Experimental tests of garnet peridotite oxygen barometry

Guðmundsson, Garðar; Wood, B. J.

doi:10.1007/s004100050027

Cited by 22 publications

(34 citation statements)

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“…In this study, a recent calibration of the olivine‐orthopyroxene‐garnet oxybarometer (Stagno et al, ) is used to establish the oxygen fugacity values of cratonic mantle peridotites. Compared with previous calibration performed at pressures of 3 and 3.5 GPa (Gudmundsson & Wood, ), the new oxybarometer was constructed at pressures from 3 to 7 GPa (Stagno et al, ) and was able to reproduce experimental data more precisely. A key parameter in this oxybarometer is the Fe 3+ /∑Fe ratio in garnet (i.e., the andradite end‐member), which can be obtained by phase equilibrium modeling in the Fe 3+ ‐bearing system.…”

Section: Methodsmentioning

confidence: 99%

Making Cratonic Lithospheric Mantle

Chen

2018

JGR Solid Earth

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The origin of cratonic lithospheric mantle has been attributed to either high‐pressure (5–7 GPa) melting in hot mantle plumes or low‐pressure (<5 GPa) melting in mid‐ocean ridges or suprasubduction zones. To resolve this long‐standing debate, it is necessary to confirm under what depths the incipient cratonic mantle melted. Compared with most cratonic mantle xenoliths and xenocrysts, which commonly experienced metasomatic modification after melt extraction, diamond inclusions with predominantly harzburgitic compositions can better track the compositional signature of pristine cratonic mantle. This paper presents thermodynamic calculations performed with THERMOCALC software to establish a quantitative relationship between garnet and cratonic peridotite compositions. Along the normal cratonic geotherm (40 mW/m2), the XCa [atomic Ca/(Ca + Mg + Fe2+)] and Cr# [atomic Cr/(Cr + Al) × 100] values in garnet depend mainly on the bulk CaO/Al2O3 and Cr# values, respectively. Furthermore, mantle melting modeling shows that the Cr# of the residue displays a negative correlation with melting pressure at melt fractions of greater than ~15%. Therefore, the high Cr# values (mostly 12–36) of global garnet inclusions in diamond support a low‐pressure (<4 GPa) origin for cratonic lithospheric mantle. More importantly, the incipient cratonic mantle calculated from the garnet inclusions exhibits similar bulk CaO/Al2O3 and Cr# compositions to oceanic lithosphere but different values from arc lithosphere with higher CaO/Al2O3 and Cr# values. These results imply that cratonic mantle was initially formed by the extensive melting of hot ambient mantle in the Archean ocean ridge environments. The shallow oceanic lithosphere was subsequently stacked to generate the thick and stable cratonic lithospheric mantle.

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Section: Methodsmentioning

confidence: 99%

Making Cratonic Lithospheric Mantle

Chen

2018

JGR Solid Earth

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“…We calculated the oxygen fugacity values using the monomineral versions of the ilmenite-olivine, spinel-olivine (Taylor et al, 1998) and garnet (Gudmundsson and Wood, 1995) oxybarometers and corrected equations for clinopyroxene (Ashchepkov et al, 2012).…”

Section: Monomineral Ilmenite Thermobarometrymentioning

confidence: 99%

Picroilmenites in Yakutian kimberlites: variations and genetic models

et al. 2014

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Abstract. Major and trace element variations in picroilmenites from Late Devonian kimberlite pipes in Siberia reveal similarities within the region in general, but show individual features for ilmenites from different fields and pipes. Empirical ilmenite thermobarometry (Ashchepkov et al., 2010), as well as common methods of mantle thermobarometry and trace element geochemical modeling, shows long compositional trends for the ilmenites. These are a result of complex processes of polybaric fractionation of protokimberlite melts, accompanied by the interaction with mantle wall rocks and dissolution of previous wall rock and metasomatic associations. Evolution of the parental magmas for the picroilmenites was determined for the three distinct phases of kimberlite activity from Yubileynaya and nearby Aprelskaya pipes, showing heating and an increase of Fe# (Fe# = Fe / (Fe + Mg) a.u.) of mantle peridotite minerals from stage to stage and splitting of the magmatic system in the final stages. High-pressure (5.5–7.0 GPa) Cr-bearing Mg-rich ilmenites (group 1) reflect the conditions of high-temperature metasomatic rocks at the base of the mantle lithosphere. Trace element patterns are enriched to 0.1–10/relative to primitive mantle (PM) and have flattened, spoon-like or S- or W-shaped rare earth element (REE) patterns with Pb > 1. These result from melting and crystallization in melt-feeding channels in the base of the lithosphere, where high-temperature dunites, harzburgites and pyroxenites were formed. Cr-poor ilmenite megacrysts (group 2) trace the high-temperature path of protokimberlites developed as result of fractional crystallization and wall rock assimilation during the creation of the feeder systems prior to the main kimberlite eruption. Inflections in ilmenite compositional trends probably reflect the mantle layering and pulsing melt intrusion during melt migration within the channels. Group 2 ilmenites have inclined REE enriched patterns (10–100)/PM with La / Ybn ~ 10–25, similar to those derived from kimberlites, with high-field-strength elements (HFSE) peaks (typical megacrysts). A series of similar patterns results from polybaric Assimilation + fractional crystallization (AFC) crystallization of protokimberlite melts which also precipitated sulfides (Pb < 1) and mixed with partial melts from garnet peridotites. Relatively low-Ti ilmenites with high-Cr content (group 3) probably crystallized in the metasomatic front under the rising protokimberlite source and represent the product of crystallization of segregated partial melts from metasomatic rocks. Cr-rich ilmenites are typical of veins and veinlets in peridotites crystallized from highly contaminated magma intruded into wall rocks in different levels within the mantle columns. Ilmenites which have the highest trace element contents (1000/PM) have REE patterns similar to those of perovskites. Low Cr contents suggest relatively closed system fractionation which occurred from the base of the lithosphere up to the garnet–spinel transition, according to monomineral thermobarometry for Mir and Dachnaya pipes. Restricted trends were detected for ilmenites from Udachnaya and most other pipes from the Daldyn–Alakit fields and other regions (Nakyn, Upper Muna and Prianabarie), where ilmenite trends extend from the base of the lithosphere mainly up to 4.0 GPa. Interaction of the megacryst forming melts with the mantle lithosphere caused heating and HFSE metasomatism prior to kimberlite eruption.

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“…From the Fe 3+ /ΣFe ratios determined by EPMA the oxygen fugacity relative to FMQ was calculated for the conditions of solidification of the breccia (= partial crystallization of the melt) at 35 kb and 1150 °C by using the composition of the actual garnet and an average Mg# of 90.5 and 90 for the newly grown orthopyroxenes and olivines resp. (after Gudmundsson and Wood, 1995; Table 1). The BSE image of xenocryst 1 in Fig.…”

Section: Resultsmentioning

confidence: 99%

Oxygen fugacities of the metasomatizing melt in a polymict peridotite from Kimberley

International Kimberlite Conference Extended Abstracts: 2008

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Experimental tests of garnet peridotite oxygen barometry

Cited by 22 publications

References 0 publications

Making Cratonic Lithospheric Mantle

Making Cratonic Lithospheric Mantle

Picroilmenites in Yakutian kimberlites: variations and genetic models

Oxygen fugacities of the metasomatizing melt in a polymict peridotite from Kimberley

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