Olivine in an_unexpected_location_on_vesta_surface


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Olivine in an_unexpected_location_on_vesta_surface

  1. 1. LETTER doi:10.1038/nature12665 Olivine in an unexpected location on Vesta’s surface E. Ammannito1, M. C. De Sanctis1, E. Palomba1, A. Longobardo1, D. W. Mittlefehldt2, H. Y. McSween3, S. Marchi1,4, M. T. Capria1, F. Capaccioni1, A. Frigeri1, C. M. Pieters5, O. Ruesch6, F. Tosi1, F. Zambon1, F. Carraro1, S. Fonte1, H. Hiesinger6, G. Magni1, L. A. McFadden7, C. A. Raymond8, C. T. Russell9 & J. M. Sunshine10 Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System1. Only a few of these meteorites, the orthopyroxenerich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume2. Olivine was tentatively identified on Vesta3,4, on the basis of spectral and colour data, but other observations did not confirm its presence5. Here we report that olivine is indeed present locally on Vesta’s surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks6–8. Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common7,9 surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivinerich material suggest a complex evolutionary history for Vesta. The Visible and Infrared Mapping Spectrometer (VIR) on board NASA’s Dawn spacecraft10 has been used in a global search for olivine on the Vestan surface (Supplementary Information). VIR revealed a global-scale dichotomy7,8 (Fig. 1), with diogenite-rich material exposed predominantly in the deeply excavated southern hemisphere. Magmaocean models for Vesta’s differentiation yield eucritic crust overlying a diogenite layer, with olivine-rich mantle rocks and a metallic core in the deep interior11,12. These models predict mineralogical variations on a large vertical scale, with olivine-rich cumulates occurring below olivine-poor diogenite. Alternative models, more consistent with the diverse trace-element geochemistry of diogenites, posit that diogenitic plutons occur at the crust–mantle boundary or within the basaltic crust13,14, resulting in association of olivine-rich and orthopyroxenerich diogenites mixed on smaller scales. VIR spectra did not provide definitive evidence for olivine within the two large basins in the southern hemisphere6–8. However, typical olivine-bearing diogenites cannot be easily distinguished spectrally from olivine-free diogenites1 because of the difficulty of identifying olivine at low concentrations in the presence of abundant orthopyroxene15,16; thus, olivine may be present within the southern basins but only in modest amounts (=25 vol%, comparable to that reported for most olivine-bearing diogenites2). Unexpectedly, olivine-rich areas have now been discovered in the northern hemisphere. The VIR spectra of ejecta surrounding Arruntia crater and the nearby Bellicia crater (Fig. 2) reveal clear olivine signatures (Fig. 3a), with the 1-mm band (hereafter BI) centred at slightly longer wavelength than the average Vesta spectrum, and the centre of the 2-mm band (hereafter BII) is unchanged. Laboratory data demonstrate that pyroxene features dominate the spectra of olivine–pyroxene mixtures15,16. Only olivine contents of $50 vol% produce a shift in the centre of BI15,16, and the centre of BII remains unchanged with admixture of olivine (Fig. 3b). The three parameters we used to interpret olivine–pyroxene mixtures are the positions of the respective centres of BI and BII and variations in the band area ratio16–18 (BAR). In the BI–BII diagram (Fig. 3c), Bellicia and Arruntia data lie distinctly off the linear HED trend, with high values for BI centres that reveal the presence of olivine. Because the BII-centre position reflects the composition of pyroxene in olivine–pyroxene mixtures and, in the Bellicia– Arruntia area, lies between those of eucrites and diogenites, we have determined that the olivine in this area is associated with the mixed lithology, howardite. This situation is distinct from the olivine occurrence in HED meteorites, where only very small amounts of olivine (#3 vol%) occur in howardites19 (with the exception of the paired PCA 02 howardites, which nevertheless contain at