Dizhi lixue xuebao (Apr 2023)
Research on the applicability of electron spin resonance dating of the late Quaternary sinter deposits in the rift valley, southern Tibet
Abstract
Sinters in the rift valleys of southern Tibet, including silica sinter and travertine deposits, are the products of hydrothermal activity under regional tectonic movement. Their formation age is significant for studying hydrothermal activity history in this region. Electron spin resonance (ESR) dating is a practical dating method for determining the age of silica sinter and travertine deposits. However, silica sinter's ESR signals vary due to the complex composition. Meanwhile, these ESR signals are mixed, superimposed, and interfere with each other, affecting the ESR signal's measurement. Furthermore, ESR dating has been applied less in travertine samples in southern Tibet, which is not conducive to a comprehensive understanding of the hydrothermal activity history in southern Tibet. Studying the applicability of ESR dating of southern Tibetan silica sinter and travertine deposits helps obtain accurate ESR ages. It lays the chronologic foundation for researching tectonic activities in these rift valleys. This research applied ESR dating to the silica sinter and travertine deposits collected separately from the Targejia thermal field area and the Xiakangjian hot spring area, located in the Ngri-Xigaze area in southern Tibet. We performed ESR dating tests, including how to choose ESR signals, the effect of additional doses, and the thermal stability of ESR signals in travertine. Based on these tests, relatively accurate, reliable ESR ages of silica sinter and travertine were obtained. The results show that: According to the ESR dating results, the silica sinter samples collected from the fourth and third terrace of the Targejia geothermal field were formed at 177±20 and 81±16 ka, respectively, and the travertine deposits collected from the floodplain and first terrace of the Xiakangjian hot spring were formed at 106±32 ka and 264±26 ka, respectively. In terms of irradiation dose, sinter samples collected from southern Tibet respond well to irradiation dose in the range of 0~7680 Gy; In terms of temperature, silica sinter samples are less affected by closure temperature, and the thermal behavior of the ESR signal at g=2.0034 of travertine in southern Tibet is stable in the range of 20 ℃~250 ℃ that is suitable for ESR dating. Regarding mineral structure, The travertine in southern Tibet has better mineral purity and crystallinity; thus, the ESR age results are relatively accurate.
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