知识与财富的链接
新巴尔虎右旗塔木兰沟组火山岩主要由玄武岩、玄武安山岩和安山岩组成。TIMS锆石U-Pb定年结果显示,火山岩形成于约154 Ma的晚侏罗世。岩石主体属碱性系列,镁质量分数较低（w（MgO）为0.55%~3.36%）,镁值较小（Mg#为0.17~0.49）;稀土元素配分模式呈轻稀土富集右倾型,轻重稀土分馏明显（（La/Yb）N为9.51~17.21）,存在微弱的Eu异常（δEu为0.78~1.04）;微量元素以富集大离子亲石元素（如Rb、Ba、K）和轻稀土元素（LREE）、亏损高场强元素（如Nb、Ta、Ti）和相容元素（Cr、Co、Ni）为特征。综合研究表明,岩浆源区为俯冲板片流体交代过的岩石圈地幔,岩浆上升过程中未受到地壳物质的明显混染。结合区域地质构造演化特征,认为塔木兰沟组火山岩是蒙古-鄂霍茨克洋闭合造山后岩石圈伸展环境下的产物。
The volcanic rocks of Tamulangou Formation in New Barag Right Banner are mainly composed of basalt, basaltic andesite,and andesite. TIMS zircon U-Pb dating result shows that the volcanic rocks were formed in the Late Jurassic (ca. 154 Ma). The geochemical data show that the volcanic rocks belong to alkaline series, and have low contents of MgO (w(MgO)=0.55%-3.36%) and small amount of Mg# (0.17-0.49); the chondrite-normalized rare earth element (REE) patterns indicate that the volcanic rocks are enriched in light rare earth elements (LREE) with significant fractionation of HREE from LREE ((La/Yb)N=9.51-17.21) and insignificant Eu anomalies (δEu=0.78-1.04); the trace element geochemistry is characterized by enrichment of large ionic lithophile elements (e.g. Rb, Ba, K) and LREEs, depletion of high field strength elements (e.g., Nb, Ta, Ti),and compatible elements (Cr, Co, Ni). These characteristics suggest that the magma may be derived from partial melting of lithosphere mantle and metasomatized by subduction related fluids. Combined with the regional research results, we suggest that the volcanic rocks were formed under a lithospheric extension after the closure of the Mongol-Okhotsk Ocean.