Highlights on Geochemical Changes in Archaean Granitoids and Their Implications for Early Earth Geodynamics

Jaana Halla

doi:10.3390/geosciences8090353

Abstract

The Archaean (4.0–2.5 Ga) continental crust is mainly composed of granitoids, whose geochemical characteristics are a function of their formation mechanisms and components, as well as physical conditions of their source. Therefore, revealing changes in Archaean geodynamic processes requires understanding of geochemical changes in Archaean granitoids. This paper compares key geochemical signatures in granitoid occurrences from the Eoarchaean to Neoarchaean Eras and aims to highlight changes or variations in their geochemical signatures. The study is performed by exploring and comparing geochemical and geochronological datasets of Archaean granitoids compiled from literature. The results show that two end-members of sodic TTGs (tonalite–trondhjemite–granodiorite) occur throughout the Archaean: low- and high-HREE (heavy rare earth elements) types. A profound change in granitoid geochemistry occurred between 3.0 and 2.5 Ga when multi-source high-K calc-alkaline granitoid batholiths emerged, possibly indicating the onset of modern-type plate tectonics.

Highlights

It is well known that continents, covering one-third of the Earth’s surface, have grown through time
The models presented to explain the formation of TTGs include stagnant lid tectonics, plume tectonics involving mantle upwelling, or arc tectonics related to subduction, which all may cause episodic melting of basaltic precursors [1,2]
At 3.0–2.5 Ga, there was a significant change in the Earth’s geodynamics indicated by the emergence of multi-source high-K calc-alkaline granitoid batholiths, which has been related to increasing crust-mantle interactions due to the onset of modern-type plate tectonics [3,4,5]

Summary

Introduction

It is well known that continents, covering one-third of the Earth’s surface, have grown through time. The exact nature and timing of the Earth’s geodynamic changes that transformed the Hadean magma ocean to the large landmasses that rose above the sea level and attracted life are still unclear. Granitoids from the fragments of the earliest Archaean continental crust have different appearance and geochemical features from the diversified, multi-source granitoid batholiths of the present-day continents. The models presented to explain the formation of TTGs include stagnant lid (single plate) tectonics, plume tectonics involving mantle upwelling, or arc tectonics related to subduction, which all may cause episodic melting of basaltic precursors [1,2]. At 3.0–2.5 Ga, there was a significant change in the Earth’s geodynamics indicated by the emergence of multi-source high-K calc-alkaline granitoid batholiths, which has been related to increasing crust-mantle interactions due to the onset of modern-type plate tectonics [3,4,5]

Objectives

Discussion

Conclusion