东海椒江凹陷晚古新世物源变化

Provenance Change and Its Influence in Late Paleocene, Jiaojiang Sag, East China Sea Shelf Basin

摘要:

为深入分析椒江凹陷上古新统明月峰组物源，探索适用于海域的物源研究方法，对东海椒江凹陷的岩石组分、重矿物及碎屑锆石UPb定年等数据进行物源综合分析.结果显示，凹陷东部明月峰组上段和下段的物源发生了改变，其下段物源主要来自凹陷东部的海礁隆起，以过渡弧切割弧环境的酸性侵入岩为主，主要源岩时代为183～209 Ma，有少量变质岩及其他中生代火成岩贡献；至明月峰组上段沉积期，物源以过渡弧环境下的酸性喷出岩及侵入岩为主，碎屑锆石年龄集中于106~116 Ma，与围区物源特征基本相同；结合沉积体系演化分析，表明整个椒江凹陷的物源来自西部的浙闽隆起区.研究区物源变化是构造、沉积环境在晚古新世发生剧变的结果，这种物源变化对该区的盖层发育及对油气层封盖能力产生了较大影响.

关键词:椒江凹陷; 海域物源研究; 碎屑锆石; 物源变化; 浙闽隆起

Abstract:

To fully recovery provenance of Mingyuefeng Formation of Well W6 in upper Paleocene in Jiaojiang Sag and probe research methods for provenance analysis applied to sea area, this research used detrital framework grains, heavy minerals and detrital zircon UPb dating for the comprehensive provenance analysis. The result shows that the Lower Mingyuefeng Formation(LMF) and Upper Mingyuefeng Formation(UMF) have entirely different provenance in the east part of Jiaojiang Sag. The main source of LMF is from Haijiao Uplift located to the east of the sag and is mainly acid intrusive rocks formed in transitional arcdissected arc with zircon UPb age ranging from 183 to 209 Ma. In addition, there is a small amount of contribution of the metamorphic and Mesozoic igneous in other age range. The main source of UMF in Jiaojiang Sag is possibly from Zhemin Uplift to the west of the sag with acid volcanic rocks and intrusive rocks formed in transitional arc with the zircon age about 106～116 Ma. It has nearly the same source rocks with the adjacent areas whose provenance area is located in the western Minzhe Uplift. This conclusion is also supported by the depositional system evolution. The change of provenance is the resulted from the tectonic and deposition environment change in late Paleocene, which has a great impact on the cap rock and the sealing capability to the oil and gas bearing in this area.

Key words:Jiaojiang Sag; offshore provenance research; detrital zircon; provenance change; Zhemin Uplift