四川盆地晚三疊紀到始新世地層的碎屑鋯石U-Pb定年及其沉積源區的研究

Provenance study of the Late Triassic to Eocene strata in Sichuan basin using detrital zircon U-Pb dating

黃俊富(Jyun-Fu Huang)

指導教授 ： 李元希

國立中正大學/理學院/地球與環境科學系應用地球物理與環境科學研究所/碩士(2016年)

摘要

四川盆地與松潘-甘孜造山帶位於西藏東緣，受中生代與新生代造山作用影響，松潘-甘孜造山帶以龍門山斷層系統為界形成3000-5000公尺高的高原，龍門山斷層上盤的松潘-甘孜造山帶主要由中生代厚達5-15公里的晚三疊紀復理石沉積岩所組成，受中生代造山運動影響變質為綠色片岩相板岩，四川盆地主要由中生代以來的淺海相沉積岩所組成，在中生代之後轉為前陸盆地型態沉積。
　　本研究利用碎屑鋯石U-Pb定年，配合前人研究已有鋯石U-Pb年代釐清中生世到始新世間沉積物的可能來源。在松潘-甘孜造山帶的泥盆紀地層中，本研究提供了更完整的年齡譜發現除既有年代群如970 Ma與440 Ma外亦發現有2.4-2.6Ga年代群，提供新的泥盆紀地層特性資料。在晚三疊紀地層中我們發現西南側的松潘-甘孜鋯石年齡譜與東北側不同，有大量760-800 Ma源自於南中國地塊的鋯石，顯示南北松潘-甘孜盆地有不同來源。我們亦比較四川盆地內晚三疊紀的地層，發現在西南側地層松潘-甘孜西南側的地層中皆存在約270Ma年代群，此年代群未見於四川盆地西側地層中，顯示四川盆地東西兩側的來源不同，東側以秦嶺-大別山為主，西側來源可能來自盆地西側南中國地塊。四川盆地在白堊紀到始新世之後轉為前陸盆地型態，沉積物來源以龍門山造山帶的松潘-甘孜地層為主。

關鍵字

四川盆地

並列摘要

In this study we analysis the detrital zircon U-Pb ages from Late Triassic to Eocene strata of Sichuan basin and Songpan-Ganze folded belt in eastern Tibet to discuss possible sediment provenance.
The Songpan-Ganze folded belt, comprised of 5-15km thickness of late Triassic flysch deposit, was deformed by Mesozoic and Cenozoic events which formed 3-5km high plateau. It connects with Sichuan basin by Longmenshan orogenic belt. In the Sichuan basin it comprised of shallow marine deposit since Mesozoic and become foreland basin deposit after the Cenozoic.
We collected samples from Triassic to Eocene strata in SW Sichuan basin and Songpan-Ganze folded belt in different age strata and we also combined with previous studies to analysis the possible sediment provenance. In the Songpan-Ganze folded belt we obtained more comprehensive age spectrums in Devonian strata. Previous study show the age spectrum concentrates on 970 Ma and 440 Ma and we observed there exists many 2.4-2.6 Ga grains. The Triassic strata are similar with previous studies which ages concentrate on ca. 1.8Ga, 790Ma and some grains are 260-300Ma and 410-470Ma.
In Sichuan basin the preliminary data show there are quite different age spectrums from Triassic to Jurrassic. The Triassic to Jurassic strata show the age spectrums concentrate on 270Ma, 450Ma, 800Ma, and few 1800Ma. But in Jurassic strata most of grain ages concentrate on 1800Ma. In the Cretaceous strata we started to observed ca. 215 Ma peak and some on 770Ma which infer the sediments could come from Songpan-Ganze folded belt. In Eocene strata the age spectrums concentrate on 1800 Ma and 270 Ma which infers the sediments different source from Cretaceous to Eocene.

參考文獻

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