Submarine Volcanism Research Articles

A Preliminary Review of Metallogenic Regularity of Silver Deposits in China

China has widely distributed silver deposits, and is rich in silver resources. Although silver deposits are mainly associated with Pb‐Zn deposits, a number of independent silver deposits have also been discovered in recent years. Silver deposits include different types, such as submarine volcanism and continental volcanism related type, intrusion related type, and sedimentary related type. This study summarized the metallogenic regularity of China's silver deposits systematically based mainly on the data from 490 silver deposits. It is shown that submarine volcanic sedimentary type, continental volcanic or sub‐volcanic type, skarn type, hydrothermal type (including vein type and stratabound type), sedimentary metamorphic type, sedimentary type and regolith type should be regarded as the most important prediction types of silver deposit. A total of 32 silver mineralization belts and 111 silver concentration areas have been delineated. The map of “Spatial distribution of silver mineralization belts in China” and other series of maps finished in this study may provide a theoretical basis for the evaluation and prognosis of silver resources potential in China.

Segmentation and tracking of anticyclonic eddies during a submarine volcanic eruption using ocean colour imagery.

The eruptive phase of a submarine volcano located 2 km away from the southern coast of El Hierro Island started on October 2011. This extraordinary event provoked a dramatic perturbation of the water column. In order to understand and quantify the environmental impacts caused, a regular multidisciplinary monitoring was carried out using remote sensing sensors. In this context, we performed the systematic processing of every MODIS and MERIS and selected high resolution Worldview-2 imagery to provide information on the concentration of a number of biological, physical and chemical parameters. On the other hand, the eruption provided an exceptional source of tracer that allowed the study a variety of oceanographic structures. Specifically, the Canary Islands belong to a very active zone of long-lived eddies. Such structures are usually monitored using sea level anomaly fields. However these products have coarse spatial resolution and they are not suitable to perform submesoscale studies. Thanks to the volcanic tracer, detailed studies were undertaken with ocean colour imagery allowing, using the diffuse attenuation coefficient, to monitor the process of filamentation and axisymmetrization predicted by theoretical studies and numerical modelling. In our work, a novel 2-step segmentation methodology has been developed. The approach incorporates different segmentation algorithms and region growing techniques. In particular, the first step obtains an initial eddy segmentation using thresholding or clustering methods and, next, the fine detail is achieved by the iterative identification of the points to grow and the subsequent application of watershed or thresholding strategies. The methodology has demonstrated an excellent performance and robustness and it has proven to properly capture the eddy and its filaments.

Historical bathymetric charts and the evolution of Santorini submarine volcano, Greece

Historical bathymetric charts are a potential resource for better understanding the dynamics of the seafloor and the role of active processes, such as submarine volcanism. The British Admiralty, for example, have been involved in lead line measurements of seafloor depth since the early 1790s. Here, we report on an analysis of historical charts in the region of Santorini volcano, Greece. Repeat lead line surveys in 1848, late 1866, and 1925–1928 as well as multibeam swath bathymetry surveys in 2001 and 2006 have been used to document changes in seafloor depth. These data reveal that the flanks of the Kameni Islands, a dacitic dome complex in the caldera center, have shallowed by up to ∼175 m and deepened by up to ∼80 m since 1848. The largest shallowing occurred between the late 1866 and 1925–1928 surveys and the largest deepening occurred during the 1925–1928 and 2001 and 2006 surveys. The shallowing is attributed to the emplacement of lavas during effusive eruptions in both 1866–1870 and 1925–1928 at rates of up to 0.18 and 0.05 km3 a−1, respectively. The deepening is attributed to a load-induced viscoelastic stress relaxation following the 1866–1870 and 1925–1928 lava eruptions. The elastic thickness and viscosity that best fits the observed deepening are 1.0 km and ∼1016 Pa s, respectively. This parameter pair, which is consistent with the predictions of a shallow magma chamber thermal model, explains both the amplitude and wavelength of the historical bathymetric data and the present day rate of subsidence inferred from InSAR analysis.

