Active crustal differentiation beneath the Rio Grande Rift

Jacob H. Cipar, Joshua M. Garber, Andrew R.C. Kylander-Clark, Andrew J. Smye

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)758-763
Number of pages6
JournalNature Geoscience
Volume13
Issue number11
DOIs
StatePublished - Nov 1 2020

All Science Journal Classification (ASJC) codes

  • Earth and Planetary Sciences(all)

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