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The Cracked Mountain edifice is a basaltic subglacial volcano (i.e. tuya) situated in southwest British Columbia, Canada. The edifice is dominated by subaqueously deposited, massive to poorly stratified, variably palagonitized lapilli tuffs intruded by syn-eruptive dikes and lobes of peperitic pillow-lavas (15–20 vol.%); minor stacks of pillow-lava are found on the margins of the edifice. Here, we present mineralogical, textural, and physical property data for 134 sample cores from the palagonitized volcaniclastic deposits. Our sample suite includes three specific field environments defined by proximity to intrusive heat sources: (i) proximal (< 1 m) deposits (ENV1), (ii) deposits within 1–5 m of intrusions (ENV2), and (iii) deposits far removed (> 5 m) from discernible heat sources (ENV3). The dataset comprises mineralogy and measurements of density, porosity, permeability, P-wave velocity, uniaxial compressive strength, and paleomagnetism. Increased palagonitization is marked by increases in authigenic mineral abundance (smectite and analcime), density, strength, and P-wave velocity and concomitant decreases in porosity and permeability. Paleomagnetic data show a common pole direction recorded by all volcanic deposits indicating volcanism occurred within a single paleomagnetic moment (< 200 years). Palagonitization of the volcaniclastic deposits is driven by heat supplied by syn-eruptive intrusions and is most intense in ENV1, where dikes raised temperatures (> 150 °C) for a prolonged duration (< 1 year), and weakest in ENV3 deposits reheated to lower temperatures (< 150 °C). The timescale of palagonitization was short and coincident with the emplacement and cooling of syn-eruptive intrusions. The mapped intensity of palagonitization and thermal modelling are used to define a ‘palagonite window’ as a function of time and distance from heat sources (i.e. dikes). [ABSTRACT FROM AUTHOR]

The Genbudo lava, the late Pleistocene basaltic-andesitic lava flow in the southwestern part of Iwate Volcano, Japan, is a 70 m thick columnar jointed flow that can be divided into three parts from bottom to top: the colonnade, the entablature, and the partly-brecciated uppermost part. Two main types of fractures developed in the entablature: pseudopillow fractures that formed in a branching network-like pattern throughout the entablature, and sheet fractures with curved surfaces that are nearly parallel to each other. At the uppermost part of the flow, finger-like structures of lava extend upward from the coherent lava, and cogenetic autoclastic rocks form between the fingers. This occurrence suggests that hyaloclastites were generated during emplacement in the uppermost part of the flow, apparently when water from a dammed river valley covered the flow. The texture of the lava near the pseudopillow fractures in the entablature is commonly hypocrystalline, while the texture in other parts is holocrystalline. There are two types of pyroxene microlites, large prismatic (average size ~ 30 µm) and dendritic (< 10 µm in length) crystals in the lava near the pseudopillow fractures. These suggest that the cooling rate of the lava was greatest in the vicinity of the pseudopillow fractures. Networks of palagonite-filled micro-fractures (less than 10 µm in width) are found in this part of the flow, and many bubbles are observed along the fractures. This is clear evidence that the rapid cooling of the lava was caused by water infiltration through the pseudopillow fractures. From the measurement of Fe-rich droplet sizes that formed due to liquid immiscibility within the lava, we estimate the cooling rate within the colonnade as about 49 °C/h and within the entablature as 642 °C/h, consistent with much more rapid cooling by water infiltration from above. [ABSTRACT FROM AUTHOR]

Studies of the submarine alteration of basaltic glass may improve the understanding of crust-seawater interactions and the oceanic elemental cycle. Natural alteration processes such as the palagonitization of basaltic glass are complex, and their elucidation is crucial to the understanding of fluid-rock interactions. This study involves major and trace element and isotope mapping of a submarine-altered basaltic glass grain and reveals sequential development of alteration textures toward the grain core through the transition between unaltered glass and palagonite. The conversion from basaltic glass to palagonite in a low-temperature submarine environment results in enrichment in B, Rb, K, Li, H2O, U, Nb, Th, Ti, Cu, Ta, Zr, Hf, Ni, Sc, Fe, Cr, Pb, and Zn; and depletion in Si, Mg, Al, Sr, Na, Co, rare-earth elements, Ca, P, and V (in order of decreasing distribution coefficient). The glass-palagonite interface region has the highest high field strength element (HFSE) and Fe-Ti contents but the lowest Mg content, indicating that the Fe-Ti phases that host HFSE were precipitated first during initial palagonitization. At the same time, an inferred exchange of oxygen occurred, based on variation in δ18O, with values increasing from basaltic glass to palagonite. However, initial palagonite compositions were afected by subsequent precipitation and/or incorporation/adsorption of additional compounds such as Mg(OH)2 scavenged from pore water. [ABSTRACT FROM AUTHOR]

