Using environmental isotopes in the study of the recharge-discharge mechanisms of the Yarmouk catchment area in Jordan

The recharge sources, the flow mechanisms and discharge areas of the different groundwater bodies underlying the Yarmouk River catchment area in Jordan, have, until now, not been adequately explained, although a wide range of hydrological, hydrogeological, and hydrochemical studies have been done. Along the Jordanian part of the catchment area of the Yarmouk River, groundwater issues from different aquifers with a variety of chemistries and types within the same aquifer and in between the different aquifers. Conventional recharge/discharge mechanisms, water balances and chemical analyses did not adequately explain the chemical variations and the different water types found in the area. Applying environmental isotopic tools combined with their altitude effects due to topographic variations (250–1,300 m a.s.l. within a distance of 20 km), and taking into consideration re-evaporation effects on the isotopic depletion and enrichment of rainwater, has greatly helped in understanding the recharge discharge mechanisms of the different aquifers. Precipitation along the highlands of an average of 600 mm/year is found to be depleted in its isotopic content of O¹⁸ = –7.0 to –7.26 and D = –32.2 to –33.28, whereas that of the Jordan Valley of 350 mm/year is highly enriched in isotopes with O¹⁸ = –4.06 and D = –14.5. The groundwater recharged along the highlands is depleted in isotopes (O¹⁸ = ~ –6, D = ~ –30), groundwater at the intermediate elevations is enriched (O¹⁸ = ~ –5, D = ~ –23) and that of the Jordan Valley aquifers containing meteoric water is highly enriched (O¹⁸ ~ –3.8, D = ~ –18). The deep aquifers in the Jordan Valley foothills are depleted in isotopes (O¹⁸ –18 = –6, D = –30) and resemble those of the highland aquifers. Only through using isotopes as a tool, were the sources of the different groundwater bodies and recharge and discharge mechanisms unambiguously explained. It was found that recharge takes place all over the study area and produces groundwater, which, from the highlands towards the Jordan Valley, shows increasing enrichment in isotopes. The highlands aquifer, with its groundwater depleted in isotopes, becomes confined towards the Jordan Valley; and, due to its confining pressure, leaks water upwards into the overlying aquifers causing their water to become less enriched in isotopes. Water depleted in its isotopic composition also seeps upward to the ground surface at the mountain foothills through faults and fissures.

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Resumen Las fuentes de recarga, los mecanismos de flujo y las áreas de descarga de los diferentes cuerpos de agua subterránea que subyacen el área de la cuenca del Río Yarmouk en Jordania, se han explicado de manera no ambigua únicamente mediante la aplicación de los isótopos como herramienta. A lo largo de la parte Jordana del área de la cuenca del Río Yarmouk el agua subterránea emerge de diferentes acuíferos con una variedad de tipos y composiciones, ya sea que provengan del mismo acuífero o de diferentes acuíferos. Los mecanismos convencionales de recarga/descarga, balances hídricos y variaciones químicas no han podido explicar las variaciones químicas y los diferentes tipos de aguas. La aplicación de herramientas de isótopos ambientales combinadas con los efectos de altitud derivados de variaciones topográficas (250 hasta 1,300 m s.n.m. en una distancia de 20 km) y tomando en consideración los efectos de re-evaporación en el empobrecimiento de isótopos y enriquecimiento del agua de lluvia han ayudado fuertemente en el entendimiento de los mecanismos de recarga/descarga de los diferentes acuíferos. La precipitación en el área varía de 600 mm/año, a lo largo de las tierras altas, a 350 mm/año en el área del Valle Jordán. El flujo de agua subterránea ocurre de las tierras altas hacia el Valle Jordán. El agua subterránea de las tierras altas está empobrecida en isótopos (O¹⁸ =~ –6, D =~ –30), el agua subterránea de elevaciones intermedias está enriquecida (O¹⁸ =~ –5, D =~ –23), y el agua de los acuíferos del Valle Jordan contiene agua meteórica que se encuentra altamente enriquecida (O¹⁸ =~ –3.8, D =~ –18). Los acuíferos profundos que se localizan al pie de las tierras altas del Valle Jordán están empobrecidos en isótopos (O¹⁸ =~ –6, D =~ –30) y son similares a los acuíferos de las tierras altas. Solo al aplicar los isótopos ambientales como herramienta pudo explicarse de manera inequívoca las fuentes de los diferentes cuerpos de agua subterránea y los mecanismos de recarga y descarga.

