The volcanic history of the late Pleistocene Shamao complex, Tatun Volcano Group, northern Taiwan

Abstract

Abstract Although the Tatun Volcanic Group (TVG) looms over the metropolitan capital region of Taiwan, the threats it poses are only vaguely known. Here, as a first step toward improving understanding those threats, we investigate the Shamao complex, one of the youngest and smallest features of the TVG. Analysis of a high-resolution, LiDAR-based, Digital Terrain Model (DTM), augmented by sparse outcrops and a drill core, reveals an episodic, multi-event pyroclastic density currents (PDCs), particularly block-and-ash flow (BAF) succession rather than a single slump event. This demonstrates that the complex consists of overlapping West and East Domes and an older West Flow, which extends southwestward ~ 650 m from a source on the flank of the domes. High-precision 40 Ar/ 39 Ar analyses reveal that West Flow erupted at 196.4 ± 2.3 ka, long before the eruptions of East Dome at 24.2 ± 1.8 ka and West Dome likely soon thereafter. The three principal landforms of the complex consist of crystal-rich volcanic rocks with basaltic-andesitic to andesitic bulk compositions and limited Sr–Nd isotopic variations, grossly similar to other published data for the TVG. However, subtle differences in petrography and trace element geochemistry likely reflect differing mineralogy and melt fraction during magma extraction. Overall, our combined geomorphologic, geochronologic, petrologic, and geochemical approach suggests that the development of the Shamao complex involved intermittent magma extraction from one or more mush systems over 10–100 kyr timescale, in the Pleistocene.