{"id":23378,"date":"2020-08-26T15:55:39","date_gmt":"2020-08-26T13:55:39","guid":{"rendered":"http:\/\/karmaka.de\/?p=23378"},"modified":"2020-08-26T15:57:43","modified_gmt":"2020-08-26T13:57:43","slug":"evidence-for-early-asteroidal-collisions-prior-to-4-15-ga-from-basaltic-eucrite-phosphate-u-pb-chronology","status":"publish","type":"post","link":"https:\/\/karmaka.de\/?p=23378","title":{"rendered":"Evidence for early asteroidal collisions prior to 4.15 Ga from basaltic eucrite phosphate U\u2013Pb chronology<span class=\"badge-status\" style=\"background:#787878\">OPEN ACCESS<\/span>&nbsp;"},"content":{"rendered":"\n<p>Mizuho Koike, Yuji Sano, Naoto Takahata, Tsuyoshi Iizuka, Haruka Ono, Takashi Mikouchi<\/p>\n\n\n\n<p>Earth and Planetary Science Letters<br>In Press, Corrected Proof, Available online 26 August 2020<\/p>\n\n\n\n<p><a rel=\"noreferrer noopener\" href=\"https:\/\/www.sciencedirect.com\/science\/article\/pii\/S0012821X20304416\" target=\"_blank\"><strong>LINK (OPEN ACCESS)<\/strong><\/a><br><\/p>\n\n\n\n<p>&#8220;Highlights<\/p>\n\n\n\n<p>\u2022 NanoSIMS U-Pb dating of phosphates in basaltic eucrites.<br>\u2022 Unbrecciated eucrites recorded the slow cooling process of the asteroid crusts.<br>\u2022 Brecciated eucrites reveal the presence of multiple impacts on Vesta during \u223c4.4\u20134.15 billion years ago.<br>\u2022 These \u201cearly collisions\u201d may be an end tail of the earlier bombardments among the inner solar system.&#8221;<\/p>\n\n\n\n<p class=\"justify-text\">&#8220;The late heavy bombardment (LHB) hypothesis, wherein the terrestrial planets are thought to have suffered intense collisions ca. 3.9 billion years ago, is under debate. Coupled with new dynamical calculations, re-examination of geochronological data seem to support an earlier solar system instability and a smooth monotonic decline in impacts, as opposed to a \u201ccataclysm.\u201d To better understand this collisional history, records from the asteroidal meteorites are required. Here, we report a uranium\u2013lead (U\u2013Pb) chronological dataset for eucrite meteorites thought to originate from the asteroid 4 Vesta; this dataset indicates to a continuous history of collisions prior to 4.15 Ga. Our 207Pb\u204e\/206Pb\u204e model ages of apatite [Ca5(PO4)3(F,Cl,OH)] and merrillite [Ca9NaMg(PO4)7] from three brecciated basaltic eucrites\u2014Juvinas (4150.3 \u00b1 11.6 million years ago (Ma); merrillite only), Camel Donga (disturbed around 4570\u20134370 Ma), and Stannern (4143.0 \u00b1 12.5 Ma)\u2014record multiple thermal metamorphic events during the period of \u223c4.4\u20134.15 Ga. We interpret this to mean that Vesta or the vestoid cluster underwent multiple impacts and moderate high-temperature reheating during this time. The ages of \u223c4.4\u20134.15 Ga are distinctly younger than the initial magmatic process on Vesta (&gt;4.5 Ga) but are significantly older than a later \u201cimpact peak\u201d based on some interpretations of 40Ar\u201339Ar chronologies (\u223c3.9\u20133.5 Ga). The intense collisions prior to 4.15 Ga on Vesta are at odds with the conventional LHB hypothesis but not inconsistent with the much earlier bombardment and monotonic decline scenario. Different radiometric chronologies of the asteroid likely represent the different stages of a continual collisional process. Conversely, the model 207Pb\u204e\/206Pb\u204e ages of apatite in the unbrecciated basaltic eucrite, Agoult, returned an age of 4524.8 \u00b1 9.6 Ma. This may represent slow cooling from an earlier global reheating of the crust on Vesta at 4.55 Ga, as documented by other radiometric chronologies. The apatite in Juvinas recorded a coincident timing of 4516.9 \u00b1 10.4 Ma, which could be due to either slow crustal cooling or impact.&#8221;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Mizuho Koike, Yuji Sano, Naoto Takahata, Tsuyoshi Iizuka, Haruka Ono, Takashi Mikouchi Earth and Planetary Science LettersIn Press, Corrected Proof, Available online 26 August 2020 LINK (OPEN ACCESS) &#8220;Highlights \u2022 NanoSIMS U-Pb dating of phosphates&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[77,72,35,186],"tags":[759,2826,1823,355,1866,3443,1872],"_links":{"self":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/23378"}],"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=23378"}],"version-history":[{"count":2,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/23378\/revisions"}],"predecessor-version":[{"id":23380,"href":"https:\/\/karmaka.de\/index.php?rest_route=\/wp\/v2\/posts\/23378\/revisions\/23380"}],"wp:attachment":[{"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=23378"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=23378"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/karmaka.de\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=23378"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}