgrave province mark the preserved edge of the north and west australian craton these two belts show remarkable chronological links between c 1345 and 1150 ma but contrasting histories before and after that period their period of shared evolution reflects collision and accretion of the south australian craton but their tectonic setting and basement geology throughout that event were very different

the musgrave province stitching north west and south australia abstract the musgrave province in central australia is an east west trending 120 000 km2 region composed of lithologic units that range in age from earliest mesoproterozoic to neoproterozoic it is one of the few terrains in australia that records significant grenvillian aged tectonism and has a distinctly younger geological history than the surrounding fragments of proterozoic australia compared to other proterozoic terranes of australia the evolution of the musgrave province is poorly understood the region contains evidence for the development of earliest mesoproterozoic arc related magmatism with major juvenile crustal additions comprising intercalated felsic and mafic gneisses with protolith ages ranging from ca 1 60 to 1 54 ga this period of arc magmatism was followed by closure of the ocean separating the north australian craton nac from the south australian craton sac at ca 1 54 ga arc magmatism and collision was followed by a period of extension during which protoliths to the metasedimentary rocks of the eastern musgrave province were deposited at ca 1 4 ga the combined juvenile nd isotopic signature and detrital zircon ages from these metasediments suggests provenance from non australian sources with possible sources originating from laurentia granitic magmatic events occurred at ca 1 3 and 1 20 1 14 ga the latter comprising the voluminous a type granites of the pitjantjatjara supersuite the intrusion of these magmatic units provide key temporal constraints on deformational events and are coeval with the voluminous a type suites of laurentia which would invite correlation of australia with laurentia at ca 1 30 1 14 ga these magmatic episodes are accompanied by deformation at granulite facies at ca 1 30 ga unnamed event and 1 23 1 15 ga musgrave orogeny these deformation metamorphic events have completely recrystallised any primary layering within the pre 1 30 ga rocks forcing interpretations on their genesis to be inferred from geochemical and isotopic data the tectonic significance of these events is not clear however they may form part of a larger grenville aged deformational belt extending into the western australian albany fraser province and antarctica emplacement of the voluminous mafic ultramafic giles complex and associated granulite facies metamorphism of the giles event occurred at ca 1 078 ga the layered intrusions of the giles complex are generally fault bound and are considered to represent discrete bodies emplaced in an extensional regime associated with generation of the warakurna large igneous province the ca 1 08 ga alcurra dolerite unnamed ca 1 0 ga olivine dolerites and ca 0 8 ga amata dolerite dissect much of the musgrave province the alcurra dolerite and unnamed olivine dolerite dykes have been proposed as originating from a modified sub continental lithospheric mantle whereas the amata dolerite is proposed to be plume related coinciding with the initiation of rifting creating the centralian superbasin an earliest cambrian intraplate transpressional event is recorded in the ca 550 ma petermann orogeny this resulted in deep crustal exhumation of much of the northern musgrave province from beneath the centralian superbasin with mylonitic deformation recorded at pressures of 12 kbar and temperatures of 700 750 c

understanding cratonic flood basalts the origin of continental flood basalts has been debated for decades these eruptions often produce millions of cubic kilometers of basalt on timescales of only a million years although flood basalts are found in a variety of settings no locale is more puzzling than cratonic areas such as southern africa or the siberian craton where strong thick lithosphere is breached by these large basaltic outpourings conventionally flood basalts have been interpreted as melting events produced by one of two processes 1 elevated temperatures associated with mantle plumes and or 2 adiabatic decompression melting associated with lithospheric thinning in southern africa however there are severe problems with both of these mechanisms first the rifting circumstances of several wellknown basaltic outpourings clearly reflect lithospheric control rather than the influence of a deep seated plume specifically rift timing and magmatism are correlated with stress perturbations to the lithosphere associated with the formation of collisional rifts second the substantial lithospheric thinning required for adiabatic decompression melting is inconsistent with xenolith evidence for the continued survival of thick lithosphere beneath flood basalt domains as an alternative to these models we propose a new two stage model that interprets cratonic flood basalts not as melting events but as short duration drainage events that tap previously created sublithospheric reservoirs of molten basalt formed over a longer time scale reservoir creation existence stage i requires long term e g 1 ma supersolidus conditions in the sublithospheric mantle that could be maintained by an elevated equilibrium geotherm appropriate for the archean a slow thermal perturbation e g thermal blanketing or large scale mantle upwelling or a subduction related increase in volatile content the drainage event stage ii occurs in response to an abrupt stress change in the lithosphere which leads to the initiation and propagation of lithospheric dikes such a model accounts for the short eruption time of flood basalts the evidence for lithospheric control of the eruptions and the continued survival of cratonic lithosphere following these magmatic events the most notable consequence of this model is that it implies the existence of large reservoirs of magma comparable to the eruption volume of flood basalts that have been and are still likely present beneath stable continental lithopshere

pedosediments of karstic sinkholes in the eolianites of ne yucatan a record of late quaternary soil development geomorphic processes and landscape stability abstract the pedogenetic and geomorphic processes controlling soil development in tropical karstic landscapes are still poorly understood we have discovered and studied thick pedosediments in karst pockets developed in late pleistocene lithified calcareous dunes eolianites in the ne coast of the yucatan peninsula the morphological geochemical and mineralogical characteristics of the pocket fills were interpreted as a record of pedogenesis and geomorphic dynamics that shaped the soil mantle during the holocene sand fraction mineralogy and the zr ti ratio indicated a mixed origin of the soil parent material volcanic and granitic metamorphic components redeposited in the lithoral and coastal environments were identified within the soil matrix primary minerals were transformed by weathering and caused desilicification accumulation of clay hydroxy interlayered vermiculite and kaolinite and dithionite citrate bicarbonate extractable iron oxides fed reworked pedofeatures indicative of clay illuviation and redoximorphic processes were observed this set of processes points to a continuous phase of humid pedogenesis several thousand years long in the early middle holocene however the development of thick recalcified pedosediments in the pockets contrasting with the thin background rendzinas requires active soil redeposition during a late phase of geomorphic activity the available accelerator mass spectrometry ams radiocarbon date indicates that the switch of the erosion sedimentation processes could be related to ancient maya land use impact

dust impure calcite and phytoliths modeled alternative sources of chemical weathering solutes in shallow groundwater abstract in highly reactive carbonate terrains that constitute more than one fifth of critical zone landscapes quantifying bedrock weathering processes may require understanding the realities of carbonate mineral impurity on solubility biotically produced minerals as an integral part of leaky biogeochemical cycles and dust deposited minerals as important high surface area first contact solute sources the potential impact of these processes has not been thoroughly investigated as groundwater solutes are mostly thought to be sourced from chemical reactions with soil and bedrock although dust is often viewed as an important delivery mechanism of nutrients to other ecosystems including those in mountain and tropical settings we present results of computer and hand calculated manual inverse modeling of two years of stream water chemistry spanning a dry and a wet year for a groundwater fed headwater stream at the konza tallgrass prairie long term ecological research site in northeastern kansas weathering of the limestone and shale bedrock at the site provide a possible source of solutes to the groundwater fed stream but our modeling suggests an alternate source considering the pathway of groundwater recharge likely encounters highly reactive phases before encountering bedrock we used the mineralogy and geochemistry of local dust collected previously estimates of a possible chemical composition of phytolith containing potassium and an impure calcite representing measured limestone bedrock chemistry to show that chemical reactions with the current dust flux are adequate to account for the groundwater chemistry average annual amounts were about 1 380 kg ha 1 yr 1 dust dissolved 2 80 kg ha 1 yr 1 bedrock carbonate dissolved and 3 320 kg ha 1 yr 1 phytoliths precipitated small amounts of cation exchange were also required to balance the models there were only small differences between the computer and manual inverse models both methods resulted in up to 4 6 times more mass of dust dissolved than bedrock we suggest that dust weathering may be a process that occurs widely considering the ubiquitous dust flux in continental regions significance of research solutes in groundwater and in streams fed by groundwater are thought to be mostly derived from aquifer bedrock and soil water recharging the aquifer this paradigm may fail for landscapes that have been subaerially exposed for 10 s to 100 s of millions of years in terrains where relatively rapid dissolution of minerals dominates such as carbonate mineral dominated rocks like limestone here we test whether dust having high surface area and being the first inorganic solid encountered by meteoric precipitation could provide enough solutes water to reduce the amount of bedrock that dissolves extending the timeframe of landscape evolution we found through inverse modeling with phreeqc that dust can provide 4 6 times as much mass to stream water in merokarst than calcite and that the mass of dust dissolved was the same order of magnitude as local dust deposition these results give permissive evidence that dust is important to understanding groundwater chemistry

