Guocan Wang

Timing and rate of exhumation along the Litang fault system, implication for fault reorganization in Southeast Tibet

The Litang fault system that crosses the Litang Plateau, a low relief surface at high elevation (~4200–4800 m above sea level) that is not affected by regional incision, provides the opportunity to study exhumation related to tectonics in the SE Tibetan Plateau independently of regional erosion. Combining apatite and zircon fission track with apatite (U-Th)/He thermochronologic data, we constrain the cooling history of the Litang fault system footwall along two transects. Apatite fission track ages range from 4 to 16 Ma, AHe ages from 2 to 6 Ma, and one zircon fission track age is ~99 Ma. These data imply a tectonic quiet period sustained since at least 100 Ma with a slow denudation rate of ~0.03 km/Ma, interrupted at 7 to 5 Ma by exhumation at a rate between 0.59 and 0.99 km/Ma. We relate that faster exhumation to the onset of motion along the left-lateral/normal Litang fault system. That onset is linked to a Lower Miocene important kinematic reorganization between the Xianshuihe and the Red River faults, with the eastward propagation of the Xianshuihe fault along the Xiaojiang fault system and the formation of the Zhongdian fault. Such strike-slip faults allow the sliding to the east of a wide continental block, with the Litang fault system accommodating differential motion between rigid blocks. The regional evolution appears to be guided by the strike-slip faults, with different phases of deformation, which appears more in agreement with an “hidden plate-tectonic” model rather than with a “lower channel flow” model.

Neogene Source-to-Sink Relations between the Pamir and Tarim Basin: Insights from Stratigraphy, Detrital Zircon Geochronology, and Whole-Rock Geochemistry

The Tarim Basin, as the largest inland basin on the planet, provides a valuable opportunity to understand the mountain building of the northern Tibetan Plateau and its effects on basin development. Here we present a synthesis of sedimentology, zircon U-Pb geochronology, and bulk-rock geochemistry of Neogene sediments in the Qimugan section, southwest Tarim Basin. Spatial variation in zircon U-Pb age distributions from early Miocene clasts at Qimugan and Oytag suggest significant dextral strike-slip on the Kashgar-Yecheng transfer system likely commenced during the Oligocene–early Miocene. Over time, age peaks of ∼20 and ∼107 Ma in a middle Miocene sample at Qimugan suggest significant headwater erosion of the ancient Yarkand River reached the southeast Pamir–Karakoram hinterland as it does today. This is coincident with a relatively steady decrease in chemical weathering of source terranes during the middle-late Miocene, suggesting a climate transition from warm and/or humid to cool and/or dry in the Pamir-Karakoram. Under global cooling, middle Miocene changes in both provenance and geochemistry at Qimugan require topographic growth of the Pamir-Karakoram interior at that time, coeval with initial formation of the fold-thrust system and doming of the Muztaghata massif in the eastern Pamir, in addition to a prominent depocenter shift and sediment load in the southwest Tarim Basin. Subsequently, stable sediment provenance and depocenters suggest the current tectonic-sedimentary configuration in the eastern Pamir–southwest Tarim Basin has been established since the middle-late Miocene. These observations can be explained by a model of crustal contraction below the southeast Pamir–Karakoram and strain propagation to the Tarim Basin, possibly related to resumed Indian crust subduction. Our results thus support compressional deformation extended to all margins of the northern Tibetan Plateau by the middle-late Miocene.

Ordovician radiolarians from the Yinisala ophiolitic mélange and their significance in western Junggar, Xinjiang, NW China

The Yinisala ophiolitic mélange is located in the southern part of the Xiemisitai Mountains in western Junggar (NW China), and is composed of mafic-ultra mafic rocks, siliceous blocks, marble (marbleized limestone) and pyroclastic rocks, which all crop out as faulted blocks. Rich radiolarian and sponge spicule fossils are found in the siliceous rock for the first time. There are six genera of radiolarians (including one gen. et sp. Indet.) belonging to two families: Inaniguttid gen. et sp. Indet., Inanigutta sp., Inanibigutta sp., Inanihella bakanasensis (Nazarov), Triplococcus acanthicus (Danelian and Popov), Antygopora sp., which are identified to be of late Early to Middle Ordovician age, representing the upper limit of the formation age of the Yinisala ophiolite mélange. The ophiolites were developed in the Early Cambrian-Middle Ordovician oceanic environment, probably an important part of the early Paleozoic Paleo-Asian Ocean, based on the composition and structure of the siliceous rock and associated deep-water fossils. The Yinisala, Taerbahatai, and Hongguleleng ophiolitic mélange belts can be correlated as a suite of unified subduction accretionary complex, which extends eastward to the eastern Junggar. We consider that there existed an ancient ocean connecting the east and west of northern Junggar in the Early Cambrian-Middle Ordovician.