The Osborn Plateau is a large intraplate elevation in the eastern Indian Ocean, which has been poorly studied by geological and geophysical methods. On cruise SO258/1 aboard the R/V Sonne, new data were collected by Parasound seismic processing, multibeam survey, and, for the first time, dredging. Faults in the sedimentary cover, which extend to the seafloor surface, indicate high neotectonic activity in the area of the Osborn Plateau. It may have continued up to the present, as well as in the adjacent segment of the Ninetyeast Ridge, where strong earthquakes are recorded. Two reflectors A and C in the upper part of the sedimentary cover mark global regressive changes in the World Ocean level at the Pliocene–Pleistocene and Miocene–Pliocene and boundaries. Reflector B in sediments at the Lower–Upper Pliocene boundary is associated with a change in the regional hydrodynamic regime at the time in the eastern Indian Ocean. Reflector B at the Lower–Upper Pliocene boundary is associated with a change in the local hydrodynamic regime in the region of the plateau and was caused by uncompensated sedimentation. As a result of dredging, strongly altered vitroclastic tuffs were obtained, consisting of palagonized ash particles and lapilli. Analysis of geochemical data on the composition of palagonite made it possible to reconstruct the main geochemical features of the primary composition of glass in tuffs, in particular, high enrichment in incompatible elements (Nb, Zr, Ti, La, etc.). The results of studying the dredged rocks suggest that tuffs dredged on the Osborn Plateau were formed as a result of explosive volcanic eruptions of alkaline basalts under subaerial or relatively shallow conditions and represent the latest eruption products in the region. [ABSTRACT FROM AUTHOR]

Highlights • Ediacaran basalts of the East European Craton were altered by heated meteoric water. • Cyanobacteria were active on the Ediacaran land in hydrothermal systems. • Chemical changes dominated by import of Mg and H 2 O and export of Ca. • The main alteration product is a mixture of di- and trioctahedral Fe-smectites; potentially analogous to the most common Martian clays. • Most of REE in the alteration products are contained in the dioctahedral smectite. Abstract The Ediacaran continental flood basalts and associated tuffs were studied to identify and quantify alteration processes by means of XRD and chemistry, supplemented by Mössbauer and FTIR spectroscopies, petrography, oxygen and iron isotopes, K-Ar dating, and organic geochemistry. Two superimposed alteration processes were identified: the Ediacaran hydrothermal alteration, induced by meteoric waters, heated and put in motion by the cooling basalt, and the Caledonian and/or Variscan potassic alteration. The degree of basalt alteration was quantified using as an index the sum of primary minerals in the bulk rock. The sequence of minerals dissolved and crystallized during the hydrothermal alteration was established. The alteration resulted in the loss of Ca (dissolution of plagioclases), compensated by the gain of water and Mg (crystallization of clays), and proceeded from the edges of the basalt flows in an oxidizing environment, evidenced by the increasing amount of hematite and Fe3+/Fe2+ ratio of the bulk rock. Cyanobacteria were active in the hydrothermal system, most probably responsible for the measured negative δ56Fe values and more reducing conditions at the stage of intense alteration. Chlorophaeite (palagonite), following quartz as the earliest petrographically identifiable basalt alteration product was found to vary systematically from fully isotropic to birefringent. The chlorophaeite was identified as a mixture of Fe-montmorillonite and Fe-saponite, identical with griffithite and oxysmectites, probably preceded by a finer-grained ferrosaponite at the isotropic stage. REE content of chlorophaeite indicates basaltic volcanic glass (sideromelane) as the major source of material. REE in clays are contained mostly in the dioctahedral smectite, while in the bulk rock mostly in phosphates. The smectite characteristics and Mg enrichment are indicative of the hydrothermal basalt alteration process, which perhaps was dominant also on Mars. Both mineral and chemical composition of tuffs vary continuously from basaltic to felsic, the latter close to the measured rhyodacite composition, dominated by quartz and feldspars. The basaltic tuffs resemble the most altered basalts but contain also abundant albite and chlorite, indicative of higher alteration temperatures, up to 220 °C. Tuff composition indicates stronger component of felsic volcanism in the trap formation than evidenced by the preserved bodies of effusive rocks. [ABSTRACT FROM AUTHOR]

We present the results of a petrographic and geochemical study carried out on a layer of achnelithic tephra outcropping at the base of the volcanic cone of Las Herrerías (Miocene-Quaternary volcanic region of Campo de Calatrava, Spain). The tephra, with a composition of nephelinite and ash (< 1 mm) to coarse lapilli (ca. 1 cm) in size, is made of intact isolated achneliths (mostly elongated and spheroidal, including Pele's tears), achnelith fragments and rare welded achneliths. The achneliths at Las Herrerías were generated in a gas-rich fire fountain that fragmented the magma into micro- to nanometre particles. The low viscosity of the nephelinitic blebs (< 1235 Pa.s) inside the hottest (ca. 900 °C), inner zone of the fountain allowed the development of the characteristic fluidal shapes of these pyroclasts and their welding above the glass transition temperature (533–669 °C). The sideromelane glass of the achneliths, also nephelinitic in composition, is variably altered to palagonite. The palagonitization was isovolumetric and took place in a near closed system at the achnelith scale. Palagonitization involved depletion in the concentration (g/cm 3 ) of all major elements and notable increase in H 2 O content. The elements liberated by this process formed smectite with an average structural formula comprised between those of beidellite and nontronite end terms: (Na 0.01 K 0.03 Ca 0.18 ) (Mg 0.22 Fe 0.16 ) 2 + (Fe 0.48 Al 1.02 ) 3 + (Ti 0.18 ) 4 + (Si 3.58 Al 0.42 ) O 10 (OH) 2 . The degree of palagonitization in each achnelith was likely related to the amount of water incorporated by individual clasts at the moment of their deposition in a volcanic maar lake. Afterwards, there was no more water circulation through the achnelithic tephra, which was sealed from water by overlying hydrovolcanic tuff deposits. It was this isolation that made possible the preservation of glass to the present day. [ABSTRACT FROM AUTHOR]