most ,7% olivine20). Olivine in HED meteorites occurs mainly in diogenites, which range from orthopyroxenite to harzburgite to dunite21 (Extended Data Fig. 1 and Extended Data Table 1). This observation is consistent with the interpretation that HED meteorites sample lithologies from Vesta’s southern hemisphere that are associated with material ejected from the two large basins22. The Vestan olivine-rich spectra and derived parameters are consistent with a mixture of 50–80-vol% olivine with pyroxene occurring over a broad area of hundred-kilometre size, encompassing both Bellicia crater and Arruntia crater. Olivine-rich material occurs as several high-albedo patches hundreds of metres across located high on the walls of Bellicia crater (Fig. 2b–d). Some of these patches have positive relief compared with the adjacent wall, suggesting more competent material (Fig. 2f). Several fresh small craters (with diameters of order 100 m) superposed on Bellicia ejecta also have high-albedo annuli with olivine spectral signatures (Fig. 2e). Olivine-rich material at Arruntia crater is most common in the ejecta blanket (Fig. 2g, h). The geological setting suggests that olivine-rich lithologies occur as a bright layer partly obscured by slump deposits and regolith mixing of the surface. Unlike its occurrence in HED meteorites, mainly as a small volume fraction in diogenites, here a lithology rich in olivine ($50 vol%) in patches hundreds of metres in size is mixed with howarditic regolith. The detected olivine-rich materials have characteristics at odds with pre-Dawn ideas about Vestan olivine: they are not associated with diogenites, they are located far from deeply excavated terrains in the southern hemisphere and they occur in large patches extending hundreds of metres. Both exogenic and endogenic origins are possible. An exogenic origin seems unlikely, considering how uncommon xenocrystic (chondritic) olivine is in howardites20 and the rarity of olivine-rich asteroids in the main belt23 (Supplementary Information). Also, the large patches seem inconsistent with the fact that impactors are normally disaggregated. On the other hand, endogenic olivine is a component of Vesta, as 1 Istituto di Astrofisica e Planetologia Spaziali, INAF, 00133 Rome, Italy. 2NASA Johnson Space Center, Houston, Texas 77058, USA. 3Department of Earth and Planetary Sciences, University of Tennessee, ¨ Knoxville, Tennessee 37996, USA. 4NASA Lunar Science Institute, Boulder, Colorado 80302, USA. 5Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA. 6Institut fur ¨ ¨t ¨ ¨ Planetologie, Westfalische Wilhelms-Universita Munster, 48149 Munster, Germany. 7NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. 8Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA. 9University of California, Los Angeles, California 90095, USA. 10Department of Astronomy, University of Maryland, College Park, Maryland 20742, USA. 0 0 M O N T H 2 0 1 3 | VO L 0 0 0 | N AT U R E | 1 ©2013 Macmillan Publishers Limited. All rights reserved
  2. 2. RESEARCH LETTER 60º W 120º W 180º W 240º W 300º W 60º N 60º N Bellicia Arruntia Latitude 30º N * * 30º N 0º N 0º N Veneneia 30º S 30º S Rheasilvia 60º S 60º S 60º W 120º W 180º W 240º W 300º W Longitude Figure 1 | HED meteorite distribution map. Lithological map of Vesta’s surface derived from VIR spectra8,10 using all the data acquired during the Dawn orbital phases: red for diogenite, green for howardite, blue for eucrite, with overlapping fields of yellow for diogenitic howardite and cyan for eucritic howardite. The regions with magnesium-rich pyroxenes (red and yellow) correspond to a diogenite-dominated lithology. The distribution shows that the southern hemisphere is more rich in magnesiac pyroxene with areas of nearly pure diogenite, whereas the equatorial region and the northern hemisphere are more basalt-rich (eucritic). Howardites—brecciated mixtures of these lithologies—are the most abundant rocks observed on Vesta’s surface. Arruntia and Bellicia craters are indicated, as well as the rim of Rheasilvia and Veneneia basins (dashed line). Howardites enriched in diogenites are visible in the ruined northern