SUSTAIN drilling at Surtsey volcano, Iceland, tracks hydrothermal and microbiological interactions in basalt 50 years after eruption

The 2017 Surtsey Underwater volcanic System for Thermophiles, Alteration processes and INnovative concretes (SUSTAIN) drilling project at Surtsey volcano, sponsored in part by the International Continental Scientific Drilling Program (ICDP), provides precise observations of the hydrothermal, geochemical, geomagnetic, and microbiological changes that have occurred in basaltic tephra and minor intrusions since explosive and effusive eruptions produced the oceanic island in 1963–1967. Two vertically cored boreholes, to 152 and 192 m below the surface, were drilled using filtered, UV-sterilized seawater circulating fluid to minimize microbial contamination. These cores parallel a 181 m core drilled in 1979. Introductory investigations indicate changes in material properties and whole-rock compositions over the past 38 years. A Surtsey subsurface observatory installed to 181 m in one vertical borehole holds incubation experiments that monitor in situ mineralogical and microbial alteration processes at 25–124 ∘C. A third cored borehole, inclined 55∘ in a 264∘ azimuthal direction to 354 m measured depth, provides further insights into eruption processes, including the presence of a diatreme that extends at least 100 m into the seafloor beneath the Surtur crater. The SUSTAIN project provides the first time-lapse drilling record into a very young oceanic basaltic volcano over a range of temperatures, 25–141 ∘C from 1979 to 2017, and subaerial and submarine hydrothermal fluid compositions. Rigorous procedures undertaken during the drilling operation protected the sensitive environment of the Surtsey Natural Preserve

Social License to Operate in Geothermal Energy

Geothermal energy is a resource that has the potential for development in many countries around the world. Despite its versatility and economic viability, this resource faces numerous obstacles that hinder its deployment and capacity for achieving a similar market share as other renewable and clean energy sources. Both technical and non-technical barriers can be highly detrimental to the implementation of geothermal projects. A social license to operate (SLO) is a tool that can help the deployment of geothermal energy. As a new concept, SLO is little developed in the business literature but is still being adopted in many industries. Its main challenges reside in its context-dependence and the lack of clear frameworks to utilize it. This paper introduces, in a first known attempt, through a qualitative approach, a conceptual model of the social license to operate in the geothermal energy sector. For its development, three case studies, working group discussion and surveying were conducted in the framework of the H2020 funded CROWDTHERMAL project, which aims to empower EU citizens for direct participation in geothermal projects through crowdfunding. Findings of this paper also drew on existing general conceptual models of the SLO, and experiences from other sectors that have developed their own SLO models. The paper contributes to a more contextualized understanding of the social license within the geothermal sector and sheds the light on practices and challenges that influence the acquisition and maintenance of SLO in geothermal energy projects and initiatives

Unravelling the anatectic history of the lower conteninental crust through the petrology of melt inclusions and lu-hf garnet geochronology: A case study from the western Alpujárrides (Betic Cordillera, S. Spain)

