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

Abstract

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 207Pb/206Pb 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 ~2.5 Ga. In summary, all detrital zircons with age peaks at ca. 2.2–2.1 Ga, have εHf(t) value of −6.99 to +9.41 and two-stage Hf depleted mantle ages (TDM2 model ages) of 3143 to 2137 Ma. The ~2.5 Ga detrital zircons however, have εHf(t) value and TDM2 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 ~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, clastic 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.