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Home , Carbonaceous chondrite, Kaidun meteorite, Shergotty meteorite

& 38, Nr 5, 725–737 (2003) Abstract available online at http://meteoritics.org

The Kaidun : Clasts of alkaline-rich fractionated materials

Andrei V. IVANOV, 1* Nataliya N. KONONKOVA, 1 S. Vincent YANG, 2 and Michael E. ZOLENSKY 3

1Vernadsky Institute of Geochemistry and Analytical Chemistry, Moscow 117975, Russia 2Lockheed Engineering and Science Company, , Texas 77258, USA 3SN2, NASA , Houston, Texas 77058, USA *Corresponding author. E-mail: [email protected]

(Received 9 April 2002; revision accepted 11 November 2002)

Abstract–Clasts of alkaline (the second find in ) and subalkaline rocks were found in the . One of them (#d4A) is a large crystal of albite with inclusions of fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The two latter minerals were previously unknown in meteorites. Another clast (#d[3–5]D) has a melt crystallization texture of mainly feldspar (oligoclase) composition and contains relict grains of both high-Ca and low-Ca pyroxene and fluorapatite. The mineralogical characteristics of these clasts suggest a genetic relationship and an origin from the same . The textural and mineralogical characteristics of the clasts indicate origin by extensive igneous differentiation. Such processes most likely took place in a rather large differentiated body. The material of clast #d(3–5)D is similar in some mineralogical respects to basaltic shergottites.

INTRODUCTION and nature of this enigmatic meteorite lies in studying its different components. In this paper, we describe the results of The Kaidun meteorite is an extremely unusual our investigation of two clasts, #d(3–5)D and #d4A, that show heterogeneous . Kaidun, as a whole, is classified as a evidence of formation by igneous differentiation, and that CR2 carbonaceous (Ivanov 1989; Ivanov et al. appear to be genetically related. 1987; Clayton et al. 1994) and contains numerous inclusions of different types. These include CI type (Ivanov 1989; EXPERIMENTAL PROCEDURES Ivanov et al. 1987; Clayton et al. 1994), an unusual CM1 lithology containing many mineralogical features not We studied doubly-polished thin sections of the Kaidun previously reported in meteorites (Zolensky et al. 1996), and fragments #d4A and #d(3–5)D. A petrographic and fragments of different enstatite . An EL3 chondrite mineralogical study was performed by traditional optical fragment was the first such material found in any meteorite microscopy and scanning electron microscopy. We used a (Ivanov and Ulyanov 1985). An EH fragment contains many JEOL JSM-35CF at the Johnson Space Center (JSC), products of nebular condensation including the unusual Houston, Texas, and a CAMSCAN at Moscow State compound Na 2S2 (Ivanov et al. 1996), and another one shows University. Both machines were operated at 15 kV to obtain evidence for both nebular and parent body aqueous alteration backscattered electron images. of metal (Ivanov et al. 1998). We found a geode of Fe, Ni We determined the chemical composition of matrix and metal crystals which appears to have formed as a result of mineral phases using a Cameca Camebax-Microbeam carbonyl transportation (Ivanov et al. 1988). Along with the electron microprobe at the Vernadsky Institute in Moscow forementioned sodium sulfide Na 2S2, we discovered an and Cameca SX 100 at JSC. In most cases, the analyses were unusual Fe, Cr sulfide with stoichiometry close to daubreelite carried out at 30 nA and accelerating voltage of 15 kV. For but with a constantly low analytical sum and strong optical mineral phases with higher volatile composition, we anisotropy (Ivanov 1989; Ivanov et al. 1996, 1998), and the performed the analyses in a raster scanning mode with a line mineral florenskyite FeTiP, which is the first phosphide of a spacing of 2 mm, a 10 nA beam current, and a 15 kV lithophilic element found in nature (Ivanov et al. 2000b). accelerating voltage. A raster scanning mode with a line Kaidun is a unique meteorite that has no known spacing of 50 mm also was used to obtain the matrix analogues. Undoubtedly, the key to understanding the origin composition of the #d(3–5)D clast. Natural minerals and

