Crustal Volatiles Research Articles

Influence of upwelling mantle magmas on cratonic crust implied from Vp/Vs beneath South America platform

SUMMARY The crust of the South American platform recorded imprints of dynamic processes related with the opening of the Central and South Atlantic but has not been well measured. Crustal structure can be retrieved from teleseismic receiver functions using H–κ stacking, but nearly parallel stripes of high stacking values existing in stacking images for seismic stations in sedimentary area cause difficulties in identifying solutions. We show that some seemingly spurious stripes that do not point to any layer solution are helpful in the identification of the solution position. With the aid of the auxiliary stripes, we retrieved thicknesses and Vp/Vs of sedimentary and crystalline crust for 65 permanent stations of the Brazilian Seismographic Network and six new portable seismic stations in Brazil and Uruguay. The resulted sedimentary thickness and Vp/Vs exhibit a good correlation with the Phanerozoic sediments in the South American basins. The crust of Paraná–Etendeka Large Igneous Province (LIP) had been expected to be more mafic since it had ever been penetrated by mantle magma in the Cretaceous related to the south Atlantic opening. However, we found very low Vp/Vs (1.67) in the crystalline crust beneath the LIP, implying a more felsic crust and that no significant mafic intruding/underplating has occurred in the region. The more felsic crust may be formed in a special evolution early than the magmatic event, or during the magmatic event by releasing crustal volatiles. The resulted sedimentary thickness and Vp/Vs ratios exhibit a good correlation with the Phanerozoic sediments in the South American basins, which implies that Triassic–Jurassic and Cretaceous magmatism did not cause significant metamorphism in sediments formed before the magmatic events.

Volatile characteristics and fluxes of He-CO2 systematics in the southeastern Tibetan Plateau: Constraints on regional seismic activities

The spatial and temporal evolutionary mechanisms of volatile components at plate boundaries and their potential as earthquake precursors are not well understood. Based on observations of He–CO2 from 19 hot-spring gases in the Lancang River fault zone, Yunnan Province, the results show that the volatiles mainly come from the crust. The combined He isotope, He–CO2 relationships, and δ13C–CO2 values of the hot-spring volatiles indicate that it is a mixture of mantle and crustal fluids. These are related to the radiogenic He production caused by crustal U and Th elements with <5% mantle-derived He, whereas C is mainly from the metamorphic decarbonization of Tethyan marine carbonate rocks. Based on the He–CO2 isotopic relationship, crustal volatiles flux with a significant proportion were determined within a non-volcanic area, which was estimated to be 9–132 mol a−1, and CO2 degassing was estimated to be 2–120 × 109 mol a−1. These results are comparable to those of some volcanic areas and large seismically-active fault zones (such as the San Andreas Fault zone). The compressional stress field of the rigid crust near the study area leads to the low permeability of large faults and CO2 degassing from the hydrothermal system, resulting in chemical precipitation that further blocks the shallow crust conduits and deduced overpressure below the hydrothermal reservoir, which may be the cause of the presence of earthquakes with magnitudes greater than 7 in the Lancang River fault zone. The results are significant for elements cycling of converging plate boundaries and earthquake hazards monitoring.

Deep CO2 and N2 emissions from Peruvian hot springs: Stable isotopic constraints on volatile cycling in a flat-slab subduction zone

