Abstract
The diamondiferous Renard kimberlites are located in the eastern portion of the Superior Province, in the northern Otish Mountains of Quebec. To better constrain the cratonic lithospheric mantle beneath Renard, 116 microxenoliths and xenocrysts, and 56 diamonds were collected.
Based on the single clinopyroxene geothermobarometer [1] a cold ‘Slave-type’ geotherm was present during Neoproterozoic kimberlite emplacement. Common Pb dating of clinopyroxene xenocrysts indicates an age of ~2.7 Ga for the underlying lithospheric mantle, broadly coinciding with a major phase of global continental crust generation.
Compositionally, garnet xenocrysts mainly fall in the on craton lherzolite field (G9A of [2]). Considerable variability in the chondrite normalized trace element patterns of the peridotitic garnets is observed and three principal patterns have been identified: sinusoidal, humped, and sloped. Sinusoidal patterns follow the fluid metasomatism trend of [3] whilst garnets with humped patterns fall on a melt metasomatic trend. Sloped patterns fall along a trend of increasing Y with little to no associated increase in Zr, a trend not observed in the Kaapvaal samples of [3].
Calculated REEN patterns of the metasomatising agents indicate that sinusoidal patterns likely reflect metasomatism by a highly fractionated fluid. The agent associated with sloped patterns is similar to typical mantle melts. Evolution of this melt through interaction with garnet peridotite wall rocks
produced the metasomatic agent reflected by humped garnet patterns.
Renard diamonds have nitrogen contents and aggregation states similar to worldwide data. Two distinct inclusion assemblages have been determined: A peridotitic (olivine, Mg-chromite and a G10 garnet), and an SiO2 assemblage. The latter may represent an eclogitic silica rich source or a peridotitic source with SiO2 forming during localised carbonation reactions along veins.
Based on the single clinopyroxene geothermobarometer [1] a cold ‘Slave-type’ geotherm was present during Neoproterozoic kimberlite emplacement. Common Pb dating of clinopyroxene xenocrysts indicates an age of ~2.7 Ga for the underlying lithospheric mantle, broadly coinciding with a major phase of global continental crust generation.
Compositionally, garnet xenocrysts mainly fall in the on craton lherzolite field (G9A of [2]). Considerable variability in the chondrite normalized trace element patterns of the peridotitic garnets is observed and three principal patterns have been identified: sinusoidal, humped, and sloped. Sinusoidal patterns follow the fluid metasomatism trend of [3] whilst garnets with humped patterns fall on a melt metasomatic trend. Sloped patterns fall along a trend of increasing Y with little to no associated increase in Zr, a trend not observed in the Kaapvaal samples of [3].
Calculated REEN patterns of the metasomatising agents indicate that sinusoidal patterns likely reflect metasomatism by a highly fractionated fluid. The agent associated with sloped patterns is similar to typical mantle melts. Evolution of this melt through interaction with garnet peridotite wall rocks
produced the metasomatic agent reflected by humped garnet patterns.
Renard diamonds have nitrogen contents and aggregation states similar to worldwide data. Two distinct inclusion assemblages have been determined: A peridotitic (olivine, Mg-chromite and a G10 garnet), and an SiO2 assemblage. The latter may represent an eclogitic silica rich source or a peridotitic source with SiO2 forming during localised carbonation reactions along veins.
| Original language | English |
|---|---|
| Pages (from-to) | A439-A439 |
| Number of pages | 1 |
| Journal | Geochimica et Cosmochimica Acta |
| Volume | 74 |
| Issue number | 12, Supplement |
| DOIs | |
| Publication status | Published - Jun 2010 |
| Externally published | Yes |
| Event | Goldschmidt Conference (20th : 2010) - Knoxville, United States Duration: 13 Jun 2010 → 18 Jun 2010 |