下扬子PTB界线深水相区粘土岩的火山成因研究及其对LPME的指示意义

全球,尤其是特提斯域二叠—三叠纪之交(PTB)剖面中普遍发育火山成因的粘土岩,对理解晚二叠世末生物大灭绝(LPME)的触发机制及相关基础地质问题具有重要意义。本文报道了在华南下扬子区新发现两条深水PTB剖面(皖南牛山和蔡村)的粘土岩工作,包括岩石学、矿物学和全岩地球化学等,填补了区域研究空白。研究结果发现,粘土岩主要由伊利石等粘土矿物,以及石英、岩浆锆石、长石等斑晶矿物组成。在地球化学上具有高K_2O、低Na_2O、相对富集大离子亲石元素(LILE)、相对亏损高场强元素(HFSE)等特征。据此,认为这些粘土岩为火山成因的钾质斑脱岩,其原岩可能为中酸性流纹英安岩,具有弧岩浆作用的源区背景。对比华南其他地区已发现的PTB界线粘土岩,发现它们成因类似,可能来源于古特提斯洋周缘陆陆碰撞,抑或是泛大洋俯冲潘吉亚大陆东缘(包括华南板块)所导致的长英质火山岩浆喷发,且具有多期多源性特点。PTB时期全球活跃的火山岩浆活动(包括镁铁质火山作用和华南地区火山灰所指征的长英质火山作用)可能是导致LPME的主要原因。     

Initiation of large-volume silicic centers in the Yellowstone hotspot track: insights from H<Subscript>2</Subscript>O- and F-rich quartz-hosted rhyolitic melt inclusions in the Arbon Valley Tuff of the Snake River Plain

During the onset of caldera cluster volcanism at a new location in the Snake River Plain (SRP), there is an increase in basalt fluxing into the crust and diverse silicic volcanic products are generated. The SRP contains abundant and compositionally diverse hot, dry, and often low-δ¹⁸O silicic volcanic rocks produced through time during the formation of individual caldera clusters, but more H₂O-rich eruptive products are rare. We report analyses of quartz-hosted melt inclusions from pumice clasts from the upper and lower Arbon Valley Tuff (AVT) to gain insight into the initiation of caldera cluster volcanism. The AVT, a voluminous, caldera-forming rhyolite, represents the commencement of volcanism (10.44 Ma) at the Picabo volcanic field of the Yellowstone hotspot track. This is a normal δ¹⁸O rhyolite consisting of early and late erupted members (lower and upper AVT, respectively) with extremely radiogenic Sr isotopes and unradiogenic Nd isotopes, requiring that ~50 % of the mass of these elements is derived from melts of Archean upper crust. Our data reveal distinctive features of the early erupted lower AVT melt including: variable F concentrations up to 1.4 wt%, homogenous and low Cl concentrations (~0.08 wt%), H₂O contents ranging from 2.3 to 6.4 wt%, CO₂ contents ranging from 79 to 410 ppm, and enrichment of incompatible elements compared to the late erupted AVT, subsequent Picabo rhyolites, SRP rhyolites, and melt inclusions from other metaluminous rhyolites (e.g., Bishop Tuff, Mesa Falls Tuff). We couple melt inclusion data with Ti measurements and cathodoluminescence (CL) imaging of the host quartz phenocrysts to elucidate the petrogenetic evolution of the AVT rhyolitic magma. We observe complex and multistage CL zoning patterns, the most critical being multiple truncations indicative of several dissolution–reprecipitation episodes with bright CL cores (higher Ti) and occasional bright CL rims (higher Ti). We interpret the high H₂O, F, F/Cl, and incompatible trace element concentrations in the context of a model involving melting of Archean crust and mixing of the crustal melt with basaltic differentiates, followed by multiple stages of fractional crystallization, remelting, and melt extraction. This multistage process, which we refer to as distillation, is further supported by the complex CL zoning patterns in quartz. We interpret new Δ¹⁸O(Qz-Mt) isotope measurements, demonstrating a 0.4 ‰ or ~180 °C temperature difference, and strong Sr isotopic and chemical differences between the upper and lower AVT to represent two separate eruptions. Similarities between the AVT and the first caldera-forming eruptions of other caldera clusters in the SRP (Yellowstone, Heise and Bruneau Jarbidge) suggest that the more evolved, lower-temperature, more H₂O-rich rhyolites of the SRP are important in the initiation of a caldera cluster during the onset of plume impingement.     

