长江中下游重要成矿区带及邻区大地电磁测深三维反演研究

Study for MT 3D Inversion in the middle and lower reaches of the Yangtze river important mineralization zones and its adjacent area

当前,大地电磁测深法一维、二维反演技术是实际资料处理和解释主要应用的技术手段,三维反演技术随着算法的改进和硬件设施的提升也取得重要进展,但三维反演计算还存在计算速度慢、消耗大量内存等问题,导致其在实际应用中并不多见.本文以长江中下游重要成矿区带及邻区大地电磁资料为例,以REBOCC三维反演算法作为计算手段,在具有16G内存的普通计算机工作站上开展了武汉图幅面积约25.68万km2的大面积区域范围的大地电磁三维反演工作,计算耗时约一个半月,取得较为理想的三维反演结果.研究区内共布置完成大地电磁测深点425个,由于测点数目较多,工区范围较大,单台工作站一次性进行全部数据三维反演计算根本无法运行,这就导致必须选择采用分区块、抽稀频点的解决办法.课题组首先将整个工区划分为6个子区块,相邻2个子区块之间保留一定的重叠区域,同时将每个测点抽稀使用20个频点;其次,将每个子区块依次轮流在工作站上进行三维反演计算,分别取得相应子区块三维反演结果;最后,将每个子区块的三维反演结果在重叠区域按照一定的加权规则进行拼接,最终得到长江中下游地区岩石圈三维电性结构模型.长江中下游地区是我国重要的铁铜矿产业基地,揭露岩石圈的三维空间电性结构特征,为下一步找矿突破与预测具有重要指导意义.本文通过对长江中下游重要成矿区带及邻区大地电磁测深资料的三维反演研究表明:三维电磁探测技术可行、优势明显,通过三维反演计算可以得到研究区内纵向和横向上的电性分布特征;在现代观测设备和先进的计算技术的支撑下,深部三维电性结构模型可以为认识地下三维地质结构提供丰富信息;针对大面积区域范围的大地电磁资料在单台工作站上先实行分块反演计算再进行拼接的工作方法同样可以取得较为理想的三维反演结果,其在工作成本和时效性等方面均可以接受.

Currently,magnetotelluric sounding one dimensional and two dimensional inversion technique is a major application of actual data processing and interpretation techniques,3d inversion technique with the improvement of algorithm and hardware facilities of ascension also made important progress,but in actual application of three dimensional inversion there is slow speed of calculation,consuming large amounts of memory and other problems.This article take magnetotelluric data acquired from the important mineralization belt in middle and lower reaches of the Yangtze river and its adjacent area for example. Using REBOCC three-dimensional inversion algorithm as a means of calculation,it took about a month and a half to do magnetotelluric 3dinversion in common with computer workstation with 16 gb memory in the wuhan area of about 25.68 square kilometers.The study area completed magnetotelluric sounding station 425.Due to the number of measuring station is more,scope of work area is larger,work area 3dinversion calculation need great memory to store the middle data.In order to make the three dimensional inversion can work on the workstation run smoothly,our work team evenly picked out the best 290 stations from all stations in the work area first.Second the entire work area is divided into six children work area,adjacent to retain a certain overlap between two child work area.At the same time,each measuring station selected out 20 sounding frequency.To each work area on the workstation,in turn,three-dimensional inversion calculated separately,finally the 3dinversion result of each work area in the overlapping area according to certain weight proportion for Mosaic,end up with the middle and lower reaches of the Yangtze river region lithosphere three-dimensional electrical structure model.The middle and lower reaches of the Yangtze river is China＇s important iron copper industry base,expose the lithosphere three-dimensional electrical structure characteristics,for the next step prospecting breakthrough and prediction has important guiding significance. This article through 3 d inversion research of magnetotelluric sounding data in the middle and lower reaches of the Yangtze river important mineralization zones and its adjacent area shows that：Threedimensional electromagnetic detection technology is feasible andhas obvious advantages,through 3dinversion calculation can get the order on the vertical and horizontal electrical distribution characteristics;In modern observation equipment and advanced computing technology,under the support of deep three-dimensional electrical structure model can provide rich information for recognizing the underground three dimensional geological structure;On a large area range of magnetotelluric data on a single workstation to implement partitioned inversion calculation for splicing methods can also be obtained more ideal three dimensional inversion results,in the work cost and timeliness,etc are acceptable.