basins and in Rheasilvia (see Supplementary Information for further details and Extended Data Fig. 2). demonstrated by its occurrence in diogenites and even in the PCA 02 howardites, where the target rock for olivine-bearing impact melts in these breccias was olivine-rich diogenite20. Two main models for the origin of endogenic olivine are serialmagmatism models that consider fractional crystallization in diogenite plutons emplaced at the base of, or within, the Vestan crust13,14, and magma-ocean models that predict an olivine-dominated mantle at depths of .20–40 km underlying an orthopyroxene-dominated (diogenitic) lower crust11,12. In the serial-magmatism hypothesis, a mixed region of eucrite, diogenite and olivine-rich material could have been sampled by impacts that did not excavate to great depth. The magma-ocean hypothesis a Arruntia h Arruntia g 5 5 6 f Bellicia 1 b d 2 1 c e 2 1 3 4 4 Bellicia 2 | N AT U R E | VO L 0 0 0 | 0 0 M O N T H 2 0 1 3 ©2013 Macmillan Publishers Limited. All rights reserved Figure 2 | Olivine-rich region in the visible and near-infrared wavelengths. a, Infrared mosaics of VIR data (longitudes 30u–77u W, latitudes 25u–60u N). Bellicia crater (38 km 3 43 km, longitude 48u W, latitude 38u N) and Arruntia crater (,11-km diameter, longitude 72u W, latitude 40u N) are enclosed in black squares. Coordinates in Claudia system. The mosaics have been made using VIR data from different observation cycles. The false colours (red, 1.25 mm; green, 1.93 mm; blue, 1.64 mm), emphasize in green the olivine-rich region. b, Stretched view of Bellicia crater in false colours (same as in a) showing in green the purest olivine exposures. c–f, Framing Camera images of Bellicia crater. c, Image (,65 m per pixel) highlighting example locations of bright materials carrying the olivine-rich spectral signature (arrows). Numbered arrows show (1) olivine-rich material associated with a slump deposit downslope from a small crater; (2) comingled bright and dark materials on the crater wall; (3) relatively dark material adjacent to olivine-rich material; and (4) small craters on Bellicia ejecta that expose olivine-rich material. d, Image (,22 m per pixel) showing details of a portion of the crater wall. e, Image (,65 m per pixel) highlighting the small craters with olivine annuli. f, Image (,22 m per pixel) showing details of (1) portion of the crater wall. g, h, Framing Camera images of Arruntia crater. g, Image (,22 m per pixel) showing locations of concentrations of olivine-rich material (arrows) in Arruntia ejecta. h, Image (,65 m per pixel) showing details of crater wall geology. Lenses of bright material are present (5), and dark materials are comingled with bright materials (6).
  3. 3. a 1.1 Continuum-removed reflectance LETTER RESEARCH 1 0.9 0.8 0.7 Average Vesta 0.6 Olivine-rich area 0.5 0.4 0.65 0.85 1.05 1.25 1.45 1.65 1.85 2.05 2.25 Wavelength (μm) Continuum-removed reflectance b 1.1 1 0.9 0.8 0.7 0.6 0.5 100% Ortho-Pyx 0.4 90% Ortho-Pyx/10% Ol 30% Ortho-Pyx/70% Ol 0.3 70% Ortho-Pyx/30% Ol 10% Ortho-Pyx/90% Ol 50% Ortho-Pyx/50% Ol Olivine rich 0.2 0.65 0.85 1.05 1.25 1.45 1.65 1.85 2.05 2.25 Wavelength (μm) c 0.98 Ol/Ortho-Pyx Olivine-rich area +Olivine 0.97 Test area Bellicia walls Diogenite 0.96 BI centre (μm) Figure 3 | Spectral characteristics of the olivine-rich areas. a, Continuumremoved average Vestan spectrum and continuum-removed spectrum of the olivine-rich area in Bellicia. Olivine-rich spectra show a large asymmetric BI, typical of olivine-rich mixtures, whereas BII indicates that pyroxene is also present. The BI centre is at a slightly longer wavelength with respect the average spectrum, but the BII centre does not shift, as would be the case for iron-rich pyroxenes typical of eucrites or for high-calcium clinopyroxenes. b, Coloured lines show spectra of mixtures of olivine (Ol) and orthopyroxene (Ortho-Pyx) (data from the RELAB database) and the green points show the spectrum of the olivine-rich area. Laboratory olivine spectra exhibit only a broad, asymmetric 1-mm feature due to the overlapping of three individual absorptions29, whereas orthopyroxene exhibits two