Coexistence of garnet blueschist and eclogite in South Tianshan,NW China: dependence of P–T evolution and bulk‐rock composition     

Z. L. Tian  C. J. Wei 《Journal of Metamorphic Geology》2014,32(7):743-764

Coexisting garnet blueschist and eclogite from the Chinese South Tianshan high‐pressure (HP)–ultrahigh‐pressure (UHP) belt consist of similar mineral assemblages involving garnet, omphacite, glaucophane, epidote, phengite, rutile/sphene, quartz and hornblendic amphibole with or without paragonite. Eclogite assemblages generally contain omphacite >50 vol.% and a small amount of glaucophane (<5 vol.%), whereas blueschist assemblages have glaucophane over 30 vol.% with a small amount of omphacite which is even absent in the matrix. The coexisting blueschist and eclogite show dramatic differences in the bulk‐rock compositions with higher X(CaO) [=CaO/(CaO + MgO + FeO_total + MnO + Na₂O)] (0.33–0.48) and lower A/CNK [=Al₂O₃/(CaO + Na₂O + K₂O)] (0.35–0.56) in eclogite, but with lower X(CaO) (0.09–0.30) and higher A/CNK (0.65–1.28) in garnet blueschist. Garnet in both types of rocks has similar compositions and exhibits core–rim zoning with increasing grossular and pyrope contents. Petrographic observations and phase equilibria modelling with pseudosections calculated using thermocalc in the NCKMnFMASHO system for the coexisting garnet blueschist and eclogite samples suggest that the two rock types share similar P–T evolutional histories involving a decompression with heating from the P_max to the T_max stage and a post‐T_max decompression with slightly cooling stage, and similar P–T conditions at the T_max stage. The post‐T_max decompression is responsible for lawsonite decomposition, which results in epidote growth, glaucophane increase and omphacite decrease in the blueschist, or in an overprinting of the eclogitic assemblage by a blueschist assemblage. Calculated P–X(CaO), P–A/CNK and P–X(CO₂) pseudosections indicate that blueschist assemblages are favoured in rocks with lower X(CaO) (<0.28) and higher A/CNK (>0.75) or fluid composition with higher X(CO₂) (>0.15), but eclogite assemblages preferentially occur in rocks with higher X(CaO) and lower A/CNK or fluid composition with lower X(CO₂). Moreover, phase modelling suggests that the coexistence of blueschist and eclogite depends substantially on P–T conditions, which would commonly occur in medium temperatures of 500–590 °C under pressures of ~17–22 kbar. The modelling results are in good accordance with the measured bulk‐rock compositions and modelled temperature results of the coexisting garnet blueschist and eclogite from the South Tianshan HP–UHP belt.  相似文献   

布谷马西钾盐矿区卜育矿段盐系地层沉积旋回划分     

栾元滇  田宁  刘东义  岳伟佳  王宏伟 《化工矿产地质》2020,42(3):225-230

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One-dimensional consolidation of soil under multistage load based on continuous drainage boundary     

Yi--> Tian  Wenbing Wu  Guosheng Jiang  M. Hesham El Naggar  Guoxiong Mei  Meijuan Xu  Rongzhu Liang 《国际地质力学数值与分析法杂志》2020,44(8):1170-1183

In engineering practice, a rapid loading rate can result in ground failure when the strength of soft soils is relatively low, and a multistage loading scheme is always utilized to deal with this situation. Firstly, under a multistage load and the continuous drainage boundary, an analytical solution of excess pore-water pressure and consolidation degree is obtained by virtue of the superposition formula of excess pore-water pressure, and a more general continuous drainage boundary under arbitrary time-dependent load is developed. Then, a comparison with existing analytical solutions is conducted to verify the present solution. A preliminary attempt on applying the continuous drainage boundary into the finite element model is made, and the feasibility of the numerical model for the one-dimensional consolidation under the continuous drainage boundary is verified by comparing the results calculated by FEM with that from present analytical solution. Finally, the consolidation behavior of soil is investigated in detail for different int erface parameters or loading scheme. The results show that, in land reclamation projects, a horizontal drain should be placed close to the boundary with a smaller interface parameter to improve the consolidation efficiency. The degree of consolidation is also related to the applied time-dependent load and interface parameters.  相似文献   