implications of replacement for reaction transport modeling abstract mineral replacement in rocks consists of growth of guest mineral and dissolution of host the two reactions are coupled by the grain grain stress generated by growth of the guest grain in a rigid or very viscous rock in which it has initially no available room this stress self adjusts to make the volumetric rates of guest growth and host dissolution equal to each other which accounts for the volume conservation typical of replacement volume preservation during replacement is required by conservation of mass and momentum as well the two reactions are also simultaneous and proceed by a sequence of many tiny alternating increments where these increments are small enough internal textural details of the host grain or grain aggregate are morphologically preserved as ghost textures by the replacement the strong variation of mineral reaction rates with stress required by replacement is evidenced also experimentally reported widespread replacement in many rocks laterites diagenesis of siliciclastics and carbonates metasomatic ores metamorphic rocks and hydrothermal alteration warrants creating water rock reactive transport models that predict when and where in a system replacement should take place current geochemical models implicitly view replacement as sequential uncoupled dissolution of host and growth of guest this sequence of reactions may also occur in rocks but crucially differs from replacement implications of replacement for water rock reaction modeling include 1 balancing of replacement reactions on volume 2 use of helmholtz rather than gibbs free energies of minerals involved in replacement 3 taking account of the strong stress dependence of mineral growth and dissolution rates in rocks and 4 taking account of possible accommodation of growth by local deformation as well as pressure solution of the host rock and of the effect of strain rate growth rate on local rock viscosity

mapping and defining sources of variability in bioavailable strontium isotope ratios in the eastern mediterranean abstract the relative contributions of bedrock and atmospheric sources to bioavailable strontium sr pools in local soils was studied in northern israel and the golan regions through intensive systematic sampling of modern plants and invertebrates to produce a map of modern bioavailable strontium isotope ratios 87 sr 86 sr for regional reconstructions of human and animal mobility patterns the study investigates sources of variability in bioavailable 87 sr 86 sr ratios in particular the intra and inter site range of variation in plant 87 sr 86 sr ratios the range of 87 sr 86 sr ratios of plants growing on marine sedimentary versus volcanic geologies the differences between ligneous and non ligneous plants with varying growth and water utilization strategies and the relative contribution of atmospheric sr sources from different soil and vegetation types and climatic zones results indicate predictable variation in 87 sr 86 sr ratios inter and intra site differences in bioavailable 87 sr 86 sr ratios average of 0 00025 while the range of 87 sr 86 sr ratios measured regionally in plants and invertebrates is 0 7090 in pleistocene calcareous sandstone and 0 7074 in mid pleistocene volcanic pyroclast the 87 sr 86 sr ratios measured in plants growing on volcanic bedrock show time dependent increases in atmospheric deposition relative to bedrock weathering the 87 sr 86 sr ratios measured in plants growing on renzina soils depends on precipitation the spacing between bedrock 87 sr 86 sr ratios and plants is highest in wet conditions and decreases in dry conditions the 87 sr 86 sr ratios measured in plants growing on terra rossa soils is relatively constant 0 7085 regardless of precipitation ligneous plants are typically closer to bedrock 87 sr 86 sr ratios than non ligneous plants since the bioavailable 87 sr 86 sr ratios currently measured in the region reflect a mix of both exogenous and endogenous sources changes in the relative contribution of exogenous sources can cause variation over time precipitation the age of the bedrock and the overall sr concentration must to be taken into consideration when interpreting geographical variation in strontium isotopes throughout a region because these factors can change through time we recommend that sr data from time periods older than the holocene be interpreted with caution

evidence for the development of a superpermeability flow zone by bioturbation in shallow marine strata upper jubaila formation central saudi arabia abstract superpermeability super k flow zones in carbonate reservoirs are thought to be controlled by bioturbation related burrow networks e g burrow pores of thalassinoides to improve the current understanding this study investigated thalassinoides and associated passive fill in the upper jubaila member of the upper jurassic jubaila formation central saudi arabia analysis of the elemental and mineralogical compositions of powder samples from the passive fill and burrow matrix and thin sections of selected burrow matrix samples were conducted to determine the origin of the passive fill the goal herein is to infer the flow properties of the bioturbated strata of the upper jubaila member based on the occurrence of this passive fill in the burrow pores of the thalassinoides compared to the burrow matrix the analyzed passive fill exhibit marked differences in elemental composition suggesting a much younger and different origin than that of the marine carbonates of the upper jubaila member a cao plus mgo concentration below 28 and an elevated sio2 plus al2o3 concentration above 45 suggest a clay dominated passive fill the reddish and brownish colorations of the passive fill are attributed to the presence of iron oxyhydroxides as indicated by the elevated fe2o3 concentration a mean of 5 8 1 7 and a mineralogical composition with elevated percentages of goethite and hematite the normalized rare earth element ree pattern of the passive fill is consistent with that of lithogenous siliciclastic sources which are likely deposited in a well oxygenated environment as suggested by the redox sensitive elements and normalized rees these sources probably originate in hot humid environment as indicated by the chemical index of alteration cia 80 the above geochemical data suggest that the passive fill was derived from soils similar to mediterranean terra rossa soils and postdate the formation of burrow pores in the thalassinoides bearing strata this could have occurred after exposure of the upper jubaila member terra rossa soil most likely reached the thalassinoides bearing strata from the surface through vertical fractures and karst features filled burrow pores fractures along bedding plains and even intercrystalline pores the occurrence of terra rossa soil in the burrows and intercrystalline pores of the thalassinoides bearing strata implies that the pore system of the upper jubaila member possessed connected pathways that enabled soil infiltration followed by simultaneous precipitation in the burrows and intercrystalline pores the presence of these connected burrow pores containing shafts with diameters ranges from 1 to 5 cm suggests a superpermeable storage capacity and presence of a superflow unit in the upper jubaila member this study provides an excellent example to better understand the controls of super k zones in carbonate reservoirs

diagenetic replacement controlled by force of crystallization many diagenetic replacements in sedimentary rocks occur along thin solution films between the authigenic and host phases rather than conventionally invoking bulk pore water undersaturation for host phase dissolution we propose that many diagenetic replacements occur by a force of crystallization controlled replacement mechanism whereby nonhydrostatic stresses resulting from authigenic crystal growth are principally responsible for host phase dissolution this model explains diagenetic features such as the restriction of host phase dissolution to authigenic host crystal contacts and euhedral authigenic crystal faces in planar contact with unreplaced host phases as well as the relative replacement tendencies of some common authigenic minerals

elemental and strontium isotopic geochemistry of the soil profiles developed on limestone and sandstone in karstic terrain on yunnan guizhou plateau china implications for chemical weathering and parent materials abstract the limestone and yellow sandstone soil profiles from sw china were measured for chemical and sr isotope compositions of the bulk soils and their sequential leachates labile carbonate and residue or silicate fraction aiming to characterize the parent materials of the soils to understand the soil weathering and formation processes and to discuss the origin of the red residua terra rossa the studied yellow sandstone soil yellow limestone soil and black limestone soil show different ph values sio 2 contents rb sr abundance ratios and 87 sr 86 sr ratios the sequential leachates of different soil types also have different 87 sr 86 sr and ca sr ratios the major chemical compositions of the studied soil profiles suggest that all the sandstone and limestone soils are developing at a stage that feldspar is exhausting and the clay minerals are changing from smectite to kaolinite and gibbsite as compared with the red residua distributed in the karst region the soils studied here show lower cia values 58 84 but both higher na 2 o k 2 o 0 9 2 7 and na 2 o al 2 o 3 concentration ratios 0 07 0 26 on average suggesting a lower weathering intensity than that of the red residua the depth profiles of soil cia values na 2 o k 2 o and rb sr ratios and 87 sr 86 sr ratios indicate that the weathering intensity is slightly lower for the upper and higher for the deeper soils which suggest that the sandstone and limestone soil profiles were formed through both accumulation and weathering of in situ weathering residue and input of external detritus or soil from upper land during weathering of the soils preferential release of ca and retention of sr in soil result in higher ca sr ratios in both labile and carbonate fractions than those in the residue fractions of all soil profiles the co variations of hf nb and zr nb ratios together with those rb sr and 87 sr 86 sr ratios of limestone soils sandstone soils and the red residua demonstrate that their parent materials are distinct and support the point that the widely distributed red residua is originated from the weathering residua of both carbonate and silicate clastic rocks and further weathering of the weathering residua resulted in intensive release of si na ca and relative enrichment of al k and other immobile elements in the red residua

