Details of Award
NERC Reference : NE/J019372/2
How were the first stable continents formed?
Fellowship Award
- Fellow:
- Dr AR Hastie, University of Birmingham, Sch of Geography, Earth & Env Sciences
- Grant held at:
- University of Birmingham, Sch of Geography, Earth & Env Sciences
- Science Area:
- Earth
- Overall Classification:
- Earth
- ENRIs:
- Natural Resource Management
- Global Change
- Science Topics:
- Palaeoenvironments
- Volcanic Processes
- Mantle & Core Processes
- Tectonic Processes
- Abstract:
- How were the first continents formed? This is a fundamental question regarding the evolution of the Earth, and yet, scientists can still not conclusively answer it. Nevertheless, resolving this question is essential for earth scientists, chemists and biologists as the generation of the continents are ultimately responsible for the chemical evolution of the planet's interior, hydrosphere and atmosphere throughout geological time. The first continents were formed by partial melting of an older igneous protolith; however, both the composition of the protolith and its tectonic affinity are controversial. Field and analytical studies suggest that the early continents were formed by partial melting of oceanic crust in primitive subduction zones. If true, early convergent margins would compositionally modify the Earth by recycling chemically fractionated crustal material back into the planet's interior. Also, early volcanic arcs would release volatile elements and chemically modify the early atmosphere and oceans, which would have implications for the emergence and evolution of life. Thus, understanding the generation of the continents is important to several scientific disciplines and this project aims to determine the affinity of the protolith that underwent partial melting to form the first continents and, if successful, may support the viability of subduction zones on the early Earth. The early continental crust is composed of the trondjhemite tonalite and granodiorite/dacite (TTG/D) suite of igneous rocks. The oldest TTG/Ds are thought to be derived from a metamorphosed amphibole-plagioclase-garnet-bearing basic igneous protolith. For metabasic rocks, pressures of ~1.0-1.6 GPa (30-50 km) are required to stabilise a mineralogy of amphibole, plagioclase and garnet. Today basic oceanic crust generated at mid-ocean ridges (MOR) is ~7 km thick and subducts beneath younger oceanic crust to form island arcs. Away from plate boundaries, basaltic oceanic islands are common, and many are thought to be generated from hot mantle plumes that ascend from deep within the Earth to erupt on the surface. Past attempts at identifying the basic igneous protolith that underwent partial melting to form the TTG/Ds has involved partial melt experiments on metabasic material from MORs, island arcs and intraplate oceanic islands at pressure ranges of 0.1-32 GPa. Unfortunately, the resultant melts do not match the compositions of the earliest TTG/Ds and few experiments have been performed within the essential 1.0-1.6 GPa pressure interval. Beneath the Earth's early MORs the mantle was hotter and chemically more enriched than mantle beneath today's MORs, and when it underwent partial melting, it formed thicker (>20 km) and more enriched MOR crust. Oceanic plateaus are derived from large scale partial melting of mantle plumes and, relative to modern MOR crust, have thicker crust (8-30 km) and are compositionally more enriched. Thus, oceanic plateaus may be a modern-day analogue for oceanic plates on the early Earth. Accordingly, this study aims to (1) analyse rocks above the subducting Ontong Java oceanic plateau, Solomon Islands and (2) perform experimental partial melt experiments on modern oceanic plateau rocks in the pressure range of 1.0-1.6 GPa to determine if lavas with identical compositions to the Earth's early continental crust can be generated form an oceanic plateau basaltic protolith. If successful, the source region of the oldest continental crust can be identified and generated at depths of ~30-50 km. Also, by identifying that the source region has to be in this pressure range, this research will suggest that primitive subduction zones could be viable processes for forming the first continental crust. This is because alternative models to explain the formation of the continents (intracrustal melting and large scale resurfacing) involve both higher and lower pressures that results in garnet and plagioclase not being stabilised together.
- NERC Reference:
- NE/J019372/2
- Grant Stage:
- Completed
- Scheme:
- Postdoctoral Fellow (FEC)
- Grant Status:
- Closed
- Programme:
- Postdoctoral Fellowship
This fellowship award has a total value of £216,801
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DI - Staff | DA - Estate Costs | DI - T&S | DA - Other Directly Allocated |
|---|---|---|---|---|---|
| £44,404 | £53,500 | £83,696 | £27,068 | £6,624 | £1,508 |
If you need further help, please read the user guide.