Mantle metasomatism and kimberlite emplacement recorded in the dissolution and reaction products on diamond and other mantle minerals

Diamond forms deep in the mantle and is carried upwards to the Earth’s surface by the deepest known magma, kimberlites. Our modern knowledge of diamond internal structure and inclusions implies a complex history of interaction with melts and fluids, which percolate through the mantle beneath the continents modifying its composition. The complexity of the diamond carrier, kimberlite magma, precludes the usage of conventional methods to study kimberlites leaving their origin ambiguous. The proposed research offers a novel approach for investigating deep magmas and fluids by uncovering the record, which they leave on the surface of diamond and other mantle minerals during interaction. Experiments carried out at the conditions simulating the natural environments will explore development of surface features on diamond during dissolution. Comparing these features to those on natural diamonds will test the exiting hypotheses of the complex chemical processes in the different domains of subcontinental mantle and the hypotheses of the composition of kimberlite melt, the behavior of volatiles, and their effect on kimberlite emplacement. The proposed study will use diamonds obtained from different sections of composite kimberlite pipes. This unique opportunity to study diamond parcels with geological control is possible due to the support of my research by diamond industry. In order to derive a predictive model applicable to natural kimberlites, I am developing a quantitative method to study diamond morphology using atomic force microscopy. This approach provides three-dimensional dataset of mineral surface and allows to quantify the H2O:CO2 ratio and temperature of diamond-destructive fluids. The results of this work will complement the studies of diamond mineral inclusions and isotope systematic to resolve fundamental questions related to the origin of kimberlite magmatism, processes triggering diamond growth, and complex chemical processes modifying the subcontinental mantle. The anticipated results will establish the mechanism of diamond interaction with fluids and explain the variety of surface features observed on natural diamonds, which origin is not yet understood. The project will advance modeling of the oxidation state of the Earth’s mantle, provide new robust constraints on the nature of fluids in different mantle environments, and compare the evolution of the deep continental roots beneath North America and Africa. The study will address important exploration problem of diamond preservation. Diamond dissolution may result in significant diamond loss and decrease in diamond grade. If substantial dissolution occurs in the kimberlite magma the decrease in diamond grade may not be apparent from the existing methods for diamond potential assessment. The proposed research will provide new tools for improving exploration techniques and assessment of kimberlite bodies.