Intensive variables in kimberlite magmas, Lac de Gras, Canada and implications for diamond survival
Intensive variables in kimberlite magmas, Lac de Gras, Canada and implications for diamond survival
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DOI：
10.1093/petrology/egh031
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发表时间：
2004-09-01
影响因子：
3.9
通讯作者：
Canil, D
中科院分区：
文献类型：
--
作者：
Fedortchouk, Y;Canil, D
根据加拿大中部奴隶省Leslie、Aaron、Grizzly和Torrie金伯利岩管橄榄石斑晶中的氧化物，估算了金伯利岩岩浆的结晶温度(T)和氧逸度（fO(2)）。在假设压力为1.0 GPa时，橄榄石-铬铁矿对记录的结晶温度为1030-1170℃+/- 50℃，平均温度接近1080℃。在此温度下，共存橄榄石和铬铁矿的fO(2)比镍-镍氧化物（NNO）缓冲液的氧化程度低2-3 log单位，氧化活性受到蒙脱石存在的限制。与橄榄石斑晶边缘平衡的橄榄石、大块岩石和液体成分的质量平衡表明，这些金伯利岩是由含有11-28 mol %液体、10 mol %早期沉淀橄榄石斑晶和62-79 mol %地幔异晶橄榄石的岩浆结晶而成的。计算的T-fO(2)值表明，Lac de Gras金伯利岩中的金刚石可能在石墨稳定场内运移到地表，但靠近石墨- co2边界。
Crystallization temperatures (T) and oxygen fugacities (fO(2)) of kimberlite magma are estimated from oxides included in olivine phenocrysts from the Leslie, Aaron, Grizzly and Torrie kimberlite pipes in the central Slave Province, Canada. Crystallization temperatures recorded by olivine-chromite pairs at an assumed pressure of 1.0 GPa are 1030-1170degrees C +/- 50degrees C, with a mean of similar to1080degrees C. At these temperatures, the fO(2) of coexisting olivine and chromite is 2-3 log units less oxidized than the nickel-nickel oxide (NNO) buffer at a silica activity limited by the presence of monticellite. Mass balance of olivine, bulk-rock and liquid compositions in equilibrium with olivine phenocryst rims suggests that these kimberlites represent crystallization from a magma with 11-28 mol % of liquid, 10 mol % of earlier precipitated olivine phenocrysts and 62-79 mol % of mantle xenocryst olivine. The calculated T-fO(2) values indicate that diamonds entrained in the Lac de Gras kimberlites were probably transported to the surface within the stability field of graphite but close to the graphite-CO2 boundary.