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首次利用锆石LA-ICP-MSU-Pb法测得甘肃火石山东北部侵位于长城系、蓟县系以及志留系中的哈尔根头口布花岗岩形成于中泥盆世早期(同位素年龄为387.6±8.2Ma),同时发现该花岗岩体内存在晚蓟县世产物(继承性锆石年龄1172±7Ma)。哈尔根头口布花岗岩体主要由钾长花岗岩、二长花岗岩、花岗岩组成,岩石具有高硅(SiO2含量为70.28%～79.4%)、富碱(Na2O+K2O为6.52%～9.11%)、低铝(Al2O3含量为8.82%～14.05%)、低Sr(含量为40～150×10-6,平均为101.5×10-6)的特征、岩石的δ<3.3、A/CNK值为0.8～1.1,为钙碱性准铝质到弱过铝质岩石;稀土元素具有明显的LREE富集(LREE/HREE=2.89～16.4,LaN/YbN=1.82～25.18)和Eu亏损,相对富集Rb、Th、Ce和Sm,而亏损Ta、Nb、Zr、Hf。综合分析认为该花岗岩为A型花岗岩,产于构造挤压向构造伸展转换的地质背景之中。
The zircon-LA-ICP-MSU-Pb method was used for the first time to find that the Haergen head mouth cloth granitoids in the Changcheng, Jixian and Silurian systems in the northeastern Huoshe Mountains of Gansu Province were formed in the early Middle Devonian (isotopic age 387.6 ± 8.2Ma). It is also found that there is the artifact of late thistle in this granite (inherited zircon age 1172 ± 7Ma). The Haergen head mouth cloth granite body is mainly composed of potash-bearing granite, monzogranite and granite. The rock has high contents of silicon (SiO2: 70.28% -79.4%) and alkali-rich (Na2O + K2O: 6.52% -9.11% Low alumina (Al2O3 content of 8.82% ~ 14.05%), low Sr (content of 40 ~ 150 × 10-6, an average of 101.5 × 10-6) characteristics of rock δ <3.3, A / CNK value of 0.8 ~ 1.1 for Ca-Alkali-to-weak permalloy; Rare earth elements have obvious LREE enrichment (LREE / HREE = 2.89 ~ 16.4, LaN / YbN = 1.82 ~ 25.18) and depletion of Eu, Th, Ce and Sm, and loss Ta, Nb, Zr, Hf. The comprehensive analysis shows that the granite is A-type granite, which is produced in the geological background from compressional to tectonic extension and transformation.