725 © , 2003. Printed in USA. 726 A. V. Ivanov et al. synthetic compounds were used as standards and ZAF- The clast’s overall texture is defined by an ophitic main corrections were applied. mass speckled with large apatite and pyroxene grains. Section The bulk chemical composition of clast #d(3–5)D was #d3D contains 3 grains each of pyroxene and apatite, #d4D calculated using matrix and mineral composition data and the contains 5 pyroxene grains and 2 apatite grains, and #d5D results of a quantitative mass balance mineralogical contains 1 pyroxene grain. We note that #d3D is the first thin calculation. section to contain this clast. It appears to contain the edge of the clast. At its edge, #d3D contains a rounded, amoebae- DESCRIPTION AND TEXTURE OF CLASTS shaped piece of Kaidun’s carbonaceous matrix in contact with the clast material, which, at this site, is a uniform, crystal-free Clast #d4(3–5)D glassy mass (Fig. 2). The large pyroxene grains have irregular shapes ranging Clast #d(3–5)D is present in 3 polished thin sections— from equant to elongate and are 400 × 300 to 140 × 80 mm in #d3, #d4, and #d5—obtained by sequential cutting of a size. The pyroxene grains are characteristically rounded. fragment of Kaidun. According to a predefined system, we Eight of the 9 pyroxene grains found in the thin sections are named the clast #d(3–5)D and its thin sections #d3D, #d4D, high-Ca and one (190 × 80 mm) is low-Ca. and #d5D. The thin sections of this clast are irregular and are In section #d3D, the apatite grains are 70–120 mm in size 1.9 × 2.1, 2.6 × 3.0, and 2.2 × 4.0 mm in size, respectively. The and are equant to slightly elongate. The apatite grains show clast’s texture, mineral assemblage, and mineral compositions clear faces and corners, and one of the grains is a regular are essentially identical in all 3 sections (Fig. 1). hexagon. In section #d4D, an apatite grain ~100 mm across

Fig. 1. Backscattered electron image of Kaidun fragment #d(3–5)D, section #d3D. The clast’s overall texture is defined by an ophitic main mass speckled with large apatite and pyroxene grains. The dark irregular areas are holes, the large light-gray grains with roundish outlines are high-Ca pyroxenes, and the small white grains are apatite. The apatite grain at the center is a regular hexagon with clear faces and corners. The scale bar is 0.5 mm. The Kaidun meteorite 727

Fig. 2. Backscattered electron image of a piece of carbonaceous matrix at the edge of fragment #d(3–5)D, section #d3D. The rounded contact between the body of the clast and the carbonaceous inclusion indicate that the material of the clast was liquid during formation of the contact. The scale bar is 50 mm. also has a hexagonal shape but with rounded corners. One diameter. The layering has two structural types— in some fragment of a second apatite grain in section #d4D is located cases the layer is made from a brushy mass of thin needle- at the very edge of the clast. shaped crystals (Fig. 4), and in others, it is colloform. Layers The main mass of clast #d(3–5)D consists of crystals of with a fine crystal structure occur primarily near the edges of plagioclase submerged in a finely crystalline mass of complex the clast and are found primarily in section #d3D. Both types composition (Fig. 3). The finely crystalline mass becomes of coating commonly occur in a single void in which the glassy toward the edges of the clast. The plagioclase crystals colloform coating overlaps and covers the crystalline coating. are commonly lath-shaped, ~400 × 40 mm in size, and are In these cases, the boundary between the coatings is usually skeletal to rectangular. Some laths are curved. Plagioclase irregular and indistinct. We found a few plagioclase laths laths commonly intergrow in various shapes, including - interrupted by voids with coated walls. shaped. Regular plagioclase rhombuses with a long axis up to 130 mm are common. All types of plagioclase crystals are Clast #d4A usually surrounded by thin pyroxene crystals. Inclusions of composition similar to pyroxene— and usually rich in In thin section #d4, about 4 mm from #d4D, we found a phosphorus—are common in the inner areas of the twinned crystal of plagioclase (clast #d4A) 1.2 × 0.7 mm in plagioclase crystals. Potassium-rich grains with anorthoclase size (Fig 5). The crystal contains irregular 30– 40 micron composition are ubiquitous in the matrix. No opaque phases inclusions of apatite. The crystal is intersected by a fractured were found in the clast. Clast #d(3–5)D contains voids zone containing 3–8 micron calcium phosphate grains. ranging from a few tens of microns up to ~0.5 mm in size. The The central part of an albite crystal contains an elongate large voids have complex, irregular shapes. In many cases, the 150 × 50 mm polymineralic inclusion (Fig. 6). The inclusion’s voids interrupt or completely crosscut plagioclase laths. We main phase is aenigmatite in the form of an elongated, did not note any patterns in the locations of the voids. Small partially fragmented grain 85 × 20 mm in size and several voids <~100 mm occur preferentially but not exclusively in adjacent small grains (<10 mm). Small, rounded phosphate the finely crystalline areas of the main mass of the clast. The inclusions are present in the middle of the largest aenigmatite small voids often have a rounded or elongated almond shape. grain. Aenigmatite also occurs intergrown with apatite. Sometimes these elongated voids aligned. Among the small aenigmatite grains are several small (<5 The walls of the small voids, in many cases, are covered mm) grains of wilkinsonite, which is a mineral of the with a thin mineralized layer having a typical thickness of <10 aenigmatite group (Fig. 7). In one case, wilkinsonite occurs as µm, but varying up to 18 mm. The varying thickness may be thin exsolution-like inclusions within an aenigmatite grain. due to the plane of the section not being parallel to the voids’ This is the first time aenigmatite and wilkinsonite have been 728 A. V. Ivanov et al.

