【摘要】 苦橄岩是一种超镁铁质熔岩 ,它在大火成岩省中虽然只占很小的比例 ,但具有非常重要的意义。苦橄岩通常产于火山岩系的底部和下部 ,其中有的苦橄岩具有原始岩浆的特点 ,另有一些为堆积成因 ,也有少部分代表了演化岩浆。对它的岩石学、矿物学、元素和同位素地球化学以及橄榄石包裹体中挥发份的研究可以为研究大火成岩省和地幔柱的关系、地幔柱的热成分结构模式、大火成岩省和全球生物灭绝事件以及预测Cu Ni PGE硫化物矿床的成矿潜力提供重要约束。更多还原

【Abstract】 Picrite is a special ultramafic lava. Although it has a little production in large igneous provinces (LIPs), it plays a crucial role in many respects. In general, picrites are found in the early parts of LIP successions. Olivine phenocryst compositions and whole-rock chemical compositions can be used to identify primitive picrite. The calculated results show that some of them are believed to represent the primary mantle-derived melts, and others may be generated by accumulation of olivines, whereas minor may be relatively evolved magmas. Based on the melting experiments under high-temperature and high-pressure condition, the liquidus temperatures and pressures can be estimated. We obtained a liquidus temperature of 1 600 ℃ and pressure of 4.5 GPa for the Emeishan picrites by this method, suggesting that the Emeishan large igneous province are related to mantle plume because such high temperature is about 250 to 320℃ higher than the potential asthenospheric temperature. It might support the model that the plume head is hotter than the plume tail. Major, trace element and Sr, Nd and Pb geochemistry of picrites can provide some important constraints on their source regions. Oxygen isotope of phenocryst olivine in picrites is an available tool for discriminating crustal contaminations whereas He isotope is a powerful tool for identifying MORB-deriving and plume-derived sources. In addition, combination of highly siderophile elements and Os isotope geochemistry can provide a dominant constraint on the structure model of mantle plume, i.e., whether it originates from core-mantle boundary or upper-lower boundary. Recently, relations of LIPs to global mass extinction events are paid much attention. However, whether they played a crucial or little role in global mass extinction events is quite debated. Estimation of degassing quantity and ratios by petrological method can provide a dominant evidence on the issue. In addition, the relation between LIPs and Cu-Ni-PGE sulfide deposits are focused in recent ten years. The chalcophile element and PGE concentrations in picrites can provide a key clue to prospect for the potential of Cu-Ni-PGE sulfide deposits.更多还原