Structural states of Mg-cordierite I: Order parameters from synchrotron X-ray and NMR data

The hexagonal to orthorhombic phase transition in synthetic Mg-cordierite has been studied by (i) measuring the spontaneous strain associated with the transition using Synchrotron X-ray powder diffraction and (ii) measuring the degree of Al, Si order in terms of the number of Al-O-Al bonds per formula unit using solid state NMR spectroscopy. This defines the two order parametersQ andQ _od respectively, and their relationship as a function of annealing temperature and time is used to define the structural states of cordierite during the ordering sequence. The formation of modulated hexagonal cordierite within which a high degree of Al, Si order can be attained, results in a strongly non-linear relationship betweenQ andQ _od .The transition from modulated to orthorhombic cordierite is strongly first-order under all temperature conditions studied and involves a large step inQ, whileQ _od changes continuously throughout the ordering sequence with no marked discontinuity at the phase transition. The lattice distortion, traditionally defined in cordierite by the Δ index provides no full information on the degree of Al, Si order in anhydrous Mg-cordierite, and both order parameters must be used to define its structural state. Transmission electron microscopy has been used to study the mechanism of the transformation from hexagonal to modulated to orthorhombic cordierite.     

Omphacite in Californian metamorphic rocks

Omphacite is a common mineral in greenstones, metasediments and related Franciscan rocks of the glaucophane schist facies. It also occurs in late veins cutting amphibolites, glaucophane schists, eclogites, greenstones, and occasionally metagraywackes. It is apparent that this mineral is stable under glaucophane schist facies conditions in rocks of a suitable bulk composition, and is not restricted to the eclogite facies. Association with albite, quartz and lawsonite, and late veining of omphacite veins by aragonite indicates that pressures necessary to form omphacite are reasonably close to those calculated from an ideal solution model.     

On the occurrence of eclogite in Western Norway

Recent experimental data show that eclogites may form in the crust under conditions where total pressure exceeds water pressure. The regional distribution of eclogites in Western Norway and their association with crustal rocks makes their formation in the crust the most attractive hypothesis. Before a mantle origin should be assigned to any rock within this eclogite and garnet peridotite area it should be demonstrated that their country rocks are in a metamorphic state incompatible with the load pressures required for eclogite stability. Criteria for ascertaining eclogite formation in the crust are discussed.Publication no. 8 in the Norwegian geotraverse project.     

大洋环流型式转换在冰期旋回中的作用及经典第四纪冰期理论质疑(续)

大洋环流型式转换在冰期旋回中的作用及经典第四纪冰期理论质疑(续)汉景泰Ｗ．Ｓ．Ｆｙｆｅ(加拿大西安大略大学地质系)４问题及讨论大洋环流－气候学说认为从冰期到间冰期海洋－大气系统全球性巨型再组合导致了末次冰期的终止。     

地球科学新的优先考虑的问题：自然科学、工程学、经济学的联合和知识发展的必要性

文章从分析生命支持系统的基本组成着手,指出愈来愈多的人类活动促使大气中ＣＯ２、ＣＨ４、Ｈ２Ｏ、Ｎ２Ｏ…含量不断增加,气候变暖;水资源危机愈加严重;对土壤产出的要求越来越高;地质灾害对人类自身的冲击更加严重;能源和原材料更大程度的短缺;废物的排放量增大及生物变异等新问题和生物种类的新发现。对上述现象的深入研究或解决,均是地球科学优先和急于考虑的问题。而这需要大批高素质,既具自然科学、工程学、经济学,又具管理知识的人才,因而这些优先考虑问题的重中之重是教育。     

Kyanite-andalusite equilibrium

The solubilities of macrocrystalline andalusite and kyanite have been measured in water between 400 and 550 °C and at pressures of 1–3 kilobars. Resulting data indicate that the phases are in equilibrium at 398 °C (1 kb,), 472 °C (2 kb) and 534 °C (3 kb). Due to the inherent difficulty of measuring small solubility differences errors in these temperatures could be as much as ±40 °C although experimental reproducibility suggests greater precision.     

Pan-African plates: Additional evidence from igneous events in Saudi Arabia

The chemical and geological nature of thec. 600 m.y. igneous complex of the Al-Hadah escarpment of Saudi Arabia is fitting to that of a modern subduction environment. It appears that plate motions were occurring during this Pan-African tectonic event but the scale of both plates and motions was smaller than that of the present time.     

Experimental introduction of excess Ar40 into a granitic melt

Samples of a Precambrian granite were melted in sealed capsules to produce a radiogenic Ar⁴⁰ atmosphere over the melt. The amount of Ar⁴⁰ incorporated in the quenched charge was then determined. Under these experimental conditions the amount of argon dissolved in the quenched melt was appreciable and could be an important source of error in potassiumargon dating.Publication authorized by the Director, U.S. Geological Survey.