Discrepant age records of Permian thermal overprint in metapelite in the Neoproterozoic Kang-Dian Orogenic Belt (SW China)

Abstract

Metapelite within a ∼2.5 km-long transect from the southern Neoproterozoic Kang-Dian Orogenic Belt (SW China) was investigated. Metamorphic zircon and monazite of a plagioclase absent sample yielded Permian ages of 268±4.5 Ma and 265.4±1.5 Ma, respectively. Metamorphic zircon from the other three samples yielded Neoproterozoic ages of ca. 874-778 Ma but no Permian age, while monazite from one of them yielded both Neoproterozoic (811±8 Ma) and Permian (259.3±1.7 Ma) ages. The garnet growth / breakdown and plagioclase consumption / K-feldspar growth might account for the different Y and heavy rare earth element (HREE) content and negative Eu anomaly trend in monazite over time. The garnet was interpreted to be formed in the Neoproterozoic, while the preserved mineral assemblages represent the reworked products during Permian overprint. The synchronous magmatic activities might account for the Permian ages of monazite and zircon and the resorbed and diffused garnet zoning. These data indicate the Permian magmatic-thermal pulse affected the preexisted Neoproterozoic metamorphic rocks differentially. Such phenomenon is important and should be carefully considered in orogenic research.