high al gabbros in the laramie anorthosite complex wyoming implications for the composition of melts parental to proterozoic anorthosite high al gabbro represents one of the latest phases of magmatism in the 1 43 ga laramie anorthosite complex lac in southeastern wyoming this lithology which is mineralogically and geochemically the most primitive in the lac forms dikes and small intrusions that cross cut monzonitic and anorthositic rocks high al gabbro is characterized by high al2o3 15 19 wt ree patterns with positive europium anomalies eu eu 1 2 3 8 and the lowest initial 87sr 86sr as low as 0 7033 and highest initial nd up to 2 in the lac their sr and nd isotopic characteristics indicate a mantle origin followed by crustal assimilation during ascent intermediate plagioclase an50 60 and mafic silicate fo54 63 compositions suggest that they are not primary mantle melts and that they differentiated prior to final emplacement high al gabbros of the lac are similar compositionally to gabbros from several other proterozoic anorthosite complexes including rocks from the harp lake complex and the hettasch intrusion in labrador and the adirondack mountains of new york these gabbros are considered to be parental to their associated anorthositic rocks a theory that is supported by recent experimental work we interpret lac high al gabbros to represent mantle derived melts produced by the differentiation of a basaltic magma in an upper mantle chamber continued evolution of this magma eventually resulted in the formation of plagioclase rich diapirs which ascended to mid crustal levels and formed the anorthositic rocks of the lac because these gabbros intrude the anorthositic rocks they do not represent directly the magma from which anorthosite crystallized and instead are younger samples of magma formed by identical processes

gypsum caves as indicators of climate driven river incision and aggradation in a rapidly uplifting region detailed geomorphological analysis has revealed that subhorizontal gypsum caves in the northern apennines italy cut across bedding planes these cave levels formed during cold periods with stable river beds and are coeval with fluvial terraces of rivers that flow perpendicular to the strike of bedding in gypsum monoclines when rivers entrench renewed cave formation occurs very rapidly resulting in the formation of a lower level river aggradation causes cave alluviation and upward dissolution paragenesis in passages nearest to the river beds the u th dating of calcite speleothems provides a minimum age for the formation of the cave passage in which they grew which in turn provides age control on cave levels the ages of all speleothems coincide with warmer and wetter periods when co 2 availability in the soils covering these gypsum areas was greater this climate driven speleogenetic model of epigenic gypsum caves in moderately to rapidly uplifting areas in temperate regions might be generally applicable to karst systems in different geological and climatic conditions

depleted mantle source for the ulungur river a type granites from north xinjiang china geochemistry and nd sr isotopic evidence and implications for phanerozoic crustal growth abstract the ulungur river granites from north xinjiang china display two petrological trends 1 a peralkaline trend composed of alkali amphibole and alkali pyroxene bearing granites and dykes and 2 an aluminous trend represented by alkali granites monzogranites and aluminous granite dykes within the peralkaline granites rb sr whole rock isochron dating yielded an age of 300 ma for the emplacement of the peralkaline granites and 270 ma for the aluminous granites the ulungur river granites share all the geochemical features common to a type granites of the world the ulungur river granites are post orogenic and emplaced in a post collisional extensional environment the peralkaline and aluminous rocks have indistinguishable nd isotopic compositions they have unusually positive and relatively uniform nd t values ranging from 5 1 to 6 7 for the peralkaline rocks at 300 ma and from 5 5 to 5 9 for the aluminous rocks at 270 ma the initial 87sr 86sr ratios cannot be determined precisely by the whole rock isochron technique mainly because most samples are highly radiogenic and have high rb sr ratios in addition the large variation in sr isotopic compositions can partly be explained by crustal contamination during magma differentiation the nd isotopic data clearly indicate that both the peralkaline and aluminous rocks were derived from a long lived depleted mantle reservoir the formation of the ulungur river a type granites is hypothesized as follows 1 a depleted mantle was first metasomatised then subjected to partial melting leading to the generation of basic magmas now represented by the kalatongke mafic ultramafic complex in the ulungur river area 2 the basic magmas have undergone high degrees of fractional crystallisation with separation of biotite hornblende plagioclase potassium feldspar and other accessory phases such as apatite and ilmenite with the residual magmas forming the peralkaline granites during the magmatic differentiation the liquids were probably contaminated by crustal materials as evidenced by nb depletion and nd sr isotopic systematics on the other hand the formation of aluminous granites involved a replenishment of new mantle derived magmas into the differentiating magma chamber and followed by fractional crystallisation with retention of hydrous phases hornblende and biotite the petrological evolution of the ulungur river granites is thus from peralkaline to calc alkaline and not from calc alkaline to peralkaline as more often observed elsewhere the ulungur river granites in common with the voluminous granitoids occurring in the central asian orogenic belt represent a significant juvenile addition of the continental crust in the phanerozoic

thermal genesis of dissolution caves in the black hills south dakota jewel cave 118 km of mapped passages beneath an area of 2 7 km 2 and wind cave 70 km beneath 1 8 km 2 are respectively the fourth and tenth longest known cave systems and the world9s foremost examples of three dimensional rectilinear networks of solutional passages other caves in the black hills are similar they occur in 90 140 m of well bedded mississippian limestone and dolomite walls throughout jewel cave are lined with euhedral calcite spar as much as 15 cm thick wind cave displays lesser encrustations and remarkable calcite boxwork since 1938 opinion has favored cave excavation by slowly circulating meteoric waters in artesian confinement similar to that surrounding the black hills we believe that the caves were developed by regional thermal waters focusing on paleospring outlets in outlying sandstones four sets of criteria are evaluated 1 morphological the three dimensional one phase maze form having convectional features is similar to known and supposed thermal caves in europe 2 petrographic and mineralogical study of the chief precipitates shows a record of carbonate solution calcite precipitation consonant with a model of cooling then degassing waters 3 a thermal anomaly at regional hot springs is shown to extend beneath wind cave where basal lake water samples show chemical and isotopic affinities with the thermal waters and 4 13 c and 18 o measurements place all suspected paleothermal water precipitates in the domain of thermal calcites reported by others and being deposited at the modern hot springs finally u series dates show that the wind cave deposits are quaternary and that the cave is still draining jewel cave is truly relict and divorced from the modern thermal ground water system its great calcite spar sheets are probably older than 1 25 1 50 ma

precise and accurate isotope fractionation factors α17o α18o and αd for water and caso4 2h2o gypsum gypsum caso4 2h2o is a hydrated mineral containing crystallization water also known as gypsum hydration water ghw we determined isotope fractionation factors 17o 18o and d between ghw and free water of the mother solution in the temperature range from 3 c to 55 c at different salinities and precipitation rates the hydrogen isotope fractionation factor dgypsum water increases by 0 0001 units per c between 3 c and 55 c and salinities 150 g l of nacl the dgypsum water is 0 9812 0 0007 at 20 c which is in good agreement with previous estimates of 0 981 0 001 at the same temperature the 18ogypsum water slightly decreases with temperature by 0 00001 per c which is not significant over much of the temperature range considered for paleoclimate applications between 3 c and 55 c 18ogypsum water averages 1 0035 0 0002 this value is more precise than that reported previously e g 1 0041 0 0004 at 25 c and lower than the commonly accepted value of 1 004 we found that nacl concentrations below 150 g l do not significantly affect 18ogypsum water but dgypsum water increases linearly with nacl concentrations even at relatively low salinities suggesting a salt correction is necessary for gypsum formed from brines unlike oxygen isotopes the dgypsum water is affected by kinetic effects that increase with gypsum precipitation rate as expected the relationship of the fractionation factors for 17o and 18o follows the theoretical mass dependent fractionation on earth 0 529 0 001 we provide specific examples of the importance of using the revised fractionation factors when calculating the isotopic composition of the fluids

isotope and trace element evolution of the naica aquifer chihuahua mexico over the past 60 000 yr revealed by speleothems the espada speleothems of cueva de las espadas naica mine chihuahua mexico comprise a high purity selenite core overlain by successive deposits of calcite gypsum and aragonite gypsum precipitated under water from a hydrothermal solution 58 c when the water table was above the cave level ca 57 ka during the last glaciation and some intervals during deglaciation and the holocene aragonite was deposited at lower temperatures 26 c in a perched lake occupying the cave bottom when the water table dropped below the cave level during brief dry intervals during deglaciation and the early holocene the isotopic composition of gypsum water of crystallization shows that the deglaciation holocene aquifer water was enriched in deuterium by 12 8 8 7 relative to water from the last glaciation this is attributed to an increased relative moisture contribution from the gulf of mexico during deglaciation and the holocene compared to the last glaciation this indicates that drier conditions occurred in the naica area during the holocene than around 57 ka furthermore trace element analyses of gypsum served to deduce the circulation regime of the naica aquifer during the past 60 000 yr and also suggest that higher aquifer recharge occurred during the last glaciation

the use of topographic scale models in predicting eolian dust erosion in hilly areas field verification of a wind tunnel experiment abstract eolian erosion of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel erosion simulations on a topographic scale model and in the field the wind tunnel results and the field results show good agreement indicating that wind tunnel simulations of eolian dust erosion on scale models of complex topography may predict at least to an acceptable level the erosion sensitive areas in a hilly landscape of nearly uniform surface roughness the experiments also indicate that a restricted height distortion of scale models may be acceptable to determine the areas of highest erosion in addition wind tunnel blockage percentages up to 10 may be allowed to obtain acceptable erosion patterns on the model when surface roughness is more or less uniform eolian erosion of dry dusty sediments is almost entirely determined by macro topography if however surface roughness is highly variable over the field the initiation of eolian erosion is also largely a function of local micro topography

wind tunnel experiments and field measurements of aeolian dust deposition on conical hills abstract the spatial pattern of short term aeolian dust deposition on and around cone shaped hills is investigated via the simulation in a wind tunnel of dust storms over a topographic scale model of a conical hill in the negev desert israel the results are tested during a full scale dust storm in the negev the wind tunnel experiments adequately predict the field pattern although some problems may arise on steep windward slopes where the accumulation threshold is more quickly exceeded on the scale model than in the field conical hills create an elongated area of low deposition dust shadow in their lee downwind from the shadow zone a local area of more than normal compared to the undisturbed surroundings deposition occurs on the lateral flanks of the hill and also on the small convex windward slope just upstream of the top and at the top itself dust deposition remains low to very low it is the lowermost concave windward slope that receives the largest amounts of dust the pattern described above refers to short term deposition only water erosion may seriously alter the final accumulation pattern since it will clean the slopes of important amounts of dust that accumulate in the wadis

