内蒙古哈珠地区晚古生代花岗岩类成因及其构造意义

系统研究了北山造山带北部哈珠地区花岗岩类的年代学、地球化学和锆石Hf同位素特征，并据此探讨了岩体的成因及其对晚古生代构造岩浆演化的制约.锆石LA-MC-ICP-MS U-Pb测年结果显示花岗闪长岩（298.6±1.7 Ma）和二长花岗岩（306.0±1.3 Ma）、碱长花岗岩（289.3±1.3 Ma）分别为晚石炭世晚期、早二叠世岩浆活动的产物.花岗闪长岩、二长花岗岩化学组成上表现为中钾钙碱性、Mg#值较低，分异程度中等（D.I.=79.2~86.9），属准铝质、镁质岩石；碱长花岗岩则表现高硅、富碱、准铝，贫钙、镁、铁，分异程度高（D.I.=94.4~96.5）.三者均富集Rb、Ba、Th、U、La、Ce等，不同程度亏损高场强元素Nb、Ta、P、Ti、Sr、Eu.花岗闪长岩、碱长花岗岩样品的ε_Hf（t）均为正值，T_DMC主要集中于450~800 Ma.本文和最近获得的数据表明，俯冲板块脱水交代新生下地壳，并诱发新生地壳的部分熔融，形成晚石炭世花岗岩类；早二叠世由于后碰撞伸展作用导致岩石圈拉伸减薄，促使新生地壳部分熔融，再经高程度的分异演化形成本文碱长花岗岩. 

Petrogenesis and Tectonic Significance of the Late Palaeozoic Granitoids in Hazhu Area,Inner Mongolia

The chronology, geochemistry and zircon Hf isotopes of granitoids in Hazhu area of the northern Beishan belt are systematically studied, and the genesis of the plutons and their restrictions on the tectonic magma evolution in Late Paleozoic are discussed. The zircon LA-MC-ICP-MS U-Pb dating results show that the granodiorites and monzogranites formed during the late Late Carboniferous in 298.6±1.7 Ma and 306.0±1.3 Ma, and the alkali-feldspar granites formed in Early Permian 289.3±1.3 Ma. Chemically, the granodiorites and monzogranites are characterized by middle potassium calc alkaline, low Mg# value and middle degree of differentiation (D.I.=79.2-86.9), metaluminum and enriched-magnesium. And alkali-feldspar granites show high contents of silica and alkalis, metaluminum, low abundances of calcium, magnesium and iron, and high degree of differentiation (D.I.=94.4-96.5). All of them are enriched in Rb, Ba, Th, U, La, Ce, and so on, and depleted in high field strength elements, Nb, Ta, P, Ti, Sr, and so on. The ε_Hf(t) values in this paper are all positive. The Hf isotopic crustal model age T_DMC is mainly concentrated from 800 Ma to 450 Ma. According to the data obtained in this paper and other regional geological data acquired recently, the subduction plate dehydrated, after then, the subduction fluid entered into the juvenile crust, and induced partial melting of the juvenile crust, forming the granitoids in Late Carboniferous. The extension resulted in the thinning and stretching of the lithosphere due to the post collisional extension in Early Permian, which caused the partial melting of the new crust, and then the alkali-spar granites were formed by a high degree of differentiation and evolution.