When the traditional supercontinent Gondwana was torn asunder 83 million years in the past, an enormous chunk of it sank beneath the waves because it drifted away.
In line with some geologists, this submerged chunk – referred to as Zealandia – could be thought of Earth’s eighth continent, it weren’t for a thick layer of ocean water obscuring our view.
As a substitute, all that now peeks above the ocean’s floor is New Zealand and surrounding islands, so Zealandia itself has lengthy remained enigmatic. About 94 p.c of the 4.9 million km2 continent is submerged, hiding particulars of the northern a part of the land mass.
Utilizing geochemical and isotope knowledge from newly dredged samples of rocks in addition to seismic readings, GNS Science geologist Andy Tulloch and colleagues created a refined map of that area to analyze how the continent got here to be.
Samples of rocks, some as previous because the dinosaurs, have been taken from exploration drill websites and plenty of South Zealandia’s uncovered peaks, comparable to Chatham and Antipodes islands.
An evaluation of their chemical make-up, together with different geological clues, revealed similarities in patterns with geology in West Antarctica, suggesting a subduction of Zealandia’s edge as much as 1 / 4 of a billion years in the past, throughout what’s now the Campbell Plateau off New Zealand’s west coast.
Subduction is when two edges of Earth’s crust push in opposition to each other forcing one edge down into Earth’s mantle. However opposite to earlier ideas, magnetic anomalies present in the identical area aren’t associated to this occasion.
This removes “the unique argument for a strike‐slip “Campbell Fault,” Tulloch and workforce clarify of their paper. “Zealandia and Antarctica are each considerably internally deformed.”
As a substitute, they suggest, the Campbell Magnetic Anomaly System arose from in depth stretching between totally different components of Gondwana that finally snapped aside to create Zealandia’s surrounding sea flooring.
First the mixed areas of Zealandia/West Antarctica and Antarctica/Australia cracked, permitting the Tasman sea to hurry in about 83 million years in the past.
Subsequent, in the course of the Late Cretaceous round 79 million years in the past, Zealandia and West Antarctica ripped away creating the Pacific ocean.
How Zealandia’s crust managed to stretch so skinny earlier than breaking away, has lengthy puzzled geologists. Comparable thinness can also be obvious in West Antarctica.
Tulloch and colleagues discovered proof that the stretching course different by as much as 65 levels between 100 to 80 million years in the past. They suppose this may occasionally have allowed the in depth thinning of the continental crust.
Collectively these findings create a strong basis for a extra detailed evaluation for this unusual stretching of the earth.
This analysis was revealed in Tectonics.
