Where is tibetan plateau

Cartoon cross-section of Tibet simplified from [ 7 ] invoking a stepwise formation of the Tibetan region. Similar to the stepwise model [ 7 ] is the concept of uplift beginning in the southwest of the region and progressing north-eastward: a pattern that seemingly emerges from stable isotope paleoaltimetry [ 32 , 33 ].

Here, an area encompassing much of the modern Himalaya, the YTSZ and much of southern Tibet was envisaged to have risen to above 4 km by 40 Ma, then another zone to the northeast to have achieved 4 km at around 30 Ma and so on to the northeast, where only recent uplift was invoked Fig. However, this model, like the soft Tibet model before it, largely ignores the pre-existing deep-rooted structures within Tibet: boundaries of the uplifted regions do not coincide with major suture zones and seemingly reflect supposed progressive crustal thickening as if Tibet behaved as a coherent entity.

Progressive uplift of Tibet as illustrated in a commentary [ 32 ] on a review of stable isotope paleoaltimetry [ 33 ]. Note that as in Fig. Based on an extensive review of the literature, Wang et al.

Progressive outward growth model of Wang et al. In this model, a central core of Tibet was elevated early in the Paleogene, while the Qilian Shan in the north and the Himalaya in the south are very recent constructs.

The evidence for a high core of Tibet is multi-stranded. Numerous authors agree that the southern edge of Tibet featured an Andean-type Gangdese mountain range before the India—Asia collision e.

The lack of crustal shortening in the late Cenozoic, low precipitation, cool temperatures and minimal erosion, as well as lithospheric processes, were all invoked to explain the flatness of central Tibet [ 10 ].

It has long been known that Tibet is not a single monolithic block but an amalgam of Gondwanan terranes successively accreted onto the Eurasia plate. This assembly began in the early Mesozoic and continued to the early Cenozoic [ 2 , 5 , 18 , 31 , 34 , 35 , 41 ], India being the most recent of these terranes to arrive. The sizes of the blue arrows represent the relative motion today as measured by GPS [ 10 ].

The onset of these collisions has been dated to the late Triassic to early Jurassic for the Kunlun—Qaidam and Qiangtang terranes [ 42 , 43 ], the early Cretaceous for the Qiangtang and Lhasa collision [ 44 ] and the early Paleogene for the initiation of the India—Lhasa block collision, which is ongoing see [ 10 ] and references therein. However, there are significant outliers in the timing of the initial India—Lhasa terrane collision spanning 65 Ma [ 41 , 45 ] to 20 Ma [ 46 ].

The timing of the onset of continental collision and establishment of a land bridge facilitating terrestrial biotic exchange between India and Eurasia has long been a topic of contention and debate [ 1 , 2 , 10 ] and knowing when this event occurred is important because, apart from the biotic consequences, contact curtails pre-existing oceanic circulation patterns, sea temperatures and sea surface isotopic compositions.

A recent molecular phylogenetic study using dated fossils to constrain an analysis of 50 mammalian lineages argues for free exchange between India and Eurasia as early as As with the India—Lhasa block collision, each of the previous accretion events would have thickened the crust, subducted ocean and continental lithosphere, and resulted in some increase in surface relief, so when India arrived Tibet already exhibited an inherited range of surface heights and complex underlying geology.

Unsurprisingly the terrane amalgam shot-through by deep-rooted suture zones and faults was never likely to produce a Tibet that behaved coherently under compression [ 7 , 48 ]. Guillot et al. While the crust on average may have been thus thickened and, on average, isostatic compensation may result in such mean elevations, the process of shortening produced by India's northward motion will have produced different responses in different parts of the Tibetan region at different times in an idiosyncratic manner [ 48 ].

Recent improvements in our understanding of regional geology, fossil biotas and, crucially, radiometric dating have transformed our understanding of Tibetan orography and a new pattern of topographic evolution across the Tibetan region is emerging. At the start of the Paleogene, Tibet exhibited significant topography relief as a result of prior accretions of the Songpan Ganzi—Hoh Xil, Qiangtang and Lhasa terranes [ 1 , 2 ].

For the Lhasa terrane to have drifted southward since then is unlikely considering India's northward passage. The Gangdese mountain system long predated the Lhasa—Qiangtang terrane collision, where suturing was diachronous from east to west and closure occurred in the Nima region by Ma [ 1 ].

