冀东幔枝构造的地球物理特征分析

Geophysical Characteristics Analysis of the Mantle Branch Structure in Eastern Hebei

幔枝构造是地幔热柱的第三级构造单元,是地幔热柱多级演化在岩石圈浅部的综合表现形式,是重要的成矿控矿构造。冀东幔枝构造的核部主要为太古宙—古元古代变质岩及侵入其内的燕山期岩浆岩组成的岩浆-变质杂岩。表壳岩和岩浆岩分布区在区域上多表现为重磁的低值异常,深变质岩尤其磁铁石英岩广泛分布区,表现为巨幅强磁异常和明显的高重力异常,可作为寻找铁矿建造的重要依据。冀东幔枝构造盖层主要为中新元古界碳酸盐岩—碎屑岩建造,重磁在区域上多表现为重磁负异常。核部与盖层之间拆离滑脱层(带)在航磁ΔT等值线平面图上表现为极低的负异常,是区内最低的弱磁场,在布格重力异常图上表现为正异常向负异常过渡的特征。冀东火山断陷盆地内岩石磁性变化较大,常引起局部的航磁异常,在区域上显示重力负异常。冀东地区金矿多集中于在航磁负异常区,尤其是正异常向负异常过渡的地区,即航磁等值线梯度变化区。在布格重力异常图上多分布于重力低值异常区。对应1:20万区域地质图,金主要分布于出露和隐伏的燕山期中酸性岩体与围岩接触带外围,尤其变质岩发育区,构造上为近EW向、NNE向和NW向构造展布区,尤其交汇处及次级断裂发育区。

Mantle branch structure is the third level tectonic unit of mantle thermal column,which is the comprehensive expression of multi-level evolution of mantle thermal column in the shallow part of lithosphere,and is an important mineralization control structure.The core of the mantle branch structure of Eastern Hebei is mainly magmatic-metamorphic miscellaneous rocks composed of metamorphic rocks of Tauric and Paleozoic age and Yanshan period magmatic rocks intruded in it.The deep metamorphic rocks,especially the magnetite quartz rocks,are widely distributed in the area,and show huge strong magnetic anomalies and obvious high gravity anomalies,which can be used as an important basis for finding iron ore construction.The caprock of mantle branch structure of Eastern Hebei is mainly carbonate-clastic rock construction in the middle and late meta-paleocene,and the heavy magnetism is mostly negative anomalies in the area.The detached slip layer(zone)between the core and the cover shows very low negative anomalies on the aeromagneticΔT contour map,which is the lowest weak magnetic field in the area.The transition from positive anomaly to negative anomaly is characteristic.The magnetic variation of rocks in Eastern Hebei volcanic fault basin is large,which often causes localized aeromagnetic anomalies and shows negative gravity anomalies in the region.Gold is mostly concentrated in the area of negative aeromagnetic anomalies,especially in the area of transition from positive to negative anomalies,that is the area of gradient changes in aeromagnetic contours.In the Bouguer gravity anomaly map,it is mostly distributed in the area of low gravity anomalies.Corresponding to the 1:200,000 regional geological map,gold is mainly distributed in the periphery of the contact zone between the outcropping and hidden Yanshan period medium acidic rocks and the surrounding rocks,especially in the area of metamorphic rock development,and the tectonic spreading is near EW direction,NNE direction and NW direction.