U-P DATING OF ZIRCONS FROM CENOZOIC SANDSTONE: CONSTRAIN ON THE GEODYNAMIC SETTING OF EAST CHINA SEA SHELF BASIN
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摘要: 东海陆架西部凹陷带古新统砂岩锆石的U-P年龄表明,陆架西部古新世物源以中生代母岩为主,其次为元古代变质岩及少量古生代母岩。东海陆架东部凹陷带渐新统砂岩锆石的U-P年龄表明陆架东部渐新世物源以元古代变质岩为主,其次为中生代母岩及少量太古代变质岩与古生代母岩。陆架西部古新统砂岩锆石的U-P年龄与闽浙隆起带露头及钻孔揭示的基岩一致,而陆架东部渐新统砂岩锆石的U-P年龄比西部老。根据上述砂岩锆石U-P年龄,可以推测古近纪东海陆架盆地发育过程中,东海陆架东部地势较高。单颗粒锆石REE配分模式表明元古代锆石轻稀土(LREE)明显比其他样品高且含量相近,Ce正异常不明显;中生代锆石Ce正异常明显,但同时Eu负异常也很明显,与中生代基岩锆石相似;古生代锆石稀土元素含量偏低,La含量明显超过其他轻稀土元素。根据上述特征可以清晰指示砂岩的母岩类型与年代,推断古新世东海大陆架的基底性质与构造背景。Abstract: The U-P dating data of zircon from Paleocene sandstones in the west of East China Sea shelf indicate that most zircon grains are of Mesozoic origin, and then are Proterozoic, including sporadic Paleozoic ones. The U-P dating data of zircons from Oligocene sandstones in the east of East China Sea shelf indicate that most zircon grains are Proterozoic, and then are Mesozoic, including sporadic Archean and Paleozoic ones. The dating result indicates that the basement is different between the west and the east of East China Sea shelf basin. The western basement is consistent with the outcrop data in Fujian-Zhejiang offshore area. The U-P dating data of zircons imply that topography was low in the west and high in the east of East China Sea shelf during the development of Eogene basin. Chondrite-normalized REE patterns of the individual zircons determined by ICPMS show that the Proterozoic zircons have high content of LREE and invisible Ce anomalies, whereas Mesozoic zircons have large positive Ce and small negative Eu anomalies, and Paleozoic zircons are characterized by low content of LREE in which La is higher in content than other LREE elements. The LAM-ICPMS data give chronological evidence to us to previously identify basement rocks and to probe into tectonic property of the shelf of East China Sea.
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Keywords:
- sandstone /
- U-P dating /
- REE /
- basement /
- zircon /
- East China Sea shelf
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