Halmahera Arc is the

volcanic arc A volcanic arc (also known as a magmatic arc) is a belt of volcanoes formed above a subducting oceanic tectonic plate, with the belt arranged in an arc shape as seen from above. Volcanic arcs typically parallel an oceanic trench, with the arc ...

of the

Halmahera Halmahera, formerly known as Jilolo, Gilolo, or Jailolo, is the largest island in the Maluku Islands. It is part of the North Maluku province of Indonesia, and Sofifi, the capital of the province, is located on the west coast of the island. H ...

region of eastern

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

. It is considered to belong to the

Halmahera Plate Halmahera Plate has recently (1990s) been postulated to be a microplate within the Molucca Sea Collision Zone of eastern Indonesia. Regional tectonics The tectonic setting of the Molucca Sea region is unique. It is the only global example of an ac ...

within the

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 The tectonic relationship of the Sangihe Plate, Halmahera Plate, ...

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 Plate Located in the western Pacific Ocean near Indonesia, the Molucca Sea Plate has been classified by scientists as a fully subducted microplate that is part of the Molucca Sea Collision Complex. The Molucca Sea Plate represents the only known example ...

beneath the

Philippine Sea Plate The Philippine Sea Plate or the Philippine Plate is a tectonic plate comprising oceanic lithosphere that lies beneath the Philippine Sea, to the east of the Philippines. Most segments of the Philippines, including northern Luzon, are part of ...

as it arrived at the Eurasian margin. The distribution of ages within the

Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago (Mya) to the beginning of the present Quaternary Period Mya. ...

arc indicates a northward migration of volcanic activity during the

Late Miocene The Late Miocene (also known as Upper 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, which lasted from 11.63 Ma (million years ago) to 5.333 Ma. The ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Australian 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 Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

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 The Bacan Islands, formerly also known as the Bachans, Bachians, and Batchians, are a group of islands in the Moluccas in Indonesia. They are mountainous and forested, lying south of Ternate and southwest of Halmahera. The islands are administe ...

and Halmahera throughout the Late Miocene to

Early Pliocene Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

. Limestone deposition was curtailed as arc activity migrated north while

volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the Earth#Surface, surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the su ...

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 Sorong fault also (Sorong Fault Zone, SFZ) 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 Pl ...

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.

References

{{reflist Tectonic plates Geology of the Pacific Ocean Island arcs Geology of Indonesia Geology of the Philippines Molucca Sea Volcanism of the Philippines

Origin

See also

References