The helium and carbon isotope characteristics of the Andean Convergent Margin

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Barry, P. H., De Moor, J. M., Chiodi, A., Aguilera, F., Hudak, M. R., Bekaert, D. V., Turner, S. J., Curtice, J., Seltzer, A. M., Jessen, G. L., Osses, E., Blamey, J. M., Amenabar, M. J., Selci, M., Cascone, M., Bastianoni, A., Nakagawa, M., Filipovich, R., Bustos, E., Schrenk, M. O. , Buongiorno, J., Ramírez, C. J., Rogers, T. J., Lloyd, K. G. & Giovannelli, D. The helium and carbon isotope characteristics of the Andean Convergent Margin. Frontiers in Earth Science, 10, (2022): 897267, https://doi.org/10.3389/feart.2022.897267.Subduction zones represent the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively cycled between Earth reservoirs by plate tectonics. Helium is a sensitive tracer of volatile sources and can be used to deconvolute mantle and crustal sources in arcs; however it is not thought to be recycled into the mantle by subduction processes. In contrast, carbon is readily recycled, mostly in the form of carbon-rich sediments, and can thus be used to understand volatile delivery via subduction. Further, carbon is chemically-reactive and isotope fractionation can be used to determine the main processes controlling volatile movements within arc systems. Here, we report helium isotope and abundance data for 42 deeply-sourced fluid and gas samples from the Central Volcanic Zone (CVZ) and Southern Volcanic Zone (SVZ) of the Andean Convergent Margin (ACM). Data are used to assess the influence of subduction parameters (e.g., crustal thickness, subduction inputs, and convergence rate) on the composition of volatiles in surface volcanic fluid and gas emissions. He isotopes from the CVZ backarc range from 0.1 to 2.6 RA (n = 23), with the highest values in the Puna and the lowest in the Sub-Andean foreland fold-and-thrust belt. Atmosphere-corrected He isotopes from the SVZ range from 0.7 to 5.0 RA (n = 19). Taken together, these data reveal a clear southeastward increase in 3He/4He, with the highest values (in the SVZ) falling below the nominal range associated with pure upper mantle helium (8 ± 1 RA), approaching the mean He isotope value for arc gases of (5.4 ± 1.9 RA). Notably, the lowest values are found in the CVZ, suggesting more significant crustal inputs (i.e., assimilation of 4He) to the helium budget. The crustal thickness in the CVZ (up to 70 km) is significantly larger than in the SVZ, where it is just ∼40 km. We suggest that crustal thickness exerts a primary control on the extent of fluid-crust interaction, as helium and other volatiles rise through the upper plate in the ACM. We also report carbon isotopes from (n = 11) sites in the CVZ, where δ13C varies between −15.3‰ and −1.2‰ [vs. Vienna Pee Dee Belemnite (VPDB)] and CO2/3He values that vary by over two orders of magnitude (6.9 × 108–1.7 × 1011). In the SVZ, carbon isotope ratios are also reported from (n = 13) sites and vary between −17.2‰ and −4.1‰. CO2/3He values vary by over four orders of magnitude (4.7 × 107–1.7 × 1012). Low δ13C and CO2/3He values are consistent with CO2 removal (e.g., calcite precipitation and gas dissolution) in shallow hydrothermal systems. Carbon isotope fractionation modeling suggests that calcite precipitation occurs at temperatures coincident with the upper temperature limit for life (122°C), suggesting that biology may play a role in C-He systematics of arc-related volcanic fluid and gas emissions.This work was principally supported by the NSF-FRES award 2121637 to PB, KL, and JM. Field work was also supported by award G-2016-7206 from the Alfred P. Sloan Foundation and the Deep Carbon Observatory to PB, KL, DG, and JM. Additional support came from The National Fund for Scientific and Technological Development of Chile (FONDECYT) Grant 11191138 (The National Research and Development Agency of Chile, ANID Chile), and COPAS COASTAL ANID FB210021 to GJ. DG was partially supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program Grant Agreement No. 948972—COEVOLVE—ERC-2020-STG

Multivariate Analysis Applied to Aquifer Hydrogeochemical Evaluation: A Case Study in the Coastal Significant Subterranean Water Body between “Cecina River and San Vincenzo”, Tuscany (Italy)