origin and evolution of fault controlled hydrothermal dolomitization fronts a new insight abstract dolomitization is one of the most significant diagenetic reactions in carbonate systems occurring where limestone caco3 is replaced by dolomite camg co3 2 under a wide range of crystallization temperatures and fluids the processes governing its formation have been well studied but the controls on the position of dolomitization fronts in ancient natural settings particularly in a fault controlled hydrothermal system htd have received remarkably little attention hence the origin and evolution of htd dolomitization fronts in the stratigraphic record remain enigmatic here a new set of mineralogical and geochemical data collected from different transects in a partially dolomitized cambrian carbonate platform in western canada are presented to address this issue systematic patterns of sudden decrease in the magnesium content mol mgco3 and increase in porosity were observed towards the margin of the body furthermore fluid temperatures are cooler and 18 owater values are less positive at the dolomitization front than within the core of the body these changes coincide with a change from poorly ordered planar e dolomite with multiple crystal zonations at the margin to an unzoned well ordered interlocking mosaic of planar s to nonplanar dolomite in the core of the body these phenomena are hypothesized to reflect dynamic self limiting processes in the formation and evolution of htd dolomitization fronts through i plummet of dolomitization potential at the head of dolomitizing fluids due to progressive consumption of magnesium and fluid cooling and ii retreat of dolomitization fronts towards the fluid source during subsequent recrystallization of the dolomite body inboard of the termination once overdolomitization took place this new insight illustrates how dolomitization fronts can record the oldest phase of dolomitization instead of the youngest as is often assumed formation of porosity is interpreted to occur as the result of acidification induced grain leaching during the development of dolomitization fronts this mechanism coupled with retrogradation of dolomitization fronts may help to explain the apparent enhancement of porosity in proximity to dolomitization fronts

residence resorption and recycling of zircons in devils kitchen rhyolite coso volcanic field california zircons from the devils kitchen rhyolite in the pleistocene coso volcanic field california have been analyzed by in situ pb u ion microprobe shrimp rg and by detailed cathodoluminescence imaging the zircons yield common pb corrected and disequilibrium corrected pb u ages that predate a previously reported k ar sanidine age by up to 200 kyr and the range of ages exhibited by the zircons is also approximately 200 kyr cathodoluminescence imaging indicates that zircons formed in contrasting environments most zircons are euhedral and a majority of the zircons are weakly zoned but many also have anhedral embayed cores with euhedral overgrowths and multiple internal surfaces that are truncated by later crystal zones concentrations of u and th vary by two orders of magnitude within the zircon population and by 10 20 times between zones within some zircon crystals indicating that zircons were transferred between contrasting chemical environments a zircon saturation temperature of 750 c overlaps within error a previously reported phenocryst equilibration temperature of 740 25 c textures in zircons indicative of repeated dissolution and subsequent regrowth are probably caused by punctuated heating by mafic magma input into rhyolite the overall span of ages and large variation in u and th concentrations combined with calculated zircon saturation temperatures and resorption times are most compatible with crystallization in magma bodies that were emplaced piecemeal in the crust at coso over 200 kyr prior to eruption and that were periodically rejuvenated or melted by subsequent basaltic injections

synchronization of dissolution and precipitation fronts during infiltration driven replacement in porous rocks coupled dissolution precipitation reactions where two minerals share a common ion occur frequently in geological replacement the reactions are driven by an inflow of precipitating secondary ions and an outflow of dissolved primary ions although crystallization pressure is frequently invoked to explain volume preserving replacement it cannot be operative if the chemical reactions lead to a loss of mineral volume here the host rock that should confine the precipitating mineral is dissolving faster than the grains are growing in this paper we propose two chemical mechanisms by which a rapid dissolution front and a slower precipitation front can be synchronized and volume for volume replacement preserved we analyze these mechanisms within the framework of reactive transport theory and show that morphological features observed in calcite replacement can be correlated with predictions of the models

on ferroan a type granitoids their compositional variability and modes of origin we recognize eight types of ferroan granitoid that can be distinguished on the basis of major element chemistry these include alkalic granitoids that may be metaluminous or peralkaline alkali calcic granitoids that may be metaluminous peraluminous or peralkaline calc alkalic granitoids that may be metaluminous or peraluminous and rare calcic ferroan granitoids these granitoids may form by two distinct end member processes extreme differentiation of basaltic melts results in ferroan granitoids that are either peralkaline alkalic and alkali calcic or metaluminous alkalic alkali calcic and calc alkalic with alkalinity increasing with increasing pressure of differentiation partial melting of tonalitic to granodioritic crust produces alkali calcic to calc alkalic granitoids that are metaluminous at low pressures and peraluminous at high pressures it is likely that a combination of these two processes plays some role in the formation of most ferroan granitoids most granitoids that are referred to as ferroan however the term has become more confusing than edifying because it has been applied to a broad spectrum of granitoid compositions with varying petrogenesis for this reason we recommend that the term be discontinued and ferroan used in its stead

controls on denudation rates in tectonically stable mediterranean carbonate terrain using cosmogenic isotopes and solute load analysis we quantify chemical weathering solutional erosion and denudation rates over variable time scales in a tectonically stable moderate relief carbonate terrain soreq drainage judea hills israel located in a semihumid mediterranean climate long term 10 4 yr denudation rates were calculated from 36 cl concentrations in 51 bedrock and sediment samples bedrock samples range in elevation 340 850 m hillslope gradient 0 30 and mean annual precipitation map 500 630 mm and vary in soil cover thickness 0 75 cm mg ca ratio 0 0 1 0 mol clay mineral contents 0 6 wt and mechanical strength 41 58 schmidt hammer rebound units soil pco2 values at a single location during the course of 1 yr range between 0 4 and 9 0 mmol mol 1 average long term denudation rate of exposed bedrock samples is 21 7 mm k y 1 field observations and 36 cl measurements indicate that soil pockets undergo cycles in the rate of deepening and that over 10 5 yr time scale average denudation rates beneath soil pockets are similar to those of exposed bedrock sediment samples yield even higher denudation rates which are probably anthropogenically induced but could also indicate that the sediment source is soil pockets long term denudation rates are decoupled from hillslope gradient elevation and rock strength denudation rates show a positive correlation with present day map values exhibit a complex relation with rock mg content and show a weak correlation with clay content annual chemical weathering rates were calculated from modern day solute load measured in waters of perched springs and the regional carbonate aquifer our results indicate that on annual decadal and 10 4 yr time scales chemical weathering and denudation are controlled by carbonate dissolution while mechanical processes are far less signifi cant overlap between the distributions of hco3 concentrations measured in runoff springs and the regional aquifer water suggests that chemical weathering focuses at the bedrock surface and therefore is comparable with solutional denudation this result is in contrast to the features of ancient fl uvial and colluvial activity steep nonconcave hillslopes and stream profi les and knickzones in the streams preserved in the present landscape such features were formed in response to mid pleistocene uplift and could have been preserved due to a decrease in stream power following the formation of subsurface drainage and the lowering in abrasive clast supply that followed the stabilization of hillslopes in the drainage long term denudation rates calculated from exposed bedrock samples are higher by factor of 1 4 relative to annual contemporary chemical weathering rates increased precipitation by a similar factor averaged over the last glacial and present interglacial can explain this difference

the sahara east mediterranean dust and climate connection revealed by strontium and uranium isotopes in a jerusalem speleothem this paper explores the potential of sr and u isotope systems in speleothems as tracers of eolian dust transport and hydrological conditions the study focuses on a speleothem from jerusalem spanning the past 220 kyr this speleothem provides a precisely dated record of dust flux from the sahara to the east mediterranean enhanced dust flux and terra rossa soil development are reflected by elevated 87sr 86sr ratios in the speleothem 0 7082 0 7086 while lower 87sr 86sr ratios 0 7078 indicate higher contribution of the local bedrock due to low dust flux and low soil accumulation the strontium isotope system in the speleothem is a robust monitor of the sahara monsoon modulated climate since dust uptake is related to development or reduction in vegetation cover of sahara soil the 234u 238u activity ratios in the speleothem range between 1 12 and 1 0 the high activity values may indicate selective removal of 234u from the soil while the low values converge to the bedrock the migration of 234u to the cave reflects mainly the regional hydrological conditions that are modulated by the north atlantic mediterranean climate system thus the speleothem provides a combined record of the monsoon north atlantic climatic systems long term stability in glacial 87sr 86sr ratios 0 7083 0 0001 over the past 220 kyr suggests an overall similarity in eolian dust sources and uniformity in the synoptic conditions that dominate the dust storm tracks during glacial periods

contrasting punctuated zircon growth in two syn erupted rhyolite magmas from tarawera volcano insights to crystal diversity in magmatic systems abstract two mineralogically and chemically distinct rhyolite magmas t1 and t3 were syn erupted from the same conduit system during the 21 9 ka basalt intrusion triggered okareka eruption from tarawera volcano new zealand high spatial resolution u th disequilibrium dating of zircon crystals at the 3 5 m scale reveals a protracted yet discontinuous zircon crystallization history within the magmatic system both magma types contain zircon whose interiors predate the eruption by up to 200 ka the dominant age peak in the t1 magma is 30 ka with subordinate peaks at 45 75 and 100 ka whereas the t3 magma has a dominant zircon interior age peak at 90 ka with smaller modes at 35 and 150 ka these patterns are consistent with isolated pockets of crystallization throughout the evolution of the system crystal rim analyses yield ages ranging from within error of the eruption age to at least 90 ka prior to eruption highlighting that zircon crystallization frequently stalled long before the eruption continuous depth profiling from crystal rims inward demonstrates protracted growth histories for individual crystals up to 100 ka that were punctuated by asynchronous hiatuses of up to 30 ka in duration disparate zircon growth histories can result from localized thermal perturbations caused by mafic intrusions into a silicic reservoir the crystal age heterogeneity at hand sample scale requires considerable crystal transport and mixing we propose that crystal mixing was achieved through buoyancy instabilities caused by mafic magma flow through crystal mush a terminal pre eruptive rejuvenation event was capable of mobilizing voluminous melts that erupted but was too short

