关键词: 孔兹岩带, 大青山地区, 集宁—凉城地区, 石榴花岗岩, 地球化学, 华北克拉通

Abstract: Garnet granites and anatectic source rocks (pelitic gneiss) in Daqingshan and Jining-Liangcheng areas at the northern margin of the North China craton gradually transition and closely coexist in the field. The garnet granites contain many source rock enclaves, residual bodies and residual mineral phases/peritectic minerals. There are also a large number of garnet granite blocks in anatectic source rock. All these migmatites have heterogeneity macroscopically. Petrographic studies show that the mineral composition of garnet granites and the anatectic source rocks are similar and both contain garnet with similar characteristics. This can be considered a residual mineral/peritectic minerals facies type. Geochemical studies indicate that garnet granites are relatively well integrated with their anatectic source rocks, both have high Al2O3 values and TFeO/MgO ratio, with a large variation in CaO values and K2O/Na2O ratio. They are relatively enriched in light REE and large ion lithophile elements, and relatively depleted in Ta, Nb, Ti  and P. Deviating from the composition range of typical S-type granites in the world, garnet granites have lower SiO2(50.30%-73.10%) and greater MgO+TFeO(1.6%-14.8%). It is believed that this deviation from the normal S-type granite compositon is related to the introduction of residual garnet and the addition of mantle-derived materials. The garnet granites in the Daqingshan  and the Jining-Liangcheng areas were formed by two episodes of anatexis at the 2.45-2.37 Ga and 1.95-1.90 Ga respectively, consistent with the regional mantle-derived magma underplating in this area. This indicates that garnet granites are the products of large-scale partial melting of metasedimentary rocks caused by mantle-derived basic magma intruding into granulite facies metasedimentary rocks.

Key words: khondalite belt, Daqingshan area, Jining-Liangcheng area, garnet granites, geochemistry, North China craton