Ungrouped C and CM carbonaceous chondrites

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On the other hand, from Figure 4.9, there is no any evidence to show that the positive Tm anomaly in our REE pattern (the red REE pattern) is present, whereas, the REE patterns for CI-chondrite obtained by Barrat et al. (2012) and Dauphas and Pourmand (2015) are shown the visibly positive Tm anomalies. These positive Tm anomalies may be not real. From Figure 4.10, we can easily see that our data (24.1 ppb) and Anders and Grevesse (1989) data (24.2 ppb) are perfectly consist to each other for Tm abundance. From these evidences, we suggest that the abundance values of Tm in CI-chondrite reported by Barrat et al. (2012) and Dauphas and Pourmand (2015) are overestimated.

For Tb and Ho cases, hypothesizing that CI-normalized HREE pattern for CI chondrite is smooth and our values for other REE are correct, then the reported CI values of Tb and Ho should be lowered by 3.4% and 5.7%, respectively. This hypothesis could be verified by the Figure 4.10, showing the CI-normalized REE, Th and U patterns for Allende (obtained by this work) with two different normalized CI values. Moreover, our compiled data of Tb and Ho for CI chondrite can also explain the zigzag patterns of Allende in the range from Gd to Er (Figure 4.10) that was mentioned by Shinotsuka et al. (1995) for the case of ordinary chondrites. As a result, we suggest that the reported abundances of Tb and Ho for CI chondrite given by Anders and Grevesse (1989) should be reviewed and revised for further studies.

Thorium and uranium in CI chondrite

In general, our compiled abundance for Th is consistent with that by Anders and Grevesse (1989), whereas, our value for U is slightly lower than the values reported by Anders and Grevesse (1989), and consistent with that by Barrat et al. (2012). Our Th/U ratio for CI chondrite is 3.72 ± 0.13, and slightly higher than that (3.63) given by Anders and Grevesse (1989). Rocholl and Jochum (1993) suggested that the Th/U ratio for solar system is 3.9 ± 0.2, while this value given by Barrat et al. (2012) is 3.67. Rocholl and Jochum (1993) have shown that U and Th are heterogeneously distributed in CIs at a low scale, and that some small samples display a noticeable U enrichment. This enrichment could be explained by a local redistribution of U from phosphates by aqueous fluids. Although the databases used for the estimations of the abundances of U and Th were filtered to avoid the anomalous samples, the results could be somewhat disturbed by this redistribution.

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Figure 4.11 Mg and mean CM-normalized abundances for Murchison chondrite. The elements were ordered from left to right according to decreasing nebular condensation temperatures. The mean CM-normalized values are taken from Wasson and Kallemeyn

(1988)

Chemical compositions of B-7904, Y-86720, PCA 02012 and Y-793321 are compared with those for Murchison, given in Figure 4.12. Based on mineralogical study, Nakamura (2005) reported the degree of heating for several carbonaceous chondrites including 793321. Y-793321 has experienced the thermal metamorphism at the stage II (300^oC – 500^oC), while B-7904 and Y-86720 have undergone the thermal metamorphism at the stage IV (> 750^oC).

Moreover, as mentioned in the previous section, Nakato et al. (2013) suggested that PCA 02012 was also experienced a short duration heating event at temperature of ~ 900^oC.

Even though Y-793321 was metamorphosed, there is no any noticeable difference between Y-793321 and Murchison (Figure 4.12). Figure 4.13 shows the REE, Th and U abundance patterns for two Antarctic ung-C chondrites (B-7904 and Y-86720), two Antarctic CM chondrites (PCA 02012 and Y-793321 (mean)) and Murchison meteorites obtained in this study. It is easily to recognize that the REE, Th and U abundance patterns of Y-793321 and Murchison are very similar to each other (Figure 4.13). Therefore, we suggest that Y-793321 is not only a typical CM2 chondrite, but also the terrestrial weathering of Y-793321 is insignificant. On the other hand, in Table 3.7b, we report three data sets with the three corresponding positions of 52, 67 and 75 of Y-793321. The RSD (%) of mean value for ICP-AES and ICP-MS data is better than 5% except Cu (5.4%) and 3.5% except U (5.9%), respectively. This observation indicates that the chemical composition of Y-793321 is highly homogeneous distributed in spite of different positions.