Fission Track Geochronology of Xiaonanchuan Pluton and the Morphotectonic Evolution of Eastern Kunlun since Late Miocene

ABSTRACT Apatite fission track (AFT) thermochronology of seven samples from the Xiaonanchuan ( ) pluton in the Kunlun ( ) pass area was carried out, for the purpose of determining the timing of cooling and the relation between the exhumation and the morphotectonic processes. The AFT ages yield low denudation rates of 0.020–0.035 mm/a during the late Miocene, which correspond to a stable geomorphic and weak tectonic uplifting environment. The low denudation rates can be considered as the approximate tectonic uplifting rates. The AFT geochronology shows paroxysmally rapid cooling since the Pliocene and an apparent material unroofing of more than 3 km in the Xiaonanchuan area. This was not the result of simple denudation. The rapid cooling was coupled with the intensive orogeny since the Pliocene, which was driven by tectonic uplifting. The accelerated relief building was accompanied by a series of faulting, which caused the basin and the valley formation and sinking. The space pattern of the AFT ages also shows differential uplifting, which decreases northwardly. This trend is supported by the regional AFT data, which indicate that the exhumation decreases northwardly in eastern Kunlun. This trend also exists in east-west orientation from the western Kunlun range to the eastern. The uplifting trend is also supported by geomorphic characteristics including the elevation and the relief differences as well as the distribution of the Late Cenozoic volcanism.

On the Geodynamic Mechanism of Episodic Uplift of the Tibetan Plateau during the Cenozoic Era

: Multi-stage uplift of the Tibetan Plateau during the Cenozoic implies a complex geodynamic process. In this paper, we review main geodynamic models for the uplift of the plateau, and, in particular, analyze the spatio-temporal framework of the Cenozoic deformation structures, which are closely related to the deep geodynamic mechanism for the plateau uplift. From this perspective, significant change of the deformation regime over the Tibetan Plateau occurred by the middle-late Miocene, while thrust and thrust-folding system under NS compression was succeded by extension or stress-relaxation. Meanwhile, a series of large-scale strike-slip faults commenced or was kinemtically reversed. Based on a systematic synthesis of the structure deformation, magmatism, geomorphological process and geophysical exploration, we propose a periodical model of alternating crustal compression and extension for episodic uplift of the Tibetan Plateau.

Controls on Cenozoic exhumation of the Tethyan Himalaya from fission‐track thermochronology and detrital zircon U‐Pb geochronology in the Gyirong basin area, southern Tibet

The Gyirong basin, southern Tibet, contains the record of Miocene-Pliocene exhumation, drainage development, and sedimentation along the northern flank of the Himalaya. The tectonic controls on basin formation and their potential link to the South Tibetan Detachment System (STDS) are not well understood. We use detrital zircon (ZFT) and apatite (AFT) fission-track analysis, together with detrital zircon U-Pb dating to decipher the provenance of Gyirong basin sediments and the exhumation history of the source areas. Results are presented for nine detrital samples of Gyirong basin sediments (AFT, ZFT, and U-Pb), two modern river-sediment samples (ZFT and AFT), and six bedrock samples (ZFT) from transect across the Gyirong fault bounding the basin to the east. The combination of detrital zircon U-Pb and fission-track data demonstrates that the Gyirong basin sediments were sourced locally from the Tethyan Sedimentary Sequence. This provenance pattern indicates that deposition was controlled by the Gyirong fault, active since ~10 Ma, whose vertical throw was probably < ~5000 m, rather than being controlled by normal faults associated with the STDS. The detrital thermochronology data contain two prominent age groups at ~37–41 and 15–18 Ma, suggesting rapid exhumation at these times. A 15–18 Ma phase of rapid exhumation has been recorded widely in both southern Tibet and the Himalaya. A possible interpretation for such a major regional exhumation event might be detachment of the subducting Indian plate slab during the middle Miocene, inducing dynamic uplift of the Indian plate overriding its own slab.

