Northern Qinghai-Tibet Plateau Research Articles

New Rock Magnetism and Magnetic Fabrics Studies on the Late Triassic Volcanic Rocks from Qaidam Block, Northern Tibetan Plateau

The Qaidam Block, located at the northern Qinghai–Tibet Plateau, is a pivotal area in unraveling the closure time of the Kunlun Ocean basin which might have recorded the transformation process between the Proto-Tethys and Paleo-Tethys Ocean basins. However, the late Triassic position of the Qaidam Block remains enigmatic, largely due to the scarcity of paleomagnetic data essential for quantitatively determining its paleolatitude. The widespread presence of the Elashan formation, particularly along the southern periphery of the Qaidam block, presents good material for conducting paleomagnetic work. Nevertheless, the primary magnetic carriers preserved within the Elashan formation might be influenced by multiple tectonic thermal events, particularly those associated with collisions between southern blocks and the Qaidam Block. Here we present rock magnetism and magnetic fabrics studies to identify the content and composition of magnetic minerals within the Elashan formation. The rock magnetic and petrologic results show that the magnetic carriers in the samples from the Elashan formation are dominated by magnetite with a small amount of goethite, pyrrhotite, and hematite. The results of Anisotropy in Magnetic Susceptibility indicate that the south of the Longwalangku section might not be obviously influenced by the tectonic events. Our results also provided guidance for future paleomagnetic research, emphasizing the importance of conducting further sampling away from adjacent faults, particularly in the southern Longwalangku area.

Late Holocene vegetation diversity change and potential response to climate variations on the northern Qinghai-Tibetan Plateau

Biodiversity change under current global warming scenario has attracted wide attentions, representing general stability and balance in ecosystems. Understanding the temporal patterns and potential driving mechanisms of biodiversity changes would provide significant knowledge for ecosystem sustainability, which requires necessary investigations on long-term records during the late Holocene. The high elevation and specific environment on the Qinghai-Tibetan Plateau (QTP) promote the development of fragile alpine ecosystems, responding sensitively to regional climate variations. Based on a high-resolution fossil pollen record retrieved from Lake Kusai on the northern QTP, late Holocene vegetation diversities were estimated based on the Hill number indices, which were subsequently evaluated at three time scales, i.e., millennial, centennial and multi-decadal time scales. The results indicate that Hill number indices could represent vegetation diversity changes on the northern QTP. Reconstructed vegetation diversity indices indicate gradual variations on millennium scale in each diversity index, along with different responses to environmental factors of regional moisture and total solar irradiance. On the centennial time scale, high consistencies were identified among the vegetation diversity indices as well as correlations with environmental factors, revealing overall positive responses between diversity variations and environmental changes. Rather complicated correspondences to environmental factors appeared on the multi-decadal scale, showing different patterns in diversity indices, which illustrates variations through time as well. Accordingly, vegetation diversity changes of the alpine communities on the northern QTP experienced serious variations during the late Holocene, and revealed complicated responses to regional environmental changes, that further investigations particularly at different time scales would be necessary in the future.

Source and Formation of Boron Deposits in Mahai Basin on the Northern Qinghai-Tibet Plateau: Clues from Hydrochemistry and Boron Isotopes

Source and Formation of Boron Deposits in Mahai Basin on the Northern Qinghai-Tibet Plateau: Clues from Hydrochemistry and Boron Isotopes

N limitation may inhibit the effectiveness of close-to-nature restoration measures for degraded alpine meadows on the northern Qinghai‒Tibet Plateau

