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

大陆岩石圈有一层薄薄的硅质地壳(约10-40公里)，下面是较致密的富铁镁(超镁铁质)大陆岩石圈地幔。上地壳在成分上大致为花岗岩类。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窗口。大多数研究人员同意，大型花岗岩类侵入体形成于俯冲带(大洋岩石圈倾斜下降到下地幔)上方的大陆弧中。然而，许多根本性的问题仍然存在，即岩浆的产生和侵位是否跨越俯冲过程，或者岩浆侵位是否集中在反映碰撞造山作用和碰撞后地壳松弛的离散时期。岩浆的形成和侵位是连续的还是间歇性的？如果岩浆成因是连续的，那么上地壳的岩浆侵位是否是幕式的，并受到离散的构造-岩浆事件的促进？为了回答这些问题，我将把重点放在欧洲西北部的加里东山带上。在爱尔兰和苏格兰，田野关系得到了很好的保存和良好的记录。挪威特殊的垂直暴露使人们能够对花岗岩类侵入进行三维调查。推断花岗岩类岩浆产生和侵位的过程需要将野外观察与岩石地球化学、精确的年龄限制和记录岩浆来源的敏感同位素比率相结合(S)。当单个矿物在岩浆中生长时，它们会形成带状，它们的地球化学和同位素成分从核心到边缘记录了地幔和再循环地壳不断演变的相对贡献。直到最近，分析技术才变得足够精确，能够提供对岩浆生成和侵位过程的基本见解。我和我的HQP将使用岩石年代学(岩石或矿物随时间增长的测定)来研究花岗岩类岩浆的成因，在俯冲、碰撞和后碰撞阶段的岩浆源的演化，以及岩浆过程的时间尺度。我们将分析坚固矿物的微量元素和同位素组成，这些矿物系统地记录了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颗粒尺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拟议的研究计划的基础，该计划包括许多HQP机会。其目的是促进对山区岩浆作用的性质和时间尺度的了解。地壳再循环与新的地壳增长的比例对于地壳演化模型和研究地壳增长时期、气候、生命演化和金属天赋之间的潜在联系是必不可少的。

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.