Giant plagioclase growth during storage of basaltic magma in Emeishan Large Igneous Province,SW China     

Li-Lu?Cheng  Zong-Feng?Yang  Ling?Zeng  Yu?Wang  Zhao-Hua?LuoEmail author 《Contributions to Mineralogy and Petrology》2014,167(2):971

Giant plagioclase basalts (GPBs) reflect the storage of flood basalt magma in subvolcanic magma chambers at crustal depths. In this study of the Late Permian Emeishan large igneous province in southwest China, we focus on understanding the plumbing system and ascent of large-volume basaltic magma. We report a quantitative textural analysis and bulk-rock geochemical composition of clustered touching crystals (CT-type) and single isolated crystal (SI-type) GPB samples from 5- to 240-m-thick flows in the Daqiao section. Both types of GPBs are evolved (<6 MgO wt%), but have high Ti/Y ratios (>500) and high total FeO content (11.5–15.2 wt%). The mineral chemistry of the two types of plagioclase displays a small range of anorthite content (<5 mol%), which is consistent with their unzoned characteristics. The two types of GPBs have S-type crystal size distributions but have quite different slopes, intercepts, and characteristic lengths. The characteristic lengths of the five flows are 1.54, 2.99, 1.70, 3.22, and 1.86 mm, respectively. For plagioclase growth rates of 10^?11 to 10^?10 mm/s, steady-state magma chamber models with simple continuous crystal growth suggest that CT-type plagioclase megacrysts have the residence time of about 500–6,000 years, whereas the residence time for SI-type plagioclase is significantly longer, about 1,000–10,000 years. By combining field geology, quantitative textural data with geochemistry, we suggest that CT- and SI-type crystals grew and were coarsened in the outer part and inner part of a magma chamber, respectively. Magma evolution during storage is controlled by crystallization, crystal growth, and magma mixing, and pulsating eruptions occur in response to the continuous supply of hot magma.  相似文献   

Petrogenesis of the Yangchang Mo‐bearing granite in the Xilamulun metallogenic belt,NE China: geochemistry,zircon U–Pb ages and Sr–Nd–Pb isotopes     

Qingdong Zeng  Jinhui Yang  Zuolun Zhang  Jianming Liu  Xiaoxia Duan 《Geological Journal》2014,49(1):1-14

The Yangchang granite‐hosted Mo deposit is typical of the Xilamulun metallogenic belt, which is one of the important Mo–Pb–Zn–Ag producers in China. A combination of major and trace element, Sr, Nd and Pb isotope, and zircon U–Pb age data are reported for the Yangchang batholith to constrain its petrogenesis and Mo mineralization. Zircon LA‐ICPMS U–Pb dating yields mean ages of 138 ± 2 and 132 ± 2 Ma for monzogranite and granite porphyry, respectively. The monzogranites and granite porphyries are calc‐alkaline with K₂O/Na₂O ratios of 0.75–0.92 and 1.75–4.42, respectively. They are all enriched in large‐ion lithophile elements (LILEs) and depleted in high‐field‐strength elements (HFSEs) with negative Nb and Ta anomalies in primitive‐mantle‐normalized trace element diagrams. The monzogranites have relatively high Sr (380–499 ppm) and Y (14–18 ppm) concentrations, and the granite porphyries have lower Sr (31–71 ppm) and Y (5–11 ppm) concentrations than those of monzogranites. The monzogranites and granite porphyries have relatively low initial Sr isotope ratios of 0.704573–0.705627 and 0.704281, respectively, and similar ²⁰⁶Pb/²⁰⁴Pb ratios of 18.75–18.98 and 18.48–18.71, respectively. In contrast, the ε_Nd(t) value (−3.7) of granite porphyry is lower than those of monzogranites (−1.5 to −2.7) with Nd model ages of about 1.0 Ga. These geochemical features suggest that the monzogranite and granite porphyries were derived from juvenile crustal rocks related to subduction of the Paleo‐Pacific plate under east China. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