凤太矿集区东塘子铅锌矿床S、Pb同位素组成对成矿物质来源的示踪     

张革利  田涛  王瑞廷  高卫宏  常宗东 《中国地质》2020,47(2):472-484

东塘子铅锌矿床是秦岭成矿带中典型的铅锌矿床之一,前人对东塘子铅锌矿床成矿作用研究较多,但受限于测试手段及认识的局限性,多年来对其物质来源的认识仍未统一。本文在充分研究东塘子铅锌矿床地质特征的基础上,开展了相关样品的S、Pb同位素分析,分析对象包括了不同类型的铅锌矿石,讨论了该铅锌矿床的成矿物质来源、区内岩浆岩与铅锌成矿的关系等。研究表明:东塘子铅锌矿床矿石硫化物δ34S值变化范围为1.8‰～12.5‰,平均7.50‰,计算获得成矿流体中总硫δ34S∑S为7.7‰,显示海水硫酸盐(蒸发膏岩)与岩浆硫的混合来源特征。矿石铅同位素组成稳定,铅源主要来自富U-Th-Pb的上地壳与深部,可能与深部岩浆活动有关。研究结果表明,东塘子铅锌矿床的成矿过程与南秦岭印支期大规模多阶段构造-岩浆-流体活动密切相关,为下一阶段区内找矿工作提供了新的思路。  相似文献   

赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化     

马天  齐义泉  程旭华 《热带海洋学报》2019,38(5):18-31

利用2002—2015年ARGO网格化的温度、盐度数据, 结合卫星资料揭示了赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化特征, 探讨了其变化机制。结果表明, 障碍层厚度变化的两个高值区域出现在赤道东印度洋和孟加拉湾北部。在赤道区域, 障碍层同时受到等温层和混合层变化的影响, 5—7月和11—1月受西风驱动, Wyrtki急流携带阿拉伯海的高盐水与表层的淡水形成盐度层结, 同时西风驱动的下沉Kelvin波加深了等温层, 混合层与等温层分离, 障碍层形成。在湾内, 充沛的降雨和径流带来的大量淡水产生很强的盐度层结, 混合层全年都非常浅, 障碍层季节内变化和准半年变化主要受等温层深度变化的影响。上述两个区域障碍层变化存在关联, 季节内和准半年周期的赤道纬向风驱动的波动过程是它们存在联系的根本原因。赤道东印度洋地区的西风(东风)强迫出向东传的下沉(上升)的Kelvin波, 在苏门答腊岛西岸转变为沿岸Kelvin波向北传到孟加拉湾的东边界和北边界, 并且在缅甸的伊洛瓦底江三角洲顶部(95°E, 16°N)激发出向西的Rossby波, 造成湾内等温层深度的正(负)异常, 波动传播的速度决定了湾内的变化过程滞后于赤道区域1~2个月。  相似文献   

Pressure-dependent Raman spectra of β-Ca3(PO4)2 whitlockite     

Shuangmeng Zhai  Xiang Wu  Weihong Xue 《Physics and Chemistry of Minerals》2015,42(4):303-308

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Hydrological cycle and water balance estimates for the megadune–lake region of the Badain Jaran Desert,China          下载免费PDF全文

Yan‐Dong Ma  Jing‐Bo Zhao  Xiao‐Qing Luo  Tian‐Jie Shao  Zhi‐Bao Dong  Qi Zhou 《水文研究》2017,31(18):3255-3268

The hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content, and grain size reveal 3 types of important natural phenomenon: (a) vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone; (b) seepage, wet sand deposits, and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone; (c) zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation, but it is still able to maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long‐term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts.  相似文献   

The role of anthropogenic activities in karst spring discharge volatility          下载免费PDF全文

Jing Wu  Jian Yin  Yonghong Hao  Yan Liu  Yonghui Fan  Xueli Huo  Youcun Liu  Tian‐Chyi J. Yeh 《水文研究》2015,29(13):2855-2866

