Induced Thermoluminescence and Cathodoluminescence Studies of Meteorites

Sears, D. W. G.; Dehart, J. M.; Hasan, F. A.; Lofgren, G. E.

doi:10.1021/bk-1990-0415.ch011

Cited by 8 publications

(13 citation statements)

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“…Consistent with this, the distribution of Cr 2 O 3 in olivine is bimodal, with a strong mode in the same range as type 3.6 Tieschitz and type 3.7 Bremervˆrde and a weaker mode similar to that found in type 3.0 Semarkona. There is no spatial relationship in the Ngawi thin section between chondrules with olivine in the type 3.0 range of Cr contents; these chondrules were dispersed among chondrules with low Cr in olivine, consistent with the CL images of "host" Ngawi material shown by Sears et al (1990) and not the type 3.1 clasts in these images.…”

Section: The Distribution Of Cr In Olivinesupporting

confidence: 69%

“…At the same time, induced TL rises in the bulk meteorites. This has long been attributed to progressive devitrification of glass to form sodic feldspars (e.g., Sears et al 1982;Sears et al 1990;Sears et al 1991b;DeHart et al 1992). The source of blue CL in one chondrule has now been confirmed as crystalline albite, verifying this long line of reasoning.…”

Section: Classification Of Chondrulesmentioning

confidence: 75%

“…With increasing levels of metamorphism, matrix shows increasing levels of blue CL, indicating that feldspar is forming in that location (Sears et al 1990). The only possible source for the Na that enters matrix is chondrules, possibly the same ones that gained Na during the earliest stages of metamorphism.…”

Section: Alkali Mobility In Matrixmentioning

confidence: 98%

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The onset of metamorphism in ordinary and carbonaceous chondrites

Grossman

Brearley

2005

Meteorit & Planetary Scien

342

441

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Received May 18, 2004; revision accepted November 3, 2004) Abstract-Ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by Xray mapping techniques. A variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) methods. The matrix in the least metamorphosed chondrites is rich in S and Na. The S is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains. Progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules. Alkalis initially leave the matrix and enter chondrules during early metamorphism. Feldspar subsequently nucleates in the matrix and Na re-enters from chondrules. These metamorphic trends can be used to refine classification schemes for chondrites. Cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3.0 and 3.1 into types 3.00 through 3.15. On this basis, the most primitive ordinary chondrite known is Semarkona, although even this meteorite has experienced a small amount of metamorphism. Allan Hills (ALH) A77307 is the least metamorphosed CO chondrite and shares many properties with the ungrouped carbonaceous chondrite Acfer 094. Analytical problems are significant for glasses in type II chondrules, as Na is easily lost during microprobe analysis. As a result, existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised.

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Section: The Distribution Of Cr In Olivinesupporting

confidence: 69%

Section: Classification Of Chondrulesmentioning

confidence: 75%

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The onset of metamorphism in ordinary and carbonaceous chondrites

Grossman

Brearley

2005

Meteorit & Planetary Scien

342

441

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“…[13] Semarkona is unique in its CL properties as it is in many chemical, isotopic and mineralogical properties [e.g., Sears et al, 1990;Matsunami et al, 1993]. Large chondrules and other structural components in Semarkona are surrounded by a fine-gained (almost ''smoky'') matrix with red CL characteristic of Fe-free olivine.…”

Section: Ordinary Chondrites (Cathodoluminescence Figures A8 --A28)mentioning

confidence: 99%

Photomosaics of the cathodoluminescence of 60 sections of meteorites and lunar samples

Akridge¹

2004

J. Geophys. Res.

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[1] Cathodoluminescence (CL) petrography provides a means of observing petrographic and compositional properties of geological samples not readily observable by other techniques. We report the low-magnification CL images of 60 sections of extraterrestrial materials. The images we report include ordinary chondrites (including type 3 ordinary chondrites and gas-rich regolith breccias), enstatite chondrites, CO chondrites and a CM chondrite, eucrites and a howardite, lunar highland regolith breccias, and lunar soils. The CL images show how primitive materials respond to parent body metamorphism, how the metamorphic history of EL chondrites differs from that of EH chondrites, how dark matrix and light clasts of regolith breccias relate to each other, how metamorphism affects eucrites, the texture of lunar regolith breccias and the distribution of crystallized lunar spherules (''lunar chondrules''), and how regolith working affects the mineral properties of lunar soils. More particularly, we argue that such images are a rich source of new information on the nature and history of these materials and that our efforts to date are a small fraction of what can be done.

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“…The TL apparatus and procedures and the cathodoluminescence (CL) imaging were described by Sears and Weeks (1983) and Sears et al (1989). The natural TL was removed by heatin'k>the sample to 500 "C in the TL apparatus and TL induced by a 250 mCi Sr p source was measured.…”

Section: Thermoluminescence Measurementsmentioning

confidence: 99%

Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

et al. 1995

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— In order to investigate the relative importance of dry metamorphism and aqueous alteration in the history of chondrules, chondrules were hand‐picked from the Semarkona (petrographic type 3.0), Bishunpur (3.1), Chainpur (3.4), Dhajala (3.8) and Allegan (5) chondrites, and matrix samples were extracted from the first three ordinary chondrites. The thermoluminescence (TL) properties of all the samples were measured, and appropriate subsets of the samples were analyzed by electron‐microprobe and radiochemical neutron activation and the water and H‐isotopic composition determined. The TL data for chondrules from Semarkona and Bishunpur scatter widely showing no unambiguous trends, although group B1 chondrules tend to have lower sensitivities and lower peak temperatures compared with group A5 chondrules. It is argued that these data reflect the variety of processes accompanying chondrule formation. The chondrules show remarkably uniform contents of the highly labile elements, indicating mineralogical control on abundance and volatile loss from silicates and loss and recondensation of mobile chalcophiles and siderophiles in some cases. Very high D/H values (up to ∼8000‰ SMOW) are observed in certain Semarkona chondrules, a confirmation of earlier work. With increasing petrographic type, mean TL sensitivities of the chondrules increase, the spread of values within an individual meteorite decreases, and peak temperatures and peak widths show trends indicating that the TL is mainly produced by feldspar and that dry, thermal metamorphism is the dominant secondary process experienced by the chondrules. The TL sensitivities of matrix samples also increase with petrographic type. Chainpur matrix samples show the same spread of peak temperatures and peak widths as Chainpur chondrules, indicating metamorphism‐related changes in the feldspar are responsible for the TL of the matrix. The TL data for the Semarkona and Bishunpur matrix samples provide, at best, only weak evidence for aqueous alteration, but the matrix contains H with approximately terrestrial D/H values, even though it contains much water. Secondary processes (probably aqueous alteration) presumably lowered the D/H of the matrix and certain chondrules. While chondrule properties appear to be governed primarily by formation processes and subsequent metamorphism, the matrix of Semarkona has a more complex history involving aqueous alteration as a meteorite‐wide process.

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Induced Thermoluminescence and Cathodoluminescence Studies of Meteorites

Cited by 8 publications

References 0 publications

The onset of metamorphism in ordinary and carbonaceous chondrites

The onset of metamorphism in ordinary and carbonaceous chondrites

Photomosaics of the cathodoluminescence of 60 sections of meteorites and lunar samples

Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

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