塔里木盆地晚志留世-石炭纪伸展构造的发现及其地质意义   总被引：1，自引：0，他引：1       下载免费PDF全文

李日俊  孙龙德  杨海军  张光亚  曾昌民  冯晓军  文磊  张强  贾铁干 《地质科学》2014,(1):30-48

通过精细的地震资料解释,在塔里木盆地中部的满西地区发现晚志留世-石炭纪伸展构造。伸展构造由一系列规模不大的正断层组成,平面上组成两条北东-南西向的左行雁列状正断层带,剖面上构成负花状构造和堑垒构造。根据生长系数计算结果,正断层形成于晚志留世,在泥盆纪和石炭纪持续活动,于石炭纪末停止活动。正断层活动的高峰期为晚志留世。该期伸展构造在塔中和塔北地区也有发育,反映当时塔里木盆地处于区域性伸展构造背景。塔里木盆地晚志留世-石炭纪的伸展构造,是昆仑早古生代晚期（晚奥陶世-中志留世）碰撞造山后构造应力松弛作用的产物。  相似文献   

三峡库区巴东地震(M_s5.1)成因机制及次声波信号          下载免费PDF全文

李献瑞  曾佐勋  周强  贺赤诚  刘江平  赵娟  潘黎黎 《地球科学》2014,39(12):1793-1806

2013年12月16日三峡库区巴东发生M_s5.1地震.根据eigen-6c2模型研究了巴东地区的8-638阶卫星重力异常, 结果表明: 该地区场源深度为10 km的地壳为局部重力低异常, 反映了该处物质密度较周围偏低, 形成低密度层.同时, 研究了该地区速度结构剖面, 结果表明: 巴东地区地壳5~9 km及10~15 km深处存在上下两个低速层, 上部低速层与水库渗水有关, 下部低速层与地幔热流体的上涌有关.低密度层和低速层的确定为韧性流变层的存在提供了证据.巴东地震是地壳深部能量的长期集聚与突发释放, 属构造地震.然而, 库水下渗引起的上部低速异常降低了断层活动的阈值, 震前库水载荷的变化对此次巴东地震的发生起到了触发作用.通过对比次声波和地震波, 我们得出次声波仪记录到的异常信号为本地次声波.   相似文献   

电､磁综合方法在云南北衙铁金矿勘查中的应用   总被引：3，自引：1，他引：2       下载免费PDF全文

杨剑王绪本  王永华王桥 曾琴琴 《中国地质》2014,41(2):602-610

北衙金矿位于西南三江富碱斑岩成矿带区域,地质构造复杂,华里西期海相玄武岩和喜山期富碱斑岩极为发育;前者普遍具有热液型铜矿化,后者与金、铁、铅、锌、银等多金属矿床具有密切成因关系。本文针对北衙铁金矿,利用高精度磁测圈定的磁异常,结合音频大地电磁法,两种方法互补,遵循"从已知矿床到未知的原则",紧密结合地质资料,较好地探测深部地质构造以及矿体的空间位置,为工程布置提供了有力的指导。  相似文献   

Particle size shapes the prokaryotic microbial communities in mangrove sediments: A case study of Sanya,China     

Wu Qu  Michael Vicent Shija  Jie Wu  Min Jin  Jianxin Wang  Runying Zeng  Zhuhua Chan 《海洋学报(英文版)》2022,41(8):120-128

The prokaryotic microbial communities in the sediments play crucial roles in the ecological functions of mangrove ecosystems. Therefore, the environmental factors that affect the structures of these prokaryotic microbial communities could indirectly participate in the regulation of mangrove functions, which is of great value for mangrove studies. The particle size (PS) of soils is recently demonstrated as a key environmental factor for shaping the microbial communities; however, this hypothesis has rarely been tested for mangrove environments. A case study of three tropical mangroves from Sanya, China was performed in this work to assess the influence of PS on the prokaryotic microbial community structures of bacteria, archaea, diazotrophs, and denitrifiers in the sediments. Results showed the variability in the spatial scale and the stability in the temporal scale for the prokaryotic communities, indicating that the tropical mangrove sediments could be a versatile but stable environment. Among the collected environmental factors, PS, salinity, and humidity had the greatest impacts, and PS mostly affected the structures of these prokaryotic communities based on its highest R2 values of canonical correspondence analysis, Mental test, and linear fitting (p≤0.05). Furthermore, PS was positively correlated with the diversity and abundance of diazotrophic communities and negatively correlated with the abundances of methanogenic communities including Methanobacteriaceae, Methanospirillaceae, Methanoregulaceae, and Methanosaetaceae. Former studies show the increasing trend of PS caused by the rise of sea level and the intensification of human activities. Therefore, our findings indicate that PS could be a potential intermediate that links climate change and human activities with the possible ecological function migration of mangroves; meanwhile, the increase of PS could in turn release the stress of these environmental changes by increasing the abundance and diversity of the diazotrophic community and decreasing the abundances of methanogens.  相似文献   