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Résumé Les zones de recharge, les mécanismes découlement et les zones de décharges des différentes masses deau souterraine sous le bassin versant de la rivière Yarmouk en Jordanie, étaient expliquées de manière ambiguë par les seuls outils isotopiques. Le long de la parti Jordanienne du bassin versant de la rivière Yarmouk leau souterraine provient de différents aquifères et se distinguent par leur type et leur composition chimique, selon que leau provient du même ou des différents aquifères. Les mécanismes conventionnels de recharge et de décharge, bilan hydrologique ne donnaient pas dexplications satisfaisantes concernant les variations chimiques et les différents types deau. En appliquant les isotopes environnementaux combinés aux effets de laltitude sur les variations des teneurs isotopiques (laltitude varie de 250 à 1,300 m sur une distance de 20 km.) et en prenant en considération les effets de ré-évaporation sur lappauvrissement et lenrichissement isotopique des eaux pluviales ont fortement contribués à une meilleure compréhension des mécanismes de recharge des différents aquifères. Les précipitations annuelles sont comprises entre 600 mm dans les zones en altitude et 350 mm dans la vallée de la Jordanie. Les écoulements de leau souterraine sont dirigés des zones en altitude vers la vallée de la Jordanie. Les eaux souterraines des zones en altitude sont isotopiquement appauvries (O¹⁸ = ~ –6, D = ~ –30), les eaux souterraines des zones de moyenne altitude sont enrichies (O¹⁸ = ~ –5, D = ~ –23) et les eaux de la vallée très enrichies (O¹⁸ ~ –3.8, D = ~ –18). Les aquifers profonds dans la vallée de la Jordanie sont appauvris (O¹⁸ –18 = –6, D = –30) et se confondent avec les eaux des zones situées en altitude. En appliquant uniquement les isotopes environnementaux comme des outils de compréhension des phénomènes hydrogéologiques, la source des différentes masses deau souterraines, les mécanismes de la recharge et de la décharge pourraient être expliqués de manière ambiguë.

     

Geochemical,and stable and radiogenic isotope records in Devonian and Early Carboniferous carbonates from Valle de Tena,central Pyrenees (Spain): evidence for their diagenetic environments

Mineralogical, textural and geochemical investigations were made to determine the post-depositional evolution of Devonian and Early Carboniferous carbonates from Valle de Tena. The carbonate association is made up of low-Mg calcite, which occurs as micrite, spar cements, neomorphic patches and spar filling veinlets. Non-stoichiometric dolomite and ankerite occur as cements (dolomite also as replacements) in the Middle Devonian, post-dating calcite types. All these phases pre-date tectonic stylolites, indicating compaction after stabilization of the carbonate minerals. Strontium concentrations indicate that Early Devonian and Early Carboniferous micrites initially precipitated as aragonite; Middle and Late Devonian micrites precipitated as high-Mg calcites. Both precursors were diagenetically stabilized to low-Mg calcites through interaction with meteoric waters in phreatic environments. Trace elements in dolomite and ankerite indicate precipitation from Sr-enriched meteoric water. All studied carbonates, except Middle Devonian limestones, precipitated in reducing environments, which favoured incorporation of Fe and Mn. Late calcite generations precipitated from more saline waters than micrites. Light ¹⁸O values in micrites suggest alteration mainly in meteoric-phreatic environments. The dolomites and ankerites precipitated from more ¹⁸O-depleted fluids than the calcites, suggesting a greater contribution from meteoric waters. Variations in ¹³C of micrites represent primary secular trends, according to published ¹³C variations. The ¹³C oscillations within each succession probably relate to sea-level oscillations. Strontium isotopes also point to a meteoric origin of diagenetic fluids. Model calculations suggest that O and Sr isotopes equilibrated between calcites and fluid at relatively low water/rock ratios, whereas C isotopic signatures are inherited from limestones.     

Oxygen-isotope ratios in metamorphic eclogites

Rocks having O¹⁸-values less than those of normal basalts (5 to 7 permil) are very rare. However, anomalously low -values are common in European B-type eclogites, including those from N. W. Spain (1.5 to 5.6 permil), W. France, S. Germany, and W. Norway. Since isotopic exchange with sediments during metamorphism would have increased their -values, we tentatively conclude that the isotopically light eclogites descended from basaltic rocks which interacted with light meteoric waters at high temperatures, as did the Tertiary igneous rocks of W. Scotland. Isotopically heavy eclogites from S. Germany (8.6 to 10.5 permil) are isotopically similar to calc-silicate rocks from N. W. Spain and are possibly derived from dolomitic pelites.Coexisting quartz and rutile effectively fractionate the isotopes of oxygen and thereby constitute a potentially useful geothermometer. The average quartz-rutile fractionation in B-type eclogites is 6.5 permil.Lamont-Doherty Geological Observatory of Columbia University Contrib. No. 1559.     

Genesis of upper proterozoic stratabound copper mineralization,Kapunda, South Australia

Chalcopyrite-rich bedded and vein mineralization at Kapunda occurs in two locally developed dolosiltstone units within a sequence of generally darker-coloured, finer-grained calcmudstones and siltstones. The Mine Series accumulated in shallow water to supratidal, sabkha-like environments; there is no evidence for igneous activity in the region. Isotope data for bedded sulphides are characteristic of biological sulphate reduction in a restricted basin. It is likely that iron sulphides were produced initially, and that copper was introduced subsequently in mildly oxidizing, highly saline groundwaters, the influence of which is seen in the ¹³C-¹⁸O correlation for dolomite in the mineralized siltstones. Isotopic data support derivation of the veins from their host sediments, and this appears to have occurred before lithification.     

