Geophysical Identification and Characterization of Mafic-Ultramafic Intrusions in Plume Centre Regions

Abstract

Gravity and magnetic data from the EGM2008 and EMAG2 datasets are used for a global study of geophysical anomalies in LIP plume centre regions with the goal of identifying maficultramafic intrusions linked to those LIPs. Geophysical anomalies within eighteen LIPs are investigated. Four of these LIPs are selected for detailed modelling: the Mackenzie, High-Arctic, Kunene-Kibaran, and Deccan LIPs.Modelling supports that these anomalies are produced by large (radius >30 km) and generally deep-seated crustal intrusions, with densities consistent with mafic-ultramafic rock and magnetic susceptibilities consistent with serpentinized ultramafic rock. Modelling also indicates that these values remain consistent within a LIP, particularly regarding density and depth. Lastly, we recognize three types of spatial distributions for intrusions in plume centre regions: 1) intrusions that circumscribe the plume centre emplaced along circular fault systems, 2) intrusions emplaced along rifts, in some cases rifts that converge towards the plume centre, and 3) single/unclassified intrusions.ii Acknowledgments I would like to thank my supervisors Dr. Richard Ernst and Dr. Claire Samson. Your knowledge, enthusiasm and generous support over the past two years has been unwavering and is sincerely appreciated. I would also like to thank Alan King, who provided the data used in the project and insight into developing the project.

Gravity and magnetic modelling of layered mafic–ultramafic intrusions in large igneous province plume centre regions: case studies from the 1.27 Ga Mackenzie, 1.38 Ga Kunene–Kibaran, 0.06 Ga Deccan, and 0.13–0.08 Ga High Arctic events

“…An excellent case is the shallow Muskox intrusion on the Canadian Arctic mainland that is a part of the Mackenzie LIP (section 3.1) and its link to one of the deep intrusions to the north identified from gravity data. The other large intrusions that circumscribe the plume centre may have also produced secondary chambers with similar economic potential as the Muskox (Blanchard 2016 We recognize three distinct spatial distribution types for regional-scale layered maficultramafic intrusions within LIP plume centre regions. These are: 1) Intrusions that circumscribe a plume centre (formed as a result of plume-induced uplift and subsequent subsidence), located at 150 -500 km from the plume centre and spaced at regular intervals around the plume centre.…”

“…It has been suggested that the gravity anomalies D1, D2 and D3 coincide with minor exposures of alkaline and acidic intrusions (Karanth and Sant 1995;Mishra et al 2001); however it's unclear whether these exposures are components of the main intrusive bodies, or if they are instead shallow intrusions sourced from deeper units. Both scenarios were considered (Blanchard 2016) and the preferred model is presented here.…”

“…A key question we address is whether layered intrusions are distributed in regular patterns within plume centre regions, and we attempt to characterize these geometries in this study. The overarching goal is to develop a better understanding of LIP plumbing systems and the setting of intrusions within these systems (Blanchard 2016).…”

Hot Rocks from Cold Places: A Field, Geochemical and Geochronological Study from the High Arctic Large Igneous Province (HALIP) at Axel Heiberg Island, Nunavut

“…U-Pb age determinations from this intrusion show that emplacement occurred at 92 Ma based on determinations from the gabbroic and microgranite phases Estrada and Henjes-Kunst, 2013). Lastly, on the basis of aeromagnetic and gravity anomalies in the vicinity of Kleybolte Peninsula, extreme northwestern Ellesmere Island, another mafic intrusion has been geophysically identified and interpreted as a part of the HALIP (Blanchard, 2016).…”