Generation of felsic crust in the Archean: A geodynamic modeling perspective
Generation of felsic crust in the Archean: A geodynamic modeling perspective
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DOI：
10.1016/j.precamres.2015.10.005
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发表时间：
2015-04
影响因子：
3.8
通讯作者：
E. Sizova;T. Gerya;K. Stüwe;Michael Brown
中科院分区：
文献类型：
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作者：
E. Sizova;T. Gerya;K. Stüwe;Michael Brown
由于地球长期变冷，一般没有现代的类比来帮助理解太古代可能发生的构造样式。太古宙较高的地幔温度和较高的放射性生热会影响地壳的厚度和组成。因此，基于地质记录中保存的碎片证据的约束良好的数值模拟是评估太古宙地壳形成假说的最合适工具。太古宙灰色片麻岩杂岩的主要岩性为钠质闪长岩-闪长岩-花岗闪长岩（TTG）套。石榴石角闪岩、麻粒岩或榴辉岩相条件下的水合玄武岩熔融作用被认为是太古宙TTGs形成的主导作用。考虑到地幔对某些TTGs可能贡献的地球化学特征，提出了太古宙地壳形成的模式，包括俯冲作用、加厚大陆地壳底部的熔融作用和水饱和条件下地幔衍生熔体的分离结晶作用。我们使用一个初始条件适合于太古宙-中太古宙的二维岩石-热力耦合构造-岩浆数值模型对这些假设进行了评估。根据实验结果，我们确定了水合原始玄武岩地壳可能产生中-长英质熔体的三种构造过程：(1)下基性地壳拆沉滴入地幔；(2)地壳局部增厚；(3)小尺度地壳翻转。在一个由短暂的俯冲作用终止的停滞变形的盖子构造-岩浆地球动力学体系的背景下，我们确定了两种不同类型的大陆地壳。第一种类型为原始花岗岩-绿岩状地壳，呈圆顶-龙骨状，形成于脱层上升流地幔之上，主要受垂直构造作用的影响。第二种类型是由强烈变形的花岗岩-绿岩和俯冲相关层序组成的再加工（增生）地壳，受强烈的水平缩短和垂直构造作用的影响。因此，我们的研究已经确定了一个可能的时空转变，从原始的花岗岩-绿岩状地壳，具有圆顶和龙骨的几何形状，到在太古代形成更多的长质片麻岩地体的重加工（增生）地壳。我们认为这些机制的同代性可以解释太古代地质记录的多样性和复杂性。
As a consequence of secular cooling of the Earth, there is generally no modern analog to assist in understanding the tectonic style that may have operated in the Archean. Higher mantle temperatures and higher radiogenic heat production in the Archean Earth would have impacted the thickness and composition of the crust. For this reason, well-constrained numerical modeling, based on the fragmentary evidence preserved in the geological record, is the most appropriate tool to evaluate hypotheses of Archean crust formation. The main lithology of Archean gray gneiss complexes is the sodic tonalite–trondhjemite–granodiorite (TTG) suite. Melting of hydrated basalt at garnet amphibolite, granulite or eclogite facies conditions is considered to be the dominant process that generated the Archean TTGs. Taking into account geochemical signatures of possible mantle contributions to some TTGs, models proposed for the formation of Archean crust include subduction, melting at the bottom of thickened continental crust and fractional crystallization of mantle-derived melts under water-saturated conditions. We evaluated these hypotheses using a 2D coupled petrological-thermomechanical tectono-magmatic numerical model with initial conditions appropriate to the Eoarchean–Mesoarchean. Based on the result of our experiments, we identify three tectonic processes by which intermediate to felsic melts may be generated from hydrated primitive basaltic crust: (1) delamination and dripping of the lower mafic crust into the mantle; (2) local thickening of the crust; and (3) small-scale crustal overturns. In the context of a stagnant-deformable lid tectono-magmatic geodynamic regime that is terminated by short-lived subduction, we identify two distinct types of continental crust. The first type is a pristine granite–greenstone-like crust with dome-and-keel geometry formed over delaminating–upwelling mantle which is mostly subjected to vertical tectonics processes. By contrast, the second type is a reworked (accreted) crust comprising strongly deformed granite–greenstone and subduction-related sequences and subjected to both strong horizontal shortening and vertical tectonics processes. Thus, our study has identified a possible spatial and temporal transition from pristine granite–greenstone-like crust with dome-and-keel geometry to reworked (accreted) crust forming more felsic gneiss terranes in the Archean. We suggest that the contemporaneity of the proposed mechanisms can explain the variety and complexity of the Archean geological record.