LINK<\/strong><\/a><\/p>\n\n\n\n“Laser ablation inductively coupled plasma\u2010mass spectrometry (LA\u2010ICP\u2010MS) U\u2013Pb geochronology of shocked zircon grains in a vesicular\u2010fluidal impact melt rock from the \u226554 km Charlevoix impact structure, Qu\u00e9bec, Canada, suggests an Ordovician to Silurian age of 450 \u00b1 20 Ma for the impact. This age is anchored by concordant U\u2013Pb results of ~450 Ma for a U\u2010rich, cryptocrystalline zircon grain in the melt rock, interpreted as a recrystallized metamict zircon crystal; the U\u2013Th\u2013Pb system of the metamict grain was seemingly chronometrically reset by the Charlevoix impact, but withstood later tectonometamorphic events. The new zircon age for Charlevoix is in agreement with a stratigraphically constrained Late Ordovician maximum age of ~453 Ma and corroborates earlier suggestions that the impact occurred most likely in the Ordovician, and not ~100 Myr later, as indicated by previous K\/Ar and 40Ar\/39Ar geochronologic results. The latter may reflect postimpact thermal overprint of impactites during the Salinian (Late Silurian to Early Devonian) and\/or Acadian (Late Devonian) orogenies. U\u2013Pb geochronology of zircon crystals in anorthosite exposed in the central uplift of the impact structure yielded a Grenvillian crystallization age of 1062 \u00b1 11 Ma. The preferred Ordovician age for the Charlevoix impact structure, which is partially overthrusted by the Appalachian front, suggests the impact occurred during a phase of Taconian tectonism and an episode of enhanced asteroid bombardment of the Earth. Our results, moreover, demonstrate that (recrystallized) metamict zircon grains may be of particular interest in impact geochronology.”<\/p>\n","protected":false},"excerpt":{"rendered":"
Martin Schmieder, Barry J. Shaulis, Thomas J. Lapen, Elmar Buchner, David A. Kring Meteoritics & Planetary Science First Published: 19 June 2019 LINK “Laser ablation inductively coupled plasma\u2010mass spectrometry (LA\u2010ICP\u2010MS) U\u2013Pb geochronology of shocked zircon…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[90],"tags":[5043,92,321,1934,4635],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/19822"}],"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=19822"}],"version-history":[{"count":1,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/19822\/revisions"}],"predecessor-version":[{"id":19823,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/19822\/revisions\/19823"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=19822"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=19822"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=19822"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}