Partial melting (anatexis) plays a fundamental role in the generation, differentiation and the rheology of Earth’s continental crust. “Migmatitic” terranes constitute the main geological record of crustal anatexis throughout Earth’s history. Unravelling the mechanisms of crustal anatexis from these terranes has proven to be challenging particularly when it comes to unveiling the primary chemical composition of anatectic melts. The main aim of this thesis is to better understand lower crustal anatexis through the study of “nanogranite inclusions” —microscopic droplets of melt that formed via incongruent melting reactions— in metamorphic minerals, and its relationship with lithospheric scale tectonomagmatic processes. The originality of my Thesis resides in the combination of a petrological, thermodynamical and experimental study of anatexis on the basis of the study of nanogranite inclusions in garnets from high-pressure granulitic migmatites. The case study is migmatitic gneisses from the Jubrique unit, a complete —though strongly thinned— crustal section in the westernmost Alpujárrides (Betic Cordillera, S. Spain). These gneisses overlie the Ronda peridotites —the largest exposure of subcontinental lithospheric mantle on Earth— and provide a unique opportunity to investigate the nature and age of crustal melting events and their timing with mantle processes in the westernmost Mediterranean. Melt inclusions (≈ 30-40 μm) —now recrystallized to nanogranites— in Jubrique gneisses are present in garnet cores and rims throughout the entire sequence. Thermodynamic modeling and conventional thermobarometry provide peak conditions of ≈ 850 ºC and 1.2-1.4 GPa, corresponding to garnet cores with kyanite and rutile inclusions. Post-peak conditions of ≈ 800-850 ºC and c. 0.5 GPa are recorded in rims of garnet porphyroblast/clasts. The study of nanogranite inclusions shows that most garnet grew in the presence of melt. To constrain the primary composition and the P-T conditions of formation of nanogranitoids, we have carried out an experimental study of nanogranitoids in garnets, which were melted at 1.5 GPa and 850, 825 and 800 ºC in a piston cylinder apparatus. Experiments show that anatexis and entrapment of nanogranites occurred at c. 800 ºC. Electron microprobe and NanoSIMS analyses indicate that experimental glasses are leucogranitic and peraluminous and define two compositional groups: Type I corresponds to K-rich, Ca- and H2O-poor leucogranitic melts, whereas type II represents K-poor, Ca- and H2O-rich granodioritic to tonalitic melts. They are found, respectively, at cores and rims of garnet porphyroblasts/clasts, and show that Jubrique migmatites underwent two anatectic events under contrasting fluid regimes. To determine the age of crustal melting events and their timing with lithospheric mantle processes, we have analyzed Lu-Hf in whole rocks and garnets of Jubrique gneisses and garnet pyroxenites from the Ronda peridotite. The Lu-Hf isochrons confirm that the growth of garnet in Jubrique gneisses occurred in the Early Permian (c. 289 Ma) during the latest stages of the Variscan orogeny, most likely in a context of continental collision and overthickened continental crust. We found no Alpine Lu-Hf ages, indicating either that this event is not resolvable with our sampling and dating techniques, or that the Lu-Hf of garnet was not equilibrated in the Alpine orogeny. The Lu-Hf whole rock-garnet isochrons of mantle garnet pyroxenites provide Jurassic- Cretaceous (144 Ma), Paleogene (53 Ma) and Miocene (21 Ma) ages. We interpret early Miocene ages as recording the waning stages of an Alpine extensional-related thermal event before emplacement of peridotites. Mantle garnet pyroxenites do not record Lu-Hf Variscan ages that may suggest that this system was reset by later mantle events or that garnet in mantle rocks grew in geodynamic events later than the Variscan orogeny.Tesis Univ. Granada. Programa Oficial de Doctorado en: Ciencias de la TierraMy Ph.D. Thesis is supported by a “Formación del Personal Investigador-FPI” Fellowship (BES-2011-045283) funded by the Spanish Government (Ministerio de Economia y Competitividad). I also acknowledge an earlier MAE-AECID fellowship funded by the “Agencia Española de Cooperación Universitaria y Científica para el Desarrollo”. The research of my Ph.D. Thesis has been funded by research grants from the “Ministerio de Economia y Competitividad” (Grants CGL2010-14848 and CGL2013-42349-P), Junta de Andalucía (research groups RNM-131 and Proyecto de Excelencia P09-RNM-4495), and has benefited from EU Cohesion Policy funds from the European Regional Development Fund (ERDF) and the European Social Fund (ESF) in support of human resources, innovation and research capacities, and research infrastructures

Microstructures and petrology of melt inclusions in the anatectic sequence of Jubrique (Betic Cordillera, S Spain): Implications for crustal anatexis

