The TAIGER (Taiwan Integrated Geodynamics Research) project is a joint USA-Taiwan program that seeks to model the complex collision processes and the tectonic development of Taiwan, based on extensive observation. Funded by the NSF Continental Dynamics Program and by Taiwan's National Science Council and involving investigators at SUNY/Binghamton, UTIG, USC, Cornell, and Wisconsin, this project has acquired more than twice as much data as originally proposed due to synergistic contributions by Taiwan scientists and Taiwanese government science funding. From FY2006-2009, deployments of seismic instruments on land (IRIS) and at ocean-bottom (OBSIP) maximized the recording of local events and teleseisms, as well as artificial sources specially set off for TAIGER, in order to obtain high resolution 3-D images. To map the areas around Taiwan the PIs were able to use the NSF-supported research ship, the R/V Langseth, to create seismic waves that were recorded by a 6-km long streamer and also ocean-bottom and land recorders. These seismic and magnetotelluric profiles as well as petrologic lab data are currently being analyzed. TAIGER project data combined with geodynamics methods will be used to test a set of existing tectonic models that range from a thin skinned model, in which subduction of continental Eurasian mantle and lower crust is separated from a deforming crustal wedge by a plate boundary decollement, from a thick skinned model, where deformation of crust and mantle occurs within a vertically contiguous system, with progressive thickening of continental mantle beneath the core of the mountain belt.
The current project (TAIGER?s TALE), will expand on thier initial studies to carry out in-depth and advanced studies using the extensive TAIGER data volumes (no new data will be acquired). This work will lead to significant advances in understanding deformational processes associated with the evolution of Taiwan due to plate collision. Studies will focus primarily on seismological analyses to obtain physical properties and rheological indicators as well as the integrative ties with geodynamical modeling efforts. The over-arching strategy is to take advantage of the unique aspects of the acquired data sets, the tectonic environment, and the diverse and complementary participating/collaborating personnel. They will perform their analyses of various data sets in such a way that higher frequency/higher resolution results are nested in the context of broader scale results. They will make extensive use of ?crossover? seismological data sets recorded during TAIGER (active sources collected by passive-source arrays, and earthquakes collected in active-source arrays). Also, analysis/interpretation of these data will be closely tied to geodynamic modeling.
The continental island of Taiwan is currently under construction due to plate tectonics. The northwestern corner of the Philippine Sea tectonic plate is colliding with the larger continental Eurasian plate. In addition, a linear island arc embedded into the Philippine Sea plate is also running into Taiwan. This net collision is responsible for the appearance of and current new growth of the Central Ranges that dominate the eastern half of the island. The active tectonics of Taiwan offers an excellent laboratory to study how a mountain orogen evolves through time and the role of a colliding island arc to produce mountain building. More specific questions include: - What is the role of the Eurasian continental lithosphere in the collision: does this continental plate subduct? - Do both the Philippine Sea and Eurasian colliding plates experience pervasive deformation? - In the case of the collision between a continental plate and an island arc, how is the subduction zone geometry that defines the upper and lower plates modified after the introduction of continental lithosphere into the collision zone? - What are the 3-D rheological and mechanical properties of the crust and the mantle in the orogen and what are the deformation processes involved? - Does the orogenic process extend to upper mantle depths of 100-200 km? - Is the known pervasive crustal rock fabrics in the heart of the collision zone sufficient to affect lithospheric-scale seismic studies in terms of seismic anisotropy overprints or alteration? This project is one of a set of funded projects that composed an international collaboration involving several USA and Taiwanese universities and academic institutions. This collaboration, the Taiwan Integrated Geodynamics Research (TAIGER) project, addressed the above scientific questions using geophysical methods. The collaboration collected new marine and land geophysical observations over a span of five years and carried out disciplinary analyses and integration. The Central Ranges grow at one of the most rapid rates of exhumation in the world due to the arc-continent collision. The combination of fast uplift and erosion brings to the mountain surface metamorphic rocks that were once at least 10 km deep. These metamorphic rocks are organized into regional trends that define geological terranes. Conventional thinking about these terranes based on earlier geological studies are that the metamorphic rocks are bulk oriented in a near vertical dip, striking parallel to the long direction of the island. These metamorphic rocks produce crustal seismic anisotropy, and the near-vertical dip is optimal to create seismic anisotropy signals with azimuthal variation. Local earthquakes and controlled seismic sources recorded in the TAIGER seismic experiments have evidence of this seismic anisotropy. This project developed new computer tools to analyze these seismic signals. TAIGER rock studies involving petrophysical laboratory measurements provided calibration of the amounts of anisotropy provided by the metamorphic rocks. Integration of TAIGER studies revealed that the metamorphic rocks at depth are complex and that standard assumptions that are typically used for seismic analysis are too simplified. This project hosted an early career post-doc that was supported via a collaborating TAIGER institution. The overall TAIGER data volume that is publically available via IRIS DMC and the Taiwan TEC data center provided new research for young investigators and graduate students. American and in particular Taiwanese early career scientists have had opportunities to carry out scientific research of significance due to the acquisition of the data in a manner designed to address first-order topics.