In basaltic glass from the southern Mid-Atlantic-Ridge conducive environmental conditions for biogenic weathering resulted in excellent preserved microbial morphologies on glass surfaces. The distinct glass interface and open spaces between palagonite sheet and glass indicate a dissolution-reprecipitation mechanism of glass alteration potentially supported by microorganisms. On internal fracture surfaces, branching channels with widths at 20–30 μm containing longish structures with targeted dissolution of the glass by growing tips were observed. Alteration resulted in enrichment of Fe, Ti, P, and K in palagonite in amorphous mineral forms. [ABSTRACT FROM AUTHOR]

Between 30 August and 15 December 2006, Mt Etna, Italy, underwent both effusive and explosive activity which took place from the South-East Crater, one of its summit craters. Several paroxysmal episodes followed in succession, separated by a few days of minor activity and characterised by dissimilar explosive style and intensity. Here, we report one of the most studied and powerful episodes, which started early in the morning on 24 November 2006 and lasted about 13h. Excellent weather conditions enabled reconstructing in detail the onset and evolution of the eruptive phenomena both by live-camera recordings and direct observations. The explosive activity consisted of powerful Strombolian activity alternating with short periods of lava fountains. A weak volcanic plume rose up to ~2km above the volcanic vent, followed by tephra fallout which covered the SE and S flanks of Etna. Campaigns allowed collecting about 40 tephra samples and mapping the fallout deposit. The clockwise shifting of the volcanic plume during the eruption caused the different timing of the fallout on the ground, thus widening the dispersal area. Voronoi's method was used to evaluate: i) the total grain-size distribution, indicating that the fallout deposit peaked at 1 ϕ, and, for the first time at Etna, ii) the total componentry distribution, finding that most of the particles were lithics, with a low proportion of juvenile vs. lithics (34:65). The total erupted mass was estimated ~1.9×108 kg, corresponding to a mass eruption rate of ~5×103 kgs−1. Physical parameters and textural features of the erupted products suggest that the 24 November 2006 explosive event may be classified as small-sized in the recent history of Etna, and that the eruptive dynamic was mainly governed by magma/gas decoupling, which produced relatively fine-grained fallout deposits containing unusual elongated sideromelane ash particles. [ABSTRACT FROM AUTHOR]

Occurrence of well crystallized nontronite in a megaporphyritic basalt flow from Nighoj area, Maharashtra, India is reported. Thin section studies of the vesicles from periphery to the centre reveal the presence of greenish palagonite, probably indicating the stages of devitrification of glass and the weathering of palagonite to the formation of nontronite. The centre of the vesicles is marked by the presence of dark greenish-brown, radiating and fibrous sheets of nontronite. X-ray diffraction (XRD) analysis reveals the dominant presence of smectite (nontronite) as the major phase with traces of pyroxene. Scanning Electron Microscopy (SEM) shows well developed sheets of nontronite within the gas vesicles of the megaporphyritic basalt flows. In the present investigation, the nontronite within the gas vesicles of the megaporphyritic basalts at Nighoj was formed in-situ due to the devitrification of glass containing palagonite. Palagonite is an intermediate step in the alteration that may be accomplished by the steam generated in quenching of the lava. Weathering of palagonite under conditions of poor drainage is essential to the genesis of nontronite as has been suggested by Victor and Vernon (1946). [ABSTRACT FROM AUTHOR]

Abstract: The incipient alteration of basaltic glass to palagonite in recent seafloor lavas from the arctic Mohns Ridge was studied by complimentary high-spatial-resolution geochemical techniques: TEM-EDS (transmission electron microscopy energy dispersive X-ray spectroscopy) and NanoSIMS (nano-scale secondary ion mass spectrometry). Rounded to elongated pores 0.5–2μm across were found embedded in compact palagonite that have sizes and shapes comparable to microbial cells. In-situ elemental mapping revealed that the micropore rims are comparable in composition to the bulk palagonite and that some are enriched in manganese. Elevated concentrations of carbon and nitrogen were also found in some of the micropores. Hence these structures are interpreted as fossilised bacteriomorphs of endolithic microorganisms that inhabited fractures in the basaltic glass. The preferential accumulation of Mn in some of the cell encrustations suggests the mineralisation of Mn-oxidising bacteria. These data provide further evidence for the involvement of microorganisms in the colonisation and chemical alteration of recent seafloor volcanic glass and identify micro-scale Mn enrichments associated with micropores as a promising biosignature in such rocks. [Copyright &y& Elsevier]

