Induced thermoluminescence (TL) images of ordinary chondrites, ALH-77214 (L3.4-3.5), Y-74191 (L3.6), ALH-77216 (L3.8) and ALH-78043 (L6), were measured by the TL spatial distribution readout system combined with a microscope and TL characteristics [peak temperature and peak width] of mesostases were analyzed. Their chemical compositions were also analyzed by an electron probe X-ray microanalyzer. We found that; (1) The mesostasis was responsible for much of the TL in the ordinary chondrites, (2) A mesostasis of normative anorthite compositions showed low peak temperature (&acd;90℃) and narrow width (&acd;65℃), while a mesostasis of normative albite compositions showed high peak temperature (&acd;125℃) and wide width (&acd;100℃), (3) A main phosphor in a low petrologic grade chondrite 3.5 was a high albite mesostasis, (4) Some chondrules in the same fragments of the type 3 chondrites showed no or weak TL emission and these mesostases had high normative albite. These facts suggest that in type 3 ordinary chondrites; (1) The post-accretional metamorphism cannot account for the coexistence of high albite mesostases with TL emission and no emission and a high anorthite mesostasis with TL emission, (2) Low petrologic grade chondrites 3.5 have a large population of slowly cooled chondrules

Fujimura,Shin-ichi

Kubo,Hideyuki

Matsunami,Satoshi

Ninagawa,Kiyotaka

Nishimura,Hiroshi

Wada,Tomonori

Yamamoto, Isao

National Institute of Polar Research Repository

Proc. NIPR Symp. Antarct. Meteorites, 4, 344-351, 1991 THERMOLUMINESCENCE CHARACTERISTICS AND CHEMICAL COMPOSITIONS OF MESOSTASES IN ORDINARY CHONDRITES Kiyotaka NINAGAWA1 , Hideyuki KUB01 , Shin-ichi FUJIMURA1 , Isao Y AMAMOT01 , Tomonori WADA�, Satoshi MATSUNAMI3 and Hiroshi NISHIMURA3 1 0kayama University of Science, 1-1, Ridai-cho, Okayama 700 �Okayama University, 1-1, Tsushimanaka 3-chome, Okayama 700 3 Naruto University of Education, Takashima, Naruto 772 Abstract: Induced thermoluminescence (TL) images of ordinary chondrites, ALH-77214(L3.4-3.5), Y-7419I(L3.6), ALH-77216(L3.8) and ALH-78043(L6), were measured by the TL spatial distribution readout system combined with a microscope and TL characteristics [peak temperature and peak width] of meso­stases were analyzed. Their chemical compositions were also analyzed by an electron probe X-ray microanalyzer. We found that; (1) The mesostasis was responsible for much of the TL in the ordinary chondrites, (2) A mesostasis of normative anorthite compositions showed low peak temperature ("' 90°C) and narrow width ("' 65°C), while a mesostasis of normative al bite compositions showed high peak temperature ("' 125°C) and wide width ("' 100°C), (3) A main phosphor in a low petrologic grade chondrite <3.5 was a high anorthite mesosta­sis and that in high grade chondrites > 3.5 was a high albite mesostasis, (4) Some chondrules in the same fragments of the type 3 chondrites showed no or weak TL emission and these mesostases had high normative albite. These facts suggest that in type 3 ordinary chondrites; (1) The post-accretional metamorphism cannot account for the coexistence of high albite mesostases with TL emission and no emission and a high anorthite mesostasis with TL emission, (2) Low petrologic grade chondrites < 3.5 have a large population of rapidly cooled chondrules and high petrologic grade chondrites > 3.5 have a large population of slowly cooled chondrules. 1. Introduction SEARS et al. have made great progress in quantitative classification of chondrites, using the induced TL property of meteorites (SEARS et al., 1980, 1990, 1991). The natural TL of meteorites has been used to estimate meteorite orbits (MELCHER, 1981a), terrestrial age (SEARS and DURRANI, 1980; MELCHER, 1981b; NINAGAWA et al., 1983; BHANDARI and SENQUPTA, 1988), heat penetration on atmospheric passage (MELCHER, 1979) and shock heating (HASAN et al., 1987). These TL studies have been performed using ground samples with a photomultiplier. On the other hand, TL spatial distribu­tion readout systems have been developed (WALTON and DEBENHAM, 1980; !MAEDA et al., 1985). Our system was improved to provide a quantitative glow curve of a local area using a two-dimensional photon counting method (YAMAMOTO et al., 1987) and 344 TL and Chemical Compositions