discriminating fluid source regions in orogenic gold deposits using b isotopes abstract the genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions however there is considerable debate as to the ultimate source of these fluids and the metals they transport tourmaline is a common gangue mineral in orogenic gold deposits it is stable over a very wide p t range demonstrates limited volume diffusion of major and trace elements and is the main host of b in most rock types we have used texturally resolved b isotope analysis by secondary ion mass spectrometry sims to identify multiple fluid sources within a single orogenic gold ore district the loulo mining district in mali west africa hosts several large orogenic gold ore bodies with complex fluid chemistry associated with widespread pre ore na and multi stage b metasomatism the gara deposit as well as several smaller satellites formed through partial mixing between a dilute aqueous carbonic fluid and a hypersaline brine hydrothermal tourmaline occurs as a pre ore phase in the matrix of tourmalinite units which host mineralization in several ore bodies clasts of these tourmalinites occur in mineralized breccias disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation tourmalines show a large range in 11 b values from 3 5 to 19 8 which record a change in fluid source between paragenetic stages of tourmaline growth pre mineralization tourmaline crystals show heavy 11 b values 8 19 8 and high x site occupancy na ca 0 69 1 apfu suggesting a marine evaporite source for hydrothermal fluids syn mineralization and replacement phases show lighter 11 b values 3 5 to 15 1 and lower x site occupancy 0 62 0 88 apfu suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments the large overlapping range in isotopic compositions and a skew toward the opposing population in the 11 b data for both tourmaline groups reflects continual tourmaline growth throughout mineralization which records the process of fluid mixing a peak in 11 b values at 8 largely controlled by tourmalines of syn to post ore timing represents a mixture of the two isotopically distinct fluids this paper demonstrates that b isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems the importance of b as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes b isotope analysis a powerful tool for testing the level of source region variability in these fluids and by extension that of metal sources

genesis of the late eocene bedded halite in the qaidam basin and its implication for paleoclimate in east asia abstract it has long been suggested that the eocene climate in east asia was characterized by three latitudinally distributed zones one middle arid zone and two humid zones to its north and south the middle arid zone was firstly proposed based on the widespread red beds and evaporites in a nww trending zone of china however this long standing model has recently been challenged by increasing doubts about the effectiveness of these arid climate indicators the qaidam basin as one of the eocene evaporites bearing basins in china can be studied to test whether the bedded evaporites can validly indicate arid climate over 300 m halite beds have been found in the late eocene upper xiaganchaigou uxg formation in a local saline center shizigou area of the qaidam basin its coexistence with source rocks and limited distribution together with the absence of red beds make it difficult to explain the halite genesis with the conventional climatic controlled playa model based on stratigraphic correlation lithological and mineralogical observation and oxygen carbon and chlorine isotopic analysis we identify several characteristics about the shizigou saline center 1 undulated lake floor 2 shallow water 3 limited hydrothermal impact 4 evaporation induced precipitation 5 high eolian influence and 6 fluctuated climate background according to these investigations we suggest a new model for the genesis of the bedded halite in the qaidam basin the tectonic climatic model the key point for this model is that the undulated topography caused by tectonic activity and the fluctuated climate together leaded to the hydrological isolation of the shizigou area the shizigou area was isolated from the larger brackish qaidam paleolake for independent evaporation during arid climate stage while connected with it during humid climate stage causing alternatively water influx and evaporation and inducing the occurrence of interbedded halite and source rocks thus the widespread bedded halite in the eocene strata over china may indicate fluctuated rather than arid climate in east asia

applications of organic geochemistry to paleolimnological reconstructions a summary of examples from the laurentian great lakes the organic matter content of lake sediments contains information that helps to reconstruct past environmental conditions evaluate histories of climate change and assess impacts of humans on local ecosystems the elemental isotopic and molecular compositions of organic matter buried in sediment provide evidence of the biota that have lived in a lake and its catchment area and they serve as proxies of organic matter delivery and accumulation sedimentary records from the north american great lakes provide examples of applications of organic geochemistry to paleolimnological reconstructions the records of these lakes date from retreat of the laurentide ice sheet around 12 ka include the mid holocene hypsithermal and show consequences of recent human changes low corg ntotal ratios indicate that most of the sediment organic matter in the great lakes is from algal production yet changes in biomarker molecule compositions also show that varying amounts of land plant organic matter have been delivered to the lakes elevated algal productivity that accompanies nutrient enrichments of lake waters is recorded as excursions to less negative 13c values in the organic matter of sediments that were deposited in the 1960s and 1970s increased organic carbon mass accumulation rates mirror the isotopic excursions in most parts of the great lakes accumulations of petroleum residues and pyrogenic polycyclic aromatic hydrocarbons in sediments identify fluvial and eolian delivery of organic matter components to different parts of the great lakes emerging applications of multiple and novel organic geochemical proxies to paleolimnological reconstructions are promising yet some potentially important measurements remain underutilized

origin and residence time of groundwater in the tadla basin morocco using multiple isotopic and geochemical tools summary groundwater resources in the tadla basin stem from surface water recharge and different groundwater inflows forming a multilayered aquifer system which hosts one of morocco s most important groundwater reservoirs the hydrodynamic infrastructure i e the relationship between all regional aquifers recharge and the residence time of waters poses a serious challenge for current water management and future exploitation in aiming for a long term sustainable utilization a combined hydrogeologic and isotopic investigation using hydrochemical and isotopic tracers such as 18 o 2 h 3 h 13 c and 14 c was carried out in order to determine the sources of water recharge to the aquifers the groundwater flow system and the residence time of these waters more than one hundred point measurements throughout the study area in varying wells boreholes springs and rivers were investigated chemical compositions of the groundwater indicate an important influence by the host carbonate rocks from each of the tadla aquifers stable isotope results indicate the existence of two groups of groundwater corresponding to the unconfined aquifer in the north and the confined aquifer in the south the 18 o 2 h 3 h and 14 c data indicate that the high atlas mountains in the south and east of the basin which are characterized by high rainfall and low 18 o and 2 h values are currently the major source of recharge for the tadla aquifers a significant recharge zone lies in the northern part of the basin where all the aquifers outcrop the confined zones show depleted 18 o values corresponding to the signature of recharge water from the atlas mountains moreover all isotope data demonstrated clearly that the tassaout springs which are located in the southwest of the basin and were previously interpreted as representing natural outlet of the deep aquifers are comprised of young waters with depleted 18 o and 2 h signatures suggesting a high altitude recharge from the atlas mountain in contrast the unconfined parts of the aquifers show higher values of 18 o indicating an evaporation phenomenon which occurs during infiltration or recharge from irrigation the mixing process of old and recent waters is confirmed by 14 c and 3 h the isotopic data also indicates probable interaction and flow between the different aquifers the isotopic and hydrochemical data is therefore essential in confirming possible mixing relationships between aquifers whereas traditional hydraulic data is not capable to provide a quantitative assessment of these relationships the data generated in this study will certainly encourage the revision and improvement of the current hydrological water resources model for the tadla basin the results provide a framework for development of a comprehensive management plan in which water exploitation shifts towards areas with modern recharge and where young and high quality groundwater is found

boron isotope signatures in the coastal groundwaters of french guiana 1 drinking water used by the population of french guiana comes mostly from rivers and can induce major health impacts consequently groundwaters are being studied in terms of an alternative drinking water supply in this context boron isotopes were applied to the coastal aquifers to better constrain the water rock interactions we found that the 1 1 b signatures vary between 2 98 and 49 35 o in the groundwaters and between 36 35 and 42 41 o in the river waters and that the local seawater gave a value of 40 76 o we also noted an inverse correlation between groundwater ph and 1 1 b this relationship previously demonstrated experimentally is particularly well defined in the french guiana coastal aquifer because of the wide ph range 4 18 to 7 64 naturally present in the groundwaters it would appear that the variations in 1 1 b values are linked to water rock interaction processes e g dissolution precipitation of silicates

geochemical evidence for possible natural migration of marcellus formation brine to shallow aquifers in pennsylvania the debate surrounding the safety of shale gas development in the appalachian basin has generated increased awareness of drinking water quality in rural communities concerns include the potential for migration of stray gas metal rich formation brines and hydraulic fracturing and or flowback fluids to drinking water aquifers a critical question common to these environmental risks is the hydraulic connectivity between the shale gas formations and the overlying shallow drinking water aquifers we present geochemical evidence from northeastern pennsylvania showing that pathways unrelated to recent drilling activities exist in some locations between deep underlying formations and shallow drinking water aquifers integration of chemical data br cl na ba sr and li and isotopic ratios 87sr 86sr 2h h 18o 16o and 228ra 226ra from this and previous studies in 426 shallow groundwater samples and 83 northern appalachian brine samples suggest that mixing relationships between shallow ground water and a deep formation brine causes groundwater salinization in some locations the strong geochemical fingerprint in the salinized cl 20 mg l groundwater sampled from the alluvium catskill and lock haven aquifers suggests possible migration of marcellus brine through naturally occurring pathways the occurrences of saline water do not correlate with the location of shale gas wells and are consistent with reported data before rapid shale gas development in the region however the presence of these fluids suggests conductive pathways and specific geostructural and or hydrodynamic regimes in northeastern pennsylvania that are at increased risk for contamination of shallow drinking water resources particularly by fugitive gases because of natural hydraulic connections to deeper formations

rapid growth and strain rates inferred from synkinematic garnets penokean orogeny minnesota recent reinterpretations of the early proterozoic penokean orogeny in minnesota invoke a plate tectonic model with characteristics similar to phanerozoic collisional belts deformation during collision produced large flattening strains 89 and the development of a tectonic foliation and progressive metamorphism up to amphibolite facies as indicated by the presence of synkinematic s1 garnets biotite garnet thermometry and plagioclase garnet biotite muscovite barometry give southward increasing temperatures and pressures and indicate burial to depths of 21 25 km similar to medial and internal zones of collisional orogens worldwide gibbs method modeling on zoned synkinematic garnets indicates virtually no change in pressure p or temperature t during garnet growth growth and rotation of garnets at a point in p t space in an actively evolving deformational and thermal regime are surprising and suggest rapid garnet growth rates and high rates of strain during orogeny this is consistent with previous studies that indicate more rapid rates of tectonometamorphic processes in the precambrian relative to younger orogenic belts

