التفاصيل البيبلوغرافية
| العنوان: |
Expedition 368X summary. |
| المؤلفون: |
Childress, L. B., Alvarez Zarikian, C. A., Briais, A., Dadd, K. A., Deng, J.-M., Höfig, T. W., Huang, X.-L., Li, B., Lin, J., Liu, C., Liu, Z., Nirrengarten, M. F. R., Peate, D. W., Qiu, N., Satolli, S., Stock, J. M., Sun, Z., van der Zwan, F. M., Xiang, R., Yi, L. |
| المصدر: |
Proceedings of the International Ocean Discovery Program, Expedition Reports; 9/28/2018, Vol. 367/368, p1-16, 16p |
| مستخلص: |
International Ocean Discovery Program (IODP) Expedition 368X is the third of three expeditions 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. Seismic profiles across the margin in the IODP study area show from continent to ocean a wide extended continental margin, an outer margin high (OMH), and a continent–ocean transition (COT) zone displaying different ridges of unknown nature. Four primary sites were selected for the overall program: one in the 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 COT zone ranging from the OMH to the interpreted steady-state oceanic crust 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 the 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. Also, 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 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. A 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 Versatile 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 completed the operational objectives in Hole U1503A that were started 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. Postcruise research on the sediments and basalt recovered from Hole U1503A will allow for determination of emplacement age, 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. [ABSTRACT FROM AUTHOR] |
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