The frontal accretionary prism of the Hikurangi subduction margin is composed mostly of interbeds of hemipelagic mud and silty turbidites that were deposited on the floor of Hikurangi Trough during the Pleistocene. Expedition 375 of the International Ocean Discovery Program included coring those deposits at Sites U1518 and U1520, which are located on the frontal accretionary prism and the trench wedge, respectively. This report provides the results of 208 X-ray diffraction analyses of the clay-sized fraction (<2 mm spherical settling equivalent). Sampling focused on the background lithology of hemipelagic mud. Normalized weight percent values for common clay-sized minerals (where smectite + illite + undifferentiated [chlorite + kaolinite] + quartz = 100%) exhibit unusual amounts of scatter in all of the lithostratigraphic units. Furthermore, the results reveal neither depth-dependent trends nor excursions at unit boundaries, and compositional differences among sites, lithologic units, and subunits are insignificant. At Site U1520, the mean (µ) and standard deviation (σ) values for Units I–III are smectite = 31.4 wt% (σ = 11.1), illite = 41.5 wt% (σ = 6.9), chlorite + kaolinite = 11.6 wt% (σ = 3.6), and quartz = 15.5 wt% (σ = 6.1). At Site U1518, the mean and standard deviation valuesmore »
Data report: clay mineral assemblages within biocalcareous and volcaniclastic inputs to the Hikurangi subduction zone, IODP Expedition 372B/375 Sites U1520 and U1526, offshore New Zealand
Inputs to the Hikurangi subduction zone, offshore North Island, New Zealand, include volcaniclastic conglomerates that were deposited during the Late Cretaceous on the flanks of the subducting basement of Hikurangi Plateau. The overlying succession of pelagic carbonates is early Paleocene to early Pleistocene in age and ranges in composition from calcareous mudstone to muddy chalk and chalk. A thick wedge of Quaternary trench sediments occupies the top of the stratigraphic succession. International Ocean Discovery Program Expedition 375 cored those subduction inputs at two sites. Site U1520 is located on the distal edge of the trench, and Site U1526 is located near the crest of Tūranganui Knoll, where a highly condensed section of pelagic-hemipelagic sediment covers the basalt basement. This report provides the results of 128 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent), where smectite + illite + undifferentiated (chlorite + kaolinite) + quartz = 100%. Clay minerals in the altered volcaniclastic conglomerates and basalt consist almost exclusively of smectite. At Site U1520, the normalized abundance of smectite in overlying biocalcareous sediments ranges from 28.3 to 72.9 wt% (mean = 54.2 wt%), whereas the abundance of illite ranges from 16.1 to 49.0 wt% (mean = 32.0 more »
- Award ID(s):
- 1326927
- Publication Date:
- NSF-PAR ID:
- 10299638
- Journal Name:
- Proceedings of the International Ocean Discovery Program
- Volume:
- 372B/375
- ISSN:
- 2377-3189
- Sponsoring Org:
- National Science Foundation
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Sediments deposited on the upper slope of the Hikurangi subduction margin, offshore New Zealand, are composed mostly of hemipelagic mud with interbeds of silt to sand that were modified after deposition by strong bottom currents. Some of those deposits were spot cored at Site U1519 during International Ocean Discovery Program (IODP) Expedition 375. This report provides the results of 76 X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent). Sampling focused on the background lithology of hemipelagic mud. Normalized weight percent values for common clay-sized minerals (where smectite + illite + undifferentiated [chlorite + kaolinite] + quartz = 100%) reveal unusually small amounts of scatter both within and between the two lithostratigraphic units. The mean and standard deviation (σ) values for Unit I are smectite = 44.1 wt% (σ = 3.7), illite = 34.0 wt% (σ = 2.8), undifferentiated (chlorite + kaolinite) = 10.7 wt% (σ = 1.3), and quartz = 11.2 wt% (σ = 2.2). The mean and standard deviation values for Unit II are smectite = 49.9 wt% (σ = 5.5), illite = 31.9 wt% (σ = 4.0), undifferentiated (chlorite + kaolinite) = 5.8 wt% (σ = 1.8), and quartz = 12.3 wt% (σ =more »
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This report provides a reconnaissance-scale assessment of bulk mineralogy and clay mineral assemblages in sediments and sedimentary rocks that are entering the Hikurangi subduction zone, offshore North Island, New Zealand. Samples were obtained from three sites drilled during Leg 181 of the Ocean Drilling Program (Sites 1123, 1124, and 1125) and 38 piston/gravity cores that are distributed across the strike-length of the margin. Results from bulk-powder X-ray diffraction show large variations in normalized abundances of total clay minerals and calcite. The typical lithologies range from clay-rich hemipelagic mud (i.e., mixtures of terrigenous silt and clay with lesser amounts of biogenic carbonate) to calcareous mud, muddy calcareous ooze, and nearly pure nannofossil ooze. Basement highs (Chatham Rise and Hikurangi Plateau) are dominated by biocalcareous sediment, whereas most deposits in the trench (Hikurangi Trough and Hikurangi Channel) and on the insular trench slope are hemipelagic. Clay mineral assemblages (<2 µm) change markedly as a function of geographic position. Sediment entering the southwest side of the Hikurangi subduction system is enriched in detrital illite (>60 wt%) relative to chlorite, kaolinite, and smectite. Normalized proportions of detrital smectite increase significantly toward the northeast to reach values of 40–55 wt% offshore Hawkes Bay and acrossmore »
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Holes C0002Q–C0002T were drilled in the inner accretionary prism of the Nankai Trough during International Ocean Discovery Program (IODP) Expedition 358. Sample depths range 2827.5–3067.5 meters below seafloor (mbsf). This report provides the results of X-ray diffraction analyses of the clay-sized fraction (<2 µm spherical settling equivalent) from 33 specimens of bulk cuttings (1–4 mm size fraction). Four core samples from Hole C0002T were also analyzed. Mean weight percent values for common clay-sized minerals are smectite = 20.0 wt%, illite = 54.5 wt%, undifferentiated (chlorite + kaolinite) = 13.8 wt%, and quartz = 11.7 wt%. The average value of the illite crystallinity index is 0.64Δ°2θ. Values of expandability for smectite + illite/smectite (I/S) mixed-layer clay average 57%, and the average proportion of illite in I/S clay is 46%. Depth-dependent trends are not evident in either the clay mineral assemblages or diagenetic indicators. Significant discrepancies exist between these new results and data from the overlapping depth intervals in Hole C0002P. A total of 18 core samples from IODP Hole C0025A in the central Kumano Basin were also analyzed, covering a depth range of 406.12–571.94 mbsf. In Lithologic Unit I (lower fore-arc basin facies), the mean values are smectite = 16.5 wt%,more »
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- Publisher's Version of Record
- https://doi.org/10.14379/iodp.proc.372B375.207.2021
