The stable isotope signature of kilometre-scale fracturedominated metamorphic fluid pathways, Mary Kathleen, Australia

Abstract Large calcite veins and pods in the Proterozoic Corella Formation of the Mount Isa Inlier provide evidence for kilometre-scale fluid transport during amphibolite facies metamorphism. These 10- to 100-m-scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 × 10-km Mary Kathleen Fold Belt, despite the isotopic heterogeneity of the surrounding wallrocks. The fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks. The pods have δ¹³C_calcite values of –2 to –7% and δ¹⁸O_calcite values of 10.5 to 12.5%. Away from the pods, metadolerite wallrocks have δ¹⁸O_whole-rock values of 3.5 to 7%. and unaltered banded calc-silicate and marble wallrocks have δ¹³C_calcite of –1.6 to –0.6%, and δ¹⁸O_calcite of 18 to 21%. In the alteration zones adjacent to the pods, the δ¹⁸O values of both metadolerite and calc-silicate rocks approach those of the pods. Large calcite pods hosted entirely in calc-silicates show little difference in isotopic composition from pods hosted entirely in metadolerite. Thus, 100- to 500-m-scale isotopic exchange with the surrounding metadolerites and calc-silicates does not explain the observation that the δ¹⁸O values of the pods are intermediate between these two rock types. Pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc-silicates. These data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the Corella Formation at the presently exposed crustal level, although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc-silicates, or thermal fluctuations attending deformation and metamorphism. The overall L-shaped trend of the data on plots of δ¹³C vs. δ¹⁸O is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc-silicate rocks. Localization of the vein systems in dilatant sites around metadolerite/calc-silicate boundaries indicates a strong structural control on fluid flow, and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km. The ultimate source for the external fluid is uncertain, but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle. Intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism.     

宁远保安地区基性─超基性火山岩基本特征

本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系，作了初步探讨。     

辽西中生代火山岩岩浆成因——稀土元素配分及同位素定量模式

本文通过对辽西及邻区中生代盆地火山岩稀土元素配分特征的研究及模拟运算，探讨了其岩浆成因及过程。结果显示南北岩区岩浆成因不同，南岩区岩源为MORB地幔和长期富集型幔熔融混合而成，北岩区为MORB和近期亏损型地幔熔融混合而成。     

Sedimentary environment and development controls of the hydrocarbon source beds:Middle and Upper Proterozoic in northern North China

Problem on development control of marine source bed hold in Chinese petroleum industry progression. The Hongshuizhuang Formation,Tieling Formation and Xiamaling Formation in the Middle and Upper Proterozoic are important hydrocarbon source beds in northern North China, and investigation of their sedimentary environments and the controls has great significance for petroleum exploration in North China. Based on sedimentology (sequence stratigraphy), palaeoecology, sedimentary geochemistry, and sedimentary palaeogeography, their development pattern is discussed. All these studies indicate that the development controls of the hydrocarbon source beds include a favorite palaeogeographic location, exceeding propagation of biomes in low and middle latitudes, anoxic environments, enrichment of phosphorus element and the adsorption of clay minerals during the preservation of organic matter in the marine carbonates.     

豫西济源谭庄组河流沉积中的Stipsellus遗迹组构

豫西济源盆地上三叠统谭庄组下段为曲流河沉积。本文通过描述和分析谭庄组河流沉积特征，划分了4种不同河流沉积组合类型，识别出Stipsellus遗迹组构，并发现该遗迹组构常与曲流河沉积物伴生，可作为此类沉积的典型生物遗迹标志。其中，Stipsellus sp．A代表发育在河漫滩较浅水体下或潮湿的软底细粒沉积物中的一种遗迹组构类型；Stipsellus sp．B则代表发育在曲流砂坝上部的男一种遗迹组构类型。     

Composition of plagioclases in volcanic rocks of King George Island, Antarctica with reference to the petrogenetic significance

Plagioclases occur mainly as phenocrysts in volcanic rocks of King George Island, South Shetland Islands, West Antarctica. In basaltic andesites and andesites of Keller Peninsula and Ullman Spur (Admiralty Bay), they are high structure state labradorite-andesines; and in high-A1 basalts and basaltic andesites of Barton and Weaver peninsulas (Maxwell Bay), they are high structure state bytownite-anorthites.∑REE, La/Yb ratios and δEu values of plagioclases from Admiralty Bay are higher than those from Maxwell Bay. All plagioclases have rather identical chondritenormalized transitional element distribution patterns, probably reflecting that crystal structure rather than composition of plagioclase controls their diversity. Compositions of plagioclases depend chiefly on those of their host rocks, compositional differences of plagioclases reveal that basaltic magmas in the Admiralty Bay area are more evolved than in the Maxwell Bay area.     

