Yarlung River Research Articles

Late Oligocene to Pleistocene thermo-tectonic evolution of the Karakoram Fault Zone: New insights from basement and detrital apatite fission track thermochronology

The Karakoram Fault Zone displays distinctive topographic and tectonic characteristics, with intricate river drainage systems. Although there are extensive thermochronological datasets for the western Tibetan Plateau, limited investigations have been carried out to uncover the low-temperature thermal history of the Karakoram Fault Zone, which connects the Lhasa terrane with the Pamir. In this contribution, apatite fission track (AFT) thermochronology was conducted on 13 basement and 4 conglomerate samples collected from the western Gangdese batholith and the Ayi Mountain Range, on either side of the Karakoram fault. Inverse thermal history modeling results reveal that the western Gangdese batholith experienced two stages of rapid basement cooling at 27–23 Ma (late Oligocene-early Miocene) and 16–4 Ma (middle Miocene-Pliocene). The adjacent Ayi Mountain Range experienced cooling in the late Miocene (∼8 Ma) and during the Pliocene to Pleistocene (4–1 Ma). We suggest that tectonic forces associated with rollback and lateral break-off of the Indian continental lithosphere, and the dextral strike-slip activity of the Karakoram fault were responsible for the first cooling phase. The second accelerated cooling phase was due to the deep fragmentation of the Indian slab, the activity of the Karakoram normal fault, and associated ∼E-W extension. Additionally, since the late Oligocene, the Indus River incision has likely also contributed to the exhumation of the western Tibetan Plateau. Subsequently, the western Gangdese batholith reached high elevations, resulting in the reversal of the Yarlung River. The dextral-normal motion of the Karakoram fault, which is still active today, was the main cause of the Pliocene to Pleistocene accelerated cooling detected in the Ayi Mountain Range.

Interaction of surface processes and crustal flow in the Eastern Himalayan Syntaxis

The syntaxes at the eastern and western ends of the Himalaya located in the Tsangpo and Indus gorge regions provide examples of the interplay between tectonics and erosion. A previous borehole study along the Yarlung River in the Eastern Himalayan Syntaxis (EHS) revealed an ∼1 km thick sedimentary wedge upstream of the Tsangpo gorge with a >2.5 Ma depositional age. However, the mechanism of formation of this sedimentary wedge remains under debate. Here, we combine low-temperature thermochronology data and thermomechanical modelling to discuss how a sedimentary wedge formed at the highly eroded EHS. Our low-temperature thermochronology results show late Miocene fast cooling episodes focused at the Gyaca and Tsangpo gorges, which are interpreted to be related to coeval rifting at the former and rapid erosion and hot-crust upwelling at the latter. Constrained by the geological and geophysical observations, we apply thermomechanical models to illustrate the mechanism of formation of the sedimentary wedge and present high relief of the EHS. The numerical geodynamic model shows that localized erosion triggers middle ‘crust extrusion’ and regional topographic adjustment at the EHS. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7008098 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Deciphering differential exhumation in the Gangdese orogen in southern Tibet using exposed porphyry alteration systems and geomorphic analysis

Topography and exhumation vary strongly in the Tibetan Plateau, reflecting different geodynamics and surface processes. The Gangdese orogen in southern Tibet is characterized by west-to-east variations in topography and occurrences of the Miocene porphyry copper deposits. We integrated remote sensing based hydrothermal alteration mapping and geomorphological analysis to detect patterns of differential exhumation since the Miocene. High abundances of propylitic and potassic alteration of the eastern Miocene granitoids are identified, indicating >2 km of exhumation since the Miocene. The western Gangdese has intensive phyllic and argillic alteration representing ∼1 km of exhumation. Geomorphic analyses also show E-W changes that most likely resulted from differential rock uplift histories. Channel steepness index values indicate the eastern Gangdese has channel gradients between 211 m1.02 and 457 m1.02, compared to values between 30 m1.02 and 160 m1.02 in the west. Linear inversion of tributaries of the Yarlung river shows a pulse of rock uplift between 25 Ma and 7 Ma with a maximum rate of 110 m/ m.y. in the east. In contrast, the western Gangdese exhibits slower and persistent rock uplift rates between 20 m/m.y. and 40 m/m.y. since 20 Ma. The integrated results record differential exhumation and rock uplift since the Miocene. We invoke the geometric variations of the subducted Indian lithosphere to interpret the E-W differential exhumation since the Miocene. Steeper subduction of the Indian lithosphere beneath the eastern Gangdese induced mantle upwelling, triggering rapid rock uplift and deep exhumation. Conversely, the shallower subduction of the Indian slab in the west generated slow and prolonged rock uplift with less exhumation. Our study refines the exhumation process of the Gangdese since the Miocene.

