Abstract
Ferroan granitoid intrusions are rare in the Archaean rock record, but have played a large role in the evolution of the Proterozoic crust, particular in relation to anorthosite-mangerite-charnockite-granite suites. Here we discuss the petrogenesis of the ca. 2785–2805 Ma ferroan Ilivertalik Intrusive Complex, which has many geochemical similarities to Proterozoic iron rich granitoids. We present major and trace element whole rock chemistry and combined in-situ zircon U-Pb, Hf and O isotope data. The intrusive complex divides into: (i) minor tabular units of mainly diorite-tonalite compositions, which are typically situated along contacts to the host basement and (ii) interior larger, bodies of mainly granite-granodiorite composition. Geochemically these two unites display continuous to semi-continuous trends in Haker-diagrams. Whole rock REE enrichment display increases from Yb to La, from 10–25 to 80–100 times chondrite, respectively. The diorite-tonalite samples are generally more enriched in REE compared to the granite-granodiorite samples. The complex has hafnium isotope compositions from around +1.5 to −2.5 epsilon units and δ18O compositions in the range of 6.3 to 6.6‰. The complex is interpreted to be derived from partial melting in a crustal source region during anomalously high crustal temperatures.
Highlights
Igneous intrusive rocks from intra-cratonic settings make up a prominent part of the Paleoand Meso-proterozoic crust, e.g., [1,2]; these intrusive rocks are characterised by anorthosite massifs, mangerites, charnockites and ferroan granitoids, referred to as the anorthosite-mangerite-charnockitegranite (AMCG) suites, e.g., [1,2,3,4,5]
These rock types are, e.g., abundant in the major Mesoproterozoic belts running across North America through south Greenland to Scandinavia, that make-up one of the largest continental magmatic provinces on Earth, e.g., [1,5,6]
The charnockite and ferroan (A-type) granitoids represent high-temperature granites that are characteristic of intra-cratonic Proterozoic crust; no AMCG suites with Archean age are known which might suggest a temporal evolution of crustal magmatic systems on Earth [2]
Summary
Igneous intrusive rocks from intra-cratonic settings make up a prominent part of the Paleoand Meso-proterozoic crust, e.g., [1,2]; these intrusive rocks are characterised by anorthosite massifs, mangerites, charnockites and ferroan granitoids, referred to as the anorthosite-mangerite-charnockitegranite (AMCG) suites, e.g., [1,2,3,4,5] These rock types are, e.g., abundant in the major Mesoproterozoic belts running across North America through south Greenland to Scandinavia, that make-up one of the largest continental magmatic provinces on Earth, e.g., [1,5,6]. Complex, where it occurs as intrusive sheets and lenses up to 500 m wide within the felsic TTG basement [7,9]. Another recently described possibly ferroan granitoid is from the Acasta Gneiss
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