¹⁴C AGES OF SOME QUARTERNARY EXPLOSIVE ERUPTIONS IN SOUTHERN PHILIPPINES

F.G. Delfin, Jr.¹, C.G. Newhall², D. Trimble³, M.L. Martinez-Villegas⁴, Syed Hussain⁵, F.E.B. Bayon¹, R.D.C. Leynes¹, J.E.A. Caranto¹ and W.P.C. Pioquinto^1
1PNOC Energy Development Corp., Merritt Road, Ft. Bonifacio, Metro Manila, Philippines 1201
²US Geological Survey, Dept. of Geological Sciences Box 351310,
University of Washington, Seattle, WA 98195, USA
³Radiocarbon Laboratory, US Geological Survey, Menlo Park, CA 94025, USA
⁴Philippine Institute of Volcanology and Seismology, Diliman, Quezon City, Philippines 1104
⁵Pakistan Institution of Nuclear Science and Technology, Islamabad, Pakistan

ABSTRACT

        14C age-determinations in four southern Philippine volcanoes document the absolute ages of some Quaternary explosive eruptions in the region, spanning from late Pleistocene to the 17^th century. Seven ¹⁴C dates indicate at least four explosive eruptive events in the Lake Leonard center, a solfataric andesitic to dacitic dome complex. These ages are 25ka, 12ka, 6ka, and ~1.8ka. The youngest event corresponds to a major explosive eruption about 1,800 ybp that ejected dacitic tephra over a wide region and formed the 2.5 km-wide Lake Leonard caldera.

        A 7.5 ka ¹⁴C age obtained in a pyroclastic deposit on Mt. Apo’s northwest slope represents an eruptive event from "modern" Apo’s present summit crater. In Mt. Matutum, three ages indicate at least two distinct recent explosive eruptions: ~2.2 ka and ~600 ypb. These indicate that the explosive eruptions that produced the widespread pyroclastic apron around Matutum are most likely younger than the formation of Matutum's summit cone.

        In Mt. Parker, fourteen ¹⁴C age-dates have established at least four major explosive eruptions: 23- 27 ka, 3.8 ka, ~600 ypb, and ~300 ybp. All four events involved dacitic magma erupted largely as pyroclastic flows. The ~300 ybp event formed Mt. Parker’s 3 km-wide caldera and coincides with the giant eruption of January 4, 1641 described in Spanish-era documents. Parker's eruptive characteristics are remarkably similar to Pinatubo and the potential eruption of juvenile silicic magma in Parker needs to be carefully assessed by additional studies.

        Although far from comprehensive, our available ¹⁴C data, combined with field studies of the four volcanoes, suggest that: 1) the oldest dated explosive events in Lake Leonard and Parker are roughly contemporaneous, ~25ka, 2) explosive volcanism in southcentral Mindanao, associated with the extinct Sangihe trench and the active Cotabato trench is younger and more voluminous compared to that in southeastern Mindanao which is related to the subduction along the Philippine Trench.