The norite belt in the Mesoarchaean Maniitsoq structure, southern West Greenland: conduit-type Ni-Cu mineralisation in impact-triggered, mantle-derived intrusions?

Abstract

With the recent discovery of the giant, deeply eroded, 3 Ga Maniitsoq impact structure in southern West Greenland (Garde 2010), an enigmatic, c. 75 by 15 km large, curvilinear belt of undeformed norite intrusions with Ni-Cu mineralisation was re-interpreted as representing crustally contaminated melts derived from the mantle in the wake of the impact (Fig. 1; Garde et al. 2012). The norite belt (Nielsen 1976; Secher 1983) was discovered in the early 1960s by the mining and exploration company Kryolitselskabet Øresund A/S, and more than one hundred shallow exploration holes were drilled by the company in the period 1965–1971. The mineralisation has subsequently been investigated by Cominco Ltd., Falconbridge Ltd. and NunaMinerals A/S. In 2011, the re-interpretation of the norite belt, and recent availability of improved airborne geophysical exploration tools, prompted the Canadian company North American Nickel Inc. (NAN) to resume exploration.

Complete hydrothermal re‐equilibration of zircon in the Maniitsoq structure, West Greenland: A 3001 Ma minimum age of impact?

“…These intrusions were reinterpreted by Garde et al. (, ) as representing mantle melts with continental crustal contamination, triggered by the proposed impact. One of them yielded three poorly defined 207 Pb/ 206 Pb age groups at 3016 ± 23 Ma, 3006 ± 13 Ma, and 2976 ± 13 Ma (Garde et al.…”

“…These include a regional aeromagnetic anomaly; a thoroughly comminuted core (Finnefjeld domain) measuring 35 by 50 km; extensive in situ lower crustal crush zones with segregation of K‐feldspar melt veins; a surrounding, approximately 20 km wide melt zone with direct melting of feldspar; the above‐mentioned belt of noritic intrusions, which are interpreted as representing crustally contaminated mantle melts (Garde ; Garde et al. ); and superimposed, very intense, high‐temperature hydrothermal alteration in large parts of the structure.…”

“…Garde et al. (, ) studied the field relationships between some of the intrusions in the “norite belt” and their host orthogneisses, and concluded that they postdate the intense crushing, but were locally affected by ductile shearing together with crushed rock volumes. The previously published age data cited above are in agreement with an intrusion age of approximately 3000 Ma with minor partial resetting and are thus compatible with the 3000.9 ± 1.9 Ma minimum age of the Maniitsoq event obtained here.…”

Geodynamic Implications of Synchronous Norite and TTG Formation in the 3 Ga Maniitsoq Norite Belt, West Greenland

“…Garde et al (2012) and (2013) suggested a genetic link to the "post-kinematic diorites" of the Fiskefjord region (Garde, 1991), which along with recently discovered norite outcrops to the north of the main norite belt (Ravenelle et al, 2017) imply norite magmatism occurred over length scales >100 km. Norite bodies range in size from kilometre-scale (e.g., the 8 km 2 Fossilik body; Ravenelle et al, 2017) to meter-scale pods (Garde et al, 2013). Unlike other mafic-ultramafic complexes further south in the Akia Terrane (Garde, 1997;Szilas et al, 2015), the norites are not closely associated with other ultramafic cumulates.…”

“…Despite significant interest in the ∼2.7-2.0 Ga noritic suite, there are few documented occurrences of "boninite-like" noritic rocks older than 2.7 Ga. In this regard, the exposed North Atlantic Craton in West Greenland may be unusual, with norites reported in the ∼3 Ga Maniitsoq Norite Belt and associated "diorite" of the Fiskefjord region (Garde, 1991;Garde et al, 2013;Ravenelle et al, 2017), the ∼3 Ga Amikoq Complex (Aarestrup et al in press), and ∼3.4 Ga noritic dykes in the Isua region (Nielsen et al, 2002). In this study, we present new field observations, petrography, geochemical and isotopic data, and phase equilibrium modelling for the ∼3 Ga Maniitsoq Norite Belt, with the aim of understanding its petrogenesis.…”