Honda, MasahikoPhillips, DavidHarris, Jeffrey WMatsumoto, Takuya2015-12-070012-821Xhttp://hdl.handle.net/1885/18978We have undertaken helium, neon and argon step-heating, isotopic analyses of eleven polycrystalline diamonds of known peridotite/eclogite paragenesis from the Jwaneng kimberlite pipe, Botswana. In contrast to the findings of crustal noble gases in framesites from the same kimberlite pipe (Honda et al., 2004. Unusual noble gas compositions in polycrystalline diamonds: preliminary results from the Jwaneng kimberlite, Botswana. Chem. Geol. 203, 347-358.), the Jwaneng polycrystalline diamonds appear to contain similar noble gas isotopic compositions (particularly Ne) to those representing a mantle source for MORBs. This implies that the Jwaneng polycrystalline diamonds may have formed in recent times, possibly close to the time of kimberlite emplacement at ~. 235. Ma. In contrast, Jwaneng framesites could be as old as gem diamonds (mineral inclusion ages of ~. 2.9. Ga). Furthermore, the data indicate that the sub-continental mantle lithosphere in the region has heterogeneous Ne isotopic compositions, or that these compositions changed over time from crustal Ne (as observed in the framesites) to MORB-like (as observed in the polycrystalline diamonds).Keywords: Botswana; Continental mantle; Diamond formation; Gem diamond; Isotopic analysis; Isotopic composition; Kimberlite pipes; Mantle evolution; Mantle lithosphere; Mantle source; Mineral inclusions; Noble gas; Noble gas isotopic composition; Polycrystalline di Diamond; Mantle evolution; Mantle lithosphere; Noble gas201110.1016/j.epsl.2010.10.0082016-02-24