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Himalayan geology

The movement of the Indian plate toward the Eurasian plate starting 71 million years ago at the average speed of 5–15 centimetres (2.0–5.9 in) per year, which closed the Neo-Tethys Ocean above and opened the Indian Ocean below.

Cimmeria, having rifted from Gondwana shown drifting towards Eurasia, closing the Paleo-Tethys Ocean above, opening the Neo-Tethys Ocean below, and carrying parts of what is today the Tibetan Plateau

The accretions of the Karakoram, the Kohistan-Ladakh island arc, and the Gangdese belt to Eurasia preceded the final India-Eurasia collision.

The Indus River in the foreground and the Nanga Parbat peak, the western anchor of the Himalayas, far in the background, a little faint but towering well above the cloud layer

The Indus-Yarlung suture zone, shown in green, separates the Himalayas from the Tibet transhimalaya

Folded layers of Himalayan rock, exposed in a cliff about 3 kilometres (1.9 mi) northeast of Jomsom, in the Kali Gandaki Gorge in Nepal

Tectonics, the recurring physical changes that affect the arrangement of the Earth's crust, and plate tectonics, the movement of large regions of the Earth's crust in the manner of planar rigid bodies, are key to understanding the formation of the Himalayas. The Earth's crust rests directly on its mantle. Tectonic plates, comprising the crust and the upper portions of their underlying mantle, are moved around by convection in the asthenosphere. The oceanic crust, found beneath oceans, is, on average, 7 km thick. It is created from upwelling magma at mid-ocean ridges and predominantly consists of basalt, the principal igneous rock on Earth. In contrast, the continental crust underlying dry land has an average thickness of 35 km and is rich in silica, which is less dense than basalt. It makes the continental tectonic plates more buoyant than the oceanic.

India's defining geologic processes, which began 70 million years ago, had involved India rifting, or splitting away, from Gondwana, and the Indian continental plate along with the Neo-Tethys oceanic plate above it jointly moving northward. As these eventually reached the Eurasian plate, the less buoyant oceanic plate subducted, or slid under Eurasia and was carried into the deeper asthenosphere. In contrast, the Indian continental plate was obstructed because of its thickness and buoyancy. The lateral compression generated by the obstruction caused the plate to be sheared horizontally. Its lower crust and mantle slid under, but one layer of the upper crust piled up in sheets (called nappes) ahead of the subduction zone. Geophysicist Peter Molnar noted that most of the Himalayas are "slices of rock that once were the top part of India's crust." This is the process of mountain building, or orogeny, in the Himalayas.

Before the orogeny, the Eurasian coastline had been similar to today's Central Andes. Along such coastlines, the adjoining oceanic plate subducts and erupts as volcanoes. Magma, which eventually crystallizes into granite, rises into the Earth's crust below the active volcanoes but not to the surface. However, when India's continental plate pushed against Eurasia, not only did a part of the upper crust fold in nappes, but another stiffer part began to push against (or drag) Eurasia's ancient volcanic mountains farther north. As a result, the crust of this formerly coastal region shortened under compression and thickened. Isostatic equilibrium, or the balance between the gravitational force pulling down on the crust and the force of buoyancy pushing up from the mantle, gives the Tibetan Plateau its notable thickness and altitude.

The Indian plate was not the only landmass that had been a part of Gondwana, and subsequently rifted, drifting northward toward Eurasia. Before the India-Eurasia collision in Middle Paleocene (60 Mya) and subsequent Himalayan orogeny, two other landmasses, the Qiangtang terrane and Lhasa terrane, had drifted up from Gondwana. Qiangtang, a geological region in what is today northern Tibet, had done so in Late Triassic (237–201 Mya). The Lhasa terrane collided with the southern boundary of the Qiangtang in the Early Cretaceous (145–100 Mya). The collision caused the lithospheric mantle of the Lhasa terrane to thicken and shorten, forming a barrier that later prevented the Indian lithosphere from fully subducting under Tibet. The suture zones, or remains of the subduction zone and the terranes that are joined, are found in the Tibetan plateau. The Qiantang and Lhasa terranes were part of the string of microcontinents Cimmeria, today constituting parts of Turkey, Iran, Pakistan, China, Myanmar, Thailand and Malaysia, which had rifted from Gondwana earlier, closing the Paleo-Tethys Ocean above them and opening the Neo-Tethys Ocean between them and Gondwana, eventually colliding with Eurasia, and creating the Cimmerian Orogeny.

The collision of India with Eurasia closed the Neo-Tethys Ocean. The suture zone (in this instance, the remnants of the Neo-Tethys subduction zone pinched between the two continental crusts), which marks India's welding to Eurasia, is called the Indus-Yarlung suture zone. It lies north of the Himalayas. The headwaters of the Indus River and the Yarlung Tsangpo (later in its course, the Brahmaputra) flow along this suture zone. These two Eurasian rivers, whose courses were continually diverted by the rising Himalayas, define the western and eastern limits, respectively, of the Himalayan mountain range.

During the India-Eurasia collision, two elongated protrusions located on either side of the northern border of the Indian continent generated areas of extreme deformation. A point where mountain ranges with different directions of extension, and thus formed by tectonic forces at varying angles, converge is called a syntaxis (Greek: convergence). The two syntaxes, Nanga Parbat and Namche Barwa, on the northwestern and northeastern corners of the Indian continent, respectively, are characterized by the quick upward movement of land or rocks that were once deeply buried and significantly altered by extreme heat and pressure. Geologists have estimated the rate of uplift of these rocks to be 7 millimetres (0.28 in) per year, or 7 kilometres (4.3 mi) per million years. The protruding regions have some of the highest mountain peaks at 8,125 metres (26,657 ft) and 7,756 metres (25,446 ft), respectively. The regions also have the greatest topographical relief in the interior of a continent, approximately 7,000 metres (23,000 ft) over a horizontal distance of 20–30 kilometres (12–19 mi). Nanga Parbat has a narrow, anticline, or arch-shaped fold whose crest dips sharply to the north, perpendicular to the general direction along which the Himalayas extend. The Indus and Yarlung Tsangpo, which originally emptied into the New-Tethys, now bend around the Nanga Parbat and Namche Barwa, respectively, to eventually empty into the Indian Ocean.

