TY - JOUR

T1 - Carbonatite melt-peridotite interaction at 5.5-7.0 GPa

T2 - Implications for metasomatism in lithospheric mantle

AU - Sokol, Alexander G.

AU - Kruk, Alexey N.

AU - Chebotarev, Dimity A.

AU - Palyanov, Yury N.

PY - 2016/4/1

Y1 - 2016/4/1

N2 - Interaction between carbonatite melt and peridotite is studied experimentally by melting samples of interlayered peridotite-carbonatite-peridotite in graphite containers at 1200-1350 °C and 5.5-7.0 GPa in a split-sphere multianvil apparatus. Starting compositions are lherzolite and harzburgite, as well as carbonatite which may form in the upper part of a slab or in a plume-related source. Most experimental runs were of 150 h duration in order for equilibrium to be achieved.The interaction produced carbonatitic melts with low SiO2 (≤7 wt.%) and high alkalis. At 1200 °C, melt-peridotite interaction occurs through Mg-Ca exchange, resulting in elimination of orthopyroxene and crystallization of magnesite and clinopyroxene. At 1350 °C hybridization of the carbonatite and magnesite-bearing peridotite melts occurred with consumption of clinopyroxene and magnesite, and crystallization of orthopyroxene at MgO/CaO ≥ 4.3. The resulting peridotite-saturated melt has Ca# (37-50) depending on primary carbonatite composition. Compositions of silicate phases are similar to those of high-temperature peridotite but are different from megacrysts in kimberlites. CaO and Cr2O3 changes in garnet produced from the melt-harzburgite interaction at 1200 and 1350 °C perfectly match the observed trend in garnet from metasomatized peridotite of the Siberian subcontinental lithospheric mantle. K-rich carbonatite melts equilibrated with peridotite at 5.5-7.0 GPa and 1200-1350 °C correspond to high-Mg inclusions in fibrous diamond. Carbonatite melt is a weak solvent of entrained xenoliths and therefore cannot produce kimberlitic magma if temperatures are ~1350 °C on separation from the lithospheric peridotite source and ~1000 °C on eruption.

AB - Interaction between carbonatite melt and peridotite is studied experimentally by melting samples of interlayered peridotite-carbonatite-peridotite in graphite containers at 1200-1350 °C and 5.5-7.0 GPa in a split-sphere multianvil apparatus. Starting compositions are lherzolite and harzburgite, as well as carbonatite which may form in the upper part of a slab or in a plume-related source. Most experimental runs were of 150 h duration in order for equilibrium to be achieved.The interaction produced carbonatitic melts with low SiO2 (≤7 wt.%) and high alkalis. At 1200 °C, melt-peridotite interaction occurs through Mg-Ca exchange, resulting in elimination of orthopyroxene and crystallization of magnesite and clinopyroxene. At 1350 °C hybridization of the carbonatite and magnesite-bearing peridotite melts occurred with consumption of clinopyroxene and magnesite, and crystallization of orthopyroxene at MgO/CaO ≥ 4.3. The resulting peridotite-saturated melt has Ca# (37-50) depending on primary carbonatite composition. Compositions of silicate phases are similar to those of high-temperature peridotite but are different from megacrysts in kimberlites. CaO and Cr2O3 changes in garnet produced from the melt-harzburgite interaction at 1200 and 1350 °C perfectly match the observed trend in garnet from metasomatized peridotite of the Siberian subcontinental lithospheric mantle. K-rich carbonatite melts equilibrated with peridotite at 5.5-7.0 GPa and 1200-1350 °C correspond to high-Mg inclusions in fibrous diamond. Carbonatite melt is a weak solvent of entrained xenoliths and therefore cannot produce kimberlitic magma if temperatures are ~1350 °C on separation from the lithospheric peridotite source and ~1000 °C on eruption.

KW - Diamond formation

KW - Experiment

KW - Kimberlite

KW - Magma

KW - Mantle

KW - Metasomatism

UR - http://www.scopus.com/inward/record.url?scp=84960330563&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2016.01.013

DO - 10.1016/j.lithos.2016.01.013

M3 - Article

AN - SCOPUS:84960330563

VL - 248-251

SP - 66

EP - 79

JO - Lithos

JF - Lithos

SN - 0024-4937

ER -