大别山北缘中生代火山-侵入岩锶-钕同位素组成特征及其物质来源

Sr and Nd isotopic composition and material sources of Mesozoic volcano_intrusive rocks in the northern margin of Dabie Mountains

报道了大别山北缘中生代 (早白垩世 )不同成因系列火山 -侵入岩的 14个Rb -Sr、Sm -Nd同位素分析数据 ,其中正长岩类ISr值为 0 .70 84 3～ 0 .710 14 ,εNd值为 - 14 .7～ - 15 .8,亏损地幔两阶段模式年龄TDM为 2 .12～ 2 .2 0Ga ;高钾钙碱性系列岩石ISr值为 0 .70 75 0～ 0 .710 5 4,εNd值为 - 17.2～ - 19.1,TDM 为 2 .32～ 2 .4 8Ga ;橄榄安粗岩系列岩石ISr值为 0 .70 873～0 .70 912 ,εNd值为 - 2 0 .7～ - 2 1.7,TDM为 2 .6 0～ 2 .6 8Ga。通过与基底变质岩Sm -Nd同位素组成对比 ,认为高钾钙碱性系列主要由类似于大别群的地壳岩石衍生而成 ,正长岩类是由大别群和少量较年轻地壳岩石 (卢镇关群和佛子岭群 ?)衍生而成的 ,而橄榄安粗岩系列则来源于富集地幔并可能混入少量更古老的类似于泰山群的地壳组分。

Volcano_intrusive rocks in the Mesozoic volcanic belt along the northern margin of Dabie Mountains can be subdivided into three rock series, i.e., high_potassium calc_alkaline series (HKCA), alkaline series (A) and shoshonitic (SHO) series. 14 samples were measured for the Rb_Sr and Sm_Nd isotopic compositions, and the results show that the initial Sr ratios ( I Sr ) are 0.707?50～0.710?54, 0.708?43～0.710?14 and 0.708?73～0.709?12, the initial Nd ratios (εNd) are -17.2～-19.1, -14.7～-15.8 and -20.7～-21.7, and the two_stage depleted_mantle model ages ( T? DM ) are 2.32～2.48Ga, 2.12～2.20 Ga and 2.60～2.68 for HKCA, A and SHO, respectively. A comparison of Nd isotopic composition between these volcano_in_trusive rocks and the basement metamorphic rocks shows that the HKCA rocks were mainly derived from the Dabie Group_like crustal rocks, alkaline rocks were mainly derived from Dabie Group with small amounts of younger crustal rocks (Luzhenguan Group and Foziling Group ?), and the shoshonitic rocks were mainly derived from enriched mantles probably with incorporation of small amounts of even older Taishan Group_like crustal rocks.