Abstract: The suggestion that radon could be used as a radioactive tracer of regolith-atmosphere exchanges and as a proxy for subsurface water on Mars, as well as its indirect detection in the Martian atmosphere by the rover Opportunity, have raised the need for a better characterization of its production process and transport efficiency in the Martian soil. More specifically, a proper estimation of radon exhalation rate on Mars requires its emanation factor and diffusion length to be determined. The dependence of the emanation factor as a function of pore water content (at 267 and 293K) and the dependence of the adsorption coefficient on temperature, specific surface area and nature of the carrier gas (He, He+CO2) have been measured on a Martian soil analogue (Hawaiian palagonitized volcanic ash, JSC Mars-1), whose radiometric analysis has been performed. An estimation of radon diffusion lengths on Mars is provided and is used to derive a global average emanation factor (2–6.5%) that accounts for the exhalation rate inferred from the 210Po surface concentration detected on Martian dust and from the 214Bi signal measured by the Mars Odyssey Gamma Ray Spectrometer. It is found to be much larger than emanation factors characterizing lunar samples, but lower than the emanation factor of the palagonite samples obtained under dry conditions. This result probably reflects different degrees of aqueous alteration and could indicate that the emanation factor is also affected by the current presence of pore water in the Martian soil. The rationale of the “radon method” as a technique to probe subsurface water on Mars, and its sensitivity to soil parameters are discussed. These experimental data are useful to perform more detailed studies of radon transport in the Martian atmosphere using Global Climate Models and to interpret neutron and gamma data from Mars Odyssey Gamma Ray Spectrometer. [Copyright &y& Elsevier]

Abstract: The colonization and weathering of young seafloor basaltic glass from the mid-Atlantic Ridge was examined. Microorganisms were localised to fractures in the surface of the basalt and grew on the surfaces of material in the fractures. XAS, Raman spectroscopy and NanoSIMS analysis of the fracture-filling material shows that it contains non-crystallised iron-enriched altered glass and poorly ordered iron oxides. Organisms, which in places develop into contiguous biofilms, develop on the surface of the material. No putative biogenic alteration textures were observed in the basaltic glass at the fracture boundaries suggesting that the microbial community is restricted to the secondary alteration products. Microbial culturing shows the presence of heterotrophic bacteria including Sufitobacter and Halomonas consistent with observations of photic zone detritus associated with fracture-filling material. These data show that the interior of fresh basaltic glass is an endolithic habitat for microorganisms, but that the glass itself is not a primary source of cations or energy for the developing communities. [ABSTRACT FROM AUTHOR]

Abstract: To better understand glass alteration mechanisms, especially alteration layers formation, leaching experiments of a borosilicate glass (SON68) doped with a different rare earth element (La, Ce, or Nd) with solutions rich in 29Si and 18O were carried out. The coupled analyses of glass, alteration products, and solution led to a complete elemental and isotopic (29Si and 18O) budget. They revealed different behaviours of elements that depend not only on their structural role in the glass, but also on their affinity for alteration products (gel, phyllosilicates, phosphates). However, analyses of both glass and solution are not sufficient to describe the real exchanges occurring between glass and solution. The use of 29Si and 18O tracers gives new insights on the formation of alteration layers. During alteration the phyllosilicates records the isotopic variations of the leaching solution. Their isotopic signatures highlight a mechanism of dissolution/precipitation, which implies equilibrium between the secondary phases and the solution. On the other hand the gel isotopic signature, that is intermediate between the glass and the solution, substantiates the hypothesis that the gel is formed by hydrolysis/condensation reactions. This mechanism can thus explain the influence of the gel formation conditions (alteration conditions, solution saturation) on the structure (reorganisation) and texture (porosity) of this layer and on its protective effect. These hydrolysis/condensation reactions are also certainly involved in the aluminosilicate glass alteration and in the formation of palagonite. [Copyright &y& Elsevier]

The composition of sand-silt and pelite fractions of deep-sea sediments deposited under different hydrodynamic conditions was studied. Assemblages of clastic, clayey, biogenic, and authigenic minerals formed under the influence of surface and bottom currents were traced. It is shown that biogenic opal, fine-dispersed celestobarite, and authigenic protosyngenetic ferromanganese micronodules, which are composed of only manganese phases, represent indicators of cyclonic gyres characterized by enhanced bioproductivity. Collophane (bone detritus), phillipsite, palagonite, and large celestobarite crystals prevail in mineral assemblages below the anticyclonic gyres, whereas ore micronodules are depleted in manganese. Surface and bottom currents control the distribution of clastic (terrigenous edaphogenic, terrestrial-volcanogenic) and clay minerals, as well as biogenic opal in the form of Ethmodiscus frustules in sediments. Edaphogenic mineral assemblages represent the reliable indicators of bottom currents. [ABSTRACT FROM AUTHOR]

