塔里木盆地古董山火山岩地球化学特征及可能的时代

Geochemistry and possible age of Gudongshan volcanic rocks,Tarim Basin

前人原将塔里木盆地中部古董山地区划为二叠纪的地层中夹有4层火山岩,但对该处火山岩至今没有详细的地球化学和同位素年代学研究。笔者经过详细的野外考察和室内的实验测试,揭示了古董山火山岩的野外特征、地球化学特征和K-Ar定年及锆石SHRIMP U–Pb定年数据,并对古董山火山岩可能的时代和形成时的构造环境进行了讨论。认为在塔里木盆地古董山地区白垩纪发生过多次岩浆活动事件,锆石SHRIMP U–Pb定年记录的最新岩浆活动是在晚白垩世,而且可能还有更新的岩浆活动,古董山火山岩的时代可能要重新考虑,或许应为白垩纪。地球化学特征显示古董山火山岩显著富集TiO2,并且FeO+Fe2O3、P2O5含量较高,Al2O3、MgO、CaO含量较低,主量、微量元素特征均反映出古董山火山岩为典型的板内玄武岩,形成于板内拉张环境。

There are 4 volcanic rock interlayers in the Permian strata of Gudongshan area,southern central Tarim Basin,but there exists no geochemical data and isotopic age constraint on the Gudongshan volcanic rock at present.Based on detailed field mapping and experiments,this paper reports field characteristics,geochemical characteristics,K-Ar dating results and zircon SHRIMP U–Pb dating results of Gudongshan volcanic rocks in the study area and also discusses the possible age and tectonic setting of Gudongshan volcanic rock.The preliminary results obtained by the authors indicate that igneous activities occurred repeatedly in Cretaceous.The youngest igneous activity age recorded by zircon SHRIMP U–Pb dating is Late Cretaceous（80.1 ± 4.3 Ma）.The authors hold that the age of Gudongshan volcanic rock should be reconsidered,and is probably Cretaceous.Geochemical data show that Gudongshan volcanic rocks are rich in TiO2,FeO＋Fe2O3 and P2O5,and poor in Al2O3,MgO and CaO.Both main elements and trace elements indicate that Gudongshan volcanic rocks are intraplate basalts（WPB） formed in an extensional intraplate setting.