Strontium chemistry of anhydrite from DSDP/ODP Hole 504B

A unique record of the chemical evolution of seawater during hydrothermal recharge into oceanic crust is preserved by anhydrite from the volcanic sequences and sheeted dike complex in ODP Hole 504B. Chemical and isotopic analyses 87Sr/86Sr, delta18O, delta34S of anhydrite constrain the changing composition of fluids due to reaction with basalt. There is a general trend of decreasing 87Sr/86Sr of anhydrite, corresponding to the minor incorporation of basaltic strontium with depth in the volcanic rocks. 87Sr/86Sr ratios decrease rapidly with depth in the dikes to values identical to host basalt (0.7029). Sr/Ca ratios (<0.1 mmol/mol) suggest that recharge fluids have very low Sr concentrations and fluids evolve by first precipitating Sr-bearing phases before extensive exchange of Sr with the host basalt. There is a background trend of decreasing sulfate delta18O with depth from +12-13? in the lower volcanics to +7? in the lower sheeted dikes recording an increase in recharge fluid temperature from c. 150° to c. 250°C, and confirming the presence of sulfate in hydrothermal fluids at elevated temperatures. From the amount of anhydrite recovered from Hole 504B and the amount of seawater sulfur that has been reduced to sulfide, a minimum seawater recharge flux can be calculated. This value is 4-25 times lower than estimates of high-temperature fluid fluxes based on either thermal constraints or global chemical budgets and suggests that there is significant deficit of seawater-derived sulfur in the oceanic crust. Only a minor proportion of the seawater that percolates into the crust near the axis is heated to high temperatures and exits as black smoker-type fluids. A significant proportion of the axial heat loss must be advected at 200-250°C by sulfate-bearing hydrothermal solutions that egress diffusely from the crust. These fluids penetrate into the dikes and exchange both heat and chemical tracers without the extensive clogging of porosity by anhydrite precipitation, which would halt hydrothermal circulation for any reasonable fluid flux. The heating of the major proportion of hydrothermal fluids to only moderate temperatures (c. 250°C) reconciles estimates of hydrothermal fluxes derived from thermal models and global geochemical budgets. The flux of hydrothermal sulfate would be of a magnitude similar to the riverine input, and oxygen-isotopic exchange at 200-250°C between dissolved sulfate and recharge fluids during hydrothermal circulation provides a mechanism to continuously buffer seawater sulfate oxygen to the light isotopic composition observed.

Summary of shipboard physical properties of mudstones, carbonates, and clastic at DSDP Holes 72-515B and 72-516F

Compressional-wave velocity, wet-bulk density, and porosity were measured on sediments and rocks recovered from Deep Sea Drilling Project Holes 515B and 516F. Wet-bulk densities were measured by both gravimetric and GRAPE methods. Velocities were measured on trimmed samples with the Hamilton frame velocimeter. The shipboard measurement techniques are discussed in the explanatory notes chapter (Coulbourn, this volume) and are described in detail by Boyce (1976a). Only the shipboard measurements are reported here.

Chemistry of Globigerinoides ruber shells from ODP Site 160-963

Here we present a high-resolution faunal, floral and geochemical (stable isotopes and trace elements) record from the sediments of Ocean Drilling Program Site 963 (central Mediterranean basin), which shows centennial/millennial-scale resemblance to the high-northern latitude rapid temperature fluctuations documented in the Greenland ice cores between 20 and 70 kyr BP. Oxygen and carbon isotopes, planktic foraminifera and calcareous nannofossil distributions suggest that Dansgaard-Oeschger (D/O) and Heinrich events (HE) are distinctly expressed in the Mediterranean climate record. Moreover, recurrent though subdued oscillations not previously identified in the Lateglacial Mediterranean sediments document a significant centennial-scale climate variability in the basin that is greater than previously thought. Alternations between climate regimes dominated by polar outbreaks during D/O stadials and warm D/O interstadials, with associated intensification of continental runoff, are well expressed in the ODP Site 963. These place the Mediterranean basin as an often overlooked recorder of the interplay between large- and regional- scale climate controls at intermediate latitudes, and of the possible interactions between different components of the climate system. Significant changes in Ba/Ca values measured in Globigerinoides ruber shells from a number of D/O stadials and interstadials suggest enhanced freshwater input from the north-eastern Mediterranean borderland during the D/O interstadials. However, the short duration of 3D stratification events never led to complete oxygen consumption along the water column, but clear effects of sluggish 3D circulation in the basin are testified to by negative excursions in d13C measured in selected species of planktic and benthic foraminifera. HEs are constantly associated with lightening in the d18O record of planktic foraminifera, possibly because of the impact of iceberg melting in the Iberian Margin on Mediterranean thermohaline circulation. Interestingly, in two cases in particular, HE2 and HE5, fresher water inputs also affected deeper horizons of intermediate waters, suggesting a basin-wide impact.

