Carbon and oxygen isotopic constraints on paleoclimate and paleoelevation of the southwestern Qaidam basin,northern Tibetan Plateau     

Lin-Lin Li  Chao-Dong Wu  Chang-Fu Fan  Ji-Jun Li  Chang-Hao Zhang 《地学前缘(英文版)》2017,8(5):1175-1186

We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction and isotopic studies reveal that the carbonate minerals are mainly authigenic and they do not preserve any evidence for detrital carbonate and diagenesis. The isotope data show large fluctuations in the δ¹⁸O and δ¹³C values in the middle–late Eocene, indicating relatively warm and seasonal dry climate. The positive correlation of the δ¹⁸O and δ¹³C values in the Oligocene and the positive shift of the δ¹³C values from the Eocene to Oligocene suggest that the climate changed to arid in the Oligocene. However, the δ¹⁸O values show negative shift, which is closely related to the global cooling event. During the Miocene, the δ¹³C values vary between –2‰ and –4‰, whereas the δ¹⁸O values show continuous negative shift. The mean δ¹⁸O values decrease from –8.5‰ in the early Miocene to –10.0‰ in the late Miocene. The stable isotope-based paleoaltimetry results suggest that the elevation of the southwestern Qaidam basin was approximately 1500 m in the middle–late Eocene and Oligocene. Subsequently, during Miocene the crustal uplift process started and the elevation reached approximately 2000 m in the early Miocene and 2500 m in the late Miocene, which suggests large-scale growth of the northern Tibet Plateau during the Miocene.  相似文献   

Zircon geochronology reveals polyphase magmatism and crustal anatexis in the Buchan Block,NE Scotland: Implications for the Grampian Orogeny     

T.E. Johnson  C.L. Kirkland  D.R. Viete  S. Fischer  S.M. Reddy  N.J. Evans  B.J. McDonald 《地学前缘(英文版)》2017,8(6):1469-1478

The type locality for high-temperature,low-pressure regional metamorphism,the Buchan Block in NE Scotland,exhibits profound differences to the rest of the Grampian Terrane.These differences have led some to regard the Buchan Block as an exotic crustal fragment comprising Precambrian basement gneisses and cover rocks thrust into their current position during Grampian orogenesis.Although rocks of the Buchan Block are now generally correlated with Dalradian strata elsewhere,the origin of the gneisses and the cause of the high heat flow and associated magmatism is debated.We report SIMS U-Pb and LA-ICPMS Hf isotopic data in zircon from high-grade rocks from the northeast(Inzie Head Gneiss)and northwest(Portsoy)corners of the Buchan Block.Around Inzie Head,upper amphibolite to granulite facies metasedimentary gneisses coexist with diorite sheets that were emplaced contemporaneously with partial melting of their host rocks,at least locally.U-Pb geochronology indicates a crystallisation age for the diorite of 486±9 Ma.Highly-deformed diorites within the Portsoy Gabbro have a crystallisation age of 493±8 Ma.Ages of ca.490 Ma for magmatism and high-grade metamorphism,which are broadly contemporaneous with ophiolite obduction and the onset of orogenesis,are significantly older than the established peak of Grampian metamorphism(ca.470 Ma).We propose a new model for the Grampian Orogeny involving punctuated tectonothermal activity due to tectonic switching during accretionary orogenesis.Rollback of a NW-dipping subduction zone at ca.490 Ma produced a back-arc environment(the Buchan Block)with associated arc magmatism and high dT/dP metamorphism.Arrival of an outboard arc resulted in shortening(the initial phase of the Grampian Orogeny)at ca.488 Ma.Rollback of a NW-dipping subduction zone to the SE of the ca.488 Ma suture began at 473 Ma and led to lithospheric-scale extension,decompression melting and advective heating of the middle crust,producing the widespread ca.470 Ma Grampian(classic Barrovian and Buchan)regional metamorphism.Resumed hinge advance and the final phase of shortening cut off the heat supply at ca.465 Ma,marking the end of the Grampian Orogeny.  相似文献   

柴北缘胜利口东地区白云母二长花岗岩锆石U-Pb年代学、地球化学及Hf同位素          下载免费PDF全文

张金明  王秉璋  薛万文  付彦文  田成秀  雷晓清 《中国地质》2022,49(2):620-630

[研究目的]柴北缘地区分布着大量早古生代花岗岩,是否存在与大陆深俯冲和早期碰撞阶段的岩浆活动,截至目前研究资料较少,制约了对柴北缘地区大地构造背景演化的认识.[研究方法]本文对胜利口东地区白云母二长花岗岩进行锆石U-Pb年代学、岩石地球化学及Hf同位素研究.[研究结果]通过LA-ICP-MS锆石U-Pb同位素测年,获得...  相似文献   

δ15N variation in Ulva lactuca as a proxy for anthropogenic nitrogen inputs in coastal areas of Gulf of Gaeta (Mediterranean Sea)     

