臺灣中央山脈向陽山至新康山地區變質火山岩之研究

Study of Metavolcanic rocks on the Area from Hsiangyangshan to Shinkangshan of Central Range, Taiwan

呂婉瑄(Wan-Syuan Lyu)

指導教授 ： 羅 偉 、宋聖榮

國立臺北科技大學/工程學院/資源工程研究所/碩士(2010年)

摘要

臺灣中央山脈面積佔全島近三分之一，主要由變質岩所組成，地質構造複雜。其中，有許多火成岩體零星分布，此些火成岩體的成因與臺灣島的造山過程有密不可分的關係。本研究選定中央山脈向陽山至新康山地區的變質火山岩進行分析，期望對探討中央山脈的岩漿活動與地體構造演化提供重要的資訊。
臺灣中央山脈向陽山至新康山地區出露之岩性為板岩偶夾千枚岩、變質砂岩和變質火山岩，變質火山岩其原岩產狀以火山熔岩和凝灰岩為主，其中，野外觀察新康山和八通關古道石洞之變質火山岩部份具枕狀構造，推測此區原岩形成於海洋環境，並且與沉積岩同時期生成。根據岩象學分析，向陽山至新康山地區之變質火山岩礦物群屬於綠色片岩變質相，僅經歷一次的變質作用。
依照主要元素結果顯示，向陽山地區變質火山岩二氧化矽含量在49.79~65.93 wt.%；新康山地區變質火山岩二氧化矽含量在48.29~51.35 wt.%。另由全岩地球化學之微量元素和稀土元素分析結果顯示，向陽山地區之變質火山岩，(La/Sm)N為1.23~2.07，(La/Yb)N為1.42~2.68，其稀土元素分佈型態為平坦型，銪(Eu)普遍呈現負異常，且釷(Th)富集，鈮(Nb)、鉭(Ta)和鈦(Ti) 虧損，具有火山島弧玄武岩的地球化學特性；新康山地區之變質火山岩，(La/Sm)N為1.88~2.87，(La/Yb)N為3.41~5.89，其稀土元素型態分佈近似於洋島玄武岩，且高場力鍵結元素(HFSE)和輕稀土元素(LREE)比重稀土元素(HREE)富集，而大離子半徑元素(LILE)虧損，具有板塊內部玄武岩的地球化學特性。

關鍵字

中央山脈 ； 板岩 ； 變質火山岩 ； 地球化學

並列摘要

The area of the Central Range is about one-third of the Taiwan. The major rocks exposed on the Central Range are metamorphic rocks which composed slate, schist, gneiss, marble, and some metavolcanic rocks. These metavolcanic rocks are exposed at widely scattered places on the Central Range. Therefore, the petrogenesis of the metavolcanic rocks has the inseparable relation with the orogenic process of the Taiwan Island. This research is intended to analyze these metavolcanic rocks from Hsiangyangshan to Shinkangshan area of Central Range. We expect that the results of this study is believed to be significant for the future study of magmatism and tectonic history in the Central Range of Taiwan.
The rocks exposed on the study area consist of slate, phyllite, metasandstone and metavolcanic rocks, these rocks are all undergone greenschist facies metamorphism. From the field investigation along the road from Shinkangshan to shihdung area, these metavolcanic rocks are composed of some lavas and volcanic tuffs, there are also some pillow structures can be observed. It is believed that the metavolcanic rocks are contemporaneous with the meta-sedimentary wallrocks.
According to the major elements geochemistry analysis, the silica contents of the metavolcanic rocks in the Hsiangyangshan area and the Shinkangshan area are 49.79~65.93 wt. % and 48.29~51.35 wt. %, respectively. While the whole-rock trace elements and rare earth elements geochemistry analysis indicate that the rare earth elements distribution patterns of the Hsiangyangshan area are flat type, the ratio of (La/Sm)N is about 1.23 to 2.07, and (La/Yb)N is 1.42 to 2.68, Eu element is slightly negative anomalies, Th element is enrichment, while the Nb, Ta and Ti are all depletion This result suggests that the geochemical characteristics of the metavolcanic rocks exposed on the Hsiangyangshan area is belonged to volcanic arc basalts. On the other hand, the metavolcanic rocks on the Shinkangshan area with the rare earth elements ratio (La/Sm)N =1.88~2.87 and (La/Yb)N =3.41~5.89 are similar to the oceanic basalts. Based on the geochemical characteristics of the high field strength elements (HFSE), light rare earth elements (LILE) relation to heavy rare earth elements (HREE) and depletion in light rare earth elements (LREE), it is suggested that the metavolcanic rocks of the Shinkangshan area are the intra-plate basalts.

並列關鍵字

Central Range ； Slate Formation ； metavolcanic rocks ； geochemistry

參考文獻

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