新甘交界红柳河地区二叠纪玄武岩年代学、地球化学及构造意义

Geochronology,geochemistry and tectonic implications of Permian basalts in Hongliuhe area on the border between Xinjiang and Gansu.

新甘交界红柳河地区二叠系剖面中发育有块状和枕状玄武岩,激光ArAr定年确定的玄武岩形成时间在280～300Ma之间;玄武岩SiO_2含量为44.71%～49.27%,Mg~#为42.4～52.4,(^(87)Sr/^(86)Sr)_i为0.703834～0.706819,(^(143)Nd/^(144)Nd)_i为0.518861～0.5121220,ε_(Nd)(t)为-3.01～3.67。玄武岩微量元素、稀土元素和Sr-Nd同位素均显示出与OIB性质相似的特征。其弱富集的不相容元素和轻稀土元素,显示出源区富集的特点。而Zr/Nb(14.63)和Th/U(2.83)则指示岩浆中可能有少量循环原始地幔和亏损地幔物质的加入。综合对比北山南部柳园地区二叠纪玄武岩源区特征,提出红柳河地区早二叠世OIB型玄武岩主要来源于北山地区晚古生代裂谷带下伏已被不同程度改造的富集地幔。

Laser Ar-Ar dating indicates that the Permian basalts in Hongliuhe area on the border between Xinjiang and Gansu Provinces were erupted at 280 - 300Ma. SiO2 =44.71% - 49.27 % ,Mg^＊ = 42.4 -52.4, （^87Sr/^86Sr）l =0. 703834 -0. 706819, （^143 Nd/^144 Nd） i = 0.518861 - 0.5121220, εNd （t） = - 3.01 ～ ＋ 3.67. The trace element, REE and Sr-Nd isotope of Permian Basalts in Hongliuhe area show the similar style to OIB. It is characterized by lightly enrichment in light rare earth elements and incompatible elements, which indicate an enriched mantle source. And the ratios of Zr/Nb （ 14.63 ） and Th/U （2.83） show that some recycled primitive and depleted mantle material might be interfused into the enriched source. Analyzing integrally with the Liuyuan basahs, we point out that the Lower Permian basalts in Hongliuhe area are similar to OIB from the modified enriched mantle which were derived from the rift zone during Late Paleozoic.