北山北带黄丘泉地区早泥盆世花岗岩的岩石成因及构造意义  

Petrogenesis and tectonic significances of Early Devonian granites in Huangqiuquan area from the northern Beishan Orogenic Belt,NW China

作　　者：卜涛 王国强[1,2] 黄博涛 过磊[1,2] 邹璇 BU Tao;WANG Guoqiang;HUANG Botao;GUO Lei;ZOU Xuan(Xi,an Center,China Geological Survey(Geosciences Innovation Center of Northwest China),Xi’an,710119;Center for Orogenic Belt Geology,China Geological Survey,Xi’an,710119;Central South Geological Survey Institute of China Metallurgical Geology Bureau,Wuhan,430080)

机构地区：[1]中国地质调查局西安地质调查中心(西北地质科技创新中心),西安710119 [2]中国地质调查局造山带地质研究中心,西安710119 [3]中国冶金地质总局中南地质调查院,武汉430080

出　　处：《地质论评》2024年第6期2193-2211,共19页Geological Review

基　　金：中国地质调查局地质调查项目(编号:DD20243411、DD20240029、DD20230005、DD20230215、DD20190812);陕西省自然科学基金资助项目(编号:2023-JC-YB-267)的成果。

摘　　要：北山造山带在早泥盆世是否存在构造体制转换一直是该地区大地构造演化研究的关键。笔者等选取北山北带黄丘泉地区的石英二长岩和正长花岗岩进行了岩石学、元素地球化学、锆石U-Pb年代学和Hf同位素分析,结果显示,石英二长岩和正长花岗岩的LA-ICP-MS锆石U-Pb年龄的加权平均值分别为411.9±2.2 Ma和409.6±1.7 Ma;全岩样品具有准铝质—弱过铝质、碱性—碱钙性及铁质等地球化学特征;稀土元素总量中等,轻重稀土弱到中等分馏且相对富集轻稀土,石英二长岩具有弱的负Eu异常,正长花岗岩具有明显的负Eu异常;微量元素富集Rb、K、U,亏损Sr、Ta、P、Ti;锆饱和温度计算黄丘泉岩体的结晶温度在828~888℃,平均856℃;以上这些岩石地球化学特征与A型花岗岩一致。锆石ε_(Hf)(t)值介于-7.02~4.42,二阶段模式年龄(t_(DM2))介于1.84~1.12 Ga,平均1.42 Ga,表明岩浆源区以古老地壳物质为主,但也有新生物质的加入,可能为新生幔源熔体上侵并与壳源熔体发生不同程度岩浆混合的产物。构造环境判别显示石英二长岩为A2型花岗岩,正长花岗岩为A1型花岗岩。结合区域地质资料及前人研究成果,认为黄丘泉地区A型花岗岩均形成于后碰撞伸展环境,A1型花岗岩和A2型花岗岩的共同出现,标志着北山造山带的构造体制于早泥盆世已进入后碰撞伸展环境,并具向板内构造阶段演化的趋势。The existence of structural system transformation in the Beishan orogenic belt during the Early Devonian has always been a key issue in the study of tectonic evolution in the region.In this paper,the granites from the Huangqiuquan area in the northern belt of Beishan is selected for petrology,zircon U-Pb chronology,element geochemistry and Hf isotope analysis.The results show that the weighted average values of zircon U-Pb ages obtained by LA-ICP-MS for quartz monzonite and syenogranite are 411.9±2.2 Ma and 409.6±1.7 Ma,respectively.The quartz monzonite and syenogranite in the research area were characterized by quasi aluminous to weakly peraluminous,alkaline to alkaline calcium and iron.TheΣREE is moderate,relatively enriched in LREE and depleted in HREE with weak to moderate fractionation between LREE and HREE.The quartz monzonite display small negative Eu anomalies,whereas the syenogranite show more obviously negative Eu anomalies.The trace elements are rich in Rb,K,U and poor in Sr,Ta,P and Ti.Calculated by zirconium saturation temperature,the crystallization temperature of Huangqiuquan granite is 828~888℃,average 856℃.Combined with the geochemical characteristics above,the Huangqiuquan granite should be defined as A-type granite.The zirconε_(Hf)(t)values ranges from-7.02 to-4.42.TDM2 modle ages from 1.84 to 1.12 Ga,average 1.42 Ga.It indicates that the magma source area is mainly composed of ancient crustal materials,but there is also the addition of new biomass,which may be the product of the upwelling of new mantle derived melts and varying degrees of magma mixing with ancient crustal melts.The tectonic environment discrimination shows that the quartz monzonite is A2 type granite and the syenite granite is A1 type granite.Based on regional geological data and previous research results,it is believed that the A-type granite in the Huangqiuquan area was formed in a post collision extension environment.The simultaneous occurrence of A1 type granite and A2 type granite indicates that the tectonic syste

关 键 词：早泥盆世 A型花岗岩 锆石U-PB年龄 地球化学 北山 

分 类 号：P542[天文地球—构造地质学] P588.121[天文地球—地质学] P534.44