Magnetic anomalies in the Shikoku Basin: a new interpretation

Chamot‐Rooke, Nicolas; Renard, Vincent; Pichon, Xavier Le

doi:10.1016/0012-821x(87)90067-7

Cited by 112 publications

(83 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Present-day heat flow is at a maximum near Site 808, and this is due, at least in part, to its location near the crest of the extinct spreading ridge (Ashi and Taira, in press). The last phase of volcanic activity in the Shikoku Basin ended about 12 Ma (Chamot-Rooke et al, 1987). Empirical models of thermal decay for oceanic lithosphere predict heat-flow values of 136 mW/m 2 (Parsons and Sclater, 1977) to 145 mW/m 2 (Lister, 1977) for a crustal age of 12 Ma.…”

Section: Subunit Ivbmentioning

confidence: 99%

“…The stratigraphic interval in question contains nannofossils that are 11.1 to 12.2 Ma in age (Shipboard Scientific Party, 1991b). According to Chamot-Rooke et al (1987), the central region of Shikoku Basin experienced a final phase of highly disorganized volcanic activity between 15 and 12 Ma. Thus, the sediments could share some of the characteristics of ophiolite-related umbers (e.g., Robertson and Hudson, 1974), which are broadly analogous to the metalliferous sediments associated with hydrothermal circulation at many mid-ocean spreading centers (e.g., Bonatti, 1975).…”

Section: Hydrothermal Anomalymentioning

confidence: 99%

See 1 more Smart Citation

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Underwood¹,

Pickering²,

Gieskes³

et al. 1993

Proceedings of the Ocean Drilling Program

View full text Add to dashboard Cite

This paper presents a synthesis of data from X-ray diffraction analyses of clay minerals and X-ray fluorescence analyses of bulk mudstones from Ocean Drilling Program Site 808. The samples come from three closely spaced holes drilled through the toe of the Nankai accretionary prism offshore Shikoku, Japan. Detrital assemblages of clay minerals are unusually uniform throughout the Nankai trench-wedge facies. Illite is the most abundant detrital clay mineral, followed by chlorite, smectite, and traces of kaolinite. Relative percentages of smectite increase within the upper subunit of the Shikoku Basin stratigraphy. This subunit contains abundant layers of volcanic ash, and the corresponding change in clay mineralogy probably was caused by synvolcanic weathering in source areas during the Pliocene, together with in-situ alteration of disseminated glass shards within the Shikoku Basin.At a depth of ~555 mbsf, the detrital and/or authigenic smectite component begins its transformation to illite/smectite mixed-layer clay. With increasing depth below this horizon there is a monotonic increase in illite interlayers. The onset of illitization occurs at an estimated temperature of ~65°C. Ordered (R = 1) illite/smectite interlayering first appears at depths of -1220 mbsf (<2-µm size fraction) and -1100 mbsf (<0.2-µm size fraction). The depth interval of the smectite-to-illite transformation coincides with a reduction in pore-water chlorinity; however, the absolute abundance of smectite appears to be insufficient to account for the changes in aqueous chemistry via in-situ dehydration reactions. Instead, significant volumes of diluted pore water probably were transported to Site 808, either from sources located deeper in the accretionary prism (where bulk mudstone porosities are lower) or from lateral sources where mudstones originally deposited in the Shikoku Basin may contain higher percentages of smectite. Significantly, we did not detect any anomalies in clay mineralogy or clay-mineral diagenesis within or near the décollement zone (945-964 mbsf).X-ray fluorescence analyses show that hemipelagic muds and mudstones at Site 808 are chemically uniform throughout most of the section. There are no geochemical perturbations, for example, within the décollement zone. Data from interbeds of volcanic ash demonstrate that the chemical effects of mud/ash dissemination and/or in-situ alteration of pyroclastic material are limited. In addition, ash layers are chemically heterogeneous within Unit III and Subunit IVa, which indicates that tephra was transported from a variety of andesitic to rhyolitic sources on the Japanese Islands during the Pliocene. In contrast, Miocene rocks of Unit V display a clear chemical divergence (little mixing) between rhyolitic tuffs and interbeds of multicolored mudstone.The most significant geochemical anomaly at Site 808 occurs well below the décollement zone between 1087 and 1111 mbsf. Variegated mudstones in this interval contain unusually high ratios of MgO/Al 2 O 3 , Fe total /Al 2 O 3 , Mn...

