The importance of iron speciation (Fe+2/Fe+3) in determining mineral assemblages: an example from the high‐grade aluminous metapelites of southeastern Madagascar

Metapelitic granulites from the Anosyen domain of southeastern Madagascar are exposed in three intercalated formations: the Amparihy, Bakika and Ihosy formations. Although mineralogically distinct from each other, the rocks from these formations show very similar bulk‐rock compositions when measured on a Fe_T basis. The preserved mineral assemblages thus do not reflect differences in the ratios of the main rock‐forming oxides (i.e. Al₂O₃:Fe_T:MgO), but instead reflect variations in the pre‐metamorphic oxidation state of the protolith rocks. These differences in oxidation state are manifested via differences in iron speciation – either Fe⁺² or Fe⁺³. The relatively reduced rocks of the Amparihy Formation preserve the assemblage bi–sp–sill–g–cd, which contrasts markedly with the mostly garnet and spinel‐absent bi–cd–sill–mt assemblages preserved in the strongly oxidized rocks of the Ihosy Formation. Compositionally intermediate rocks of the Bakika Formation are garnet bearing, but sillimanite‐absent, and contain the assemblage sp–g–cd–mag. Modelling of these rocks in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O system suggests that they evolved along a heating and cooling P–T path with only limited decompression accompanying cooling on the retrograde path. Peak temperatures and pressures of ～880–920 °C and 6–6.5 kbar are inferred for the majority of the Anosyen domain, with slightly lower peak temperatures (～840 °C) estimated in the extreme northwest of the area. The high‐temperature and relatively low‐pressure nature of metamorphism suggests high geothermal gradients existed during orogenesis, which in southern Madagascar is related to the amalgamation of Gondwana (580–520 Ma). Although metamorphic temperatures may have been augmented via thermal advection from the emplacement of the syn‐ to post‐tectonic Ambalavao suite, the high geothermal gradients nevertheless suggest thin and consequently hot lithosphere existed prior to orogenesis.     

Sunrise Hill unconformity: A newly discovered regional hiatus between Archaean granites and greenstones in the northeastern Pilbara Craton

Contacts between Archaean granites and greenstones in the northeastern part of the Pilbara Craton have been described as intrusive and tectonic. New field observations in the Shay Gap region demonstrate that greenstones of the Gorge Creek Group unconformably overlie the Muccan and Warrawagine batholiths. Regionally, the unconformity is marked by a persistent but relatively thin basal clastic sequence, locally with a granite boulder conglomerate, overlain by ore‐bearing banded iron‐formation, fine‐grained clastic rocks and chert. The granite basement is dated at 3443 ± 6 Ma. The precise age of the hiatus is unknown but its maximum effect might have been the removal of a substantial thickness of Early to Middle Archaean strata.     

Nitric oxide profiles measured in situ during the Globus '85 campaign

Nitric oxide profiles obtained from three flights of chemiluminescent instruments during the Globus '85 campaign held in France in the autumn of 1985 are reported. When the profile obtained in the early morning of 20 September is compared with the flight made the previous afternoon, an average morning to midday NO ratio of 0.7 for the region between 26 and 33 km is obtained. This value is in good agreement with theoretical studies involving the photolysis of N₂O₅ and the establishment of the NO₂–NO equilibrium.     

Iron porphyrins in the Permian Kupferschiefer of the lower Rhine Basin, N.W. Germany

Immature samples of the Permian Kupferschiefer from the Lower Rhine Basin in N.W. Germany were analysed for tetrapyrrole pigment type and abundance. The sediment, thought to have been deposited in a marine regime with enhanced salinity, was found to contain high concentrations of metalloporphyrins. The porphyrins are complexed to nickel (Ni) and oxovanadium (V=0), but high abundances of iron (Fe) porphyrins were also detected using UV/visible spectroscopy and mass spectrometry. The presence in the latter of series of aetioporphyrins, cycloalkanoporphyrins, di-cycloalkanoporphyrins and benz-cycloalkanoporphyrins was confirmed by accurate mass measurements; HPLC co-injection of deoxophylloerythroetioporphyrin (C₃₂ DPEP) with the demetallated iron porphyrins indicated its presence in the sediment as an iron complex. The study provides the first evidence for the occurrence of Fe porphyrins in geological samples other than coals and lignites, and reports the highest concentrations in sedimentary organic matter to date.     