boron occurrence in halite and boron isotope geochemistry of halite in the qarhan salt lake western china abstract previous studies have investigated boron b isotope composition of salt lake brines in the qaidam basin western china however the research on b isotope geochemistry of halite from a sediment core in a typical sedimentary basin has been very limited in this study a 102 m long drill core isl1a was recovered from qarhan salt lake in eastern qaidam basin forty three halite samples from upper 44 0 m in isl1a were collected and analyzed for chemical compositions k na ca 2 mg 2 cl so 4 2 sr 2 and b 3 and b isotopes in order to investigate their relationships and b isotope fractionation between halite and brines in the qarhan salt lake the results show that 1 more b 3 and mg 2 values in halite are low concentrations and more concentrated and low b 3 concentrations have a strong correlation with low mg 2 in halite which imply that they might be the same source 2 low mg 2 values in halite from isl1a have a similar trend with m mg 2 molarity of fluid inclusion brines from two sediment cores east to isl1a about 50 km in the study area suggesting that low b 3 and mg 2 concentrations should derive from fluid inclusions in halite based on x ray diffraction results in isl1a that no borate and small amount of magnesium salts were deposited 3 11 b values of halite in isl1a range from 0 35 to 5 84 which are in the range of those of river water and brines 1 0 to 9 6 and almost overlapped with those of brines 2 9 to 7 5 in the qarhan salt lake these results suggest that no or minor b isotope fractionation between halite and brine occurred

boron isotope variations in nature a synthesis the large relative mass difference between the two stable isotopes of boron 10b and 11b and the high geochemical reactivity of boron lead to significant isotope fractionation by natural processes published 11b values relative to the nbs srm 951 standard span a wide range of 90 the lowest 11b values around 30 are reported for non marine evaporite minerals and certain tourmalines the most 11b enriched reservoir known to date are brines from australian salt lakes and the dead sea of israel with 11b values up to 59 dissolved boron in present day seawater has a constant world wide 11b value of 39 5 in this paper available 11b data of a variety of natural fluid and solid samples from different geological environments are compiled and some of the most relevant aspects including possible tracer applications of boron isotope geochemistry are summarized

the effect of ph and temperature on the isotopic fractionation of boron between saline brine and sediments the effects of ph and temperature on the adsorption distribution of boron in sediment and the boron isotopic fractionation factor between saline brine and sediment were studied the results show that the adsorption and isotopic fractionation of boron between saline brine and sediment are similar to that between seawater and marine or pure sediments in a certain ph range the adsorption distribution factor kd and isotopic fractionation factor of boron are controlled by the ph of the saline brine kd increases with ph while decreases an unusual aspect of this study was that 11b enrichment in the solid was seen during boron adsorption by clay at high ph these results have been used to study the distribution of boron isotopes in salt lakes of qaidam basin

boron isotopic geochemistry of the mcmurdo dry valley lakes antarctica abstract the geochemistry of boron was investigated in the ice covered lakes and glacier meltwater streams within taylor and wright valley of the mcmurdo dry valleys mcm antarctica in order to achieve a greater understanding of the source of boron to these aquatic systems and how in lake processes control boron concentration selected lake depths surface and bottom water and streams were analyzed for boron geochemistry boron stable isotope values in these waters span the range of 12 3 to 51 4 which corresponds to the variations from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake the data demonstrate that the major sources of b to the aquatic system are via terrestrial chemical weathering of aluminosilicates within the stream channels and a marine source either currently being introduced by marine derived aerosols or in the form of ancient seawater lakes fryxell hoare and upper waters of lake joyce which experience more terrestrial influence of aluminosilicate chemical weathering via glacial meltwater streams display a mixture of these two major sources while the source of b in the bottom waters of lake joyce appears to be primarily of marine origin lakes bonney and vanda and the blood falls brine have a marine like source whose 11b values have become more positive by mineral precipitation and or adsorption don juan pond displays a terrestrial aluminosilicate influence of a marine like source these hypersaline lake waters from antarctica are similar in 11b to other hypersaline lake waters globally suggesting that similar processes control their b geochemistry

tectonic denudation of the darwin metamorphic core complex in the andes of tierra del fuego southernmost chile implications for cordilleran orogenesis cordillera darwin in the southernmost chilean andes is a tectonically denuded metamorphic core complex similar to those widely developed in the north american cordillera detailed comparison can be drawn with the shuswap metamorphic core complex in british columbia and washington analysis of the geotectonic history of the darwin complex reinforces the view that the presence of tectonically thickened continental crust is critical for development of most if not all known core complexes and also suggests that inversion of a marginal basin during a compressional regime is one way of initiating such a crustal welt the cordillera darwin complex is unique in the andes and antarctandes this indicates that although low angle normal faulting occurs at high levels in convergent plate settings such as the central andes and the himalayas extensional denudation of deep crustal levels in active andean type orogens may require special tectonic circumstances uplift of the darwin complex began at about 70 ma in a localized extensional setting within the developing transform zone between the south american and antarctic plates this strike slip setting is analogous to some metamorphic core complexes in north america and possibly to a recently identified core complex in new zealand it is likely to be a common one for core complexes in convergent orogens

proterozoic metamorphism and cooling in the southern lake superior region north america and its bearing on crustal evolution abstract metamorphism along the southern margin of the archean superior province has been historically attributed to the penokean orogeny a narrow corridor of amphibolite facies rocks north of the main suture does record 1 83 1 80 ga metamorphic monazite u th pb ages that mark the culmination of arc accretion however subsequent widespread amphibolite facies metamorphism and associated magmatism is recorded along the regions of greatest penokean crustal thickening the tectonically buried archean proterozoic continental margin in minnesota new monazite geochronology reveals a profound midcrustal metamorphic imprint caused by emplacement of the 1 775 ga east central minnesota batholith at moderate depths in northern wisconsin and upper peninsula michigan metamorphic monazite growth at 1 78 1 745 ga and far from geon 17 intrusions reflect a previously little recognized regional amphibolite facies metamorphic event associated with ca 1 76 ga yavapai interval accretion not solely penokean induced crustal collapse south of the penokean suture penokean terrane rocks were twice metamorphosed to upper greenschist facies first during yavapai accretion and again during geon 16 mazatzal accretion geon 16 overprinting also affected a small part of the continental margin in the northeast orogen the peavy metamorphic node south directed basement thrusts there likely accommodated substantial mazatzal foreland shortening suggesting thick skinned deformation mazatzal amphibolite facies metamorphism occurred throughout iowa and southernmost wisconsin south of the baraboo quartzite 40 ar 39 ar mineral cooling ages from eastern wisconsin reveal a limited metamorphic aureole associated with the intrusion of the 1 47 ga wolf river batholith in part reflecting its rapid emplacement at shallow crustal levels a local area of anomalously young 40 ar 39 ar mica ages away from known midcontinent rift exposures probably reflect shallow crustal level reheating during rifting not exhumation the pattern and degree of proterozoic metamorphism preserved across the northern interior of the north american midcontinent is highly variable and is a reflection of multiple accretionary and intrusive events between 1 87 and 1 47 ga collectively the geo and thermochronologic data reveal a progressive tectonic younging toward the south and overall waning of proterozoic metamorphism in this region these results demonstrate a changing tectonic environment from active margin to continental interior as laurentia grew southward and stabilized over a few hundred million years

a world in a grain of sand regional metamorphic history from 40ar 39ar laser probe analyses of proterozoic sediments from the canadian shield abstract a reconnaissance examination using the 40ar 39ar laser probe for step heating analysis of millimeter size whole rock chips representing a variety of huronian sediments from northern ontario has demonstrated several novel and surprising features most of the samples show one to three linear segments on the 36ar 40ar versus 39ar 40ar correlation diagram but about half of these have a positive slope these linear segments represent mixing of argon from distinct components one of which is always a virtually pure radiogenic component mixing of this radiogenic component with unradiogenic argon produces lines with the normal negative slope isochrons whereas mixing with a relatively young high k component is required to generate lines with a positive slope such positive slopes are rare in the literature and they are termed here as ambichrons all of the x intercepts of these linear segments indicate significantly younger ages than the deposition age of the sediments 2200 2450 ma intercept ages are recorded a at 1800 1850 ma corresponding to the peak of the penokean orogeny and subsequent cooling b at 1700 1760 ma probably representing a previously postulated period of rapid post penokean uplift and c at 1480 1570 ma representing either further uplift and cooling or heating in the killarney orogeny despite the relatively mild chemical and textural effects of metamorphism all pre depositional indeed pre penokean history has been eradicated from the k ar systematics in addition to the isochrons and ambichrons two of the samples show very significant recoil effects displayed as horizontal line segments in the correlation diagrams even this preliminary study clearly demonstrates that important geo history is recorded by the k ar system in precambrian sedimentary rocks and that the laser step heating approach obviously has much potential for revealing this history

solution weathering rate and origin of karst landforms and caves in the quartzite of auyan tepui gran sabana venezuela abstract the paper reports the results of sio 2 analyses in the aonda cave system located on the auyan tepui one of the widest table mountains of the gran sabana south venezuela characterised by karst landforms developed in siliceous rock chemical analyses underline the very low concentration of sio 2 of the surface water percolation and cave drip waters have a sio 2 concentration of about 1 mg l the mean silica load of the cave stream is 184 mg s mainly derived from surface solution removal in the allogenic recharge area in the aonda cave system the mean sio 2 dissolved load is 40 mg s in part from surface solution 15 and mainly from underground processes 85 the low solubility of sio 2 in slightly acidic water implies the importance of the time factor in the formation of cave systems with the present dissolution rate about 10 ma would be necessary to form the known karst system this estimation can be significant only if we assume that climate has been stable in the last few tens of millions of years furthermore this age can be taken as a minimum estimate while according to the geomorphic evolution of the area the origin of the aonda cave system could be reasonably dated back to at least 20 30 ma that is to the oligocene

chlorine isotopic geochemistry of salt lakes in the qaidam basin china abstract the isotopic compositions of chlorine in salt lake brine coexisting with halite oil field water and river water from the qaidam basin qinghai china have been examined using high precision measurement of chlorine isotopes based on thermal ionization mass spectrometry of the cs 2 cl ion 37 cl values vary from 2 05 to 2 94 with average values of 2 94 for hot spring water 1 35 for river water 0 38 for oil field brine 0 40 for saline water and 0 63 for salt lake brine the preliminary results show isotopic fractionation of chlorine in salt lake brine during salt precipitation the variation of the 37 cl value in these salt lakes is mainly associated with brine evaporation and halite precipitation and with the hydrochemistry of the input water the chlorine isotopic composition may reflect the degree of evaporation of the salt lake brine and may be used to distinguish brines that are in equilibrium with precipitating salts and brines that have dissolved earlier evaporates

