Megamonsoons Were Present in Tibet Multiple Times From the Late Permian Through the Middle Triassic

Mesozoic litho- and magneto-stratigraphic evidence from the central Tibetan Plateau for megamonsoon evolution and potential evaporites

Authors:

Fang et al

Abstract:

The megamonsoon was a striking event that profoundly impacted the climatic environment and related mineral sources (salts, coals and oil-gases) in the Mesozoic. How this event impacted Asia is unknown. Here, we firstly reported a Mesozoic stratigraphic sequence in the northern Qiangtang Basin, in the central Tibetan Plateau, based on lithofacies and chronologies of paleontology and magnetostratigraphy. How the planetary and megamonsoon circulations controlled the Asian climate with time has been recorded. Using the basic principles of physical geography, present analogs and a newly developed model, the evolution of the stratigraphic sequence was interpreted to demonstrate that the Qiangtang Basin has been subjected to a megamonsoon climate with heavy precipitation during its northward movement since the Latest Permian but has been subjected to a dry environment due to moving into the northern hemisphere subtropic high zone in the Middle Triassic and monsoonal retreat in the early Late Jurassic (early Oxfordian) approximately 161 Ma. The coupling of the hot-dry climate and the close of the Meso-Tethys, along with sea retreat in the Late Jurassic, ensured a large potential time window for evaporite (potash) formation in the Qiangtang Basin, while the tropic megamonsoon rain forest in the Late Permian to the Early Triassic and in the Late Triassic to Middle Jurassic favored the formation of coal and hydrocarbon source rocks.

What Environment did Miocene Neogene ape Lufengpithecus lufengensis Live in?

Pollen evidence of the palaeoenvironments of Lufengpithecus lufengensis in the Zhaotong Basin, southeastern margin of the Tibetan Plateau

Authors:

Chang et al

Abstract:

Evolutionary processes in hominoid primates were closely related to global and/or regional environmental changes, and therefore palaeoenvironmental reconstruction is fundamental for understanding how environmental changes shaped their evolution. Here, we present pollen data from the 16-m-thick Shuitangba (STB) section, Yunnan Province, southwestern China, bearing remains of the hominoid Lufengpithecus lufengensis of the terminal Miocene; and use principal component analysis to reconstruct the palaeovegetation and palaeoclimate during the key period when the hominoid lived. Our results show that before the STB hominoid appeared (Zone A), the vegetation was dominated by subtropical evergreen broad-leaved taxa with a few temperate deciduous taxa (e.g., Quercus, Castanea/Castanopsis, Alnus). The development of aquatic plants commencing at the ~ 12 m depth is a prominent feature, indicating a warm and humid climate. During the time when the hominoid lived (Zone B), evergreen broad-leaved forests with evergreen Quercus were predominant, while grasses including Poaceae began to expand, and simultaneously conifers decreased, indicating a warm climate. The significant presence of aquatic pollen taxa in subzone A-2 and Zone B suggests the occurrence of lacustrine or swampy environments. In contrast, in Zone C, the vegetation changed to coniferous forest, indicating cooler and drier conditions. These results provide substantive evidence of the vegetation conditions when the hominoid lived, suggesting that the greater diversity of vegetation and the warm humid climate, compared to the present day, would have favoured its survival.

Pollen Evidence Suggests Late Eocene Paleogene Hoh Xil Basin (Tibet) was Below 2,000 m

A Late-Eocene palynological record from the Hoh Xil Basin, northern Tibetan Plateau, and its implications for stratigraphic age, paleoclimate and paleoelevation

Authors:

Miao et al

Abstract:

