Zircons from kimberlite: New insights from oxygen isotopes, trace elements, and Ti in zircon thermometry

Zircon from the East Orebody of the Bayan Obo Fe–Nb–REE deposit, China, and SHRIMP ages for carbonatite-related magmatism and REE mineralization events

“…Some characteristics of zircons from known kimberlite-alkalinecarbonatite systems documented in the literature (Belousova et al 1998;Claesson et al 2000;Belousova et al 2002;Corfu et al 2003;Chakhmouradian and Williams 2004) are that they tend to form large (>250 μm), bipyramidal, stubby forms. The work of Page et al (2007) on kimberlitic zircons from four continents supports these observations and confirms further the common occurrence of oscillatory growth zoning with sharp truncations where only fragments of the megacrysts remain. The zircons of the present study compare well with some of these characteristics, especially with respect to the lack of prism face development and the low elongation ratios ("stubby" forms).…”

“…The zircons of the present study compare well with some of these characteristics, especially with respect to the lack of prism face development and the low elongation ratios ("stubby" forms). While the ~700 μm lengths of the largest Bayan Obo zircons do not approach the megacrystic, cm-scale proportions of the kimberlitic zircons described by Belousova et al (1998) and Page et al (2007), they do tend to exceed the upper limit of ~200 μm for zircons in "common rocks" as reported by Corfu et al (2003).…”

“…The Bayan Obo zircon with its high Hf content (up to 7wt% HfO 2 and Zr/Hf ratios averaging only 24 in the cores with a median of 16) is not consistent with this pattern, and instead, might indicate a fractionated melt where the Zr/Hf ratio has decreased relative to chondritic values of 37 (Hoskin and Schaltegger 2003). High Th/U ratios (or very low U) are reported in zircons from kimberlitealkaline-carbonatite systems (Davis 1977;Belousova et al 1998Belousova et al , 2002Chakhmouradian and Williams 2004;Page et al 2007). Specifically, Yuan et al (2008) list U concentrations in zircon averaging 50 ppm for the Mud Tank carbonatite and 9 ppm for the Monastery kimberlite.…”

Isotopic fractionation of oxygen and carbon in decomposed lower-mantle inclusions in diamond

“…Mattey et al (1994); Lowry et al (1999); Spetsius et al (2008); analyses of eclogitic association minerals after Deines et al (1991);Jacob et al (1994Jacob et al ( , 1998Snyder et al (1995); Lowry et al (1999); Schulze et al (2003Schulze et al ( , 2013; Viljoen et al (2005); Spetsius et al (2008); Ickert et al (2013). Analyses of zircon from kimberlites after Valley et al (1998) and Page et al (2007). Number of analyses is shown in brackets at mineral names: Ol -olivine, Opx -orthopyroxene, Cpx -clinopyroxene, Grt -garnet, Coe -coesite, Cal -calcite, WoIIwollastonite II, CaSiPrv -CaSi-perovskite, Mtc -monticellite.…”

Tracking continental-scale modification of the Earth’s mantle using zircon megacrysts

“…Their trace element patterns (Valley et al, 1998, Belousova et al, 2002 and low δ 18 O (Page et al, 2007) indicate that they are not of crustal origin, but crystallised within the mantle and experienced only minimal chemical interaction with the host magmas that transported them to the surface. While details of their petrogenesis (and the origin of megacryst suites more broadly) remain a subject of active research, there is agreement that zircon megacrysts are produced by metasomatic melts in some way related to kimberlite magmas (e.g., Kinny et al, 1989;Nowell et al, 2004;Page et al, 2007). They record precise U-Pb ages and initial 176 Hf/ 177 Hf isotope ratios providing important constraints on the age and nature of the metasomatic events occurring in their mantle sources.…”