湖北省随州花山蛇绿混杂岩Sm-Nd、Rb-Sr同位素年代研究

A Study on Sm-Nd and Rb-Sr Isotopic Chronology of the Huashan Ophiolitic Melange in the Suizhou Area,Hubei Province

对湖北省随州地区组成花山蛇绿混杂岩的杨家棚MORB型火山岩、小阜岛弧型火山岩进行了Sm-Nd、Rb-Sr同位素分析。由杨家棚地区火山岩样品得出的全岩Sm-Nd等时线年龄为1736±37(2σ)Ma,I_(Nd)=0.510582±42(2σ),ε_(Nd)(t)=+3.7;由小阜火山岩样品得出的全岩Sm-Nd等时线年龄为1197±170(2σ) Ma,I_(Nd)=0.51125±18(2σ),ε_(Nd)(t)=+3.1;小阜火山岩样品全岩Rb-Sr等时线年龄为737±31(2σ)Ma,I_(sr)=0.7052±13(2σ)。这些结果表明花山洋盆的形成时间可能为中元古代,而非古生代;737Ma指示了其后期的变质年龄。

This paper reports the Sm-Nd and Rb-Sr isotopic chronology of the main melange blocks and the MORB volcanic rocks from the Yangjiapeng area and the IAT volcanic rocks from the Xiaofu area, which comprise the ophiolitic melange of Huashan. The whole-rock samples of the volcanic rocks from the Yangjiapeng area give a Sm-Nd isochron age of 1736±37(2σ)Ma, with INd = 0. 510582 + 42(2σ) ,εNd(t) = +3. 7; the whole-rock samples of the volcanic rocks from the Xiaofu area present a Sm-Nd isochron age of 1197±170(2σ)Ma,with INd = 0. 51125+18(2σ),εNd(t) = +3. 1 and a Rb-Sr isochron age of 737±31 (2σ)Ma,with ISr = 0. 7052± 13(2σ). The results indicate that the Huashan Ocean basin was formed in the Mesoproterozoic, not the Paleozoic, and that a strong metamorphism of volcanic rocks took place in the Neoproterozoic.