南海北部隱沒-碰撞過渡帶的地體構造及沈積研究

The Taiwan orogen has formed by
oblique collision from north to south
between the Luzon Arc and the Chinese
margin since about 5 Ma. West of the
Taiwan orogen the western Taiwan
foreland basin has formed during the
Late Pliocene as the flexural response of
the Eurasian plate to loading of the
Taiwan orogen. Tectonics of the South
China Sea near southern Taiwan
exhibits a progressive northward
transition from oceanic subduction
along the Manila Trench to the incipient
collision zone offshore southern Taiwan
where the continental crust of the
Eurasian plate subducts beneath the
Philippine Sea plate. North of 21 N, dip
angles of the Benioff zone incease up to
80 degrees in the incipient collision
zone where the Manila Trench becomes
shallower and gradually loses its
morphological identify and finally
mergers into the nearly N-S trending
Penghu Submarine Canyon. Convegent
tectonics in the initial collision mainly
represented by the beginning of flexure
of the Chinese margin with westward
migrating overthrust belt of Taiwan,
forming two distinct basins. On the
3
Chinese side, the marginal sea basin
becomes smaller and is underlain by the
South China Sea Slope but on the
Taiwan margin a wedge-top basin has
formed above the frontal thrust sheets of
the Taiwan orogenic wedge. Sediments
derived from the Taiwan orogen
progressively overlie strata of the
Chinese margin, resulting in increasing
sediment thickness and shallowing of
the floor of the wedge-top basin from
south to north. Sedimentary facies
shows that offshore deep-water mud is
gradationally overlain by sahllow
marine sediments. Sediments of the
wedge-top basin are being actively
deformed into mud diapiric intrusions
and a series of west-vergent thrusts and
folds and associated piggyback basins,
resulting in irregular topography of sea
floor with alternating sea ridges and
troughs. Pliocene-Quaternary strata of
the Chinese margin are little deformed
by the westward compression induced
by the arc-continent collision in the
southern Taiwan. The slope profile of
the Chinese margin is characterized by a
sigmoidal curvature, representing a
typical primary depositional setting of
the passive margin. Slope canyons occur
mainly on the upper slope and cut sea
floor, resulting in irregular topography
and representing effects of erosion.