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先前根据松潘带广泛分布的花岗岩类研究,已提出了松潘带印支期岩石圈拆沉作用模型,但这一模型的建立尚缺少该区火山岩类研究的支持,在松潘带印支期岩石圈拆沉作用过程中是否存在岩石圈地幔物质的部分熔融值得关注.对产于松潘带中部的阿坝和洼赛火山岩进行了LA-ICP-MS锆石U-Pb定年、地球化学和Sr-Nd-Hf同位素组成研究.结果表明,阿坝和洼赛火山岩属于钙碱性安山岩类,它们的岩浆结晶年龄分别为(210±3)和(205±1)Ma,与松潘带印支晚期花岗岩类的形成时代相一致,形成于松潘带碰撞后构造背景.阿坝和洼赛火山岩显示有明显差异的地球化学特征,前者高Al2O3,K2O和Rb,低Na2O,Ba和Sr,表明它们不存在统一的岩浆演化.在全岩Sr和Nd同位素组成上,阿坝火山岩ISr=0.7070～0.7076,εNd(t)=-5.3～-3.9;洼赛火山岩ISr=0.7075～0.7077,εNd(t)=-3.9～-3.6.锆石Lu-Hf同位素组成指示,阿坝火山岩εHf(t)=-3.7～0.3,洼赛火山岩εHf(t)=-2.7～5.5.分析表明,阿坝火山岩和洼赛火山岩化学组成代表了它们原始熔体的组成,在岩浆演化过程中地壳物质的同化混染作用不明显.阿坝火山岩的岩浆源以壳源物质为主,含有少量幔源物质,其岩浆源区可能位于壳幔边界,而洼赛火山岩的岩浆起源于岩石圈地幔的部分熔融,岩石圈地幔可能受到含角闪石流体的交代作用.阿坝和洼赛火山岩的岩石成因为松潘带印支期岩石圈发生拆沉作用提供了又一新的证据,表明松潘带印支期岩石圈拆沉作用导致残留岩石圈地幔部分的熔融作用.
Previously, based on the study of the granodiorites widely distributed in the Songpan belt, the model of Indosinian lithosphere delamination has been proposed in the Songpan belt. However, the establishment of this model lacks the support of volcanic research in the area. The partial melting of lithospheric mantle material deserved attention during the delamination process.The LA-ICP-MS zircon U-Pb dating, geochemistry and Sr-Nd- Hf isotopic composition.The results show that the Aba and Waaisai volcanic rocks belong to calc-alkaline andesite and their magmatic ages are (210 ± 3) and (205 ± 1) Ma, respectively, which are consistent with the formation of the late Songpan-Indosinian granitoids Era and Vaisai volcanic rocks show obvious differences in geochemical characteristics.The former are high in Al2O3, K2O and Rb, low in Na2O, Ba and Sr, indicating that they do not have uniform magmatic evolution In the whole rock Sr and Nd isotopic compositions, the ISAB values of Aba volcanic rocks range from 0.7070 to 0.7076 and εNd (t) = -5.3 to -3.9 respectively. ISR = 0.7075 ~ 0.7077 and εNd (t) = -3.9 ~ -3.6. The zircon Lu-Hf isotopic composition indicates that Aba volcanic rock εHf (t) = -3.7 ~ 0.3, εHf (t) = -2.7 ~ 5.5. The analysis shows that the chemical composition of the Aba volcano and the Waaisai volcanic rock represent the composition of their original melts and the assimilation and contamination of crustal materials during the magmatic evolution The magmatic source of Aba volcanic rocks is dominated by crustal materials and contains a small amount of mantle source materials, and the magma source area may be located at crust and mantle boundary. The magma of Waai volcanic rocks originated from the partial melting of lithospheric mantle and the lithospheric mantle may Which is interpreted by the amphibolite fluid.The rock genesis of Aba and Waai volcanic rocks provided another new evidence for the detachment of the Indosinian lithosphere in the Songpan belt, indicating that the Indosinian lithosphere delamination in the Songpan belt led to Remaining lithospheric mantle melting.