well-defined, symmetric absorptions near 1 mm and, respectively, 2 mm (refs 17, 30). Spectra of mixtures of olivine–orthopyroxene show that large olivine contents (.50%) produce distortion of the band shape near 1 mm from that of pure pyroxene. More sensitive indications of olivine in a mixture are a shallow depression near 1.3 mm and a reduction in depth of BII pyroxene absorption. c, Scatter plot of band centres. HED meteorite data are represented as coloured circles and lie on a linear correlation trend: eucrites and diogenites data are well separated, with the howardite data between them. For olivine–orthopyroxene mixtures (30– 70%, 50–50%, 70–30%; orange squares), the BI centre shifts towards longer wavelengths for increasing olivine content as illustrated by the arrow, but little or no shift is registered in the BII centre. The olivine-rich area inside Bellicia (green squares), Bellicia walls (brown cross) and a control area nearby Bellicia (cyan cross) are also represented. The olivine-rich points scatter above the HED meteorite trend and separate from the control area, which lies in the HED meteorite field. The Bellicia walls data lie between the olivine-rich area and the control area, suggesting a mixing of both. Howardite Eucrite 0.95 0.94 0.93 0.92 –Olivine 0.91 1.88 1.9 1.92 1.94 1.96 1.98 2 2.02 BII centre (μm) implies that mantle olivine would be excavated only by large, basinforming impacts. In the Bellicia–Arruntia region, we see patches of nearly pure olivine, hundreds of metres in size, in a background of howarditic material that suggest a large olivine-dominated source, with coherent sub-kilometresize ejecta. The serial-magmatism model envisions smaller scales of petrologic variation14,24, suggesting a mixed lithology of olivine and orthopyroxene that is not observed. The occurrence of several olivine spots a few hundreds of metres across, as seen in the walls of Bellicia, seems hard to reconcile with the plutonic origin. In the magma-ocean model, the Rheasilvia basin, superimposed on the older Veneneia25,26 basin, could have excavated and redistributed mantle material across Vesta27. The mineralogical diversity of the equatorial regions versus southern regions7,8 indicates that the lower crust and upper mantle, which are dominated by diogenitic material, were exposed by these impacts and were deposited as an extensive area of Rheasilvia ejecta in the northwest direction (Fig. 1), but most probably not extending to the Bellicia–Arruntia region. The presence of the olivine in the hemisphere opposite the large southern basins raises the question of antipodal focusing of energy leading to excavation of olivine-rich materials from depth. However, a large, high-velocity metallic core, such as in Vesta1, should defocus and deflect the energy away from the collision28. Thus, the olivine is probably not due to antipodal excavation. Diogenite-rich materials in the northern regions are concentrated in an area broadly corresponding to a 180-km ruined crater25 near Bellicia and in other large craters farther north (Fig. 1). Thus, the northern diogenitic material might have been ejected by these other ancient large impacts. However, the depths of the old basins near Bellicia and Arruntia are 10 and 15 km (ref. 25), respectively, possibly making the basins too shallow to reach the mantle. A generalized geologic history for these olivine-rich materials could be as follows: ancient large impacts excavated and incorporated large blocks of diogenite-rich and olivine-rich material into the eucritic crust, and subsequent impacts exposed this olivine-rich material in Arruntia and Bellicia. This produced olivine-rich terrains in a howarditic background, with diogenite-rich howardites filling nearby, eroded, older basins. The large exposures of olivine-rich material and their association with howardite may favour a magma-ocean model for the origin of the olivine. However, the apparent absence of olivine concentrations in Rheasilvia, where the excavation depth is greater, may suggest that the internal distribution of lithologies was heterogeneous, perhaps supporting the serial-magmatism model, or that the crust–mantle boundary was deeper in the region excavated by Rheasilvia than in the Bellicia– Arruntia region. In any case, the lack of pure olivine in the southern deeply excavated basins and its unexpected discovery in the northern hemisphere of Vesta indicate a more complex evolutionary history than inferred from pre-Dawn models. Online Content Any additional Methods, Extended Data display items and Source Data are available in the online version of the paper; references unique to these sections appear only in the online paper. Received 10 April; accepted 13 September 2013. Published online 6 November 2013. 