Abstract
Eclogite xenoliths from the mantle have experienced a wide variety of processes and P-T conditions, many of which are recorded in the mineral compositions and textures. Exsolution of garnet from clinopyroxene is one such texture, occurring in a minority of mantle eclogites. New analyses of clinopyroxene and garnet of eclogite xenoliths from kimberlites at Bellsbank (South Africa) and Obnazhënnaya (Yakutia, Russia) are presented here, and these are combined with data from the literature. Exsolution of garnet from clinopyroxene is generally lamellar, although lens-shaped garnets are also present. Major- and trace-element characteristics show a wide range of compositions and include eclogite Groups A, B, and C. Rare-earth element (REE) concentrations of garnet and pyroxene were determined by SIMS, and the REE patterns are subtly different from those in “ordinary” eclogites. Differences include the absence of prominent Eu anomalies in samples of this study and differences in the slopes of chondrite-normalized REE patterns. It is possible that these “signatures” are unique to exsolved eclogites, a result of subsolidus elemental partitioning during exsolution. Some reconstructed whole-rock compositions are aluminuous; comparison with ordinary eclogites shows only minor differences, implying a similar origin. If the immediate precursor to the exsolved eclogites was a monomineralic pyroxenite, the excess aluminium was tied up in Tschermak's molecule, although the occasional presence of kyanite exsolution lamellae is indicative of a Ca-Eskola component. Reconstructed “pyroxenes” from kyanite- and corundum-rich samples contain unrealistic amounts of aluminium for mantle pyroxenes. A protolith (or parental pyroxene) “threshold” of ∼24% Al2O3 may exist, above which (as in a plagioclase cumulate) the final assemblage is kyanite- and/or corundum-bearing.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Aoki K-I, Fujimaki H, Kitamura M (1980) Exsolved garnet-bearing megacrysts from some South African kimberlites. Lithos 13:269–279
Ashwal LD, Morrison DA, Phinney WC, Wood J (1983) Origin of Archean anorthosites: evidence from the Bad Vermillion Lake anorthosite complex, Ontario. Contrib Mineral Petrol 82:259–273
Basu AR, Ongley JS, MacGregor ID (1986) Eclogites, pyroxene geotherm, and layered mantle convection. Science 233:1303–1305
Bobrievich AP, Smirnov GI, Sobolev VS (1960) The mineralogy of xenoliths of a grossular-pyroxene-disthene rock (grospydite) from the Yakutian kimberlites (in Russian) Geol Geofiz 3:18–24
Borley GD, Suddaby P (1975) Stressed pyroxenite nodules from the Jagersfontein kimberlite. Mineral Mag 40:6–12
Caporuscio FA, Smyth JR (1990) Trace element crystal chemistry of mantle eclogites. Contrib Mineral Petrol 105:550–561
Carswell DA, Dawson JB, Gibb FGF (1981) Equilibration conditions of upper-mantle eclogites: implications for kyanite-bearing and diamondiferous varieties. Mineral Mag 44:79–89
Coleman RG, Lee DE, Beatty LB, Brannock WW (1965) Eclogites and eclogites: their differences and similarities. Geol Soc Am Bull 76:483–508
Dawson JB (1980) Kimberlites and their xenoliths. Springer, Berlin Heidelberg New York
Desnoyers C (1975) ExsoIntions d'amphibole, de grenat et de spinelle dans les pyroxenes de roches ultrabasiques: peridoties et pyroxenolites. Bull Soc Fr Mineral Cristalogr 98:65–72
Freer R, Carpenter MA, Long JVP, Reed SJB (1982) “Null result” diffusion experiments with diopside: implications for pyroxene equilibria. Earth Planet Sci Lett 58:285–292
Gasparik T (1984) Experimentally determined stability of clinopyroxeneegarnet +corundum in the system CaO−MgO−Al2O3−SiO2. Am Mineral 69:1025–1035
Green DH (1966) The origin of “eclogites” from Salt Lake Crater Hawaii. Earth Planet Sci Lett 9:367–389
Griffin WL, Carswell DA, Nixon PH (1979) Lower-crustal granulites and eclogites from Lesotho, southern Africa. In: Boyd FR, Meyer HOA (eds) The mantle sample: inclusions in kimberlites and other volcanics, vol 2. Am Geophys Union, Washington, DC, pp 59–86
Flarte B, Gurney JJ (1975) Evolution of clinopyroxene and garnet in an eclogite nodule from the Roberts Victor kimberlite pipe, South Africa. Phys Chem Earth 9:367–387
Hays JF (1966) Lime-alumina-silica. Carnegie Inst Washington Yearb 65:234–239
Jagoutz E (1988) Nd and Sr systematics in an eclogite xenolith from Tanzania: evidence for frozen mineral equilibria in the continental lithosphere. Geochim Cosmochim Acta 52:1285–1293
Jagoutz E, Carlson RW, Lugmair GW (1980) Equilibrated ndunequilibrated Sr isotopes in mantle xenoliths. Nature 286:708–710
Kurat G, Palme H, Spettel B, Baddenhausen H, Hoffmeister H, Palme C, Wanke H (1980) Geochemistry of ultramafic xenoliths from Kapfenstein, Austria; evidence for a variety of upper mantle processes. Geochim Cosmochim Acta 44:45–60
Lappin MA (1978) The evolution of a grospydite from the Roberts-Victor mine, South Africa. Contrib Mineral Petrol 66:229–241