ISSN:0024-493

Social License to Operate in Geothermal Energy

Geothermal energy is a resource that has the potential for development in many countries around the world. Despite its versatility and economic viability, this resource faces numerous obstacles that hinder its deployment and capacity for achieving a similar market share as other renewable and clean energy sources. Both technical and non-technical barriers can be highly detrimental to the implementation of geothermal projects. A social license to operate (SLO) is a tool that can help the deployment of geothermal energy. As a new concept, SLO is little developed in the business literature but is still being adopted in many industries. Its main challenges reside in its context-dependence and the lack of clear frameworks to utilize it. This paper introduces, in a first known attempt, through a qualitative approach, a conceptual model of the social license to operate in the geothermal energy sector. For its development, three case studies, working group discussion and surveying were conducted in the framework of the H2020 funded CROWDTHERMAL project, which aims to empower EU citizens for direct participation in geothermal projects through crowdfunding. Findings of this paper also drew on existing general conceptual models of the SLO, and experiences from other sectors that have developed their own SLO models. The paper contributes to a more contextualized understanding of the social license within the geothermal sector and sheds the light on practices and challenges that influence the acquisition and maintenance of SLO in geothermal energy projects and initiatives

Subduction initiation and recycling of Alboran domain derived crustal components prior to the intra-crustal emplacement of mantle peridotites in the Westernmost Mediterranean: isotopic evidence from the Ronda peridotite

International audienceDuring Late Oligocene-Early Miocene different domains formed in the region between Iberia and Africa in the westernmost Mediterranean, including thinned continental crust and a Flysch Trough turbiditic deposits likely floored by oceanic crust [1]. At this time, the Ronda peridotite likely constituted the subcontinental lithospheric mantle of the Alboran domain, which mantle lithosphere was undergoing strong thinning and melting [2] [3] coevally with Early Miocene extension in the overlying Alpujárride-Maláguide stacked crust [4, 5].Intrusive Cr- rich pyroxenites in the Ronda massif records the geochemical processes occurring in the subcontinental mantle of the Alboran domain during the Late Oligocene [6]. Recent isotopic studies of these pyroxenites indicate that their mantle source was contaminated by a subduction component released by detrital crustal sediments [6]. This new data is consistent with a subduction setting for the late evolution of the Alboran lithospheric mantle just prior to its final intracrustal emplacement in the early Miocene Further detailed structural studies of the Ronda plagioclase peridotites—related to the initial stages of ductile emplacement of the peridotite—have led to Hidas et al. [7] to propose a geodynamic model where folding and shearing of an attenuated mantle lithosphere occurred by backarc basin inversion followed by failed subduction initiation that ended into the intracrustal emplacement of peridotite into the Alboran wedge in the earliest Miocene. This hypothesis implies that the crustal component recorded in late, Cr-rich websterite dykes might come from underthrusted crustal rocks from the Flysch and/or Alpujárrides units that might have been involved in the earliest stages of this subduction initiation stage

The composition of nanogranitoids in migmatites overlying the Ronda peridotites (Betic Cordillera, S Spain): the anatectic history of a polymetamorphic basement

