Timescales of magmatic processes in accretionary orogens: Implications for crustal growth

大陆岩石圈有一个薄的硅质地壳帽（~10-40 km），下面是致密的富铁镁（超镁质）大陆岩石圈地幔。上地壳的成分大致为花岗岩类。花岗岩类岩浆起源于地壳深部，为研究地壳深部过程提供了一个窗口。大多数研究人员都认为，大型花岗岩类侵入物形成于俯冲带（海洋岩石圈向下地幔倾斜）上方的大陆弧。然而，许多基本问题仍然存在，如岩浆的产生和侵位是否跨越了俯冲的持续时间，或者岩浆侵位是否集中在反映碰撞造山运动和碰撞后地壳松弛的离散事件中。岩浆的形成和侵位是连续的还是偶发的？如果岩浆的成因是连续的，那么岩浆在上地壳的侵位是否是偶发的，是否是由离散的构造岩浆事件促成的？为了回答这些问题，我将把重点放在欧洲西北部的加里多尼亚山带上。在爱尔兰和苏格兰，这种田间关系得到了很好的保存和记录。挪威独特的垂直暴露使得花岗岩类侵入的三维调查成为可能。推断花岗岩岩浆生成和侵位的过程需要将现场观测与岩石地球化学、精确的年龄约束和记录岩浆来源的敏感同位素比率相结合。当单个矿物在岩浆中生长时，它们被分带，它们的地球化学和同位素组成从核心到边缘记录了地幔和再循环地壳的演化相对贡献。直到最近，分析技术才变得足够精确，可以为岩浆的产生和就位过程提供基本的见解。我的HQP和我将使用岩石年代学（确定岩石或矿物随时间的生长）来研究花岗岩岩浆的成因，在一个增生山带的俯冲、碰撞和碰撞后阶段岩浆源的演化，以及岩浆过程的时间尺度。我们将分析强健矿物的微量元素和同位素组成，系统地记录岩浆生长过程中的演化。这些耦合的岩石学和时间框架将被纳入将粒度过程与复杂的构造和岩浆历史联系起来的模型中。我的研究经验构成了包括许多HQP机会在内的拟议研究计划的基础。其目的是促进对山带岩浆过程的性质和时间尺度的认识。地壳再循环与新地壳生长的比例是建立地壳演化模式和研究地壳生长时期与气候、生命演化和金属禀赋之间潜在联系的必要条件。

The continental lithosphere has a thin cap of siliceous crust (~10-40 km) underlain by a denser Fe-Mg rich (ultramafic) continental lithospheric mantle. The upper crust is broadly granitoid in composition. The granitoid magmas originate in the deep crust and provide a window for studying deep crustal processes. Most researchers agree that large, granitoid intrusions form in continental arcs above subduction zones (the angled descent of oceanic lithosphere into the underlying mantle). However, many, fundamental questions persist as to whether magma generation and emplacement spans the duration of subduction or whether magma emplacement is concentrated in discrete episodes that reflect collisional orogeny and post-collisional crustal relaxation. Are magma genesis and emplacement continuous or episodic processes? If magma genesis is continuous, is magma emplacement in the upper crust episodic and facilitated by discrete tectonomagmatic events? To address these questions, I will focus on the Caledonian mountain belt in northwestern Europe. In Ireland and Scotland, the field relationships are remarkably preserved and well documented. Norway's exceptional vertical exposures allow a three-dimensional investigation of granitoid intrusions. Deducing the processes responsible for granitoid magma generation and emplacement requires combining field observations with lithogeochemistry, precise age constraints, and sensitive isotopic ratios that record the magma source(s). As individual minerals grow in magmas, they become zoned and their geochemical and isotopic compositions from core to rim record the evolving relative contributions from the mantle and recycled crust. Only recently have analytical techniques become sufficiently precise to provide fundamental insights into magma generation and emplacement processes. My HQP and I will use petrochronology (the determination of rock or mineral growth with time) to investigate the genesis of granitoid magmas, the evolution of magma sources during the subduction, collision, and post-collisional phases of an accretionary mountain belt, and the timescales of the magmatic processes. We will analyze the trace element and isotopic compositions of robust minerals, which systematically record magma evolution as they grow. These coupled petrological and temporal frameworks will be incorporated into models that link grain-scale processes to complex tectonic and magmatic histories. My research experiences form the foundation of the proposed research program that includes many HQP opportunities. The objectives are to contribute to the understanding of nature and timescales of magmatic processes in mountain belts. The proportion of crustal recycling to new crustal growth is perquisite for models of crustal evolution and for investigating potential connections between episodes of crustal growth, climate, the evolution of life, and metal endowments.