petrography and composition of authigenic feldspars oligocene frio formation south texas abstract detrital feldspar assemblages 1 to 4 km burial depth in oligocene sandstones from south texas are extensively altered by dissolution in some samples cementation in secondary pores principally by albite but also by authigenic k feldspar and other minerals occurs subsequent to the dissolution and can lead to wholesale replacement textures solid state diffusion of cations has not been important in the replacement process information from conventional light microscopy sem examination and back scattered electron imaging suggests that relative rates of dissolution versus replacement varied widely among different detrital grains through time even on the scale of a thin section dissolution of detrital feldspars and precipitation of relatively pure albite and k feldspar take place ver a large depth interval and thus can be markedly separated in time vacuolized albite occurring as irregular veins within detrital grains is associated with little visible secondary porosity and forms when precipitation is rapid relative to dissolution of the detrital grain more rapid dissolution results in formation of larger scale intragranular secondary pores commonly filled by subsequent precipitation of clear albite within the former grain volume electron microprobe analyses show that the composition of vacuolized albite and authigenic k feldspar deviate somewhat from ideal compositions presumed typical for authigenic feldspars regardless of their cause these subtle variations in composition have important ramifications for basin scale mass balance calculations requiring accurate estimates of the volume of authigenic feldspar

constraints on crystal storage timescales in mixed magmas uranium series disequilibria in plagioclase from holocene magmas at mount hood oregon abstract uranium series crystal ages interpreted within a textural and geochemical framework can provide insight into crystal storage timescales especially in cases where crystals may derive from multiple sources we report here 230 th 226 ra model ages of two distinct populations of plagioclase from low silica dacites from mount hood oregon a volcano where previous studies show that the compositions of erupted magmas are controlled by magma recharge mixing and incorporation of plagioclase derived from mafic and silicic end member magmas we have measured trace element concentrations and 238 u 230 th 226 ra disequilibria in four plagioclase size fractions from the timberline 1500 a and old maid 215 a eruptive sequences after correction for groundmass and apatite contamination average 230 th 226 ra model ages of large 500 m plagioclase are 4 5 ka timberline and 5 5 ka old maid with ages of cores that are 10 ka in each case indicating that plagioclase derived from silicic magmas crystallized thousands of years before eruptions these model ages are longer than timescales of repose between eruptions indicating that these crystals resided in the sub surface over multiple eruptions likely stored in a silicic crystal mush zone that periodically interacts with mafic recharge magmas remobilizing a fraction of the large plagioclase crystals during each eruptive event after correction for large plagioclase contamination small 226 ra ba relative to equilibrium with liquid proxies groundmass and mafic inclusion leading to 230 th 226 ra model ages that are 230 th 226 ra disequilibria require that the majority of crystals in the separate are young 226 ra ba could potentially be explained by rapid crystallization immediately prior to and or during mixing events consistent with evidence of rapid crystallization of rims rapid crystallization of mafic intrusions may trigger eruption at mount hood by producing a partially crystalline mafic magma capable of mixing with a reheated silicic crystal mush

the potential influence of dust flux and chemical weathering on hillslope morphology convex soil mantled carbonate hillslopes in the eastern mediterranean abstract convex soil covered hillslopes are ubiquitous in various tectonic and climatic settings and their morphologic characteristics can be significantly altered by dust flux and chemical weathering carbonate hillslopes across the eastern mediterranean display a classic convex morphology despite high rates of dust deposition which are apparently similar in magnitude to denudation rates and despite a highly soluble bedrock lithology these high rates of dust flux and bedrock dissolution result in soil composition which is strikingly different from the underlying bedrock in this study we apply a modified regolith mass balance equation which includes dust input and chemical depletion and utilize a combination of field work and geochemical methods immobile and major elements xrd to estimate the fraction of dust derived materials in the soil and the fraction of the soil that was lost via dissolution soil and bedrock were sampled at 7 eastern mediterranean study sites across a prominent north to south gradient in both precipitation 250 to 900 mm yr 1 and dust flux 150 to 40 g m 2 yr 1 and compared with dust composition our results indicate that the dust fraction in the soil correlates with modern measurements of dust deposition rates and decrease from nearly 100 of the 2 mm indicating that mechanical weathering of the underlying bedrock contributes to regolith formation and plays a role in shaping carbonate hillslopes using a commonly used soil transport model we show that the observed dust fraction and chemical weathering can potentially account for a 50 change in hillslope curvature furthermore the predicted steady state hilltop curvature based on our results fits well the observed curvature based on high resolution lidar derived topographic data our results highlight the potential importance of dust and chemical weathering in soil production formulations and hillslope evolution models and we propose that these contributors to soil mass balance could also be relevant for silicate terrain in addition we also demonstrate that the source material of mediterranean soils varies with environmental factors such as rainfall dust deposition rates and bedrock mechanical properties

constraints on the nature of the subvolcanic reservoir at south sister volcano oregon from u series dating combined with sub crystal trace element analysis of plagioclase and zircon abstract we present sub crystal scale 238u 230th zircon ages and 238u 230th 226ra plagioclase ages of bulk mineral separates from the holocene 2 0 2 3 ka eruptions of the rock mesa rm and devil s hills dh rhyolites at south sister volcano oregon we link these age data with sub crystal trace element analyses of zircon and plagioclase to provide insight into the subvolcanic system at south sister as an example of a small volume continental arc volcano our results document the presence of coeval yet physically distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed zircons from the rm and dh dominantly record ages from 20 to 80 ka with some grains recording ages 350 ka whereas plagioclase records 230th 226ra ages of 2 3 6 8 ka rm and 4 0 9 6 ka dh 3 and a 238u 230th age of 10 34 ka dh 3 we interpret zircons with ages 50 ka within a heterogeneous magmatic system and coexisted as physically distinct dominantly liquid bodies prior to eruption thus we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous largely crystalline reservoir similarities in crystal age and chemical data to that at other young silicic systems e g mount st helens okataina caldera complex suggest that this model may be more generally applicable to silicic magmas

snake river sr type volcanism at the yellowstone hotspot track distinctive products from unusual high temperature silicic super eruptions a new category of large scale volcanism here termed snake river sr type volcanism is defined with reference to a distinctive volcanic facies association displayed by miocene rocks in the central snake river plain area of southern idaho and northern nevada usa the facies association contrasts with those typical of silicic volcanism elsewhere and records unusual voluminous and particularly environmentally devastating styles of eruption that remain poorly understood it includes 1 large volume lithic poor rhyolitic ignimbrites with scarce pumice lapilli 2 extensive parallel laminated medium to coarse grained ashfall deposits with large cuspate shards crystals and a paucity of pumice lapilli many are fused to black vitrophyre 3 unusually extensive large volume rhyolite lavas 4 unusually intense welding rheomorphism and widespread development of lava like facies in the ignimbrites 5 extensive fines rich ash deposits with abundant ash aggregates pellets and accretionary lapilli 6 the ashfall layers and ignimbrites contain abundant clasts of dense obsidian and vitrophyre 7 a bimodal association between the rhyolitic rocks and numerous coalescing low profile basalt lava shields and 8 widespread evidence of emplacement in lacustrine alluvial environments as revealed by intercalated lake sediments ignimbrite peperites rhyolitic and basaltic hyaloclastites basalt pillow lava deltas rhyolitic and basaltic phreatomagmatic tuffs alluvial sands and palaeosols many rhyolitic eruptions were high mass flux large volume and explosive vei 6 8 and involved h2o poor low 18o metaluminous rhyolite magmas with unusually low viscosities partly due to high magmatic temperatures 900 1 050 c sr type volcanism contrasts with silicic volcanism at many other volcanic fields where the fall deposits are typically plinian with pumice lapilli the ignimbrites are low to medium grade non welded to eutaxitic with abundant pumice lapilli or fiamme and the rhyolite extrusions are small volume silicic domes and coulees sr type volcanism seems to have occurred at numerous times in earth history because elements of the facies association occur within some other volcanic fields including trans pecos texas etendeka parana lebombo the english lake district the proterozoic keewanawan volcanics of minnesota and the yardea dacite of australia

