相山火山-侵入杂岩Nd-Sr-Pb同位素地球化学特征

Nd-Sr-Pb isotope geochemistry of the volcanic-intrusive complex at Xiangshan, Jiangxi province.

对相山火山 -侵入杂岩 Nd、Sr、Pb同位素组成及基底变质岩 Pb同位素组成的研究表明 :相山两旋回火山岩及火山期后的次火山岩具有较低的 εNd(t)值 (- 7.4 6～ - 9.4 0 )、较高的 ISr值 (0 .70 80 1～ 0 .712 0 1)和较古老的 Nd模式年龄 (1.5 4～ 1.70 Ga) ,且相对富集放射成因铅 (2 0 6 Pb/2 0 4 Pb、2 0 7Pb/2 0 4 Pb、2 0 8Pb/2 0 4 Pb分别为 17.6 86～ 18.32 3、15 .5 2 3～ 15 .730、38.14 3～38.936 )。相山火山 -侵入杂岩与该区出露的基底变质沉积岩在 Nd、Pb同位素组成上既有明显的相似性 ,又有一定差别。因此 ,相山火山 -侵入杂岩的源区主要为地壳岩石 。

This paper presents study on Nd, Sr and Pb isotope geochemistry of the volcanic-intrusive complex at Xiangshan. The volcanic rocks of the two main eruption cycles (140 Ma) and the late subvolcanic rocks (135 Ma) have lower epsilon (Nd) (t) values (-9.40 similar to -7.46), higher initial Sr-87/Sr-86 ratios (0.70801 similar to0.71201) and older Nd model ages (1.54 similar to1.70 Ga). These rocks are also relatively riched in radiogenic Pb (Pb-206/Pb-204 = 17.686 similar to 18.323, Pb-207/Pb-204 = 15.523 similar to 15.730, Pb-208/Pb-204 = 38.143 similar to 38.936). There exist evident similarities and also minor differences in Nd and Pb isotope compositions between the complex and the basement meta-sedimentary rocks. The volcanic-intrusive complex may have been derived mainly from partial melting of crustal rocks resembling the basement meta-sedimentary rocks. However, minor mantle-derived materials may have also been involved in formation of these rocks.