Lappin MA, Dawson BD (1975) Two Roberts-Victor cumulate eclogites and their re-equilibration. Phys Chem Earth 9:351–365
Lundberg LL, Crozaz G, McKay G, Zinner E (1988) Rare earth element carriers in the Shergotty meteorite and implications for its chronology. Geochim Cosmochim Acta 52:2147–2163
Lundberg LL, Crozaz G, McSween HY (1990) Rare earth elements in minerals of the ALHA 77005 shergottite and implications for its parent magma and crystallization history. Geochim Cosmochim Acta 54:2535–2547
MacGregor ID, Manton WI (1986) the Roberts-Victor ecologies: ancient oceanic crust. J Geophys Res 91:14063–14079
McCormick TC (1984) Crystal chemistry and breakdown reactions of aluminous mantle-derived omphacites. PhD dissertation, Arizona State Univ
Neal CR, Taylor LA (1990) Comment on “Mantle eclogites: evidence of igneous fractionation in the mantle” by JR Smyth, FA Caporuscio, and TC McCormick. Earth Planet Sci Lett 101:112–119
Neal CR, Taylor LA, Davidson JP, Holden P, Halliday AN, Nixon PH, Paces JB, Clayton RN, Mayeda TK (1990) Eclogites with oceanic crustal and mantle signatures from the Bellsbank kimberlite, South Africa, part 2: Sr, Nd, and O isotope geochemistry. Earth Planet Sci Lett 99:362–379
Oberti R, Caporuscio FA (1991) Crystal chemistry of clinopyroxenes from mantle eclogites: a study of the key role of the M2 site population by means of crystal-structure refinement. Am Mineral 76:1141–1152
O'Hara MJ, Yoder HS (1967) Formation and fractionation of basic magmas at high pressure. Scott J Geol 3:67–117
Pearson DG, Shirey SB, Carlson RW, Taylor LA (1992) Os isotope constraints of the petrogenesis of eclogite xenoliths. AGU 1992 Spring Meeting, Trans Am Geophys Union EOS 73:376
Sautter V, Harte B (1988) Diffusion gradients in an eclogite xenolith from the Roberts-Victor kimberlite pipe; 1: mechanism and evolution of garnet exsolution in Al2O3-rich clinopyroxene. J Petrol 29:1325–1352
Sautter V, Harte (1990) Diffusion gradients in an eclogite xenolith from the Roberts-Victor kimberlite pipe: (2) kinetics and implications for petrogenesis. Contrib Mineral Petrol 105:637–649
Shervais JW, Taylor LA, Lugmair GW, Clayton RN, Mayeda TK, Korotev RL (1988) Early Proterozoic oceanic crust and the evolution of subconinental mantle: ecologites and related rocks from southern Africa. Geol Soc Am Bull 100:411–423
Smyth JR, Caporuscio FA (1984) Petrology of a suite of eclogite inclusions from the Bobbejaan kimberlite, II: primary phase compositions and origin. In: Kornprobst J (ed) Kimberlites II: the mantle and crust-mantle relationships. Elsevier, Amsterdam, pp 121–131
Smyth JR, McCormick TC, Caporuscio FA (1984) Petrology of a suite of eclogite inclusions from the Bobbejaan kimberlite, I: two unusual corundum-bearing kyanite eclogites. In: Kornprobst J (ed) Kimberlites II: the mantle and crust-mantle relationships. Elsevier, Amsterdam, pp 121–132
Smyth JR, Caporuscio FA, McCormick TC (1989) Mantle eclogites: evidence of igneous fractionation in the mantle. Earth Planet Sci Lett 93:133–141
Sobolev NV (1977) Deep-seated inclusions in kimberlites and the problem of the composition of the upper mantle. Am Geophys Union, Washington, D.C.
Sobolev VS, Sobolev NV (1964) Xenoliths in kimberlites of northern Yakutia and the structure of the mantle. Dok Akad Nauk SSSR Ser Seol 158:22–26
Sobolev NV, Kuznetsova IK, Zyuzin NI (1968) The petrology of grospydite xenoliths from the Zagadochnaya kimberlite pipe in Yakutia. J Petrol 9:253–280
Stosch H-G (1982) Rare earth element partitioning between minerals from anhydrous spinel peridotite suites from Dreiser Weiher, West Germany. Geochim Cosmochim Acta 46:793–812
Taylor LA, Neal CR (1989) Eclogites with oceanic crustal and mantle signatures from the Bellsbank kimberlite South Africa, part I. mineralogy, petrography, and whole rock chemistry. J Geol 97:551–567
Taylor LA, Eckert JO, Neal CR, Crozaz G (1991) Crustal signatures in mantle eclogites: REE patterns of clinopyroxene and garnet by SIMS and INAA (abstract). 5th Int Kimb Conf extended abstr, CPRM Spec Publ 2/91, Brasilia, pp 410–414
Tuttle OF, Bowen NL (1958) Origin of granite in the light of experimental studies in the system NaAlSi3O8−KAlSi3O8−SiO2−H2O. Geol Soc Am Mem 74
Weiblen PW, Morey GB (1980) A summary of the stratigraphy, petrology, and structure of the Duluth Complex. Am J Sci 280-A:88–133
Zinner E, Crozaz G (1986) A method for the quantitative measurement of rare earth elements in the ion microprobe. In J Mass Spectrom Ion Processes 69:17–38
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Jerde, E.A., Taylor, L.A., Crozaz, G. et al. Exsolution of garnet within clinopyroxene of mantle eclogites: major- and trace-element chemistry. Contr. Mineral. and Petrol. 114, 148–159 (1993). https://doi.org/10.1007/BF00307752
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00307752