Anhydrite in Hydrothermally Altered Basalts: Deep Sea Drilling Project Hole 504B, Leg 83

Alt, JC; Saltzman, ES; Price, DA

doi:10.2973/dsdp.proc.83.111.1985

Cited by 7 publications

(2 citation statements)

References 19 publications

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“…7; Alt et al, 1985aAlt et al, , 1985bAlt et al, , 1986aAlt et al, , 1986bAlt et al, , 1989aAlt et al, , 1989bHonnorez et al, 1985). First, chlorite and actinolite formed in veins and greenschist minerals (chlorite, actinolite, albite-oligoclase, titanite, and local talc) formed in the host rocks during axial hydrothermal alteration by seawater hydrothermal fluids at temperatures of ~200°C to >300°C.…”

Section: Alteration Processesmentioning

confidence: 99%

Hydrothermal Alteration of a Section of Upper Oceanic Crust in the Eastern Equatorial Pacific: A Synthesis of Results from Site 504 (DSDP Legs 69, 70, and 83, and ODP Legs 111, 137, 140, and 148)

Alt¹,

Laverne²,

Vanko³

et al. 1996

Proceedings of the Ocean Drilling Program

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152

255

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Mineralogical, chemical, and isotopic results from seven drilling legs that visited DSDP/ODP Hole 504B over 14 years are compiled here to present an integrated view of hydrothermal alteration of oceanic crust at Site 504. Hole 504B reaches to 2111 mbsf, through 274.5 m sediment, 571.5 m of volcanic rocks, a 209 m transition zone, and 1050 m into a sheeted dike complex. The volcanic section was altered through a series of processes involving interaction with seawater at low temperatures, with the effects of cold, oxidizing seawater decreasing downward. These processes and their effects on the volcanic section are generally similar to those in other oceanic upper crustal sections.The transition zone and upper dikes were altered in a subsurface mixing zone, where hydrothermal fluids upwelling through the dikes mixed with cooler seawater circulating in the overlying more permeable volcanic rocks. Alteration of the transition zone and upper dikes (down to 1500 mbsf) occurred in a series of stages, reflecting the thermal and chemical evolution of the hydrothermal system from (1) early chlorite, actinolite, albite-oligoclase, and titanite, to (2) quartz, epidote and sulfides, to (3) anhydrite, and finally to (4) zeolites and local calcite. The maximum temperature estimated for the first two stages is 350°-380°C, and the inferred mineral assemblages for these early stages are typical of the greenschist facies.The lower dikes (1500-2111 mbsf) underwent an early, high-temperature (>400°C) alteration stage, resulting in the formation of hornblende and calcic secondary plagioclase, consistent with reactions inferred to occur in deep subsurface reaction zones, where hydrothermal vent fluids acquire their final compositions. Much of the subsequent reactions produced greenschist assemblages at ~300°-400°C. The lower dikes have lost metals and sulfur and are a source of these elements to hydrothermal vent fluids and seafloor sulfide deposits. The lower dikes underwent subsequent alteration stages similar to the upper dikes, with rare epidote + quartz veins recording the presence of upwelling hydrothermal fluids, and limited late off-axis effects (zeolites and prehnite). Anhydrites in the lower dikes indicate more reacted fluid compositions than in the upper dikes.Alteration of the sheeted dikes from Hole 504B is heterogeneous, with recrystallization controlled by fracturing and access of fluids. Defining the position of the seismic Layer 2/3 transition depends upon the scale of observation, but the change at Site 504 occurs within the sheeted dikes and is correlated with progressive changes in porosity and hydrothermal alteration. However, we still do not know the nature of the transition from sheeted dikes to gabbros in in situ ocean crust, or the nature of the inferred fault at the base of Hole 504B and its role in fluid flow and alteration.

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Section: Alteration Processesmentioning

confidence: 99%

Hydrothermal Alteration of a Section of Upper Oceanic Crust in the Eastern Equatorial Pacific: A Synthesis of Results from Site 504 (DSDP Legs 69, 70, and 83, and ODP Legs 111, 137, 140, and 148)

Alt¹,

Laverne²,

Vanko³

et al. 1996

Proceedings of the Ocean Drilling Program

Self Cite

152

255

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“…The lower end Jambon and Zimmermann (1990). SO 2 : from Alt et al (1985). CO 2 : from Marty and Tolstikhin (1998).…”

Section: Volatile Fluxes From Ridges and Plumesmentioning

confidence: 99%

Fluxes of volatiles (H2O, CO2, N2, Cl, F) from arc volcanoes

2008

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This review gives an overview of the estimates of volatile emissions from arc and mid-ocean ridge volcanoes to the atmosphere and hydrosphere with particular focus on H 2 O, CO 2 , N 2 , Cl and F. The gas compositions of high temperature (>500°C) fumaroles are compiled and used to derive magmatic H 2 O/SO 2 , CO 2 /SO 2 , HCl/SO 2 and HF/SO 2 ratios on an arcby-arc basis to obtain new estimates of major volatile fluxes from arcs globally. The estimate of F flux from arcs is two orders of magnitude smaller than the amount of F released from mid ocean ridges whereas the arc Cl flux exceeds the ridge flux. An important observation is that globally the water budget of subduction zones seems to be balanced and the amount of water degassed through arc volcanism is within the estimates of the amount of water released from the slab below the volcanic front. Recent work that focused on the Central American arc shows that detailed knowledge of the subduction input compositions, coupled with gas emission studies is critical to further constrain the fate of volatiles during the subduction processes.

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Archean sulphur cycle: Evidence from sulphate minerals and isotopically fractionated sulphides in superior province, Canada

Cameron¹,

Hattori²

1987

Chemical Geology: Isotope Geoscience section

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Anhydrite in Hydrothermally Altered Basalts: Deep Sea Drilling Project Hole 504B, Leg 83

Cited by 7 publications

References 19 publications

Hydrothermal Alteration of a Section of Upper Oceanic Crust in the Eastern Equatorial Pacific: A Synthesis of Results from Site 504 (DSDP Legs 69, 70, and 83, and ODP Legs 111, 137, 140, and 148)

Hydrothermal Alteration of a Section of Upper Oceanic Crust in the Eastern Equatorial Pacific: A Synthesis of Results from Site 504 (DSDP Legs 69, 70, and 83, and ODP Legs 111, 137, 140, and 148)

Fluxes of volatiles (H2O, CO2, N2, Cl, F) from arc volcanoes

Archean sulphur cycle: Evidence from sulphate minerals and isotopically fractionated sulphides in superior province, Canada

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