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

the origin of the palaeoproterozoic amcg complexes in the ukrainian shield new u pb ages and hf isotopes in zircon the ukrainian shield hosts two palaeoproterozoic anorthosite mangerite charnockite granite amcg complexes the korosten and korsun novomyrhorod complexes that intruded palaeoproterozoic continental crust in north western and central parts of the shield respectively we report results of u pb zircon and baddeleyite dating of 16 samples from the korosten plutonic complex kpc and 6 samples from the korsun novomyrhorod plutonic complex knpc fifteen zircon samples from both complexes were also analysed for hf isotopes these new together with previously published data indicate that the formation of the kpc started at c 1815 ma and continued until 1743 ma with two main phases of magma emplacement at 1800 1780 and 1770 1758 ma each of the main phases of magmatic activity included both basic and silicic members the emplacement history of the knpc is different from that of the kpc the vast majority of the knpc basic and silicic rocks were emplaced between c 1757 and 1750 ma the youngest stages of the complex are represented by monzonites and syenites that were formed between 1748 and 1744 ma both ukrainian amcg complexes are closely associated in space and time with mantle derived mafic and ultramafic dykes the hf isotope ratios in the zircons indicate a predominantly crustal source for the initial melts with some input of juvenile hf from mantle derived tholeiite melts the preferred model for the formation of the ukrainian amcg complexes involves the emplacement of large volumes of hot mantle derived tholeiitic magma into the lower crust this resulted in partial melting of mafic lower crustal material mixing of lower crustal and tholeiitic melts and formation of ferromonzodioritic magmas further fractional crystallization of the ferromonzodioritic melts produced the spectrum of basic rocks in the amcg complexes emplacement of the ferromonzodioritic and tholeiitic melts into the middle crust and their partial crystallization caused abundant melting of the ambient crust and formation of the large volumes of granitic rocks present in the complexes

chronology of multiphase emplacement of the salmi rapakivi granite anorthosite complex baltic shield implications for magmatic evolution the u pb dating of 18 samples representing the principal rock types of the 4000 km2 salmi anorthosite rapakivi granite complex and its satellite uljalegi pluton southeastern baltic fennoscandian shield reveals that six temporally distinct episodes of igneous activity occurred in a timespan of 17 million years from oldest to youngest they are 1 gabbronorite and monzonite at 1546 7 ma 2 syenogranite at 1543 4 ma 3 early wiborgite and pyterlite at 1540 6 1537 9 ma 4 biotite granite and more evolved granite at 1538 4 1535 ma 5 late pyterlite at 1535 2 ma 6 olivine gabbro and biotite amphibole granite at 1530 ma the resolvable intervals between magmatic episodes are 3 5 5 0 million years early wiborgite and pyterlite 3 above and biotite granite 4 above probably crystallized from multiple magma intrusions age differences of 3 4 1 5 million years between zircon and baddeleyite in olivine gabbro 6 above are probably a result of xenocrystic origin of baddeleyite extracted from an earlier mafic phase of the salmi complex the ages and chemical features of early and late zircon populations together with our modeling of magma crystallization and zircon growth show that the duration of magma crystallization and pb diffusion in zircon was short lived and insignificant compared to the precision of dating of about 1 2 million years hence the range of u pb ages for each of the major rock types may approximate the emplacement intervals of their respective magmas average rate of magma emplacement was about 0 01 km3 year for the most voluminous phase of early biotite amphibole rapakivi granite and about 0 0024 km3 year for the salmi complex as a whole compositional changes of the salmi magmas over time are in agreement with the model of magmatism related to lithospheric extension

boxwork and ferromanganese coatings in hypogenic caves an example from sima de la higuera cave murcia se spain abstract this paper examines the greyish blue deposits that were recently discovered in the lower levels of the sima de la higuera cave murcia se spain which occur as patinas over the walls and ceilings as well as coating boxwork formations their mineralogy was determined using xrd and micro raman spectroscopy while edx microanalysis was used to determine their elemental composition the mineralogical analyses revealed the presence of mn oxides todorokite and pyrolusite and fe with a low degree of crystallinity whereas edx microprobe showed elevated concentrations of mn 38 2 wt fe 15 2 wt and pb 8 1 wt the ferromanganese oxyhydroxides occur as botryoidal aggregates overlying blades of calcite that have a visibly sugary texture the speleogenetic model proposed describes 1 an initial phase of precipitation of hydrothermal calcite veins of hypogenic origin within the fissures of the host rock under phreatic conditions and 2 a subsequent vadose phase involving preferential corrosion of the carbonate host rock caused by lowering of the ph resulting from co 2 diffusion in condensed water and oxidation of fe and mn under aerobic conditions probably mediated by microorganisms it is this later phase that gave rise to the boxwork the boxwork of the sima de la higuera cave is a singular example of a formation that is generated by dissolution corrosion of the rock due to acidification caused by oxidation of iron and manganese

evolution of the gypsum karst of sorbas se spain the gypsum karst of sorbas is developed within messinian gypsum characterized by an interbedded sequence of selenitic gypsum beds and marls this geological configuration has led to the development of an interstratal karst in which galleries have developed in the marl levels but not in the gypsum ones up to six cave passage levels have been detected in the gypsum caves following stratification planes between the impervious intercalated marls and the pervious gypsum strata the explanation for this lies in the hydrogeological history of the area initially the gypsum karst evolved as a multi layer semi confined aquifer under phreatic conditions enabling the formation of small proto conduits in the individual gypsum beds while the intervening marls and clays acted as impervious barriers during a second stage after lowering of the piezometric level vadose conditions were established in which mechanical erosion processes in the intercalated marls and clays became predominant this genetic duality means that the gypsum karst at sorbas can be taken as an example of interstratal karstification where the contemporary underground erosion processes and those of karstic evolution should be considered products of the hydrogeological development the total lowering of the piezometric level during the quaternary is at least of 120 m in the centre of the basin interstratal vadose caves more than 120 m below the surface possess phreatic proto channels in their upper levels which identify the past phreatic conditions in the genesis of the caves

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

the role of condensation in the evolution of dissolutional forms in gypsum caves study case in the karst of sorbas se spain abstract the karst of sorbas se spain is one of the most important gypsum areas worldwide its underground karst network comprises over 100 km of cave passages rounded smooth forms condensation cupola and pendant like features appear on the ceiling of the shallower passages as a result of gypsum dissolution by condensation water meanwhile gypsum speleothems formed by capillarity evaporation and aerosol deposition such as coralloids gypsum crusts and rims are frequently observed closer to the passage floors the role of condensation dissolution mechanisms in the evolution of geomorphological features observed in the upper cave levels has been studied by means of long term micro erosion meter mem measurements direct collection and analysis of condensation waters and micrometeorological monitoring monitoring of erosion at different heights on gypsum walls of the cueva del agua reveals that the gypsum surface retreated up to 0 033 mm yr 1 in mem stations located in the higher parts of the cave walls the surface retreat was negligible at the lowest sites suggesting higher dissolution rates close to the cave ceiling where warmer and moister air flows monitoring of microclimatic parameters and direct measurements of condensation water were performed in the covadura cave system in order to estimate seasonal patterns of condensation direct measurements of condensation water dripping from a metal plate placed in the central part of the el bosque gallery of covadura cave indicate that condensation takes place mainly between july and november in coincidence with rainless periods the estimated gypsum surface lowering due to this condensation water is 0 0026 mm yr 1 microclimatic monitoring in the same area shows differences in air temperature and humidity of the lower parts of the galleries colder and drier with respect to the cave ceiling warmer and wetter this thermal sedimentation controls the intensity of the condensation evaporation mechanisms at different heights in the cave

rapakivi granites and related rocks an introduction abstract this article is an introductory chapter for the proceedings of the last seventh meeting of the international geological correlation programme igcp project 315 correlation of rapakivi granites and related rocks on a global scale 1991 1996 based on current knowledge progress made during the six years of the project and the seven papers published in this special issue a synthesis of the age distribution geotectonic environment petrogenesis geochemistry and metallogeny of the rapakivi granites and related rocks is presented

geochronological constraints on the emplacement history of an anorthosite rapakivi granite suite u pb zircon and baddeleyite study of the korosten complex ukraine u pb zircon baddeleyite ages obtained for the korosten anorthosite rapakivi granite complex ukrainian shield suggest that different magmatic phases were emplaced during a period of ca 30 million years as a series of distinct igneous episodes the earliest 1789 1 2 0 ma anorthosites were followed by 1781 3 3 2 ma dykes of plagiogranite porphyries the emplacement of a major rapakivi granite phase took place at 1767 4 2 2 ma and was followed by emplacement of layered intrusions of anorthosites gabbronorites diabases and ultrabasic rocks between 1761 and 1758 ma the minimum duration of magmatism of about 30 million years the 6 15 million years interval between igneous pulses and alternation of discrete episodes of basic and felsie magmatism are common features of major anorthositemangerite charnockite rapakivi granite complexes temporal distribution of igneous activity in the korosten complex shows that the gabbro anorthosites and the granites are not comagmatic although they are possibly cogenetic and that at least four portions of granitic and basic magmas were generated during a relatively long period of at least 30 million years the time gap of about 20 25 million years between early basic and later and more voluminous granitic magmatism characteristic of the korosten pluton wiborg and salmi batholiths probably reflects the duration of extensional processes before the generation of large volumes of magma in the lower crust

the effect of surface curvature on the deposition of loess a physical model summary a physical model for the deposition of fine dusty material loess on curved surfaces is presented the model is tested in a sedimentation experiment with a symmetrical hill with length axis perpendicular to the flow direction in a wind tunnel it appears both from the model and the experiment that loess deposition will occur preferably on windward slopes and not on leeward ones in contrast to the widespread wind shadow concept below the deflation threshold loess deposition increases as wind speed increases above the deflation threshold an effective accumulation of the loess layer on the surface will occur within a well defined wind speed interval the loess layer on the surface will erode away only if wind speed has exceeded this interval for flat and dry surfaces free of roughness elements the upper limit of the interval is 7 m s free stream velocity for wet surfaces however it may be considerably higher 15 m s and more

