The Great Unconformity is an iconic geologic feature that coincides with an enigmatic period of Earth's history that spans the assembly and breakup of the supercontinent Rodinia and the Snowball Earth glaciations. We use zircon (U-Th)/He thermochronology (ZHe) to explore the erosion history below the Great Unconformity at its classic Grand Canyon locality in Arizona, United States. ZHe dates are as old as 809 ± 25 Ma with data patterns that differ across both long (∼100 km) and short (tens of kilometers) spatial wavelengths. The spatially variable thermal histories implied by these data are best explained by Proterozoic syn-depositional normal faulting that induced differences in exhumation and burial across the region. The data, geologic relationships, and thermal history models suggest Neoproterozoic rock exhumation and the presence of a basement paleo high at the present-day Lower Granite Gorge synchronous with Grand Canyon Supergroup deposition at the present-day Upper Granite Gorge. The paleo high created a topographic barrier that may have limited deposition to restricted marine or nonmarine conditions. This paleotopographic evolution reflects protracted, multiphase tectonic activity during Rodinia assembly and breakup that induced multiple events that formed unconformities over hundreds of millions of years, all with claim to the title of a “Great Unconformity.”The Great Unconformity is exposed along the length of the Grand Canyon in northwestern Arizona, United States (Fig. 1) and separates the Cambrian Tonto Group from the underlying Paleoproterozoic basement or Mesoproterozoic-Neoproterozoic Grand Canyon Supergroup. It represents as much as 1.2 b.y. of missing time (Timmons and Karlstrom, 2012). Recent studies have identified various events potentially associated with the Great Unconformity erosion surface that include >800 Ma Rodinia amalgamation, ca. 800 Ma early Rodinia breakup, 717–635 Ma Cryogenian Snowball glaciations, and ca. 580–500 Ma late Rodinia breakup and the Pan-African Orogeny (e.g., DeLucia et al., 2018; Keller et al., 2019; Flowers et al., 2020). Evidence of erosion during all of these periods is preserved in the Grand Canyon Supergroup of the Upper Granite Gorge (UGG; Fig. 1C); in unconformities within the Unkar Group (>800 Ma), disconformities between the Cardenas Basalt, Nankoweap Formation and the Chuar Group (ca. 800 Ma), and the unconformity separating the Chuar Group and Sixtymile Formation/Tapeats Sandstone (spanning ca. 730–520 Ma; Karlstrom et al., 2020). The Lower Granite Gorge (LGG) does not preserve the Grand Canyon Supergroup, which makes it unclear whether the LGG and UGG share a common Neoproterozoic history. Together, these geologic relationships suggest a multiphase and possibly spatially variable history of Great Unconformity development. Here we present ZHe data to decipher the origin of this feature in its iconic Grand Canyon exposure.The UGG and LGG of the Grand Canyon expose 1.8–1.4 Ga basement, which remained at depths consistent with temperatures >400 °C (∼12–15 km) until ca. 1.4 Ga (Williams and Karlstrom, 1996; Dumond et al., 2007). In the UGG, the Proterozoic Grand Canyon Supergroup occurs on top of basement, and the full Supergroup and Sixtymile Formation (∼3 km thick in total) are only preserved in the easternmost part of the gorge (Fig. 1). The region is cut by faults that offset the basement and Supergroup (Timmons et al., 2005), but only small offsets are apparent in the Phanerozoic units, which indicates that Precambrian tectonism is responsible for most of the observed displacement. In the LGG, the Great Unconformity is defined by Tonto Group Tapeats Sandstone overlying basement, whereas in the UGG, ca. 1255 Ma, Unkar Group rests on basement. It is unclear whether the Supergroup originally extended over the LGG and was largely removed by the sub-Tapeats unconformity or if the unconformity in the LGG is a composite surface with the Tapeats capping older topography. Previous studies have suggested that the Chuar basin was restricted in mid-Chuar time from the proposed Tonian intracontinental seaway (e.g., Dehler et al., 2017; Rooney et al., 2017). This restriction could have been caused by paleotopography. Throughout the Grand Canyon, the Tapeats is succeeded by Paleozoic strata with an Ordovician-Devonian hiatus. These units were buried by Mesozoic foreland deposits that