碩士 / 國立臺灣大學 / 地質學研究所 / 88 / The core, MD972142 raised from offshore northwestern Palawan in the South China Sea during the IMAGES III-IPHIS-Leg II Cruise, contained 18 distinct tephra layers. The thickness of the tephra layer ranges from 2 cm to 50 cm. The major components of these tephra layers are volcanic glass, pumice, mineral crystals and lithic fragments. The topest tephra layer, which is near core top and obviously dragged, is not analyzed in this study. The other 17 tephra layers from core depth of 170-2408 cm were sampled for size and geochemical analysis. According to the oxygen isotope stratigraphy, the estimated ages of these 17 tephra layers are from 40-490 ka.
Combined with the detailed core description and the result of size analysis, we can conclude that the particle sizes of most volcanic pyroclasts are bigger than ~30-40 μm and limit in the size range of 60-125 μm. The size distribution pattern of the tephra layers would indicate the settling condition of tephra and may follow the experiment results of Carey (1997).
The geochemical data of pumice in tephra layers clearly show medium K2O and high K2O calc-alkali series in the variation diagram of SiO2 vs. K2O plot. The data reveal a wide range of SiO2 (SiO2= 57~80 wt.%). Comparing with the other data, the data of pumice in tephra layer 3 (~80 ka) show the highest SiO2 and lower K2O content. Some data of pumice in layer11 (~300 ka) and layer17 (~485 ka) show a high-K trend clearly different from data of other tephra layers. It implies that the layer 3, 11, and 17 may not erupt from the same volcanic province with other tephra layers.
Meanwhile, the volcanic glass from tephra layers (L3, L4, L5, L6, L7, L8, L9, L12, L13, L14, L15) exhibit typical geochemical arc signature of Ta-Nb-Ti depletions. Comparing with the available geochemical data of on-land lavas around this area, the Macolod Corridor of Southern Luzon arc may be considered as the most possible sources for most tephra layers except layer3.
The pumice in tephra layer 11 (L11) exhibits unusual high K2O contents (K2O=3.5~5.8%) indicating it may have different sources from the others. The age (~485 ka) and geochemical data of pumice in tephra layer 17 are similar with the Middle Toba Tuff (MTT), although we need more evidences to confirm its source. The major element data of pumice in tephra layer 3 fall into the composition range of Mt. Pinatubo eruption, 1991. In addition, the trace element data of L3 are similar with the data of rhyolite sample of Mt. Pinatubo. Hence, it implies that Mt. Pinatubo may be the eruptive source for L3.
| Identifer | oai:union.ndltd.org:TW/088NTU00138009 |
| Date | January 2000 |
| Creators | Rong-Hao Tsai, 蔡榮浩 |
| Contributors | , 楊燦堯, 陳中華, 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 | 59 |
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