The role of mantle ultrapotassic fluids in diamond formation

doi:10.1073/pnas.0608134104

The role of mantle ultrapotassic fluids in diamond formation

Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Pr. Koptuyga 3, 630090 Novosibirsk, Russia

Edited by Ho-kwang Mao, Carnegie Institution of Washington, Washington, DC, and approved January 1, 2007 (received for review September 15, 2006)

Abstract

Analysis of data on micro- and nano-inclusions in mantle-derived and metamorphic diamonds shows that, to a first approximation, diamond-forming medium can be considered as a specific ultrapotassic, carbonate/chloride/silicate/water fluid. In the present work, the processes and mechanisms of diamond crystallization were experimentally studied at 7.5 GPa, within the temperature range of 1,400–1,800°C, with different compositions of melts and fluids in the KCl/K₂CO₃/H₂O/C system. It has been established that, at constant pressure, temperature, and run duration, the mechanisms of diamond nucleation, degree of graphite-to-diamond transformation, and formation of metastable graphite are governed chiefly by the composition of the fluids and melts. The experimental data suggest that the evolution of the composition of deep-seated ultrapotassic fluids/melts is a crucial factor of diamond formation in mantle and ultrahigh-pressure metamorphic processes.

high-pressure experiment

Footnotes

*To whom correspondence should be addressed. E-mail: palyanov{at}uiggm.nsc.ru
Author contributions: Y.N.P., V.S.S., N.V.S., and A.G.S. designed research; Y.N.P. and A.G.S. performed research; A.G.S. contributed new reagents/analytic tools; Y.N.P., V.S.S., N.V.S., and A.G.S. analyzed data; and Y.N.P., V.S.S., N.V.S., and A.G.S. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
↵ † Under conditions of complete miscibility between water-containing melts and aqueous fluids, we will conventionally refer to water-poor and water-rich compositions as melts and fluids, respectively.
Abbreviations:

FG,

film growth;

TGG,

temperature-gradient growth;

UHP,

ultrahigh-pressure.