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Arculus, Richard J; Pearce, Julian A; Murton, Bramley J; van der Laan, Sieger R (1992): Geochemistry of igneous rock samples of ODP Site 125-786 [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.763139, Supplement to: Arculus, RJ et al. (1992): Igneous stratigraphy and major element geochemistry of Holes 786A and 786B. 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, 143-169, https://doi.org/10.2973/odp.proc.sr.125.137.1992

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Abstract:
A morphologically complex igneous basement was penetrated at Leg 125 Site 786 beneath approximately 100 m of Eocene-Pleistocene sediments at 31°52.45 'N, 141°13.59'E in a 3082-m water depth. The site is located on the forearc basement high (FBH) of the Izu-Bonin (Ogasawara) Arc. In the broadest terms, the sequence in Hole 786B consists of a basal sheeted dike complex, heavily mineralized in places, with overlying pillow lavas giving way to a complex and repeated sequence of interlayered volcanic breccias and lava flows with some thin sedimentary intervals. The sequence has been further cut by dikes or sills, particularly of high-Ca and intermediate-Ca boninite, and is locally strongly sheared by faulting. The whole basement has been covered with middle Eocene-early Pleistocene sediments. A monomict breccia forms the shallowest portion of Hole 786B and a polymict breccia having Mn-oxide-rich clast coatings and matrix forms the deepest part of Hole 786A (-100-160 mbsf). The basement is tectonized in some places, and a mineralized stockwork is present in the deepest part of Hole 786B. A wide variety of rock types form this basement, ranging from mafic to silicic in character and including high-, intermediate-, and low-Ca boninites, intermediate- and low-Ca bronzite andesites, andesite, dacite, and rhyolite groups. Intragroup and intergroup relationships are complicated in detail, and several different upper mantle source(s) probably were involved. A significant role for orthopyroxene-clinopyroxene-plagioclase fractionation is indicated in the mafic-intermediate groups, and the most probable complementary cumulates should be noritic gabbros.
Many overall similarities but some subtle differences are noted between the igneous basement at Site 786 and the subaerial outcrops of the FBH to the south in the type boninite locality of Chichijima. Both suites were derived by hydrous melting of a relatively shallow, refractory (harzburgitic) upper mantle source. These Bonin forearc basement rocks are similar in many respects to those of Eocene-Oligocene age now forming the forearc of the Marianas at Leg 60 Site 458 and on Guam. In sharp distinction, the geochemistry of the Eocene-Pleistocene ash sequences overlying the Bonin FBH must have been derived from a very different upper mantle source, implying considerable across-strike differences in sub-arc mantle composition.
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: 1989-04-04T12:00:00 * Date/Time End: 1989-04-16T17:00:00
Event(s):
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:
4 datasets

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Datasets listed in this publication series

  1. Arculus, RJ; Pearce, JA; Murton, BJ et al. (1992): (Table 3) Major- and trace element analyses of ODP Site 125-786 samples. https://doi.org/10.1594/PANGAEA.763134
  2. Arculus, RJ; Pearce, JA; Murton, BJ et al. (1992): (Table 4) Normalized major- and trace element analyses of ODP Site 125-786 samples. https://doi.org/10.1594/PANGAEA.763137
  3. Arculus, RJ; Pearce, JA; Murton, BJ et al. (1992): (Table 1) Comparative major- and trace element content for duplicate samples of ODP Hole 125-786A. https://doi.org/10.1594/PANGAEA.763132
  4. Arculus, RJ; Pearce, JA; Murton, BJ et al. (1992): (Table 2) Major- and trace element analyses of ODP Hole 125-786B samples. https://doi.org/10.1594/PANGAEA.763133