Flow of Mantle Fluids Through the Duct,le Lower Crust: Helium Isotope Trends I B. Mack Kennedyl andlMatthijs C. van Soest ICenter for Isoto~e Geochemistry Earth Scienoes Division Lawrence Berkeley National Laboratory Berkeley, (:A 94720 2Noble Gas Geochemistry and Geochronology Laboratory School of Earth and Space Exploration Arizona State University Tempe, AZ 85287-1404 Abstract Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3 He /4 He ratios in surface fluids from the northern Basin and Range province, western North America increase systematically from low, crustal values in the east to high, mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active trans-tensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere in regions even where there is no significant magmatism. Superimposed on the regional trend are local, high- He/ He anomalies signifying hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.

Flow of mantle fluids through the ductile lower crust: Helium isotope trends

The continental lithosphere is a vast store for carbon. The carbon has been added and reactivated by episodic freezing and re-melting throughout geological history. Carbon remobilization can lead to significant variations in CO2 outgassing and release in the form of magmas from the continental lithosphere over geological timescales. Here we use calculations of continental lithospheric carbon storage, enrichment and remobilization to demonstrate that the role for continental lithosphere and rifts in Earth’s deep carbon budget has been severely underestimated. We estimate that cratonic lithosphere, which formed 2 to 3 billion years ago, originally contained about 0.25 Mt C km–3. A further 14 to 28 Mt C km–3 is added over time from the convecting mantle and about 43 Mt C km–3 is added by plume activity. Re-melting focuses carbon beneath rifts, creating zones with about 150 to 240 Mt C km–3, explaining the well-known association of carbonate-rich magmatic rocks with rifts. Reactivation of these zones can release 28 to 34 Mt of carbon per year for the 40 million year lifetime of a continental rift. During past episodes of supercontinent breakup, the greater abundance of continental rifts could have led to short-term carbon release of at least 142 to 170 Mt of carbon per year, and may have contributed to the high atmospheric CO2 at several times in Earth's history. Continental rifts are stores and sources of abundant carbon, according to calculations of carbon storage, enrichments and mobilization in rift systems. Continental rift systems are likely to play an important role in Earth’s deep carbon cycle.

An essential role for continental rifts and lithosphere in the deep carbon cycle

http://www.jlakes.org/config/hpkx/news_category/2015-05-10/1-s2.0-S037702731400002X.pdf

Past, present and future of volcanic lake monitoring

The present-day topography of the Italian peninsula results from the interactions between crustal-mantle and surface processes occurring since the Late Miocene. Analysis of exhumation and cooling of crustal rocks, together with Quaternary drainage evolution,helps to unravel the tectonic-morphologic evolution of the Apennines by distinguishing end-member models,and hence describing the orogenic belt evolution. The pattern of regional topography, erosional history and present-day distribution of active deformation suggests that the eastward migrating extensional-compressional paired deformation belts may still control the topogra-phy of the northern Apennines, albeit at slower rates than in the past. Conversely, Quaternary drainage evo-lution in the central and southern Apennines suggests that the topography of these regions underwent a Quaternary regional arching, which is only partly con-sistent with the persisting migration of the compres-sional-extensional pair.

Topography, exhumation, and drainage network evolution of the Apennines

The current situation of inorganic elements in marine turtles: A general review and meta-analysis.

Active degassing of mantle-derived fluid: A geochemical study along the Vulture line, southern Apennines (Italy)

Mantle CO2 degassing at Mt. Vulture volcano (Italy): Relationship between CO2 outgassing of volcanoes and the time of their last eruption

[1] We report on the first geochemical investigation of the Monticchio maar lakes (Mt. Vulture volcano, southern Italy) covering an annual cycle that aimed at understanding the characteristic features of the physical structures and dynamics of the two lakes. We provide the first detailed description of the lakes based on high-resolution conductivity-temperature-depth (CTD) profiles, chemical and isotopic (H and O) compositions of the water, and the amounts of dissolved gases (e.g., He, Ar, CH4, and CO2). The combined data set reveals that the two lakes, which are separated by less than 200 m, exhibit different dynamics: one is a meromictic lake, where the waters are rich in biogenic and mantle-derived gases, while the other is a monomictic lake, which exhibits complete turnover of the water in winter and the release of dissolved gases. Our data strongly suggest that the differences in the dynamics of the two lakes are due to different density profiles affected by dissolved solutes, mainly Fe, which is strongly enriched in the deep water of the meromictic lake. A conceptual model of water balance was constructed based on the correlation between the chemical composition of the water and the hydrogen isotopic signature. Gas-rich groundwaters that feed both of the lakes and evaporation processes subsequently modify the water chemistry of the lakes. Our data highlight that no further potential hazardous accumulation of lethal gases is expected at the Monticchio lakes. Nevertheless, geochemical monitoring is needed to prevent the possibility of vigorous gas releases that have previously occurred in historical time.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/ggge.20111

Geochemical insight into differences in the physical structures and dynamics of two adjacent maar lakes at Mt. Vulture volcano (southern Italy)

Among the chemical elements and chemical compounds that promote life and its evolution on the earth, there are some which have toxic effects on plant life, animals and human beings. A lot of the chemicals released follow more or less complex cycles of different duration, during the course of which they are transported and disseminated, by means of various interactions, throughout the environment, including the biosphere. Natural processes ascribable to magmatism form a powerful system that discharge a large amount of substances which can contaminate waters and soils, even though there are generally only trace elements. In this paper, some of the main contamination processes linked to magmatism, such as the hydrothermalism of black and white smokers at the bottom of oceans, are described, as are other examples in the Mediterranean area and Italy, including volcanic ash deposition, CO2 soil saturation and emission of radioactive radon. Furthermore, their toxic effects on the population are also highlighted, bearing in mind their implications and relevance in planning the use and management of both the soils and waters of a given area.

Pasquale Mario Nuccio

Papers

Active degassing of mantle-derived fluid: A geochemical study along the Vulture line, southern Apennines (Italy)

Mantle CO2 degassing at Mt. Vulture volcano (Italy): Relationship between CO2 outgassing of volcanoes and the time of their last eruption

Geochemical insight into differences in the physical structures and dynamics of two adjacent maar lakes at Mt. Vulture volcano (southern Italy)

Pollution of waters and soils by contaminants of magmatic origin

Muddy 1: prototipo di un robot per il campionamento “step by step” di gas dai sedimenti lacustri