摘要
辽吉地区地处华北克拉通胶-辽-吉带北部,区域内发育有相对完整的古元古代沉积作用与岩浆活动。本文对辽吉地区2个古元古代条痕状花岗岩体(鸡冠山岩体和老黑山岩体)进行了岩石学、地球化学和成因学研究。研究表明,条痕状花岗岩(二长花岗片麻岩)样品具有高的K_2O/Na_2O、FeOT/MgO比值和Ga、Zr、Y含量以及低的CaO、MgO、Sr、Cr、Co、Ni含量,全碱(K_2O+Na_2O)含量变化于7.97%~9.08%。在SiO_2-K_2O图中,条痕状花岗岩主要位于高钾钙碱系列区域,样品A/CNK值介于0.84~1.03之间,A/NK值为1.11~1.17,10000Ga/Al比值全部大于2.6,为高钾钙碱性铝质A型花岗岩。其中6个样品的εNd(t)为-3.3^-0.9,Nd同位素两阶段模式年龄tDM2=2860~2669Ma,暗示其形成于太古宙地壳的部分熔融。条痕状花岗岩富集Rb、U、K等大离子亲石元素和轻稀土元素,亏损Nb、Ta、Ti等高场强元素,具有明显的俯冲带岩浆特征,在Rb/30-Hf-Ta×3图中落入火山弧区域;其Y相对于Nb更富集,具有与岛弧玄武岩相似的Y/Nb等元素比值,在Y/Nb-Rb/Nb和Nb-Y-Ce图解中落入A_2型花岗岩区域。古元古代早期,辽吉地区处于大陆弧后盆地构造环境,强烈的弧后伸展作用产生了条痕状花岗岩;在后期的地体拼贴过程中,条痕状花岗岩与周围岩石共同变形并最终构造挤压在一起。
As the northern segment of Jiao-Liao-Ji Belt of North China Craton,the Liaoji region preserves good exposure of Paleoproterozoic sedimentation and magmatism. In this contribution,we conducted petrologic,geochemical and petrogenesis study on two Paleoproterozoic monzogranitic gneisses（ Jiguanshan pluton and Laoheishan pluton） in the Liaoji region. The study shows that the monzogranites have relatively higher K2O/Na2 O,Fe OT/Mg O ratios and Ga,Zr,Y contents,while low contents of Ca O,Mg O,Sr,Cr,Co and Ni. Concentration of the total alkali（ K2O ＋ Na2O） is 7. 97% - 9. 08%. In the diagram of SiO2-K2O,monzogranites mainly lie in the high-K calc-alkaline series. A/CNK values of the monzogranites are 0. 84 - 1. 03,while their A/NK values are 1. 11 - 1. 17.10000Ga/Al values of all the samples are higher than 2. 6,thus,these monzogranites are classified as aluminous A-type granites with high-K calc-alkaline affinity. εNd（t） values of six samples from the monzogranites are-3. 3 --0. 9,corresponding to tDM2 of 2860 -2669Ma. Thus,the monzogranites originated from partial melting of Archean crust. The monzogranites are characterized by enrichment in large ion lithophile elements（ such as Rb,U,K） and light rare earth elements,and depletion in high field strength elements（ such as Nb,Ta,Ti）,showing evident signature of subduction-zone magmatism. The monzogranites plot in the region of volcanic arc in the Rb/30-Hf-Ta × 3 diagram. In the diagrams of Y/Nb-Rb/Nb and Nb-Y-Ce,the monzogranites are located in the region of A2-type granites due to theirs relatively higher Y than Nb,which is similar to island-arc basalts in terms of Y/Nb ratios. The Liaoji region was a continental back-arc basin in the Early Paleoproterozoic,and strong extension generated the monzogranites in this back-arc basin. The monzogranites were later deformed and pushed together with their surrounding rocks in later processes of terrane amalgamation.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第3期963-977,共15页
Acta Petrologica Sinica
基金
国家重点基础研究发展计划项目(2012CB416603)资助
关键词
古元古代
华北克拉通
花岗岩
胶辽吉带
构造演化
Paleoproterozoic
North China Craton
Granites
Jiao-Liao-Ji Belt
Tectonic evolution
