Magmatic cyclicity and episodic continental growth of the Australian Tasmanides

Abstract

The hafnium isotopes of zircon have recently been identified as a new means of detecting magmatic cyclicity. A hierarchy of possible magmatic cycles has been verified, ranging from the ∼600 Myr supercontinent cycle to 10–20 Myr plutonic cycles. While the supercontinent cycle is well-established, the shorter mantle convective and plutonic cycles require further work to understand how magmatic dynamics may give rise to such cyclicity. In this study, we analyze in detail the long-lived orogenic system of the Australian Tasmanides, and a hierarchy of cycles is visible, including a ∼ 290 Myr accretionary/orogenic cycle, a ∼ 65 Myr upper mantle cycle, and 20–10 Myr magmatic and plutonic cycles. These cycles correlate with the evolution of the orogens and episodic continental growth of eastern Gondwana. The surprising similarity in period length between the opening/closing of a typical Atlantic-like Wilson cycle to the case here of the lifecycle of a West Pacific-type arc system may imply that the two distinct tectonic settings have a similar mantle convective effect, which requires further empirical testing and theoretical study. Similar to magmatic cycles identified in the Hadean and in modern arc settings, the hierarchy of cycles in the Tasmanides implies a uniformitarian similarity in arc magmatism throughout Earth history.