{"id":4338,"date":"2015-04-13T22:58:34","date_gmt":"2015-04-13T20:58:34","guid":{"rendered":"http:\/\/karmaka.de\/?p=4338"},"modified":"2015-04-13T23:03:22","modified_gmt":"2015-04-13T21:03:22","slug":"meteorite-zircon-constraints-on-the-bulk-lu%e2%88%92hf-isotope-composition-and-early-differentiation-of-the-earth","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=4338","title":{"rendered":"Meteorite zircon constraints on the bulk Lu\u2212Hf isotope composition and early differentiation of the Earth"},"content":{"rendered":"<p>Tsuyoshi Iizuka, Takao Yamaguchi, Yuki Hibiya, and Yuri Amelin <\/p>\n<p>PNAS 2015 ; published ahead of print April 13, 2015, doi:10.1073\/pnas.1501658112 <\/p>\n<p><a href=\"http:\/\/www.pnas.org\/content\/early\/2015\/04\/08\/1501658112.abstract\" target=\"_blank\"><strong>LINK<\/strong><\/a><\/p>\n<p><a href=\"http:\/\/www.pnas.org\/content\/suppl\/2015\/04\/08\/1501658112.DCSupplemental\/pnas.201501658SI.pdf\" target=\"_blank\"><strong>Supporting information (PDF)<\/strong><\/a><\/p>\n<div class=\"su-quote su-quote-style-default\"><div class=\"su-quote-inner su-u-clearfix su-u-trim\">Significance: The radioactive decay of lutetium-176 to hafnium-176 has been used to study Earth\u2019s crust\u2212mantle differentiation that is the primary agent of the chemical and thermal evolution of the silicate Earth. Yet the data interpretation requires a well-defined hafnium isotope growth curve of the bulk Earth, which is notoriously difficult to reconstruct from the variable bulk compositions of undifferentiated chondrite meteorites. Here we use lutetium\u2013hafnium systematics of meteorite zircon crystals to define the initial hafnium isotope composition of the Solar System and further to identify pristine chondrites that are the best representative of the lutetium\u2013hafnium system of the bulk Earth. The established bulk Earth growth curve provides evidence for Earth\u2019s crust\u2212mantle differentiation as early as 4.5 billion years ago. <\/div><\/div>\n<div class=\"su-quote su-quote-style-default\"><div class=\"su-quote-inner su-u-clearfix su-u-trim\">Knowledge of planetary differentiation is crucial for understanding the chemical and thermal evolution of terrestrial planets. The 176Lu\u2212176Hf radioactive decay system has been widely used to constrain the timescales and mechanisms of silicate differentiation on Earth, but the data interpretation requires accurate estimation of Hf isotope evolution of the bulk Earth. Because both Lu and Hf are refractory lithophile elements, the isotope evolution can be potentially extrapolated from the present-day 176Hf\/177Hf and 176Lu\/177Hf in undifferentiated chondrite meteorites. However, these ratios in chondrites are highly variable due to the metamorphic redistribution of Lu and Hf, making it difficult to ascertain the correct reference values for the bulk Earth. In addition, it has been proposed that chondrites contain excess 176Hf due to the accelerated decay of 176Lu resulting from photoexcitation to a short-lived isomer. If so, the paradigm of a chondritic Earth would be invalid for the Lu\u2212Hf system. Herein we report the first, to our knowledge, high-precision Lu\u2212Hf isotope analysis of meteorite crystalline zircon, a mineral that is resistant to metamorphism and has low Lu\/Hf. We use the meteorite zircon data to define the Solar System initial 176Hf\/177Hf (0.279781 \u00b1 0.000018) and further to identify pristine chondrites that contain no excess 176Hf and accurately represent the Lu\u2212Hf system of the bulk Earth (176Hf\/177Hf = 0.282793 \u00b1 0.000011; 176Lu\/177Hf = 0.0338 \u00b1 0.0001). Our results provide firm evidence that the most primitive Hf in terrestrial zircon reflects the development of a chemically enriched silicate reservoir on Earth as far back as 4.5 billion years ago. <\/div><\/div>\n","protected":false},"excerpt":{"rendered":"<p>Tsuyoshi Iizuka, Takao Yamaguchi, Yuki Hibiya, and Yuri Amelin PNAS 2015 ; published ahead of print April 13, 2015, doi:10.1073\/pnas.1501658112 LINK Supporting information (PDF)<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[922,112],"tags":[1247,1248,1243,1250,1246,1244,1245,1249,184],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/4338"}],"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=4338"}],"version-history":[{"count":4,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/4338\/revisions"}],"predecessor-version":[{"id":4342,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/4338\/revisions\/4342"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4338"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4338"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4338"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}