Volcaniclastic Deposits Research Articles

Structural evolution of an inner accretionary wedge and forearc basin initiation, Nankai margin, Japan

Core recovered during Integrated Ocean Drilling Program (IODP) Expedition 319 from below the Kumano forearc basin of Japan's Nankai margin provides some of the only in situ samples from an inner accretionary wedge, and sheds light on the tectonic history of a seismically hazardous region. The 84m of core comprises Miocene-age well-bedded muds, silts, and volcaniclastic sediments. Beds increase in dip with depth, and are cut by (i) soft-sediment deformation bands (“vein structures”), (ii) ∼1-cm thick shear zones within ∼10-cm thick regions of high shear strain, and (iii) <1-mm thick slickensided faults which are the youngest structures in the core and highly localized. Microstructural analyses of the shear zones suggest that they formed via multiple increments of shear localization and a mixed granular and cataclastic flow. Kinematic analysis of slip indicators in shear zones further reveals that they formed via north–south shortening. In contrast, the faults cut the shear zones with mixed slip kinematics, and accommodated northwest–southeast shortening, roughly parallel to the modern shortening direction. The entire section was also rotated ∼15° counterclockwise about a roughly vertical axis. Therefore the principle strain axes and stratigraphic section rotated during or postdating development of the major sub-basin (∼5.6–3.8Ma) unconformity, a time that generally coincides with a change in the Philippine Sea plate convergence direction. Forearc basin development therefore postdates a protracted geologic evolution of shear-zone development, tectonic rotations, and inner-wedge development, the last of which coincides with a rheological evolution toward localized frictional faulting.

High resolution 3D P wave velocity structure beneath Tenerife Island (Canary Islands, Spain) based on tomographic inversion of active‐source data

We present a high resolution 3 dimensional (3D) P wave velocity model for Tenerife Island, Canaries, covering the top of Teide volcano (3,718 m a.s.l.) down to around 8 km below sea level (b.s.l). The tomographic inversion is based on a large data set of travel times obtained from a 3D active seismic experiment using offshore shots (air guns) recorded at more than 100 onshore seismic stations. The obtained seismic velocity structure is strongly heterogeneous with significant (up to 40%) lateral variations. The main volcanic structure of the Las Cañadas‐Teide‐Pico Viejo Complex (CTPVC) is characterized by a high P wave velocity body, similar to many other stratovolcanoes. The presence of different high P wave velocity regions inside the CTPVC may be related to the geological and volcanological evolution of the system. The presence of high P wave velocities at the center of the island is interpreted as evidence for a single central volcanic source for the formation of Tenerife. Furthermore, reduced P wave velocities are found in a small confined region in CTPVC and are more likely related to hydrothermal alteration, as indicated by the existence of fumaroles, than to the presence of a magma chamber beneath the system. In the external regions, surrounding CTPVC a few lower P wave velocity regions can be interpreted as fractured zones, hydrothermal alterations, porous materials and thick volcaniclastic deposits.

Cryptic eruption of Mount Ruapehu revealed by deposits of sediment laden streamflow in a steep mountain valley: The 4 ka Kiwikiwi Formation, Whangaehu Valley, NZ

A distinctive deposit of unaltered reworked volcaniclastic sediment, here designated the Kiwikiwi Formation, is described from the upper Whangaehu Valley at Mount Ruapehu, New Zealand. The grain-size distribution and sedimentary features of the unit suggest deposition from a sheetflow-dominated alluvial system, but simple sediment entrainment calculations show that the unit's granulometry is inconsistent with normal streamflow deposition at the observed steep depositional slope. Streams have produced deposits at Mount St. Helens and Mount Pinatubo under similarly anomalous conditions following debris avalanche and/or volcanic eruptions, when highly charged with sediment and subject to common lahars (debris flows and hyperconcentrated flows). Reported sediment transport rates from Mount St. Helens' Toutle River, and Pinatubo's Pasig–Potrero River, show that a virtually unlimited supply of relatively fine-grained (sand-range) tephra renders some established sediment transport formulae inapplicable because the volume of available material effectively exceeds the transport capacity of the system. We use simple equilibrium flow calculations to demonstrate that this sedimentary unit, which has open porosity, framework grain support and bedding characteristics compatible with alluvial sheet flows, would not have been deposited under normal streamflow conditions. This approach provides a means to confirm the role of capacity limitations on stream behaviour during the post-eruptive sedimentary response phase in catchments overwhelmed by pyroclastic material, and is particularly useful given the lack of clear depositional fingerprints for hyperconcentrated flow. We further infer that because the material in the Kiwikiwi Formation is uniform, unaltered and minimally abraded, differs from older sediment in the valley, overlies a 4.6ka debris-avalanche deposit, and was emplaced from an over-capacity stream by hyperconcentrated flows or extremely thinned ones, and without evidence of interruption, it represents the previously unidentified proximal products of an unstudied Holocene eruption of Ruapehu.

