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The growth of Glasgow from a small town into a heavily industrialised conurbation depended greatly on its local geological riches. Extensive mining and quarrying of a range of minerals took place from the 18th century onwards. The early underground stoop and room (pillar and stall) workings, and the backfilled quarries, together with variably consolidated natural superficial deposits, have bequeathed to the city a heritage of unwanted engineering problems which cannot easily be quantified. Recent work by the British Geological Survey (BGS) illustrates the scale of both geological and man-made problems. 相似文献
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Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan 总被引：5，自引：0，他引：5
BROWNE BRANDON L.; EICHELBERGER JOHN C.; PATINO LINA C.; VOGEL THOMAS A.; DEHN JONATHAN; UTO KOZO; HOSHIZUMI HIDEO 《Journal of Petrology》2006,47(2):301-328
Mafic to intermediate enclaves are evenly distributed throughoutthe dacitic 1991–1995 lava sequence of Unzen volcano,Japan, representing hundreds of mafic recharge events over thelife of the volcano. This study documents the morphological,textural, chemical, and petrological characteristics of theenclaves and coexisting silicic host lavas. The eruptive productsdescribed in this study appear to be general products of magmamingling, as the same textural types are seen at many othervolcanoes. Two types of magmatic enclaves, referred to as Porphyriticand Equigranular, are easily distinguished texturally. Porphyriticenclaves display a wide range in composition from basalt toandesite, are glass-rich, spherical and porphyritic, and containlarge, resorbed, plagioclase phenocrysts in a matrix of acicularcrystals and glass. Equigranular enclaves are andesitic, non-porphyritic,and consist of tabular, medium-grained microphenocrysts in amatrix glass that is in equilibrium with the host dacite magma.Porphyritic enclaves are produced when intruding basaltic magmaengulfs melt and phenocrysts of resident silicic magma at theirmutual interface. Equigranular enclaves are a product of a moreprolonged mixing and gradual crystallization at a slower coolingrate within the interior of the mafic intrusion. KEY WORDS: mafic enclaves; quenched mafic inclusions; magma mingling; Unzen volcano; Unzen Scientific Drilling Project; resorbed plagioclase 相似文献
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The Boss Point Formation of Maritime Canada comprises alternating successions of braidplain sandstone, lacustrine mudstone, and lacustrine fluvio-deltaic sandstone and mudstone. These rocks were deposited within an active strike-slip basin during the early Pennsylvanian (Westphalian A), at a palaeolatitude of 8°S. Palaesols comprise a small but distinct proportion of the formation, and typically occur at the tops of fining upward sandstone-siltstone cycles. Spherulitic siderites from the Boss Point Formation occur within sandy and silty palaeosols. They occur as ‘large’ (>200 μm) and ‘small’ (<200 μm) diameter spherulitic nodules within calcrete, and show either a radially arranged ferroan calcite and siderite spar morphology, or contain a core of ferroan calcite, surrounded by a later formed sheath of siderite. Analytical data indicate that with respect to Ca-Mg-Mn, wide compositional variation occurs within the siderites. The Boss Point Formation siderites are similar to, but contain less Ca for a given Mg/Mn ratio, than previously published siderite compositional data. Published data, together with the results from the Boss Point Formation, indicate that a continuum exists in freshwater siderites, between the relatively Mn-depleted and the Mg-enriched analytical fields that were previously reported. The relatively low Ca values determined in the Boss Point Formation samples reflect the general lack of calcium in the sedimentary basin during sedimentation. Both chlorite and smectite clays may have been important sources of iron. It is concluded that the spherulitic siderites are eogenetic, and formed within small anoxic ponds rich in organic matter, under reducing and low dissolved sulphate conditions. With time these pools dried up, ferroan calcite precipitating as calcrete nodules around the earlier formed siderite spherulites. 相似文献
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