山东齐河—禹城地区深部地质构造特征——来自大地电磁的证据

Characteristics of the geological deep structure in QiHe-Yucheng area of Shandong:evidence from magnetotelluric method

近年来,山东齐河—禹城地区矽卡岩型铁矿找矿工作取得重大进展,有望成为山东省内重要的富铁矿基地.但该地区覆盖层厚,深部异常信息难以获取,因此对控矿岩体的研究仍然相对薄弱.为此在该区布设了4条大地电磁剖面,采用夜间12 h采样时长、G-B阻抗张量分解法、二维非线性共轭梯度反演技术措施,并与航重、航磁、钻孔资料,联合反演获得了各剖面厚覆盖层之下侵入岩体的顶界面、岩体的侵入边界、地层结构及断层位置.依据所推断的岩体边界和断层位置处磁异常Tilt梯度特征,重新圈定了研究区内岩体的边界和断层位置,共圈定隐伏岩体5个,断层9条.断层间相互关系表明在岩体侵入之后,本区地质构造运动仍然比较显著,要重视后期构造作用对区内铁矿体的改造,区内构造活动剧烈部位是今后重点研究对象.通过研究发现,在厚覆盖区,利用大地电磁、航重、航磁、钻探资料综合反演解释,进行隐伏地质构造研究,是一种有效的方法组合.

In recent years, a great progress has been achieved in prospecting of iron ore as a skarn type in Qihe—Yucheng area where is expected to be an important iron ore base with high grade in Shandong province. In the region, formation of the sediments above are of huge thick, information of its ore-bearing is still lack of enough research. Four magnetotelluric profiles were designed in the area. The 12-hour of sampling at night, the G-B impedance tensor of decomposition method, and the 2-D NLCG of inversion technique were used. Combined airborne gravity, aeromagnetic, and drilling data, joint inversion obtained the top interface of the intrusion rock mass under the thick overburden of each section, the intrusive boundary of the rock mass and stratum structure, and determined the location of the section interruption layer. According to the characteristics of the tilt derivative of the magnetic anomaly modulus at the boundary of rock masses and location of fault provided by gravity-magnetic-resistivity joint inversion results, the boundary of the rock mass and location of fault in the study area were redefined. Five hidden rock masses and nine faults were delineated. The correlation between faults indicates that the geological tectonic movement in the area is still significant after an intrusion of rock mass, it is necessary to pay attention to the transformation of bodies of iron ore in the area by late tectonic action, and the area with an intense tectonic activity will be a key research object in the future. Output from this research show that approach used is an effective method to study the hidden geological structure in a thick-covered area by the comprehensive interpretation with magnetotelluric, airborne gravity, aeromagnetic and drilling data.