New interpretation of tectonic model in south Tibet

We present a new interpretation of tectonic evolution in southern Tibet that is drastically different from the existing models. A detailed tectono-sedimentary study crossing the Yarlung Zangpo ophiolite zone shows that many geological features are different from those commonly described in large subduction collision models. For example, no N–S oriented shear zones are found between the ophiolitic sequence and country flysch strata, whereas a conformable contact relationship is recognized between them. A tectonic window exists inside the ophiolite body in the Bailang region. Some intrusion-like mafic–ultramafic bodies occurred in the Renbu region, where the country strata are in sub-concordant contact with these bodies and show contact metamorphic aureole. Toward the west, the ophiolite zone was separated by flysch sequences into sub-parallel branches. In the Lhasa region, the sedimentary facies are similar on both sides of the Zangpo Valley, and have preserved an intact Mesozoic basin system. Instead of ophiolite rocks, volcaniclastic deposits occurred in the corresponding location of the ophiolite in the Zangpo Valley. Consequently, we conclude that the Zangpo ophiolite zone has a tectonic affinity of back-arc basin with its spasmodic growth of juvenile oceanic crust. The real tectonic suture, or the closure zone of the Neotethys, should be represented by the High Himalaya Central Gneiss Unit, which shows a large scale strong shearing in same orientation, high metamorphism and protracted re-mobilization. The oceanic crust subducted northward and split off the Himalaya continental front arc, created the Zangpo back-arc basin since Late Triassic. The collapse of the Zangpo back-arc basin by supra-subduction occurred since the Eocene. The final collision between India and the Himalayan arc took place since Late Eocene with a re-mobilized large shear system. The major mylonitic zones migrated progressively southward with bulk of shear slip absorbing the crust of north India and south Tibet.

New Avian tracks from the lower to middle Eocene at Fossil Hill, King George Island, Antarctica

AbstractTrace fossils are long known to exist in the Fossil Hill Formation (lower to middle Eocene) at Fildes Peninsula, King George Island, Antarctica. During fieldwork in 2009, abundant new avian tracks were recovered, which are analysed here. Three avian ichnotaxa are distinguished. The most common impressions are tridactyls and tetradactyls with slender digit imprints II–IV and a posterior hallux. They are included in the ichnogenus Gruipeda. In addition tridactyl and tetradactyl footprints with short and thick digit impressions are conferred to Uhangrichnus. The third ichnotaxon is a tridactyl impression with broad and short digits assigned to Avipeda. The latter taxon is here documented for the first time from Antarctica. These avian tracks are preserved in volcaniclastic sediments consisting in reddish-brown layers of mudstone intercalated with coarse sandstone. The sequence represents lacustrine environments which seasonally dried and were episodically refilled.

