基于正演模拟的火山岩重磁响应特征研究:以川西地区二叠系为例

近期的川西地区深层火山岩勘探成果表明该地区二叠系火山岩具有巨大勘探潜力,但目前以地震为主的勘探手段在精细刻画火山岩分布范围等方面尚存在困难,本研究尝试通过重磁方法为火山岩勘探提供更多有利证据。利用川西地区最新的重磁资料,结合现有地质认识分析川西地区重磁物性特征;根据不同模型的重磁正演模拟结果,总结川西地区深层火山岩重磁响应特征。通过实测重磁资料处理,分析研究区断裂分布特征和高磁异常分布规律。研究表明:(1)正演结果显示磁力异常对火山岩的反应敏感,重力异常对断裂构造反应明显,但对火山岩无明显反应;(2)磁力异常对火山岩的刻画能力较为突出,能够识别出厚度大于45 m的火山岩,但对于火山岩埋深、岩性变化的识别存在困难;(3)通过研究区重力异常解译出的断裂构造与研究区已知断裂构造吻合度较高,同时利用磁力异常刻画的火山岩分布情况与现有认识也具有可比性。重磁勘探在四川盆地火山岩勘探中具有重要作用,重力勘探可探明控制火山岩分布的深大断裂的发育情况,磁力勘探能够识别出火山岩平面分布特征,快速圈定有利靶区,进而为火山岩勘探提供有力的重磁依据。

Study on Gravity and Magnetic Response Characteristics Based on Forward Modeling: An Example from Permian Volcanic Rocks in the Western Sichuan Basin

Recent exploration results of deep volcanic rocks in the western Sichuan Basin indicate that the Permian volcanic rocks in this region have great exploration potential. However, it is still difficult for seismic exploration methods to describe the distribution of volcanic rocks in detail. Therefore, it is necessary to provide more favorable evidence for volcanic exploration through gravity and magnetic methods. This paper takes advantage of the latest gravity and magnetic data to analyze the characteristics of gravity and magnetic properties in the western Sichuan Basin based on existing geological knowledge, and summarizes the gravity and magnetic response characteristics of deep volcanic rocks in this region based on the gravity and magnetic forward simulation results of different models. Through the processing of measured gravity and magnetic data, the distribution characteristics of faults and the distribution law of high magnetic anomalies in the study area are analyzed. The results show that: (1) The forward modeling results show that magnetic anomalies are sensitive to volcanic rocks, and gravity anomalies are sensitive to faulted structures, but not to volcanic rocks. (2) Magnetic anomaly has an outstanding ability to depict volcanic rocks, which can identify the volcanic rocks with a thickness of more than 45 m, but it is difficult to identify the buried depth and lithology changes of volcanic rocks. (3) The fault structures interpreted by gravity anomalies in the study area are in good agreement with the known fault structures in the study area. Meanwhile, the distribution of volcanic rocks described by magnetic anomalies is comparable to the existing understanding. It is concluded that gravity and magnetic exploration plays an important role in volcanic exploration in Sichuan Basin. Gravity exploration can identify the development of deep and large faults that control the distribution of volcanic rocks, and magnetic exploration can identify the plane distribution characteristics of volcanic rocks and quickly delineate the favorable target areas, thus providing favorable gravity and magnetic basis for volcanic exploration.