鄱阳湖生态环境动态监测服务系统

针对目前生态环境监测中多源多尺度数据获取、定量遥感模型半自动化条件制约海量数据的快速处理与分析以及静态的时空快照服务难以表达动态变化过程等问题,该文从基于传感网的数据多元化实时感知获取、基于数据仓库的生态信息主题化动态汇聚、基于多尺度WFS的智能化服务、基于动态数据驱动的仿真动态模拟知识化应用方面考虑,设计湖泊流域生态环境动态监测服务系统。以鄱阳湖为例进行验证,为鄱阳湖流域的生态监测以及江西省生态文明试验区建设提供服务。     

Recursive algorithm for fast GNSS orbit fitting

Gaussian elimination is an efficient and numerically stable algorithm for estimating parameters and their precision. However, before estimating the parameters, it is often prudent to perform statistical tests to achieve the best fitting model. We use Gaussian elimination to select the best fitting model among candidate models. A succinct relationship between the weighted sum of squared residuals and the previous one is revealed by a volume formula. For quick parameter estimation and determination of weighted sum of squared residuals, a recursive elimination algorithm is proposed in the context of Gaussian elimination. In order to improve the model selection efficiency, the parameter estimation and the determination of the weighted sum of squared residuals are carried out in parallel using the proposed recursive elimination algorithm in which the improvement at each recursive stage is judged by the Bayesian information criterion. Ultimately, the computational complexity and numerical stability of the recursive elimination proposed are briefly discussed, and a GNSS orbit interpolation example is used to verify the results. It shows that the proposed recursive elimination algorithm inherits the numerical stability of the Gaussian elimination, and this algorithm can be used to examine the gain from the newly introduced parameter, dynamically assess the fitting model, and fix the optimal model efficiently. The optimal fitting model with the lowest information is very close to the real situation verified by checkpoints.     

A new method for specular and diffuse pseudorange multipath error extraction using wavelet analysis

Multipath remains one of the major challenges in Global Navigation Satellite System (GNSS) positioning because it is considered the dominant source of ranging errors, which can be classified into specular and diffuse types. We present a new method using wavelets to extract the pseudorange multipath in the time domain and breaking it down into the two components. The main idea is an analysis-reconstruction approach based on application of both continuous wavelet transform (CWT) and discrete wavelet transform (DWT). The proposed procedure involves the use of L1 code-minus-carrier (CMC) observable where higher-frequency terms are isolated as residuals. CMC residuals are analyzed by applying the CWT, and we propose the scalogram as a technique for discerning time–frequency variations of the multipath signal. Unlike Fourier transform, the potential of the CWT scalogram for examining the non-stationary and multifrequency nature of the multipath is confirmed as it simultaneously allows fine detection and time localization of the most representative frequencies of the signal. This interpretation of the CWT scalogram is relevant when choosing the levels of reconstruction with DWT, allowing accurate time domain extraction of both the specular and diffuse multipath. The performance and robustness of the method and its boundary applicability are assessed. The experiment was carried out using a receiver of Campania GNSS Network. The results are given in which specular multipath error is achieved using DWT level 7 approximation component and diffuse multipath error is achieved using DWT level 6 denoised detail component.     

Optimization and Parametrical Investigation to Assess the Reconstitution of Different Types of Indian Sand Using Portable Travelling Pluviator

By using the air pluviation technique, it is aimed to achieve the desired relative density with uniform void ratio throughout the specimen in order to maintain the homogeneity and to avoid the spatial variability. Further, in order to achieve the maximum deposition intensity, a systematic optimization study has been carried out rigorously in a test tank to determine the diameter of the orifice to be employed for the sieve plates of different porosity and the number of sieve plates to be installed in the diffuser sieve sets. The study has been conducted with four different patterns of sieves with different porosity to achieve a wide range of relative densities for four different uniformly graded Indian sands. The dynamic penetrometer which is considered to be one of the cost effective instruments has been efficiently used to determine the soil resistance at various locations of the test tank for every given height of fall in order to check the uniformity of placement density throughout the sand bed. The study reveals that the sand beds of different relative densities could be achieved using different patterns of diffuser sieves at optimum sand flow rate without compromising the uniformity. The effect of height of fall as well as porosity of diffuser sieves on the relative density of different sands has been studied in detail. The deposition intensity and the relative density obtained from the present study are compared with the values available in the literature.     

Assessment and Prediction of Liquefaction Potential Using Different Artificial Neural Network Models: A Case Study

Soil liquefaction as a transformation of granular material from solid to liquid state is a type of ground failure commonly associated with moderate to large earthquakes and refers to the loss of strength in saturated, cohesionless soils due to the build-up of pore water pressures and reduction of the effective stress during dynamic loading. In this paper, assessment and prediction of liquefaction potential of soils subjected to earthquake using two different artificial neural network models based on mechanical and geotechnical related parameters (model A) and earthquake related parameters (model B) have been proposed. In model A the depth, unit weight, SPT-N value, shear wave velocity, soil type and fine contents and in model B the depth, stress reduction factor, cyclic stress ratio, cyclic resistance ratio, pore pressure, total and effective vertical stress were considered as network inputs. Among the numerous tested models, the 6-4-4-2-1 structure correspond to model A and 7-5-4-6-1 for model B due to minimum network root mean square errors were selected as optimized network architecture models in this study. The performance of the network models were controlled approved and evaluated using several statistical criteria, regression analysis as well as detailed comparison with known accepted procedures. The results represented that the model A satisfied almost all the employed criteria and showed better performance than model B. The sensitivity analysis in this study showed that depth, shear wave velocity and SPT-N value for model A and cyclic resistance ratio, cyclic stress ratio and effective vertical stress for model B are the three most effective parameters on liquefaction potential analysis. Moreover, the calculated absolute error for model A represented better performance than model B. The reasonable agreement of network output in comparison with the results from previously accepted methods indicate satisfactory network performance for prediction of liquefaction potential analysis.     

