Subduction of Neo-Tethys oceanic lithosphere beneath the Iranian plate during the Mesozoic formed several igneous bodies of ultramafic to intermediate and felsic composition. Intrusion of these magmas into a regional metamorphic sequence (the Sanandaj-Sirjan Zone) caused partial melting and formation of migmatites with meta-pelitic protoliths. The Alvand complex (west Iran) is a unique area comprising migmatites of both mafic and pelitic protoliths. In this area, the gabbroic rocks contain veins of leucosome at their contact with pyroxenite and olivine gabbro. These leucosomes are geochemically and mineralogically different from leucosomes of the meta-pelitic migmatites and clearly show properties of I-type granites. Microscopic observations and whole rock compositions of the mafic migmatite leucosomes show that migmatization occurred through partial melting of biotite, hornblende and plagioclase. Thermobarometric calculations indicate 800 °C and 3.7 kbar for partial melting, although phase diagram modeling demonstrates that the presence of water could decrease the solidus temperature by about 40 °C. Our results suggest an asthenospheric magma upwelling as the source of heat for partial melting of the gabbroic rock during subduction of Neo-Tethys oceanic crust under the western edge of the Iranian plate. The present study also reveals relationships between migmatization and formation of S- and I -type granites in the area.

中文翻译：

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伊朗板块下新特提斯俯冲过程中的高温-低压变质作用：Alvand 杂岩体（伊朗西部）镁铁质混合岩形成的证据

中生代伊朗板块下方的新特提斯大洋岩石圈俯冲形成了几个超镁铁质至中质和长英质成分的火成岩体。这些岩浆侵入区域变质层序（Sanandaj-Sirjan 带）导致部分熔融并形成混合岩和变泥质原岩。Alvand 复合体（伊朗西部）是一个独特的区域，包含基性原岩和泥质原岩的混合岩。在该地区，辉长岩在与辉石岩和橄榄石辉长岩接触时含有白体脉。这些白体在地球化学和矿物学上与变泥质混合岩的白体不同，并且清楚地显示了 I 型花岗岩的特性。镁铁质混合岩白体的显微观察和全岩组成表明，混合作用是通过黑云母、角闪石和斜长石的部分熔融发生的。热气压计算表明部分熔化为 800 °C 和 3.7 kbar，尽管相图模型表明水的存在可以将固相线温度降低约 40 °C。我们的结果表明，在伊朗板块西缘下的新特提斯洋壳俯冲期间，软流圈岩浆上涌作为辉长岩部分熔化的热源。本研究还揭示了混杂作用与该地区 S 型和 I 型花岗岩的形成之间的关系。尽管相图模型表明水的存在可以将固相线温度降低约 40 °C。我们的研究结果表明，在伊朗板块西缘下的新特提斯洋壳俯冲期间，软流圈岩浆上涌作为辉长岩部分熔化的热源。本研究还揭示了混杂作用与该地区 S 型和 I 型花岗岩的形成之间的关系。尽管相图模型表明水的存在可以将固相线温度降低约 40 °C。我们的研究结果表明，在伊朗板块西缘下的新特提斯洋壳俯冲期间，软流圈岩浆上涌作为辉长岩部分熔化的热源。本研究还揭示了混杂作用与该地区 S 型和 I 型花岗岩的形成之间的关系。