内蒙古西乌旗努和特A型花岗岩位于贺根山缝合带内,侵位于晚石炭世梅劳特乌拉蛇绿岩带、中二叠统哲斯组和晚石炭世英云闪长岩中,岩性为正长花岗岩.努和特A型花岗岩富硅、富钾、富碱、贫Al2O3、CaO、MgO、TiO2、P2O、Sr、Ba、Eu、Ti和P,具有较高的Ga/Al、(Na2O+K2O)/CaO、K2O/MgO、TFeO/MgO、Rb/Nb、Y/Nb、Sc/Nb值,稀土元素配分曲线为海鸥式分布,δ Eu值为0.25～0.54,负Eu异常明显,地球化学特征明显不同于I、S和M型花岗岩,为铝质A型花岗岩.在地球化学分类判别图解上,努和特A型花岗岩显示后造山A2型花岗岩特征,反映其形成于后造山伸展环境.LA-ICP-MS锆石U-Pb测年表明,该花岗岩的侵位年龄为130.4±1.2Ma和130.4±1.4Ma,其形成时代为早白垩世.根据蛇绿岩、俯冲-岛弧型-碰撞型和后造山型岩浆岩的时空分布与演化特征,贺根山缝合带在早白垩世可能处于后造山伸展阶段.%Located along the Hegenshan colhsional orogenic suture zone in Xi Ujimqin Banner of Inner-Mongoha,the Nuhete Atype granite intruded into Late Carboniferous Meilaotewula ophiohte,Middle Permian Zhesi Formation and Late Carboniferous tonalite and consists mainly of syenogranites.The granite is geochemically characterized by high SiO2(72.92％～76.18％),K2O(4.1％～5.03％)and absolute alkali values (Na2O+K2O=8.01％～8.64％),low Al2O3,CaO,MgO,TiO2,P2O5,Sr,Ba,Eu,Ti,P values,and relatively high Ga/Al,(Na2O + K2O)/CaO,K2O/MgO,TFeO/MgO,R.b/Nb,Y/Nb,Sc/Nb ratios.It is characterized by a slightly right-inclined gull-wing shaped REE patterns with negative Eu anomalies (δ Eu=0.25～0.54).The Nuhete syenogramte exhibits the typical geochemical characteristics of aluminous A-type granites,being significantly different from I,S and M type granites in geochemistry.According to the chemical subdivision diagrams of the A-type granitoids,the Nuhete A-type granite belongs to aluminous A2-type granitoid formed and emplaced in a post-orogenic extension setting.The LA-ICP-MS zircon U-Pb dating shows that the age of the granite is 130.4 ±1.2 Ma and 130.4 ±1.4Ma,suggesting early Cretaceous.According to the temporal and spatial distribution and evolution characteristics of the ophiolites,subductional arc granitoids,collisional granites and post orogenic granitoids in the Hegenshan colhsional orogenic suture zone,the authors hold that the Hegenshan suture zone was in a post orogenic extension stage in the Early Cretaceous period.
展开▼
