Detrital Zircon U—Pb Age Characteristics and Provenance Analysis of Submarine Fan of Middle Miocene in the Qiongdongnan Basin
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摘要: 【目的】琼东南盆地中中新统海底扇是南海北部天然气勘探的重要目标,但长期以来对该海底扇沉积物的物源并未达成共识,因此,物源分析将对该区天然气勘探有利目标优选具有重要意义。【方法】本文通过钻井取心,开展碎屑锆石U—Pb年龄谱特征研究,并与周缘潜在物源区锆石U—Pb年龄进行对比分析,示踪研究区中中新统海底扇物源。【结果】结果表明,①盆地北部N-1、N-2、N-3、N-4等4口井碎屑锆石U—Pb年龄表现为燕山期(160 Ma、157 Ma、133 Ma、107 Ma、102 Ma、99Ma)、印支期(249 Ma、241 Ma、239 Ma)、加里东期(466 Ma、455 Ma)的年龄峰值特征,且与海南岛碎屑锆石U—Pb年龄特征相似度高,但与红河、越南中部碎屑锆石U—Pb年龄特征相似度低。②盆地南部S-1、S-2、S-3等3口井碎屑锆石U—Pb年龄特征表现为印支期(242 Ma、238 Ma、237 Ma)、加里东期(435 Ma、431 Ma、425 Ma)、海西期(396 Ma、392 Ma)以及燕山期(143 Ma)的年龄峰值特征,且S-2井具有较年轻的喜马拉雅期(21 Ma)单峰年龄特征。【结论】琼东南盆地北部中中新统沉积物源主要来自海南岛,红河及越南中部物源对其影响非常有限,盆地南部中中新统为红河和海南岛双物源供给,且以红河物源为主,自西向东差异明显。Abstract: [Objective]The middle Miocene submarine fan in the Qiongdongnan Basin is an important target for natural gas exploration in the northern South China Sea. However, for a long time, there has been no consensus on the source of the submarine fan sediments, The provenance analysis will be of great significance to the optimization of natural gas exploration in this area. [Methods]In this paper, the detrital zircon U—Pb age spectrum characteristics of drilling cores of the middle Miocene submarine fan in the Qiongdongnan Basin was analyzed and compared with the U—Pb age of the zircon in the potential provenance area to trace the source of submarine fan in the study area. [Results]The results show that : ①The U—Pb ages of detrital zircons from N-1, N-2, N-3 and N-4 wells in the northern part of the basin are characterized by the age peaks of Yanshanian (160 Ma, 157 Ma, 133 Ma, 107 Ma, 102 Ma, 99 Ma), Indosinian ( 249 Ma, 241 Ma, 239 Ma ) and Caledonian ( 466 Ma, 455 Ma ), and have high similarity with the U—Pb age characteristics of detrital zircons from the Hainan Island sediments, but with low similarity with the U—Pb age characteristics of detrital zircons from Red River and central Vietnam sediments. ②The detrital zircon U—Pb age characteristics of three wells ( S-1, S-2, S-3 ) in the southern part of the basin show the peak age characteristics of Indosinian ( 242 Ma, 238 Ma, 237 Ma ), Caledonian (431 Ma, 431 Ma, 425 Ma,), Hercynian (392 Ma, 392 Ma) and Yanshan ( 143 Ma ). The S-2 well has a younger unimodel Himalayan ( 21 Ma ) age peak. [Conclusion] It is confirmed that the sediment source of the middle Miocene in the northern part of the basin is mainly from Hainan Island. The influence of the provenance in the Red River and Central Vietnam are very limited. The provenance of the middle Miocene in the southern Qiongdongnan Basin has a double-source supply from the Red River and Hainan Island, and is dominated by the former one, with an apparent difference from west to east.
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Key words:
- zircon U-Pb age /
- provenance /
- submarine fan /
- Meishan Formation /
- Qiongdongnan Basin
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