SUMMARY Two years of continuous recordings of ambient seismic noise observed at 354 stations in South China from 2009 to 2010 are used to estimate Rayleigh wave group and phase velocity maps from 6 to 40 s period. These results are merged with Rayleigh wave phase velocity maps from 25 to 70 s period derived from earthquakes in the same time frame. Eikonal tomography generates the dispersion maps, which, by Monte–Carlo inversion, are used to estimate a 3‐D Vsv model of the crust and upper mantle down to a depth of 150 km across all of South China with attendant uncertainties. A clear image emerges of the ‘West Yangtze Block’, a region of the western Yangtze Craton characterized by relatively thick crust (∼40 km) overlying a seismic mantle lithosphere that extends to at least 150 km that may have been the nucleus for the formation of the Yangtze craton in the Archean and may present a present‐day obstacle to the eastward expansion of Tibet. The West Yangtze Block contrasts with the thinner crust (∼30 km) and mantle lithosphere (∼70–80 km) beneath the eastern Yangtze Craton and South China Foldbelt. These observed differences are consistent with processes associated with flat slab subduction in the Mesozoic that may have eroded the lithosphere of the eastern Yangtze Craton and the South China Foldbelt.

Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.LI ET AL.

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