Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts
Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose mel...
Ausführliche Beschreibung
Gespeichert in:
| Autor*in: |
Stephen F. Foley [verfasserIn] Isra S. Ezad [verfasserIn] Sieger R. van der Laan [verfasserIn] Maik Pertermann [verfasserIn] |
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| Format: |
E-Artikel |
|---|---|
| Sprache: |
Englisch |
| Erschienen: |
2022 |
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| Schlagwörter: |
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| Übergeordnetes Werk: |
In: Geoscience Frontiers - Elsevier, 2016, 13(2022), 4, Seite 101380- |
|---|---|
| Übergeordnetes Werk: |
volume:13 ; year:2022 ; number:4 ; pages:101380- |
| Links: |
|---|
| DOI / URN: |
10.1016/j.gsf.2022.101380 |
|---|
| Katalog-ID: |
DOAJ039816710 |
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| 245 | 1 | 0 | |a Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts |
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| 520 | |a Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. | ||
| 650 | 4 | |a Hydrous pyroxenite | |
| 650 | 4 | |a Experimental petrology | |
| 650 | 4 | |a Mantle melts | |
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| 650 | 4 | |a Lamproite | |
| 650 | 4 | |a Mantle metasomatism | |
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| 700 | 0 | |a Sieger R. van der Laan |e verfasserin |4 aut | |
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10.1016/j.gsf.2022.101380 doi (DE-627)DOAJ039816710 (DE-599)DOAJ2e18a0781f7b4a4186e8024b6ea629fe DE-627 ger DE-627 rakwb eng QE1-996.5 Stephen F. Foley verfasserin aut Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts 2022 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism Geology Isra S. Ezad verfasserin aut Sieger R. van der Laan verfasserin aut Maik Pertermann verfasserin aut In Geoscience Frontiers Elsevier, 2016 13(2022), 4, Seite 101380- (DE-627)DOAJ000091189 25889192 nnns volume:13 year:2022 number:4 pages:101380- https://doi.org/10.1016/j.gsf.2022.101380 kostenfrei https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe kostenfrei http://www.sciencedirect.com/science/article/pii/S1674987122000330 kostenfrei https://doaj.org/toc/1674-9871 Journal toc kostenfrei GBV_USEFLAG_A SYSFLAG_A GBV_DOAJ AR 13 2022 4 101380- |
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10.1016/j.gsf.2022.101380 doi (DE-627)DOAJ039816710 (DE-599)DOAJ2e18a0781f7b4a4186e8024b6ea629fe DE-627 ger DE-627 rakwb eng QE1-996.5 Stephen F. Foley verfasserin aut Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts 2022 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism Geology Isra S. Ezad verfasserin aut Sieger R. van der Laan verfasserin aut Maik Pertermann verfasserin aut In Geoscience Frontiers Elsevier, 2016 13(2022), 4, Seite 101380- (DE-627)DOAJ000091189 25889192 nnns volume:13 year:2022 number:4 pages:101380- https://doi.org/10.1016/j.gsf.2022.101380 kostenfrei https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe kostenfrei http://www.sciencedirect.com/science/article/pii/S1674987122000330 kostenfrei https://doaj.org/toc/1674-9871 Journal toc kostenfrei GBV_USEFLAG_A SYSFLAG_A GBV_DOAJ AR 13 2022 4 101380- |
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10.1016/j.gsf.2022.101380 doi (DE-627)DOAJ039816710 (DE-599)DOAJ2e18a0781f7b4a4186e8024b6ea629fe DE-627 ger DE-627 rakwb eng QE1-996.5 Stephen F. Foley verfasserin aut Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts 2022 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism Geology Isra S. Ezad verfasserin aut Sieger R. van der Laan verfasserin aut Maik Pertermann verfasserin aut In Geoscience Frontiers Elsevier, 2016 13(2022), 4, Seite 101380- (DE-627)DOAJ000091189 25889192 nnns volume:13 year:2022 number:4 pages:101380- https://doi.org/10.1016/j.gsf.2022.101380 kostenfrei https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe kostenfrei http://www.sciencedirect.com/science/article/pii/S1674987122000330 kostenfrei https://doaj.org/toc/1674-9871 Journal toc kostenfrei GBV_USEFLAG_A SYSFLAG_A GBV_DOAJ AR 13 2022 4 101380- |
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10.1016/j.gsf.2022.101380 doi (DE-627)DOAJ039816710 (DE-599)DOAJ2e18a0781f7b4a4186e8024b6ea629fe DE-627 ger DE-627 rakwb eng QE1-996.5 Stephen F. Foley verfasserin aut Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts 2022 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism Geology Isra S. Ezad verfasserin aut Sieger R. van der Laan verfasserin aut Maik Pertermann verfasserin aut In Geoscience Frontiers Elsevier, 2016 13(2022), 4, Seite 101380- (DE-627)DOAJ000091189 25889192 nnns volume:13 year:2022 number:4 pages:101380- https://doi.org/10.1016/j.gsf.2022.101380 kostenfrei https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe kostenfrei http://www.sciencedirect.com/science/article/pii/S1674987122000330 kostenfrei https://doaj.org/toc/1674-9871 Journal toc kostenfrei GBV_USEFLAG_A SYSFLAG_A GBV_DOAJ AR 13 2022 4 101380- |
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10.1016/j.gsf.2022.101380 doi (DE-627)DOAJ039816710 (DE-599)DOAJ2e18a0781f7b4a4186e8024b6ea629fe DE-627 ger DE-627 rakwb eng QE1-996.5 Stephen F. Foley verfasserin aut Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts 2022 Text txt rdacontent Computermedien c rdamedia Online-Ressource cr rdacarrier Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism Geology Isra S. Ezad verfasserin aut Sieger R. van der Laan verfasserin aut Maik Pertermann verfasserin aut In Geoscience Frontiers Elsevier, 2016 13(2022), 4, Seite 101380- (DE-627)DOAJ000091189 25889192 nnns volume:13 year:2022 number:4 pages:101380- https://doi.org/10.1016/j.gsf.2022.101380 kostenfrei https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe kostenfrei http://www.sciencedirect.com/science/article/pii/S1674987122000330 kostenfrei https://doaj.org/toc/1674-9871 Journal toc kostenfrei GBV_USEFLAG_A SYSFLAG_A GBV_DOAJ AR 13 2022 4 101380- |
