Pulsed rise and growth of the Tibetan Plateau to its northern margin since ca. 30 Ma.

The onset of mountain building along margins of the Tibetan Plateau provides a key constraint on the processes by which the high topography in Eurasia formed. Although progressive expansion of thickened crust underpins most models, several studies suggest that the northern extent of the plateau was established early, soon after the collision between India and Eurasia at ca. 50 Ma. This inference relies heavily on the age and provenance of Cenozoic sediments preserved in the Qaidam basin. Here, we present evidence in the northern plateau for a considerably younger inception and evolution of the Qaidam basin, based on magnetostratigraphies combined with detrital apatite fission-track ages that date the basin fills to be from ca. 30 to 4.8 Ma. Detrital zircon-provenance analyses coupled with paleocurrents reveal that two-stage growth of the Qilian Shan in the northeastern margin of the Tibetan Plateau began at ca. 30 and at 10 Ma, respectively. Evidence for ca. 30 and 10 to 15 Ma widespread synchronous deformation throughout the Tibetan Plateau and its margins suggests that these two stages of outward growth may have resulted from the removal of mantle lithosphere beneath different portions of the Tibetan Plateau.

Upward and outward growth of north-central Tibet: Mechanisms that build high-elevation, low-relief plateaus.

Large orogenic plateaus, such as the Tibetan Plateau, are characterized by high-elevation, low-relief topography, in contrast to the rugged terrains of narrower mountain belts. A key question is how low-elevation hinterland basins, characteristic of broad regions of shortening, were raised while regional relief was flattened. This study uses the Hoh Xil Basin in north-central Tibet as an analogue for late-stage orogenic plateau formation. The precipitation temperatures of lacustrine carbonates deposited between ~19 and ~12 million years ago record an early to middle Miocene phase of surface uplift of 1.0 ± 0.7 km. The results of this study demonstrate the contribution of sub-surface geodynamic processes in driving regional surface uplift and redistribution of crustal material to flatten plateau surfaces during the late stage of orogenic plateau formation.

Pre-Quaternary decoupling between Asian aridification and high dust accumulation rates.

Theories of late Cenozoic climate cooling assume that central Asian aridification and high dust accumulation rates in the Chinese Loess Plateau and the North Pacific Ocean are genetically related. On the basis of detailed sediment provenance analysis, we show that high dust accumulation rates in the Chinese Loess Plateau and the North Pacific Ocean during the late Miocene-Pliocene were mainly caused by increased erosion in the Qilian Mountains and low-elevation eastern Asia areas, driven by the effects of East Asian summer monsoon intensification. We conclude that precipitation-driven erosion increased dust input to the North Pacific Ocean and may have played a pivotal role in late Cenozoic climate cooling.

Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin.

The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ(18)O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time.

Rise of the Andes.

The surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening, leading to their gradual rise. Recent studies of the Andes indicate that their elevation remained relatively stable for long periods (tens of millions of years), separated by rapid (1 to 4 million years) changes of 1.5 kilometers or more. Periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable, dense lower lithosphere after long-term thickening of the crust and lithospheric mantle.

Rapid uplift of the Altiplano revealed through 13C-18O bonds in paleosol carbonates.

The elevation of Earth's surface is among the most difficult environmental variables to reconstruct from the geological record. Here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters, constrained by measurements of abundances of 13C-18O bonds in soil carbonates. We use this approach to show that the Altiplano plateau in the Bolivian Andes rose at an average rate of 1.03 +/- 0.12 millimeters per year between approximately 10.3 and approximately 6.7 million years ago. This rate is consistent with the removal of dense lower crust and/or lithospheric mantle as the cause of elevation gain.