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Figure 4.12 Mg and mean CM-normalized abundances for the two Antarctic ung-C (B-7904 and Y-86720), two Antarctic CM chondrites (PCA 02012 and Y-793321), and Murchison, a typical CM2 chondrite obtained in this work. The elements were ordered from left to right according to decreasing nebular condensation temperatures. The mean CM-normalized values

are taken from Wasson and Kallemeyn (1988).

Although B-7904, Y-86720 and PCA 02012 have similar chemical compositions to those for other CM chondrites, their Zn abundances are strongly depleted (Figure 4.12). Considering that these meteorites were strongly metamorphosed (Nakamura, 2005; Nakato et al., 2013), these depletions of Zn may be due to thermal metamorphism on their parent body. However, Th, U and P abundances of B-7904,115 are higher than those of CM mean at the relative values of 20%, 30% and 30%, respectively. As shown in Figure 4.13, B-7904,115 exhibited an unusual REE, Th and U pattern, displaying a prominence between Gd and Ho. This kind of unusual pattern could not be explained by parent body processes such as thermal metamorphism and aqueous alteration, but an impact-metamorphosed process on its parent body is a possibly plausible explanation (Choe et al., 2010). Thus, this feature was probably either inherited from nebular material from which its parent was formed or resulted of complexities of impact processing on its parent body (Choe et al., 2010). The appearances of two REE patterns for Y-86720 with different positions (63 and 69) were similar to each other but their magnitudes were different (the relative values of Y-86720,63 and Y-86720,69 were ~1.5 and 1.8 × CI, respectively). The REE, Th and U abundance pattern of PCA 02012 is very similar to that of Y-86720,63 sample except for U.

In brief, we suggest that: (1) chemically, B-7904 and Y-86720 are the ung-C chondrites;

(2) the host phases of REE (e.g. apatite, melilite) are heterogeneously distributed in Y-86720

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chondrite; (3) PCA 02012 is an unusual CM chondrite or ung-C chondrite; and (4) the parent bodies of Y-86720 and PCA 02012 may somewhat share some common features.

Figure 4.13 A comparison REE, Th and U abundance patterns between two Antarctic ung-C chondrites (B-7904 and Y-86720), two Antarctic CM chondrites (PCA 02012 and Y-793321) and Murchison meteorites obtained in this study. The CI-normalized values are taken form

this work.

In Figure 4.14, we showed the Mg and mean CM-normalized abundance patterns of several elements for Jbilet Winselwan and the three Antarctic CM (LEW 90500,25, Y-791198,77 and PCA 91008,10) chondrites and compared with those of Murchison obtained in this work. The chemical composition of Jbilet Winselwan is similar to that of mean CM chondrites except for Th, Sr and P. Remarkably, comparing with CM mean value, the Sr abundance of Jbilet Winselwan is extremely high (~ 5 × CM). Reviewing the ICP-AES analytical procedure for the experiment number 11^th (Exp-11), other samples such as Allende (control sample), Murchison (Mur-6, ME 1129), Y-793321,52 (and several CV-chondrite samples) which have normal Sr contents, these appear to be reliable values. Although the enrichment of Sr abundance in Jbilet Winselwan may be caused by terrestrial weathering of hot desert through developing of iron hydroxides and calcite in the soil in very short time (Barrat et al., 1999; Stelzner et al., 1999), we have no good explanation for the high Sr abundance in Jbilet Winselwan.

Among three Antarctic CM chondrites (Figure 4.14), LEW 90500,25 and Y-791198,77 have the similar chemical compositions to those of mean CM and Murchison chondrites, whereas, the chemical composition of PCA 91008,10 is relatively lower than that of mean CM chondrites. Especially, Ca, Ni and Co abundances are approximately 25%, 30% and 23% lower than those of mean CM, respectively.

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Figure 4.14 Mg and mean CM-normalized abundances for Jbilet Winselwan and the three Antarctic CM (LEW 90500,25, Y-791198,77 and PCA 91008,10) chondrites are compared with those of Murchison, a typical CM2 chondrite obtained in this work. The elements were

ordered from left to right according to decreasing nebular condensation temperatures. The mean CM-normalized values are taken from Wasson and Kallemeyn (1988).

In general, refractory lithophile elements (Al, Sc, Ca, REE) are not much affected by parental aqueous alteration. Calcium may be an exception: it appears to have been mobilized during CM alteration to form phosphate (i.e., Brearley and Chizmadia, 2005; Rubin et al., 2007).

