华北克拉通北缘中段古元古代造山作用的岩浆记录:S型花岗岩地球化学特征及锆石SHRIMP年龄

Magma recording of Paleoproterozoic orogeny in central segment of northern margin of North China Craton:Geochemical characteristics and zircon SHRIMP dating of S-type granitoids

华北克拉通北缘中段沿集宁-凉城-千里山一带分布着大量S型花岗岩,主要为强过铝花岗岩,少量为偏(亚)铝质花岗岩。S型花岗岩岩石地球化学的特点是SiO2含量较低(大部分<74%),Al2O3/TiO2比值低(<100),CaO/Na2O比值高(>0.3),Rb/Sr和Rb/Ba比值较低,稀土元素和微量元素特征复杂,如Eu正异常、Eu负异常和Eu异常不明显均出现,具有中等程度的轻稀土元素富集。这种地球化学特征暗示该区S型花岗岩的源区成分为杂砂岩,形成于主动大陆边缘,且熔融温度较高,来源较深,相当于澳大利亚拉克伦造山带S型花岗岩,为高温型热造山带产物。通过对该区不同岩体锆石SHRIMP测定,该区S型花岗岩形成年代为1904～1921Ma,该时代代表华北克拉通北缘古元古代一次造山作用的时代。

There are many Paleoproterozoic S-type granitoid intrusions distributing along Jining-Liangcheng- Qianlishan in the central segment of northern margin of North China Craton, and they are mainly strongly peraluminous granitoids （SPGs）, and a few are metaluminous granitoids. Most of the S-type granitoid rocks have lower SiO2 contents （mainly less than 74% ）, lower Al2O3/TiO2 ratios （〈 100） and Rb/Sr ratios as well as Rb/ Ba ratios, but higher CaO/Na2O ratios （〉 0. 3）. The REEs and trace elements are very complex, for example, some samples are characterized by positive Eu anomalies, some by negative Eu anomalies and others by weak Eu anomalies, but all samples are moderate LREE enrichment. This kind of geochemistry characteristic suggests that the S-type granitoids were generated by melting of psammites （meta-graywackes） that aggraded in active plate margin like forearc basin, with hot and deep source, and it is like the S-type granitoids in Lachlan orogenic belts, Australia. After dating the strongly peraluminous granitoid intrusions distributing from the center to margin by zircon SHRIMP U-Pb technique, it is suggested that SPGs were formed at （1921 ± 16） Ma to （1904±10） Ma, and it represented one orogeny time in Paleoproterozoic in North China Craton.