The Hoh Xil Basin, lying in the central Tibetan Plateau, is key to understanding the Cenozoic tectonics, paleoelevation and paleoclimate changes that have occurred in the Tibetan Plateau since the collision of the Indian and Asian tectonic plates. However, the stratigraphic age and paleoelevation indicated by the sediments of the Hoh Xil Basin remain hotly debated. Here we report on one palynological record from the TTH-C section, extracted from the Yaxicuo Group (the stratigraphic unit between the Fenghuoshan and Wudaoliang groups), and analyze its implications for stratigraphic age, paleoclimate and paleoelevation in the Hoh Xil Basin. The record shows that palynological taxa are mainly dominated by xerophytic Ephedripites, Nitrariadites (Nitrariapollis) and Chenopodipollis, with few ferns and conifers. Rich morphologies correspond well with those in the Xia Ganchaigou Formation (Fm) of the Qaidam Basin to the north. Palynological percentages are well correlated with the middle member of the Xia Ganchaigou Fm in the Qaidam Basin as well as the lower member of the Mahalagou Fm in the Xining Basin to the northeast. The ages of the middle member of the Xia Ganchaigou and lower member of the Mahalagou Fms from these two basins are both identical to the Bartonian Stage (~ 40-37 Ma) of the Late Eocene, according to their respective high-resolution magnetostratigraphic dating. This means that the age of the Yaxicuo Group at least covers the Bartonian Stage. Besides the Qaidam and Xining basins, the palynological assemblages of the TTH-C section are also similar to those of three other sites (the Jiuquan, Tu-ha and Hetao basins), indicating similarly arid climates dominated by a northwestern Chinese subtropical high, and a relatively low paleoelevation in the Hoh Xil Basin (mostly less than 2,000 m a.s.l.) in the Late Eocene.

Miocene Neogene Tarim Basin Drying due to Tibetan Plateau Uplift

Late Miocene episodic lakes in the arid Tarim Basin, western China

Authors:

Liu et al

Abstract:

The Tibetan Plateau uplift and Cenozoic global cooling are thought to induce enhanced aridification in the Asian interior. Although the onset of Asian desertification is proposed to have started in the earliest Miocene, prevailing desert environment in the Tarim Basin, currently providing much of the Asian eolian dust sources, is only a geologically recent phenomenon. Here we report episodic occurrences of lacustrine environments during the Late Miocene and investigate how the episodic lakes vanished in the basin. Our oxygen isotopic (δ18O) record demonstrates that before the prevailing desert environment, episodic changes frequently alternating between lacustrine and fluvial-eolian environments can be linked to orbital variations. Wetter lacustrine phases generally corresponded to periods of high eccentricity and possibly high obliquity, and vice versa, suggesting a temperature control on the regional moisture level on orbital timescales. Boron isotopic (δ11B) and δ18O records, together with other geochemical indicators, consistently show that the episodic lakes finally dried up at ∼4.9 million years ago (Ma), permanently and irreversibly. Although the episodic occurrences of lakes appear to be linked to orbitally induced global climatic changes, the plateau (Tibetan, Pamir, and Tianshan) uplift was primarily responsible for the final vanishing of the episodic lakes in the Tarim Basin, occurring at a relatively warm, stable climate period.

The Effects of Tibetan Plateau Uplift on the Asian Monsoon

The impact of regional uplift of the Tibetan Plateau on the Asian monsoon climate

Authors:

Zhang et al

Abstract:

The climatic effect of Tibetan Plateau (TP) uplift is a hot topic in paleoclimate research. In this paper, the results of a set of numerical simulations are reported to analyze the impact of regional TP uplift on the Asian monsoon climate. The focus is on the impact of the regional uplift in the west and east parts on South Asian summer monsoon, as well as the impact of regional uplift on East Asian winter monsoon. The results show that the uplifts of the Himalaya and the central-southern TP have little effect on summer precipitation increasing over South Asia. Whereas, the further uplifts of the TP in the west and east parts, including the uplifts of both the eastern and western TP, have important effects on the strengthening of the South Asian summer monsoon. The uplift of the eastern TP leads to low-level cyclonic circulation anomalies appearing in the Bay of Bengal, accompanied by anomalous upward movement, and in turn precipitation markedly increases in the Bay of Bengal. Whereas, the uplift of the western TP produces low-level cyclonic circulation anomalies around the uplifted region and intensifies the moisture transport from the tropical ocean, and thus precipitation further increases in South Asia, especially in the northern Arabian Sea. The strengthened summer monsoon in South Asia is coupled with the intensification in diabatic heating and moisture convergence. For the East Asian winter monsoon, the intensification of winter monsoon winds is related more to the regional uplifts than the uplift of the whole TP. The uplifts of the central-southern TP, the northern TP and other northern topography have greater effects on the strengthening of the winter monsoon winds.