Nevertheless, the refractory lithophile elements can be considered as important indicators of the original (i.e., pre-alteration) composition of the CM chondrites (Rubin et al., 2007). The mean CM- and Mg-normalized refractory lithophile abundances of the typical CM chondrites such as Murchison, Y-793321, etc. (Figure 4.12 and 4.14), range from 0.90 to 1.10, indicating that the samples are basically isochemical irrespective of their degree of alteration. Therefore, the low Ca, Ni and Co abundances in PCA 91008,10 may have been caused by terrestrial weathering (Rubin et al., 2007; Choe et al., 2010).

Figure 4.15a displays approximately chondritic Ni/Co ratios in most of CM and ung-C chondrites obtained in this work. Exceptions are PCA 91008,10 and PCA 02012. The PCA 91008,10 has a lower Ni/Co ratio with low Ni content compared to that of CI, whereas, PCA 02012 shows the opposite trend with a higher Ni/Co ratio at high Ni content. For PCA 91008,10, it indicates metal loss from bulk meteorite that would affect Ni much more than Co. In contrast, the PCA 02012 is enriched of Ni relative to Co at high Ni content. In Figure 4.15b, we show the Fe-Co plot for bulk CM and ung-C chondrites obtained in this work and compared with availably corresponding literature values. There is a correlation between Fe and Co in CM and ung-C chondrites. A similar correlation would be obtained for Fe and Ni. In general, Co/Fe

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ratios in CM chondrites are slightly lower than those of CI. Exceptions are again PCA 91008,10 and PCA 02012. At the lower Fe contents, PCA 91008,10 has a Co abundance too low for a chondritic Co/Fe ratio, whereas, PCA 02012 appears on the opposite trend. Indicating that PCA 91008 and PCA 02012 seem to be the unusual CM chondrites.

Figure 4.15 Ni-Co (a) and Fe-Co (b) plots for bulk CM and ung-C chondrites and compare with those of literatures. CI-compiled value from the present work and CM-mean value from

Wasson and Kallemeyn (1988).

4.4 CO-CV carbonaceous chondrites 4.4.1 Major and minor elements

Figure 4.16 shows Mg- and mean CO-normalized abundances for several elements in Colony and compared with those of Rubin et al., (1985). There is good agreement between our data and those of Rubin for Al, V, Ni, Fe, Mn, and Zn. However, for some REEs (i.e. Sm, La and Eu), our data are much higher than data reported by Rubin.

From the Figure 4.16, it can be seen that REEs, Th, U and Ba in Colony are highly enriched;

the elements of Al, Ti, V, Co, Mn and Zn are consistent with CO mean within 26%, whereas Ca and Ni are depleted by 31.6% and 19.5%, respectively. Although Al/Mn vs. Zn/Mn ratios (Figure 4.4) indicated that Colony is classified into CO chondrite group, the above observations and REE pattern of Colony (Figure 3.14) reveal that Colony is not a normal CO chondrite. This suggestion agrees well with that of Rubin et al., (1985) and Noguchi et al., (1999).

Data from the other CO chondrites are shown in Figure 4.17. The ratio of each sample over mean CI is plotted in order of assumed decreasing nebular volatility for lithophile elements (a) and for siderophile and chalcophile elements (b). Most lithophile elements in the samples are

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in proportions consistent with a CO chondrite classification (Wasson and Kallemeyn, 1988), except for Sc in Y-82050 and REEs and Mn in Y-82094,90 sample. For siderophiles and chalcophiles agree well to CO mean except Cu in Felix and Ni, Co, Fe and Cu in Y-82094,90.

Figure 4.16 Mg and mean CO-normalized abundances for Colony (CO3.0, this work) are compared with those of Rubin et al., (1985). The elements were ordered from left to right according to decreasing nebular condensation temperatures. The mean CO-normalized values

are taken from Wasson and Kallemeyn (1988).

Y-82094 was classified as a C03 chondrite on the basis of its major petrological features.

However, it possesses a number of unique characteristics which being suggested that it is not a normal CO chondrite (Kimura et al., 2014). Indeed, for Y-82094,90 sample, it can be seen in the Figure 3.20 (Results section) and Figure 4.17 that, compared to CO mean, REEs are relatively enriched (by 2.7% - 21.6 %), whereas Mn is depleted by 33.4%. On the other hand, Figure 4.4 shows also that Y-82094,90 is not a normal CO chondrite. For the siderophiles and chalcophiles, the Ni, Co, Fe and Cu are depleted by 12.3%, 18.7%, 15.5% and 26.3% relative to CO, respectively, whereas Zn is consistent with CO mean. Depletion in siderophiles are probably due to weathering.

