Multisystem dating of modern river detritus from Tajikistan and China: Implications for crustal evolution and exhumation of the Pamir

Abstract

The Pamir is the western continuation of Tibet and the site of some of the highest mountains on Earth, yet comparatively little is known about its crustal and tectonic evolution and erosional history. Both Tibet and the Pamir are characterized by similar terranes and sutures that can be correlated along strike, although the details of such correlations remain controversial. The erosional history of the Pamir with respect to Tibet is significantly different as well: Most of Tibet has been characterized by internal drainage and low erosion rates since the early Cenozoic; in contrast, the Pamir is externally drained and topographically more rugged, and it has a strongly asymmetric drainage pattern. Here, we report 700 new U-Pb and Lu-Hf isotope determinations and >300 40 Ar/ 39 Ar ages from detrital minerals derived from rivers in China draining the northeastern Pamir and >1000 apatite fission-track (AFT) ages from 12 rivers in Tajikistan and China draining the northeastern, central, and southern Pamir. U-Pb ages from rivers draining the northeastern Pamir are Mesozoic to Proterozoic and show affinity with the Songpan-Ganzi terrane of northern Tibet, whereas rivers draining the central and southern Pamir are mainly Mesozoic and show some affinity with the Qiangtang terrane of central Tibet. The ε Hf values are juvenile, between 15 and −5, for the northeastern Pamir and juvenile to moderately evolved, between 10 and −40, for the central and southern Pamir. Detrital mica 40 Ar/ 39 Ar ages for the northeastern Pamir (eastern drainages) are generally older than ages from the central and southern Pamir (western drainages), indicating younger or lower-magnitude exhumation of the northeastern Pamir compared to the central and southern Pamir. AFT data show strong Miocene-Pliocene signals at the orogen scale, indicating rapid erosion at the regional scale. Despite localized exhumation of the Mustagh-Ata and Kongur-Shan domes, average erosion rates for the northeastern Pamir are up to one order of magnitude lower than erosion rates recorded by the central and southern Pamir. Deeper exhumation of the central and southern Pamir is associated with tectonic exhumation of central Pamir domes.Deeper exhumation coincides with western and asymmetric drainages and with higher precipitation today, suggesting an orographic effect on exhumation. A younging-southward trend of cooling ages may reflect tectonic processes. Overall, cooling ages derived from the Pamir are younger than ages recorded in Tibet, indicating younger and higher magnitudes of erosion in the Pamir.

Thermochronological insights into the structural contact between the Tian Shan and Pamirs, Tajikistan

“…The ~10 Ma AFT/AHe cooling signal confirms recent data by Kässner et al () and Carrapa et al. (), suggesting a phase of rapid cooling during the late Miocene. This cooling event is thought to be related to the northward motion of the Pamirs (Cao, Wang, van der Beek, Bernet, & Zhang, ; Kässner et al, ; Thiede et al., ), which induced deformation and intense mountain building throughout the entire Tian Shan (e.g.…”

The Alichur Dome, South Pamir, Western India–Asia Collisional Zone: Detailing the Neogene Shakhdara–Alichur Syn‐collisional Gneiss‐Dome Complex and Connection to Lithospheric Processes

“…In the East Pamir, the onset of ~E–W extension along the active KSES at ~10 Ma exhumed the Kongur Shan dome and, due to a southward decrease in slip magnitude, augmented the earlier, ~N–S‐extension‐related exhumation of the Muztaghata dome (Arnaud et al, ; Brunel et al, ; Cai et al, ; Cao, Wang, et al, ; Robinson et al, ; Robinson et al, ; Thiede et al, ). Bedrock retrograde‐metamorphic and/or cooling ages (Brunel et al, ; Cao, Bernet, et al, ; Hacker et al, ; Hubbard et al, ; Robinson et al, ; Rutte, Ratschbacher, Khan, et al, ; Stearns et al, ; Stearns et al, ), which are consistent with the broader signal from detrital cooling ages (Cao, Bernet, et al, ; Carrapa et al, ; Lukens et al, ), indicate southward propagation of convergence‐parallel gneiss‐dome exhumation from the Central to the South Pamir. This was followed by cross‐cutting, orogen‐parallel (~E–W) gneiss‐dome exhumation along the KSES and the SKFS.…”

Miocene Volcaniclastic Sequence Within the Xiyu Formation from Source to Sink: Implications for Drainage Development and Tectonic Evolution in Eastern Pamir, NW Tibetan Plateau

“…Figure shows the previously published detrital zircon U‐Pb age spectra of both modern river sand of potential source regions of the Tashkorgan‐Yarkand River and the sedimentary rocks that might record the river evolution (Blayney et al, ; Carrapa et al, ; Clift et al, ; Lukens et al, ; Rittner et al, ). In Figure , we only present the ≤1,000 Ma ages as they are critical components for provenance identification in this region (e.g., Blayney et al, ; Clift et al, ).…”

“…from both modern sand and older sandstone samples considered in this study. Data of modern sand are from compilation of Blayney et al (), Carrapa et al (), Clift et al (), Lukens et al (), and Rittner et al (). Data of older sedimentary rocks from the Aertashi section and the Qimugan section are from Blayney et al () and Cao et al (), respectively.…”