1971—2010年三江源地区水汽输送变化分析     

曾小凡  苏布达  易善桢  周建中  翟建青 《气候变化研究进展》2013,(3):187-191

在利用三江源地区及邻近区域探空资料对NCEP/NCAR I再分析资料进行适用性分析的基础上,采用1971—2010年再分析资料的逐日风场和比湿数据,分析三江源地区水汽输送的变化。结果表明:1971—2010年,经向流入三江源地区的水汽显著减少,使区域总水汽收支也呈显著减少趋势。水汽通量在1970年代和1980年代的变化相对较小,在1990年代和2000年代的变化幅度则较大。三江源地区总水汽收支在春季、夏季和秋季均呈明显减少趋势,冬季则无明显变化。三江源地区水汽输入明显减少,特别是6月和9月显著减少,对该地区降水形成不利。  相似文献   

湖南省三级天气预报会商辅助系统的设计与实现     

唐杰  周慧  刘炼烨  曾欣  何正阳  李象玉 《气象研究与应用》2013,34(1):37-40,111

针对天气预报会商业务,基于VB、Fortran90、Perl、C#、Bash shell综合编程技术和Curl、NCL、Surfer外部程序包,设计和开发了湖南省三级天气预报会商辅助系统,从技术上实现了天气预报会商气象信息产品的优化,和湖南各级会商发言PPT制作与传输的快速化、自动化;为增强湖南天气预报技术、思路交流,和提高全省各级天气会商质量和预报质量,提供了有效的业务技术支持。  相似文献   

Holocene lake level variations on the Qinghai-Tibetan Plateau   总被引：1，自引：0，他引：1  

Xiang-Jun Liu  Zhong-Ping Lai  Fang-Ming Zeng  David B. Madsen  Chong-Yi E 《International Journal of Earth Sciences》2013,102(7):2007-2016

Paleoshorelines indicative of multiple high lake stages can be found around many lakes on the Qinghai-Tibetan Plateau (QTP). Conspicuous paleoshorelines associated with the most recent highstands can be readily observed on satellite images and during field investigations. However, earlier paleoshorelines have been identified at only a few sites around these lakes due to a lack of clear shoreline features and limited spatial extension of those that can be identified. We investigated past lake highstands using published chronologies, Aster-DEM, Google Earth, and ArcGIS 9.2 software. These data suggest that (1) paleoshorelines of the most recent lake highstand were formed during the Holocene; (2) during this highstand, lake levels reached more than 90, 60–90, and 30–60 m higher than present in the central Gangdise and western Qiangtang areas, while in the eastern Qiangtang, Holxil-Yushu, and northeastern QTP areas highstands did not exceed 30 m above modern; (3) during the early Holocene, some lakes on the southwestern QTP combined to form large lakes, while lakes in the inland areas of the QTP were only a little larger during the Holocene high lake level stages.  相似文献   

Comparison of metal(loid) concentrations in water, sediments and fish from two large shallow lakes   总被引：2，自引：0，他引：2  

J. Zeng  L. Y. Yang  X. M. Chuai  X. F. Chen  H. Y. Zhao  Q. L. Wu 《International Journal of Environmental Science and Technology》2013,10(6):1209-1218

Hulun Lake and Taihu Lake are both large shallow lakes in China. In summer and winter of 2009, water, sediments and fish samples were collected from the two lakes and the concentrations of metal(loids) were analyzed. The results demonstrated that aqueous concentrations of arsenic (As), chromium (Cr), cadmium (Cd), nickel (Ni) and copper (Cu) in Hulun Lake were significantly higher than those in Taihu Lake. Especially, the As concentrations (about 130 μg/L) in Hulun Lake dramatically exceeded the permissible level of drinking water. Compared with Taihu Lake, metal(loid) concentrations in the sediments of Hulun Lake were significantly lower, which might have less impacts on the metal exchanges between water and sediments. In contrast, concentrations of the measured metal(loids) (including As) in fish from Hulun Lake and Taihu Lake were comparable, suggesting that the dramatic difference in aqueous and sediment metal(loid) concentrations had less influence on the metal(loid) bioavailability. The higher concentrations of dissolved organic carbon (DOC) and cations (e.g., Na⁺, K⁺ and Mg²⁺) in lake water might contribute to the reduced metal(loid) bioavailability to fish in Hulun Lake.  相似文献