comparison of proterozoic and phanerozoic rift related basaltic granitic magmatism abstract this paper compares the 1 67 1 47 ga rapakivi granites of finland and vicinity to the 1 70 1 68 ga rapakivi granites of the beijing area in china the anorogenic 130 ma granites of western namibia and the 20 15 ma granites of the colorado river extensional corridor in the basin and range province of southern nevada in finland and china the tectonic setting was incipient aborted rifting of paleoproterozoic or archean continental crust in namibia it was continental rifting and mantle plume activity that led to the opening of southern atlantic at 130 ma the 20 15 ma granites of southern nevada were related to rifting that followed the triassic paleogene subduction of the farallon plate beneath the southwestern united states in all cases extension related magmatism was bimodal and accompanied by swarms of diabase and rhyolite quartz latite dikes rapakivi texture with plagioclase mantled alkali feldspar megacrysts occurs in varying amounts in the granites and the latest intrusive phases are commonly topaz bearing granites or rhyolites that may host tin tungsten and beryllium mineralization the granites are typically ferroan alkali calcic metaluminous to slightly peraluminous rocks with a type and within plate geochemical and mineralogical characteristics isotope studies nd sr suggest dominant crustal sources for the granites the preferred genetic model is magmatic underplating involving dehydration melting of intermediate felsic deep crust juvenile mafic magma was incorporated either via magma mingling and mixing or by remelting of newly hybridized lower crust in namibia partial melting of subcontinental lithospheric mantle was caused by the tristan mantle plume in the other cases the origin of the mantle magmatism is controversial for the fennoscandian suites extensive long time mantle upwelling associated with periodic migrating melting of the subcontinental lithospheric mantle governed by heat flow and deep crustal structures is suggested

gypsum speleothems in lava tubes from lanzarote canary islands ion sources and pathways abstract lava tubes from lanzarote island in the canary archipelago commonly show white speleothems that stand out from the black basaltic rock mineralogical analyses of the speleothems from el covon and chifletera lava tubes show that gypsum is the dominant mineral with minor amounts of halite speleothems composed of microcrystalline gypsum up to 150 m long are coatings globules or extensive white powder accumulations covering the tube floor those composed of macrocrystalline gypsum with millimetric size tabular and lenticular crystals are crusts and stalactites uranium series dating of speleothems show ages ranging from 6217 1644 yr to 40 039 4748 yr 34s and the 18o of gypsum speleothems 34s is 20 97 v cdt and 18o is 9 78 v smow is similar to that of sulphate dissolved in seawater 87sr 86sr from speleothems 0 708665 0 708976 suggests that the main source of ca is seawater but additional ca contributions from aeolian dust have reduced the sr isotope values these data support the idea that gypsum precipitates in the lava tube by evaporation of marine spray or solutions derived from marine spray two probable vias for ions input into the lava tube are considered 1 sea spray circulating through the lava tube 2 low frequency rain infiltration leaching the marine spray salts precipitated at the surface the constant supply of ions from sea spray air currents in the cave and the fast but partial evaporation due to the high relative humidity in the lava tube favours accumulation of major amounts of gypsum and subordinately halite scarcity of precipitation in the western canary islands prevents dissolution of gypsum speleothems

1 88 1 87 ga post kinematic intrusions of the central finland granitoid complex a shift from c type to a type magmatism during lithospheric convergence abstract the evolution of the svecofennian orogen spans from 1 95 ga to 1 80 ga with the main crust forming activity having taken place 1 90 1 87 ga ago subsequent deformation was largely concentrated to southern finland where transpressional structures indicate lithospheric convergence until 1 80 ga much of the svecofennian orogen in finland is occupied by the central finland granitoid complex cfgc that mainly consists of i type granodiorite and granite these 1 89 1 88 ga intrusive rocks are typically foliated and considered synkinematic a distinct suite of post kinematic undeformed or slightly foliated plutons crosscut the synkinematic rocks they are predominantly quartz monzonites and monzogranites and have been divided into three types according to their petrographic mineral and chemical characteristics compared to the calc alkaline synkinematic granitoids the post kinematic suite generally has an alkaline affinity with higher fe ti k ba zr and nb and lower mg ca and sr at a given sio 2 content the type 1 post kinematic plutons are peraluminous and contained a prominent sedimentary component in their source the types 2 and 3 plutons are marginally metaluminous to peraluminous the type 2 granites especially those in the western cfgc approach the classic 1 65 1 54 ga rapakivi granites of southern finland in their petrographic characteristics magmatic association tholeiitic mafic rocks and elevated contents of incompatible elements and hence have a type characteristics the type 3 plutons contain a pyroxene bearing margin type 3a or contain pyroxene throughout type 3b the type 3b rocks have c type charnockite magma type affinities and some plutons of this subgroup are alkaline the type 3a plutons appear to be transitional between the type 2 and type 3b plutons the synkinematic magmatic episode in the cfgc area probably involved partial melting of intermediate high k rocks in the lower crust with a magmatic addition from a mafic underplate this magmatic episode left a hornblende and biotite poor granulitic residue in the lower crust heat from the mafic underplate triggered partial melting of the granulite to produce the post kinematic magmatism and also introduced mafic material into the post kinematic magmas the post kinematic magmatism took place over quite a short time period ca 15 ma during overall lithospheric convergence it extended beyond the cfgc area and registers a temporal shift from the northeast toward the west and a general change in the character of magmatism from c type to a type the post kinematic magmatism probably resulted from extensional or transtensional events modifying the tectonically thickened crust partial melting of the mafic lower crust produced c type magmatism soon after the first melting episode the crust was already rather rigid and allowed the mafic magmas to follow a tholeiitic trend when the bimodal a type magmas were formed in the western cfgc

evidence for a concealed midcontinent rift related northeast iowa intrusive complex abstract large amplitude aeromagnetic and gravity anomalies over a 16 000 km2 area of northeast iowa and southeast minnesota have been interpreted to reflect the northeast iowa intrusive complex neiic a buried intrusive igneous complex composed of mafic ultramafic rocks in the yavapai province 1 8 1 7 ga hundreds of meters of paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the neiic long considered but not proven to be related to the 1 1 ga midcontinent rift system mrs the neiic is comparable in areal extent to the richly mineralized duluth complex and is similarly located near the margin of the mrs new geochronological and geophysical data together support an mrs affinity for the neiic a dike swarm imaged in aeromagnetic data is cut by intrusions of the neiic and a new apatite u pb date of 1170 ma on one of the dikes thus represents a maximum age for the neiic a minimum age constraint is suggested by 1 large volume magmatism associated with the mrs that was the last such event to affect the region and 2 the presence of reversely magnetized dikes similar in character to mrs related dikes elsewhere that cut several intrusions of the neiic the neiic is largely characterized by the presence of multiple zoned intrusions many of which contain large volumes of mafic ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere including the mrs related coldwell complex of ontario the largest of the zoned intrusions are 40 km in diameter and are interpreted to have thicknesses of many kilometers suspected faults alignments of intrusions and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the belle plaine fault zone and fayette structural zone both previously interpreted as pre mrs possibly lithospheric scale discontinuities that may have controlled neiic emplacement these interpretations collectively imply notable potential for the neiic to host several different types of undiscovered base metal and critical mineral deposits

grenville age a type and related magmatism in southern laurentia texas and new mexico u s a abstract large grenville age plutons are known to be present in the 1340 1370 ma basement in texas and eastern new mexico but their distribution and compositional ranges are poorly known new u pb zircon dates shrimp rg stanford university on subsurface samples have identified widespread presence of compositionally diverse grenville age 1070 1110 ma plutonic rocks in the texas panhandle core from a 175 m thick sill like gabbroic intrusion yielded a date of 1081 8 3 ma in situ differentiation of this tholeiitic magma led to a 7 fold increase in incompatible element concentrations as ree patterns remained essentially flat trace element data suggest an e morb like source to the south alkali feldspar granite with a type affinities was recovered from drill core from the abilene gravity minimum near albany texas it yielded a date of 1078 23 ma similar to undeformed post orogenic granites in the llano uplift further west an anorthosite xenolith from the eocene three sisters intrusion in el paso texas yielded a date of 1068 30 ma which is within error of the 1110 19 ma age determined for the main stage of the nearby a type red bluff granitic suite xenoliths from potrillo maar volcano in the center of the southern rio grande rift include monzonitic xenoliths with granulitic texture which yielded dates of 1072 ma in contrast potrillo maar xenoliths with igneous textures yielded u pb dates of 27 ma development of the granulitic texture is interpreted to reflect granulite facies metamorphism during tertiary time 26 27 ma on the basis of age zoning and u concentrations in the zircon crystals our results show that grenville age magmatism in the texas and new mexico subsurface was widespread and was coeval with syn and post deformation granites in the llano uplift of central texas the compositions of dated samples suggest that mafic magmas were broadly tholeiitic in character and that granitic magmas were a type these magmatic affinities are thought to be associated with crustal extension rather than with subduction moreover the presence of anorthosite xenoliths in the el paso kilbourne hole region the broadly tholeiitic character of mafic rocks and the a type nature of the granitic rocks are broadly similar to amcg anorthosite mangerite charnockite granite suites present in the grenville province of eastern laurentia

petrogenesis of a mid proterozoic anorthosite mangerite charnockite granite amcg complex isotopic and chemical evidence from the nain plutonic suite the nain plutonic suite nps about 1 30 ga underlies some 19 000 km intruding the boundary between middle to late archean rocks in the east nain province and late archean and early proterozoic rocks in the west churchill province nd isotopic compositions in most igneous units of the nps reflect their geographic position relative to the inferred boundary between the nain and churchill provinces rare exceptions are local intrusions of olivine bearing basic rocks with highest epsilon nd 1 3 ga near 3 0 present in both eastern and western sectors of the nps anorthositic rocks have variable and significant contributions of crustal nd but notably lower i sr than granitoid rocks ferrodiorites are similar isotopically to the anorthositic group and have chemical and mineral compositions more akin to the anorthositic group than the granitoids aluminous orthopyroxene megacrysts in nps anorthositic rocks indicate crystallization pressures of 6 2 to 11 0 kbar consistent with lower cru

makhavinekh lake pluton labrador canada geological setting subdivisions mode of emplacement and a comparison with finnish rapakivi granites abstract makhavinekh lake pluton is an oval elsonian 1322 ma granitic intrusion within the nain plutonic suite of central coastal labrador the pluton comprises at least five textural mineralogical subdivisions dominated by quartz monzonite and granite and it is surrounded by a well defined pyroxene hornfels thermal aureole fayalite and clinopyroxene are common constituents of the eastern half of the makhavinckh lake pluton hornblende is present throughout the whole pluton and is the dominant mafic mineral in the western half of the intrusion the hornblende rich parts of the intrusion appear to be a consequence of late to post emplacement hydration of originally olivine bearing rocks textural mineralogical and geochemical features are similar to the rapakivi granites of finland the makhavinekh lake pluton has the morphology of a sheath separating an external gneissic country rock complex from an internal basic plutonic suite it is proposed that the makhavinekh lake pluton developed through cumulate processes and was emplaced as a hot dry crystal charged mush via a mechanism of cauldron subsidence block faulting that allowed ascent of the pluton may have been related to crustal bulging from an underlying mafic magma pond

