Small degree of partial melting on peridotites and gabbros from the upper mantle.

辉长岩层和辉长岩袋通常存在于上地幔衍生的橄榄岩中（例如，日本Horoman橄榄岩杂岩中的辉长岩; Ronda橄榄岩中的镁铁质层）。有一个普遍的共识，辉长岩与幔源橄榄岩不显示任何同源的化学成分的关系，残留物和部分熔融熔体。研究了小熔体对辉长岩和橄榄岩的变质作用。(1)MORB地幔岩的H_2O-不饱和固相线在T=1000 ℃时位于28 kb的压力下，在P=18 ~ 23 kb时位于1075 ℃的温度下。该固相线与MORB地幔岩成分中部分角闪石的稳定极限相吻合，固相线的位置可由橄榄岩中Na_2 O + K_2 O含量控制。(2)在T=950 ° C附近，测定了霍罗曼辉长岩的10 kb H_2O不饱和固相线。辉长岩中部分气化角闪石的最大温度稳定性出现在P=10 kb时的T=1075 ℃，比MORB地幔岩的温度稳定性高50 ℃左右。在固相线附近的P-T条件下，角闪石可以作为控制水化橄榄岩分解和变质的媒介。(3)在上地幔橄榄岩的岩浆通道附近，可以观察到少量熔体对橄榄岩的影响，在那里，在少量的部分熔融的壁橄榄岩以及从通道的熔体添加过程中可以产生置换。

Gabbroic layers and pockets are commonly found in upper mantle-derived peridotites (e.g., gabbros in the Horoman peridotite complex, Japan; mafic layers in the Ronda peridotites). There is a general consensus that gabbros in association with the mantle-derived peridotites do not show any co-genetic relationships in chemical compositions as residues and the partially fused melts. Effects of small melts on the modification of the gabbros as well as peridotites were investigated in this research.(1) H2O-undersaturated solidus of MORB pyrolite locates at a pressure of 28 kb at T=1000ﾟC and at a temperature of 1075ﾟC between P=18 and 23 kb. This solidus coincides with the stability limit of pargasitic amphibole in MORB pyrolite composition and the location of solidi can be controlled by the Na2O+K2O content of peridotites.(2) 10 kb H2O-undersaturated solidus of the Horoman gabbro was determined near T=950ﾟC from the sandwich-type melting experiments. The maximum temperature stability of pargasitic amphibole in gabbros occurs at T=1075ﾟC under P=10 kb, which is approximately 50ﾟC higher than that for MORB pyrolite. It is clear that the amphibole can be an agent controlling the decomposition and modification on hydrated peridotites under the P-T conditions near solidus.(3) Effect of small amounts of melt on peridotites is observable near magma channels in the upper mantle-derived peridotites, where a replacement can be generated during small degree of partial melting of the wall peridotites as well as melt addition from the channel.