Tapponier and Robert Hall South East Asia tectonic model

Two theories from both on opening of South China sea. One is using extension and subduction concept and the others is tectonic extrusion between India-Asia tectonic plate.

Robert Hall proposed the earlier theory while Paul Tapponier the latter theory.

This model considers the existence of a Proto-South China Sea during the Eocene which started subducting beneath the Pacific Ocean and the continental crust of Borneo. Crucial evidence for the Eocene-age Proto-South China Sea comes from the subduction complex and deepwater sediments of north-west Borneo (the Rajang-Crocker outcrops of Sarawak and Sabah). The pull of the eastward subducting slab is believed to have caused sufficient extension in the continental crust, which eventually led to the opening of a new oceanic basin – the SCS – during the Oligocene-Miocene.

While this model provides a reasonable framework for the origin of the SCS, geologists have also attempted to incorporate certain valid aspects of the India indentation model for an integrative scenario. For example, Ian Longley (1997, Geological Society of London Special Publication 126) has suggested that the widespread crustal extension of Sundaland in the Eocene was back-arc rifting induced by the Indian plate collision and contemporaneous oceanic subduction beneath the southern margin of Sundaland (Sunda arc). Tung-Yi Lee and Lawrence Lawver (1995, Tectonophysics, vol. 251) have argued that the extrusion of the Indochina Block induced the subduction of the pre-existing Proto-South China Sea, thus providing a mechanism for crustal extension in addition to the slab pull. Several geologists have extended the strike-slip faults of extrusion tectonics in the Indochina Block to major faults in north-western Borneo. For instance, Christopher Morley (2002, Tectonophysics, vol. 347) proposed a right-lateral transform system by linking the Red River Fault to the Lupar and West Baram Lines in Borneo, thus explaining the south-east movement of the Luconia carbonate platform from the Chinese margin in the north to the Borneo margin to the south.

One popular tectonic model for the origin of the SCS was proposed by Paul Tapponnier and his French colleagues (Geology, 1982, Vol. 10). In an experiment involving indentation of a rigid block against a deformable plastic material, these researchers examined the effect of the collision of the Indian plate (a Precambrian shield) against the relatively ‘soft body’ of Asian continent, a basement-sedimentary complex which was subjected to multiple phases of tectonic deformation in Palaeozoic and Mesozoic times. This idea was based on the Swiss geologist Emil Argand’s interpretation in his La Techtonique de l’Asie (1924): that the collision of the rigid India with the plastic Asia during the ‘Alpine [Himalayan] orogeny’ caused not only north-south dipping folds and thrusts (in the direction of the collision) but also eastward ‘flow’ of rocks in eastern Asia.

The India-Asia collision took place at about 55–50 Ma, and since then the Indian plate has been pushing against Asia at a rate of about 5 cm per year, resulting in 2,500–2,000 km of continental deformation. Tapponnier and his colleagues, based on a comparison of their experimental results with a tectonic map of Asia, suggested that after the collision, between 50 and 20 Ma, the Indochina Block was extruded south-eastward (out of the way of the indenter) for 800 km along the then left-lateral Red River Fault, which spans from eastern Tibet to northern Vietnam. This tectonic escape and clockwise rotation of the Indochina Block was interpreted to be responsible for the opening of the SCS during this period. After 20 Ma, the extrusion tectonics shifted to other strike-slip faults in central Asia, thus terminating the seafloor spreading in the SCS and opening new extensional basins in continental Asia.

This elegant model has been elaborated on by many other researchers, and it indeed offers a useful perspective on the strike-slip motions and associated pull-apart basins in Central and South East Asia as a result of the Indian collision in Cenozoic times. Geochronological data from rocks along the Red River Fault suggest fault activity to be in the Oligocene-Early Miocene, and total movements on the fault have been estimated to be several hundreds of kilometres. Nevertheless, the direct relevance of the Red River fault activity for the opening of the SCS has also been questioned. For one thing, it is not clear how the Red River Fault extends offshore and is linked to the seafloor spreading structures. Moreover, magnetic lineations of the SCS show that the seafloor spreading began in the east to north-east (far from the Red River Fault) and then ‘unzipped’ in a west to south-west direction, thus creating a wedge-shaped sea with its maximum width in the north-east.