Phanerozoic evolution of Asia : Lessons from Tertiary geodynamics of SE Asian basins

Category Geodynamic
Group GSI.IR
Location International Geological Congress,oslo 2008
Source www.۳۳igc.org
Holding Date 18 August 2008

Phanerozoic evolution of Asia : Lessons from Tertiary geodynamics of SE Asian basins

Pubellier, Manuel1; Ringenbach, Jean-Claude2
1Ecole Normale Sup, CNRS, France;
2Total Exploration Production, France


The large belts and related sutures of Eurasia were formed as part of the late stages of closure of ocean basins and include units belonging to both the subducted and the overriding plates. International correlation and joint mapping programs (e.g. IGMA5000) have allowed the definition of the continuity of the tectonic belts.
Some of these belts are still under construction and show the relicts of marginal basins incorporated into the orogen. In specific examples, it can be shown that tectonic events are often short-lived (1 to 2 Ma), whereas the subduction is a long-lasting process. In the case of the southern Philippines or the New Guinea orogen, mountain building started in the Pliocene and was completed around 2 Ma ago. Since then, the geodynamic environment changed drastically and evolved towards the installation of a partitioned system and a subduction jump.
The starting phase is the opening of marginal basins. The Sunda Plate in Southeast Asia concentrated most of the deformation as a back-arc extension. The marginal (back-arc) basins are remarkably diachronous and apparently have relayed through time. We performed a sorting of the major faults of the basins based on geological and seismic data which allowed us to identify areas of the Sunda Plate with distinct deformation styles, and to propose an evolution of the geodynamic context through the Tertiary.
The extensional evolution of the Sunda basins was interrupted by the arrival of crustal asperities of various natures. Active examples such as Sumba Island illustrate how a slight perturbation of the subduction instantaneously provoked subduction jump and reversal. The reversal marks the beginning of the shortening of the back-arc basins which ultimately get incorporated into mountain ranges as back-arc ophiolites.
Unravelling the Phanerozoic evolution of Eurasia shows that back-arc basins often developed during convergence (e.g. Tien Shan). The closure of the main ocean basins is generally known from the metamorphosed (cratonized) wedges and ophiolite assemblages which nowadays appear as large lithologic entities, between the continental crustal fragments. Unfortunately, the post accretion tectonics generally involves strike-slip faults which tend to fragment the suture zones and obscure the former basins, as is observed in the Altaïds Kazakhstan orogens during Caledonian times, or Songpan Garze during Indonesian times. Such an evolution emphasises the importance of making use of actualistic models to understand how cumulated tectonic events form a larger orogeny and how subduction is responsible for both the opening and the shortening of the back-arc basins.