In Iceland, hyaloclastites form thick masses generated as a result of subglacial eruptions during Pliocene-Pleistocene surface glaciations. The formation of hyaloclastites and features of their alterations during lithogenesis were investigated. Hyaloclastites are extremely heterogeneous in their physical and physical-mechanical properties. A sequence of hyaloclastites secondary transformations was established from virgin, only slightly palagonitized hyaloclastites with contact-type cement to thoroughly transformed rocks with secondary minerals forming porous cement and partially substituting volcanic glass. A general tendency towards an increase in elasticity, density, strength, and thermal characteristics and towards a decrease in porosity and permeability has been observed with progression of secondary alterations, with the growth of age, from newer to more ancient deposits, and the depth of hyaloclastite burial. [ABSTRACT FROM AUTHOR]

Bacteria play an important role in rock weathering and yet their diversity and potential activity in the terrestrial rock weathering environment is poorly understood. Culture and culture-independent methods (16S rDNA) were used to investigate the populations of bacteria inhabiting a basaltic glass/palagonite subglacial (hyaloclastite) deposit subject to weathering in Iceland. The rock hosts a diverse microbial community. The 16S rDNA clones were dominated by Actinobacteria, Proteobacteria, Bacteroidetes and Acidobacteria. Representatives of Gemmatimonadetes and Verrucomicrobia were present. Isolation of organisms on basalt/palagonite yielded only two isolates, an actinobacterium and a Bacteroidetes, showing that the active species, at least in the time scale of laboratory cultivation, are a small proportion of the total diversity. Firmicutes and Actinobacteria were isolated when basalt/palagonite was supplemented with an organic source. Many of the isolates demonstrated tolerance to transition metals (Cr, Cu, Zn, Ni, Co) naturally present in the rock. The growth of the isolates was inhibited at typical pH values for Icelandic rain, which suggests that the increase in pH caused by the consumption of protons in rock weathering, for example by palagonite formation, may play a role in defining which organisms are active. Colonization experiments show that the filamentous growth habit of the actinobacterium isolated on basalt/palagonite allows it to actively invade and colonise the basaltic glass. The filamentous growth of some actinobacteria may be an important contributor to their role in systemic interstitial rock weathering in the natural environment. [ABSTRACT FROM AUTHOR]

Abstract: Volcanic rocks in southern Uruguay are linked to an extensional tectonic regime related to the post-collisional Brasiliano–Pan African orogenic cycle. The ca 580 Ma magmatic event is recorded in the Playa Hermosa Formation. In the upper section of this formation several units were defined. The basal unit is a quartz–syenite brecciated deposit, interpreted as the result of explosive episodes of shallow plutonic quartz–syenite intrusion with signs of hydrothermal alteration. Sedimentary and basaltic lithoclasts are occasionally present in the breccia, implying the emplacement of basalts before of that magmatic event. The middle unit is composed of trachytic hyaloclastites. Local distribution and textural evidence indicate that trachytic volcanic pulses have been followed by an explosive event that produced brecciated deposits. The upper unit of the studied sequence is composed of basalts with thin sedimentary intercalations. Most of the outcropping basalts display the typical micro- and macro-features of hyaloclastites; distinctive of extrusions occurred in wet sediments previous to lithification. Basaltic feeder dikes are common in the lower unit. The study of flow structures in the quartz–syenite brecciated deposits led to the recognition of two basaltic inputs. Such differences are related to the intensity of chloritic alteration, which would be related to water contamination. Basaltic peperites are one of the most impressive features of the Playa Hermosa Formation. Hyaloclastites and peperites largely represented among the studied volcanic rocks, and devitrification textures are all evidences of magma/seawater interactions. In the basaltic fragments of the peperites well preserved orange palagonite appears, while the sandstone fractions have lithic clasts of felsic volcanic rocks, such as rhyolitic lavas with perlitic cracks and lithophysae-like structures. Palagonite chemical analyses suggest marine environment and, at the same time, it proves that the studied section lacks of regional metamorphism. The felsic volcanic lithoclasts contained in sandstones could be related to the felsic volcanic lobes intercalations. The studied magmatic event is important in order to formulate correlations with other Neoproterozoic units distributed around the Dom Feliciano belt, like Camaquã and Campo Alegre basins (Brazil), and in the Kaoko belt (NW Namibia) in Africa. Also, Playa Hermosa Formation presents glacigenic features that are well documented, and reinforce the volcanism around 580 Ma in the Rio de la Plata Craton. [Copyright &y& Elsevier]

