TY  - JOUR
A1  - Ozawa, Ayako
A1  - Tagami, Takahiro
A1  - Listanco, Eddie L.
A1  - Arpa, Carmencita B.
A1  - Sudo, Masafumi
T1  - Initiation and propagation of subduction along the Philippine Trench : evidence from the temporal and spatial distribution of volcanoes
N2  - K-Ar ages of 37 samples collected from the Bicol peninsula, the Luzon island, Philippines, were determined by the unspiked sensitivity method in order to constrain the timing of initiation of subduction along the Philippine Trench. The measured K-Ar ages range from 0 to 7 Ma with two old outliers of 27 and 43 Ma. Together with K-Ar ages previously reported on volcanics in Leyte and eastern Mindanao, subduction volcanism has likely propagated from north to south: similar to 6.6 Ma in Bicol and similar to 3.5 Ma in Leyte and its vicinity. The temporal and spatial distribution suggests that the subduction volcanism started earlier in the north than in the south. This is consistent with the southern propagation of subduction along the Philippine Trench from similar to 8 Ma. (C) 2003 Elsevier Ltd. All rights reserved
Y1  - 2004
SN  - 1367-9120
ER  - 
TY  - JOUR
A1  - Ozawa, Ayako
A1  - Tagami, T.
A1  - Sudo, Masafumi
T1  - K-Ar geochronology of the temporal change of eruptive style in the eastern Izu peninsula, central Japan
N2  - A recent K-Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3-0.2 Ma. To narrow down the time of change, we determined 10 K-Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26- 0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29-0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism
Y1  - 2004
SN  - 1038-4871
ER  -