International Ocean Discovery Program; Expedition 368X preliminary report; South China Sea rifted margin; testing hypotheses for lithosphere thinning during continental breakup; drilling at the South China Sea rifted margin; 15 November-8 December 2018

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doi: 10.14379/iodp.pr368X.2019
Author(s): Childress, Laurel; Briais, Anne; Deng, Jia-Ming; Lin, Jian; Nirrengarten, Michael F. R.; Qiu Ning; Satolli, Sara; Sun Zhen; Yi Liang; Zhong Lifeng
International Ocean Discovery Program, Expedition 368X Scientists, Colleg Station, TX
Author Affiliation(s): Primary:
Texas A&M University, International Ocean Discovery Program, College Station, TX, United States
Geosciences Environnement Toulouse, France
Taiwan Ocean Research Institute, Taiwan
Woods Hole Oceanographic Institution, United States
Institut de Physique du Globe de Strasbourg, France
Chinese Academy of Science, Key Laboratory of Marginal Sea Geology, China
University of Chieti-Pescara, Italy
South China Sea Institute of Oceanology, China
Tongji University, China
Sun Yat-Sen University, China
Source: Preliminary Report - International Ocean Discovery Program, Vol.368X, 27p. Publisher: International Ocean Discovery Program, College Station, TX, United States. ISSN: 2372-9562
Note: In English. 33 refs.
Summary: International Ocean Discovery Program (IODP) Expedition 368X is the third of three cruises that form the South China Sea Rifted Margin program. Expeditions 367, 368, and 368X share the common key objectives of testing scientific hypotheses of breakup of the northern South China Sea (SCS) margin and comparing its rifting style and history to other nonvolcanic or magma-poor rifted margins. Four primary sites were selected for the overall program: one in the outer margin high (OMH) and three seaward of the OMH on distinct, margin-parallel basement ridges informally labeled Ridges A, B, and C from north to south. The ridges are located in the continent-ocean transition (COT) zone ranging from the OMH to the interpreted steady-state oceanic crust (Ridge C) of the SCS. The main scientific objectives include 1. Determining the nature of the basement in crustal units across the COT of the SCS that are critical to constrain style of rifting, 2. Constraining the time interval from initial crustal extension and plate rupture to the initial generation of igneous ocean crust, 3. Constraining vertical crustal movements during breakup, and 4. Examining the nature of igneous activity from rifting to seafloor spreading. In addition, sediment cores from the drill sites targeting primarily tectonic and basement objectives will provide information on the Cenozoic regional environmental development of the Southeast Asia margin. Expedition 368X was planned to reoccupy a site started during Expedition 368. Because of repeated breakdowns of the low clutch diaphragm in the drawworks, Hole U1503A was abandoned after installing casing to 991.5 m. Despite this setback to Expedition 368 and the South China Sea Rifted Margin program, Hole U1503A was completed during Expedition 368X. The overarching scientific goal of IODP Expeditions 367 and 368 was to unveil the mechanisms of continental breakup at the northern SCS margin from rifting through steady-state spreading. A key operational objective of Site U1503 was to sample the lowermost ∼300 m of sediments on top of basement to constrain the age and subsidence history of the crust at this location, the timing of normal faulting, and the environment of the early half-graben fill. A second important goal was to sample at least 100 m of the igneous basement. Deep representative sampling of the igneous material at this site will provide an important reference frame for the modeling of breakup and early ocean spreading. In Hole U1503A, the sediment sequence was cored with the rotary core barrel (RCB) system from 995.1 to 1597.84 m (602.74 m penetration; 128.01 m recovered; 21%) and then the underlying basement was continuously cored from 1597.84 to 1710.1 m (112.26 m penetration; 47.91 m recovered; 43%). Although logging deeper than 991.5 m (bottom of casing) was not possible because of unstable hole conditions, Hole U1503A was logged with the Vertical Seismic Imager in the cased portion of the hole. No days were lost to waiting on weather, and the only mechanical downtime was a 1.5 h period when an electrical malfunction caused the top drive to shut down for repairs. Expedition 368X successfully completed the operational objectives in Hole U1503A that were abandoned during Expedition 368. In the SCS margin science program, material recovered during Expedition 368X will contribute toward meeting the four specific objectives of Expeditions 367 and 368. Postexpedition research on the sediments and basalt recovered from Hole U1503A will allow for determination of emplacement age and geochemical analyses of rock composition and assessment of melting processes and age of crystallization. The combination of such analyses will contribute to geochemical or thermomechanical modeling that will constrain mantle origin and melting processes leading to the formation of these basalts.
Year of Publication: 2019
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Basalts; Basement; Biostratigraphy; Boreholes; Cenozoic; Chemostratigraphy; Continental margin; Cores; Crust; Crustal thinning; Expedition 368; Expedition 368X; Geophysical methods; Geophysical profiles; Geophysical surveys; IODP Site U1503; Igneous rocks; International Ocean Discovery Program; Lithostratigraphy; Magnetostratigraphy; North Pacific; Northwest Pacific; Oceanic crust; Pacific Ocean; Physical properties; Plate tectonics; Rifting; Sea-floor spreading; Sedimentary rocks; Seismic methods; Seismic profiles; South China Sea; Surveys; Tertiary; Volcanic rocks; Well logs; West Pacific
Coordinates: N180900 N180900 E1161900 E1161900
Record ID: 2019012114
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.