New evidence for the structure of conical seamounts and hills at the foot of the Sea of Okhotsk margin of the Kuril island arc: Continuous seismic-profiling data

This paper is concerned with results from the interpretation of continuous seismic profiling (CSP) data that were acquired during the 21st cruise of the R/V Pegas in 1980. The data are of relevance for the structure of conical seamounts and sea-hills at the foot of the Sea of Okhotsk margin of the Kuril island arc. The seamounts are extrusive domes (volcanoes) or magmatic diapirs with thick sedimentary caps of contrasting (at the top) and transparent (at the bottom) Cenozoic deposits. They were mostly formed in the Cenozoic, largely during Pliocene to Quaternary time; they resulted from viscous magma being emplaced into the sediments. There are also several small, buried domes with flattened bottoms that were formed by liquid magma being emplaced into the sediments (laccoliths or subvolcanoes). We also touch on questions relating to the terminology, geography, and history of submarine volcanism in the region and its relationship to the Benioff zone.

Transient Changes in Bacterioplankton Communities Induced by the Submarine Volcanic Eruption of El Hierro (Canary Islands)

The submarine volcanic eruption occurring near El Hierro (Canary Islands) in October 2011 provided a unique opportunity to determine the effects of such events on the microbial populations of the surrounding waters. The birth of a new underwater volcano produced a large plume of vent material detectable from space that led to abrupt changes in the physical-chemical properties of the water column. We combined flow cytometry and 454-pyrosequencing of 16S rRNA gene amplicons (V1–V3 regions for Bacteria and V3–V5 for Archaea) to monitor the area around the volcano through the eruptive and post-eruptive phases (November 2011 to April 2012). Flow cytometric analyses revealed higher abundance and relative activity (expressed as a percentage of high-nucleic acid content cells) of heterotrophic prokaryotes during the eruptive process as compared to post-eruptive stages. Changes observed in populations detectable by flow cytometry were more evident at depths closer to the volcano (~70–200 m), coinciding also with oxygen depletion. Alpha-diversity analyses revealed that species richness (Chao1 index) decreased during the eruptive phase; however, no dramatic changes in community composition were observed. The most abundant taxa during the eruptive phase were similar to those in the post-eruptive stages and to those typically prevalent in oceanic bacterioplankton communities (i.e. the alphaproteobacterial SAR11 group, the Flavobacteriia class of the Bacteroidetes and certain groups of Gammaproteobacteria). Yet, although at low abundance, we also detected the presence of taxa not typically found in bacterioplankton communities such as the Epsilonproteobacteria and members of the candidate division ZB3, particularly during the eruptive stage. These groups are often associated with deep-sea hydrothermal vents or sulfur-rich springs. Both cytometric and sequence analyses showed that once the eruption ceased, evidences of the volcano-induced changes were no longer observed.

Modulation of oxygen production in Archaean oceans by episodes of Fe(II) toxicity

Earth’s initial oxygenation took several hundred million years. Experiments and geochemical modelling suggest that early photosynthetic marine microbes may have been repeatedly stressed by Fe(II) delivered by submarine volcanism. Oxygen accumulated in the surface waters of the Earth’s oceans1 and atmosphere2 several hundred million years before the Great Oxidation Event between 2.4 and 2.3 billion years ago3. Before the Great Oxidation Event, periods of enhanced submarine volcanism associated with mantle plume events4 supplied Fe(II) to sea water. These periods generally coincide with the disappearance of indicators of the presence of molecular oxygen in Archaean sedimentary records5. The presence of Fe(II) in the water column can lead to oxidative stress in some organisms as a result of reactions between Fe(II) and oxygen that produce reactive oxygen species6. Here we test the hypothesis that the upwelling of Fe(II)-rich, anoxic water into the photic zone during the late Archaean subjected oxygenic phototrophic bacteria to Fe(II) toxicity. In laboratory experiments, we found that supplying Fe(II) to the anoxic growth medium housing a common species of planktonic cyanobacteria decreased both the efficiency of oxygenic photosynthesis and their growth rates. We suggest that this occurs because of increasing intracellular concentrations of reactive oxygen species. We use geochemical modelling to show that Fe(II) toxicity in conditions found in the late Archaean photic zone could have substantially inhibited water column oxygen production, thus decreasing fluxes of oxygen to the atmosphere. We therefore propose that the timing of atmospheric oxygenation was controlled by the timing of submarine, plume-type volcanism, with Fe(II) toxicity as the modulating factor.

