Permian High Ba-Sr Granitoids: Geochemistry, Age and Tectonic Implications of Erlangshan Pluton, Urad Zhongqi, Inner Mongolia

Abstract: Erlangshan Pluton from Urad Zhongqi, central Inner Mongolia, is located in the middle segment of the northern margin of the North China Plate. The rocks consist mainly of diorites with gneissic structure. Petrochemical characteristics reveal that the diorites belong to metaluminous, high-potassium calc-alkaline series, with chemical signatures of I-type granites. They are characterized by low SiO2 contents (56.63%–58.53%) and A/CNK (0.90–0.96), high Al2O3 contents (17.30%–17.96%) and Na2O/K2O ratios (1.20–1.70), enrichment in large ion lithophile elements (LILE, e.g., Ba=556–915 ppm, Sr=463–595 ppm), and relative depletion in high field strength elements (HFSE, e.g., Nb, Ta, Ti) in primitive mantle-normalized spidergram, and right-declined rare earth element patterns with slightly negative Eu anomalies (d?Eu=0.72–0.90). They have Sr/Y ratios (20–25) evidently less than Kebu Pluton (49–75) to its east. Sensitive high resolution ion micro-probe U-Pb zircon dating of the diorites has yielded an intrusive age of 270±8?Ma. This leads us to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal-derived magma and minor mantle-derived mafic magma, followed by fractional crystallization, which was trigged by crustal extension and fault activity in post-collisional setting.     

Application of Fractal Models to Distinguish between Different Mineral Phases

Fractal modeling is demonstrated to be an effective and rapid tool to distinguish between mineral phases in rock samples. It supplements work that previously could be performed only by observing the interpenetrational or metasomatic phenomena between different minerals with the aid of mineralographic microscope. The Gejiu tin district in southwestern China was chosen as a study area for the recognition and characterization of the spatial distribution of two phases (Types I and II) of cassiterite. Vector patterns used for this study were extracted from digital photomicrographs and analyzed with the aid of MapGIS. Perimeter–area fractal dimension, cumulative number–area exponent, and shape index were determined in order to quantify geometrical irregularities and spatial cassiterite phase distribution characteristics. The results show that fractal dimensions based on area and perimeter are larger for crystals of Type I than for those of Type II. The mean shape index (SI) increases from 0.54 (Type I) to 0.64 (Type II), indicating an increase in regularity. The number–area exponent also increases from 0.88 to 1.15, indicating the smaller crystals of Type II. The cumulative number–shape index log–log plot shows two separate straight-line segments. One of these probably represents a background shape realized during the original process of natural crystallization, whereas the other likely represents anomalous shapes because of weathering or other superimposed processes. Two parallel lines can be constructed on the perimeter–area log–log plots. The upper line, with a larger intercept, represents crystals with lower SI. The lower line represents crystals with higher SI, indicating that the intercept provides a measure of the irregularity of grains. By combining the perimeter–area model with cumulative number–area plot and shape index, the two phases of cassiterite can be distinguished and characterized. One phase has fewer crystals of large size, and the other has smaller crystals. This difference can be explained by assuming that under higher-temperature conditions, the large cassiterite crystals formed earlier than the smaller crystals. Consequently, the large cassiterites underwent longer, high-intensive weathering than the small crystals so that their shapes became more irregular. The younger, more abundant small cassiterites retained their original regular shapes.     

河南省济源沙沟铅锌矿的发现及意义

根据化探异常所圈定的靶区,采用化探和物探相结合的方法,在河南省西北部上寒武统白云岩中发现了类似于MVT的铅锌矿床.矿体赋存于上寒武统的厚层状白云岩中,矿体的产出部位与层位和构造关系密切.不同级别和不同时期的构造相互交汇和切割,对铅锌矿床的形成起着明显的控制作用.通过矿床特征、找矿标志的分析研究,对该类型铅锌矿床的找矿标志和找矿方法有了新的认识和发现,为寻找此类型的铅锌矿床提供了经验.     