In Aptian—Albian times — The Shexing sediments were mainly derived from the south, i. These transitions, coupled with the onset of development of the Xigatse fore-arc basin at — Ma [ 60 ], suggest that the Gangdese arc exhibited a significant rise in mid-Cretaceous time, but there are no quantitative estimates of its crest height.

This confidence in a high topography arises from oxygen isotope analyses conducted on well-dated diagenetically unaltered paleosols, lacustrine calcareous carbonates and marls from the Linzizong Group, in the Linzhou Basin [ 37 ]. In the Eocene, the Gangdese Mountains were the first obstacle for moist air drawn northward in summer by the Siberian low: a seasonal depression that exists by virtue of Eurasia's position and size and the thermal capacity of land versus sea.

On the windward side of the Gangdese, a Rayleigh isotope fractionation process would have operated, and because this process is predicable the height estimates are likely to be reliable [ 61 ]. This Gangdese highland did not extend northward to occupy the whole of the Lhasa terrane but was confined to its southern margin. In the northern part of the Lhasa block, rapid rock uplift must have been taking place between 80 and 70 Ma [ 62 ], but evidently was matched by erosion because there is evidence of large-scale bedrock peneplain formation between 70 and 50 Ma, and this surface has survived to the present [ 62 ].

The planation process by laterally migrating rivers appears, initially, to have eroded 3—6 km of rock, suggesting the erosional surface remained at low elevation until the erosion rate reduced. This late Cretaceous rock uplift, and subsequent surface uplift, was presumably in response to crustal thickening produced by the India collision [ 62 ]. Throughout the late Cretaceous and early Paleogene, the Gangdese mountain system likely stretched along most of, if not all, the full east—west extent of the Lhasa terrane along its southern flank.

The northern Lhasa terrane was evidently at a lower elevation and was being subducted below the Qiangtang terrane along the BNSZ [ 1 ]. The proto-Tibetan Plateau model [ 10 ] Fig.

To test these models, it is essential to measure the surface height changes over time, especially in central Tibet. Paleoaltimetry for central Tibet has mostly relied on stable isotopic compositions of rainfall and their relationships with elevation [ 63 ], but these are subject to significant uncertainty away from the windward slope of the southern flank of Tibet [ 61 , 64 ] and until recently this approach lacked the rigor imposed by climate model mediation.

For example, micritic calcium carbonate paleosol nodules from the upper Niubao Formation in the Lunpola Basin Fig. In the nearby Nima Basin Fig. How this proposed high-elevation plateau is supposed to have remained stable for so long has not been fully explained. Other isotope systems have yielded similar results. Subsequent review and re-examination of these results did not substantially alter the conclusions that Tibet was high in the Eocene, but neither was there evidence for a progressive northward elevation change [ 66 ].

Contrasting with these high elevations, which are virtually indistinguishable from those of the present, are the fossil finds from the BNSZ basins. The Lunpola Basin Fig. The Cenozoic sediments within the basin are some 4 km thick and comprise paleosols, fluvial, fluvio-deltaic and lacustrine units, some indicative of freshwater and some saline conditions [ 67 ].

The Cenozoic succession is divisible into a predominantly fluvial Paleocene—Eocene Niubao Formation and an overlying predominantly lacustrine Oligocene—Miocene Dingqing Formation [ 67 , 68 ]. Radiometrically constrained [ 69 ] magnetostratigraphy, cyclostratigraphy [ 68 ] and palynology [ 14 ] provide the chronology for the Dingqing Formation, but the surface geology is often complex as beds are folded and faulted [ 70 ]. Among the fossil finds from the Chattian late Oligocene lower Dingqing Formation is a climbing perch, Eoanabas thibetana Anabantidea [ 71 ], whose modern relatives occupy tropical lowlands of South Asia and sub-Saharan Africa below m, while higher in the succession early Miocene—Aquitanian a primitive form of the cyprinid fish Plesioschizothorax macrocephalus has been recovered, whose modern relatives are restricted to elevations below m.

The palynology of the Dingqing Formation [ 14 ] spanning Such a taxonomic mix does not reflect co-occurrence in the vegetation but mixing of palynomorphs during transport into the lake sediments. However, this reflects not the elevation of the lake margins but the blended heights of the source vegetation communities, including montane taxa, and thus represents the height of an undefined location between the basin lake and the crests of the surrounding mountains [ 70 ] even though the estimated height is lower than that given by isotopes.

