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  • 1
    Publication Date: 2019-02-01
    Description: New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.
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  • 2
    Publication Date: 2019-02-01
    Description: We examine the importance of dispersed volcanic ash as a critical component of the aluminosilicate sediment entering the Nankai Trough, located south of Japan’s island of Honshu, via the subducting Philippine Sea plate. Multivariate statistical analyses of an extensive major, trace, and rare earth element data set from bulk sediment and discrete ash layers at Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 quantitatively determine the abundance and accumulation of multiple aluminosilicate inputs to the Nankai subduction zone. We identify the eolian input of continental material to both sites, and we further find that there are an additional three ash sources from Kyushu and Honshu, Japan and other regions. Some of these ash sources may themselves represent mixtures of ash inputs, although the final compositions appear statistically distinct. The dispersed ash comprises 38 ± 7 weight percent (wt%) of the bulk sediment at Site C0011, and 34 ± 4 wt% at Site C0012. When considering the entire sediment thickness at Site C0011, the dispersed ash component supplies 38000 ± 7000 g/cm2 of material to the Nankai subduction system, whereas Site C0012 supplies 20000 ± 3000 g/cm2. These values are enormous compared to the ~2500 g/cm2 (C0011) and ~1200 g/cm2 (C0012) of ash in the discrete ash layers. Therefore, the mass of volcanic ash and chemically equivalent alteration products (e.g., smectite) that are dispersed throughout the stratigraphic succession of bulk sediment appears to be up to 15–17 times greater than the mass of discrete ash layers. The composition of the dispersed ash component at Site C0011 appears linked to that of the discrete layers, and the mass accumulation rate for dispersed ash correlates best with discrete ash layer thickness. In contrast, at Site C0012 the mass accumulation rate for dispersed ash correlates better with the number of ash layers. Together, the discrete ash layers, dispersed ash, and clay-mineral assemblages present a complete record of volcanism and erosion of volcanic sources; and indicate that mass balances and subduction factory budgets should include the mass of dispersed ash for a more accurate assessment of volcanic contributions to large-scale geochemical cycling.
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  • 3
    Publication Date: 2018-06-28
    Description: During the “Azores Tephra” cruise M141 on the German research vessel RV Meteor in September 2017 we carried out pore fluid analyses of 28 gravity cores recovered from the Azores Plateau. The pore fluids were analysed for total alkalinity, ammonium, methane and other major elements such as Na, Ca, Cl, B, Mg and Sr and allow, for the first time, to perform a thorough analysis of sub-seafloor fluid origin and secondary alteration processes in this area of intense tectonic and volcanic activity. Pore fluids in sediments of the Azores Plateau are generally affected by the alteration of marine volcanic deposits. Moreover, due to local heating of the plateau, shallow hydrothermal fluid venting occurs e.g. known at the D. Joao de Castro seamount in the Terceira Rift (Cardigos et al., 2005). Here, for the first time, we present fluid geochemistry data from deep-water hydrothermal seepage areas of the Azores Plateau. The present status of geochemical analyses, suggests that there are two different types of hydrothermal seepage systems: In many places on the plateau a slightly acidic (CO2-rich) hydrothermal fluid percolates through the sediments; Along the Terceira Rift, which marks the northern border of the plateau, also methane-rich fluid seeps are suspected. We will present a comprehensive interpretation of the available data set, with respect to geochemical processes occurring at the hydrothermally-driven seepage systems, fluid and gas sources, the activity of the seeps, and the role of ash alteration. References Cardigos, F., Colaço, A., Dando, P. R., Ávila, S. P., Sarradin, P. M., Tempera, F., Conceição, P., Pascoal, A., and Serrão Santos, R., 2005, Shallow water hydrothermal vent field fluids and communities of the D. João de Castro Seamount (Azores): Chemical Geology, v. 224, no. 1-3, p. 153-168.
