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A. G. Shtukenberg Yu. O. Punin E. Haegele H. Klapper 《Physics and Chemistry of Minerals》2001,28(9):665-674
Optical anomalies (deviations of the symmetry of optical properties from the ideal symmetry of the crystal) occur in many
minerals and synthetic compounds and have been under investigation since the last century. An important feature of optically
anomalous mixed crystals is a high degree of optical inhomogeneity, whereas the optical patterns of mixed crystals without
anomalies are usually rather uniform. This work is devoted to the study of this phenomenon. As a model object we have chosen
mixed alum crystals, which were known for their anomalous birefringence and which revealed the following types of optical
inhomogeneities: (1) sector zoning; (2) concentric zoning; (3) subsector zoning; (4) stripes normal to growth front.
The inhomogeneity of anomalous birefringence of mixed crystals of alums can be explained by superposition of several effects:
mismatch strain, strain along dislocations and growth ordering of isomorphous components. Optical inhomogeneities due to the
sector zoning of crystals and their dislocation structure arise even under stationary growth conditions and stationary micromorphology
of the growing face. Both variable growth conditions and the relief of the growing face strongly intensify the optical inhomogeneity
due to three interrelated factors: (1) a significantly inhomogeneous mismatch strain; (2) a variable degree of ordering of
isomorphous components due to the compositional inhomogeneities; (3) different degrees of ordering of isomorphous atoms caused
by different orientations, heights and velocities of growth steps. These effects lead to the formation of subsector zoning
and zoning superimposed on the optical sector zoning. These optical structures are crossed by birefringent stripes arising
from dislocations.
Received: 29 March 2000 / Accepted: 11 March 2001 相似文献
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Giorgio Graziani Sergio Lucchesi Eugenio Scandale 《Physics and Chemistry of Minerals》1990,17(5):379-384
Growth marks of pegmatite beryls can be divided into general and specific in relation to their types and distributions. Dislocation absence and growth bands have been recognized as general growth marks of the environment while minor element concentrations and optical anomalies as specific to the local growth medium. 相似文献
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《Journal of Structural Geology》2002,24(6-7):1109-1123
This study uses compositional analyses of garnet porphyroblasts to test a previously published microstructure-based model of garnet growth in the Fleur de Lys Supergroup. X-ray maps reveal significant compositional anomalies within garnet, including zoning reversals and steepened compositional gradients. These anomalies occur at the margin of the proposed first stage of garnet growth (G1), and coincide with truncations of inclusion trails and changes in the inclusion assemblage. Intervals of reversed composition zoning and steepened compositional gradients across this boundary are interpreted to represent a hiatus in garnet growth, possibly accompanied by garnet consumption, during which changes in the garnet-forming reaction, P–T conditions and deformation kinematics occurred. The junction of the proposed second and third stages of garnet growth (G2 and G3) coincides with the transition between successive crenulation cleavages, without substantial microstructural truncations or changes in the inclusion assemblage. The G2–G3 boundary is generally marked by uninterrupted normal zoning, with subtle compositional anomalies in some samples. This boundary may in fact record continuous garnet growth, or alternatively mark a relatively short intra-orogenic pause in garnet growth with minimal affect on zoning patterns. Individual porphyroblasts with contrasting inclusion trail microstructures also have different zoning patterns, and this supports the previous recognition of contrasting growth histories between individual porphyroblasts. A combined structural–metamorphic model is presented that integrates the timing of garnet growth and foliation development, reaction history and the P–T–t path in the Fleur de Lys Supergroup. 相似文献
