Scientists at The University of Texas at Austin have conducted a study using zircons as geologic timekeepers to describe a potential overlooked step in the process of raising seafloors into mountains. Zircons are tiny minerals that record chemical signatures of the geological environment where they formed, and in this study, researchers found zircons from the Andes mountains of Patagonia with a chemical signature associated with the movement of tectonic plates apart, despite forming when the plates were colliding. This unexpected signature suggests a previously undescribed tectonic step involving oceanic crust mixing in a magma chamber to influence zircon formation.
The theory of oceanic magma mixing is significant as it represents a transitional step in the formation of back arc basins, essential geological structures shaping landscapes and the planet’s climate regulation. Back arc basins form between oceanic and continental tectonic plates, opening as the plates move apart and closing as they come back together. Understanding this process, which brings a geologic record of Earth history to the surface, is crucial as it plays a role in carbon dioxide storage through weathering of ocean crust. Coauthor Matt Malkowski collected zircons from the Rocas Verdes Basin in Patagonia, capturing the entire record of the back arc basin from opening to closing.
In analyzing the chemical signatures of the zircons, researchers found that while zircons associated with the basin’s opening had the expected signature, those linked with the basin’s closing did not undergo the typical chemical shift. The absence of a pull down signature until 200 million years later suggested a scenario where tectonic forces underthrust parts of the oceanic crust, pushing it towards the magmatic chamber where zircons form. As the continents continue to squeeze together, the oceanic crust gets replaced by continental crust, reflecting in the zircon signature. This transitional phase could be present in back arc basins worldwide, but its observation has been limited due to the fast closure of most basins.
Following the discovery of this zircon signal in Patagonia, researchers are now exploring if this influence of oceanic crust on zircon formation can be found in zircons from other locations, such as the Sea of Japan. By analyzing zircons from modern back arc basins, scientists aim to further understand the processes affecting the formation of mountain belts from seafloor spreading and closure. The study builds upon a history of research on back arc basins at UT Austin, with earlier work by Professor Ian Dalziel recognizing the Andes of Patagonia as a result of back arc basin closure. This research contributes to ongoing efforts to expand knowledge about these geological processes and their implications for Earth’s history.
The study, funded by the National Science Foundation and UT Austin, highlights the importance of zircons as geological timekeepers in unraveling the complexities of mountain-building processes and the tectonic forces at play. By examining zircons and their chemical signatures, researchers can uncover new insights into the mechanics of plate tectonics and the formation of geological structures that shape the Earth’s surface. Through ongoing research, scientists aim to further refine their understanding of back arc basins and their role in Earth’s geological history.
