Implications of Crystal Zoning for Magma Reservoir Processes at the Tatun Volcanic Group, Taiwan

The current state of the Tatun Volcanic Group (TVG), situated within the capital of Taiwan, has been under heavy debate for decades. Officials have long since declared it to be inactive, while many geologists believe it to be active. In 2016, using seismological methods, Lin et al. detected what is believed to be a magma reservoir seated 20 kilometers beneath the Taipei metropolis; consequently, some began to believe its existence is evidence that the TVG remains active and future eruptions may still occur, others speculate the great depth of the reservoir implies that the magma is subsiding, therefore, inactive. However, the magmatic system of the TVG is not well understood, thus, the debate remains inconclusive.

In this study, we attempt to identify the magmatic processes of the TVG magma reservoir to better explain the patch of magma deep under the city of Taipei found by Lin et al. (2016).Thin sections of andesites and basalts were analyzed by an SEM and a synchrotron nanoprobe. Preliminary results revealed chemical zoning present within a number of plagioclase and amphibole crystals that may indicate an event in the reservoir the crystals recorded prior to eruption. Iron and chromium content are higher in the outer rims of the amphibole crystals, while calcium content is higher in plagioclase cores.