Evidence of Iceberg Dropstones From Carboniferous/Permian Tibet

Features, provenance, and tectonic significance of Carboniferous-Permian glacial marine diamictites in the Southern Qiangtang–Baoshan block, Tibetan Plateau

Authors:

Fan et al

Abstract:

In this study, we conducted profile measurements, gravel composition analyses, and U-Pb dating on detrital zircons from a representative glacial marine diamictite in the Gangmaco–Dabure area of the Southern Qiangtang–Baoshan block, Tibetan Plateau. We conclude that the diamictite was formed in a glacial marine environment from the outer edge of the continental shelf to the continental slope and deep sea, in what is now the Southern Qiangtang–Baoshan block. Four distinct glacial-interglacial cycles were identified in the diamictite, which record a minimum of four stages of Gondwana glaciation in the area of the Southern Qiangtang–Baoshan block. Combined with regional geological information, we also conclude that during the Carboniferous-Permian, sediments containing the glacial marine diamictite derived from Gondwana, in the region extending from India to the Tethys Himalaya area, Lhasa and Southern Qiangtang–Baoshan blocks, recorded the transition from continental, neritic to abyssal environments. Gravel assemblages and U-Pb dating of detrital zircons in the glacial marine diamictite indicate that the provenance of the diamictite was Indian Gondwana. We infer that during the Late Paleozoic, the northern margin of the Indian Gondwana continued to be influenced by the Early Palaeozoic tectonic set-up, when Indian Gondwana was under an erosional regime, and the Tethys Himalaya area, Lhasa and Southern Qiangtang–Baoshan blocks were deposited on a passive continental margin.

Tibet was the Cradle of Pleistocene Quaternary's Megafauna

Cenozoic vertebrate evolution and paleoenvironment in Tibetan Plateau: Progress and prospects

Authors:

Wang et al

Abstract:

Due to its lofty height, the Tibetan Plateau features some of the harshest environments in the world with extreme coldness, low oxygen, high UV radiation, and in places, severe aridity. These harsh environments have served as the main driver of vertebrate evolution during the Cenozoic that produced a low productivity, low diversity, high endemicity community – environmental forcing seems to be a dominant mechanism for mammalian evolution in marginal habitats. Mammals have acquired special adaptations for thermal insulation, oxygen transport, DNA damage repair, and others. While broadly similar to faunal assemblages in North China and Central Asia, Tibetan faunas often show initiation of cold-adapted lineages that predate Ice Age megafauna. Our “out of Tibet” hypothesis thus postulates that cold-tolerant species in Pliocene high Tibet were pre-adapted to conditions that were to become widespread during the subsequent Pleistocene Ice Age and Tibet had thus become a cradle for Ice Age megafauna. The best examples of the “out of Tibet” scenario include the Tibetan woolly rhinoceros (Coelodonta thibetana), Tibetan bharal (Pseudois), Asian hunting dog (Sinicuon), and ancestral snow leopard (Panthera blytheae). Our “Third Pole to North Pole” linkage of an extinct Pliocene Tibetan fox, Vulpes qiuzhudingi, with the late Pleistocene and extant arctic fox, V. lagopus, is a subset of the “out of Tibet” hypothesis. One of the iconic Tibetan mammals, the endemic Tibetan antelope (Pantholops) has the longest residence in Tibet going back to the late Miocene, suggesting a long history of perfecting its adaptations to cold environments.

Stable carbon and oxygen isotope analyses of fossils from the Tibetan Plateau reveal significant spatial and temporal variations in the evolution of herbivores’ diets and environments during the late Cenozoic. The diets of modern Tibetan herbivores consist primarily of C3 plants, reflecting the present-day C3 dominance in high-elevation cold habitats. The available carbon isotope data, however, show that warm-climate C4 grasses were a significant dietary component of ancient herbivores in the Gyirong Basin (central Himalayas) in the late Miocene and in Shangri-La (southeastern Tibetan Plateau) in the early Pleistocene, and likely in the Qaidam Basin (NE Tibetan Plateau) from late Miocene to early Pliocene and in Kunlun Pass Basin (northeastern Tibetan Plateau) in the early Pleistocene. This suggests that C4 grasses spread into the Tibetan Plateau in the late Miocene and had persisted in some places to early Pleistocene, but have since disappeared or become insignificant in the region. The retreat of C4 grasses from the Tibetan Plateau is most likely driven by decreases in local temperatures to below the cross-over temperature unfavorable to C4 grasses, as a result of tectonic uplift and/or global climate change. The available isotope data also show that high-elevation cold climatic conditions that favor C3 over C4 grasses arrived earlier in southwestern Tibetan Plateau than in southeastern and northeastern parts of the plateau. This would imply that the Tibetan Plateau had not uniformly reached its present height as recent as early Pleistocene. Future research should focus on determining intra-regional patterns of ecological and climatic change in order to tease apart the effects of tectonic uplift and global climate change on local and regional environmental change and to better understand the linkage between tectonics and climatic and biotic changes.