Hydrogeochemical investigation of surface and groundwater composition in an irrigated land in Central Tunisia

Major element concentrations, stable (δ¹⁸O and δ²H) and radiogenic (³H, ¹⁴C) isotopes determined in groundwater provided useful initial tracers for understanding the processes that control groundwater mineralization and identifying recharge sources in semi-arid Cherichira basin (central Tunisia).Chemical data based on the chemistry of several major ions has revealed that the main sources of salinity in the groundwaters are related to the water–rock interaction such as the dissolution of evaporitic and carbonate minerals and some reactions with silicate and feldspar minerals.The stable isotope compositions provide evidence that groundwaters are derived from recent recharge. The δ¹⁸O and δ²H relationships implied rapid infiltration during recharge to both the Oligocene and Quaternary aquifers, with only limited evaporation occurring in the Quaternary aquifer.Chemical and isotopic signatures of the reservoir waters show large seasonal evolution and differ clearly from those of groundwaters.Tritium data support the existence of recent recharge in Quaternary groundwaters. But, the low tritium values in Oligocene groundwaters are justified by the existence of clay lenses which limit the infiltration of meteoric water in the unsaturated zone and prolong the groundwater residence time.Carbon-14 activities confirm that groundwaters are recharged from the surface runoff coming from precipitation.     

Oxygen and hydrogen isotopes for the characteristics of groundwater recharge: a case study from the Chih-Pen Creek basin,Taiwan

Assessing the seasonal variation of groundwater recharge is important for effective management of groundwater resources. Stable isotopes of oxygen and hydrogen were used to estimate the sources of groundwater and seasonal contributions of precipitation to groundwater recharge in Chih-Pen Creek basin of eastern Taiwan. Based on the isotopes of precipitation (n = 177), two different local meteoric water regression lines (LMWL) can be obtained for the different seasons: δD = 8.06¹⁸O + 10.08 for wet season precipitation (May through October) and δD = 8.65δ¹⁸O + 17.09 for dry season precipitation (November through April). The slope and intercept of regression line for wet season precipitation are virtually identical to the global meteoric water line (GMWL) of Craig (1961). In contrast to during dry season precipitation due to evaporation effect the intercept of 17.09 is much higher than of the GMWL of 10. The results show the stable isotopes compositions of precipitation decrease with increasing rainfall amount and air temperature, due to the amount effect of precipitation is pronounced. The amount effect is clearly but do not show the temperature effect from January to December 2007. Using a mass-balance equation, a comparison of deuterium excess or d values of precipitation and groundwater indicates the groundwater consist of 76% wet season precipitation and 24% dry season precipitation, representing a distinct seasonal variation of groundwater recharge in study area. About 79% of the groundwater is recharged from the river water of the mountain watershed and 21% is from the rain that falls on the basin.     

Fluid regimes in the deformation of the Helvetic nappes,Switzerland, as inferred from stable isotope data

The stable isotope composition of veins, pressure shadows, mylonites and fault breccias in allochthonous Mesozoic carbonate cover units of the Helvetic zone show evidence for concurrent closed and open system of fluid advection at different scales in the tectonic development of the Swiss Alps. Marine carbonates are isotopically uniform, independent of metamorphic grade, where ¹³C=1.5±1.5 (1 ) and ¹⁸O=25.4±2.2 (1 ). Total variations of up to 2 in ¹³C and 1.5 in ¹⁸O occur over a cm scale. Calcite in pre- (Type I) and syntectonic (Type II) vein arrays and pressure shadows are mostly in close isotopic compliance with the matrix calcite, to within ±0.5, signifying isotopic buffering of pore fluids by host rocks during deformation, and closed system redistribution of carbonate over a cm to m scale. This is consistent with microstructural evidence for pressure solution — precipitation deformation.Type III post-tectonic veins occur throughout 5 km of structural section, extend several km to the basement, and accommodate up to 15% extension. Whereas the main population of Type III veins is isotopically undistinguishable from matrix carbonates, calcite in the largest of these veins is depleted in ¹⁸O by up to 23 but acquired comparable ¹³C values. This generation of veins involved geopressurized hydrothermal fluids at 200 to 350° C where ¹⁸O H₂O=–8 to +20, representing variable mixtures of ¹⁸O enriched pore and metamorphic fluids, with ¹⁸O depleted meteoric water. Calc-mylonites ( ¹⁸O=25 to 11) at the base of the Helvetic units, and syntectonic veins from the frontal Pennine thrust are characterized by a trend of ¹⁸O depletion relative to carbonate protoliths, due to exchange with an isotopically variable reservoir ( ¹⁸O H₂O=20 to 4). The upper limiting value corresponds to carbonate-buffered pore fluid, whereas the lower value is interpreted as ¹⁸O-depleted formation brines tectonically expelled at lithostatic pressure from the crystalline basement. Carbonate breccias in one of the large scale late normal faults exchanged with infiltrating ¹⁸O-depleted meteoric surface waters ( ¹⁸O=–8 to –10).During the main ductile Alpine deformation, individual lithological units and associated tectonic vein arrays behaved as closed systems, whereas mylonites along thrust faults acted as conduits for tectonically expelled lithostatically pressured reservoirs driven over tens of km. At the latest stages, marked by 5 to 15 km uplift and brittle deformation, low ¹⁸O meteoric surface waters penetrated to depths of several km under hydrostatic gradients.     

