Provenance and metamorphic PT conditions of Cryogenian–Ediacaran metasediments from the Kid metamorphic complex, Sinai, NE Arabian–Nubian Shield: Insights from detrital zircon geochemistry and mineral chemistry

Abstract

The Malhaq and Um Zariq formations occupy the northern part of the Neoproterozoic Kid metamorphic complex of SE Sinai, NE Arabian–Nubian Shield. This study presents new mineral chemistry data and LA-ICP-MS analyses of the trace element concentrations on zircons separated from metapelites from these formations. The detrital zircons of Um Zariq Formation are more enriched in ΣREE, whereas Malhaq Formation zircons are markedly HREE-enriched with strongly fractionated HREE patterns. The quite differences in the overall slope and size of the Eu and Ce anomalies between REE patterns of the two zircon suites provide a robust indication of different sources. The Ti-in-zircon thermometer has revealed that the zircons separated from Malhaq Formation were crystallized within the 916–1018°C range, while those from Um Zariq Formation exhibit higher range of crystallization temperatures (1084–1154°C). The detrital zircons of Malhaq Formation were derived mainly from mafic source rocks (basalt and dolerite), whereas Um Zariq Formation zircons have varied and more evolved parent rocks. Most of the investigated zircons from both formations are concluded to be unaltered magmatic that were lately crystallized from a high LREE/HREE melt. All the studied detrital zircon grains show typical trace elements features of crustal-derived zircons. All of the Um Zariq Formation and most of Malhaq Formation detrital zircons are geochemically discriminated as continental zircons. Both formation metapelites record similar, overlapping peak metamorphic temperatures (537–602°C and 550–579°C, respectively), and pressures (3.83–4.93kbar and 3.69–4.07kbar, respectively). The geothermal gradient, at the peak metamorphic conditions, was quite high (37–41°C/km) corresponding to metamorphism at burial depth of 14–16km. The peak regional metamorphism of Um Zariq and Malhaq formations is concluded to be generated during extensional regime and thinning of the lithosphere in an island arc setting with heat flow from the underlying arc granitoids.