The Petrogenesis of late Archaean anorthositic chromitites: New insights from Fiskenæsset, Greenland and Sittampundi, India

We present the trace element data for chromites from the anorthositic chromitites at Fiskenæsset, Greenland and Sittampundi, India, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), along with new major element analyses. Anorthositic chromitites are a rare petrological association consisting of highly calcic plagioclase (>An90), calcic-amphibole, and iron-rich chromite, primarily restricted to the late Archaean (2900–2500 Ma). Unlike chromitites in komatiitic, oceanic, and layered intrusion settings, their formation remains poorly understood. Our study demonstrates that the Fiskenæsset and Sittampundi chromites have strikingly similar minor and trace element chemistry: although the Fiskenæsset chromites contain higher Mn, V and Ga and lower Ti, Ni, Zn, and Co than the Sittampundi chromites. UG2 Bushveld chromite normalized multi-element plot indicates that these chromites are depleted in Ti and Sc, consistent with crystallization from a melt undergoing amphibole fractionation. Cr#-Fe# variations further suggest that chromite composition was controlled by amphibole fractionation, reinforcing the role of magmatic amphibole in the genesis of anorthositic chromitites. We propose that the presence of water in the parent magma was critical for chromite crystallization, and as amphibole crystallized, reducing the water content of the melt, Cr solubility decreased, triggering chromite precipitation.