As a consequence, they are unreliable proxies for quantitative paleoaltimetry, unlike larger and more delicate plant parts such as leaves, which readily show signs of transport prior to burial and thus better reflect vegetation nearby the site of fossilization.

These include a palmate palm leaf, Koelreuteria lunpolaensis , K. The flora as a whole consists of intact leaves and leaflet clusters and shows no sign of long-distance transport, so represents vegetation growing spatially and altitudinally very close to the large margin [ 73 ]. Because palms are intrinsically cold-intolerant, they can indicate a maximum possible elevation for the basin floor provided that the cold month mean terrestrial thermal lapse rate is known [ 70 ].

This model-mediated approach avoids the use of inappropriate free air lapse rates and automatically compensates for secular climate change, in terms of both temperatures at a sea level datum and thermal terrestrial lapse rates.

While the lowermost Paleocene units of the Niubao Formation host aeolian sands and other indicators of aridity, the middle Eocene Lutetian part has recently yielded a diversity of plant remains including leaves, fruits and seeds [ 74 , 75 ] from lacustrine units within an otherwise fluvially dominated succession in the Bangor Basin Fig.

These remains point to a humid subtropical and therefore low elevation flora with floristic links to the Eocene Green River flora, western USA, and the middle Eocene Messel flora, Germany [ 76 ]. One additional piece of evidence pointing to lowland thermophilic humid forests in the Paleogene of central Tibet includes finds of amber from dipterocarps tropical lowland forest dominants across South and Southeast Asia today that might have been reworked from the Niubao into the Dingqing Formation [ 77 ], but so far no definitive dipterocarp megafossils have been found.

The continental effect on the isotopic composition of rainfall is complex in this inland setting and can only be properly resolved using appropriately configured isotope-enabled climate models. Furthermore, it is not yet possible to say when this elevation was achieved, but the uplands were shedding sediment northward in the Paleogene as evidenced by deposits in the Hoh Xil Basin [ 8 , 79 ] and suggest that the Qiangtang terrane may have supported an east—west mountain chain throughout the Eocene.

However, the surface height of this upland needs to be re-examined using appropriately configured isotope-enabled models that allow not only time-specific isotopic values of source waters but also trajectories of source moisture to be more accurately determined, something that was not available when the original elevation estimate [ 78 ] was made.

There have been few instances of multiproxy cross-calibration, but one location that has been studied intensively is the mid-Miocene 15 Ma Namling—Oiyug Basin Fig. Subsequently, this was revised to — m using a calibration more suited to potentially monsoonal climates and a near sea level datum from a similar-aged flora in the Siwaliks, northeast India, corrected for paleolatitude [ 80 ]. All these measurements, both paleontological and isotopic, are identical within methodological uncertainties, so why do isotope and paleontological proxies give such divergent results in central Tibet?

Instead, the fossils evidence a diverse lowland ecosystem. We envisage a predominant Indian Ocean moisture source to the south and a summer northward air parcel trajectory driven by an Asian interior Siberian low-pressure system Fig. Here, moisture-laden winds would encounter the east—west Gangdese mountain system and be forced upward preferentially raining out the heavy isotopes, leaving light isotope enriched moisture to crest the mountain tops and enter the lowland to the north.

Similarly, in winter cool dry air from the north, passing over land and the Qiangtang mountains, will have depleted heavy isotope content Fig. This effect is shown by isotope-enabled computer models Fig. Because prior to the rise of the Himalaya the Gangdese formed a southern highland of a similar height to today's plateau, and conceivably hosted peaks approaching the heights of many modern Himalayan peaks, the sediments preserve isotopic ratios indicative of paleoelevations similar to those of today.

Maps of southern Asia India is in the lower left corner showing the results of an isotope-enabled climate model simulation for the Lutetian middle Eocene. There is no valley signature in c , which appears very similar to the high-plateau scenario d showing that the isotopes entering such a valley reflect the height of the bounding mountain systems and the lowland between them appears as a plateau.

Stable isotope paleoaltimetry indicates the Qaidam Basin Fig. However, there is some evidence that uplift in parts of northern Tibet occurred much earlier, e. This implies an Eocene uplift of the region or a pre-existing uplift derived from pre-Cenozoic terrane collisions. Additionally, other areas of northern Tibet also seem to have risen in the Paleogene [ 83 ]. Taken together, this implies significant deformation and uplift in parts of northern Tibet during the Eocene, seemingly simultaneous with eastward extrusion of Tibet and the building of the Hengduan Mountains.

