The Miocene elevation of Mount Everest (original) (raw)
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Greater Himalayan exhumation triggered by Early Miocene monsoon intensification
Although most data suggest that the India-Eurasia continental collision began ∼45-55 Myr ago, the architecture of the Himalayan-Tibetan orogen is dominated by deformational structures developed in the Neogene period (<23 Myr ago). The stratigraphic record and thermochronometric data indicate that erosion of the Himalaya intensified as this constructional phase began and reached a peak around 15 Myr ago. It remained high until ∼10.5 Myr ago and subsequently slowed gradually to ∼3.5 Myr ago, but then began to increase once again in the Late Pliocene and Pleistocene epochs. Here we present weathering records from the South China Sea, Bay of Bengal and Arabian Sea that permit Asian monsoon climate to be reconstructed back to the earliest Neogene. These indicate a correlation between the rate of Himalayan exhumation-as inferred from published thermochronometric data-and monsoon intensity over the past 23 Myr. We interpret this correlation as indicating dynamic coupling between Neogene climate and both erosion and deformation in the Himalaya.
From tectonically to erosionally controlled development of the Himalayan orogen
Geology, 2005
Whether variations in the spatial distribution of erosion influence the location, style, and magnitude of deformation within the Himalayan orogen is a matter of debate. We report new 40 Ar/ 39 Ar white mica and apatite fission-track (AFT) ages that measure the vertical component of exhumation rates along an ϳ120-km-wide NE-SW transect spanning the greater Sutlej region of northwest India. The 40 Ar/ 39 Ar data indicate that first the High Himalayan Crystalline units cooled below their closing temperature during the early to middle Miocene. Subsequently, Lesser Himalayan Crystalline nappes cooled rapidly, indicating southward propagation of the orogen during late Miocene to Pliocene time. The AFT data, in contrast, imply synchronous exhumation of a NE-SW-oriented ϳ80 ؋ 40 km region spanning both crystalline nappes during the Pliocene-Quaternary. The locus of pronounced exhumation defined by the AFT data correlates with a region of high precipitation, discharge, and sediment flux rates during the Holocene. This correlation suggests that although tectonic processes exerted the dominant control on the denudation pattern before and until the middle Miocene; erosion may have been the most important factor since the Pliocene.
Earth and Planetary Science Letters, 2023
The involvement of meteoric water in orogens dynamics through surface processes is well known as for example in the Himalayas where erosion, resulting of the interplay between climate and tectonics shapes the most spectacular landscapes on the planet. But what about more internal and deepest surface fluid infiltration? Here we report analysis of the δ 18 O (water) and δD (water) of extracted water from fluid inclusions hosted into Cenozoic quartz veins sampled in the core of the Himalayan range, near the Main Central Thrust and the South Tibetan Detachment. Isotopic and microthermometric values suggest a meteoric origin for the fluids trapped in the quartz of syn-to post-kinematic veins formed between 10 to 20 km depth. Moreover, the isotopic compositions obtained in this study on quartz fluid inclusions water collected along a transect across the Himalayan range evolved with the topography in a similar manner than the modern meteoric water. Considering the age of formation of the quartz veins between 18 and 12 Ma, we deduce that the morphology of the Himalayan topographic front was already shaped during the Miocene but located further north.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2012
The Himalayan foreland basin sediments were deposited during a crucial time period in the Himalayan orogeny. This period, in the Tertiary, has become major focus of research because of the large scale uplift of the Himalayan range which has greatly modified the climate of the Asian continent. The present South Asian monsoonal climate is believed to be a consequence of Himalayan uplift during this period. Also the Himalayan orogeny comprises a major regional tectonic event of the Earth. Hence, the study of these Himalayan foreland basin sediments are not only significant in revealing the palaeoclimatic history of the Asian continent but also paves a way for understanding of the effects of Himalayan orogeny on global climate. Here we report a palaeoprecipitation history of the Ramnagar sub-basin since Miocene times and its regional correlation to other subbasins of the Himalayan mountain belt. An attempt has been made to use oxygen isotope ratios of pedogenic carbonates in Siwalik palaeosols as proxy palaeo-recorders to deduce the palaeoclimatic history of the Jammu region in the Ramnagar sub-basin for the first time. A total of 141 pedogenic carbonates have been analyzed from three Siwalik sections covering a lateral stretch of approximately 40-50Km along strike. The δ 18 O values vary from − 12.31‰ to − 5.89‰ and, when plotted against age, indicate that δ 18 O values, on average, become~2‰ enriched from the oldest to the youngest analyzed sediments except for largely depleted δ 18 O values around 10 Ma, 5 Ma and 1.8 Ma. This~2‰ increase in calculated δ 18 O values could have been possible by an~3°C increase in mean annual air temperature; conversely the largely negative δ 18 O values indicate periods of intense rainfall or stronger monsoonal conditions. An increase of 2.6‰ in δ 18 O values has been found from the 10 Ma rainfall event to that at 1.8 Ma which indicates a reduction of~173 mm in rainfall intensity and amount. Hence, precipitation reconstructions indicate a progressive increase in aridity from~12 Ma to Recent excluding a short term increases in rainfall or monsoon intensity at around 10 Ma, 5 Ma and 1.8 Ma. This pattern of palaeoprecipitation change is similar to the changes documented in other sub-basins of the Himalayan mountain range. Further, monsoon intensification at around 10 Ma, 5 Ma and 1.8 Ma is also observable in various other proxy records, thereby suggesting the role of significant regional tectonism in the evolution and intensification of the present South Asian monsoon climate. Our results indicate that from the Mid-Miocene to Recent, except for the periods of largely depleted δ 18 O values, the average δ 18 O value increased by~2‰. The general increase in average δ 18 O values from Lower to Upper Siwalik sediments can be explained by changes in both continentality and latitude of the moisture source. It seems likely that this long term increase in δ 18 O values was due to the uplift of the Himalayas and the Tibetan Plateau in the north which acted as a barrier to the passage of airmasses from Central Asia in the north, thereupon with time restricting the source of airmasses to the south from the Indian Ocean.
