Short communication: age2exhume – a MATLAB/Python script to calculate steady-state vertical exhumation rates from thermochronometric ages and application to the Himalaya

Abstract

Abstract. Interpreting cooling ages from multiple thermochronometric systems and/or from steep elevation transects with the help of a thermal model can provide unique insights into the spatial and temporal patterns of rock exhumation. Although several well-established thermal models allow for a detailed exploration of how cooling or exhumation rates evolved in a limited area or along a transect, integrating large, regional datasets in such models remains challenging. Here, we present age2exhume, a thermal model in the form of a MATLAB or Python script, which can be used to rapidly obtain a synoptic overview of exhumation rates from large, regional thermochronometric datasets. The model incorporates surface temperature based on a defined lapse rate and a local relief correction that is dependent on the thermochronometric system of interest. Other inputs include sample cooling age, uncertainty, and an initial (unperturbed) geothermal gradient. The model is simplified in that it assumes steady, vertical rock uplift and unchanging topography when calculating exhumation rates. For this reason, it does not replace more powerful and versatile thermal–kinematic models, but it has the advantage of simple implementation and rapidly calculated results. We also provide plots of predicted exhumation rates as a function of thermochronometric age and the local relief correction, which can be used to simply look up a first-order estimate of exhumation rate. In our example dataset, we show exhumation rates calculated from 1785 cooling ages from the Himalaya associated with five different thermochronometric systems. Despite the synoptic nature of the results, they reflect known segmentation patterns and changing exhumation rates in areas that have undergone structural reorganization. Moreover, the rapid calculations enable an exploration of the sensitivity of the results to various input parameters and an illustration of the importance of explicit modeling of thermal fields when calculating exhumation rates from thermochronometric data.

Phases of Enhanced Exhumation During the Cretaceous and Cenozoic Orogenies in the Eastern European Alps: New Insights From Thermochronological Data and Thermokinematic Modeling

“…Furthermore, PECUBE allows inverse modeling for a set of samples taken along an elevation profile, that is, it considers the spatial position of the samples relative to each other. A summary and comparison of the capabilities of the different codes mentioned above can be found in van der Beek & Schildgen (2023).…”

Elevation‐Dependent Periglacial and Paraglacial Processes Modulate Tectonically‐Controlled Erosion of the Western Southern Alps, New Zealand

“…Reported AFT cooling ages of 0 Myr were excluded; these ages are indicative of fast exhumation but do not provide quantitative constraints on exhumation rates. Cooling ages were converted to steady‐state, vertical exhumation rates using the age2exhume script (van der Beek & Schildgen, 2023), with an initial geotherm of 25°C/km, a thermal diffusivity of 30 km 2 /Myr, a model thickness of 25 km, a temperature at 0 masl elevation of 14°C and a lapse rate of 5°C/km. To correct for local topographic relief and surface‐temperature variations, we follow Willett and Brandon (2013) in considering each sample's position relative to a smoothed version of the topography, with a smoothing radius defined by π × z c , with z c being an estimated closure depth.…”

“…The estimated z c for each system was as follows: 2,000 m (AHe), 3,500 m (AFT), 5,000 m (ZHe), and 6,000 m (ZFT). Details on the model and parameters of each thermochronological system can be found in van der Beek & Schildgen (2023). Because the model assumes steady rock uplift and constant topography, it provides only first‐order estimates of exhumation rates and regional patterns of exhumation.…”

Impact of Quaternary Glaciations on Denudation Rates in North Pamir—Tian Shan Inferred From Cosmogenic 10Be and Low‐Temperature Thermochronology

“…We assume a (default) thermal diffusivity of 30 km 2 Myr −1 , and a model thickness of 30 km. Model results are not sensitive to the assumed model thickness (see sensitivity tests in Van der Beek & Schildgen, 2023); this value was chosen as a rough estimate of the starting thermal field for the model, which encompasses typical depths from which rocks were tectonically exhumed in the Tian Shan. Kinetic parameters for the AHe system are derived from Farley (2000) and for the AFT system from Reiners and Brandon (2006).…”

“…To estimate long‐term exhumation rates across the Tian Shan, we compile AFT ( n = 705, Table S3 in Supporting Information S2) and apatite (U‐Th‐Sm)/He (AHe, n = 211, Table S4 in Supporting Information S2) ages available in the published literature (see Tables S3 and S4 in Supporting Information S2 for list of publications). We calculate one‐dimensional, steady‐state exhumation rates from the published AFT and AHe cooling ages using the age2exhume MATLAB code (Van der Beek & Schildgen, 2023).…”