Journal ArticleDOI
Phase relations in peridotite+CO2 Systems to 12 GPa: Implications for the origin of kimberlite and carbonate stability in the Earth's upper mantle
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The phase relations of synthetic peridotites in the systems CaO-MgO-SiO2-CO2 (CMS-CO 2 ), CaOmGO-Al2O3- SiO2 -CO 2 (CMASCO 2 ) and CMAS-H2O were studied from 4 to 12 GPa using a multanvil apparatus.Abstract:
The phase relations of synthetic peridotites in the systems CaO-MgO-SiO2-CO2 (CMS-CO2), CaO-MgO-Al2O3-SiO2-CO2 (CMAS-CO2) and CaO-MgO-SiO2-CO2-H2O (CMS-CO2-H2O) were studied from 4 to 12 GPa using a multi-anvil apparatus. Peridotite solidi in both the CMS-CO2 and CMAS-CO2 systems have similar topologies. Carbonates are the first phases consumed at, or above, the solidus in peridotite+CO2 at pressures above 4 GPa. Magnesite solid-solutions are stable subsolidus phases in peridotite+CO2 to pressures of at least 12 GPa. It is demonstrated that if uncontaminated, diamond-bearing kimberlites emplaced in the Earth's crust are primary magmas, then they could be derived by partial melting of carbonated peridotite at 5 to 7 GPa in the upper mantle beneath the cratonic areas of continents. “Proto-kimberlites” may be generated at pressures above 7 GPa in the upper mantle, but no such magmas are represented on the Earth's surface. Mineral chemical data from experimental run products indicate that: 1) the discrete sub-calcic clinopyroxene nodules found in some kimberlites represent phenocrysts which crystallized at high pressure in the kimberlite magma and, 2) the spatial association of kimberlite and melilitite observed in the field is not related to a common source region for both these magmas in the mantle. If the oxygen fugacity recorded in samples from the upper 150 km of the mantle is maintained at greater depths, then carbonates are potential hosts for carbon in the mantle to depths of at least 350 km.read more
Citations
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Water in the oceanic upper mantle: implications for rheology, melt extraction and the evolution of the lithosphere
Greg Hirth,David L. Kohlstedt +1 more
TL;DR: In this paper, the influence of water on the dynamics of the oceanic upper mantle is re-evaluated based on recent experimental constraints on the solubility of water in mantle minerals and earlier experimental studies of olivine rheology.
Journal ArticleDOI
Melting in the Earth's deep upper mantle caused by carbon dioxide
TL;DR: It is inferred that carbon, helium, argon and highly incompatible heat-producing elements are efficiently scavenged from depths of ∼200–330 km in the upper mantle and argued that these melts promote recrystallization and realignment of the mineral matrix, which may explain the geophysical observations.
Journal ArticleDOI
Deep global cycling of carbon constrained by the solidus of anhydrous, carbonated eclogite under upper mantle conditions
TL;DR: In this paper, the phase relations of carbonate-bearing eclogite assemblages from 2.5 to 8.5 GPa were investigated and the results indicated that carbonated peridotite is a more likely source of magmatic carbon in oceanic provinces.
Journal ArticleDOI
Geochemistry of South African On- and Off-craton, Group I and Group II Kimberlites: Petrogenesis and Source Region Evolution
Megan Becker,Anton P. le Roex +1 more
TL;DR: In this paper, the authors used bulk-rock geochemical compositions of hypabyssal kimberlites, emplaced through the Archaean Kaapvaal craton and Proterozoic Namaqua-Natal belt, to estimate close-to-primary magma compositions of Group I kimbers.
Journal ArticleDOI
The Continuum of Primary Carbonatitic-Kimberlitic Melt Compositions in Equilibrium with Lherzolite: Data from the System CaO-MgO-Al2O3-SiO2-CO2 at 6 GPa
John A. Dalton,Dean C. Presnall +1 more
TL;DR: In this article, the authors trace the compositional path of the line and determine the compositions of coexisting phases in a CMAS solidus system, and then construct bulk compositions that maximize the amount of liquid to facilitate analysis.
References
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Journal ArticleDOI
Melting of a dry peridotite KLB‐1 up to 14 GPa: Implications on the Origin of peridotitic upper mantle
TL;DR: In this paper, a diapiric model was proposed for the genesis of komatiite magma by partial melting of mantle peridotite at 150-200 km depth.
Journal ArticleDOI
The bearing of phase equilibria studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks
TL;DR: In this article, a revised closed system model of basalt evolution is presented, based upon these controlling factors; depth of partial melting, extent of part melting, speed of movement towards the surface, and olivine extraction.
Journal ArticleDOI
An experimental determination of primary carbonatite magma composition
TL;DR: In this paper, the phase relationship of carbonate and amphibole-bearing peridotite (containing 0.3% H2O and 0.5-2.5% CO2) is investigated.
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