Structural Features and Function of the Karst Critical Zone

正1 Major achievements of IGCP 661 The IGCP661 project"Processes,Cycle,and Sustainability of the Critical Zone in Karst Systems (2017-2021)"has been carried out for two years.Besides five International karst meetings and two training courses for karst that have been held,some scientific achievements include the basic roles of the function and structural evolution of the karst critical zone have been determined.In various types of karst critical zone,the different forms of calcite and HCO_3~-cycling were determined.A     

青田山口叶蜡石传压介质初步研究

采用青田山口叶蜡石作为超高压高温合成金刚石的传压介质，分析了其主要化学成分和矿物组成。对青田山叶蜡石粉压块粒度效应进行了研究，确定了该传压介质的粒度组成。超高压高温人造金刚石试验表明，青田山口叶蜡石的传压介质理想，金刚石合成效果较好。     

白山、丰满水库群实时洪水联合调度系统设计与开发

利用面向对象程序设计技术,在中文窗口平台下,设计开发了功能齐全、界面友好、操作灵活、信息丰富,具有很强实用性的白山、丰满水库群实时洪水联合调度系统,可迅速完成从实时遥测降雨信息的采集到两库产、汇流预报和洪水联合调度方案的制定、评价、选择的全过程,简要介绍了系统开发策略及系统设计中的一些主要关键技术及其实现过程,对开发其它水库及水库群防洪调度系统具有重要参考价值。     

Cation diffusion in aluminosilicate garnets: experimental determination in pyrope-almandine diffusion couples

Diffusion couples made from homogeneous gem quality natural pyrope and almandine garnets were annealed within graphite capsules under anhydrous conditions at 22–40 kbar, 1057–1400 °C in a piston-cylinder apparatus. The concentration profiles that developed in each couple were modeled to retrieve the self diffusion coefficients [D(I)] of the divalent cations Fe, Mg, Mn and Ca. Because of their usually low concentrations and lack of sufficient compositional change across the interface of the diffusion couples, only a few reliable data can be obtained for D(Ca) and D(Mn) from these experiments. However, nine sets of D(Fe) and D(Mg) data were retrieved in the above P-T range, and cast in the form of Arrhenian relation, D=D ₀exp{−[Q(1 bar)+PΔV ⁺]/RT}. The values of the activation energy (Q) and activation volume (ΔV ⁺) depend on whether f _O2 is constrained by graphite in the system C-O or held constant. For the first case, we have for Fe:Q(1 bar)=65,532±10,111 cal/mol, D ₀=3.50 (±2.30)×10⁻⁵ cm²/s, ΔV ⁺=5.6(±2.9) cm³/mol, and for Mg:Q(1 bar)=60,760±8,257 cal/mol, D ₀=4.66 (±2.48)×10⁻⁵ cm²/s, ΔV ⁺=5.3(±3.0) cm³/mol. Here the ΔV ⁺ values have been taken from Chakraborty and Ganguly (1992). For the condition of constant f _O2, the Q values are ∼9 kcal lower and ΔV ⁺ values are ∼4.9 cm³/mol larger than the above values. Lower temperature extrapolation of the Arrhenian relation for D(Mg) is in good agreement with the Mg tracer diffusion data (D ^* _Mg) of Chakraborty and Rubie (1996) and Cygan and Lasaga (1985) at 1 bar, 750–900 °C, when all data are normalized to the same pressure and to f _O2 defined by graphite in the system C-O. The D ^* _Mg data of Schwandt et al. (1995), on the other hand, are lower by more than an order of magnitude than the low temperature extrapolation of the present data, when all data are normalized to the same pressure and to f _O2 defined by the graphite buffer. Comparison of the D(Fe), D(Mg) and D(Mn) data in the pyrope-almandine diffusion couple with those in the spessartine-almandine diffusion couple of Chakraborty and Ganguly (1992) shows that the self diffusion of Fe and Mn are significantly enhanced with the increase in Mn/Mg ratio; the enhancement effect on D(Mg) is, however, relatively small. Proper application of the self diffusion data to calculate interdiffusion coefficient or D matrix elements for the purpose of modeling of diffusion processes in natural garnets must take into account these compositional effects on D(I) along with the effects of thermodynamic nonideality, f _O2, and pressure. Received: 8 May 1997 / Accepted: 2 October 1997