International audienceThe study of the composition of primary melts during anatexis of high-pressure granulitic migmatites is relevant to understand the generation and differentiation of continental crust. Peritectic minerals in migmatites can trap droplets of melt that forms via incongruent melting reactions during crustal anatexis. These melt inclusions commonly crystallize and form nanogranitoids upon slow cooling of the anatectic terrane. To obtain the primary compositions of crustal melts recorded in these nanogranitoids, including volatile concentrations and information on fluid regimes, they must be remelted and rehomogenized before analysis. A new occurrence of nanogranitoids was recently reported in garnets of mylonitic metapelitic gneisses (former high pressure granulitic migmatites) at the bottom of the prograde metamorphic sequence of Jubrique, located on top of the Ronda peridotite slab (Betic Cordillera, S Spain). Nanogranitoids within separated chips of cores and rims of large garnets from these migmatites were remelted at 15 kbar and 850, 825 or 800 °C and dry (without added H2O), during 24 h, using a piston cylinder apparatus. Although all experiments show glass (former melt) within melt inclusions, the extent of rehomogenization depends on the experimental temperature. Experiments at 850–825 °C show abundant disequilibrium microstructures, whereas those at 800 °C show a relatively high proportion of rehomogenized nanogranitoids, indicating that anatexis and entrapment of melt inclusions in these rocks likely occurred at pressures ≤1.5 GPa and temperatures close to 800 °C. Electron microprobe and NanoSIMS analyses show that experimental glasses are leucogranitoid and peraluminous, though define two distinct compositional groups. Type I melt inclusions correspond to K-rich, Ca- and H2O-poor leucogranitic melts, whereas type II melt inclusions represent K-poor, Ca- and H2O-rich granodioritic to tonalitic melts. Type I and II melt inclusions are found in most cases at the cores and rims of large garnets porphyroclasts, respectively. We tentatively interpret these two distinct melt compositions as suggesting that these former migmatites underwent two melting events under contrasting fluid regimes, possibly during two different orogenic periods. This study demonstrates the strong potential of melt inclusions studies in migmatites and granulites in order to unravel their anatectic history, particularly in strongly deformed rocks where most of the classical anatectic microstructures and macrostructures have been erased during deformation

Subduction initiation, recycling of lower continental crust, and intracrustal emplacement of subcontinental lithospheric mantle in the westernmostMediterranean

International audienceThe geochemistry of high-Mg pyroxenite dykes in the Ronda peridotite (S Spain) shows that the subcontinental lithospheric mantle in the westernmost Mediterranean evolved above a subducting slab shortly before its intracrustal emplacement. We present new SrNd-Pb isotopic data of crustal rocks in the western Betics that might account for the isotopic signature of Ronda high-Mg pyroxenite. We show that lower crustal garnet granulites from the Alpujarride complex, which overly the peridotites, account for the characteristic relatively high 207Pb-208Pb/204Pb and low 206Pb/204Pb subductioncomponent of Ronda high-Mg pyroxenite. The involvement of fluids/melts derived from lower crust in the genesis of high-Mg Ronda pyroxenite indicates that the peridotites in the westernmost Mediterranean were placed in a forearc position above a newly initiated subduction zone, followed by underthrusting of the lower crust. This possibly occurred during the late Oligocene due to the inversion of an extensional back-arc continental basin.As subduction progressed, the thinned subcontinental mantle was emplaced over the foreland following its collision with the trench

Sr-Nd-Pb isotopic systematics of crustal rocks from the western Betics (S. Spain): Implications for crustal recycling in the lithospheric mantle beneath the westernmost Mediterranean

International audienceWe present new Sr-Nd-Pb isotope data of the western Alpujárride metamorphic basement and the pre-Miocene Flysch sediments of the Betic Cordillera (southern Spain). Nd model ages are consistent with an increasing detrital input from the Alborán domain to the Flysch Trough in the western Mediterranean during the late Oligocene. The Alpujárride metamorphic crustal rocks derived from Archean-Paleoproterozoic terranes located along the northern margin of Gondwana in the Neoproterozoic. The heterogeneous isotopic signatures of the Alpujárride units indicate that they have different sedimentary protoliths and underwent contrasted Variscan and pre-Variscan tectono-magmatic evolutions. Melts/fluids derived from the western Alpujárride gneisses contaminated the mantle source of the Ronda high-Mg pyroxenite dykes, implying that the Alpujárride lower crust underthrusted the subcontinental lithospheric mantle of the Alborán domain generating subduction-like magmatism in the late Oligocene. The western Alpujárride upper crust is involved in the Neogene volcanism of the Alborán Sea basin, but only contaminated some LREE-enriched calc-alkaline lavas erupted along the continental margins. On the other hand, tholeiitic lavas in the center of the basin show no isotopic evidence of crustal assimilation. This indicates that most of the crust in the central Alborán Sea accreted by Miocene tholeiitic magmatism and that Alpujárride lower crust is absent and likely foundered close to the continental margins of the basin