The Himalayan mountain range consists of three sub-ranges: (1) the Higher- or "Tethys" Himalayas, (2) the Lesser Himalayas, and (3) the Siwaliks. The nappes—large, stacked sheets of rock—found in the Tethys Himalayan mountain range, are primarily composed of sedimentary rocks, such as limestone formed from the accumulation and compression of sediments like sand, mud, and shells deposited in the Neo-Tethys seabed during the Paleogene" (66 Mya–23 Mya). Below the sedimentary rocks in the Higher and Lesser Himalayas is a bottom layer, or basement, composed of metamorphic rock formed much earlier during the Pan-African-Cadomian orogeny between 650 Mya and 550 Mya. The lowest subrange, the Siwaliks, represents the sedimentary rock deposits washed off the rising Himalayas in a foreland basin, a low-lying crustal region, at their foot. It primarily consists of sandstones, shales, and conglomerates formed during the Neogene period (23 Mya to 2.6 Mya).

Christmas card

		Season's Greetings
		(He) enjoyed himself very much and explained a lot of things to (us), and helped us to put away the Dictionary when we had done with it. When he took up his hat to go, he gave one long look round the library. Then he turned ... (and Saxon took advantage of this to wag his way in and join the party), and said, "It's a rare privilege, the free entry of a book chamber like this. I'm hoping ... that you are not insensible of it." (Text on page 17 illustrated in the frontispiece in Juliana Horatia Ewing's Mary's Meadow and Other Tales of Fields and Flowers, illustrated by Mary Wheelhouse, London: G. Bell and Sons, 1915.) Fowler&fowler«Talk» 04:03, 23 December 2024 (UTC)

Sources

General

• Wester, Philippus; Mishra, Arabinda; Mukherji, Aditi; Shrestha, Arun Bhakta, eds. (2019), The Hindu Kush Himalya Assessment: Mountains, Climate Change, Sustainability and People, Springer Open, ICIMOD, HIMAP, ISBN 978-3-319-92287-4, LCCN 2018954855
• Zurick, David; Pacheco, Julsun (2006), Illustrated Atlas of the Himalayas, with Basanta Shrestha and Birendra Bajracharya, Lexington: University Press of Kentucky, ISBN 9780813123882, OCLC 1102237054

Geography

• Price, Martin F.; Byers, Alton C.; Friend, Donald A.; Kohler, Thomas; Price, Larry W., eds. (2013). Mountain Geography: Physical and Human Dimensions. Berkeley, Los Angeles, and London: University of California Press. ISBN 9780520254312. OCLC 841227048.
• Gerrard, John (1990). Mountain environments: an examination of the physical geography of mountains. MIT Press. ISBN 978-0-262-07128-4. OCLC 20637538.

Geology

• Chakrabarti, B. K. (2016). Geology of the Himalayan Belt: Deformation, Metamorphism, Stratigraphy. Amsterdam and Boston: Elsevier. ISBN 978-0-12-802021-0.
• Davies, Geoffrey F. (2022). Stories from the Deep Earth: How Scientists Figured Out What Drives Tectonic Plates and Mountain Building. Cham, Switzerland: Springer Nature. doi:10.1007/978-3-030-91359-5. ISBN 978-3-030-91358-8. S2CID 245636487.
• Frisch, Wolfgang; Meschede, Martin; Blakey, Ronald (2011). Plate Tectonics: Continental Drift and Mountain Building. Heidelberg: Springer. doi:10.1007/978-3-540-76504-2. ISBN 978-3-540-76503-5.
• Johnson, Michael R. W.; Harley, Simin L. (2012). Orogenesis: The Making of Mountains. Cambridge, UK and New York: Cambridge University Press. ISBN 978-0-521-76556-5.
• Molnar, Peter (2015). Plate Tectonics: A Very Short Introduction. Oxford University Press. ISBN 9780198728269.

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References

• Bourbaki, Nicolas (1998), Elements of the History of Mathematics, Berlin, Heidelberg, and New York: Springer-Verlag, 301 pages, ISBN 3540647678
• Giosan, L.; Clift, P. D.; Macklin, M. G.; Fuller, D. Q.; Constantinescu, S.; Durcan, J. A.; Stevens, T.; Duller, G. A. T.; Tabrez, A. R.; Gangal, K.; Adhikari, R.; Alizai, A.; Filip, F.; VanLaningham, S.; Syvitski, J. P. M. (2012), "Fluvial landscapes of the Harappan civilization", Proceedings of the National Academy of Sciences, 109 (26): E1688 – E1694, doi:10.1073/pnas.1112743109, ISSN 0027-8424
• Schmidt, J.; Piper, P. (March 27 1996), "Letter to Home", in Grimm, P.; Bob, T. (eds.), Jonesing for Jones, vol. 12, New York: Fred Books, ISBN 1-55555-555-5 {{citation}}: Check |isbn= value: checksum (help); Check date values in: |date= and |year= / |date= mismatch (help); Unknown parameter |publication-year= ignored (help)
• Hill, Marvin S. (1976), "Joseph Smith and the 1826 Trial: New Evidence and New Difficulties" (PDF), BYU Studies, 12 (2): 1–8, archived from the original (PDF) on 2006-09-21, retrieved 2007-05-17