Expansion of the South China Sea basin:Constraints from magnetic anomaly stripes,sea floor topography,satellite gravity and submarine geothermics

The widely distributed E-W-trending magnetic anomaly stripes in the central basin and the N-Etrending magnetic anomaly stripes in the southwest sub-basin provide the most important evidence for Neogene expansion of the South China Sea.The expansion mechanism remains,however,controversial because of the lack of direct drilling data,non-systematic marine magnetic survey data,and irregular magnetic anomaly stripes with two obvious directions.For example,researchers have inferred different ages and episodes of expansion for the central basin and southwest sub-basin.Major controversy centers on the order of basinal expansion and the mechanism of expansion for the entire South China Sea basin.This study attempts to constrain these problems from a comprehensive analysis of the seafloor topography,magnetic anomaly stripes,regional aeromagnetic data,satellite gravity,and submarine geothermics.The mapped seafloor terrain shows that the central basin is a north-south rectangle that is relatively shallow with many seamounts,whereas the southwest sub-basin is wide in northeast,gradually narrows to the southwest,and is relatively deeper with fewer seamounts.Many magnetic anomaly stripes are present in the central basin with variable dimensions and directions that are dominantly EWtrending,followed by the NE-,NW- and NS-trending.Conversely such stripes are few in the southwest sub-basin and mainly NE-trending.Regional magnetic data suggest that the NW-trending Ailaoshan-Red River fault extends into the South China Sea,links with the central fault zone in the South China Sea,which extends further southward to Reed Tablemount.Satellite gravity data show that both the central basin and southwest sub-basin are composed of oceanic crust.The Changlong seamount is particularly visible in the southwest sub-basin and extends eastward to the Zhenbei seamount.Also a low gravity anomaly zone coincides with the central fault zone in the sub-basin.The submarine geothermic distribution demonstrates that the southwest sub-basin has a higher geothermal value than the central basin,and that the central fault zone is defined by a low thermal anomaly.This study suggests that NW-SE expansion of the southwest subbasin is later than the N-S expansion of the central basin with the sub-basin extending into the central basin and with both expansions ending at the same time.The expansion of southwestern sub-basin,similar to the Japanese Sea,is likely caused by left-lateral strike slip on the central fault zone in the South China Sea,which may have significance for finding oil and gas in this region.

Non-Isothermal Dissolutive Wetting of Al-Ni and Cu-Ni Alloy Nanodroplets on a Cu(100)Substrate

The kinetics of Al-Ni and Cu-Ni nanodroplets spreading over a Cu substrate in the presence of a temperature difference between them is studied via molecular dynamics simulations.The simulations show that significant dissolution reactions occur for the two systems and there is no precursor film generated during spreading.The spreading rate significantly increases when nanodroplets contain less Ni atoms in the Al-Ni/Cu wetting systems.However,a different trend is observed in the Cu-Ni/Cu wetting systems.The spreading rate remains unchanged regardless of the ratio of Cu to Ni atoms owing to the fact that Cu and Ni have almost the same lattice constants.The simulations also demonstrate that,because of the temperature gradient between the nanodroplet and substrate,local solidification takes place in the later spreading stage,which significantly hinders spreading.Due to the mismatch of lattice constants between Al and the Cu atoms in the Al-Ni/Cu wetting systems,hexagonal closest packed(hcp),body centered cubic(bcc),and face centered cubic(fcc)arrangements of atoms are observed when the Al-Ni nanodroplets solidify completely,whereas there is only a fcc arrangement in the Cu-Ni/Cu wetting systems.