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Arculus, Richard J; Bloomfield, A L (1992): Geochemistry of ash layers from the Bonin Forearc [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.770729, Supplement to: Arculus, RJ; Bloomfield, AL (1992): Major element geochemistry of ashes from Sites 782, 784, and 786 in the 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, 277-292, https://doi.org/10.2973/odp.proc.sr.125.149.1992

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Abstract:
Many ash-rich layers, varying from a few millimeters to several centimeters thick, were identified in the sedimentary sequences penetrated during Ocean Drilling Program Leg 125 at Sites 782, 784, and 786, located about 400 to 500 km south of Tokyo in the Bonin forearc. The total age range of the ash layers is from Eocene to Pleistocene, although not all sites cover this full span.
The ashes consist of vitric, microlite-bearing, and crystal-rich components; the glassy shards are typically highly vesicular, with elongate, flattened bubbles. The dominant crystalline phases are orthopyroxene, clinopyroxene, and plagioclase.
The major-element compositions of individual vitric shards collected from selected layers of Holes 782A, 784A, and 786A were determined by electron microprobe analyses; particular care was taken to ensure that the analytical results were not compromised by electron beam damage to the glasses.
Compositions range from basalt through andesite and dacite to rhyolite and generally belong to a tholeiitic, low-K suite. There is no indication of any regular secular change during the evolution of the Bonin arc from tholeiitic through calc-alkalic to alkali compositions with time. In Holes 782A and 784A, some high-K rhyolite compositions of late Miocene and Pleistocene age are present. A clear chemical distinction has existed since arc inception between the source(s) of these ashes and the upper mantle source(s) tapped during construction of the igneous basement that formed the forearc.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: 31.346733 * Median Longitude: 141.386053 * South-bound Latitude: 30.861000 * West-bound Longitude: 141.226000 * North-bound Latitude: 31.875000 * East-bound Longitude: 141.738000
Date/Time Start: 1989-03-16T18:00:00 * Date/Time End: 1989-04-04T12:00:00
Event(s):
125-782A * Latitude: 30.861000 * Longitude: 141.314200 * Date/Time Start: 1989-03-16T18:00:00 * Date/Time End: 1989-03-17T07:30:00 * Elevation: -2958.9 m * Penetration: 476.8 m * Recovery: 282 m * Location: North Pacific Ocean * Campaign: Leg125 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 50 cores; 476.8 m cored; 0 m drilled; 59.1 % recovery
125-784A * Latitude: 30.908000 * Longitude: 141.738000 * Date/Time Start: 1989-03-26T15:30:00 * Date/Time End: 1989-03-31T10:00:00 * Elevation: -4912.0 m * Penetration: 425.3 m * Recovery: 218.28 m * Location: North Pacific Ocean * Campaign: Leg125 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 45 cores; 425.3 m cored; 0 m drilled; 51.3 % 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
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
3 datasets

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Datasets listed in this publication series

  1. Arculus, RJ; Bloomfield, AL (1992): (Table 1) Occurrence and age of ash layers in ODP Leg 125 holes. https://doi.org/10.1594/PANGAEA.770725
  2. Arculus, RJ; Bloomfield, AL (1992): (Table 2) Major element composition of ash layers in ODP Leg 125 holes. https://doi.org/10.1594/PANGAEA.770727
  3. Arculus, RJ; Bloomfield, AL (1992): (Table 3) Representative pyroxene composition of ash layers in ODP Leg 125 holes. https://doi.org/10.1594/PANGAEA.770728