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

Mantle volatiles are mainly lost from the Earth to the atmosphere through subaerial and submarine volcanism. Recent studies have shown that degassing of mantle volatiles also occurs from inactive volcanic areas and in tectonically active areas. A new challenge in Earth science is to quantify the mantle-derived flux of volatiles (e.g., CO2) which is important for understanding such diverse issues as the evolution of the atmosphere, the relationships between magma degassing and volcanic activity, gas pressure and seismogenic processes, and the hazards posed by volcanic lakes. Here we present a detailed study of mantle-derived CO2 budget from Mt. Vulture volcano in the Apennines, Italy, whose latest eruption occurred 141±11 kyr ago.The relationship between δ13CCO2 and total dissolved carbon at Mt. Vulture volcano indicates that the emitted CO2 is a mixture of a biogenic end-member with an average δ13CCO2 of about −17‰ and a mantle-derived CO2 end-member with δ13CCO2 values from −3‰ to +2‰. These values of mantle-derived δ13CCO2 are in the range of those for gas emitted from active volcanoes in the Mediterranean. We calculated the contribution of individual components (CO2 in groundwater, in lakes and from main pools) to the total CO2 budget in the area. We used new measurements of water flow, combined with literature data, to calculate the CO2 flux associated with groundwater, and measured the gas flux from the main pools on the volcanic edifice. Finally, we calculated the CO2 flow in the lakes based on the gradient concentration and eddy diffusivity. The total mantle-derived CO2 budget in the area is 4.85×108 molyr−1, which is more than double previous estimates. This is higher than those observed in younger volcanic systems elsewhere, thereby supporting the existence of actively degassing mantle melts below Mt. Vulture volcano.A structural map highlights the tectonic control on CO2 flow across the Mt. Vulture volcanic edifice. Indeed, the tectonic discontinuities that controlled the magma upwelling during the most recent volcanic activity are still the main active degassing structures.The new estimate of CO2 budget in the Mt. Vulture area, together with literature data on CO2 budget from historically active and inactive Italian volcanoes, suggests a power-law functional relationship between the age of the most recent volcanic eruption and both total discharged CO2 (R2=0.73) and volcano size-normalized CO2 flux (R2=0.66). This relation is also valid by using data from worldwide volcanoes highlighting that deep degassing can occur over very long time too. In turn, the highlighted relation provides also an important tool to better evaluate the state of activity of a volcano, whose last activity occurred far in time.Finally, our study highlights that in the southern Apennines, an active degassing of mantle-derived volatiles (i.e., He, CO2) occurs indiscriminately from west to east. This is in contrast to the central–northern Apennine, which is characterized by a crustal radiogenic volatile contribution, which increases eastward, coupled to a decrease in deep CO2 flux. This difference between the two regions is probably due to lithospheric tears which control the upwelling of mantle melts, their degassing and the transport of volatiles through the crust.