Abstract: The recent detection of up to ∼10 wt% water-equivalent H heterogeneously distributed in the upper meter of the equatorial regions of the martian surface and the presence of the 3-μm hydrations feature across the entire planet raises the question whether martian surficial dust can account for this water-equivalent H. We have investigated the H2O and CO2 adsorption properties of palagonitic dust (<5 μm size fraction of phyllosilicate-poor palagonitic tephra HWMK919) as a martian dust analog and two smectites under simulated martian equatorial surface conditions. Our results show that the palagonitic dust, which contains hydrated and hydroxylated volcanic glass of basaltic composition, accommodates significantly more H2O under comparable humidity and temperature conditions than do the smectites nontronite and montmorillonite. [Copyright &y& Elsevier]

Abstract: We present measurements of ratios of elements of the scattering matrix of martian analogue palagonite particles for scattering angles ranging from 3° to 174° and a wavelength of 632.8 nm. To facilitate the use of these measurements in radiative transfer calculations we have devised a method that enables us to obtain, from these measurements, a normalized synthetic scattering matrix covering the complete scattering angle range from 0° to 180°. Our method is based on employing the coefficients of the expansions of scattering matrix elements into generalized spherical functions. The synthetic scattering matrix elements and/or the expansion coefficients obtained in this way, can be used to include multiple scattering by these irregularly shaped particles in (polarized) radiative transfer calculations, such as calculations of sunlight that is scattered in the dusty martian atmosphere. [Copyright &y& Elsevier]

Abstract: In this study are discussed new SEM-EDS analyses performed on glass shards from five cores collected in the Central Adriatic Sea and two cores recovered from the South Adriatic Sea. A total of 26 tephra layers have been characterized and compared with the geochemical features of terrestrial deposits and other tephra archives in the area (South Adriatic Sea and Lago Grande di Monticchio, Vulture volcano). The compositions are compatible with either a Campanian or a Roman provenance. The cores, located on the Central Adriatic inner and outer shelf, recorded tephra referred to explosive events described in the literature: AP3 (sub-Plinian activity of the Somma-Vesuvius, 2710±60 14C years BP); Avellino eruption (Somma–Vesuvius, 3548±129 14C years BP); Agnano Monte Spina (Phlegrean Fields, 4100±400 years BP); Mercato eruption (Somma–Vesuvius, 8010±35 14C years BP; Agnano Pomici Principali eruption (Phlegrean Fields, 10,320±50 14C years BP); Neapolitan Yellow Tuff (Phlegrean Fields, 12,100±170 14C years BP). Some of these layers were also observed in the South Adriatic core IN68-9 in addition to younger (AP2, sub-Plinian eruption, Somma–Vesuvius, 3225±140 14C years BP), and older layers (Pomici di Base eruption, Somma–Vesuvius, 18,300±150 14C years BP). Significant is the tephra record of core RF95-7 that, for the first time in the Adriatic Sea, reports the occurrence of tephra layers older than 60 ka: the well known Mediterranean tephra layers X2 (ca. 70 ka), W1 (ca. 140 ka) and V2 (Roman origin, ca. 170 ka) as well as other tephra layers attributed, on the basis of geochemistry and biostratigraphy, to explosive eruptions occurred at Vico (138±2 and 151±3 ka BP) and Ischia (147–140 ka BP). Previous tephra correlations performed on other cores in the Central Adriatic Sea were also critically revised according to new available data, and integrated with the results of this study for a correlation at a regional scale. The most important key beds for correlation are the “Agnano Monte Spina” and “Neapolitan Yellow Tuff” tephra layers, which occur in both Central and South Adriatic sea. Other tephra layers, younger than 15 ka, are relatively less frequent: the Y1 (Etna, 14,180±260 14C years BP) and “Agnano Pomici Principali”. In the more recent record, in the shelf cores north of Gargano Promontory, the AP3 tephra layer is also frequent. [Copyright &y& Elsevier]

Elongate, fine tubes, ~1 µm wide and up to 200 µm long, extend from fractured surfaces, vesicle walls, and internal fractures into fragments of basalt glass in samples from the Hawaii Scientific Drilling Project #2 phase 1 (HSDP #21) core and the Hilina slope, Hawaii. Several features indicate that these tubes are microbial endolithic microborings: the tubes resemble many described microborings from oceanic basalt glass, their formation is postdepositional but restricted to certain but different ranges of time in the two sets of samples, and they are not uniformly distributed throughout glass fragments. Microtubules record several characteristic behaviors including boring into glass, mining, seeking olivine, and avoiding plagioclase. They also are highly associated with a particular form of glass-replacing smectite. Evidence of behavior should join morphological and geochemical criteria in indicating microbial alteration of basalt glass. In some samples, steeply conical tubes, ~10–20 µm in diameter tapering to 1 µm and commonly filled with smectite, appear to be modifications or elaborations of the microtubules. These also curve toward olivine and are associated with replacement smectite. In HSDP #21 samples, microtubules initiated at margins of shards before palagonite replaced those margins and are preserved during palagonitization. In fact, microtubules appear to have provided routes that enhanced the efficiency of water's reaching of unaltered glass. In Hilina Slope samples, the microtubules appear to postdate palagonitization because they initiate at the boundary between palagonite and unaltered sideromelane. Preservation of microtubules during palagonitization in samples together with recognition of other associated characteristics representing behavior suggests that such features may be recognizable in more heavily altered ancient rocks. [ABSTRACT FROM AUTHOR]

