(Table 1) Chemical composition of segregations and groundmass seperates of ODP Leg 135 samples

Concentrations of dark-colored, highly vesicular, quench-textured mesostasis occur commonly in volcanic rocks drilled in the Lau Basin during Leg 135. These segregations occur as veins, patches, and vesicle linings in rocks with 49%-54% SiO2. The segregations are depleted in Mg, Ca, Al, Sc, Ni, and Cr and enriched in Ti, Ba, Y, and Zr compared to the groundmass with which they occur. Many of the segregations are unusually enriched in copper. The elemental variations show that the segregations are residual liquids produced by 12%-55% crystallization of plagioclase and clinopyroxene, with minor olivine, opaques, or orthopyroxene from the groundmass melt. The liquids forming the segregations are mobilized and emplaced in earlier formed vesicles during the rapid crystallization of the groundmass. The dominant process in this mobilization and emplacement is volatile exsolution from crystallizing melts constrained by a rigid crystalline framework. This exsolution produces significant overpressures within the late-stage melts; the overpressure drives the residual melts through the walls of the older vesicles, along planes of weakness, and into voids. This mechanism is consistent with the occurrence of bimodal vesicle populations in many of the host lavas.

劳盆地（Lau Basin）第135航次钻取的火山岩中，普遍发育深色、高泡孔状、具淬火结构的填隙物（mesostasis）富集体。这类分凝体以脉体、斑块及泡孔衬壁的形式产出在SiO₂含量为49%~54%的岩石中。相较于其赋存的火山岩基质（groundmass），该类分凝体贫Mg、Ca、Al、Sc、Ni及Cr，而富Ti、Ba、Y及Zr。诸多分凝体的铜含量异常偏高。
元素地球化学变化特征表明，这些分凝体是由基质熔体经斜长石（plagioclase）、单斜辉石（clinopyroxene）及少量橄榄石（olivine）、不透明矿物（opaques）或斜方辉石（orthopyroxene）经历12%~55%的结晶分异作用后形成的残余熔体。在基质快速结晶过程中，形成分凝体的残余熔体被迁移并充填至先期形成的泡孔中。
该迁移与就位作用的主导机制为：受刚性结晶格架约束的结晶熔体发生挥发分出溶（volatile exsolution）。该挥发分出溶作用会在晚期熔体内部产生显著超压，超压驱使残余熔体穿过先期泡孔的壁体、沿薄弱面裂隙运移并充填至各类空隙中。该机制与诸多寄主熔岩中发育的双峰式泡孔群（bimodal vesicle populations）的产出特征高度吻合。