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Mathematical Model to Define Eruptive Stages of Young Volcanic Rocks

Achieving high-precision dating of young volcanic rocks in Southeast China, Tengchong, using Gaussian mathematical modelling based on Argon-Argon dating.

The Tengchong volcanoes in Southeast China is home to one of the youngest volcanic areas and is characterized by multi-stage eruptions and complex overlapping relationships. Stages of volcanic eruption within this area has been largely contentious.

In a recent research funded by the Geological Survey Project of the China Geological Survey Bureau, the team used radiometric dating to the main volcanic units in the Tengchong area and obtained ages ranging from 0.025 to 5.1 million years based on conventional data processing methods.

Traditionally, dating of young volcanic rocks is a challenging task and requires high-precision in the process. Many variables that contribute to age deviation include the low radiogenic content, inconsistency in Argon-Argon ratios, precision of instruments used, errors that arise during preparation and measurement. The lack of a unified timescale caused conventional methods to be unable to strictly define the stages of the Tengchong volcanic eruptions. Such uncertainty related to using a single age as an eruption age in the absolute chronological study of volcanic eruptions can even be misleading.

To solve these issues, the researchers adopted a Gaussian mathematical model, dealing with all 378 original ages from 13 samples. An apparent age-probability diagram, consisting of three independent waveforms, have been obtained. The corresponding isochron ages of these three waveforms suggest there were three volcanic eruptive stages, namely during the Pliocene, early Middle Pleistocene and late Middle Pleistocene to early Late Pleistocene.

This new method proposed by the team for identifying stages within the same timescale has the advantage of controlling variables, reducing deviation, approaching the true age value, weakening the influence of subjective factors and precisely defining the eruptive stages in young volcanic rocks. Increasing the number of testing data, the final result will be more representative of the real volcanic history, with reproducible and verifiable eruptive stages. [APBN]