Diamond forms during low pressure serpentinisation of oceanic lithosphere
Metadata
Show full item recordEditorial
European Assoc Geochemistry
Date
2020-09-10Referencia bibliográfica
Pujol-Sola, N., Garcia-Casco, A., Proenza, J. A., Gonzalez-Jimenez, J. M., del Campo, A., Colas, V., ... & Roque-Rosell, J. (2020). Diamond forms during low pressure serpentinisation of oceanic lithosphere. GEOCHEMICAL PERSPECTIVES LETTERS, 15, 19-24. [doi: 10.7185/geochemlet.2029]
Sponsorship
European Union (EU); Spanish Projects CGL2015-65824 RTI2018-099157-A-I00 PID2019-105625RB-C21 A.RNM.186.UGR18; Spanish Government RYC-2015-17596; Mexican research program CONACYT-Ciencia Basica A1-S-14574; Mexican research program UNAM-PAPIIT IA-101419Abstract
Diamond is commonly regarded as an indicator of ultra-high pressure conditions in
Earth System Science. This canonical view is challenged by recent data and interpretations
that suggest metastable growth of diamond in low pressure environments.
One such environment is serpentinisation of oceanic lithosphere, which produces
highly reduced CH4-bearing fluids after olivine alteration by reaction with infiltrating
fluids. Here we report the first ever observed in situ diamond within olivine-hosted,
CH4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samples
from the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated in
voids below the polished mineral surface forming a typical serpentinisation array,
with methane, serpentine and magnetite, providing definitive evidence for its metastable
growth upon low temperature and low pressure alteration of oceanic lithosphere
and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage at
a reference P-T point appropriate for serpentinisation (350 °C and 100 MPa) is consistent with extreme reduction of the fluid
to logfO2 (MPa) = −45.3 (ΔlogfO2[Iron-Magnetite] = −6.5). These findings imply that the formation of metastable diamond at
low pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioning
a generalised ultra-high pressure origin for ophiolitic diamond.