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  • 學位論文

利用碎屑鋯石鈾鉛定年分析墾丁與利吉混同層砂岩岩塊之源區

Provenance analysis by U-Pb dating of detrital zircons of sandstone blocks on the Kenting and Lichi Mélanges

指導教授 : 陳文山

摘要


墾丁層與利吉層是歐亞板塊與菲律賓海板塊碰撞產生的混同層,分別分布於恆春半島及海岸山脈,產狀為泥岩夾雜各種岩性的外來岩塊。本研究利用碎屑鋯石鈾鉛定年,輔以岩象、超微化石(砂頁岩塊)分析混同層中砂岩岩塊的沉積年代與其沉積物來源,為了解蛇綠岩的來源另外採集利吉層的蛇綠岩,亦進行鋯石鈾鉛定年、鉿同位素與鈾含量的分析。此外,為了解利吉層與墾丁層沉積岩塊的來源,亦分析恆春半島中新世地層砂岩。分析7個恆春半島中新世地層、28個混同層砂岩岩塊、4個東台灣蛇綠岩樣品。 根據碎屑鋯石年齡族群分析,里龍山層和石門層的特徵與台灣地區中北部中新世地層相似,而樂水層顯示不同的特徵。根據古水流向以及岩象組成中所含的硬頁岩岩屑、變質砂岩岩屑和蛇綠岩岩屑,里龍山層與石門層的沉積物來源為古增積岩體,其中含有蛇綠岩和陸源物質。根據碎屑鋯石年齡與岩象組成顯示,樂水層的沉積物來源與華夏古陸相似。 本研究根據鋯石年齡的比例與岩象特徵,將混同層中的砂岩分成4個類型。Type 1砂岩與石門層和里龍山層的特徵相似,沉積物源區為古增積岩體。Type 2砂岩與樂水層的特徵相似,沉積物源區為華夏古陸。Type 3蛇綠岩系砂岩的沉積物源區為古增積岩體,其內所含的年輕鋯石族群來自南中國海海洋地殼,老鋯石來自陸源物質。Type 4火成岩岩屑砂岩的沉積物源區為火山島弧,其中所含的年輕鋯石族群來自火山島弧,老鋯石為原始火成岩形成時岩漿上湧所捕獲。利吉層中含有Type 1、Type 2、Type 3和Type 4的岩塊,而墾丁層中含有Type 1和Type 3的岩塊。 利吉層中的東台灣蛇綠岩(ETO),鋯石鈾鉛定年結果顯示有兩個年齡族群(1)17.4~16.3 Ma和(2)14.8~13.9 Ma。鉿同位素分析結果顯示,東台灣蛇綠岩的岩漿來自高度虧損的地函,且隨著年代越年輕,岩漿來源有越來越虧損的趨勢。

並列摘要


The Kenting and Lichi Mélanges formed at the subduction system of Eurasian plate and Philippine Sea plate, located in Hengchun Peninsula and southern Coastal Range, respectively. Mélange is a body of rock characterized by exotic blocks, contained in a fine-grained deformed matrix. The purpose of this study is to analyse provenance of the sandstone blocks on the Mélanges, by using detrital zircon U-Pb dating, petrography, nannofossil biostratigraphy, and Hf isotope analysis. In addiction, in order to understand the sources of ophiolite, and the sandstone blocks of the Kenting and Lichi Mélanges, this study also collected samples from Eastern Taiwan Ophiolite and Miocene strata of Hengchun Peninsula. We analysed 7 Miocene strata samples from Hengchun Peninsula, 28 sandstone blocks from the Mélanges and 4 Eastern Taiwan Ophiolite. According to U-Pb age assemblage analysis, Lilungshan Formation and Shimen Formation have the same character with Central and Norther Taiwan Miocene Strata, but Loshui Formation has a different character. According to paleocurrent data and petrography results, contains argillite, quazite, and ophiolitic lithics, the provenance of Lilungshan Formation and Shimen Formation is the old accretionary wedge. According to U-Pb age assemblage analysis and petrography results, the provenance of Loshui Formation is the Cathaysia. According to zircon U-Pb age assemblage and petrography results, we classified sandstone blocks of the Mélanges into four types. Type 1 sandstone has the same character with Lilungshan Formation and Shimen Formation, the provenance of Type 1 sandstone represent the old accretionary wedge. Type 2 sandstone has the same character with Loshui Formation, the provenance of Type 2 sandstone is the Cathaysia. The provenance of Type 3 ophiolitic sandstone is the old accretionary wedge. The young zircon age population of Type 3 is derived from South China Sea oceanic crust, which been scratched and uplifted by the subduction system, and the old zircons are from continental material. The provenance of Type 4 volcanic lithics sandstone is volcano arc. The young zircon age population of Type 4 is from the volcanic arc, and the old zircons are captured from sedimentary strata, when the original magma upwelling. The Lichi Mélange contains Type 1, Type 2, Type 3 and Type 4 sandstone blocks. The Kenting Mélange contains Type 1 and Type 3 sandsone blocks. The zircon U-Pb age of Eastern Taiwan Ophiolite of the Lichi Mélange, include two age populations (1)17.4~16.3 Ma, and (2)14.8~13.9 Ma, which zircon Hf isotopic data indicated the magmas are from depleted mantal.

參考文獻


Andersen, T., 2002, Correction of common lead in U–Pb analyses that do not report 204Pb: Chemical Geology, v. 192, p. 59-79.
Andersen, T., 2005, Detrital zircons as tracers of sedimentary provenance: limiting conditions from statistics and numerical simulation: Chemical Geology, v. 216, p. 249-270.
Barrier, E., and J. Angelier, 1986, Active collision in eastern Taiwan: the Coastal Range: Tectonophysics, v. 125, p. 39-72.
Blichert-Toft, J., and F. Albarède, 1997, The Lu-Hf isotope geochemistry of chondrites and the evolution of the mantle-crust system: Earth and Planetary Science Letters, v. 148, p. 243-258.
Chang, C. P., J. Angelier, T. Q. Lee, and C. Y. Huang, 2003, From continental margin extension to collision orogen: structural development and tectonic rotation of the Hengchun peninsula, southern Taiwan: Tectonophysics, v. 361, p. 61-82.

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