Orographic rainfall drives the Himalaya drainage divide to move north

The Yarlung River flows between the east-trending Himalayan and Gangdese orogens, and across several north-trending rifts. It carries rich information on the Indian-Asian collisional tectonics and the Asian monsoon. The tectonic activity and the intensified monsoon would increase topographic uplift and rainfall, respectively, thereby driving drainage reorganization and divide migration. However, how and when the river network formed and adjusted remains controversial. Knowledge of its drainage-divide stability can provide a new and independent perspective for the river network reorganization and the tectonic and climatic changes behind it. Here, we reveal the drainage-divide stability of the Yarlung River using χ-plot and Gilbert metrics methods and simulate the river's formation process. We find that the Himalaya drainage divide is primarily moving north, which is driven by the spatiotemporal variations in precipitation across the Himalayas. The northward drainage-divide migration will further enhance the fluvial incision in the southern flank of the Himalayas. The drainage-divide migration and numerical simulation results support an early (>20 Ma) formation of the modern, orogen-parallel Yarlung River. The Gangdese drainage divide shows predominantly northward and southward migration of the Endorheic-Yarlung and Nu-Yarlung divides, respectively. Such mobility is controlled by base-level rise within the endorheic drainage and eastern downstream reaches of the Yarlung River, respectively. Moreover, the north-trending rifts separate the drainage divides into five zones, each with a distinct migration pattern. This demonstrates a surficial response to the along-strike tectonic variations, especially underthrusting Indian slab tears.

The extraordinary Namche Barwa sediment factory in the Eastern Himalayan Syntaxis

AbstractThe Namche Barwa Syntaxis (NBS) is one of the most productive detrital factories on Earth. Previous studies have shown that the NBS supplies large amounts of sediment to the Brahmaputra River, although the sources and controlling factors of sediment production have not been ascertained in detail. This study presents petrographic and heavy‐mineral data for 43 sand samples collected in the Yarlung and Parlung river catchments covering the entire NBS and surrounding areas. Combined with U–Pb ages of detrital zircons, our data indicate that 89 ± 11% of Yarlung River sediments downstream of the NBS are produced in the Yarlung and Parlung gorges. The annual sediment flux of the Yarlung River increases by a factor of 20 within ca. 250 km from upstream of the NBS (ca. 10 Mt) to downstream (ca. 200 Mt/a). The Yarlung and Parlung gorges, representing only ca. 1% of the Yarlung‐Brahmaputra catchment area, contribute 74 ± 9% of the total Brahmaputra sediment flux. Average interannual erosion rates in the Yarlung and Parlung gorges corresponding to these fluxes are calculated to be 9.2 ± 1.2 mm/a and 6.5 ± 2.1 mm/a respectively. Focused erosion of the Namche Barwa Complex and Yarlung Suture Zone in the gorge, where high‐grade metamorphic rocks are exposed, is a consequence of high channel steepness (ksn values up to 800–1800), high stream power and extreme events including frequent earthquakes and landslides. The coupling between surface erosion and tectonic uplift in the Yarlung Gorge is in full agreement with the tectonic aneurism model of NBS evolution.

Fault systems impede incision of the Yarlung river into the Tibetan plateau

It is widely accepted that tectonics generally enhances river incision. However, why rivers have not incised further into orogenic plateaus to destroy terrains over long-time scales remains ambiguous. Here we hypothesize that the diverse nature of regional tectonics could have impeded river erosion, taking Yarlung River in Tibetan Plateau as a case. We constrain the incision history and effect of a tectonic rift on fluvial incision by low-temperature thermochronology. Results show focused cooling near the rift, but markedly reduced cooling in the upstream and downstream regions since ~7 Ma. This coincides with an episode of rapid exhumation of Eastern Himalaya Syntaxis downstream. We propose that these two co-phased tectonic systems resulting from accelerated extension of southern Tibetan Plateau prevented upstream migration of river knickpoints. Our study highlights that the activity of fault systems may hinder regional erosion, thereby facilitating the preservation of topography and high plateaus in active orogenic belts.