The late Pleistocene Pilauco site, Osorno, south-central Chile

Paleontological and archaeological sites have frequently been found in open locations of the Intermediate Depression of south-central Chile. This paper presents the results of two field sampling seasons carried out at the Pilauco Site (ca. 39°S) and compares them with those of three well known sites in Chile: Quereo, Tagua-Tagua and Monte Verde, ca. 32°, 34° and 41°S, respectively. Stratigraphic data collected at Pilauco and the resulting radiocarbon age model suggest that before 12,540 ± 90 BP the old Damas River eroded an older volcaniclastic hill, which was followed by a bog formation in an ox-bow lake. The site was developing up to 11,004 ± 186 BP, the date of the youngest vertebrate fossil. Two younger peat beds seal the site. As in Tagua-Tagua and Monte Verde, Gomphotheres are the most represented megafauna. Fossils of Equidae, Camelidae, Cervidae, Mephitidae, Muridae, Myocastoridae and Xenarthra are also found in Pilauco. As a whole, 718 bones, 30 teeth and 11 coprolites represent the extinct and extant vertebrates. Preliminary taphonomic results suggest action of various agents in the bones, i.e. trampling, root etching, abrasion, and carnivore gnawing. The spatial analysis suggests the transfer of smaller anatomical units (e.g. bones of camelids and horses) and the rearrangement of some pieces comparatively large (e.g. gomphothere bones). Similar to the present day north Patagonian landscape, the area where Pilauco site is located had a variety of animal resources, plants and stones in an ecotone between hills, floodplains and wetlands. A total of 101 lithics were recorded: basalt and quartzite were collected from nearby fluvial deposits and dacitic obsidian from the local volcaniclastic deposits. Debitage is the most represented lithic item (75%); cores and marginal edge-trimmed artifacts represented 12 and 13%, respectively. Artifacts and flakes are spatially and temporality associated in the same PB-7 bed with high bone concentrations in some specific areas, between 361 and 424 cm of local altitude. This industry is characterized by a recurrent lithic expedite technology with production of flakes and chips which mastered marginal retouches over the bifacial trimming. This seems to be connected to strategic conditions of high resource diversity, especially of human groups with a high or medium mobility across land. Pilauco represents a site contemporaneous to Monte Verde related as well to the first human occupation in the southern cone of South America, but with higher mammal diversity.

IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough

Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10–30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime. doi:10.2204/iodp.sd.13.03.2011

Large-scale internal structure of the Sanbongi Fan–Towada Volcano, Japan: Putting the theory to the test, using GPR on volcaniclastic deposits

The Towada Caldera Volcano is located between the prefectures of Aomori and Akita — Northeast Honshu Island, Japan. The caldera, today filled by a lake, has produced 15,000years ago a complex eruption emplacing an ignimbrite topped by the lake outburst flood deposit, through which the present Oirase River erodes. This flood deposit has shaped the geomorphologic feature named Sanbongi Fan, on which Towada City extends. This flood event hypothesis is mainly based on sedimentological and geomorphological evidences of floods mainly from outcrops retrieved from the Sanbongi Fan area. Because of the lack of extended outcrops – typical of the Japanese environment – the present paper has therefore put the theory to the test using GPR (Ground Penetrating Radar) radargram extending along a 640m length. The GPR used for the survey was a Pulse-ekko-Pro with 50MHz antennas, and the software Reflex was used to process the data. The radargrams have displayed a sole unit, which the GPR could not penetrate. It can be interpreted as the ignimbrite. On top of this deposit a series of subhorizontal layers, with the alternation between a backset and a foreset extends between 5m and 3m depth. Above 3m, the units are regular and subhorizontal. The deposit is also characterized by the extensive presence of boulders, which are located along three bands: (1) on top of the ignimbrite; (2) in the units deposited by the outburst flood, between 3 and 5m depths; (3) and in the units close to the surface, although part of these punctual elements are most certainly anthropogenic. Compared with the outcrops, the present research confirms that the material located above the ignimbrite material have been deposited by the outburst flood, creating large-sheet patterns, which have transported boulders. These sheets display backset and foreset patterns, depending on the position of the deposit, indicating flow pulsation or surges under a ‘high-energy-flow’ condition.

IODP Expedition 331: Strong and Expansive Subseafloor Hydrothermal Activities in the Okinawa Trough

