- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 1 (36.99 KiB) Viewed 16 times
- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 2 (43.22 KiB) Viewed 16 times
- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 3 (55.91 KiB) Viewed 16 times
- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 4 (55.91 KiB) Viewed 16 times
- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 5 (45.95 KiB) Viewed 16 times
- A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 6 (23.48 KiB) Viewed 16 times
Temperature (°C) 600 700 800 900 1000 1100 1200 1300 1400 1 SIO2 TiO2 Al2O3 Mgo Сао Mno Feo Nazo Total o CPX 54.59 0.38 6.77 12.08 14.29 0.12 6.23 4.22 98.68 6 GA 39.90 0.30 22.91 14.68 4.22 0.52 17.17 0.08 99.78 12 N 3 Graphite Pressure (GPa) 6 Diamond 7 Si Ti AI Mg Ca Mn Fe Cratonic conductive geotherm 1.9910 2.9504 0.0083 0.0133 0.2928 2.0090 0.6566 1.6178 0.5584 0.3344 0.0037 0.0326 0.1900 1.0618 0.2984 0.0115 3.9993 8.0308 8 00 40mW/m2 9 9 Na Total
A diamondiferous eclogite xenolith from a kimberlite contains both garnet (GA) and omphacitic clinopyroxene (CPX). The compositions of these minerals are listed in the table below, along with the cation formulas. GA Temperature (°C) 600 700 800 900 1000 1100 1200 1300 1400 1 SIO2 TiO2 Al2O3 Mgo Cao Mno Feo Nazo Total O CPX 54.59 0.38 6.77 12.08 14.29 0.12 6.23 4.22 98.68 6 39.90 0.30 22.91 14.68 4.22 0.52 17.17 0.08 99.78 2 3 4 12 Graphite Pressure (GPa) 5 Diamond CO 7 Cratonic conductive geotherm Si Ti ΑΙ Mg Ca Mn Fe Na Total 1.9910 2.9504 0.0083 0.0133 0.2928 2.0090 0.6566 1.6178 0.5584 0.3344 0.0037 0.0326 0.1900 1.0618 0.2984 0.0115 3.9993 8.0308 8 40mW/m 9
The diagram above is a pressure-temperature plot showing a conductive geotherm (green line) for the cratonic mantle lithosphere through which the host kimberlite erupted. It which was determined using data from garnet peridotite xenoliths. The univariant reaction graphite diamond is also shown (blue line). (a) Assuming the eclogite xenolith was originated from the mantle lithosphere at some pressure-temperature condition lying on the geotherm, before it was entrained in the kimberlite, what is the minimium pressure in GPa from which it could have originated? (4 marks) (b) Calculate the mole fraction of grossular (Xco Gt) in the garnet from this eclogite. Show your working. (4 marks) (c) Calculate the Ka for Fe-Mg distribution between garnet and the clinopyroxene in the eclogite. Ks = (Fe/Mg)/(Fe/Mg)cex (4 marks)
(d) Using the geothermometer formula below from Ellis and Green (1979), calculate the minimum temperature at which the eclogite equilibrated in the lithosphere, using your minimum pressure estimate from above. Express the answer in °C (note that 0°C = 273.15 K and that 1 GPa = 10 kb) (8 marks) 3104 X6 + 3030 + 10.86 P(kb) T("K)= In K, +1.9034 Ca 1