2004
New geologic mapping in the Marsyandi Valley of central Nepal reveals the existence of tectonically significant Quaternary thrust faults at the topographic front of the Higher Himalaya. The zone of recent faulting is coincident with an abrupt change in the gradient of the Marsyandi River and its tributaries, which is thought to mark the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. Uplift of the Higher Himalaya during the Quaternary is not entirely due to passive uplift over a deeply buried ramp in the Himalayan sole thrust, as is commonly believed, but partially reflects active thrusting at the topographic front. The zone of active thrusting is also coincident with a zone of intense monsoon precipitation, suggesting a positive feedback relationship between focused erosion and deformation at the front of the Higher Himalayan ranges.
Himalayan tectonic evolution determined from the sedimentary record, Nepal
2003
Ar^3 9 Ar dating of detrital white micas, petrography and heavy mineral analysis and whole-rock geochemistry has been applied to three time-equivalent sections through the Siwalik Group molasse in SW Nepal [Tinau Khola section (12^6 Ma), Surai Khola section (12^1 Ma) and Karnali section (16^5 Ma)]. 40 Ar^3 9 Ar ages from 1415 single detrital white micas show a peak of ages between 20 and 15 Ma for all the three sections, corresponding to the period of most extensive exhumation of the Greater Himalaya. Lag times of less than 5 Myr persist until 10 Ma, indicating Greater Himalayan exhumation rates of up to 2.6 mm year À 1 , using one-dimensional thermal modelling.There are few micas younger than 12 Ma, no lag times of less than 6 Myr after 10 Ma and whole-rock geochemistry and petrography show a signi¢cant provenance change at 12 Ma indicating erosion from the Lesser Himalaya at this time.These changes suggest a switch in the dynamics of the orogen that took place during the 12^10 Ma period whereby most strain began to be accommodated by structures within the Lesser Himalaya as opposed to the Greater Himalaya. Consistent data from all three Siwalik sections suggest a lateral continuity in tectonic evolution for the central Himalayas.
Dominance of tectonics over climate in Himalayan denudation
Landscape denudation in actively deforming mountain ranges is controlled by a combination of rock uplift and surface runoff induced by precipitation. Whereas the relative contribution of these factors is important to our understanding of the evolution of orogenic topography, no consensus currently exists concerning their respective influences. To address this question, denudation rates at centennial to millennial time scales were deduced from 10Be concentrations in detrital sediments derived from 30 small basins (10–600 km 2 ) in an 200-km-wide region in central Nepal. Along a northward, strike-perpendicular transect, average denudation rates sharply increase from <0.5 mm/yr in the Lesser Himalayas to ~1 mm/yr when crossing the Physiographic Transition, and then accelerate to 2–3 mm/yr on the southern fl ank of the high peaks in the Greater Himalayas. Despite a more than fi ve-fold increase in denudation rate between the southern and northern parts of this transect, the corresponding areas display similar precipitation rates. The primary parameter that presents a signifi cant co-variation with denudation is the long-term rock-uplift rate that is interpreted to result from the ramp-fl at transition along the Main Himalayan Thrust. We propose that, in this rapidly uplifting mountain range, landscapes adjust quickly to changing climatic conditions, such that denudation is mainly limited by the rate at which material is pushed upward by tectonic processes and made available for removal by surface processes. In this particular context, variations in precipitation appear to have only a second-order role in modulating the denudation signal that is primarily set by the background rock-uplift rate.
A Late Miocene acceleration of exhumation in the Himalayan crystalline core
Earth and Planetary Science Letters, 2008
Unraveling the relative roles of erosion and tectonics in shaping the modern topography of active orogens requires datasets documenting spatial and temporal patterns of exhumation, surface uplift and climatic forcing throughout orogenic growth. Here we report the results of biotite 40 Ar/ 39 Ar incremental heating and single-grain laser-fusion experiments from a nearly vertical, ∼ 1000 m age-elevation transect in the central Nepalese Himalaya. Age-elevation relationships constructed from these data suggest very slow cooling in this part of the Himalayan crystalline core during the Early Miocene, accelerating to only moderate rates at ∼ 10 Ma. If we assume purely vertical exhumation and a steady-state thermal structure, the exhumation rates implied by these data are ≪0.1 mm/yr prior to 10 Ma and ∼0.5 mm/yr from ∼10-7 Ma. The acceleration in cooling rate at 10 Ma requires a change in kinematics that may be linked to large-scale changes in climate, or to more local tectonic perturbations. Although we do not presently have enough data to assess the relative roles of regional vs. local drivers, these data provide a new constraint on exhumation through the Miocene that must be honored by any model of Himalayan evolution.
Earth and Planetary Science Letters, 2004
New geologic mapping in the Marsyandi Valley of central Nepal reveals the existence of tectonically significant Quaternary thrust faults at the topographic front of the Higher Himalaya. The zone of recent faulting is coincident with an abrupt change in the gradient of the Marsyandi River and its tributaries, which is thought to mark the transition from a region of rapid uplift in the Higher Himalayan ranges to a region of slower uplift to the south. Uplift of the Higher Himalaya during the Quaternary is not entirely due to passive uplift over a deeply buried ramp in the Himalayan sole thrust, as is commonly believed, but partially reflects active thrusting at the topographic front. The zone of active thrusting is also coincident with a zone of intense monsoon precipitation, suggesting a positive feedback relationship between focused erosion and deformation at the front of the Higher Himalayan ranges. ß