Origin and its constraint to tectonic evolution of Paleoproterozoic granitoids in the eastern Liaoning and Jilin province, North China

Abstract

Hornblende monzogranite and porphyritic granites are major Paleoproterozoic granitoids in the Eastern Liaoning and Southern Jilin Provinces. Their genesis and tectonic settings are still argued. This argument resulted in unclear knowledge to Paleoproterozoic tectonic evolution in this area. This paper describes mainly their geochemistry of these two granites. Hornblende monzogranite is characterized by striae structure composed of hornblende, magnetite and/or other dark minerals, and by weak negative Eu anomalies(Ea/Eu*=0. 47 - 0. 65). The tDM of hornblende monzogranite ranges from 2.40 Ga to 2.82 Ga. Its crystallization age is about 2.175 Ga. Porphyritic granite is characterized by porphyritic structure, and negative Eu anomalies (Eu/Eu*= 0.30 - 0.86). The tDM of the porphyritic granite ranges from 2.42 Ga to 2.57Ga. The crystallization age of porphyritic granite is about 1.875Ga. The N (tDM)-t relation shows that there are perhaps twice Paleoproterozoic underplatings. The peak tDM ages of these two underplatings are 2.5 - 2.4Ga and around 2.1 Ga, respectively. In Pearce' s diagram and εND (t)-t figure, we concluded that the former underplated pluton and other crust components are heated to melt by the latter one so that large-scale hornblende monzogranite (A-type granite) formed and intruded in the rift setting. However, porphyritic granite emplaced after the following orogenesis. Twice underplatings and one orogenesis are main evolutionary processes of the Paleoproterozoic Jiao-Liao-Ji orogen.