quartz grain surfaces a potential microarchive for sedimentation processes and parent material identification in soils of jordan abstract using sem supported microsurface and analytical methods we studied quartz and rare feldspar grains of the sand fraction 250 m from three soil profiles in jordan the soils including a lithosol are of different maturity and diagenetic alteration of their bed rocks which are sandstone limestone and basalt the profiles had been investigated during projects on the environmental history of the region whereas the quartz grain surface analysis qgsa that has been applied for the first time to jordan soils is an essential part of a supplementary study that was initiated when findings of unusual mineral components in a red basalt soil raised questions of their source and the history of this soil the major transport processes and environments that were reconstructed for the sandstone regosol and the red mediterranean soil rms on early tertiary limestone are documented by successions and types of grain morphological features that apparently reflect varying water dynamics partly alternating with aeolian motion a result which matches with the known sedimentary history of their bedrocks and supports the reliability of the quartz grain surface analysis qgsa the microtexture pattern for the exotic quartz grain community in the basalt soil on an early quaternary basaltic rock showed a high similarity to those of the limestone samples part of the quartz grains from the basalt soil turned out to be chert as is present in the rms profile and was an essential indication for the source of quartz a sufficient explanation for the presence of quartz is that the outcropping weathered eocene umm rijam chert limestone formation among them chert nodules was reworked and transported to the top of the weathering basalt while a feldspar grain from the sandstone regosol shows a conformable pattern to the quartz grains plagioclase single grains from the red basalt soil in contrast are primary mineral components of the source rock these preserved plagioclases exhibit only minor features of chemical weathering corresponding to the young non diagenetic bedrock the size of the grains and situation of the basalt cap in the landscape as well as preliminary dating suggest a period of heavy storms in jordan at some time during the pleistocene

mineral growth in rocks kinetic rheological models of replacement vein formation and syntectonic crystallization abstract we model three cases of coupling between mineral growth kinetics and mechanical response of the rock i dispersed spherical crystals growing by replacement in a hydrostatically stressed elastic rock ii growth of veins or vein networks accommodated by viscous relaxation of surrounding rock and iii syntectonic crystallization in a rock undergoing bulk pure shear such models for the microscopic environment of mineral growth together with additional assumptions or knowledge about rheological behavior and aggregate geometry provide refined estimates of the behavior of a macroscopic volume element which could be combined with geochemical reaction transport models crucial in the models are the various consequences pressure solution creep fracturing of the local stress that is necessarily generated by mineral growth in rocks other than in pores in the first model the dispersed spherical crystals of mineral a are assumed to grow within a spherical volume of rock consisting of mineral b the mineralized zone mz itself embedded in elastic rock the macroscopic stress in the mz and the far field stress in the surrounding rock are uniform and hydrostatic mineral growth of the a crystals is driven by supersaturation with respect to mineral a is accommodated by replacement of b grains and leads to an expansion of the mz described by an infinitesimal strain the radial growth rate of a spherical crystal of mineral a with replacement of mineral b is da dt k a r tln a k b v 0 b k b v 0 b k a v 0 a where ka and kb are kinetic constants r is the gas constant t the temperature in kelvin and v0a and v0b are specific volumes reference saturation states of mineral a a 1 and host mineral b b 1 are specified at the far field hydrostatic stress 0 the microscopic environment of each crystal of a is modeled by a representative volume element rve consisting of a sphere of mineral a embedded in a spherical shell of mineral b in each rve stress is neither uniform nor hydrostatic the model links the local microscopic stress with the macroscopic stress in the mz and surrounding rock the second model refers to veins that make room for themselves by growing not to veins that form by cementation of previously opened or opening cracks if the growth of mineral a as propagating veins or as an interconnected vein network takes place by deformation and expansion of the mz with the deformation itself driven by the stress arising from the supersaturation driven growth the surrounding rock undergoes deformation and is treated as viscous the rate of growth in vein width w is dw dt 2 k a rtln a sv 0 a 1 m where m 16 kav0ac2 3b3 is the medium viscosity c is the vein radius and each vein is treated as centered in a spherical rve of radius b s is an effective tensile stress required for vein propagation for a vein network in which veins surround equant polyhedra of rock of radius b we set c b and drop the term in s for simplicity veins may also widen by replacement the ratio of vein widening by expansion to that by replacement is dw dt expansion dw dt replacement 3 b 16 3 b 16 k a v 0 a k b v 0 b k b v 0 b k a v 0 a both mechanisms of accommodation contribute equally when 3b 16kbv0b at higher viscosity replacement is dominant the incipient growth of a cylindrical crystal with circular cross section in a medium deforming in pure shear simulates syntectonic crystallization both dissolution and deformation of the host accommodate growth in the model the crystal tends to grow faster in the direction of maximum rate of extension in this direction the host mineral may either dissolve to accommodate growth or precipitate to form a pressure shadow accommodation by host dissolution is greatest in the direction of maximum rate of shortening

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

terra rossa genesis implications for karst and eolian dust a geodynamic thread abstract although terra rossa has long been thought to form by residual dissolution of limestone and or by accumulation of detrital mud ash or dust on preexisting karst limestones we present conclusive new field and petrographic evidence that terra rossa forms by replacement of limestone by authigenic clay at a moving metasomatic front several centimeters wide the red clay s major chemical elements al fe and si probably come from dissolved eolian dust the replacement of calcite by clay exhibits a serrated microstylolitic texture that helps prove that replacement happens not by dissolution precipitation as conventional wisdom has it but by pressure solution of calcite driven by the crystallization stress generated by the growth of clay crystals the acid produced by the isovolumetric replacement of limestone by clay quickly dissolves out additional porosity permeability in an adjacent slice of limestone within the front triggering a reactive infiltration instability that should theoretically

tectonic evolution of proterozoic australia proterozoic australia has long been interpreted as a single intact continent in which all tectonic and magmatic activity was intracratonic this paper proposes an alternative hypothesis in which numerous fragments of continental crust were assembled by plate tectonic processes the assembly was completed between 1300 and 1100 ma when the crustal fragments were combined as an early component of the rodinian supercontinent rifting and fragmentation of archaean continents began in the late archaean and continued into the proterozoic passive margin deposits such as those of the hamersley basin accumulated on isolated fragments of archaean crust these numerous fragments were subsequently assembled into three cratons by 1830 ma a west australian craton was established by collision of the archaean pilbara and yilgarn cratons which were joined along the capricorn orogen similarly a south australian craton developed by amalgamation of the proto gawler and proto curnamona cratons along the kimban orogen a north australian craton appears to have formed by accretion of numerous crustal fragments including the kimberley pine creek lucas and altjawarra cratons with sutures marked by the king leopold halls creek tennant creek and proto isan orogens the southern margin of the north australian craton was the site of repeated terrane accretion and orogenic activity between 1880 ma and 1400 ma this included an orogenic event at 1880 1850 ma the strangways 1780 1730 ma argilke 1680 1650 ma and chewings 1620 1580 ma orogenies and the intracratonic anmatjira uplift 1500 1400 ma intracratonic rifting at 1750 to 1710 ma and 1640 to 1600 ma produced the mcarthur basin and related minor basins parts of which were deformed by the isan orogeny at 1600 and 1530 ma rifting along the line of the capricorn orogen led to deposition in the overlying intracratonic bangemall basin between 1630 and 1300 ma along the eastern margin of the south australian craton the 1670 to 1600 ma olarian orogeny marks interaction with now obscured continental crust to the east tectonic activity between 1300 and 1100 ma led to the assembly of proterozoic australia as an early component of the supercontinent of rodinia this first involved the amalgamation of the west australian and north australian cratons followed by collision with the south australian craton the centralian superbasin developed over the junction of the north south and west australian cratons between 830 and 750 ma rifting to the east formed the adelaide geosyncline at 830 ma this was followed by the breakup of rodinia with the rifting apart of laurentia and gondwanaland along the eastern margin of proterozoic australia at 750 ma and the subsequent formation of the palaeo pacific ocean after the breakup of rodinia a series of northeast southwest compressional events followed by periods of relaxation reflect the assembly of a new supercontinent old lines of weakness were reactivated culminating in the intracratonic king leopold paterson petermann ranges and pinjarra orogenies between 620 and 540 ma subsequent reactivation continued into the phanerozoic with the widespread eruption of continental flood basalts and the formation of intracratonic basins 540 530 ma

accretion of asian dust to hawaiian soils isotopic elemental and mineral mass balances hawaiian soils contain a mixture of material derived from in situ weathering of parent material plus atmospheric inputs including sea salt aerosols and asian dust we use soil mineralogy and radiogenic isotope geochemistry sr and nd to evaluate the impact of asian dust on a chronosequence of hawaiian soils dust becomes an important constituent of soils 20 ky and older near surface 50 cm depth horizons contain as much as 30 quartz a mineral absent from local parent material basaltic sr and nd isotope signatures in these horizons have been completely overprinted by asian dust signatures with 87sr 86sr ratios as high as 0 723 and end values as low as 7 ree patterns in these soils are indistinguishable from that of average upper continental crust quartz abundance and nd isotopes provide two independent tracers of long term dust additions to the chronosequence soils the two tracers indicate a minimum long term average dust accretion rate of 125 mg cm 2 ky 1 at the 150 ka chronosequence site roughly a factor of three higher than holocene dust accumulation rates estimated from north pacific sediment cores we find that the mass of dust preserved in these soil profiles does not increase with age in soils 150 ka and older requiring a loss mechanism for accreted dust on the basis of the geomorphic stability of these sites observed preferential loss of dust derived mica relative to quartz and estimates of soil si leaching rates we argue that chemical weathering is the dominant loss mechanism for dust from these soils dust has a profound effect on the budgets of elements that are susceptible to leaching losses dust becomes the dominant source of soil nutrients si and p in the oldest most intensely weathered soils we calculate a dust derived p input flux of 0 8 mg cm 2 ky 1 and a dust derived si input flux of 35 mg cm 2 ky 1 si leaching fluxes are high 1400 mg cm 2 ky 1 in the youngest 2 ka soils and drop systematically with soil age to a value that closely balances the dust derived si input flux by 4100 ka extremely refractory elements such as nb which are concentrated in soils by residual enrichment processes are much less readily impacted by dust addition although dust has had a pronounced impact on sr and nd isotopic budgets and on soil mineral composition at the 150 ka site dust cannot have contributed 4 of the total nb contained in this soil profile