进积型三角洲交汇区沉积模式--以东营凹陷沙三中亚段为例

作为碎屑岩储层发育的最主要沉积相类型之一,进积型三角洲在油气勘探领域具有举足轻重的地位;加强对进积型三角洲沉积模式的研究,对于油气储层预测具有重要现实意义。渤海湾盆地东营凹陷古近纪湖盆内发育的东营三角洲和永安三角洲在沙河街组三段中亚段沉积期发生了交汇,而有关两个三角洲的交汇方式、沉积特征及交汇区储层的预测尚未引起足够的重视。以岩芯观测、录井和地震资料为基础,分析了东营凹陷古近系沙三段中亚段三角洲交汇区沉积特征,探讨了沉积期次、交汇过程,建立了三角洲交汇区沉积模式。研究表明,东营凹陷沙河街组三段中亚段主要发育湖泊、进积型三角洲沉积;储集砂体主要形成于三角洲前缘水下分流河道,河口坝微相次之,浊积岩主要分布于深湖区。认为此前界定的东营三角洲的分布范围可能被夸大,而永安三角洲的沉积规模可能被低估。东营凹陷古近系沙三中亚段可划分为9个期次,其作用过程可分为局部交汇阶段和完全交汇阶段。三角洲水下交汇区是水流汇聚和沉积物卸载的有利场所,叠置砂体可成为有利的油气储层,因而具有重要的油气勘探价值。     

朝鲜半岛古元古代摩天岭群的碎屑锆石U-Pb年龄及其地质意义

克拉通内部活动带变质沉积建造蕴藏了早期超大陆形成中地体聚-散动力学过程的重要信息,碎屑锆石年代学则是揭示这种信息的最佳工具之一。针对华北(中-朝)克拉通最具代表性的古元古代活动带(辽-吉-朝活动带)中巨量沉积建造精细表征方面的空白区域,本文开展了朝鲜半岛检德地区摩天岭群的碎屑锆石年代学研究。SIMS U-Pb定年结果显示,北大川组变火山碎屑岩样品的锆石年龄谱记录了约2.53Ga的主要年龄峰值和约2.19Ga的最年轻峰值,说明北大川组开始沉积的时代应该晚于2.2Ga。南大川组变沉积岩样品碎屑锆石记录的最年轻峰值年龄为约2.02Ga,说明南大川组的沉积时代应该不早于2.02Ga;其锆石年龄谱记录了一个主要年龄峰值区域(2.02~2.18Ga)、一个次要年龄峰值(约2.46Ga)和一些2.78~3.30 Ga的古老年龄,指示其物质源区主要为同区古元古代地质体和邻近地体上的太古宙变质基底。区域对比表明,摩天岭群与中国境内辽吉活动带中的辽河群及集安群/老岭群具有基本一致的碎屑锆石年龄谱,说明它们不仅是同一时代的产物,而且分享类似的物质源区。这些时代一致、物源相近的沉积建造可以为甄别古元古代辽-吉-朝活动带的大地构造属性提供重要参考。与沉积年龄相近的碎屑锆石占据主导的碎屑锆石年龄谱反映了汇聚板块边缘各类盆地的典型特征,而相悖于大部分碎屑锆石年龄远大于地层沉积年龄的裂谷型盆地。     

滇西马登地区晚二叠世-早三叠世地层组合及年代学:火山岩锆石U-Pb定年证据

在西南"三江"造山带中段的兰坪盆地内,由于露头状况不好,盆地基底岩石出露状况不详,导致地层划分、归属相当混乱。详细的野外地质调查揭示,盆地东缘马登地区出露的基底岩石主要由2个构造地层单元组成,上部为火山-沉积序列,下部为浅海相泥岩、灰岩及生物碎屑灰岩。上部火山-沉积序列出露厚约1200m,可分为4个喷发-沉积韵律,由英安质熔岩、流纹质熔岩与晶屑凝灰岩、火山集块岩、火山角砾岩、流纹质凝灰岩、火山碎屑岩及少量泥岩相间组成。火山岩锆石LAICP-MS U-Pb法测年数据显示,岩浆活动始于250Ma,持续至244Ma,总体处于早三叠世,构成江达-维西-云县弧火山岩带的一部分。强烈变形的海相地层与火山岩二者呈断层接触,其时代老于250Ma。结合砂岩中碎屑锆石年龄结果(大于260Ma)判定,这套沉积岩应属于晚二叠世,其与早三叠世-中三叠世火山岩一起组成兰坪盆地的基底岩石。