Stable isotope organic chemistry of ODP Leg 105 sites

Stable carbon and nitrogen isotopic compositions as well as organic carbon and total nitrogen contents are reported for Site 645 in Baffin Bay and Sites 646 and 647 in the Labrador Sea. Both low-resolution analyses (1 sample/section) and high-resolution results (up to 7 samples/section) are presented. These records indicate that large-scale changes in productivity since the middle Miocene have occurred in Baffin Bay. Such changes are not evident in samples from the Labrador Sea. Isotopic records of all the sites are influenced strongly by rapidly changing influxes that combine terrigenous debris with planktonic production. In parts of the cores, relationships to other phenomena, such as ice stages, are present. However, these correlations are not common and indicate that these events were masked by the dynamic changes in sources of organic matter occurring in this complex system.

Chemistry of minerals of ODP Hole 103-637A peridotites

The Galicia margin lies northwest of the Iberian Peninsula and is a passive ocean margin with thin sedimentary cover. Altered peridotite was recovered from ODP Site 637, on the north-trending ridge at the western edge of the margin, near the oceanic/continental crust boundary. The altered ultramafics were originally clinopyroxene-rich upper mantle harzburgites and are now extensively serpentinized (>85%) and cut by very late-stage carbonate veins. Despite pervasive late, low-temperature alteration, evidence of early, high-temperature alteration remains. Alteration is apparent as (1) amphibole rims on clinopyroxene (>800°C), (2) hornblende + tremolite (450° to 800°C), (3) breakdown of hornblende to form tremolite + chlorite (<450°C), (4) zoned Cr-spinels, (5) hydration of orthopyroxene and olivine to serpentine, (6) serpentine veins, (7) replacement of pyroxene and olivine by calcite, and (8) calcite veins and vugs. Both the relict igneous and the high-temperature alteration minerals (amphiboles) show evidence of brittle deformation. Subsequent low-temperature alteration veins and minerals are deformed only in faulted and brecciated zones. This textural evidence suggests that the low-temperature alteration occurred after emplacement of the ultramafics at the surface. Serpentine fills tension fractures in orthopyroxene, and both serpentine and calcite fill tension cracks in olivine. The high-temperature alterations in these samples are similar to those found in oceanic fracture zone and ophiolite ultramafics. This widespread occurrence of high-temperature alteration suggests that hot fluids were pervasive in these ultramafic blocks. Localization of high-temperature alteration close to large carbonate veins suggests channelization of the late, low-temperature fluids. Earlier hydrations (e.g., high-temperature alterations and serpentinization) were pervasive.

Physical oceanography of CTD stations in the Persian Gulf

The following tables show physical and chemical data observed by the "Meteor" in the Persian Gulf and the Strait of Hormus. This study was performed in accordance with the general programme of the International Indian Ocean Expedition (IIOE) during the oeriod from March 25th until April 16th, 1965. The water temperature was measured by reversing thermometers; in most cases two instruments were used simultaneously. The absolute mean temperature difference of this double measurement is 0.0153 °C. The salinity was determined both by salinometer and by titration. In this case of the density, the specific volume anomaly, the dynamic depth anomaly, the sound velocity and the interpolation for standard depths were carried out by the National Oceanographic Data Center (NODC), Washington.

Water chemistry of lakes from the Antarctic

This paper reviews Japanese limnological studies mainly in the McMurdo and Syowa oases, with special emphasis on the nutrient distribution. Generally, the chemical composition of the major ionic components in the coastal lakes and ponds is similar to that in seawater, while that in inland Dry Valley lakes and ponds of the McMurdo Oasis is abundant in calcium, magnesium and sulfate ions. The former can be explained by the direct influences of sea salts, while the latter is mainly attributable to the accumulation of atmospheric salts. Most saline lakes are meromictic. Dissolved oxygen concentrations in the upper layers are saturated or supersaturated, but the bottom layers are anoxic and often hydrogen sulfide occurs. The concentrations of nutrients vary largely not only among the lakes but also with depth. Silicate-Si, which is generally abundant in all freshwater and saline lakes, may be due to erosions of soils and rocks. Nitrite-N concentrations in both freshwater and saline lakes are generally low. Nitrate-N concentrations in the oxic layers of the inland saline lakes in the McMurdo Oasis arc often high, but not high in the coastal saline lakes of the Syowa and Vestfold oases. The abundance of phosphate-P and ammonium-N in the bottom stagnant layers of saline lakes can be explained by the accumulation of microbially released nutrients due to the decomposition of organic substances. Nutrients are supplied mainly from meltstreams in the catchment areas, and are proved to play an important role in primary production.

