Tectonic Controls of Volcanism and Complex Movements Along the Sumatran Fault System

Abstract

Recent geological work within the Contract Area of P.T. Riotinto Bethlehem Indonesia in West Sumatra, including aerial photographic and aeromagnetic surveys by Lockwood Survey Corporation, have yielded much new data on the Sumatran Fault Zone and have revealed its intimate connection with volcanism. Three major fault zones each characterized by complex wrench, thrust and subordinate normal faulting can be recognized from aerial photographic interpretation. During the Quaternary significant di splacements along the Sumatran Fault Zone occurred and are still continuing, and in consequence morphological features and especially drainage patterns are in the closes t correspondence to the fracture systems. Strong E-W magnetic lineaments thought to represent major intermediate intrusives at depth are found associated with volcanic centres. Where these lineaments are cut by strands of the fault zones volcanoes are located. Igneous activity along original E-W a lignments and dextral tranSCUlTent faulting along NNW trending zones interact to produce a barrier range of volcanic rocks along the active fault zone with evenly spaced active volcanic centres at 75-100 km. distances along it. The total horizontal shift along the fault is approximately 130 km. since the inception of the present volcanic cycle. The fault system is thought to be a fundamental fracture whose full explanation is to be sought within the concept of a plate tectonic interpretation of the geology of Southeast Asia. 12 0 Volcano wilh hiltorlcal .rocord 01 activity. } From Mop by B. G. Esdl!r (111511) \'flth odditions from Von B.mm.Hn (1949) Alter. J. Kat~r. 1969. Figur •. I .

Subsurface structures of Sianok Segment in the GSF (Great Sumatran Fault) inferred from magnetic and gravity modeling

“…This study serves as the first investigation of subsurface structures in the volcanic centers of the Central Barisan Fault identified by Posavec et al (1973). The Marapi volcanic center of this study is in the vicinity of the boundary between the Sianok and Sumani segments.…”

“…Acocella et al (2018) identified that some of the volcanoes are likely controlled by GSF structures, while others are probably and possibly linked to GSF. Posavec et al (1973) named seven volcanic centers (from north to south) as follows: Marapi, Talang, Kerintji, Hulumajang, Pandan, Kaba, and Dempo after their most striking or active members. At each volcanic center, there is a series of active and dormant volcanoes that stretch in the E-W direction.…”

“…At each volcanic center, there is a series of active and dormant volcanoes that stretch in the E-W direction. The line connecting the volcanoes forms an angle of about 70 in the direction of the GSF (Posavec et al, 1973). The Marapi Centre, located in the Sianok segment, is one of the more active centers (Figure 1A).…”

“…The other important feature of the Marapi Center is Lake Maninjau, a 16 by 7 km caldera with a maximum depth of 169 m (Wills et al, 2021). According to Posavec et al (1973), this caldera is the product of three major eruptions that generated extensive tuff cover in the surrounding area. The extent of tuff cover could be appreciated in the Sianok canyon in Bukittinggi.…”

Subsurface Structure of Singkarak Pull Apart Inferred from Magnetic and Gravity Modeling

“…The subduction between the Indian-Australian plate under the Eurasian plate on the island of Sumatra occurs obliquely [1][2][3][4][5][6]. This has an impact on the emergence of tectonic activity in the form of faults and magmatism.…”