As important terrestrial ecosystems on the Qinghai‒Tibet Plateau with important ecological and economic value, alpine meadows in some regions are in a degraded state due to climate change and unsustainable grazing. Due to the fragile ecological environment, exploring sustainable restoration models of degraded alpine meadows using close-to-nature restoration measures is the direction of ongoing efforts. Thus, in this study, three close-to-nature restoration measures, namely, manure application (M), Poa annua, Elymus dahuricus, and Puccinellia distans mixed with non-tillage reseeding (R), and the combined treatments (MR), were used to restore degraded alpine meadows from 2019 to 2021. The results showed that the M and MR treatments significantly enhanced plant biomass and reduced forbs dominance, thus improving community structure. Moreover, the M and MR treatments significantly affected plant and bacterial alpha diversity. However, the three restoration measures did not alter the correlation between the plant and bacterial communities. Furthermore, these three measures resulted in a significant increase in the plant carbon:nitrogen ratio and a significant decrease in the nitrogen:phosphorus ratio, while neither the plant carbon:phosphorus ratio nor the soil stoichiometric ratio changed significantly, indicating that nitrogen limitation was an important factor that limited the recovery process of the alpine meadows. The structural equation model indicated that the plant nitrogen:phosphorus ratio may regulate the response of plant and bacterial diversity to different restoration measures in alpine meadows. Our findings emphasize that the management of degraded alpine meadows using close-to-nature restoration measures should be a long-term effort, with more attention given to changes in the nitrogen content of meadow ecosystems.

Topographic Drivers of Permafrost Organic Carbon Accumulation on the Northern Qinghai–Tibet Plateau

ABSTRACTLarge amounts of soil organic carbon (SOC) have accumulated over thousands of years in the northern permafrost regions. However, the SOC accumulation rates and the effects of topography, vegetation, and soil properties on SOC storage remain poorly constrained, leading to large uncertainties in the estimation of SOC storage and its response to warming. Here, we examined SOC stocks, densities, and accumulation rates using field sampling and radiometric dating in areas with different topographic parameters on the northern Qinghai–Tibet Plateau. Results show that SOC density and stock increases with elevation on south‐facing slopes but decreases with elevation on north‐facing slopes. The carbon accumulation rates in the upper 6 m soil are highest (16.32 g C m−2 year−1) in the north‐facing alpine wet meadow and lowest (1.07 g C m−2 year−1) in the south‐facing alpine steppe. Elevation‐, slope‐, and slope aspect‐induced variations in soil properties and vegetation type are the main factors controlling the spatial SOC distribution. These results imply that the topography strongly affects the spatial heterogeneity of SOC in mountainous permafrost regions. Overall, our findings highlight that topographic factors should be further integrated into carbon models of carbon responses to climate change in permafrost‐affected soils.

Re-intensification of flash drought in western China over the past decade: Implications of fluctuating wetting trend

Climate changes and human activities have led to a rise of frequency and intensity of the global flash droughts, resulting in severe consequences for ecosystems, agriculture, and human societies. However, research dedicated to flash droughts in the dryland of western China is relatively limited, leaving their evolutionary characteristics and development processes of these phenomena unclear. To bridge this gap, this study analyzed the spatiotemporal characteristics of flash droughts in western China from 1981 to 2020, based on the standardized evapotranspiration stress index. Additionally, we investigated the development mechanisms by taking meteorological conditions and soil moisture into account. The findings revealed that the northern Qinghai-Tibet Plateau, western Qilian Mountains, and western and southern Loess Plateau are hotspots of flash droughts, characterized by rapid development rates. Across most of the study area, flash drought events persisted between 25 and 30 days. Adequate precipitation is necessary before the onset of flash droughts in western China, while water scarcity and high temperatures played crucial roles in driving the mid-stage of flash droughts. Within the context of the observed “warming and wetting” trend, the average flash droughts occurrence from 2011 to 2020 was approximately 16 % lower than that from 1981 to 1990, and there was a significant annual decrease in spatial coverage of 0.01 % per year. However, in the “wetting in west, drying in east” trend, the spatial coverage of flash droughts has shifted from a declining trend to an insignificant increasing trend since 2000 in the study area, with significant regional differences between the western and eastern regions. Over the past decade, flash droughts had once again intensified in the central Qinghai-Tibet Plateau and the Loess Plateau due to warming and fluctuating wetting trends, raising significant concerns for future ecosystem and agricultural water management in these regions.

