The Geological Link Between Northern Australia and Northern China

The history of Earth’s continental crust is a saga of drifting and colliding landmasses, forming and breaking apart through immense geological forces. The continental crust refers to the thick, outermost layer of the Earth that forms the continents, composed primarily of granitic rocks, in contrast to the thinner and denser oceanic crust. Among the earliest recognized supercontinents, Nuna, which existed between 1.8 to 1.2 billion years ago, represents a key period in Earth’s tectonic evolution, which refers to the ongoing processes of plate movements and interactions that shape the Earth’s surface over geological time. A crucial aspect of its configuration is the long-standing connection between the North China Craton and the North Australian Craton. A craton is a large, stable block of the Earth’s crust that has remained relatively unchanged for billions of years. These two ancient continental fragments, once thought to be isolated entities, have been revealed through paleomagnetic, geological, and geochemical evidence to have been intimately linked for nearly 450 million years. This connection played a fundamental role in shaping the geological character of both cratons and provides insight into the broader processes governing supercontinent assembly, which refers to the merging of smaller landmasses into a larger one, and fragmentation, the subsequent breakup of such landmasses.

Paleomagnetic studies offer a window into the past, tracing the ancient latitudes, or positions relative to the equator, of continents through the magnetization locked in their rocks. When igneous and some sedimentary rocks form, they acquire a magnetic signature that aligns with the Earth's magnetic field at the time, which provides crucial data for reconstructing past continental positions. Data from both cratons show that at around 1.78 billion years ago, their paleopoles, which are the positions of the ancient magnetic poles recorded in rocks, align, suggesting that they occupied a common geographic domain within Nuna. The significance of this alignment cannot be overstated, as it indicates that these two landmasses were not only close in proximity but also moved as part of a unified tectonic system, meaning they were likely part of the same lithospheric plate or adjacent plates undergoing similar movements. At approximately 1.32 billion years ago, further paleomagnetic evidence confirms their continued association, revealing that their relative positions remained stable for much of Nuna’s existence. The orientations of coeval dyke swarms, which are groups of parallel igneous intrusions that formed simultaneously, in both regions suggest that they were affected by the same mantle plume, a rising column of hot rock from deep within the Earth that can cause extensive volcanic activity, further reinforcing the idea of a shared tectonic history.

Geological records from both cratons paint a strikingly similar picture. The Yanliao Rift in North China and the McArthur Basin in North Australia exhibit remarkable sedimentary parallels. A rift is a region where the Earth's crust is being stretched and thinned, often associated with faulting and basin formation. A basin is a low-lying geological structure that accumulates sediments over millions of years. Between 1.70 and 1.60 billion years ago, both regions experienced extensive clastic sedimentation, which refers to the deposition of sediments derived from pre-existing rock material, interspersed with minor carbonates, sedimentary rocks composed primarily of carbonate minerals such as limestone and dolostone. Notably, dolostone deposits, a type of carbonate rock rich in the mineral dolomite, found in both basins have been dated at 1.64 billion years, suggesting parallel marine depositional environments. This depositional pattern suggests that both regions were subjected to similar environmental conditions, including similar water depths, salinity, and climate, and may have been part of an extensive, interconnected basin system. The presence of early eukaryotic microfossils, microscopic fossils of cells with a nucleus, including Valeria lophostriata, in both the lower Changcheng Group of the North China Craton and the Mallapunyah Formation of the North Australian Craton suggests that these environments fostered similar biological evolution. Fossil evidence provides one of the most tangible connections between these two regions, highlighting their shared ecological and oceanic conditions during the Proterozoic, the geological eon spanning from 2.5 billion to 541 million years ago.

Geochemical studies provide further confirmation of this deep connection. Mafic magmatic events, which involve eruptions of iron- and magnesium-rich volcanic rock, in both cratons occurred synchronously, with strikingly similar geochemical signatures, meaning the chemical composition of rocks from both regions is nearly identical. At around 1.73 billion years ago, the Miyun dolerite dykes of the Yanliao Rift share mineralogical, or rock-forming mineral content, and chemical affinities with the Oenpelli dolerite sills in the McArthur Basin, suggesting they originated from the same deep mantle source. The most compelling evidence, however, comes from the massive 1.32-billion-year-old Large Igneous Province (LIP) event. A LIP is a vast region covered in volcanic rock produced by rapid and voluminous magmatism over a short geological period. During this time, the Datong dyke and Yanliao sills in North China and the Galiwinku dyke swarm and Derim-Derim sills in North Australia erupted in unison, marking a widespread magmatic event likely triggered by the same mantle plume. The presence of these geochemical fingerprints across both cratons offers a compelling narrative of their shared evolution within Nuna.

The enduring link between the North China Craton and the North Australian Craton within Nuna is one of the most compelling examples of long-lived cratonic association in Proterozoic history. Their connection is evident through an extraordinary alignment of paleomagnetic poles, sedimentary and fossil records, geochemical signatures, mineral deposits, and tectonic histories. For nearly half a billion years, these two landmasses moved as a unified entity within Nuna, sharing geological processes and environmental conditions that shaped their evolution. The eventual breakup of Nuna around 1.32 billion years ago marked the end of this long-standing connection, yet the geological legacy of their shared past remains preserved in the rocks. Understanding the profound link between these cratons offers deeper insights into the processes that governed early supercontinent formation, helping to unravel the mysteries of Earth’s distant past. Their connection is a testament to the power of deep time, where continents may drift apart, but the traces of their union remain etched in the fabric of the Earth.

Here's the video we made on the geological link between North Australia and North China on the OzGeology YouTube channel: