Product Code Database
The Banda Arc (main arc, Inner, and Outer) is a dual chain of islands in eastern Indonesia that is around 2,300 km long. It is the result of the collision of a continent and an intra-oceanic island arc.
The presently active volcanic arc is mounted on stretched continental and oceanic crust whereas the associated subduction trench is underlain by continental crust, which has subducted deep enough to contaminate the volcanic arc with continental melts. The island of Timor is notable for the lack of volcanic activity. This is due to the island representing the zone of fore-arc and continental collision which prevents volcanic activity from occurring.
The convergence of the Indo-Australian Plate tectonics and Eurasia resulted in the formation of the Sunda and Banda . The transitional zone between the arcs is located south of Flores and is characterized by the change in the Tectonics regime along the boundary in the Timor Region. (2025). 9783540885573 ISBN 9783540885573
The basic stratigraphy of Timor is layers of young volcanics and sedimentary rocks overlaying metamorphic complexes. The sedimentary and metamorphic layers together form what is called the "Banda Terrane". These layers were thrust on top of the Australian passive continental margin as the arc and continent collided, so Australian lithologies, like the Gondwana sequence, underlie the island of Timor. Compressive forces continue to duplex the Australian sequences under the island, leading to as much as 2,500 meters of uplift of the Banda Terrane.
Because they are metamorphic, the Banda Terrane sequences could be from a number of sources. Likely sources are 1) rifted metamorphic material from the ancient Great Indonesian Arc, 2) they are part of the original Australian continental basement, or 3) They are metamorphosed exposures of the subducted passive continental margins of Australia.
Petrology studies show that the Banda Terrane was formed as a clay-rich sedimentary unit derived from mafic continental and oceanic arc Protolith. As such, detrital zircons are part of its composition. There are two groups of zircons found in Banda Terrane rocks: euhedral zircons, and weathered spherical zircons. The age of these zircons, as derived from U-Pb dating, are 87 Ma, and 113 Ma, respectively. On the other hand, the three major groups of zircon ages found in colliding Australian sediments are 301 Ma, 1882 Ma, and 2400-2700 Ma. The difference in zircon ages indicates that the Banda Terrane is likely not of Australian origin, but rather of Asian origin from the Great Indonesian Arc.
Similar event-age relationships using Lu-Hf dating and fission-track analysis indicate the Banda Terrane likely rifted from the Great Indonesian Arc, collided with the Australian continent 3 Mya, and has been uplifted through duplexing of the underlying Gondwana sequence. Volcanic and sedimentary layers on top of the metamorphic rocks weathered away, leaving the metamorphic cores as Klippe now visible on the surface.
However, the results of the collision are much larger than just Timor. The collision has created a 180-degree island arc, which is more than long. Geographically, it stretches across eastern Indonesia, and is delimited by an active inner Volcano arc. The outer arc contains numerous , and its internal geologic structure contains young oceanic crust exclusively.
|
|
