T. Fujiwara et al., MORPHOLOGICAL-STUDIES OF THE AYU TROUGH, PHILIPPINE-SEA CAROLINE PLATE BOUNDARY, Geophysical research letters, 22(2), 1995, pp. 109-112
The Ayu Trough lies on the southern boundary between the Philippine Se
a Plate and Caroline Plate. Although this trough may be the best place
to study the evolution and kinematics of the Philippine Sea Plate, th
e origin and evolution of this trough are poorly understood. Our geoph
ysical and morphological surveys in the northern part of the Ayu Troug
h revealed that the trough shares morphological similarities with slow
-spreading mid-ocean ridges. The seafloor ages and an average spreadin
g rate of the trough were inferred from the average length of the ridg
e segments, distribution of sediment thickness, and basement subsidenc
e. Based on the seismic section at 3 degrees 30'N, the opening of the
trough started about 25 Ma with an average half-spreading rate 4.1 mm/
yr. This spreading rate is much slower than some previous estimates. T
he present magma production rate and activity of the trough is estimat
ed to be even lower than the 25 m.y. average. The seafloor depth of th
e trough axis and relief of the axial valley are approximately twice a
s deep as that of active mid-ocean ridges. The trough axis valley is c
overed with sediment in contrast with the axial valleys of active mid-
ocean ridges. Sedimentation at the trough axis shows that the spreadin
g rate has been quite slow for the last 2.5 Ma.