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Naslund, Howard Richard (1993): Geochemistry of minerals in medium-grained diabase from ODP Holes 137-504B and 140-504B [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.805320, Supplement to: Naslund, HR (1995): Grain-size, morphological, and compositional variations in igneous silicates in medium-grained diabase from Hole 504B. In: Erzinger, J; Becker, K; Dick, HJB; Stokking, LB (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 137, 3-17, https://doi.org/10.2973/odp.proc.sr.137140.001.1995

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Abstract:
Samples recovered from Hole 504B during Leg 140 include a number of medium-grained, holocrystalline diabases that appear to represent the cores of thick dikes. The plagioclase and pyroxene in these samples occur in a variety of crystal morphologies. Plagioclase occurs as phenocrysts, microphenocrysts, elongate crystals, skeletal crystals, and branching radial clusters. Pyroxene occurs as phenocrysts, microphenocrysts, ophitic crystals, and poikilitic crystals. Plagioclase compositions became progressively poorer in anorthite and MgO and progressively richer in FeO as crystallization proceeded, while the average grain volume decreased and the aspect ratio of individual grains increased. Pyroxene compositions are largely independent of crystal morphology.
The diabase dikes recovered from Hole 504B during Leg 140 appear to have crystallized in situ. Crystal compositions and morphologies are consistent with a rapid cooling rate and solidification times for individual dikes on the order of hours or days. The crystallization rate and nucleation rate of plagioclase lagged behind the cooling rate so that the degree of undercooling progressively increased as crystallization proceeded. Plagioclase crystal morphologies indicate much greater degrees of supersaturation than do pyroxene or olivine crystal morphologies. The 504B diabase magmas appear to have been emplaced with abundant preexisting pyroxene and olivine nuclei, but with few preexisting plagioclase nuclei. The suppression of plagioclase nucleation and crystallization relative to that of pyroxene and olivine could provide a mechanism by which the actual fractionation assemblage is more pyroxene-rich and plagioclase-poor than that predicted from thermodynamic models, or that observed in isothermal crystallization experiments.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Latitude: 1.226900 * Longitude: -83.730300
Date/Time Start: 1991-04-07T13:10:00 * Date/Time End: 1991-11-12T04:10:00
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
10 datasets

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Datasets listed in this publication series

  1. Naslund, HR (1993): (Table 4) Geochemistry of elongate plagioclase of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805312
  2. Naslund, HR (1993): (Table 9) Geochemistry of ophitic pyroxene of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805317
  3. Naslund, HR (1993): (Table 3) Geochemistry of plagioclase microphenocrysts of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805311
  4. Naslund, HR (1993): (Table 2) Geochemistry of plagioclase phenocrysts of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805309
  5. Naslund, HR (1993): (Table 10) Geochemistry of poikilitic pyroxene of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805318
  6. Naslund, HR (1993): (Table 8) Geochemistry of pyroxene microphenocrysts of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805316
  7. Naslund, HR (1993): (Table 7) Geochemistry of pyroxene phenocrysts of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805315
  8. Naslund, HR (1993): (Table 5) Geochemistry of skeletal plagioclase of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805313
  9. Naslund, HR (1993): (Table 11) Geochemistry of olivine phenocrysts of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805319
  10. Naslund, HR (1993): (Table 6) Geochemistry of plagioclase radial clusters of ODP Holes 137-504B and 140-504B. https://doi.org/10.1594/PANGAEA.805314