8,000 Year Old Mutation Key to Tibetan High Altitude Adapation

In an environment where others struggle to survive, Tibetans thrive in the thin air on the Tibetan Plateau, with an average elevation of 14,800 feet. A University of Utah led discovery that hinged as much on strides in cultural diplomacy as on scientific advancements, is the first to identify a genetic variation, or mutation, that contributes to the adaptation, and to reveal how it works. The research appears online in the journal Nature Genetics on Aug. 17, 2014.

“These findings help us understand the unique aspects of Tibetan adaptation to high altitudes, and to better understand human evolution,” said Josef Prchal, M.D., senior author and University of Utah professor of internal medicine.

For his research, Prchal needed Tibetans to donate blood, from which he could extract their DNA, a task that turned out to be more difficult than he ever imagined. It took several trips to Asia, meeting with Chinese officials and representatives of exiled Tibetans in India, to get the necessary permissions to recruit subjects for the study. But he quickly learned that official documents would not be enough. Wary of foreigners, the Tibetans refused to participate.

To earn the Tibetans’ trust, Prchal obtained a letter of support from the Tibetan spiritual leader, the Dalai Lama. “The Dalai Lama felt that a better understanding of the adaptation would be helpful not only to the Tibetan community but also to humanity at large,” said Prchal. He also enlisted the help of native Tibetan Tsewang Tashi, M.D., an author and clinical fellow at the Huntsman Cancer Institute at the University of Utah. More than 90 Tibetans, both from the U.S. and abroad, volunteered for the study.

Published in Science in 2010, Prchal’s group was the first to establish that there was a genetic basis to Tibetan high altitude adaptation. In the intervening years, first author Felipe Lorenzo, M.D., Ph.D., pioneered new techniques to tease out the secret to one of the adaptations from a “GC-rich” region of the Tibetans’ DNA that was particularly difficult to penetrate.

Their efforts were worth it; the DNA had a fascinating story to tell. About 8,000 years ago, the gene EGLN1 changed by a single DNA base pair. Today, a relatively short time later on the scale of human history, the vast majority of Tibetans – 88 percent - have the genetic variation, and it is virtually absent from closely related lowland Asians. The findings indicate the tiny genetic change endows its carriers with a selective advantage.

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Chinese Afforestation Plans for Tibetan Plateau may be Problematic

Political risks arising from the impacts of large-scale afforestation on water resources of the Tibetan Plateau

Authors:

Cao et al

Abstract:

With rapid economic and population growth, water scarcities and conflicts over the available water are becoming worse, while climate change makes the potential risk to society unpredictable. To deal with a growing water scarcity and improve the quality of water, China’s government launched a large-scale afforestation program in the Tibetan Plateau—the birthplace of Asia’s primary rivers, which lies upstream of 40% of the world’s population, at a high altitude and with fragile ecosystems. However, this program could aggravate the conflict for water between humans and nature, because tree plantations consume 1.7 × 109 m3 more water annually than the equivalent area of the region’s natural vegetation. The shrinkage of glaciers caused by climate warming will exacerbate the water resource scarcity caused by these plantations and may soon become a primary source of conflict between regions that depend on river discharge from the plateau. To mitigate these problems, China’s government should change its policy to conserve natural vegetation instead of planting more trees.

