(Table 1) Apparent ages from 40Ar/39Ar heating steps for DSDP Hole 72-516F basalts

Submarine basalts are difficult to date accurately by the potassium-argon method. Dalrymple and Moore (1968) and Dymond (1970), for example, showed that, when the conventional K-Ar method is used, pillow lavas may contain excess 40Ar. Use of the 40Ar/39Ar step-heating method has not overcome the problem, as had been hoped, and has produced some conflicting results. Ozima and Saito (1973) concluded that the excess 40Ar is retained only in high temperature sites, but Seidemann (1978) found that it could be released at all temperatures. Furthermore, addition of potassium, from seawater, to the rock after it has solidified can result in low ages (Seidemann, 1977), the opposite effect to that of excess 40Ar. Thus, apparent ages may be either greater or less than the age of extrusion. Because of this discouraging record, the present study was approached pragmatically, to investigate whether self-consistent results can be obtained by the 40Ar/39Ar step-heating method.

Silicate mineralogy of basalts at DSDP Leg 54 Holes

Basalts drilled from the East Pacific Rise, OCP Ridge, and Siqueiros fracture zone during Leg 54 are texturally diverse. Dolerites are equigranular at Sites 422 and 428 and porphyritic, with phenocrysts of plagioclase (An69.73) and Ca-rich clinopyroxene (Ca42Mg48Fe10) at Site 427. The East Pacific Rise lavas and some of those from the OCP Ridge are fine-grained and porphyritic. The majority of the large crystals are clustered skeletal glomerocrysts of plagioclase An64-77), together with olivine (Fo80-87), Ca-rich clinopyroxene, or both. Euhedral phenocrysts of plagioclase, together with olivine, Carich clinopyroxene, and Cr-Al spinel in some cases, occur in most of the fine-grained lavas. These phenocrysts are small (maximum dimension <1 mm in all but one sample), sparse (combined modal amount <1% in all samples), and distinctive from the megacrysts which characterize many ocean-floor lavas. In two East Pacific Rise lavas, zoned plagioclase (An83 cores) is the sole phenocryst phase. In other porphyritic lavas from all the main East Pacific Rise and OCP Ridge units drilled during Leg 54, the plagioclase phenocrysts contain cores of bytownite (An79-87) surrounded by more-sodic feldspar (An67-77). Core/rim relationships vary from continuous normal zoning, through discontinuous zoning, to extensive resorption of the calcic cores in some samples. The compositions of the plagioclase calcic cores are systematically related to those of the glomerophyric plagioclase and olivine in the lavas containing them. Furthermore, only one compositional population of calcic cores occurs in each rock. The possible causes of these relationships are far from clear. Magma mixing, although superficially applicable, is inconsistent with important aspects of the phenocryst mineralogy of these particular lavas. A more satisfactory model to explain both phenocryst zoning and rapid glomerocryst growth immediately before extrusion may be constructed by postulating influx of water into the upwelling magmas within Layer 3 of the oceanic crust beneath the East Pacific Rise, and subsequent loss of part of this water during effervescence within feeder dykes between Layer 3 and the ocean floor. It is shown that this model is fully consistent with published data on water and carbon dioxide contents and ratios in the pillow-margin glasses, vesicles, and phenocryst inclusions of ocean-floor basalts. The evidence for the precipitation of plagioclase- dominated crystalline assemblages from these magmas in the upper part of Layer 3 is concordant with recent geophysically based modeling of the structure of the East Pacific Rise. Calcium-rich clinopyroxenes in dolerites from the OCP Ridge and Siqueiros fracture zone show radial, oscillatory, and sector-zoning. In Sample 428A-5-2 (Piece 5a), the compositional trends resulting from this zoning closely resemble those of the pyroxenes in some lunar lavas. The controls on crystallization of interstitial pigeonite - epitaxial upon augite - in this rock are discussed. Both sector-zoning of the augite and nucleation of pigeonite within microvolumes of magma with a low Ca(Mg + Fe) ratio appear to be important factors.