Fig. 3. Backscattered electron image of the texture of the main part of fragment #d(3–5)D, section #d4D. The elongate lath-shaped plagioclase crystals are submerged in a finely crystalline mass. At the center is a void with a colloform coating. Part of a high-Ca pyroxene grain is at the upper left. The scale bar is 100 mm.

found in meteorites and only the second time wilkinsonite has compositions. Plagioclase (average An 21.8Ab76.7Or1.5) varies been found in nature (Duggan 1990). widely in composition (An 16.0–34.5Ab64.6–82.1Or0.8–1.2). Zoning In this inclusion, we also identified rounded grains of is absent in plagioclase crystals. arfvedsonite about 15 mm in diameter. On one side, the grains Wide variations in composition also were noted in the fine of aenigmatite are coated with Fe and Mg phyllosilicates subcalcic augite crystals of the matrix (En 27.9–40.6Fs36.3–53.7 containing calcium phosphate inclusions. Wo14.7–26.7). Matrix pyroxenes are characterized by high phosphorus, which is not typical of pyroxenes. Some portions CHEMICAL COMPOSITION OF THE COMPONENTS of the matrix had a potassium-rich anorthoclase composition. In these areas, the potassium content reached 2.5 wt%. Clast #d(3–5)D A peculiarity of the chemical composition of the matrix of clast #d(3–5)D is the extremely high and variable content Table 1 shows the chemical composition of the of alkaline elements and phosphorus. For example, the components of clast #d(3–5)D. average and maximum K 2O content in the matrix In all 3 sections of clast #d(3–5)D, the large grains of substantially exceed those in the plagioclase crystals. In high-Ca pyroxene contain nearly constant major element normalized composition, the matrix of the clast is more than compositions (augite En 42.4Fs21.6Wo36.0). The variations of 83.5 vol% plagioclase (Ab 82.2An14.2Or3.6), 9 vol% pyroxene, the minor element compositions in these pyroxene grains are and 5.8 vol% . typical for augite. The only low-Ca pyroxene grain we found The collomorphic coatings covering the walls of the has a pigeonite composition of En 47.2Fs42.9Wo9.9. Chemical small voids have a consistently low analytical sum (85–92 zoning is absent in these crystals. Apatite grains in clast #d(3– wt%) and, based upon the composition (Table 2), consist of 5)D have a fairly constant chlorfluorapatite composition phyllosilicates of the chlorite-serpentine group. The (Table 1). composition of these coatings is substantially different in Matrix plagioclase of all morphological types is usually different voids but fairly constant within a given void. We did characterized by a high content of foreign components such not observe chemical zoning in these coatings. as TiO2, FeO, MgO, P 2O5. Table 1 shows only the purest A characteristic of the composition of the finely The Kaidun meteorite 729

Fig. 4. Backscattered electron images of voids with coatings of different structural types in fragment #d(3–5)D, section #d4D: two voids with crystalline coating (above, scale bar 10 mm) and a void with colloform coating (below, scale bar 30 mm). The coatings also differ widely in chemical composition (see Table 2). crystalline coatings within voids is a high content of MgO, measurements for the finely crystalline coating may include FeO, and Al 2O3, with a very low SiO 2 content and the nearly some contribution of SiO 2 from the collomorphic coating. total lack of almost all other analyzed components. The We have performed additional calculations to attempt to analytic sums are also consistently low (Table 2, Fig.8). The correct for this effect. As shown in Table 2, we have crystalline coating is very thin and its boundary with the subtracted the suspected contribution of the collomorphic collomorphic coating is irregular. As a result, microprobe coating from the measured composition of the finely analyses of the crystalline coating inevitably pick up a crystalline coating. The resulting calculated compositions are contribution from the collomorphic coating because the well-approximated by the formula (Mg, Fe, microprobe spot size (~3 microns) is larger than the thickness Mn)5Al2O8•nH2O. Both coating types contain sulfur, which of the crystalline coating. Specifically, we believe that our SiO 2 was not observed in the other components of clast #d(3–5)D. 730 A. V. Ivanov et al.