Submarine Volcanism: a Review of the Constraints, Processes and Products, and Relevance to the Cabo de Gata Volcanic Succession

Understanding of submarine volcanism still lags behind understandingof subaerial volcanism for the obvious reason that eruptionsare usually not, or only partially visible, and deposits are largelyinaccessible. In addition, our understanding of the effects of theambient water mass and the way in which erupting magma andwater interact, and the ways in which the physical properties of thewater mass control and influence eruption styles, dispersal processesand deposit characteristics, is still at a relatively early stage. In particular,in the past there has been a very simplistic approach to assessingconstraints on eruption styles using only ambient hydrostaticpressure, whereas equally important properties such as bulk modulus,compressibility, deformability, attenuation properties, thermalconductivity, heat capacity, have not been adequately considered.This review summarises our understanding on these issues, andbriefly summarises varying eruption conditions, styles and depositcharacteristics.The origin of pumice deposits preserved in subaqueous settingsneeds to be interpreted with care. They could represent local explosiveevents, but could also represent pumice sourced from distantexplosive events and vents, even subaerial, and deposited by falloutthrough water, the passage of pyroclastic flows into water fromsubaerial vents, long distance rafting of buoyant pumice by currents,reworking and resedimentation, and even non-explosive subaqueousvesiculation and quench fragmentation of subaqueously eruptedlavas in shallow or even deep water.The Miocene Cabo de Gata volcanic succession of southeasternSpain was deposited in shallow marine environments based on interbeddedfossiliferous limestones, which represent periods of volcanichiatus. The volcanic facies are consistent with a shallow marine setting,involving eruption of low volatile bearing magmas to formandesite and dacite lava flows, domes and associated hyaloclastites,as well as eruptions of volatile rich rhyolitic magmas that producedpumice deposits erupted from subaerial vents or vents at waterdepths that were too shallow to suppress explosive eruptionsthrough the effects of hydrostatic pressure, but were then reworkedand resedimented.

Groundwater flow in a relatively old oceanic volcanic island: The Betancuria area, Fuerteventura Island, Canary Islands, Spain

The island of Fuerteventura is the oldest of the Canary Islands' volcanic archipelago. It is constituted by volcanic submarine and subaerial activity and intrusive Miocene events, with some residual later volcanism and Quaternary volcanic deposits that have favored groundwater recharge. The climate is arid, with an average rainfall that barely attains 60mm/year in the coast and up to 200mm/year in the highlands. The aquifer recharge is small but significant; it is brackish due to large airborne atmospheric salinity, between 7 and 15gm−2year−1 of chloride deposition, and high evapo-concentration in the soil. The average recharge is estimated to be less than about 5mm/year at low altitude and up to 10mm/year in the highlands, and up to 20mm/year associated to recent lava fields. Hydrochemical and water isotopic studies, supported by water table data and well and borehole descriptions, contribute a preliminary conceptual model of groundwater flow and water origin in the Betancuria area, the central area of the island. In general, water from springs and shallow wells tends to be naturally brackish and of recent origin. Deep saline groundwater is found and is explained as remnants of very old marine water trapped in isolated features in the very low permeability intrusive rocks. Preliminary radiocarbon dating indicates that this deep groundwater has an apparent age of less than 5000years BP but it is the result of mixing recent water recharge with very old deep groundwater. Most of the groundwater flow occurs through the old raised volcanic shield of submarine and subaerial formations and later Miocene subaerial basalts. Groundwater transit time through the unsaturated zone is of a few decades, which allows the consideration of long-term quasi-steady state recharge. Transit times are up to a few centuries through the saturated old volcanics and up to several millennia in the intrusive formations, where isolated pockets of very old water may exist.

Constraining the age and origin of the seamount province in the Northeast Indian Ocean using geophysical techniques

