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Petrology and PGE Abundances of High-Cr and High-Al Podiform Chromitites and Peridotites from the Bulqiza Ultramafic Massif, Eastern Mirdita Ophiolite, Albania
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This study was financially supported by the National Natural Science Foundation of China (grants No. 41541017, 41641015, 41720104009), the China Geological Survey (grants No. DD20160023-01, 201511022), and the Research funding from the Chinese Academy of Geological Sciences (grant No. YYWF201702).

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    Abstract:

    The Bulqiza ultramafic massif, which is part of the eastern Mirdita ophiolite of northern Albania, is world renowned for its high-Cr chromitite deposits. High-Cr chromitites hosted in the mantle section are the crystallized products of boninitic melts in a supra-subduction zone (SSZ). However, economically important high-Al chromitites are also present in massive dunite of the mantle-crust transition zone (MTZ). Chromian-spinel in the high-Al chromitites and dunites of the MTZ have much lower Cr# values (100Cr/(Cr+Al)) (47.7–55.1 and 46.5–51.7, respectively) than those in the high-Cr chromitites (78.2–80.4), harzburgites (72.6–77.9) and mantle dunites (79.4–84.3). The chemical differences in these two types of chromitites are reflected in the behaviors of their platinum-group elements (PGE). The high-Cr chromitites are rich in IPGE relative to PPGE with 0.10–0.45 PPGE/IPGE ratios, whereas the high-Al chromitites have relatively higher PPGE/IPGE ratios between 1.20 and 7.80. The calculated melts in equilibrium with the high-Cr chromitites are boninitic-like, and those associated with the high-Al chromitites are MORB-like but with hydrous, oxidized and TiO2-poor features. We propose that the coexistence of both types of chromitites in the Bulqiza ultramafic massif may indicates a change in magma composition from MORB-like to boninitic-like in a proto-forearc setting during subduction initiation.

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QIU Tian, YANG Jingsui, MILUSHI Ibrahim, WU Weiwei, MEKSHIQI Nezir, XIONG Fahui, ZHANG Cong, SHEN Tingting.2018. Petrology and PGE Abundances of High-Cr and High-Al Podiform Chromitites and Peridotites from the Bulqiza Ultramafic Massif, Eastern Mirdita Ophiolite, Albania[J]. Acta Geologica Sinica(),92(3):1063-1081

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History
  • Received:May 18,2020
  • Revised:April 08,2018
  • Online: June 19,2018
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