Fig. 5. Backscattered electron image of Kaidun fragment #d(4)A. The fragment is composed largely of a single crystal of albite. The elongate light area in upper center is an inclusion of complex composition (see Fig. 6). The small white grains are apatite. The scale bar is 300 mm.

Clast #d4A analyses, one of a separate grain and one of an exsolution-like inclusion in a grain of aenigmatite. Both compositions are Table 3 shows the chemical composition of the practically identical and can be approximated by the formula 2+ 3+ components of clast #d4A. Clast #d4A is a single plagioclase Na1.97(Fe 3.59, Mg0.21, Mn0.09, Ca0.05)(Fe 1.87, Al0.12, crystal with intergrowths. It has an albitic composition and Ti0.01)Si5.97O20. weak chemical zoning, from Ab 89An5.4Or5.6 near the center to Wilkinsonite from the Kaidun clast has noticeably higher Ab90.5An2.4Or7.1 at the edges. MgO and lower MnO in comparison with the only known In clast #d4A, apatite is present as fluorapatite. terrestrial wilkinsonite (MgO <0.1 wt% and MnO >1.0 wt%; Aenigmatite is present in clast #d4A in two settings—within Duggan 1990). a multiphase inclusion (aenigmatite 1) and in an intergrowth Arfvedsonite is MgO-rich and has the formula (Na 1.93, 2+ 3+ with a relatively large apatite crystal (aenigmatite 2). The Fe Ca0.74, K0.25)(Mg2.41, Fe 1.62, Mn0.08)(Fe 0.94, Al0.06)Si8.01 and Mg contents of the mineral vary somewhat in the O22(OH)20. different positions (Table 3). The formulas are: The phyllosilicates are characterized by a variable 2+ Na1.98(Fe 4.13, Mg0.75, Ca0.08, Mn0.08)Ti1.00(Si5.86, Al0.16)O20 composition and notable phosphorus content. Small inclusions 2+ and Na2.07(Fe 3.42, Mg1.36, Ca0.11, Mn0.06)Ti0.99(Si5.93, of phosphates in the aenigmatite grain, in phyllosilicates, and Al0.12)O20, for aenigmatite 1 and 2, respectively. The Mg and in the fractured zone of the albite are characterized by a low Mn contents of aenigmatites from clast #d4A differ analytic sum and by significant Si, Al, Fe, and Mg. noticeably from those of terrestrial aenigmatites. The content of MgO in terrestrial aenigmatite from alkaline rocks never DISCUSSION exceeds 3 wt% and is usually smaller than 1.5 wt% (Mitrofanova and Afanas’eva 1966; Kostyleva-Labuntsova et Formation of the Clasts al. 1978; Jones 1984; Stolz 1986, and many others), while the MgO contents in aenigmatite from the Kaidun clast are 3.6 The texture of the main mass of clast #d(3–5)D is finely and 6.8 wt%. The MnO content in terrestrial aenigmatite crystalline to glassy containing skeletal and subangular usually exceeds 1 wt% and quite often exceeds 2 wt%, while plagioclase crystals. This texture probably formed by rapid the MnO content in Kaidun aenigmatite is 0.5–0.8 wt%. cooling of a melt. The rounded contact between the body of As noted above, wilkinsonite occurs only as very small the clast and the inclusion of carbonaceous matrix seen in grains. For this reason, we were able to obtain only 2 good #d3D clearly indicates that the material of the clast was in The Kaidun meteorite 731