《Marine pollution bulletin》2014,85(1-2):76-82

We tested the capacity of Ulva lactuca to mark N sources across large marine areas by measuring variation in its δ¹⁵N at several sites in the Gulf of Gaeta. Comparisons were made with the macroalga Cystoseira amentacea. Variation of δ¹⁵N values was assessed also in the coastal waters off the Circeo Natural Park, where U. lactuca and C. amentacea were harvested, as these waters are barely influenced by human activities and were used as reference site. A small fragment from each frond was preserved before deployment in order to characterize the initial isotopic values. After 48 h of submersion, U. lactuca was more responsive than C. amentacea to environmental variation and δ¹⁵N enrichment in the Gulf of Gaeta was observed. The spatial distribution of δ¹⁵N enrichment indicated that different macro-areas in the Gulf were affected by N inputs from different origins. Comparison of the δ¹⁵N values of fragments taken from the same transplanted frond avoided bias arising from natural isotopic variability.  相似文献   

Selenium and mercury concentrations in harbor seals (Phoca vitulina) from central California: Health implications in an urbanized estuary     

Elizabeth A. McHuron  James T. Harvey  J. Margaret Castellini  Craig A. Stricker  Todd M. O’Hara 《Marine pollution bulletin》2014

We measured total selenium and total mercury concentrations ([TSe] and [THg]) in hair (n = 138) and blood (n = 73) of harbor seals (Phoca vitulina) from California to assess variation by geography and sex, and inferred feeding relationships based on carbon, nitrogen, and sulfur stable isotopes. Harbor seals from Hg-contaminated sites had significantly greater [THg], and lesser [TSe] and TSe:THg molar ratios than seals from a relatively uncontaminated site. Males had significantly greater [THg] than females at all locations. Sulfur stable isotope values explained approximately 25% of the variability in [THg], indicating increased Hg exposure for seals with a greater use of estuarine prey species. Decreased [TSe] in harbor seals from Hg-contaminated regions may indicate a relative Se deficiency to mitigate the toxic effects of Hg. Further investigation into the Se status and the potential negative impact of Hg on harbor seals from Hg-contaminated sites is warranted.  相似文献   

Anthropogenic lead concentrations and sources in Baltic Sea sediments based on lead isotopic composition     

Agata Zaborska 《Marine pollution bulletin》2014

The Gulf of Gdańsk is influenced by heavy metals of anthropogenic origin. In this study, temporal concentration changes of Pb, Zn, Cd, and Cu were studied in six, 50 cm long sediment cores. The main aim of the study was to concentrate on the history of Pb fluxes and Pb isotopic composition (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) to trace Pb sources. The lowest Pb concentrations (19 μg g⁻¹) were measured in sediments deposited circa 1860, while the highest Pb concentrations (63–147 μg g⁻¹) were measured in sediments deposited between 1960s and 70s. Pre-industrial Pb fluxes were 7 Pb m² year⁻¹, while after WWII they reached 199 Pb m² year⁻¹. Highest ²⁰⁶Pb/²⁰⁷Pb ratios (∼1.22) were measured in the oldest sediment layers, and the lowest ²⁰⁶Pb/²⁰⁷Pb ratios (∼1.165) were measured in the sediments deposited in 1970s–90s. During the period of highest Pb contamination, the anthropogenic Pb fraction reached up to 93%. A general discussion of the Pb sources, emissions, and loads for Poland is included.  相似文献   

Anthropogenic land-use signals propagate through stream food webs in a California,USA, watershed     

《Limnologica》2014

Human development of watersheds can change aquatic ecosystems via multiple pathways. For instance, human rural development may add nutrients to ecosystems. We used naturally occurring stable isotopes in stream food webs to investigate how land use affects stream ecosystems across a gradient of land development in the San Lorenzo watershed, California. Road density was used as a proxy for land development. We found that streams in watersheds with higher road densities had elevated concentrations of phosphate and nitrate. Furthermore, algal δ¹⁵N values increased as a function of nitrate concentration, but saturated at approximately 6‰. This saturating pattern was consistent with a two-source mixing model with anthropogenic and watershed sources, fit using Bayesian model fitting. In sites that had >2.6 km roads km⁻², anthropogenic sources of N were estimated to represent >90% of the N pool. This anthropogenic N signal was propagated to stream consumers: rainbow trout (Oncorhynchus mykiss), signal crayfish (Pacifasticus leniusculus), and benthic invertebrate δ¹⁵N were positively correlated with algal δ¹⁵N. Even relatively low density rural human land use may have substantial impacts on nutrient cycling of stream ecosystems.  相似文献   

Analysis of water stable isotopes fingerprinting to inform conservation management: Lake Urema Wetland System,Mozambique     

