Geomorphological mapping, 40Ar/39Ar geochronology, and geochemistry of the Huangzuei complex (Tatun Volcanic Group, Taiwan): Implications for volcanic architecture and magma generation

The Huangzuei complex is a volcanic complex within the 25 km-wide Tatun Volcanic Group (TVG), which is situated on the northern tip of Taiwan and poses significant potential hazards to the Taipei metropolitan area. The Huangzuei complex has well-preserved landforms with three sets of lava flows that radiate northwestward, northeastward and southeastward up to several kilometers from Mt. Huangzuei, the 250-m-high cratered summit of the Huangzuei complex.

High-resolution topography from a LiDAR-based bare-earth DEM enables detailed demarcation and characterization of individual flows, including volume, thickness, and profiles. Results of our geomorphological mapping and ⁴⁰Ar/³⁹Ar dating of volcanic matrix reveal that eruption of the Huangzuei complex began at 139 ka, was most vigorous from ~129 ka to 133 ka and resumed at ~116 ka. The south-eastern branch of lavas partially overlap ~264-298 ka lavas that may have erupted from Dajianhou, another neighboring volcanic complex. It is likely that the Huangzuei volcanism ended in the formation of domes and a summit crater at 85 ka or later.

Disequilibrium textures, including oscillatory zoning, reverse zoning, partial resorption, and development of reaction rims, are common in samples from the Huangzuei complex. These textures, together with the wide ranges of mineral compositions (Mg# of pyroxenes and An content of plagioclase), indicate that the magma that formed the Huangzuei complex underwent intense magma hybridism, likely involving periodic replenishment by more primitive magmas during crystallization differentiation. We propose the latter as the cause of the voluminous lava emplacement from ~129 to ~133 ka.