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Tibetan
uplift
At the INQUA Congress in Peijing in 1991, Mörner organised a symposium
on “The Tibetan Uplift”. It was concluded that the main uplift
had occurred in the last 3.0 ma. Later, Mörner summarised the information
of the Tibetan uplift as well as crustal movements elsewhere in the
last 3.0 ma, and proposed that the period was so characteristic with
respect to strong crustal movement that it merited the term “the
Neotectonic Period”.
The
Beijing 1991 symposium: A symmary
During the 13th INQUA Congress in Beijing, August 2-9, 1991, a symposium
was held on "The Uplift of the Tibetan Plateau" (with the
present author as convenor).
The Tibetan Plateau is the largest high-plateau in the world. It is
located at about Lat. 30-40o N and covers some 30-40 longitudinal degrees:
i.e. about 1/9 of the Earth's equatorial circle. The average elevation
is in the order of 4000-5000 m with many peaks reaching well above 7000
m and a few even 8000 m. It is known as "the roof of the world".
During the last years the Tibetan Uplift has become interesting in a
new perspective. At around 2.5 Ma ago, the Milankovitch insolation variables
suddenly started to generate alternations between glacials (ice ages)
and interglacials. It has been proposed that the formation of a high
Tibetan Plateau caused a general atmospheric circulation change so that
the Milankovitch variables from that time onwards were able to generate
glacial/interglacial alternations (but were not able to do so before
that stage).
During the Beijing symposium, it became clear that the uplift of the
Tibetan Plateau was not a long-term uniform process but essentially
had occurred by intensified step-wise uplifting in the last 3.0-2.5
Ma.
Chen Xuebo spoke about "the origin of the Tibetan Plateau which
has been uplifted by violent compression since 2.5 Ma before present".
Li Jijun claimed that an intense upheaval of the plateau occurred at
about 2 Ma ago and that this was "the starting factor to induce
Asian monsoon" and loess deposition. He identified four main pulses
in the uplift beginning at around 2-1.5, 1.0, 0.6 and 0.15 Ma ago.
Williams et al. showed that "sedimentation dramatically increased
in Qaidam Basin" during the periods 2.4-1.6 Ma and 0.8-0.6 Ma ago
which they attributed to "rapid uplifting of the Tibetan Plateau".
Liu Chenglin identified the onset of slow uplifting at about 15 Ma with
the major uplift taking place in four episodes during the last 2.8 Ma;
viz. 2.8-2.0, 1.6-1.1, 0.8/0.4-0.16 and 0.03-0 Ma BP (the last phase
of uplift must apparently be longer than the last 30 Ka; probably to
some infinite radiocarbone dates)
Zhang Qingsong et al. presented new evidence that "intensive uplifting
of the Kunlun-Karakorum Mountains began at the end of Pliocene-early
Pleistocene period" and amounted to 2600-3100 m. This induced drastic
changes of the environmental conditions.
Nikonov and Pakhonov used botanical evidence to show that the uplift
of the Pamirs Highlands occurred in two main phases; (1) 3.0-2.5 Ma
the area was uplifted 1 km at a mean rate of about 2 mm/yr, and (2)
during the last 0.3-0.4 Ma the area was uplifted 1.5 km at a mean rate
of about 4 mm/yr.
Zhang Qingsong et al. reported the results of repeated levelling in
the Tibetan Plateau. They showed that "main parts of the Plateau
is still going up with mean rates of 5.8 mm/a". This is in full
agreement with the proposition that the uplift of the Tibetan Plateau
primarily took part in the last 2–3 million years
Qian Fang had undertaken magnetostratigraphic analyses of Hipparion
beds. The studies enabled him to show that the main uplift is younger
than 4.9 Ma and may have culminated in the last 1.5 Ma.
Taken together, our symposium effectively demonstrated that available
information (previously only fragmentarily known outside China) indicates
that the Tibetan Plateau is much younger than generally assumed and
now can be dated at about 3.0–2.5 Ma. Later, it has become clear
that this rapid and young Tibetan uplifting is a part of a general intensification
of global geodynamics in the last 3 Ma. Furthermore, there is a clear
link between the initial main uplift phase 3.0–2.5 Ma ago and the
onset of Asian monsoon and general climatic change within the region
including the change from red clay formation to onset of loess deposition
at the Gauss/Matuyama boundary 2.5 Ma ago.
