TY - JOUR

T1 - Eclogitic diamonds from variable crustal protoliths in the northeastern Siberian craton

T2 - Trace elements and coupled δ13C-δ18O signatures in diamonds and garnet inclusions

AU - Zedgenizov, Dmitry

AU - Rubatto, Daniela

AU - Shatsky, Vladislav

AU - Ragozin, Alexey

AU - Kalinina, Victoria

PY - 2016/3/1

Y1 - 2016/3/1

N2 - Diamonds of eclogitic assemblages are dominant in the placer diamond deposits of the northeastern Siberian platform. In this study we present new trace elements and stable isotopes (δ13C and δ18O) data for alluvial diamonds and their garnet inclusions from this locality. Cr-rich garnets of peridotitic affinity in the studied diamonds have a narrow range of δ18O values from 5.7‰ to 6.2‰, which is largely overlapping with the accepted mantle range. This narrow range suggests that the garnet inclusions showing different REE patterns and little variations in oxygen isotopes may have formed by different processes involving fluid/melts that, however, were in oxygen isotopic equilibrium with the mantle. The trace element composition of the eclogitic garnet inclusions supports a crustal origin for at least the high-Ca garnets, which show flat HREE patterns and in some cases a positive Eu-anomaly. High-Ca eclogitic garnets generally show heavier oxygen isotope compositions (δ18O 6.5-9.6‰) than what is observed in low-Ca garnets (δ18O 5.7-7.4‰). The variability in oxygen isotopes and trace elements is suggested to be inherited from contrasting crustal protoliths. The relationship between the high δ18O values of inclusions and the low δ13C values of the host diamonds implies that the high-Ca garnet inclusions were derived from intensely hydrated (e.g., δ18O >7‰) and typically oxidised basaltic rock close to the seawater interface, and that the carbon for diamonds was closely associated with this protolith.

AB - Diamonds of eclogitic assemblages are dominant in the placer diamond deposits of the northeastern Siberian platform. In this study we present new trace elements and stable isotopes (δ13C and δ18O) data for alluvial diamonds and their garnet inclusions from this locality. Cr-rich garnets of peridotitic affinity in the studied diamonds have a narrow range of δ18O values from 5.7‰ to 6.2‰, which is largely overlapping with the accepted mantle range. This narrow range suggests that the garnet inclusions showing different REE patterns and little variations in oxygen isotopes may have formed by different processes involving fluid/melts that, however, were in oxygen isotopic equilibrium with the mantle. The trace element composition of the eclogitic garnet inclusions supports a crustal origin for at least the high-Ca garnets, which show flat HREE patterns and in some cases a positive Eu-anomaly. High-Ca eclogitic garnets generally show heavier oxygen isotope compositions (δ18O 6.5-9.6‰) than what is observed in low-Ca garnets (δ18O 5.7-7.4‰). The variability in oxygen isotopes and trace elements is suggested to be inherited from contrasting crustal protoliths. The relationship between the high δ18O values of inclusions and the low δ13C values of the host diamonds implies that the high-Ca garnet inclusions were derived from intensely hydrated (e.g., δ18O >7‰) and typically oxidised basaltic rock close to the seawater interface, and that the carbon for diamonds was closely associated with this protolith.

KW - Carbon isotopes

KW - Diamond

KW - Eclogite

KW - Garnet

KW - Mantle

KW - Oxygen isotopes

KW - Siberian craton

UR - http://www.scopus.com/inward/record.url?scp=84953261790&partnerID=8YFLogxK

U2 - 10.1016/j.chemgeo.2015.12.018

DO - 10.1016/j.chemgeo.2015.12.018

M3 - Article

AN - SCOPUS:84953261790

VL - 422

SP - 46

EP - 59

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

ER -