of Mesostases 345 was applied to meteorites (NINAGAWA et al., 1990). So far the relation between the TL characteristics and bulk composition of sep­arated chondrules has been studied (SEARS et al., 1984) and the main mineral, which is responsible for the TL in meteorites, is known to be a mesostasis [feldspar] (LALOU et al., 1970). But the TL petrography has not been possible until the present. In this report, we firstly measured the TL images of ordinary chondrites in several petrologic grades by the TL spatial distribution readout system and analyzed local glow curves. Next, we analyzed the chemical compositions of mesostases by an electron probe X-ray microanalyzer [EPMA]. The correlation between the locally analyzed TL characteristics and chemical compositions of mesostases was compared directly. 2. Samples and Experiments Antarctic ordinary chondrites, ALH-77214 (L3.4-3.5), Y-74191 (L3.6), ALH-77216 (L3.8) and ALH-78043 (L6) were examined. The sample preparation and the TL spatial distribution readout system combined with a microscope were described previously (NINAGAWA et al., 1990). ALH-77214 (L3.4-3.5), Y-74191 (L3.6), ALH-77216 (L3.8) and ALH-78043 (L6) were irradiated by r-rays of doses of 1320, 660, 120 and 120 krad, respectively, because a low petrologic grade meteorite had low TL sensitivity. The TL measurements were done immediately after r-rays irradiation, at the rate of temperature rise 0.25°C/s with a Corning band pass filter 4-96. An EPMA, JCXA-733 (JEOL LTD.) was used for the chemical composition analysis, operated at 15 kV accelerating voltage and 12 nA beam absorption on PCD. 3. Results and Conclusions Figure l shows backscattered electron images (BEI) and TL images of the me­teorites at the temperature interval 100-110°C. The position of high TL intensity in TL image is put by deep black points. The regions of which local glow curves were analyzed were squared in figures. Most TL comes from the mesostasis. A silica phase was found to be also responsible for the TL in ALH-77214 (L3.4-3.5) and had a TL glow peak at ,..,., 265°C. The typical glow curves of mesostases are shown in Fig. 2. The glow curve of square region I in ALH-77214 has a peak at 81 °C and peak width of 59°C. The glow curve of square region I in ALH-78043 has a peak at l 26°C and peak width of I03°C. The TL characteristics [peak temperature and peak width] of the mesostases are described in Table la. The mesostasis in ALH-78043 (L6) has become feldspar. The slow rate of temperature rise, 0.25°C/s makes TL peak temperature lower than that of SEARS's measurements (7.5°C/s). Figure 3 shows the correlation between peak temperature and peak width. This figure shows the higher the peak temperature, the wider the peak width. The TL emissions from ALH-77216 (L3.8) and ALH-78043 (L6) concentrate on high peak temperature and wide temperature region. GUIMON et al. have classified the TL characteristics into two groups, "low peak temperature and narrow width' and 'high peak temperature and wide width', and attributed the difference of these TL characteristics to the feld-346 NINAGAWA et al. a, ) �6 li""l L:J 1 mm 1 mm TL and Chemical Compositions of Mesostases 347 spar forms (GuIMON et al., 1985). The chemical compositions of region were analyzed by the EPMA. mesostases at several pos1t10ns in each square We obtained the quantity of normative minerals en 600 -,--,-r--i-,-i--,----r-r,---.,.----,-,-r-,,---,---,-T----,-­a l ALH-77214 I mesostasis C 0 0 ..c a.. Q) 0 C Q) 0 en Q) 4-00 .: 200 E :::, 0 E Q) ..c I-C 0 0 ..c a.. Q) 0 C Q) 0 en Q) 4-00 �' 100 200 300 Te mp e r at u r e ( • C) bl ALH-78043 I mesostas is 4-00 .: 200 \ E :::, 0 E Q) ..c I- 100 200 300 Te mp e r at u r e ( • Cl 400 Fig. 2. TL glow curves by the two-dimensional photon counting method. a) square region I [mesostasis] of ALH-772!4(L3.4-3.5), b) square region I [mesostasis] of ALH-78043(L6). Fig. I (opposite). BE/s and induced TL images. Long dimension is 2.9 mm. The position of high TL intensity is put by deep black points. The squares show the regions, where local TL glow curves were analyzed and chemical compositions of mesostases were analyzed by EPMA. The circles show the regions where the mesostases showed no or weak TL and chemical compositions were analyzed hy EPMA. A) a