Integrated Ocean Drilling Program (IODP) Expedition 331 drilled into the Iheya North hydrothermal system in the middle Okinawa Trough in order to investigate active subseafloor microbial ecosystems and their physical and chemical settings. We drilled five sites during Expedition 331 using special guide bases at three holes for reentry, casing, and capping, including installation of a steel mesh platform with valve controls for postcruise sampling of fluids. At Site C0016, drilling at the base of the North Big Chimney (NBC) mound yielded low recovery, but core included the first Kuroko-type black ore ever recovered from the modern subseafloor. The other four sites yielded interbedded hemipelagic and strongly pumiceous volcaniclastic sediment, along with volcanogenic breccias that are variably hydrothermally altered and mineralized. At most sites, analyses of interstitial water and headspace gas yielded complex patterns with depth and lateral distance of only a few meters. Documented processes included formation of brines and vapor-rich fluids by phase separation and segregation, uptake of Mg and Na by alteration minerals in exchange for Ca, leaching of K at high temperature and uptake at low temperature, anhydrite precipitation, potential microbial oxidation of organic matter and anaerobic oxidation of methane utilizing sulfate, and methanogenesis. Shipboard analyses have found evidence for microbial activity in sediments within the upper 10–30 m below seafloor (mbsf) where temperatures were relatively low, but little evidence in the deeper hydrothermally altered zones and hydrothermal fluid regime. &lt;br&gt;&lt;br&gt; doi:&lt;a href="http://dx.doi.org/10.2204/iodp.sd.13.03.2011" target="_blank"&gt;10.2204/iodp.sd.13.03.2011&lt;/a&gt;

Basalt mounds and adjacent depressions attract contrasting biofacies on a volcanically active Middle Miocene coastline (Porto Santo, Madeira Archipelago, Portugal)

Small basalt mounds with encrusting corals and inter-mound carbonate sandy zones with abundant rhodoliths corresponding to an ancient intertidal to shallow-water sea floor are exhumed from overlying volcaniclastic deposits and basalt lava flows at Pedra de Agua on Ilheu de Cima off Porto Santo, one of the islands of the northeastern Atlantic Madeira Archipelago (Portugal). The mounds rise above the surrounding surface to attain a height of about half a meter. The mounds exhibit an in situ assemblage of hermatypic corals, dominated by Tarbellastrae and Solenastrea. They formed as massive (4.2 × 1.9 m average length), isolated patches in a protected bay close to shore eroded from an uneven basalt substrate dated to the Middle Miocene (14–15 Ma). The slightly deeper zones between basalt mounds, which alternate with them over a distance of more than 20 m, are covered mainly by coarse carbonate sand on which rhodoliths up to 14.8 cm in diameter are preserved in situ. Many rhodoliths have grown around a basalt core, which indicates a local, near-shore source for development. Complete burial of the elevated coral settlements and intervening low zones populated by rhodoliths occurred when volcanic lapilli and other tephra catastrophically buried this part of the rocky shore. The rhodoliths and coral assemblages exposed in an area of 12 m2 were canvassed systematically using census quadrats to quantify community relationships.

Anisotropy in seafloor flange, slab, and crust samples from measurements of permeability and porosity: Implications for fluid flow and deposit evolution

Seafloor hydrothermal vents accommodate the convective transfer of fluids from subsurface environments to the oceans. In addition to black smoker chimneys, a variety of other deposit‐types form. Flanges protrude from the sides of edifices as horizontal ledges, below which vent fluids pool. Slabs are hydrothermally silicified layered volcaniclastic deposits. Crusts are deposits composed of previously deposited material underlain by hot fluids. Permeability and porosity measurements were conducted on flanges from Guaymas Basin and the Main Endeavour Vent Field, slabs from the Lucky Strike Vent Field, and a crust sample from the Trans‐Atlantic Geotraverse (TAG) active mound. Cores taken parallel to textural layers have high permeabilities (≈10−12 m2) and porosities (30–40%) that follow a power law relationship with exponent α ≈ 1 to 2. Cores taken perpendicular to layering have permeabilities from 10−16 to 10−12 m2 and porosities from 20 to 45%, with α ≈ 5 to 8. The two distinct trends result from the heterogeneity of textural layers within these deposits. Microstructural observations show large variations in grain packing and pore distributions between layers, consistent with flow perpendicular to layering being more susceptible to changes in permeability that result from mineral precipitation than flow parallel to layering. These results imply that the primary flow direction in these deposits is parallel to layering, whereas flow perpendicular to layering is more restricted. Quantification of anisotropic permeability provides important constraints for determination of fluid flux from these layered deposits, and temperatures, chemistry, and availability of nutrients to organisms living in and at exteriors of deposits.

