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van der Laan, Sieger R; Arculus, Richard J; Pearce, Julian A; Murton, Bramley J (1992): Petrology and geochemistry of the basement boninite series of ODP Site 125-786 [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.767632, Supplement to: van der Laan, SR et al. (1992): Petrography, mineral chemistry, and phase relations of the basement Boninite series of Site 786, Izu-Bonin Forearc. In: Fryer, P; Pearce, JA; Stokking, LB; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 125, 171-201, https://doi.org/10.2973/odp.proc.sr.125.139.1992

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Abstract:
The 720 m of igneous basement that was penetrated at Site 786 of Ocean Drilling Program Leg 125 consists of boninite-series volcanics. Bronzite andesites dominate the lithology and primitive magmas of high-Ca, intermediate-Ca, and low-Ca boninite are present in subordinate amounts. Sparsely phyric boninites typically contain olivine and orthopyroxene phenocrysts with Mg numbers [= Mg/(Mg + Fe) in moles] between 86% and 87%. Their high whole-rock Mg numbers, and the absence of zonation in the phenocrysts, imply equilibration at temperatures probably between 1200° and 1250°C, and 20° to 50°C below their liquidus. Equilibrium olivine and orthopyroxene have identical Mg numbers, and Mg/Fe partitioning between these minerals and the melt thus can be described with a single Kd. The invariably phenocryst-rich bronzite andesites contain Plagioclase that has spectacular zoning and mafic phases that can be as magnesian as those of the boninite parent. The most evolved melts are rhyolites with hypersthene, Plagioclase (An50), and magnetite. Eruption temperatures for the rhyolites are estimated at about 1000°C. Some magmas contain ferroactinolite in the groundmass, which is most likely a secondary, low-temperature phase.
The locally large contrasts in degree of alteration are consistent with multiple episodes of magmatic activity. However, all igneous events produced boninite volcanics. Only the first, the edifice-building episode, gave rise to differentiated magmas. Differentiation of parental boninites took place by limited fractional crystallization, producing bronzite andesites. The erupted andesites, dacites and rhyolites are filter pressed extracts from these bronzite andesite magmas, which, as a result, have accumulated crystals. Subsequent younger igneous events produced high-Ca and intermediate-Ca boninites which intruded as dikes and sills throughout the basement sequence. The mineralogy of the dikes and sills reflects variable degrees of subliquidus cooling of the magma before emplacement.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: 31.874600 * Median Longitude: 141.226250 * South-bound Latitude: 31.874200 * West-bound Longitude: 141.226000 * North-bound Latitude: 31.875000 * East-bound Longitude: 141.226500
Date/Time Start: 1989-04-04T00:00:00 * Date/Time End: 1989-04-16T17:00:00
Event(s):
125-786 * Latitude: 31.874600 * Longitude: 141.226250 * Date/Time Start: 1989-04-04T00:00:00 * Date/Time End: 1989-04-16T00:00:00 * Elevation: -3076.0 m * Penetration: 995.1 m * Recovery: 275 m * Location: North Pacific Ocean * Campaign: Leg125 * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 91 cores; 832.6 m cored; 0 m drilled; 33% recovery
125-786A * Latitude: 31.875000 * Longitude: 141.226000 * Date/Time Start: 1989-04-04T12:00:00 * Date/Time End: 1989-04-04T12:00:00 * Elevation: -3070.0 m * Penetration: 166.5 m * Recovery: 84.95 m * Location: North Pacific Ocean * Campaign: Leg125 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 19 cores; 166.5 m cored; 0 m drilled; 51 % recovery
125-786B * Latitude: 31.874200 * Longitude: 141.226500 * Date/Time Start: 1989-04-04T12:00:00 * Date/Time End: 1989-04-16T17:00:00 * Elevation: -3082.0 m * Penetration: 828.6 m * Recovery: 190.07 m * Location: North Pacific Ocean * Campaign: Leg125 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 72 cores; 666.1 m cored; 0 m drilled; 28.5 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
6 datasets

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Datasets listed in this publication series

  1. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Table 1) Geochemistry of olivines in ODP Site 125-786. https://doi.org/10.1594/PANGAEA.767620
  2. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Table 2) Geochemistry of orthopyroxene in ODP Site 125-786. https://doi.org/10.1594/PANGAEA.767624
  3. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Table 3) Geochemistry of clinopyroxene in ODP Site 125-786. https://doi.org/10.1594/PANGAEA.767625
  4. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Appendix) Detailed petrology of ODP Site 125-786 samples. https://doi.org/10.1594/PANGAEA.767631
  5. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Table 4) Geochemistry of plagioclase in ODP Site 125-786. https://doi.org/10.1594/PANGAEA.767626
  6. van der Laan, SR; Arculus, RJ; Pearce, JA et al. (1992): (Table 5) Geochemistry of Cr-spinel, glass, and amphibole in ODP Site 125-786. https://doi.org/10.1594/PANGAEA.767628