Artist's depiction of a solar nebula and subsequent evolution of our solar system (image taken from panoramicuniverse.com)
Chondrites contain distinct, millimeter-sized objects called chondrules. These chondrules originated as free-floating molten droplets that were flash heated and later crystallized. In this study, I used a petrographic microscope to characterize the textures of the chondrules within NWA-6104, a chondritic meteorite, to help determine the degree of thermal and aqueous alteration. I also used a Cameca SX100 electron microprobe to analyze its chemistry and classify it, as it had not been previously studied.
Photomicrograph of an olivine chondrule from NWA-6104
Textural observations and the chemistry of NWA-6104 classified it as an L5/6 ordinary chondrite. L stands for low iron bearing and 5/6 characterizes the degree of alteration, with 3 being the lowest; values above or below 3 experience either thermal or aqueous alteration, respectively. The degree of alteration (5/6) was determined petrographically by certain textural criterion. Chemical analyses constrained the peak metamorphic temperatures that the parent body of NWA-6104 experienced to 800-900 +50 oC. This range of temperatures is consistent with the degree of metamorphism that would be expected for a 5/6 ordinary chondrite.
To see the original paper from which this post was whittled, please go here.
I think that the post gives a good introduction to meteorites and the information they might contain about the early conditions of our solar system. What I took out of the post is that textural observations of this meteorite are consistent with certain chemical constraints in classifying the meteorite's degree of alteration (particularly thermal metamorphism). However, it is not clear to me what the significance is of this particular degree of thermal metamorphism. Can this be elaborated on?
ReplyDeleteThis post provides good background and detail to explain the significance of studying chondrites. This is especially helpful to a general audience. I would only suggest adding some more detail regarding the sample itself and the implications of the analysis of this specific sample as it is not immediately evident from the sample description. This would help place the sample in context of early solar system evolution.
ReplyDeleteThe post does a good job introducing the background material on meteorites in an understandable manner, and the photo's are excellent. However I think the main component missing is what the importance of the topic is. What information can you obtain that is pertinent to your questions from this meteorite? Is the classification not ordinary or of particular interest?
ReplyDeleteI like the general description of chondrites and chondrules. However, I'm not sure how the discussion about the metamorphic grade of a specific chondrite fits in to the big picture. It almost seems like this should be broken up into two different posts; one on how chondrites/chondrules are formed and another on all the information that can be gleaned from NWA-6104.
ReplyDeleteI think it's a little confusing when you say chondrites have not undergone significant melting or differentiation, and then say that they have undergone alteration with fluids and heating. I would make the distinction very clear between thermal processing and alteration. Maybe you could say the composition is mostly primitive (you could even draw people in by saying their composition is practically that of the sun, minus volatiles), rather than say they were altered. Also, I think it would be useful to explain how they formed in the first place (generally). Very cool topic!
ReplyDeleteThe post seemed both interesting and understandable to me. I particularly liked the inclusion of the photomicrograph, though, come to think of it, what is being shown could use some further elaboration in the caption.
ReplyDeleteAnything with a thin section photo is OK in my books! I would remove the reference to the microprobe as it just complicates the story. I would just say 'the chemistry of these tell us....' and leave out the methods for the general audience.
ReplyDeleteThis post is written in an understandable language and clearly structured in three parts about chondrites, chondrules and the new findings to NWA-6104. However, the last part could be improved by explaining the reader the importance of this study and how the data contribute to a more detailed picture of the processes in Early Solar System.
ReplyDeletealteration of geological smaple is common. a furthur inference about the solar nebula is self-contained for this post.
ReplyDeleteYour post has a strong start; you do a good job of introducing why meteorite observations can be important. However, I would like to see more about the implications of the heating of your sample-- a broader picture view that incorporates your observations, rather than simply stating them, would lend the post a strong finish.
ReplyDelete