1. Russell, C. T. et al. Dawn at Vesta: testing the protoplanetary paradigm. Science 336, 684–686 (2012). 0 0 M O N T H 2 0 1 3 | VO L 0 0 0 | N AT U R E | 3 ©2013 Macmillan Publishers Limited. All rights reserved
  4. 4. RESEARCH LETTER 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. Beck, A. W. & McSween, H. Y. Diogenites as polymict breccias composed of orthopyroxenite and harzburgite. Meteorit. Planet. Sci. 45, 850–872 (2010). Gaffey, M. J. Surface lithologic heterogeneity of asteroid 4 Vesta. Icarus 127, 130–157 (1997). Binzel, R. P. et al. Geologic mapping of Vesta from 1994 Hubble Space Telescope Images. Icarus 128, 95–103 (1997). Li, J. Y. et al. Photometric mapping of asteroid (4) Vesta’s southern hemisphere with Hubble Space Telescope. Icarus 208, 238–251 (2010). McSween, H. J. et al. Composition of the Rheasilvia basin, a window into Vesta’s interior. J. Geophys. Res. 118, 335–346 (2013). De Sanctis, M. C. et al. Spectroscopic characterization of mineralogy and its diversity across Vesta. Science 336, 697–700 (2012). Ammannito, E. et al. Vestan lithologies mapped by the visual and infrared spectrometer on Dawn. Meteorit. Planet. Sci. http://dx.doi.org/10.1111/ maps.12192 (13 September 2013). De. Sanctis, M. C. et al. Vesta’s mineralogical composition as revealed by the visible and infrared spectrometer on Dawn. Meteorit. Planet. Sci. http://dx.doi.org/ 10.1111/maps.12138 (8 July 2013). De Sanctis, M. C. et al. The VIR spectrometer. Space Sci. Rev. 163, 329–369 (2011). Righter, K. & Drake, M. J. A magma ocean on Vesta: core formation and petrogenesis of eucrites and diogenites. Meteorit. Planet. Sci. 32, 929–944 (1997). Ruzicka, A., Snyder, G. A. & Taylor, L. A. Vesta as the howardite, eucrite and diogenite parent body: implications for the size of a core and for large-scale differentiation. Meteorit. Planet. Sci. 32, 825–840 (1997). Barrat, J.-A. et al. Relative chronology of crust formation on asteroid Vesta: insights from the geochemistry of diogenites. Geochim. Cosmochim. Acta 74, 6218–6231 (2010). Mittlefehldt, D. W. Petrology and geochemistry of the Elephant Moraine A79002 diogenite: a genomict breccia containing a magnesian harzburgite component. Meteorit. Planet. Sci. 35, 901–912 (2000). Singer, R. B. Near-infrared spectral reflectance of mineral mixtures: systematic combinations of pyroxenes, olivine, and iron oxides. J. Geophys. Res. 86, 7967–7982 (1981). Cloutis, E. A. et al. Calibration of phase abundance, composition, and particle size distribution for olivine–orthopyroxene mixtures from reflectance spectra. J. Geophys. Res. 91, 11641–11653 (1986). Adams, J. B. Visible and near-infrared diffuse reflectance spectra of pyroxenes as applied to remote sensing of solid objects in the solar system. J. Geophys. Res. 79, 4829–4836 (1974). Gaffey, M. J. et al. Mineralogic variations within the S-type asteroid class. Icarus 106, 573–602 (1993). Delaney, J. S. et al. The polymict eucrites. J. Geophys. Res. 89, C251–C288 (1984). 20. Beck, A. W. et al. Petrologic and textural diversity among the PCA 02 howardite group, one of the largest pieces of the Vestan surface. Meteorit. Planet. Sci. 47, 947–969 (2012). 21. Beck, A. W. et al. MIL 03443, a dunite from asteroid 4 Vesta: evidence for its classification and cumulate origin. Meteorit. Planet. Sci. 46, 1133–1151 (2011). 22. Marchi, S. et al. High-velocity collisions from the lunar cataclysm recorded in asteroidal meteorites. Nature Geosci. 6, 303–307 (2013). 23. DeMeo, F. et al. An extension of the Bus asteroid taxonomy into the near-infrared. Icarus 202, 160–180 (2009). 