Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin
| dc.contributor.author | Dludla, Siyanda | |
| dc.contributor.author | Le Roex, Anton P | |
| dc.contributor.author | Gurney, John J | |
| dc.date.accessioned | 2016-08-05T13:33:19Z | |
| dc.date.available | 2016-08-05T13:33:19Z | |
| dc.date.issued | 2006 | |
| dc.date.updated | 2016-06-06T08:44:12Z | |
| dc.description.abstract | A suite of mantle eclogite hosted within the Premier kimberlite on the Kaapvaal craton can be classified on the basis of Na2O content in garnets as group I type, although textures are ambiguous. No accessory phases of note occur, but rutile and phlogopite are found in a few samples. Clinopyroxenes show variable light rare element (LREE) enrichment (La/Ybn = 2–48), and the garnets are strongly LREE depleted relative to chondrites (La/Ybn = <0.04). Four pyroxenite samples include both garnet clinopyroxenite and garnet orthopyroxenite; clinopyroxenes in these samples are strongly LREE enriched (La/Ybn = 57–65). Calculated equilibration temperatures of the eclogites range from 999 ± 32 to 1168 ± 14° C with an average temperature of 1102 ± 37° C, assuming a pressure of 50 kbar. Relative to a shield geotherm of 40mW/m2, these temperatures suggest a sampling depth of 135 to 165 km. A single, calcium-rich sample gives an equilibration temperature of 1296 ± 32° C at the same assumed pressure. Calculated equilibrium temperatures and pressures for the garnet pyroxenites are 887 to 987° C and 26 to 39 kbar (clinopyroxenite) and 1135 to 1156° C and 48 ± 2 kbar (orthopyroxenite). Reconstituted bulk rock compositions of the eclogites indicate the presence of low- and high-MgO groups. The MgO-poor eclogites (8 to10.5 weight % MgO) have jadeite-rich clinopyroxenes and except for lower silica contents are similar to mid-ocean ridge basalts in major element composition, with slight negative Euanomalies (Eu/Eu*=0.83 to 0.96), indicative of (low-P) plagioclase fractionation. The MgO-rich eclogites (13.6 to 18 weight % MgO) are similar in composition to oceanic gabbro. In combination the geochemical data suggest that the Premier eclogite suite represents a fragment of a once composite oceanic crustal section; the protolith to the low-MgO eclogites was recycled oceanic crustal layer two metabasalt, which experienced silicic melt loss during subduction; the protolith to the high-MgO suite was oceanic crustal layer three cumulate gabbro/pyroxenite. | |
| dc.identifier | http://dx.doi.org/10.2113/gssajg.109.3.353 | |
| dc.identifier.apacitation | Dludla, S., Le Roex, A. P., & Gurney, J. J. (2006). Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin. <i>South African Journal of Geology</i>, http://hdl.handle.net/11427/21160 | en_ZA |
| dc.identifier.chicagocitation | Dludla, Siyanda, Anton P Le Roex, and John J Gurney "Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin." <i>South African Journal of Geology</i> (2006) http://hdl.handle.net/11427/21160 | en_ZA |
| dc.identifier.citation | Dludla, S., Le Roex, A. P., & Gurney, J. J. (2006). Eclogite xenoliths from the Premier kimberlite, South Africa: geochemical evidence for a subduction origin. South African Journal of Geology, 109(3), 353-368. | |
| dc.identifier.ris | TY - Journal Article AU - Dludla, Siyanda AU - Le Roex, Anton P AU - Gurney, John J AB - A suite of mantle eclogite hosted within the Premier kimberlite on the Kaapvaal craton can be classified on the basis of Na2O content in garnets as group I type, although textures are ambiguous. No accessory phases of note occur, but rutile and phlogopite are found in a few samples. Clinopyroxenes show variable light rare element (LREE) enrichment (La/Ybn = 2–48), and the garnets are strongly LREE depleted relative to chondrites (La/Ybn = <0.04). Four pyroxenite samples include both garnet clinopyroxenite and garnet orthopyroxenite; clinopyroxenes in these samples are strongly LREE enriched (La/Ybn = 57–65). Calculated equilibration temperatures of the eclogites range from 999 ± 32 to 1168 ± 14° C with an average temperature of 1102 ± 37° C, assuming a pressure of 50 kbar. Relative to a shield geotherm of 40mW/m2, these temperatures suggest a sampling depth of 135 to 165 km. A single, calcium-rich sample gives an equilibration temperature of 1296 ± 32° C at the same assumed pressure. Calculated equilibrium temperatures and pressures for the garnet pyroxenites are 887 to 987° C and 26 to 39 kbar (clinopyroxenite) and 1135 to 1156° C and 48 ± 2 kbar (orthopyroxenite). Reconstituted bulk rock compositions of the eclogites indicate the presence of low- and high-MgO groups. The MgO-poor eclogites (8 to10.5 weight % MgO) have jadeite-rich clinopyroxenes and except for lower silica contents are similar to mid-ocean ridge basalts in major element composition, with slight negative Euanomalies (Eu/Eu*=0.83 to 0.96), indicative of (low-P) plagioclase fractionation. The MgO-rich eclogites (13.6 to 18 weight % MgO) are similar in composition to oceanic gabbro. In combination the geochemical data suggest that the Premier eclogite suite represents a fragment of a once composite oceanic crustal section; the protolith to the low-MgO eclogites was recycled oceanic crustal layer two metabasalt, which experienced silicic melt loss during subduction; the protolith to the high-MgO suite was oceanic crustal layer three cumulate gabbro/pyroxenite. DA - 2006 DB - OpenUCT DP - University of Cape Town J1 - South African Journal of Geology LK - https://open.uct.ac.za PB - University of Cape Town PY - 2006 T1 - Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin TI - Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin UR - http://hdl.handle.net/11427/21160 ER - | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11427/21160 | |
| dc.identifier.vancouvercitation | Dludla S, Le Roex AP, Gurney JJ. Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin. South African Journal of Geology. 2006; http://hdl.handle.net/11427/21160. | en_ZA |
| dc.language.iso | eng | |
| dc.publisher.department | Department of Geological Sciences | en_ZA |
| dc.publisher.faculty | Faculty of Science | en_ZA |
| dc.publisher.institution | University of Cape Town | |
| dc.source | South African Journal of Geology | |
| dc.source.uri | http://sajg.geoscienceworld.org/ | |
| dc.subject.other | Eclogite | |
| dc.subject.other | Kimberlite | |
| dc.subject.other | Garnet | |
| dc.subject.other | Rutile | |
| dc.subject.other | Phlogopite | |
| dc.subject.other | Temperature | |
| dc.title | Eclogite xenoliths from the Premier kimberlite, South Africa: Geochemical evidence for subduction origin | |
| dc.type | Journal Article | en_ZA |
| uct.type.filetype | Text | |
| uct.type.filetype | Image | |
| uct.type.publication | Research | en_ZA |
| uct.type.resource | Article | en_ZA |