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Evolution of the Songshan complex (Tatun Volcanic Group, northern Taiwan) from geomorphological mapping, 40Ar-39Ar dating, petrology and geochemistry

Shih-Jui Shrek Lin 1†, Sheng-Yu (Welson) Li1†, Kerry Sieh1,2, Brian Jicha3, Kwan-Nang Pang2, Tai Truong Nguyen2,4, Hao-Yang Lee2, Yoshiyuki Iizuka2

  • Affiliations: 1Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan; 2Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan; 3Department of Geoscience, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA; 4Department of Geology, Hanoi University of Mining and Geology, Vietnam; †these authors contributed equally to this work as co-first authors

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 176

  • Programme No: 3.5.35

  • Theme 3 > Session 5

Abstract

The Tatun Volcanic Group (TVG) is a cluster of young volcanic centers on the northern flank of Taiwan's capital, Taipei. It is too poorly understood to reliably and quantitatively evaluate the hazards it poses. Here we report initial results from a multi-disciplinary study of one of these volcanic centers, the Songshan complex. Analysis of high-resolution LiDAR-based topography reveals a ten-km long array of at least six overlapping lava flows that extends from Mt. Songshan northward to the coast. Several new 40Ar-39Ar dates reveal that these six flows erupted over about 35,000 years, between 279.8 ± 3.3 and 246.1 ± 1.3 ka. Ages of 329.7 ± 1.8 and 437.6 ± 1.8 ka on andesitic boulders within a set of younger lahars on the western flank of the flows point to still older, highly eroded and buried flows in the headwaters of the Songshan drainage. Whole-rock geochemical analyses show that the samples share the following features: (i) intermediate SiO₂ contents (54--60 wt.%), and (ii) all belong to the calc-alkaline series. Furthermore, geochemical and petrographic analyses suggest that the flows can be grouped into basaltic andesitic and andesitic, reflecting distinct compositional trends. Initial evidence suggests a dual-magma-chamber, episodic model for the Songshan complex, with compositional diversity likely tied to separate magmatic sources or evolutionary pathways. We will test this model via further examination of volcanic stratigraphy, geomorphology, and geochronology. By placing the Songshan complex within a robust framework, we will provide more reliable, quantitative assessments of the hazards posed by the TVG.