scholarly journals Lithospheric foundering and underthrusting imaged beneath Tibet

2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Min Chen ◽  
Fenglin Niu ◽  
Jeroen Tromp ◽  
Adrian Lenardic ◽  
Cin-Ty A. Lee ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Wave Speed ◽  
The Tibetan Plateau ◽  
Uppermost Mantle ◽  
Southern Tibet ◽  
Surface Uplift ◽  
South Central ◽  
Plateau Uplift ◽  
Central Tibet ◽  
Potassic Volcanism

Abstract Long-standing debates exist over the timing and mechanism of uplift of the Tibetan Plateau and, more specifically, over the connection between lithospheric evolution and surface expressions of plateau uplift and volcanism. Here we show a T-shaped high wave speed structure in our new tomographic model beneath South-Central Tibet, interpreted as an upper-mantle remnant from earlier lithospheric foundering. Its spatial correlation with ultrapotassic and adakitic magmatism supports the hypothesis of convective removal of thickened Tibetan lithosphere causing major uplift of Southern Tibet during the Oligocene. Lithospheric foundering induces an asthenospheric drag force, which drives continued underthrusting of the Indian continental lithosphere and shortening and thickening of the Northern Tibetan lithosphere. Surface uplift of Northern Tibet is subject to more recent asthenospheric upwelling and thermal erosion of thickened lithosphere, which is spatially consistent with recent potassic volcanism and an imaged narrow low wave speed zone in the uppermost mantle.

scholarly journals Record of Crustal Thickening and Synconvergent Extension from the Dajiamang Tso Rift, Southern Tibet

Geosciences ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 209
Author(s):  
William B. Burke ◽  
Andrew K. Laskowski ◽  
Devon A. Orme ◽  
Kurt E. Sundell ◽  
Michael H. Taylor ◽  
...  
Keyword(s):  
Dynamic Models ◽  
Hanging Wall ◽  
Crustal Thickness ◽  
Suture Zone ◽  
Crustal Thickening ◽  
Southern Tibet ◽  
South Central ◽  
Crustal Thinning ◽  
Indian Lithosphere ◽  
Central Tibet

North-trending rifts throughout south-central Tibet provide an opportunity to study the dynamics of synconvergent extension in contractional orogenic belts. In this study, we present new data from the Dajiamang Tso rift, including quantitative crustal thickness estimates calculated from trace/rare earth element zircon data, U-Pb geochronology, and zircon-He thermochronology. These data constrain the timing and rates of exhumation in the Dajiamang Tso rift and provide a basis for evaluating dynamic models of synconvergent extension. Our results also provide a semi-continuous record of Mid-Cretaceous to Miocene evolution of the Himalayan-Tibetan orogenic belt along the India-Asia suture zone. We report igneous zircon U-Pb ages of ~103 Ma and 70–42 Ma for samples collected from the Xigaze forearc basin and Gangdese Batholith/Linzizong Formation, respectively. Zircon-He cooling ages of forearc rocks in the hanging wall of the Great Counter thrust are ~28 Ma, while Gangdese arc samples in the footwalls of the Dajiamang Tso rift are 16–8 Ma. These data reveal the approximate timing of the switch from contraction to extension along the India-Asia suture zone (minimum 16 Ma). Crustal-thickness trends from zircon geochemistry reveal possible crustal thinning (to ~40 km) immediately prior to India-Eurasia collision onset (58 Ma). Following initial collision, crustal thickness increases to 50 km by 40 Ma with continued thickening until the early Miocene supported by regional data from the Tibetan Magmatism Database. Current crustal thickness estimates based on geophysical observations show no evidence for crustal thinning following the onset of E–W extension (~16 Ma), suggesting that modern crustal thickness is likely facilitated by an underthrusting Indian lithosphere balanced by upper plate extension.

Revised chronology of central Tibet uplift and its implications

2021 ◽  
Author(s):  
Xiaomin Fang ◽  
Guillaume Dupont-Nivet ◽  
Chengshan Wang ◽  
Chunhui Song ◽  
Qingquan Meng ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Tibetan Plateau ◽  
International Society ◽  
Regional Climate ◽  
Surface Processes ◽  
The Tibetan Plateau ◽  
Fossil Plants ◽  
Growth Mechanisms ◽  
Southern Tibet ◽  
Central Tibet

<p>Understanding the Tibetan Plateau (TP) topographic history is essential to determining its building mechanisms and its role in driving regional climate, environments and biodiversity. The Lunpola Basin (central-southern Tibet) is the key place to constrain the Tibet building because it deposits the most complete Cenozoic stratigraphy sequence in the central TP and bears many layers of tuffs, abundant fossil plants and mammals and paleosols. It is also the first place that stable isotope based paleoaltimetry was applied to, which suggested that similar to present elevation was attained in the central TP at least 35 Ma ago, implying a much earlier uplift of the TP than before. This view was soon widely accepted by international society but was challenged by recent discoveries of low elevations tropical fossil apparently deposited at 25.5 Ma. However, we use magnetostratigraphic and radiochronologic dating to robustly revise the chronology of regional elevation estimates both from the stable isotope and fossils in the Lunpola Basin. The results indicate that both ages estimated for the stable and fossil based elevations are wrong with the former from ~40 Ma revising to ~26-21 Ma and the later from ~26 Ma to ~40 Ma. Thus this revised chronology demonstrates that central Tibet was generally low (<2.3 km) since at least ~40 Ma and became high (3.5-4.5 km) since at least ~26 Ma. This supports the Eocene existence of a lowland between the Gangdese Shan and Tanggula Shan until their early Miocene uplift. This later uplift of central-southern Tibet has important implications for Tibetan Plateau (TP) growth mechanisms and agrees well with recently updated studies of the TP-imposed impacts on Asian atmospheric circulations, surface processes and biotic evolution and diversification differentiation.</p>

scholarly journals Three main stages in the uplift of the Tibetan Plateau during the Cenozoic period and its possible effects on Asian aridification: A review