The breakup of western margin of Australia from Greater India started around 155 Ma and progressed southwards. After the separation, the interceding intraplate region experienced large volumes of submarine volcanism, extending over 100 Myrs. The Christmas Island Seamount Province (CHRISP, as it has been dubbed) lies south of the Java-Sunda Trench, and contains numerous submerged volcanic seamounts, and two sub-aerially exposed island groups—Cocos (Keeling) Islands, and Christmas Island. While recent geochronological investigations have shed light on the diverse eruption ages of the volcanics of this region, some islands/seamounts have demonstrated protracted volcanic histories, and it is not clear how the volcanic loading, tectonic subsidence, and subsequent emergence history of the islands relates to these discrete volcanic episodes. This study utilises a number of geophysical techniques to determine the crustal structure, loading and subsidence history, and last sub-aerial exposure age for the CHRISP. The study shows that flexural and subsidence modelling are reliable techniques in constraining the age of the seamounts when geochronological techniques are not possible. Utilising regional gravity signatures, we model the crustal structure underneath the Cocos (Keeling) Island, and constrain the thickness of the limestone cover between 900 and 2,100 m. Using age-depth subsidence curves for oceanic lithosphere the time since these seamounts were exposed above sea-level was determined, and a trend in exposure ages that youngs towards the west is observed. Two episodes of volcanism have been recorded at Christmas Island and they are of different origin. The younger phase in the Pliocene is a manifestation of flexure induced cracks produced in the lithosphere as it rides the subduction fore-bulge, whereas a low velocity seismic zone rising from the lower mantle, and tectonic reorganization, may be associated with the older Eocene volcanic phase, as well as much of the rest of the province. Our modelling also supports the existence of an older, undated volcanic core to Christmas Island, based on the loading ages from flexural modelling.

Exploration of the 1891 Foerstner submarine vent site (Pantelleria, Italy): insights into the formation of basaltic balloons

On October 17, 1891, a submarine eruption started at Foerstner volcano located within the Pantelleria Rift of the Strait of Sicily (Italy). Activity occurred for a period of 1 week from an eruptive vent located 4 km northwest of the island of Pantelleria at a water depth of 250 m. The eruption produced lava balloons that discharged gas at the surface and eventually sank to the seafloor. Remotely operated vehicle (ROV) video footage and high-resolution multi-beam mapping of the Foerstner vent site were used to create a geologic map of the AD 1891 deposits and conduct the first detailed study of the source area associated with this unusual type of submarine volcanism. The main Foerstner vent consists of two overlapping circular mounds with a total volume of 6.3 × 105 m3 and relief of 60 m. It is dominantly constructed of clastic scoriaceous deposits with some interbedded pillow lavas. Petrographic and geochemical analyses of Foerstner samples by X-ray fluorescence and inductively coupled plasma mass spectrometry reveal that the majority of the deposits are vesicular, hypocrystalline basanite scoria that display porphyritic, hyaloophitic, and vitrophyric textures. An intact lava balloon recovered from the seafloor consists of a large interior gas cavity surrounded by a thin lava shell comprising two distinct layers: a thin, oxidized, quenched crust surrounding the exterior of the balloon and a dark gray, tachylite layer lying beneath it. Ostwald ripening is proposed to be the dominant bubble growth mechanism of four representative Foerstner scoria samples as inferred by vesicle size distributions. Characterization of the diversity of deposit facies observed at Foerstner in conjunction with quantitative rock texture analysis indicates that submarine Strombolian-like activity is the most likely mechanism for the formation of lava balloons. The deposit facies observed at the main Foerstner vent are very similar to those produced by other known submarine Strombolian eruptions (short pillow flow lobes, large scoriaceous clasts, spatter-like vent facies). Balloons were likely formed from the rapid cooling of extremely vesicular magma fragments as a result of a gas-rich frothy magma source. The exterior of these fragments hyperquenched forming a vesicular glassy shell that acted as an insulating layer preventing magmatic gas in its interior from escaping and thus allowing flotation as densities reached less than 1,000 kg/m3. We believe that lava balloons are a common eruptive product, as the conditions required to generate these products are likely to be present in a variety of submarine volcanic environments. Additionally, the facies relationships observed at Foerstner may be used as a paleoenvironmental indicator for modern and ancient basaltic shallow submarine eruptions because of the relatively narrow depth range over which they likely occur (200–400 m).

