Early Cambrian oceanic island-arc magmatism at the paleo-Pacific margin of East Gondwana: Evidence from northern Victoria Land (Antarctica)

• Published in: Lithos
• Main Authors: Henjes-Kunst F., Tribuzio R., Gerdes A.
• Other Authors: Henjes-Kunst, F., Tribuzio, R., Gerdes, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: continental margin; boninite; metavolcanic rocks; mafic ultramafic sequence; Victoria Land; Pacific; Antarc*; Antarctica
• Online Access: http://hdl.handle.net/11571/1423974; https://doi.org/10.1016/j.lithos.2020.105925; https://www.sciencedirect.com/science/article/pii/S0024493720305600

We present new geochemical, isotopic and geochronological data for two Cambrian magmatic sequences exposed in northern Victoria Land (Antarctica) at the eastern margin of the Ross-orogenic Wilson Terrane: (i) the metavolcanic and metaplutonic rocks from the Dessent tectono-metamorphic complex, and (ii) the boninite-derived mafic-ultramafic Niagara Icefalls igneous complex. The Dessent metaigneous rocks are subdivided into three main types. Type I metavolcanites show LREE-depleted chondrite-normalized patterns and high initial ɛNd (mostly +6 to +7). Metavolcanic and metaplutonic type II rocks show low MREE-HREE concentrations and initial ɛNd ranging from +2 to +4. Type III metavolcanites mostly differ from type II rocks in the somewhat elevated MREE-HREE abundances. Type I, II and III rocks geochemically resemble forearc basalts, boninites s.l. and firstarc volcanites, respectively, from the Izu-Bonin-Mariana island arc system. Zircon separated from two metaplutonic rocks documents a crystallization age of ~516 Ma. The Niagara Icefalls rocks display a wide range of Nd–Sr isotopic compositions (e.g., initial ɛNd + 5 to −8). Zircons separated from a gabbronorite and from a granitoid vein allowed us to date the building of the Niagara Icefalls igneous complex at ~537 Ma. The melts forming the Niagara Icefalls igneous complex were most likely sourced in a supra-subduction zone mantle wedge, which included both depleted mantle and slab-derived sedimentary components. We propose that the mafic-ultramafic Niagara Icefalls igneous complex and the metaigneous rocks of the Dessent tectono-metamorphic complex are fossil analogues of two distinct oceanic island arcs, which formed in the earliest and the late early Cambrian, respectively.