Crustal thickness, elevation, and Sr/Y and (La/Yb)N of magmatic rocks are strongly correlated for subduction‐related and collision‐related mountain belts. We quantitatively constrain the paleo‐elevation of the Tibetan Plateau since the Cretaceous using empirically derived equations. The results are broadly consistent with previous estimates based on stable isotope and structural analyses, supporting a complex uplift history. Our data suggest that a protoplateau formed in central Tibet during the Late Cretaceous and was higher than the contemporaneous Gangdese arc. This protoplateau collapsed before the India‐Asia collision, during the same time period that elevation in southern Tibet was increasing. During the India‐Asia collision, northern and southern Tibet were uplifted first followed by renewed uplift in central Tibet, which suggests a more complicated uplift history than commonly believed. We contend that a broad paleovalley formed during the Paleogene in central Tibet and that the whole Tibetan Plateau reached present‐day elevations during the Miocene.
The redox evolution of Archean upper mantle impacted mantle melting and the nature of chemical equilibrium between mantle, ocean and atmosphere of the early Earth. Yet, the origin of these variations in redox remain controversial. Here we show that a global compilation of ∼3.8-2.5 Ga basalts can be subdivided into group B-1, showing modern mid-ocean ridge basalt-like features ((Nb/La)PM ≥ 0.75), and B-2, which are similar to contemporary island arc-related basalts ((Nb/La)PM < 0.75). Our V-Ti redox proxy indicates a more reducing upper mantle, and the results of both ambient and modified mantle obtained from B-1 and B-2 samples, respectively, exhibit a ∼1.0 log unit increase in their temporal evolution for most cratons. Increases in mantle oxygen fugacity are coincident with the changes in basalt Th/Nb ratios and Nd isotope ratios, indicating that crustal recycling played a crucial role, and this likely occurred either via plate subduction or lithospheric drips.
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