Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia

Konstantin D. Litasov, Vladimir G. Malkovets, Sergey I. Kostrovitsky, Lawrence A. Taylor

Research output: Contribution to journalArticle

Abstract

Ilmenite-bearing symplectite, typically ilmenite-clinopyroxene, occurs in rare mantle xenoliths from kimberlite and other alkaline rocks. Two major hypotheses have been proposed for their origin: (1) exolution from high-pressure pyroxene or garnet; and (2) cotectic or eutectic co-precipitation from evolved "proto-kimberlite" melt, producing megacrysts. Here we present new findings about these ilmenite-clinopyroxene symplectites in the Miocene picrobasalts and Pleistocene basanites of the Vitim volcanic field, central Siberia. For comparison, we have described unusual ilmenite-clinopyroxene symplectites from Yakutian kimberlites: the Mary pipe (Kuoisk field) and the Mir pipe (Malo-Botuobinsk field). Symplectite clinopyroxene from Vitim alkaline basalts corresponds to the low-Mg end of the clinopyroxene megacryst trend. They have an Mg# of 70-72 and contain 1.5-2.0 wt% TiO2. Ilmenites from Vitim symplectites are Cr-poor and contain 5.3-6.3 wt% MgO, whereas ilmenites from kimberlite symplectites contain 0.1-1.4 wt% Cr2O3 and 8-13 wt.% MgO. However, trace-element patterns of symplectitic clinopyroxene in both kimberlites and alkaline basalts are similar. Clinopyroxenes from Vitim symplectites have more evolved trace-element patterns (Lan = 3.1-3.8, normalized to primitive mantle) relative to the majority of megacrysts (Lan = 1.0-3.8). Modeling of fractional crystallization of clinopyroxene from alkaline basaltic melt indicates that clinopyroxenes from symplectites correspond to the residual melt fraction of 20-40%, which is high for eutectic crystallization. Symplectites from the Mary pipe can be divided into Cr-rich (Cr2O3cpx = 0.20-0.39 wt.% and Cr2O3ilm = 0.7-1.3 wt%) and Cr poor (Cr2O3cpx = 0.04-0.16 wt.% and Cr2O3ilm = 0.1-0.4 wt.%) subgroups. However trace-element patterns in clinopyroxenes from both groups of symplectites are similar. This may indicate a symplectite origin from different pulses of magma. Cr-enrichment in the Cr-rich group can be related to contamination by adjacent peridotites. Compositional and textural variations in symplectites from both the alkaline basalts and kimberlites reveal similarities in genesis and a clear connection with megacryst assemblages. We suggest that ilmenite-clinopyroxene symplectites characterize the initial stage of simultaneous precipitation of ilmenite and clinopyroxene. They crystallize after the majority of the clinopyroxene megacrysts and before normal Ilm-Cpx intergrowths and ilmenite megacrysts. This indicates a possible cotectic rather than eutectic precipitation of ilmenite and clinopyroxene in symplectites. Pressure and temperature estimations indicate that Ilm-Cpx symplectites from the Mir and Mary kimberlite pipes formed at pressures of 40-50 kbar, whereas those from Vitim basalts formed at lower pressures of 12-17 kbar. Coexisting Fe-Ti oxides in Vitim ilmenites from symplectites and megacrysts suggest equilibration temperatures of 690-1025°C at fO2 = 0.22-1.88 log units below the QFM buffer. This redox state is similar to that of spinel peridotites in the same localities.

Original languageEnglish
Pages (from-to)976-997
Number of pages22
JournalInternational Geology Review
Volume45
Issue number11
Publication statusPublished - Nov 2003
Externally publishedYes

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symplectite
petrogenesis
ilmenite
clinopyroxene
basalt
kimberlite
pipe
megacryst
trace element
melt
mantle
alkaline rock
fractional crystallization
spinel
pyroxene
low pressure
garnet
crystallization

ASJC Scopus subject areas

  • Geology

Cite this

Litasov, K. D., Malkovets, V. G., Kostrovitsky, S. I., & Taylor, L. A. (2003). Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia. International Geology Review, 45(11), 976-997.

Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia. / Litasov, Konstantin D.; Malkovets, Vladimir G.; Kostrovitsky, Sergey I.; Taylor, Lawrence A.

In: International Geology Review, Vol. 45, No. 11, 11.2003, p. 976-997.