Tectono-Sedimentary evolution and geochronology of the Middle Miocene Altınapa Basin, and implications for the Late Cenozoic uplift history of the Taurides, southern Turkey

The Tauride range in southern Turkey is flanked and overlain by Neogene sedimentary basins. To the south and on top of the high range, these basins are mainly marine, whereas poorly studied intramontane basins dominated by continental deposits are exposed to the north. In this paper, we study the stratigraphy and structure of the continental Altınapa Basin, and provide 40Ar/39Ar geochronology for volcanic deposits in the stratigraphy. The stratigraphy can be subdivided into a Lower Group, displaying ~400m of fining upward fluvio-lacustrine sediments, unconformably overlain by an Upper Group with ~500m of lacustrine deposits, andesitic lavas and volcaniclastic sediments. 40Ar/39Ar dating of three volcaniclastic samples across the Upper Group provide 11.8–11.6Ma ages. The Altınapa Basin is an extensional basin, which formed predominantly due to N–S to NE–SW directed stretching. The main basin forming phase occurred during deposition of the Lower Group, prior to 11.8Ma. Paleostress inversion analyses demonstrate uniaxial stress, with highly variable extension directions that are consistent with currently observed seismicity patterns. The Middle Miocene extension history of the Altınapa Basin is consistent with a regional pattern of Middle Miocene NE–SW to NW–SE extension north of the Cyprus subduction zone. This suggests that the Cyprus subduction zone has been in retreat relative to central Anatolia since at least Middle Miocene time. The continental Altınapa Basin is currently at an elevation of ~1km, whereas partly contemporaneous marine sediments in the Mut Basin that lies on top of the Tauride range are elevated to 2km. This shows strong late Cenozoic differential uplift in southern Turkey, with at least 1km more uplift of the Tauride range than of the intramontane basins to the north. We conclude that the current high elevation of the Taurides is related to late Neogene extension and does not result from the late Cretaceous to perhaps Oligocene folding and thrusting that deformed the rocks in the range.

Alternating diatomaceous and volcaniclastic deposits in Milos Island, Greece. A contribution to the upper Pliocene–lower Pleistocene stratigraphy of the Aegean Sea

In the northern part of Milos Island, South Aegean Volcanic Arc, a stratigraphic succession spanning the late Pliocene and early Pleistocene exceeds 300m in thickness and records an alternation of products from submarine volcanic explosive events and fossiliferous, both siliceous and carbonate marine sedimentary rocks. The accumulation of volcaniclastic deposits took place under subaqueous marine conditions as evidenced by sedimentary features, scarce fossil remains and the local presence of burrow traces.Each major volcanic event was represented by the accumulation of thick-bedded pumice and glassy tuffs, succeeded by the deposition of marine sediments composed mainly of laminated diatomaceous marlstone and sandy limestone. The silica content of the diatomaceous sediments varies from 39% to 70%, mostly in the form of biogenic opal-A. SiO2/Al2O3 ratios ranging from 5 to 21 indicate a varied contribution of reworked volcanic grains. The sequential arrangement of basinal diatomaceous marlstone and shoreface sandy limestone deposits suggests that the depth of water was not great, which is also consistent with features observed in the volcaniclastic deposits.Calcareous nannofossils from the upper part of the succession of northern Milos allow biostratigraphic correlation with nannofossil biozones MNN19a–MNN19b across the Gelasian/Calabrian boundary within the early Pleistocene. A late Pliocene (Piacenzian) age has been estimated for the lower part of the section, where biozone MNN16a has been documented. Diatoms, planktonic foraminifera and calcareous nannofossil assemblages in the diatomaceous beds point to deposition in a partially closed, relatively shallow marine environment. In this setting, warm and stratified water conditions can be concluded for the Piacenzian diatomaceous beds whereas highly productive cool waters are inferred from the Gelasian/Calabrian diatomite.

Stratigraphy, sedimentary petrology and provenance of the Sobral and Cross Valley formations (Paleocene), Marambio (Seymour) Island, Antarctica.

