Sr-Nd-Pb isotopes of fluids in diamond record two-stage modification of the continental lithosphere

Abstract

Sample Description Seven microinclusion-bearing fibrous diamonds from a single source in Canada were selected for the present study from a private collection of M. Schrauder (Vienna, Austria). The exact origin of these diamonds is unknown; however, based on the year of first mine production compared to when these diamonds were originally acquired (2009), potential mines are Diavik (with an emplacement age of 55‒56 Ma; Graham et al., 1999; Creaser et al., 2004), Ekati (45‒75 Ma; Lockhart et al., 2003; Creaser et al., 2004), Jericho (~172 Ma; Heaman et al., 2002), Victor (170‒180 Ma; Januszczak et al., 2013) or Snap Lake (523‒535 Ma; Agashev et al., 2001; Heaman et al., 2004). The diamonds are all 3 to 4 mm in diameter, vary in weight between 91 to 116 mg, have cubic morphology, and are white to dark grey in colour. Five of the diamonds are fully fibrous whereas two (515 and 516) have a fibrous coat overgrowth on a small microinclusion-free octahedral core (<800 μm across). Each diamond was laser-cut twice to create two parallel side sections and a central thin plate that was polished on both sides; all parts were then cleaned ultrasonically in a mixture of concentrated HF (29 N) and HNO3 (16 N) for >2 h and washed with ethanol and distilled water.