Cenozoic low temperature cooling history of the eastern Lhasa terrane: Implications for high-relief topography of external drainage area in the southern Tibetan Plateau

The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments. The internal and external drainage areas display similar high-elevations, while their topographic reliefs are not comparable; the former shows a large low-relief surface, whereas the latter is characterized by relatively high relief. The eastern Lhasa terrane is a key tectonic component of the Tibetan Plateau. It is characterized by high topography and relief, but the thermal history of its basement remains relatively poorly constrained. In this study we report new apatite fission track data from the eastern part of the central Lhasa terrane to constrain the thermo-tectonic evolution of the external drainage area in the southern Tibetan Plateau. Twenty-one new AFT ages and associated thermal history models reveal that the basement underlying the external drainage area in southern Tibet experienced three main phases of rapid cooling in the Cenozoic. The Paleocene-early Eocene (∼60–48 Ma) cooling was likely induced by crustal shortening and associated rock exhumation, due to accelerated northward subduction of the NeoTethys oceanic lithosphere. A subsequent cooling pulse lasted from the late Eocene to early Oligocene (∼40–28 Ma), possibly due to the thickening and consequential erosion of the Lhasa lithosphere resulted from the continuous northward indentation of the India plate into Eurasia. The most recent rapid cooling event occurred in the middle Miocene-early Pliocene (∼16–4 Ma), likely induced by accelerated incision of the Lhasa River and local thrust faulting. Our AFT ages and published low-temperature thermochronological data reveal that the external drainage area experienced younger cooling events compared with the internal drainage area, and that the associated differentiated topographic evolution initiated at ca. 30 Ma. The contributing factors for the formation of the high-relief topography mainly contain active surface uplift, fault activity, and the enhanced incision of the Yarlung River.

