Meeting

Qiu Zhong¹, Jian Lin^{1, 2, 3}, Tingting Zheng³

Ling Chen^a,b, Jihao Zhu^*a, Fengyou Chu

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Lartaud F.^1, Nedoncelle K. ¹, de Rafelis M.², Le Bris N. ¹

1 UPMC Univ Paris 06, CNRS UMR 8222, LECOB, Observatoire Océanologique, F-66650 Banyuls-sur mer, France.

The study of hydrothermal sulfide in the Okinawa Through can help to uncover the hydrothermal mineralization characteristics of back-arc basins that are in the early expansion. In this study, the mineralogical characteristics of the sulfide from the midland and south of the Okinawa Through are carried out. First of all, using optical microscope and electron microscope to confirm the mineral composition, characteristics of crystal shape, syntagmatic relation and crystallization order. Analyze the chemical composition in virtue of electron probe.

Magnetic mapping is of increasing interest in studies of seafloor hydrothermal systems because such data can promote the understanding of the location and spatial extent of hydrothermal alteration zones. Previous studies reported both reduced and enhanced magnetization at hydrothermal fields of different tectonic settings, suggesting that the destruction and production of magnetic minerals are controlled by geological and tectonic background.

JiabiaoLi, AiguoRuan, XiongweiNiu, Minhui Zhao,Xuelin Qiu, Y. John Chen,Hanchao Jian

1) Second Institute of Oceanography, State Oceanic Administration, Hangzhou 3100122) South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301

3)Institute of Theoretical and Applied Geophysics, School of Earth and Space Science, Peking University, Beijing 100871 

The neotectono-sedimentary processes of the South China Sea abyssal basin have long been a puzzling issue and are still debated because of the lack of drilling evidence. In this study, we interpreted four multi-channel seismic profiles across the Southwest Sub-basin (SWSB), integrated for stratigraphic correlation with new drilling data from the Integrated Ocean Discovery Program （IODP） 349 Expedition. Results show that the Neogene sediments are divided into four stratigraphic units, each with distinctive seismic reflectors.

We investigate the characteristics of turbulent flows within near-bottom hydrothermal plumes at mid-ocean ridges through quantitative analysis of video images from manned submersibles using the Particle Image Velocimetry (PIV) method. High-quality video images of near-bottom hydrothermal vents were selected from the Data Library and Archives of the Woods Hole Oceanographic Institution (WHOI), consisting of multiple examples of vent fields in the Atlantic, Pacific, and Indian Oceans.

Marine magnetic lineation is an important media to interpret the age and spreading process of the oceanic crust. But there are many difficulties to identify the lineation from sea surface observation in a deep and narrow inactive ocean basin located in the low-latitude. Located in such a tectonic position, the spreading history of the Southwest subbasin of the South China Sea became a long time controversy. the deeptow data were able to increase observed anomaly amplitudes by a factor of ~4.

Oblique spreading occurs when the direction of relative motion between two rigid plates is oblique to the mid-ocean ridge trend. The main oblique spreading ridges are the Southwest Indian Ridge (Dick et al., 2003), Sheba Ridge (Lepvrier et al., 2002), Reykjanes Ridge (Dauteuil and Brun, 1993), Mohns Ridge (Wijk and Blackman, 2007), and Knipovich Ridge (Okino et al., 2002).

Oceanic crust undergoes rapid transformation in both its thermal and physical structure within the first 10 Ma from the ridge axis. Large departures in observed heat flow measurements from global depth and heat flow models reveal the importance of hydrothermal systems in heat dissipation and crustal alteration. Hydrothermal systems have the greatest influence on young oceanic crust due to its high porosity and permeability and low sediment cover. Much is still unknown about the scale and processes involved, especially the interaction between the solid Earth and the oceans.

We investigate the relationship among hotspot influence, local magma supply, and asymmetric topography and crustal structure of the conjugate flanks of the slow-spreading Mohns Ridge. Residual mantle Bouguer anomaly (RMBA) was calculated by subtracting from free-air gravity the predicted attractions of water-sediment, sediment-crust, and crust-mantle interfaces as well as the effects of lithospheric cooling.

The NERC-funded joint geophysical and oceanographic OSCAR project aims to develop understanding of the interactions between relatively young oceanic crust and the overlying abyssal ocean through heat transfer and fluid flow. The movement of hydrothermal fluids through the oceanic crust causes changes in its structure and composition: circulating heat, precipitating minerals in open cracks and fractures, and forming alteration fronts which influence permeability and seismic properties, though little is known about the rate and extent of these processes.