Research output: Contribution to journalArticle

Litasov, KD, Malkovets, VG, Kostrovitsky, SI & Taylor, LA 2003, 'Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia', International Geology Review, vol. 45, no. 11, pp. 976-997.
Litasov, Konstantin D. ; Malkovets, Vladimir G. ; Kostrovitsky, Sergey I. ; Taylor, Lawrence A. / Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia. In: International Geology Review. 2003 ; Vol. 45, No. 11. pp. 976-997.
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abstract = "Ilmenite-bearing symplectite, typically ilmenite-clinopyroxene, occurs in rare mantle xenoliths from kimberlite and other alkaline rocks. Two major hypotheses have been proposed for their origin: (1) exolution from high-pressure pyroxene or garnet; and (2) cotectic or eutectic co-precipitation from evolved {"}proto-kimberlite{"} melt, producing megacrysts. Here we present new findings about these ilmenite-clinopyroxene symplectites in the Miocene picrobasalts and Pleistocene basanites of the Vitim volcanic field, central Siberia. For comparison, we have described unusual ilmenite-clinopyroxene symplectites from Yakutian kimberlites: the Mary pipe (Kuoisk field) and the Mir pipe (Malo-Botuobinsk field). Symplectite clinopyroxene from Vitim alkaline basalts corresponds to the low-Mg end of the clinopyroxene megacryst trend. They have an Mg# of 70-72 and contain 1.5-2.0 wt{\%} TiO2. Ilmenites from Vitim symplectites are Cr-poor and contain 5.3-6.3 wt{\%} MgO, whereas ilmenites from kimberlite symplectites contain 0.1-1.4 wt{\%} Cr2O3 and 8-13 wt.{\%} MgO. However, trace-element patterns of symplectitic clinopyroxene in both kimberlites and alkaline basalts are similar. Clinopyroxenes from Vitim symplectites have more evolved trace-element patterns (Lan = 3.1-3.8, normalized to primitive mantle) relative to the majority of megacrysts (Lan = 1.0-3.8). Modeling of fractional crystallization of clinopyroxene from alkaline basaltic melt indicates that clinopyroxenes from symplectites correspond to the residual melt fraction of 20-40{\%}, which is high for eutectic crystallization. Symplectites from the Mary pipe can be divided into Cr-rich (Cr2O3cpx = 0.20-0.39 wt.{\%} and Cr2O3ilm = 0.7-1.3 wt{\%}) and Cr poor (Cr2O3cpx = 0.04-0.16 wt.{\%} and Cr2O3ilm = 0.1-0.4 wt.{\%}) subgroups. However trace-element patterns in clinopyroxenes from both groups of symplectites are similar. This may indicate a symplectite origin from different pulses of magma. Cr-enrichment in the Cr-rich group can be related to contamination by adjacent peridotites. Compositional and textural variations in symplectites from both the alkaline basalts and kimberlites reveal similarities in genesis and a clear connection with megacryst assemblages. We suggest that ilmenite-clinopyroxene symplectites characterize the initial stage of simultaneous precipitation of ilmenite and clinopyroxene. They crystallize after the majority of the clinopyroxene megacrysts and before normal Ilm-Cpx intergrowths and ilmenite megacrysts. This indicates a possible cotectic rather than eutectic precipitation of ilmenite and clinopyroxene in symplectites. Pressure and temperature estimations indicate that Ilm-Cpx symplectites from the Mir and Mary kimberlite pipes formed at pressures of 40-50 kbar, whereas those from Vitim basalts formed at lower pressures of 12-17 kbar. Coexisting Fe-Ti oxides in Vitim ilmenites from symplectites and megacrysts suggest equilibration temperatures of 690-1025°C at fO2 = 0.22-1.88 log units below the QFM buffer. This redox state is similar to that of spinel peridotites in the same localities.",
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T1 - Petrogenesis of ilmenite-bearing symplectite xenoliths from vitim alkaline basalts and yakutian kimberlites, Russia

AU - Litasov, Konstantin D.

AU - Malkovets, Vladimir G.

AU - Kostrovitsky, Sergey I.

AU - Taylor, Lawrence A.

