福建西南地區古生代至中生代地層的碎屑鋯石鈾鉛年代

Detrital Zircon U-Pb Age Study of the Paleozoic－Mesozoic Sedimentary Rocks, Southwestern Fujian

李瑞清(Zugeerbai Zul)

指導教授 ： 陳文山

國立臺灣大學/理學院/地質科學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02166

摘要

本研究區域主要位在福建省西南部的寒武紀至奧陶紀的輕度變質岩，以及泥盆紀至侏儸紀的沉積岩，採集的岩石樣本從古生代至中古生代地層中共10個樣本的碎屑鋯石進行利用LA-ICP-QMS測量鈾-鉛定年分析。
由於華南地區，經歷數期與多個板塊的碰撞，產生了多期構造活動，造成地層層序，大地構造與沉積環境的多變性。綜合本研究分析結果，討論碎屑鋯石年代的變化，了解華南東側地區晉寧運動、加里東運動、印支運動與燕山運動岩漿岩碎屑鋯石再堆積的地質意義。各運動期的碎屑鋯石含量的比較，加里東、印支與燕山運動前後似乎有些微變化。將晉寧運動（850-750Ma）之前經過多次堆積的碎屑鋯石的總合來討論，此作法是推測這些時代的碎屑鋯石都經多次侵蝕循環而堆積在晉寧運動之後的地層中。
從加里東運動之前的碎屑鋯石總和比例來看，以＞2400 Ma（五台運動）、1700-1000 Ma、1000-930 Ma（四堡運動）所佔比例較高約95%。而在不屬於構造運動期間仍有來自火成岩碎屑鋯石堆積（1700-1000 Ma）。本研究認為其間存在零星的火成活動所致，如750-450 Ma 期間在福建地區可以發現零星的火成岩分布。
加里東運動之後，由於有將近40%來自此時期的火成岩碎屑鋯石，所以造成＞750 Ma 碎屑鋯石的總和比例大幅降低，但是此期間是以＞2400 Ma 與850-750 Ma 的碎屑鋯石比例為多。原因是加里東運動可能造成早古生代與震旦系岩層的出露，以致750-450 Ma與850-750 Ma的比例較高，而老於＞2400 Ma的碎屑鋯石較多的原因，本研究尚無法解釋。
印支運動時期與之前，＞750 Ma的碎屑鋯石有降低趨勢，可能是地表逐漸被大量火山岩覆蓋所致。但印支運動時期1900-1700 Ma（呂梁運動）的碎屑鋯石比例有非常高的比例約18%；呂梁運動是華夏古陸主要的形成時期，構成華夏古陸主要基底，目前出露在閩西北地區，稱為麻源群。印支運動期間，華南地區形成大區域的斷層與褶皺作用，造成華夏古陸基底大面積出露地表，而成為主要來源。

關鍵字

碎屑鋯石 ； U-Pb dating ； 中生代至古生代

並列摘要

Abstract

The study is in located in the Southwest of Fujian Province, sandstone samples were collected from the Cambrian to Ordovician metamorphic rocks, and the Devonian to Jurassic sedimentary rocks. Detrital zircons of the Paleozoic-Mesozoic strata rocks were separated from10 samples by LA-ICP-MS measurements for U-Pb dating.
The Southern China region undergo several plate collision, results in many phase tectonic activities, causing the variabilities of sequence stratigraphy, tectonic, and sedimentary environment.
Result from the U-Pb dating, it indicates that the Jinning orogeny, Caledonian orogeny, Indosinian and Yanshanian magmatic detrital zircons re-accumulation of geological sigifcance. The comparison of these tectonic movements Caledonian, Indosinian and Yanshanian seems to slightly change of detrital zircon ages.
The detrital zircon age assemblidge of Caledonian indicates that ＞2400 Ma (Wutai movement), 1700-1000 Ma, 1000-930 Ma (Sibao movement) higher proportion of about 95%. Some of igneous zircons deposite in the time without tectonic movement (1700-1000Ma). This study suggests that there remain sporadic igneous activity, such as the 750-450 Ma can be found in Fujian province during the sporadic distribution of igneous rocks.
From the Caledonian movement and after, because nearly 40% from this period of igneous detrital zircons , with the result ＞750 Ma detrital zircons significantly reduced the proportion of the total, but this period is ＞2400 Ma and 850-750Ma for proportion of detrital zircon and more. The reason is Caledonian movement may cause the early Paleozoic, and Sinian strata exposed, resulting in 750-450 Ma and 850-750 Ma a higher proportion of the old in ＞2400 Ma detrital zircons more reasons, this study still can’t explain.
Indosinian movement period, ＞750 Ma detrial zircon tended to decrease, probably a lot of volcanic rocks covering the surface gradually caused. But Indosinian movement 1900-1700 Ma (Luliang movement) the proportion of detrital zircons have a very high proportion of about 18%; Luliang movement is the main formation period the Catashyia, constitute the main base Catashyia, now exposed in Fujian northwest region, knows as Mayuan group.
During the Indosinian movement, South China region the formation of large areas fault and folding result in a large basement area Cathaysia exposed surface, and become the main source.

並列關鍵字

Detrital zircon ； U-Pb dating ； Paleozoic to Mesozoic

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