The unconformity bounded Paleocene Sobral and Cross Valley formations represent part of the uppermost infill of the James Ross Basin of northeastern Antarctic Peninsula. Both units have been subdivided into allomembers since they also present internal unconformities. The Sobral Formation represents silicoclastic sedimentation on a marine shelf during at least two transgressive-regressive cycles. The Cross Valley Formation fills in a narrow valley with volcaniclastic deposits representing an incised valley system with estuarine and finally deltaic facies. Sandstones of the Sobral Formation are feldspathic litharenites and lithic arkoses while those of the Cross Valley Formation are feldspathic litharenites to litharenites (volcanic). The sandstone composition (petrofacies) of the Sobral and Cross Valley formation suggest provenance from a dissected volcanic arc that increased its activity during the Danian but decline again towards the late Thanetian. A detailed analysis of the sandstone compositional trends allowed to differentiate two petrofacies (S and CV) and two sub-petrofacies (S I, S II, CV I and CV II respectively). The sub-petrofacies suggest a control from the sedimentary environments upon the detrital modes and their interference with the true provenance signal. The increase in quartz and glaucony in some units may be related with the unconformities and reworking of the underlying sedimentary units as well as development of high energy environments. On the other hand, volcanic, plutonic and metamorphic rock fragments are related to the provenance area. The overlap of two main sources of sediments, one from the basin edge and other within the basin is then envisaged. The first one represents the unroofing of a volcanic arc located at the present day position of the Antarctic Peninsula. This source shed volcanic rock fragments and minor metamorphic rock fragments with variable amount of quartz and feldspars. This composition plots within the recycled orogen and dissected arc fields of the provenance diagrams representing periods of arc inactivity and deep erosion and plots within the volcanic arc fields after times of volcanic activity. On the other hand, sandstones with high proportion of quartz recorded at specific levels within the sequence suggest breakdown of less resistant components and reworking of the loose underlying sedimentary rocks favoured by low sedimentary rates and/or in high energy environments.

Early Miocene volcanic activity and paleoenvironment conditions recorded in tephra layers of the AND-2A core (southern McMurdo Sound, Antarctica)

The ANtarctic geological DRILLing Program (ANDRILL) successfully recovered 1138.54 m of core from drill hole AND-2A in the Ross Sea sediments (Antarctica). The core is composed of terrigenous claystones, siltstones, sandstones, conglomerates, breccias, and diamictites with abundant volcanic material. We present sedimentological, morphoscopic, petrographic, and geochemical data on pyroclasts recovered from core AND-2A that provide insights on eruption styles, volcanic sources, and environments of deposition. One pyroclastic fall deposit, 12 resedimented volcaniclastic deposits and 14 volcanogenic sedimentary deposits record a history of intense explosive volcanic activity in southern Victoria Land during the Early Miocene. Tephra were ejected during Subplinian and Plinian eruptions fed by trachytic to rhyolitic magmas and during Strombolian to Hawaiian eruptions fed by basaltic to mugearitic magmas in submarine and/or subglacial to subaerial environments. The long-lived Mount Morning eruptive center, located ∼80 km south of the drill site, was recognized as the probable volcanic source for these products on the basis of volcanological, geochemical, and age constraints. The study of tephra in the AND-2A core provides important paleoenvironment information by revealing that the deposition of primary and moderately reworked tephra occurred in a proglacial setting under generally open-water marine conditions.

Intrusion of basalt into frozen sediments and generation of Coherent-Margined Volcaniclastic Dikes (CMVDs)

Coherent-Margined Volcaniclastic Dikes (CMVDs) are described for the first time from Askja (Dyngjufjöll), Iceland. These dikes display continuous, coherent glassy margins 5cm thick and have a variety of clastic interiors comprising vitric tephra, pillow and pillow-fragment bearing lapilli tuffs. CMVDs are interpreted to form when basaltic dikes interact with subglacial ice-cemented volcaniclastic sediments. Formation requires chilling of dike margins, drainage of the dike interior and flooding of the cavity by meltwater, followed by non-explosive mingling of magma, clastics and water. Evidence for ice-cementation includes minimal interaction with the host (<3mm peperite), local pillowed dike margins and the preservation of continuous glassy coherent margins along the edge of a drained dike cavity. CMVDs should be present at other volcanic centers with ice-cemented sediments, including the Martian cryosphere.