The traditional hydrological time series methods tend to focus on the mean of whichever variable is analysed but neglect its time‐varying variance (i.e. assuming the variance remains constant). The variances of hydrological time series vary with time under anthropogenic influence. There is evidence that extensive well drilling and groundwater pumping can intercept groundwater run‐off and consequently induce spring discharge volatility or variance varying with time (i.e. heteroskedasticity). To investigate the time‐varying variance or heteroskedasticity of spring discharge, this paper presents a seasonal autoregressive integrated moving average with general autoregressive conditional heteroskedasticity (SARIMA‐GARCH) model, whose the SARIMA model is used to estimate the mean of hydrological time series, and the GARCH model estimates its time‐varying variance. The SARIMA‐GARCH model was then applied to the Xin'an Springs Basin, China, where extensive groundwater development has occurred since 1978 (e.g. the average annual groundwater pumping rates were less than 0.20 m³/s in the 1970s, reached 1.20 m³/s at the end of the 1980s, surpassed 2.0 m³/s in the 1990s and exceeded 3.0 m³/s by 2007). To identify whether human activities or natural stressors caused the heteroskedasticity of Xin'an Springs discharge, we segmented the spring discharge sequence into two periods: a predevelopment stage (i.e. 1956–1977) and a developed stage (i.e. 1978–2012), and set up the SARIMA‐GARCH model for the two stages, respectively. By comparing the models, we detected the role of human activities in spring discharge volatility. The results showed that human activities caused the heteroskedasticity of the Xin'an Spring discharge. The predicted Xin'an Springs discharge by the SARIMA‐GARCH model showed that the mean monthly spring discharge is predicted to continue to decline to 0.93 m³/s in 2013, 0.67 m³/s in 2014 and 0.73 m³/s in 2015. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

SONG-China Project: A Global Automated Observation Networktwo     

Yan Zheng-zhou  Lu Xiao-meng  Tian Jian-feng  Zhang Chun-guang  Wang Kun  Deng Li-cai 《Chinese Astronomy and Astrophysics》2018,42(4):609-625

Driven by the technological advancements and scientific objectives, the data acquisition in observational astronomy has been changed greatly in recent years. Fully automated or even autonomous ground-based network of telescopes has now become a tendency for time-domain observational projects. The Stellar Observations Network Group (SONG) is an international collaboration with the participation and contribution of the Chinese astronomy community. The scientific goal of SONG is time-domain astrophysics, such as the astroseismology and the research of variable stars in open clusters. The SONG project aims to build a global network of one-meter telescopes equipped with high-precision and high-resolution spectrographs, and two-channel lucky-imaging cameras. It is the Chinese initiative to install a 50 cm binocular photometry telescope at each SONG node to share the network platform and infrastructure. This work is focused on the design and implementation of SONG/50BiN in technology and methodology, for the ground-based network composed of multiple sites and a variety of instruments.  相似文献   

Photosynthetic response of <Emphasis Type="Italic">Scirpus validus</Emphasis> and <Emphasis Type="Italic">Typha orientalis</Emphasis> to elevated temperatures in Dianchi Lake,Southwestern China     

Jun-ping Xu  Mei Sun  Hang Wang  Yun Zhang  Xiao-tang Zhang  Kun Tian 《山地科学学报》2018,15(12):2666-2675

Understanding the effects of simulated warming on photosynthetic performance of aquatic plants may provide strong supports for predicting future dynamics of wetland ecosystems in the context of climate change. The plateau wetlands located in Yunnan province are highly sensitive to climate warming due to their high altitude and cold temperature. Here, we conducted a temperaturecontrolled experiment using two temperature manipulations (ambient temperature as the control and 2°C higher than ambient temperature as the warmed treatment) to determine the photosynthetic characteristics of two lakeside dominant species (Scirpus validus Vahl and Typha orientalis C. Presl.) in Dianchi Lake. Net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), and transpiration rate of S. validus that grew under warmed treatment were all significantly higher than those under the control. G_s and C_i of T. orientalis showed similar patterns as S. validus did. For the response curves of P_n to photosynthetic active radiation (Pn-PAR) and intercellular CO₂ concentration (P_n-C_i), S. validus had higher P_n values under elevated temperatures than the control, while P_n-PAR and P_n-C_i curves of T. orientalis did not separate clearly under two temperature scenarios. Both S. validus and T. orientalis had higher maximum net photosynthetic rate, light saturation point, dark respiration rate, the maximum rate of RuBP carboxylation (V_cmax), maximum electron transport rate driving RuBP regeneration (J_max), the ratio of V_cmax to J_max, triosephosphate utilization, and 1, 5-bishosphate carboxylase ribulose content under warmed treatment than those under the control. This study provides a preliminary step for predicting the future primary production and vegetation dynamics of plateau wetlands in Yunnan province.  相似文献