Geolgoical investigationson the Oceanic crust of the philPPines sea

This report deals with the preliminary results obtained by the
international working group of the LG.C.P. project "Ophiolits" ,
during their 3rd session in which the author participated .
The work has been carried out with help of the USSR's Research vessel;
"Dmitry Mendeleev "during June - August 1976, which enabled the
inference of some of the structure and rock types of the crust, of
phlilippine ,Sea.
The philippine Sea has a ragged bottom, and is very complicated
from the tectonic point of view. It is dissected by the Kyushu-palau ridge
to eastern and western sectors:
In the eastern part, four trenches ; palau, Yap, Mariana and Bonin, and
several Island Arcs, four Marginal Seas, and west Mariana ridge are
situceed.
The western part comprise phillipine and Ryuku trenches and phillipine
Basin , which is tectonically still , not clear.
The eastern part is covred by the sediments of the first layer of oceanic
crust, with the oldest rock having an Eocene age. The morphostructurs,
magnetic anomalis, and the central philiphine fault which cut through. This
part have an uniform N-SE trend.
The kyushu-Balau ridge, cuts through all the tectonic elements of
the philippine Sea, and make an acute angle with Central phillipine Fault.
The rock samples obtained from this ridge show that this ridge has been
an Island Are, and hase sinked at late olifocene. The heat flow is very
low in this zone .
The parece-Vela Basin, SitUated at the east of kyushu-palau
ridge has a particular structure . It has a ragged bottom, and the magnetic
anomalies have a southern trend, the heat flow is above normal at its
northern part. No sediments older than Miocene is recorded.
The Morphology of the Yap structeral Zone is similar to those of
Mid-Oceanic ridges . Rocks from second and third layers of Oceanic crust
were dredged here.
The Mariana Trench has an assvmetric structure. The easterR wall
(Ocean side) is formed of basalts and diabases, while the western wall
show a complete section of an oceanic crust.
Rocks obtained from the bottom of the philippine sea are similar
to those Ophiolites which are actually found in different continents• The
results of the muineralogy ,studies and the chemical analyses of
the Ophiolites are given.