Publication Date:
2021-05-12
Description:
The formation of diamonds within eclogitic rocks has been widely linked to the fate of carbon during subduction and,
therefore, referred to conditions of pressure, temperature, and oxygen fugacity (fo2). Mantle-derived eclogite xenoliths from
Udachnaya kimberlite pipes represent a unique window to investigate the formation of carbon-free, graphite–diamondbearing
and diamond-bearing rocks from the Siberian craton. With this aim, we exploited oxy-thermobarometers to retrieve
information on the P–T–fo2 at which mantle eclogites from the Siberian craton equilibrated along with elemental carbon.
The chemical analyses of coupled garnet and omphacitic clinopyroxene were integrated with data on their iron oxidation
state, determined both by conventional and synchrotron 57Fe Mössbauer spectroscopy. The calculated fo2s largely vary for
each suite of eclogite samples from 0.10 to − 2.43 log units (ΔFMQ) for C-free eclogites, from − 0.01 to − 2.91 (ΔFMQ)
for graphite–diamond-bearing eclogites, and from − 2.08 to − 3.58 log units (ΔFMQ) for diamond-bearing eclogites. All
eclogite samples mostly fall in the fo2 range typical of diamond coexisting with CO2-
rich water-bearing melts and gaseous
fluids, with diamondiferous eclogites being more reduced at fo2 conditions where circulating fluids can include some methane.
When uncertainties on the calculated fo2 are taken into account, all samples essentially fall within the stability field of
diamonds coexisting with CO2-
bearing melts. Therefore, our results provide evidence of the potential role of CO2-
bearing
melts as growth medium on the formation of coexisting diamond and graphite in mantle eclogites during subduction of the
oceanic crust.
Description:
Published
Description:
107
Description:
1T. Struttura della Terra
Description:
JCR Journal
Keywords:
redox, eclogite, diamond, magmas
;
04.01. Earth Interior
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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