astrochronology for the messinian sorbas basin se spain and orbital precessional forcing for evaporite cyclicity the sorbas basin of se spain contains one of the most complete sedimentary successions of the mediterranean reflecting the increasing salinity during the messinian salinity crisis a detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves here we present an astrochronological framework for the messinian of the central part of the sorbas basin this framework will form a solid basis for high resolution correlations to the marginal carbonate facies and to the central mediterranean area the early messinian abad member contains 55 precession induced sedimentary cycles marked by homogeneous marl opalrich bed alternations in the lower abad and by homogeneous marl sapropel alternations in the upper abad astronomical tuning results in an age of 5 96 ma for the transition to the yesares evaporites and thus for the onset of the messinian salinity crisis the marl sapropel cycles of the upper abad are replaced by gypsum sapropel cycles 14 in the yesares member indicating that the evaporite cyclicity is related to precession controlled oscillations in circum mediterranean climate as well as a consequence gypsum beds correspond to precession maxima insolation minima and relatively dry climate sapropelitic marls to precession minima insolation maxima and relatively wet climate an alternative glacio eustatic obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high sedimentation during the abad yesares and the overlying coastal sequences of the sorbas member took place in a continuously marine environment indicating that marine conditions in the sorbas basin prevailed at least until 5 60 5 54 ma according to our scenario deposition of the yesares and sorbas member took place synchronously with deposition of the lower evaporites in the central mediterranean finally the continental zorreras member consists of 8 sedimentary cycles of alternating reddish silts dry climate and yellowish sands wet climate which correlates very well with the upper evaporites and lago mare facies of the mediterranean q 2001 elsevier science b v all rights reserved

the contemporary physical and chemical flux of aeolian dust a synthesis of direct measurements of dust deposition abstract the deposition of aeolian or windblown dust is widely recognized as an important physical and chemical flux to ecosystems dust deposition adds exogenous mineral and organic material to terrestrial surfaces and can be important for the biogeochemical cycling of nutrients there have been many studies that characterize the physical and chemical composition of dust however few studies have synthesized these observations in order to examine patterns geochemical fluxes we have compiled observations of dust deposition rates particle size distributions psd mineralogy and bulk elemental and organic chemistry the rates of dust deposition observed across the globe vary from almost 0 to greater than 450 g m 2 yr 1 sites receiving dust deposition can be partitioned into broad categories based on there distance from dust source regions when compared to global dust models our results suggest some models may underestimate dust deposition rates at the regional and local scales the distance from the source region that dust is deposited also influences the particle size distributions mineralogy and chemical composition of dust however more consistent dust sampling and geochemical analyses are needed to better constrain these spatial patterns on average the concentrations of most major elements si al fe mg ca k in aeolian dust tend to be similar 20 to the composition of the upper continental crust ucc but there is substantial variability from sample to sample in contrast some elements tend to be depleted na or enriched ti in dust likely as a result of soil weathering processes prior to dust emissions trace elements especially heavy metals are consistently enriched in dust relative to the ucc ecologically important nutrients such as n and p are also present in dust deposition the geochemical flux attributable to dust deposition can be substantial in ecosystems located proximal to dust source regions we calculate estimates of elemental flux rates based on the average chemical composition of aeolian dust and varying rates of deposition these estimated flux rates are useful as a rough gauge of the degree to which dust deposition may influence biogeochemical cycling in terrestrial ecosystems and should be utilized to better constrain deposition estimates of global dust models

the svecofennian orogen a tectonic model abstract recent geological studies have provided new concepts concerning the timing of the final break up of the archaean craton age data on detrital zircons from sedimentary rocks in sweden and finland show marked similarities and indicate pervasive homogenization of accumulated material geochemical and isotopic studies in sweden and finland suggest the existence of two volcanic belts separated by an area dominated by sedimentary rocks however the ages of metamorphism and plutonism differ in particular the late post 1 85 ga granitoid magmatism was more voluminous in sweden than in finland the svecofennian crust in finland is anomalously thick up to 65 km and is characterized by a high velocity lower crust of variable thickness the evolution of the svecofennian orogen is modelled by opening of the pre svecofennian ocean at 1 95 ga and progressive accretion of two arc complexes to the archaean craton between 1 91 1 87 ga initial accretion at 1 91 ga led to thrusting of the slices of an island arc complex and proterozoic marine strata onto the thickening craton margin subduction reversal with simultaneous anti clockwise rotation of the converging plate or convergence of another plate resulted in subduction below the newly accreted arc complex the tectonic style at the craton margin changed from thrusting to lateral displacement in the east in finland in the west in sweden the subduction zone retreated along a transform fault a large sedimentary basin closed in the east 1 89 ga ago when another arc complex collided against the accreted one collision resulted in lithospheric thickening subsequent delamination of the thickened lithosphere and compensation by a hot mantle underplate and large scale granitoid magmatism as a result of mixing between mantle magma and remelted arc complex material the thick dense layer that formed in the lower crust as the result of underplating kept the thickened crust in isostatic balance thus the exhumation rate in this area was similar to the rate in areas of thinner crust subduction and sediment accumulation continued in the west until at least 1 87 ga when large areas in the east were already stabilized an intracratonic transpressional zone developed as the result of continued convergence subsequent extensional collapse along the transpressional zone caused melting of svecofennian sedimentary rocks migmatization and generation of the 1 84 1 82 ga anatectic granites of southern finland and central sweden the voluminous post 1 85 ga granitoid magmatism in sweden is tentatively associated with an east west extension that is not related to the extensional collapse

baddeleyite zro2 and zircon zrsio4 from anorthositic rocks of the laramie anorthosite complex wyoming petrologic consequences and u pb ages

what lies beneath geophysical mapping of a concealed precambrian intrusive complex along the iowa minnesota border large amplitude gravity and magnetic highs over northeast iowa are interpreted to reflect a buried intrusive complex composed of mafic ultramafic rocks the northeast iowa intrusive complex neiic intruding yavapai province 1 8 1 72 ga rocks the age of the complex is unproven although it has been considered to be keweenawan 1 1 ga because only four boreholes reach the complex which is covered by 200 700 m of paleozoic sedimentary rocks geophysical methods are critical to developing a better understanding of the nature and mineral resource potential of the neiic lithologic and cross cutting relations interpreted from high resolution aeromagnetic and airborne gravity gradient data are presented in the form of a preliminary geologic map of the basement precambrian rocks numerous magnetic anomalies are coincident with airborne gravity gradient agg highs indicating widespread strongly magnetized and dense rocks of likely mafic ultramafic composition a yavapai age metagabbro unit is interprete

quaternary soils and dust deposition in southern nevada and california eoliandustconstitutesmuchofthepedogenic material in late pleistocene and holocene soils of many arid regions of the world comparisonofthecompositionsand influx rates of modern dust with the eolian component of dated soils at 24 sites in southern nevada and california yields informationon 1 thecompositionandinflux rate of dust in late pleistocene and holocene soils 2 paleoclimate and its effects on the genesis of aridic soils especially with regard to dustfall events 3 the timing and relative contribution of dust from playa sources versus alluvial sources and 4 the effects of accumulation of dust in soil horizons the 2mmfractionsofaandbhorizons of soils formed on gravelly alluvial fan deposits in the study area are similar to moderndustingrainsize contentofcaco3and salt majoroxides andclaymineralogy thus they are interpreted to consist largely of dust the major oxide compositions of the shallow soil horizons are nearly identical to that of the modern dust but the compositions of progressively deeper horizons approachthatoftheparentmaterial theclay mineralogyofmoderndustatagivensiteis similar to that of the av horizons of nearby holocene soils but is commonly different from the mineralogies of deeper soil horizonsandoftheavhorizonsofnearbypleistocenesoils theseresultsareinterpretedto indicate that dust both accumulates and is transformed in av horizons with time changes in soil accumulation rates provide insights into the interplay of paleoclimate dustsupply andsoil formingprocesses modern dust deposition rates are more than large enough to account for middle and late holocene soil accumulation rates at nearly all sites however the early holocene soil accumulation rates in areas near late pleistocene pluvial lakes are much higher than modern rates and clearly indicate a dust deflation and deposition event that caused rapid formation offine grained shallow soil horizons on uppermost pleistocene and lower holocene deposits we interpret late pleistocene soil accumulation rates to indicate that dust deposition rates were low during this period but that increased effective moisture during the late wisconsinan favored translocation of clay andcaco3fromnearthesurfacetodeeper inthesoilprofile pre latepleistocenerates are very low in most areas mainly due to a pedogenic threshold that was crossed when accumulations of silt clay and caco3 began to inhibit the downward transport of eolian material but in part due to erosion

flash flood events recorded by air temperature changes in caves a case study in covadura cave se spain summary on 28th september 2012 more than 150 mm rain fell in just two hours in some points of southeastern spain triggering intense flash floods that resulted in the death of ten people and widespread material damage in the gypsum karst of sorbas rainfall intensity reached 33 mm h air temperature monitoring in different levels of covadura cave down to 85 m depth enabled the effect of this extreme episode on the cave microclimate to be evaluated in real time the cave air temperature increased by between 0 9 and 4 1 c as a result of water flow into the cavity and intense mixing of air masses in addition to the displacement of deeper air masses toward shallower levels produced by fast recharge of the surrounding karst aquifer the lag between peak rainfall intensity and the highest cave air temperature was 5 6 h indicating the response time of the karst to this rainfall event no trends with depth were observed suggesting that water not only flowed in through the main cave entrance but also through secondary accesses and fractures furthermore the size of the cave passages and the intensity of air turbulence generated by waterfalls in the cave played an important role in producing these temperature differences even though the rainfall event lasted 10 h cave air temperature did not return to pre flash flood values until more than 20 days later this indicates that while waterflow through the cave might stop a few hours after the rainfall event cave air temperature can be affected over a longer period this can be explained by slow groundwater level decreasing of the surrounding karst aquifer and latent heat liberation produced by moisture condensation on the cave walls our results show how continuous monitoring of air temperature in caves can be a useful tool for evaluating the short term effects of flash floods in subterranean karst systems