the role of loamy sediment terra rossa in the context of steady state karst surface lowering abstract reddish loamy material terra rossa found on many karstified surfaces has long been accepted as a characteristic karst feature two basic views of terra rossa formation were distinguished related to either a residual or a detrital origin more recently it has been suggested that it could derive from isovolumetric reactions between the parent carbonate rock and airborne material this paper reviews possible sources of terra rossa explores its behaviour on the karst surface from the karst geomorphology viewpoint and considers whether its existence is better explained in terms of a closed or open karst geomorphic system two approximately west east traverses were laid out across slovenia and the czech republic comprising nine sample locations in each country previously known to be characterized by terra rossa general geomorphic speleomorphic conditions were estimated and loamy material and parent rock samples were collected insoluble residues extracted from the rock were processed in the same ways as the loamy material basic geochemical and mineralogical investigations were run the data obtained were processed statistically results show that statistical relationships between the adjacent rock insoluble residues and adjacent terra rossa bodies exist only at sampling sites recognised as vertical most such sites are cutters which are karren like grooves formed beneath the soil more commonly referred to as subsoil karren us environmental protection agency 2002 a lexicon of cave and karst terminology field m s ed p 53 possible sources of terra rossa material as well as the possibilities of material accumulating on the karst surface are discussed in detail with special emphasis upon cutters theoretical considerations indicate that cutters are the only features that can collect sufficient insoluble residue to be detectable after a period of evolution within a surface that is lowering under steady state conditions all other accumulations of similar appearance must be admixed materials of diverse origins or be completely allogenic in origin the most recent approach which considers terra rossa as an active karst surface agent is temporarily put aside though its explanatory potential in the future is acknowledged

pedogenesis of red soils overlaid coral reef terraces in the southern taiwan abstract red soils developed above the reef limestones are commonly observed in the world their characteristic properties of high contents in clays and iron oxides reddish hue are usually classified themselves as inceptisols alfisols ultisols or mollisols in soil taxonomy the genetic contexts between the soils and beneath limestone have been revealed for gauging paleo landform surface processes relating to paleoclimatic shifts since the late pleistocene there are levels of reef marine terraces in altitude in the hengchun peninsula of taiwan their surfaces are covered by thick reddish soil enriched with iron oxides however these terra rossa like soils distributed on the reef limestone are actually developed from heterogeneous detrital materials instead of developing from the insoluble residue of the limestone according to the soil taxonomy the soils on the higher terraces are classified as the typic paleudults or typic kandiultults they are equivalent to the alisols in wrb system the soils on the lower terraces are classified as typic udipsamments and lithic eutrudepts and they are equivalent to the arenosols and cambisols respectively this study suggests that the terra rossa like soils in the study are developed from the parent materials of fluvial deposits which are subject to the landform surface processes during the interglacial

multiscale magmatic cyclicity duration of pluton construction and the paradoxical relationship between tectonism and plutonism in continental arcs abstract the close relationship between crustal magmatism an expression of heat dissipation and tectonics an expression of stress dissipation leads to the question of their mutual relationships indeed the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas and then possible magmatic initiation of structures at a wide range of scales however new data about 3 d pluton shape and duration of pluton construction perturb this simple geological image and indicate some independence between magmatism and tectonics in some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics in other cases we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric plate dynamics a simple explanation of this complexity follows directly from the pulsed incremental assembly of plutons and its spatial and temporal characteristics the size of each pluton is related to a magmatic pulsation at a particular time scale and each of these coupled time space scales is related to a specific process in small plutons we can observe the incremental process the building block of plutons in larger plutons the incremental process is lost and the pulsation which consists of a cycle of injections at different timescales must be related to the composition and thermal regime of the source region itself driving magmatic processes melting segregation and transfer that interact with tectonic boundary conditions the dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes from our data and a review of published work we find a positive corelation between volume and duration of pluton construction the larger a pluton the longer its construction time large fast or small slow plutons have not been identified to date one consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans a second consequence of this correlation is that small plutons which are constructed in a geologically short length of time commonly record little about tectonic conditions and result only from the interference between magma dynamics and the local geologic setting the fast rate of magma transfer in the crust on the order of cm s relative to tectonic rates on the order of cm yr explain why the incremental process of pluton construction is independent of but not insensitive to the tectonic setting however in large plutonic bodies which correspond to longer duration magmatic events regional deformation has time to interact with the growing pluton and can be recorded within the pluton wall rock structure magma transfer operates at a very short timescale comparable to volcanic timescales which can be sustained over variable periods depending on the fertility of the magma source region and its ability to feed the system the fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below

contribution of saharan dust to mediterranean soils assessed by sequential extraction and pb and sr isotopes abstract measurements of the concentrations and isotopic composition of pb and sr in al silicates and fe oxides of two soil profiles developed in the guadalquivir river basin andalusia southwestern spain are used in order to estimate the significance of local versus foreign sources lead concentrations are 10 6 mg kg in deep more than 100 cm soil samples and reach 30 60 mg kg near the surface 206 pb 207 pb values range from 1 200 to 1 206 in deep samples and from 1 186 to 1 191 in the upper most samples sr concentrations range from 30 to 69 mg kg showing no systematic trend with depth 87 sr 86 sr ratios range from 0 71753 to 0 72526 also with no systematic changes with depth in the fe oxide fraction but with a systematic increase in values with depth in the al silicate fraction of one of the soil profiles in all the samples the isotopic composition of pb in the al si fraction is slightly more radiogenic than its value in the fe oxide fraction the isotopic composition of sr exhibits the opposite behavior and 87 sr 86 sr values in the fe oxide fraction are always higher than in the al silicate fraction based on our data we calculate that al silicates in the fine soil fraction less than 5 m in both sites contain 33 86 of saharan dust and that the fe oxides contain less saharan dust and more material released by the weathering of basement granitoid type rocks in the case of pb a third source is present in the upper part of the soil i e anthropogenic pb probably added to the soil over millennia the results of the present study suggest that saharan dust makes up a significant fraction in al silicates and fe oxides of mediterranean soils but that local sources both natural rock derived and anthropogenic are not trivial

terra rossa genesis by replacement of limestone by kaolinite iii dynamic quantitative model abstractwe model quantitatively the chemical dynamics of terra rossa formation that we deduced earlier from new field and petrographic evidence the key phenomenon is that authigenic kaolinite a proxy for kaolinite solid solutions and other clays replaces limestone at a downward moving reaction front at the base of the existing terra rossa the chemical elements needed to make the authigenic clay are assumed to come from dissolution of eolian clay dust deposited at the surface the model consists of equations of mass conservation in one spatial dimension that incorporate infiltration diffusion and replacement and dissolution reactions distinctive elements of the model are that 1 the kinetics of the kaolinite for calcite replacement is dominated by the crystallization stress generated by the kaolinite growth in accordance with the view that replacement happens not by dissolution precipitation but by guest mineral growth driven pressure solution of the host 2 the field observation that the terr

quartz features constrain the origin of terra rossa over dolomite on the yunnan guizhou plateau china abstract the origin of terra rossa and the relationship between terra rossa and its underlying carbonate rocks pose long standing and controversial questions little insoluble residue content in carbonate rocks makes it difficult to believe that the terra rossa derives only from their underlying carbonates this study focuses on one 4 05 m thick pingba farm terra rossa profile over dolomite on the yunnan guizhou plateau china it is characterized by its ferromanganese concretion gibbsite and terra rossa coexistence in profile the al2o3 contents in the terra rossa rise to 34 the authors examined the quartz content particle size distribution of quartz surface micro textures and quartz morphology quartz oxygen isotope ratios mineral composition chemical composition and other tracers in the terra rossa and dolomite to determine the derivation of the terra rossa the results indicate that terra rossa in the pingba farm profile is an in situ weathering solum the terra rossa comes partly but not completely from insoluble residues from the underlying dolomite the debris minerals quartz feldspar etc derive completely from the underlying dolomite the clay minerals and the al fe and mn oxides and hydroxides likely have three origins one portion derives from insoluble residues of the underlying dolomite a second portion transforms from primary minerals in the underlying dolomite the final portion possibly comes from antigenic minerals which formed from aqueous solutes imported by the leaching water the terra rossa is mainly composed of antigenic minerals