Biocrust-reduced soil water retention and soil infiltration in an alpine Kobresia meadow

Abstract. Biocrust is a key component of ecosystems and plays a vital role in altering hydrological processes in terrestrial ecosystems. The impacts of biocrust on hydrological processes in arid and semi-arid ecosystems have been widely documented. However, the effects and mechanisms of biocrust on soil hydrological processes in alpine ecosystems are still poorly understood. In this study, we selected two meadow types from the northern Qinghai–Tibet Plateau: normal Kobresia meadow (NM) and biocrust meadow (BM). Both the soil hydrological and physicochemical properties were examined. We found that, in the 0–30 cm soil layer, soil water retention and soil water content in NM were higher than those in BM, whereas the 30–40 cm layer's soil water retention and soil water content in NM were lower than those in BM. The topsoil infiltration rate in BM was lower than that in NM. Furthermore, the physicochemical properties were different between NM and BM. The 0–10 cm soil layer's clay content in BM was 9 % higher than that in NM, whereas the 0–30 cm layer's soil capillary porosity in NM was higher than that in BM. In addition, the 0–20 cm layer's soil total nitrogen (TN) and soil organic matter (SOM) in NM were higher than those in BM, implying that the presence of biocrust may not favor the formation of soil nutrients owing to its lower soil microbial biomass carbon and microbial biomass nitrogen. Overall, soil water retention was determined by SOM by altering the soil capillary porosity and bulk density. Our findings suggest that the establishment of cyanobacteria crust biocrust may not improve soil water retention and infiltration, and the soil in cyanobacteria crust meadows could be more vulnerable to runoff generation and consequent soil erosion. These results provide a systematic and comprehensive understanding of the effects of biocrust on the soil hydrology of alpine ecosystems.

The Ahadawa deposit—A newly discovered porphyry Cu–Mo system in the North Qaidam, Northern Qinghai-Tibet Plateau, NW China

Ongoing exploration in the North Qaidam, Northern Qinghai-Tibet Plateau, NW China, has led to the identification of a porphyry Cu-Mo system centered on Ahadawa. In this study, we conducted a detailed geochronological and geochemical study on porphyritic monzogranite from the Ahadawa deposit, which hosts the Cu-Mo mineralization. The weighted mean zircon U-Pb ages for three mineralized porphyritic monzogranite samples from different sites range from 218.8 ± 1.2 Ma (MSWD = 1.5) to 224.7 ± 1.6 Ma (MSWD = 1.8), and finally to 233.1 ± 0.9 Ma (MSWD = 1.4, n = 23). These results, combined with antecrystic grains as old as ∼ 245.7 Ma, collectively indicate more than 25 Ma multi-stage magmatic emplacement activity in the Ahadawa deposit. Corresponding to complex magma episodes, six studied molybdenite samples yielded variable Re-Os model ages ranging from 436.7 ± 6.6 to 232.6 ± 1.2 Ma, with the three youngest dates constraining a weighted mean Re-Os age of 234.0 ± 6.8 Ma. The 234 Ma mineralization age is consistent with the observed Late Triassic magmatism, whereas the Re-Os model ages of 436.7 to 245.7 Ma, if they remain robust through future investigation, may highlight a long-lived hydrothermal activity in the Ahadawa deposit. Whole-rock and zircon compositions indicate that the Late Triassic porphyries occurring at the surface display distinct geochemical features, with the early porphyritic monzogranite of 233.1 Ma characterized by much higher whole-rock Sr/Y, and zircon Eu/Eu* and Ce/Ce* than the younger (218.8 Ma and 224.7 Ma, respectively) porphyritic monzogranite. This suggests that the Late Triassic magmas were initially characterized by high water content and high oxidation state and the differences between the old and two younger groups might be related to plagioclase-dominated fractionation. The finding of the Ahadawa porphyry system highlights the need for ongoing exploration (especially in poorly studied remote areas) and systematically geochronological and geochemical studies to constrain the temporal and spatial evolution of mineralized episodes within a complex, protracted magmatic history.