geochemical and isotopic oxygen hydrogen carbon strontium constraints for the origin salinity and residence time of groundwater from a carbonate aquifer in the western anti atlas mountains morocco summary groundwater in many arid basins particularly in developing countries is the only available water resource that sustains local communities yet information on the basic hydrological parameters and the sustainability of the groundwater exploitation are often lacking this study investigates the origin of groundwater from the lower cambrian carbonate aquifer of the lakhssas plateau in the anti atlas mountains of southwestern morocco the study aims to reveal the origin of the groundwater salinity sources and the residence time of the water the study is based on a comprehensive geochemical and isotopic oxygen hydrogen carbon and strontium investigation of groundwater from different parts of the basin the hydrochemical and isotopes results indicated three types of groundwater in the lakhssas plateau 1 thermal water in the southern part of the basin with solute composition that reflects dissolution of calcium sulfate and calcium carbonate minerals 2 low temperature groundwater at the southern margin of the basin with low salinity chloride content up to 100 mg l and chemical composition that is expected from equilibrium with limestone dolomite rocks and 3 low temperature groundwater in the northern western and eastern margins of the basin with a wide range of salinity chloride up to 800 mg l the different water types had also different stable isotope composition the thermal water was depleted in 18 o and 2 h 18 o as low as 7 6 relative to the southern 5 9 to 5 3 and northern waters 5 7 to 3 8 the differences in 18 o and 2 h between the southern and northern waters are related to elevation that induced fractionation of oxygen and hydrogen isotopes in recharge water originated from coastal moisture the data suggest that the high salinity in groundwater from the northern western and eastern margins of the lakhssas plateau is related to the presence of schist rocks in these areas the distinctive low na cl and br cl ratios coupled with high silica contents and high 87 sr 86 sr ratios up to 0 713 in the saline groundwater provide additional evidences for the link between salinity and the schist rocks in contrast the thermal water had relatively low 87 sr 86 sr ratio 0 7089 which is identical to the secular seawater sr isotope ratio during the early cambrian period and presumably reflects interaction with the early cambrian carbonate and sulfate aquifer rocks in the northern and southern groundwater the 87 sr 86 sr ratios were higher and correlated with the mg ca ratios inferring mixing between the early cambrian limestone and other rocks with higher 87 sr 86 sr such as the schist rocks the radiocarbon data showed 14 c activities ranging from 6 pmc in the thermal water to 62 pmc in the southern water age modeling corrected for dissolution of the carbonate rocks with dead carbon simulated mean residence time of 10 15 ka bp for the thermal water and a range of 0 to 3 ka bp for the northern and southern waters depending on the used models the integration of the data enables us to establish a conceptual model for the origin of groundwater in the lakhssas plateau 1 recharge to the aquifer from relatively heavy isotope depleted recharge water presumably during wetter conditions about 10 15 ka bp the recharge water interacted at high depth with limestone and calcium sulfate minerals and emerged to the surface as thermal water at the southern part of the basin 2 more recent recharge from coastal moisture originated from the atlantic ocean the stable isotope composition of groundwater was controlled by the elevation of their recharge areas recharge at higher elevation particularly in the southern margin resulted in lower 18 o and 2 h values 3 the recharge water interacted with the carbonate aquifer rocks particularly with calcite and dolomite minerals in areas of exposure of schist rocks the water rock interaction induced salinization of the groundwater overall our data reveal that the limited water resources in this semi arid zone of morocco could be in some parts less renewable and also saline future exploitation of this basin will have to account the salinity factor and the suggested contribution of water recharged some thousands years ago

evolution of lithospheric strength after thrusting modeling of an eroding thrust belt indicates that immediately after thrusting the lithosphere is about twice as strong as unthickened cratonic lithosphere but after 10 to 20 m y it becomes weaker than cratonic lithosphere reaching a minimum of 40 to 70 of cratonic strength 30 to 100 m y after thrusting this may explain why rifting of thrust belts commonly occurs several tens of million years after thrusting ceases relative weakening results from 1 elevation of the geotherm caused by burial of radioisotope enriched surface rocks and 2 replacement of strong mantle rocks by weak crustal rocks in the lithospheric column low denudation rates enhance weakening by allowing radioisotope enriched rocks to remain buried longer our modeling indicates that 1 magmatism after thrusting is favored by high concentrations of heat producing elements in the lower plate and by slow denudation rates and 2 factors that affect denudation rate such as climate and the development of external drainage can significantly influence evolution of a thrust belt

stable isotope geochemistry of sediment hosted groundwater from a late paleozoic early mesozoic section in central europe abstract the boron isotopic composition in combination with oxygen hydrogen and sulfur isotopes and hydrochemical tracers is utilized to investigate the evolution of groundwaters from a late paleozoic permian to early mesozoic triassic section of the sedimentary cover in central europe n switzerland sw germany four distinct groundwater types have been identified a saline groundwater from permian rotliegend sediments 11b 13 7 to 33 0 18o 6 7 to 5 3 d 53 4 to 37 8 34s 16 4 to 17 1 b brackish to saline groundwater from lower triassic buntsandstein sediments 11b 6 4 to 22 3 18o 10 3 to 6 9 d 71 8 to 60 5 34s 18 2 to 18 4 c fresh to saline groundwater from middle triassic muschelkalk sediments 11b 10 2 to 7 7 18o 11 8 to 8 8 d 86 6 to 63 0 34s 15 8 to 21 4 and d saline groundwater from upper triassic keuper sediments 11b 26 3 18o 6 4 d 41 2 34s 16 1 as evidenced by b o h s stable isotope and hydrochemical e g na cl br cl ca so4 ca mg so4 k b and li b constraints interactions with sedimentary host rocks and inter aquifer mixing have contributed to the evolution of the investigated groundwaters

boron isotopic compositions of brine sediments and source water in da qaidam lake qinghai china abstract the isotopic compositions of boron in da qaidam lake quinghai have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate the brines are enriched in 11b with an average 11b of 5 49 2 34 compared with those of lake sediments and boron minerals produced by the lake the apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0 988 0 001 and 0 986 0 001 respectively source water 11b values range from 11 72 to 16 69 depending on their origin

a transdisciplinary analysis of water problems in the mountainous karst areas of morocco water management and engineering in the karstic high atlas of morocco are difficult tasks under the prevailing geological hydrogeological geomorphological vegetational and climatic conditions it is important to be able to understand and predict the characteristics and availability of water for future water planning in the region under changing climatic and agricultural conditions an interdisciplinary analysis of problems and adequate hydrological modelling tools developed by geologists hydrologists and biologists are necessary the karst areas of the high atlas mountains are characterised by impermeable triassic basalt underlying substantial subsurface reservoirs with high potential discharge rates the karst groundwater aquifers are extensive but largely unknown in dimension probably with a hierarchical network of groundwater flow paths it is estimated that approximately 70 of the surface water is directly lost to groundwater steep landslide and debris flow prone slopes exist next to coarse grained highly porous river beds infrequent high intensity rainfall or snowmelt causes a particularly high flood risk to these karst areas in addition agriculture and land use changes have degraded the karst areas the most important driving forces for degradation include permanent overgrazing even during droughts and the use of firewood by a continually growing population large scale degradation of vegetation has occurred in the oro mediterranean mountainous mediterranean zone between 2600 and 3400 m which coincides with the most important zone for karstic groundwater creation the combination of high amounts of groundwater flow and rapid surface flow due to sparse vegetation has increased the problems of flood flow

boron concentration and isotopic composition of halite from experiments and salt lakes in the qaidam basin abstract the concentration and isotopic abundance of boron in salt can be used to trace paleosalinities and depositional environments for marine and non marine evaporites however the mechanism of incorporating boron into halite during evaporation of salt lake brines is subject to dispute and there have been few studies of boron concentrations and isotopic compositions during this process due to the low boron concentration in halite a group of evaporation experiments from artificial solutions and salt lake brines have been analyzed in this study the results of boron concentration and isotopic analyses demonstrate that the boron in halite comes mainly from fluid inclusions with a lesser amount from coprecipitation the isotopic fractionation factors between the brine and halite are from 0 9857 to 1 0000 for the evaporation experiments and 0 9945 to 1 0009 for natural samples from the salt lake the 11b values of halite from the qaidam basin salt lakes vary from 4 7 to 25 8 compared to 4 7 to 31 4 in the salt lake brines these values are controlled by the boron isotopic composition of the boron sources ph values and na ca ratios in the salt lake brines the variation of boron isotopes in halite may be used to trace the hydrochemical evolution and paleoevaporation environment in salt lakes

the boron isotope geochemistry of the kirka borate deposit western turkey abstract we have measured the boron isotope composition of seventeen samples of borate minerals colemanite ulexite and borax and the 87sr 86sr ratio in thirteen borate samples from the kirka borate deposit in western anatolia turkey these neogene deposits were formed by evaporation of playa lakes fed by geothermal springs the 11b values range from 14 9 o in colemanite to 1 6 o in borax to a first approximation the relative differences in the 11b values of the borate minerals are consistent with their basic boron atomic configuration but the magnitude of the boron isotope fractionation between the three minerals precludes their simultaneous precipitation from a brine with the same boron isotope composition and ph rather the data are consistent with precipitation of colemanite from a brine with lower ph than that required for ulexite precipitation which in turn requires a lower ph than is needed for borax precipitation the boron isotope data also suggest that the borate minerals did not maintain boron isotopic equilibrium with the brine after they precipitated rayleigh fractionation models indicate that during borax precipitation the 11b value of the brine was slightly heavier than during precipitation of ulexite and colemanite

the goodman swell a lithospheric flexure caused by crustal loading along the midcontinent rift system rb sr biotite ages of archean and early to middle proterozoic crystalline rocks in northern wisconsin and adjacent upper peninsula of michigan describe a regionally systematic pattern related to differential uplift an age low occurs in northern wisconsin where values range from 1070 1172 ma for rocks with crystallization ages of 1760 to 1865 ma these values overlap with the main episode of mafic igneous activity 1090 to 1120 ma along the midcontinent rift system mrs we interpret these low biotite ages as registering closure due to cooling below the 300 c isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the goodman swell the position of the goodman swell is independent of the archean and early proterozoic regional geologic framework but closely linked with the curvilinear concave to the south mrs we interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the mrs the southward concavity of load axes resulted in flexural interaction that localized the swell because of rapid uplift the swell may have been a source area for clastic sediments in the rift sequence

active and passive tectonic controls for transverse drainage and river gorge development in a collisional mountain belt dades gorges high atlas mountains morocco abstract transverse drainages are discordant river patterns whose flow directions cut across geological structures such as faults folds and the regional tectonic fabric strike of mountain belts such drainages can form spectacular geomorphological features with reaches often occupying narrow and deeply dissected canyons gorges that cut through prominent topographic barriers within collisional plate margins e g foreland basin systems studies have frequently examined transverse drainage development in response to active tectonics e g thrusting here transverse drainage will develop via incision or become deflected and fixed in response to oblique fault fold growth structures particularly within wedge top thrust front and foredeep basin settings within this paper the development of transverse drainage within the little studied fold thrust component of an orogen is examined using a spectacular series of river gorges along the river dades from the high atlas mountains of morocco integrated field derived geological and geomorphological data are used to explore the interplay between active tectonics lithology and structural configuration passive tectonics of bedrock for the creation of transverse drainage and associated river gorge reaches at the southern edge of the high atlas fold thrust belt the river dades passes through the deeply dissected tarhia n dades and main dades gorges before emerging into the ait seddratt wedge top basin fluvial incision is principally controlled by plio quaternary uplift of the high atlas mountains the larger main dades gorge has formed a deeply dissected antecedent course via drainage inheritance into structurally thickened jurassic bedrock via uplift between two key structural components of the foreland basin system the fold thrust belt and the wedge top basin the smaller tarhia n dades gorge involves a more complex interplay between active tectonics and the passive structural arrangement of an asymmetric plunging syncline combined with the stratigraphic arrangement and strength of the jurassic bedrock the drainage network is configured to the fold and associated fault joint structures to form respective nw se and ne sw orientated dip slope and strike drainage progressive incision by tributary dip slope streams cutting down through resistant limestone bedrock into underlying weaker mudstone bedrock has resulted in accelerated headward erosion and drainage network expansion by river captures this has resulted in a minor re routing of the river dades as a transverse drainage through a former dip slope tributary stream to form the tarhia n dades gorge