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  • 4
    Publication Date: 2018-09-10
    Description: Slow slip events (SSEs) at the northern Hikurangi subduction margin, New Zealand, are among the best-documented shallow SSEs on Earth. International Ocean Discovery Program Expedition 375 was undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi Trough by (1) coring at four sites, including an active fault near the deformation front, the upper plate above the high-slip SSE sourc e region, and the incoming sedimentary succession in the Hikurangi Trough and atop the Tūranganui Knoll Seamount, and (2) installing borehole observatories in an active thrust near the deformation front and in the upper plate overlying the slow slip source region. Logging-while-drilling (LWD) data for this project were acquired as part of Expedition 372 (26 November 2017-4 January 2018; see th e Expedition 372 Preliminary Report for further details on the LWD acquisition program). Northern Hikurangi subduction margin SSEs recur every 1-2 years and thus provide an ideal opportunity to monitor deformation and associated changes in chemical and physical properties throughout the slow slip cycle. Sampling of material from the sedimentary section and oceanic basement of the subducting plate reveals the rock properties, composition, lithology, and structural character of material that is transported downdip into the SSE source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate all the way to the trench, indicating that the shallow thrust fault zone targeted during Expedition 375 may also lie in the SSE rupture area. Hence, sampling at this location provides insights into the composition, physical properties, and architecture of a shallow fault that may host slow slip. Expedition 375 (together with the Hikurangi subduction LWD component of Expedition 372) was designed to address three fundamental scientific objectives: (1) characterize the state and composition of the incoming plate and shallow plate boundary fault near the trench, which comprise the protolith and initial conditions for fault zone rock at greater depth and which may itself host shallow slow slip; (2) characterize material properties, thermal regime, and stress conditions in the upper plate above the core of the SSE source region; and (3) install observatories at an active thrust near the deformation front and in the upper plate above the SSE source to measure temporal variations in deformation, temperature, and fluid flow. The observatories will monitor volumetric strain (via pore pressure as a proxy) and the evolution of physical, hydrological, and chemical properties throughout the SSE cycle. Together, the coring, logging, and observatory data will test a suite of hypotheses about the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface.
    Type: Report , NonPeerReviewed
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  • 5
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    In:  [Poster] In: 97th Annual Meeting of the Geologische Vereinigung (GV) - The Oceans in the Earth System, International Conference 2007, 03.-05.10, Bremen .
    Publication Date: 2012-02-23
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  • 6
    Publication Date: 2012-02-23
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  • 7
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    In:  [Poster] In: 97th Annual Meeting of the Geologische Vereinigung (GV) - The Oceans in the Earth System, International Conference 2007, 01.-05.10, Bremen .
    Publication Date: 2012-02-23
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  • 8
    Publication Date: 2012-02-23
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  • 9
    Publication Date: 2017-08-08
    Description: The Masaya Caldera Complex has been the site of three highly explosive basaltic eruptions within the last six thousand years. A Plinian eruption ca. 2 ka ago formed the widespread deposits of the Masaya Triple Layer. We distinguish two facies within the Masaya Triple Layer from each other: La Concepción facies to the south and Managua facies to the northwest. These two facies were previously treated as two separated deposits (La Concepción Tephra and the Masaya Triple Layer of Pérez and Freundt, 2006) because of their distinct regional distribution and internal architectures. However, chemical compositions of bulk rock, matrix and inclusion glasses and mineral phases demonstrate that they are the product of a single basaltic magma batch. Additionally, a marker bed containing fluidal-shaped vesicular lapilli allowed us to make a plausible correlation between the two facies, also supported by consistent lateral changes in lithologic structure and composition, thickness and grain size. We distinguish 10 main subunits of the Masaya Triple Layer (I to X), with bulk volumes ranging between 0.02 and 0.22 km3, adding up to 0.86 km3 (0.4 km3 DRE) for the entire deposit. Distal deposits identified in two cores drilled offshore Nicaragua, at a distance of ∼ 170 km from the Masaya Caldera Complex, increase the total tephra volume to 3.4 km3 or ∼ 1.8 km3 DRE of erupted basaltic magma. Isopleth data of five major fallout subunits indicate mass discharges of 106 to 108 kg/s and eruption columns of 21 to 32 km height, affected by wind speeds of 〈 2 m/s to ∼ 20 m/s which increased during the course of the multi-episodic eruption. Magmatic Plinian events alternated with phreatoplinian eruptions and phreatomagmatic explosions generating surges that typically preceded breaks in activity. While single eruptive episodes lasted for few hours, the entire eruption probable lasted weeks to months. This is indicated by changes in atmospheric conditions and ash-layer surfaces that had become modified during the breaks in activity. The Masaya Triple Layer has allowed to reconstruct in detail how a basaltic Plinian eruption develops in terms of duration, episodicity, and variable access of external water to the conduit, with implications for volcanic hazard assessment.
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  • 10
    Publication Date: 2019-01-21
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