Zircon U-Pb Age Determination of Volcanic Eruptions in Lutao and Lanyu in the Northern Luzon Magmatic Arc

This paper reports for the first time zircon U-Pb ages of volcanic rocks and sands from Lutao and Lanyu, two islets off SE Taiwan in the north Luzon arc. The samples include (1) seven andesites from four volcanic units and three river/beach sands from Lutao and (2) five basaltic andesites from four volcanic units and two river/beach sands from Lanyu. The Lutao andesites contain abundant magmatic zircons, aging from similar to 1.54 to similar to 1.24 Ma for individual sample, which yielded an overall mean Pb-206/U-238 age of 1.31 +/- 0.03 Ma (n = 190, MSWD = 2.6). This is slightly older than, or broadly coincident with, a mean Pb-206/U-238 age of 1.23 +/- 0.03 Ma (n = 103, MSWD = 1.9) given by detrital zircons from the three sands. The Lanyu volcanics appear to have less abundant magmatic zircons, aging from similar to 2.72 to similar to 2.35 Ma for individual sample, which yielded an overall mean Pb-206/U-238 age of 2.61 +/- 0.13 Ma (n = 11, MSWD = 1.8). This accords with a mean Pb-206/U-238 age of 2.69 +/- 0.11 Ma (n = 34, MSWD = 4.7) obtained by detrital zircons from the two sands. The age data suggest that in Lutao and Lanyu the major volcanic eruptions occurred at similar to 1.3 and similar to 2.6 Ma, respectively. Moreover, volcanic samples from both islets contain various amounts of older inherited zircons, similar to 11% in Lutao and up to similar to 82% in Lanyu, which together with detrital zircons from the sands show main age peaks at similar to 150 Ma and similar to 1.9 and similar to 2.5 Ga, consistent with the notion for a hidden continental crust involved in the genesis of the northern Luzon magmatic arc.