大兴安岭北部斯木科地区晚侏罗世斑状正长花岗岩年代学、地球化学特征及其成因

对斯木科斑状花岗岩进行了锆石LA-ICP-MS U-Pb年代学及岩石地球化学特征研究。测年结果显示,该岩体年龄为(144±0.85)Ma,为晚侏罗世。岩石地球化学分析表明,斯木科斑状正长花岗岩为准铝质-过铝质岩石,属于高钾钙碱性系列;稀土元素丰度总量较高,轻稀土富集且轻重稀土分馏较明显[(La_N/Yb_N=3.15~6.63)],表现为"右倾型"的稀土配分模式,岩石具有轻度的负Eu异常(δEu=0.54~0.66);微量元素以相对富集Rb、K等大离子亲石元素,而相对亏损Nb、Ta、P、Ti等高场强元素为特征。斯木科斑状正长花岗岩具有高分异I型花岗岩的特征,来源于地壳中火山岩的部分熔融。对Nb-Y构造环境判别图解及构造环境讨论,结合其所具有的I型花岗岩的特征,斯木科斑状正长花岗岩应为伸展构造体制下的产物,形成于造山后伸展构造环境。

Chronology,geochemical characteristics and petrogenesis of Late Jurassic porphyritic syenogranite in Simuke area,northern Da Hinggan Mountains

LA-ICP-MS zircon U-Pb dating and geochemical data of Simuke porphyritic syenogranite have been studied.The results indicate that the diagenetic age of porphyritic syenogranite is (144±0.85)Ma,belonging to Late Jurassic.The geochemical study shows that the porphyritic syenogranite belongs to high-K calc-alkaline series and high aluminum rocks. The rare earth elements are characterized by rich light rare earth elements and significant fractionation of LREE and HREE[(La/Yb)N=3.15～6.63].The REE distribution patterns are right deviated, with weak negative europium anomalies(δEu=0.54～0.66). For trace elements, the porphyritic syenogranites are enriched in Rb and K,but depleted in Nb,Ta,P and Ti.The porphyritic granite in Simuke area is high differentiation I type granite,derived from partial melting of basic volcanic rocks in the crust.Based on Nb-Y tectonic environment discrimination diagram and tectonic environment,combined with the characteristic of I type granite,the porphyritic granite in Simuke area should be the product of extensional tectonic system and it is formed in post-orogenic extensional tectonic environment.