tectonic setting of the midcontinent rift system abstract the continental lithosphere which hosts the midcontinent rift mcr system comprises a crustal assemblage ranging in age from 3 6 to 1 5 ga the most voluminous igneous activity along the mcr occurred within late archean 2 7 ga crust presumably due to magmatism associated with a rising mantle plume two major arms of the rift extend to the southeast and the southwest where rifting magmatism and sedimentation were confined to a 2000 km long rift that cuts through the various crustal provinces ranging in age from 3 6 to 1 5 ga tensional reactivation of pre existing crustal discontinuities may have influenced the location of parts of the mcr however direct cause and effect are difficult to distinguish for want of sufficient exposures the most active phases of magmatism and rifting occurred between 1109 and 1087 ma a u pb age of 1097 ma for the southern end of the mcr shows that magmatic activity was synchronous throughout its length there is evidence of rifting and magmatism prior to 1109 ma but there is little evidence of magmatism after 1087 ma rifting may have effectively ceased by that time rifting may have ceased as a result of compressional forces being exerted on the foreland during the grenville collisional event spanning 1030 970 ma and compressional reactivation of normal faults may have resulted in partial inversion of the mcr chemical data and u pb and sm nd isotopic data for igneous rocks along the rift are similar to those for mcr rocks in the lake superior area which are best explained in terms of a mantle plume model however since the distal arms of the mcr were developed in proterozoic lithosphere and did not involve nearly as much magmatism as in the lake superior area mantle plume sources may not have been as important in formation of the distal magmas data from the buried arms are also consistent with the mafic magmas being derived by decompression melting of proterozoic lithosphere during rifting

genesis and evolution of gypsum tumuli tumuli are hollow subcircular domes of the most superficial stratum of gypsum principally found in outcrops of macrocrystalline gypsum they vary from a few centimetres to several metres in diameter and reach maximum heights of a little more than 1 m the relationships between the morphostatistical parameters that define these formations are h r 3 and e r 9 where h is the elevation of the raised layer e its thickness and r the mean radius their genesis has caused some controversy over the involvement of phenomena such as hydration of anhydrite or tectonic processes capable of explaining this folding this paper shows their genesis linked to the dissolution of macrocrystalline gypsum and reprecipitation of microcrystalline gypsum within the same gypsiferous layer it has been calculated that to reach the theoretical saturation within the few centimetres thickness of the cap of the tumulus water infiltration velocities are required of between 0 002 cm s 1 for an uplifted stratum of 2 cm thickness and 0 03 cm s 1 for 30 cm thickness these velocities imply the existence of very slow rates of infiltration and or capillary movement of water within the gypsiferous layer the secondary microcrystalline gypsum is precipitated in the intercrystalline and intracrystalline voids of the gypsum crystals producing an increase in porosity and associated volume that causes the doming of the gypsiferous layer the development of tumuli is a cyclic process which is favoured by a sequence of short wet and dry intervals which in turn facilitate the almost simultaneous processes of dissolution and precipitation these conditions predominate in arid and semiarid climates where intense evaporation can occur suddenly following sporadic infiltration copyright 1999 john wiley sons ltd

speleothems in gypsum caves and their paleoclimatological significance this article highlights the relationship between speleothems growing inside gypsum caves and the particular climate that existed during their development speleothems in gypsum caves normally consist of calcium carbonate calcite or calcium sulphate gypsum and the abundance of such deposits greatly differs from zone to zone observations carried out over the last 20 years in gypsum caves subjected to very different climates italy spain new mexico northern russia cuba argentina highlight wide variation in their cave deposits in arid or semi arid climates the speleothems are mainly composed of gypsum whilst in temperate humid or tropical regions carbonate formations are largely predominant in polar zones no speleothems develop these mineralogical details could be useful paleoclimatic indicators of climate change the interpretation proposed is based on the fact that in gypsum karst the kind of speleothems deposited is determined by competition between the two principal mechanisms that cause precipitation of calcite and gypsum these mechanisms are completely different calcite speleothem evolution is mainly controlled by co2 diffusion while gypsum deposits develop mostly due to evaporation therefore the prevalence of one kind of speleothem over the other and the relationship between the solution precipitation processes of calcite and gypsum may provide evidence of a specific paleoclimate additionally other non common deposits in gypsum caves like moonmilk cave rafts and dolomite speleothems can be used as markers for the prevalence of long dry periods in humid areas seasonal changes in climate or rainfall trends in some gypsum areas moreover the dating of gypsum speleothems could contribute paleoclimatic data relating to dry periods when calcite speleothems are not deposited in contrast the dating of calcite speleothems in gypsum caves could identify former wet periods in arid zones

contemporary geochemical composition and flux of aeolian dust to the san juan mountains colorado united states 1 dust deposition in the rocky mountains may be an important biogeochemical flux from upwind ecosystems seasonal winter spring dust mass fluxes to the san juan mountains during the period from 2004 to 2008 ranged from 5 to 10 g m 2 with individual deposition events reaching as high as 2 g m 2 dust deposited in the san juan mountains was primarily composed of silt and clay sized particles indicating a regional source area the concentrations of most major and minor elements in this dust were similar to or less than average upper continental crustal concentrations whereas trace element concentrations were often enriched in particular dust collected from the san juan mountain snowpack was characterized by enrichments of heavy metals including as cu cd mo pb and zn the mineral composition of dust partially explained dust geochemistry however based on results of a sequential leaching procedure it appeared that trace element enrichments were associated with the organic and not the mineral fraction of dust our observations show that the dust derived fluxes of several nutrients and trace metals are substantial and because many elements are deposited in a mobile form could be important controls of vegetation soil or surface water chemistry the flux measurements reported here are useful benchmarks for the characterization of ecosystem biogeochemical cycling in the rocky mountains

crust and upper mantle structure along the dss baltic profile in se finland summary the 430 km long dss baltic profile in se finland runs through the rapakivi intrusion the svecokarelian geosynclinal complex including the ladoga bothnian bay zone and the archean basement complex a brief description of field operations in 1982 is presented record sections of p and s waves were used for the interpretations a starting model was constructed by inverse methods and improved by dynamic ray tracing modelling three blocks are indentified on the cross section from sw to ne these are the southern associated with the rapakivi massif depth to moho m about 40 km the central ladoga bothnian bay zone with m of approximately 55 60 km and the northern archean crystalline basement with m about 40 45 km the average crustal velocity is 6 6 6 7 kms the crustal structure along the baltic profile is compared with the surrounding dss profiles finnish sveka and soviet kern tulos and ladoga profiles the eastern border of the ladoga bothnian bay zone was located and specific features of the crust and uppermost mantle along the profile area are discussed

triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo humidity reconstruction abstract atmospheric relative humidity is an important parameter affecting vegetation yet paleo humidity proxies are scarce and difficult to calibrate here we use triple oxygen 17 o and 18 o and hydrogen d isotopes of structurally bound gypsum hydration water ghw extracted from lacustrine gypsum to quantify past changes in atmospheric relative humidity an evaporation isotope mass balance model is used together with monte carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of ghw and with statistically robust estimates of uncertainty we apply this method to reconstruct the isotopic composition of paleo waters of lake estanya ne spain and changes in normalized atmospheric relative humidity rh n over the last glacial termination and holocene from 15 to 0 6 cal kyrs bp the isotopic record indicates the driest conditions occurred during the younger dryas yd 12 13 cal kyrs bp we estimate a rh n of 40 45 during the yd which is 30 35 lower than today because of the southward displacement of the polar front to 42 n it was both windier and drier during the yd than the bolling allerod period and holocene mean atmospheric moisture gradually increased from the preboreal to early holocene 11 to 8 cal kyrs bp 50 60 reaching 70 75 rhn from 7 5 cal kyrs bp until present day we demonstrate that combining hydrogen and triple oxygen isotopes in ghw provides a powerful tool for quantitative estimates of past changes in relative humidity

triple oxygen isotope signatures in evaporated water bodies from the sistan oasis iran natural samples from water bodies in the arid and semiarid environment of the sistan oasis iran demonstrate a systematic evolution of 17o excess and 18o as a result of nonequilibrium fractionation during extreme evaporation residual water samples exhibit a significant and systematic decrease of 17o excess with progressive evaporation loss reaching values of 160 per meg over a 35 range of 18o waters from heavily evaporated volume limited natural bodies with limited or no recharge fall on the theoretically predicted isotopic evolution curve in agreement with ambient relative humidity of 30 to 35 recharged water bodies appear to follow a different trend these new results demonstrate the potential of 17o excess for the estimation of evaporation loss and ambient conditions in an arid environment

aeolian deposition of dust over hills the effect of dust grain size on the deposition pattern wind tunnel experiments were conducted to investigate the effects of topography on the grain size characteristics of aeolian dust deposits experiments were performed on three isolated hills having various size and aspect ratios the longitudinal profile of the median grain diameter was investigated for each hill the longitudinal dust deposition profile was also studied for nine grain size classes of between 10 and 104 m as were wind and dust concentration profiles in the atmosphere upwind of over and downwind of a hill the wind tunnel experiments show that the grain size characteristics of aeolian dust deposits are affected by topography most apparent is the occurrence of a zone of reduced grain size on the leeside of hills which extends from just upwind of the summit to a distance of several times the height of the hill slightly coarser than normal dust is deposited on the concave windward hill slope and in a zone downwind of the area of reduced grain size but the increase in grain size in these zones remains very small although the normalized dust deposition profile for a hill does not vary substantially as a function of grain size systematic trends are observed the most important tendencies are 1 a progressive extension in the downwind direction of a zone of decreased dust deposition on the leeside of a hill the coarser the grains the further downwind the zone of reduced deposition extends 2 a progressive increase in dust deposition immediately upwind of a hill the finer the grains the higher the deposition value upwind of a hill becomes both tendencies are explained by the difference in inertia of the grains which is controlled by grain size copyright 2005 john wiley sons ltd

fluorite bearing early and middle proterozoic granites okak bay area labrador geochronology geochemistry and petrogenesis three discrete age groups of relatively fractionated fluorite bearing post tectonic proterozoic granitoid rocks have been identified in the okak bay area of labrador on the basis of u pb zircon geochronology two of the groups occur entirely within the archean nain province the third occurs largely within the early proterozoic churchill province torngat orogen none of the three episodes of granitoid magmatism can be directly linked to orogenic activity in its immediate surroundings although all three granite groups are broadly similar petrologically and chemically to the felsic rocks of the anorogenic elsonian 1450 1290 ma nain plutonic suite nps only one of the dated units can be correlated confidently with elsonian magmatism the other two groups represent significantly older anorogenic or postorogenic magmatism the oldest unit the wheeler mountain granites of the nain province has yielded a u pb age of about 2135 2134 31 2137 2 ma a major tectonothermal event of this age has not been previously identified in northern labrador and the origin of the granites is uncertain three small intrusions on offshore islands white bear saddle opingiviksuak in the nain province were intruded about 1775 1774 21 1776 42 1774 21 ma these granites may have been intruded post kinematically into a stable archean foreland representing a delayed effect of a preceding collisional event torngat orogeny between nain and churchill province to the west the youngest unit dated at about 1318 1319 2 1316 23 ma is umiakovik lake batholith which crops out largely within the eastern churchill province and is one of the largest granitoid intrusions of the nps the age confirms that it formed an integral part of the elsonian magmatic event but both umiakovik lake batholith and nearby 1320 ma makhavinekh lake pluton are significantly older than some basic members of the nps in the coastal area to the southeast nd and sr isotopic data demonsrate that archean protoliths formed significant components of the source materials for all three of these proterozoic granitoid magmas this source was supplemented by one or more proterozoic episodes of lower crustal intrusion and underplating by juvenile mantle derived magmas that occurred in the region