Fig. 6. Backscattered electron image of a part of fragment #d(4)A. At the center is a complex multiphase inclusion containing aenigmatite, wilkinsonite, arfvedsonite, and phyllosilicates. A part of a rather large apatite with 2 small aenigmatite grains at the edges is at the upper left. The chemical compositions of aenigmatite in the multiphase inclusion and the intergrowths with apatite crystal are different (see Table 3). Abbreviations: ab = albite, aen = aenigmatite, arf = arfvedsonite, phy = phyllosilicates. The scale bar is 30 mm. liquid form during formation of the contact. We suggest that 1974, 1980), the shape of plagioclase crystals during the melt could have interacted with the water-bearing crystallization from a melt reflects the degree of supercooling carbonaceous matrix at this time, producting a hydrous melt. of the melt and its cooling rate. The presence in clast #d(3– The presence of phyllosilicate coatings within voids supports 5)D of tablet-shaped, skeletal, and subangular crystals of this supposition. plagioclase suggests that the crystals formed from a rapidly At the same time, the nearly complete lack of sulfur in the cooling, supercooled melt. High rates of cooling and matrix and the low content (typical components of crystallization are also suggested by the above mentioned matrix) suggests that very little high content of foreign ions in the plagioclase and pyroxene contamination of the melt by the material of the carbonaceous of the matrix, as well as the observation that most potassium matrix occurred. Interactions were apparently limited did not partition into albite during crystallization. According primarily to contamination by water and very water-soluble to experimental results (Lofgren 1974, 1980), the level of components. supercooling DT appears to have been ~150°C/ hr, with a Clearly, the formation of clast #d(3–5)D occurred during cooling rate of ~5–10° C/ hr. a high-velocity . During this event, the material The formation of the clast’s voids appears to be related to of the impactor was heavily melted. However, the smooth, the presence of a fluid phase and occurred during cooling and rounded edges of most of the large mineral grains in clast crystallization of the melt. This is also supported by the above #d(3–5)D are incompatible with their formation by mentioned cases of plagioclase laths being interrupted by crystallization of this melt but suggest the opposite process voids, including voids with coated walls. The presence of a of resorption of crystals in the melt. W e suggest that the fluid phase may be related to contamination by water and large mineral grains of the clast are the remains of a other from the carbonaceous matrix of the meteorite. previously existing fragment or fragments that have However, we cannot exclude the possibility of a high volatile undergone melting. content in the primary material of the clast. As the results of experimental studies show (Lofgren The formation of the coatings on the void walls must 732 A. V. Ivanov et al.

Fig. 7. Backscattered electron image of the wilkinsonite-containing part of the complex inclusion in the #d(4)A fragment. Wilkinsonite of the same composition presents as separate grains and as exsolution-like inclusions in aenigmatite. Abbreviations: wlk = wilkinsonite, others = see caption to Fig. 6. The scale bar is 10 mm.

have occurred during the final stage of formation of the clast, does not show evidence of significant secondary changes and with the formation of the colloform coatings following that of appears to have retained its original texture from before its the crystalline coatings. incorporation into the Kaidun parent body. As mentioned The composition of the crystalline coatings of the voids above, the crystal’s fractured zone may be result of an impact of clast #d(3–5)D— (Mg, Fe, Mn) 5Al2O8•nH2O—is similar if event. The hydrated phases present in the clast— not identical to the Mg 11Fe4Al6O24•nH2O composition of the phyllosilicates and hydrous phosphates—may be linked to thin, elongated individual crystals found in the cavities of the hydrous alteration in the parent body of the meteorite. Note chondritic clast #d3A (Ivanov et al. 2000a). We note that no that during this hydrous alteration, the characteristics of the mineral phase of this composition has been observed clast—the alkaline character of the clast’s components—were previously in nature. The formation of crystals of this phase in preserved. both cases appears to have occurred from a fluid of identical or extremely similar composition, and most likely they share Chemistry and Origin of the Clasts a single process of formation. The difference in morphology of this phase in clasts #d3A and #d(3–5)D— elongated The mineral association of clast #d4A—albite, apatite, individual crystals in the first case and a finely crystalline aenigmatite, wilkinsonite, and arfvedsonite—clearly indicate brush in the second case—could reflect differences in its alkaline igneous nature. The formation of this clast formation temperature. In turn, this appears to suggest that the probably resulted from extreme differentiation of the source formation of this phase in clast #d(3–5)D occurred at higher material. We must emphasize that arfvedsonite, aenigmatite temperature than in clast #d3A. We assume the mineral- and wilkinsonite are represented by MgO-rich varieties and forming fluid was formed in clast #d(3–5)D during cooling of that the latter 2 minerals are notably distinct chemically from the melt. In clast #d3A, this phase may have formed from the their terrestrial analogues. same fluid after its further cooling during filtration through Four alkaline rock clasts were found previously in the meteorite material. LL3–6 chondritic breccia Adzhi-Bogdo (Bischoff et al. 1993). In contrast to the previous clast (#d[3–5]D), clast #d4A The main minerals of these clasts are K-feldspar and SiO 2- The Kaidun meteorite 733 7 4 5 4 . . . . r 2 4 2 3 O 2 4 – 5