late neogene paleoclimate and paleoenvironment reconstructions from the pipe creek sinkhole indiana usa abstract the late neogene represents warm earth conditions immediately prior to the development of extensive northern hemisphere glaciation and this period in earth history may therefore provide the best available analog for the projected outcome of continued global warming there are few interior continental sites of late neogene age from the eastern half of north america and subsequently very little is known about the conditions characterizing climate the early pliocene 5 ma pipe creek sinkhole pcs includes the sediment fill of a complex karst environment that developed in north central indiana usa lat 40 27 25 4 long 85 47 37 2 the site includes more than 3 m of high chroma red colored silty clay sediment interpreted to be terra rossa the terra rossa 13c values average 20 0 7 pdb and are interpreted to represent sediment deposited in a closed cave system under high summer temperatures and with well drained soils an in situ paleosol at the top of the terra rossa represents a transition from a closed cave to an open environment that eventually flooded thereby becoming a small pond 13c values from lacustrine sediments with organic matter derived dominantly from algae average 20 6 and suggest the pond was stagnant and enriched with bicarbonate from the underlying limestones or via aquifers pond sediments include abundant vertebrate fossils which are broadly consistent with those inhabiting an open ecosystem such as a savannah or parkland however the pcs pollen includes low taxonomic diversity that is dominated by pine with some hickory and flowering plants but no grass pollen we propose two hypotheses to explain the pcs stratigraphic record 1 the pollen assemblage may represent a local pine dominated ecosystem associated with the pond paleoenvironment such as a riparian community and that the greater landscape was drier and open 2 alternatively the climate may have became wetter raising the elevation of the groundwater table and initiating the formation of the pond then in response to the wetter conditions an early succession forest ecosystem developed

spatial distribution and development of soils in tropical karst areas from the peninsula of yucatan mexico abstract better understanding of soil formation requires knowing the spatial distribution of the soils that allows constructing models of soil sequences in multiple directions along various types of gradients this approach was applied to comprehend the soil formation from the soil distribution in the tropical karst areas of the peninsula of yucatan mexico for soil mapping a two step methodology was followed first a geomorphic analysis was performed subsequently 382 soil profiles were reclassified and integrated into a geopedologic map additional soil survey was carried out in areas where soil information was lacking 123 soil profiles satellite images were used to identify flooded areas after conducting numerous field verifications and analyses landforms and soils were combined to make a soilscape map based on field observations and the soilscape map soil development was analyzed on soil sequences four geomorphic environments were identified karstic plains and hills with leptosols cambisols luvisols and vertisols coastal plains with arenosols regosols solonchacks and histosols fluvio paludal plains with gleysols histosols leptosols and solonchacks and tectono karstic plains and hills with leptosols cambisols luvisols and vertisols relevant soil forming factors in the peninsula of yucatan include time of emersion of the limestone platforms climate rock type and macro and micro relief other factors such as groundwater level fractures also have an influence on soil formation karst development can be considered as a complex soil and relief forming factor terra rossa soils as leptosols cambisols luvisols nitisols and vertisols in the peninsula of yucatan may be polygenic in some cases the theory of residual origin fits better the data than the theory of allochthonous origin in other cases it is the other way around

mineralogical and chemical variability of mountain red brown mediterranean soils the purpose of the current study was to quantitatively explore the dynamics of clay pedogenesis in red brown soils of the terra rossa type and associated soils mainly rhodoxeralfs of the mediterranean region with respect to bedrock and dust composition and the impact of the vegetation translocated elements silicon and potassium fifteen non cultivated shallow and leached mountain pedons were sampled in israel along three transects that represent various rainfall ranges and bedrock lithologies bulk and clay fraction chemical and mineralogical compositions as well as grain size were determined quantitative relative analysis of clay minerals displayed a large variability that was largely affected by leaching leaching was dependent on rainfall amount and bedrock soil permeability in general if the better soils were drained and leached the higher were the amounts of both kaolinite and illitic phases soil clay assemblages lay between two mineralogical end members one with dominance of smectite and the second with high values of kaolinite and illitization parameters potassium and silicon were mobile in soils relative to aluminum but under high rainfall or certain vegetation translocation by vegetation reached a degree that promoted illite or smectite formation local combinations of rainfall bedrock soil permeability and vegetation translocation of potassium and silicon dictated a large variability in clays including illite formation within a restricted group of red brown mediterranean soils

reduced rapakivi type granites the tholeiite connection reduced rapakivi type granites are the most iron enriched and reduced i e least oxidized of the anorogenic granite association the low oxygen fugacity and chemical composition of these granites severely limit their sources in this paper we argue that reduced rapakivi type granites and their eruptive equivalents high potassium fayalite rhyolites are derived from mafic sources because tholeiitic magmas and their derivatives have the required low oxygen fugacity reduced rapakivi type granites are produced either by extreme differentiation of basaltic melts or by partial melting of underplated basalts and their differentiated equivalents they form in extensional environments where the asthenosphere is present at shallow depths we envision three stages in the origin of these rocks 1 tholeiitic melts are emplaced at the base of the crust 2 continued introduction of heat partially remelts these tholeiitic rocks and 3 the hot dry melts so produced migrate into the middle crust to produce rapakivi batholiths or erupt as rhyolites partial melting of felsic continental crust may accompany the intrusion of rapakivi type magmas thereby producing the other metaluminous and peraluminous granite compositions of the anorogenic suite

the mesoproterozoic thermal evolution of the musgrave province in central australia plume vs the geological record abstract the 1090 to 2 of western and central australia it also included one of the most voluminous additions of juvenile felsic material to earth s crust with the development of one of the world s longest lived rhyolitic centres including the talbot supervolcano previous suggestions that the event was the result of a deep mantle plume cannot adequately account for the 50 m y duration of mantle derived magmatism or the fact that isolated localities such as the talbot sub basin preserve the entire magmatic record with no discernible regional age progressive spatial trend for at least 100 m y before the giles event the musgrave region experienced high to ultra high crustal temperatures possibly as an ultra hot orogen born from a c 1300 ma back arc granitic magmatism prior to the giles event also involved a significant mantle derived component and was accompanied by mid crustal ultra high temperature 1000 c metamorphism reflecting a thin and weak lithosphere this magmatism also resulted in a mid crustal 25 km deep layer greatly enriched in radiogenic heat producing elements that strongly augmented the already extreme crustal geotherms over a prolonged period the giles event may have been triggered when this regional musgrave thermal anomaly was displaced and again significantly destabilised along the mundrabilla shear zone a continent scale structure that juxtaposed the musgrave province against the easterly extension of the capricorn orogen where pre existing orogen scale structures were in extension these orogen scale structures funnelled the magmas that produced the warakurna large igneous province and the intersection of the musgrave thermal anomaly and the mundrabilla shear zone was the site of the talbot supervolcano although previously thought to be a result of a deep mantle plume the giles event was more likely the product of intra plate tectonic processes involving an anomalous and prolonged thermal pre history a magma focussing lithospheric architecture and large scale tectonic movements

melting of a subduction modified continental lithospheric mantle evidence from late proterozoic mafic dike swarms in central australia geochemical and nd isotopic studies of two postorogenic late proterozoic 1083 23 ma high mg tholeiitec dike swarms in central australia indicate that the dike swarms were derived by partial melting of the continental lithospheric mantle which was modified by subduction processes during major crust formation events in the region both dike swarms stuart and kulgera which intrude the arunta and musgrave inliers respectively resemble island arc tholeiites in terms of geochemical features they yield whole rock sm nd ages of 1853 189 ma with nd 4 2 4 2 stuart and 1589 165 ma with nd 1 7 3 6 kulgera the two whole rock ages and initial nd values are remarkably similar to the oldest u pb zircon ages and initial nd values obtained from the corresponding basement blocks these isotopic data are interpreted as recording sm nd fractionation events in the continental lithospheric mantle associated with major episodes of crust formation in the early proterozoic

what caused the denudation of the menderes massif review of crustal evolution lithosphere structure and dynamic topography in southwest turkey the deformation of earth s lithosphere in orogenic belts is largely forced externally by the sinking slab but can also be driven by internal delamination processes caused by mechanical instabiliti

