Papers by Daniele L . Pinti
Computers & Geosciences, 1998
ABSTRACT
Earth and Planetary Science Letters, 2020
The Monteregian Hills are an alignment of magmatic intrusions of Cretaceous age located in the St... more The Monteregian Hills are an alignment of magmatic intrusions of Cretaceous age located in the St. Lawrence Lowlands, Quebec, Canada. Their origin is controversial and numerous studies have failed to decipher between a hotspot trail or sub-continental magmatism related to the opening of the North Atlantic Ocean. Here, we show that 17.7 ± 9.6% of the helium of the modern to Holocene-aged groundwater from the regional aquifer is of mantle origin, with a 3 He/ 4 He (R) of up to 1.42 times the atmospheric ratio (Ra). It suggests that a fossil Monteregian Hills magmatic signal, diluted by local radiogenic helium and preserved in the Monteregian Hills intrusions, is leached locally by flowing modern or sub-modern groundwater. Helium isotopic measurements by pyrolysis in Monteregian Hills bulk rocks and clinopyroxene separates show R/Ra values of up to 4.96, suggesting that fossil mantle helium has been partially preserved in these rocks and their mineral phases. Monte Carlo simulations of a magma aging model shows that the initial 3 He/ 4 He ratio in these Cretaceous intrusions could have been between 21 ± 10Ra and 33 ± 28Ra (2σ), favoring the hypothesis that the Monteregian Hills are the product of the passage of the North American plate over the New England hotspot. This study raises the prospect of using modern groundwater as an archive of mantle He over a hundreds of millions of years timescale.
[1] To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar for... more [1] To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar formation, Western Australia, and to gain insights on their origin and potential biogenicity, we conducted nuclear reaction analyses (NRA) and carbon and nitrogen isotope ratio measurements on various samples from the 3460-Myr-old Fe-rich Marble Bar chert. The Marble Bar chert formed during the alteration of basaltic volcanoclastic rocks with Fe-and Si-rich hydrothermal fluids, and the subsequent precipitation of magnetite, carbonates, massive silica, and, locally, sulfides. At a later stage, the magnetite, sulfides, and carbonates were replaced by Fe-Mn-oxyhydroxides. Nuclear reaction analyses indicate that most of the N and C resides within these Fe-Mn-oxyhydroxides, but a minor fraction is found in K-feldspars and Ba-mica dispersed in the silica matrix. The N and C isotopic composition of Fe-oxides suggests the presence of a unique biogenic source with d 15 N AIR values from +6.0 ± 0.5% to 7.3 ± 1.1% and a d 13 C PDB value of À19.9 ± 0.1%. The C and N isotope ratios are similar to those observed in Proterozoic and Phanerozoic organic matter. Diffusion-controlled fractionation of N and C released during high combustion temperatures indicates that these two elements are firmly embedded within the iron oxides, with activation energies of 18.7 ± 3.7 kJ/mol for N and 13.0 ± 3.8 kJ/mol for C. We propose that N and C were chemisorbed on iron and were subsequently embedded in the crystals during iron oxidation and crystal growth. The Fe-isotopic composition of the Marble Bar chert (d 56 Fe = À0.38 ± 0.02%) is similar to that measured in iron oxides formed by direct precipitation of iron from hydrothermal plumes in contact
We report the discovery of anomalies in the xenon isotopic composition of Archean cherts belongin... more We report the discovery of anomalies in the xenon isotopic composition of Archean cherts belonging to the metasedimentary sequences of Pilbara Craton, Western Australia. The cherts show contemporary excesses of 129 Xe and 131 – 136 Xe, compared to atmospheric Xe. The 129 Xe excesses are comparable to those observed in mantle-derived samples, such as MORBs, xenoliths, diamonds and CO-rich well gases and correlate with excesses of 238 U fissiogenic-produced 2 136 Xe, close to the mantle ratio. However, isotope 131 Xe is in excess of 238 U fissiogenic-Xe production. The 129 Xer 131 Xe ratio ranges from 0.7 to 3.2 and it is consistent with production of these two isotopes by neutron-capture reactions with Ž. tellurium. These anomalies are analogous to those measured in metamorphic rocks gneisses and amphibolites in the KTB borehole in Germany and probably were produced by reactions with Te. q