probabilistic sinkhole modelling for hazard assessment a method for quantitatively assessing sinkhole susceptibility spatial probability and hazard spatio temporal probability has been developed and independently tested in a 50 km2 sector of the ebro valley evaporite karst three genetic types of sinkholes have been mapped in the floodplain and a terrace surface 947 small cover collapse sinkholes type 1 terrace large collapse sinkholes type 2 floodplain and large subsidence depressions type 3 floodplain the type 1 sinkhole inventory includes two temporal populations 447 sinkholes formed before 24 november 2005 and 500 between that date and 2 november 2006 sinkhole susceptibility models have been elaborated analysing the statistical relationships between the sinkholes of the 2005 inventory and a set of potential conditioning factors the independent evaluation validation of the susceptibility models by means of several strategies random sequentially excluded and temporal has allowed us to select the most significant variables for each sinkhole type and assess quantitatively the quality of models which are reasonable for the three sinkhole types validation has also provided information on the contribution of specific variables and the effect of changing their accuracy to the prediction capability of models susceptibility models for type 3 sinkholes have been validated satisfactorily with the 2006 sinkhole inventory temporal validation the best susceptibility model has been transformed into a hazard map considering the frequency of sinkholes that occurred in each susceptibility class between 2005 and 2006 as well as their average size the susceptibility and hazard models obtained could be used as an objective basis for the application of mitigation measures either of preventive or corrective nature copyright 2008 john wiley sons ltd

new u pb ages from the wiborg rapakivi area constraints on the temporal evolution of the rapakivi granite anorthosite diabase dyke association of southeastern finland abstract new u pb data on zircons monazites and baddeleyite suggest that the wiborg rapakivi batholith and associated mafic rocks in southeastern finland were emplaced mainly between 1650 and 1625 ma the earliest anorogenic magmatism related to the intrusion of the rapakivi granites was the emplacement of some diabase dykes about 1665 ma ago while the youngest porphyries intruded the rapakivi granites at 1615 ma the process involved three peaks of diabase activity at 1665 1645 and 1635 ma and two major granite events at 1640 5 and 1630 5 ma the former of which comprises also the intrusion of minor gabbroic anorthosite bodies on the whole the result was the emplacement of at least 105 km3 of rock material over a period of 50 ma within southern finland the rapakivi magmatism continued until 1540 ma by emplacement of the west finnish intrusions which combined are as extensive as the wiborg area globally the proterozoic rapakivi event probably represents the largest pulse of intracratonic magmatism which occurred during geological history and may be a consequence of rapid growth of continental masses in the early proterozoic

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

scale model simulations of the deposition of loess in hilly terrain the sedimentation of loess in a 40 km2 area on the northern border of the belgian loess belt is investigated by means of wind tunnel experiments loess deposition is simulated on a relief scale model for different wind directions it appears that simulation with northeast winds produces a loess deposition pattern that coincides closely to the field pattern which may be an indication that the loess bearing winds at the end of the weichselian came from the northeast loess deposition occurs preferably on windward slopes and not on leeward ones the wind shadow concept which is important in the case of sand deposition may therefore not necessarily apply to fine materials such as fine silt and clay

using stable isotopes δ 17 o δ 18 o and δd of gypsum hydration water to ascertain the role of water condensation in the formation of subaerial gypsum speleothems abstract we analyzed the stable isotopes 17 o 18 o and d of gypsum hydration water ghw in a variety of speleothems as well as condensation and infiltration waters in five caves of the semiarid gypsum karst of sorbas basin almeria se spain microclimate parameters air temperature relative humidity and effective condensation rate were also monitored over an annual cycle we found that the mother solution from which the majority of gypsum speleothems grow is composed of a mixture of condensation 60 and infiltration water 40 that undergoes evaporation although evaporation of infiltration water alone was thought to be responsible for secondary gypsum precipitation in vadose caves our results suggest that condensation can be a major source of water for the formation of gypsum speleothems the modelled d excess and 17 o trajectories of water during the evaporative process confirm that the majority of speleothems precipitate from a mixture of condensation and infiltration water under relative humidity of 75 85 similar to that measured in the cave atmosphere during winter these findings have important implications for future studies of gypsum speleothems as paleoenvironmental archives

variations of 17o 16o and 18o 16o in meteoric waters the variations of d 17 o and d 18 o in recent meteoric waters and in ice cores have proven to be an important tool for investigating the present and past hydrologic cycle in order to close significant information gaps in the present distribution ofd 17 o and d 18 o of meteoric water we have run precise measurements with respect to vsmow on samples distributed globally from low to high latitudes based on the new and existing data we present the global meteoric water line gmwl ford 17 o andd 18 o as ln d 17 o 1 0 528 ln d 18 o 1 0 000033 r 2 0 99999 in addition to meteoric water we carried out the first measurements of seawater from the pacific and atlantic oceans with respect to vsmow the obtained results show that the slope of the trend line ln d 17 o 1 vs ln d 18 o 1 of seawater samples is 0 528 the same as for meteoric water but the regression intercept is 5 per meg thus the positive intercept in the gmwl indicates an excess of 17 o in meteoric waters with respect to the ocean an excess or depletion of 17 o in water is defined as 17 o excess ln d 17 o 1 0 528 d 18 o 1 most meteoric water samples have positive 17 o excess of varying magnitudes with an average of 37 per meg with respect to vsmow we explain how these positive values originate from evaporation of sea water into marine air which is undersaturated in water vapor and how subsequent increase of 17 o excess occurs when atmospheric vapor condenses to form liquid and solid precipitation we also clarify the effect of excessive evaporation on 17 o excess finally based on the new results on 17 o excess of seawater we recalculated the relationship of d 17 o vs d 18 o in vapor diffusion in air as 18 adiff 1 0096

petrogenesis of the igneous mucajai amg complex northern amazonian craton geochemical u pb geochronological and nd hf o isotopic constraints abstract the ca 1525 ma igneous mucajai anorthosite monzonite granite amg complex in northern brazil is a rare manifestation of mesoproterozoic intraplate magmatism in the northern amazonian craton the complex comprises a two phase rapakivi granite batholith with subordinate quartz fayalite monzonites and syenites and the closely associated repartimento anorthosite zircon u pb id tims geochronology reveals that the anorthosite 1526 2 ma monzonite 1526 2 ma and the main phase biotite hornblende granite 1527 2 ma of the complex intruded the paleoproterozoic 1 94 ga country rocks simultaneously at 1526 ma and that the more evolved biotite granite is marginally younger at 1519 2 ma intraplate magmatism in the mucajai region was relatively short lived and lasted 12 million years 1529 1517 ma at maximum the nd whole rock id tims e nd from 1 9 to 2 8 hf zircon lam icp ms e hf from 2 0 to 3 1 and o zircon sims 18 o from 6 1 to 7 0 isotopic compositions of the studied rocks are fairly uniform but still reveal a small degree of isotopic heterogeneity in the paleoproterozoic crust enclosing the complex the small isotopic differences observed in the two types of rapakivi granites biotite hornblende granite and biotite granite may result either from an isotopically heterogeneous lower crustal source or more likely from contamination of the granitic magma derived from a lower crustal source during prolonged residence at upper crustal levels

40ar 39ar biotite and hornblende geochronology from the oskarshamn area se sweden discerning multiple proterozoic tectonothermal events twelve 40ar 39ar biotite and four hornblende age determinations have been carried out to constrain the cooling history of the proterozoic bedrock near oskarshamn se sweden an area identified as a possible site for long term nuclear waste storage the bedrock hosts 1 80 ga granites granodiorites quartz monzodiorites and diorites gabbros of the transscandinavian igneous belt and two 1 45 1 44 ga granite intrusions the gotemar and uthammar plutons biotite was selected from three surface samples representing both the older rocks and the younger granites and from three cored boreholes at nine different depth levels hornblende was extracted from samples at the top and bottom of one borehole and at two sub surface levels of another borehole three age groups were distinguished 1 62 ga 1 51 1 47 ga and 1 43 1 42 ga in the first group two hornblende analyses yielded ages of 1799 4 ma and 1773 13 ma which indicate initial fast cooling after emplacement of the 1 80 ga rocks of the transscandinavian igneous belt two biotite ages of 1618 7 ma and 1621 3 ma are interpreted to date final cooling through 300 c after the youngest suite 1 67 ga of the transscandinavian igneous belt in southcentral sweden seven biotite ages in the range 1 51 1 47 ga are enigmatic to interpret but largely coincide with the cessation of widespread rapakivi magmatism in fennoscandia and the initiation of the danopolonian event the 1 44 1 42 ga hornblende and biotite ages reflect cooling after thermal heating from the 1 45 1 44 ga gotemar and uthammar plutons later events thermally affected the bedrock in the oskarshamn area as indicated by a poorly defined biotite age of 928 6 ma and other disturbed 40ar 39ar ages of samples bordering a complex deformation zone less

physical weathering of carbonate host rock by precipitation of soluble salts in caves a case study in el oron arco cave region of murcia se spain abstract the dissolution of carbonate host rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves however circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role we studied the stable isotope composition 18o and 34s of sulfate 18o and d of structurally bound gypsum hydration water and 87sr 86sr and salinity of fluid inclusions in gypsum speleothems found in el oron arco cave cartagena se spain we suggest that physical weathering of carbonate host rock was driven by precipitation of soluble sea salts mostly gypsum and halite and this process controlled the recent geomorphological evolution of the cave the triassic carbonate host rock shows clear evidence for salt weathering including gypsum halite infillings in cracks of the bedrock mechanical spalling of the carbonate and detachment of rock fragments that lead to the formation cave voids and in situ accumulations of piles of unsorted rubble sulfur and oxygen isotopes of gypsum sulfate 3 0

