The supercontinent cycle seen from a hafnium isotope perspective in the Mongolian Accretionary Collage

Traditionally, the Wilson cycle is regarded as a convincing theory to explain plate tectonics; however, the links between long-lived accretionary orogens and supercontinent assemblies remain unclear. Long-lived accretionary orogens are proposed to have evolved around external oceans, potentially persisting for up to two billion years. In this paper, we revisit the supercontinent cycle based on hafnium isotope trends of the Precambrian Mongolian Ribbon (PMR) and the Mongolian Accretionary Collage (MAC), which possibly highlight the evolution of two consecutive external oceans in the Central Asian Orogenic Belt (CAOB). By considering these proposed external oceans, we suggest that extroversion, rather than orthoversion or introversion, could be the dominant mechanism for the formation of supercontinents. Compilation of 5706 Hf zircon isotopes from magmatic and detrital data from subduction-related rocks in the PMR and MAC reveals two distinct external advancing and retreating modes of subduction trends that switch at the assembly of each presumed supercontinent (2000, 1000, 540 and 260 Ma; millions of years ago). The subduction-related Hf trends connected to external geodynamics record the evolution of the PMR from ca. 2500 to 550 Ma and the MAC from ca. 550 to 300 Ma. Two phases of the retreating mode are observed ca. 2000 Ma to 1000 Ma and ca. 400 Ma to 300 Ma, while three phases of the advancing mode occurred ca. 2500 Ma to 2000 Ma, ca. 750 Ma to 550 Ma and ca. 550 Ma to 400 Ma. Therefore, we propose a cycle of extroversion modulated by alternating periods of advancing and retreating modes of subduction between the assemblies of Columbia, Rodinia, and Gondwana, which terminated with the assembly of Pangea. While the Cryogenian–Ediacaran period is characterised by a snowball Earth, the Ediacaran to Cambrian transition is not marked by a change in subduction mode despite the assembly of Gondwana. The Gondwana supercontinent was stable after ca. 540 Ma, and a subduction girdle developed in advancing mode. The stability of this supercontinent is supported by well-known evidence, such as the formation of a slab graveyard after assembly. Nonetheless, no explanation exists for why the advancing/advancing mode phenomenon occurred. Our hafnium model suggests that an interconnected cycle may govern the Earth's evolution and speculates that a feedback loop exists between advancing and retreating modes and between “top-down” and “bottom-up” processes, leading to a fully operative supercontinent cycle. In addition, tectonic switching from these processes might control extreme magmatism and metamorphism during supercontinent assembly. For instance, these two latter extreme proxies are observed in the assembly of Eurasia within the collisional belts as well as in the subduction girdle of the external ocean at ∼40 Ma to ∼20 Ma. Our model not only predicts future plate movements but also speculates their eventual amalgamation into a supercontinent, Pangea Proxima, through extroversion. Therefore, it is proposed that the Pacific Ocean will close. The main message is that the supercontinent cycle has exerted first-order control on the evolution of long-lived accretionary orogens since the Palaeoproterozoic era. • Hafnium isotopes and extreme metamorphism calibrate the supercontinent cycle. • The supercontinent cycle exerts primaeval control on long-lived accretionary orogens. • The hafnium model suggests that the next supercontinent could form through extroversion.