内蒙古察右后旗红格尔图花岗岩岩体位于索伦缝合带以南，主要为正长花岗岩和二长花岗岩，富硅（70.44%~78.80%），富碱（7.46%~10.74%），贫镁、铁、钛等，A/CNK值在0.95~1.41之间，碱铝指数AKI值在0.68~0.97之间，碱度率AR值在3.30~6.68之间，为弱过铝质-过铝质类碱性系列花岗岩；稀土元素总量变化范围大，轻稀土元素富集，重稀土元素亏损，Eu呈负异常（δEu=0.03~0.89）；富集高场强元素Th、U、Hf、Ta、Y等，亏损大离子亲石元素Sr、Ba、Eu等；高场强元素和值（（Zr+Nb+Ce+Y）＜350×10-6）明显偏低，该岩体属于高分异I型花岗岩，形成于后造山（后碰撞）伸展构造环境。LA-ICP-MS锆石同位素测年，获得锆石206Pb/238U年龄加权平均值分别为267.2±1.4Ma、269.2±1.6Ma和272.1±1.2Ma，表明该岩体形成于中二叠世，因此研究区内两大板块碰撞缝合的时间应该至少早于该岩体的形成时代，即应该至少早于267.2~272.1Ma。%Honggeertu granites, located in central Inner Mongolia and belonging to southern Solon-Linxi fault, is mainly composed of middle-fine to middle-coarse grained syenite granites and monzonitic granites. These granites have high SiO 2 (70.44%~78.80%) and are enriched in alkali (Na2O+K2O=7.46%~10.74%) but depleted in Mg, Fe and Ti. The A/CNK ratios are in the range of 0.95~1.41, alkali aluminum indexes (AKI) are 0.68~0.97, and alkalinities (AR) are 3.30~6.68, suggesting that the granites belong to weakly peraluminous-peraluminous alkaline series. The granite intrusion has widely varying total REE values (∑REE=25.96×10-6~654.50× 10-6), and is enriched in LREE and depleted in HREE with negative Eu anomaly (δEu=0.03~0.89). It is relatively enriched in high field strength elements (Th, U, Hf, Ta and Y) and depleted in large ion lithophile elements (Ba, Eu and Sr). The values of high field strength elements (Zr+Nb+Ce+Y) are higher than 350 × 10-6. The rocks belong to highly fractionated I-type granites formed in a post orogenic tectonic environment. Zircon LA-ICP-MS dating yielded 206Pb/238U weighted average ages, i.e., 267.2Ma ± 1.4Ma (MSWD=1.5), 269.2 ± 1.6Ma (MSWD=1.7) and 272.1 ± 1.2Ma (MSWD=0.38), indicating that the rock was formed in the Middle Permian. The new data suggest that the collision between NCC and Siberian Craton was earlier than the formation of the rock, and should be at least as early as 267.2~272.1Ma.
展开▼