Evolution of the trace element contents (Sr and Mn) of hemipelagic carbonates from the Zumaia Paleocene section (Gipuzkoa, Spain): implications for the knowledge of seawater chemistry during the Selandian

AbstractWell exposed and stratigraphically well constrained by numerous studies, the Zumaia section is one of the best places to conduct studies on the Palaeocene in basin facies. Thus, this section has been chosen [Schmitz et al., 2011] as a stratotype of Selandian basal and terminal limits (GSSP: Global boundary Stratotype Section and Point). The sediments consist of carbonate hemipelagites interbedded with fine carbonate (Maastrichtian to Selandian) and siliciclastic (Thanetian to Eocene) turbidites.The purpose of this work is to geochemically characterize the Selandian by trace element contents (strontium and manganese) and to try to assess the chemical composition of seawater during the Paleocene. Analysis of various separated granulometric fine fractions show that hemipelagic sediments from the Zumaia section present a high preservation quality of the original records of trace-element contents. Late burial diagenesis plays only a minor role and geochemical breaks are not reducible to a change in the nature of carbonate producers.The strontium contents of Paleocene sediments require that the Sr/Ca ratio of seawater was lower than that in the present ocean. The Selandian is characterized by a positive excursion of the strontium curve. This accident is also recognized in several worldwide sections and is related to the platform/basin carbonate sedimentation budget and the intensity of oceanic hydrothermalism.The Mn content of hemipelagites is very high and can reach 2500–3000 ppm in the Paleocene. A comparison of analyses by atomic absorption spectrometry (AAS) and electron paramagnetic resonance (EPR) shows that both Mn2+ (in the calcite lattice) and Mn4+ (as oxide micro nodules) coexist. The Mn content fluctuations are related to the opening phases of the North Atlantic during the Paleocene by submarine volcanism and hydrothermalism in the North Atlantic Igneous Province (NAIP).

Eruption of South Sarigan Seamount, Northern Mariana Islands: Insights into Hazards from Submarine Volcanic Eruptions

are grateful to the NOAA Vents Program (now Earth Oceans Interaction Program) and the NOAA Office of Ocean Exploration and Research for long-term funding support of the Mariana arc explorations. JAMSTEC provided funding for Y. Tamura, the Hyper-Dolphin ROV dives, and the support vessel Natsushima. This work was supported in part by the JSPS Grant-in-Aid for Scientific Research (B) (23340166)]. The 2002 and 2013 mapping cruises were supported by the National Science Foundation (2013 cruise OCE-0841074). We thank the crews and science teams on the research vessels T.G. Thompson, Ewing, Melville, and Natsushima for their hard work at sea. We are grateful to J. White, M. Perfit, G. McGimsey, and J. Chaytor for their helpful reviews and C. Searcy and D.N. Greene for informative discussions about the history of seismic and hydro-acoustic monitoring in the southern Mariana arc. PMEL contribution number 4139.

Geochemical constraints on the evolution of mafic and felsic rocks in the Bathani volcanic and volcano-sedimentary sequence of Chotanagpur Granite Gneiss Complex

The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, cross-cutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC.

Autonomous Underwater Vehicles (AUVs): Their past, present and future contributions to the advancement of marine geoscience

Autonomous Underwater Vehicles (AUVs) have a wide range of applications in marine geoscience, and are increasingly being used in the scientific, military, commercial, and policy sectors. Their ability to operate autonomously of a host vessel makes them well suited to exploration of extreme environments, from the World’s deepest hydrothermal vents to beneath polar ice sheets. They have revolutionized our ability to image the seafloor, providing higher resolution seafloor mapping data than can be achieved from surface vessels, particularly in deep water. This contribution focuses on the major advances in marine geoscience that have resulted from AUV data. The primary applications are i) submarine volcanism and hydrothermal vent studies, ii) mapping and monitoring of low-temperature fluid escape features and chemosynthetic ecosystems, iii) benthic habitat mapping in shallow- and deep-water environments, and iv) mapping of seafloor morphological features (e.g. bedforms generated beneath ice or sediment-gravity flows). A series of new datasets are presented that highlight the growing versatility of AUVs for marine geoscience studies, including i) multi-frequency acoustic imaging of trawling impacts on deep-water coral mounds, iii) collection of high-resolution seafloor photomosaics at abyssal depths, and iii) velocity measurements of active submarine density flows. Future developments in AUV technology of potential relevance to marine geoscience include new vehicles with enhanced hovering, long endurance, extreme depth, or rapid response capabilities, while development of new sensors will further expand the range of geochemical parameters that can be measured.