Gas-rich hot springs throughout the Peruvian Andes contain a surprising contribution of mantle and crustal volatiles (CO2 and N2) despite being located along a volcanic gap associated with modern flat-slab subduction. Similar mantle and crustal volatile degassing is observed in springs from the backarc region of the northern Altiplano Plateau which experienced flat-slab subduction in the Oligocene. We constrain the sources of deeply-derived volatiles using C, N, O and H stable isotope analyses alongside previously reported helium isotope (3He/4He) and gas abundance data. δ18O and δ2H values of spring waters are consistent with regional meteoric water, with deviations towards higher values due to fluid mixing and high-temperature fluid-rock interaction. δ15N values of N2 gas range from −0.5 to +4.4‰ (vs AIR), indicating contributions of mantle and crustal (sedimentary) nitrogen. δ13C values of dissolved inorganic carbon (DIC) and CO2 gas from bubbling springs are used to model initial δ13C values before degassing, with resulting values ranging from −13.6 to −0.3‰ (vs VPDB) and an average value of −6.9‰. DIC concentrations range from 1 to 57 mmol/kg, of which carbonate dissolution accounts for only a small fraction (average of 15%). The remaining carbon (1 to 44 mmol/kg) is derived from a mixture of deep CO2 sources with endmember δ13C values of −7‰ and −14‰ which, in light of relationships with 3He/4He ratios, are interpreted to be the subcontinental lithospheric mantle (SCLM) and metamorphic crustal carbon, respectively. These results are consistent with previous interpretations that slab-to-lithosphere fluid transfer is mobilizing volatiles from the SCLM to the continental crust above the flat slab and confirms that mantle CO2 is migrating with mantle helium. Metamorphic CO2 and N2 are mobilized from the continental crust and entrained by mantle fluids on their way to the surface. In the backarc region, similar geochemical patterns suggest that volatiles are released by dehydration and/or partial melting of previously hydrated lithosphere. We estimate a CO2 flux of ~3 × 108 mol yr−1 (34 t d−1) from 45 springs with available discharge values. If scaled to all reported thermal springs in Peru, then the total CO2 emissions from Peruvian thermal springs may approach 2 × 109 mol yr−1 (203 t d−1), or ~ 0.2% of global emissions from subaerial volcanism. Regional CO2 emissions may be 10 to 100 times greater when considering CO2 diffusely lost along fault zones or temporarily dissolved near-surface aquifers. These results demonstrate that flat-slab subduction leads to an efficient and unexpected transfer of mantle and crustal volatiles to Earth's surface, and more generally, that deep volatile fluxes in subduction zones are not limited to active volcanism.

Origin of the degassing pipes at the Ries impact structure and implications for impact‐induced alteration on Mars and other planetary bodies

AbstractThe impact melt‐bearing breccias at the Ries impact structure, Germany, host degassing pipes: vertical structures that are inferred to represent conduits along which gases and fluids escaped to the surface, consistent with hydrothermal activity that occurs soon after an impact event. Although the presence of degassing pipes has been recognized within the well‐preserved and long‐studied ejecta deposits at the Ries, a detailed mineralogical study of their alteration mineralogy, as an avenue to elucidate their origins, has not been conducted to date. Through the application of high‐resolution in situ reflectance imaging spectroscopy and X‐ray diffraction, this study shows for the first time that the degassing pipe interiors and associated alteration are comprised of hydrated and hydroxylated silicates (i.e., Fe/Mg smectitic clay minerals with chloritic or other hydroxy‐interlayered material) as secondary hydrothermal mineral phases. This study spatially extends the known effects of impact hydrothermal activity into the ejecta deposits, beyond the crater rim. It has been suggested that the degassing pipes at the Ries are analogous to crater‐related pit clusters observed in impact melt‐bearing deposits on Mars, Ceres, and Vesta. The results of this work may inform on the presence of crustal volatiles and their interaction during the impact process on rocky bodies throughout the solar system. The Mars 2020 Perseverance rover may have the opportunity to investigate impact‐related features in situ; if so, this work suggests that such investigations may provide key information on the origin and formation of clay minerals on Mars as well as hold exciting implications for future Mars exploration.

