内蒙古固阳地区新太古代变质侵入岩地球化学特征及意义

Geochemistry Characteristics and Significance of Metamorphic Intrusions in Guyang Region,Inner Mongolia

内蒙古固阳地区新太古代变质侵入岩具明显TTG岩系特征，符合钙碱性系列岩石的演化趋势，且具有由早期富钙向晚期富钠演化的趋势．其SiO2含量介于49．99％～76．08％（绝大多数为51％～67％之间），全碱含量高（NazO＋KzO〉7％），富钠（Na20〉3％），Na20／K20〉1，铝含量高（A12（）3含量通常在13％～18％之间），Mg#值较高（Mg#变化范围为33～50，均值为45）．微量元素显示岩石较低的Rb／Sr比值（0．02％Rb／Sr％0．22，均值为0．08），具有明显的Nb、P和Ti负异常以及Sr正异常．稀土元素配分曲线为右倾型，岩石强烈富集LREE，亏损HREE，具弱Eu正异常．利用激光等离子体质谱（LA-ICP-MS）对其锆石进行了U-Pb定年，测得其年龄在2500-2520Ma之间，属新太古代晚期．另外，二长花岗岩的不一致线下交点年龄为410~576Ma，代表着引起Pb从矿物中丢失的热事件的时间，即可以作为“早古生代华北地台应祁连山褶皱带的闭合而向南增生”这一事件在该区的时间响应．

The Neoarchean intrusions in Guyang area, Inner Mongolia, with obvious characteristics of TTG rock series, are in line with the calc-alkaline series in the rock evolution, reflecting the trend of rock evolution from the early Ca-enriched one to later Na-enriched one. The SiOz content of these intrusive rocks is in the range of 49. 99--76.08 （mostly 51--67//0）, with a high alkali content （Na2 O＋ K2 O〉 7 if0 ）, enriched in Na （Na2 O〉 3 if0 ）, Na2 O/K2 O〉 1, high-alumina （A12 03 content usually between 13--18%）, high Mg value （Mg ranging from 33--50, average 45）. Trace elements show low Rb/Sr ratio （0. 02Rb/Sr-0. 22, average 0. 08）, with significant Nb, P and Ti negative anomalies and a positive Sr anomaly. REE distribution curves show that the rocks with a weak positive Eu anomaly are strongly LREE enriched, HREE loss, belonging to a right-inclined type. The laser ablation-inductively coupled plasma-mass spectrometry （LA-ICP-MS） was used for the zircon U-Pb dating of the intrusive rocks, and the isotope age is between 2 500 and 2 520 Ma, belonging to the Late Neoarchaean. Moreover, monzogranite in obtaining inconsistent U-Pb age settlement under the curve （410--576 Ma） represents the cause of the loss of Pb from the mineral-thermal event of the time, that can be used as the time limit of the incident in this area, what is the southward hyperplasia of North China platform in Early Paleozoic should be with the closure of Qilian fold belt.