Himalayan geology

Le chamane est un guérisseur et un guerrier. Lors des séances de cures, il s’applique pour le bien de sa com- munauté à renverser l’emprise des entités malfaisantes sur les humains, afin de rétablir la protection du groupe. Pour ce faire, le guerrier-guérisseur part à la recherche d’un diagnostic, d’une âme ou d’une bataille à livrer, évo- luant dans un monde sauvage, peuplé d’aïeux et d’esprits bienfaiteurs, de créatures démoniaques et de fantômes sournois. Afin de devenir le réceptacle des êtres invisibles et de montrer sa force d’intervention, le chamane se pare d’accessoires et de vêtements rituels. Ce couple d’attributs élabore le costume du chamane, véritable ar- mure, où réside dans chaque élément qui le compose le pouvoir des ancêtres. Et c’est ce rattachement transgéné- rationnel du costume à une lignée de chamanes qui anime le guérisseur d’un concentré de force, accumulé à travers les âges.

Erosion is a key step in the destruction and recycling of the continental crust, yet its primary drivers continue to be debated. The relative balance between climatic and solid Earth forces in determining erosion patterns and rates, and in turn orogenic architecture, is unresolved. The monsoon-dominated frontal Himalaya is a classic example of how surface processes may drive focused denudation and potentially control structural evolution. We investigate whether there is a clear relationship between climate and erosion in the drier Himalayan rain shadow on the periphery of the Tibetan Plateau, where a coupled climate-erosion relationship is less clear. We present a new integrated data set combining bulk petrography, geomorphometric analysis, detrital U-Pb zircon geochronology, and bulk Nd and Sr isotope geochemistry from modern river sediments that provides constraints on spatial patterns of sediment production and transport in the Zanskar River. Zanskar River sands are dominated by Greater Himalayan detritus sourced from the glaciated Stod River catchment, which represents only 13% of the total basin area. Prevalent zircon peaks from Cambrian– Ordovician (440–500 Ma) and Mississippian– Permian (245–380 Ma) units indicate more abundant pre-Himalayan granitoids in the northwest Indian Himalaya than in the central and eastern Himalaya. Erosion from the widely exposed Tethyan Himalaya, however, appears modest. Spatial patterns of erosion do not correlate with highest channel steep

The geomorphic, tectonic and seismic aspects of the Ganga plain have been studied by several workers in the recent decades. However, the northern part of this tectonically active plain has been the prime focus in most of the studies. The region to the south of the Ganga River requires necessary attention, especially, regarding the seismic activities. The region lying immediately south of the Outer Himalayas (i.e. the Ganga plain) responds to the stress regime of the Himalayan Frontal Thrust Zone by movement along the existing basement faults (extending from the Indian Peninsula) and creating new surface faults within the sediment cover as well. As a result, several earthquakes have been recorded along these basement faults, such as the great earthquakes of 1934 and 1988 associated with the East Patna Fault. Large zones of ground failure and liquefaction in north Bihar (close to the Himalayan front), have been recorded associated with these earthquakes. The present study reports the soft sediment deformation structures from the south Bihar associated with the prehistoric earthquakes near the East Patna Fault for the first time. The seismites have been observed in the riverine sand bed of the Dardha River close to the East Patna Fault. Several types of liquefaction-induced deformation structures such as pillar and pocket structure, thixotropic wedge, liquefaction cusps and other water escape structures have been identified. The location of the observed seismites within the deformed zone of the East Patna Fault clearly indicates their formation due to activities along this fault. However, the distance of the liquefaction site from the recorded epicenters suggests its dissociation with the recorded earthquakes so far and hence possibly relates to any prehistoric seismic event. The occurrence of the earthquakes of a magnitude capable of forming liquefaction structure in the southern Ganga plain indicates the transfer of stress regime far from the Himalayan front into the peninsular region through these basement faults. Northward extension of the East Patna Fault coincides with the region of the Himalayan front, which corresponds to a less slip potential. Therefore, an association of frequent earthquakes in this region indicates strain release along the East Patna Fault.

Najman et al., 2010), has resulted in formation of the largest mountain ranges on Earth. The Himalaya have continued to evolve both in topography and structure as a result of ongoing tectonic deformation coupled with erosion, which is partly modulated by the strength of summer monsoon rains (Bookhagen et al., 2005; Clift, Hodges, et al., 2008; Wobus et al., 2003). Sediments eroded from the Western Himalaya has been deposited in the Arabian Sea where they form the second largest sediment body on Earth, the Indus submarine fan (Clift et al., 2001; Kolla & Coumes, 1987). Despite extensive studies on the foreland basin, a regional erosion history for the Western Himalaya has not yet been generated, hampering efforts to understand what controls orogenic evolution on multi-million year timescales.

