碩士 / 國立臺灣大學 / 地質科學研究所 / 92 / The core, MD972143 raised from the West Philippine Sea during the IMAGES III-IPHIS-Leg II Cruise in 1997, contained ten distinct tephra layers. They were sampled for geochemical and size analyses. Thickness of these tephra layers ranges from 1 to 12 cm. The shape of grains in tephra layers is angular and the average of particle size is about 10-30μm suggest that they may be directly deposited from nearby volcanic eruptions. According to the magnetostratigraphic records and oxygen isotopic stratigraphy, these tephra layers provide the evidence of volcanic activities near Luzon arc in last 2 Myrs.
The geochemical data of pumices and glassy shards in ten tephra layers reveal a wide range of SiO2 from 58% to 80%. However, these of Layer-2 (ca. 260 ka) and Layer-3 (ca. 280 ka) are clearly distinguished into 2 parts — one shows the highest SiO2 (ca. 80%), while the other is medium (ca. 58-66%). The contents of K2O range from 2 to 5% and most plot into the field of HKCA (High-K Calc-Alkaline Series), e.g. Layer-1, part of Layers 4, 5, 6, 7, 8 and 10. However, the Layers 2 and 3 have lower K2O value than the average and in the feld of MKCA (Medium-K Calc-Alkaline Series), while the Layers 8 and 9 are higher than 5% and in the field of shoshonitic series. The ratio of Sr-isotope are between 0.703838±16 and 0.704793±16.
Based on the available geochemical data of on-land lavas around this area, and the results of particle occurrence and size, geochemical analyses and ages in the core MD972143, the tephra layers may dominantly come from the volcanism in the “Macolod Corridor” of southern Luzon arc, e.g. Layer-1, and intermediate part of Layers 3, 4, 6, 7, 8 and 10. In addition, the acidic part of Layer-2 may have relations with Mt. Pinatubo in the Bataan Segment. However, the Layer-5 and HKCA part of Layers 8 and 9 can’t correlate to the volcanic deposits of the Philippine arcs.
The thickness and particle size of tephra layer in the deep-sea basin are resulted from the magnitude of the eruption. The thicker bed and larger size deposited, the larger magnitude erupted. Assuming the same conditions of wind direction and strength in this area in last 2 Myrs, the order of eruptive magnitude of the Layers 1, 4, 6, 7,and 10, come from the same source — Macolod Corridor, are Layer 4 (ca. 296 ka), Layer 1 (ca.163 ka), Layer 10 (ca.1980 ka), Layer 7 (ca. 1520 ka), and Layer 6 (ca. 1500 ka), respectively.
There is a well-correlated tephra layer in the Layer 10 of the Core MD972142, located in South China Sea and the Layer 3 of the Core MD972143 in terms of geochemical, particle size and age data. The good relationship suggests that they may be from the same source, the Macolod Corridor of central Luzon.
| Identifer | oai:union.ndltd.org:TW/092NTU00138002 |
| Date | January 2003 |
| Creators | I-Hsuan Huang, 黃宜萱 |
| Contributors | Sheng-Rong Song, 宋聖榮 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 0 |
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