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Significance of Calcium-Rich Differentiates in Chondritic Meteorites Pyrite-Haematite Alteration As a Source of Colour in Red Be

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Significance of Calcium-Rich Differentiates in Chondritic Meteorites Pyrite-Haematite Alteration As a Source of Colour in Red Be Nature Vol. 255 June 5 1975 471 ' Walker, G. P. L., in Geodynamics of Iceland and the North Atlamic area (edit. elements makes confirmation of this impossible. Accepting by Kristjansson, L.), 189-201 (Reidel, Dordrecht, 1974). 9 Jakobsson, S. P., Lithos, 5, 365-386 (1972). this, it is likely that at least one planetary body had been 10 Sigurdsson H. Earth planet. Sci. Lett., 10, 129-135 (1970). 11 Ward, P. L., P~lmason, G., and Drake, C., J. geophys. Res., 74, 665-684 (1969). differentiated and partially fragmented so that its disrupted 12 Walker, G. P. L., in Geodynamics of lcel:md and the North Atlantic area (edit. material was incorporated into an L-group, chondritic, parent by Kristjansson, L.), 177-188 (Reidel, Dordrecht, 1974). 13 Walker, G. P. L., Q. Jl geol. Soc. Land., 119,29-60 (1963). body. Goodland has a short gas retention age which precludes 14 Einarsson, T., J. geophys. Res., 73, 7561-7576 (1968). 12 15 Hast, N., Tectonophysics, 8, 169-211 (1969). speculation about its early history ; the age of Bovedy is 16 Brander, J., and Wadge, G., Nature, 244,496-498 (1973). currently under investigation in the hope that it will provide a 17 Johnston, G. L .. in Geodynamics of Iceland and the North Atlantic area (edit. by Kristjansson, L.), 49-62 (Reidel, Dordrecht 1974). younger limit to the time of differentiation of the parent of its 18 Serson, P. H., Hannaford, W., and Haines, G. V., Science, 162, 355-357 (1968). 19 Sigurdswn, H., Rit. visindafjelags islendinga, 38, 162-179 (1967). calcic feldspar glasses. There seem to have been two distinct periods of heating among planetary bodies in the early Solar System. The first caused the melting and differentiation which led to the pro­ duction of calcic plagioclase on a planetary body. Portions of Significance of calcium-rich this were subsequently available for incorporation into the differentiates in chondritic meteorites chondritic parent body which was at this time still relatively undifferentiated. The second heating event caused the meta­ KNOWLEDGE of conditions in the early Solar System is based morphism4·11 of at least one (L-group) ordinary chondrite largely on results from the study of meteorites. We have found parent body. Differences in the initial 87Srj86Sr ratios betw~en in two chondritic meteorites 'chondrules' or inclusions con­ the metamorphosed (H6) chondrite Guarena and the eucntes taining material with the composition of a calcic plagioclase. are also indicative of the occurrence of two heating events We believe that this may be evidence of differentiation on a separated in time'3• planetary body before compaction of the chondritic parent Four general sources of energy have been proposed to body(ies) occurred (see also ref. I). account for these heating events, namely: the release of The Bovedy Meteorite fell in Northern Ireland in 1969 accretional energy, the decay of short lived radionuclides, the (refs 2 and 3) and is an unequilibrated ordinary chondrite of decay of long lived radionuclides, and intense solar the low iron group (L3 in the classification of Van Schmus and 14 radiation • At least two of these are required to account for 4 Wood ). Microprobe analysis of the meteorite showed that one the two heating cycles outlined above, as each could have large chondrule, 4 mm in diameter, comprises phenocrysts of been effective once only. Whichever combination of heat low calcium-pyroxene (Fs17_ 28) with included grains of olivine sources was responsible for these heating events, evidence for (Fa24) and a clear isotropic interstitial phase with the com­ the earlier should best be seen in the least metamorphosed position of a plagioclase (An85). Part of a large bleb, approxi­ chondrites. It is in these meteorites that the products of the mately 2 mm