珠江沉积物碎屑锆石UPb年龄

Characteristics of Detrital Zircon UPb Geochronology of the Pearl River Sands and Its Implication on Provenances

摘要:

通过对珠江流域主要支流和干流河流砂进行碎屑锆石UPb定年分析，建立了珠江流域的碎屑锆石年龄谱，发现主要分为8组峰值，分别为2 800—2 300 Ma，2 000—1 800 Ma，1 800—1 300 Ma，1 100—700 Ma，600—400 Ma，380—230 Ma，200—80 Ma，<65 Ma，分别对应陆壳增长期、吕梁期、晋宁期、加里东期、印支期、燕山期及喜山期等构造活动.各支流碎屑锆石年龄谱特征不同，且具有分带性：上游北盘江、南盘江、红水河、右江、左江及西江干流样品具有明显的380—230 Ma主峰，碎屑锆石主要来自右江造山带.右江和左江具有独特的2 000—1 800 Ma峰值，碎屑锆石可能来自更老的基底.中游柳江样品具有1 000—800 Ma峰值，碎屑锆石来自扬子地块.桂江样品除1 000—800 Ma峰值外，还具有660—400 Ma和2 800—2 300 Ma峰值，碎屑锆石来自江南造山带和华夏地块.下游北江、东江及珠江三角洲样品碎屑锆石主要来自东南沿海花岗岩带，具有明显的200—90 Ma峰值.西江干流样品以印支期380—230 Ma峰值为主，同时也受到燕山期岩浆活动影响而含较多中生代锆石.研究结果显示，利用碎屑锆石年龄的不同峰值可以示踪珠江不同支流沉积物，对进一步研究南海北部沉积物源汇对比和揭示珠江流域演变过程具有重要意义.

Abstract:

The detrital zircon dating of the modern river sands from the tributaries and mainstream of the Pearl River reveals age spectra with eight major age groups: 2 800—2 300 Ma, 2 000—1 800 Ma, 1 800—1 300 Ma, 1 100—700 Ma, 600—400 Ma, 380—230 Ma, 200—80 Ma and <65 Ma, corresponding to tectonic events within the drainage e.g. crustal growth, Lüliangian, Jinningian, Caledonian, Indosinian and Yanshanian. The tributaries are characterized with different age spectra and can be classified by their location. The Beipanjiang River, the Nanpanjiang River, the Hongshuihe River, the Youjiang River, the Zuojiang River and the mainstream of Xijiang River from the upstream feature a 380—230 Ma age peak, indicating that these zircons were mainly from the Youjiang Orogenic Belt. The 2 000—1 800 Ma age peak only occurs in the Youjiang River and the Zuojiang River, suggesting that those zircons probably come from an ancient basement. The Liujiang River from the middle stream is characterized with a 1 000—800 Ma age peak, which represents zircons from the Yangtze Block. Besides this 1 000—800 Ma age peak, another two age peaks of 660—400 Ma and 2 800—2 300 Ma are found in the Guijiang River, suggesting provenances from the Jiangnan Orogenic Belt and the Cathaysia Block. The detrital zircons from the North River, the East River and the Pearl River delta of the downstream are mainly deprived from the granite belt along the southeast coast. This result shows that the peaks of the detrital zircon ages can be used to identify the sediment from the tributaries, which may be helpful for studying the provenance of the northern South China Sea sediment and its relationship with the evolution of the Pear River.