Bloomer, Sherman H; Ewart, Anthony; Hergt, Janet M; Bryan, Wilfred B (1994): Geochemistry of ODP Hole 135-841B [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.798412, Supplement to: Bloomer, SH et al. (1994): Geochemistry and origin of igneous rocks from the outer Tonga forearc (Site 841). In: Hawkins, J; Parson, L; Allan, J; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 135, 625-646, https://doi.org/10.2973/odp.proc.sr.135.129.1994
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Abstract:
Two igneous rock units were recovered at Site 841. More than 200 m of island-arc rhyolites, rhyolitic tuffs, lapilli tuffs, and pumice breccias, divided into five units, compose the basement at the site. These rhyolitic volcanics are late middle Eocene or older and formed part of a subaerial rhyolitic volcano. These low-K rhyolites were produced by fractional crystallization of a more mafic arc-tholeiitic lava or by dehydration melting of lower crustal arc tholeiites. The Site 841 basement rocks are similar in composition to high-SiO2 lavas in the Eocene basement on 'Eua and crystallized from depleted island-arc-tholeiitic basalts like those exposed on 'Eua. No evidence is present in the rhyolites, or in the clasts enclosed within them, for boninite series magmas at Site 841. The Site 841 rhyolitic complex bears no resemblance to Cretaceous rhyolites from the Lord Howe Rise, which are enriched in K and incompatible elements. The volcanic rocks at Site 841 are part of a widely distributed Eocene volcanic episode that marked the earliest phases of subduction in the Tonga region; they are not part of an older crustal fragment.
The second igneous sequence is a series of basaltic dikes and sills that intruded Miocene sediments. These basalts have trace element abundances and ratios identical to upper Miocene lavas from the Lau Ridge. The Site 841 basalts do not have any geochemical characteristics that suggest they were generated by unusual thermal conditions in the shallow sub-forearc mantle. They are most reasonably interpreted as intrusions fed by basement dikes propagated from the associated active arc.
No evidence for local serpentinite exposures, like those that are common in the Mariana forearc, was found at Site 841. The results from Site 841 provide strong support for hypotheses of forearc evolution that have been advanced for the Izu-Bonin-Mariana system.
Project(s):
Deep Sea Drilling Project (DSDP)
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: -23.906100 * Median Longitude: -177.572720 * South-bound Latitude: -36.962500 * West-bound Longitude: 165.434300 * North-bound Latitude: -18.501000 * East-bound Longitude: -175.297000
Date/Time Start: 1971-12-12T00:00:00 * Date/Time End: 1991-02-10T20:30:00
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
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5 datasets
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Datasets listed in this publication series
- Bloomer, SH; Ewart, A; Hergt, JM et al. (1994): (Table 2) Major and trace element analyses of ODP Hole 135-841B Unit I samples. https://doi.org/10.1594/PANGAEA.798408
- Bloomer, SH; Ewart, A; Hergt, JM et al. (1994): (Table 6) Analysis of rhyolitic volcanic rocks from ODP Hole 135-841B Units 2-6 and DSDP Hole 21-207A. https://doi.org/10.1594/PANGAEA.798410
- Bloomer, SH; Ewart, A; Hergt, JM et al. (1994): (Table 8) Analysis of clasts from ODP Hole 135-841B basement and sediments. https://doi.org/10.1594/PANGAEA.798411
- Bloomer, SH; Ewart, A; Hergt, JM et al. (1994): (Table 4) Isotopic analyses of volcanic rocks from ODP Hole 135-841B. https://doi.org/10.1594/PANGAEA.798409
- Bloomer, SH; Ewart, A; Hergt, JM et al. (1994): (Table 1) Comparison of major and trace element analyses of ODP Leg 135 samples. https://doi.org/10.1594/PANGAEA.798407