Active crustal differentiation beneath the Rio Grande Rift

• Published in: Nature geoscience 2020-11, Vol.13 (11), p.758-763
• Main Authors: Cipar, Jacob H., Garber, Joshua M., Kylander-Clark, Andrew R. C., Smye, Andrew J.
• Format: Article
• Language: English
• Subjects: 704/2151/209; 704/2151/210; 704/2151/431; 704/2151/562; Attenuation; Conductive heat transfer; Continental crust; Continents; Differentiation; Earth; Earth and Environmental Science; Earth crust; Earth mantle; Earth Sciences; Earth System Sciences; Geochemistry; Geology; Geophysics/Geodesy; Heat transfer; High temperature; Isotopes; Metamorphism; Metamorphism (geology); Modelling; Orogeny; Stability; Tectonics; Temperature; Thickening; Ultrahigh temperature; Uranium
• ISSN: 1752-0894; 1752-0908
• DOI: 10.1038/s41561-020-0640-z

Silicon-rich continental crust is unique to Earth. Partial melting during high- to ultrahigh-temperature metamorphism (700 °C to >900 °C) promotes the long-term stability of this crust because it redistributes key elements between the crust and mantle and ultimately produces cooler, more-differentiated continents. Granulites—rocks formerly at high- to ultrahigh-temperature conditions—preserve a record of the stabilization of Earth’s continents, but the tectonic mechanisms that drive granulite formation are enigmatic. Here we present an analysis of lower-crustal xenoliths from the Rio Grande Rift—a nascent zone of extension in the southwestern United States. Uranium–lead geo- and thermochronology combined with thermobarometric modelling show that the lower 10 km of the crust currently resides at granulite-facies conditions, with the lowermost 2 km at ultrahigh-temperature conditions. Crust and mantle xenoliths define a continuous pressure-and-temperature array, indicating that a thin lithospheric mantle lid mediates elevated conductive heat transfer into the crust. These findings establish a direct link among ultrahigh-temperature metamorphism, collapse of the Laramide orogen and lithospheric mantle attenuation. Other indicators of modern ultrahigh-temperature metamorphism are consistent with these conditions prevailing over thousands of square kilometres across the US–Mexico Basin and Range province. Similarities between the pressure-and-temperature path from the Rio Grande lower crust and those from exhumed granulite terranes imply that post-thickening lithospheric extension is a primary mechanism to differentiate Earth’s continental crust. A link between post-thickening lithospheric extension and the differentiation of continental crust is implied by granulite conditions beneath the Rio Grande Rift, inferred from analysis of lower-crustal xenoliths and thermobarometric modelling.