雅鲁藏布江三大支流流域小花水柏枝种群结构及动态特征

PDF HTML阅读 XML下载 导出引用 引用提醒 雅鲁藏布江三大支流流域小花水柏枝种群结构及动态特征 DOI: 10.5846/stxb202110132894 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（32060087） Population structure and dynamic characteristics of Myricaria wardii in the basin of three branches of Yarlung Zangbo River Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:小花水柏枝（Myricaria wardii）为西藏特有物种，是重要的藏药资源，主要分布于雅鲁藏布江（简称雅江）三大支流河谷流域。为探索小花水柏枝种群结构及分布特征，在雅江三大支流拉萨河、年楚河和尼洋河流域设定15个样点，每个样点5个样方，测量小花水柏枝的基径大小，用径级大小划分年龄结构，通过编制静态生命表并绘制存活曲线来描述种群结构，并使用种群动态量化和时间序列分析预测小花水柏枝种群数量变化。结果表明：雅江三大支流小花水柏枝种群径级结构均为底部狭窄中部膨大的非典型金字塔结构。动态指数显示三大支流小花水柏枝种群均为增长型但增长趋势不明显，并且对外界干扰比较敏感，抗干扰能力较差。静态生命表及相关曲线显示三大支流小花水柏枝种群存活数量和生命期望随着径级增大逐渐下降，三大流域小花水柏枝种群均发生不同程度的波动，整体呈现不稳定的状态。生存分析和时间序列分析均表明缺乏幼苗是导致未来小花水柏枝衰退的主要原因，且预测年楚河和拉萨河小花水柏枝种群将更快进入衰退期，尼洋河流域小花水柏枝种群衰退期较晚。同时，幼苗所占比例与居群所在地降水量显著正相关，因此高降水量的尼洋河流域更适合小花水柏枝的生存。然而此环境的小花水柏枝种群数量对干扰较敏感，建议在雅江三大支流流域经济发展的同时加强对小花水柏枝种群幼苗保护，保护和改善小花水柏枝种群生境，以维持其种群的天然更新和恢复。 Abstract:Myricaria wardii is one of species of Myricaria,which is endemic to Tibet and an important resource of Tibetan medicine. It is mainly distributed in the basin of three branches of Yarlung Zangbo River (or Yarlung River, for short), namely Niyang River, Lhasa River and Nianchu River. In order to explore the population structure and distribution characteristics of M.wardii species, 15 sample plots and 5 sample sites in each plot, were determined, and from which we collected basic diameter of M.wardii. Population dynamics quantization and time sequence analysis were used to predict potential population changes of M.wardii. Characteristics of the population structure were described by establishing a static life table and drawing a population survival curve. The results showed that the population diameter class structure of M.wardii species in the basin of three branches of Yarlung River was atypical pyramid structure with narrow bottom and enlarged middle. The dynamic index showed that the population of M.wardii. in the three tributaries were all growing, but the growth was not obvious, and they were sensitive to external disturbances and had poor anti-interference ability. The static life table and the correlation curve showed that the survival number and life expectancy of the populations of M.wardii in the three tributaries gradually decreased with the increase of diameter class. The populations of M.wardii in the three tributaries all fluctuated to varying degrees, showing an unstable state as a whole. Both survival analysis and time series analysis showed that the lack of seedlings was the main reason for the decline of M.wardii in the future, and it was predicted that the populations of M.wardii in the Nianchu River and Lhasa River would enter the decline period sooner, while the decline period of the populations of M.wardii in the Niyang River were relatively later. At the same time, the proportion of seedlings was significantly positively correlated with the precipitation where the population was in, so that the Niyang River Basin with high precipitation was more suitable for the survival of M.wardii. However, the population of Myricaria wardii is more sensitive to disturbance in this environment. It is recommended to strengthen the protection of the seedlings of M.wardii population while developing economy of the three tributaries of the Yarlung River, then protect and improve the population environment of M.wardii, so as to maintain its natural renewal and recovery. 参考文献 相似文献 引证文献

Two Stages of Accelerated Exhumation in the Middle Reach of the Yarlung River, Southern Tibet Since the Mid‐Miocene

AbstractClimate change and tectonic activity through erosion control Earth’s topography, much of which is shaped by river incision. The Yarlung River has dissected the Indian‐Asian Collision Zone, and is one of the Earth’s largest rivers. However, its erosion rate history and how it interacts with regional tectonics remain ambiguous. Here, we apply low‐temperature thermochronometry and thermal‐kinematic models for bedrock samples from the Yarlung River. Our analysis reveals two stages of relatively fast exhumation occurred in different parts of the middle reach of the Yarlung River followed by remarkedly slow exhumation rate. First, a mid‐Miocene period (15–9 Ma) of rapid exhumation occurred along much of the Yarlung River, including within wide portions of the valley and its tributaries. This period of rapid exhumation coincides with the stage of high precipitation rates recorded in the Asian marginal basins and the timing of the east‐west extensional faults. In combination with extensional faults, the enhanced precipitation due to the onset of Asian monsoon would increase river discharge and thus accelerate mid‐Miocene exhumation rates. Second, a Pliocene‐Pleistocene (5–2 Ma) period of accelerated exhumation limited to gorges occurred in response to north‐south normal faulting, implying local tectonics as a first‐order control. Our results highlight roles of climatic and tectonic processes in shaping fluvial topography and how these change with time.

Aeolian sand dunes alongside the Yarlung River in southern Tibet: A provenance perspective

The potential interactions between aeolian and fluvial systems are critical in understanding environmental change. Whether aeolian products originated from the river depends on the river characteristics and wind regimes. In southern Tibet, aeolian sand dunes are widespread along the Yarlung River, and thus provide an ideal example to explore the relationships between large fluvial systems and aeolian products. Although previous studies postulated that those aeolian products were originated from the Yarlung River, few empirical data actually exist to support this idea. We analysed the spatial pattern, sand transportation directions, and granulometric characteristics of the sand dunes to evaluate the potential influence of the Yarlung River on the aeolian processes. Comparison of the dune field distribution against channel width and longitudinal profile of the Yarlung River shows that sand dunes are clustered at the wide and flat segments of the river. Analyses of >4,600 sand dune orientations using Google Earth imagery show that the dunes located at the southern and northern sides of the Yarlung River demonstrate opposite sand transportation directions that generally point against the river. This suggests that the sand grains probably originated from the river. Grain size distributions from dune samples show unimodal or unimodal‐like patterns. This means that each sand dune field was dominantly fed by a simple transportation process rather than by compound processes from smaller‐level fluvial systems, which in turn implies that the Yarlung River was the most possible candidate for the provenance of these aeolian deposits. This study provides new constraints to demonstrate that the Yarlung River provides both accommodation space and sorted fluvial sand for the aeolian sand dunes along the river.

