Djerfisherite is a K-Cl-bearing sulfide that is present in both ultra-reduced extraterrestrial enstatite meteorites (enstatite chondrites or achondrites) and reduced terrestrial alkaline intrusions, kimberlites, ore deposits, and skarns. Major element chemistry of two terrestrial occurrences of djerfisherite (from the Ilímaussaq and Khibina alkaline igneous suites) and three extraterrestrial examples of djerfisherite have been determined and combined with petrographic characterization and element mapping to unravel three discrete modes of djerfisherite formation. High Fe/Cu is characteristic of extraterrestrial djerfisherite and low Fe/Cu is typical of terrestrial djerfisherite. Ilímaussaq djerfisherite, which has high-Fe contents (~55 wt%) is the exception. Low Ni contents are typical of terrestrial djerfisherite due to preferential incorporation of Fe and/or Cu over Ni, but Ni contents of up to 2.2 wt% are measured in extraterrestrial djerfisherite. Extensive interchange between K and Na is evident in extraterrestrial samples, though Na is limited (<0.15 wt%) in terrestrial djerfisherite. We propose three setting-dependent mechanisms of djerfisherite formation: primitive djerfisherite as a product of nebula condensation in the unequilibrated E chondrites; formation by extensive K-metasomatism in Khibina djerfisherite; and as a product of primary "unmixing" due to silicate-sulfide immiscibility for Ilímaussaq djerfisherite. There are several important reasons why a deeper understanding of the petrogenesis of this rare and unusual mineral is valuable: (1) its anomalously high K-contents make it a potential target for Ar-Ar geochronology to constrain the timing of metasomatic alteration; (2) typically high Cl-contents (~1.1 wt%) mean it can be used as a valuable tracer of fluid evolution during metasomatic alteration; and (3) it may be a potential source of K and magmatic Cl in the sub-continental lithospheric mantle (SCLM), which has implications for metal solubility and the generation of ore deposits.
Sheet intrusions represent important magma conduits and reservoirs in subvolcanic systems. Constraining the emplacement mechanisms of such intrusions is crucial to understanding the physiochemical evolution of magma, volcano deformation patterns, and the location of future eruption sites. However, magma plumbing systems of active volcanoes cannot be directly accessed and we therefore rely on the analysis of ancient systems to inform the interpretation of indirect geophysical and geochemical volcano monitoring techniques. Numerous studies have demonstrated that anisotropy of magnetic susceptibility (AMS) is a powerful tool for constraining magma flow patterns within such ancient solidified sheet intrusions. We conducted a high-resolution AMS study of seven inclined sheets exposed along the Ardnamurchan peninsula in northwest Scotland, and examined how magma flow in sheet intrusions may vary along and perpendicular to the magma flow axis. The sheets form part of the Ardnamurchan Central Complex, which represents the deeply eroded roots of an ∼58-m.y.-old volcano. Our results suggest that the inclined sheets were emplaced via either updip magma flow or along-strike lateral magma transport. It is important that observed variations in magnetic fabric orientation, particularly magnetic foliations, within individual intrusions suggest that some sheets were internally compartmentalized, i.e., different along-strike portions of the inclined sheets exhibit subtle differences in their magma flow dynamics. This may have implications for the flow regime and magma mixing within intrusions.
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