Revised three-dimensional geometry of the platiniferous Hekeia Gabbro, Longwood Range, Southland

Abstract

The Hekeia Gabbro in the Longwood Range of Southland is prospective for platinum group elementmineralisation. Recently acquired geological and isotopic data, combined with reinterpreted aeromagneticdata, provide new constraints on the three dimensional extent and internal structure of the gabbro. Directobservations of in situ subvertical igneous layering give confidence that most curvilinear aeromagneticpatterns are largely caused by macroscopic primary igneous layering. Steep magnetic gradients can be usedto reliably define the areal limits of the Hekeia Gabbro and show that it extends to depths >1 km. Nd isotoperatios distinguish Hekeia Gabbro from younger gabbros and confirm the presence of at least two surfaceoutcrops of Hekeia Gabbro a few km west of the main body. Hekeia Gabbro is interpreted to be part of a 5km thick Late Permian lopolith that was subsequently deformed and intruded by other Late Permian andTriassic plutons.

The Thermal Structure of Central Te Riu a Māui/Zealandia Continent as Determined From the Depth to Base of Magnetic Sources

“…For many decades, the SMAS and JMA have been the principal geophysical markers that define an oroclinal bend in the New Zealand basement and are offset c. 460 km along the Alpine Fault to the southern South Island (Sutherland, 1999; Wellman, 1973). Detailed aeromagnetic surveys and local‐scale modeling of different parts of the SMAS show it comprises a series of closely spaced steeply dipping magnetic bodies extending 12–20 km deep (e.g., Eccles et al., 2005; Mortimer et al., 2016).…”

“…These correspond to Permian‐Jurassic gabbroic and dioritic plutons of the Median Batholith, and basalt‐ and andesite‐rich lavas of the adjacent Permian Brook Street Terrane (Edbrooke et al., 2015). The plutonic and volcanic rocks carry modal magnetite and have a high magnetic susceptibility with corresponding contrast in TMI relative to adjacent units (Mortimer et al., 2016, and references therein). The eastern part of the SMAS is a more sharply defined, positive linear anomaly of c. 10 km wavelength, the Junction Magnetic Anomaly (JMA) (Hatherton, 1969) which is associated with serpentinized peridotites of the Dun Mountain Ophiolite Belt (DMOB).…”