A secretive mechanical exchange between mantle and crustal volatiles revealed by helium isotopes in 13C-depleted diamonds

Fluid inclusions trapped in fast-growing diamonds provide a unique opportunity to examine the origin of diamonds, and the conditions under which they formed. Eclogitic to websteritic diamondites from southern Africa show 13C-depletion and 15N-enrichment relative to mantle values (δ13C = -4.3 to -22.2 ‰ and δ15N = -4.9 to +23.2 ‰). In contrast the 3He/4He of the trapped fluids have a strong mantle signature, one sample has the highest value so far recorded for African diamonds (8.5 ± 0.4 Ra). We find no evidence for deep mantle He in these diamondites, or indeed in any diamonds from southern Africa. A correlation between 3He/4He ratios and 3He concentration suggests that the low 3He/4He are largely the result of ingrowth of radiogenic 4He in the trapped fluids since diamond formation. The He-C-N isotope systematics can be best described by mixing between fluid released from subducted altered oceanic crust and mantle volatiles. The high 3He/4He of low δ13C diamondites reflects the high 3He concentration in the mantle fluids relative to the slab-derived fluids. The presence of post-crystallisation 4He in the fluids means that all 3He/4He are minima, which in turn implies that the slab-derived carbon has a sedimentary organic origin. In short, although carbon and nitrogen stable isotope data show strong evidence for crustal sources for diamond-formation, helium isotopes reveal an unambiguous mantle component hidden within a strongly 13C-depleted system.

Comparison of central pit craters on Mars, Mercury, Ganymede, and the Saturnian satellites

AbstractWe report on the first results of a large‐scale comparison study of central pit craters throughout the solar system, focused on Mars, Mercury, Ganymede, Rhea, Dione, and Tethys. We have identified 10 more central pit craters on Rhea, Dione, and Tethys than have previously been reported. We see a general trend that the median ratio of the pit to crater diameter (Dp/Dc) decreases with increasing gravity and decreasing volatile content of the crust. Floor pits are more common on volatile‐rich bodies while summit pits become more common as crustal volatile content decreases. Uplifted bedrock from below the crater floor occurs in the central peak upon which summit pits are found and in rims around floor pits, which may or may not break the surface. Peaks on which summit pits are found on Mars and Mercury share similar characteristics to those of nonpitted central peaks, indicating that some normal central peaks undergo an additional process to create summit pits. Martian floor pits do not appear to be the result of a central peak collapse as the median ratio of the peak to crater diameter (Dpk/Dc) is about twice as high for central peaks/summit pits than Dp/Dc values for floor pits. Median Dpk/Dc is twice as high for Mars as for Mercury, reflecting differing crustal strength between the two bodies. Results indicate that a complicated interplay of crustal volatiles, target strength, surface gravity, and impactor energy along with both uplift and collapse are involved in central pit formation. Multiple formation models may be required to explain the range of central pits seen throughout the solar system.

Post-earthquake anomalies in He–CO2 isotope and relative abundance systematics of thermal waters: The case of the 2011 Van earthquake, eastern Anatolia, Turkey

We report the helium and carbon isotope (3He/4He, δ13C) and relative abundance (CO2/3He) characteristics of hydrothermal gases from eastern Anatolia sampled ~1month after the October 23, 2011 Van earthquake (Mw: 7.2, focal depth: 19km). Seven sites were sampled which comprise three localities along the Çaldıran Fault Zone, at a distance of 58–66km to the epicenter (Group I), two localities north of the Çaldıran Fault, about 90–113km from the epicenter (Group II), and two localities in the vicinity of the historically-active Nemrut Caldera at a distance of 110–126km from the epicenter (Group III). All sites were previously sampled for their He–CO2 systematics in 2009 (Mutlu et al., 2012) facilitating direct comparison with the post-earthquake dataset.The post-earthquake values cover a wide range of 3He/4He, δ13C and CO2/3He ratios, from 0.84 to 6.37RA (where RA=air 3He/4He), −5.30 to +0.49‰ (vs. VPDB), and 4.9×1010 to 6.85×1013, respectively. Group I samples show a consistent post-earthquake increase in 3He/4He whereas both Group II localities decreased in 3He/4He. No change was recorded for the two Group III localities. He isotope variations are consistent with simple changes in the proportions of mantle and crustal volatiles, with all Group I sites showing an increase in the mantle He contribution. We hypothesize that the enhanced mantle He signal is derived from asthenospheric melts intruded into the crust, with seismic perturbations responsible for bubble formation and growth leading to overpressure and gas loss. The strike–slip Çaldıran Fault Zone provides the permeable pathway for the liberated volatiles to reach hydrothermal systems at shallow levels of the crust and the surface. Release of crustal He dominates the He mass balance of Group II samples as locations are further from the earthquake epicenter. Group III samples are even further away from the earthquake and show no perturbations in He isotopes. Whereas binary mixing dominates the He isotope systematics, CO2 shows additional effects involving the hydrothermal system. Consequently, changes in the balance between mantle and crustal CO2 are masked and more difficult to discern. The results emphasize the sensitivity of He isotopes to seismic perturbations in the crust and illustrate how location of sampling sites – on permeable segments of faults – and distance from seismic events influence resulting changes involving gas chemistry.

