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| :::Geology Of The Hengchun Peninsula |
Geologic History
The Miocene turbiditic rocks forming the backbone of the Hengchun Peninsula were deposited in a basin on the
southeastern side of the Chinese passive continental margin. All the turbiditic sediments were transported
from west to east or from north to south into the basin. Clastic sedimentation originated mainly from the
continental margin in early Miocene time. In middle Miocene time, ophiolitic fragments (mafic to ultramafic
oceanic materials) increased suddenly in the turbidite deposits. These magmatic materials were derived
chiefly from the South China Sea. A large amount of continental detrital sediments were deposited in this
basin in late Miocene time, but were still mixed with oceanic magmatic detritus. These magmatic constituents
increased again at the end of Miocene sedimentation, possibly derived from the same oceanic rocks or from
reworking of middle Miocene magmatic components.
According to Page and Lan (1983), the ophiolitic materials were incorporated in an accreting wedge on the
western edge of the Philippine Sea plate during the eastward subduction of the South China Sea on the
Asiatic continental margin. At the beginning of plate collision, the wedge must have become emergent and
these ophiolitic rocks were subaerially eroded and were deposited as pebbles in basins on the west and the
east of the wedge separately. The ophiolitic materials in the Kenting melange as well as in the Lichi
melange were thus formed in a similar manner.
Pelletier and Stephan (1986) suggested a different scenario. They indicated that the South China Sea opened
along a spreading center from 32 to 12 Ma in an east-west direction but cut by a series of north-south
transform faults. During this period, clastic sediments from the Chinese continent were deposited on the
young Chinese passive margin. In middle Miocene time, a slice of oceanic crust from the South China Sea was
abducted upon the Chinese passive continental margin along a north-south transform fault. As a result of
abduction, ophiolitic pebbles and blocks slumped and slipped down the slope in the Hengchun area. From
middle Miocene to late Miocene, the basin subsided steadily by continuous arrival of Asian detrital
sediments. At that time, the South China Sea oceanic crust was being subducted underneath the Luzon Arc
along the Manila Trench. The Luzon Arc began to collide with the Asiatic continental margin in late Miocene
time in the northern part of Taiwan. The ophiolites were then uplifted, exposed and eroded. The erosional
debris were added to the turbiditic sediments of the Hengchun Peninsula. Collision became more intense
toward the end of Miocene. A west-vergent deformation event affected the margin and created a series of
imbricate thrust sheets. As a result of uplift caused by accretion, southward gravity sliding from the
uplifted Central Range occurred in the Hengchun Peninsula. The collision extended to the southern part of
Taiwan at the Mio-Pliocene boundary, at which time the turbidities on the passive margin were folded and
thrust westward. The Kenting melange was formed in front of the thrust beneath the sole of a large nape. In
the opinion of Pelletier and Stephan (1986), the main episode of deformation on the Hengchun Peninsula is
latest Miocene or near the Mio-Pliocene boundary.
The Kenting Park anticline was formed in this main orogenic stage. If the age of the Kenting melange is late
Pliocene or younger as suggested by T.C, Huang and others (1983), the main orogenic episode is late Pliocene
to Pleistocene, This age corresponds with the Penglai Orogeny which is the major orogenic movement in Taiwan.
After the main orogenic episode, the late Pliocene to Pleistocene Maanshan Formation and Hengchun Limestone
were deposited unconformably over the Miocene strata. Gentle folds in the younger sediments demonstrate that
recent deformation is still going on, accompanied by slow uplift of the hills and mountains.
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