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e e c a b a e l l l l l l 1 e t n o o n , o l s c 2

* a n o t i m s , e f f m a a a a a a e n 6 a o c e p 5 e a m 4 h t t t t t t e n e a t x s u l o o e u a e 2 o 9 t 3 p t t i i , e 5 3 x u e s s s s s s s c l l o i e i r i t l r u 5 1 1 6 1 m n l l l F l k t r n = o e t F o y y y y y y g g a o m l c

= r a = e a p f o o o r r r r r r b a l g a l l b = = = = = b u p n o u = i l y = l p e l b e e a h

a C C n C n C C C C C C a C A n P n A n P n P n A M n B c n R A A D n T A R T a b c d e T a b c d 734 A. V. Ivanov et al.

Fig. 8. Backscattered electron image of fragment #d(3–5)D, section #d3D (a) and corresponding X-ray maps Al K a (b), Mg Ka (c), and Si K a (d) of the void covered with a crystalline coating. The coating is enriched in Al and Mg and does not contain Si, which is present only on the surface of the crystals as a component of the colloform coating. The scale bar is 10 mm.

phases (tridymite and quartz). The minor phases include albite, of the data without additional correction could result in an chlorapatite, whitlockite, ilmenite, zircon, Ca-poor pyroxene, overestimated sodium content in aenigmatite. If we assign the and a poorly characterized Na, Ti-bearing silicate ([Na, Na2O content of the aenigmatite 1 Kaidun #d4A (7.3 wt%) to Ca]2.7[Fe, Mg]6Ti1.3Si7O24). The sizes of the quartz and K- the Na, Ti-bearing silicate in Adzhi-Bogdo, the formula of the feldspar grains are up to 700 mm. These clasts were classified silicate will correspond to aenigmatite and can be written as 2+ as alkali-granitoids. Besides the alkali-granitoid clasts, Adzhi- Na1.98(Fe 4.16, Mg0.77, Ca0.04, Mn0.03)Ti1.06(Si5.90, Al0.04)O20. Bogdo also contains pyroxene-rich clasts containing both Ca- Kaidun clast #d4A and the alkali-granitoid clasts of poor and high-Ca pyroxenes. Judging from the similarities of Adzhi-Bogdo are the only alkaline rock clasts found in the minor phase compositions, granitoids and pyroxene-rich meteorites to date. The mineral compositions of these clasts in clasts are related (Bischoff et al. 1993). both meteorites are considerably different. However, the We emphasize the significant similarities of the Kaidun clast #d4A is a single large albite crystal with composition of aenigmatite 1 from Kaidun #d4A (Table 3) and inclusions of other minerals. Kaidun #d4A is evidently a of the unidentified Na, Ti-bearing silicate from alkali- fragment of an alkaline rock and is more coarse-grained granitoid clasts of Adzhi-Bogdo (42.1 wt% SiO 2, 10.1 TiO2, compared to the parent rock of granitoid clasts in Adzhi- 0.26 Al2O3, 35.5 FeO, 0.24 MnO, 3.7 MgO, 0.27 CaO, 8.2 Bogdo. The composition of the parent rock of Kaidun #d4A is Na2O; Bischoff et al. 1993). The SiO 2, FeO, and MgO unknown. However, the presence of compositionally similar contents are similar in both phases, although, Na 2O shows a aenigmatite in both Kaidun #d4A and granitoid clasts of marked difference. Na 2O content in the Na, Ti-bearing silicate Adzhi-Bogdo (or, in Adzhi-Bogdo, a similar mineral phase) of Adzhi-Bogdo is possibly overestimated, particularly if suggests a genetic relationship. albite was used as the Na standard during microprobe analysis The matrix of clast #d(3–5)D, as mentioned above, has and if measurements of both standard and sample were made probably been insignificantly contaminated by material from under standard conditions. Sodium is very unstable under the matrix of the meteorite. This allows us to evaluate the electron beam in albite but very stable in aenigmatite. The use character of the primary material that underwent melting. The Kaidun meteorite 735

c When determining the nature of the melted primary material,

6 7 2 6 8 8 5 9 4 l 6 7 4 5 9 7 2 9 6 ...... the key parameters appear to be: 1) relict character of the a t 9 9 0 1 8 9 8 8 3 o 9 9 0 0 9 9 9 8 8

T 1 1 large grains of the clast under study—two different pyroxenes and apatite; 2) the high content of alkali plagioclase in the 7 3

. 2 clast; and 3) the lack of significant amounts of olivine. These 1 0 4 – – 0 2 7 6 3 5 parameters indicate a strongly differentiated character for the 7 5 2 1 4 1 3 ...... O 2 0 – 9 0 0 0 – – – 1 0

P 4 3 melted material. Based on the bulk SiO 2 content and the sum of Na2O + K2O in clast #d(3–5)D, in reference to earthlike 8 9 3 2 .