《Physics and Chemistry of the Earth》2014

The present study focusses on the analysis of water stable isotopes to contribute to understanding the hydrology of the Lake Urema wetland system in central Mozambique towards conservation management.Lake Urema Wetland is located in the Gorongosa National Park at the southernmost extent of the East African Rift System and is situated entirely within the Urema catchment. Of particular concern to the park’s management is the understanding of hydrological processes as these may trigger transformations of ecosystems, habitat losses and wildlife migrations. Concerns over the Lake Urema wetland’s drying up and the trapping of sediments in the floodplain have been raised for some time by conservationists.Water samples were collected for stable water isotope analyses during the wet and the dry seasons for the period 2006–2010 from springs, boreholes, rivers, and Lake Urema. In addition monthly composite precipitation was collected at two rain gauges.The results show that Lake Urema is maintained throughout the dry season merely from water generated during the wet season. It receives water from wet season precipitation and the runoff generated from this precipitation. The water source areas of the lake are the Gorongosa Mountain and the Barue Basement geomorphological units. Consequently, the source of the sediments which have been trapped into the lake and the floodplain has to be identified in these two catchment areas and urgent action is required to rescue the lake. This water body constitutes a groundwater buffer system which supports a unique wetland landscape. The annual inundations’ processes leading to the recharge-drainage cycle in the floodplain are most sensitive to the deposition of sediments, changing hydraulic gradients, and reducing wet season inflows and increasing drainage rates.  相似文献   

Organic carbon isotope gradient and ocean stratification across the late Ediacaran-Early Cambrian Yangtze Platform     

WANG XinQiang  SHI XiaoYing  JIANG GanQing  TANG DongJie 《中国科学:地球科学(英文版)》2014,57(5):919-929

Organic carbon isotope(δ13Corg) data from two well-preserved sections across a shallow-to-deep water transect of the late Ediacaran-Early Cambrian Yangtze Platform in South China show significant temporal and spatial variations. In the shallow-water Jiulongwan-Jijiapo section, δ13Corg values of the late Ediacaran Dengying Formation range from -29‰ to -24‰. In the deep-water Longbizui section, δ13Corg values from time-equivalent strata of the Dengying Formation are mostly between –35‰ and -32‰. These new data, in combination with δ13Corg data reported from other sections in South China, reveal a 6‰–8‰ shallow-to-deep water δ13Corg gradient. High δ13Corg values(-30‰) occur mostly in shallow-water carbonate rocks, whereas low δ13Corg values(-32‰) dominate the deep-water black shale and chert. The large temporal and spatial δ13Corg variations imply limited buffering effect from a large dissolved organic carbon(DOC) reservoir that was inferred to have existed in Ediacaran-Early Cambrian oceans. Instead, δ13Corg variations between platform and basin sections are more likely caused by differential microbial biomass contribution to total organic matter. High δ13Corg values(-30‰) documented from shallow-water carbonates are within the range of typical Phanerozoic δ13Corg data and may record the isotope signature of organic matter from primary(photosynthetic) production. In contrast, low δ13Corg values(-32‰) from deep-water sections may have resulted from higher chemoautotrophic or methanotrophic biomass contribution to bulk organic matter in anoxic environments. The δ13Corg data provide indirect evidence for ocean stratification and episodic chemocline fluctuations in the Ediacaran-Early Cambrian Yangtze Platform.  相似文献   

太行山木吉村斑岩铜(钼)矿床岩石地球化学、Sr-Nd-Pb同位素特征及其地质意义   总被引：2，自引：0，他引：2  

曲凯  董国臣  李胜荣  申俊峰  王艳娟  王霞  罗薇 《现代地质》2014,28(3):449-460

木吉村斑岩铜(钼)矿床位于太行山北段涞源杂岩体的腰部,是太行山构造-岩浆-成矿带的一个重要矿床。在野外调研的基础上,对木吉村斑岩铜(钼)矿床含矿岩体进行了系统的岩石学、地球化学和Sr-Nd-Pb同位素研究。结果表明：木吉村矿床的含矿岩体闪长玢岩为高钾钙碱性I型侵入岩,具有较高的SiO₂、Al₂O₃、Sr含量和Sr/Y比值以及(La/Yb)_N,较低的Yb、Y的特征;稀土元素配分曲线呈右倾趋势,轻稀土相对富集,轻重稀土分异明显,具微弱的正Eu异常;微量元素蛛网图中富集大离子亲石元素Ba、K、U、Sr,亏损高场强元素Nb、Ta、P、Ti,总体显示出与埃达克岩相似的地球化学特征。闪长玢岩的I_Sr为0.705 386~0.706 838,ε_Nd(t)为-16.7~-14.9,²⁰⁸Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb、²⁰⁶Pb/²⁰⁴Pb的平均值分别为36.614、15.226、16.545,与木吉村矿床矿石中的硫化物铅同位素数值基本一致,Sr-Nd-Pb同位素共同表明其岩浆形成可能与有深源基性物质参与的古老下地壳部分熔融有关。结合研究区地质背景,认为木吉村含矿岩体可能主要来自古老下地壳的部分熔融,并受到幔源物质的混染作用。  相似文献