Argon geochronology lab
Research Field
Specialties: Structural Geology, Microstructural Geology, Tectonic evolution, Geochronology
Research interests: Applying multiscale structural evolution reconstruction of orogeny and or shear belts in southeast Asia. In charge of NTNU Ar-Ar Lab facility.
personal webpage https://twstemhime.wixsite.com/maryyeh
please visit the lab web page: https://ntnuararlab.wixsite.com/ararlab
The exploration and pursuit of geological ages have always been a distinctive aspect of geology. The 40Ar/39Ar dating method, an extension of the K-Ar dating method, is one of the techniques used to determine the ages of rock minerals. Potassium is widely present in various types of rocks and minerals, while argon is an inert gas that does not readily react with other chemicals. This makes these two elements suitable for analysis. Solid potassium, when irradiated with neutrons, undergoes isotope decay and transforms into argon. By using high temperature or laser fusion methods, argon gas trapped in minerals and rocks can be released and the "absolute age" of the rock or mineral can be measured. The argon-argon dating laboratory in this department inherits from the former National Taiwan University Department of Geology's argon-argon dating laboratory. It consists of three sets of mass spectrometers, each paired with a step-heating furnace, CO2 laser, and 193nm excimer laser. The laboratory was transferred to Shih Hsin University in 2017.
Step-heating dating system: This system uses the VG1200S mass spectrometer as the main analytical instrument, equipped with dual vacuum systems. It can be heated up to 1700oC using a Mo high-temperature furnace under ultra-high vacuum conditions for sample analysis. Between the sample system and the mass spectrometer, there is an ultra-high vacuum stainless steel automatic gas purification system. The VG1200S uses a Faraday cup to detect charged particles and measures the signals of 40Ar, 39Ar, 38Ar, 37Ar, and 36Ar to calculate the age of the sample. This method is suitable for minerals and rocks with complex ages, metamorphism, or tectonic events.
Laser fusion dating system: This system uses the VG3600 mass spectrometer as the main analytical instrument, coupled with a state-of-the-art CO2 laser and an ultra-high vacuum sample chamber as the sampling system. It can be used in continuous or pulse mode for single-grain sample fusion dating and step-heating analysis. The VG3600 uses a Faraday cup and a multiplier to detect charged particles, measuring the signals of 40Ar, 39Ar, 38Ar, 37Ar, and 36Ar to calculate the age of the sample. Due to the multiplier's sensitivity being 100 times that of the Faraday cup, this analysis system is suitable for geologic events with a single event, young ages, and small sample sizes, although it may require a large number of analyses for minerals and rocks.
Laser ablation dating system: This system uses the Nu Noblesse mass spectrometer as the main instrument, employing patented focusing equipment for multiple isotope reception. It is coupled with the UP193-FX excimer laser and an ultra-high vacuum sample chamber for spot micro-area dating and single mineral fusion dating experiments. This technique provides a convenient and direct method to measure the distribution of argon isotopes within minerals, allowing for the determination of age profiles within minerals. It enables direct comparison and linkage between structures, metamorphic conditions, pressure, and age.
This laboratory welcomes collaboration in natural science research and analysis.
Please note:
Argon-argon dating method applicable to minerals: Potassium-rich minerals such as potassium feldspar, mica minerals, amphibole, etc., as well as altered minerals and whole-rock analysis of volcanic rocks. Weathering can disrupt the potassium-argon isotope system, so only fresh samples can be analyzed. All sampling and mineral purification processes must avoid contamination with oils. The mass spectrometer operates under ultra-high vacuum conditions, and oil contamination not only increases background values but can also lead to significant errors in sample age due to the similar molecular weights of some hydrocarbons and argon isotopes. Mineral samples such as potassium feldspar, mica minerals, amphibole, etc., require approximately 50 mg (>95%), and whole-rock samples of volcanic rocks require around 500 mg (>95%).
The main research procedures we apply are as follows: The development of analytical techniques that integrate structural geology, petrology, and argon-argon dating, and the establishment of a research methodology that involves clarifying large-scale structures → microstructures → combining petrology to understand temperature and pressure conditions during rock deformation → incorporating isotope dating (U-Pb zircon and various mineral Ar-Ar dating) → to conduct a comprehensive four-dimensional (spatial and temporal) study of the structural and tectonic evolution history of the study area.
For the evolution of the Tibetan Plateau and Southeast Asian tectonics, a mechanism of exhumation followed by retrograde fluid-assisted tectonic movement has been proposed (Chiu et al., 2018, 2023). By reconstructing the structure and tectonic evolution across the Red River Shear Zone from Yunnan to Vietnam, the initiation age of the left-lateral movement of the Red River Shear Zone has been revised to postdate the South China Sea rifting event. The exhumation slab model has been revised to clarify the interaction dynamics and tectonic framework between the Red River Shear Zone, the Tibetan Plateau, and the South China Sea Rift (Yeh et al., 2008; 2014). Regarding the spatiotemporal distribution of Mesozoic magmatic events around the South China Sea, the relationship between the retreat of the ancient Pacific Plate and the weakening and thinning of the Southeast Asian continental crust has been elucidated. It has been proposed that the extension in the South China Sea during the Cenozoic is related to the subduction zone from the Sunda Trench to Indonesia, rather than the escape of the Indochina Block (Mai et al., 2018). The latest achievement is the clarification of the structure and metamorphic evolution of the Kinmen multi-phase magmatic complex, providing detailed insights into the timing and sequential evolution of crustal thinning along the southeastern margin of South China since the Mesozoic (Huang & Yeh, 2020).
The above represents the most significant research outcomes under my leadership. Additionally, there are collaborative achievements in various areas, such as the significance of plate tectonics in the central African magmatic evolution (Shellnutt et al., 2017, 2019), the impact of glacier retreat on the evolution of the Gangwana Block (Yeh and Shellnutt, 2016), the evolution of the Appalachian Mountains in North America, paleocontinental reconstruction, and more (Yeh and Bell., 2004; Shellnutt et al., 2018, 2019), and others.
- 2014 NTNU Excellent Research Achievement Award for the Year 2013
- 2013 National Science Council Outstanding Contribution to Technology Transfer Award
- National Taiwan Normal University Incentive Awards for Increasing the Number of Ministry of Science and Technology Projects for the Year 103 (2014)
- National Taiwan Normal University Incentive Awards for Increasing the Number of Ministry of Science and Technology Projects for the Year 104 (2015)
PhD in Structural geology from School of Earth Sciences, James Cook University, Australia
Bs in Geology Department, University of Maryland college park, USA
1 Vacancy
Job Description
The intern posistion is open for 2024 Oct ~2024 Dec, not for other time period
Preferred Intern Education Level
Master with informatic, mathmatic, or statistic backgroud is prefered. Must be familier with phython and R language.
Skill sets or Qualities
Had experience to develop database system. Can develop custom made software. Good communication ability.