The Architecture of a Root Zone of a Large Magmatic Conduit System From High Resolution Magnetic, Gravity and Petrophysical Data: The Reinfjord Ultramafic Complex

• Published in: Journal of geophysical research. Solid earth 2024-04, Vol.129 (4), p.n/a
• Main Authors: Pastore, Z., Church, N. S., Fichler, C., Michels, A., ter Maat, G. W., Larsen, R. B., McEnroe, S. A.
• Format: Article
• Language: English
• Subjects: Cores; Depth; Dunite; Economics; faults; Gabbros; Geological history; Geomagnetic field; Gravity; gravity anomaly; Gravity data; History; Iapetus; Lava; Localization; Magma; magnetic anomaly; Mineralization; Platinum; remanent magnetization; Root zone; Sea level; Sediment samples; Sedimentary rocks; serpentinization; Sulphides; Tectonics; Three dimensional models; Ultramafic materials; Ultramafic rocks
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB027991

The Seiland Igneous Province (SIP) is a large province of mafic and ultramafic (UM) complexes interpreted to be relics of a giant plumbing system feeding the Ediacaran Central Iapetus Magmatic Province. The Reinfjord Ultramafic Complex (RUC) is one of the four major ultramafic complexes of the SIP. The RUC has a younger dunite core surrounded by wehrlite and lherzolite embedded in country rocks consisting of layered gabbros with sub‐horizontal layering and metamorphosed sedimentary rocks. Here, we develop a 3D subsurface model for the RUC using high‐resolution magnetic and gravity data and extensive petrophysical measurements from oriented surface samples and drill core samples. Our model indicates that the RUC narrows in depth, extending a minimum of 1.4 km below sea level, and plunges eastwards below the country rock. This model allows us to decipher the lithologic heterogeneities, and the depth and lateral extent of ultramafic rocks, which we interpret in the context of the geologic history of the area. The RUC is spatially separated from other UM complexes of the SIP and the result of this study indicates a smaller depth extent. Combining these findings with the previously reported distribution of the SIP rocks based on the regional gravity data, we propose that the uplift of the crustal block hosting the RUC is larger than for ultramafic complexes in the northwestern part of the SIP. Plain Language Summary Worldwide, mafic and ultramafic intrusions are considered potential hosts for economic Ni‐Cu and platinum group elements. Magma‐conduit systems are particularly interesting for such mineralization, because they provide an ideal environment for the formation of large economic sulfide occurrences such as the Norilsk Talnakh deposits. We investigate one of the ultramafic complexes of a large magmatic province considered to represent a deep root zone where transient melts passed en route to upper crustal levels. The RUC is an ideal magma‐conduit system for research of large igneous provinces. Here, we construct a subsurface model of the ultramafic complex using gravity and geomagnetic field data constrained by petrophysical data sets from rock samples. We identified the different mafic and ultramafic units, and the alteration of rocks linked to later tectonic events. The localization and the estimation of relative volumes of altered and unaltered mafic and ultramafic rocks provide information about the geodynamic history and the ore potential of these r