Geochemistry and mineralogy of ultramafic rocks from conical seamount

The Mariana arc-trench system, the easternmost of a series of backarc basins and intervening remnant arcs that form the eastern edge of the Philippine Sea Plate, is a well-known example of an intraoceanic convergence zone. Its evolution has been studied by numerous investigators over nearly two decades (e.g., Kang, 1971; Uyeda and Kanamori, 1979; LaTraille and Hussong, 1980; Fryer and Hussong, 1981; Mrosowski et al., 1982; Hussong and Uyeda, 1981; Bloomer and Hawkins, 1983; Karig and Ranken, 1983; McCabe and Uyeda, 1983; Hsui and Youngquist, 1985; Fryer and Fryer, 1987; Johnson and Fryer, 1988; Johnson and Fryer, 1989; Johnson et al., 1991). The Mariana forearc has undergone extensive vertical uplift and subsidence in response to seamount collision, to tensional and rotational fracturing associated with adjustments to plate subduction, and to changes in the configuration of the arc (Hussong and Uyeda, 1981; Fryer et al., 1985). Serpentine seamounts, up to 2500 m high and 30 km in diameter, occur in a broad zone along the outer-arc high (Fryer et al., 1985; Fryer and Fryer, 1987). These seamounts may be horsts of serpentinized ultramafic rocks or may have been formed by the extrusion of serpentine muds. Conical Seamount, one of these serpentine seamounts, is located within this broad zone of forearc seamounts, about 80 km from the trench axis, at about 19°30'N. The seamount is approximately 20 km in diameter and rises 1500 m above the surrounding seafloor. Alvin submersible, R/V Sonne bottom photography, seismic reflection, and SeaMARC II studies indicate that the surface of this seamount is composed of unconsolidated serpentine muds that contain clasts of serpentinized ultramafic and metamorphosed mafic rocks, and authigenic carbonate and silicate minerals (Saboda et al., 1987; Haggerty, 1987; Fryer et al., 1990; Saboda, 1991). During Leg 125, three sites were drilled (two flank sites and one summit site) on Conical Seamount to investigate the origin and evolution of the seamount. Site 778 (19°29.93'N, 146°39.94'E) is located in the midflank region of the southern quadrant of Conical Seamount at a depth of 3913.7 meters below sea level (mbsl) (Fig. 2). This site is located in the center of a major region of serpentine flows (Fryer et al., 1985, 1990). Site 779 (19°30.75'N, 146°41.75'E), about 3.5 km northeast of Site 778, is located approximately in the midflank region of the southeast quadrant of Conical Seamount, at a depth of 3947.2 mbsl. This area is mantled by a pelagic sediment cover, overlying exposures of unconsolidated serpentine muds that contain serpentinized clasts of mafic and ultramafic rocks (Fryer et al., 1985, 1990). Site 780 (19°32.5'N, 146°39.2'E) is located on the western side of Conical Seamount near the summit, at a depth of 3083.4 mbsl. This area is only partly sediment covered and lies near active venting fields where chimney structures are forming (Fryer et al., 1990).

(Table 2) Asphalt samples taken in the surveyed area at Chapopote Knoll, Southern Gulf of Mexico

