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

该项目的重点是伊朗东南部马克兰带南部中心（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，马克兰带是一个活跃的俯冲带，上面覆盖着地球上最广泛的新生代增生楔。虽然已经开展了一些研究，但对其演化的许多方面仍然知之甚少，如俯冲起始、后续发展、岛弧岩浆作用的时间和演化、岛弧岩浆作用对大陆地壳产生的贡献、岛弧碰撞和增生、和分离和挖掘（超）在俯冲带中，特别是年轻和薄的海洋板块的一个常见过程是最上面的玄武岩地壳的一部分的分离和它们的增生到底部。增生杂岩除了沉积物沿着沿着下沉的海洋板块被刮走之外，其他物质也可以被转移并增生到上覆的板块上。这可能发生在弧下的深度，涉及（超）基性岩弧根材料和高压变质岩（蓝片岩），或在楔内和楔下的较浅层次，通常涉及（非常）低级变质岩，或根本没有变质的岩石。伊朗SMZ中心的沉积物含有（非常）大的（层状）辉长岩、辉石岩和橄榄岩，以及体积较小的长英质至中等岩浆岩、斜长角闪岩和蓝片岩。这些不连续地暴露在距离海沟约200公里的一个200公里乘40公里的大区域内。由于加积楔是加积速率高、热流低且通常缺乏岩浆活动的区域，因此需要对楔中心出现大量岩浆岩和变质岩作出解释。本研究的目的是建立楔内的吸积和拆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/或洋壳的残余。蓝片岩的岩石学和40 Ar/39 Ar定年可提供活动俯冲带高压变质岩分离深度和折返速率的信息。这些结果将允许在更广泛的喜马拉雅俯冲-碰撞带的可比岩石类型的相关性。新特提斯洋在伊朗东南部尚未关闭，通过研究SMZ的地质方面，我们可以更好地研究这些过程，如俯冲，增生，碰撞，变质和折返，发生在阿尔卑斯-喜马拉雅造山带的其他部分。重要的是，马克兰楔的大部分都暴露在陆地上，可以接触到楔状结构和岩石，也可以接触到其他活动俯冲系统无法接触到的结晶岩。事实上，SMZ很可能是地球上唯一一个对活跃的俯冲洋壳进行陆基研究的地方。

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.