Passive Continental Margin
Passive Continental Margin develops where plates rift and separate as a result of seafloor spreading. Alternatively, a continental boundary formed by rifting and continental rupture. They are among the most common type of continental margins found in present day ocean margin. They can also be considered as Atlantic Ocean type continental margin. It is difficult to classify continental margin of Bangladesh directly into passive (divergent) or convergent margin. The eastern continental margin offshore of Chittagong, Cox's Bazar and Teknaf behaves like a convergent continental margin where the Indian Plate subducted under the Burmese Plate and a foreland type of basin formed west of the present day suture line. These plates are still tectonically quite active. The eastern folded and faulted belt is frequently affected by earthquakes. Further south, the Andaman-Nicobar islands represent the island arc complex associated with the subduction of Indian Plate under the Burmese Plate. The continental margin of the East Coast of India and south shore of Bangladesh (off Sundarban, Khulna, Patuakhali) behaves like a Passive Continental Margin. This part of the continental margin is tectonically less active and can be considered with Atlantic coast of USA, especially with the coast of the Mississippi Delta. The south shore of Bangladesh is going through active delta building process. There is an active submarine canyon extending on the continental shelf off the south shore of Bangladesh, known as swatch of no ground. Sediments from the continental shelf are transported through this submarine canyon to the deeper part of the bay of bengal. [Mahmood Alam]
See map in tectonic framework.