Oxygen and hydrogen isotope studies on the basal complexes of the Canary Islands: implications on the conditions of their genesis

¹⁸O/¹⁶O and D/H ratios have been measured in rocks and mineral separates from the basal complexes of Fuerteventura, Gomera and La Palma. These complexes comprise alkali plutonic rocks ranging from olivine gabbros to syenites and dikes of various mineralogy cutting them, all metamorphosed under greenschist conditions. K-Ar determinations gave ages from 48 to 17 My. The ¹⁸O's and D's of these rocks range from –1,4 to +11 and –113 to –45 respectively, with a majority of rocks depleted in heavy isotopes relative to normal, deep seated values. These values do not correspond to those found in ophiolitic sequences, which, for a comparable temperature range, give minimum ¹⁸O's>3. These values are explained in terms of water-rock interactions involving limited amounts of meteoric waters from high elevations. This implies the existence of a very important volcanic edifice over Fuerteventura in the Miocene Oligocene period with elevations between 2,500 and a maximum of more than 4,000 m.     

Characteristics and chronology of fracture — fluid infiltration in the Archean,Eye Dashwa Lakes pluton,Superior Province: evidence from H,C, O-isotopes and fluid inclusions

The Archean Eye Dashwa Lakes pluton (2672±24 Ma) has domains of mineralogically fresh isotropic granite, domains that have undergone bulk hydrothermal alteration, and at least eleven sets of sequential fracture arrays, each with distinctive mineral assemblages. Fresh granite is characterized by whole rock ¹⁸O=8.1 to 8.6 and primary magmatic quartz-feldspar (+1.3), quartz-biotite (5.2 to 5.4) and quartz-magnetite (+9.8) fractionations. Magmatic fluids had a calculated isotopic composition of ¹⁸O=7.9±0.5, and D=–80±5. These isotropic volumes of the granite have not experienced significant incursion of external thermal waters. Pegmatites, quartz-molybdenite veins, and phlogopite-muscovite coated fractures are sporadically distributed in the granite, and were precipitated from high-temperature magmatic fluids where ¹⁸O=8.0 to 10.3 and D=–80±5.The most abundant variety of fracture filling assemblage is epidote-quartz-chlorite±muscovite: fractures are bounded by domains of mineralogically similar bulk hydrothermal alteration of the granite. These minerals formed at 160 to 280° C, in the presence of NaCl, and NaCl-MgCl₂ brines (up to 25 wt% NaCl equivalent) of probable evolved marine water origin ( ¹⁸O=+0.4 to +3.8, D=–10 to –35) undergoing transient boiling. Upper plateau ⁴⁰Ar/³⁹Ar ages for the muscovite are 2650±15 Ma. Sequentially in the chronology of fracture-infiltration events, calcite-fluorite veins were deposited from boiling fluids at 340 to 390° C, isotopically characterized by ¹⁸O=4.7 and ¹³C=–5; and rare prehnite-chlorite lined fractures formed at 250 to 290° C. A generation of adularia-bearing veins precipitated at 140 to 230° C, from CaCl₂-NaCl brines, where ¹⁸O=0 to –6.5 and D=–10 to –30. Incremental ⁴⁰Ar/³⁹Ar age spectra on the K-feldspar yield an upper plateau of 1100 Ma. Subsequently, hematite developed during reactivation of earlier fractures, at 140 to 210° C in the presence of fluids characterized by ¹⁸O=–0.4 to –5.4 and D=–15 to –25. Arrays of open fractures partially occupied by gypsum and goethite reflect a fluid infiltration event at temperatures <50° C. Many of the earlier generations of fracture minerals have transgranular fracture infillings which record the presence of low temperature (88–190° C), hypersaline CaCl₂-NaCl brines. Narrow fractures lined with clays±calcite are sites for seepage of modern ground-waters. The isotopic signature of clay ( ¹⁸O=12 to 20, D=–80±5) plots near the line for modern kaolinites, confirming its formation in the presence of recent surface waters. Calcites coexisting with the clay minerals, and in fractured pegmatite show a common isotopic signature ( ¹⁸O=23±0.5, ¹³C=–13.6), indicating precipitation from modern groundwaters, where reactivated fractures have acted as conduits for infiltration of surface waters to depths of 200 m. Intermittent fracture-infiltration has occurred over 2.7 Ga. The early sequences of fracture-related fluid flow are interpreted in terms of devolatilization of the granite, followed by thermal contraction fracturing, incursion of marine water and convective cooling in the Archean. Hematite and adularia fracture fillings correspond to a stage when meteoric water infiltrated the volcanicplutonic terrain during Proterozoic and later times. Episodic fracture-fluid expulsion events may have been driven by seismic pumping, in response to magmatically and tectonically induced stresses within the Shield, with surface waters penetrating to depths of 15 km in the crust.     