Provenance and erosional impact of Quaternary megafloods through the Yarlung-Tsangpo Gorge from zircon U-Pb geochronology of flood deposits, eastern Himalaya

Holocene and Upper Pleistocene sediments in the eastern Himalayan syntaxis represent an extraordinary record of glacial outburst megafloods in one of the most tectonically active landscapes on Earth. Glacial damming and outburst floods in the syntaxis may have focused erosion in the steep Tsangpo Gorge and inhibited river incision into the margin of the Tibetan Plateau. However, few flood slackwater deposits have been studied, and it is unknown which of the hundreds of known glacial impoundments in Tibet may have sourced the floods. Here we report n=1438 new detrital zircon U-Pb data from individual ancient megaflood and historical outburst flood slackwater deposits to examine the provenance and erosive potential of these events. Detrital zircon U-Pb geochronology of megaflood deposits show that megaflood provenance is more consistent with impoundment of the Yarlung River drainage at or west of the Namche Barwa massif, than impoundment of eastern drainages along the Yigong and Parlung Rivers. Compared to active bedload in the Siang River, and historical floods within the same drainage area, megaflood samples overall contain a disproportionately large amount of zircons eroded from the Tsangpo Gorge. We interpret this preferential derivation to reflect preferential erosion during large discharge events—supporting the hypothesis that Quaternary megafloods are a primary contributor to rapid exhumation of the eastern Himalayan syntaxis.

Mio-Pliocene piracy, relict landscape and drainage reorganization in the Namcha Barwa syntaxis zone of eastern Himalaya

The presence of unique elevated low relief relict landscape in the transient Dibang catchment, at the orographic edge of Tibet-Himalaya in the tectonically active Namcha Barwa syntaxial zone, is modelled to understand evolving regional landscape, drainage reorganization and tectonics. This elevated low relief landscape represents a Mio-Pliocene abandoned paleo-channel of the Yarlung river, which was captured by the headward eroding Siang river owing to >600 m base level advantage. The river capture caused isolation of the Dibang river, which evolved as a transient parched catchment since 3–6 Ma after loss of ~17 times drainage area and 4–17 times discharge. The drainage area and discharge gained by the Siang river triggered enormous incision causing aneurysm leading to the accelerated growth of the Tsangpo gorge and affected regional tectonics. This paleo-drainage reorganization is reflected in the Mio-Pliocene sedimentation pattern in the southern Tibet-Himalaya and foreland basins.

The Ancestral Lhasa River: A Late Cretaceous trans-arc river that drained the proto–Tibetan Plateau

Abstract Late Cretaceous trench basin strata were deposited in the subduction zone that consumed Neo-Tethyan oceanic lithosphere along the southern margin of the proto–Tibetan Plateau. We conducted detrital zircon (DZ) U-Pb geochronology on six trench basin samples (n = 1716) collected near Dênggar, Tibet (∼500 km west of Lhasa), to assess the provenance of these rocks and reconstruct Late Cretaceous sediment transport pathways. They contained DZ ages that point to a unique source around Lhasa city, north of the Late Cretaceous Gangdese magmatic arc. The modern Lhasa River catchment contains the requisite sources, and its main trunk transects the Gangdese magmatic arc, joining with the Yarlung River at a barbed junction at the India-Asia suture. We infer that the Lhasa River is an ancient feature that transported sediment to the subduction zone in Late Cretaceous time and persisted during India-Asia collision.