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At Segura, granitic pegmatite veins with cassiterite and lepidolite, hydrothermal Sn–W quartz veins and Ba–Pb–Zn quartz veins intruded the Cambrian schist–metagraywacke complex and Hercynian granites. Cassiterite from Sn–W quartz veins is richer in Ti and poorer in Nb and Nb+Ta than cassiterite from granitic pegmatite. Wolframite from Sn–W quartz veins is enriched in ferberite component. The Sn–W quartz veins contain pyrrhotite, arsenopyrite, sphalerite, chalcopyrite, stannite, matildite and schapbachite and the Ba–Pb–Zn quartz veins have cobaltite, pyrite, sphalerite, chalcopyrite, galena and barite, which were analyzed by electron microprobe. The presently abandoned mining area was exploited for Sn, W, Ba and Pb until 1953. Stream sediments and soils have higher concentrations of metals than parent granites and schists. Sn, W, B, As and Cu anomalies found in stream sediments and soils are associated with Sn–W quartz veins, while Ba, Pb and Zn anomalies in stream sediments and soils are related to Ba–Pb–Zn quartz veins. Sn, W, B, As, Cu, Ba, Pb and Zn anomalies in stream sediments and soils are also related to the respective old mining activities, which increased the mobility of trace metals from mineralized veins to soils, stream sediments and waters. Stream sediments and soils are sinks of trace elements, which depend on their contents in mineralized veins and weathering processes, but Sn, W and B depend mainly on a mechanic process. Soils must not be used for agriculture and human residence due to their Sn, B, As and Ba contents. Waters associated with mineralized veins were analyzed by flame atomic absorption spectroscopy (FAAS) and ICP-AES have high As, Fe and Mn and should not be used for human consumption and agriculture activities. The highest As values in waters were all related to Sn–W quartz veins and the highest Fe and Mn values were associated with the Ba–Pb–Zn quartz veins. No significant acid drainage was found associated with the old mine workings. 相似文献
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《International Geology Review》2012,54(10):1157-1171
Intensities and anomalies of radiometric (gamma) natural fields are related to structures in geologic sections. Positive and negative anomalies in the overburden of petroliferous as well as of "sterile" structures are essentially functions of lithologic and/or mineral composition of the rocks which, in turn, depend on tectonic structure of the area. These and still other complexities, suited as they may be for interpreting radiometric expressions of various structures, are still in need of further research. -- AGI Staff. 相似文献
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Pierre Nehlig Fawsia Asfirane Antonin Genna Catherine Guerrot Nadège Nicol Ignace Salpeteur Mohammed Shanti & Denis Thiéblemont 《地学学报》2001,13(5):347-353
A new aeromagnetic map together with new geological and geochronological data has led to a reinterpretation of the geological history of the Arabian Shield.
The magnetic anomalies outline an orogenic complex containing a network of mostly left-lateral strike-slip faults, including the Nabitah Belt and several peripheral mountain ranges. Oblique accretion resulted in obliteration of early volcanic-arc magnetic fabrics, which were almost completely replaced by a NW–SE magnetic fabric in the northern Shield; the southern Shield, however, reveals extensive E–W anomalies related to post-accretion magmatic intrusions. This complex web of orogenic zones is intimately associated with synchronous molasse basins that formed 680–610 Ma.
The distribution and chronology of orogenic zones, related to the closing of East and West Gondwana, brings into question several earlier assumptions, such as high continental growth rates, palaeogeodynamic reconstructions, the definitions of the Nabitah and Najd faults, and the significance of molasse basins. 相似文献
The magnetic anomalies outline an orogenic complex containing a network of mostly left-lateral strike-slip faults, including the Nabitah Belt and several peripheral mountain ranges. Oblique accretion resulted in obliteration of early volcanic-arc magnetic fabrics, which were almost completely replaced by a NW–SE magnetic fabric in the northern Shield; the southern Shield, however, reveals extensive E–W anomalies related to post-accretion magmatic intrusions. This complex web of orogenic zones is intimately associated with synchronous molasse basins that formed 680–610 Ma.
