印尼西爪哇碎屑鋯石及繼承鋯石之鈾-鉛定年學研究

U-Pb geochronology of detrital and inherited zircons from West Java, Indonesia

羅琳(Lo Ling)

指導教授 ： 賴昱銘

國立臺灣師範大學/理學院/地球科學系/碩士(2022年)

https://doi.org/10.6345/NTNU202201551

摘要

爪哇島位於中生代巽他大陸核心的邊緣，是一平行隱沒帶之東西向島嶼。印澳板塊自中生代起開始向北漂移，並隱沒至歐亞板塊下方，產生多次的隱沒作用。期間也曾發生微陸塊貼合事件，造成爪哇島東西兩側之地體架構有所不同。依照其特徵可將爪哇島分為西爪哇、中爪哇和東爪哇。西爪哇北部的火成活動，為蘇門答臘向東延伸的白堊紀火山島弧。其他區域則以新生代火山島弧為主，火山活動年代包括第三紀及第四紀至今。前人針對西爪哇Jatibarang地層與南蘇門答臘出露之新近系火成岩進行研究，發現兩者具有相似的岩性與特徵，但並未提出年代的證據。本研究於西爪哇採集砂岩(包括河口砂質沉積物)，進行碎屑鋯石鈾-鉛定年分析，並搭配火成岩中分析所得的繼承鋯石，依據鋯石年代在時間與空間上的分布情形，試比對西爪哇在不同時期之鋯石來源區域，以及西爪哇各期火山活動之年代。
本研究共分析5個砂岩，分別採自Ciletuh、Jasinga和Bayah地區；以及1個位於Ci Pamuhulan河口的砂質沉積物，總計分析627顆碎屑鋯石；並於Danau火山、Bayah(north)火山及Ciletuh地區採集的3個火成岩中，挑選繼承鋯石共62顆。年代分析結果指出：(1)西爪哇西北部具有約140 Ma之鋯石紀錄，可對比至蘇門答臘同時期的岩漿活動年代做對比，且此年代並未見於西爪哇南部樣本，(2) 西爪哇新生代以來之岩漿活動，具有遠離隱沒帶越趨年輕的現象，由南向北分別記錄了23 Ma、17 Ma及11 Ma三期事件，(3) 本研究於Bayah地區的砂岩及河口砂質沉積物中獲得始新世、白堊紀和三疊紀之碎屑鋯石年代訊號，結果顯示物源分別來自現地火山活動、婆羅洲的施瓦納山脈及馬來半島花岡岩。

關鍵字

碎屑鋯石 ； 鈾鉛定年 ； 西爪哇 ； 巽他大陸 ； 新生代岩漿活動

並列摘要

Sundaland is the Mesozoic continental core of Southeast Asia, and the Java island locates at it’s southern margin which is an east-west island and parallel to a subduction zone. Since the Mesozoic Era, the Indo-Australian Plate began to drift northward, and subducted beneath the Eurasian Plate. During this period, several subduction events occurred and microcontinental blocks accreted to the margin of Sundaland. According to the characteristics of basement rocks, Java can be divided into three parts: West Java, Central Java and East Java. The igneous activity in the northern West Java is related to the Cretaceous volcanic arc, which extended eastward from Sumatra Island. The other areas are mainly Cenozoic volcanic arcs from Tertiary to Recent. Different to the East Java, there were few age constrains and no detrital zircon studies from previous works in the West Java.
In this study, we sampled sandstones, river sand, and andesites from West Java. According to the detrital zircon ages from sediment and sedimentary rocks and inherited zircons from igneous rocks, the volcanism with temporal and spatial distribution and the sources of detrital zircons can be identified in West Java. A total of 627 zircons from five sandstones from the Ciletuh, Jasinga, and Bayah areas, and one river sand from the Ci Pamuhulan were analyzed, moreover, 62 inherited zircons from three igneous rocks (Danau, Bayah (North) volcano and Ciletuh areas) were processed. The age results show: (1) The Cretaceous zircon ages (140 Ma) from the northwest West Java might be correlated with the magmatic activity in Sumatra, but they are not found in south West Java. (2) The Cenozoic magmatic activities in West Java are divided into three stages, i.e., 23 Ma, 17 Ma and 11 Ma from south to north. (3) The Triassic, Cretaceous, and Eocene detrital zircon signatures were identifeid from the sandstones and river sand in the Ciletuh and Bayah areas, and it is reasonable to suggest that their sources were from Malaya granites, Schwaner Mountains, and the volcanism in West Java.
In this study, we sampled sandstones, river sand, and andesites from West Java. According to the detrital zircon ages from sediment and sedimentary rocks and inherited zircons from igneous rocks, the volcanism with temporal and spatial distribution and the sources of detrital zircons can be identified in West Java. A total of 627 zircons from five sandstones from the Ciletuh, Jasinga, and Bayah areas, and one river sand from the Ci Pamuhulan were analyzed, moreover, 62 inherited zircons from three igneous rocks (Danau, Bayah (North) volcano and Ciletuh areas) were processed. The age results show: (1) The Cretaceous zircon ages (140 Ma) from the northwest West Java might be correlated with the magmatic activity in Sumatra, but they are not found in south West Java. (2) The Cenozoic magmatic activities in West Java are divided into three stages, i.e., 23 Ma, 17 Ma and 11 Ma from south to north. (3) The Triassic, Cretaceous, and Eocene detrital zircon signatures were identifeid from the sandstones and river sand in the Ciletuh and Bayah areas, and it is reasonable to suggest that their sources were from Malaya granites, Schwaner Mountains, and the volcanism in West Java.

並列關鍵字

Detrial zircon ； U-Pb geochronology ； West Java ； Sundaland ； Cenozoic island arc magmatism

參考文獻

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