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齐齐哈尔纳克玄武岩与哈拉布拉克玄武岩出露于南天山阔克萨勒岭区,两组玄武岩均属碱性玄武岩系列,样品富集大离子亲石元素和高场强元素,轻重稀土分馏明显,(La/Yb)N=5.4～7.0,Ce/Y=18.04～24.52,Eu/Eu*=0.96～1.13,无负Eu异常,总体特征与洋岛型玄武岩(OIB)的特点类似。Mg#与高场强元素Ni,Sr,Cr,V与Nb/La值无相关性,Ti*(1.02～1.7)与Nb*(1.77～2.14)表明以单斜辉石为主的分离结晶是岩浆演化的主要趋势,与岩相学观察一致。将Zr/Nb,La/Nb,Ba/Nb,Ba/Th等比值与OIB端元及主要化学库不相容元素比值进行对比,发现源区类似EMI和EMII。Zr/Nb=7.4～8.38,Ce/Yb=16.11～24.52,高(La/Yb)N和(Gd/Yb)N值表明岩浆是含石榴子石相橄榄岩与尖晶石相橄榄岩富集过渡地幔源区低部分熔融的产物。对玄武岩稀土元素运用分离结晶部分熔融过程(CL/CO=(1-F)(1/Do-1)/DO)反演计算,模拟结果表明齐齐哈尔纳克玄武岩经1.57%～3.27%部分熔融形成,地幔源区Gt∶Sp=5∶95;哈拉布拉克玄武岩经4.09%部分熔融形成,地幔源区Gt∶Sp=25∶75。模拟结果表明南天山洋深部地幔可能并不是均一的。结合玄武岩年代(晚泥盆系—石炭系)、南天山中部库勒湖蛇绿混杂带的硅质岩、黑英山阿尔腾卡什组硅质岩中大量中泥盆—早石炭世放射虫化石、与玄武岩共生的蛇绿岩富大离子亲石元素,亏损Nb、富集Ce和P等边缘海岛弧特点及出露弧后盆地中沉积碳酸盐岩,表明玄武岩产于弧后盆地,弧后洋盆在晚泥盆世消减并最终于早石炭世末期闭合。
Qiqiharnak basalt and Halabulak basalt are exposed in the southern Keshan Mountains. The two basalts are alkaline basalt series. The samples are enriched in large ion lithophile elements and high field strength elements, and the light and heavy rare earth fractions are obviously fractionated , (La / Yb) N = 5.4-7.0, Ce / Y = 18.04-24.52, and Eu / Eu * = 0.96-1.13 without negative Eu anomalies. The general characteristics are similar to those of OIB. There is no correlation between Mg # and the Ni, Sr, Cr, V and Nb / La values of the high field strength elements. Ti * (1.02-1.7) and Nb * (1.77-2.14) indicate that the separation crystallization of clinopyroxene is The main trend of magmatic evolution, consistent with the petrographic observation. Comparing the incompatible element ratios of Zr / Nb, La / Nb, Ba / Nb, Ba / Th, etc. with the OIB terminal and main chemical library, we found that the source region is similar to EMI and EMII. Zr / Nb = 7.4 ~ 8.38, Ce / Yb = 16.11 ~ 24.52. The values of (La / Yb) N and (Gd / Yb) N indicate that the magma is enriched with garnet-bearing peridotite and spinel peridotite Transitional mantle source area of the lower part of the molten product. The results show that the Qiqihar-Narn basalts are partially melted by 1.57% ~ 3.27% by the inversion of fractional crystallization process (CL / CO = (1-Do) / DO) , The mantle source Gt: Sp = 5:95; the Halabulak basalts were partially melted by 4.09%, and the mantle source Gt: Sp = 25:75. The simulation results show that the deep mantle in the southern Tianshan Mountains may not be uniform. In combination with the basaltic rocks (Late Devonian-Carboniferous), the chert of the Kühler ophiolite belt in the central part of the southern Tianshan Mountains, a large number of mid-Devonian-Early Carboniferous radiolarian Fossils, rich ion-lithophile elements of ophiolite coexist with basalts, depleted Nb, enriched marginal island arcs such as Ce and P, and the deposition of carbonate rocks in exposed back-arc basins indicate that basalts are produced in back-arc basins, arcs The ocean basin was subducted in the Late Devonian and eventually closed at the end of the Early Carboniferous.