ÐDuring the recharge of an aquifer, atmosphere-derived noble gases are dissolved in ground water.... more ÐDuring the recharge of an aquifer, atmosphere-derived noble gases are dissolved in ground water. The dissolved amount of gas depends on the relative noble gas solubilities, which in turn are inversely proportional to the ambient temperature. Therefore, paleotemperatures prevailing at the time of the aquifer recharge can be calculated from precise measurements of the amount of noble gases in ground water samples. However, the initial noble gas concentrations can be modi®ed by several physical factors, such as the NaCl content of water, the elevation of the recharge area, the radiogenic in situ production of noble gas isotopes, air contamination and degassing, all of which make paleotempera-tures dicult to estimate. The amount of air added or gas lost are unknown parameters which must be evaluated through iterative methods. Here, we present a program written with Mathematica 1 , which calculates paleotemperatures using atmosphere-derived noble gas corrected from the above mentioned factors. The program involves root ®nding methods and minimization of functions which has been speci®cally developed for this application. #
Considerable information on oil exploration can be gained from the isotopic measurement of noble ... more Considerable information on oil exploration can be gained from the isotopic measurement of noble gases dissolved in petroleum. However, this analysis is complicated by (i) incomplete degassing, due to the high solubility of noble gas in petroleum, and (ii) pollution of the analytical devices by organic compounds. Here, a specific facility for the separation of noble gases from petroleum is described. The separation is based on the release of the gases dissolved in petroleum into the headspace of an evacuated container (flashing). Purification of noble gases from reactive gases is performed by using CuO furnaces and Ti–Zr alloy getters.
Noble gases, inert elements having isotopes produced by the decay of long half-life radionuclides... more Noble gases, inert elements having isotopes produced by the decay of long half-life radionuclides, offer a powerful approach for tracing fluid circulation and dating groundwa-ters.The (U + Th)-4He water ages-calculated from the accumulation rate in water of radio-genic 4He produced by decay of U and Th contained in the aquifer rocks-is frequently higher than the hydrological ages. This discrepancy is generally interpreted by two contrasting models: (i) heterogeneities of the aquifers, which allow water stagnation and accumulation of large amounts of radiogenic 4He, or (ii) addition of 4He produced in deeper regions of the continental crust. In this contribution, we propose that the apparent contrast between (U + Th)-4He ages and hydrological ages in the Paris Basin reflects the mixing of different types of water, having different residence times. We show, using the helium isotopic signatures of waters, that this mixing occurs between three aquifers, the Middle Jurassic, the Triassic and the Palaeozoic basement, which have contrasting helium contents and heterogeneous chemical compositions and permeabilities. The difference of radiogenic 4He/4~ ratios between the aquifers of Triassic and Middle Jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks. This implies residence times for groundwaters circulating in the Middle Jurassic carbonate aquifer much longer than those obtained from hydrological studies. Independent fluid age estimates, based on the ground palaeotemperatures recorded in the same groundwaters by the atmosphere-derived noble gases, seem to confirm the presence of very old groundwaters in the Paris Basin.
The increasing number of studies on the determination of natural methane in groundwater of shale ... more The increasing number of studies on the determination of natural methane in groundwater of shale gas prospection areas offers a unique opportunity for refining the quantification of natural methane emissions. Here methane emissions, computed from four potential sources, are reported for an area of ca. 16,500 km 2 of the St. Lawrence Lowlands, Quebec (Canada), where Utica shales are targeted by the petroleum industry. Methane emissions can be caused by 1) groundwater degassing as a result of groundwater abstraction for domestic and municipal uses; 2) groundwater discharge along rivers; 3) migration to the surface by (macroand micro-) diffuse seepage; 4) degassing of hydraulic fracturing fluids during first phases of drilling. Methane emissions related to groundwater discharge to rivers (2.47 × 10 −4 to 9.35 × 10 −3 Tg yr −1 ) surpass those of diffuse seepage (4.13 × 10 −6 to 7.14 × 10 −5 Tg yr −1 ) and groundwater abstraction (6.35 × 10 −6 to 2.49 × 10 −4 Tg yr −1 ). The methane emission from the degassing of flowback waters during drilling of the Utica shale over a 10-to 20-year horizon is estimated from 2.55 × 10 −3 to 1.62 × 10 −2 Tg yr −1 . These emissions are from one third to sixty-six times the methane emissions from groundwater discharge to rivers. This study shows that different methane emission sources need to be considered in environmental assessments of methane exploitation projects to better understand their impacts.
Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from un... more Hydraulic fracturing is becoming an important technique worldwide to recover hydrocarbons from unconven-tional sources such as shale gas. In Quebec (Canada), the Utica Shale has been identified as having unconventional gas production potential. However, there has been a moratorium on shale gas exploration since 2010. The work reported here was aimed at defining baseline concentrations of methane in shallow aquifers of the St. Lawrence Lowlands and its sources using δ 13 C methane signatures. Since this study was performed prior to large-scale fracturing activities, it provides background data prior to the eventual exploitation of shale gas through hydraulic fracturing. Groundwater was sampled from private (n = 81), municipal (n = 34), and observation (n = 15) wells between August 2012 and May 2013. Methane was detected in 80% of the wells with an average concentration of 3.8 ± 8.8 mg/L, and a range of <0.0006 to 45.9 mg/L. Methane concentrations were linked to groundwater chemistry and distance to the major faults in the studied area. The methane δ 13 C signature of 19 samples was > −50‰, indicating a potential thermogenic source. Localized areas of high methane concentrations from predominantly biogenic sources were found throughout the study area. In several samples, mixing, migration, and oxidation processes likely affected the chemical and isotopic composition of the gases, making it difficult to pinpoint their origin. Energy companies should respect a safe distance from major natural faults in the bedrock when planning the localization of hydraulic fracturation activities to minimize the risk of contaminating the surrounding groundwater since natural faults are likely to be a preferential migration pathway for methane.
Groundwater vulnerability mapping provides useful but limited information for developing protecti... more Groundwater vulnerability mapping provides useful but limited information for developing protection plans of the resource. Classical vulnerability ranking methods often do not take into account complex hydros-tratigraphy and never consider groundwater flow dynamics.
To elucidate the source of an air-like component in fluid inclusions of xenoliths from the subcon... more To elucidate the source of an air-like component in fluid inclusions of xenoliths from the subcontinen-tal mantle, we measured N, He and Ar elemental and isotopic composition in gases released by crushing from spinel-lherzolites of the Newer Volcanics, southeastern Australia. Gas released from fluid inclusions in olivine separates shows δ 15 N ranging from –6.0 ± 1.2‰ to +2.0 ± 1.7‰. The range of measured δ 15 N values are in contrast with a remarkably uniform 3 He/ 4 He ratio of 10.1 ± 0.2 × 10 –6. The lightest δ 15 N value of –6.0 ± 1.2‰ is consistent with the measured MORB-like 3 He/ 4 He ratio of 10.1 ± 0.2 × 10 –6 and suggests that gases in xenoliths of southeast Australia are derived from a well-mixed upper mantle reservoir. The heavier nitrogen isotopic signatures (from ~0 to +2‰) and elemental ratio of argon to nitrogen could be explained by the addition of 30% to 40% of a recycled sedimentary component. Nitrogen is indeed recycled more efficiently in the mantle than helium, preserving the trace of present or past subduction. The heavy N component has been observed in xenoliths from the eastern side of the Newer Volcanic province. Sedimentary nitrogen may result from subduction along the eastern margin of Australia, during Paleozoic time. The present nitrogen results, together with the relatively low 40 Ar/ 36 Ar ratios and apparently correlated 3 He and 36 Ar contents in those xenoliths, suggest the long-term preservation of recycled surface volatiles in the continental lithospheric mantle.