Abstract: The subsurface biosphere in the basaltic ocean crust is potentially of major importance in affecting chemical exchange between the ocean and lithosphere. Alteration of the oceanic crust commonly yields secondary pyrite that is depleted in 34S relative to igneous sulfides. Although these 34S depleted sulfur isotope ratios may point to signatures of biological fractionation, previous interpretations of sulfur isotope fractionation in altered volcanic rocks have relied on abiotic fractionation processes between intermediate sulfur species formed during basalt alteration. Here, we report results for multiple S-isotope (32S, 33S, 34S) compositions of altered basalts at ODP Site 801 in the western Pacific and provide evidence for microbial sulfate reduction within the volcanic oceanic crust. In-situ ion-microprobe analyses of secondary pyrite in basement rocks show a large range of δ 34S values, between −45‰ and 1‰, whereas bulk rock δ 34S analyses yield a more restricted range of −15.8 to 0.9‰. These low and variable δ 34S values, together with bulk rock S concentrations ranging from 0.02% up to 1.28% are consistent with loss of magmatic primary mono-sulfide and addition of secondary sulfide via microbial sulfate reduction. High-precision multiple sulfur-isotope (32S/33S/34S) analyses suggest that secondary sulfides exhibit mass-dependent equilibrium fractionation relative to seawater sulfate in both δ 33S and δ 34S values. These relationships are explained by bacterial sulfate reduction proceeding at very low metabolic rates. The determination of the S-isotope composition of bulk altered oceanic crust demonstrates that S-based metabolic activity of subsurface life in oceanic basalt is widespread, and can affect the global S budget at the crust–seawater interface. [Copyright &y& Elsevier]

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula. [ABSTRACT FROM AUTHOR]

Abstract: The Plio-Pleistocene Llancanelo Volcanic Field, together with the nearby Payun Matru Field, comprises at least 800 scoria cones and voluminous lava fields that cover an extensive area behind the Andean volcanic arc. Beside the scoria cones in the Llancanelo Field, at least six volcanoes show evidence for explosive eruptions involving magma–water interaction. These are unusual in the context of the semi-arid climate of the eastern Andean ranges. The volcanic structures consist of phreatomagmatic-derived tuff rings and tuff cones of olivine basalt composition. Malacara and Jarilloso tuff cones were produced by fallout of a range of dry to wet tephra. The Malacara cone shows more evidence for a predominance of wet-emplaced units, with a steep slump-slope characterized by many soft-sediment deformation structures, such as: undulating bedding planes, truncated beds and water escape features. The Piedras Blancas and Carapacho tuff rings resulted from explosive eruptions with deeper explosion loci. These cones are hence dominated by lapilli tuff and tuff units, emplaced mainly by wet and/or dry pyroclastic surges. Carapacho is the only centre that appears to have started with phreatomagmatic eruptions, with lowermost tephra being rich in non-volcanic country rocks. The presence of deformed beds with impact sags, slumping textures, asymmetrical ripples, dunes, cross- and planar lamination, syn-volcanic faulting and accretionary lapilli beds indicate an eruption scenario dominated by excessive water in the transportational and depositional regime. This subordinate phreatomagmatism in the Llancanelo Volcanic Field suggests presence of ground and/or shallow surface water during some of the eruptions. Each of the tuff rings and cones are underlain by thick, fractured multiple older lava units. These broken basalts are inferred to be the horizons where rising magma interacted with groundwater. The strong palagonitization at each of the phreatomagmatic cones formed hard beds, resistant to erosion, and therefore the volcanic landforms are well-preserved. [Copyright &y& Elsevier]

Abstract: Frequent observations of tubular to vermicular microchannels in altered basalt glass have led to increasing appreciation of a possible significant role of microbes in the low-temperature alteration of seafloor basalt. We have examined such microchannel alteration features at the nanoscale in basalt glass shards from the Ontong Java Plateau using a combination of focused ion beam milling, transmission electron microscopy and scanning transmission X-ray microscopy. Three types of materials were found in ultrathin cross-sections cut through the microchannels by FIB milling: fresh basalt glass, amorphous Si-rich rims surrounding the microchannels, and palagonite within the microchannels. X-ray absorption spectroscopy at the C K-edge and Fe L2,3-edges showed the presence of organic carbon in association with carbonates within the microchannels and partial oxidation of iron in palagonite compared with basalt glass. Although these observations alone cannot discriminate between a biotic or abiotic origin for the microchannels, they provide new information on their mineralogical and chemical composition and thus better constrain the physical and chemical conditions prevailing during the alteration process. [Copyright &y& Elsevier]

