Distributed crustal shortening followed by transpressional shearing in the Superior Province, northeastern Canada: A Late Archean analogy to modern accretionary plate margins?
Distributed crustal shortening followed by transpressional shearing in the Superior Province, northeastern Canada: A Late Archean analogy to modern accretionary plate margins?
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DOI：
10.1016/j.precamres.2021.106322
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发表时间：
2021-08
影响因子：
3.8
通讯作者：
J. Žák;F. Tomek;M. Svojtka;F. Vacek;V. Kachlík;L. Ackerman;J. Jezek;M. Petronis
中科院分区：
文献类型：
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作者：
J. Žák;F. Tomek;M. Svojtka;F. Vacek;V. Kachlík;L. Ackerman;J. Jezek;M. Petronis
加拿大上级省已成为探讨晚太古代构造过程和地壳生长机制的重要试验区之一。该省由一个> 2.8Ga的原榴辉岩核组成，被大量的弧形岩体侵入，并被一系列狭窄，细长的ca。2.8-2.7 Ga的幼年带，也被称为次生带或域。这些彗星似乎环绕着原彗星核，并且通常向外年轻，但它们聚集的运动学和地球动力学原因仍然存在争议。在本文中，我们研究了魁北克东北部的Radisson岩体，它侵入了假定的岩浆弧（比恩维尔域）的南部，外缘沿着其~ WNW-ESE-走向的构造边界与原岩浆地壳（拉格兰德域）。该岩体以斑状二长花岗岩至石英二长岩为主，侵位于2712 Ma左右，并表现出复杂的内部结构，由叠加的岩浆至固态变形造成。磁化率各向异性（AMS）表明，早期边缘平行的~WNW-ESE岩浆面理中含有陡峭的线理，它记录了高结晶岩浆的垂直伸展和水平压扁，这可能是侵位作用和/或剪切作用主导的平移挤压作用的结果。然而，更普遍的是同一叶理内的水平线理，被解释为记录侵位后，但仍然同岩浆，构造应变（~NNE-SSW缩短和边界平行拉伸）。冷却后，本地化的右旋S-C糜棱岩区容纳进一步缩短的岩体内，而未变形的晚期长英质岩脉横切的固态结构在一个角度的岩体边缘。我们认为，这种结构的继承，也再现了数值组构建模，是一个本地规模的信号的两个阶段的组装东北部上级省：正面，NNE向的ESTNE收敛和附件的ESTNE核，在一个“热”的制度与大量的弧形深成作用，其次是更本地化的右旋剪切平行ESTNE边界。后一阶段记录在原克拉通边缘，但也在外侧Abitibi绿岩带几乎在同一时间（约2000年）。2700-2690 Ma）。两个阶段的演化和类似的变形分布在一个广泛的区域相结合，类似于现代大型热造山带中形成的板块构造体制。
The Canadian Superior Province has become one of the key test pieces to discuss tectonic processes and mechanisms of crustal growth in the Late Archean. The Province consists of a >2.8 Ga proto-cratonic core intruded by voluminous arc-like plutons and surrounded by a series of narrow, elongate ca. 2.8–2.7 Ga juvenile belts, also referred to as terranes or domains. The terranes seem to wrap around the proto-cratonic core and generally young outward, but the kinematics and geodynamic causes of their assembly remain debated. In this paper, we examine the Radisson pluton in northeastern Québec, which intruded the southern, outer edge of the presumed magmatic arc (Bienville domain) along its ~WNW–ESE-trending tectonic boundary with the proto-cratonic crust (La Grande domain). The pluton, dominated by porphyritic monzogranite to quartz monzonite, was emplaced at around 2712 Ma and exhibits complex internal structure resulting from superposed magmatic to solid-state deformations. An early margin-parallel ~WNW–ESE magmatic foliation containing a steep lineation, recognized by the anisotropy of magnetic susceptibility (AMS), is interpreted as recording vertical stretching and horizontal flattening of highly crystallized magma, either due to emplacement and/or pure shear dominated transpression. More widespread, however, is a horizontal lineation within the same foliation that is interpreted as recording post-emplacement, but still syn-magmatic, tectonic strain (~NNE–SSW shortening and boundary-parallel stretching). Upon cooling, localized dextral S–C mylonite zones accommodated further shortening within the pluton whereas undeformed late-stage felsic dikes cross-cut the solid-state fabric at an angle to the pluton margins. We suggest that this structural succession, also reproduced by numerical fabric modeling, is a local-scale signal of a two-stage assembly of the northeastern Superior Province: the frontal, NNE-directed terrane convergence and attachment to the cratonic nucleus, operating in a ‘hot’ regime with voluminous arc-like plutonism, was followed by more localized dextral shearing parallel to terrane boundaries. The latter phase is recorded at the proto-craton margin but also in the outboard Abitibi greenstone belt virtually at the same time (ca. 2700–2690 Ma). In combination, the two-stage evolution and similar deformation distributed over a broad region resemble modern large hot orogens formed in a plate-tectonic regime.