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GEOTECTONIC DEVELOPMENT OF THE PHILIPPINES

FROILAN C. GERVASIO
National Research Council of the Philippines

 

 

 

 

ABSTRACT



The geotectonic development of the Philippines involves at least two long-term and several short-term cycles of crustal reorganization traceable from Paleozoic to Recent.

The long-term cycles are manifested by the reorganization of the preexisting crustal plate into geosynclinal systems and (or) mobile belts and their gradual transformation into platforms. The gradual change into platforms, which involved a series of short-term cycles, is essentially characterized at depths, by an ongoing crystallization of primary magma generated during the initial geosynclinal stage.

The short-term cycles are demonstrated by the cyclic occurrences of transgression sedimentation followed by regression and orogenic movement yielding mountain systems and (or) elements of island arcs and emplacement at near surface of quasi-solid plutons, usually within geosyncline/platform background.

The span of time covering the better known Mesozoic-Tertiary geotectonic cycle is about 100 to 130 million years while that of the Paleozoic seems much longer. The short-term cycles involved periods of 10 to 60 million years becoming shorter from geosynclinal to platform stage.

The development of various cycles of activity are considered effects of reorganization of the earth’s interior region which seems to have coeval relationship to the earth’s orbital movement around the center of the Milky Way galaxy.

The essential differences of crustal development between the Paleozoic anal the Mesozoic-Tertiary geotectonic cycles may also be premised on the possible differences in orbital radius and speed of travel of the earth during the two cycles.

The recognized formation of Barrovian type metamorphics and granites during Paleozoic, being of an earlier orbital cycle, could have been due to weaker gravitational field setting and slower pace of orbital travel of the earth. Under such conditions conducive to more pronounced magmatic differentiation, anatexis and regional metamorphism even at shallow depths were developed in the presence of strong contractive force and greater hydrostatic pressure.

 

 

 

 

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