Differential crustal deformation across the Cona-Oiga rift, southern Tibetan Plateau

The Cona-Oiga rift (COR) is the easternmost member of a series of ∼N-S trending Cenozoic rifts in the southern Tibetan Plateau. The Yarlung River flows from west to east, across the COR and exhibits diverse river morphology along strike. We analyze tributary fluvial longitudinal profiles in the Yarlung drainage and the published strain rate field on both sides of the rift in order to gain knowledge about its development and crustal deformation patterns within the plateau interior. Tributaries on the western side of the rift have relatively low normalized steepness index (ksn). Concave curves in χ-elevation plots and cross-divide contrasts in χ, mean relief, and mean gradient, indicate ongoing river reorganization in this region. In contrast, high topographic relief and steep stream channels developed on the eastern side. In addition, spatial variations in negative dilatational strain rates indicate diverse crustal shortening and regional uplift across the COR. We suggest that the Cona-Oiga rift plays an important role in accommodating deformation associated with the continuing indentation of the eastern Himalayan syntaxis. Tectonic forcing might be the dominant factor controlling landscape evolution across the COR.

Differential exhumation histories between Qulong and Xiongcun porphyry copper deposits in the Gangdese copper metallogenic Belt: Insights from low temperature thermochronology

The Qulong and Xiongcun porphyry deposits in the Gangdese Copper (Molybdenum) Metallogenic Belt (GCMB) are both giant porphyry deposits. They were located in the eastern and the central GCMB (about 400 km apart), and were generated in the Miocene and the Jurassic, respectively. In order to reveal why the two asynchronous deposits could occur in the same metallogenic belt, the in-situ zircon U-Pb, zircon and apatite fission track (ZFT and AFT), and apatite (U-Th)/He (AHe) dating were conducted. Their associated exhumation amounts and histories were compared, and finally the prospecting significance was evaluated. AHe ages of the Qulong deposit indicate it underwent an amount of at least 1.3–2.8 km exhumation since 13.8–13.1 Ma. However, AFT data and modeling results reveal that the Xiongcun deposit experienced two stages of rapid cooling at 20–13 Ma and 13–8 Ma, respectively. The temperature decreases from 160 °C to 40 °C after ∼20 Ma and the corresponding exhumation amount is about 4–6 km. Integrated the regional thermochronological data, exhumation amounts of 4–6 km and <2 km in the southern and northern parts of the central Gangdese Magmatic Arc (GMA) and up to 6–8 km in the eastern GMA during 20–13 Ma were assumed, while exhumation amounts of both the eastern and central GMA post ∼13 Ma were <2 km, except for north–south rifting zone and river valley. These observations imply that porphyry deposits formed prior to 20 Ma should sparsely preserve, whereas those generated after Early Miocene should preserve well and thus have preservation potential. However, the occurrence of Xiongcun porphyry deposit with intensive exhumation indicates it had been buried by post-mineralization volcano-sedimentary rocks. Therefore, the temporal-spatial distribution of the porphyry deposit in the GCMB is largely controlled by the combination of burial, uplift, and exhumation. The two stages of exhumation in the Xiongcun deposit resemble with those of the entire GCMB. The Early Miocene rapid exhumation might be regulated by Xietongmen-Lhasa-Oiga brittle-ductile shear (XLOBDS), while the Late Miocene rapid exhumation might be associated with incision of Yarlung River.

Post-collisional exhumation of the Indus-Yarlung suture zone and Northern Tethyan Himalaya, Saga, SW Tibet

The Cretaceous-Eocene sedimentary sequences of the Sangdanlin section at Saga, SW Tibet, within the India-Asia collisional zone, have been studied in detail for constraining the timing of initial collision. However, the post-depositional history has not been investigated. Here, we report new low temperature thermochronology data along the classic Sangdanlin section, to reveal the cooling/exhumation history of the Indus-Yarlung suture zone (IYSZ) and northern Tethyan Himalaya. Samples from the IYSZ, all yield latest Oligocene-Miocene ages, with most zircon (U-Th)/He ages ranging between ~18 and 27 Ma and apatite fission track (AFT) ages of ~12–9 Ma. Thermal history modelling indicates a consistent Middle-Late Miocene cooling episode related to post-Great Counter Thrust (GCT) incision of the Yarlung River. To the south, samples from the northern Tethyan Himalaya Mesozoic sequences yield older ZHe ages of ~32–36 Ma, signifying activity of the Tethyan Himalayan fold-thrust zone, while two granites linked to formation of the North Himalayan gneiss domes yield Late Miocene AFT ages. The regional low temperature thermochronology data reveal different cooling patterns for tributaries on the northern and southern sides of the Yarlung River. This points to the strong influence of Early Miocene tectonism along the GCT, as a major controlling factor on river drainage reorganization at this time.