Figure 4.18 presents the Ni/Co (a) and Fe/Co (b) ratios in CO chondrites obtained in this work. Generally, there is a positive correlation between Ni-Co, and Fe-Co, except for those in Colony sample. In Figure 4.18a, the Ni/Co ratio for most samples distributed quite evenly around the CI ratio. The Colony has a lower Ni/Co ratio with low Ni content compared to that of CI. It could indicate metal loss from bulk meteorite that would affect Ni much more than Co.

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Figure 4.17 Mg and CI-normalized abundances ratio of CO carbonaceous chondrites (except Colony) analyzed by ICP-AES and ICP-MS. Elements are separated into lithophiles in the left

of the diagram (a) and siderophiles and chalcophiles in the right (b). In each portion, elements are ordered from left to right in terms of decreasing nebular condensation temperature. The CI-normalized values are from this work, and The CM-, CO-, CV-mean values are taken from

Wasson and Kallemeyn (1988).

In Figure 4.18b, we show the Fe-Co plot for bulk CO obtained in this work. A similar correlation would be obtained for Fe and Ni. Similar to CM chondrite case, the Co/Fe ratios in CO chondrites are slightly lower than those of CI. Exception is again the Colony which has too low Co abundance while the Fe concentration is maximum. The ratios of Ni/Co and Fe/Co for Y-82094,90 are lower than those of the other CO chondrites. In Figure 4.19, the CI- and Mg-normalized lithophile (a) and siderophile and chalcophile (b) abundances of CV chondrites are given. In general, the lithophiles are in range of CM-CO mean and below CV mean line, except for La of Bali sample, whereas siderophile and chalcophile elements plotted in the CV chondrites form a tight array of the CV mean except Cu in Mokoia, Grosnaja and A-880835,81 and Zn in Grosnaja.

From Figure 4.19, it is clear that the refractory lithophiles (Al to V) are diverse in a wide range of CM-CO-CV, whereas the moderate volatile (Mn), siderophiles and chalcophiles (Ni, Co, Fe, Cu, Zn) concentrated around CV-line. Indeed, from Figure 4.5, it can also be seen that the ratio of refractory lithophile (Al/Mn) vs. volatile (Zn/Mn) distribute in a wide area between CM-CO-CV.

As discussed in section 4.1 (Figure 4.5), Bali (USNM 4839) meteorite is a typical CV3 chondrite and Grosnaja (BM 63624, NHMW_#2745_B) is a typical heterogeneous CV chondrite. These imply that the refractory lithophile abundances in CV are distributed in a wider range than those of CM and CO chondrites. Figure 4.20 presents the Ni/Co (a) and Fe/Co (b) ratios in CV chondrites obtained in this work.

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Figure 4.18 Ni-Co (a) and Fe-Co (b) plots for bulk CO chondrites. CI-compiled value from the present work and CO-mean value from Wasson and Kallemeyn (1988).

Figure 4.19 Mg and CI-normalized abundances ratio of CV carbonaceous chondrites analyzed by ICP-AES and ICP-MS. Elements are separated into lithophiles in the left of the

diagram (a) and siderophiles and chalcophiles in the right (b). In each portion, elements are ordered from left to right in terms of decreasing nebular condensation temperature. The

CI-normalized values are from this work, and The CM-, CO-, CV-mean values are taken from Wasson and Kallemeyn (1988).

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Figure 4.20 Ni-Co (a) and Fe-Co (b) plots for bulk CV chondrites. CI-compiled value from the present work and CV-mean value from Wasson and Kallemeyn (1988).

There is a quite good correlation between abundances of Ni and Co in CV. On the other hand, the correlation between Fe and Co is relatively unclear and arranged in a wide range.

From data obtained in this study for three groups: CM (Figure 4.14 and 4.15), CO (Figure 4.17 and 4.18) and CV (Figure 4.19 and 4.20), we suggest that the bulk chemical compositions of CM, CO, CV chondrites are independent of the petrologic subtypes.

4.4.2 REE, Th and U abundance patterns

Figure 4.21 shows the REE, Th and U abundance patterns for the usual CO chondrites (a) and unusual CO chondrites (b). It is easily recognized that the REE abundance patterns for usual CO chondrites are mostly flat and varied in a narrow range (1.5 – 1.7 × CI), whereas the REE abundance patterns for unusual CO chondrites are prominent in the range of Gd-Er with different magnitude (1.75 – 3.5 × CI). Especially, the Tb abundance in Lancé (BM 1294,24) is anomalously high (16.6 × CI). For Th and U abundances, the variations are mostly similar between usual and unusual CO chondrites.