The Candelaria silver deposit,Nevada — preliminary sulphur,oxygen and hydrogen isotope geochemistry

The pre-Cenozoic geology at Candelaria, Nevada comprises four main lithologic units: the basement consists of Ordovician cherts of the Palmetto complex; this is overlain unconformably by Permo-Triassic marine clastic sediments (Diablo and Candelaria Formations); these are structurally overlain by a serpentinitehosted tectonic mélange (Pickhandle/Golconda allochthon); all these units are cut by three Mesozoic felsic dike systems. Bulk-mineable silver-base metal ores occur as stratabound sheets of vein stockwork/disseminated sulphide mineralisation within structurally favourable zones along the base of the Pickhandle allochthon (i.e. Pickhandle thrust and overlying ultramafics/mafics) and within the fissile, calcareous and phosphatic black shales at the base of the Candelaria Formation (lower Candelaria shear). The most prominent felsic dike system — a suite of Early Jurassic granodiorite porphyries — exhibits close spatial, alteration and geochemical associations with the silver mineralisation. Disseminated pyrites from the bulk-mineable ores exhibit a ³⁴S range from — 0.3 to + 12.1 (mean ³⁴S = +6.4 ± 3.5, 1, n = 17) and two sphalerites have ³⁴S of + 5.9 and + 8.7 These data support a felsic magmatic source for sulphur in the ores, consistent with their proximal position in relation to the porphyries. However, a minor contribution of sulphur from diagenetic pyrite in the host Candelaria sediments (mean ³⁴S = — 14.0) cannot be ruled out. Sulphur in late, localised barite veins ( ³⁴S = + 17.3 and + 17.7) probably originated from a sedimentary/seawater source, in the form of bedded barite within the Palmetto basement ( ³⁴S = + 18.9). Quartz veins from the ores have mean ¹⁸O = + 15.9 ± 0.8 (1, n = 10), which is consistent, over the best estimate temperature range of the mineralisation (360°–460°C), with deposition from ¹⁸O-enriched magmatic-hydrothermal fluids (calculated ¹⁸O fluid = + 9.4 to + 13.9). Such enrichment probably occurred through isotopic exchange with the basement cherts during fluid ascent from a source pluton. Whole rock data for a propylitised porphyry ( ¹⁸O = + 14.2, D = — 65) support a magmatic fluid source. However, D results for fluid inclusions from several vein samples (mean = — 108 ± 14, 1, n = 6) and for other dike and sediment whole rocks (mean = — 110 ± 13, 1, n = 5) reveal the influence of meteoric waters. The timing of meteoric fluid incursion is unresolved, but possibilities include late-mineralisation groundwater flooding during cooling of the Early Jurassic progenitor porphyry system and/or meteoric fluid circulation driven by Late Cretaceous plutonism.     

Stable isotope systematics in mesozoic granites of Central and Northern California and Southwestern Oregon

¹⁸O, D, and H₂O⁺ contents were measured for whole-rock specimens of granitoid rocks from 131 localitics in California and southwestern Oregon. With 41 new determinations in the Klamath Mountains and Sierra Nevada, initial strontium isotope ratios are known for 104 of these samples. Large variations in ¹⁸O (5.5 to 12.4), D (–130 to –31), water contents (0.14 to 2.23 weight percent) and initial strontium isotope ratios (0.7028 to 0.7095) suggest a variety of source materials and identify rocks modified by secondary processes. Regular patterns of variation in each isotopic ratio exist over large geographical regions, but correlations between the ratios are generally absent except in restricted areas. For example, the regular decrease in D values from west to east in the Sierra Nevada batholith is not correlative with a quite complex pattern of ¹⁸O values, implying that different processes were responsible for the isotopic variations in these two elements. In marked contrast to a good correlation between (⁸⁷Sr/⁸⁶Sr)_o and ¹⁸O observed in the Peninsular Ranges batholith to the south, such correlations are lacking except in a few areas. D values, on the other hand, correlate well with rock types, chemistry, and (⁸⁷Sr/⁸⁶Sr)_o except in the Coast Ranges where few of the isotopic signatures are primary. The uniformly low D values of samples from the Mojave Desert indicate that meteoric water contributed much of the hydrogen to the rocks in that area. Even so, the ¹⁸O values and ¹⁸O fractionations between quartz and feldspar are normal in these same rocks.This reconnaissance study has identified regularities in geochemical parameters over enormous geographical regions. These patterns are not well understood but merit more detailed examination because they contain information critical to our understanding of the development of granitoid batholiths.     

