Mafic and ultramafic mantle and deep crustal xenoliths from Banks Peninsula, South Island, New Zealand

Abstract

Mafic and ultramafic xenoliths of spinel lherzolite, wehrlite, websterite, pyroxenite, and metagabbro (mafic granulite) occur in a basanite plug forming Le Bons Bay Peak on the eastern flanks of Akaroa volcano, Banks Peninsula. Spinel lherzolites are assigned to the Cr-diopside xenolith suite and are interpreted to represent fragments of depleted upper mantle derived from a depth of c. 60 km. Pyroxenites belong to the wehrlite series Al-augite xenolith suite and may represent basaltic cumulates derived from differentiation of mafic magma intruded at or near the crust/ mantle boundary. Mafic granulite of gabbroic composition represents a tectonised and partly recrystallised lower crustal basaltic cumulate. Mineral and bulk rock chemistry of the xenoliths suggests that chemical and mineralogical variation in Banks Peninsula magmas could reflect the development of a subcrustal basaltic "underplate". This might explain the trend from extensively modified to relatively unmodified mantlederived magmas through time. The Le Bons Bay Peak xenolith suite may be explained in terms of rapidly rising basanite magma, with entrained spinel lherzolite xenoliths, which incorporated ultramafic cumulates and metagabbro while passing through the crust/mantle boundary region.

High‐ to ultrahigh‐temperature metamorphism in the lower crust: An example resulting from Hikurangi Plateau collision and slab rollback in New Zealand

“…However, garnet–orthopyroxene–spinel–sillimanite‐bearing granulite xenoliths occur in Late Cretaceous volcanic rocks at Mt. Somers (Barley, ; Figure inset), and clinopyroxene–orthopyroxene granulite xenoliths occur in Miocene volcanic rocks on Banks Peninsula (Sewell et al., ; Figure inset). There is insufficient published modal and chemical data to accurately calculate the equilibration pressures of these other xenoliths but their occurrences point to granulite likely being widespread in the lower crust of the South Island.…”

“…Granulite xenoliths have been found in volcanic rocks erupted through the Eastern Province in the North Island (Graham, 1987;Gruender, Stewart, & Foley, 2010) and South Island (Barley, 1987;Dickey, 1968a;Reay & Sipiera, 1987;Sewell, Hobden, & Weaver, 1993). In situ granulite facies rock occurs in the exhumed lower crust of the Cretaceous arc preserved in Fiordland within the Western Province (Figure 1 inset).…”

Metasomatized ancient lithospheric mantle beneath the young Zealandia microcontinent and its role in HIMU-like intraplate magmatism

“…Previous investigation of Zealandia peridotitic xenoliths has been at reconnaissance level at best. Brief petrographic descriptions and/or mineral chemistries have been reported by Brown [1954], Wright [1967], Wallace [1975], Price and Wallace [1976], Reay and Sipiera [1987], Brodie and Cooper [1989], Tulloch and Nathan [1990], Sewell et al [1993], Hoke et al [2000], Duclos et al [2005], McCoy-West et al [2013], and Scott et al [2014]. He isotopes were reported for 10 samples [Hoke et al, 2000] and Duclos et al [2005] reported seismic anisotropy measurements on eight of those specimens.…”

“…Brief petrographic descriptions and/or mineral chemistries have been reported by Brown [], Wright [], Wallace [], Price and Wallace [], Reay and Sipiera [], Brodie and Cooper [], Tulloch and Nathan [] , Sewell et al . [], Hoke et al . [], Duclos et al .…”

The Interplay between Melting, Refertilization and Carbonatite Metasomatism in Off-Cratonic Lithospheric Mantle under Zealandia: an Integrated Major, Trace and Platinum Group Element Study

“…In the northern half of the island, isolated occurrences are found within the Cookson Volcanics in Marlborough (Reay, 1993) and sporadic dykes in Westland (Tulloch & Nathan, 1990). Further south, mantle xenoliths are more common, having been entrained in a range of small-scale basaltic volcanic edifices, including the Akaoroa Volcano (Sewell et al, 1993;McCoy-West et al, 2013), Deborah Volcanics (Reay et al, 2002), Waipiata Volcanics (Wright, 1966;Price & Green, 1972;Rae, 1990;Reay et al, 1991;Scott et al, 2014a), and Dunedin Volcano (Hoke et al, 2000;Price et al, 2003). Additionally, mantle xenoliths are also observed within the Alpine Dyke Swarm (Wallace, 1975;Cooper et al, 1987;Scott et al, 2014b).…”