The onset of continuous plate subduction and the rise of alkali magmatism
Recently, the international journal Nature Communications published a research article entitled “Continuous Plate Subduction Marked by The Rise of Alkali Magmatism 2.1 Billion Years Ago”, accomplished by Professor Wei-dong Sun and his supervised postdoc Dr He Liu, affiliated to the Center for Ocean Mega-Science Chinese Academy of Sciences, as well as two geoscientists from the United States.
Over the Earth’s evolutionary history, the style of plate subduction has evolved through time due to the secular cooling of the mantle. While continuous subduction is a typical feature of modern plate tectonics, a stagnant-lid tectonic regime with localized episodic subduction likely characterized the early Earth. As a result of the secular cooling of the mantle, the subduction style was later transitioned into the self-sustaining continuous subduction. The continuous subduction that dominates at the modern convergent plate boundaries, is characterized by long-lived recycling of oceanic plate into the mantle along the subduction zone.
Although the onset of plate tectonics has been highly contested, little is known about the pace of subduction style evolution, particularly the transition from episodic to continuous plate subduction. The timing of the transition between these two subduction styles bears important insights into Earth’s cooling history, influencing on orogenic processes, continent evolution, and mass exchange between the shallow and deep Earth.
An important consequence of continuous subduction is the enhanced cooling of the mantle caused by the increasing volume of subducting oceanic crust, which, in turn, would result in lower degrees of mantle partial melting. Liu et al. evaluate ~55,000 mafic igneous rocks spanning the last 3.5 Ga to track the initiation and consequence of continuous plate subduction, showing an increasing magnitude of alkali basaltic magmatism beginning at ca. 2.1 Ga. The rapid rise of continental alkali basalts correlates with an abruptly decreasing degree of mantle melting resulting from the enhanced cooling of the mantle at ca. 2.1 Ga. Therefore, the start time of continuous plate subduction is estimated as ca. 2.1 Ga.
Diff (HFSE) and proportion of alkali basalts in relation to all mafic rocks over the geological time.
This study was supported by Strategic Priority Research Program of the Chinese Academy of Sciences (XDB18020102), National Key R & D Program of China (2016YFC0600408) and NSFC 41473029.
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