Khondalite series - geochronology and geochemistry of the Jiehekou Group in Luliang area

The Jiehekou Group is distributed in Luliang area, Shanxi Province, and com posed mainly of meta-argillo-arenaceous rocks, marbles and small amounts of amphibolite. They underwent amphibolite-facies metamorphism. The meta-argi llo-arenaceous rocks show large Variations in major element compositions, b ut have similar REE patterns and trace element compositions, with TREE = 15 1. 9 similar to 322. 3 mu g/g, Eu/Eu* = 0. 24 similar to 0. 58, (La/Yb)(a) = 8. 91 similar to 12. 23, Ba/Ba* = 0. 18 similar to 0. 71. The rocks have Nd isotopic model age t(DM) varying among 2. 50 and 2. 77 Ga. Metamorphosed detrital zircons from them yield two discordia with upper intercepts of 2. 80+/-0. 11 Ga and 2. 03+/-0. 05 Ga, respectively. Some main conclusions ar e as follows: (1) The Jiehekou Group, being of khondalite series properties , was likely formed in a tectonic environment of the passive continental ma rgin of the North China Craton; (2) The Jiehekou Group was formed in the Ea rly Proterozoic, rather than in the Neoarchaean or Mesoarchaean; (3) The so urce region, from which the argillo-arenaceous rocks of the Jiehekou Group were derived, was composed dominantly of Al and K-rich granitic or/and sedi mentary rocks of Neoarchaean.