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Hiscott, Richard N; Gill, James B (1992): Geochemistry of sands and sandstones in ODP Leg 126 sites [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.774232, Supplement to: Hiscott, RN; Gill, JB (1992): Major and trace element geochemistry of Oligocene to Quaternary volcaniclastic sands and sandstones from the Izu-Bonin Arc. In: Taylor, B; Fujioka, K; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 126, 467-485, https://doi.org/10.2973/odp.proc.sr.126.150.1992

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Abstract:
During Ocean Drilling Program Leg 126, six sites were cored in a young backarc rift basin and its flanks (rift onset 1.1-3.56 Ma) and in the forearc basin of the Izu-Bonin Arc. In the backarc area, strata are younger than about 4.5 Ma, whereas in the forearc, ages are about 0-31 Ma in sections punctuated by important Miocene unconformities. Bulk chemical analyses of volcaniclastic turbidite sands and sandstones, derived directly from the arc, were obtained from 271 atomic absorption analyses (major elements), 253 XRF analyses (trace elements) and 16 ICP-MS analyses (trace and rare-earth elements). Of the 271 samples, 78 come from the backarc area and the remainder from the forearc.
The sands and sandstones reflect the igneous compositions of their sources. Most are formed of materials derived from subalkaline, low-K andesites, and dacites, although compositions range from basalt to rhyolite. Basic and acid andesites are predominant in Oligocene rocks; in contrast, Pliocene-Pleistocene sediments were derived from acid andesitic to rhyolitic sources. The oldest sandstones, estimated to have an age of about 31 Ma, were derived from an arc tholeiitic, not boninitic, source. The 26-31 Ma sandstones furthest to the north, at Sites 787 and 792, have higher relative concentrations of Ti, Zr, and Y than do those at southern Site 793. Data from younger samples indicate that, for more than 30 m.y., the average composition of volcaniclastic sediments and volcanism near Aoga Shima was more basic than to the south, near Sumisu Jima.
Using the sandstones as igneous proxies, we conclude that magmas erupted along the arc have become more depleted in light-rare-earth elements (LREE) with time. There was a major change in rare-earth-element (REE) concentrations in the late Oligocene, from essentially flat patterns (normalized La/Yb about 1-1.5) to LREE-depleted patterns (normalized La/Yb about 0.5). At the same time, Zr/Y ratios decreased from about 2-4 to about 1.5-2.5. These changes may reflect a shift in provenance, or changes in the composition of the mantle wedge beneath the arc.
In the backarc area, lithic clasts and glass shards of rift-facies basalt are present in sediments as old as 2.35-3.15 Ma. Two samples of mafic sand from the backarc basin have flat REE patterns (normalized La/Yb about 1.0), like some of the <1-Ma rift lavas and unlike pre-rift sand and sandstone samples. These possibly represent the local effects of sedimentary mixing of detritus from arc and backarc eruptions because no evidence from the arc itself exists to suggest a recent change in the REE content of magmas.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: 31.347528 * Median Longitude: 140.279904 * South-bound Latitude: 30.914133 * West-bound Longitude: 139.841733 * North-bound Latitude: 32.399400 * East-bound Longitude: 140.888200
Date/Time Start: 1989-04-15T03:15:00 * Date/Time End: 1989-06-17T18:55:00
Event(s):
126-787 * Latitude: 32.375700 * Longitude: 140.749400 * Date/Time Start: 1989-04-23T00:00:00 * Date/Time End: 1989-04-27T00:00:00 * Elevation: -3265.0 m * Penetration: 354.6 m * Recovery: 159.9 m * Location: North Pacific Ocean * Campaign: Leg126 * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 34 cores; 320.1 m cored; 0 m drilled; 49.9% recovery
126-787B * Latitude: 32.375700 * Longitude: 140.749400 * Date/Time Start: 1989-04-24T14:55:00 * Date/Time End: 1989-04-27T12:00:00 * Elevation: -3265.0 m * Penetration: 320.1 m * Recovery: 159.88 m * Location: North Pacific Ocean * Campaign: Leg126 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 34 cores; 320.1 m cored; 0 m drilled; 49.9 % recovery
126-788 * Latitude: 30.922133 * Longitude: 140.003617 * Date/Time Start: 1989-04-28T00:00:00 * Date/Time End: 1989-05-16T00:00:00 * Elevation: -1112.5 m * Penetration: 717.4 m * Recovery: 159.7 m * Location: Philippine Sea * Campaign: Leg126 * Basis: Joides Resolution * Method/Device: Composite Core (COMPCORE) * Comment: 53 cores; 493.8 m cored; 0 m drilled; 32.3% recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
5 datasets

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Datasets listed in this publication series

  1. Hiscott, RN; Gill, JB (1992): (Table 5) Comparison of sand composition with igneous clasts of ODP Hole 126-788C. https://doi.org/10.1594/PANGAEA.774230
  2. Hiscott, RN; Gill, JB (1992): (Table 6) La/Yb ratios of ODP Leg 126 sites. https://doi.org/10.1594/PANGAEA.774231
  3. Hiscott, RN; Gill, JB (1992): (Table 2) Volatil-free major element content in volcaniclastic sands of ODP Leg 126 sites. https://doi.org/10.1594/PANGAEA.774227
  4. Hiscott, RN; Gill, JB (1992): (Table 4) Volatil-free trace and rare-earth element content in volcaniclastic sands of ODP Leg 126 sites. https://doi.org/10.1594/PANGAEA.774229
  5. Hiscott, RN; Gill, JB (1992): (Table 3) Volatil-free trace element content in volcaniclastic sands of ODP Leg 126 sites. https://doi.org/10.1594/PANGAEA.774228