It has long been recognized that a significant proportion of north—south shortening under compression from the India—Asia collision may have been accommodated by extrusion of parts of Tibet to the east and southeast [ 23 , 91—93 ]. This extrusion was originally envisaged to have taken place in a somewhat rigid manner but the low-relief, high-elevation topography in eastern Tibet has been used as evidence for ductile flow of the lower crust [ 94 , 95 ].

A slightly different model based on paleomagnetic analysis envisages extrusion, translation to the south and rotation of the Indo-China block.

Tong et al. Most recently, based on a high-resolution paleomagnetic study and previous work, Li et al. Controversy surrounds not only the building of SE Tibet but also the timing of its rise. Recently, a multi-phased rapid uplift of SE Tibet, starting as early as the late Cretaceous [ 96 — ], has been suggested based on low-temperature thermochronological studies, following on from earlier work that suggested a predominantly Miocene uplift of the region based on river incision measurements [ 95 , ].

Rapid incision of major river systems as revealed by low-temperature thermochronology is estimated to have taken place between 15 and 10 Ma and used as evidence for lower crustal flow [ , ]. However, incision may not be associated with surface uplift but an intensification of monsoon rainfall [ ].

Eocene to Miocene provenance shifts have been studied to determine changes in river drainages e. Such a dating framework is also essential for paleoaltimetric studies, and until recently the baseline dating reference for the region has been geological maps lacking absolute age constraints.

Instead, dating, and thus uplift studies, relied heavily on biostratigraphy, with an inherent element of circular reasoning. The first clue that regional dating required revision came from a study of the Jianchuan Basin Fig.

Re-analysis shows a paleoelevation somewhere between these two estimates [ 64 ], but awaits further investigation in conjunction with isotope-enabled climate modeling.

These ages are also consistent with those of detrital zircons found in fluvial sands higher within a mine section [ ]. The Mankang Markam Basin Fig. There are numerous plant fossils from several horizons within the basin, but two within the Lawula Formation are of particular note because they record climate and elevation at the end of the Eocene.

An overlying assemblage characterized by much smaller leaves and indicative of cooler temperate vegetation is similarly constrained to be between It is difficult to determine whether the apparent 1 km elevation increase in at most 3.

These uncertainties, spanning 2. Furthermore, because Miocene isotope lapse rates and air trajectories were assumed, the estimate has to be regarded as unreliable despite its similarity to that obtained from the leaf fossils.

In recognition of the problems posed by incorrect age assumptions, Hoke [ 64 ] noted that, irrespective of the dating issue but using an estimated Paleogene isotopic lapse rate, the differences in preserved oxygen isotopes along NNW—SSE transect across Yunnan to SE Tibet yield an elevation difference of 4. However, if near-modern relief across SE Tibet and northwest NW Yunnan was achieved by the end of the Eocene, when did most of the regional uplift occur?

This is exemplified in Fig. However, this completely ignores the existence of the Yarlung—Tsangpo suture that marks the junction of the Indian and Eurasian plates and the geodynamics associated with the collision process. It is therefore essential that, when considering the orogeny of the Tibetan region, the formation of the Himalaya is treated separately from the development of Tibet.

In the Tapponnier et al. Support for this Neogene rise of the Himalaya is long-standing and one of the first attempts at quantitative paleoaltimetry in the region was conducted nearly 50 years ago with the discovery of Quercus semecarpifolia Quercus sect. Heterobalanus remains of supposed Pliocene age at a reported modern elevation of 5. This seemed to indicate a very recent rise of the Himalaya, but unfortunately these remains were not found in situ and their precise origin and exact age remain unknown.

As with other paleoaltimetric work in the Tibetan region, useful insights come from a combination of paleontological and stable isotope proxies. This shift was accompanied by a rapid acceleration in Himalayan uplift [ ] and a slowdown in India's northward motion [ ] Fig. Ding et al. A similar elevation was obtained from oxygen isotopes from the same deposits 2.

Thus, the influence of the Himalaya on atmospheric circulation deflection of air parcel trajectories and a rain shadow effect over Tibet only really began to operate from the middle Miocene onward [ ].

Similar work along the length of the Himalaya is required to understand their lateral growth and their effect on climate and biotic systems.

The red line is the inferred elevation of the Himalaya, while the blue line is the elevation of the Gangdese highlands. Shading is indicative of uncertainties. Modified from Xu et al. The rates of India's northward motion dotted lines are taken from Molnar and Stock [ ].