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They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. 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Stephen F. Foley |
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Stephen F. Foley misc QE1-996.5 misc Hydrous pyroxenite misc Experimental petrology misc Mantle melts misc Phlogopite misc Lamproite misc Mantle metasomatism misc Geology Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts |
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QE1-996.5 Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts Hydrous pyroxenite Experimental petrology Mantle melts Phlogopite Lamproite Mantle metasomatism |
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Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts |
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Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts |
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melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. melting relations and major element compositions of melts |
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Melting of hydrous pyroxenites with alkali amphiboles in the continental mantle: 1. Melting relations and major element compositions of melts |
| abstract |
Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. |
| abstractGer |
Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. |
| abstract_unstemmed |
Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium.Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO2 and especially K2O but low CaO and Al2O3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al2O3 and do not resemble lamproites. These experiments show that low CaO and Al2O3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P2O5 or TiO2 depending on the phases present and are unlike any melts seen at the Earth’s surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. |
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The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons.Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths < 130 km: minor perturbations of the stable geotherm at <150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases.</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Hydrous pyroxenite</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Experimental petrology</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Mantle melts</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Phlogopite</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Lamproite</subfield></datafield><datafield tag="650" ind1=" " ind2="4"><subfield code="a">Mantle metasomatism</subfield></datafield><datafield tag="653" ind1=" " ind2="0"><subfield code="a">Geology</subfield></datafield><datafield tag="700" ind1="0" ind2=" "><subfield code="a">Isra S. Ezad</subfield><subfield code="e">verfasserin</subfield><subfield code="4">aut</subfield></datafield><datafield tag="700" ind1="0" ind2=" "><subfield code="a">Sieger R. van der Laan</subfield><subfield code="e">verfasserin</subfield><subfield code="4">aut</subfield></datafield><datafield tag="700" ind1="0" ind2=" "><subfield code="a">Maik Pertermann</subfield><subfield code="e">verfasserin</subfield><subfield code="4">aut</subfield></datafield><datafield tag="773" ind1="0" ind2="8"><subfield code="i">In</subfield><subfield code="t">Geoscience Frontiers</subfield><subfield code="d">Elsevier, 2016</subfield><subfield code="g">13(2022), 4, Seite 101380-</subfield><subfield code="w">(DE-627)DOAJ000091189</subfield><subfield code="x">25889192</subfield><subfield code="7">nnns</subfield></datafield><datafield tag="773" ind1="1" ind2="8"><subfield code="g">volume:13</subfield><subfield code="g">year:2022</subfield><subfield code="g">number:4</subfield><subfield code="g">pages:101380-</subfield></datafield><datafield tag="856" ind1="4" ind2="0"><subfield code="u">https://doi.org/10.1016/j.gsf.2022.101380</subfield><subfield code="z">kostenfrei</subfield></datafield><datafield tag="856" ind1="4" ind2="0"><subfield code="u">https://doaj.org/article/2e18a0781f7b4a4186e8024b6ea629fe</subfield><subfield code="z">kostenfrei</subfield></datafield><datafield tag="856" ind1="4" ind2="0"><subfield code="u">http://www.sciencedirect.com/science/article/pii/S1674987122000330</subfield><subfield code="z">kostenfrei</subfield></datafield><datafield tag="856" ind1="4" ind2="2"><subfield code="u">https://doaj.org/toc/1674-9871</subfield><subfield code="y">Journal toc</subfield><subfield code="z">kostenfrei</subfield></datafield><datafield tag="912" ind1=" " ind2=" "><subfield code="a">GBV_USEFLAG_A</subfield></datafield><datafield tag="912" ind1=" " ind2=" "><subfield code="a">SYSFLAG_A</subfield></datafield><datafield tag="912" ind1=" " ind2=" "><subfield code="a">GBV_DOAJ</subfield></datafield><datafield tag="951" ind1=" " ind2=" "><subfield code="a">AR</subfield></datafield><datafield tag="952" ind1=" " ind2=" "><subfield code="d">13</subfield><subfield code="j">2022</subfield><subfield code="e">4</subfield><subfield code="h">101380-</subfield></datafield></record></collection>
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