Stable isotopic evidence for large-scale seawater infiltration in a regional metamorphic terrane; the Trois Seigneurs Massif,Pyrenees, France

Oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a Hercynian metamorphic sequence in the Trois Seigneurs Massif, Pyrenees, France, indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous ¹⁸O values. The extent of homogenization is shown by the similarity of ¹⁸O values in metacarbonates, metapelites and granitic rocks (+11 to +13), and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies. These values contrast with the ¹⁸O values of metapelites of lower metamorphic grade ( ¹⁸O about +15). Homogenization was caused by a pervasive influx of hydrous fluid. Mass-balance calculations imply that the fluid influx was so large that its source was probably high-level groundwaters or connate formation water. Hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at D=–25 to –30, suggesting a seawater origin. Many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6–12 km in the presence of this water-rich fluid, the composition of which was externally buffered. Deep penetration of surface waters in such environments has been hitherto unrecognized, and may be a key factor in promoting major anatexis of the continental crust at shallow depth. Three types of granitoid are exposed in the area. The leucogranites and the biotite granite-quartz diorite are both mainly derived from fusion of local Paleozoic pelitic metasediment, because all these rocks have similar whole-rock ¹⁸O values (+11 to +13). The post-metamorphic biotite granodiorite has a distinctly different ¹⁸O (+9.5 to +10.0) and was probably derived from a deeper level in the crust. Rare mafic xenoliths within the deeper parts of the biotite granite-quartz diorite also have different ¹⁸O (+8.0 to +8.5) and possibly represent input of mantle derived magma, which may have provided a heat source for the metamorphism.Contribution No. 4192, Publications of the Division of Geological and Planetary Sciences, California Institute of Technology     

Stable isotope study of carbonate-cemented rocks from the Pobitite Kamani area,north-eastern Bulgaria

The Precipitation of carbonate cements in the Pobitite Kamani area (Lower Eocene) began during early diagenesis of sediments. There is evidence, however, that calcite is still forming today.The negative ¹³C values to –29.2 suggest that the carbonate formed during degradation of ¹²C-enriched organic matter (perhaps partly from oxidation of methane). The ¹⁸O values of –0.9 to –1.6 reflect the marine origin of the early diagenetic carbonate cements. Most of the carbonates, however, formed during late diagenesis (at approximately 1300 m burial depth) and/or recently (after uplift) from percolating groundwaters. These carbonates have an isotopic composition characteristic of carbonates which precipitated from meteoric waters under normal sedimentary temperatures in isotopic equilibrium with ¹²C-enriched soil carbon dioxide.     

Stable isotope relations in an open magma system,Laacher See,Eifel (FRG)

¹⁸O/¹⁶O and D/H ratios have been measured for matrix glasses and phenocrysts from the zoned phonolitic Laacher See tephra sequence (11000 y.b.p., East Eifel volcanic field, FRG) to study open-system behaviour of the associated magma system. Mineral and glass ¹⁸O values appear to be largely undisturbed by low-temperature, secondary alteration, record isotopic equilibrium and confirm previous conclusions, based on radiogenic isotope evidence, of early, small-scale crustal assimilation during differentiation of parental magmas in a crustal magma chamber. One sanidine-glass pair possibly documents the late stage influx of meteoric fluids into the topmost magma layer prior to eruption. A sealing carapace of chilled magma, which itself was strongly contaminated, prevented large-scale fluid exchange up to the point prior to eruption when this carapace was fractured and meteoric water gained access to parts of the magma system. D/H measurements of various glass types (glass inclusions, dense and pumiceous glass) and amphiboles gave conflicting results suggesting a combination of degassing, volatile exchange with country rocks and hydration. Stable isotope ratios for primitive parental magmas ( ¹⁸O=+5.5 to 7.0) and mantle megacrysts ( ¹⁸O=+ 5.5 to +6.0, D=–21 to –38, for amphiboles and phlogopite, resp.) suggest a rather variable fluid composition for the sub-Eifel mantle.     

Contrasting fluid/rock interaction between the Notch Peak granitic intrusion and argillites and limestones in western Utah: evidence from stable isotopes and phase assemblages

The Jurassic Notch Peak granitic stock, western Utah, discordantly intrudes Cambrian interbedded pure limestones and calcareous argillites. Contact metamorphosed argillite and limestone samples, collected along traverses away from the intrusion, were analyzed for ¹⁸O, ¹³C, and D. The ¹³C and ¹⁸O values for the limestones remain constant at about 0.5 (PDB) and 20 (SMOW), respectively, with increasing metamorphic grade. The whole rock ¹⁸O values of the argillites systematically decrease from 19 to as low as 8.1, and the ¹³C values of the carbonate fraction from 0.5 to –11.8. The change in ¹³C values can be explained by Rayleigh decarbonation during calcsilicate reactions, where calculated is about 4.5 permil for the high-grade samples and less for medium and low-grade samples suggesting a range in temperatures at which most decarbonation occurred. However, the amount of CO₂ released was not anough to decrease the whole rock ¹⁸O to the values observed in the argillites. The low ¹⁸O values close to the intrusion suggest interaction with magmatic water that had a ¹⁸O value of 8.5. The extreme lowering of ¹³C by fractional devolatilization and the lowering of ¹⁸O in argillites close to the intrusion indicates oxgen-equivalent fluid/rock ratios in excess of 1.0 and X(CO₂)_F of the fluid less than 0.2. Mineral assemblages in conjunction with the isotopic data indicate a strong influence of water infiltration on the reaction relations in the argillites and separate fluid and thermal fronts moving thru the argillites. The different stable isotope relations in limestones and argillites attest to the importance of decarbonation in the enhancement of permeability. The flow of fluids was confined to the argillite beds (argillite aquifers) whereas the limestones prevented vertical fluid flow and convective cooling of the stock.     