The hydrogeochemical characteristics of the significant subterranean water body between “Cecina River and San Vincenzo” (Italy) was evaluated using multivariate statistical analysis methods, like principal component analysis and self-organizing maps (SOMs), with the objective to study the spatiotemporal relationships of the aquifer. The dataset used consisted of the chemical composition of groundwater samples collected between 2010 and 2018 at 16 wells distributed across the whole aquifer. For these wells, all major ions were determined. A self-organizing map of 4 × 8 was constructed to evaluate spatiotemporal changes in the water body. After SOM clustering, we obtained three clusters that successfully grouped all data with similar chemical characteristics. These clusters can be viewed to reflect the presence of three water types: (i) Cluster 1: low salinity/mixed waters; (ii) Cluster 2: high salinity waters; and (iii) Cluster 3: low salinity/fresh waters. Results showed that the major ions had the greater influence over the groundwater chemistry, and the difference in their concentrations allowed the definition of three clusters among the obtained SOM. Temporal changes in cluster assignment were only observed in two wells, located in areas more susceptible to changes in the water table levels, and therefore, hydrodynamic conditions. The result of the SOM clustering was also displayed using the classical hydrochemical approach of the Piper plot. It was observed that these changes were not as easily identified when the raw data were used. The spatial display of the clustering results, allowed the evaluation in a hydrogeological context in a quick and cost-effective way. Thus, our approach can be used to quickly analyze large datasets, suggest recharge areas, and recognize spatiotemporal patterns

Standard operating procedure for the analysis of major ions in hydrothermal fluids by ion chromatography

Repository containing the Standard Operating Procedures for the analysis carried out in the Giovannelli Lab at the University of Naples Federico II, Ital

Standard Operating Procedure for the analysis of trace elements in hydrothermal fluids by Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

This SOP validates an inductively coupled plasma mass spectrometry (ICP-MS) procedure for the determination of biometals and trace elements in hydrothermal fluids and sediments. Hydrothermal fluids are aqueous solutions with a wide range of temperature, salinity, pH and trace elements that can be used by a set of microbial proteins containing redox-sensitive transition metals as their catalytic core. Due to the high variability of these samples, we have developed this protocol taking into account the special features of the matrices analyzed. Our methods focus primarily on a subset of trace metals, Trace metals such as Fe, Co, Ni, Mo, W, V and Cu referred to as biometals, used by biology as cofactors in proteins. An ICP-MS 7900 Agilent system was used, with calibration curves linear in the 0.01 to 100 μg/L concentration range

CARACTERIZACIÓN GEOQUÍMICA DE ROCAS EN UNA SECUENCIA CRETÁCICA DE LA CUENCA DEL LAGO DE MARACAIBO / Geochemical Characterization of Rocks in a Cretaceous Sequence in Lago de Maracaibo Basin

