陽明山國家公園小油坑安山岩熱液蝕變作用

Hydrothermal Alteration of Andesitic Rock at the Siaoyoukeng Area, Yangmingshan National Park

方建能(Jiann-Neng Fang)

《臺灣鑛業》 63卷1期 (2011/03) Pp. 1-11

https://doi.org/10.30014/TMI.201103.0002

摘要

本研究分析陽明山國家公園小油坑地區硫氣孔周圍安山岩質岩石，並進行岩象觀察、次生礦物鑑定及化學成分分析，目的在了解經熱液蝕變作用後，岩石中組成礦物的蝕變行為、次生礦物種類及岩石化學成分的變化趨勢。研究結果發現安山岩中斑晶礦物，斜長石比輝石斑晶容易受熱液蝕變作用溶蝕，且具有化學環帶構造的斜長石斑晶，其結晶中央含鈣高處較邊緣含鈣低處易受到溶蝕。在四個岩樣中皆發現低溫方英石、低溫石英與鉀明礬石等三種次生礦物存在。經由岩石的化學分析得知，在越接近硫氣孔位置時，岩石中SiO2 成分逐漸增加，Al2O3、TiO2、Fe2O3、CaO、MgO、MnO和P2O5等成分皆因被淋蝕而呈逐漸減少的趨勢。

關鍵字

小油坑 ； 安山岩 ； 硫氣孔 ； 低溫方英石 ； 鉀明礬石

並列摘要

The study performed a petrographic analysis on the andesitic rock near the fumaroles at the Siaoyoukeng Area of the Yangmingshan National Park, aiming at understanding the behaviors of the primary minerals, the kinds of secondary minerals, and the changes in chemical composition in andesites undergoing hydrothermal alteration.Results indicate that, of the porphyritic crystals in the andesitic rock, plagioclase, and pyroexene crystals tend to experience dissolution in the presence of hydrothermal alteration. For plagioclase crystals with zoning structure of chemical composition, the core crystal with richer calcium is more vulnerable to dissolution than the peripheral crystals with lower calcium. Secondary minerals found in all four rock samples include alunite, α-cristobalite, and α-quartz. Results of chemical analysis suggest that the weight of SiO2 grows greater in location nearer to the fumaroles. On the other hand, Al2O3, TiO2, Fe2O3, CaO, MgO, MnO and P2O5 betray decrease due to leaching.

並列關鍵字

Siaoyoukeng ； andesite ； solfatara ； α-cristobalite ； alunite