Recent fossil discoveries have shown that Tibet hosts a wealth of paleontological data attesting to a past where diverse Paleogene forests seemingly existed in subtropical intermontane lowlands in a great central valley along the Bangong—Nujiang suture zone between the Gangdese and Qiangtang uplands. These forests, with floristic links across the Northern Hemisphere, also provided a range of habitats for an abundant fauna.

This suggests that only in the Neogene did a high plateau begin to form across Tibet by raising the valley floor to near the height of the bounding mountains through a combination of compressional uplift and sediment fill. The Tibetan Plateau was never uplifted as a monolithic entity but has evolved in a piecemeal fashion since early in the Mesozoic. Mesozoic terrane collisions formed a topographically complex landscape with deep valleys and high mountains providing a high ecological niche diversity that contributed to, and nurtured, modern Asian biodiversity.

This progressive building of Tibet also thickened the crust, collision by collision, with the inevitable consequence that not all of that thickness, and elevation, can be attributed to the arrival of the Indian plate. This also means that the size of greater India was likely much smaller than often envisaged. When the Indian plate did arrive, Tibet already had a complex, and in places high, relief, the most dominant features being the east—west trending mountain ranges of the Gangdese and Tanggula Qiangtang uplands Fig.

In the Eocene, more moisture entered the valley Fig. Cartoons illustrating the topographic development of central and southern Tibet as well as the Himalaya. Tibet experienced significant north—south deformation during the Eocene, perhaps progressively halving the width of the central valley and causing localized uplift to near present heights in the north of Tibet, as well as uplift in the eastern Tanggula range.

This compression was also translated eastward, forming the uplands of NW Yunnan that today comprise the Hengduan Mountains and host globally exceptional biodiversity. As the Himalaya passed through 5 km, they imposed an increasing rain shadow effect on central Tibet. All the phytopaleoaltimetry cited here, and some of the more recent isotope paleoaltimetry, has benefitted from various forms of climate model mediation.

The pre-existing surface height estimates that did not use such an approach need to be re-examined with, and validated using, high-resolution coupled ocean—atmosphere—isotope—vegetation models before we can have a definitive understanding of the topographic development of Tibet.

Knowing past topography is essential for disentangling the complex interactions between orography, climate and biodiversity, and future investigations of such interactions will require a move away from treating Tibet as a simple plateau rising as a block, but instead use paleotopographies that are as realistic as possible.

Such work can be undertaken empirically and iteratively, but as model spatial resolution increases so does the requirement for accurate multiple quantitative paleoaltimetric proxies to be used in conjunction with each other in order to exploit their various different, but complementary, characteristics. Tibet is not a monolithic entity but assembled piecemeal during the Mesozoic by successive terrane accretions. This produced a complex high-relief landscape harboring subtropical biotas in deep valleys.

Stable isotope and paleontological paleoaltimeters measure different aspects of the topography: isotopes tend to reflect high elevations, while fossils tend to reflect lowland elevations. In valley systems, isotopes seem to reflect the heights of the bounding mountain crests and the valley appears as a high plateau. Contrary to previous conceptual models, Tibet did not rise as a pre-formed plateau, or by crustal thickening driven solely by the India—Eurasia collision, but evolved gradually through tectonic compression and internally drained basin sediment infill.

The Tibetan Plateau did not form until the Neogene, concurrently with the Himalaya rising above 5 km and the establishment of a strong rain shadow affect. Future paleotopography will be best quantified using multiple altimetric proxies stable isotope and paleontological in combination, mediated by climate or Earth system models.

Existing stable isotope paleoaltimetry needs to be re-assessed using isotope-enabled climate models and empirical evaluation of past landscapes. To fully understand the contribution the Tibetan region has made to Asian biodiversity and monsoon evolution requires further well-dated fossil collections in conjunction with Earth system modeling using realistic paleotopographies and not simple block-like representations of Tibet.

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Geology ; 40 : — It towers over southwestern China at an average elevation of m above sea level and is known as "the roof of the world. The plateau has a highland continental climate and a very complex topography with great variations. Second, at what altitude do Tibetans live? Fairly large numbers about , live at an altitude exceeding m in the Chantong-Qingnan area.

People of Tibetan ethnic descent are lifelong high-altitude residents and cannot easily move to higher or lower elevations. The upper altitude limit of crops is around m, while the nomads reside above m and m.