Halmahera Arc
Encyclopedia
Halmahera Arc is the volcanic arc
of the Halmahera
region of eastern Indonesia
. It is considered to belong to the Halmahera Plate
tectonics, within the Molucca Sea Collision Zone
.
beneath the Philippine Sea Plate as it arrived at the Eurasian margin. The distribution of ages within the Neogene
arc indicates a northward migration of volcanic activity during the Late Miocene
to Pliocene
. Results of the dating work show that after collision with the Australian margin at c. 22 Ma there was a period of volcanic quiescence and limestone deposition before a new arc formed. This arc began erupting at around 11 Ma on Obi
as a result of subduction
of the Molucca Sea plate. Initiation of subduction is thought to have occurred around 15–17 Ma and may have been responsible for disturbing potassium-argon ages of pre-Neogene rocks. Dates from fresh rocks show that the volcanic front migrated northwards through Bacan
and Halmahera throughout the Late Miocene to Early Pliocene. Limestone deposition was curtailed as arc activity migrated north while volcanism
died out from the south. No Neogene volcanism younger than 8 Ma is observed in the Obi area while on Bacan subduction-related volcanism ceased at c. 2 Ma.
Late Pliocene crustal deformation caused a 30–40 km westward shift of the volcanic front. Quaternary
volcanic rocks exposed in Bacan and the extreme south of Halmahera are not direct products of subduction but, rather, display geochemical characteristics of both subduction and fault-related magmatism. These volcanic rocks are distributed along splays of the Sorong Fault
system. The formation and propagation of the Halmahera arc is a consequence of the clockwise rotation of the Philippine Sea plate as the southern edge moved across the northern Australian margin and impinged on the east Eurasian margin. The ages of initiation of volcanism and subduction track the developing plate boundary as subduction propagated northwards.
Volcanic arc
A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...
of the Halmahera
Halmahera
Halmahera is the largest island in the Maluku Islands. It is part of the North Maluku province of Indonesia.Halmahera has a land area of 17,780 km² and a population in 1995 of 162,728...
region of eastern Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. It is considered to belong to the Halmahera Plate
Halmahera Plate
Halmahera Plate has recently been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.-Regional tectonics:...
tectonics, within the Molucca Sea Collision Zone
Molucca Sea Collision Zone
The Molucca Sea Collision Zone is postulated by paleogeologists to explain the tectonics of the area based on the Molucca Sea in Indonesia, and adjacent involved areas.-Tectonics:...
.
Origin
Potassium-argon ages of Neogene to Recent igneous rocks from the Halmahera region record a history of intra-oceanic arc development since the late Middle Miocene following an earlier phase of collisional plutonism. Arc formation from the Middle Miocene onwards was due to the east-directed subduction of the Molucca Sea PlateMolucca Sea Plate
-Earlier theory:The Molucca Sea Plate was theorised to be a small tectonic plate carrying northern Sulawesi, the Molucca Sea and a portion of the Banda Sea in a region littered with numerous small plates. The theory suggested a subduction zone lies along its northern border with the Sunda Plate...
beneath the Philippine Sea Plate as it arrived at the Eurasian margin. The distribution of ages within the Neogene
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
arc indicates a northward migration of volcanic activity during the Late Miocene
Late Miocene
The Late Miocene is a sub-epoch of the Miocene Epoch made up of two stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch....
to Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. Results of the dating work show that after collision with the Australian margin at c. 22 Ma there was a period of volcanic quiescence and limestone deposition before a new arc formed. This arc began erupting at around 11 Ma on Obi
Obi
Obi may refer to:* Obi , a sash worn with a kimono or with the uniforms used by practitioners of Japanese martial arts* Obi-Wan Kenobi, fictional character from the Star Wars universe...
as a result of subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
of the Molucca Sea plate. Initiation of subduction is thought to have occurred around 15–17 Ma and may have been responsible for disturbing potassium-argon ages of pre-Neogene rocks. Dates from fresh rocks show that the volcanic front migrated northwards through Bacan
Bacan
Bacan refers to a group of islands in the Maluku Islands of Indonesia and to that group's largest island. The islands are mountainous and forested. The islands lie south of Ternate and west of Halmahera's southernmost arm...
and Halmahera throughout the Late Miocene to Early Pliocene. Limestone deposition was curtailed as arc activity migrated north while volcanism
Volcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
died out from the south. No Neogene volcanism younger than 8 Ma is observed in the Obi area while on Bacan subduction-related volcanism ceased at c. 2 Ma.
Late Pliocene crustal deformation caused a 30–40 km westward shift of the volcanic front. Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
volcanic rocks exposed in Bacan and the extreme south of Halmahera are not direct products of subduction but, rather, display geochemical characteristics of both subduction and fault-related magmatism. These volcanic rocks are distributed along splays of the Sorong Fault
Sorong Fault
Sorong fault also is an active, broad zone of inferred left lateral shear at the triple junction of the Australian plate, Eurasian plate, and Pacific plates, where many plate fragments exist, such as the Philippine Sea Plate, Bird's Head Plate, Halmahera Plate and the Molucca Sea Plate. It has...
system. The formation and propagation of the Halmahera arc is a consequence of the clockwise rotation of the Philippine Sea plate as the southern edge moved across the northern Australian margin and impinged on the east Eurasian margin. The ages of initiation of volcanism and subduction track the developing plate boundary as subduction propagated northwards.
See also
- Philippine Mobile BeltPhilippine Mobile BeltThe Philippine Mobile Belt is a complex portion of the tectonic boundary between the Eurasian Plate and the Philippine Sea Plate, comprising most of the country of the Philippines. It includes two subduction zones, the Manila Trench to the west and the Philippine Trench to the east, as well as the...
- Australian Plate
- Halmahera PlateHalmahera PlateHalmahera Plate has recently been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.-Regional tectonics:...
- Molucca Sea PlateMolucca Sea Plate-Earlier theory:The Molucca Sea Plate was theorised to be a small tectonic plate carrying northern Sulawesi, the Molucca Sea and a portion of the Banda Sea in a region littered with numerous small plates. The theory suggested a subduction zone lies along its northern border with the Sunda Plate...
- Sangihe PlateSangihe PlateSangihe Plate has recently been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia.-Regional tectonics:...