decoupled crystallization and eruption histories of the rhyolite magmatic system at tarawera volcano revealed by zircon ages and growth rates we obtained u th disequilibrium age data on zircons from each of the four rhyolite eruptions that built tarawera volcano in the last 22 ka within the okataina volcanic center ovc caldera new zealand secondary ion mass spectrometry analyses on unpolished euhedral crystal faces that lack resorption features show that crystal growth variously terminated from near eruption age to 100 ka prior to eruption age depth profiling of crystals reveals long periods of continuous 34 ka and discontinuous growth 90 ka growth hiatuses of up to 40 ka duration occur but do not all relate to obvious resorption surfaces age differences up to similar magnitude are found on opposing faces of some crystals suggesting episodes of partial exposure to melts these features are best explained by periodic complete or partial sub solidus storage and or inclusion in larger crystal phases followed by rapid liberation prior to eruption this is supported by high abundances of u and th 500 2 000 ppm in some zircons consistent with periods of high crystallinity 70 in the magmatic system based on crystal melt partitioning contemporaneous but contrasting rim ward trends of these elements within crystals even in the same lava hand sample require synchronous growth in separate melt bodies and little connectivity within the system but also significant crystal transport and mixing prior to eruption many crystals record continuity of growth through the preceding 60 ka ovc caldera collapse and subsequent eruptions from tarawera this demonstrates a decoupling between eruption triggers such as shallow crustal extension and mafic intrusion and the crystallization state of the ovc silicic magmatic system the data highlights the need to distinguish between the time for accumulation of eruptible magma and the long term magma residence time based on the age of crystals with high closure temperatures when assessing the potential for catastrophic eruptions

cave fills in miocene pliocene strata on cayman brac british west indies implications for the geological evolution of an isolated oceanic island abstract an 8 m high wall in a quarry on the west end of cayman brac exposes the upper part of the cayman formation miocene the lower part of the overlying pedro castle formation pliocene and the cayman unconformity which is a karstic unconformity that separates these formations the modern day karst surface caps the pedro castle formation this exposure also includes cross sections through two filled caves the lower cave 8 m long up to 2 5 m high and upper cave 23 m long up to 2 m high that are housed in the cayman formation and pedro castle formation respectively the lower cave is filled with caymanite which is formed of laminated varicolored dolomitized mudstones and grainstones that contain scattered marine fossils e g foraminifera red algae this cave connected to the cayman unconformity by a small diameter tunnel evolved as part of the karst system that developed during the messinian lowstand 7 3 5 3 ma the cave was filled and dolomitized prior to deposition of the pedro castle formation the upper cave is filled with a wide spectrum of lithotypes including dolostones calcareous mudstones terra rossa gastropod coquina coated grains and speleothems u th dating indicates that some of the flowstones are 500 000 years old whereas others are only 21 000 years old dolostones and mudstones in the basal part of the upper cave contain marine fossils foraminifera red algae whereas the younger deposits are devoid of such fossils the upper cave and its deposits developed after the sediments of the pedro castle formation had been deposited and lithified development of the cave filling deposits which includes a clear transition from marine to non marine influences was controlled by eustatic sea level changes and or westward tectonic tilting of cayman brac that occurred after the pedro castle formation became exposed probably during the late pliocene

geochemistry of istrian lower palaeogene bauxites is it relevant to the extent of subaerial exposure during cretaceous times abstract investigation of the origin and occurrence of istrian lower palaeogene bauxites discussed in this work relies on adoption of the recent perspectives on development of the collision induced diachronous discontinuity surface in the istrian part of the adriatic dinaric carbonate platform this process related to the forebulge uplift at the latest stages of alpine orogenesis is amply recorded in the geochemical signature of contemporaneous bauxites in order to elucidate the patterns of bauxite formation a discriminant function model based on the compositional data analysis major and trace elements is constructed providing the solid ground for separation of the bauxite groups deposited in the subaerially exposed istrian palaeoenvironment complete distinction between the four a priori defined istrian lower palaeogene bauxite groups achieved by the analysis demonstrates the highest degree of efficiency in characterizing environmental conditions marked by the unique suite of geochemical variables compositions

an inverse conglomerate paleomagnetic test and timing of in situ terra rossa formation at bloomington indiana directions of remanent magnetism in an 2 m interval of terra rossa claystone at bloomington indiana cluster around the current earth magnetic field direction a fact consistent with authigenic formation of the terra rossa over the last 0 78 m yr the date of the latest earth s magnetic field reversal and suggesting a minimum terra rossa formation rate of 2 5m m yr paleomagnetic directions in limestone floaters within the terra rossa are indistinguishable from directions of the bedrock mississippian harrodsburg limestone indicating that the floaters are in situ and perfectly preserve their original stratigraphic position thus the red claystone containing the floaters is interpreted as an authigenic isovolumetric replacement of the harrodsburg the replacement of which the floaters escaped and precludes the possibility that the floaters and the surrounding claystone are a mudflow that had carried limestone blocks in it the implication that the claystone is authigenic independently confirms the petrographic observations reported previously that the red clay grew in situ replacing the underlying limestone at a moving metasomatic front rock magnetic studies of the terra rossa clays show evidence of both goethite and maghemite as main magnetic carriers of this remanence both minerals are independently known to occur in pisolites of the terra rossa the ferric ironbearing red clays also are weakly magnetic

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

genesis and mineralogy of soils formed on uplifted coral reef in west timor indonesia many scientists believe that soils forming on or in association with limestone are derived from consolidated limestone rocks or the limestone residuum the objective of this study was to determine the genesis of reddish alfisols and black mollisols formed on uplifted coral reefs in west timor indonesia a total of 24 alfisols and 23 mollisols were studied and sampled rock samples were also collected from the surface from within the profile and from the bedrock of representative profiles dissolution of the coral limestones yielded 1 7 insoluble residue oxides of si k ca and mg were present at higher concentrations in the insoluble rock residues than in the bulk soils and clay fractions concentrations of al and fe oxides were higher in the soils than in the residues considering these possibility exists that exogenic materials atmospheric dusts or volcanic ash may have also contributed to the formation of these soils studied alfisols were dominated by kaolinite followed in a decreasing order by vermiculite gibbsite and quartz whereas mollisols were predominantly smectite and mica followed by kaolinite and quartz the mineralogy of the insoluble residues was similar to that of the clay of mollisols the presence of kaolinite in residues and in the clay of both soils suggests that kaolinite may have been derived from the residue therefore we concluded that weathering of the underlying limestone is the main source contributed to the development of both the alfisols and the mollisols based on the principles of mineral transformation in the soil particularly higher kaolinite content we conclude that alfisols occurring in more stable surfaces and are strongly weathered than mollisols

piggy back supervolcanoes long lived voluminous juvenile rhyolite volcanism in mesoproterozoic central australia the talbot sub basin is one of several bimodal volcanic depositional centres of the mesoproterozoic bentley basin in central australia it is dominated by rocks of rhyolitic composition and includes ignimbrites some forming large to super eruption size deposits ferroan incompatible trace element enriched a type compositions anhydrous mineralogy and clear evidence for local rheomorphism indicate high eruption temperatures with apparent zircon saturation temperatures suggesting crystallization at 900 degrees c comagmatic basalt is of mantle origin with minor proterozoic basement contamination the rhyolites cover the same range of nd isotope compositions epsilon nd 1070 1 24 to 0 96 and la nb ratios 1 2 2 1 as the basalts epsilon nd 1070 2 1 to 1 1 la nb 1 2 2 3 and are compositionally far removed from all older basement and country rock components average epsilon nd 1070 4 la nb 10 the rhyolites and basalts are cogenetic through a process probably involving both fractional crystallization of mafic magmas and partial melting of recently crystallized mafic rock in a lower crustal intraplate extraction of dacitic magmas to a voluminous upper crustal chamber system and separation of rhyolite by processes involving rejuvenation and cannibalization of earlier chamber material more than 230 000 km 3 of parental basalt is required to form the 22 000 km 3 of preserved juvenile rhyolite in the talbot sub basin alone which represents one of the most voluminous known felsic juvenile additions to intracontinental crust zircon u pb age components are complex and distinct from those of basement and country rock and contain antecrystic components reflecting dissolution regrowth processes during periodic rejuvenation of earlier emplaced chamber material without any significant interaction with country rock the overall duration of magmatism was 30 myr but can be divided into between two and four separate intervals each probably of a few hundred thousand years duration and each probably reflecting one of the distinct lithostratigraphic groups defined in the sub basin neither the composition nor style of felsic and mafic volcanism changes in any significant way from one volcanic event to the next and the range of zircon u pb ages indicates that each period utilized and cannibalized the same magma chamber this volcanism forms a component of the 1090 1040 ma giles event in central australia associated with magma dominated extension at the nexus of the cratonic elements of proterozoic australia this event cannot be reasonably reconciled with any putative plume activity but rather reflects the 200 myr legacy of enhanced crustal geotherms that followed the final cratonic amalgamation of central australia

can crystallization of olivine tholeiite give rise to potassic rhyolites an experimental investigation experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica saturated potassic suites could be genetically related through crystallization extreme crystallization 96 97 of a high mgo 10 62 wt olivine tholeiite from the snake river plain with an initial bulk water content of 0 4 wt at a mid crustal pressure of 4 3 kbar generated potassic rhyolitic liquids similar in major element chemistry to those found in the quaternary rhyolite domes of the snake river plain and their plutonic equivalents in the proterozoic laramie anorthosite complex residual liquids comparable in composition to the bulk rock compositions of intermediate rocks found at the craters of the moon and cedar butte eruptive centers in the snake river plain are also generated along this crystallization path