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Kempton, Pamela D; Autio, Laurie K; Rhodes, J M; Holdaway, M J; Dungan, Michael A; Johnson, P (1985): Petrology of basalts from DSDP Hole 83-504B [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.804749, Supplement to: Kempton, PD et al. (1985): Petrology of basalts from Hole 504B, Deep Sea Drilling Project, 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, 129-164, https://doi.org/10.2973/dsdp.proc.83.104.1985

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Abstract:
Basalts from Hole 504B, Leg 83, exhibit remarkable uniformity in major and trace element composition throughout the 1075.5 m of basement drilled. The majority of the basalts, Group D', have unusual compositions relative to normal (Type I) mid-ocean ridge basalts (MORB). These basalts have relatively high mg values (0.60-0.70) and CaO abundances (11.7-13.7%; Ca/Al = 0.78-0.89), but exhibit a marked depletion in compatible trace elements (Cr and Ni); moderately incompatible trace elements (Zr, Y, Ti, etc.); and highly incompatible trace elements (Nb, LREE, etc.). Petrographic and compositional data indicate that most of these basalts are evolved, having fractionated significant amounts of plagioclase, olivine, and clinopyroxene. Melting experiments on similar basalt compositions from the upper portion of Hole 504B (Leg 70; Autio and Rhodes, 1983) indicate that the basalts are co-saturated with olivine and plagioclase and often clinopyroxene on the 1-atm. liquidus.
Two rarely occurring groups, M' and T, are compositionally distinct from Group D' basalts. Group T is strongly depleted in all magmaphile elements except the highly incompatible ones (Nb, La, etc.), while Group M' has moderate concentrations of both moderately and highly incompatible trace elements and is similar to Type I MORB. Groups M' and T cannot be related to Group D' nor to each other by crystal fractionation, crystal accumulation, or magma mixing. The large differences in magmaphile element ratios (Zr/Nb, La/Yb) among these three chemical groups may be accounted for by complex melting models and/or local heterogeneity of the mantle beneath the Costa Rica Ridge.
Xenocrysts and xenoliths of plagioclase and clinopyroxene similar in texture and mineral composition to crystals in coarse-grained basalts from the lower portion of the hole are common in Hole 504B basalts. These suggest that addition of solid components either from conduit or magma chamber walls has occurred and may be a common source of disequilibrium crystals in these basalts. However, mixing of plagioclase-laden depleted melts (similar to the Costa Rica Ridge Zone basalts) with normal MORB magmas could provide an alternate source for some refractory plagioclase crystals found out of equilibrium in many phyric MORB.
The uniformity of major element compositions in Hole 504B basalts affords an ideal situation for investigating the effects of alteration on some major and trace elements in oceanic basalts. Alteration observed in whole-rock samples records primarily two events - a high-temperature and a low-temperature phase. High-temperature phases include: chlorite, talc, albite, actinolite, sphene, quartz, and pyrite. The low-temperature phases include smectite (saponite), epistilbite or laumontite, and minor calcite. Laumontite may actually straddle the gap between the low- and high-temperature mineral assemblages. Alteration is restricted primarily to partial replacement of primary phases. Metamorphic grade, in general, increases from the top to the bottom of Hole 504B (Legs 69, 70, and 83) as seen in the change from a smectiteto- chlorite-dominated secondary mineral assemblage. However, a systematic progression for the interval recovered during Leg 83 is not apparent. Rather, the extent of alteration appears to be a function of the initial texture and fracture density. Variations in whole-rock major and trace element concentrations cannot be attributed convincingly to any differences in alteration observed. Compositional characteristics of the secondary minerals indicated that extensive remobilization of elements has not occurred; local redistribution is suggested in most cases. Thus, the major and trace element signature of these basalts remains effectively the same as the original composition prior to alteration.
Project(s):
Deep Sea Drilling Project (DSDP)
Coverage:
Latitude: 1.227200 * Longitude: -83.730200
Date/Time Start: 1981-11-22T00:00:00 * Date/Time End: 1982-01-02T00:00:00
Event(s):
83-504B * Latitude: 1.227200 * Longitude: -83.730200 * Date/Time Start: 1981-11-22T00:00:00 * Date/Time End: 1982-01-02T00:00:00 * Elevation: -3460.0 m * Penetration: 1350 m * Recovery: 107.7 m * Campaign: Leg83 * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL) * Comment: Leg 83 of DSDP was devoted entirely to coring and experiments in Hole 504B, the deepest borehole to date into the oceanic crust. Hole 504B now extends over a kilometer into basement, nearly twice as far as any other DSDP hole, and it is the only DSDP hole to have clearly penetrated into the intrusive sheeted dikes that underlie the extrusive pillow lavas of the upper oceanic crust. At Hole 504B, Leg 83 continued an ongoing DSDP effort that began during Legs 68, 69, and 70 in 1979, and also included part of Leg 92 in 1983. 71 cores; 514 m cored; 0 m drilled; 21 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
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Datasets listed in this publication series

  1. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 9) Geochemistry of alteration minerals at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804748
  2. Kempton, PD; Autio, LK; Rhodes, JM et al. (1983): (Table 6) Geochemistry of basalts at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804746
  3. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 1) Geochemistry of clinopyroxenes at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804741
  4. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 2) Geochemistry of FeTi oxides at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804742
  5. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 3) Geochemistry of plagioclase at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804743
  6. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 4) Geochemistry of spinels, at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804744
  7. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 5) Geochemistry of whole-rock basalts at DSDP Hole 83-504B. https://doi.org/10.1594/PANGAEA.804745
  8. Kempton, PD; Autio, LK; Rhodes, JM et al. (1985): (Table 7) Trace element abundances in selected samples at DSDP Hole 83-504B basalts. https://doi.org/10.1594/PANGAEA.804747