Contributions to Mineralogy and Petrology

, Volume 160, Issue 4, pp 489–510

Mineral inclusions in sublithospheric diamonds from Collier 4 kimberlite pipe, Juina, Brazil: subducted protoliths, carbonated melts and primary kimberlite magmatism

  • Galina P. Bulanova
  • Michael J. Walter
  • Chris B. Smith
  • Simon C. Kohn
  • Lora S. Armstrong
  • Jon Blundy
  • Luiz Gobbo
Original Paper

DOI: 10.1007/s00410-010-0490-6

Cite this article as:
Bulanova, G.P., Walter, M.J., Smith, C.B. et al. Contrib Mineral Petrol (2010) 160: 489. doi:10.1007/s00410-010-0490-6

Abstract

We report on a suite of diamonds from the Cretaceous Collier 4 kimberlite pipe, Juina, Brazil, that are predominantly nitrogen-free type II crystals showing complex internal growth structures. Syngenetic mineral inclusions comprise calcium- and titanium-rich phases with perovskite stoichiometry, Ca-rich majoritic-garnet, clinopyroxene, olivine, TAPP phase, minerals with stoichiometries of CAS and K-hollandite phases, SiO2, FeO, native iron, low-Ni sulfides, and Ca–Mg-carbonate. We divide the diamonds into three groups on the basis of the carbon isotope compositions (δ13C) of diamond core zones. Group 1 diamonds have heavy, mantle-like δ13C (−5 to −10‰) with mineral inclusions indicating a transition zone origin from mafic protoliths. Group 2 diamonds have intermediate δ13C (−12 to −15‰), with inclusion compositions indicating crystallization from near-primary and differentiated carbonated melts derived from oceanic crust in the deep upper mantle or transition zone. A 206Pb/238U age of 101 ± 7 Ma on a CaTiSi-perovskite inclusion (Group 2) is close to the kimberlite emplacement time (93.1 ± 1.5 Ma). Group 3 diamonds have extremely light δ13C (−25‰), and host inclusions have compositions akin to high-pressure–temperature phases expected to be stable in pelagic sediments subducted to transition zone depths. Collectively, the Collier 4 diamonds and their inclusions indicate multi-stage, polybaric growth histories in dynamically changing chemical environments. The young inclusion age, the ubiquitous chemical and isotopic characteristics indicative of subducted materials, and the regional tectonic history, suggest a model in which generation of sublithospheric diamonds and their inclusions, and the proto-kimberlite magmas, are related genetically, temporally and geographically to the interaction of subducted lithosphere and a Cretaceous plume.

Keywords

BrazilCollier 4 kimberliteSublithospheric diamondsInclusionsCarbon isotopesSubductionCarbonatite melt

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Galina P. Bulanova
    • 1
  • Michael J. Walter
    • 1
  • Chris B. Smith
    • 1
  • Simon C. Kohn
    • 1
  • Lora S. Armstrong
    • 1
  • Jon Blundy
    • 1
  • Luiz Gobbo
    • 2
  1. 1.Department of Earth SciencesUniversity of BristolBristolUK
  2. 2.Rio Tinto Desenvolvimentos Minerais LtdaBrasíliaBrazil