Detrital zircon U-Pb geochronology and Hf isotopes of the Liaohe Group, Jiao-Liao-Ji Belt: Implications for the Paleoproterozoic tectonic evolution

The Jiao-Liao-Ji Belt (JLJB) is one of the most important Paleoproterozoic orogenic belts, which is intervening between the Longgang and Nangrim-Liaonan blocks. The Liaohe Group is an important research subject for understanding the Paleoproterozoic tectonic setting and evolution of the JLJB. However, the relationship of depositional spatial and chronological distributions between the North and South Liaohe groups are still under debates. In this paper, we present geochronological and zircon Lu-Hf isotopic results of meta-sedimentary rocks from the Liaohe Group to decipher their provenance depositional ages and environment, as well as their tectonic significance on the JLJB. The detrital zircons from the corresponding formations, including the Li'eryu, Gaojiayu and Dashiqiao formations of the North and South Liaohe groups, show similarities in age patterns and Hf isotopic compositions. The detrital zircons from the Li'eryu Formation of the two groups display unimodal Pb-207/Pb-206 age peaks at ca. 2.2-2.1 Ga. On the other hand, detrital zircons from the Gaojiayu and Dashiqiao formations of the two groups, yield two dominating age peaks at ca. 2.2-2.1 and similar to 2.5 Ga. In summary, all detrital zircons with age peaks at ca. 2.2-2.1 Ga, have epsilon(Hf)(t) value of -6.99 to +9.41 and two-stage Hf depleted mantle ages (T-DM2 model ages) of 3143 to 2137 Ma. The similar to 2.5 Ga detrital zircons however, have epsilon(Hf)(t) value and T-DM2 model ages which widely range from -9.37 to +10.13 and from 349 to 2367 Ma, respectively. Geochronological results indicate that ca. 2.2-2.1 Ga zircons were derived from the Liaoji granitoids. The adjacent basement rocks of the Longgang and Liaonan-Nangrim blocks provide the major sources to detrital zircons that yield an age peak at similar to 2.5 Ga. Combined with previous studies, the new geochronological data suggest that the protoliths of the corresponding formations of the North and South Liaohe groups deposited their detritus progressively in a back-arc basin. The Liaoji granitoids are the main sources providing detritus for the Li'eryu Formation. Subsequently, elastic sediments transported from the Longgang and Liaonan blocks, as well as from the Liaoji granitoids, were successively deposited and provided sources to the Gaojiayu and Dashiqiao formations.