Miocene Neogene Tibetan Plateau Uplift Drove Chinese Floral Diversity

Late Miocene southwestern Chinese floristic diversity shaped by the southeastern uplift of the Tibetan Plateau

Authors:

Jacques et al

Abstract:

In southwestern China and Southeast Asia modern geology and topography have been influenced strongly by the collision between the Indian and Eurasian plates. The southeastern margin of the Tibetan Plateau is well known for its high biodiversity and diverse vegetation types. While the present diversity is explained by the geological history of this region, to date no study has looked at how past vegetation was shaped by geological and topographical history. In this study, we focus on three coeval late Miocene leaf assemblages from Yunnan: Lincang, Xiaolongtan and Xianfeng. The palaeoelevation of these three sites is reconstructed using enthalpy as a palaeoaltimeter. Enthalpy at the fossil site is reconstructed based on leaf physiognomy; the difference between this enthalpy and enthalpy at sea-level is used as a proxy for altitude. The palaeoaltitudes are resolved as 214 ± 901 m asl for Lincang, 530 ± 901 m asl for Xiaolongtan, and 1936 ± 901 m asl for Xianfeng. The floristic components of these floras are analysed for their geographical elements. There is a gradient in the percentage of tropical genera between the three floras from Lincang, at the lowest elevation, to Xianfeng, at the highest level. For Lincang, this percentage exceeds the threshold used to define present day tropical regions. Our results demonstrate that there was already a floristic differentiation in Yunnan during the late Miocene. Floras with tropical affinities were at low altitude, whereas floras with temperate affinities were at high altitude. With the later uplift of southern Yunnan, floras with tropical affinities retreated to the south where they are still present. The uplift framework reconstructed in this paper gives a tectonic context for further studies on the impact of uplift on biodiversity.

Climate Fluctuations at the Eocene-Oligocene Transition in Xining (Tibetan Plataeu)

Clay mineral changes across the Eocene–Oligocene transition in the sedimentary sequence at Xining occurred prior to global cooling

Authors:

Zhang et al

Abstract:

During the Cenozoic, high-quality long-term sedimentary sequences formed in Xining basin at the northeastern margin of the Tibetan Plateau, which are characterized by alternating gypsiferous layers and reddish mudstone beds. The Tashan section was previously dated in detail by magnetostratigraphy, which yielded an age span of 16 to 35.7 Ma. In this study, bulk and clay mineral assemblages and magnetic parameters of the 33.1–35.7 Ma portion were analyzed using X-ray diffraction and magnetic methods to determine the behavior of the Eocene–Oligocene climate transition. Quartz, calcite, feldspar and clay fractions in sediments that are mainly derived from the surrounding catchments, gypsum and dolomite are authigenic minerals. Illite, chlorite, irregular mixed-layer illite-smectite and smectite are the four main clay-sized fractions (< 2 μm) in the gypsum/gypsiferous layers and the reddish mudstone beds, which suggest that no significant tectonic activity occurred in the catchment area of the Xining basin during the period of 35.7–33.1 Ma. Dominant hematite, illite and gypsum in the sediments indicate that the climate was dominantly hot and dry in the Xining basin. This was controlled by a “planetary” subtropical aridity zonal pattern; the variations in gypsum, dolomite and smectite content are mainly controlled by the climate changes. The characteristics of the clay mineral assemblages suggest that warm and humid fluctuations with hot and dry conditions prevailed during ~ 35.7–34.1 Ma in inner Asia. This changed to cold and dry conditions at ~ 34.1 Ma and remained so from ~ 34.1 to 33.1 Ma. Comparisons with open ocean marine records and Northern Hemisphere continental records indicate that the climate cooling in continental records occurred prior to the main drop of δ18O in foraminifera preserved in marine sediments at Oi-1 (33.545 Ma). This demonstrates that the magnitude of Antarctic ice growth during the EOT was not the major contributor to inner Asian aridification, possibly due to the northward moving of subtropical highs that existed in northwest China and was induced by temperate zones moving during the late Eocene to early Oligocene.

Did Tibetans Get Hemoglobin Gene From Denisovan Hominins?

Tibetans were able to adapt to high altitudes thanks to a gene picked up when their ancestors mated with a species of human they helped push to extinction, according to a new report by University of California, Berkeley, scientists.

An unusual variant of a gene involved in regulating the body's production of hemoglobin – the molecule that carries oxygen in the blood – became widespread in Tibetans after they moved onto the high-altitude plateau several thousand years ago. This variant allowed them to survive despite low oxygen levels at elevations of 15,000 feet or more, whereas most people develop thick blood at high altitudes, leading to cardiovascular problems.