a critical evaluation of the available measurements for the stable isotopes of boron abstract the reported measurements for the stable isotopes of b 11b and 10b in natural materials are compiled critically reviewed and evaluated the selected values along with a discussion of the error indicate the potential exists for using b isotopes in interpreting geochemical environments the isotopic values for 11b range from 31 0 for terrestrial rocks to 40 0 for sea water relative to nbs srm 951 which has a reported 11b 10b ratio of 4 04362 0 00137 2 furtherm the isotope ratios generally form a narrow cluster of values for specific rock types in some instances the reported 11b may be shifted substantially from the mean of unaltered rock as a result of weathering or reaction such as the progressive enrichment of 11b in marine sediments over time due to reaction with sea water an application of widespread interest is the use of b isotopes in environmental studies boron is a contaminant derived from numerous sources such as municipal and industrial waste the 11b in these wastes or processed waters is often significantly different from the 11b of the local ground water which will likely reflect the 11b values of the nearby rocks this modification by contaminated water can be 20 0 different from the 11b of the unaffected water providing a useful tool in delineating the source of contamination and the direction of migration

40ar 39ar ages for minerals from the amphibolite dynamothermal aureole mont albert gaspe quebec new 40ar 39ar ages are presented for two hornblendes and one biotite from the dynamothermal aureole that is situated at the base of the mont albeit ophiolite analysis by the incremental release technique reveals a small component of excess 40ar in one hornblende though both exhibit plateau type spectra the biotite was analyzed by the total fusion technique all apparent ages are concordant and average 456 3 ma dynamothermal aureoles form during the obduction process which juxtaposes ophiolites and amphibolite protoliths during a compressional tectonic event at a plate margin in this instance thrusting of the mont albert ophiolite over rocks of the shickshock group the concordance of biotite and hornblende ages indicates rapid postmetamorphic cooling and firmly dates obduction at 456 3 ma ago an age younger than any of the other northern appalachian ophiolites the high pressure metamorphism of the amphibolite is inconsistent with the present high structural level of the composite mont albert

on the origin of early proterozoic gneiss domes and metamorphic nodes northern michigan biotite 40 r 39 r cooling ages from medium pressure 500 600 mpa rocks in the watersmeet district northern michigan suggest significant cooling uplift and concomitant deformation during gneiss dome formation at 1755 ma well after the close of the 1870 1830 ma penokean orogeny however an 1822 ma hornblende plateau date indicates that the isograds surrounding the dome are penokean in age we attribute gneiss dome formation and doming of penokean aged isograds to an episode of orogenic collapse superimposed on an earlier history of crustal shortening this contrasts with the compressional origin for gneiss domes preserved in the low pressure 200 300 mpa republic district the different origins may reflect the fact that collapse was localized along the overthickened region of the orogenic belt in contrast to the watersmeet area hornblende and biotite 40ar 39ar ages obtained from the republic area are 1720 1680 ma given the relatively shallow depth of this region it is unlikely that temperatures re

role of underground fissure flow in near surface rainfall runoff process on a rock mantled slope in the karst rocky desertification area abstract because of the complex near surface double layer geologic structure i e surface and underground fissures of slopes in karst regions it is difficult to collect data on all flows especially the flows generated in underground fissures this lack of information leads to a poor understanding of the rainfall runoff process associated with soil loss in karst landscapes the goal of this study was to determine the output characteristics of surface subsurface and underground fissure flows and their conversion relationships as well as the role of underground fissure flow in the near surface rainfall runoff process using rainfall experiments the results revealed the following findings light rainfall intensities 15 and 30 mm h generated subsurface lateral flow and underground fissure flow whereas greater rainfall intensities generated surface runoff in addition to subsurface and underground flows ii the runoff drainage depths of all the above flows increased with increasing rainfall intensity while the runoff drainage coefficient exhibited no obvious regular change except for the surface runoff moreover the distribution ratio of surface runoff to total flow also increased with increasing rainfall intensity but decreased with increasing underground fissure degree while the distribution ratio of underground fissure flow exhibited the opposite trend iii underground fissure flow with distribution ratios of 27 8 78 0 dominated the total flow yield this study has significance for controlling soil erosion and water shortage in the karst rocky desertification region and also improves the understanding of the near surface rainfall runoff process in this region

karst landscape and hydrology in morocco research trends and perspectives moroccan karst has been the subject of study over the last two decades as a system where landforms interact with groundwater springs and human action the literature review gone through in this article focuses on international publications including french journals it shows the complexity of the karst area and its local model diversity the regimes of the aquifers landforms and springs were reported in most mountain terrains and the local interactions between the karst aquifer karst springs landforms and human action were discussed even the rif mountain presents some karst aspects mainly in its central part the atlas domain is more dominated by karst the substrate types tectonics altimetry climate and vegetation roles are important in karst dynamics human factors impact the landscapes and the equilibrium of the hydro karst system via resources overuse and management indicators of the present day disequilibrium were evoked turbidity of water in karst springs geotechnical problems erosion of the soil etc these problems will be more complex in the future due to the human density increase and probable intense human activity in the rural areas sustainable management is therefore a challenging priority in the karst domain

chemical and boron isotope compositions of non marine brines from the qaidam basin qinghai china the general chemistry and boron isotope composition were investigated in fresh waters and hypersaline brines from the qaidam basin northern qinghai xizang tibet plateau china this basin is a large tectonically active system isolated from the ocean and composed of thick clastic and evaporite sediments the modern playas are subject to intense evaporation and are characterized by hypersaline brines as well as potash and borate evaporites the chemical composition of the dissolved solutes in the modern brines and waters reveals three main sources 1 inflow of hot springs enriched in sodium sulphate and boron evaporation of these waters leads to a high na cl ratio 1 a na cl so4 brine and an evaporite mineral assemblage of halite mirabilite borate lakes daqaidam and xiaoqaidam 2 inflow surface river waters which are modified by preferential dissolution of halite and potassium and magnesium salts characterized by a na mg cl solute type with low na cl 1 brcl licl and bcl ratios and 3 ca chloridic subsurface brines which are controlled by both salt dissolution and dolomitization processes evaporation and salt crystallization of mixtures of the latter two types leads to a marine like brine e g na mg cl type nacl ratio 1 and mineral assemblages similar to that predicted for progressive evaporation of seawater e g qarhan playa halite sylvite carnallite bischofite the 11 b values of the input waters to the qaidam basin range of 0 7 to 10 9 vs nbs 951 and brines from salt lakes 0 5 to 15 0 are similar to those of associated granitic rocks 11b 2 3 to 3 7 n 3 and hence indicate the non marine origin of these fluids the highest 11b values are associated with fluids with low bli ratios indicating selective removal of elemental boron and 10b by adsorption onto clay minerals the magnitude of 11b enrichment due to adsorption is 15 20 and thus non marine brines are well distinguished from marine derived brines 11b of 39 to 59 preserving the large isotopic difference 40 of their source waters it is proposed to use this distinctive isotopic signature for tracing the origin of ancient evaporite environments

postcollisional cooling of the penokean orogen in east central minnesota new 40ar 39ar thermochronologic data from the internal zone of the penokean orogen in east central minnesota indicate rapid cooling from mid crustal temperatures early proterozoic metamorphosed cover rocks yield concordant hornblende and biotite plateau ages of 1755 ma underlying archean basement gneiss yields concordant muscovite and biotite plateau ages of 1705 ma these are some of the oldest cooling ages recorded in rocks buried during the 1830 1860 ma penokean collisional orogeny cooling was coeval with regional rhyolitic volcanism and granite emplacement suggesting a period of tectonic activity in this region during mid to late 1700 ma based on similarities with phanerozoic extensional regimes we suggest preliminarily that these data might be explained by a previously unrecognized major extensional episode in the lake superior region

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

origin of the late cretaceous potash bearing evaporites in the vientiane basin of laos δ11b evidence from borates abstract the evaporites on the khorat plateau comprise one of the largest potash deposits in the world and their origin has long been a controversial problem based on boron isotope measurements from borate as a good indicator to distinguish marine and nonmarine evaporites the borates of potash layers were identified and the results were used to indicate the source of evaporites in the study area as representative of the whole khorat plateau the results show that the main borates include boracite and hilgardite the boracites occur as crystals and ooids with minor amounts of hilgardite aggregates the range of 11b values is from 21 30 to 32 94 averaging 29 74 and falls in the range of marine borates the 11b values in the potash layer are seemingly variable because of the influence of fluvial influx when salts were precipitating although the composition of seawater has possibly been modified the evidence from boron isotopic composition implies that the evaporites in the study area or in the whole khorat plateau are marine deposits

thermal history of low metamorphic grade paleoproterozoic sedimentary rocks of the penokean orogen lake superior region evidence for a widespread 1786 ma overprint based on xenotime geochronology abstract paleoproterozoic strata in northern michigan wisconsin and minnesota were deposited between 2 3 and 1 75 ga within the rifted margin and subsequent foreland basin of the penokean orogen these strata show evidence for multiple regional metamorphic events previously attributed entirely to the penokean orogeny 1875 1835 ma metasandstones from the marquette range supergroup and the animikie mille lacs and north range groups were sampled at multiple localities across minnesota wisconsin and michigan for metamorphic xenotime suitable for in situ shrimp u pb geochronology all samples are from the northern penokean foreland basin where the metamorphic grade is greenschist to sub greenschist and the strata are virtually undeformed xenotime u pb ages in these samples have a bimodal population with means of 1786 4 ma n 32 and 1861 10 ma n 9 xenotime of both ages are contained in metasandstones from the basal chocolay group in michigan and wisconsin and the mille lacs group and north range groups in minnesota the older age records a regional low temperature thermal event that is slightly older than the overlying menominee group in michigan and the animikie group in minnesota and ontario this 1861 ma event coincides with regional uplift that led to the formation of the unconformity between the menominee group and the overlying baraga group in michigan hence xenotime growth must have occurred at shallow burial depths younger units from the menominee and baraga groups in michigan and the animikie group in minnesota record only the 1786 ma event a dominant 1800 1790 ma metamorphic monazite population that overprints penokean interval monazite has been documented within amphibolite to granulite facies rocks immediately north of the niagara fault zone within the vicinity of gneiss domes and granitic plutons in contrast the 1786 ma xenotime ages are from low grade virtually undeformed rocks 50 150 km from the high grade zones and thus do not appear to reflect a local thermal imprint rather the geographic extent of the 1786 ma xenotime growth event suggests that it reflects a basin wide subtle thermal pulse it is proposed that the xenotime ages record widespread subtle heating triggered by renewed subduction along the orogen due to yavapai interval convergence the 1800 1700 ma yavapai terrane forms an accretionary belt throughout the central and southwestern u s and truncates the southern part of the penokean orogen in central wisconsin and southeastern minnesota about 200 km south of the sample sites alternatively an 1800 1765 ma interval of gravitational collapse of overthickened crust of the penokean orogen immediately north of the niagara fault zone may have driven a northward flow of hydrothermal fluids which subtly but pervasively altered the northern parts of the penokean foreland and resulted in xenotime growth