Insights into mantle-type volatiles contribution from dissolved gases in artesian waters of the Great Artesian Basin, Australia

The geochemical features of the volatiles dissolved in artesian thermal waters discharged over three basins (Millungera, Galilee and Cooper basin) of the Australian Great Artesian Basin (GAB) consistently indicate the presence of fluids from multiple gas sources located in the crust (e.g. sediments, oil reservoirs, granites) as well as minor but detectable contributions of mantle/magma-derived fluids. The gases extracted from 19 water samples and analyzed for their chemical and isotopic composition exhibit amounts of CO2 up to about 340mlSTP/LH2O marked by a δ13CTDC (Total Dissolved Carbon) ranging from −16.9 to +0.18‰ vs PDB, while CH4 concentrations vary from 4.4×10−5 to 4.9mlSTP/LH2O. Helium contents were between 9 and >2800 times higher than equilibrium with Air Saturated Water (ASW), with a maximum value of 0.12mlSTP/LH2O. Helium isotopic composition was in the 0.02–0.21 Ra range (Ra = air-normalized 3He/4He ratio). The three investigated basins differ from each other in terms of both chemical composition and isotopic signatures of the dissolved gases whose origin is attributed to both mantle and crustal volatiles. Mantle He is present in the west-central and hottest part of the GAB despite no evidence of recent volcanism. We found that the partial pressure of helium, significantly higher in crustal fluids than in mantle-type volatiles, enhances the crustal He signature in the dissolved gases, thus masking the original mantle contribution. Neotectonic activity involving deep lithospheric structures and magma intrusions, highlighted by recent geophysical investigations, is considered to be the drivers of mantle/magmatic volatiles towards the surface. The results, although pertaining to artesian waters from a vast area of >542,000km2, provide new constraints on volatile injection, and show that fluids' geochemistry can provide additional and independent information on the geo-tectonic settings of the Great Artesian Basin and its geothermal potential.

Reprint of: Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

Crustal volatile release at Merapi volcano; the 2006 earthquake and eruption events

High‐temperature gas in volcanic island arcs is widely considered to originate predominantly from the mantle wedge and from subducted sediments of the down‐going slab. Over the decade (1994–2005) prior to the 2006 eruption of Merapi volcano, summit fumarole CO2 gas δ13C ratios are relatively constant at −4.1 ± 0.3‰. In contrast, CO2 samples taken during the 2006 eruption and after the May 26th 2006 Yogyakarta earthquake (M6.4) show a dramatic increase in carbon isotope ratios to −2.4 ± 0.2‰. Directly following the earthquake (hypocentre depth 10–15 km), a 3–5‐fold increase in eruptive intensity was observed. The elevated carbon isotope gas data and the mid‐crustal depth of the earthquake source are consistent with crustal volatile components having been added during the 2006 events, most probably by the thick local limestone basement beneath Merapi. This ‘extra’ crustal gas likely played an important role in modifying the 2006 eruptive behaviour at Merapi and it appears that crustal volatiles are able to intensify and maintain eruptions independently of traditional magmatic recharge and fractionation processes.

