Oxygen Isotope Evidence for Chemical Interaction of Ki lauea Historical Magmas with Basement Rocks

K<IMG SRC="http://petrology.oxfordjournals.org/math/imacr.gif" ALT="i" BORDER="0">lauea historical summit lavas have a wide range in matrix <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O_VSMOWvalues (4·9–5·6<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">). The disequilibriumbetween matrix and olivine <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and K<IMG SRC="http://petrology.oxfordjournals.org/math/imacr.gif" ALT="i" BORDER="0">lauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of K<IMG SRC="http://petrology.oxfordjournals.org/math/imacr.gif" ALT="i" BORDER="0">lauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. K<IMG SRC="http://petrology.oxfordjournals.org/math/imacr.gif" ALT="i" BORDER="0">lauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">) based on thenew olivine <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values. KEY WORDS: Hawaii; K<IMG SRC="http://petrology.oxfordjournals.org/math/imacr.gif" ALT="i" BORDER="0">lauea; basalt; oxygen isotopes; crustal contamination     

正常菌与可吸入矿物细颗粒作用致突变性研究

采用Ames试验分别对蒙脱石、石英、方解石、钠长石4种可吸入矿物细颗粒及其与大肠杆菌、表皮葡萄球菌相互作用48 h后的混悬液作为受试物进行检测,分析IMG是否具有致突变性,及其与人体正常细菌群作用后,IMG/正常菌复合体是否有致突变性毒力改变。结果显示石英以及石英/大肠杆菌复合体对TA98、TA100菌株Ames试验呈阳性反应;石英/表皮葡萄球菌复合体对TA98菌株Ames试验呈阳性反应;而蒙脱石、方解石、钠长石纯矿及其与正常菌作用后的复合体Ames试验结果均为阴性。结果表明石英具有直接致突变作用;石英与正常菌菌作用后复合体依然具有致突变性,但石英表现出的碱基置换突变作用在与表皮葡萄球菌作用后消失,其机制有待进一步研究。     

几种遥感影像数据读写及其在地理国情普查中的应用

随着地理国情普查和1∶50000动态更新等国家指令性项目的开展,不同类型的遥感影像应用越来越广泛,因此遥感影像图像文件的数据读写就显得更为必要和急切。本文以TIFF,IMG为例,就几种常见遥感影像格式及其读写做以说明,以便大家在影像读取、裁切等操作中应用。     

Petrogenesis of the Swaziland and Northern Natal Rhyolites of the Lebombo Rifted Volcanic Margin, South East Africa

The Jozini and Mbuluzi rhyolites and Oribi Beds of the southernLebombo Monocline, southeastern Africa, have geochemical characteristicsthat indicate they were derived by partial melting of a mixtureof high-Ti/Zr and low-Ti/Zr Sabie River Basalt Formation types.Compositional variations within the different rhyolite typescan largely be explained by subsequent fractional crystallization.The Sr- and Nd-isotope composition of the rhyolites is uniqueamongst Gondwana silicic large igneous provinces, having <IMG SRC="http://petrology.oxfordjournals.org/math/epsiv.gif" ALT="{varepsilon}" BORDER="0">_Ndvalues close to Bulk Earth (–0·94 to 0·35)and low, but more variable, initial ⁸⁷Sr/⁸⁶Sr ratios (0·7034–0·7080).Quartz phenocryst <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values indicate that the rhyolite magmashad <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values between 5·3 and 6·7<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">, consistentwith derivation from a basaltic protolith with <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values between4·8 and 6·2<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">. The low-<IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O rhyolites (< 6·0<IMG SRC="http://petrology.oxfordjournals.org/math/permil.gif" ALT="{per thousand}" BORDER="0">)come from the same stratigraphic horizon and are overlain andunderlain by rhyolites with more ‘normal’ <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O magmavalues. These low-<IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O rhyolites cannot have been produced byfractional crystallization or partial melting of mantle-derivedbasaltic material. The rhyolites have low water contents, makingit unlikely that the low <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O values are the result of post-emplacementalteration. Modification of the source by fluid–rock interactionat elevated temperatures is the most plausible mechanism forlowering the <IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O magma value. It is proposed that the low-<IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸Orhyolites were derived by melting of earlier altered rhyolitein calderas situated to the east, which were not preserved afterGondwana break-up. KEY WORDS: rhyolite; Lebombo; stable and radiogenic isotopes; low-<IMG SRC="http://petrology.oxfordjournals.org/math/delta.gif" ALT="{delta}" BORDER="0">¹⁸O magmas; partial melting