oblique subduction footwall deformation and imbrication a model for the penokean orogeny in east central minnesota the penokean orogeny was a major early proterozoic 1875 1825 ma tectonic event in the great lakes region in east central minnesota it is marked by multiply deformed and highly metamorphosed supracrustal rocks of the early proterozoic denham and thomson formations structural features similar to those in the supracrustal rocks also exist in the basement archean 2700 ma mcgrath gneiss such features are here explained in a tectonic model consisting of southward directed oblique subduction along the great lakes tectonic zone intense deformation occurred in the footwall of the major thrust which marked the boundary between downgoing and overriding plates during a type continental subduction sedimentary rocks thomson formation deposited on the footwall during loading caused by thrusting eventually became incorporated into the deformation zone early formed structures related to footwall deformation are a dominantly well developed foliation in the gneiss and isoclinal recumbent folds with a bedding subparallel foliation in the denham and lower thomson formations progressive metamorphism during subduction reached the garnet zone of the amphibolite facies various deformation inversions show that this early phase of deformation involved extreme flattening with z vertical and large amounts of extension in both the north south and east west directions footwall deformation was followed by imbrication and accretion onto the hanging wall during uplift associated with continued compression and isostatic rebound later formed structures associated with imbrication and deformation within the hanging wall consist of folding of the foliation and development of shear zones in the mcgrath gneiss and open to close upright to overturned folds in the denham and thomson formations the peak metamorphic event represented by staurolite occurred after the later deformation at temperatures of about 470 530 c and a minimum pressure of 3 4 kbar minimum depth of 12 4 km increasing temperature associated with decreasing pressure uplift is explained by conductive relaxation caused by crustal thickening and erosion this tectonic model may have more widespread implications for explaining similar structural features found in many precambrian terranes worldwide

behaviour of boron and strontium isotopes in groundwater aquifer interactions in the cornia plain tuscany italy abstract the cornia plain alluvial aquifer in tuscany is exploited intensely to meet the demand for domestic irrigation and industrial water supplies the b concentration of groundwater however is often above the european limit of 1 mg l 1 with the result that exploitation of these water resources requires careful management boron and sr isotopes have been used as part of a study on the origin and distribution of b dissolved in groundwater and indirectly as a contribution to the development of appropriate water management strategies the geochemistry of the cornia plain groundwater changes from a hco3 facies in the inland areas to a cl facies along the coastal belt where seawater intrusion takes place the b concentration of groundwater increases towards the coastal areas while the 11b 10b ratio decreases this indicates that there is an increasing interaction between dissolved b and the sediments forming the aquifer matrix whose b content is in the order of 100 mg kg 1 adsorption desorption exchanges take place between water and the sediment fine fraction rich in clay minerals with a net release of b from the matrix into the groundwater and a consequent 11b shift from positive to negative values the aquifer matrix sediments therefore seem to be the major source of b dissolved in the groundwater the groundwater matrix interactions triggered by the ionic strength increase caused by seawater intrusion can also be detected in the ca na ion exchanges dissolved sr follows a trend similar to that of ca while the 87sr 86sr ratio is equal to that of the exchangeable sr of the aquifer matrix and therefore does not change significantly these results have helped to define a new strategy for groundwater exploitation with the final objective of reducing b concentration in the water extracted from the aquifer

tectono stratigraphic evolution of the early proterozoic wisconsin magmatic terranes of the penokean orogen the early proterozoic penokean orogen developed along the southern margin of the archean superior craton the orogen consists of a northern deformed continental margin prism overlying an archean basement and a southern assemblage of oceanic arcs the wisconsin magmatic terranes the south dipping niagara fault suture zone separates the south facing continental margin from the accreted arc terranes the suture zone contains a dismembered ophiolite the wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure the northern pembine wausau terrane contains a major succession of tholeiitic and calc alkaline volcanic rocks deposited in the interval 1860 1889 ma and a more restricted succession of calc alkaline volcanic rocks deposited about 1835 1845 ma granitoid rocks ranging in age from about 1870 to 1760 ma intrude the volcanic rocks the older succession was generated as island arcs and or closed back arc basins above the south dipping subducti

fractionation of boron isotopes during erosion processes the example of himalayan rivers abstract the boron isotopic composition of 5 rain waters and 35 river waters running from the high himalayas 5050 m down to the bay of bengal were measured by ion microprobe to make a first survey of the boron isotopic fractionations present in a major erosion system the rains have rather homogeneous b concentrations and isotopic compositions 0 09 0 09 mol l and 5 4 1 7 at the exception of the two kathmandu samples which probably reflect a significant anthropic contamination the river waters show a large range of b concentrations from 0 09 to 28 68 mol l and of b isotopic compositions 11b values ranging from 7 0 to 29 4 no systematic correlation between the 11b values and the major ion chemistry of the river waters is present at the exception of the most b and cl rich rivers which have systematically the highest 11b values likely controlled by evaporite dissolution after correction for the evaporite contribution from 9 4 to 64 4 of dissolved b with a systematic decrease southwards the riverine b concentrations and 11b values are still highly variable from 0 10 to 5 83 mol l and from 5 8 to 24 1 respectively this variation reflects mostly different conditions of silicate weathering congruent and incongruent silicate dissolution the contribution from the dissolution of carbonates being quite negligible 5 of the dissolved b on the river b budget at variance with congruent silicate dissolution incongruent dissolution occurs with a large b isotope fractionation which depends on ph clay water 31 2 at acidic ph and 5 8 at higher ph the b systematic suggests strongly that these fractionations are produced over a wide range of ph from 7 to 9 5 in soils and don t result from reactions between the dissolved and suspended load in rivers the net result of himalayan erosion for the global b cycle is the input to the sea of waters with highly variable b concentrations and isotopic compositions 0 67 and 0 29 mol l 5 0 and 21 0 for the ganga and the brahmaputra during the monsoon period respectively

a boron isotopic study of a mineralogically zoned lacustrine borate deposit the kramer deposit california u s a abstract an investigation of the boron isotopic composition of hydrated borates in the kramer lacustrine deposit of southern california was undertaken in an effort to better inderstand the origins of mineralogically zoned deposits of this type twenty one samples from fifteen depths along a drill core through the deposit reveal that isotopic zoning accompanies mineral zoning the range of 11 b for borax through the 24 9 m thick na borate core facies is 0 1 to 1 7 except for samples inand just below a clay rich 6 m interval where 11 b varies from 5 1 to 2 3 the 11 b of three cottonball ulexite samples in a 3 0 m thick na ca borate facies above the na borate facies ranges from 5 5 to 4 6 whereas two samples from a 6 1 m thick basal na ca borate facies both yield 2 1 the 11 b of colemanite from near the top of the upper na ca borate facies is 8 6 the small range of 11 b through much of the na borate facies indicates that the source waters of the borax precipitating lake varied little in 11 b for a time interval of 5 7 10 4 yr the 11 b variations within and among borax crystals in the 6 m clay rich interval some of which are estimated to have occurred over a period of weeks were probably produced by a combination of ph change and rayleigh effect during partial desiccation cycles the distinctly different ranges of 11 b exhibited in the upper and lower na ca borate facies and the distinctive cottonball habit of the crystal aggregates indicate that ulexite originated through growth in the lake margin muds

tourmaline b isotopes as tracers of fluid sources in silicified palaeoarchaean oceanic crust of the mendon formation barberton greenstone belt south africa pervasive silicification is a common phenomenon in early archaean volcano sedimentary sequences reflecting the interaction between si rich fluids and the archaean oceanic crust in the palaeoarchaean barberton greenstone belt south africa the silicified zones locally contain abundant tourmaline in order to constrain the source of fluids responsible for the alteration six tourmaline bearing samples from the 3 3 ga mendon formation were investigated by in situ analyses of mineral chemistry and boron isotopes the samples comprise a silicified finely laminated sedimentary chert and five highly altered and silicified komatiites electron microprobe analysis empa indicates that tourmaline is mostly dravitic with one sample between dravite and mg foitite tourmaline has a weakly developed patchy colour and chemical zonation with variations in al fe and mg composition some samples show strong zoning in cr concentration with cr enrichment in the core and locally the high cr domains are at contacts with other cr rich phases such as magnesiochromite and chromian muscovite fuchsite overall the boron isotope composition 11b ranges from 20 7 to 10 2 two groups of tourmaline are distinguished based on the variation in 11b ratios within single samples 1 those with small 4 range in 11b values spinifex textured komatiites and silicified sediment and 2 those with a large range in 11b values of up to 18 brecciated and foliated samples positive boron isotope values 6 to 10 are found in one spinifex textured komatiite and are interpreted as being derived from seawater interacting with archaean oceanic crust in shallow hydrothermal systems the intermediate boron isotope values 5 to 8 found in all other samples are similar to morb and may represent boron derived from the archaean oceanic crust the rare and exceptionally light boron isotope values 10 to 21 were found in rims of group 2 tourmaline these values cannot be produced by fractionation alone and point to the presence of another fluid source the source of the light boron has yet to be identified but possible candidates are remobilized boron either derived from granitic crust or from marine evaporites that precipitated from seawater enriched in 10b in any case the isotopically light boron appears to have been present during seafloor hydrothermal alteration and deposition of the mendon formation at ca 3 3 ga

boron isotopic composition as a provenance indicator for the flux raw material in roman natron glass abstract boron is a trace element present in natron glass which largely enters the glass via the flux therefore the b isotope ratio is targeted as a means of provenancing this flux in this work 33 greco roman natron glasses and 18 natron samples were analysed for their b isotopic composition expressed as 11b all glasses except one of mixed flux origin show a 11b value close to the average value of 29 11 natron samples from the wadi natrun show an average 11b of 29 8 while the sample from al barnuj shows a 11b of 28 5 the average for 4 fezzan samples from libya is 25 3 and that for the 2 samples from lake pikrolimni in greece 10 5 there is an influence of the sand on the 11b of natron glass complicating the picture but in general the silica source will slightly lower the 11b of the glass compared to that of the natron source the high melting temperature has no significant effect on the b isotope ratio it can be concluded that greco roman natron glasses show a rather homogenous 11b the wadi natrun salts analysed fit a model in which the 11b of the glasses is somewhat lower than that of the natron source due to the input of low 11b sand the samples from lake pikrolimni in greece analysed in this study show too low 11b values to be used in glass making according to this model

