准噶尔盆地陆梁地区基底火山岩的岩石地球化学及其构造环境

Basement volcanic rocks in Luliang uplift in the central region of the Junggar basin are dominated by soda-rich basalts and rhyolites and shows a bimodal, intraplate suite. The basalts are characterised by the occurrence of olivine in phenocrysts and groundmass. Pyroxenes in samples are augite. Feldspars are acid plagioclases (An:30∼50). The whole-rock CIPW results show that most samples contain Ne(2.8%∼4.6%), Ol(19.3%∼10.1%), and Di(10.2%∼24.6%). The mineral- assemblage is Ne+Ol+Di+An. Basalts plotted in the alkalic area on the diagram are Si-Alkaline. Mg^# numbers are smaller than 65. The total REE ranges from 110.29∼158.06 μg/g, (La/Y)_N varies from 3.10-4.51. δEu varies from 0.93∼1.04. Trace elements of basalts are characterized by moderate enrichment in LILE ralative to LREE, moderate depletion in Nb, Ta relative to LREE and LILE, Ni and Gr are lower than that of reference value of primitive magma. These characteristics indicate that basalts in Luliang belong to alkali-olivine basalt. Basalt has higher positive initial ε_Nd(7.20∼8.38) and lower ⁸⁷Sr/⁸⁶Sr, while rhyolite has lower initial positive ε_Nd (5.64∼6.60) and higher ⁸⁷Sr/⁸⁶Sr. These differences are attributable to the absence or presence respectively of a significant crustal component, but basalt and rhyolite were derived from the same depleted mantle source. Rb-Sr isochron age and zircon crystal ages vary from 323Ma∼395Ma. The conclusions can be made that basalts were originated from a depleted mantle and then differentiated and contaminated by crust, and the basement volcanics were formed in the continental rifting environment which was related to limited extension during D-C. Therefore, the Luliang uplifting in basin can be explained to be a continental rift.