Diamonds and the Geology of Mantle Carbon

Transcription

1 Diamonds and the Geology of Mantle Carbon Steven B. Shirey 1 Pierre Cartigny 2 Daniel J. Frost 3 Shantanu Keshav 4 Fabrizio Nestola 5 Paolo Nimis 5 D. Graham Pearson 6 Nikolai V. Sobolev 7 Michael J. Walter 8 1 Department of Terrestrial Magnetism,USA 2 Institut de Physique du Globe de Paris, France 3 Bayerisches Geoinstitut, Germany 4 Geosciences Montpellier, France 5 University of Padua, Italy 6 University of Alberta, Canada 7 Sobolev Institute of Geology and Mineralogy, Russia 8 University of Bristol, UK RiMG chapter of Carbon in Earth

2 Unique aspects of diamonds The flagship of carbon minerals in Earth Deepest samples (120 to 800 km) Old samples ( million years old) Most resistant to later geologic processes Unique potential to trace mantle processes Form under special conditions, (e.g. metasomatic)

3 Fronts for diamond research Element partitioning during diamond growth Inclusion paragenesis and diamond age Source of carbon and its geologic significance, Speciation of diamond-forming fluids and mantle fo 2 Deep diamonds and relation to geodynamic processes Experiments on diamond formation by fluids and melts Nanostructural characteristics of diamond

4 Components of Diamonds and the Mantle Geodynamics of Carbon (DMGC) project Crystallography P,T conditions for diamond crystallization and inclusion-host relationships Experimental petrology movement of C through the mantle with melt and fluid into diamond Geochemistry age and geochemical constraints on C-bearing fluids in the mantle Stable isotopes detect primitive and recycled components and isotopic fractionation Nanostructure diamond formation at the crystal chemical level

5 Diamonds of the world Diamond types lithospheric superdeep alluvial UHP crustal impact exposed Archaean crust well-defined cratons, part of composite cratons composite craton outline; Proterozoic amalgamation craton correlations from Pangea RiMG Chapter 12 of Carbon in Earth

6 Diamonds in relation to mantle keels and subduction volcanic chain mid-ocean ridge subduction 140 km 420 km 670 km 900 km G D kimberlite upper mantle transition zone lower mantle LAB Ol + Maj + Cpx Wds/Rwd + Maj + CaPv MgPv + FePer + CaPv basalt/eclogite Grt + Ol + Chr ± Cpx ± Opx ± Sf craton lithospheric mantle Grt + Cpx + Sf Maj + Sti ± CaTiPv ± CaPv upper mantle Maj + Cpx + CaTiPv transition zone lower mantle MgPv(FeAl) + CaPv + CaFrt + NAL + Sti G D lithospheric mantle convecting mantle RiMG Chapter 12 of Carbon in Earth

7 Internal textures of diamonds coated moncrystalline superdeep RiMG Chapter 12 of Carbon in Earth (some original photos from Kopylova et al. (2010; Bulanova et al. 2010)

8 Fluids in diamonds (silicic) Si+Al Si+Al Ca MgAPoorBYaku7an Brazil MgARichBYaku7an Diavik Koffiefontein Panda Botswana K+Na (saline) K+Na Ca+Mg+Fe (carbona77c) Ca+Mg+Fe Mg Fe 1 RiMG Chapter 12 of Carbon in Earth (original from Kopylova et al. (2010)

9 Diamonds, fo2, fluid speciation, P, T RiMG Chapter 12 of Carbon in Earth

10 Carbon isotopic compostions of diamonds main mantle-range (fibrous diamonds, mid-ocean ridge basalts carbonatites and kimberlites) Peridotitic diamonds (n = 1357) lowest value highest value Polycrystalline from kimberlites (n = 120) Eclogitic diamonds (n = 997) Komatiitic from Dachine French Guyana (n=181) Eclogitic from Jericho, Slave Craton, Canada (n=42) Fibrous diamonds and diamond coats (n = 127) Carbonados (n=54) Lower mantle diamonds (n = 78) F) Metamorphic diamonds (n = 120) Transition Zone (n = 31) Jagersfontain (South Africa) Sao Luiz (Brazil) Kankan (Guinea) Recycled carbon δ13c ( ) δ13c ( ) RiMG Chapter 12 of Carbon in Earth

11 Diamonds as characterized by their silicate inclusions Stachel and Harris (2008) Ore Geology Reviews 34, The relative abundance of diamond source regions in the Earth's mantle bas

12 Diamonds and mantle geology depth = 150 km P-wave velocity anomaly (%) O M LE V K Z L F D KO JW R JA P P Latitude South E-TYPE SILICATE INCLUSIONS 32 P-TYPE 0.9SILICATE INCLUSIONS BORDER OF 2.5 Ga PERIDOTITES Longitude East RiMG Chapter 12 of Carbon in Earth

13 Geothermobarometry on mineral inclusions in diamonds RiMG Chapter 12 of Carbon in Earth

14 of carbon. If the above hypothesis is correct, then the carbon from which the diamonds formed Downloaded from on Novem only about 100 million years old, on the of a dated sublithospheric inclusion from Basaltic minerals at high pressure in the deep mantle Fig. 3. (A)Estimatedmodalmineralogyinsubductedbasaltic oceanic crust as a function of depth i mantle (17, 18). MgPv, Mg-perovskite; CaPv, Ca-perovskite; CF, CF phase; NAL, NAL phase; St, stish Gt, garnet; Cpx, clinopyroxene. The inclusion mineralogy in diamonds from Juina-5, including M CaPv, CF phase, NAL phase, and stishovite, is stable at depths of ~700 to 1400 km in the lower mantl AschematicmodelfordiamondformationandascentbeneaththeBrazilianlithosphere.Wesugges the diamonds and inclusions initially formed from subducted oceanic crustal components in the u part of the lower mantle and were transported in an upwelling plume to the upper mantle, where clusions in diamonds from Juina-5. (A) inel (Mg,Fe)Al 2 O 4 (Sp) and nepheline unmixed into composite inclusions according to lower-pressure phase relations. Sf) in one corner that we interpret as an participate Redrafted in diamond from Walter, crystallization Kohn, Araujo, Bulanova, Smith, Gaillou, Wang, Steele, and Shirey (2011). Science 334, ninclusionindiamondju5-67thatis

15 Diamond capture and inclusion unmixing Walter, Kohn, Araujo, Bulanova, Smith, Gaillou, Wang, Steele, and Shirey (2011). Science 334,

16 Diamond formation, deep to shallow crust Craton Formation and Modification ~ Ga 50 amalgamated cratonic lithosphere accreted lithosphere ~ EMOG -2 kilometers metasomatism Fe-Ni metel/carbide E-type P-type graphite diamond redox crystallization from primordial and recycled fluids and melts rich in CH 4, H 2 O, CO 3-, CO 2, S, Cl, etc sub-lithospheric mantle -3-4 kilometers ΔFMQ diamond resporbtion/ growth redox melting and freezing cratonic root uplift (plume?) diamond precipitation via redox freezing inclusion unmixing melting of carbonated crust (hydrous?) inclusions crystallized from melts subducted lithosphere diamond formation in slab? Fe-Ni metel/carbide -5 <-5 ΔFMQ stranding and themalization of slab RiMG Chapter 12 of Carbon in Earth