TY - JOUR

T1 - Chromitites from the Vavdos ophiolite (Chalkidiki, Greece): Petrogenesis and geotectonic settings; constrains from spinel, olivine composition, PGE mineralogy and geochemistry

AU - Sideridis, Alkiviades

AU - Zaccarini, Federica

AU - Koutsoviti, Petros

AU - Grammatikopoulos, Tassos

AU - Tsikouras, Basilios

AU - Garuti, Giorgio

AU - Hatzipanagiotou, Kostantinos

N1 - Publisher Copyright: © 2021 Elsevier B.V.

PY - 2021/10

Y1 - 2021/10

N2 - Podiform chromitites of the Vavdos ophiolite are associated with dunite bodies hosted within residual mantle harzburgite. The mantle source is highly depleted and apparently developed at fore-arc settings as inferred from the presence of boninitic melts. The ascendance of these melts through dunite pathways and their subsequent interaction with the depleted harzburgite instigated chromitite mineralization within dunite. Spinel occurs in a) massive accumulations (Mg# = 0.56–0.68 and Cr# = 0.69–0.77), b) in non-massive disseminated textures (Mg# = 0.52–0.61 and Cr# = 0.80–0.81) and c) in schlieren chromitite deposits within dunite bodies (Mg# = 0.43–0.48 and Cr# = 0.79–0.82). Olivine is the main silicate inclusion in chromitites, whereas the absence of hydrous mineral phases is linked with crystallization at relatively deeper parts of the mantle. Olivine inclusions in spinel are enriched in Fo, Ni and Ca compared to the interstitial olivine grains. No compositional gaps were noted between the mineral analyses of chromitites and dunites; the calculated parental melts are also homogeneous, reinforcing the view for production of melt batches by similar processes. Platinum-group elements (PGE) concentrations and platinum-group minerals (PGM) demonstrate high (Os + Ir + Ru)/ (Rh + Pt + Pd) ratios, typical of many Tethyan ophiolitic chromitites. The main PGM phase is laurite that forms an extended solid solution series with substitution of Ru for Os + Ir, linked to the cooling of the system. Massive chromitites contain Ru-rich laurite and Os-Ir alloys whereas non-massive ores contain Ru-poor laurite. The PGM were included in fresh magnesiochromite favoring their magmatic origin and initial entrapment at ~ 1200 °C and low sulfur fugacity.

AB - Podiform chromitites of the Vavdos ophiolite are associated with dunite bodies hosted within residual mantle harzburgite. The mantle source is highly depleted and apparently developed at fore-arc settings as inferred from the presence of boninitic melts. The ascendance of these melts through dunite pathways and their subsequent interaction with the depleted harzburgite instigated chromitite mineralization within dunite. Spinel occurs in a) massive accumulations (Mg# = 0.56–0.68 and Cr# = 0.69–0.77), b) in non-massive disseminated textures (Mg# = 0.52–0.61 and Cr# = 0.80–0.81) and c) in schlieren chromitite deposits within dunite bodies (Mg# = 0.43–0.48 and Cr# = 0.79–0.82). Olivine is the main silicate inclusion in chromitites, whereas the absence of hydrous mineral phases is linked with crystallization at relatively deeper parts of the mantle. Olivine inclusions in spinel are enriched in Fo, Ni and Ca compared to the interstitial olivine grains. No compositional gaps were noted between the mineral analyses of chromitites and dunites; the calculated parental melts are also homogeneous, reinforcing the view for production of melt batches by similar processes. Platinum-group elements (PGE) concentrations and platinum-group minerals (PGM) demonstrate high (Os + Ir + Ru)/ (Rh + Pt + Pd) ratios, typical of many Tethyan ophiolitic chromitites. The main PGM phase is laurite that forms an extended solid solution series with substitution of Ru for Os + Ir, linked to the cooling of the system. Massive chromitites contain Ru-rich laurite and Os-Ir alloys whereas non-massive ores contain Ru-poor laurite. The PGM were included in fresh magnesiochromite favoring their magmatic origin and initial entrapment at ~ 1200 °C and low sulfur fugacity.

KW - Chromitites

KW - Greece

KW - Olivine

KW - Ophiolite

KW - Platinum-group elements

KW - Platinum-group minerals

UR - http://www.scopus.com/inward/record.url?scp=85107927910&partnerID=8YFLogxK

U2 - 10.1016/j.oregeorev.2021.104289

DO - 10.1016/j.oregeorev.2021.104289

M3 - Article

VL - 137

JO - Ore geology reviews

JF - Ore geology reviews

SN - 0169-1368

IS - October

M1 - 104289

ER -