BEi of ALH-77214(L3.4-3.5), a) B) TL image of ALH-77214 at the temperature interval JOO-I JO"C, a BEi of Y-7719/(LJ.6), b) TL image of Y-7719 I at the temperature interval 100--JJO"C, C) a BEi of ALH-77216(L3.8), c) TL image of ALH-77216 at the temperature interval JOO-I JO'"C, D) a BEi of ALH-78043(L6), d )  TL image of ALH-78043 at the temperature interval JOO-I J0°C. 348 NINAGAWA et al. Table I. TL characteristics and normative ratio of albite/(alhite+ anorthite). a) Square regions in Fig. 1 Induced thermoluminescence Meteorite region peak temperature (°C) ALH-77214 81 II 78 Ill 100 IV 104 Y-77191 I 101 II 133 Ill 133 IV 114 V 113 ALH-77216 I 125 II 134 Ill 128 IV 134 V 118 ALH-78043 I 126 II 133 Ill 126 IV 126 V 119 VI 121 b) Circled regions in Fig. 1 ALH-77214 Y-77191 -- -- -- - --- --�-- --�---V VI VII no TL no TL no TL ALH-77216 VI weak TL peak width (°C) 59 57 82 70 71 115 102 93 80 JOO 98 107 99 98 103 113 IOI 111 96 93 Normative ratio of albite/(albite+anorthite) (mole % ) 40. 7 ±2.2 28.6± 1. 8 79.8±2. 7 28. 7±7.7 21.1 100 100 98.2±1.4 93.9±8.7 84.5± 1.8 89.2± 1.0 86.5±2.1 93.9±8.2 84.4±0. 3 81.1±1.1 82.4±0.5 80.8±0.6 82.2± 1.3 78.1 ±1.7 77 .9±2.2 98. 7 ± 1. 8 100 100 98.1 ±1.9 in these mesostases. The average ratio, albite/(albite+anorthite) (mole %), was calculated and was also listed in Table I a. We obtained that high normative anorthite mesostases >50% in ALH-77214 (L3.4-3.5) and Y-77191 (L3.6) have low peak tem­peratures and narrow widths, and high normative albite mesostases >50% in all TL measured chondrites had high peak temperatures and wide widths. In our result, the difference of TL characteristics can be attributed to the chemical compositions of mesostases, not to the feldspar forms. As a bulk TL characteristics the ordinary chondrites under petrologic type 3.5 belong to the group of 'low peak temperature and narrow width' and those above type 3.5 belong to the group of 'high peak temperature and wide width' (GUIMON 200 150 0 0 -..s::; ..... 100 -0 � ...:.;: ., CP 0.. 50 TL and Chemical Compositions of Mesostases Hesostasis • m .. II) z X ALH-77214(L3.4-3.5) 1,11,IV normative anorthite ALH-77214(L3.4-3.5) III normative albite Y -74191(L3.6) I normative anorthite Y -74191(L3.6) II,III,IV,V normative albite ALH-77216(L3.8) I,II,III,IV,V normative albite ALH-78043(L6) I,II,III,IV,V,VI normative albite X � X (!)\,, C!J (!) ... •• 50 100 150 Pe a k Te mp e r at u r e ( • C) >501 >SOI >501 >501 >501 >501 Fig. 3. The correlation between TL peak temperature and peak width. 349 200 et al., 1985). We found that the high anorthite mesostasis is mainly responsible for the TL under the petrologic type 3.5, ALH-77214 (L3.4-3.5) and that the high albite mesostasis is mainly responsible for the TL above type 3.5, Y-74191 (L3.6), ALH-77216 (L3.8) and ALH-78043 (L6). We recognized that there were some chondrules which showed no or weak TL emission in the same fragments of the type 3 ordinary chondrites. These chondrules are shown with circles in Fig. I, region V in ALH-77214, regions VI and VII in Y-74191, and region VI in ALH-77216. It is considered that glass shows no or weak TL and crystallized mesostasis [feldspar] shows intense TL (SEARS, 1988). The chem­ical compositions of these mesostases were also analyzed and we obtained the quantity of normative minerals in these mesostases. The average ratio, albite/(albite+anor­thite) (mole %), was calculated and was listed in Table lb. They had a large content of albite. What dose the coexistence of high albite mesostases with TL emission and no emission and high anorthite mesostasis with TL emission in the same fragments of type 3 ordinary chondrites mean? The melting temperature of albite is lower than that of anorthite. If type 3 ordinary chondrites suffered from a post-accretional metamorphism, the coexistence of crystallized and glassy mesostasis of albite conflicts 350 NINAGA WA et al. with the existence of crystallized anorthite mesostasis in the same fragments. Then the coexistence of them means that the type 3 chondrites maintain a state of the forma­tion of each chondrule without suffering from the post-accretional metamorphism. The glassy mesostasis is made by rapid cooling and crystallized mesostasis is by slow cooling in their formation. These