ABSTRACT

The interaction between migrating melts and the upper mantle largely affects the composition of the ascending melt and residual peridotites. In island arcs, melt-rock interactions and products which involved highly depleted mantle peridotites are still largely undocumented despite their petrological importance. In this contribution, the petrographic and geochemical signatures of refractory and refertilized peridotites comprising the mantle section of the southern Palawan Ophiolite, Philippines are investigated. The peridotites are dominantly comprised of residual spinel harzburgites with minor dunite and plagioclase peridotites. Spinel harzburgites are similar to other highly depleted residual mantle materials of other suprasubduction zone ophiolites. Plagioclase peridotites, which are cut by gabbroic intrusions, preserve distinct petrological characteristics indicating melt-rock interaction. The melts preserved as gabbroic dikes have signatures transitional between mid-ocean ridge and island arc, and are comparable to back-arc basin lavas. We therefore propose that the plagioclase peridotites were formed due to the reaction between highly depleted mantle peridotites beneath an intraoceanic arc and migrating BABB-like magmas possibly during the incipient stages of back-arc rifting.

摘要

迁移熔体与上地幔之间的相互作用在很大程度上影响了上升熔体和残余橄榄岩的组成。在岛弧中，熔岩相互作用和涉及高度枯竭的地幔橄榄岩的产物，尽管具有重要的岩石学意义，但在很大程度上仍未被记录。在这篇文章中，研究了构成菲律宾巴拉望蛇绿岩南部地幔部分的耐火橄榄岩和再肥橄榄岩的岩石学和地球化学特征。橄榄岩主要由残余尖晶石斜长岩和少量纯晶岩和斜长石橄榄岩组成。尖晶石方辉石类似于其他超俯冲带蛇绿岩的其他高度耗竭的残余地幔物质。斜长石橄榄岩，被辉长岩侵入体切割，保留明显的岩石学特征，表明熔岩相互作用。保存为辉长岩脉的熔体具有洋中脊和岛弧之间的过渡特征，可与弧后盆地熔岩相媲美。因此，我们提出斜长石橄榄岩的形成是由于洋内弧下高度枯竭的地幔橄榄岩与可能在弧后裂谷的初期阶段迁移的 BABB 状岩浆之间的反应。