"We have very clear evidence that this version of the gene came from Denisovans," a mysterious human relative that went extinct 40,000-50,000 years ago, around the same time as the more well-known Neanderthals, under pressure from modern humans, said principal author Rasmus Nielsen, UC Berkeley professor of integrative biology. "This shows very clearly and directly that humans evolved and adapted to new environments by getting their genes from another species."

This is the first time a gene from another species of human has been shown unequivocally to have helped modern humans adapt to their environment, he said.

Nielsen and his colleagues at BGI-Shenzhen in China will report their findings online July 2 in advance of publication in the journal Nature.

The gene, called EPAS1, is activated when oxygen levels in the blood drop, triggering production of more hemoglobin. The gene has been referred to as the superathlete gene because at low elevations, some variants of it help athletes quickly boost hemoglobin and thus the oxygen-carrying capacity of their blood, upping endurance. At high altitude, however, the common variants of the gene boost hemoglobin and its carrier, red blood cells, too much, increasing the thickness of the blood and leading to hypertension and heart attacks as well as low-birth-weight babies and increased infant mortality. The variant or allele found in Tibetans raises hemoglobin and red blood cell levels only slightly at high elevation, avoiding the side-effects seen in most people who relocate to elevations above 13,000 feet.

"We found part of the EPAS1 gene in Tibetans is almost identical to the gene in Denisovans and very different from all other humans," Nielsen said. "We can do a statistical analysis to show that this must have come from Denisovans. There is no other way of explaining the data."

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Evidence From Cambrian Tibet of an Andean-like Mountain Building on the Active Margin of Gondwana

Cambrian ultrapotassic rhyolites from the Lhasa terrane, south Tibet: Evidence for Andean-type magmatism along the northern active margin of Gondwana

Authors:

Ding et al

Abstract:

The petrogenesis and tectonic significance of early Paleozoic magmatic rocks in south Tibet is debated. In this paper, we report Cambrian ultrapotassic felsic volcanics from the Lhasa terrane. Petrographic and whole-rock geochemical studies indicate that these rocks are rhyolite and rhyolitic ignimbrite, and have varying SiO2 (69.56–82.09 wt.%), Al2O3 (9.52–16.61 wt.%) and Fe2O3t (1.0–7.9 wt.%). The rocks are ultrapotassic (high K2O 4.19–6.90 wt.%, and very low Na2O 0.01–0.06 wt.%) and peraluminous (A/CNK = 1.41–2.22). They are enriched in Rb, Th, U, Pb, Zr and Y, and showenegative Ba, Sr, P, Nb, Ta and Ti anomalies, and slightly fractionated REE patterns with moderately negative Eu anomalies, typical of A-type granitoids. Zircons from six samples yielded crystallization ages of ca. 512 Ma. These zircons show εHf(t) values in the range of − 4.7 to + 1.3, and two-stage Hf model ages of 1734–1392 Ma. Combining with previous results, we propose that these ultrapotassic rhyolites were derived from the partial melting of middle Proterozoic crustal rocks in the lower crust under high-temperature and water-absent conditions in an extensional environment of active magmatic arc. Thus, this study provides new insights into early Paleozoic Andean-type orogeny along the northern margin of Gondwana supercontinent.

Tibet Already 10,000 Feet (3,000 m) Elevation in Neogene

Palynological evidence for the latest Oligocene−early Miocene paleoelevation estimate in the Lunpola Basin, central Tibet

Authors:

Sun et al

Abstract:

Uplift of the Tibetan Plateau is ultimately driven by the Cenozoic collision between the Indian and Eurasian plates and their continued convergence. One approach for studying the Tibetan Plateau uplift is to verify the paleoelevation changes from collision to present day. This is important for understanding both the tectonics and the climatic effects. The new high resolution palynological record of the uppermost Oligocene to the lowest Miocene strata from the Lunpola Basin indicates that the vegetation types during the latest Oligocene–earliest Miocene was dominated by mixed coniferous–broadleaved forests being different from the modern steppe vegetation. By using the Coexistence Approach to the fossil pollen records, after calibration the effects of temperature difference and the lapse rate, a maximum paleoelevation of 3190 ± 100 m asl was estimated in the Lunpola Basin in the latest Oligocene − earliest Miocene, being 1500 to 2000 m lower compared with the previous oxygen isotope paleoelevation in the same region.