La cuenca petrolífera del Lago de Maracaibo, ubicada al noroeste de Venezuela ha sido catalogada como una de las más importantes a nivel mundial, siendo la Formación La Luna (FLL) su roca madre por excelencia. Sin embargo, las formaciones Apón y Maraca incluidas en el grupo Cogollo, han sido definidas como rocas madre de cierta importancia. El objetivo del trabajo consistió en determinar y comparar parámetros geoquímicos para caracterizar la secuencia Cretácica representada en el núcleo 26D-2. Para esto fue realizado en primer lugar la descripción de las muestras de mano y análisis mineralógico, la determinación de las concentraciones de carbono total, inorgánico (carbonático) y carbono orgánico total (COT), además de realizar pirólisis Rock-Eval, para obtener información acerca del tipo de kerógeno y el grado de madurez térmica. A continuación fue extraído el bitumen, para separarlo en maltenos y asfaltenos. Los maltenos fueron separados a su vez, en hidrocarburos saturados, aromáticos y resinas. Los biomarcadores presentes en los hidrocarburos saturados y los marcadores aromáticos fueron identificados por cromatografía de gases acoplada a espectrometría de masas (CG/EM). A los asfaltenos se les determinaron los pesos moleculares en número (Mn) y en peso (Mw) por cromatografía de permeación de gel. En base a los resultados obtenidos pudo concluirse que en la secuencia Cretácica evaluada, el aporte de materia orgánica resultó ser mixta y se sugieren facies sedimentarias marinas, carbonáticas y siliciclásticas. Las muestras presentan una madurez térmica que va de temprana a intermedia de acuerdo tanto a los biomarcadores y marcadores aromáticos como a los resultados obtenidos a través de pirólisis Rock-Eval y de los asfaltenos.ABSTRACTThe Maracaibo basin has been catalogued as one of the most important basins worldwide, the La Luna Formation (FLL) being the main source rock. Nonetheless, other formations have been defined as source rocks of secondary importance. This is the case of some of the formations included in the Cogollo group (Apón and Maraca formations). The purpose of this study was to determine and compare geochemical parameters in order to characterize the Cretaceous sequence represented in the well core 26D-2. In order to do that, first a physical description of the samples was made, together with mineralogical analyses and the determination of the total carbon, inorganic (carbonate) and total organic carbon (TOC). Rock-Eval pyrolysis analyses were also made to determine the type of kerogen and the maturity range of the samples. The bitumen was extracted and separated into maltenes and asphaltenes. The maltene fraction was then separated in saturate and aromatic hydrocarbons and resins. To obtain both biomarkers and aromatic markers, a gas chromatography coupled with mass spectrometry (GC/MS) analysis was done. Lastly the asphaltene fraction was analyzed using gel permeation chromatography to determine the molecular weight in number (Mw) and in weight (Mw). Considering the results obtained through pyrolysis, biomarkers and aromatic markers, the Cretaceous sequence analyzed presented a mixed organic matter input, the sedimentary facies were marine, carbonatic and siliciclastic and the samples show an early to intermediate maturity range.Keywords: Geochemistry, Carbon, Asphaltenes of bitumen, Biomarkers, La Luna, Apón, Lisure, Maraca

Mapping the microbial diversity associated with different geochemical regimes in the shallow-water hydrothermal vents of the Aeolian archipelago, Italy

: Shallow-water hydrothermal vents are unique marine environments ubiquitous along the coast of volcanically active regions of the planet. In contrast to their deep-sea counterparts, primary production at shallow-water vents relies on both photoautotrophy and chemoautotrophy. Such processes are supported by a range of geochemical regimes driven by different geological settings. The Aeolian archipelago, located in the southern Tyrrhenian sea, is characterized by intense hydrothermal activity and harbors some of the best sampled shallow-water vents of the Mediterranean Sea. Despite this, the correlation between microbial diversity, geochemical regimes and geological settings of the different volcanic islands of the archipelago is largely unknown. Here, we report the microbial diversity associated with six distinct shallow-water hydrothermal vents of the Aeolian Islands using a combination of 16S rRNA amplicon sequencing along with physicochemical and geochemical measurements. Samples were collected from biofilms, fluids and sediments from shallow vents on the islands of Lipari, Panarea, Salina, and Vulcano. Two new shallow vent locations are described here for the first time. Our results show the presence of diverse microbial communities consistent in their composition with the local geochemical regimes. The shallow water vents of the Aeolian Islands harbor highly diverse microbial community and should be included in future conservation efforts

Surface Bacterioplankton Community Structure Crossing the Antarctic Circumpolar Current Fronts

The Antarctic Circumpolar Current (ACC) is the major current in the Southern Ocean, isolating the warm stratified subtropical waters from the more homogeneous cold polar waters. The ACC flows from west to east around Antarctica and generates an overturning circulation by fostering deep-cold water upwelling and the formation of new water masses, thus affecting the Earth’s heat balance and the global distribution of carbon. The ACC is characterized by several water mass boundaries or fronts, known as the Subtropical Front (STF), Subantarctic Front (SAF), Polar Front (PF), and South Antarctic Circumpolar Current Front (SACCF), identified by typical physical and chemical properties. While the physical characteristics of these fronts have been characterized, there is still poor information regarding the microbial diversity of this area. Here we present the surface water bacterioplankton community structure based on 16S rRNA sequencing from 13 stations sampled in 2017 between New Zealand to the Ross Sea crossing the ACC Fronts. Our results show a distinct succession in the dominant bacterial phylotypes present in the different water masses and suggest a strong role of sea surface temperatures and the availability of Carbon and Nitrogen in controlling community composition. This work represents an important baseline for future studies on the response of Southern Ocean epipelagic microbial communities to climate change