The Chromite Record of Mafic Crustal Growth

Introduction

Understanding Earth's crustal growth is crucial to understanding the evolution of its tectonics, the birth of the first continents, and the fundamental changes that transformed Earth into a habitable planet. However, much of our understanding of Earth's crustal growth is predicated on a single mineral - zircon - that is strongly biased towards detecting felsic crustal growth.

Problem Statement

This is particularly problematic for the early Earth, where average crustal compositions were far more mafic than today, and the very first protocrust may be entirely undetectable using conventional methods.

Proposed Solution

I propose to access the mafic to ultramafic crustal growth record using detrital chromite preserved in sedimentary rocks from Archaean Cratons. Like zircon, chromite chemical compositions reflect the magmas that they crystallised from, and can be used to identify the provenance of the mafic portions of a sedimentary rock. Furthermore, they can be dated using Re-Os isotopes, to identify the age of eroded mafic terranes.

Project Objectives

This project has three main objectives:

1. Develop techniques to identify the age and composition of chromite sources in ancient sedimentary rocks.
2. Use a range of detrital chromite samples from sedimentary sequences in the Superior Craton, to reconstruct a mafic-ultramafic crustal growth curve for the craton.
3. Search for evidence of Earth's mafic protocrust in some of the oldest known chromite-bearing sedimentary rocks.

Expected Outcomes

These achievements will open a new avenue for studying sedimentary provenance, unlock the archive of mafic crustal growth throughout Earth history, and provide insights on the nature and survival of Earth's earliest crust. The techniques developed will be broadly applicable, paving the way for a better understanding of Earth's crustal evolution.