Intercomparison of NO column measurements during MAP/GLOBUS 1985

Column measurements of nitric oxide were made using several techniques during the MAP/GLOBUS campaign in France in September 1985. The data sets are nearly co-located and simultaneous, therefore allowing a valid intercomparison of the various measurement methods. The range of altitudes sampled differs from instrument to instrument. This complicates the comparison because the data sets are to some extent complementary. The NO distributions apparently vary significantly from day to day, and possibly over shorter timescales. Changes in dynamics may be responsible for these variations. The results from the instruments which measure in the infrared and the ultraviolet are self-consistent, and show good agreement with photochemical predictions. On 19 September, when the intercomparison was made, the profile measured by the in-situ chemiluminescent instrument differed significantly from the predicted profile, and the measured columns were generally higher.     

攀西地区铁钛氧化物矿物的显微结构

本文用矿石显微镜及单晶X射线分析方法,研究了攀枝花—西昌地区铁钛氧化物矿物的显微结构共生组合特点、各出溶相间的关系和分布方位以及不同岩石和矿石显微结构共生组合上的差异。业已查明它们受岩浆旋回和岩石类型所控制。本文指出了磁铁矿-钛铁晶石固溶体显微出溶结构可能是拐点分解经调制结构后的终期产物。     

游离氧化铁形态转化对红粘土工程性质的影响

本文通过模拟环境中的有机质使游离氧化铁形态转化对典型红粘土工程性质的影响试验,系统地测试了游离氧化铁的形态分布与物性指标的关系。试验结果表明,在渍水条件下,游离氧化铁的形态转化对红粘土性质的影响不显著,但在渗水条件下,由于游离氧化铁的流失使得胶结作用减弱,它对红粘土工程性质的影响逐渐明显,其潜在的危害仍然是不容忽视的。     

微波等离子体炬原子发射光谱法测定铁和铝的研究

研究了低功率微波等离子体炬原子发射光谱法（ＭＰＴ－ＡＥＳ）对Ｆｅ，Ａｌ的测定。样品经气动雾化后，分别以流动注射与连续式两种方式引入ＭＰＴ。考察了用这两种进样方式时ＭＰＴ－ＡＥＳ的分析性能，证明低功率ＭＰＴ－ＡＥＳ具有良好的分析特性。     

辉碲铋矿单矿物的化学分析

辉碲铋矿物经ＨＮＯ３－ＫＣｌＯ３溶解，用火焰原子吸收法或乙二胺四乙酸二钠事滴定法测定Ｂｉ，火焰原子吸收法测定Ｔｅ、Ｆｅ、Ｃｕ，３，３＇－二氨基联苯胺光度法测定Ｓｅ，硫酸重量法测定Ｓ。其结果与矿物化学成分理论值十分接近，主、次量元素平行测定６次，其ＲＳＤ小于０．８％，痕量元素ＲＳＤ（ｎ＝６）小于１０％。     

Studies of Nitrous Oxide Emission from Farmlands in North China

Measurements of nitrous oxide emission from agricultural lands were conducted. The results show that nitrous oxide fluxes on several soils are at the range of 2-60 μg . N / m2 h. Factors influencing the production rates of nitrous oxide from the soils, such as soil temperature, soil moisture and fertilization, are discussed. The calculated amount of nitrous oxide emission from China farmlands is 9.8 × 107 Kg . N per year, which accounts for about 10% of the total source strength in China areas.