Abstract
As a Quaternary repository of wind-reworked Indus River sand at the entry point in the Himalayan foreland basin, the Thal Desert in northern Pakistan stores mineralogical information useful to trace erosion patterns across the western Himalayan syntaxis and the adjacent orogenic segments that fed detritus into the Indus delta and huge deep-sea fan throughout the Neogene. Provenance analysis of Thal Desert sand was carried out by applying optical and semi-automated Raman spectroscopy on heavy-mineral suites of four eolian and 11 fluvial sand samples collected in selected tributaries draining one specific tectonic domain each in the upper Indus catchment. In each sample, the different types of amphibole, garnet, epidote and pyroxene grains—the four dominant heavy-mineral species in orogenic sediment worldwide—were characterized by SEM-EDS spectroscopy. The chemical composition of 4249 grains was thus determined. Heavy-mineral concentration, the relative proportion of heavy-mineral species, and their minerochemical fingerprints indicate that the Kohistan arc has played the principal role as a source, especially of pyroxene and epidote. Within the western Himalayan syntaxis undergoing rapid exhumation, the Southern Karakorum belt drained by the Hispar River and the Nanga Parbat massif were revealed as important sources of garnet, amphibole, and possibly epidote. Sediment supply from the Greater Himalaya, Lesser Himalaya, and Subhimalaya is dominant only for Punjab tributaries that join the Indus River downstream and do not contribute sand to the Thal Desert. The detailed compositional fingerprint of Thal Desert sand, if contrasted with that of lower course tributaries exclusively draining the Himalaya, provides a semi-actualistic key to be used, in conjunction with complementary provenance datasets and geological information, to reconstruct changes in paleodrainage and unravel the relationship between climatic and tectonic forces that controlled the erosional evolution of the western Himalayan-Karakorum orogen in space and time.
Highlights
Heavy minerals provide detailed information on the geology of source areas, which is useful in the study of modern sand unmodified by diagenesis [1]
The detailed compositional fingerprint of Thal Desert sand, if contrasted with that of lower course tributaries exclusively draining the Himalaya, provides a semi-actualistic key to be used, in conjunction with complementary provenance datasets and geological information, to reconstruct changes in paleodrainage and unravel the relationship between climatic and tectonic forces that controlled the erosional evolution of the western Himalayan-Karakorum orogen in space and time
The studied river sands derived from the Karakorum contain moderately poor to rich transparent-heavy-mineral suites dominated by amphibole, with subordinate epidote, clinopyroxene, titanite and rare clinozoisite, apatite, and garnet
Summary
Heavy minerals provide detailed information on the geology of source areas, which is useful in the study of modern sand unmodified by diagenesis [1]. The detailed compositional fingerprint of Thal Desert sand, if contrasted with that of Punjab tributaries exclusively draining the Himalayan belt, provides an additional actualistic key to trace changes in erosion patterns within the huge catchment that has fed detritus to the Indus delta and deep-sea fan throughout the late Neogene [19,20]. Other studies investigating provenance of Indus sediments focused on Pb isotopes in detrital K-feldspar and bulk-sediment Nd and Sr isotope fingerprints [24,25,26], zircon U-Pb or mica 39 Ar/40 Ar geochronology and apatite fission-track or (U–Th)/He thermochronology [27,28,29], sand petrography, heavy minerals, 10 Be cosmogenic nuclides [18,30], and clay mineralogy [31] Such multi-technique approaches have shed new light on the relative role played by the interacting climatic and tectonic forces that controlled the erosional evolution of the western Himalayan-Karakorum orogen. Other rivers are minor and mostlyBelt flow during flash floods
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