reductive weathering of black shale and release of barium during hydraulic fracturing abstract hydraulic fracturing is an important technological advance in the extraction of natural gas and petroleum from black shales but water injected into shale formations in the fracturing process returns with extraordinarily high total dissolved solids tds and high concentrations of barium ba it is generally assumed that high tds comes from the mixing of surface water injected fluid with na ca cl formation brines containing elevated ba but the mechanisms by which such mixing might occur are disputed here we show that ba in water co produced with gas could originate from water rock reactions with ba levels observed in produced waters reached on a time scale relevant to hydraulic fracturing operations we examined samples from three drill cores from the marcellus shale in pennsylvania and new york to determine the possible water rock reactions that release barium during hydraulic fracturing two samples one containing microcrystalline barite baso 4 and one without barite contain elevated concentrations of ba relative to the crustal average for shale rocks a third sample is slightly depleted in ba relative to the crustal average micro xrf measurements and sem eds analysis combined with chemical sequential extraction methods reveal that a majority of the ba in all samples 55 77 wt is present in clays and can only be leached from the rock by dissolution in hydrofluoric acid thus a majority of barium in our samples is relatively inaccessible to leaching under hydraulic fracturing conditions however the balance of ba in the rocks is contained in phases that are potentially leachable during hydraulic fracturing e g soluble salts exchangeable sites on clays carbonates barite organics we next studied how shale reacts with water at elevated temperatures 80 c low eh 100 to 200 mv and a range of ionic strengths is 0 85 6 4 that emulate conditions prevalent at depth during hydraulic fracturing our experimental results indicate that the amount of ba released from the bulk rock has a positive correlation with the ionic strength of the reacting fluid between 5 and 25 of the total ba in the rock can be leached from shale under ionic strength conditions and leachate compositions typical of produced waters over a contact time of just 7 days we suggest that reductive weathering of black shale occurs during hydraulic fracturing due to 1 ba 2 in clays exchanging with na and ca 2 ions that are present in high concentrations in produced water and 2 increased solubility and dissolution kinetics of barite under high ionic strength conditions at the low eh conditions prevalent during hydraulic fracturing the sulfate deficient water allows ba to be dissolved into the produced water based on ba yields determined from laboratory leaching experiments of marcellus shale and a reasonable estimate of the water rock mass ratio during hydraulic fracturing we suggest that all of the ba in produced water can be reconciled with leaching directly from the fractured rock

factors controlling carbonate dissolution rates quantified in a field test in the austrian alps carbonate dissolution rates were investigated by measuring the mass difference of carbonate tablets exposed to natural dissolution for 1 year 70 tablets were distributed over 13 test sites on the north slope of the hochschwab massif in the austrian alps the influences of altitude subsoil vs sub aerial exposure vegetation karst morphology soil humidity sample lithology and sample surface morphology were investigated the observed dissolution rates varied between 13 and 40 m a for subcutaneous samples and about 11 m a for sub aerial exposure outstandingly high rates of 48 m a were observed in a doline and nearly zero rates were measured at a site influenced by seeping spring water a mass balance using high resolution hydrological data was calculated for the klaffer spring which has an average outflow of 4 8 m3 s it indicated a loss of 21 106 kg of carbonate rock per year which gives an average dissolution rate of 95 m a for the catchment area of 83 km2 the dissolution rates of 10 m a from the sub aerially exposed samples are comparable to values from limestone pedestals which were protected from dissolution by glacial erratics for the past 15 ka

impact of water rock interactions on indicators of hydraulic fracturing flowback fluids produced from the jurassic shale of qaidam basin nw china abstract water rock interactions occurring during fracturing and flowback in shale gas reservoirs may dominate some chemical and isotopic compositions of hydraulic fracturing flowback fluids hfff by imparting characteristic compositions of the continental shale to the hfff in this paper a simple conservative mixing model scmm and a progressive conservative mixing model pcmm were developed to evaluate and understand the impacts of geochemical processes on forensic indicators 11b 87sr 86sr and ba sr of hfff produced from the dameigou shale application of the paired sample t test showed that the measured values of 11b 87sr 86sr ba and sr in hfff produced from the dameigou shale were all significantly p 1 45 in hfff therefore 87sr 86sr and ba sr show potential as indicators of continental hfff produced from carbonate poor shales and provide a clear distinction from rapidly circulating shallow groundwater mainly recharged by rainwater 87sr 86sr 0 70903 0 70914 and ba sr

boron isotopic composition of marine and nonmarine evaporite borates abstract here we present the results of the boron isotopic analysis of borates from some well known marine and nonmarine evaporite deposits combining new analyses with analyses from the literature yields a mean 11 b value for nine marine evaporite borate analyses of 25 4 permil 11 b 10 b 4 15 0 02 and a mean for twenty five nonmarine evaporite borates of 7 10 permil 11 b 10 b 4 02 0 04 previous studies have shown that the boron isotopic composition of seawater 11 b 40 permil 11 b 10 b 4 20 is about four percent heavier than the boron isotopic composition of most crustal rocks and minerals we suggest that our results for marine and nonmarine evaporite borates reflect this difference thus it should be possible to use boron isotopic composition as a tracer for boron of marine evaporitic origin applications include borate bearing evaporite deposits and perhaps borate and or borosilicate bearing metamorphic rocks

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

boron isotopic composition of fumarolic condensates from some volcanoes in japanese island arcs boron samples from 40 fumarolic condensates from volcanoes in the ryukyu arc satsuma iwo jima and shiratori iwo yama and the north east japan arc usu shinzan showa shinzan esan and issaikyo yama all have 11b10b ratios close to 4 07 higher values from 4 09 to 4 13 were only observed in condensates from volcanoes in the southernmost end of the north east japan arc nasu dake the northern part of the izu bonin arc hakone and the north mariana arc ogasawara iwo jima these higher values suggest geological interaction of the magmas with sea water enriched in 11b

boron isotopic composition of tourmaline from massive sulfide deposits and tourmalinites boron isotope ratios 11b 10b have been measured on 60 tourmaline separates from over 40 massive sulfide deposits and tourmalinites from a variety of geologic and tectonic settings the coverage of these localities is global 5 continents and includes the giant ore bodies at kidd creek and sullivan canada broken hill australia and ducktown usa overall the tourmalines display a wide range in 11b values from 22 8 to 18 3 possible controls over the boron isotopic composition of the tourmalines include 1 composition of the boron source 2 regional metamorphism 3 water rock ratios 4 seawater entrainment 5 temperature of formation and 6 secular variations in seawater 11b the most significant control appears to be the composition of the boron source particularly the nature of footwall lithologies variations in water rock ratios and seawater entrainment are of secondary importance the boron isotope values seem especially sensitive to the presence of evaporites marine and non marine and carbonates in source rocks to the massive sulfide deposits and tourmalinites

the chocolay group lake superior region u s a sedimentologic evidence for deposition in basinal and platform settings on an early proterozoic craton the early proterozoic chocolay group in the lake superior region is a cratonal sequence consisting of a basal unit overlain successively by quartzite dolomite and slate formations two regional depositional environments are described 1 present day structural troughs marquette menominee and felch michigan show evidence of having sedimentary basin precursors and 2 other areas gogebic range michigan show evidence of sedimentation in platform settings the basal unit in the marquette and menominee troughs is as much as 160 m thick and was probably deposited by alluvial processes in the gogebic range the basal unit is less than 10 m thick and resembles lag deposits at the base of transgressive sequences the overlying quartzite contains cross beds that show two regional sedimentary vector paleocurrent distributions 1 unimodal low variance distributions with sedimentary vectors oriented subparallel to local structural trough axes marquette menominee and felch troughs and 2 polymodal distributions with sedimentary vectors showing greater dispersion about the mean gogebic range as indicated by many varieties of sedimentary structures silicified evaporites cryptalgal structures intraclast breccias and so on the carbonates and interstratified siliciclastics of the chocolay group were deposited in subtidal to supratidal conditions taylor noted in 1972 that certain members of the chocolay group carbonates thicken toward the center of the marquette trough with concomitant facies changes the uppermost pelite unit of the chocolay group was probably deposited below normal wave base it is concluded that the basins and platforms were formed on a craton undergoing rift type tectonism

occurrence of rare borate minerals veatchite a tunellite teruggite and cahnite in the emet borate deposits turkey the emet borate deposits were formed in two separate basins possibly part of an interconnected lacustrine playa lake in areas of volcanic activity fed partly by thermal springs and partly by surface streams the borates are interlayered with tuff clay and marl limestone occurs above and below the borate lenses sediments in both basins are similar but borate minerals show different mineralogical and geochemical features in the two basins

climate and cave control on pleistocene holocene calcite to aragonite transitions in speleothems from morocco elemental and isotopic evidence the occurrence of aragonite in speleothems has commonly been related to high dripwater mg ca ratios because mg is known to be a growth inhibitor for calcite laboratory aragonite precipitation experiments however suggested a more complex array of controlling factors here we present data from pleistocene to holocene speleothems collected from both a dolostone and a limestone cave in northern morocco these stalagmites exhibit both lateral and stratigraphic calcite to aragonite transitions aragonite fabrics are well preserved and represent primary features in order to shed light on the factors that control alternating calcite and aragonite precipitation elemental mg sr ba u p y pb al ti and th abundances were measured using la icp ms and analysed with principal component analysis samples were analyzed at 100 200 m resolution across stratigraphic and lateral transitions carbon and oxygen isotope ratios were analysed at 100 m resolution covering stratigraphic calcite to aragonite transitions results show that the precipitation of aragonite was driven by a decrease in effective rainfall which enhanced prior calcite precipitation different geochemical patterns are observed between calcite and aragonite when comparing data from the grotte de piste and grotte prison de chien this may be explained by the increased dripwater mg ca ratio and enhanced prior aragonite precipitation in the dolostone cave versus lower dripwater mg ca ratio and prior calcite precipitation in the limestone cave a full understanding for the presence of lateral calcite to aragonite transitions is not reached trace elemental analysis however does suggest that different crystallographic parameters ionic radius amount of crystal defect sites adsorption potential may have a direct effect on the incorporation of sr mg ba al ti th and possibly y and p