Following the discovery of asphalt volcanism in the Campeche Knolls a research cruise was carried out in 2006 to unravel the nature of the asphalt deposits at Chapopote. The novel results support the concept that the asphalt deposits at the seafloor in 3000 m of water depth originate from the seepage of heavy petroleum with a density slightly greater than water. The released petroleum forms characteristic flow structures at the seafloor with surfaces that are 'ropy' or 'rough' similar to magmatic lava flows. The surface structures indicate that the viscosity of the heavy petroleum rapidly increases after extrusion due to loss of volatiles. Consequently, the heavy petroleum forms the observed asphalt deposit and solidifies. Detailed survey with a remotely operated vehicle revealed that the asphalts are subject to sequential alterations: e.g. volume reduction leading to the formation of visible cracks in the asphalt surface, followed by fragmentation of the entire deposit. While relatively fresh asphalt samples were gooey and sticky, older, fragmented pieces were found to be brittle without residual stickiness. Furthermore, there is evidence for petroleum seepage from below the asphalt deposits, leading to local up-doming and, sometimes, to whip-shaped extrusions. Extensive mapping by TV-guided tools of Chapopote Asphalt Volcano indicates that the main asphalt deposits occur at the south-western rim that borders a central, crater-like depression. The most recent asphalt deposit at Chapopote is the main asphalt field covering an area of ~2000 m**2. Asphalt volcanism is distinct from oil and gas seepage previously described in the Gulf of Mexico and elsewhere because it is characterized by episodic intrusions of semi-solid hydrocarbons that spread laterally over a substantial area and produce structures with significant vertical relief. As Chapopote occurs at the crest of a salt structure it is inferred that asphalt volcanism is a secondary result of salt tectonism.

Boron contents and boron, carbon, and oxygen isotope data for ODP Sites 160-970 and 160-971

Products of two mud volcanoes from the distal part of the Mediterranean Ridge accretionary complex have been investigated regarding their B, C, and O stable isotope signatures. The mud breccias have been divided into mud matrix, lithified clasts, biogenic deposits, and authigenic cements and crusts related to fluid flow and cementation. Isotope geochemistry is used to evaluate the depth of mobilization of each phase in the subduction zone. B contents and isotope ratios of the mud and mud clasts show a general trend of B enrichment and decreasing d11B values with increasing consolidation (i.e., depth). However, the majority of the clast and matrix samples relate to moderate depths of mobilization within the wedge (1-2 km below seafloor). The carbonate cements of most of these clasts as well as the authigenic crusts, however, provide evidence for a deep fluid influence, probably associated with the décollement at 5-6 km depth. This interpretation is supported by d13C ratios of the crust, which indicate precipitation of C from thermogenic methane, and by the d11B ratios of pore-water samples of mud-breccia drill cores. Clams (Vesicomya sp.) living adjacent to fluid vents have d11B and d18O values corresponding to brines known in the area, which acted as the parent solution for shell precipitation. Such brines are most likely Miocene pore waters trapped at deep levels within the backstop to the accretionary prism, probably prior to desiccation of the Mediterranean in the Messinian (6-5 Ma). Combining all results, deep fluid circulation and expulsion are identified as the main processes triggering mud liquefaction and extrusion, whereas brines contribute only locally. Given the high B contents, mud extrusion has to be considered a major backflux mechanism of B into the hydrosphere.

Late Oligocene rapid transformations in the South China Sea

Lithobiostratigraphic data indicate that the double reflectors on the seismic profile through Ocean Drilling Program (ODP) Site 1148 represent two unconformities that coincide, respectively, with the lower/upper Oligocene boundary at ~488 mcd, and Oligocene-Miocene boundary at 460 mcd. Two other unconformities, at ~478 and 472 mcd, respectively, were also identified within the upper Oligocene section. Together they erased a sediment record of about 3 Ma from this locality in a period of very active seafloor spreading. The existence of 32.8 Ma marine sediment at the terminated depth (850 mcd) indicates that the initial breakup of the South China Sea (SCS) was probably during 34-33 Ma, close to the Eocene-Oligocene boundary. High sedimentation rates of 60-115 m/my from the much expanded, N350 m lower Oligocene section resulted from rifting and rapid subsidence between 33 and 29 Ma. The mid-Oligocene unconformity at ~28.5 Ma, which also occurred in many parts of the Indo-West Pacific region, was probably related to a significant uplift of the Himalayan-Tibetan Plateau to the west and the initial collision between Indonesia and Australia in the south. A narrowed Indonesian seaway may have accounted for the late Oligocene warming and chalk deposition in the northern South China Sea including the Site 1148 locality. The unconformities and slumps near the Oligocene-Miocene boundary indicate a very unstable tectonic regime, probably corresponding to changes in the rotation of different land blocks and the seafloor spreading ridge from nearly E-W to NE-SW, as recognized earlier at magnetic Anomaly 7. This 25 Ma event also saw the first New Guinea terrane docking at the northern Australian craton. The low sedimentation rate of ~15 m/my in the early to middle Miocene may correspond to another period of rapid seafloor spreading and rapid widespread subsidence that effectively caused sediment source areas to retreat with a rapidly rising sea level. The isostatic nature of these late Oligocene unconformities and slumps with several major collision-uplift events indicate that the rapid changes in the early evolutionary history of the South China Sea were mainly responding to regional tectonic reconfiguration including the uplift-driven southeast extrusion of the Indochina subcontinent.

