Sm-Nd age and Sr, Nd isotopic characteristics of the Fanshan potassic alkaline ultramafite-syenite complex in Hebei province, China.
Sm-Nd age and Sr, Nd isotopic characteristics of the Fanshan potassic alkaline ultramafite-syenite complex in Hebei province, China.
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作者：
Mu Bao
河北矾山侵入杂岩是由层状钾质碱性超镁铁岩和碱性正长岩组成的，以产大型磁铁磷灰石矿床而闻名于世。然而，它们的形成时间仍然存在争议。大多数地质学家认为矾山杂岩的岩石和矿床形成于三叠纪250 ~ 200 Ma，也有人认为其形成于二叠纪。对矾山杂岩体进行了Sm-Nd测年，获得了其年龄。矾山杂岩体中4个矿物样品和2个全岩样品的Sm-Nd等时线年龄为243.4±9.7Ma，I-Nd =0.512045，e-Nd（t）=-5.4;矾山杂岩体中4个矿物样品和7个全岩样品的Sm-Nd等时线年龄为239± 19 Ma，I-Nd =0.512055。e Nd（t）=-5.3。这些年龄数据表明矾山杂岩的侵位开始于早三叠世。而矾山杂岩的Rb-Sr等时线年龄为218± 8 Ma，I-Sr = 0.70554，e-Sr =18.4，表明矾山杂岩可能在中三叠世完全固化。上述矾山杂岩的Sr、Nd同位素事实表明矾山杂岩是由富集的地幔物质形成的。
The intrusive complex in the Fanshan, Hebei province, China, consisting of layered patassic alkaline ultramafite and alkaline syenite, is know in the world for its containing large magnetite apatite deposits, and the rocks and deposits have been investigated and a lot of data have been accumulated over the past twenty years. However, their formation timing is still in dispute. Most geologists consider that the rocks and deposits in the Fanshan intrusive complex originated in Triassic Period between 250Ma and 200Ma, but some believe that they were formed in Permian Period. Sm Nd dating of the Fanshan intrusive complex has been performed, and its age have been obtained. The Sm Nd isochron age of four mineral samples and two whole rock samples from the Fanshan intrusive complex is 243.4±9.7Ma with I Nd =0.512045, e Nd ( t )=-5.4, and the Sm Nd isochron age of four mineral samples and seven whole rock samples from the Fanshan intrusive complex is 239±19Ma with I Nd =0.512055, e Nd ( t )=-5.3. These age data indicate that emplacement of the Fanshan complex started at early Triassic period. However, the Rb Sr isochron age in the Fanshan complex is 218±8Ma with I Sr =0.70554,e Sr =18.4, suggesting possibly that the Fanshan complex was solidified completely in the middle Triassic Period. The Sr, Nd isotope fact of the Fanshan complex above shows that the Fanshan complex was derived from enriched mantle materials.