Precambrian Research ( IF 3.8 ) Pub Date : 2021-09-20 , DOI: 10.1016/j.precamres.2021.106391 Xiaohui Zhou 1 , Bruno Lafrance 1 , Mostafa Naghizadeh 1 , David B. Snyder 2 , Ademola Q. Adetunji 1 , Rajesh Vayavur 1 , Michael A. Hamilton 3 , John A. Ayer 1
Our understanding of crustal architecture and tectonic evolution has advanced due to integrated geological and geophysical research on Precambrian cratons. However, it is still a heated debate whether Archean crust structure developed by an allochthonous model similar to modern plate tectonics or autochthonous model emphasizing in-situ evolution of supracrustal belts. The < ca. 2696 Ma Chicobi belt is a sedimentary basin in the central Abitibi Subprovince of the Superior Province, and as such provides a unique opportunity to contribute to this debate. It comprises both Porcupine-type turbidite and Timiskaming-type polymictic conglomerate and cross-bedded sandstone, and unconformably overlies ca. 2728–2711 Ma metavolcanic rocks, including the Amos Group to the south. The metasedimentary rocks were deposited after an early (D1 > ca. 2696 Ma) deformation event, which is expressed by internally foliated clasts in conglomerate. The Chicobi belt was regionally folded and cut by shear zones during a second (D2) deformation event, and was re-folded by Z-shaped folds during a third (D3) dextral shearing event. The D2 event is constrained between ca. 2696 Ma, the pre-existing age of detrital zircon in the Scapa Group along strike of the Chicobi belt, and ca. 2681 Ma, the new age of the cross-cutting syenitic Gémini-Saint-Éloi Pluton.
New high-resolution seismic reflection and magnetotelluric surveys were conducted along the same transect across the Chicobi belt. The seismic reflection survey imaged subhorizontal to shallowly north-dipping reflective bands at depths of 3–7 km. Regional-scale inversion of new and pre-existing gravity data indicates that these reflective bands are linked to the Beauchamp Fault south of the Amos Group. Magnetotelluric inversion model shows high resistivity (>1000 Ω·m) zones under metasedimentary rocks, as well as a synform defined by low resistivity (10–100 Ω·m) zones, which aligns with folded metavolcanic rocks south of the Chicobi belt.
Integration of the geophysical data with surface mapping suggests that the upper-middle crustal architecture of the Chicobi belt is dominated by D2 upright folds overlying a fault zone. We suggest that deformation of the Chicobi belt is dominated by thrusting and folding, a deformation style compatible with allochthonous growth of the Abitibi Subprovince.
中文翻译:
新太古代沉积盆地的地壳结构和构造演化:来自加拿大魁北克省阿比提比副省金属地球奇科比横断面的地质和地球物理证据
由于对前寒武纪克拉通的综合地质和地球物理研究,我们对地壳结构和构造演化的理解有所提高。然而,太古宙地壳结构究竟是由类似于现代板块构造的外来模式发展起来的,还是强调上地壳带原位演化的本土模式,仍然是一个激烈的争论。<约。2696 Ma Chicobi 带是苏必利尔省阿比蒂比省中部的一个沉积盆地,因此提供了一个独特的机会来为这场辩论做出贡献。它由豪猪型浊积岩和蒂米斯卡明型混杂砾岩和交错层状砂岩组成,并且不整合地覆盖在约 2728-2711 Ma 变质火山岩,包括南部的 Amos 群。变质沉积岩是在早期(D1 > 大约 2696 Ma)变形事件,由砾岩中的内部叶状碎屑表示。Chicobi 带在第二次 (D 2 ) 变形事件期间被剪切带区域折叠和切割,并在第三次 (D 3 ) 右旋剪切事件期间被 Z 形褶皱重新折叠。D 2事件被限制在大约之间。2696 Ma,沿 Chicobi 带走向的 Scapa 群碎屑锆石的预先存在年龄,约 2681 Ma,横切正长岩双子座-圣埃洛伊冥王星的新时代。
新的高分辨率地震反射和大地电磁调查是沿着奇科比带的同一横断面进行的。地震反射勘测在 3 至 7 公里深度处对亚水平至浅北倾反射带成像。新的和先前存在的重力数据的区域尺度反演表明,这些反射带与阿莫斯群以南的 Beauchamp 断层相连。大地电磁反演模型显示变质沉积岩下的高电阻率 (>1000 Ω·m) 带,以及由低电阻率 (10-100 Ω·m) 带定义的同形体,与 Chicobi 带以南的褶皱变质火山岩对齐。
地球物理数据与地表测绘的整合表明,奇科比带的中上地壳结构以覆盖断裂带的D 2直立褶皱为主。我们认为 Chicobi 带的变形以逆冲和折叠为主,这种变形方式与 Abitibi 子省的异地生长相适应。