Organic carbon analyses of ODP Site 160-971 in the Mediterranean Sea

Mud volcanism on the Mediterranean Ridge is caused by extrusion of overpressured sediments, with consequent formation of spectacular dome-shaped features composed of mud breccias at the seafloor. The organic material in the mud breccia of the Napoli mud volcano is a mixture of different facies, stratigraphic origin and thermal maturities. One portion is synsedimentary organic material with only minor diagenetic alterations and represents sedimenting material that was embedded into the mud volcano during its extrusion. The mud breccia also contains thermally mature organic material of mainly terrestrial provenance with algae of fresh- and brackish-water origin. Vitrinite reflectance data of this maturity generation range from 0.65 to 0.90% R(oil) and thus characterize thermally mature source rocks, a rank which is corroborated by fluorescence and molecular characteristics. The predominance of vitrinite in the maceral assemblages and the occurrence of biomarkers of terrigenous origin suggest that the major part of the mud matrix derives from a lacustrine or riverine sedimentary unit in the subsurface, possibly from the Messinian stage. A third generation of organic material includes inertinites and vitrinites of high reflectance, which represent recycled organic matter present in any marine sediment. By use of the Lopatin method for modelling the thermal maturation of hydrocarbon source rocks from the vitrinite reflectance data, we calculated that the depth of mobilization ranges from 4900 m to 7500 m, depending upon the temperature gradient used.

Chemical analyses and results of sediments from different DSDP Holes from the North Atlantic

Chemical analyses of North Atlantic D.S.D.P. (Deep Sea Drilling Project) sediments indicate that basal sediments generally contain higher concentrations of Fe, Mn, Mg, Pb, and Ni, and similar or lower concentrations of Ti, Al, Cr, Cu, Zn, and Li than the material overlying them. Partition studies on selected samples indicate that the enriched metals in the basal sediments are usually held in a fashion similar to that in basal sediments from the Pacific, other D.S.D.P. sediments, and modern North Atlantic ridge and non-ridge material. Although, on average, chemical differences between basal sediments of varying ages are apparent, normalization of the data indicates that the processes leading to metal enrichment on the crest of the Mid-Atlantic Ridge appear to have been approximately constant in intensity since Cretaceous times. In addition, the bulk composition of detrital sediments also appears to have been relatively constant over the same time period. Paleocene sediments from site 118 are, however, an exception to this rule, there apparently having been an increased detrital influx during this period. The bulk geochemistry, partitioning patterns, and mineralogy of sediments from D.S.D.P. 9A indicates that post-depositional migration of such elements as Mn, Ni, Cu, Zn, and Pb may have occurred. The basement encountered at the base of site 138 is thought to be a basaltic sill, but the overlying basal sediments are geochemically similar to other metalliferous basal sediments from the North Atlantic. These results, as well as those from site 114 where true oceanic basement was encountered, but where there was an estimated 7 m.y. hiatus between basaltic extrusion and basal sediment deposition, indicate that ridge-crest sediments are not necessarily deposited during active volcanism but can be formed after the volcanism has ceased. The predominant processes for metal enrichment in these deposits and those formed in association with other submarine volcanic features is a combination of shallow hydrothermal activity, submarine weathering of basalt, and the formation of ferromanganese oxides which can scavenge metals from seawater. In addition, it seems as though the formation of submarine metalliferous sediments is not restricted to active-ridge areas.

