Petrogenesis of andalusite–kyanite–sillimanite veins and host rocks, Sanandaj-Sirjan metamorphic belt, Hamadan, Iran

Quartz‐rich veins in metapelitic schists of the Sanandaj‐Sirjan belt, Hamadan region, Iran, commonly contain two Al₂SiO₅ polymorphs, and, more rarely, three coexisting Al₂SiO₅ polymorphs. In most andalusite and sillimanite schists, the types of polymorphs in veins correlate with Al₂SiO₅ polymorph(s) in the host rocks, although vein polymorphs are texturally and compositionally distinct from those in adjacent host rocks; e.g. vein andalusite is enriched in Fe₂O₃ relative to host rock andalusite. Low‐grade rocks contain andalusite + quartz veins, medium‐grade rocks contain andalusite + sillimanite + quartz ± plagioclase veins, and high‐grade rocks contain sillimanite + quartz + plagioclase veins/leucosomes. Although most andalusite and sillimanite‐bearing veins occur in host rocks that also contain Al₂SiO₅, kyanite‐quartz veins crosscut rocks that lack Al₂SiO₅ (e.g. staurolite schist, granite). A quartz vein containing andalusite + kyanite + sillimanite + staurolite + muscovite occurs in andalusite–sillimanite host rocks. Textural relationships in this vein indicate the crystallization sequence andalusite to kyanite to sillimanite. This crystallization sequence conflicts with the observation that kyanite‐quartz veins post‐date andalusite–sillimanite veins and at least one intrusive phase of a granite that produced a low‐pressure–high‐temperature contact aureole; these relationships imply a sequence of andalusite to sillimanite to kyanite. Varying crystallization sequences for rocks in a largely coherent metamorphic belt can be explained by P–T paths of different rocks passing near (slightly above, slightly below) the Al₂SiO₅ triple point, and by overprinting of multiple metamorphic events in a terrane that evolved from a continental arc to a collisional orogen.     

Tectonic controls on metamorphism, partial melting, and intrusion: timing and duration of regional metamorphism and magmatism in the Ni de Massif, Turkey

Mafic high-pressure granulite, eclogite and pyroxenite xenoliths have been collected from a Mesozoic volcaniclastic diatreme in Xinyang, near south margin of the Sino-Korean Craton (SKC). The high-pressure granulite xenoliths are mainly composed of fine-grained granoblasts of Grt+Cpx+Pl+Hbl±Kfs±Q±Ilm with relict porphyritic mineral assemblage of Grt+Cpx±Pl±Rt. P–T estimation indicates that the granoblastic assemblage crystallized at 765–890 °C and 1.25–1.59 GPa, corresponding to crustal depths of ca. 41–52 km with a geotherm of 75–80 mW/m². Calculated seismic velocities (V_p) of high-pressure granulites range from 7.04 to 7.56 km/s and densities (D) from 3.05 to 3.30 g/cm³. These high-pressure granulite xenoliths have different petrographic and geochemical features from the Archean mafic granulites. Elevated geotherm and petrographic evidence imply that the lithosphere of this craton was thermally disturbed in the Mesozoic prior to eruption of the host diatreme. These samples have sub-alkaline basaltic compositions, equivalent to olivine– and quartz–tholeiite. REE patterns are flat to variably LREE-enriched (La_N/Yb_N=0.98–9.47) without Eu anomaly (Eu/Eu*=0.95–1.11). They possess 48–127 ppm Ni and 2–20 ppm Nb with Nb/U and La/Nb ratios of 13–54 and 0.93–4.75, respectively, suggesting that these high-pressure granulites may be products of mantle-derived magma underplated and contaminated at the base of the lower crust. This study also implies that up to 10 km Mesozoic lowermost crust was delaminated prior to eruption of the Cenozoic basalts on the craton.     

Analysis and study of the large earthquake risk in Yanqing-Huailai basin

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Relationship of manganese-iron oxides and associated heavy metals to grain size in stream sediments

The distribution of ammonium citrate-leachable lead, zinc and cadmium among size fractions in stream sediments is strongly influenced by the presence of hydrous Mn-Fe oxides in the form of coatings on sediment grains. Distribution curves showing leachable metals as a function of particle size are given for eight samples from streams in New York State. These show certain features in common; in particular two concentrations of metals, one in the finest fractions, and a second peak in the coarse sand and gravel fraction. The latter can be explained as a result of the increasing prevalence and thickness of oxide coatings with increasing particle size, with the oxides serving as collectors for the heavy metals. The distribution of Zn and Cd in most of the samples closely parallels that of Mn; the distribution of Pb is less regular and appears to be related to Fe in some samples and Mn in others. The concentration of metals in the coarse fractions due to oxide coatings, combined with the common occurrence of oxide deposition in streams of glaciated regions, raises the possibility of using coarse materials for geochemical surveys and environmental heavy-metal studies.     

Two-feldspar geothermometry in granulite facies metamorphic rocks

A geothermometric technique based on equilibria between coexisting plagioclase and alkali feldspar was applied to quartzo-feldspathic granulites from Salvador, BA, Brazil. The conditions of metamorphism were determined to be in the range 750 ° C–800 ° C, 4–8 Kb, by comparison with experimental data on the stabilities of sapphirine, phlogopite and other minerals occurring in the associated rocks. Selected feldspar data gives temperatures near, but slightly below, this range. Several variants of the Wood and Banno model, as well as an empirical two-pyroxene geothermometer, were also tested and found to give temperatures which were apparently 50 °–100 ° high. The solubility of Al₂O₃ in orthopyroxene indicates temperatures which are about 200 ° to high, suggesting that Fe in the natural assemblages significantly changes relationships observed experimentally in MgO-Al₂O₃-SiO₂ systems.     

基于特征指数合成影像的不透水面提取和分析

不透水面作为表征一个地区城市化水平的关键性指标,其时空变化特征与城市建设密切相关.以济南市重要的泉水补给区南部山区为研究对象,根据植被-不透水面-土壤(V-I-S)城市地表组分模型选取了NDVI、BCI、SBAI、MNDWI和NDUI 5种遥感特征指数构成合成影像,利用最大似然法对特征指数合成影像进行分类获取不透水面信...