Chrono- and lithostratigraphy of a Mesozoic–Tertiary fore- to intra-arc basin: Adelaide Island, Antarctic Peninsula

AbstractThe Mesozoic fore-arc of the Antarctic Peninsula is exposed along its west coast. On Adelaide Island, a 2–3 km succession of turbiditic coarse sandstones and volcanic rocks is exposed. Four U–Pb (zircon) ages are presented here that, in combination with a new stratigraphy, have permitted a robust chrono- and lithostratigraphy to be constructed, which in turn has allowed tentative correlations to be made with the Fossil Bluff Group of Alexander Island, where the ‘type’ fore-arc sequences are described. The lithostratigraphy of Adelaide Island includes the definition of five volcanic/sedimentary formations. The oldest formation is the Buchia Buttress Formation (149.5 ± 1.6 Ma) and is correlated with the Himalia Ridge Formation of Alexander Island. The sandstone–conglomerate dominated succession of the Milestone Bluff Formation (113.9 ± 1.2 Ma) is tentatively correlated with the Pluto Glacier Formation of Alexander Island. Three dominantly volcanic formations are recognized on Adelaide Island, akin to the volcanic rocks of the Alexander Island Volcanic Group; the Mount Liotard Formation is formed of 2 km of basaltic andesite lavas, whilst the Bond Nunatak Formation is also dominated by basaltic andesite lavas, but interbedded with volcaniclastic rocks. The Reptile Ridge Formation has been dated at 67.6 ± 0.7 Ma and is characterized by hydrothermally altered rhyolitic crystal-lithic tuffs. Tentative correlations between Adelaide Island and Alexander Island preclude the two areas forming part of distinct terranes as has been suggested previously, and a proximal source for volcaniclastic sediments also indicates an exotic terrane origin is unlikely.

Multiple controls on rift basin sedimentation in volcanic settings: Insights from the anatomy of a small Early Cretaceous basin in the Yanshan belt, northern North China

This paper deals with a small continental rift basin in a volcanic setting and tries to decipher potential controls on its synrift sedimentation. The Luanping basin, which is a well-exposed Early Cretaceous rift basin in the Yanshan belt on the northern periphery of the North China block, was chosen as a case study. We show that extensive and vigorous volcanism took place just prior to the onset of basin formation and continued into a synrift period. Basin fills consist predominantly of lacustrine, fan-delta, braid-delta, and volcaniclastic deposits. Lacustrine facies are composed mostly of deep-lake deposits that appear to have been established soon after basin initiation. Fan-delta systems developed along two high-angle border faults, the master northern Hongqi fault and the secondary western Xiaobaiqi fault. Fan-delta fronts were built up primarily by gravelly and sandy debrites and turbidites. Braid-delta deposits are restricted to the eastern corner of the basin and are characterized by an aggregation of braid-plain conglomeratic deposits. Underwater extrusions of magma and pyroclastic flows are inferred from the presence of volcanic breccias, ignimbrites, andesitic pillows, and peperites, which are enclosed by host lacustrine deposits. Deep-lake and fan-delta systems persisted throughout the synrift period, indicating a rapid subsidence rate, with both adequate sediment and water supply. The high-angle border faults are thought to have played a critical role in creating large accommodation space, and simultaneous displacements of the Hongqi and Xiaobaiqi faults led to the localization of a major depocenter in the western part of the basin. One-dimensional backstripping analysis of three stratigraphic sections shows that the Luanping basin experienced marked synrift tectonic subsidence up to 2 km at a subsidence rate close to 0.2 mm yr −1 . We propose that the high rate of basin subsidence might have been caused mainly by left-lateral transtensional faulting and was enhanced by the superposition of basement downsag induced by underlying magma withdrawal. A predominance of volcanic particles in both debrites and sandstones suggests that source areas were erodible volcanic edifices. A humid paleoclimate is inferred, which not only provided enough water supply, but also promoted weathering of volcanic rocks in source areas, thus maintaining both the deep-lake environment and sediment influx. We conclude that relatively small and isolated rift basins in volcanic settings can experience both rapid subsidence and receive thick lacustrine deposits if they are under the combined control of favorable structure, climate, and magmatism. The model proposed here is believed to be applicable to other rift basins in similar volcano-tectonic settings.