Impact craters with ejecta flows and central pits on Mercury

Impact craters with ejecta flows and/or central pits have been found on Venus, the Moon, Earth, Mars, and some icy satellites. Using the MESSENGER camera data obtained during the orbital mission, we found craters with ejecta flows and central pits on Mercury. The ejecta flows differ from normal ballistically emplaced ejecta deposits in their long mobilized distances. They all flowed in downslope directions and exhibited a layered morphology. Analog study suggests that the ejecta flows probably have formed by fluidization in the ejecta deposits. Crustal volatiles are not required to form the ejecta flows on Mercury, although they may have helped. The ejecta flows are most likely to be a type of avalanche features in forms of dry granular flows. Central pits in impact craters on Mercury are located on summits of central peaks when viewing in sufficiently high-resolution images, but some of the central pits may occur on crater floors. The central pit craters are all fresh craters located on smooth plains and intercrater plains. The pits are different from the other forms of rimless and irregularly-shaped depressions on Mercury in the size, morphology, and/or occurrence. Crustal volatiles are not required in forming the central pit craters and they may form in a similar way with the central pit craters on the Moon.

Peridotitic and websteritic diamondites provide new information regarding mantle melting and metasomatism induced through the subduction of crustal volatiles

Diamondites are mantle xenoliths comprised of polycrystalline diamond intergrown with garnet and minor clinopyroxene. Diamondites have some geochemical characteristics distinct from monocrystalline diamonds. Examples include 13C-depletion with modal δ13C value at −18‰ containing a high abundance of websteritic garnets (73%). This is in contrast to monocrystalline diamonds that show a strong mean δ13C value at −5‰ and low abundance of websteritic inclusions (2%). At present, geochemical studies focusing on diamondites are lacking, relative to coated and monocrystalline diamond. As a consequence, there exists a substantial volume of abundant mantle material that has been largely overlooked. We have determined the coupled δ13C–δ15N values and N-concentrations for 20 samples of mantle diamondite. Although their provenance is uncertain, these diamondites are thought to originate from Southern Africa because the major and rare Earth element (REE) compositions for the garnets are consistent with other Southern African diamondites.The coupled δ13C–δ15N values, N-concentrations in the diamond and REE patterns for the garnets we conclude that the source of the 13C-depleted carbon and 15N-enriched nitrogen is crustal in origin. This is by way of recycling subducted oceanic lithosphere beneath a stable craton, possibly the Kaapvaal craton in southern Africa. The peridotitic and websteritic garnet intergrowths have REE patterns similar to eclogitic garnets and we propose their petrogenesis due to mixing between a volatile saturated eclogitic melt and mantle peridotite. We propose that diamondites represent distinct diamond-forming event(s) related to mantle melting in the sub-cratonic mantle. Diamondite-formation events are proposed to be unrelated to most monocrystalline and coated diamonds formed by metasomatic processes involving little to no mantle melting.

Helium and carbon isotope systematics of cold “mazuku” CO2 vents and hydrothermal gases and fluids from Rungwe Volcanic Province, southern Tanzania

