OCEAN - OCEAN CONVERGENCE : FORMATION OF ISLAND ARCS

CONCEPT : The Islands Arcs are narrow chains of islands which is originated the active volcanoes along the oceanic- oceanic convergence tectonics boundary.The oceanic - oceanic boundary is formed due to the movement of plates towards each other and more dense oceanic plate is subducted under less dense oceanic crust, forming a trench along the boundary. However, the ocean floor is loaded with sediment into the trench.The subducted plate reaches 100 km and enters viscous asthenosphere,melting subducted plates become less dense and push the magma upward due to buoyant force.the flowing of magma is up warded violently and is created new crust along the boundary. Continuous up welling of magma and creating new crust formed a chain of volcanic islands.

OCEAN OCEAN CONVERGENCE BOUNDARY

TECTONISM AND VOLCANISM

TECTONICAL ACTIVITY AND FORMATION :

Islands Arcs are formed due to convergence boundary.The denser oceanic plate is subducted into the lesser oceanic crust at 45 degree angle and enters asthenosphere which is viscous in nature.After forming a trench, the sediments is loaded on the ocean floor , up welling magma pushes the sediments upward , forming a new crust along the boundary.this process is repeated again and formed a narrow chains of active volcanoes.

STRUCTURE OF ISLAND ARCS

FORMATION OF ISLAND ARCS

SOME NOTABLE EXAMPLE OF ISLAND ARCS

FORMATION OF PHILIPPINE ISLAND ARCS

The Philippine Island Arcs formed due to minor plate i.e. Sunda plate which is part of Eurasian plate( continental plate) and Philippine plate ( oceanic plate) ,forming Philippine plate.

PHILIPPINE TRENCH

FORMATION OF MARIANA TRENCH

The formation of Mariana Trench,two most oceanic plate i.e. Pacific plate and Philippine collides each other and Philippine plate is subducted beneath the Pacific plate,forming Mariana Trench and challenger deep.

MARIANA TRENCH

FORMATION OF JAPAN ISLAND ARCS

Japan island arc formed due to triple junction .i.e. in the northern part Pacific Plate is subducted under Eurasian Plate,forming Japan Trench.in the southern part Philippine plate subducted underneath the Eurasian Plate, Ryukyu Trench formed.The force exerted by the Philippine plate and Eurasian plate give rise to east china sea.in the central part give rise to Izu Trench due to pacific plate and Philippine plate. Japan sea originated due to enforcement of pacific plate and Philippine plate.

JAPAN ISLAND ARCS

JAPAN SEA

JAPAN TRENCH

FORMATION OF INDONESIAN ARCHIPELAGO

The term of Archipelago means a extensive group of islands. The formation of The Indonesia Archipelago,The two plates i.e Indo - Australian plate subducted below Sunda Plate, Forming a Sunda Trench ( Java Trench is part of Sunda.)

INDONESIAN ARCHIPELAGO

FORMATION OF CARIBBEAN ISLANDS

Caribbean Islands formed due collision of North American plate and Caribbean oceanic plate respectively.the trench which is formed there is Puerto Rico.