A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 1 (36.99 KiB) Viewed 18 times
A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 2 (43.22 KiB) Viewed 18 times
A Diamondiferous Eclogie Xenolith From A Kimberlite Contains Both Gamet Ga And Omphacitic Clinopyroxene Cpx The Com 3 (21.15 KiB) Viewed 18 times
A diamondiferous eclogie xenolith from a kimberlite contains both gamet (GA) and omphacitic clinopyroxene (CPX). The compositions of these minerals are listed in the table below, along with the cation formulas CPX SIO 54.59 Temperature (°C) 600 700 800 900 1000 1100 1200 1300 1400 TIO AJO MgO СО Mno Feo Na o Total O 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 Pressure (GPa) 7 Si TI AI 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 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 gamet peridotte xenoliths. The univariant reaction graphite diamond is also shown (blue line) (a) Assuming the eclogite xenolith was originated from the mandle thosphere at some pressure-temperature condition lying on the geotherm, before was entrained in the kimberlite, what is the minimum pressure in GPa from which it could have originated? (4 marks) (b) Calculate the mole fraction of grossular (X) in the garnet from this eclogte. Show your working (4 marks) (c) Calculate the K for Fe-Mg distribution between game and the clinopyromene in the eclogiteko - (Fe/go/Fe Mcpx (4 marks)
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
(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) 3104X6 + 3030+10.86 P(kb) T(K) In K, +1.9034
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