We report new helium and carbon isotope (3He/4He and δ13C) and relative abundance (CO2/3He) characteristics of a suite of 20 gases and fluids (cold mazuku-like CO2 vents, bubbling mud-pots, hot and cold springs) from 11 different localities in Rungwe Volcanic Province (RVP), southern Tanzania and from 3 additional localities in northern Tanzania (Oldoinyo Lengai Volcano and Lake Natron). At RVP, fluids and gases are characterized by a large range in He-isotope compositions (3He/4He) from 0.97 RA to 7.18 RA (where RA = air 3He/4He), a narrow range in δ13C ratios from −2.8 to −6.5‰ (versus VPDB), and a large range in CO2/3He values spanning nearly four orders of magnitude (4×109 to 3.2×1013). Oldoinyo Lengai possesses upper‐mantle-like He–CO2 characteristics, as reported previously (Fischer et al., 2009), whereas hot springs at Lake Natron have low 3He/4He (~0.6 RA), CO2/3He (~5–15×108) and intermediate δ13C (~−3.7 to −4.9 ‰). At RVP, fluid phase samples have been modified by the complicating effects of hydrothermal phase-separation, producing CO2/3He and δ13C values higher than postulated starting compositions. In contrast, gas-phase samples have not been similarly affected and thus retain more mantle-like CO2/3He and δ13C values. However, the addition of crustal volatiles, particularly radiogenic helium from 4He-rich reservoir rocks, has modified 3He/4He values at all but the three cold CO2 gas vent (i.e., mazuku) localities (Ikama Village, Kibila Cold Vent and Kiejo Cold Vent) which retain pristine upper-mantle He-isotope (~7 RA) and He–CO2 characteristics. The extent of crustal contamination is controlled by the degree of interaction within the hydrothermal system, which increases with distance from each major volcanic center. In contrast, we propose that pristine cold CO2 mazuku gases collected at stratigraphic contacts on the flanks of RVP volcanoes may potentially tap isolated gas pockets, which formed during previous eruptive events and have remained decoupled from the local hydrothermal system. Furthermore, by identifying and utilizing unmodified gas samples, we determine mantle versus crustal provenance of the CO2, which we use to estimate mantle-derived CO2 fluxes at both Rungwe and Lake Natron. Finally, we investigate the origin of the apparent discrepancy in He isotopes between fluids/gases and mafic phenocrysts at RVP (from Hilton et al., 2011), and discuss the tectonic (i.e., rift zone dynamics) and petrogenic conditions that distinguish RVP from other plume-related subaerial rift zones.

Isotopic evidence for the infiltration of mantle and metamorphic CO 2–H 2O fluids from below in faulted rocks from the San Andreas Fault system

To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ( 3He/ 4He) of 0.1–2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault (Kennedy et al., 1997). Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C- and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite δ 13C and fluid inclusion 3He/ 4He is consistent with a mantle origin for a fraction of the infiltrating CO 2. Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H 2O and CO 2 in faulting, supporting the involvement of deep fluids percolating through and perhaps weakening the fault zone. There is no clear evidence for a significant contribution from meteoric water, except for overprinting related to late weathering.

What we know about Mars from its impact craters

Martian impact craters provide insights into formation ages of terrain units, nearsurface properties, and the planet’s degradational history. Crater size-frequency distribution analyses allow determination of terrain unit relative ages, and extrapolation of the lunar crater chronology can provide estimates of absolute ages for these units. Such analyses indicate that Mars has been geologically active throughout its history, but it also retains extensive regions dating back to ca. 4 Ga. Higher cratering rates during the Late Heavy Bombardment (LHB) helped to create the Martian regolith, and formation of large impact basins helped to erode the initially denser Martian atmosphere and may have created the hemispheric dichotomy. Low global degradation rates since the end of LHB (ca. 3.8 Ga) resulted in well-preserved impact crater morphologies. The presence of layered ejecta blankets and central pits associated with fresh to moderately eroded craters suggests a volatile-rich crust. Impact crater depth-diameter relationships allow estimation of the vertical extent of crustal volatiles to depths greater than those probed by current spacecraft instrumentation. Temporal changes in subsurface ice reservoir depths are revealed by differences in layered ejecta onset diameter as a function of crater age. An understanding of the morphology and morphometry of pristine impact craters facilitates efforts to determine the amount and types of degradation and the periods over which they operated. Impact craters therefore play a major role in unraveling the climatic and geologic history of Mars.

