Collision Initiation in South-East Asia – COLLISEA

Collision initiation is defined by the onset of accretion of the marginal part of continents. Compared to subduction initiation and mature collision stages, collision initiation is not integrated in plate tectonic models. This limits the interpretation of crustal mass budget in mountain belts, which in turn impacts the CO2 budget on Earth and climate of the past, and of earthquake mechanisms and growth of subaerial topography at subduction-collision transition. We hypothesize that pre-convergence architecture and thermo-mechanical properties inherited from former tectonic and magmatic evolution of the continental margins are key factors controlling the initial steps of continental cycling and mountain building. The physical parameters at play at collision initiation has been so far indirectly determined based on tectonic reconstruction and processes fossilized in orogens. Only a limited number of orogens show these processes taking place and have preserved markers of this specific stage that lies at the transition from offshore subduction to initial subaerial collision, which is essentially a transient phenomenon. COLLISEA project aims at expanding our knowledge of collisional processes by determining how strength, density and architecture of continental margins control collision initiation. The proposal is designed to image the deep structure of subduction-collision transition, quantify the kinematics, exhumation and thermo-mechanical behaviour of incipient arc-continent collision zones covering more than 1000 km along the plate boundary between PSP and EU in South East Asia. COLLISEA takes advantage of using to a new dense seismological network in Taiwan, new and continuously growing low-temperature thermochronological dataset in Palawan and Mindoro in the Philippines, and the first 3D thermo-mechanical models of arc-continent collision designed to integrate complexities of plate motions to fill a knowledge gap on continental initiation. As a collaborative team, three laboratories (GET, ISTEP, LG-ENS) will supervise the work performed in COLLISEA. The decision-making body includes the Project Coordinator (Mouthereau) and co-leads from each lab (Le Pourhiet, Pubellier). External to the 11-person strong COLLISEA research team are our international collaborators in Taiwan and the Philippines, including two post-docs hired in Taiwan. ANR funding is requested for 2 post-docs with numerical modelling and plate reconstructions expertise, and 1 Phd at GET for thermochronology and modelling. COLLISEA is organized around five work packages. COLLISEA will image the deep structure of collision initiation in Taiwan based on modelling of body and surface waveforms to provide information on Moho depths and variations of crust and mantle velocities across the arc-continent collision and subducted slabs. The seismic waveforms modelling approach will be complemented by the analysis of reflection/refraction seismic profiles and geophysical data off Taiwan. This study will be extended to the whole of the N-S directed plate boundary between the PSP and EU plates, by integrating our understanding of the evolution of the accreted arcs and rift domains. To establish a precise picture of the PSP/EU kinematics, and unveil the possible control by the SCS margin, we will determine the timing and duration of cooling and exhumation using low-temperature thermochronological analyses and will be used to further constrain 3D thermo-mechanical models of oblique collision initiation. Results of ambitious and highly novel COLLISEA scientific program will be transferrable to other collision zones. COLLISEA is expected to have an important and positive impact at a fundamental and economic level by integrating and further developing technologies and strategies for the energy industry and observational techniques and modelling approaches designed at resolution and dimension not reached before with aimed at improving forecasting of geohazards.