Except the old Jack Hills zircon crystals, it does not exit direct record of the first 500 Ma of ... more Except the old Jack Hills zircon crystals, it does not exit direct record of the first 500 Ma of the Earth history. Consequently, the succession of events that took place during this period is only indirectly known through geochemistry, comparison with other telluric planets, and numerical modelling. Just after planetary accretion several episodes were necessary in order to make life apparition and development possible and to make the Earth surface habitable. Among these stages are: the core differentiation, the formation of a magma ocean, the apparition of the first atmosphere, oceans and continents as well as the development of magnetic field and of plate tectonics. In the same time, Earth has been subject to extra-terrestrial events such as the Late Heavy Bombardment (LHB) between 3.95 and 3.8 Ga. Since 4.4–4.3 Ga, the conditions for pre-biotic chemistry and appearance of life were already met (liquid water, continental crust, no strong meteoritic bombardment, etc...). This does not mean that life existed as early, but this demonstrates that all necessary conditions assumed for life development were already present on Earth.
On Earth, the Archaean aeon lasted from 4.0 to 2.5 Ga; it corresponds to a relatively stable peri... more On Earth, the Archaean aeon lasted from 4.0 to 2.5 Ga; it corresponds to a relatively stable period. Compared with today, internal Earth heat production was several times greater resulting in high geothermal flux that induced the genesis of rocks such as komatiites and TTG suites, which are no more generated on Earth since 2.5 Ga. Similarly, the details of plate tectonic modalities (plate size, plate motion rate, plate thickness, tectonic style, irregular crustal growth, etc...) were different of modern plate tectonics. Both atmosphere and ocean compositions have been progressively modified and the greater heat production favoured the development of hydrothermalism and therefore created niches potentially favourable for the development of some forms of life. Catastrophic events such as giant meteorite falls or world-sized glaci-ations drastically and suddenly changed the environment of Earth surface, thus being able to strongly affect development of life. Even if specialists still debate about the age of the oldest indubitable fossil trace of life, Archaean can be considered as having been extremely favourable for life development and diversification. After the Late Heavy Bombardment (see chapter 4.5), the Earth entered in a relative stability period that lasted until now. This does not mean that at 4.4 Ga, the Earth was similar to modern Earth, on the contrary, it was archaic and the internal as well as external processes were significantly different of those active on our modern Earth. For instance, if plate tectonics existed, the
Keywords: banded iron formation lamination nitrogen isotope organic productivity iron isotope iro... more Keywords: banded iron formation lamination nitrogen isotope organic productivity iron isotope iron reduction Banded iron formations (BIFs) exhibit alternating silica-and iron-rich laminae, potentially reflecting the dynamics of the paleo-environments in which they were formed, although the exact mechanism remains unclear. Here the formation of a 2.7–2.9 Ga BIF from Dharwar Craton, India, is deciphered by analyzing the inter-band variations of the redox-sensitive isotope biomarkers, 15 N/ 14 N and 56 Fe/ 54 Fe. Organic matter with δ 15 N values as high as +12.0 ± 0.8h appears to be trapped in silica. Iron oxides exhibit systematically positive δ 56 Fe values, ranging between +0.80 ± 0.05h and +1.67 ± 0.02h. Compared to the iron-rich bands, silica-rich bands, which show higher δ 56 Fe values, exhibit an order of magnitude higher concentrations of 15 N-rich organic nitrogen, normalized by the abundances of its host silica. The presence of 15 N-rich organic matter may imply the emergence of a modern-like biological nitrogen cycle that requires the formation of oxidized nitrogen compounds. The higher concentration of 15 N-rich organic nitrogen for the silica-rich bands possibly suggests that the photosynthetic activity was higher during the formation periods of these bands. The heavier iron isotope compositions of the silica-rich bands cannot be explained alone by iron oxidation through probable pathways. The relative 56 Fe-enrichment in silica-rich bands is explained here by the progressive dissolution of iron oxides to the ocean, through iron reduction by 15 N-rich organic matter actively produced at the ocean surface. The formation of iron-rich bands possibly corresponds to periods of reduced biological productivity, when precipitated iron was not effectively dissolved to the ocean. The observed shift in the organic concentration between Fe-and Si-rich bands could be the switch that triggered the BIF laminations. This shift could conceivably represent periodic fluctuations in the oxygen generation, which possibly occurred over periods of millennia, at the dawn of the Great Oxidation Event.