Regional tectonic uplift indicated by geomorphological parameters in the Bahe River Basin, central China

Abstract Multiple uplifts of the Qinghai-Tibet Plateau since the late Cenozoic have generated large effects on the geomorphology and environment over Asia. However, how the basin responded to the uplifted Tibetan Plateau remains unknown. Here, we examined the digital geomorphology of the Bahe River basin, the greatest first-order tributary in the southern Weihe River basin. The geomorphogenesis of the watershed, the far-field effects, and the long-range consequences of the elevation from the Tibetan Plateau were thoroughly discussed. We found that there were five layers of terraces, which were mainly controlled by tectonic activity. The geomorphological characteristics suggested that Bahe basin was influenced by a severe tectonic activity prime, with intense river erosion. The Lishan-North Qinling Mountains uplift, facilitated by the horizontal expansion of the northern Qinghai-Tibet Plateau, was also responsible for the development of the Bahe River basin.

Conservation Effectiveness Assessment of the Three Northern Protection Forest Project Area

The Three-North Shelterbelt Project is the largest ecological engineering initiative in China to date, distinguished by its immense scale, extended construction period, and widespread benefits for the population. The gross ecosystem product (GEP) serves as a crucial indicator for assessing ecological benefits. This study focuses on the Three Northern Protection Forest Project Area, utilizing GEP calculations for the years 2000 to 2020. This study evaluates variations in the production values of different ecosystem services to reflect the ecological conservation benefits of the restoration project. Additionally, it analyzes the spatiotemporal evolution and trends of the GEP calculations, offering data references and decision support for the enduring efficacy of ecological restoration projects. The findings are as follows. (i) Between 2000 and 2020, the GEP of the Three-North region exhibited significant growth with continuous enhancement of various ecosystem service functions; the most substantial rate of change was observed in the water conservation function, followed by carbon sequestration and oxygen release, soil retention, windbreak and sand fixation, flood regulation, and environmental purification functions. (ii) The per-unit area value of different ecosystem types generally increased; the forest ecosystem displayed the largest growth rate at 61.18%, followed by shrubland ecosystems at 49.84%. (iii) The spatial distribution of ecosystem service in the Three-North region displayed a clustering trend alongside notable spatial heterogeneity. High-high clustering zones were identified in areas such as the Tianshan Mountains, Altai Mountains, Qilian Mountains, and Greater and Lesser Khingan Mountains. Conversely, low-low clustering areas were scattered, forming patchy distributions in regions like the Tarim Basin, northern Qinghai-Tibet Plateau, and the Hexi Corridor. This study, by analyzing the gross ecosystem product of the Three-North Shelterbelt Project region, unveils the spatial distribution characteristics, trends, and variations in ecosystem service values over the past two decades. It provides data support and decision guidance for the long-term efficacy of future ecological conservation and restoration projects. This study incorporates the GEP accounting method into the assessment of the effectiveness of major conservation projects. Compared to the traditional methods of effectiveness assessment, this represents a significant exploration and innovation.

Impacts of climate change on herpetofauna diversity in the Qinghai-Tibetan Plateau.

Although numerous studies on the impacts of climate change on biodiversity have been published, only a handful are focused on the intraspecific level or consider population-level models (separate models per population). We endeavored to fill this knowledge gap relative to the Qinghai-Tibetan plateau (QTP) by combining species distribution modeling (SDMs) with population genetics (i.e., population-level models) and phylogenetic methods (i.e., phylogenetic tree reconstruction and phylogenetic diversity analyses). We applied our models to 11 endemic and widely distributed herpetofauna species inhabiting high elevations in the QTP. We aimed to determine the influence of environmental heterogeneity on species' responses to climate change, the magnitude of climate-change impacts on intraspecific diversity, and the relationship between species range loss and intraspecific diversity losses under 2 shared socioeconomic pathways (SSP245 and SSP585) and 3 future periods (2050s, 2070s, and 2090s). The effects of global climatic change were more pronounced at the intraspecific level (22% of haplotypes lost and 36% of populations lost) than the morphospecies level in the SSP585 climate change scenario. Maintenance of genetic diversity was in general determined by a combination of factors including range changes, species genetic structure, and the part of the range predicted to be lost. This is owing to the fact that the loss and survival of populations were observed in species irrespective of the predicted range changes (contraction or expansion). In the southeast (mountainous regions), climate change had less of an effect on range size (>100% in 3 species) than in central and northern QTP plateau regions (range size <100% in all species). This may be attributed to environmental heterogeneity, which provided pockets of suitable climate in the southeast, whereas ecosystems in the north and central regions were homogeneous. Generally, our results imply that mountainous regions with high environmental heterogeneity and high genetic diversity may buffer the adverse impacts of climate change on species distribution and intraspecific diversity. Therefore, genetic structure and characteristics of the ecosystem may be crucial for conservation under climate change.

