POST-COLLISIONAL TECTONIC ESCAPES IN INDONESIA : FASHIONING THE CENOZOIC HISTORY

PROCEEDINGS PIT IAGI RIAU 2006
The 35^th IAGI Annual Convention and Exhibition
Pekanbaru – Riau, 21 – 22 November 2006

POST-COLLISIONAL TECTONIC ESCAPES IN INDONESIA : FASHIONING THE CENOZOIC HISTORY

Awang Harun Satyana^1
1BPMIGAS
ABSTRACT

Post-collisional tectonic escape refers to the lateral escape or extrusion of fault-bounded geological blocks as a result of collision or compression away from the collision zone and towards free edge of oceanic margin. While the collision zone is represented by fold-thrust belts, the tectonic escape is accommodated by large strike-slip faults and rifting and spreading of basement.

There are five significant collisional events fashioning the Cenozoic tectonics of Indonesia. The first was collision of India to Eurasia started at 50 or 45 Ma (early-middle Eocene). The collision resulted in the Himalayan Fold-Thrust Belt and was followed by the escape of the Sundaland southeastwards through major strike-slip faults and the formation of sedimentary basins in the Sundaland as well as the opening of marginal seas of the South China Sea and Andaman Sea. The faults occupied and reactivated Mesozoic sutures within the Sundaland. The faults are Red River Fault-Sabah Shear, Tonle-Sap-Mekong (Mae Ping) Fault, Three Pagoda Fault-Malay-Natuna-Lupar Line-Adang Fault, and the Sumatran Faults.

The second collision occurred at about 25 Ma (late Oligocene) when an oceanic island arcs constructed on the southern margin of the Philippine Sea Plate collided with the northern margin of Australia Continent. The collision resulted in fold-thrust belt of the Papua Central Ranges and was followed by tectonic escapes of strike-slip faults and basin formation. The faults are Sorong-Yapen Fault, Waipoga Fault, Gauttier Offset, and Apauwar-Nawa Fault. Opening of the North Irian Basin in northern Papua also shows the post-collision tectonic escapes.

The third collision was the collision of the Bird’s Head microcontinent with Papua at 10 Ma (late Miocene). The Lengguru Fold-Thrust Belt marks the collision zone. Strike-slip faults away from the collision zone like the Tarera-Aiduna, Sorong, Waipoga, and Ransiki Faults may demonstrate the post- collision tectonic escape. The Bintuni Basin located just to the west of the Lengguru Fold-Thrust Belt is a foreland basin developing as a response to post-collision extensional structure.

The fourth collision occurred from 11 to 5 Ma (late Miocene to earliest Pliocene) when the Buton-Tukang Besi and the Banggai-Sula microcontinents collided East Sulawesi ophiolite. The microcontinents were detached from the Bird’s Head of Papua and escaped westwards by the Sorong Fault. The collision has formed Batui Fold-Thrust Belt and was followed by post-collision tectonic escapes in forms of rotation of arms of Sulawesi, formation of major strike-slip faults of Palu-Koro, Kolaka, Lawanopo, Hamilton, Matano, and Balantak Faults, and the opening of the Gulf of Bone. More recent transtensional movement is responsible for the opening of pull-apart basins of Poso, Matano and Towuti Lakes, as well as the Palu Depression.

The last collision commenced at about 3 Ma (mid-Pliocene) when northern margin of Australia Continent collided Banda Island Arc. The collision resulted in foreland fold-thrust belt from Timor, Tanimbar to Seram. Lateral extension is observed to follow the arc-continent collision indicating a tectonic escape. Major strike-slip faults were formed sub-paralleling the Timor Island and may relate to the escape of the Sumba Island westwards. Extensional crustal collapse followed the arc-continent collision and has resulted in the formation of the Weber Deep, Savu Basin, and opening of the Banda Sea. The cases in Indonesia show that tectonic escape is a widespread process and may have been very important in the evolution of convergent region like Indonesia. The concept of tectonic escape can contribute to the understanding of the process by which continents are assembled and slivered