Infrared Spectroscopic Characterization of Organic Matter Associated with Microbial Bioalteration Textures in Basaltic Glass

Microorganisms have been found to etch volcanic glass within volcaniclastic deposits from the Ontong Java Plateau, creating micron-sized tunnels and pits. The fossil record of such bioalteration textures is interpreted to extend back ∼3.5 billion years to include meta-volcanic glass from ophiolites and Precambrian greenstone belts. Bioalteration features within glass clasts from Leg 192 of the Ocean Drilling Program were investigated through optical microscopy and Fourier transform infrared (FTIR) spectroscopy of petrographic thin sections. Extended depth of focus optical microscopic imaging was used to identify bioalteration tubules within the samples and later combined with FTIR spectroscopy to study the organic molecules present within tubule clusters. The tubule-rich areas are characterized by absorption bands indicative of aliphatic hydrocarbons, amides, esters, and carboxylic groups. FTIR analysis of the tubule-free areas in the cores of glass clasts indicated that they were free of organics. This study further constrains the nature of the carbon compounds preserved within the tubules and supports previous studies that suggest the tubules formed through microbial activity.

High SO2 flux, sulfur accumulation, and gas fractionation at an erupting submarine volcano

Research Article| September 01, 2011 High SO2 flux, sulfur accumulation, and gas fractionation at an erupting submarine volcano David A. Butterfield; David A. Butterfield 1University of Washington, Joint Institute for the Study of the Atmosphere and Ocean (JISAO), Box 354925, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Ko-ichi Nakamura; Ko-ichi Nakamura 2National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 3058567, Japan Search for other works by this author on: GSW Google Scholar Bokuichiro Takano; Bokuichiro Takano 3University of Tokyo, Graduate School of Arts and Sciences, Tokyo, Japan Search for other works by this author on: GSW Google Scholar Marvin D. Lilley; Marvin D. Lilley 4University of Washington, School of Oceanography, Box 357940, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar John E. Lupton; John E. Lupton 5National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory (NOAA/PMEL), 2115 SE OSU Drive, Newport, Oregon 97365, USA Search for other works by this author on: GSW Google Scholar Joseph A. Resing; Joseph A. Resing 1University of Washington, Joint Institute for the Study of the Atmosphere and Ocean (JISAO), Box 354925, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Kevin K. Roe Kevin K. Roe 1University of Washington, Joint Institute for the Study of the Atmosphere and Ocean (JISAO), Box 354925, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Geology (2011) 39 (9): 803–806. https://doi.org/10.1130/G31901.1 Article history received: 12 Nov 2010 rev-recd: 15 Mar 2011 accepted: 28 Mar 2011 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David A. Butterfield, Ko-ichi Nakamura, Bokuichiro Takano, Marvin D. Lilley, John E. Lupton, Joseph A. Resing, Kevin K. Roe; High SO2 flux, sulfur accumulation, and gas fractionation at an erupting submarine volcano. Geology 2011;; 39 (9): 803–806. doi: https://doi.org/10.1130/G31901.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Strombolian-style volcanic activity has persisted for six years at the NW Rota-1 submarine volcano in the southern Mariana Arc, allowing direct observation and sampling of gas-rich fluids produced by actively degassing lavas, and permitting study of the magma-hydrothermal transition zone. Fluids sampled centimeters above erupting lava and percolating through volcaniclastic sediments around an active vent have dissolved sulfite >100 mmol/kg, total dissolved sulfide <30 μmol/kg, pH as low as 1.05, and dissolved Al and Fe >1 mmol/kg. If NW Rota is representative of submarine arc eruptions, then volcanic vent fluids from seawater-lava interaction on submarine arcs have a significant impact on the global hydrothermal flux of sulfur and Al to the oceans, but a minimal impact on Mg removal. Gas ratios (SO2, CO2, H2, and He) are variable on small spatial and temporal scales, indicative of solubility fractionation and gas scrubbing. Elemental sulfur (Se) is abundant in solid and molten form, produced primarily by disproportionation of magmatic SO2 injected into seawater. Se accumulates within the porous rock surrounding the lava conduit connecting the magma source to the seafloor. Accumulated Se can be heated, melted, and pushed upward by rising magma to produce molten Se flows and lavas saturated with Se. Molten Se near the top of the lava conduit may be ejected up into the water column by escaping gases or boiling water. This mechanism of Se accumulation and refluxing may underlie the relatively widespread occurrence of Se deposits of many sizes found on submarine arc volcanoes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.