Supergene Hydrous Sulfates in the Tuolugou Co-Au Deposit, Northern Qinghai–Tibet Plateau: Implications for Genetic Mechanism and Exploration

Supergene hydrous sulfate minerals form through the oxygenation and weathering of primary sulfides. In the Qinghai–Tibet Plateau region, with an alpine and dry environment, hydrous sulfate minerals oxidized from pyrite-bearing ore bodies provide important clues regarding the mineralization and environment. The Tuolugou sedimentary-exhalative (SEDEX) Co-Au deposit is located in the East Kunlun metallogenic belt of the northern Qinghai–Tibet Plateau in China. In the mining district, pyrite is the prevalent Co-hosting sulfide mineral, and is partially exposed on the surface to weathering and oxidation. Herein, we document the mineral assemblages in the supergene oxidation zone in the Tuolugou deposit, probe the genesis of supergene assemblage, and explore the implications for exploration. Three zones can be recognized in the oxidation zone of the Tuolugou deposit, including the outer zone (natrojarosite), intermediate zone (rozenite and aplowite), and inner zone (roemerite and melanterite). The mechanism of oxidation under aerobic and anaerobic conditions, as well as zoning with different oxidation degrees, are described in detail. Hydrous sulfates such as natrojarosite can be used as possible indicators of the exploration of albitite-related SEDEX deposit in this region.

Warming and increasing precipitation induced greening on the northern Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP) has a fragile ecosystem that is sensitive to climate change. Due to the amplifying effect of climate change, the QTP has experienced rapid warming and shifting precipitation in recent decades, profoundly impacting the local ecosystem. However, the specific details of how vegetation responds to these changes were unclear, and the corresponding contributions were poorly quantified. Here, we employed an elastic net regression model to investigate the sensitivity of vegetation to climate factors across multiple time scales and various seasons. The vegetation activity was represented by the enhanced vegetation index (EVI), while climate change was represented by temperature, precipitation, photosynthetically active radiation (PAR), and soil moisture fraction (SMF). During 2000–2020, approximately 50 % of the QTP area showed greening, mainly concentrated in the northern region. Climate change explained approximately 70 % of the variation in vegetation during the growing season, 39 % in spring and 66 % in autumn. Grasslands exhibited the highest sensitive to climate change, with a relative contribution of 83 %, followed by mixed forests (70 %), forests (53 %) and deserts (52 %). Both temperature and precipitation significantly affected vegetation, with relative contributions of 29 % and 22 %, respectively, during the growing season. PAR and SMF had less impact on vegetation, with relative contributions of 8 % and 12 %, respectively. In the greening region, precipitation (26 %) was more important for vegetation growth compared to temperature (25 %). These findings emphasize the importance of precipitation on vegetation on the QTP, providing valuable insights for improving regional ecosystem assessment model and promoting the restoration of fragile ecosystems.

Sedimentary evolution of the embayed beach from Qinghai Lake, northern Qinghai-Tibetan Plateau, China

Sedimentary evolution of the embayed beach from Qinghai Lake, northern Qinghai-Tibetan Plateau, China

Exploring the spatial heterogeneity of ecosystem services and influencing factors on the Qinghai Tibet Plateau