Abstract: Core samples recovered during the Hawaiian Scientific Drilling Project (HSDP) drilling project reveal that the upper 1 km of the submarine flank of Mauna Kea is comprised mainly of hyaloclastites. Progressive, very low-temperature alteration of these hyaloclastites has been accompanied by systematic transformations in physical properties of these deposits. Hyaloclastite deposits which directly underlie ca. 1 km of subaerially-emplaced lavas are very poorly consolidated. But over a depth interval of ca. 500 m, compaction and, especially, precipitation of zeolitic, pore-filling cements associated with palagonitization of sideromelane, have eliminated porosity as well as promoted the consolidation of these hyaloclastites. The latter is reflected in unconfined compressive strengths which increase from mean values, respectively, of 2.5 and 4.6 MPa in weakly consolidated, smectite-rich hyaloclastites from the incipient (1080 to 1335 mbsl) and smectitic (1405–1573 mbsl) alteration zones, to a mean value of 10.0 MPa in the more highly consolidated hyaloclastites of the palagonitic zone of alteration (from 1573 mbsl to the bottom of the drill hole). Conversely, overlying, intercalated, and underlying lava flows are generally much less altered, and have mean compressive strengths which are 1 to 2 orders of magnitude greater then hyaloclastites at equivalent depths. The shear strengths of the hyaloclastites also increase with depth and grade of alteration, but are uniformly and substantially lower in the lavas. Those hyaloclastites exhibiting the highest grade of alteration (i.e., palagonitic) also exhibit the highest measured strengths, and thus the alteration of hyaloclastites appears to strengthen as opposed to weaken the flanks of the edifice. However, the contrast in strength between hyaloclastites and lavas may be a primary factor in localizing destabilization, and the zones of weak and poorly consolidated hyaloclastites may facilitate slumping by servings as hosts for shallow detachment surfaces on the unsupported flanks of these volcanoes. [Copyright &y& Elsevier]

The visible to near-infrared spectral reflectance properties of intimate and areal pyroxene + palagonitic material mixtures as well as pure mafic silicates (low-calcium pyroxene, high-calcium pyroxene, pigeonite, olivine) and mixtures of these minerals were analyzed at high spectral resolution (5 nm) as well as with non-contiguous band passes equivalent to recent HST observations and the Pathfinder IMP in order to determine the quality and quantity of mineralogical information (end member compositions, abundances, and grain sizes) derivable in the presence of palagonitic material. In the case of pyroxene + palagonitic material mixtures, pyroxene is detectable at abundances as low as 10 wt%, and its composition can be constrained because (a) its diagnostic absorption feature (located near 1000 nm) persists even for high palagonitic material abundances, and (b) palagonitic material does not appreciably alter the wavelength position of this band (<4 nm variation). For broad band data (such as Pathfinder IMP band passes), different mafic silicates can be discriminated and palagonitic material abundances constrained using a variety of reflectance ratios and three-point “absorption band depths.” However, other properties of mafic silicate ± palagonitic material assemblages, such as mafic silicate major element compositions, grain sizes, and end member abundances, generally cannot be rigorously quantified. The use of multiple reflectance ratios can, however, be used to identify relative changes in these properties, as most changes in mafic silicate ± palagonitic material assemblage properties are characterized by a unique corresponding set of reflectance ratio variations. The observed spectral-assemblage property trends are consistent with those expected from the known spectral properties of the end members. [Copyright &y& Elsevier]

This paper provides an overview of the geochemical alteration of basaltic glass, considered for over 20 years as a suitable natural analogue for nuclear borosilicate glasses. The available data show that natural basaltic glasses may survive for million of years under subsurface conditions. Mineralogical studies show that an alteration layer called palagonite forms on the surface of the basaltic in response to the chemical attack by water. Under some environmental conditions, the alteration layer consists of an amorphous gel-like material, leading many authors to suspect hydration of the glass by water permeation and alkali interdiffusion. In other cases, the alteration layer is crystallized to some extent and contains clay minerals (smectite). Such layers are formed mainly on the younger natural glass samples (<1 My) by a process of coprecipitation of the elements dissolved from the glass. On samples older than 1 My, the alteration layers also contain zeolites. In the presence of these hydrated aluminosilicates, a hydrated residual glass is systematically observed, which thus forms as a consequence of interdiffusion processes. Leach tests conducted under controlled laboratory conditions at temperatures up to 200 °C on both natural glass samples and synthetic basaltic glass provide identical kinetic results and alteration mechanisms. When compared with the data for SON68 nuclear borosilicate glass, the initial dissolution rates show the same activation energy (about 72 kJ mol−1) and consequently similar dissolution mechanisms. Moreover, when altered under static conditions at high reaction progress, both basaltic glass and nuclear glass have similar behavior characterized by a significant drop in the dissolution rate, up to three to five orders of magnitude lower than the initial dissolution rate. The time-dependence of the thickness of the altered layers measured on natural glass samples confirms this kinetic trend over time: the long-term dissolution rate is very low. This decrease may be related to diffusion mechanisms involving key chemical species and controlled by the mineralogy of the palagonite layer. [Copyright &y& Elsevier]