Major- and Minor Element Chemistry of Antarctic Clay-Rich Sediments: Sites 322, 323, and 325, DSDP Leg 35

A chemical study of 200 meters of highly altered basalt from Hole 417A shows that potassium is strikingly enriched in these rocks, and that calcium, magnesium, and sodium are all depleted. Manganese is very slightly depleted and phosphorus slightly enriched. A comparison of these rocks with fresher examples from nearby Hole 417D suggests that they were originally the same materials. Silicon, titanium, total iron, and aluminum cannot be shown to have moved during alteration; a small difference in estimated original aluminum composition is explained on the basis of original variation in plagioclase content. Of the minor elements, lithium, boron, and barium are strongly enriched, and none of the elements can be shown to be generally depleted, although several (yttrium, strontium, nickel) are slightly redistributed during alteration.A calculation of the budget of alteration shows that about 690 grams of potassium have been introduced for a 200-meter column of rock that is 1 cm 2 in cross-section. Because hydrogen ion is needed to maintain electrical balance, bicarbonate is probably consumed, yielding carbonate ion. If sea water is the altering fluid, then differing assumptions as to the original porosity show that an amount equal to 700 to 1600 volumes of the original void space must have been supplied, if potassium is the limiting chemical species and if it is completely removed from the water. Assuming a low temperature of alteration (on the basis of mineralogy and oxygen isotopes), the amount of heat necessary to drive the required volume of water through the rock must come from a crustal section in excess of what was drilled.

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“…The corrections were very small. The accuracy of these techniques has been reported elsewhere (Donnelly et al, 1973;Donnelly and Wallace, 1976).…”

Section: Sample Selection and Techniquesmentioning

confidence: 91%

The Chemistry of Altered Basalts at Site 417, Deep Sea Drilling Project Leg 51

Donnelly¹,

Thompson²,

Salisbury³

1980

Initial Reports of the Deep Sea Drilling Project

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“…For the chemical analysis of the bulk sediments we utilized wet chemical methods similar to those described by Donnelly and Wallace (1976). Sediment standards were those prepared by E. R. Sholkovitz, which were then standardized against U.S.G.S.…”

Section: Bulk Sedimentsmentioning

confidence: 99%

Geochemistry of Interstitial Waters and Sediments, Leg 64, Gulf of California

Gieskes¹,

Elderfiled²,

Lawrence³

et al. 1982

Initial Reports of the Deep Sea Drilling Project

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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 δ 18 θ (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.

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