李通藝楊智宇2019-09-052017-06-092019-09-052013http://etds.lib.ntnu.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=id=%22GN060044010S%22.&%22.id.&http://rportal.lib.ntnu.edu.tw:80/handle/20.500.12235/101241臺灣西部桂竹林層沉積年代為中新世到早上新世，部分學者視其為沉積於臺灣西部前陸盆地，某些學者則認為其仍屬於被動大陸邊緣沉積層序。因此，本研究嘗試利用碎屑鋯石鈾-鉛定年來探討苗栗出磺坑背斜附近桂竹林層沉積物源的演變，採樣地層由老至新分別為北寮砂岩、打鹿頁岩、觀音山砂岩、東坑層、上福基砂岩、桂竹林層 (關刀山砂岩段、十六份頁岩段、魚藤坪砂岩段)、及錦水頁岩。研究結果顯示，早中新世-晚中新世早期北寮砂岩、打鹿頁岩、觀音山砂岩、東坑層，具有相似的95-165 Ma、200-250 Ma、750-850 Ma峰值年代；到了晚中新世晚期上福基、關刀山砂岩其碎屑鋯石的鈾-鉛年代有了改變，90-190 Ma與200-250 Ma峰值年齡的鋯石大量出現；而到了上新世時十六份、魚藤坪砂岩、錦水頁岩層碎屑鋯石的鈾-鉛年代又有了不同，顯示200-300 Ma、400-450 Ma、750-850 Ma、1750-1950 Ma及2400-2550 Ma的峰值，其中1750-1950 Ma峰值年齡的鋯石大量出現，由此可知自中新世以來沉積物來源供應於晚中新世晚期-上新世時發生改變。 對比大陸可能沉積物源區碎屑鋯石定年結果，本研究結果與其年齡頻譜具有高度相似性，推論臺灣西部前陸盆地主要沉積物源自華夏陸塊。且本研究中鋯石鈾-鉛年齡與大陸閩浙地區出露的岩盤年代相當吻合，進一步顯示沉積物可能主要來自閩浙地區。依前人所提出的演化模式，推論於晚中新世晚期時(上福基砂岩及關刀山砂岩沉積時期)，臺灣西部前陸盆地開始發育，或許肇因於相對海水面變深或沉積坡度變陡，故沉積了大量來自鄰近地區的閩浙沿海的沉積物；到了早上新世時 (十六份頁岩沉積時期)，前陸盆地穩定發育，亦開始沉積來自臺灣島本身的沉積物。由本研究可見，苗栗地區中新世至上新世地層中碎屑鋯石的組成確實反應了臺灣新第三紀造山帶的演變歷程。The sediments of the Kueichulin Formation were deposited during Late Miocene to Early Pliocene. This formation should be able to shed some lights on the records of the transition from passive margin to foreland basin sedimentary environment in western Taiwan. This study presents U–Pb dating results of detrital zircons by single collector Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer (LA-ICP-MS) to investigate the evolution of sedimentary source region during the deposition of the Kueichulin Formation near Chuhuangkeng Anticline in Miaoli. Samples were collected all the way from the Miocene Peiliao Sandstone to the Pliocene Chinshui Shale. The U-Pb dating of zircons from the Early Miocene Peiliao Sandstone to the Late Miocene Tongken Fomation display age spectra with similar major peaks at 95-165 Ma, 200-250 Ma, and 750-850 Ma. Then U-Pb dating of zircons from the terminal Miocene Shangfuchi Sandstone and Kuantaoshan Sandstone shows similar age spectra with peaks of 90-190 Ma and 200-250 Ma, which suggest that sediment supply should have changed since the terminal Miocene. According to the correlation with detrital zircon age spectra of possible sources, sediment supply of Miocene formations with abundant Proterozoic zircons should have come from the Cathaysia basement. On the contary, for that of the terminal Miocene formations, the sources would have dominantly derived from Yanshanian and granitic plutons in East Cathaysia. The results of this study suggest that the Shangfuchi Sandstone and Kuantaoshan Sandstone should have been deposited in the initial arc-continent collision between Luzon Arc and Eurasian passive continental margin. The arc-continental collision might have induced a sudden increase of the depositional slope which may have led of the noticeable change of sediment source in the terminal Miocene.前陸盆地碎屑鋯石鈾-鉛定年桂竹林層沉積岩物源分析foreland basinU-Pb dating of detrital zirconKueichulin formationsediment source analysis