Identifying the spatial heterogeneity characteristics of ecosystem services (ESs) and their influencing mechanisms is crucial for regional ecological management and sustainable development. This study quantified net primary production (NPP), water yield (WY), soil conservation (SC), sand fixation (SF), habitat quality (HQ) and total ecosystem service (TES) on the Qinghai Tibet Plateau (QTP), and then analyzed the spatial–temporal characteristics of ESs. The geographical detector model (GDM), geographically weighted regression (GWR) model, and constraint lines were used to explore the effects of influencing factors on ESs. The results showed that (1) NPP, WY, SC, HQ and TES showed an increasing trend from 2000 to 2018, while SF showed a decreasing trend. NPP, WY, SC and TES showed a spatial distribution pattern of “high values in the southeast and low values in the northwest”, while the high values of SF were located in the northern QTP and the high values of HQ were located in the southern QTP. (2) NDVI was the key factor influencing NPP, SC, HQ and TES, and precipitation dominated WY, and SF was mainly influenced by Largest patch index (LPI). (3) In most of the study areas, the natural factors (precipitation, temperature, DEM, slope and NDVI) had positive effects on NPP, SC and TES and both positive and negative effects on WY, SF and HQ. The human factors (Resident, Road and LPI) had positive effects on HQ and both positive and negative effects on other ESs. There were mainly non-monotonic constraint effects of influencing factors on ESs. Overall, natural factors had a much stronger influence on ESs than human factors, and the interactions among factors were much stronger than their independent effects. The results of this study can provide a basis for ecological protection on the QTP.

Carbon loss and emissions within a permafrost collapse chronosequence

Permafrost carbon release is potentially the largest terrestrial feedback contributing to climate change. However, the changes in carbon release caused by the abrupt thawing of permafrost and their controlling factors remain largely unknown. Here, we measured soil organic carbon (SOC), total nitrogen (TN) concentrations, and carbon dioxide (CO2) and methane (CH4) emission rates among seven permafrost collapse features over 3 years in the northern Qinghai-Tibetan Plateau (QTP). The results showed soil carbon and nitrogen loss caused by permafrost collapse ranged from − 12% to 28% and − 1% to 38%, respectively. We found there was a nonlinear relationship between soil carbon loss and permafrost collapse chronosequence. Permafrost collapse significantly reduced ecosystem respiration (Reco) and weakened carbon sinks. The net ecosystem exchange (NEE) decreased from − 2.59 to − 0.21 µmol CO2 m−2 s−1. The Reco and NEE values showed no significant changes over time after the initial permafrost collapse. In contrast, the CH4 fluxes increased over time following permafrost collapse, and the CH4 fluxes significantly increased 2 to 10 times in the exposed area compared with that in the control area. Soil temperature, moisture, and nutrient availability exerted the most controls over the carbon emission during permafrost collapse. This study provides the patterns of carbon loss and emissions in different permafrost collapse landscapes, which will provide deep insights and reliable data for future prediction of the abrupt thawing of permafrost-carbon feedback.

Genesis of the world-class Dachang gold deposit, northern Qinghai-Tibet Plateau: A multiproxy approach

Dachang is a world-class gold deposit that occurs in the Bayan Har Terrane, northern Qinghai-Tibet Plateau, with Au resources of 121 t at an average grade of 3.0 g/t. Although this deposit was investigated in some previous studies, its genesis remains debated. The deposit is controlled by the Gande-Maduo anticlinorium and thrust fault zone, and the orebodies occur in subsidiary interlayer faults or fractures in thin-bedded, stratatoid, lenticular and vein forms. The host strata belong to the Lower Triassic Bayan Har Shan Group consisting of metasandstone, metasiltstone, slate, and carbonaceous slate interlayered with phyllite. The mineralization of Dachang can be divided into the following four stages. Stage 1 gold-sulfide-quartz veins, stage 2 gold-sulfide-carbonate-quartz veins, stage 3 stibnite-quartz veins and stage 4 quartz-carbonate veins. There are two types of ores: altered rocks and quartz veins. The main ore minerals are pyrite, arsenopyrite, stibnite and native gold, with trace amounts of tetrahedrite, chalcopyrite, galena and sphalerite. The wallrock alteration comprises mainly sulfidation, silicification, carbonatization, and sericitization. The element association is As, Sb, Au, Te, Bi, Ag, W and Pb in order of enrichment factors, whereas Cu, Mo, and Sn are depleted relative to their crustal abundances.In this study, we identified three types of primary fluid inclusions in quartz from veins of the four mineralization stages as follows: type 1 liquid-dominated two-phase aqueous inclusions; type 2 aqueous-carbonic inclusions, including aqueous-dominated (type 2a) and carbonic-dominated inclusions (type 2b); and type 3 two-phase hydrocarbon inclusions. Microthermometric measurements of fluid inclusion assemblages (FIAs) and bulk fluid inclusion analyses show that the ore-forming fluids had similar low-salinity compositions (1.7 to 6.9 wt% NaCl equiv.) in the H2O-CO2-N2 system with trace amounts of hydrocarbons. The mineralization temperatures range from 150 to 200 °C, and estimated depths are approximately 5 to 6.5 km. Fluid/wallrock reactions and immiscibility or boiling during mineralization in response to pressure fluctuations in a brittle faults were the main triggers for gold precipitation at Dachang.The hydrogen, oxygen, carbon and He-Ar isotopic compositions indicate that the ore-forming fluids originated from metamorphic devolatilization of immediate- and deep-level country rocks and no meteoric water or mantle volatiles were involved. The organic carbon proportions account for 42 to 53% of the total carbon in ore-forming fluid, and carbon fractions from sedimentary carbonates range from 47 to 58%. The gold mineralization followed immediately after the regional metamorphism (240–225 Ma) and occurred when the host rocks had exhumated into a brittle environment. The Dachang deposit is an epizonal orogenic gold deposit.

