Tectonics drives rapid exhumation of the western Himalayan syntaxis: Evidence from low-temperature thermochronometry of the Neelum valley region, Pakistan

Abstract

Reconstructing the geometry of exhumation in the western Himalayan syntaxis region around Nanga Parbat is of critical importance to understanding how tectonics and surface processes interact during orogenesis. In order to determine the role played by the main Himalayan thrusts, we combine apatite U-Pb dating with apatite and zircon (U-Th-[Sm])/He analyses as well as apatite fission track dating from the Neelum valley region of Azad Jammu and Kashmir, Pakistan. Apatite U-Pb ages range from Proterozoic to mid-Miocene and can be separated into three age groups depending on the degree to which they have been affected by Himalayan tectonothermal events. Pooled fission track ages range from 7.0 ± 0.4 to 2.2 ± 0.4 Ma (1σ), apatite He ages range from 8.7 ± 0.2 to 2.0 ± 0.2 Ma, and zircon He ages range from 20.0 ± 0.4 to 6.1 ± 0.1 Ma. The data support rapid regional cooling at 10-8 Ma caused by the removal of 5-6 km of crust. This is synchronous with the initiation of movement along the Main Boundary thrust. Stream power analysis of the Neelum River catchment indicates a high normalized steepness index (k sn) of >500 m 0.9 along the major river and lower k sn in the headwaters. The boundary between the different apatite U-Pb age groups and the transition from high k sn to lower k sn values coincide with the mapped trace of the Main Central thrust, corroborating the presence of the thrust in the southwestern part of the region. Compiling all apatite fission track cooling ages from the Nanga Parbat syntaxis region shows that cooling age contours are parallel to the major thrusts. Collectively these data provide convincing support for the contention that the well-established pattern of exhumation known from much of the Himalayan front continues around to the western syntaxis of the Himalayas.

Spatial and temporal trends in exhumation of the Eastern Himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the Bengal Fan

“…15 Ma youngest grains recorded from modern river sediments draining Eastern Himalayan regions outside the syntaxis. Similarly older ages are recorded in the western Himalaya outside of the Nanga Parbat syntaxis, where all grains are older than 18 Ma (Turab et al, 2017).…”

“…In this study, we employed U-Pb analyses on detrital rutile and apatite, 40 Ar/ 39 Ar analyses on detrital white mica, and fission-track analyses on detrital zircon from Himalayan-derived Bengal Fan sediment. Existing data are summarized below, apart for the apatite U-Pb system, for which no published data exist for the Eastern Himalaya (but note also Govin, 2017), and only one data set is available for the western Himalaya (Turab et al, 2017); thus, we present new apatite U-Pb data we produced to characterize the source region's characteristics in terms of the U-Pb isotopic system.…”

“…For both the white mica 40 Ar/ 39 Ar and apatite U-Pb data: (1) there is a difference in grain ages between modern sediments from rivers draining the syntaxis and those draining regions outside the syntaxis (for the only data set from the Western Himalaya, see Turab et al, 2017). For both micas and apatites, the youngest peak is younger in rivers draining the syntaxis, and there are uncommon grains with very short lag times.…”

Palaeozoic and Pliocene tectonic evolution of the Salt Range constrained by low‐temperature thermochronology

“…The Pakistan Subhimalaya is defined by the Kohat and Potwar (Figure 1). These are bounded to the north by the Main Boundary Thrust (MBT), which formed at around ~10 Ma (Brozovic & Burbank, 2000; Meigs et al., 1995; Turab et al., 2017). At the southern border of the Potwar, the SRT lifts up Precambrian to Pliocene strata above the SRT ramp and exposes them in a fault bend fold above Quaternary sediments of the Punjab Plain (Figure 1; Baker et al., 1988; Ghani et al., 2018).…”

Respuesta del sistema erosivo fluvial en las cuencas Ameca y Santiago, centro-occidente de México, ante el control tectónico y volcánico

“…Tales técnicas permiten estimar las tasas de exhumación (p. ej. Margirier et al, 2015;Turab et al, 2017), erosión (p. ej. Vanacker et al, 2007 e incisión (p. ej.…”