Microorganisms in the Zone of Submarine Volcanic Eruptions at 535-513 Ma

New anatomical features revealed in some Early Cambrian calcareous microfossils suggest comparison with Rhodophyta (red algae), which makes it possible to define their taxonomic position. A taxonomically rich Early Cambrian paleobiocoenosis has been discovered in northern Tien Shan, which exemplifies the existence on earth at 535-513 Ma (million years) of morphologically complex fungiform microorganisms and red algae in a shallow-water biotope where environmental conditions favorable for life were created as a result of submarine volcanic eruptions.

Texture, mineralogy and geochemistry of hydrothermally altered submarine volcanics recovered southeast of Cheshire Seamount, western Woodlark Basin

The western Woodlark Basin lies within a gold-rich metallogenic province. This area is characterized by detachment faults that record ongoing extension and act as major pathways for the circulation of hydrothermal fluids. Dredging from the flanks of a submarine ridge southeast of Cheshire Seamount, western Woodlark Basin retrieved hydrothermally altered monomictic to polymictic crackle, mosaic and chaotic breccias with at least 30% clasts N2 mmin diameter. The precursor rocks are andesitic to rhyolitic in composition, but have been intensely hydrothermally altered, with about 90% of the volcanic glass replaced by secondaryminerals. The breccias show five generations of quartz growth, with the first being related to magmatic processes and the remaining four to alteration stages including silicification, chloritization, illitization, sericitization, albitization, and sulfidation. Needle-like crystals ofmordenite (zeolite)withmultiple growth centers growon the fourth generation of quartz. Notable textural variants in the breccias are vesicles, perlitic cracks, and zoned alteration halos that mantle the rims of clasts. Electron microprobe analyses on chlorite from breccia samples have identified clinochlore as the main chlorite type and indicate a formation temperature in the range of 210–304 °C. This and the elevated Au–As–Ag–Hg–Zn–Pb–Sb contents of a mineralized sample indicate hydrothermal alteration temperatures N200 °C suggesting that these breccias may represent the upflow zone of a hydrothermal system and highlight the potential for seafloor massive sulfides in the area. The breccias show elevated contents of immobile trace elements and LREE as well as a depletion in Ta and Nb suggesting that the precursor rocks were formed in a rift-related suprasubduction environment.

Fluid inclusion study of the Horní Luby cinnabar deposit, Saxothuringian Zone, Bohemian Massif: clues for the metamorphic remobilization of mercury

The stratiform deposit of mercury at Horni Luby near Cheb (Czech Republic) is hosted by Ordovician phyllites of Vogtland–Saxony Paleozoic Unit in the Saxothuringian Zone of the Bohemian Massif. Ore is represented by cinnabar disseminated within the phyllite and by lenticular bodies rich in massive cinnabar (lenses with a thickness of up to 1 m and length along the strike varying from less than 1 m up to 20 m). Cinnabar is accompanied by pyrite and locally also siderite. The P–T history of the mineralization was deciphered by the study of fluid inclusions. Early fluids are represented by a homogenous H2O–CO2 fluid trapped in secretion quartz. This fluid underwent several heterogenization events starting from approximately 300 °C and continued down to 200–150 °C. Metamorphic quartz of secretion origin crystallized at ~300 °C, while hydrothermal pyrite crystallized at 220–210 °C and cinnabar at 195–160 °C. The formation of the richest ore was associated with the replacement of metamorphic quartz in phyllites by the cinnabar in weakly alkaline solutions. The cinnabar is pure phase, free of admixtures (Bi, Sb, Zn, Fe, and Cu). It is accompanied by minute blebs of Hg-bearing sphalerite (11–12 wt. % Hg) that might indicate earlier presence of the zincian metacinnabar and more complex metamorphic history of the ore. The primary source of mercury is thought to be Lower Paleozoic submarine volcanism. The formation of ore bodies is, however, associated with metamorphic mobilization of mercury during the late stages of the Variscan orogeny. Despite being relatively small, the mercury deposit at Horni Luby competed with the mines in Idrija (Slovenia) and Almaden (Spain) in the 16th century. The production of mercury at Horni Luby is estimated to have corresponded to c. 10–30 % of the mercury production in the mines of Idrija and Almaden at that time. In addition to Venice, the mercury from Horni Luby was also supplied to Nurnberg, Antwerp and Lyon. In 1520–1540, the production of mercury from the Horni Luby mines was 6 to 15 tons per annum. The mines were abandoned in 1597. Attempts to reinstitute mining activity in the 17th, 18th and 19th centuries were not very extensive and always failed. The total production of the Horni Luby mines during the whole mining history is estimated to have been at least 200 tons of mercury. Much of this amount was extracted between 1520 and 1540, with a minor portion between 1560–1570.