Overexploitation status of groundwater and induced geological hazards in China

Abstract During the process of urbanization and industrialization, groundwater has been extensively overexploited, with the direct result of continuously decreasing groundwater level, followed by the appearance of large scale of depression cones, which is furthermore followed by land subsidence, seawater intrusion, and increasing difficulties in subsequent groundwater exploitation. This paper makes an analysis on the geological disasters caused by overexploitation of groundwater. The consumption and overexploitation status of groundwater in representative regions in China is discussed first, with the distribution and development of depression cones elaborated the next. And the problems of land subsidence, seawater intrusion, and increasing difficulties caused by overexploitation of groundwater are analyzed at last. Results show that overexploitation of groundwater is positively related to economic development. Moreover, geological disasters such as land subsidence and seawater intrusion caused by long term of overexploitation also aggregate, posing threats, and losses to people’s lives and production. According to the analysis, the fundamental resolution for overexploitation of groundwater as well as consequential geological damages is to properly control city size and to utilize groundwater rationally and efficiently.

Wet tropical climate in SE Tibet during the Late Eocene

Cenozoic climate cooling at the advent of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago, was stamped in the ocean by a series of climatic events albeit the impact of this global climatic transition on terrestrial environments is still fragmentary. Yet archival constraints on Late Eocene atmospheric circulation are scarce in (tropical) monsoonal Asia, and the paucity of terrestrial records hampers a meaningful comparison of the long-term climatic trends between oceanic and continental realms. Here we report new sedimentological data from the Jianchuan basin (SE Tibet) arguing for wetter climatic conditions in monsoonal Asia at ~35.5 Ma almost coevally to the aridification recognized northwards in the Xining basin. We show that the occurrence of flash-flood events in semi-arid to sub-humid palustrine-sublacustrine settings preceded the development of coal-bearing deposits in swampy-like environments, thus paving the way to a more humid climate in SE Tibet ahead from the EOT. We suggest that this moisture redistribution possibly reflects more northern and intensified ITCZ-induced tropical rainfall in monsoonal Asia around 35.5 Ma, in accordance with recent sea-surface temperature reconstructions from equatorial oceanic records. Our findings thus highlight an important period of climatic upheaval in terrestrial Asian environments ~2–4 millions years prior to the EOT.

Environmental evolution of the south margin of Qaidam Basin reconstructed from the Holocene loess deposit by n-alkane and pollen records

This study provides the n-alkane and pollen records of the Holocene loess at Balong (巴隆) Town, Dulan (都兰) County, Qinghai (青海) Province, and the environmental changes reconstructed from both records agreed well. Three stages of past climate change were deciphered by variations of the n-alkane and pollen proxies. Before 5 370 a BP, the climate was warm-dry but slightly humid, corresponding to the Mid-Holocene climatic optimum; 5 370–3 830 a BP, the climate changed alternatively between warm-dry slightly humid and warm-dry, indicating the transition from the Mid-Holocene climatic optimum to the Late Holocene cold period; after 3 830 a BP, the climate was mainly warm-dry. The warm cool and extremely dry climate during 3 040–2 600 a BP was recorded by both the n-alkane and pollen proxies, suggesting the environment evolved into desert or salt lake, in accordance with the cold and highly frequent natural disaster period in the Western Zhou Dynasty (ca. 2 996–2 721 a BP) in China.

Palaeogene–Neogene Stratigraphic Sequences of the Tibetan Plateau and Their Response to Plateau Uplift

A total of 98 remnant basins and 5 stratigraphic domains with 13 stratigraphic subdomains have been recognized on the Tibetan Plateau. Through investigating the types of remnant basin, the tectonic setting, the stratigraphic sequences and sedimentary characteristics, and the evolution of the sediments, we divide the uplift process and sedimentary response for the Tibetan Plateau into three stages and eight substages. These are the subduction–collision uplift stage (65–34 Ma) with three substages, the intercontinental convergence and compressive uplift stage (34–13 Ma) with three substages, and the intercontinental isostatic adjustment uplift stage (since 13 Ma) with two substages.