Altitudinal variations of the rate and temperature sensitivity of soil nitrogen mineralization on the Qinghai-Tibetan Plateau

Abstract Changes in soil nitrogen mineralization can impact nutrient availability, and further affect plant growth. It is unclear, however, how temperature elevation in alpine grassland will affect soil net N mineralization rate (Nmin) across altitudes. At six altitudes (3200–4200 m with an interval of 200 m) along a slope in Lenglong mountain in the northern Qinghai-Tibetan Plateau, we performed an in situ soil incubation experiment by using the resin-core method to assess altitudinal variations of Nmin. Meanwhile, we evaluated the effects of temperature elevation on Nmin and its temperature sensitivity (Q10) through a soil downward transplantation experiment based on three reference baseline altitudes (3800, 4000 and 4200 m). The results showed that high altitudes generally led to low values of Nmin. Structural equation modeling analysis revealed that Nmin along the altitude was mainly controlled by soil temperature. Increased temperature caused by the altitude transplantation significantly elevated Nmin for all of the three reference altitudes. The value of Q10 was 3.4 for soil samples transplanted from the reference altitude of 4200 m, which was about twice that of the lower reference altitudes of 4000 and 3800 m.

Miocene Equisetum tubers from the Wulan Basin, Northeast Qinghai-Tibetan Plateau and their paleoecological significance

Equisetum fossils are often reported from the Cenozoic strata in the Northern Hemisphere, but their occurrence in the Qinghai-Tibetan Plateau (QTP) region is scarce. In this investigation, two new species of tuber fossils of Equisetum — Equisetum wulanense Zhang and Xie, n. sp. and Equisetum kekeense Zhang and Xie, n. sp. from the Miocene Youshashan Formation of the Wulan Basin, Qinghai Province are reported. The extant Equisetum plants are usually living in wet habitats. Therefore, fossil species, E. wulanense and E. kekeense, were likely to live in moist environments during Miocene too. The discovery of E. wulanense and E. kekeense in the late Middle Miocene (∼13.4 Ma) indicates that the local climate of the Wulan Basin was more favorable during this period. This new finding confirmed the previous view that the Neogene aridification in the northern QTP was varying: the climate in the Early Miocene and the Middle Miocene were relatively warm and humid and then the climate gradually became colder and drier since the Late Miocene. It is widely accepted that the uplift of the QTP intensified the trend of cooling and drying since the Late Miocene, and eventually formed a cold and dry climate pattern in the northeast margin of the QTP. The discovery of Equisetum fossils in this investigation improved our understanding on the Cenozoic diversity of Equisetum plants in the northern QTP, as well as on the paleoecological environments of the Wulan Basin in Miocene.

Proto-Tethys orogenic system in the northern Qinghai-Tibet Plateau: Resubdivision of lithotectonic units in Qilian-North Qaidam and discussion on several controversial scientific issues

Proto-Tethys orogenic system in the northern Qinghai-Tibet Plateau: Resubdivision of lithotectonic units in Qilian-North Qaidam and discussion on several controversial scientific issues