Preliminary investigations of 18O/16O and D/H compositions in rhyo-ignimbrites in the In Hihaou (In Zize) Magmatic Center,central Ahaggar,Algeria

The 620 M.y.-old in Hihaou (In Zize) magmatic complex located at the north-western boundary of the Archaean In Ouzzal block (western Ahaggar), is composed of massive alkaline rhyo-ignimbrites and rhyolitic domes, which are intruded by a granophyric and granitic body. The whole is preserved in a cauldron structure. Extrusive rocks are strongly ¹⁸O-depleted, with -values as low as –1.5/SMOW, while granophyres are less depleted (minimum -¹⁸O value=+2.0/SMOW. The granite has values around + 6/SMOW. D/H compositions are rather low, with D–90 to –110/SMOW. Isotopic zoning of quartz phenocrysts, ¹⁸O/¹⁶O fractionation among coexisting phases, and heterogeneity of the whole-rock -¹⁸O values, suggest that the volcanic rocks have interacted with meteoric water after the eruption. Several mechanisms of isotopic alteration are discussed. The hydrothermal alteration does not seem to have been controlled by the granitic intrusion, but rather seems to have followed the deposition of thick pyroclastic deposits on permeable arkosic sandstones and fluvio-glacial conglomerates. Pervasive circulation of water through the cooling volcanic deposits could have produced the observed ¹⁸O depletion.     

Oxygen and hydrogen isotope evidence for meteoric water infiltration during mylonitization and uplift in the Ruby Mountains-East Humboldt Range core complex,Nevada

Stable isotope analyses of rocks and minerals associated with the detachment fault and underlying mylonite zone exposed at Secret Creek gorge and other localities in the Ruby-East Humboldt Range metamorphic core complex in northeastern Nevada provide convincing evidence for meteoric water infiltration during mylonitization. Whole-rock ¹⁸O values of the lower plate quartzite mylonites (95% modal quartz) have been lowered by up to 10 per mil compared with structurally lower, compositionally similar, unmylonitized material. Biotite from these rocks has D values ranging from -125 to -175, compared to values of -55 to-70 in biotite from unmylonitized rocks. Mylonitized leucogranites have large disequilibrium oxygen isotope fractionations ( ^{quartz-feldspar} up to 8 per mil) relative to magmatic values ( ^{quartz-feldspar}1 to 2 per mil)). Meteoric water is the only major oxygen and hydrogen reservoir with an isotopic composition capable of generating the observed values. Fluid inclusion water from unstrained quartz in silicified breccia has a D value of-119 which provides a plausible estimate of the D of the infiltrating fluid, and is similar to the isotopic composition of present-day and Tertiary local meteoric water. The quartzite mylonite biotites would have been in equilibrium with such a fluid at temperatures of 480–620° C, similar to independent estimates of the temperature of mylonitization. The relatively high temperatures required for isotopic exchange between quartz and water, the occurrence of fluid inclusion trails and deformed veins in quartzite mylonites, and the spatial association of the low-¹⁸O, low-D rocks with the shear zone all constrain isotopic exchange to the mylonitic (plastic) deformation event. These observations suggest thata significant amount of meteoric water infiltrated the shear zone during mylonitization to depths of at least 5 to 10 km below the surface. The depth of penetration of meteoric fluids into the lower plate mylonites was at least 70 meters below the detachment fault. In contrast, the upper-plate unmylonitized fault slices are dominated by brittle fracture and are often intensely veined (carbonates) or silicified (volcanic rocks and breccias). The fluids associated with the veining and silicification were also meteoric as evidenced by low ¹⁸O values of the veins, which are often 10 per mil lower than the adjacent carbonate matrix, and the exceptionally low ¹⁸O values (down to-4.4) of the breccias. Several previous studies have documented the infiltration of meteoric fluids into the brittley deformed upper plate rocks of core complexes, but this study provides convincing evidence that surface fluids have penetrated lower plate rocks undergoing plastic deformation. It is proposed that infiltration took place as the shear zone began the transition from plastic flow to brittle fracture while the lower plate rocks were being uplifted. During this period, plastic flow and brittle fracture were operating simultaneously, perhaps allowing upper plate meteoric fluids to be seismically pumped down into the lower plate mylonites.     

