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Research and Development Center for Ocean Drilling Science (ODS)

Topics

ODS Open Seminar

Date/Time: Friday,July 21 15:00-17:00
Venue: Seminar room 3, Marine Ecosystem Research Building, Yokosuka HQ

Presenter 1: Dr. Xiaodong Ma(Stanford University)
Title: Temporal- and Spatial- variations of in-situ stress: a case study in the Woodford shale and modeling through viscous relaxation
Abstract:
We conducted a geomechanical case study to investigate the variations of in-situ stress and formation properties along two horizontal wells in the Woodford shale (WDFD), Oklahoma. The minimum horizontal stress (Shmin) indicated by the Instantaneous Shut-In Pressure (ISIP) of each frac stage, varies dramatically from stage to stage along both WDFD wells, which correlates well with the clay content. Variations of Shmin with lithology in these litho-facies can be plausibly explained by the viscous stress relaxation, which results in the diminishing difference between Sv and Shmin as the compliant component content increases. Prediction of Shmin through a viscoelastic model is in qualitative agreement with the measured ISIP values.

Presenter 2: Yoshihiko Tamura(ODS, JAMSTEC)
Title: Tairiku Project in the Kermadec Arc
Abstract:
A new study presents the straightforward but unexpected relationship, which relates crustal thickness to magma type in the Izu-Ogasawara (Bonin) and Aleutian oceanic arcs (Tamura et al., 2016). Volcanoes along the southern segment of the Izu-Ogasawara arc and the western Aleutian arc (west of Adak) are underlain by thin crust (10-20 km). In contrast those along the northern segment of the Izu-Ogasawara arc and eastern Aleutian arc are underlain by crust ~35 km thick. Interestingly, andesite magmas dominate eruptive products from the former volcanoes and mostly basaltic lavas erupt from the latter. The Kermadec arc is a typical oceanic arc produced by subduction of the Pacific Plate beneath the Australian Plate. The water depths between volcanoes change drastically from the northern segment (~1,000 m) to the southern segment (~3,000 m) of the Kermadec arc (Fig. 4). The crustal thickness of the Kermadec arc is not independently known. However, based on the water depth between arc front volcanoes, the crustal thickness of the northern and southern segments of the Kermadec arc cold be ~30 km and ~15 km thick, respectively. The Kermadec arc is the perfect place to see the relationships between crustal thickness and magma type and to examine the hypothesis presented through the study of the Izu-Ogasawara and Aleutian arcs.

Presenter 3: Kan-Hsi Hsiung(ODS, JAMSTEC)
Title: The South China Sea Rifted Margin program (SCSII), IODP Expedition 367 and 368: An introduction and preliminary results of the project
Abstract:
Expedition 367 and 368 are two consecutive cruises that form the South China Sea Rifted Margin program (SCSII). The South China Sea (SCS) margin is an accessible and well-imaged location where drilling of syn-rift sediment and underlying basement will provide key constraints on the processes of rifting and eventual rupturing of the continental lithosphere during breakup at a highly extended rifted margin. The key objective of the two expeditions is testing scientific hypotheses of breakup of the northern SCS margin and comparing its rifting style and history to other non-volcanic or magma-poor rifted margins. The two-expedition cored and logged a transect of drill sites across the continent–ocean transition (COT) of the northern SCS margin was implemented to understand the processes of rifting, eventual rupturing of the continental crust, and the onset of igneous oceanic crust at a highly extended rifted margin. Expedition 367 successfully completed operations at two sites (Sites U1499 and U1500), and Expedition 368 operated at five sites (Site U1501 - U1505). The secondary expedition objectives addressing the environmental history of the SCS and the southeast Asia received more focus than planned because these were located in shallower water depths and required less penetration depths. Efforts were made at every drill site to correlate the core with the seismic data and seismic stratigraphic unconformities interpreted within the Eocene to Plio-Pleistocene sedimentary sequence prior to drilling. The pre-drilling interpretation of ages of these unconformities was in general confirmed by drilling results. The preliminary results can probably be determined into four units: middle Eocene, late Eocene, early Oligocene, late Oligocene to present. The two expeditions together provided solid evidence for a process of breakup that included vigorous syn-rift magmatism as opposed to the often favored interpretation of the SCS margin as a magma-starved margin.

Contact: Research and Development Center for Ocean Drilling Science (ODS)
Saneatsu Saito +81-45-778-5265 E-mail