Extraction of basement gravity anomaly in deepwater basins: a case study in Nanweixi Basin
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摘要: 根据重力异常反演沉积盆地基底深度在区域构造研究和油气勘探等领域发挥越来越重要的作用,而有效地提取盆地基底起伏引起的重力异常是准确反演盆地基底深度的先决条件.对于地质构造较为复杂的区域,完全基于数学原理的位场分离方法较难有效提取基底起伏引起的重力异常.为此本文以南薇西盆地为例,研究了深水区盆地基底重力异常的提取方法.首先以海底地形数据为基础,采用频率域重力场正演计算方法计算海水的重力效应,并从自由空间重力异常中消除,得到布格重力异常.之后采用CRUST 1.0 莫霍面深度数据正演莫霍面重力效应,同时利用动态均衡校正方法计算莫霍面重力影响,通过与已知构造特征对比分析,确定了动态均衡校正方法更适合于研究区莫霍面重力校正,并从布格重力异常中消除莫霍面重力影响而得到了基底重力异常.最后通过对基底重力异常分析,探讨了礁滩区重力异常特征及其可能对基底深度反演带来的影响,并对南薇西盆地构造区划提出一些建议.Abstract: Gravity inversion for the basement relief of a sedimentary basin plays an increasingly important role in areas such as regional tectonic research and oil and gas exploration, and the prerequisite to accurately estimating the basement relief with gravity anomaly is effectively extracting the gravity anomaly caused by the basement. For regions with complex geological structure, it is difficult to effectively extract the gravity anomaly caused by the basement with the potential field separation methods based on mathematical principle. To address this limitation, we have considered the method of extracting the gravity anomaly caused by the basement of deepwater basins by taking the Nanweixi Basin as an example. Firstly, based on the data of the submarine topography, the gravity anomaly of seawater was calculated using a frequency domain algorithm for gravity calculation and eliminated from the free air gravity anomaly to obtain the Bouguer gravity anomaly. The depth of Moho from CRUST 1.0 was used to calculate the gravity anomaly produced by the Moho relief afterwards. The basement gravity anomaly was obtained by removing the Moho gravity anomaly. The dynamic isostatic correction was also introduced to obtain the basement gravity anomaly, which is more suitable for the Nanweixi Basin after comparing with the known geological features. Thus, the basement gravity anomaly was obtained. Finally, the gravity anomaly related to the reef and its impact on the basement relief inversion were analyzed and the division of the tectonic units of the Nanweixi Basin was discussed.
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Key words:
- Basement /
- Gravity anomalies /
- The dynamic isostatic correction /
- Deep water area /
- Reef
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