Amazing stuff! What a jigsaw puzzle!
"... Now, Gondwana is posing a new challenge. By studying the age of basement granites known to have existed near the continent’s edge, a team of geologists has found that Gondwana was much bigger than previously thought, encompassing up to 80% of the continental crust at the time, and adding some 127 million square kilometers to its extent. Such size, they suggest, makes it a true supercontinent, nearly on par with Pangea, which formed several hundred million years later.
The finding, if it holds up, challenges the notion of supercontinent cycles—the idea that the continents break apart and smoosh together, driven by shifts in the mantle, in regular cycles of 500 million years or so. ..."
"... Geologists have long gone back and forth on the status of Gondwana, which was discovered more than 100 years ago when common plant fossils were found on widely separated continents.
In 2012, Joseph Meert, a paleogeographer at the University of Florida, concluded supercontinents should at a minimum encompass 75% of all known continental crust. At the time, Gondwana was mostly thought to comprise present-day India, Australia, Africa, Antarctica, and South America—64% of known land. The 75% threshold was always arbitrary ...
In 2012, Joseph Meert, a paleogeographer at the University of Florida, concluded supercontinents should at a minimum encompass 75% of all known continental crust. At the time, Gondwana was mostly thought to comprise present-day India, Australia, Africa, Antarctica, and South America—64% of known land. The 75% threshold was always arbitrary ...
But since then, Gondwana’s size has grown, as geologists added continental fragments in the eastern United States, southern Europe, Turkey, Iran, and Pakistan. But other fragments that existed at the time, including much of China, have not traditionally been assigned to Gondwana. Magnetic signals preserved in rocks that can help determine where ancient crust was located are difficult to interpret during this period. The jigsaw puzzle is further complicated by the repeated opening and closing of narrow oceans in East Asia at the time. ..."
From the abstract:
"Profound global biogeochemical shifts marked the Ediacaran-Cambrian transition [550–500 million years (Ma)], a phenomenon often ascribed to the dynamics of supercontinent cycles.
However, Gondwana is frequently denied supercontinent status due to its perceived spatial deficit (∼64% of continental landmass). Leveraging continental-scale Nd isotopic mapping based on a vast database of 25,346 felsic-intermediate igneous rocks, we reveal extensive buried Precambrian terranes beneath Phanerozoic orogens in Asia, Europe, and North America.
Our results expand Gondwana’s reconstructed area to ∼80% of the global landmass, firmly establishing its identity as a true supercontinent—termed “Greater Gondwana.” We propose that the assembly and peripheral subduction of this “Greater Gondwana” played a pivotal role in driving the geodynamic and environmental perturbations that culminated in the Cambrian metazoan radiation."
Fig. 1. Continental-scale Nd isotopic (TDM2) map of southwestern Asia, central Europe, and southeastern North America (encompassing peri-Gondwana terranes and orogens).
Fig. 4. Reconstruction of Greater Gondwana at ca. 500 Ma or at 550 to 500 Ma compared with conventional paleogeographic interpretations (inset).
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