甘肃省区域重力场特征

CHARACTERISTICS OF REGIONAL GRAVITATIONAL FIELD IN GANSU PROVINCE

张新虎等人在区域成矿地质背景研究过程中,根据甘肃省区域地球物理新成果,对地球物理特征进行梳理。本文认为甘肃省处于中国西北地区五大板块交汇地带,地质历史漫长,地质构造复杂,在各单元间的相互作用和影响,形成了一幅复杂的应变图像。甘肃省的地球物理场特征也极为复杂。文章介绍了区域重力调查工作概况,分析了区域地层岩性的密度特征,随地层层序从新到老密度值呈递增趋势。在古生界—太古界间岩层密度接近或略高于地壳表层平均密度2.67×10~3 kg/m^3。不同期构造层之间形成密度层及密度界面,较明显的是新生界与中生界之间、中生界与古生界之间。岩体密度随岩石由酸性到基性、超基性岩密度变大;酸性花岗岩和同质火山岩熔岩较地层平均密度偏小;区域布格重力异常主要反映地壳深部信息的区域分量和浅部信息的局部分量,根据区域布格重力异常分布,划分出甘肃北山—秦岭东段重力异常带、阿克塞—张掖—永靖—舟曲弧形重力梯级带,对四顶黑山—红石山、玉门关—前红泉—旧寺墩、阿尔金山—祁连山—西秦岭、六盘山—陇山、天水—武山—临夏—尖扎、青川—阳平关、天水—武都重力梯级带特征进行了分析总结。甘肃省区域重力场特征是甘肃及邻区基础地质研究的主要组成部分,可为中大比例尺的成矿预测提供基础资料。本文试图对甘肃区域重力场特征进行系统总结,形成规律性认识供参考。

Based on the new studies of regional geophysics in Gansu Province, Zhang et al. systematically summarized the geophysical characteristics in the researches of geological setting of regional mineralization. Located at the combining zone of 5 plates, the geological evolution lasted for a relatively long time and the tectonics complicated in Gansu Province. Therefore, a complex strain pattern formed under the interactions of different tectonic units. The authors introduced the overview of regional gravity survey, concluded the characteristics of rock density from different regional strata： the values is increasing along with the stratigraphic age from new to old. The rock density in the period of Paleozoic and Archaean is near or slightly higher than the average density of crustal surface. The density layering and interface appear at tectonic layers of different ages, obviously between the Neozoic and the Mesozoic, the Mesozoic and the Paleozoic. The density of intrusive rocks gradually increases with the rock from acid to basic-ultrabasic. The density of acid granites and lava is lower than the average value of the stratum. According to the distributing characteristics of Bouguer gravity anomalies, which reflecting the regional component of deep information and local component of shallow information of the crust mainly, the Beishan-Eastern Qinling gravity anomaly belt and Aksay-Zhangye-Wuwei-Yongjing-Minxian- Zhouqu arcuate gravity cascade are defined, the 7 sub-class gravity cascades, which is the Sidingheishan- Hongshishan, Yumenguan-Qianhongquan-Jiusidun, Altyn-Qilian-Western Qinling, Liupanshan-Longshan, Tianshui-Wushan-Linxia-Jianzha, Qingchuan-Yangpingguan and Tianshui-Wudu, are derided. The characteristics of gravity cascades and relationship with geological setting are described and analysed. The results are significant to the geological researches in Gansu and adjacent areas, and the data of metallogenic prognosis of middle and large scales.