Overview
This lecture discusses the geologic history and structure of the Philippine Island Arc system, focusing on earthquake and volcanic activity, as well as the origins of various island groups.
Philippine Island Arc System: Basics
- The Philippines is an island arc system located between the Eurasian Sunderland and the Philippine Sea Plate.
- The islands are composed of igneous, sedimentary, and metamorphic rocks formed through complex geologic processes.
- The Philippine archipelago consists of more than 7,500 islands and island groups.
Earthquakes and Volcanoes
- Active tectonic processes, such as collision and subduction, cause volcanism and frequent earthquakes.
- The Philippine Institute of Volcanology and Seismology monitors 23 active volcanoes; the most active are Mayon, Taal, Kanlaon, Bulusan, and Hibok-Hibok.
- Earthquake generators include trenches and the significant Philippine Fault Zone, leading to around 20 earthquakes daily (mostly unfelt).
- Major historical earthquakes include the 1968 Casiguran (magnitude 7.3), 1990 Luzon (7.9), 2012 Negros (6.9), and 2013 Bohol (7.2) events.
Palawan Microcontinental Block
- Palawan Island and neighboring islands, including the Romblon group, Mindoro, and Buruanga Peninsula, are part of the Palawan microcontinental block.
- These areas were once part of mainland Asia before drifting and colliding with the Philippine Mobile Belt.
- Palawan and other fragments originated from the thinning of Asia's continental margin and the opening of the South China Sea.
Geological Evidence and Field Studies
- Field mapping and analysis in Romblon, Buruanga Peninsula, and Mindoro revealed quartz-rich metamorphic rocks, typical of continental origins.
- Fossils, such as radiolarians, helped date rocks in Buruanga Peninsula to the Jurassic period (~166 million years ago).
- Sandstone zircons in Mindoro indicate ages similar to southern mainland Asia (185–196 million years).
- Masbate Island rocks are younger and lack quartz grains, indicating it is not part of the Palawan microcontinental block.
Key Terms & Definitions
- Island Arc System — A chain of islands formed at a tectonic plate boundary, usually involving subduction.
- Subduction — Process by which one tectonic plate moves under another, causing earthquakes and volcanism.
- Microcontinental Block — A fragment of continental crust separated from a main continent.
- Philippine Mobile Belt — The major tectonic unit forming much of the Philippines, distinct from the Palawan block.
- Quartz — A mineral common in continental rocks.
- Radiolarians — Microscopic protozoans with silica skeletons, used to date sedimentary rocks.
- Zircon — A durable mineral used to determine the age of rocks.
Action Items / Next Steps
- Continue geological fieldwork to refine the understanding of the Philippine Island Arc system's formation.
- Review the processes and hazards related to the geologic history of the Philippines.