Geochemistry of thermal waters along fault segments in the Beas and Parvati valleys (north-west Himalaya, Himachal Pradesh) and in the Sohna town (Haryana), India

A geochemical survey on thermal waters discharging in the Beas and Parvati valleys (Kulu District, Himachal Pradesh) and in the Sohna town (Gurgaon District, Haryana) was carried out in March 2002. The Beas and Parvati area is characterized by regional seismogenetic fault segments, thrusts and complex folded structures where deep fluid circulation occurs. Thermal springs have temperatures varying between 35°C and 89°C. The wide range of surface temperatures and water chemistries suggest the mixing, at various degrees, between a deep saline end-member and a shallow freshwater. Based on the high salinity and the enrichment in halogens (Cl, Br), B and Li, the contribution of the deeper end-member seems to be larger for Kulu and Kalath relative to Manikaran and Kasol. Moreover, a large input of crustal volatiles (He, CO2, H2) is observed for Kulu and Kalath waters. The high dissolved CO2 content and its carbon isotopic composition (δ13CTDIC = -2.87 and -7.49‰ vs. PDB for Kulu and Kalath, respectively) point to a deep, prevalent thermo-metamorphic provenance of the carbon dioxide. A general shallow (i.e., organic) origin of carbon dioxide is suggested for Kasol and Manikaran. The estimated deep temperatures based on the quartz geothermometer provide values ranging between 93-114°C for all the thermal waters of the Beas and Parvati valleys. The Sohna thermal spring emerges at 42°C from joints of the seismogenetic Sohna fault. A Na-Cl-HCO3 composition characterizes this water with very low contents of all the selected minor and trace elements. High dissolved helium content points to a prolonged deep circulation, whereas calculated δ13C-CO2 (-14.23‰ vs. PDB) is indicative of the general shallow origin of carbon dioxide. The estimated deep temperatures are close to the discharge ones, not providing any valuable information about the temperature of the deeper reservoir.

Lava fountains from the 1999 Tvashtar Catena fissure eruption on Io: Implications for dike emplacement mechanisms, eruption rates, and crustal structure

The first direct evidence that patterns of basaltic eruptive activity may be very similar on Io and Earth was seen on November 26, 1999, when the solid‐state imaging system on board the Galileo spacecraft obtained high‐resolution images of a fissure eruption taking place in one of the calderas of the Tvashtar Catena complex. We analyzed the dynamics of the fissure eruption from the morphology of the lava fountains and pyroclastic deposits and derived an estimate of the eruption rate. Our best estimate of the volume eruption rate per unit length of fissure lies in the range 0.7 to 7 m3 s−1 m−1, and multiplying this rate by the fissure length of ∼25 km yields a total volume eruption rate of magma of ∼2×104 to 2×105 m3 s−1. The upper end of the inferred eruption rate is very close to the upper end of the range of eruption rates observed or inferred for fissure eruptions on Earth. Theoretical models of the possible dike systems feeding the fissure show that for eruptions of positively buoyant magma, the elastic properties of rocks are such that a magma flux of 6 to 7 m3 s−1 m−1 is the largest value that can ever be realized in such eruptions, this limiting value being independent of planetary gravity and thus the same on all silicate bodies. The eruption rate inferred for Tvashtar can also be achieved by a negatively buoyant magma, but in that case the source depth cannot be much greater than a few tens of kilometers. We find that some eruptive events are consistent with the effusion of magmas which are buoyant relative to the crust, whereas others appear to involve magmas which are not. This implies that the distribution of crustal volatiles is laterally very inhomogeneous. Our analyses suggest that the depths from which magmas make their final ascent to the surface of Io are generally of order tens, rather than hundreds, of kilometers.

