Petrochronology of the metamorphic basement units in Thailand

Abstract:

The petrochronological investigations aim at better defining the metamorphic and temporal evolution of the major plate tectonic units in Thailand (Sibumasu, Doi Inthanon, Sukhothai, Indochina) during the last 500 million years.
At present, these units are mainly characterized by their respective Mesozoic and Cenozoic evolution (younger than ca. 300 million years), mostly based on radiometric cooling ages and equilibrium thermodynamics. Modern petrochronological data describing the pressure-temperature-time-structural evolution are completely missing. This deficit results in a number of published evolution models which are largely incompatible, thus prohibiting Earth scientists to provide a comprehensive evolutionary model of SE Asia.
We aim at providing such petrochronological data in order to unravel the high-temperature and -pressure evolution of the Thai basement units, to better understand their related but also the unrelated geological development and finally to provide more consistent plate tectonic models for the evolution of SE Asia, especially in view of the escape tectonics within the Alpine-Himalayan orogeny.
The investigations are made in the frame work of a fully funded 4 year PhD project.

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Outcrop of 'old' gneisses, Ob Khan National Park, Nam Prae, Hang Dong district, Chiang Mai, Thailand, © U. Klötzli

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Implementation Period:

02.03.2023 – 20.03.2023

Project:

The terranes that form present Thailand are key for the understanding of the paleogeography of Gondwana, the Tethys oceans and the geological development of present-day SE Asia. In attempts to unravel the tectonic history of SE Asia, the region has been divided into various plate tectonic terranes, although there is no consensus on their number, the nature and location of their boundaries, the sources and characteristics of the basement, their global affinities or tectonic models for their amalgamation. This problem is accentuated by the lack of basement exposure due to the vast cover of younger sedimentary sequences, extensive jungle cover, deep lateritic weathering and the prominent lack of modern petrochronological data. Therefore, on a regional scale, the nature and evolutionary path(s) of the basement within Thailand is unknown. A very unsatisfying situation. The available basement data is limited to the three main regions of exposure: northern, southeast and on the peninsula.

The ‘basement’ rocks in Thailand, most of which are medium to high grade regional metamorphic rocks, were previously described as ‘Pre-Cambrian‘ (older than ca. 540 million years). In contrast, radiometric absolute mineral and rock dating yielded basement ages ranging from the Cambrian to the Paleogene. While there are sparse proper (i.e. metamorphic) basement exposures, granitoid plutons are more common throughout Thailand, and are useful for understanding the nature of the unexposed basement. There are two main events that led to this granite emplacement: the Permo Triassic closure of the Paleo-Tethys Ocean (and the resultant Indosinian Orogeny) and the Mesozoic–Paleogene closure of the Neo-Tethys ocean. However, the precise timing of the individual collisional events that make up the Indosinian Orogeny remains uncertain.

Our petrochronological investigations aim at better defining the metamorphic and temporal evolution of the major plate tectonic units in Thailand (Sibumasu, Doi Inthanon, Sukhothai, Indochina) during the last 500 million years.

At present, these units are mainly categorized by their respective Mesozoic and Cenozoic evolution (Indosinian and younger), mostly based on radiometric cooling ages and equilibrium thermodynamics. Modern petrochronological data describing the pressure-temperature-time-structural evolution are completely missing, as stated above.

We aim at providing such petrochronological data in order to unravel the high-temperature and -pressure evolution of the Thai basement units, to better understand their related but also the unrelated geological development and finally to provide more consistent plate tectonic models for the evolution of SE Asia, especially in view of the escape tectonics within the Alpine-Himalayan orogeny.

These investigations are made in the frame work of a fully funded 4 year PhD project.

Publications:

– Kanjanapayont, P., Klötzli, U., Charusiri, P., Klötzli-Chowanetz, E. (2011): A preliminary LA-MC-ICP-MS U-Pb zircon geochronology of the Lan Sang and Chon Buri gneisses, Thailand. GEOINDO2011, Khon Kaen, Thailand.

– Kanjanapayont, P., Klötzli, U.S., Thöni, M., Grasemann, B., Edwards, M. (2012): Rb-Sr, Sm-Nd, and U-Pb geochronology of the rocks within the Khlong Marui shear zone, southern Thailand. Journal of Asian Earth Sciences, 56, 263-275.

– Kanjanapayont, P., Kieduppatum, P., Klötzli, U., Klötzli, E., Charusiri, P. (2013): Deformation history and U-Pb zircon geochronology of the high grade metamorphic rocks within the Klaeng fault zone, eastern Thailand. Journal of Asian Earth Sciences, 77, 224-233, doi: 10.1016/j.jseaes.2013.08.027.

– Ponmanee, P., Kanjanapayont, P., Grasemann, B., Klötzli, U., Choowong, M. (2016): Quantitative finite strain analysis of high-grade metamorphic rocks within the Mae Ping shear zone, western Thailand. Austrian Journal of Earth Sciences, 109/2, 233-240 doi: 10.17738/ajes.2016.0017.

– Kanjanapayont, P., Ponmanee, P., Grasemann, B., Klötzli, U., Nantasin, P. (2018): Quantitative finite strain analysis of the quartz mylonites within the Three Pagodas shear zone, western Thailand. Austrian Journal of Earth Sciences, 111/2, 1-9, doi: 10.17738/ajes.2018.0011.

– Klötzli, U., Österle, J., Kanjanapayont, P., Neugschwentner, B., Burda, J. (2018): Geochronological research in the crystalline basement units of N Thailand: a review. GREAT 2018, Bangkok, 4-23.

– Oesterle, J., Klötzli, U., Stockli, D., Palzer-Khomenko, M., Kanjanapayont, P. (2019): New age constraints on the Lan Sang gneiss complex, Thailand, and the timing of activity of the Mae Ping shear zone from in-situ and depth-profile zircon and monazite U-Th-Pb geochronology. Journal of Asian Earth Sciences, 181, 1-21, doi: https://doi.org/10.1016/j.jseaes.2019.103886.

– Kanjanapayont, P., Klötzli, U., Frank, N. (2020): Dating multiple generation of zircons from granites and gneiss from Thailand: Implication for the crustal evolution of the Sibumasu terrane. Journal of Asian Earth Sciences, doi: https://doi.org/10.1016/j.jseaes.2019.104148.