. rocks, the clast falls among the intermediate rocks of the 1 1 – – 3 3 3 9 5 7 6 2 1 1 subalkaline series, in the family of trachyandesites 0 0 0 1 1 0 3 3 4 2 O ...... 2 0 0 0 1 1 – 0 1 1 0 0 K <

< < (Bogatikov et al. 1981). The clasts in this investigation show many similar 3 8 8

8 2 5 8 mineralogical characteristics: albitic or nearly albitic . . . . 0 0 7 6 1 – – –

– 9 2 2 2 6 8 2 3 9 6 4 plagioclase compositions and the presence of fluorapatite. O 4 1 1 1 3 9 9 5 7 6 3 1 6 2 ...... a 0 0 0 0 7 6 7 7 7 6 6 0 0 The evidence suggests that both clasts are genetically related N 1 1 and formed from the same parent body. However, the great

0 8 0 .

7 8 5 1 difference in the textures of the clasts (intensive remelting of ) . . . . 0 3 0 5 – 5 – – % clast #d(3–5)D and primary igneous character of clast #d4A) t 0 0 – 2 4 6 9 8 9 6 3 9 6 5 5 2 5 4 7 3 2 5 0 4 3 O ...... w a 0 0 3 3 0 0 0 0 0 4 4 1 0 suggests that these clasts were incorporated into the Kaidun , C 5 5 s

n parent body during different impact events. o i t Among , the show some affinities to 8 0 5 a 0 i 3 7 0 . . . . r 0 0 3 1 Kaidun clasts (Mittlefehldt et al. 1998; Y amaguchi et al. a – – – 1 3 v 8 0 4 9 1 6 4 – O

0 1 1 6 4 8 9 0 8 5 9 7

. 1996). These meteorites have essentially pyroxene- ...... g d 0 0 0 3 3 6 0 1 0 0 3 1 n M < 1 1 1 2 plagioclase compositions with little or no olivine. The size of a

e pyroxene grains in eucrites vary within wide boundaries— g 7 8 1 a 1 7 7 . . . r

0 0 0 from tens of mm to 1 mm. The compositions of some eucriric e – – – v 3 4 0 8 9 2 6 0 3 0 3 7 O 0 1 1 6 5 5 7 7 6 5 3 3 a pyroxenes are similar to the large grains of pyroxene in the ...... n ( 0 0 0 0 0 0 0 0 0 0 1 0

M < Kaidun clasts (Yamaguchi et al. 1996). Phosphates in the A 4

d eucrites are represented by fluorapatite and whitlockite 7 3 # 2 7 4 6

. . . . t (merrilite), and the size of their grains varies from 0 0 6 0 s – – 3 2 a a 7 9 0 9 – – l

1 0 6 4 4 1 4 2 6 4 3 0 2 submicrometers to ~50 mm (Delaney et al. 1984). The size of O ...... c e 0 0 0 0 5 4 0 6 6 0 0 7 4

F 3 3 3 4 4 2 2 1 1 n the plagioclase grains, in some cases, reaches 0.7 mm u d

i (Yamaguchi et al. 1996). However, unlike the plagioclase of a

1 clast #d(3–5)D, the composition of the plagioclase of the K 1 .

0 e –

3 eucrites is strongly calcic (anorthite-bytownite) and is h 3 3 3 3 3 t O 0 0 0 0 0

. . . . . 2 r 0 0 0 0 0 – – – characterized by a very low K 2O content (=0.1 wt%; m C < < < < < o

r Mittlefehldt et al. 1998). Thus, it is clear that linking the f s 6 8 formation of the Kaidun clasts with material is not t 9 3 3 . . . n 9 1 0 e 1 – –

3 warranted. – 8 7 6 6 4 3 4 9 0 n O 4 9 9 7 7 7 6 3 2 3 3 2 o ......

l Meteorites of the SNC group are of great interest, 9 8 – 0 0 0 0 0 0 0 6 7 p A 1 1 m especially the basaltic shergottites (Stolper and McSween o c

