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对湖南桃江地区江石桥辉绿岩进行了LA-ICP-MS锆石U-Pb定年,获得的岩浆侵位年龄为229±2.3Ma(n=8,MSWD=1.8,2σ)。其低钾(K_2O/Na_2O=0.14~0.16),贫碱(K_2O+Na_2O=2.89%~2.96%),富集大离子亲石元素(Rb、Ba、Th、U),亏损高场强元素(Nb、Ta、Ti),呈轻稀土元素弱富集,无Eu、Ce异常,富集放射性成因Pb,低(~(87)Sr/~(86)Sr)_i(0.706052~0.706437),较低正ε_(Nd)(t)(1.54~1.86)的特征,表明岩石来源于下地壳物质和亏损地幔的混合源区。综合前人的研究结果认为,在印支运动造山后的伸展背景下,软流圈上涌导致区域下地壳及部分地幔物质发生熔融,形成辉绿岩岩浆并向上侵位而成。
LA-ICP-MS zircon U-Pb dating of the Jiangshiqiao diabase in the Taojiang area of Hunan Province was conducted. The age of emplacement was 229 ± 2.3Ma (n = 8, MSWD = 1.8,2σ). The low K (K2O / Na2O = 0.14-0.16) and the lean alkali (K2O + Na2O = 2.89% -2.96%) enriched in LIBs (Rb, Ba, Th and U) Nb, Ta and Ti), which are weakly enriched in light rare earth elements, are absent of Eu and Ce, enriched in radiogenic Pb and low (~ 87 Sr / 86 Sr) _i (0.706052 ~ 0.706437) The positive ε_ (Nd) (t) (1.54 ~ 1.86) features indicate that the rock is derived from the mixed source region of the lower crust and the depleted mantle. According to the results of previous studies, upwelling of the asthenosphere led to the melting of the lower crust and some mantle materials in the area under the extension of orogeny during the Indosinian movement, forming the diabase magma and invaded upwards.