Oxygen isotopes in mantle related and geothermally altered magmatites of the Transhimalayan (Gangdese) ranges

In closed magma systems SiO₂ approximately measures differentiation progress and oxygen isotopes can seem to obey Rayleigh fractionation only as a consequence of the behaviour of SiO₂. The main role of ¹⁸O is as a sensitive indicator of contamination, either at the start of differentiation ( ¹⁸O_init) or as a proportion of fractionation in AFC. Plots of ¹⁸O vs SiO₂-allow to determine initial ¹⁸O values for different sequences for source comparison. For NBS-28=9.60, the ¹⁸O at 48% SiO₂-varies between a high 6.4 for Kiglapait (Kalamarides 1984), 5.9 for Transhimalaya, 5.8 for Hachijo-Jima (Matsuhisa 1979), 5.6 for Koloula (Chivas et al. 1982) and a low 5.3 for the Darran Complex, New Zealand. The Transhimalayan batholiths (Gangdese belt) were emplaced in the Ladakh-Lhasa terrane, between the present-day Banggong-Nujiang, and Indus-Yarlung Tsangbo suture zones, after its accretion to Eurasia. The gradient of the least contaminated continuous ( ¹⁸O vs SiO₂-igneous trend line is similar to that of Koloula, and AFC calculations suggest a low secondary assimilation rate of less than 0.05 times the rate of crystallisation. Outliers enriched in ¹⁸O are frequent in the Lhasa, and apparently rare in the Ladakh transsect. Low- ¹⁸O (5.0–0) granitoids and andesites on the Lhasa-Yangbajain axis are the result of present day or recent near-surface geothermal activity; their quartzes still trace the granitoids to the Transhimalaya ¹⁸O trend line, but the distribution of low total rock or feldspar ¹⁸O values could be a guide to more recent heat flow and thermally marked tectonic lineaments. Two ignimbrites from Maqiang show hardly any ¹⁸O-contamination by crustal material.     

Oxygen and hydrogen isotope compositions as indicators of granite genesis in the New England Batholith,Australia

Oxygen and hydrogen isotope studies of a number of granite suites and mineral separates from the New England Batholith indicate that O¹⁸ can be used to discriminate the major granite protoliths. The granite suites previously subdivided on the basis of mineralogical and geochemical criteria into S-type (sedimentary) and I-type (igneous) have O¹⁸ values consistently higher in the S-type granites (10.4–12.5) than in the spatially related I-type plutons (7.7–9.9). There appears to be a systematic variation in O¹⁸ from the most S-type to the most I-type granites, the dividing point between the two occuring at O¹⁸ equal to 10. A group of leucocratic granites that form about half of the batholith and difficult to classify mineralogically and geochemically is found to have low O¹⁸ values (6.4–8.1), suggesting an affinity to the most I-type granites. A single leucogranite pluton with minor muscovite has a O¹⁸ of 9.6 which is significantly higher than other leucogranites indicating a different origin perhaps involving amphibole fractionation.The behavior of D in the plutonic rocks is much less systematic than O¹⁸. Excluding samples collected adjacent to major faults, the D values show a rough positive correlation with water content similar to, but less pronounced than, the trend previously observed in the Berridale Batholith, southeastern Australia. This relation is considered to reflect an interaction between meteoric water and the granites, the largest effect being observed in samples with the least amount of water. Of note is the generally lower D values of the upper Paleozoic New England Batholith compared with the Silurian Berridale Batholith. This difference may be related to a near equatorial paleolatitude of 22 °S in the Silurian and near polar paleolatitudes in the late Carboniferous that have been inferred for these regions. Granite samples collected from near major faults, and one ignimbrite sample of rhyodacite composition, have very low D values (less than –120) suggesting a much greater degree of interaction with meteoric water.     

Modification of δD values in eastern Nevada granitoid rocks spatially related to thrust faults

Stable isotope data have been determined for 13 Mesozoic and Tertiary plutons in eastern Nevada and nearby Utah. In the southern Snake Range of eastern Nevada, where relations are best exposed and have been most intensively studied, D, ¹⁸O, and apparent K-Ar ages depend on proximity to the Snake Range decollement. Where stresses resulting from late movement on the decollement have caused cataclasis of Oligocene (37 Ma) granitoid rock, ¹⁸O, D, and K-Ar age values as low as –2.5, –155, and 18 Ma, respectively, have been determined. Where there has been no cataclasis, ¹⁸O values of Jurassic, Cretaceous, and Oligocene granitoid rocks are apparently unaffected, but both D values and K-Ar ages have been modified for distances of tens of meters below the decollement.Results similar to those in the southern Snake Range have been observed in other eastern Nevada granitoid rocks spatially related to regional thrust faults, as in the Kern Mountains, the Toana Range, and the northern Egan Range. In each of these areas cataclasis or deformation of granitoid rocks has resulted in lowered ¹⁸O, D, and K-Ar age values. Where there has been no cataclasis or deformation, ¹⁸O values are unaffected, but both D and K-Ar age values have been lowered by stresses resulting from postcrystallization movement along overlying thrust faults.Many of the plutons discussed have not been deeply eroded, and spatially related thrust faults crop out. Where thrust faults are not in evidence and the granitoid rocks give D values lower than about –130 along with spuriously low K-Ar age results, modification of the D and K-Ar age values may have been caused by stresses related to late movement along an overlying (now eroded) thrust fault.