show abstract

Section: Subunit Ivbmentioning

confidence: 99%

Section: Hydrothermal Anomalymentioning

confidence: 99%

Sediment Geochemistry, Clay Mineralogy, and Diagenesis: A Synthesis of Data from Leg 131, Nankai Trough

Underwood¹,

Pickering²,

Gieskes³

et al. 1993

Proceedings of the Ocean Drilling Program

View full text Add to dashboard Cite

show abstract

“…In the southwest Japan arc the relatively young Shikoku basin (-20 Ma) [Chamot-Rooke et al, 1987;Seno and Maruyama, 1984] subducts northwestward (Fig. la), which is suggested to be started at -15 Ma [Hibbard and Karig, 1990;Seno and Maruyama, 1984].…”

Section: Introductionmentioning

confidence: 99%

Heat flow in the Southwest Japan Arc and its implication for thermal processes under arcs

Furukawa

Shinjoe

Nishimura

1998

Geophysical Research Letters

View full text Add to dashboard Cite

Abstract. We present 35 new heat flow measurements for the Kinki district in the eastern part of the southwest Japan arc. Heat flow distribution in this region shows zonal structure parallel to the trench. In the across-arc heat flow profile there are two high heat flow peaks: one is located at the volcanic front and the other is between the south coast of this arc and the trench. The high heat flow at the volcanic front is probably caused by the induced flow in the mantle wedge. The high heat flow off the south coast is located in the zone where slab depth is 10-20 km, and is immediately to the ocean side of the boundary at which P-wave velocity increases landward in the upper crust. We thus consider the high heat flow is caused by the uplift of accreted materials along the backstop in the accretionary prism, assuming that seismic velocity is an indicator of rigidity of rocks. The upward flow velocity is estimated to be -1 mm/yr using a simple one-dimensional erosion model, which is consistent with that estimated from the present heights of marine terraces.

show abstract

“…This result confirms the presence of a high heat flow anomaly on the Kashinozaki Knoll. However, constraints on the age of the oldest sediments at the base of C0012 are compatible with Kashinozaki Knoll having the same age (about 20 Ma) as the lithosphere in this part of the Shikoku Basin as indicated from magnetic anomalies (Chamot-Rooke et al, 1987;Okino et al, 1994). When compared with models, heat flow at Site C0011 appears slightly lower that the heat flow expected for a 20-Ma lithosphere (Kinoshita et al, 2008) but can be fit within uncertainties once the effect of sedimentation in the trench is taken into account (Marcaillou et al, 2012).…”

Section: Heat Flow and Convectionmentioning

confidence: 66%

“…At the Kumano transect across the Nankai Trough, the velocity between the Philippine Sea Plate and the forearc is 4.5-5.5 cm y -1 along an azimuth of 305 q ± 3 q (Seno et al, 1993;Mazzotti et al, 2001;DeMets et al, 2010;Loveless and Meade, 2010) down an interface dipping 3 q -7 q (Kodaira et al, 2000b). The subducting lithosphere of the Shikoku Basin was formed by backarc spreading during a time period of 15-25 Ma (Chamot-Rooke et al, 1987;Okino et al, 1994). The three major seismic stratigraphic sequences identified in the northern Shikoku Basin are the lower and upper Shikoku Basin facies and local spill-over of Quaternary trench-wedge turbidites (Ike et al, 2008a).…”

Section: Geologic Setting and Previous Workmentioning

confidence: 99%