across, occurring on another specimen of the earlier planetary differentiation should be best preserved. We meteorite also has the composition of plagioclase (An 8a_ 88): suggest that this preservation has occurred and can be seen in an X-ray powder photograph showed no plagioclase lines, the calcium-rich glass in the Bovedy Meteorite and also, indicating that this bleb is mainly glass. It does, however, though less certainly, in the calcium-rich material of the contain minor whitlockite and an opaque mineral, probably chondrite Goodland. chromite, though these did not show up on the X-ray photo­ We thank D. Y. Jerome and J. C. Philippot for the neutron graph but were observed during the microprobe work. A 2.55-mg activation analysis, and I. G. Meighan for providing us with sample of this bleb was analysed for the rare earth elements by the Bovedy sample in which he pointed out the glassy bleb 5 an instrumental neutron activation technique and was found (now BM 1972,233). to have a remarkably high, positive europium anomaly. The R. HUTCHISON low abundances of rare earth elements and the magnitude of A. L. GRAHAM the europium anomaly are similar to those observed in lunar Department ofMineralogy, 6 7 anorthosites • but differ from those of the plagioclases in both 8 9 10 British Museum (Natural History), the eucritic meteorites • and the lunar mare basalts (see Cromwell Road, Table 1). LondonSW75BD, UK The second chondritic meteorite, Goodland, was found in Kansas in 1923 and is classified in the same low iron group as Received February 28; accepted April28, 1975. Bovedy but it is petrographically a type 44 and is almost 1 Hutchison, R. Nature phys. Sci., 240,58 (1972). equilibratedn. A chondrule in this stone contains some slightly 2 Meighan I. G. and Doughty, P. S., Nature, 223,24(1969). 3 Andrews: A. D:, Rackham, T. W., and Wayman, P. A., Nature, 225,727 (1969). birefringent material with the composition of a plagioclase 4 Van Schmus, W. R., and Wood,J. A., Geochim. cosmoch1m. Acta,31, 747 (1967). (An 85) interstitial to crystals of olivine (Fa25) enclosed in s Jerome, D. Y., and Philippot, J. C., Geochim. cosmoch1m. Acta,37, 909 (1973). 6 Nakamura, N., Masuda, A., Tanaka, T., and Kurasawa, H., Proc.fourth Lunar orthopyroxene (Fs16). Sci. Con[., Geochim. cosmochim. Acta. Supp/., 4, 1407 (1973). By analogy with the lunar surface, the calcic plagioclase 7 Philpotts, J. A., eta/., ibid., 4, 1427 (1973). s Schnetzler, C. C., and Philpotts, J. A., m Meteonte Research (ed1t. by M1Uman, material of Bovedy probably formed by igneous differentiation P.M.), (Reidel, Dordrecht, 1969). 9 Mason, B., and Graham, A. L., Smithsonian Contnb. Earth Scz., .3, I (1970). on a planetary scale. The same could be true of the similar 10 Schnetzler, C. C., and Philpotts, J. A., Proc. second Lunar Scz. Con[., Geochzm. material in Goodland but the absence of data on the rare earth cosmochim. Acta. Suppl., 2, 1101 (1971). 11 Dodd, R. T., Van Schmus, W. R., and Koffman, D. M., Geochzm. cosmochzm. Acta, 31,921 (1967). 12 Heymann, D., icarus, 6, 189 (1967). u Wasserburg, G. J., Papanastassiou, D. A., and Sanz, H. G., Earth planet. Sc1. Table 1 Rare earth element concentrations (p.p.m.) in Bovedy glass Lett., 7, 33 (1969). ) 6 10 compared with those of lunar and meteoritic samples - 14 Wasson,J. T.,Meteorites,181-205(Spnnger,Berlm,1974. Lunar Plagioclases Plagioclases anorthosites, from lunar from eucrites Bovedy bulk data mare basalts (average of glass (average (average 3) of 10) of 12) Pyrite-haematite alteration as Lanthanum 0.25 0.26 7.2 a source of colour in red beds and regolith Samarium 0.12 0.084 2.4 0.55 Europium 1.35 0.95 3.2 1.1 THE colour in red beds and red soils is generally acknowledged Ytterbium 0.06 0.051 1.6 0.23 to be caused by the presence of finely dispersed haematite or Lutetium 0.0068 0.0085 0.22 hydro-haematite. The origin of the haematite remains, h~w­ Europium ever, in disputet-a. In the case of present-day red weather~ng anomaly +33 +31 +3.6 +6.0 in the tropics and subtropics, the haematite or other colounng © 1975 Nature Publishing Group.
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