Geochemical Characterization of Zircon in Fyfe Hills of the Napier Complex, East Antarctica

Mami Takehara,Kenji Horie,Tomokazu Hokada

doi:10.3390/min10110943

Abstract

Ultra-high temperature (UHT) metamorphism plays an essential role in the development and stabilization of continents through accretionary and collisional orogenesis. The Napier Complex, East Antarctica, preserves UHT metamorphism, and the timing is still debated. U–Pb zircon geochronology integrated with rare earth element (REE) and oxygen isotope was applied to a garnet-bearing quartzo-feldspathic gneiss to confirm the timing of UHT metamorphism in Fyfe Hills in the western part of the Napier Complex. The zircons are analyzed using a sensitive high-resolution ion microprobe (SHRIMP). The cathodoluminescence observation and U–Pb ages allowed us to classify the analytical domains into three types: inherited domains (Group I), metamorphic domains (Group II), and U–Pb system disturbed domains (Group III). The REE patterns of Group II are characterized by a weak fractionation between the middle REE and heavy REE, which reinforces the above classification. The 207Pb*/206Pb* ages of Group II have an age peak at 2501 Ma, therefore, the gneiss experienced high temperature metamorphism at 2501 Ma. δ18O of zircons are homogeneous among the three groups (5.53 ± 0.11‰, 5.51 ± 0.14‰, and 5.53 ± 0.23‰), which suggests re-equilibration of oxygen isotopes after metamorphism at ca. 2501Ma under dry UHT conditions.

Highlights

Ultra-high temperature (UHT) metamorphism is critical to understanding the large-scale tectonic processes affecting the deep crust and lithosphere throughout Earth history
We focus on the garnet-bearing quartzo-feldspathic gneiss, collected from Fyfe Hills metamorphism
We suggest a by combining the U–Pb age, acathodoluminescence images, rare earth elements (REE) compositions, and oxygen isotope ratio

Summary

Introduction

Ultra-high temperature (UHT) metamorphism is critical to understanding the large-scale tectonic processes affecting the deep crust and lithosphere throughout Earth history. The Napier Complex in East Antarctica is the location where the regional UHT metamorphism was first recognized [2] and experienced extremely high temperatures (>1100 ◦ C) based on the mineral assemblage of sapphirine + quartz ([3] and reference therein). 1).outcrops, Archean crustal have mountain been collected at several The. Complex consists of coastal islands,records and inland ranges in Enderby localities of the Napier Complex ([8] and references therein). The Napier Complex is composed of various orthogneisses, granitic gneisses, mafic granulites, and paragneisses These granulite-facies granulite-facies metamorphic rocks, suchby asmultiple tonalitic–trondhjemitic–granodioritic (TTG) orthogneisses, metamorphic rocks have been affected thermal events, including UHT metamorphism in granitic gneisses, mafic granulites, and paragneisses. The peak temperature of the UHT metamorphism is estimated to be rocks above have been 1100 affected by multiple thermal events, including

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