(Supplementary Table 1) Proportions of methane (C1) to ethane (C2) and the stable isotope composition of methane (d13CCH4) of gas and oil collected by gas bubble sampler during cruise M 114 in the southern Gulf of Mexico

Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1-2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.

Seawater carbonate chemistry and resource allocation and extracellular acid-base status in the sea urchin Strongylocentrotus droebachiensis during experiments, 2012

Anthropogenic CO2 emission will lead to an increase in seawater pCO2 of up to 80-100 Pa (800-1000 µatm) within this century and to an acidification of the oceans. Green sea urchins (Strongylocentrotus droebachiensis) occurring in Kattegat experience seasonal hypercapnic and hypoxic conditions already today. Thus, anthropogenic CO2 emissions will add up to existing values and will lead to even higher pCO2 values >200 Pa (>2000 µatm). To estimate the green sea urchins' potential to acclimate to acidified seawater, we calculated an energy budget and determined the extracellular acid base status of adult S. droebachiensis exposed to moderately (102 to 145 Pa, 1007 to 1431 µatm) and highly (284 to 385 Pa, 2800 to 3800 µatm) elevated seawater pCO2 for 10 and 45 days. A 45 - day exposure to elevated pCO2 resulted in a shift in energy budgets, leading to reduced somatic and reproductive growth. Metabolic rates were not significantly affected, but ammonium excretion increased in response to elevated pCO2. This led to decreased O:N ratios. These findings suggest that protein metabolism is possibly enhanced under elevated pCO2 in order to support ion homeostasis by increasing net acid extrusion. The perivisceral coelomic fluid acid-base status revealed that S. droebachiensis is able to fully (intermediate pCO2) or partially (high pCO2) compensate extracellular pH (pHe) changes by accumulation of bicarbonate (maximum increases 2.5 mM), albeit at a slower rate than typically observed in other taxa (10 day duration for full pHe compensation). At intermediate pCO2, sea urchins were able to maintain fully compensated pHe for 45 days. Sea urchins from the higher pCO2 treatment could be divided into two groups following medium-term acclimation: one group of experimental animals (29%) contained remnants of food in their digestive system and maintained partially compensated pHe (+2.3 mM HCO3), while the other group (71%) exhibited an empty digestive system and a severe metabolic acidosis (-0.5 pH units, -2.4 mM HCO3). There was no difference in mortality between the three pCO2 treatments. The results of this study suggest that S. droebachiensis occurring in the Kattegat might be pre-adapted to hypercapnia due to natural variability in pCO2 in its habitat. We show for the first time that some echinoderm species can actively compensate extracellular pH. Seawater pCO2 values of >200 Pa, which will occur in the Kattegat within this century during seasonal hypoxic events, can possibly only be endured for a short time period of a few weeks. Increases in anthropogenic CO2 emissions and leakages from potential sub-seabed CO2 storage (CCS) sites thus impose a threat to the ecologically and economically important species S. droebachiensis.

High-temperature mechanical properties of aluminium alloys reinforced with titanium diboride (TiB2) particles

The physical and mechanical properties of metal matrix composites were improved by the addition of reinforcements. The mechanical properties of particulate-reinforced metal-matrix composites based on aluminium alloys (6061 and 7015) at high temperatures were studied. Titanium diboride (TiB2) particles were used as the reinforcement. All the composites were produced by hot extrusion. The tensile properties and fracture characteristics of these materials were investigated at room temperature and at high temperatures to determine their ultimate strength and strain to failure. The fracture surface was analysed by scanning electron microscopy. TiB2 particles provide high stability of the aluminium alloys (6061 and 7015) in the fabrication process. An improvement in the mechanical behaviour was achieved by adding TiB2 particles as reinforcement in both the aluminium alloys. Adding TiB2 particles reduces the ductility of the aluminium alloys but does not change the microscopic mode of failure, and the fracture surface exhibits a ductile appearance with dimples formed by coalescence.