1979; Stofler et al. 1986; McCoy et al. 1992, 1999; e 4 2 . 0 h . 0 t McSween and Treiman 1998; McSween et al. 1996; Meyer 0 1 – f – 3 3 3 8 3 8 8 0 2 o 1998; Rubin et al. 2000; Taylor et al. 2000; Zipfel 2000). 0 0 0 5 8 7 0 2

...... O . i 0 0 0 n – – 9 8 9 0 0 % T < < < o

t These meteorites consist of 40– 70 vol% of large, often >1 i w t i

1 mm, crystals of pigeonite and subcalcic augite with s 5 . 0 o 0 2 7 5 2

. . . . p homogeneous cores and strongly zoned peripheries. l 9 0 2 4 C 6 – 4 5 m

, – 2 6 – – 2 Shergottite plagioclase commonly occurs in the form of o 3 9 1 6 4 1 5 1 2 6 5 6 2 5 ...... O 3 c . i 7 7 0 0 2 1 4 2 2 3 2 7 8

. 3 l . S 6 6 4 4 4 4 4 5 5 4 3 e

zoned with composition varying within broad s t a i F e t c s a o i

y boundaries: An Ab Or . The maskelynite content in s 36–68 31–63 1–7 l l m a . a m g s

n i s , , e e various shergottite samples also varies widely: ~9–48 vol%. a f f n .

s , 1 2 n . d e e e e h f i n e y t t e e t i a e e t a l o O t t

a a t t i t i i a a C n

e Phosphates in shergottites are represented by whitlockite i i r c c r n n n t t n n e n i i i * e F . l l g a a o o

o o a n i i , b

s s n c s s 3 s s e o , e m m d

a (merrilite) and F-containing chlorapatite. In the shergottite d t o

t n n m o o e e p i i i i g g e 8 e a l l t t e t i i u t e s 3 6 2 4 l l r i i k k v l t m a c n n l l n = F a u f y y b i i l

a e QUE 94201, the apatite crystals have fluorine-rich cores and = = = = l p e e r o p b h h l b l c = l p e

e C A n A n A n A n W W A n P P a n n S A A I S T a b c d e f 736 A. V. Ivanov et al.

chlorine-rich outer layers (McSween et al. 1996). The shergottites in the peripheries of the grains, may be explained content of olivine Fa 40–97 in shergottites, as a rule, does not by their partial dissolution during melting of the clast, and exceed 10 vol% and in Sayh Al Uhaymir reaches 25 vol% also by homogenization during heating. (Zipfel 2000). Some basaltic shergottites (QUE 94201, Zagami) contain different lithologies interlinked by CONCLUSION processes of fractional crystallization (McSween et al. 1996; McCoy et al. 1999). Clasts of alkaline (the second find in meteorites) and The material of clast #d(3–5)D is similar in some subalkaline rocks were found in the Kaidun meteorite. Their characteristics to the material of the basaltic shergottites. The mineralogical characteristics suggest a mutual genetic olivine content of clast #d(3–5)D, according to norm relationship and origin from the same parent body. Clast calculations, is less than 5 vol%. The clast contains fairly #d4A is a large crystal of albite with inclusions of large grains of augite and pigeonite, which is typical for fluorapatite, arfvedsonite, aenigmatite, and wilkinsonite. The shergottites. The clast’s pyroxene compositions fall in fields latter two minerals were not previously known in meteorites. corresponding to the pyroxenes of shergottites in the Clast #d(3–5)D has a melt crystallization texture of mainly pyroxene prism (Meyer 1998) (Fig. 9). However, the average feldspar (oligoclase) composition and contains relict grains of calcium content in the augite clast is somewhat lower and both High-Ca and low-Ca pyroxene plus fluorapatite. The pigeonite is somewhat higher in comparison with the calcium textural and mineralogical characteristics of the clasts suggest content of shergottite pyroxenes. This difference may be an origin by extensive igneous differentiation. Such processes connected with the lower equilibration temperature of most likely took place in a rather large differentiated body. pyrozene clasts in comparison with the equilibration We note that the material of clast #d(3–5)D is similar in some temperature of shergottite pyroxenes (Lindsley 1983). The mineralogical characteristics to the material of the basaltic lack of the zoning, which is characteristic for the pyroxenes of shergottites.

Fig. 9. Pyroxene compositional diagram for the (Meyer 1998) and for large pyroxene grains from the Kaidun #d(3–5)D fragment. The Kaidun pyroxenes, both high-Ca and low-Ca, have rather uniform composition (see Table 1). The Kaidun points are averages of 35 analyses of several augite grains (upper point) and of 5 analyses of one pigeonite grain (lower point).

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