河北矾山钾质碱性超镁铁岩-正长岩杂岩体Sm-Nd年龄和Sr、Nd同位素特征

Sm-Nd age and Sr, Nd isotopic characteristics of the Fanshan potassic alkaline ultramafite-syenite complex in Hebei province, China.

河北矾山侵入杂岩 ,由层状钾质超镁铁岩——正长岩组成 ,已知它含有大型磁铁矿磷灰石矿床。现在已测定了岩体的岩石和矿物的 Sm - Nd同位素资料 ,并获得了杂岩体的 Sm - Nd同位素年龄。 4个矿物样品和 2个全岩样品 Sm - Nd等时线年龄为 2 4 3.4± 9.7Ma,INd=0 .5 12 0 4 5 ,εNd(t) =- 5 .4 ;4个矿物样品和 7个全岩样品等时线年龄为 2 39± 19Ma,INd=0 .5 12 0 5 5 ,εNd(t) =- 5 .3。这些年龄资料表明 ,矾山岩体可能侵位于早三叠。而矾山岩体的 Rb- Sr等时线年龄为2 18± 8Ma,ISr=0 .70 5 5 4 ,εSr=18.4的事实可能暗示矾山岩体在中三叠才完全固结并达到 Rb- Sr体系封闭的温度。上述矾山岩体的 Sr、Nd同位素特征表明 。

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, epsilon (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, epsilon (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, epsilon (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.