Ediacaran-Ordovician tectonic and geodynamic drivers of Great Unconformity exhumation on the southern Canadian Shield
Ediacaran-Ordovician tectonic and geodynamic drivers of Great Unconformity exhumation on the southern Canadian Shield
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加拿大地盾南部大不整合面折返的埃迪卡拉纪-奥陶纪构造和地球动力学驱动因素
DOI：
10.1016/j.epsl.2023.118334
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发表时间：
2023
影响因子：
5.3
通讯作者：
Macdonald, Francis A.
中科院分区：
文献类型：
--
作者：
Peak, Barra A.;Flowers, Rebecca M.;Macdonald, Francis A.
古生代沉积岩与太古宙-元古代基底之间的大不整合侵蚀面与雪球地球冰川时期的侵蚀、海平面的上升波动以及一系列的构造和地球动力学机制有关。每一类机制都预测了不同的挖掘时间和空间模式。雪球地球冰川侵蚀仅限于717-635 Ma，集中在大陆边缘狭窄的冰流中。与海平面有关的侵蚀在时间上不受限制，但在空间上也仅限于大陆边缘。相反，构造和地球动力机制可以导致发掘在时间和空间上分布更广。我们将新的锆石和磷灰石(U-Th)/He热年代学数据（ZHe, AHe）与来自加拿大安大略省东南部大陆内部位置的独立古深度信息相结合，以限制与大不整合相关的挖掘时间、规模和区域模式，这些挖掘沿着加拿大地盾南部约650公里长的样带进行。这里的不整合是由太古宙-元古代基底上的中奥陶统碳酸盐岩定义的。对7个基底样品的数据分析显示，数据范围从960±20 Ma到37.5±0.9 Ma，与辐射损伤呈负相关。AHe测年为~ 300-200 Ma，无论辐射损伤如何，样品之间的测年基本一致。独立证据支持在研究区域深度≥6 km处存在590 +2/-1 Ma Grenville堤防和577±1 Ma Callander杂岩。合并后的数据需要挖掘距离≥6公里。在我们的样带中部590-577 Ma和470 Ma，在研究区域的其他地方有超过5 km的多公里侵蚀，远远落后于caa。717-635 Ma雪球地球冰川。这些结果将埃迪卡拉纪至早古生代挖掘信号的空间范围扩大到约110万平方公里。劳伦边缘的埃迪卡拉纪厚层序是这种侵蚀的补充沉积信号。大不整合发掘在加拿大地盾大陆内部的巨大空间范围与冰川侵蚀和海平面上升变化作为主要原因是不相容的。相反，我们将挖掘归因于构造和地球动力学机制，其中可能包括均衡反弹，动态地形，与Iapetus中部岩浆省相关的羽流活动，Iapetus海洋开放期间的裂谷作用以及横贯大陆拱门的发育。
The Great Unconformity erosion surface between Paleozoic sedimentary rocks and Archean-Proterozoic basement has been related to erosion occurring during Snowball Earth glaciations, eustatic sea level fluctuations, and a range of tectonic and/or geodynamic mechanisms. Each class of mechanism predicts distinct timing and spatial patterns of exhumation. Snowball Earth glacial erosion is limited to 717-635 Ma and concentrated in narrow ice streams on continental margins. Sea-level related erosion is unconstrained in time but also spatially limited to continental margins. Tectonic and geodynamic mechanisms, in contrast, can result in exhumation distributed more broadly in time and space. We combine new zircon and apatite (U-Th)/He thermochronology data (ZHe, AHe) with independent paleodepth information from a continental interior location in southeastern Ontario, Canada to constrain the timing, magnitude, and regional pattern of exhumation associated with the Great Unconformity along a ∼650 km-long transect across the southern Canadian Shield. Here, the unconformity is defined by Middle Ordovician carbonates atop Archean-Proterozoic basement. ZHe analyses for seven basement samples display a range of dates from 960 ± 20 Ma to 37.5 ± 0.9 Ma that correlate negatively with radiation damage. AHe dates are ∼300-200 Ma and generally consistent across samples regardless of radiation damage. Independent evidence supports emplacement of both the 590 +2/-1 Ma Grenville dikes and the 577 ± 1 Ma Callander Complex in the study region at depths ≥6 km. The combined data require ≥6 km of exhumation betweenca. 590-577 Ma and 470 Ma in the middle of our transect, with multi-km erosion up to ≥5 km elsewhere in the study area, well after theca. 717-635 Ma Snowball Earth glaciations. These outcomes expand the spatial extent of an Ediacaran to early-Paleozoic exhumation signal previously inferred elsewhere across the Shield to ∼1.1 million km2. Thick Ediacaran successions on the Laurentian margins are complementary depositional signals of this erosion. The enormous spatial extent of Great Unconformity exhumation across the continental interior of the Canadian Shield is incompatible with glacial erosion and eustatic sea-level change as the primary causes. Instead, we attribute exhumation to tectonic and geodynamic mechanisms, which may include isostatic rebound, dynamic topography, plume activity associated with the Central Iapetus Magmatic Province, rifting during opening of the Iapetus Ocean, and development of the Transcontinental Arch.
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DOI：
10.1029/2020jb021243
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Journal of Geophysical Research: Solid Earth
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