24. Shearer, C. K., Burger, P. & Papike, J. J. Petrogenetic relationships between diogenites and olivine diogenites: implications for magmatism on the HED parent body. Geochim. Cosmochim. Acta 74, 4865–4880 (2010). 25. Jaumann, R. et al. Vesta’s shape and morphology. Science 336, 687–690 (2012). 26. Marchi, S. et al. The violent collisional history of asteroid 4 Vesta. Science 336, 690–694 (2012). 27. Jutzi, M. et al. The structure of the asteroid 4 Vesta as revealed by models of planetscale collisions. Nature 494, 207–210 (2013). 28. Watts, A. W. et al. The formation of terrains antipodal to major impacts. Icarus 93, 159–168 (1991). 29. Sunshine, J. M. & Pieters, C. M. Determining the composition of olivine from reflectance spectroscopy. J. Geophys. Res. 103, 13,675–13,688 (1998). 30. Burns, R. G. Mineralogical Applications of Crystal-Field Theory (Cambridge Univ. Press, 1970). Supplementary Information is available in the online version of the paper. Acknowledgements We gratefully acknowledge the support of the Dawn Instrument, Operations and Science teams, and, in particular, the Dawn Framing Camera team. This work was supported by Italian Space Agency grant I/004/12/0 and by NASA through the Dawn mission and the Dawn at Vesta Participating Scientists Program. Author Contributions M.C.D.S., E.A., E.P. and A.L. contributed to the data analysis. M.C.D.S., E.A., S.M., D.W.M., H.Y.M. and C.M.P. contributed to the data interpretation and to writing and improving the manuscript. E.A. and M.C.D.S. provided calibrated VIR data. F.T. provided geometric data. F.Z. and A.F. provided the projected and mosaicked VIR data. All authors contributed to discussion of the results. Author Information All Dawn data are available at PDS: Small Bodies Node (http://pdssbn.astro.umd.edu/data_sb/missions/dawn/index.shtml), and VIR data are also available at the ASI Data Center (http://www.asdc.asi.it/). Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests. Readers are welcome to comment on the online version of the paper. Correspondence and requests for materials should be addressed to M.C.D.S. (mariacristina.desanctis@iaps.inaf.it) or E.A. (eleonora.ammannito@iaps.inaf.it). 4 | N AT U R E | VO L 0 0 0 | 0 0 M O N T H 2 0 1 3 ©2013 Macmillan Publishers Limited. All rights reserved
  5. 5. LETTER RESEARCH Extended Data Figure 1 | Ternary diagram of orthopyroxene, olivine and clinopyroxene in diogenites. Proportions of orthopyroxene, olivine and clinopyroxene in diogenites normalized to 100%, with fields for orthopyroxenitic (red), harzburgitic (green) and dunitic diogenites (yellow). Data taken from Extended Data Table 1. ©2013 Macmillan Publishers Limited. All rights reserved
  6. 6. RESEARCH LETTER Extended Data Figure 2 | Distribution of the band centres for the HED meteorites. The difference in spectral properties of diogenites, howardites and eucrites can be quantified using a scatter plot of the BI-centre position versus the BII-centre position. We used spectra in the RELAB database to define the different HED meteorite spectral areas9. The HED meteorite distribution map has been derived as explained in refs 6, 8, 9. In this diagram, diogenites and eucrites populate distinct areas because both the BI-centre position and the BII-centre position are sensitive to the pyroxene compositions. Howardites, which are physical mixtures of diogenite and eucrite, plot between, and partly overlap, these fields. By associating a colour indication of composition with every region in the scatter plot (red for diogenite, green for howardite and purple for eucrite, with overlapping fields of yellow for diogenite–howardite and cyan for eucrite–howardite), we constructed the correspondence map in Fig. 1 using the same colour scheme. ©2013 Macmillan Publishers Limited. All rights reserved
  7. 7. LETTER RESEARCH Extended Data Table 1 | Average modal mineralogy of diogenites (vol%) Average modal mineralogy of diogenites compiled from different literature sources (refs 2, 19, 21 and refs 33–35 in Supplementary Information). ©2013 Macmillan Publishers Limited. All rights reserved