Mg-Al yttrian zirconolite in a partially melted sapphirine granulite, Vestfold Hills, East Antarctica

Abstract

A new compositional variety of zirconolite characterized by high Mg, AI, Y203 and REE, and low Fe is described from a sapphirine granulite xenolith entrained in an intrusive norite body which was emplaced into the late Arcbaean (2520-2480 Ma) Vestfold Hills high-grade terrain during the early Proterozoic. The zirconolite, and similarly Mg-AI rich perrierite-(Ce), formed as a result of sanidinite facies partial melting of the particularly magnesian and aluminous sapphirine granulite xenolith during its incorporation into the c. 1170~ basic magma at c. 2240 Ma. The high REE compared to AI cations require that a previously unrecognized coupled substitution: REE.REE.(Mg,Fe).Ca_2.Ti_t occurs in this zirconolite. Full chemical analyses are presented for zirconolite and perrierite from this unique occurrence.

Perrierite in sapphirine-quartz gneiss: geochemical and geochronological features and implications for accessory-phase paragenesis of UHT metamorphism

“…Macdonald and Belkin (2002). Mg Al rich perrierite composition reported by Harley (1994) is also given in the figure. s.d., standard deviation. n.d., not determined.…”

“…Details of the analytical conditions, including U, Th, Pb, and REE analysis are given in Hokada and Motoyoshi (2006 (Harley, 1994). However, it is relatively rich in Al 2 O 3 and MgO, but depleted in CaO and FeO (Fig.…”

“…In previous studies, the host granulite facies rocks containing the perrierite were sapphirine bearing gneisses Manton, 1979a, 1986;Harley, 1994), charnockitic pegmatites Manton, 1979a, 1979b), or quartzo feldspathic gneiss (DePaolo et al, 1982). Perrierite includes a low U and Th content, and has been used for U -Pb geochronology (Grew and Manton, 1979a, 1979b, 1986DePaolo et al, 1982).…”

“…Among these, perrierite mineral chemistry and its petrographical features have been reported only by Harley (1994). This paper presents the petrography and mineralogy of Mg -Al rich perrierite found in a sapphirine -orthopyroxene -osumilite -quartz bearing ultrahigh temperature (UHT) pelitic gneiss from Mt.…”

“…The occurrence of perrierite in granulite terranes has been studied by a few authors (Grew and Manton, 1979a, 1979b, 1986DePaolo et al, 1982;Harley, 1994), some of whom have attempted U -Pb isotopic dating of perrierite. Among these, perrierite mineral chemistry and its petrographical features have been reported only by Harley (1994).…”