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N2 - Ilmenite-bearing symplectite, typically ilmenite-clinopyroxene, occurs in rare mantle xenoliths from kimberlite and other alkaline rocks. Two major hypotheses have been proposed for their origin: (1) exolution from high-pressure pyroxene or garnet; and (2) cotectic or eutectic co-precipitation from evolved "proto-kimberlite" melt, producing megacrysts. Here we present new findings about these ilmenite-clinopyroxene symplectites in the Miocene picrobasalts and Pleistocene basanites of the Vitim volcanic field, central Siberia. For comparison, we have described unusual ilmenite-clinopyroxene symplectites from Yakutian kimberlites: the Mary pipe (Kuoisk field) and the Mir pipe (Malo-Botuobinsk field). Symplectite clinopyroxene from Vitim alkaline basalts corresponds to the low-Mg end of the clinopyroxene megacryst trend. They have an Mg# of 70-72 and contain 1.5-2.0 wt% TiO2. Ilmenites from Vitim symplectites are Cr-poor and contain 5.3-6.3 wt% MgO, whereas ilmenites from kimberlite symplectites contain 0.1-1.4 wt% Cr2O3 and 8-13 wt.% MgO. However, trace-element patterns of symplectitic clinopyroxene in both kimberlites and alkaline basalts are similar. Clinopyroxenes from Vitim symplectites have more evolved trace-element patterns (Lan = 3.1-3.8, normalized to primitive mantle) relative to the majority of megacrysts (Lan = 1.0-3.8). Modeling of fractional crystallization of clinopyroxene from alkaline basaltic melt indicates that clinopyroxenes from symplectites correspond to the residual melt fraction of 20-40%, which is high for eutectic crystallization. Symplectites from the Mary pipe can be divided into Cr-rich (Cr2O3cpx = 0.20-0.39 wt.% and Cr2O3ilm = 0.7-1.3 wt%) and Cr poor (Cr2O3cpx = 0.04-0.16 wt.% and Cr2O3ilm = 0.1-0.4 wt.%) subgroups. However trace-element patterns in clinopyroxenes from both groups of symplectites are similar. This may indicate a symplectite origin from different pulses of magma. Cr-enrichment in the Cr-rich group can be related to contamination by adjacent peridotites. Compositional and textural variations in symplectites from both the alkaline basalts and kimberlites reveal similarities in genesis and a clear connection with megacryst assemblages. We suggest that ilmenite-clinopyroxene symplectites characterize the initial stage of simultaneous precipitation of ilmenite and clinopyroxene. They crystallize after the majority of the clinopyroxene megacrysts and before normal Ilm-Cpx intergrowths and ilmenite megacrysts. This indicates a possible cotectic rather than eutectic precipitation of ilmenite and clinopyroxene in symplectites. Pressure and temperature estimations indicate that Ilm-Cpx symplectites from the Mir and Mary kimberlite pipes formed at pressures of 40-50 kbar, whereas those from Vitim basalts formed at lower pressures of 12-17 kbar. Coexisting Fe-Ti oxides in Vitim ilmenites from symplectites and megacrysts suggest equilibration temperatures of 690-1025°C at fO2 = 0.22-1.88 log units below the QFM buffer. This redox state is similar to that of spinel peridotites in the same localities.

AB - Ilmenite-bearing symplectite, typically ilmenite-clinopyroxene, occurs in rare mantle xenoliths from kimberlite and other alkaline rocks. Two major hypotheses have been proposed for their origin: (1) exolution from high-pressure pyroxene or garnet; and (2) cotectic or eutectic co-precipitation from evolved "proto-kimberlite" melt, producing megacrysts. Here we present new findings about these ilmenite-clinopyroxene symplectites in the Miocene picrobasalts and Pleistocene basanites of the Vitim volcanic field, central Siberia. For comparison, we have described unusual ilmenite-clinopyroxene symplectites from Yakutian kimberlites: the Mary pipe (Kuoisk field) and the Mir pipe (Malo-Botuobinsk field). Symplectite clinopyroxene from Vitim alkaline basalts corresponds to the low-Mg end of the clinopyroxene megacryst trend. They have an Mg# of 70-72 and contain 1.5-2.0 wt% TiO2. Ilmenites from Vitim symplectites are Cr-poor and contain 5.3-6.3 wt% MgO, whereas ilmenites from kimberlite symplectites contain 0.1-1.4 wt% Cr2O3 and 8-13 wt.% MgO. However, trace-element patterns of symplectitic clinopyroxene in both kimberlites and alkaline basalts are similar. Clinopyroxenes from Vitim symplectites have more evolved trace-element patterns (Lan = 3.1-3.8, normalized to primitive mantle) relative to the majority of megacrysts (Lan = 1.0-3.8). Modeling of fractional crystallization of clinopyroxene from alkaline basaltic melt indicates that clinopyroxenes from symplectites correspond to the residual melt fraction of 20-40%, which is high for eutectic crystallization. Symplectites from the Mary pipe can be divided into Cr-rich (Cr2O3cpx = 0.20-0.39 wt.% and Cr2O3ilm = 0.7-1.3 wt%) and Cr poor (Cr2O3cpx = 0.04-0.16 wt.% and Cr2O3ilm = 0.1-0.4 wt.%) subgroups. However trace-element patterns in clinopyroxenes from both groups of symplectites are similar. This may indicate a symplectite origin from different pulses of magma. Cr-enrichment in the Cr-rich group can be related to contamination by adjacent peridotites. Compositional and textural variations in symplectites from both the alkaline basalts and kimberlites reveal similarities in genesis and a clear connection with megacryst assemblages. We suggest that ilmenite-clinopyroxene symplectites characterize the initial stage of simultaneous precipitation of ilmenite and clinopyroxene. They crystallize after the majority of the clinopyroxene megacrysts and before normal Ilm-Cpx intergrowths and ilmenite megacrysts. This indicates a possible cotectic rather than eutectic precipitation of ilmenite and clinopyroxene in symplectites. Pressure and temperature estimations indicate that Ilm-Cpx symplectites from the Mir and Mary kimberlite pipes formed at pressures of 40-50 kbar, whereas those from Vitim basalts formed at lower pressures of 12-17 kbar. Coexisting Fe-Ti oxides in Vitim ilmenites from symplectites and megacrysts suggest equilibration temperatures of 690-1025°C at fO2 = 0.22-1.88 log units below the QFM buffer. This redox state is similar to that of spinel peridotites in the same localities.

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