Gangdese culmination model: Oligocene–Miocene duplexing along the India-Asia suture zone, Lazi region, southern Tibet

The mechanisms for crustal thickening and exhumation along the Yarlung (India-Asia) suture in southern Tibet are under debate, because the magnitudes, relative timing, and interaction between the two dominant structures—the Great Counter thrust and Gangdese thrust—are largely unconstrained. In this study, we present new geologic mapping results from the Yarlung suture zone in the Lazi region, located ∼350 km west of the city of Lhasa, along with new igneous (5 samples) and detrital (5 samples, 474 ages) U-Pb geochronology data to constrain the crystallization ages of Jurassic–Paleocene Gangdese arc rocks, the provenance of Tethyan Himalayan and Oligocene–Miocene Kailas Formation strata, and the minimum age (ca. 10 Ma) of the Great Counter thrust system. We supplement these data with a compilation of 124 previously published thermochronologic ages from Gangdese batholith, Kailas Formation, and Liuqu Formation rocks, revealing a dominance of 23–15 Ma cooling contemporaneous with slip across the Great Counter thrust system and other potentially linked structures. These data are systematically younger than 98 additional compiled thermochronologic ages from the northern Lhasa terrane, recording mainly Eocene cooling. Structural and thermochronologic data were combined with regional geological constraints, including International Deep Profiling of Tibet and the Himalaya (INDEPTH) seismic reflection data, to develop a new structural model for the Oligocene–Miocene evolution of the Tethyan Himalaya, Yarlung suture zone, and southern Lhasa terrane. We propose that a hinterland-dipping duplex beneath the Gangdese mountains, of which the Gangdese thrust is a component, is kinematically linked with a foreland-dipping passive roof duplex along the Yarlung suture zone, the Great Counter thrust system. The spatial and temporal convergence between the proposed duplex structures along the Yarlung suture zone and the South Tibetan detachment system indicate that they may be kinematically linked, though this relationship is not directly addressed in this study. Our interpretation, referred to as the Gangdese culmination model, explains why the Gangdese thrust system is only locally exposed (at relatively deeper structural levels) and provides a structural explanation for early Miocene crustal thickening along the Yarlung suture zone, relief generation along the modern Gangdese Mountains, early Miocene Yarlung River establishment, and creation of the modern internal drainage boundary along the southern Tibetan Plateau. The progression of deformation along the suture zone is consistent with tectonic models that implicate subduction dynamics as the dominant control on crustal deformation.

India‐Asia convergence: Insights from burial and exhumation of the Xigaze fore‐arc basin, south Tibet

AbstractThe composite fore‐arc/syncollisional Xigaze basin in south Tibet preserves a key record of India‐Asia collision. New apatite fission track and zircon (U‐Th)/He data from an N‐S transect across the preserved fore‐arc basin sequence near Xigaze show a consistent northward Late Cretaceous to middle Miocene younging trend, while coexisting apatite (U‐Th‐Sm)/He ages are all Miocene. Corresponding detrital zircon U‐Pb data are also reported for constraining the Cretaceous depositional ages of the Xigaze basin sequence in the region. Thermal history modeling indicates that the basin experienced northward propagating episodic exhumation, along with a northward migration of the depocenter and a pre‐existing Cenozoic syncollisional basin sequence which had been removed. In the southern part, fore‐arc exhumation commenced in the Late Cretaceous (~89 ± 2 Ma). Following transition to a syncollisional basin in the Paleocene, sedimentation in the central and northern Xigaze basin continued until the latest Eocene (~34 ± 4 Ma). Ongoing folding and thrusting (e.g., Great Counter Thrusts) caused by progressive plate convergence during late Oligocene‐early Miocene time resulted in regional uplift and considerable basin denudation, which fed two fluvial basins along its northern and southern flanks and exposed the basement ophiolite. Subsequent incision of the Yarlung River resulted in Miocene cooling in the region. Different episodes in the exhumation history of the Xigaze basin, caused by thrusting of an accretionary wedge and ophiolitic basement, can be linked to changes in India‐Asia convergence rates and the changing subduction pattern of the Indian and Neo‐Tethyan slabs.

