Seismotectonics of the Philippine Archipelago

[地球化学]为了确定菲律宾海沟俯冲的开始时间，对吕宋岛比科尔彭苏拉11座火山的37个样品进行了K-Ar年龄测定。用X-射线荧光光谱仪测定了主量元素和微量元素组成。测年结果表明，比科尔火山活动最晚开始于7 Ma，比莱特和棉兰老岛更早开始火山活动和俯冲。尽管Bicol的火山活动可按年龄差距分为三组，但常量元素和微量元素化学在这三组之间没有明显差异。测年结果表明，菲律宾海沟俯冲作用最晚开始于8~9 Ma。这一年龄与巴拉望地块与菲律宾群岛在8-9 Ma碰撞的时间一致，被认为是触发了沿菲律宾海沟的俯冲。1.确定…与菲律宾海沟三重交界区的复杂构造在更多的菲律宾海、澳大利亚和孙达兰板块，我们自1997年以来每年都实施GPS运动测量。为了估计摩卢卡海的俯冲样式，除了GPS速度场外，我们还使用了地震活动和重力异常数据。而在摩鲁加北部存在一个向西倾斜的板片。海，南部有两块向东倾斜和向西倾斜的主板。摩鲁加海的俯冲样式从北到南变化很大。从1998年9月到2001年9月，在菲律宾吕宋岛的马科洛德走廊(MC)附近进行了五次GPS定位。使用Bernese GPS软件Ver.4.0时，在研究区南部探测到2~3 cm/年的左旋运动，并有大量逆时针运动。此外，在MC中还发现了大量指向NNW-SSE或N-S的延伸。这些观察结果与最近的古地磁研究和MC及其周围火山岩的K-Ar定年研究确定的2 Ma以后的块体运动是一致的。GPS观测到的这些地壳运动可能与MC的形成过程密切相关。较少

[Geochemistry]In this study, K-Ar ages of 37 samples from eleven volcanoes in Bicolpenmsula of Luzon were measured in order to constrain the timing of the initiation of the subduction along the Philippine Trench. Major and trace element composition was also measured by XRF. Dating results show that the volcanism started at latest 7 Ma in Bicol, suggesting earlier initiation of volcanism and subduction in Bicol than in Leyte and Mindanao. Although volcanic activitiesin Bicol may be divided into three groups by age gaps, major and trace element chemistry did not show significant difference between these groups. Dating results suggest that the subduction along the Philippine Trench initiated at latest 8-9 Ma. This age is consistent with the timing of the collision of the Palawan block with the Philippine archipelago at 8-9 Ma which is considered to have triggered the subduction along the Philippine Trench.[GPS]1. For determining complicated tectonics in the triple junction region between … More the Philippine Sea, the Australian and the Sundaland plates, we have implemented GPS campaign measurementsevery year since 1997. To estimate subduction style in the Moluca Sea, we used seismicity and gravity anomaly data in addition to the GPS velocity field. While a westward dipping slab exists in the northern part of the Moluca. Sea, two main slabs that dips to the east and the west exist in the southern part. Thesubduction style in the Moluca Sea shows large variability from north to south.2. From September 1998 through September 2001, five GPS campaigns were made inand aroung the Macolod Corridor (MC), in the Luzon island, Philippines. After analyzing data using Bernese GPS software Ver. 4.0, a left lateral motion at 2-3 cm/yr with a large amount of counterclockwise motion was detected in the southern part of the study area. Furthermore, a large amount of extension, directing NNW-SSE or N-S was found in the MC. These observations are consistent with the block motion after 2Ma determined through a recent paleomagnetic research and a K-Ar dating study of volcanic rocks in andaround the MC. It is possible that these crustal movements detected by GPS observations are closely related to the formation process of the MC. Less