Nd isotopic characteristics of post-Archean sediments from the Eastern Nanling Range: Evidence for crustal evolution

摘要

A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (t_(DM)) and ε_(Nd)(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the ε_(Nd)(t) value at Neoproterozoic (ca. 0.8—0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of t_(DM) vs. t_(Str). (stratum age) and ε_(Nd)(t) vs. t_(Str.). The decrease in t_(DM) and the increase in ε_(Nd)(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.