Continental Collision Between Western/Eastern Qiangtang not Completed until Ladinian Triassic.

Late Triassic granitic magmatism in the Eastern Qiangtang, Eastern Tibetan Plateau: Geochronology, petrogenesis and implications for the tectonic evolution of the Paleo-Tethys

Authors:

Peng et al

Abstract:

Triassic granites are widely exposed in the central Qiangtang, northern Tibetan Plateau. They, therefore, made an important contribution to the growth of the Tibetan Plateau. In this paper, we present zircon U–Pb dating and Hf isotopic results, and whole-rock elemental and Sr–Nd isotopic analyses of the Dongdashan (DDS) batholith in the central Qiangtang in order to understand their petrogenesis and tectonic setting. LA-MC-ICP-MS zircon U–Pb results show that the DDS batholith was emplaced at 220.3 ± 0.7 Ma. All the granites in the DDS possess high A/CNK values (greater than 1.0) and display peraluminous characteristics, similar to S-type granite. Their strongly fractionated REE patterns ((La/Yb)N = 6.98–13.9) with conspicuous negative Eu anomalies (Eu*/Eu = 0.51–0.67), together with negative εNd(t) and εNd(t) values, and depleted Nd and Hf model ages, suggest that the DDS granitic magma had a dominantly crustal source, likely the Paleoproterozoic basement (i.e., the Ningduo and Caoqu group metasediments) in the area.

In combination with regional studies, our new geochemical data and geochronological results demonstrate that the Late Triassic magmatism was generated in a post-collisional tectonic setting. The spatial distribution pattern of the Mesozoic igneous rocks, coupled with the exhumation of high-pressure metamorphic rocks in the central Qiangtang, favors a slab breakoff model, which resulted in post-collisional extension and asthenospheric upwelling that induced large-scale partial melting of the middle-lower crust to produce voluminous amounts of felsic magma. Therefore, the occurrence of the Late Triassic post-collisional magmatism, and particularly the exhumation of high-pressure eclogites and blueschists as well as their presence in the lowermost portion of the Late Triassic volcanoclastics in the Qiangtang basin, clearly indicate that the final closure of the of Paleo-Tethys Ocean and associated continent-continent collision between the Gondwana-derived Western Qiangtang and Eastern Qiangtang terranes had not been completed until the early mid-Triassic.

What is the Crustal Structure Under Southern Tibet?

Mapping crustal structure beneath southern Tibet: Seismic evidence for continental crustal underthrusting

Authors:

Xu et al

Abstract:

Receiver function imaging along a temporary seismic array (ANTILOPE-2) reveals detailed information of the underthrusting of the Indian crust in southern Tibet. The Moho dips northward from ~ 50 km to 80 km beneath the Himalaya terrane, and locally reaches ~ 85 km beneath the Indus-Yalung suture. It remains at ~ 80 km depth across the Lhasa terrane, and shallows to ~ 70 km depth under the Qiangtang terrane. An intra-crustal interface at ~ 60 km beneath the Lhasa terrane can be clearly followed southward through the Main Himalaya Thrust and connects the Main Boundary Thrust at the surface, which represents the border of the Indian crust that is underthrusting until south of the Bangong-Nujiang Suture. A mid-crustal low velocity zone is observed at depths of 14–30 km beneath the Lhasa and Himalaya terranes probably formed by partial melt and/or aqueous fluids.

Panthera blytheae: The Old Known Great Cat Originates in Plioecene Neocene Tibet

The oldest big cat fossil ever found – which fills in a significant gap in the fossil record – was discovered on a paleontological dig in Tibet, scientists announced today.

A skull from the new species, named Panthera blytheae, was excavated and described by a team led by Jack Tseng – a PhD student at the USC Dornsife College of Letters, Arts and Sciences at the time of the discovery, and now a postdoctoral fellow at the American Museum of Natural History (AMNH) in New York.

"This find suggests that big cats have a deeper evolutionary origin than previously suspected," Tseng said.

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