塔里木西南缘棋盘河乡玄武岩锆石U-Pb年代学和地球化学研究

通过对塔西南棋盘河乡尤勒巴斯地区玄武岩进行了LA-ICP-MS 锆石 U-Pb同位素研究。获得锆石²⁰⁶ Pb/²³⁸ U同位素年龄为298.3±2.8 Ma(MSWD=2.6), 代表玄武岩的结晶年龄。本次研究的玄武岩具有高的Ti、Nb: Ti/Y为513.86~577.35、Nb含量为28×10^-6~35.7×10^-6、La/Nb为5.06~6.25以及低的Zr/Nb比值(10~10.86), 表明该玄武岩的形成与富集岩石圈地幔有关。而相对低的Nb/U(近30)和Ce/Pb(近15)比值, 指示研究区玄武岩来自大陆岩石圈或受一定程度的地壳混染。尤勒巴斯地区玄武岩具有高TiO₂和P₂O₅, 富集轻稀土和Rb、Ba, 指示具有地幔柱的地球化学成分特征。基于塔里木地区大规模的火山岩喷发以及富集不相容元素的地球化学特征和岩相古地理特征支持, 塔西南玄武岩可能是由地幔柱火山作用, 或由于地幔柱的供热和上升导致富集的岩石圈地幔部分熔融而形成。

Zircon U-Pb dating and geochemical of basalts in Qipan Country of Northwest Tarim Basin

The age of basalts in the Youlebasi of Qipan Country in the Southwest of Tarim Basin by zircon LA-ICP-MS U-Pb dating is 298.3±2.8 Ma(MSWD=2.6), which represents the crystallization age of the volcanic rocks erupted in Early Permian. The basalts have the characteristics of high Ti(Ti/Y=513.86~577.35), high Nb(28×10^-6~35.7×10^-6) and low Zr/Nb ratios(10~10.86), which indicates that the basalts were derivate from enrich mantle sources. While the slightly low Nb/U(~30)and Ce/Pb(~15)indicated that the basalts derivate from the continental lithosphere or subjected to some degree of crustal contamination. The Youlebasi basalts have higher TiO₂ and P₂O₅ contents, enrich LREE, Rb and Ba, which indicates that basalts have geochemical characteristic of mantle plume. Based on large-scale volcanic eruption Tarim area and the characteristics of enrichment incompatible elements and facies paleogeography, the basalts in the Southwest of Tarim may be caused by volcanic of mantle plume or enrichment lithospheric mantle partial melting caused by rise and heat of mantle plume.