Why are diamonds preserved in UHP metamorphic complexes? Experimental evidence for the effect of pressure on diamond graphitization

The preservation of metastable diamond in ultrahigh-pressure metamorphic (UHPM) complexes challenges our understanding of the processes taking place during exhumation of these subduction zone complexes. The presence of diamonds in UHPM rocks implies that diamonds remained metastable during exhumatio...

Full description

Saved in:
Bibliographic Details
Published in:International geology review 2019-03, Vol.61 (4), p.504-519
Main Authors: Sonin, Valeri, Leech, Mary, Chepurov, Aleksey, Zhimulev, Egor, Chepurov, Anatoli
Format: Article
Language:English
Subjects:
C-O-H fluids
carbonate melt
Carbonates
Crystals
Diamond films
Diamond stability
Diamonds
Graphite
graphite-diamond transition
Graphitization
Inclusions
Melts
multi-anvil experiment
Preservation
Pressure
Pressure effects
pressure-vessel effect
Protective coatings
Single crystals
Stability
Subduction
Subduction zones
Survival
ultrahigh-pressure (UHP) metamorphism
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The preservation of metastable diamond in ultrahigh-pressure metamorphic (UHPM) complexes challenges our understanding of the processes taking place during exhumation of these subduction zone complexes. The presence of diamonds in UHPM rocks implies that diamonds remained metastable during exhumation, and within thermodynamic stability of graphite for an extended period. This work studies the influence of pressure on the surface graphitization rate of diamond monocrystals in carbonate systems to understand the preservation of microdiamond during exhumation of UHP subduction complexes. Experiments were performed with 2-3 mm synthetic diamond monocrystals at 2-4 GPa in СаСО 3 (1550°С) and К 2 СО 3 (1450°С) melts using a high-pressure multi-anvil apparatus. The highest rate of surface graphitization took place at 2 GPa; diamond crystals were almost completely enveloped by a graphite coating. At 4 GPa, only octahedron-shaped pits formed on flat {111} diamond crystal faces. Our results demonstrate that the surface graphitization rate of diamonds in the presence of carbonate melts at 1450-1550°C increases with decreasing pressure. Decreased pressure alone can graphitize diamond regardless of exhumation rate. Metastable diamond inclusions survive exhumation with little or no graphitization because of excess pressure up to 2 GPa acting on them, and because inclusions are protected from interaction with C-O-H fluid.
ISSN:0020-6814
1938-2839
DOI:10.1080/00206814.2018.1435310