Reliable probabilistic seismic hazard analysis (PSHA) for Nepal is a long-term goal that different researchers have been working on in the last decade. Especially after the 2015 Gorkha earthquake, several classical probabilistic seismic hazard analysis studies have been carried out for the entire Nepal. Herein, an alternative simulation-based PSHA is performed for the Kathmandu basin generating a stochastic catalogue of events using information about seismogenic zones from recent research studies. Different ground motion prediction equations have been adopted. Results show the necessity for a ground motion prediction model that is tailored for Nepal.

The human-landform interaction in the region of the Ghaggar-Hakra palaeochannel in the northwest Indo-Gangetic plains during the Bronze Age Indus/Harappan civilisation (~4.6-3.9 thousand years before the present, ka BP) remains an enigmatic case due to a paucity of evidence regarding the hydrology of the then existing river. Here, we estimated the palaeohydrology of the foothill Markanda River in the sub-Himalayan catchment of the Ghaggar-Hakra (G-H) palaeochannel. Our morphology and chronology results show aggradation of a fan (57.7 ka) during the Late Pleistocene and T-1 to T-5 fluvial terraces (13.1 to 6.0 ka) during the terminal Pleistocene to Holocene, and deposition of palaeoflood sediments (3.9-3.8 ka) over the T-3 terraces during the Late Holocene. Considering the known uplift rates along the Himalayan frontal thrust, and our estimated aggradation rates, we derived channel palaeogeometry and calculated peak discharge at the site of palaeoflood deposits. We conclude that the Markanda River's peak discharge was several orders of magnitude higher during the Late Holocene than the modern-day peak discharge of 100-year return period. The palaeoflood deposits represent larger flooding of the foothill rivers that sustained flows in the downstream reaches of the Ghaggar-Hakra palaeochannel during the Late Harappan civilisation.

The Indian (southwest) summer monsoon is one of the most intense climatic phenomena on Earth. Its long-term development has been linked to the growth of high topography in South and Central Asia. The Indian continental margin, adjoining the Arabian Sea, offers a unique opportunity to investigate tectonic–climatic interactions and the net impact of these processes on weathering and erosion of the western Himalaya. During International Ocean Discovery Program Expedition 355, two sites (U1456 and U1457) were drilled in Laxmi Basin in the eastern Arabian Sea to document the coevolution of mountain building, weathering, erosion, and climate over a range of timescales. In addition, recovering basement from the eastern Arabian Sea provides constraints on the early rifting history of the western continental margin of India with special emphasis on continental breakup between India and the Seychelles and its relationship to the plume-related volcanism of the Deccan Plateau.
Drilling and coring operations during Expedition 355 recovered sediment from Sites U1456 and U1457 in the Laxmi Basin, penetrating 1109.4 and 1108.6 m below seafloor (mbsf), respectively. Drilling reached sediment dated to 13.5–17.7 Ma (late early to early middle Miocene) at Site U1456, although with a large hiatus between the lowermost sediment and overlying deposits dated to <10.9 Ma. At Site U1457, a much longer hiatus occurs near the base of the cored section, spanning from 10.9 to ~62 Ma. At both sites, hiatuses span ~8.2–9.2 and ~3.6–5.6 Ma, with a possible condensed section spanning ~2.0–2.6 Ma, although the total duration for each hiatus is slightly different between the two sites.
A major submarine fan draining the western Himalaya and Karakoram must have been supplying sediment to the eastern Arabian Sea since at least ~17 Ma. Sand mineral assemblages indicate that the Greater Himalayan Crystalline Sequence was fully exposed to the surface by this time. Most of the recovered sediment appears to be derived from the Indus River and includes minerals that are unique to the Indus Suture Zone, in particular glaucophane and hypersthene, most likely originating from the structural base of the Kohistan arc. Pliocene sandy intervals at Site U1456 were deposited in lower fan “sheet lobe” settings, with intervals of basin plain turbidites separated by hemipelagic muddy sections deposited during the Miocene. Site U1457 is more distal in facies, reflecting its more marginal setting. No major active lobe appears to have affected the Laxmi Basin since the Middle Pleistocene (~1.2 Ma).
We succeeded in recovering sections spanning the 8 Ma climatic transition, when monsoon intensity is believed to have changed strongly, although the nature of this change awaits postcruise analysis. We also recovered sediment from a large mass transport deposit measuring ~330 and ~190 m thick at Sites U1456 and U1457, respectively. This section includes an upper sequence of slump-folded muddy and silty rocks, as well as underlying calcarenites and limestone breccias, together with smaller amounts of volcanic clasts, all of which are likely derived from the western Indian continental shelf. Identification of similar facies on the regional seismic lines in Laxmi Basin suggests that these deposits form parts of one of the world’s largest mass transport deposits.
Coring of igneous basement was successful at Site U1457. Recovery of massive basalt and associated volcaniclastic sediment at this site should address the key questions related to rifting and volcanism associated with formation of Laxmi Basin. Geochemical analysis is required to understand the petrogenesis and thus the tectonic setting of volcanism that will reveal whether it is oceanic basalt or volcanic rock contaminated by underlying continental crust or continental flood basalt. However, the fact that the lavas are massive and have few vesicles implies water depths of eruption likely deeper than 2000 m. This precludes opening of the basin in the presence of a major mantle thermal anomaly, such as that associated with the Deccan Large Igneous Province. Other observations made at the two sites during Expedition 355 provide vital constraints on the rift history of this margin. Heat flow measurements at the two drill sites were calculated to be ~57 and ~60 mW/m2. Such heat flow values are compatible with those observed in average oceanic crust of 63–84 Ma age, as well as with the presence of highly extended continental crust. Postcruise analyses of the more than ~1722 m of core will provide further information about the nature of tectonic–climatic interactions in this global type area for such studies.

