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Alt, Jeffrey C; Laverne, Christine; Muehlenbachs, Karlis (1985): Geochemistry of DSDP Hole 83-504B minerals [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.804902, Supplement to: Alt, JC et al. (1985): Alteration of the upper oceanic crust: Mineralogy and processes in Deep Sea Drilling Project Hole 504B, Leg 83. In: Anderson, RN; Honnorez, J; Becker, K; et al. (eds.), Initial Reports of the Deep Sea Drilling Project, Washington (U.S. Govt. Printing Office), 83, 217-247, https://doi.org/10.2973/dsdp.proc.83.108.1985

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Abstract:
Leg 83 of the Deep Sea Drilling Project has deepened Hole 504B to over 1 km into basement, 1350 m below the seafloor (BSF). The hole previously extended through 274.5 m of sediment and 561.5 m of pillow basalts altered at low temperature (< 100°C), to 836 m BSF. Leg 83 drilling penetrated an additional 10 m of pillows, a 209-m transition zone, and 295 m into a sheeted dike complex. Leg 83 basalts (836-1350 m BSF) generally contain superimposed greenschist and zeolite-facies mineral parageneses.
Alteration of pillows and dikes from 836 to 898 m BSF occurred under reducing conditions at low water/rock ratios, and at temperatures probably greater than 100°C. Evolution of fluid composition resulted in the formation of (1) clay minerals, followed by (2) zeolites, anhydrite, and calcite.
Alteration of basalts in the transition zone and dike sections (898-1350 m BSF) occurred in three basic stages, defined by the opening of fractures and the formation of characteristic secondary minerals. (1) Chlorite, actinolite, pyrite, albite, sphene, and minor quartz formed in veins and host basalts from partially reacted seawater (Mg-bearing, locally metal-and Si-enriched) at temperatures of at least 200-250°C. (2) Quartz, epidote, and sulfides formed in veins at temperatures of up to 380°C, from more evolved (Mg-depleted, metal-, Si-, and 18O-enriched) fluids. (3) The last stage is characterized by zeolite formation: (a) analcite and stilbite formed locally, possibly at temperatures less than 200°C followed by (b) formation of laumontite, heulàndite, scolecite, calcite, and prehnite from solutions depleted in Mg and enriched in Ca and 18O, at temperatures of up to 250°C. The presence of small amounts of anhydrite locally may be due to ingress of relatively unaltered seawater into the system during Stage 3.
Alteration was controlled by the permeability of the crust and is characterized by generally incomplete recrystallization and replacement reactions among secondary minerals. Secondary mineralogy in the host basalts is strongly controlled by primary mineralogy.
The alteration of Leg 83 basalts can be interpreted in terms of an evolving hydrothermal system, with (a) changes in solution composition because of reaction of seawater fluids with basalts at high temperatures; (b) variations in permeability caused by several stages of sealing and reopening of cracks; and (c) a general cooling of the system, caused either by the cooling of a magma chamber beneath the spreading center and/or the movement of the crust away from the heat source. The relationship of the high-temperature alteration in the transition zone and dike sections to the low-temperature alteration in the overlying pillow section remains uncertain.
Project(s):
Deep Sea Drilling Project (DSDP)
Coverage:
Median Latitude: 1.227193 * Median Longitude: -83.730193 * South-bound Latitude: 1.227000 * West-bound Longitude: -83.730200 * North-bound Latitude: 1.227200 * East-bound Longitude: -83.730000
Date/Time Start: 1979-12-04T00:00:00 * Date/Time End: 1982-01-02T00:00:00
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
14 datasets

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Datasets listed in this publication series

  1. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 13) Oxygen and carbon isotopic data for vein minerals at DSDP Holes 70-504B and 83-504B. https://doi.org/10.1594/PANGAEA.804889
  2. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 11) Clay mineral descrption at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804887
  3. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 14) Bulk rock oxygen isotopes in basalts at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804890
  4. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 1) Geochemistry of actinolite and clinopyroxene at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804877
  5. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 2) Geochemistry of analcite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804878
  6. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 3) Geochemistry of calcite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804879
  7. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 12) Geochemistry of clay minerals at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804888
  8. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 4) Geochemistry of epidote at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804880
  9. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 5) Geochemistry of secondary feldspars at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804881
  10. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 6) Geochemistry of heulandite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804882
  11. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 7) Geochemistry of laumontite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804883
  12. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 8) Geochemistry of prehnite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804884
  13. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 9) Geochemistry of scolecite at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804885
  14. Alt, JC; Laverne, C; Muehlenbachs, K (1985): (Table 10) Geochemistry of sphene at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804886