influence of climate and eolian dust on the major element chemistry and clay mineralogy of soils in the northern bighorn basin u s a abstract soil chronosequences in the northern bighorn basin permit the study of chronologic changes in the major element chemistry and clay mineralogy of soils formed in different climates two chronosequences along rock creek in south central montana formed on granitic alluvium in humid and semiarid climates over the past two million years a chronosequence at the kane fans in north central wyoming formed on calcareous alluvium in an arid climate over the past 600 000 years detailed analyses of elemental chemistry indicate that the soils in all three areas gradually incorporated eolian dust that contained less zirconium considered to be chemically immobile during weathering than did the alluvium b and c horizons of soils in the wettest of the chronosequences developed mainly at logarithmic rates suggesting that leaching initially rapid but decelerating dominated the dust additions in contrast soils in the most arid of the chronosequences developed at linear rates that reflect progressive dust additions that were little affected by leaching both weathering and erosion may cause changes with time to appear logarithmic in a horizons of soils under the moist and semiarid climatic regimes clay minerals form with time in the basal b and c horizons and reflect climatic differences in the three areas vermiculite mixed layer illite smectite and smectite form in the soils of the moist climate chronosequence smectite forms in the semiarid climate chronosequence and smectite and palygorskite form in the arid climate chronosequence

wind tunnel experiments of aeolian dust deposition along ranges of hills wind tunnel experiments of aeolian dust deposition on topographic scale models of ranges of hills were conducted different hill sizes and hill spacings were used and comparisons with the deposition patterns over single isolated hills were made dust profiles over ranges of hills differ from the profiles over identical but isolated hills on isolated hills the sedimentation maximum on the windward hillslope is always single and located on the concave part of the slope in the case of ranges of hills the maximum is either single or double with the second peak on the convex part of the windward slope in the latter case the local sedimentation maximum on the convex leeslope which is rather unimportant on isolated hills is much more developed in multiple hill topography also dust deposition on the leeslopes is significantly higher in multiple hill topography than on isolated hills dust patterns on ranges of hills may be affected by the dust shadow created by the most upstream located hill if hills succeed each other quickly they are located within the shadow zone and are protected from important dust deposition the plume of high air dust concentration that is created by a hill largely determines the dust pattern on the next hill as a result of the supply of dust from above by the descending plume areas that are normally devoid of dust now experience significant dust deposition

aeolian dust transport and deposition over crete and adjacent parts of the mediterranean sea monitoring of dust deposition at several stations on crete over a three year period has shown that the present day depositional flux is of the order of 10 100 gm 2 yr 1 most of the dust deposition takes place during a few annual dust events which typically last for 1 3 days dust haze episodes are usually associated with southerly or southwesterly winds which transport fine sediment from north africa dust is raised by a wide variety of meteorological conditions which generate strong near surface winds in the source areas but major long range transport events are often associated with cold fronts linked to the passage of deep mid latitude depressions during winter and spring dust haze frequency and deposition rates are highest in western crete and decrease towards the east suggesting that transport from tunisia and neighbouring parts of north africa is particularly important the measured rate of dust deposition is well below the minimum level required for loess formation deposits which have previously been identified as loess are shown to be uncemented marine marls of tertiary age laboratory analysis of red soils surface sediments and bedrock samples has confirmed that many of the soils contain an important aeolian dust component but it is concluded that a more important source of soil parent material is provided by weathering of local rocks many of the soils contain significant amounts of quartz sand which cannot have been transported across the sea from north africa reworking of weathered material and deposited dust is extensive and is accomplished by both aeolian and fluvial processes tectonically controlled depressions in the mountains and parts of the coastal lowlands have acted as long term sinks in which a thickness of several metres of sediment and soil has accumulated during the quaternary

sinkholes in the salt bearing evaporite karst of the ebro river valley upstream of zaragoza city ne spain geomorphological mapping and analysis as a basis for risk management abstract a detailed sinkhole map has been produced in a stretch of the ebro valley 40 8 km2 including the western sector of zaragoza city ne spain during the last few decades around 70 of the original sinkhole area has been filled with anthropogenic sediments causing the disappearance of 137 ha of wetlands the interstratal karstification of salts halite and glauberite and a wnw ese trending joint set have played a major control in the development of sinkholes three morphometric types of sinkholes have been differentiated each attributed to a specific subsidence mechanism inferred from the paleosinkholes exposed in the surrounding of zaragoza city sagging of bedrock and cover collapse of bedrock and cover and collapse of cover material related to the downward migration of particles through dissolutional conduits each type of sinkhole is characterised by a distinctive behaviour in terms of controlling factors spatio temporal distribution and kinematics and consequently the proposed differentiation may have a practical utility the vast majority of the subsidence damage identified in the area occurs within the boundaries of pre existing sinkholes identifiable in old aerial photographs and topographical maps this fact demonstrates that the application of preventive planning strategies based on detailed geomorphological maps would have allowed avoidance of most of the large financial losses caused by subsidence in the area of the order of hundreds of thousands of euros per year

a wind tunnel simulation and field verification of desert dust deposition avdat experimental station negev desert the deposition of natural dust in an area of 53 ha situated in the northern negev desert is investigated in detail both in the wind tunnel dust storm simulations over a topographic scale model and in the field the wind tunnel results and the field results show a high degree of agreement indicating that scale model simulation may be considered an important technique for future loess and desert research more dust settles on windward slopes than on leeward slopes which is in contradistinction with the widespread wind shadow concept air flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too in the case of dust deposition on topographic scale models a restricted height distortion of the model will not necessarily lead to serious problems in addition wind tunnel blockage percentages up to 13 may be allowed in order to obtain acceptable dust deposition patterns for the scale model a mean gross dust deposition of about 200 250 g m 2 year 1 is calculated for the northern negev desert for 1987 thus if the settled dust can be protected against erosion in the cultivated areas in the negev the dust content of the top soil will markedly increase with time however it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and hence to a higher dust content in the atmosphere at any rate a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields from the air dust concentration data and the dust deposition data a deposition velocity of 4 7cms 1 can be calculated for avdat dust

coupled measurements of δ18o and δd of hydration water and salinity of fluid inclusions in gypsum from the messinian yesares member sorbas basin se spain we studied one cycle cycle 6 of gypsum marl deposition from the messinian yesares member in sorbas basin spain the objective was to reconstruct the changing environment of deposition and its relation to astronomically forced climate change the 18o and d of gypsum hydration water caso4 2h2o and salinity of fluid inclusions were measured in the same samples to test if they record the composition of the mother fluid from which gypsum was precipitated water isotopes are highly correlated with fluid inclusion salinity suggesting the hydration water has not exchanged after formation the relatively low water isotope values and fluid inclusion salinities indicate a significant influence of meteoric water whereas 34s 18oso4 and 87sr 86sr support a dominant marine origin for the gypsum deposits the discrepancy between water and elemental isotope signatures can be reconciled if meteoric water dissolved previously deposited marine sulfates supplying calcium and sulfate ions to the basin which maintained gypsum saturation this recycling process accounts for the marine 34s 18oso4 and 87sr 86sr signatures whereas the low 18o and d values of gypsum hydration water and fluid inclusion salinities reflect the influence of freshwater the cyclic deposition of gypsum and marl in the yesares member has previously been interpreted to reflect changing climate related to earth s precession cycle we demonstrate that the 18o d and salinity of the parent brine increased from low values at the base of the cycle to a maximum in the massive gypsum palisade and decreased again to lower values in the supercones at the top of the cycle this pattern together with changes in mineralogy calcite dolomite gypsum is consistent with a precession driven change in climate with wettest conditions summer insolation maxima associated with the base of the calcium carbonate marls and driest conditions summer insolation minima during formation of the gypsum palisade

field experiments of aeolian dust accumulation on rock fragment substrata the effect of rock fragments and rock fragment cover on the accumulation of airborne dust was examined in a long term field experiment in the negev desert of israel four parameters were studied pebble eccentricity pebble size pebble flattening and cover density the effect of these parameters on the accumulation of dust on the pebbles on the accumulation of dust between and underneath the pebbles and on total dust accumulation pebbles interpebble space was measured separately accumulation on the pebbles increased as the pebbles became larger less flattened and more elongated and as cover density increased accumulation between and underneath the pebbles increased as the pebbles became smaller more flattened and more elongated and as cover density increased although the accumulation area available became smaller total dust accumulation increased as the pebbles became smaller more flattened and more elongated and as cover density increased rock fragments act as a dust trap as dust accumulation on pebble covered surfaces is several tens of times larger than dust accumulation on similar but pebble free surfaces however less than 20 of the initially settled dust is protected from further erosion in the negev desert dust erosion by wind is of the order of 10 times larger than dust erosion by water the rate of long term dust accumulation in the negev is of the order of 15 30 g m 2 yr 1 this is considerably lower than the rates proposed elsewhere in the literature which are based upon over optimistic dust retainment percentages

isotopic constraints on emplacement age of anorthositic rocks of the marcy masiff adirondack mts new york the igneous emplacement age of anorthositic rocks comprising the marcy massif have been constrained by fixing minimum and maximum ages for their intrusion minimum ages have been fixed by a u pb dating of cores of air abraded zircons from the anorthosite 1113 ma b u pb dating of baddeleyite within the anorthosite 1087 ma c u pb dating of baddeleyite from an olivine metagabbro crosscutting marcy massif anorthosite 1109 ma d u pb zircon dating of jotunitic rocks crosscutting the marcy anorthosite massif 1143 pm 31 ma maximum emplacement ages are based upon a sheets of anorthositic rock crosscutting mangeritic charnockitic gneiss dated by u pb zircon at 1125 pm 10 ma 1134 pm 4 ma and 1135 pm 43 ma and b anorthosite related pyroxenite dikes crosscutting mangerite that contains xenoliths of identical pyroxenite these results constrain emplacement of the marcy anorthosite to 1113 1138 ma with the most probable age in the interval 1125 1135 ma this time of in

the proterozoic ahvenisto rapakivi granite massif type anorthosite complex southeastern finland petrography and u pb chronology abstract the ahvenisto complex belongs to the classic 1615 1645 ma wiborg rapakivi granite terrane of southeastern finland the complex covers an area of 350 km2 of which 70 comprises silicic rocks mainly subalkaline biotite hornblende granites and 25 gabbroic rocks mainly leucogabbronorite some olivine bearing gabbroic rocks and rare anorthosite a minor suite of monzodioritic rocks as well as silicic and mafic dike rocks is also found on outcrop the silicic rocks are usually found to cut the monzodioritic rocks whereas the silicic and monzodioritic rocks always cut the gabbroic rocks in terms of petrography and major element geochemistry the gabbroic and monzodioritic rocks of the ahvenisto complex are much like those described from the proterozoic massif type anorthosite occurrences for example the harp lake complex of labrador the ahvenisto complex was emplaced into the paleoproterozoic 1900 ma svecofennian metamorphic crust 1630 1645 ma ago and is thus one of the earliest intrusions in the wiborg terrane in particular our u pb data on zircon and baddeleyite show that a barely measurable age difference exists between a leucogabbronorite 1643 3 ma a gabbroic pegmatite in leucotroctolite 1637 2 ma a quartz monzodiorite 1642 2 ma a hornblende biotite granite 1633 6 ma and a quartz feldspar porphyry dike 1632 5 ma of the complex

