New insight into polycrystalline diamond genesis from modern nanoanalytical techniques Dorrit E. Jacob a, ⁎, Larissa Dobrzhinetskaya b , Richard Wirth c a Australian Research Council Centre of Excellence for Core to Crust Fluid Systems and Department of Earth and Planetary Sciences, Macquarie University, North Ryde, NSW 2109, Australia b Department of Earth Sciences, University of California at Riverside, Riverside, CA 92521-0412, USA c Helmholtz Centre Potsdam, GFZ German Research Center for Geosciences, Telegrafenberg, D-14473 Potsdam, Germany abstract article info Article history: Received 23 December 2013 Accepted 11 May 2014 Available online 18 May 2014 Keywords: Diamond Earth's mantle Carbonado Ultra-high pressure metamorphism TEM Subduction Technical developments in analytical methods that reach nanometer spatial resolution have enabled the interro- gation of smaller, submicron-sized inclusions in diamond that had previously been elusive. This has inspired and enabled studies of non-classical diamond species from different geological settings, resulting in a strongly faceted and dynamic picture of diamond formation. This article reviews the leap of knowledge achieved by employing state-of-the-art analytical methods with high spatial resolution to polycrystalline diamonds from different settings, i.e. from kimberlite, from crustal ultra-high pressure metamorphic terranes and alluvial carbonados. While crustal metamorphic diamonds are generally formed under oxidizing conditions, polycrystalline diamond from the Earth's mantle and carbonado have inclusion suites reflecting variable, and sometimes extreme, redox conditions. Diamond fluid compositions, however, fall in the same compositional field for worldwide diamond fluids, regardless of their geodynamic environment. On the basis of thermodynamic equilibrium data for C–H–O fluids in the mantle we argue that submicron inclusions in diamonds are products of local remobilization connected to fluid-fluxed partial melting and redox freezing. Thus, evidence from these inclusions complements information from classical work on larger inclusions and allows a unique direct insight into the medium in which diamond formed. © 2014 Published by Elsevier B.V. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2. Modern micro- and nanoanalytical techniques applied to diamond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.1. X-ray tomography and micro-X-ray computed tomography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2.2. Micro-X-ray fluorescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3. Focused ion beam (FIB) milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.4. Transmission electron microscopy (TEM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.5. NanoSIMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3. Polycrystalline diamonds from kimberlitic sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.1. Mineral intergrowths: macroinclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 3.2. Oxidation state and clues to formation mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3. Insights from nano-inclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 4. Carbonado . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 5. Polycrystalline diamonds from ultrahigh-pressure terranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 5.1. Nanoinclusions in the Erzgebirge polycrystalline diamonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 5.2. Nanoinclusions in the Kokchetav polycrystalline diamonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.2.1. Marbles and calcareous-silicate gneisses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.2.2. Feldspathic gneisses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.3. Diamond-forming fluid media and oxidation state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.4. Source of carbon and nitrogen aggregation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.5. Evidence from fluids for crust–mantle interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Earth-Science Reviews 136 (2014) 21–35 ⁎ Corresponding author. Tel.: +61 298508428; fax: +61 298508943. E-mail addresses: dorrit.jacob@mq.edu.au (D.E. Jacob), larissa.dobrzhinetskaya@ucr.edu (L. Dobrzhinetskaya), wirth@gfz-potsdam.de (R. Wirth). http://dx.doi.org/10.1016/j.earscirev.2014.05.005 0012-8252/© 2014 Published by Elsevier B.V. Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev