LINK (open access)<\/strong><\/a><\/p>\n“The CI and CI-like chondrites provide a record of aqueous alteration in the early solar system. However, the CI-like chondrites differ in having also experienced a late stage period of thermal metamorphism. In order to constrain the nature and extent of the aqueous and thermal alteration, we have investigated the bulk mineralogy and abundance of H 2 O in the CI and CI-like chondrites using thermogravimetric analysis and infrared spectroscopy.<\/p>\n
The CI chondrites Ivuna and Orgueil show significant mass loss (28.5\u201331.8 wt.%) upon heating to 1000 \u00b0C due to dehydration and dehydroxylation of abundant phyllosilicates and Fe-(oxy)hydroxides and the decomposition of Fe-sulphides, carbonates and organics. Infrared spectra for Ivuna and Orgueil have a prominent 3-\u03bcm feature due to bound \u2212OH\/H 2 O in phyllosilicates and Fe-(oxy)hydroxides and only a minor 11-\u03bcm feature from anhydrous silicates. These characteristics are consistent with previous studies indicating that the CI chondrites underwent near-complete aqueous alteration. Similarities in the total abundance of H 2 O and 3 \u03bcm\/11 \u03bcm ratio suggest that there is no difference in the relative degree of hydration experienced by Ivuna and Orgueil.<\/p>\n
In contrast, the CI-like chondrites Y-82162 and Y-980115 show lower mass loss (13.8\u201318.8 wt.%) and contain >50 % less H 2 O than the CI chondrites. The 3-\u03bcm feature is almost absent from spectra of Y-82162 and Y-980115 but the 11-\u03bcm feature is intense. The CI-like chondrites experienced thermal metamorphism at temperatures >500 \u00b0C that initially caused dehydration and dehydroxylation of phyllosilicates before partial recrystallization back into anhydrous silicates. The surfaces of many C-type asteroids were probably heated through impact metamorphism and\/or solar radiation, so thermally altered carbonaceous chondrites are likely good analogues for samples that will be returned by the Hayabusa-2 and OSIRIS-REx missions.”<\/p>\n
“Conclusions<\/p>\n
We have used TGA and IR spectroscopy to characterise bulk samples of CI and CI-like chondrites for which modal mineralogy was previously determined by King et al. ([2015]). TGA and IR spectroscopy are useful tools for quantifying hydrous and anhydrous species in these meteorites, providing new insights into the nature and extent of aqueous and thermal alteration. In summary we find the following:<\/p>\n
(1) The CI chondrites Ivuna and Orgueil contain the same abundance of H 2 O, whilst the intensity of their 3- and 11-\u03bcm features\u2014attributed to bound \u2013OH in phyllosilicates and anhydrous silicates, respectively\u2014is very similar. This is consistent with almost identical total phyllosilicate abundances and suggests that at the bulk scale, the CI chondrites experienced equal degrees of aqueous alteration.<\/p>\n
(2) The CI-like chondrites Y-82162 and Y-980115 contain >50 % less H 2 O than the CI chondrites. The 3-\u03bcm feature is almost absent from these meteorites, but the 11-\u03bcm feature is intense. This is consistent with thermal metamorphism of the CI-like chondrites that caused dehydration and dehydroxylation of the phyllosilicates and subsequent recrystallization back into olivine.<\/p>\n
(3) Peak metamorphic temperatures experienced by the CI-like chondrites exceeded 500 \u00b0C and were possibly as high as 700\u2013800 \u00b0C. Y-980115 contains more H 2 O and has an increased 3 \u03bcm\/11 \u03bcm ratio relative to Y-82162. It was either heated to a lower metamorphic temperature than Y-82162, or the duration of heating was shorter. The cause of the thermal metamorphism was probably impacts and\/or solar radiation.<\/p>\n
(4) The H 2 O abundances of CI chondrites are in reasonable agreement with those estimated for the surfaces of the most water-rich C-type asteroids. However, many C-type asteroids appear to contain significantly less H 2 O and are more consistent with the CI-like chondrites. Thermally altered carbonaceous chondrites are likely good analogues for samples that will be returned from surfaces of C-type asteroids by the Hayabusa-2 and OSIRIS-REx missions.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Ashley King, Jake Solomon, Paul Schofield, Sara Russell Earth, Planets and Space 2015, 67:198 (9 December 2015) doi:10.1186\/s40623-015-0370-4 LINK (open access) “The CI and CI-like chondrites provide a record of aqueous alteration in the early…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,10,2243,552,181],"tags":[1842,106,1809,1579,2244,815,734,110,1886,729,731],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/6350"}],"collection":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6350"}],"version-history":[{"count":2,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/6350\/revisions"}],"predecessor-version":[{"id":6352,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/6350\/revisions\/6352"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6350"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6350"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6350"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}