2018 ◽  
Author(s):  
Zhixiang Wang ◽  
Yongjin Shen ◽  
Zhibin Pang
Keyword(s):  
Tibetan Plateau ◽  
East Asian Winter Monsoon ◽  
East Asian ◽  
Winter Monsoon ◽  
The Tibetan Plateau ◽  
Asian Winter Monsoon ◽  
Plateau Uplift ◽  
Global Cooling ◽  
Tibetan Plateau Uplift ◽  
Central Tibet

Abstract. The Tibetan Plateau uplift and its linkages with the evolution of the Asian climate during the Cenozoic are a research focus for numerous geologists. Here, a comprehensive review of tectonic activities across the Tibet shows that the development of the Tibetan Plateau has undergone mainly three stages of the uplift: the near-modern elevation of the central Tibet and significant uplift of the northern margins (~ 55–35 Ma), the further uplift of the plateau margins (30–20 Ma), and a rapid uplift of the plateau margins again (15–8 Ma). The first uplift of the plateau during ~ 55–35 Ma forced the long-term westward retreat of the Paratethys Sea. The high elevation of the central Tibet and/or the Himalayan would enhance rock weathering and erosion contributing to lowering of atmospheric CO2 content, resulting in global cooling. The global cooling, sea retreat coupled with the topographic barrier effect of the Tibetan Plateau could have caused the initial aridification in central Asia during the Eocene time. The second uplift of the northern Tibet could have resulted in the onset of the East Asian winter monsoon as well as intensive desertification of inland Asia, whereas the central-eastern in China became wet. The further strengthening of the East Asian winter monsoon and the inland Asian aridification during 15–8 Ma was probably associated with the Tibetan Plateau uplift and global cooling. Therefore, the uplift of the Tibetan Plateau plays a very important role in the Asian aridification.

Combining geophysical and petrological estimates of the thermal structure of southern Tibet

2020 ◽  
Author(s):  
Tim Craig ◽  
Peter Kelemen ◽  
Bradley Hacker ◽  
Alex Copley
Keyword(s):  
Middle Miocene ◽  
Thermal Structure ◽  
The Tibetan Plateau ◽  
Crustal Material ◽  
Recent Past ◽  
Southern Tibet ◽  
Indian Lithosphere ◽  
Earthquake Distribution ◽  
Central Tibet ◽  
Geochemical Constraints

<p>The thermal structure of the Tibetan plateau remains largely unknown. Numerous avenues, both geophysical and petrological, provide fragmentary pressure/temperature information, both at the present, and on the evolution of the thermal structure over the recent past. However, these individual constraints have proven hard to reconcile with each other. This study presents a series of models for the simple underthrusting of India beneath southern Tibet that are capable of matching all available constraints on its thermal structure, both at the present day and since the Miocene. Three consistent features to such models emerge: (i) present day geophysical observations require the presence of relatively cold underthrust Indian lithosphere beneath southern Tibet; (ii) geochemical constraints require the removal of Indian mantle from beneath southern Tibet at some point during the early Miocene, although the mechanism of this removal, and whether it includes the removal of any crustal material is not constrained by our models; and (iii) the combination of the southern extent of Miocene mantle-derived magmatism and the present-day geophysical structure and earthquake distribution of southern Tibet require that the time-averaged rate of underthrusting of India relative to central Tibet since the middle Miocene has been faster than it is at present.</p>

Between Kongpo and Xanadu

2018 ◽  
Author(s):  
Ruth Gamble
Keyword(s):  
Southern Tibet ◽  
Central Tibet

The final chapter begins with Rangjung Dorjé in retreat in Kongpo, southern Tibet. Because of his growing reputation, however, he is soon forced to return to central Tibet to mediate between a group of rebels and members of the ruling Mongol-Sakya alliance. In 1329, the Mongol emperor summonses him to the capitals. He eventually arrives in Dadu nearly two years later, during the short reign of Irinjibal (1326–1332, r. 1332), and witnesses the enthronement of the final Mongol emperor, Toghon Temür (1320–1370, r. 1333–1370), who becomes his student. Once at the young emperor’s court, he is only allowed to return to Tibet briefly in 1334. He dies in Xanadu in the summer of 1339. According to his biographers, his death was enacted to facilitate his escape from the emperor’s decree that he stay in the capital. It enabled him, through rebirth, to return to his beloved mountains.

Petrology of ultramafic xenoliths from Rayfield River, south-central British Columbia

1987 ◽  
Vol 24 (8) ◽  
pp. 1679-1687 ◽  
Author(s):  
Dante Canil ◽  
Mark Brearley ◽  
Christopher M. Scarfe
Keyword(s):  
British Columbia ◽  
Phase Equilibrium ◽  
Partial Melting ◽  
Upper Mantle ◽  
Mantle Xenoliths ◽  
Spinel Lherzolite ◽  
Equilibrium Constraints ◽  
Host Magma ◽  
South Central ◽  
Ultramafic Xenoliths

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.

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