39Ar‐40Ar chronology of the enstatite chondrite parent bodies. (4th March 2014)

• Record Type: Journal Article
• Authors: Hopp, Jens; Trieloff, Mario; Ott, Uli; Korochantseva, Ekaterina V.; Buykin, Alexey I.
• Is Part Of: Meteoritics & planetary science. Volume 49:Number 3(2014:Mar.)
• Page Start: 358
• Page End: 372
• Publication Date: 2014-03-04
• Subjects: Meteorites -- Periodicals; Planetology -- Periodicals; 523.4
• DOI: 10.1111/maps.12243
• Languages: English
• ISSNs: 1086-9379

Abstract

<abstract abstract-type="main" id="maps12243-abs-0001"> <title>Abstract</title> <p>Ar‐Ar isochron ages of EL chondrites suggest closure of the K‐Ar system at 4.49 ± 0.01 Ga for EL5 and 6 chondrites, and 4.45 ± 0.01 Ga for EL3 MAC 88136. The high‐temperature release regimes contain a mixture of radiogenic <sup>40</sup>Ar* and trapped primordial argon (solar or Q‐type) with <sup>40</sup>Ar/<sup>36</sup>Ar<sub>TR</sub> ~ 0<bold>, </bold> which does not affect the <sup>40</sup>Ar budget. The low‐temperature extractions show evidence of an excess <sup>40</sup>Ar component. The <sup>40</sup>Ar/<sup>36</sup>Ar is 180–270; it is defined by intercept values of isochron regression. Excess <sup>40</sup>Ar is only detectable in petrologic types >4/5. These lost most of their primordial <sup>36</sup>Ar from low‐temperature phases during metamorphism and retrapped excess <sup>40</sup>Ar. The origin of this excess <sup>40</sup>Ar component is probably related to metamorphic Ar mobilization, homogenization of primordial and in situ radiogenic Ar, and trapping of Ar by distinct low‐temperature phases. Ar‐Ar ages of EH chondrites are more variable and show clear evidence of a major impact‐induced partial resetting at about 2.2 Ga ago or alternatively, prolonged metamorphic decomposition of major K carrier phases. EH impact melt LAP 02225 displayed the highest Ar‐Ar isochron age of 4.53 ± 0.01 Ga. This age sets a limit of about 25–45 Ma for the age bias between the K‐Ar and U‐Pb decay systems.</p> </abstract>