{"id":11606,"date":"2017-02-09T12:24:28","date_gmt":"2017-02-09T11:24:28","guid":{"rendered":"http:\/\/karmaka.de\/?p=11606"},"modified":"2017-02-09T12:34:28","modified_gmt":"2017-02-09T11:34:28","slug":"fluid-evolution-in-cm-carbonaceous-chondrites-tracked-through-the-oxygen-isotopic-compositions-of-carbonates","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=11606","title":{"rendered":"Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"<p>P. Lindgren, M.R. Lee, N.A. Starkey, I.A. Franchi<\/p>\n<p>Geochimica et Cosmochimica Acta<br \/>\nIn Press, Accepted Manuscript, Available online 9 February 2017<br \/>\ndx.doi.org\/10.1016\/j.gca.2017.01.048<\/p>\n<p><a href=\"http:\/\/www.sciencedirect.com\/science\/article\/pii\/S0016703717300728\" target=\"_blank\"><strong>LINK (OPEN ACCESS)<\/strong><\/a><\/p>\n<p>&#8220;The oxygen isotopic compositions of calcite grains in four CM carbonaceous chondrites have been determined by NanoSIMS, and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration. Two types of calcite were identified in Murchison, Mighei, Cold Bokkeveld and LaPaz Icefield 031166 by differences in their petrographic properties and oxygen isotope values. Type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration. On average, the type 1 grains have a \u03b418O of \u223c32\u201336 \u2030 (VSMOW), and \u039417O of between \u223c2 and -1 \u2030. Most grains of type 2 calcite precipitated after type 1. They contain micropores and inclusions, and have replaced ferromagnesian silicate minerals. Type 2 calcite has an average \u03b418O of \u223c21\u201324 \u2030 (VSMOW) and a \u039417O of between \u223c-1 and -3 \u2030. Such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose \u03b418O and \u03b417O values had changed by reaction with parent body silicates, as predicted by the closed-system model for aqueous alteration. Temperatures are likely to have increased over the timespan of calcite precipitation, possibly owing to exothermic serpentinisation. The most highly altered CM chondrites commonly contain dolomite in addition to calcite. Dolomite grains in two previously studied CM chondrites have a narrow range in \u03b418O (\u223c25\u201329 \u2030 VSMOW), with \u039417O \u223c-1 to -3 \u2030. These grains are likely to have precipitated between types 1 and 2 calcite, and in response to a transient heating event and\/or a brief increase in fluid magnesium\/calcium ratios. In spite of this evidence for localised excursions in temperature and\/or solution chemistry, the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions. The CM carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or, more probably, a single C-type asteroid.&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>P. Lindgren, M.R. Lee, N.A. Starkey, I.A. Franchi Geochimica et Cosmochimica Acta In Press, Accepted Manuscript, Available online 9 February 2017 dx.doi.org\/10.1016\/j.gca.2017.01.048 LINK (OPEN ACCESS) &#8220;The oxygen isotopic compositions of calcite grains in four CM&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[61,9,18,65],"tags":[2223,3273,701,105,3646,1054,3645,1758,107],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/11606"}],"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=11606"}],"version-history":[{"count":3,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/11606\/revisions"}],"predecessor-version":[{"id":11611,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/11606\/revisions\/11611"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=11606"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=11606"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=11606"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}