Origin of high-Cr podiform chromitites from Kabaena Island, Southeast Sulawesi, Indonesia: constraints from mineralogy and geochemistry

ABSTRACT

The East Sulawesi Ophiolite, one of the three largest ophiolites in the world, contains important podiform chromitites. However, the origin of these chromite deposits is not well constrained. Here, we present the detailed mineralogy and in situ chemistry of chromite and solid inclusions within chromite for podiform chromitites from the Kabaena Island, Southeast Sulawesi. Chromite grains have low TiO₂ (0.17–0.27 wt%) and Al₂O₃ (13.4–15.1 wt%) contents and high Cr# [Cr/(Cr+Al), molar] of 0.70–0.74 and Mg# [Mg/(Mg+Fe²⁺), molar] of 0.69–0.75, which resemble those of other high-Cr podiform chromitites worldwide. The MORB-normalized patterns for some selected major-trace elements of chromite show slightly positive slopes from Al₂O₃ to Mn. Chromite-hosted silicate inclusions include olivine, clinopyroxene, orthopyroxene and amphibole and are characterized by higher Mg/Fe ratios than those of host peridotites. The geothermobarometry of chromite-hosted clinopyroxene-orthopyroxene pairs indicates that the estimated T-P conditions of the parental magma of the Kabaena chromitites are 950–1010°C and 7.0–8.4 Kbar. The extreme-Mg-rich olivine inclusions (Fo >96) with extremely high Ni (5300–8200 ppm) and Cr (1500–6700 ppm) contents are interpreted to have crystallized from high-Mg and Cr boninitic melts, and the Fo contents were then elevated by subsolidus re-equilibration (Fe–Mg and Fe–Ni exchange) with chromite. Sulfide inclusions contain base metal minerals containing millerite with rare pentlandite and chalcopyrite, and platinum-group minerals that include the laurite-erlichmanite series, Ir–Ni monosulfide, irarsite and cuproiridsite. This sulfide assemblage reveals that their parental magmas experienced the evolution of high T and low f(S₂) to low T and high f(S₂) from the early to late stage. Finally, combined with the palaeogeographic reconstruction in Sulawesi, we propose that the high-Cr chromitites in this region were formed by the reaction of depleted mantle and boninitic magma beneath a juvenile island arc, implying the initiation of a new subduction in the Miocene.

KEYWORDS:

• Chromite
• Silicate inclusions
• PGM
• High-Cr chromitites
• Sulawesi

Acknowledgments

We are grateful to Editor Robert J. Stern for efficient editorial handling and constructive comments, and two anonymous reviewers for their insightful suggestions and comments that have greatly improved the manuscript. We thank Xiang Li and Wenqin Zheng for EMPA mineral major oxide analyses and Zhihui Dai for LA-ICP-MS mineral trace element analyses

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2167130.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was financially supported by the Research Fund for the Doctoral Program of Tongren University (No. trxyDH2016), the Natural Science Foundation of China (NSFC Nos. 42206051, U1603245 and 41703051), the Natural Science Foundation of Shandong Province (No. ZR2020MD070), the Chinese Academy of Sciences ―Light of West China‖ Program, and the Natural Science Foundation of Guizhou Province (No. [2018] 1171).