Chemical Indicator of Spinel During Partial Melting and Subsolidus Equilibration of Mantle Peridotite:Experimental Study and Application to Natural Rocks

Systematic experimental studies on partial melting and subsolidus equilibration of three reconstituted spinel-peridotites have been carried out at temperatures ranging from 1000 to 1380℃ and pressures of 1.0 and 1.5 GPa. The results shows (1) during partial melting, Mg# =Mg/(Mg+Fe)]and Cr# =Cr/(Cr-Al)]of spinel increase with an increase in degrees of melting) (2) during subsolidus equilibration, with increasing temperatures, Mg# of spinel increases but Cr# of spinel remains almost unchanged in dunite and increases slightly in Iherzolite and harzburgite. The negative and quasi-linear Mg# -Cr# correlation of spinel represents an isotherm of total non-equilibrium. The same results have been obtained by means of mathematical modelling. It is also proved by Mg# -Cr# correlation of spinel in natural peridotites. As a result of the spinel subsolidus equilibration, only variation of Cr# of spinel is limited, and then Cr# of spinel can be used to estimate the relative degree of melting undergone by host rocks

Chemical Indicator of Spinel During Partial Melting and Subsolidus Equilibration of Mantle Peridotite:Experimental Study and Application to Natural Rocks

Abstract Systematic experimental studies on partial melting and subsolidus equilibration of three reconstituted spinel - peridotites have been carried out at temperatures ranging from 1000 to 1380°C. and pressures of 1.0 and 1.5 GPa: The results show: (1) during partial melting, Mg# =Mg/(Mg+Fe)]and Cr# =Cr/ (Cr+Al)] of spinel increase with an increase in degrees of melting; (2) during subsolidus equilibration, with increasing temperatures, Mg# of spinel increases but Cr# of spinel remains almost unchanged in dunite and increases slightly in lherzolite and harzburgite. The negative and quasi - linear Mg# - Cr# correlation of spinel represents an isotherm of total non - equilibrium. The same results have been obtained by means of mathematical modelling. It is also proved by Mg# - Cr# correlation of spinel in natural peridotites. As a result of the spinel subsolidus equilibration, only variation of Cr# of spinel is limited, and then Cr# of spinel can be used to estimate the relative degree of melting undergone by host rocks. The bigger Cr# of spinel is, the higher the degree of melting will be. By contrast, during crystallization magma, Mg# and Cr# of spinel decrease with decreasing temperatures. Likewise, Cr# of spinel in basalts may be used to indicate the feature of Cr₂O₃/Al₂O₃ of magma, and the compositional zoning of spinel may be used to study the evolution of magma (cooling rate and contamination).