middle proterozoic uplift events in the dunbar dome of northeastern wisconsin usa isotopic ages of granitic and metamorphic rocks exposed in the dunbar structural dome of northeastern wisconsin identify a protracted series of tectonic and hydrothermal events that culminated in major regional uplift during middle proterozoic keweenawan ca 1 100 ma continental rifting and volcanism the major rock forming events and the structural development of the dome occurred during the interval 1 862 4 ma to 1 836 6 ma whole rock rb sr ages are partly reset in response to a widely recognized but cryptic event in wisconsin and michigan at about 1 630 ma the scale and systematic character of the whole rock resetting strongly suggests the presence of a fluid phase derived in situ from water dissolved in the silicates or externally from a subthrust plate of low grade metamorphic rocks the regional nature of the 1 630 ma disturbance possibly indicates that it is related to a major tectonic event such as an active plate margin far to the south rb sr biotite ages for the dunbar dome this study the southern complex of the marquette district van schmus and woolsey 1975 and the felch trough area aldrich and others 1965 provide a remarkably coherent pattern that reflects multiple episodes of differential uplift younger events superimposed on a regional 1 630 ma imprint are recorded at 1 330 ma and 1 140 ma the 1 330 ma disturbance could reflect stabilization following intrusion of the wolf river batholith at 1 485 ma the 1 140 ma uplift event occurred during keweenawan rifting and volcanism as a result of stresses imposed on a mosaic of fault bounded blocks with possible subcrustal influence the remarkably small variance in the 1 140 ma biotite age peak argues for rapid uplift and cooling and hence rapid erosion detritus from the uplift probably was being shed into nearby tectonic basins most of which did not survive subsequent uplift and erosion

evidence for nappe development during the early proterozoic penokean orogeny minnesota two major phases of early proterozoic penokean folding are now recognized in the thomson formation of east central minnesota effects of the first deformation are found only in the southern two thirds of the exposed thomson formation the second deformation affected the entire region of outcrop several lines of evidence indicate that northward directed nappes developed during the early phase of folding this evidence includes lithologic differences between the areas of one and two deformations the pervasive nature of an s 1 foliation in the area of its occurrence facing directions of f 2 folds and the refraction pattern of the s 1 foliation in graded metagraywacke slate beds taken together the data show that an area of several hundred square kilometres is on the upper limb or limbs of a large northward directed recumbent fold or folds nappes of the early phase of penokean deformation

chloride bromide δ11b systematics of a thick clay rich aquitard system boron cl and br concentrations and boron isotopic compositions 11b were used to provide insight into the sources and water sediment interactions of fossil water in a thick nonfractured aquitard system in saskatchewan canada the aquitard system consists of 80 m of late pleistocene clay rich till disconformably overlying 77 m of late cretaceous marine clay the clay is underlain by a regional sand aquifer variations in cl and br confirmed the presence of well defined conservative mixing relationships between four types of fluids present in the aquitard system 1 low cl water from the base of the fractured and oxidized till zone at 4 m depth 2 water characterized by an elevated cl peak 190 mg l at about 12 m 3 glacial meltwater present between 20 and 60 m depth and 4 more saline water cl up to 1000 mg l from the underlying cretaceous clay and sand aquifer glacial meltwater has low cl 11b 20 and cl br ratios 50 the low cl br ratio of the glacial meltwater is similar to that of modern inland precipitation which suggests that the br budget in the atmosphere 20 30 ka b p was similar to that of today and that br enrichment in the atmosphere may be a natural process the relatively low cl br ratio 150 and 11b values of the saline water in the sand aquifer 35 and 39 respectively and pore water in the cretaceous clay 25 6 and 32 6 respectively are not consistent with simple dilution of seawater but suggest dilution and modification of fifteenfold evaporated seawater with a low cl br and a high 11b value 39 this evaporitic seawater may have been entrapped in the cretaceous clay upon or after its deposition and subsequently flushed from the clay by fresher water we suggest that the refreshening process modified the original brine into na hco3 water type and extracted boron with 11b 39 from the adsorbed sites in contrast increase of cl in the upper section of the till the 12 m peak resulted in apparent depletion of dissolved boron and relative 11b enrichment which can be explained by adsorption processes the b 11b relationships can thus be used to trace water clay interactions in aquitard systems

evaporites marine or non marine division of evaporites into those types that retain information about primary mineralogy textures and structures primary evaporites and those types so extensively altered that few or no primary features remain secondary evaporites only primary evaporites can give unequivocal data bout their marine or non marine origin to help evaluate such primary deposits they have been further divided using the following attributes 1 whether the depositional setting was marine or non marine 2 whether the source water was a seawater b meteoric c hydrothermal d diagenetic e volcanogenic or f mixed specific criteria for making distinctions are 1 kinds of fossils 2 sedimentology of the associated non saline facies 3 kinds of primary saline minerals 4 association of such saline minerals both in qualitative and quantitative terms 5 trace element isotope and fluid inclusion geochemistry of such saline minerals modified journal abstract

the sedimentary cycle of the boron isotopes abstract marine sediments contain two isotopically distinct components a non desorbable fraction with 11b between 4 3 and 2 8 per mil n 10 and a desorbable component with 11b between 13 9 and 15 8 per mil n 6 the adsorption coefficient k for the uptake of b from seawater by fluvial suspended material mississippi has an experimentally determined value of 1 54 0 05 the associated isotope fractionation factor is 0 974 0 003 empirical values for k determined from the analysis of marine sediments n 6 were between 3 and 4 the amount of b adsorbed onto fluvial suspended material during estuarine mixing is about 9 109 moles yr based on pore water data adsorption experiments and comparative size fraction analyses suspended sediments from the mississippi river vs bottom deposits from the delta there is no evidence for the incorporation of b into detrital sediments at low temperature however the high b content of bauer deep metalliferous sediments must be due to incorporation of seawater b during formation of authigenic silicates the 11b of these minerals is 2 3 per mil hydrothermally altered sediments from dsdp hole 477 guaymas basin gulf of california have variable b contents from 33 ppm similar to the unaltered detritus to 1 2 ppm in the recrystallized material the latter has 11b as low as 9 0 per mil substantially lower than the unaltered material hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and 11b between 16 5 and 23 2 per mil the b mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope analysis of an oxisol profile developed over granite in the guyana shield showed that boron is partially mobilized during weathering with an isotopic offset of 2 5 per mil between bedrock and soil the observed enrichment of b in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature incorporation occurs only during burial diagenesis at temperatures greater than about 60 c however the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles

boron isotope geochemistry of salt sediments from the dongtai salt lake in qaidam basin boron budget and sources abstract dongtai salt lake in qaidam basin contains abundant boron and lithium resources and has the highest reserve of lithium found in the world but the origin of these resources is highly controversial in this study we carried out a detailed study on chemical compositions and boron isotope characteristics of salt sediments collected from a drill core in the dongtai salt lake the evaporite carbonate and silicate phases of the sediments show 11 b values of 6 4 to 2 2 17 3 to 0 5 and 14 6 to 2 8 respectively which suggest a non marine origin for the salt lake the variation of 11 b vs k identified the evolution process of the salt lake the geochemical hydrochemical signatures and the reserve estimation of boron resources approved the dominant sources of saline resources containing abundant b k and li from the inflowing nalenggele river the boron isotopic fractionation factors between evaporite and brine i e evaporite brine vary from 0 9869 to 0 9955 and the linear variation of evaporite brine vs li mg molar ratios reflects the boron isotopic fractionation during crystallization of the salts the positive correlation between 11 b and b in the carbonate phase reflects the ph control on the incorporation of boron into the carbonates and the equilibrium isotope fractionation follows the rayleigh isotope fractionation rule in a closed system the variation of 11 b values in the silicate phase behaved as an oscillating pattern and the more negative shift of 11 b values corresponds to the mudstone strata deposited under warm humid climate conditions indicating the influence of intensive weathering

geochemical and boron oxygen and hydrogen isotopic constraints on the origin of salinity in groundwaters from the crystalline basement of the alpine foreland abstract the b isotopic composition in combination with o and h isotopes and hydrochemical tracers is utilized to constrain the evolution of basement hosted groundwaters via water rock interactions and fluid infiltration from external sedimentary reservoirs two distinct groundwater types have been identified in the central european crystalline basement n switzerland sw germany 1 fresh groundwaters characterized by low values of 11b 3 5 to 0 6 18o 12 0 to 10 0 and d 86 8 to 71 9 and 2 brackish groundwaters with distinctly heavier b o and h isotopic compositions 11b 6 4 to 17 6 18o 9 4 to 5 6 d 67 6 to 60 8 fresh groundwaters show a systematic decrease in 11b related to an increase in b concentrations and degree of total mineralization along the pathway of groundwater migration which can only be interpreted in terms of leaching of crystalline host rocks a 11b value of 3 3 is inferred for the crustal b source mainly hercynian granites involved in the leaching process in agreement with the known 11b range of granitic rocks the evolution of brackish groundwaters derived from crystalline basement reservoirs with little water circulation is more complex as indicated by b o h stable isotope and hydrochemical e g b cl na cl and br cl constraints brackish groundwaters from the study area are influenced by admixture of sediment derived fluids which infiltrated from late paleozoic permo carboniferous and early mesozoic lower triassic sedimentary strata the data presented show that b isotopes are sensitive to mixing processes of fluids derived from different crustal reservoirs and hence may be utilized as a tracer for constraining the internal autochthonous vs external allochthonous origin of salinity in basement hosted groundwaters

cyclic variations of sulfate and boron concentrations and isotopes in deep groundwaters in the aquitaine basin france abstract concentrations and isotope contents of major and trace elements are principal factors in determining the origin of the chemical composition of groundwater this paper focuses specifically on the use of sulfur and boron isotopes to characterize the origin of cyclic variations in the deep eocene aquifer in the aquitaine sedimentary basin southwest of france it is part of a multi layer system mainly composed of sands and sandstone deposits groundwater contained in this deep reservoir is known to present stable chemical compositions allowing its use for various purposes like drinking water geothermal energy thermal activity and agricultural irrigation however among the dozens of wells exploiting this aquifer and despite the reservoir s substantial depth variations in sulfate concentration have been identified in a limited area of the reservoir these fluctuations are cyclic and they seem to be correlated with water level variations due to gas storage activities nearby in the same aquifer regular water samplings and analyses of major and trace elements and their isotopes have identified that bore concentration variations are correlated with sulfate variations a geochemical modelling approach based on water mixes elucidates the causes of these variations in chemical composition especially the boron and sulfate concentrations and their respective 11b and 34sso4 values from these numerical results we identify that different sources explain the variations of boron concentration one part coming from the silicates alteration present in sub layers of the exploited aquifer and the other part coming from the evaporites alteration present in the underlying molasse unit these results also confirm the existence of mass and potentially water transfers between the different sub layers of the reservoir and with the underlying molasse aquitard implying new constraints for the future hydrogeologic modelling

geochemistry and evolution of the early proterozoic post penokean rhyolites granites and related rocks of south central wisconsin u s a