The distribution and chronology of orogenic zones, related to the closing of East and West Gondwana, brings into question several earlier assumptions, such as high continental growth rates, palaeogeodynamic reconstructions, the definitions of the Nabitah and Najd faults, and the significance of molasse basins. 相似文献
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基于数字高程模型因子分析的地球化学异常提取 总被引：1，自引：0，他引：1
利用R型因子分析方法,对西北某地区1∶5万图幅岩屑样测试数据进行了分析,提取了5个代表性因子,绘制地球化学分区图。结合区域成矿地质背景、研究区地质条件及野外地质调查发现的41个矿化点,确定具有成矿意义的因子F3(Cu-Zn-Ag组合)。利用基于GIS数字高程模型对F3因子进行异常信息提取,结果显示76%的铜矿化点与异常吻合,较铜单元素圈定的异常提高了10%。异常主体位于志留系公婆泉组变质安山岩与石炭纪侵入岩的接触带(岩性偏安山岩),野外异常查证发现这些异常部位多见矿化现象。研究区北部钾长花岗岩区出现的少量弱小异常,为岩浆热液有关的黄铁矿化及黄铜矿化引起。槽探工程进一步验证了该方法在中大比例尺异常提取方面的良好效果。 相似文献
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本文介绍了三个非背斜圈闭型油气田上方进行汞量测量的试验结果,油层埋深一般在1200—3000m之间。分别属岩性圈闭、断块圈闭和岩性一断层圈闭型油气田,所用测量方法包括负压法壤中气汞量测量、累积吸附法壤中气汞量测量、土壤总汞测量、土壤吸附汞测量和水中汞量测量等。试验结果表明,各种方法在油气田上方均有清晰的异常显示。其异常特征与金属矿床上的汞气异常有其相似性。异常形态和空间分布,主要取决于导气构造的特性。汞气异常和电性异常与油气藏的关系进行了类比。这两种方法的异常有时与油气藏在地表的投影位置吻合,有时分别偏离一定距离,进一步证明了构造形态对异常的影响,并推断根据汞气异常和电性异常的特征,有可能追索油气藏的位置。 相似文献
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在粤东北某矿区进行时间域激发极化法工作时,人文干扰引起假异常。针对这种情况,通过分析地下通信光缆和地下金属供水网的平面和剖面异常特征,研究了人文干扰对时间域激发极化法观测结果的影响。经过与已知矿体异常特征的比较,区分出矿异常和干扰异常。 相似文献
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Chemical kinetics, speleothem growth and climate 总被引：7，自引：0，他引：7
WOLFGANG DREYBRODT 《Boreas: An International Journal of Quaternary Research》1999,28(3):347-356
The morphology and stratigraphy of speleothems are controlled by parameters that depend on climate. These are the water supply rates feeding the speleothem, e.g. a stalagmite, the growth rates dependent on the chemical kinetics of calcite precipitation and the supersaturation of the solution from which calcite is precipitated. To elucidate the basic principles of speleothem growth, a physical-chemical model of calcite precipitation is used to estimate growth rates under various geologically relevant conditions. Furthermore, we present a model that allows the computation of the growth history of stalagmites, i.e. their morphology and stratigraphy under varying climatic conditions. This enables us to see how climatic signals are inscribed into stalagmites. Owing to the counter-balancing effects of some parameters, it is not possible to read climatic conditions backwards from the morphology and stratigraphy of a speleothem in a simple way, but a basic understanding of the growth of speleothems can be a helpful supporting tool in the interpretation of palaeoclimatic records. 相似文献
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内蒙古额济纳旗道噶地区矿化类型为石英脉型,见含Au石英脉出露。通过对该地区进行土壤地球化学测量工作,在统计研究区各地层Cu、Ag、Au、Pb、Zn、Sb、Mo、Ni、Co、W、As、Sb等微量元素含量基础上,应用聚类分析方法分析元素间相关关系。在研究区圈定出61处单元素异常区,其中Au元素异常8处。根据地球化学异常分类规范,综合考虑地球化学异常的规模、形态、异常的强度、分带性、异常元素的组合及异常区成矿地质条件和地球化学条件,在单元素异常的基础上圈定出乙类综合异常区2个(Ⅰ号、Ⅱ号综合异常区),丙类综合异常区1个(Ⅲ号综合异常区)。在对研究区地质特征及土壤地球化学特征的基础上圈定出3个找矿靶区,并进行地表工程验证,为进一步找矿工作提供有利依据。 相似文献
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