Chemistry of interstitial waters and sediments at DSDP Leg 64 Holes

Studies of interstitial waters obtained from DSDP Leg 64 drill sites in the Gulf of California have revealed information both on early diagenetic processes in the sediments resulting from the breakdown of organic matter and on hydrothermal interactions between sediments and hot doleritic sill intrusions into the sediments. In all the sites drilled sulfate reduction occurred as a result of rapid sediment accumulation rates and of relatively high organic carbon contents; in most sites methane production occurred after sulfate depletion. Associated with this methane production are high values of alkalinity and high concentrations of dissolved ammonia, which causes ion exchange processes with the solid phases leading to intermediate maxima in Mg++, K+, Rb+, and Sr++(?). Though this phenomenon is common in Leg 64 drill sites, these concentration reversals had been noticed previously only in Site 262 (Timor Trough) and Site 440 (Japan Trench). Penetrating, hot dolerite sills have led to substantial hydrothermal alteration in sediments at sites drilled in the Guaymas Basin. Site 477 is an active hydrothermal system in which the pore-water chemistry typically shows depletions in sulfate and magnesium and large increases in lithium, potassium, rubidium, calcium, strontium, and chloride. Strontium isotope data also indicate large contributions of volcanic matter and basalt to the pore-water strontium concentrations. At Sites 478 and 481 dolerite sill intrusions have cooled to ambient temperatures but interstitial water concentrations of Li+, Rb+, Sr++ , and Cl- show the gradual decay of a hydrothermal signal that must have been similar to the interstitial water chemistry at Site 477 at the time of sill intrusion. Studies of oxygen isotopes of the interstitial waters at Site 481 indicate positive values of d18O (SMOW) as a result of high-temperature alteration reactions occurring in the sills and the surrounding sediments. A minimum in dissolved chloride at about 100-125 meters sub-bottom at Sites 478, 481, and particularly Site 479 records a possible paleosalinity signal, associated with an event that substantially lowered salinities in the inner parts of the Gulf of California during Quaternary time.

Chemistry of altered basalts from ODP Hole 123-765D

Volcanic basement recovered at Hole 765D is characterized by nonpervasive, oxidative alteration, typical of seafloor weathering. Chilled margins and the mesostasis of the lavas are variably altered to assemblages of celadonite, Fe-oxyhydroxides, zeolites, and calcite with trace saponite. Plagioclase is partially altered to Ca-Na zeolites and/or albite. Well-developed alteration halos parallel fracture surfaces and extend several centimeters into the surrounding rock. These clay-rich halos are enriched in K2O and Fe2O3 relative to the adjacent clay-poor rock. The halos and adjacent rock are characterized by d18O values 2 per mil-3 per mil higher than those of fresh MORB. The "freshness" of the samples and the scarcity of saponite suggest that the duration of seawater circulation was short-lived. Albitization of plagioclase indicates that the volcanic rocks were altered initially at low temperatures and were subsequently reheated off-axis in a closed environment. Reheating did not result in significant modification of the bulk composition of the crust.

Mineral chemistry of basalts from DSDP Holes 65-483 and 65-483B

During DSDP Leg 65, a series of holes was drilled into the oceanic basement across the mouth of the Gulf of California to study the composition of the crust and the nature of its construction at a young spreading center. In Holes 483 and 483B, two of the deepest basement holes drilled on this leg, the basement is characterized by an upper sequence of interlayered massive basalts and sediments underlain by a lower sequence of interlayered pillow and massive basalts. Electron microprobe analyses were performed on pyroxene, plagioclase, olivine, spinel, and glass from 14 representative samples of 10 of the 16 major lithologic units. These analyses along with petrographic results can be used to interpret the detailed crystallization history of the basalts. We believe from the results of this study that the basalts were formed by at least a three-stage cooling process, followed by eruption and formation of quench phases. Our data do not support magma mixing.

Petrology and chemistry of ODP Site 134-828 magmatic rocks

Petrography, major and trace elements, mineral chemistry, and Sr, Nd, and Pb isotopic ratios are reported for igneous rocks drilled on the northern flank of the North d'Entrecasteaux Ridge (NDR) during Ocean Drilling Program (ODP) Leg 134 Site 828. These rocks comprise a breccia unit beneath a middle Eocene foraminiferal ooze. Both geophysical characteristics and the variety of volcanic rocks found at the bottom of Holes 828A and 828B indicate that a very immature breccia or scree deposit was sampled. Basalts are moderately to highly altered, but primary textures are well preserved. Two groups with different magmatic affinities, unrelated to the stratigraphic height, have been distinguished. One group consists of aphyric to sparsely plagioclase + clinopyroxene-phyric basalts, characterized by high TiO2 (~2 wt%) and low Al2O3 (less than 15 wt%) contents, with flat MORB-normalized incompatible element patterns and LREE-depleted chondrite-normalized REE patterns. This group resembles N-MORB. The other group comprises moderately to highly olivine + plagioclase-phyric basalts with low TiO2 (<1 wt%) and high Al2O3 (usually >15 wt%) contents, and marked HFSE depletion and LFSE enrichment. Some lavas in this group are picritic, with relatively high modal olivine abundances, and MgO contents up to 15 wt%. Both the basalts and picritic basalts of this group reflect an influence by subduction-related processes, and have compositions transitional between MORB and IAT. Lavas with similar geochemical features have been reported from small back-arc basins such as the Mariana Trough, Lau Basin, Sulu Sea, and the North Fiji Basin and are referred to as back-arc basin basalts. However, regional tectonic considerations suggest that the spreading that produced these backarc basin basalts may have occurred in the forearc region of the southwest-facing island arc that existed in this region in the Eocene.