Tectonic and erosional history of southern Tibet recorded by detrital chronological signatures along the Yarlung River drainage

The Indus-Yarlung suture zone, within the larger Indo-Asia collision zone in southern Tibet, is characterized by a central depression with two oppositely directed axial rivers: the eastward-flowing Yarlung River and the westward-flowing Indus River. The axial valley is flanked by high-elevation ranges of the southern Lhasa terrane to the north and the Tethyan Himalaya to the south. This study analyzes the detrital geochronological and thermochronological signatures of rivers draining into the Indus-Yarlung suture zone as a proxy for the timing of tectonic, magmatic, and erosional processes in southern Tibet. Zircon U-Pb ages reflect source area crystallization ages, and their distribution is proportional to the relative area of source rocks exposed in the catchment areas. Rivers draining the northern side of the collision zone are dominated by ages between ca. 40 Ma and ca. 60 Ma, similar to ages of rocks in the Gangdese arc, whereas one river sample draining the southern side records a Tethyan Himalayan signature characterized by age clusters at ca. 500 Ma and ca. 1050 Ma. U-Pb zircon ages from the modern drainages are similar to signals preserved in the Oligocene−Miocene Liuqu and Kailas basins, suggesting that the geology of the Cenozoic drainages was similar to modern, albeit with significant erosion in the Miocene. New apatite fission-track (AFT) ages from some of the same rivers show an early Miocene regional exhumation signature, which is interpreted to record regional uplift-induced erosion coupled with efficient river incision by the Indus-Yarlung fluvial system as a result of renewed underthrusting (following rollback) of India under Asia. Late Miocene (ca. 8 Ma) apatite (U-Th)/He (AHe) ages are consistent with cooling and exhumation associated with E-W extension followed by a decrease in erosion after ca. 6 Ma.

The Liuqu Conglomerate, southern Tibet: Early Miocene basin development related to deformation within the Great Counter Thrust system

The Liuqu basin formed during the early Miocene between ophiolitic melanges (to the south) and uplifted Cretaceous forearc deposits (to the north) along a central, 150-km-long segment of the India-Asia suture zone in southern Tibet. Sedimentological analysis shows the Liuqu Conglomerate to be composed of mixed fluvial and sediment-gravity flow lithofacies assemblages locally interbedded with mature paleosols. We interpret the Liuqu Conglomerate as coarse-grained fluvial and alluvial-fan deposits. Structural analysis indicates that the Liuqu Conglomerate was deposited in a contractional setting. Paleocurrent and provenance data demonstrate that sediment was transported north-northwest from the hanging wall of a coeval thrust fault system along the southern limit of Liuqu outcrops. Detrital zircon U-Pb ages (and Hf[ t ] isotope ratios) cluster around 80–110 Ma (eHf[t] = −23.5–14.6), 120–135 Ma (eHf[t] = −12.6–13.1), 150–170 Ma (eHf[t] = −14.1–14.7), 500–600 Ma (eHf[t] = −26–3.4), and 1100–1200 Ma (eHf[t] = −27.6–2.9), requiring input from both Gangdese and melange sources. Asian zircons were recycled northward after being incorporated into accretionary melanges along the southern Asian margin prior to India-Asia collision. The age of the Liuqu Conglomerate is still somewhat uncertain, but new chronologic data, including biotite 40Ar/39Ar data, detrital zircon fission-track analyses, and δ13C compositions of soil carbonates, all converge on ca. 20–19 Ma as the most probable age. Together, these results indicate that part of the north-to-south sediment transport system that existed prior to India-Asia collision and into the Eocene was reversed by ca. 20 Ma. The Liuqu Conglomerate may represent deposits associated with the paleo–Yarlung River.