Paleoaltimetry
Paleoaltimetry
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Left: A summary of existing quantitative paleoelevation studies in the Himalayan-Tibetan Plateau
(unpublished figure, the different colors represent
different proxies, and numbers represent different studies)
My research of paeoelevations in Tibet has focused on the central (Bangong suture) and north-central (Hoh Xil-Songpan-Ganzi) parts
1. Paleoelevation studies in central Tibet (Bangong suture)
Top: Common stable isotope proxies for paleoelevation and paleoclimate studies in terrestrial settings; Right: A three-stage topographic growth history of the central Tibetan Plateau.
Significant questions:
Is stable isotope-based paleoaltimetry workable in central Tibet?
How to derive not-underestimated paleoelevations from lacustrine proxies?
What are the reasons for the discrepancies between isotope-based and fossil-based paleoelevation estimates?
Methods:
Tuff zircon U-Pb dating for age constraint;
Stable hydrogen isotopes of volcanic glass (first report in Tibet);
Used δ18O(carb) vs. δD(vg) dual isotope system to derive the stable isotopes of paleo-precipitation;
Designed a moisture mixing model for stable isotope-based paleoelevation calculation in central Tibet.
Main conclusions:
Stable isotope-based paleoaltimetry is still workable in central Tibet with necessary modifications;
Isotope-based paleoaltimetry results still reflect local elevations in central Tibet along the Bangong suture zone;
The δD of volcanic glass deposited in lakes and δ18O of lacustrine carbonate can be used to derive the stable isotopes of paleo-precipitation;
Isotope-based and fossil-based paleoelevation results can be reconciled with better age constraints and removing estimates with large uncertainties;
Central Tibet (Bangong suture) was probably a deep valley during the Eocene, and experienced two stages of surface uplift during the Oligocene and middle–late Miocene.
2. Paleoelevation reconstructions in north-central Tibet (Hoh Xil) and implications for geodynamics
U-Pb dating and petrography of the Hoh Xil Basin carbonates
Geology, to be submitted
A tectonic and topographic evolution model for the Hoh Xil Basin, north-central Tibet
Significant questions:
When did north-central Tibet obtain its current high elevation?
What are the drivers for surface uplift in north-central Tibet?
Research methods:
Carbonate clumped isotope temperatures;
Carbonate U-Pb dating;
XRD and petrography.
Main findings:
The new clumped isotope temperatures show that the Hoh Xil Basin experienced a phase of surface uplift during the early–middle Miocene;
The Hoh Xil Basin was probably low (e.g., <2 km) by the early Eocene, reached ~3 km by the late Oligocene, and experienced an additional ~1 km surface uplift during the Miocene.
Upper crustal shortening cannot account for all surface uplift, lower crustal flow and/or convective removal of the lower lithosphere are required.
3. Controlling factors of modern meteoric water stable isotopes and implications for paleoaltimetry studies
Top: Modern river water sampling across the Tibetan Plateau; Right: Back-trajectory analysis of moisture at four different locations in Tibet.
Significant questions:
What are the controlling factors of modern meteoric water stable isotopes across the Tibetan Plateau?
How reliable are stable isotope-based paleoaltimetry studies in different parts of the plateau?
Research methods:
Stable isotopes of surface waters;
HYSPLIT back-trajectory analysis of moisture;
Large data set compiling and processing;
Isotope fractionation modeling.
Main findings:
River water is a good substitute for precipitation to study large-scale spatial variations of meteoric water stable isotopes;
Discoverd a contrast difference of d-excess values between the eastern and western Tibetan Plateau;
Provided large spatial data sets of stable isotopes that can be used to verify the validity of isotope-enabled GCM modeling results;
Proposed three controlling factors of meteoric water stable isotopes: moisture mixing, surface water recycling, and sub-cloud evaporation;
Stable isotope-based paleoaltimetry is most reliable in south Tibet, while requires modification in central and north Tibet.
4. Other studies
Cenozoic paleoelevation history of the Lunpola Basin (manuscript in preparation)
Following my recent paleoelevation studies using the stable isotopes of volcanic glass in the Lunpola Basin, we further explore the elevation history using clumped isotope temperatures of lacustrine carbonates. The new data show temperature decreases around 20 Ma and after 16 Ma, which cannot be explained by global cooling. The new results refine previous paleoelevation estimates, and highlight the Neogene phase of surface uplift in central Tibet.
Paleogene topographic evolution of the northern Rockies (Tectonics, 2021)
In western North America, it has been generally accepted that surface elevations have gradually decreased during the post-orogenic extensional stage since the early Eocene. This study reports stable hydrogen isotopes of more than 60 volcanic glass samples from southwestern Montana, which shows a more than 35 per mil decrease during the late Eocene–early Oligocene. After removing the influence of global cooling, the data reflect a pulse of early Oligocene surface uplift that may be associated with sub-surface processes, e.g., convective removal of the lower lithosphere.
Late Eocene paleoelevations of the east-central Tibetan Plateau (GSA Bulletin, 2018)
With our improved understanding of the meteoric water stable isotope variations in central Tibet, we modified traditional stable isotope-based paleoaltimetry by considering the proportional mixing of two major moisture sources to infer the late Eocene paleoelevations of the Nangqian Basin, east-central Tibet. We also applied clumped isotope thermometry as an independent proxy to infer paleoelevations. This study provides a new method to reconstruct paleoelevations in continental interiors that have more than one moisture source. The results of this study also highlight the importance of crustal shortening and thickening in raising the east-central Tibetan Plateau.
5. Other related studies
Comparative clumped isotope temperature relationships in freshwater carbonates (Arnold et al., Paleoceanography and Paleoclimatology, in revision)
Stable isotopic evidence for Paleocene–Miocene paleoelevation evolution of the northern Central Andean Plateau, southern Peru (Kar et al., Journal of South American Earth Sciences, in revision)
Spatiotemporal distribution of river water stable isotope compositions and variability of lapse rate in the central Rocky Mountains: controlling factors and implications for paleoelevation reconstruction (Zhu et al., EPSL, 2018)
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