dry aeolian dust accumulation in rocky deserts a medium term field experiment based on short term wind tunnel simulations the spatial pattern of medium term a few months dry aeolian dust accumulation in rocky deserts is predicted using short term deposition and erosion experiments in a wind tunnel the predictions are tested in a field experiment set up in the northern negev desert of israel the results show that superimposing wind tunnel deposition and erosion maps usually leads to correct predictions of medium term dust accumulation the predictions are somewhat less confident near the inflection lines of windward hillslopes where small scale irregularities in the local topography make it difficult to locate the exact position of the areas of little accumulation elsewhere in the topography predictions are good and the method works satisfactorily highest accumulation occurs on concave windward slopes and to a lesser extent on slopes parallel to the wind little accumulation occurs on the convex windward slopes and in dust separation bubbles the smallest accumulation rates are observed immediately upwind of the top of pronounced hills and on leeslopes the rate of dry dust accumulation measured during the field experiment varied from 17 to 93 g m 2 a 1 depending on the topographic position of the accumulation plots for most plots it was of the order of 30 60 g m 2 a 1

techniques to measure the dry aeolian deposition of dust in arid and semi arid landscapes a comparative study in west niger seven techniques designed to measure the dry aeolian deposition of dust on a desert surface were tested during field experiments in niger central west africa deposition fluxes were measured during eight periods of 3 4 days each experimental techniques tested were the mdco marble dust collector method the frisbee method the glass plate method optical analysis of dust deposited on glass surfaces using particle imaging software the soil surface method deposition on a simulated desert floor and the capyr capteur pyramidal method theoretical techniques tested were the inferential method and the combination method gradient method extended with a deposition term for coarse dust particles the results obtained by the mdco frisbee inferential and combination methods could be directly compared by converting the data to identical standard conditions deposition on a water surface producing no resuspension the results obtained by the other methods glass plate soil surface capyr were compared relatively the study shows that the crude unconverted deposition fluxes of the five experimental techniques were similar while the crude deposition fluxes calculated by the two theoretical techniques were substantially higher of the order of four to five times as high as for the experimental techniques recalculation of the data to identical environmental conditions the standard water surface resulted in nearly identical deposition fluxes for the mdco frisbee inferential and combination techniques although the latter two still had slightly higher values but the differences remained small the measurements illustrate the need to include a grain shape factor in theoretical dust deposition models without such a factor theoretical models overestimate the deposition the paper also discusses the advantages and disadvantages of the techniques tested copyright 2007 john wiley sons ltd

predicting the thickness and aeolian fraction of soils in upland watersheds of the mojave desert abstract soil thickness and soil texture and their spatial variability at hillslope scales are important inputs for hydrologic models recent studies have demonstrated that mechanistic models can accurately predict the spatial distribution of soil thickness in areas where soil thickness varies gradually along hillslope profiles to date however these models have not been tested in arid regions where soils are often thin and highly variable at small scales i e 1 10 m and where the influence of aeolian accretion on soil thickness and soil texture may be significant in addition most of the data available for the fraction of the soil derived from aeolian deposition which can serve as a proxy for soil texture originate from soils developed on stable depositional landforms data for aeolian fractions from upland soils are scarce in this study we developed and tested a numerical model for the prediction of thickness and aeolian fraction of soils in arid upland areas the model assumes a long term balance between the rates of soil production from bedrock aeolian accretion and soil erosion rates of soil production are quantified in the model using the exponential and humped soil production functions and soil erosion rates are quantified using the nonlinear depth and slope dependent transport functions assuming that only the upper soil horizons a b are capable of transport the rate of aeolian deposition is assumed to be spatially uniform we calibrated the three free parameters of the model at a site in the mojave desert with a granite lithology using a combination of 1 field measured data for soil thickness and 2 estimation of the aeolian fraction in the soil using laboratory analysis of immobile element concentrations we validated the model results in three nearby sites using a combination of measured soil thickness in soil pits and the presence absence of soil and laboratory analysis of the aeolian fraction of soil the study area is characterized by generally thin soils

high aluminum orthopyroxene megacrysts haom in the ahvenisto complex se finland and the polybaric crystallization of massif type anorthosites the occurrence of high aluminum orthopyroxene megacrysts haoms in several massif type proterozoic anorthosite complexes has been used as evidence of their polybaric crystallization here we report such petrographic and geochemical xrf and empa evidence from haoms discovered in the 1 64 ga ahvenisto rapakivi granite massif type anorthosite complex in southeastern finland two different types of haoms were recognized type 1 haoms are individual euhedral to subhedral crystals and up to 15 cm in diameter and type 2 haoms occur in pegmatitic pockets closely associated with megacrystic up to 30 cm long plagioclase the type 1 megacrysts in particular are surrounded by complex corona structures composed of plagioclase low al orthopyroxene iddingsite after olivine and sulfides orthopyroxene crystallization pressure estimates based on an al in opx geobarometer reveal a three stage compositional evolution in both textural haom types the al content decreases significantly from the core regions of the haom 4 4 7 6 wt al2o3 through the rims 1 3 3 6 wt into the host rock 0 5 1 5 wt enstatite compositions overlap but are generally higher in the cores en 60 70 and rims en 50 70 of the haoms than in the host rock en 45 60 orthopyroxenes the highest recorded al abundances in the haom cores correspond to crystallization pressures of up to 1 1 gpa 34 km depth whereas the haom rims have crystallized at lower pressures max 0 5 gpa 20 km depth the highest pressure estimates for the host rock orthopyroxene were 0 2 gpa 7 km depth these observations confirm the polybaric magmatic evolution of the ahvenisto anorthosites and suggest that the entire 1 65 1 55 ga fennoscandian rapakivi suite was emplaced at a relatively shallow level 7 km depth in the upper crust global comparison to similar rock types reveals remarkable similarities in the petrogenetic processes controlling haom composition and evolution of anorthosite parental magmas

spatial distribution of dust deposition within a small drainage basin implications for loess deposits in the negev desert loessial colluvial sediments and aeolian aprons are common deposits in the negev desert highlands in an attempt to monitor the amounts and distributional pattern of loess monthly dust measurements were carried out during 2004 to 2006 in 10 cm diameter traps located at 18 stations along four slopes north facing south facing east facing and west facing in a second order drainage basin near sede boqer negev desert highlands israel annual total dust depositions ranged between 110 g and 178 g m 2 with an average of 151 1 g m 2 the average annual dust deposition in the catchment was 23 5 higher than the average amount recorded at the hilltops 122 4 g m 2 and may be a consequence of sheltering opportunities in the hilly topography when analysed according to season and aspect significantly higher monthly amounts were received during the wet rainy season of december to march 17 0 g m 2 in comparison with the rest of the year 8 1 g m 2 as for the aspect while no significant differences characterized north facing and south facing slopes east facing slopes received significantly higher amounts by 43 3 than west facing slopes pointing to preferential dust deposition at the leeward slope concurring with the classical model that anticipates higher dust deposition at the leeside slope but in disagreement with some reports published in the literature the findings of this study were also supported by a field survey that showed preferential loess accumulation at the eastern and north eastern aspects these findings may shed light on distributional patterns of colluvial sediments and aeolian aprons in the negev on soil forming processes and on past cycles of dust deposition

natural and human induced sinkholes in gypsum terrain and associated environmental problems in ne spain the central ebro basin comprises thick evaporite materials whose high solubility produces typically karstic landforms the sinkhole morphology developed in the overlying alluvium has been studied using gravimetry and ground penetrating radar gpr on stream terraces as well as analyzing the evolution of sinkhole morphologies observed in aerial photographs taken in 1928 1957 and 1985 the sinkhole morphologies give some idea of possible subsurface processes as well as an indication of the final mechanisms involve in sinkhole development on stream terraces and cover pediments the most commonly encountered dolines are bowl shaped in their morphology with both diffuse and scarped edges in contrast dolines developed in the gypsiferous silt infilled valleys have a funnel and well shaped morphology the diffuse edged bowl shaped dolines are developed through the progressive subsidence of the alluvial cover due to washing down of alluvial particles through small voids and cracks into deeper subsurface caves resulting in a decrease alluvial density future compaction of the alluvial cover will produce surface subsidences this type of dolines are associated with negative gravity anomalies in contrast the scarped edge dolines are formed by the sudden collapse of a cavity roof the cavities and cracks formed in the gypsum karst may migrate to the surface through the alluvial deposits by piping and they may subsequently collapse in this instance the cavities can be detected by both gravity and gpr anomalies where the voids are not deeper than 4 5 m from the surface these processes forming sinkholes can be enhanced by man induced changes in the groundwater hydrologic regime by both inflows due to irrigation ditch losses or pipe leakages and by outflows from pumping activities

zircon as a proxy for the magmatic evolution of proterozoic ferroan granites the wiborg rapakivi granite batholith se finland

late glacial temperature and precipitation changes in the lowland neotropics by tandem measurement of δ18o in biogenic carbonate and gypsum hydration water we applied a new method to reconstruct paleotemperature in the tropics during the last deglaciation by measuring oxygen isotopes of co occurring gypsum hydration water and biogenic carbonate in sediment cores from two lakes on the yucatan peninsula oxygen and hydrogen isotope values of interstitial and gypsum hydration water indicate that the crystallization water preserves the isotopic signal of the lake water and has not undergone post depositional isotopic exchange with sediment pore water the estimated lake water 18o is combined with carbonate 18o to calculate paleotemperature three paired measurements of 1200 yr old gypsum and gastropod aragonite from lake chichancanab mexico yielded a mean temperature of 26 c range 23 29 5 c which is consistent with the mean and range of mean annual temperatures mat in the region today paired measurements of ostracods gastropods and gypsum hydration water samples were measured in cores from lake peten itza guatemala spanning the late glacial and early holocene period 18 5 10 4 ka the lowest recorded temperatures occurred at the start of heinrich stadial hs 1 at 18 5 ka inferred temperatures from benthic ostracods ranged from 16 to 20 c during hs 1 which is 6 10 c cooler than mat in the region today whereas temperatures derived from shallow water gastropods were generally warmer 20 25 c reflecting epilimnetic temperatures the derived temperatures support previous findings of greater tropical cooling on land in central america during the late glacial than indicated by nearby marine records temperature increased in two steps during the last deglaciation the first occurred during the bolling allerod b a from 14 7 to 13 ka when temperature rose to 20 24 c towards the end of this period the second step occurred at 10 4 ka near the beginning of the holocene when ostracod inferred temperature rose to 26 c reflecting modern hypolimnetic temperature set during winter whereas gastropod derived temperature attained 30 c reflecting modern summer epilimnetic temperature

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