results suggest that low petrologic grade chondrites have a large population of rapidly cooled chondrules and high petrologic grade chon­drites have a large population of slowly cooled chondrules in type 3 chondrites. We would like to investigate the relationship between the devitrification process of mesostasis resulting in the formation of feldspar and the effect on thermolumines­cence as a next step. Acknowledgments The authors are indebted to Dr. K. YANAI and Dr. H. KOJIMA, National In­stitute of Polar Research, for the meteorite samples. They would like to thank Prof. N. TAKAOKA, Kyushu University, for providing opportunity to study TL of the meteorites. They are also indebted to Prof. T. HIGASHIMURA and Dr. M. NODA, the Research Reactor Institute, Kyoto University, for kindly helping us with the Co-60 gamma ray irradiation. The authors would like to thank Prof. H. HASEGAWA, Osaka Sangyo University, Prof. K. ENDO and Dr. M. KANEMAKI, Nihon University, for very useful discussions. They would like to thank Dr. T. ITAYA, Okayama University of Science, for providing a norm calculation program. The authors would like to thank Prof. D. SEARS, the University of Arkansas, for encouraging our work. References BHANDARI, N. and SENQUPTA, D. (1988): Terrestrial ages of Antarctic meteorites using the ther­moluminescence levels induced in the fusion crust. Papers Presented to the 13th Symposium on Antarctic Meteorites, June 7-9, 1988. Tokyo, Natl Inst. Polar Res., 103-105. GUIMON, R. K., KECK, B. D., WEEKS, K. s., DEHART, J. and SEARS, D. w. G. (1985): Chemical and physical studies of type 3 chondrites-IV: Annealing studies of a type 3.4 ordinary chondrite and the metamorphic history of meteorites. Geochim. Cosmochim. Acta, 49, 1515-1524. HASAN, F. A., HAQ, M. and SEARS, D. W. G. (1987): The natural thermoluminescence of mete­orites I. Twenty-three antarctic meteorites of known �8 Al content. Proc. Lunar Planet. Sci. Conf., 17th, Pt. 2, E703-E709 (J. Geophys. Res., 92, B4). !MAEDA, K., KITAJIMA, T., KUGA, K., MIONO, s., MISAKI, A., NAKAMURA, M., NINAGAWA, K., OKA­MOTO, Y., SAAVEDRA, 0., SAITO, T., TAKAHASHI, N., TAKANO, Y., TOMIYAMA, T., WADA, T., YAMAMOTO, I. and YAMASHITA, Y. (1985): Spatial distribution readout system of ther­moluminescence sheets. Nucl. Instrum. Methods, A241, 567-571. LALOU, C., BRITO, u., NORDEMANN, D. and MARY, M. (1970): Thermoluminescence induite dans des cibles epaisses par des protons de 3 GeV. C.R. Acad. Sci., Ser. B, 270, 1706-1708. MELCHER, C. L. (1979): Kirin meteorites: Temperature gradient produced during atmospheric passage. Meteoritics, 14, 309-316. MELCHER, C. L. (1981a): Thermoluminescence of meteorites and their orbits. Earth Planet. Sci. Lett., 52, 39-54. MELCHER, C. L. (1981 b): Thermoluminescence of meteorites and their terrestrial ages. Geochim. Cosmochim. Acta, 45, 615-626. TL and Chemical Compositions of Mesostases 351 NINAGAWA, K. , MIONO, s., YOSHIDA, M.  and TAKAOKA, N. ( 1983) : Measurement of terrestrial age of Antarctic meteorites by thermoluminescence technique. Mem. Natl Inst. Polar Res., Spec . Issue, 30, 251-258. NINAGAWA, K. , YAMAMOTO, I., WADA, T., MATSUNAMI, s. and NISHIMURA, H. ( 1990) : Thermolumi­nescence study of ordinary chondrites by TL spatial distribution readout system. Proc. NIPR Symp. Antarct. 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D. and Lu, J. (199 1 ) : Chemical and physical studies of type 3 chondrites-XI : Metamorphism, pairing, brecciation of type 3 ordinary chondrites. Proc . Lunar Planet. Sci., 21, 493-512. WALTON, A. J. and DEBENHAM, N. C. (1980) : Spatial distribution studies of thermoluminescence using a high gain image intensifier. Nature, 284, 42-44. YAMAMOTO, I., !MAEDA, K. , TAKAHASHI, N. , NINAGAWA, K. , TOMIYAMA, T. , WADA, T. and YAMASHITA, Y. (1987) : Spatial distribution readout system of thermoluminescence sheet II. Nucl. lnstrum. Methods, A256, 567-575. (Received August 2, 1990 ; Revised manuscript received October 3, 1990) 

Thermoluminescence characteristics and chemical compositions of mesostases in ordinary chondrites

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Thermoluminescence characteristics and chemical compositions of mesostases in ordinary chondrites

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