Petrogenesis, age and origin of (ultra)mafic, magmatic and metamorphic rocks of the Makran Accretionary Wedge, Southern Makran Zone, SE Iran

该项目主要研究位于伊朗东南部Makran带(SMZ)中心的(超)镁铁质、岩浆和变质岩的起源、性质、年龄和地球动力学背景，Makran带是一个活跃的俯冲带，覆盖着地球上最广泛的新生代增生楔形构造之一。已经开展了一些研究，但对其演化的许多方面仍知之甚少，如俯冲开始、随后的发展、岛弧岩浆作用的时间和演化、其对大陆地壳产生的贡献、弧碰撞和吸积、(超)镁铁质或深弧壳的拆离和折返。对于特别年轻和薄的大洋板块来说，俯冲带中的一个常见过程是最上面的玄武岩地壳的部分拆离，并将它们吸积到增生杂岩的底部。除了沿着沉积带从下沉的大洋板块上刮下来的沉积物外，其他物质还可以转移并附着到上覆板块上。这可能发生在弧形以下的深处，涉及(超)镁铁质弧根物质和高压变质岩(蓝片岩)，或者发生在楔形岩石内部和下方的较浅层，通常涉及(非常)低级别变质岩，或者根本没有变质的岩石。伊朗SMZ中心的沉积物含有(非常)大量的(层状)辉长岩、辉石岩和橄榄岩，以及体积较小的长英质到中级岩浆岩，以及角闪岩和蓝片岩。它们不连续地暴露在距离战壕约200公里的200乘40公里的大范围内。由于吸积楔是高吸积率、低热流和通常缺乏火成岩活动的地带，因此需要解释楔形中央大量岩浆和变质岩体的出现。这项研究旨在确定楔体内吸积和剥离过程的原因和时间，并阐明SMZ的演化。地球化学、矿物成分和锆石测年将确定这些岩石是否代表岛弧物质和/或洋壳的残留物。蓝片岩的岩石学和40Ar/39Ar测年将提供活动俯冲带高压变质岩分离深度和折返速率的信息。这一结果将允许与更广泛的喜马拉雅俯冲-碰撞带中的可比岩石类型进行对比。伊朗东南部的Neotethys洋尚未闭合，通过研究SMZ的地质方面，我们可以更好地研究阿尔卑斯-喜马拉雅造山带其他部分发生的俯冲、吸积、碰撞、变质和折返等过程。重要的是，Makran楔形的大部分暴露在陆地上，这使得可以接触到楔形结构和岩石，但也可以接触到在其他活跃的俯冲系统中无法接触到的结晶岩石。事实上，SMZ很可能是地球上唯一一个以陆地为基础研究活跃俯冲洋壳的地方。

This project focuses on the origin, nature, age and geodynamic setting of (ultra)mafic, magmatic and metamorphic rocks in the centre of the southern Makran Zone (SMZ) in SE Iran, an active subduction zone overlain by one of the most extensive Cenozoic accretionary wedges on Earth. Several studies have been carried out but many aspects of its evolution remain poorly understood, such as subduction initiation, subsequent development, the timing and evolution of island arc magmatism, its contribution to the production of continental crust, arc collision and accretion, and the detachment and exhumation of (ultra)mafic or deep arc crust.A common process in subduction zones for especially young and thin ocean plates is the detachment of parts of the uppermost basaltic crust and their accretion to the base of the accretionary complex. Besides sediments scraped off the downgoing ocean plate along décollements, other material can be transferred and accreted to the overriding plate. This can occur at depth below arcs and involve (ultra)mafic arc root material and high-pressure metamorphic rocks (blueschists), or at shallower levels within and below the wedge and generally involving (very) low-grade metamorphic rocks, or rocks not metamorphosed at all. The sediments in the centre of the Iranian SMZ contains (very) large bodies of (layered) gabbros, pyroxenites and peridotites with smaller volumes of felsic to intermediate magmatic rocks, and amphibolites and blueschists. These are discontinuously exposed over a large, 200 by 40 km area situated at a distance of about 200 kilometres from the trench. As accretionary wedges are zones of high accretion rate, low heat flow and normally lack igneous activity, the occurrence of large bodies of magmatic and metamorphic rocks in the centre of the wedge needs to be explained. This study aims to establish the causes and timing of accretion and detachment processes within wedges, and to elucidate the evolution of the SMZ. Geochemistry, mineral composition and zircon dating will establish whether the rocks represent remnants of island arc material and/or ocean crust. Petrology and 40Ar/39Ar dating of blueschists will yield information about separation depths and exhumation rates of HP metamorphic rocks in an active subduction zone. The results will allow correlation with comparable rock types in the wider Himalayan subduction-collision zone. The Neotethys ocean did not yet close in SE Iran and by studying geological aspects of the SMZ, we can better study these processes such as subduction, accretion, collision, metamorphism, and exhumation that took place in other parts of the Alpine-Himalayan orogen. Importantly, large parts of the Makran wedge are exposed on land, allowing access to wedge structures and rocks, but also to crystalline rocks that are inaccessible in other active subduction systems. In fact, the SMZ may well be the only place on Earth for a land-based study of actively subducting oceanic crust.