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題 名 | Petrogenesis of the Chilung Volcano Group Andesites in Northern Taiwan: Mixing with Shallow Sediments and Amphibole-Rich Nodules in the Andesitic Melts=臺灣北部基隆火山群安山岩之成因:安山質熔漿混入淺沈積物以及富含角閃石岩塊 |
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作 者 | 陳正宏; | 書刊名 | 中國地質學會會刊 |
卷 期 | 42:4 1999.11[民88.11] |
頁 次 | 頁559-592 |
分類號 | 358.36 |
關鍵詞 | 岩石成因; 基隆火山群安山岩; 富含角閃石岩塊; 沈積物; Petrogenesis; CVG andesites; Amphibole-rich nodules; Sediments; |
語 文 | 英文(English) |
中文摘要 | 屬於更新世之基隆火山群火成岩主要分佈於五個較大的單元,包括基隆山、武丹 山、本山、草山和雞母嶺以及一個較小的單元 - 基隆島。 其岩性特徵為含有反應程度不一 的角閃石和黑雲母、富鈣斜長石、自形磁鐵礦、以及具熔蝕逆而渾圓的石英等斑晶。二十八 個樣本的元素含量分析結束頗示各單元的化李成分差異不大 (SiO �祐t量介於 55.5 至 58.5wt %之間 ),總社而言可視為大陸邊緣隱沒帶附近鉀含量中等的鈣鹼性安山岩, 但有 些受到輕度青磐岩化的樣本具有鉀、鋰、銣、鋇含量增高之現象。其鍶、釹同位素值則顯示 形成這些火成岩的過程中應包含了富化物的介入,最可能的是上部地般物質。此等火成岩之 成因模式係以岩象觀察、微量元素和鍶、釹同位素成分來規範。岩中所含之角閃石、黑雲母 、富鈣斜長石及磁鐵礦應屬捕獲而來之富含角閃石岩塊之崩解物,而渾圓之石英顆粒可能來 自於五指山砂岩層的混染, 前者含量可達約 15 %,而後者含量約 5-12 %。 基於全岩的 SiO �祐t量低以及所含石英並非岩漿結晶分異過程形成的城物,過去對這些岩石所常用的名 詞 " 石英安山岩 (dacite)" 應予捨棄。 |
英文摘要 | Pleistocene igneous rocks in the Chilung Volcano Group(CVG) mainly distribute in five larger geographic units includingChilungshan, Wutanshan, Pensban, Tsaoshan and Chimuling(1.4-0.9 Ma), and one smaller unit in the Chilungtao (0.3 Ma).They are characterized by having highly reacted amphiboles, slightly resorbed micas, Ca-rich plagioclases, euhedral magnetites,and large corroded and rounded quartz grains as phenocrysts.Chemical compositions for 28 rock samples are rather uniform,with SiC) �� contents varying from 55.5 to 58.5 wt%. In general, these rocks can be regarded as medium-K calc-alkaline andesitesin an orogenic belt, with some slightly propylitized rocks high inK (K20=3.5-3.7 wt%), Li (45 ppm), Rb (230 ppm) and Ba (930-960 ppm). Sr and Nd-isotope ratios of CVG andesites suggestthat incorporation of an enriched component, most probably the upper crustal material, is necessary. Petrogenetically, amphibole, mica, plagioclase and magnetiteare considered to be the disintegrated member of the captur edamphibole-rich nodules, i.e., the cumulates for earlier magmatism,in the melts. Large quartz grains, on the other hand, may representthe xenocrysts originated from the underlying shallow sediments,most probably the Wuchihshan Sandstone Formation. It isestimated that CVG andesites caught ∼ 15% of such nodules andwere contaminated with 5 ∼ 12% of such sediments during theascend of magmas. Due to low SiO �� contents and irrelevance of quartz crystallization in the course of magmatic differentiation, the old usage of "dacite" for denoting these igneous rocks shouldbetter be abandoned. |
本系統中英文摘要資訊取自各篇刊載內容。