| 1. |
- Busby, CJ, et al.
(författare)
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The missing half of the subduction factory : shipboard results from the Izu rear arc, IODP expedition 350
- 2017
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Ingår i: International Geology Review. - : Informa UK Limited. - 0020-6814 .- 1938-2839. ; 59:13, s. 1677-1708
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- IODP Expedition 350 was the first to be drilled in the rear part of the Izu-Bonin, although severalsites had been drilled in the arc axis to fore-arc region; the scientific objective was to understand theevolution of the Izu rear arc, by drilling a deep-water volcaniclastic section with a long temporalrecord (Site U1437). The Izu rear arc is dominated by a series of basaltic to dacitic seamount chainsup to ~100-km long roughly perpendicular to the arc front. Dredge samples from these aregeochemically distinct from arc front rocks, and drilling was undertaken to understand this arcasymmetry. Site U1437 lies in an ~20-km-wide basin between two rear arc seamount chains, ~90-kmwest of the arc front, and was drilled to 1804 m below the sea floor (mbsf) with excellent recovery.We expected to drill a volcaniclastic apron, but the section is much more mud-rich than expected(~60%), and the remaining fraction of the section is much finer-grained than predicted from itsposition within the Izu arc, composed half of ashes/tuffs, and half of lapilli tuffs of fine grain size(clasts <3 cm). Volcanic blocks (>6.4 cm) are only sparsely scattered through the lowermost 25% ofthe section, and only one igneous unit was encountered, a rhyolite peperite intrusion at~1390 mbsf. The lowest biostratigaphic datum is at 867 mbsf (~6.5 Ma), the lowest palaeomagneticdatum is at ~1300 mbsf (~9 Ma), and the rhyolite peperite at ~1390 mbsf has yielded a U–Pb zirconconcordia intercept age of (13.6 + 1.6/−1.7) Ma. Both arc front and rear arc sources contributed tothe fine-grained (distal) tephras of the upper 1320 m, but the coarse-grained (proximal) volcani-clastics in the lowest 25% of the section are geochemically similar to the arc front, suggesting arcasymmetry is not recorded in rocks older than ~13 Ma.
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| 2. |
- Kars, Myriam, et al.
(författare)
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Impact of climate change on the magnetic mineral assemblage in marine sediments from Izu rear arc, NW Pacific Ocean, over the last 1 Myr
- 2017
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : ELSEVIER SCIENCE BV. - 0031-0182 .- 1872-616X. ; 480, s. 53-69
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Tidskriftsartikel (refereegranskat)abstract
- A rock magnetic study was conducted on upper Pleistocene marine sediments from International Ocean Discovery Program Expedition 350 Site U1437 in order to highlight the paleoenvironmental changes in the NW Pacific Ocean influenced by the East Asian monsoon regime. Remanent magnetization analyses, hysteresis properties, first-order reversal curves and low temperature magnetic measurements were carried out, along with electron microscope observations. The results indicate that coarse-grained (titano)-magnetite is the dominant magnetic phase in the magnetic mineral assemblage. Time-series analysis supports that this assemblage is modulated by global climate changes over the last 1 Myr. During the interglacial stages, magnetic minerals are more abundant; and are dominated by coarse-grained (titano)-magnetite of both terrigenous (likely from mainland China) and volcanic (Izu arc front, Japan) origin. During the glacial stages, the magnetic mineral content is lower, probably reflecting partial dissolution of (Ti)-magnetite, and the magnetic assemblage is composed of terrigenous coarse-grained (titano)-magnetite and of higher coercivity, presumably finer eolian particles (likely hematite) as a result of the enhancement of the winter monsoon in continental Asia. The magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals. Bulk organic-geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods. Additional X-ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources.
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