川西理塘第四纪盆地沉积体系、演化及古气候分析

理塘第四纪盆地以河湖相沉积为主，其形成于747ka，消亡于179～180ka。盆地内不同地点的沉积物的时空分布，揭示出古湖泊演化属于一种不连续的扩展型，在其演化过程中存在着多次的消失或萎缩时期；盆地内孢粉组合表明，其形成于一种温热湿润的气候环境，当时的海拔高度在2000m左右，以后高原气候由热变温；冰川发育加剧了古无量河的溯源侵蚀作用，最终切穿盆地，致使湖水外泄，湖泊消亡。理塘盆地的演化历程为研究青藏高原的古气候变化提供了重要证据。     

个旧锡矿区域地壳演化与成矿探讨

个旧锡多金属矿床是驰名中外的特大型矿床，过去认为是燕山晚期“花岗岩岩浆期后气液矿床”。但通过探讨区域上前震旦纪地壳演化、震旦纪-早古生代地壳演化、泥盆纪-三叠纪地壳演化以及侏罗纪-第四纪地壳演化，以及与成矿之间的关系，发现个旧矿区至少经历了印支中晚期海底基性火山-沉积成矿、印支中晚期海底喷流热水沉积成矿、燕山晚期花岗岩叠加改造成矿以及喜山期陆相表生沉积成矿作用，厘定了个旧锡矿区的印支中晚期海底基性火山．沉积Sn-Cu-Zn(Au)矿床系列、印支中晚期海底喷流-沉积Sn-Cu-Pb-Zn矿床系列、燕山晚期花岗岩叠加改造Sn-Cu-W-Be-Bi-Pb-Zn-Ag矿床系列、喜山期陆相表生沉积砂矿矿床系列等4大矿床系列及12种矿床类型。     

火山岩与地形联合约束下海岛土壤稀土元素地球化学空间分布异质性——以广西涠洲岛为例

海岛土壤地球化学特征的研究对于认识海岛表生地质环境有重要意义。本研究以我国最大的第四纪火山海岛——涠洲岛为案例,重点研究亚热带海岛环境下火山岩风化土壤的稀土元素（REE）地球化学特征,并探讨影响其空间分布的关键因素。结果表明,涠洲岛土壤REE总量（ΣREE）自然变化范围较大,介于59.07~575.30 mg/kg,平均值为285.53 mg/kg,高于中国大陆土壤背景值（163.86 mg/kg）,指示火山岩风化海岛具有较高的土壤REE丰度。反距离权重插值法（IDW）分析指示,岛内土壤的REE含量高低变化呈现出以带状和斑块状为主体形态的空间分布不均一性,推断其成因与母质岩石类型和地形位置等因素密切相关。3种不同岩性的成土母岩的ΣREE含量变化序列为：玄武岩（236.66 mg/kg）>火山碎屑岩（215.58 mg/kg）>含生物碎屑海滩沉积物（18.99 mg/kg）,对应的土壤ΣREE含量具有类似变化规律,即玄武岩土壤（307.20 mg/kg）>火山碎屑岩土壤（297.46 mg/kg）>含生物碎屑海滩沉积物土壤（89.73 mg/kg）。该证据指示母岩是控制岛内土壤REE含量变化的首位因素,玄武岩整体上易形成具有较高REE丰度的土壤,火山碎屑岩次之,而含生物碎屑海滩沉积物反之。此外,本研究还发现火山碎屑岩单一岩性区内,发育的土壤REE含量也会随地形地貌差异而出现显著变化,其原因是地形地貌制约了土壤矿物和化学风化程度,海蚀丘陵比海积平原更利于海岛土壤中REE次生富集作用的发生。