GENESIS OF THE PHILIPPINE ISLANDS The Philippine Archipelago  Emerged because of the dynamic shifting and collision of plates  Welded together in an island arc and punctuated by episodic and extensive magmatic activity  Mixture of lithospheric blocks of different ages that came from far away origins  Plate Tectonics explains where and when these terranes were formed and how they were transported to their present site Four Major Plates in the geologic and tectonic evolution of the Philippines 1. Continental Eurasian Plate 2. Indian-Australian Plate 3. Oceanic Pacific Plate 4. Philippine Sea Plate 100-65 MYA (Late Cretaceous Period)  Proto-Philippine Island arc o Volcanic and ophiolitic terranes of eastern Philippines (Bicol, Leyte, East Mindanao) 65-50 MYA (Early Cenozoic Era)  East-to-west spreading of the South China Sea floor moved the Philippines away from the mainland China toward the Pacific Ocean 55-35 MYA (Eocene Epoch)  Micro-continental terranes that will later become North Palawan, Mindoro and Zamboanga still rimmed the margins of southeastern Eurasia  Middle of Eocene – magmatic activity built the volcanic terrains of Luzon, Visayas and central Mindanao  The Philippines was divided into 3 separate island arcs: 1. Luzon arc – whose remains are found in the Sierra Madre ranges and are moving down, possibly toward Samar 2. Halmahera arc – forming the East and Central Mindanao Cordilleras 3. Sangihe arc – forming the Zamboanga peninsula and the Kudarat plateau in western Mindanao 25-10 MYA (Miocene Epoch)  Formation of the Philippine Fault  Luzon rotated 40-50˚ counterclockwise while Panay rotated 20˚ clockwise  Beginning of subduction in the Manila trench 5-2 MYA (Plio-Pleistocene Epoch)  Archipelago settled in its present position o Basin expanded and developed into flatlands and rolling hills accompanied by volcanic activity o Landmass expanded due to fluctuations of sea level o When sea level was low, land bridges were exposed, connecting Palawan- Borneo with central and western Southeast Asia