A review of the main structural and magmatic features of northern Sumatra

Abstract

Structural and magmatic features of northern Sumatra are reviewed, based on a continuing programme of reconnaissance mapping. Distinction is drawn between Tertiary sedimentation on the W and that in the centre and E, the dividing line being the main outcrop of the Sumatran Fault System (SFS) which traverses the length of the island. Large transcurrent movements on the SFS are indicated by ( a ) regional slivers of oceanic crust trapped at the leading junction of the western continental plate of Sumatra as it moved NW against the main mass of the island; ( b ) palaeomagnetic evidence (N. S. Haile) here interpreted as showing eastern Sumatra as part of the Malaya block and occupying its equatorial position since the Cretaceous in contrast to the NW tip of Sumatra, W of the SFS, for which more southerly palaeolatitudes have been determined; ( c ) juxtaposition of Li-rich and Li-poor geochemical provinces along the SFS. The Sumatran magmatic arc commenced at least in the Mesozoic. The offset of the current volcanic arc to the E at Lake Toba is ascribed to a change in the angle of the Benioff Zone, the dividing line suggested being a split in the descending plate which is coincident with prolongation of the Investigator transform fault. The SFS continues N of Sumatra as a transform of the Andaman spreading complex, and terminates in the S in the Sunda Strait area either at the edge of the continental block or against a major plate junction indicated by the commencement of deep focus earthquakes E of Sumatra.

Mantle structure and tectonic history of SE Asia

“…2) that has been a topic of considerable interest for many years. Page et al (1979) and Fauzi et al (1996) suggested there may be a slab tear beneath Sumatra, possibly linked to the Investigator Fracture Zone, which may be related to the Toba volcanic centre (Chesner, 1998(Chesner, , 2012Chesner et al, 1991). Lange et al (2010) also suggested the Investigator Fracture Zone may influence seismicity and presumably slab morphology.…”

“…Toba has been linked to subduction of the Investigator Fracture Zone on the Indian plate (e.g. Page et al, 1979), who suggested a tear at the fracture zone. Its cause could be a weakness due to the fracture zone which is being subducted subparallel to the postulated tear.…”

Tectonostratigraphic evolution of Cenozoic marginal basin and continental margin successions in the Bone Mountains, Southwest Sulawesi, Indonesia

“…They observe that this mode of terrane emplacement may be more common than generally believed, particularly in orogenic belts developed in response to oblique convergence. Examples of this type of emplacement can be found in the Philippines (Karig et al, 1986), Halmahera (Hall, 1990), and Sumatra (Page et al, 1979). A similar scenario may be applicable to the Western Sulawesi ophiolite fragments.…”

Groundmagnetic survey used to identify the weathered zone, in Blang Bintang, Aceh, Indonesia

“…Tangse valleys. This is essentially a right lateral fracture system [13]; [14]. The topographical morphology of the study area (Blang Bintang) is weak (soft) because the rocks are strongly fractured and altered.…”