evidence for east west crustal extension in the eastern alps implications for the unroofing history of the tauern window the contact between the western border of the tauern window and the overlying austroalpine nappes austria and italy is marked by a structural petrologic and geochronologic discontinuity that developed in the early stages of unroofing of the window within the window pressure temperature time paths j selverstone 1985 indicate that significant ductile thinning occurred shortly after the cessation of thrusting paleocene eocene sense of shear indicators rotated porphyroblasts asymmetric augen and pressure shadows s c fabrics associated with a west plunging stretching lineation indicate that this thinning occurred in response to top to the west low angle normal shear during metamorphism the same sense of normal shear is present in the mesozoic members of the austroalpine sequence west of the window in these rocks however west directed shear occurred at low temperatures 300 c after the thermal peak of metamorphism structural data and the regional geometry imply that the western end of the tauern window is a low angle normal fault brenner line that juxtaposed brittlely deformed rocks of the austroalpine nappes against more ductilely deformed rocks from the window biotite k ar and rb sr data suggest a miocene age for final movement on the brenner line these data indicate a prolonged history of east west extension in the eastern alps that affected all crustal levels early ductile thinning of lower crust followed by mid to upper crustal low angle normal faulting a model is presented that relates the young east west extension to displacement transfer from dextral movement on the periadriatic lineament in this model the brenner line and by analogy the simplon line can be thought of as detachment faults that tectonically unroofed the tauern window and lepontine thermal highs respectively

uplift patterns and orogenic evolution in the scottish dalradian rb sr and k ar mineral ages from the dalradian rocks of angus and perthshire indicate considerable diachronism of cooling following the caledonian regional metamorphism the oldest mineral ages 515 ma are similar to the independent estimates of peak metamorphic age and hence indicate very rapid cooling they occur in the highest grade samples of the angus region and are associated with localized uplift regional rapid uplift events at 460 440 ma and 410 390 ma may also be recognized and correlated with structural and igneous activity and metamorphic age dates within the scottish highlands thermal models show the importance of localized and discontinuous uplift in determining both the timing of metamorphism and the shape of the p t paths they suggest that the major diachronous metamorphism and granite production in the scottish highlands is depth controlled rather than representing major lateral diachronism of thickening or heat sources localized uplift may exercise considerable control on mineral facies variation within orogenic belts the local uplift in angus introduces hot high pressure tarfside nappe rocks into higher level tay nappe rocks thus the uniform block uplift models frequently used in the interpretation of metamorphic and structural phenomena in orogenic belts are an oversimplification of the real events

marine evaporites from an oceanic island in the neoproterozoic adamastor ocean abstract we report a hitherto unknown occurrence of ancient neoproterozoic evaporite deposits from an allochthonous terrane in the pan african gariep belt in namibia low contents of rb cs ba zr hf th and u flat chondrite normalised rare earth element ree patterns 87 sr 86 sr ratios as low as 0 7075 na cl br systematics of fluid inclusion leachates and high 11 b values for stratiform tourmalinites together with geologic evidence such as association with oceanic basalt gabbro and stromatolitic dolomite point to a marine evaporitic origin an atoll environment on an oceanic island is envisaged as a likely depositional setting in the associated mafic sequence we found a diamictite with metre sized ice rafted detritus suggesting the presence of sea ice cover at relatively low latitude around the time of evaporite deposition based on chemostratigraphic 87 sr 86 sr 13 c comparison with passive continental margin sediments in the para autochthonous external part of the gariep belt a correlation of the mafic diamicitite with the global varangian 590 560 ma glaciation is proposed

sediment budget of high mountain stream channels in an arid zone high atlas mountains morocco abstract in an arid zone the sediment budget is predominantly dependent on runoff which is controlled mainly by the type of rainfall sediment budget calculation is one of the indirect methods of estimating channel morphodynamics this method is advised here since it is not possible to directly measure this important hydrological indicator of environmental dynamics this is because in small mountain catchments of an arid zone it is impossible to obtain flow rates due to factors such as the amount and size of transported rock debris as well as the episodic and sudden nature of precipitation events the research was conducted in 3 catchments 2 95 km2 7 39 km2 22 73 km2 situated within the boundaries of the basin of the upper dades on the southern slopes of the high atlas in morocco the rivers of these catchments tributaries to a trunk river dades are ephemeral and mostly bedrock depending on lithology of the geology three automatic weather stations were installed there precipitation events 10 mm 51 rains in 3 catchments were used in the analysis simple rainfall typology 3 types was devised for these events during the research period seasonally repeated 6 times measurements of topography were obtained from 21 cross section profiles of streams of different order these measurements formed a basis for calculating both the intensity of flow in ephemeral rivers max 69 6 m s and the sediment budget in 70 of analysed channel cross sections erosion was dominant the average change of the surface area of the cross section profile is 82 the maximum seasonal between measurements enlargement of the surface cross section erosion is as high as 128 the lower catchment which is predominantly composed of conglomerates distinctly shows the slightest changes of the cross section profile surfaces max 24 the average volume of channel material displaced at the measurement point is 1 07 m3 max 9 81 m3 there is evidence that not only high intensity rains but also less intense but longer lasting rains amounting to high precipitation totals type c may result in the highest channel sediment budgets differences between a catchment lithology composed of limestones and marlstones and that composed of conglomerates have only a minor impact on sediment budgets in the first and second order channels whereas in the channels of the third and fourth order this impact is much higher it was found that sediment budgets calculated for individual channels were higher for the catchments composed of limestones and marlstones than for those composed of conglomerates even though the catchments of different lithology may have had the same number of tributaries this suggests that the sediment supply from slopes is comparatively larger in the catchments dominated by limestones and marlstones

pb and nd isotope and trace element constraints on the origin of basic rocks in an early proterozoic igneous complex minnesota abstract a suite of early proterozoic basic to granitic rocks exposed near st cloud minnesota are cut by northeast trending basaltic dikes pb isotope data for all of these rocks overlap and plot about an 1800 ma pb pb correlation line the basic rocks which are light ree enriched have nd values between 0 4 and 4 8 petrogenetic considerations suggest that the basic rocks were derived from a light ree enriched source which had an fe mg ratio greater than that for pyrolite the enrichment in fe mg is probably a result of the addition of basic melts to the source the light ree enrichment may have a mantle origin by the addition of mantle derived light ree enriched basic melts or fluids or a sedimentary origin by the addition of light ree enriched fluids or melts derived from subducted sediments with an early proterozoic provenance in either case the nd isotopes suggest that the light ree enriched component existed since c 2300 ma the igneous complex may have formed at a convergent margin an anorthositic gabbro near mora has an nd of 5 indicating that it was derived from a mantle source with a history of light ree depletion this gabbro may have been part of an early proterozoic ocean crust

boron isotope geochemistry of a brine carbonate system in the qaidam basin western china abstract the boron b isotope ph proxy for marine carbonates has been widely used to reconstruct past ocean ph values unlike seawater the apparent dissociation constant of boric acid kb and the 11b values of brines from the terrestrial salt lakes in western china vary however relevant studies concerning the b isotope geochemistry of brine carbonate systems in terrestrial salt lakes are limited in this study thirty nine clastic samples from a sediment core isl1a from the qarhan salt lake in the qaidam basin were collected these carbonates were analyzed for 11b b mg sr and ca using our new data as well as published ph values total dissolved solids tds element concentrations and 11b values of brines in western china we reached the following conclusions 1 during evaporation process salinity increases the 11b values of brines in salt lakes increase and the pkb logkb and ph values simultaneously decrease 2 the large heterogeneity in the 11b values of the carbonates 2 74 to 7 64 from core isl1a is mainly due to the 11b values of the brines rather than pkb and ph 3 b isotopic fractionation with a small carbonate brine of 0 997 in a brine carbonate system conforms to the rayleigh fractionation model 4 our comparison of the 11b values of these carbonates with other records from core isl1a suggests that the 11b values of the carbonates in the arid qaidam basin can be used as a new proxy for the salinity of paleo lake water

boron content and isotopic composition of tektites and impact glasses constraints on source regions abstract abundances of li be and b as well as boron isotopic compositions were determined in twenty seven tektite and impact glass samples using an ion microprobe samples included tektites from the australasian north american and ivory coast strewn fields and aouelloul and darwin impact glasses variations of b abundance and isotopic composition in a flanged australite were also studied 11 b variations of only a few permil were found within the australite flange the isotopic composition shows no correlation with the b contents or with the distance from the rim of the flange the mean 11 b value for the flanged australite is very similar to that of muong nong type tektites 1 9 1 9 thus vapor fractionation has been unimportant during tektite formation this is supported by the observation that b contents and the 11 b values of the different samples from the australasian tektite strewn field are not correlated with each other most tektites show a rather limited range of 11 b values 9 3 1 5 to 2 7 1 5 o which is small compared to the range observed for common terrestrial rocks 30 to 40 the b abundance and isotopic data can be used to place constraints on the tektite source rocks australasian tektites have high b and li abundances only clay rich sediments such as pelagic and neritic sediments as well as river and deltaic sediments have b contents up to 100 ppm and 11 b values that are in agreement with the range shown by australasian tektites 4 9 to 1 4 10 be and rb sr data indicate continental crustal source rocks and exclude pelagic and neritic sediments however deltaic sediments e g from the mekong river which are of continental crustal origin agree with 10 be rb sr and b data and support a possible source locality close to the coast of se indochina in the south china sea on the other hand one bediasite sample has a very high 11 b value of 15 1 2 1 requiring the presence of marine carbonates or evaporites among the source rocks this finding supports an offshore locality for the north american tektite source crater

the origins of the mengye potash deposit in the lanping simao basin yunnan province western china abstract the lanping simao basin lsb is a mesozoic cenozoic continental margin rift basin in western china it formed during the opening and closing of the tethys ocean this basin is also known as a metal belt as it hosts several metal deposits besides the mengye potash deposit however the exact dates of the formation either in the paleocene or the cretaceous and thus the origins of the marine continental or mixed origins of the mengye deposits remain disputed based on the basin s evolution materials of marine origin and or remnant seawater should be present but instead the salt layers of the mengye potash deposit present typically continental lithological features this study examines and reviews evaporative minerals br cl and i cl molar ratios and isotopes of s b and sr i and i cl data for this area has not been previously reported the basin s evaporative minerals are dominated by halite and sylvite the amounts of anhydrite chlorocalcite langbeinite glaserite tachyhydrite and glauberite are small all of these form in both marine and continental environments the values of i and the i cl molar ratios of halite and sylvite are from 0 07 to 0 27 ppm and from 0 03 to 0 11 10 6 respectively dependent on organic substances br and molar br cl values are from 89 08 to 555 45 ppm and from 0 06 10 3 to 0 38 10 3 respectively all of the br cl molar ratios are lower than those of seawater and most of them are 34 s 11 b and 87 sr 86 sr values for evaporative minerals indicate a continental origin for the mengye potash deposit however materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit thus the mengye potash deposit could be of continental origin with a remnant seawater trace