Noble gases, K, U, Th, and Pb in native gold

We present determinations of the noble gas and Pb isotopic abundances and of K, Th, and U concentrations of native gold. Our results demonstrate that gold is an excellent carrier for crustal volatiles, but direct dating of gold using the U, Th‐4He, 40K–40Ar, and U fission Xe methods was not successful for various reasons. The main significance of this work is the great sensitivity of gold for trapped gases as well as for gases that were produced in situ which gives the prospects of using gold and its fluid and solid inclusions for the study of paleogas composition. Numerous nuclear effects characterize the noble gas inventory of placer gold from Switzerland and Italy, vein gold from Italy, South Africa, and Venezuela, and lode gold from South Africa. The degassing patterns obtained by mass spectrometry show a low‐temperature release of volatiles around 500°C from fluid inclusions mainly in vein gold and a high‐temperature release from solid inclusions and the gold itself. The low‐temperature volatiles represent species that were trapped when the gold crystallized. We investigated the following trapped species: the isotopes of He, Ne, Ar, Kr, Xe, and Pb, and the abundances of K, U, Th, H2O, and CO2. The crustal gases trapped by gold comprise 3He from 6Li(n,α)3H → β− → 3He, 4He and 40Ar from the U, Th, and K decay, and Xe from 238U fission. We observe 4He/40Ar = 3.9 for the radiogenic trapped gases of tertiary gold and a ratio of 1.4 for Archean gold. These ratios are consistent with the production ratios from U and K at the respective times and demonstrate that gold can be used as a sampler of ancient atmospheric gases. The concentrations of U and Th range from a few parts per billion to a few parts per million, and those of K and Pb range up to some tens of parts per million. The antiquity of trapped Pb is indicated by the Pb‐Pb model age of about 3000 Ma for the lead extracted from vein gold and quartz of the Lily gold mine (South Africa). Gold also contains noble gases produced in situ by U, Th, and K decay. We obtained 4He up to the extremely high concentration of 6.8×10−2 cm3 STP/g (STP: atmospheric pressure and 0°C) for gold separated from a specimen of the Witwatersrand West Rand gold fields, indicating that this gold has a large U content.

Field gas chromatograph analyses of gases from a glowing dome at Merapi volcano, Java, Indonesia, 1977, 1978, 1979

Abstract A new field gas chromatograph (FGC) and conventional evacuated bottle (EB) techniques have been used to study high temperature (> 600°C) volcanic gases from Merapi Volcano, Indonesia during 1977, 1978, and 1979. The FGC design allows analysis of H2O, CO2, SO2, H2S, H2, COS, CH4, CO, N2, Ar, and O2 in a manner that prevents loss of sulfur and water by condensation, inhibits corrosion from reactions of gases with lead-in tubes, and minimizes atmospheric contamination. The FGC analyses are highly superior to the EB data especially with respect to prevention of sulfur loss from reaction of SO2 and H2S. In addition to providing much improved H2S data, the FGC system minimizes oxidation of H2 and CO from contaminating atmospheric O2 because of the elimination of a lengthy time interval between collection and analysis. Thermodynamic calculations indicated small errors for H2 and CH4 in the 1978 analyses provided by the proto-type FGC device. A later model FGC provided excellent analyses that were shown by thermodynamic calculations to be nearly equilibrium mixtures, requiring only minor corrections. The Merapi gases are H2O-rich (88–95%) containing small amounts of CO2 (3.5 to 7.5%), SO2 (0.3 to 1.2%), and H2S (0.3 to 1.2%). They resemble “excess volatiles” (Rubey,1955) except for too high a sulfur content. Thermodynamic calculations based on the analyses indicate that the gases were once at temperatures of at least 915°C with O2 fugacities near quartz -magnetite-fayalite and that they have not been significantly diluted by disequilibrium admixture of meteoric water below these temperatures. This conclusion takes on special importance because stable isotope studies (Allard, 1980, 1982) of Merapi gases have shown that the water is meteoric and that much of the carbon and sulfur could be from sedimentary sources. The Merapi gases, therefore, may be “magmatic” even though they are not “juvenile” but recycled crustal volatiles.