Abstract: This paper firstly discusses the feasibility of delineating the volcanic rocks distribution by gravitational and magnetic methods on the basis of the statistical results of the magnetic susceptibility and density of the different lithologies in the study area. After the separation of gravitational and magnetic fields by bandpass filter, we determined the residual gravitational and magnetic anomalies caused by volcanic rocks. The results of potential field separation show that the residual anomalies are in beaded NE-directed distribution. In the meantime, the boundary enhancement techniques such as horizontal total gradient and vertical derivative are employed to delineate the distribution of the faults, as the result, fifteen faults including four NE-striking main faults which appear as an arc protruding to the southeast and other secondary faults are distinguished. Furthermore, two fault systems with deep and superficial attribution are revealed from the inversed section of the telluric electromagnetic sounding, and their properties, characteristics and roles in the volcanic activity are fully discussed by combining with the tectonic background. Based on the comprehensive analysis of the correlation between the distribution characteristics of the residual gravitational and magnetic anomalies and the location of the faults, three volcanic activity zones are reasonably delineated. Finally, we carry out the inversion of apparent density by taking advantage of the residual gravitational anomalies and acquire the apparent density anomalies of the top part of Paleozoic. Integrated with the apparent density anomalies, the lithologies exposed from the boreholes, the observed density data of different rocks and the residual gravitational-magnetic anomalies, we elaborately delineate the lithologies of the top of Paleozoic and further define the distribution range and the lithology combination of Kekesayi group of Middle Ordovician, Tailegula group of Lower Carboniferous and Jiamuhe group of Lower Permian.

Key words: northwest margin of Junggar Basin, volcanic rock reservoir, gravitational and magnetic anomaly, magnetotelluric sounding, volcanic activity belt, lithology identification

摘要： 文中从各类岩石磁化率、密度统计数据出发，对比分析不同地层和岩性的磁性、密度，指出在研究区内开展火山岩重磁研究具有有利的物性基础。在利用带通滤波方法对重磁异常进行位场分离，消除沉积盖层和区域场影响后，获得由火山岩引起的剩余重磁异常，位场分离结果显示，反映火山岩的局部重磁异常多呈串珠状NE向分布。同时采用水平总梯度和垂向导数等边界信息增强手段，圈定研究区内的断裂构造分布情况，划分出了4条向SE弧形突出的NE向主干断裂及其他次级断裂共计15条。通过大地电磁测深了解主要断裂的垂向延伸情况，进一步厘定出深、浅2个断裂系统，并结合构造背景对2个层次断裂的性质、特征和对区内火山活动的作用进行了讨论。在综合分析剩余重磁异常分布特征和断裂构造相互关系的基础上，圈定出3条火山活动带。最后，利用剩余重力异常进行视密度反演，获得古生界顶部的视密度异常，以此为基础，结合钻孔岩性、岩石实测密度值和剩余重力异常分布规律，对古生界顶部的岩性分布进行细致的划分，确定了中奥陶统科克萨依组、下石炭统太勒古拉组和下二叠统佳木河组的分布范围及岩性组成。

关键词: 准噶尔盆地西北缘, 火山岩油气藏, 重磁异常, 大地电磁测深, 火山活动带, 岩性识别