In Figure 4.22, we present a comparison between REE, Th and U abundance patterns for ung-C and unusual CO chondrites. B-7904 has a similar REE abundance pattern with that of unusual CO chondrites which have a prominence in the medium REE area (Gd-Er). This kind of unusual pattern could not be explained by parent body processes such as thermal metamorphism and aqueous alteration, but an impact-metamorphosed process on its parent body may be a possibly plausible explanation (Choe et al., 2010). Thus, this feature was probably either inherited from nebular material from which its parent was formed or resulted of complexities of impact processing on its parent body (Choe et al., 2010).

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Figure 4.21 REE, Th and U abundance patterns for CO chondrites, (a) usual CO chondrites, (b) unusual CO chondrites. CI-normalized values are taken from this work. The closed and

opened circles represent non-Antarctic and Antarctic meteorites, respectively.

Figure 4.22 Comparison of REE, Th and U abundance patterns between (a) ung-C chondrites and (b) unusual CO chondrites. CI-normalized values are taken from this work. The closed

and opened circles represent non-Antarctic and Antarctic meteorites, respectively.

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Figure 4.23 shows the REE, Th and U abundance patterns for CV. The two Vigarano samples taken from different sources (BM 1911.174 and NHMW_#7485_B) have the anomalous REE, Th and U patterns (Figure 4.23b) with enrichment in La, Ce, Th and U (NHMW_#7485_B) and abnormal Tb abundance (~ 33 × CI, BM 1911.174). In Figure 4.23a we show the REE, Th and U abundance patterns for usual CV chondrites. It is recognized that the REE, Th and U patterns of usual CV chondrites are fractionated and comparable to those of Allende. Negative Ce and Eu anomalies, and a positive Tm anomaly along with enrichment in LREE and depletion in HREE are main features of REE abundance pattern in the SI Allende, implying that usual CV chondrites contain amount of early condensed material such as type II CAI. However, these amount of type II CAI are different in CV chondrites. A comparison of REE, Th and U abundance patterns between usual CO and usual CV chondrites are shown on Figure 4.24. It is easy to recognize the difference between REE abundance patterns of usual Co and usual CV chondrites. The REE patterns of CO chondrites are mostly flat and varied in a narrow range (1.5 – 1.7 × CI), whereas the REE abundance patterns for usual CV chondrites are fractionated patterns and varied in a wide range (1.6 – 2.8 × CI). Abundances of Th in usual CO chondrites are plotted in the range of (1.5 - 1.8 × CI), and those of usual CV chondrites are in range of (1.6 – 2.4 × CI). The variations of U abundances in usual CO and usual CV are almost similar to each other and in the range of (1.4 – 2.5 × CI). For more detailed, the Figure 4.25 shows the correlation between Tm/Tm* ratio, which represents the Tm anomaly, and La/Yb ratio, representing a fractionation between LREE and HREE, for usual Co and usual CV chondrites. The distinction between bulk REE abundance patterns of usual CO and usual CV chondrites is very clear. It indicates that the amount of early condensed material such as Type Figure 4.23 REE, Th and U abundance patterns for CV chondrites, (a) usual CV chondrites, (b) unusual CV chondrites. CI-normalized values are taken from this work. The closed and opened circles represent non-Antarctic and Antarctic meteorites, respectively.

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II CAI in usual CO is much more lower than that in usual CV chondrites. These evidences lead to the conclusions that although CO and CV chondrites have some similar characteristics (i.e.

oxygen isotopic composition, petrologic properties), their bulk REE, Th and U patterns are different, and the CO and CV chondrites come from the different parent bodies.

Figure 4.24 Comparison of REE, Th and U abundance patterns between (a) usual CO chondrites and (b) usual CV chondrites. CI-normalized values are taken from this work. The

closed and opened circles represent non-Antarctic and Antarctic meteorites, respectively.

On the other hand, we suggest that: (i) Chemical composition of CV chondrite is much more dispersive than that of CM and CO chondrites; (ii) The bulk chemical compositions of CM, CO, CV chondrites are independent of the petrologic subtypes, at least for 31 elements determined in this study.

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Figure 4.25 The correlation between [Tm/Tm*] and [La/Yb]CI for CV chondrites. CI-normalized values are taken from this work. The closed and opened circles represent

non-Antarctic and non-Antarctic meteorites, respectively.

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