NDLI: Mineralogical and geochemical investigation of layered chromitites from the Bracco–Gabbro complex, Ligurian ophiolite, Italy

Content Provider	Springer Nature Link
Author	Baumgartner, R. J. Zaccarini, F. Garuti, G. Thalhammer, O. A. R.
Copyright Year	2012
Abstract	The Bracco–Gabbro Complex (Internal Liguride ophiolite), that intruded subcontinental mantle peridotite, contains layers of chromitite that are associated with ultramafic differentiates. The chromitites and disseminated chromites in the ultramafics have Al contents similar to the Al-rich podiform chromitites [0.40 < Cr# = Cr/(Cr + Al) < 0.55]. TiO2 contents of the chromitites are unusually high and range up to 0.82 wt%. The calculated Al2O3 and TiO2 content of the parental melt suggest that the melt was a MORB type. Geothermobarometrical calculations on few preserved silicate inclusions revealed formation temperatures between 970 and 820 °C under a relatively high oxygen fugacity (ΔlogfO2 at +2.0–2.4). Chromitites were altered during the post-magmatic tectono-metamorphic uplift and the final exposure at the seafloor, as evidenced by the formation of ferrian chromite. The PGE contents of the chromitites and associated ultramafics are unusually low (PGEmax 83 ppb). The chondrite-normalized PGE spidergrams show positive PGE patterns and to some extent similarities with the typical trend of stratiform chromitites. No specific PGM have been found but low concentrations of PPGE (Rh, Pt, and Pd) have been detected in the sulphides that occur interstitially to or enclosed in chromite. Recently, it has been shown that the Internal Liguride gabbroic intrusions have formed by relatively low degrees of partial melting of the asthenospheric mantle. We conclude that the low degree of partial melting might be the main factor to control the unusual low PGE contents and the rather unique PGE distribution in the Bracco chromitites.
Starting Page	477
Ending Page	493
Page Count	17
File Format	PDF
ISSN	00107999
Journal	Contributions to Mineralogy and Petrology
Volume Number	165
Issue Number	3
e-ISSN	14320967
Language	English
Publisher	Springer-Verlag
Publisher Date	2012-10-10
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Ligurian ophiolite Bracco–Gabbro complex Layered chromitites Platinum-group elements Silicate inclusions Geothermobarometry Geology Mineral Resources Mineralogy
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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