Composition of chromian diopside megacryst in DSDP Leg 37 basalts (Table 2, 3)

Refractory megacrysts of olivine, plagioclase, chromian diopside and Cr-Al spinel, which were not in equilibrium with the host oceanic tholeiite on eruption, are present in samples from several dredge sites and DSDP drill sites in the Atlantic and Pacific Oceans. They have multiple origins: (1) cognate or accidental mantle fragments; (2) relict fragments from fractional crystallization of parental liquids considerably more primitive than oceanic tholeiite; and most commonly (3) the fractional crystallization products of such liquids mixed with oceanic tholeiite magma. Melt inclusions in chrome-spinel phenocrysts provide evidence for this postulated Mg- and Ca-rich magma which has counterparts in the Scottish Tertiary Province and in west Greenland.大西洋及太平洋的多个拖网采样站位与深海钻探计划（Deep Sea Drilling Project, DSDP）钻孔样品中，产出橄榄石、斜长石、铬透辉石及铬铝尖晶石的难熔巨晶；这类巨晶在喷发时与寄主大洋拉斑玄武岩（oceanic tholeiite）并未达到化学平衡。该类巨晶存在多种成因：(1) 同源或幔源捕虏体；(2) 源自比大洋拉斑玄武岩更为原始的母岩浆经分离结晶作用形成的残余碎块；而最常见的成因类型(3)，则是此类母岩浆与大洋拉斑玄武岩岩浆混合后，经分离结晶作用形成的产物。铬尖晶石斑晶中的熔体包裹体，为这一被提出的富镁富钙岩浆假说提供了实证依据，其对应产出见于苏格兰第三纪省及西格陵兰地区。