We use apatite fission track ages from sediments recovered by the International Ocean Discovery Program in the Laxmi Basin, Arabian Sea, to constrain exhumation rates in the western Himalaya and Karakoram since 15.5 Ma. With the exception of a Triassic population in the youngest 0.93 Ma samples supplied from western Peninsular India, apatite fission track ages are overwhelmingly Cenozoic, largely <25 Ma, consistent with both a Himalaya-Karakoram source and rapid erosion. Comparison of the minimum cooling age of each sample with depositional age (lag time) indicates an acceleration in exhumation between 7.8 and 7.0 Ma, with lag times shortening from ∼6.0 Myr at 8.5-7.8 Ma to being within error of zero between 7.0 and 5.7 Ma. Sediment supply at 7.0-5.7 Ma was largely from the Karakoram, and to a lesser extent the Himalaya, based on U-Pb zircon ages from the same samples. This time coincides with a period of drying in the Himalayan foreland caused by weaker summer monsoons and Westerly winds. It also correlates with a shift of erosion away from the Karakoram, Kohistan and the Tethyan Himalaya towards more erosion of the Lesser and Greater Himalaya and Nanga Parbat, as shown by zircon U-Pb provenance data, and especially after 5.7 Ma based on Nd isotope data. Samples younger than 5.7 Ma have lag times of ∼4.5 Myr, similar to Holocene Indus delta sediments.

Uplift of the Himalaya and Tibetan Plateau (HTP) and its linkage with the evolution of the Asian monsoon has been regarded as a typical example of a tectonic–climate linkage. Although this linkage remains unproven because of insufficient data, our understanding has greatly advanced in the past decade. It is thus timely to summarize our knowledge of the uplift history of the HTP, the results of relevant climate simulations, and spatiotemporal changes in the Indian and East Asian monsoons since the late Eocene. Three major pulses of the HTP uplift have become evident: (1) uplift of the southern and central Tibetan Plateau (TP) at ca. 40–35 Ma, (2) uplift of the northern TP at ca. 25–20 Ma, and (3) uplift of the northeastern to eastern TP at ca. 15–10 Ma. Modeling predictions suggest that (i) uplift of the southern and central TP should have intensified the Indian summer monsoon (ISM) and the Somali Jet at 40–35 Ma; (ii) uplift of the northern TP should have intensified the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM), as well as the desertification of inland Asia at 25–20 Ma; and (iii) uplift of the northeastern and eastern TP should have further intensified the EASM and EAWM at 15–10 Ma. We tested these predictions by comparing them with paleoclimate data for the time intervals of interest. There are insufficient paleoclimate data to test whether the ISM and Somali Jet intensified with the uplift of the southern and central TP at 40–35 Ma, but it is possible that such uplift enhanced erosion and weathering that drew down atmospheric CO 2 and resulted in global cooling. There is good evidence that the EASM and EAWM intensified, and desertification started in inland Asia at 25–20 Ma in association with the uplift of the northern TP. The impact of the uplift of the northeastern and eastern TP on the Asian monsoon at 15–10 Ma is difficult to evaluate because that interval was also a time of global cooling and Antarctic glaciation that might also have influenced the intensity of the Asian monsoon.