Abstract
Most of Earth’s diamonds are connected with deep-seated mantle rocks; however, in recent years, μm-sized diamonds have been found in shallower metamorphic rocks, and the process of shallow-seated diamond formation has become a hotly debated topic. Nanodiamonds occur mainly in chondrite meteorites associated with organic matter and water. They can be synthesized in the stability field of graphite from organic compounds under hydrothermal conditions. Similar physicochemical conditions occur in serpentinite-hosted hydrothermal systems. Herein, we report the first finding of nanodiamonds, primarily of 6 and 10 nm, in Hyblean asphaltene-bearing serpentinite xenoliths (Sicily, Italy). The discovery was made by electron microscopy observations coupled with Raman spectroscopy analyses. The finding reveals new aspects of carbon speciation and diamond formation in shallow crustal settings. Nanodiamonds can grow during the hydrothermal alteration of ultramafic rocks, as well as during the lithogenesis of sediments bearing organic matter.
Highlights
A high-resolution transmission electron microscope (HRTEM) image of the sample shows that this grain is an aggregate of nanodiamonds ranging from 1 to 6 nm (Fig. 3b); the dominant size is ~6 nm, and a few 10 nm-sized diamonds are observed
We propose that the temperature of nanodiamond formation during serpentinization may correspond to the range of 150–300 °C
Our results confirm that nanodiamonds can form during serpentinization in the stability field of graphite, from an organic-water system, similar to that occurring in some meteoritic parent bodies
Summary
Manuella[12] inferred that modern and fossil hydrothermal systems hosted in serpentinites, where organic matter and water coexist at a wide range of temperatures, can be considered as potential sites for the nucleation and growth of nanodiamonds On these grounds, a Hyblean serpentinized peridotite xenolith bearing asphaltene-like organic matter, which contain enigmatic clusters of tiny opaque carbonaceous flakes, was examined for the possible presence of nanodiamonds by using Raman spectroscopy and transmission electron microscopy (TEM). A Hyblean serpentinized peridotite xenolith bearing asphaltene-like organic matter, which contain enigmatic clusters of tiny opaque carbonaceous flakes, was examined for the possible presence of nanodiamonds by using Raman spectroscopy and transmission electron microscopy (TEM) The results of this investigation are reported .
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