The Origin Of Paleoproterozoic Granites In The Eastern Liaoning And Southern Jinlin Provinces And The Crustal Evolution

Hornblende monzogranite and porphyritic granite are major Paleoproterozoic granitoids in the Eastern Liaoning and Southern Jilin Provinces. Their genesis and tectonic settings are still argued. Hornblende monzogranite is characterized by striae structure consisting of hornblende, magnetite and other dark minerals, and weak negative Eu anomalies (Eu/Eu=0.47~0.65). The tDM of hornblende monzogranite is from 2.40 Ga to 2.82Ga; the forming age is around 2.175Ga. Porphyritic granite is characterized by porphyritic structure, and negative Eu anomalies (Eu/Eu = 0.30-0.86). The tDM of the porphyritic granite is from 2. 42 Ga to2. 57Ga; its forming age is around 1. 875Ga. N (ton) ~t figure shows that there seemed to have two-stage underplated in the Paleoproterozoic, and their peak ages are 2.5-2.4Ga and around 2.1Ga, respectively. From the Pearce' s diagram and e Nd(t)-t figure, we concluded that the former underplating pluton as well as other crust components should have been heated and melt by the latter underplating so that the large-scale hornblende monzogranite (A-type granite) formed and invaded in the rift setting. The porphyritic granite invaded when the orogenesis turned into post-collision stage. This studyproposes that the Paleoproterozoic geologic evolution of the crust of the Jiao-Liao-Ji nay be divided into 4 phases: earlier underplating (2.5-2.4Ga), later underplating and sedimentation of the Liaohe group ( 2. 2~2. 0 Ga) , collision (about 1.93Ga) and post-collision (1.875~1.66 Ga) . Two magma underplatings and one orogeny played a major role in the crustal evolution of the Paleoproterozoic Jiao-Liao-Ji.