论文部分内容阅读
敖包呼图仁斑状正长花岗岩体出露于内蒙北山地区石顿井北西一带,侵入古元古代北山岩群及早古生代片麻状花岗岩.该岩体富Si02(70.41％ ～ 76.05％)、K2O (3.85％～5.22％),K2O/Na2O=1.42 ～ 2.23,铝饱和指数A/CNK为0.97～ 1.10,MgO#为14～32.稀土总量较高(∑REE =179.2×10-6～332.2×10-6),轻稀土富集(La/Yb)N=11.1～22.7,Eu负异常明显(δEu 0.25～ 0.75).在微量元素原始地幔标准化图中,富集Rb、Th、K,亏损Nb、Ta、Sr、P、Ti.(Ga/Al)×104较高,为2.6～ 4.0,具A型花岗岩特征.锆石饱和温度较高,为822.8℃～893.1℃.LA-ICP-MS锆石U-Pb测年表明其形成年龄为398.15±0.85 Ma,地质时代为早泥盆世.锆石εHf(t)为0.3～ 7.8,两阶段Hf模式年龄(tDM2)为1 376～ 894 Ma.地质背景、地球化学及同位素特征显示,敖包呼图仁斑状正长花岗岩形成于早泥盆世后碰撞构造环境,是岩石圈伸展过程中软流圈上涌致使中下地壳物质增温发生部分熔融形成的.“,”The Aobaohuturen porphyritic syenite granite,intruded into the Beishan Group and the Early Paleozoic granite,outcrops in northwest of Shibanjinin Beishan area,Inner Mongolia.Major elemental analyses of the granite show that Ti is characterized by high contents of SiO2 (70.41％ ～ 76.05％) and K2O (3.85％ ～ 5.22％),and it has high K2O/Na2O ratio (1.42 ～ 2.23),an A/CNK ratio of 0.97～ 1.10,and MgO# values of 14 to 32.REE study indicates that the granite is enriched in light rare earth elements((La/Yb)N =11.06 ～ 18.54) with high total rare earth elements (∑REE =179.21 × 10-6 ～ 332.23 × 10-6).Meanwhile,the Chondrite-normalized distribution curve is right inclined with significant negative Eu anomaly (δEu =0.25 ～ 0.75).The granitic rocks are enriched in high ion lithophile element (e.g.Rb、Th and K),but depleted in Nb,Ta,Sr,P and Ti.Zircon LA-ICP-MS U-Pb dating yield edanage of 398.15 ± 0.85 Ma,respectively,indicating that the Aobaohururen granite was formed during the Early Devonian.The values εHf(t) of porphyritic syenite granite ranges from 0.3 to 7.8 with the two-stage Hf model ages (tDM2) of 1 376 ～ 894 Ma.All these characteristics indicate that the porphyritic syenite granite was formed in an extensional tectonic setting during the Early Devonian,and sourced from partial melting of cal-alkaline granodioritic protholiths derived from melting of a young crust,and it then experienced strong differentiation.