Metamorphism and the evolution of plate tectonics

Area of Science:

• Earth Science
• Geology
• Tectonics

Background:

• Earth's mantle convection drives plate tectonics and planetary heat loss.
• The timing and evolution of plate tectonics are fundamental, yet challenging, questions in Earth science.
• Metamorphic rocks record pressure-temperature (P-T) conditions, reflecting tectonic environments.

Purpose of the Study:

• To investigate the secular evolution of Earth's tectonic processes.
• To determine when and how plate tectonics emerged and developed over geological time.
• To use metamorphic P-T data as a proxy for changes in tectonic regimes.

Main Methods:

• Statistical evaluation of metamorphic P-T distributions through time.
• Analysis of apparent thermal gradients (metamorphic T/P) in rocks.
• Comparison of modern bimodal metamorphic patterns with ancient rock records.

Main Results:

• Earth's modern plate tectonic regime developed gradually since the Neoarchaean era (2.5 billion years ago).
• Metamorphic P-T distributions show a progressive widening and increased bimodality from the Neoarchaean to present.
• Average metamorphic T/P has decreased since the Palaeoproterozoic era.

Conclusions:

• Plate tectonics did not transition abruptly but evolved gradually with mantle cooling.
• The emergence of bimodal metamorphism signifies a slow development of modern tectonic processes.
• This contrasts with previous hypotheses of abrupt tectonic style changes or an earlier start for modern plate tectonics.