Investigation of the spatio-temporal relationship between normal faulting and arc volcanism on million-year time scales

The spatio-temporal evolution of normal faulting and submarine volcanism during the Mid-Miocene to Recent (<16 Ma) in the Taranaki Basin, New Zealand, provides insights into the processes driving rifting and volcanism. In the Taranaki Basin high sedimentation rates have led to the blanketing and preservation of mainly submarine volcanic edifices and normal faults. Volcanic activity gradually migrated southward along the basin and contrasts with the punctuated migration of normal faulting in the same direction. Gradual southward migration of volcanism since c . 16 Ma has been attributed to progressive steepening and SE rollback of the subducting Pacific Plate. Similarly, the location and NE–SW strike of Late Miocene and younger normal faults mainly west of the North Island appear to have been controlled by the location and NE–SW strike of the underlying subducting plate. Stepwise changes in the locus of faulting at c . 8, 4 and 2 Ma could have been triggered by increases in the rates of vertical-axis rotation of the North Island associated with changes in plate convergence rates and southward migration of the rotation pole. The disparate spatio-temporal migration histories of subduction-related faulting and volcanism indicate that, over time scales of millions of years and distances of tens of kilometres, neither process controls the timing, location and rates of activity of the other.

Unique Origin of Skarn at the Ohori Base Metal Deposit, Yamagata Prefecture, NE Japan: C, O and S Isotopic Study

AbstractThe Ohori ore deposit is one of the Cu–Pb–Zn deposits in the Green Tuff region, NE Japan, and consists of skarn‐type (Kaninomata) and vein‐type (Nakanomata) orebodies. The former has a unique origin because its original calcareous rocks were made by hydrothermal precipitation during Miocene submarine volcanism. Carbon and oxygen isotope ratios of skarn calcite and sulfur isotope ratios of sulfides were measured in and around the deposit. Carbon and oxygen isotope ratios of the skarn calcite are δ13C = −15.51 to −5.1‰, δ18O = +3.6 to +22.5‰. δ13C values are slightly lower than those of the Cretaceous skarn deposits in Japan. These isotope ratios of the Kaninomata skarn show that the original calcareous rocks resemble the present submarine hydrothermal carbonates at the CLAM Site, Okinawa Trough, than Cenozoic limestones, even though some isotopic shifts had occurred during later skarnization. δ34S ratios of the sulfide minerals from the Kaninomata and Nakanomata orebodies are mostly in a narrow range of +4.0 to +7.0‰ and they resemble each other, suggesting the same sulfur origin for the both deposits. The magnetite‐series Tertiary Kaninomatasawa granite is distributed just beneath the skarn layer and has δ34S ratios of +7.5 to 8.1‰. The heavy sulfur isotope ratio of the skarn sulfides may have been affected by the Kaninomatasawa granite.