Permanent probes to sample soil gase s were placed at the Latem geothermal field, located in the ... more Permanent probes to sample soil gase s were placed at the Latem geothermal field, located in the Volsini Mrs., Latium, Italy. Due to high uranium concentrations in the ares's alkali-potassic volcanics outcropping, quite high 222Rn values, ranging from 9,260 up to 753,000 Bq/m 3, were found. The highest radon activities match tectonic structures such as fractures and faults, and a deep high structure which constitutes the geothermal reservoir. These high radon values also conform to a major amount of 4He and CO 2. The latter gases are enriched in the gaseous phase of the geothermal fluids, and their migration is also controlled by structural features. This suggests that the enrichment of 2~Rn in the soil gases, can be linked to a direct contribution of 226Ra, carded by deep-seated fluids from the reservoir itself.
[1] To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar for... more [1] To quantify and localize nitrogen (N) and carbon (C) in Archean rocks from the Marble Bar formation, Western Australia, and to gain insights on their origin and potential biogenicity, we conducted nuclear reaction analyses (NRA) and carbon and nitrogen isotope ratio measurements on various samples from the 3460-Myr-old Fe-rich Marble Bar chert. The Marble Bar chert formed during the alteration of basaltic volcanoclastic rocks with Fe-and Si-rich hydrothermal fluids, and the subsequent precipitation of magnetite, carbonates, massive silica, and, locally, sulfides. At a later stage, the magnetite, sulfides, and carbonates were replaced by Fe-Mn-oxyhydroxides. Nuclear reaction analyses indicate that most of the N and C resides within these Fe-Mn-oxyhydroxides, but a minor fraction is found in K-feldspars and Ba-mica dispersed in the silica matrix. The N and C isotopic composition of Fe-oxides suggests the presence of a unique biogenic source with d 15 N AIR values from +6.0 ± 0.5% to 7.3 ± 1.1% and a d 13 C PDB value of À19.9 ± 0.1%. The C and N isotope ratios are similar to those observed in Proterozoic and Phanerozoic organic matter. Diffusion-controlled fractionation of N and C released during high combustion temperatures indicates that these two elements are firmly embedded within the iron oxides, with activation energies of 18.7 ± 3.7 kJ/mol for N and 13.0 ± 3.8 kJ/mol for C. We propose that N and C were chemisorbed on iron and were subsequently embedded in the crystals during iron oxidation and crystal growth. The Fe-isotopic composition of the Marble Bar chert (d 56 Fe = À0.38 ± 0.02%) is similar to that measured in iron oxides formed by direct precipitation of iron from hydrothermal plumes in contact
Nuclear reaction analyses were performed on feldspars, quartz, abiogenic and biogenic sulfides an... more Nuclear reaction analyses were performed on feldspars, quartz, abiogenic and biogenic sulfides and phosphates in organic matter-rich black shales. The goal was to study N-fractionation in black shales during diagenesis and con-temporaneous hydrothermalism. Light elements (N, C) together with heavier ones (K, Ca, Ni, Fe, Zn) were analyzed by PIXE. Due to the heterogeneous sample composition, a scanning mode was used. Each phase was identified before extracting the corresponding spectra for quantification. Six phases, carrying nitrogen (and C), have been identified. K-feldspars are the richest in N (1.0–2.4 wt.%), followed by organic carbon (0.67 wt.%). Quartz, biogenic and abiogenic sulfides and phosphates contain N in the range of 0.56–1.08 wt.%. The present N-distribution in the black shales is explained by a two-step nitrogen release: (1) organic matter decay produces N, P, S nutriments for the development of a hydrothermal vent fauna and (2) biomineralization of this vent fauna liberates nitrogen to early diagenetic fluids. The extreme N enrichment of feldspars is related to its crystal structure, favoring the potassium substitution by NH þ 4 , and the N-uptake during organic matter replacement.
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Papers by Daniele L . Pinti