Additional
notes
In opposite to the views presented in the symposium, many researchers
have previously assumed that the Tibetan uplift is a long term process
that spanned several tens of millions of years (e.g. Ruddiman et al.,
1989; Turner et al., 1993).
In agreement with the present documentation of an uplift that primarily
is confined to the last 3 Ma, there are a number of previous observations
and statements. He & He (1987) and Iwata (1987) used tilted surfaces
to demonstrate a Quaternary age of the main uplift. Zheng (1989) gave
a general review of available data on uplift and glaciations, and showed
that the main uplift refters to the period after the pre-glacial Pliocene.
Burbank (1992) showed that the sedimentary deposition south of the Himalyas
shifted direction of accumulation in the Pliocene indicating the onset
of rapid uplifting.
Below, we cite the abstract of Zheng (1989) and reproduce a redrafted
version of one of his figures (Fig. 1): "Although the succession
of glaciations and interglaciations in the Himalayas and the Qinghai-Xizang
Plateau was mainly controlled by global climatic change, large scale
and rapid uplift was an important influence on glacier development.
It significantly altered the atmospheric circulation not only of the
region itself but of the whole hemisphere. Four models of Quaternary
glaciation are described with reference to evidence on both sides of
the Himalaya. On the north side, the most extensive glaciation occurred
during the Nieniexongla stage of the Middle Pleistocene but, on the
south side, the largest glacial cover occurred during the early part
of the Upper Pleistocene. A major ice sheet covering the whole of the
Qinghai-Xizang Plateau can be ruled out on the basis of geological evidence
and climatological theory, although many medium-sized ice caps developed
on the ranges which rise above the Plateau".
Fig. 2-5-1.
Uplift of the Himalaya-Tibetean region (based on Fig. 12 of Zheng, 1989);
N2 gives the surface prior to 3 Ma, Q2 gives the level after the first
uplift pulse 3.0-2.5 Ma ago, and Q4 gives the present level with associated
snowline (thick line).
The
new global tectonic regime and the initiation of Ice Ages
When Artyushkov was introduced to this concept of a new global tectonic
regime in the last 3.0 ma, he called this “the most powerful phenomenon
in the last 100 ma”. And, indeed, so it seems to be; we have moved
into a new orogenic phase or “the Neotectonic Period”. Much
of the data are presented in my paper “Neotectonics, the new global
tectonic regime during the last 3 ma and the initiation of Ice Ages”
published in An. Acad. Bras. Ci. (1993) 65 (Supl. 2) 295-301, which
follows below as pdf-file.
Pdf 2-5 + figures 1-4 6 Tabell 1 (88k)
References (from P&G)
Mörner, N.-A., 1991. Uplift of the Tibetan Plateau. An introduction.
Abstracts, INQUA XII Congr, Beijing, p. 244.
Mörner, N.-A., 1991. Uplift of the Tibetan Plateau. A short review.
INQUA Spec. Proc. Rew. Rep., p. 78-81. Beijing.
Mörner, N.-A., 1992. Uplift of the Tibetan Plateau. INQUA Comptes
Rendus, p. 000.
Mörner, N.-A., 1992. Tibetan uplift and global climatic-geodynamic
changes. Bull. INQUA Neotectonics Comm., 15, 64.
Mörner, N.-A., 1992. The Tibetan uplift and global climatic and
geodynamic changes. Abstracts, 29th IGC, Kypto, p. 28.
Mörner, N.-A., 1994. Neotectonics in vew perspectives. Bull. INQUA
Neotectonics Comm., 17, 63-65.
Mörner, N.-A., 1995. Neotectonics. The global tectonic regiment
during the last 3 ma and the initiation of ice ages. Ann. Brazilian
Acad. Sci., 65 (1993), p. 295-301.
Mörner, N.-A., 1995. Neotectonics in new perspectives: the last
3.0 ma. Abstracts, INQUA XIII Congr., Berlin, Symp. 58.
Mörner, N.-A., 1996. New trends in global tectonics. Bull. INQUA
Neotectonics Comm., 19, 15-19.
Mörner, N.-A., 1998. New trends in global tectonics. Phys. Chem.
Earth., 23, 825-830.
Mörner, N.-A., 1998. Neotectonics and global climate. Abstracts,
EUG, Nice, Ann. Geophys., 16, I, C22.
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