were later removed (DeCelles, 2004). Previous apatite fission-track and apatite (U-Th)/He data document Phanerozoic burial temperatures >80 °C for river-level samples and help constrain subsequent erosion history (e.g., Dumitru et al., 1994; Flowers et al., 2008; Flowers and Farley, 2012; Lee et al., 2013; Winn et al., 2017).Rocks cool as they are exhumed, and this cooling history—and by proxy, exhumation history—can be recorded by ZHe thermochronology (e.g., Reiners et al., 2002). This method exploits the radioactive decay of U and Th to He. At temperatures >220 °C, He will diffuse completely out of a zircon crystal; at lower temperatures, the He will be retained. The exact temperature-diffusion relationship varies due to radiation damage, which accumulates and anneals with tim as a function of temperature (Guenthner et al., 2013; Ginster et al., 2019). Damage is proxied by effective uranium concentration (eU) for a zircon suite that underwent the same thermal history, or by α-dose estimates. With increasing eU, or α-dose up to ∼1 × 1018, zircon becomes more He retentive, but at higher damage the He retentivity decreases. This can cause positive and negative date-eU correlations at low and high damage, respectively. Thermal histories to explain a given ZHe data set can be explored using radiation damage accumulation and annealing models for He diffusion, which can include various damage annealing kinetics (Guenthner, 2021). Other factors can affect the (U-Th)/He date and include α-ejection, He implantation, inclusions, eU zonation, and grain size. With appropriate information, some of these effects can be corrected for or avoided (see the Supplemental Material1 for more detail). Especially important to this study is eU zonation. (U-Th)/He dates for zoned grains may differ from their unzoned counterparts with the same bulk eU. Variability in zonation patterns between grains can introduce dispersion into date-eU relationships, and these effects are magnified by small grain size (e.g., Hourigan et al., 2005; Farley et al., 2011; Ault and Flowers, 2012).We acquired ZHe data for four samples each from the LGG and UGG (Tables S1 and S2 in the Supplemental Material). Seven of these samples are Precambrian granitoid basement collected near river level, and one is the 729 ± 0.9 Ma Walcott Member Tuff near the top of the Chuar Group (Fig. 1D). To better understand the effects of eU zonation on ZHe dates and their interpretation, we obtained single U, Th, and Sm concentration profiles for 7–8 zircon grains per basement sample using depth-profiling by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) (Fig. S2). Zonation data were not acquired for the tuff sample because all zircon of sufficient size were dated before zonation analysis. See the Supplemental Material for details.The LGG ZHe data fall on a single negative date-eU trend spanning 740 ± 27 Ma to 69 ± 4 Ma (Fig. 2A). There is no correlation between date and grain radius (Fig. S1A). Most zircon zonation profiles for these samples have rims enriched in parent nuclides relative to cores and there is limited intrasample variability in eU zonation patterns (Figs. S2 and S3).ZHe data patterns vary among the UGG samples (Fig. 2B). Samples CP06–52 and UG90–2 yield low eU zircon with maximum dates >700 Ma and lack obvious date-eU correlations. In contrast, despite zircon with comparably low eU, the other UGG samples (UG96–1 and EGC1) yield ZHe dates all <400 Ma with one exhibiting a negative date-eU trend and the other a positive trend. As with the LGG samples, there is no apparent relationship between ZHe date and grain radius (Fig. S1B), and most zircon have rims higher in eU than cores (Figs. S2 and S3). Sample UG90–2 shows high intrasample variation in its eU zonation pattern (Fig. S2E), which may help explain its substantial ZHe date-eU scatter.ZHe data for the LGG and UGG document differences in basement thermal history. In the LGG, the Neoproterozoic dates record a portion of the Proterozoic time-temperature (t-T) path, and the consistency in the date-eU pattern across samples suggests a shared thermal history (Fig. 2A). In the UGG, data patterns differ from those in the LGG (Fig. 2B), which implies differences in t-T paths across the ∼100 km separating these sample suites. In addition, inter-sample variability in the UGG data, with spatially alternating basement samples with low eU zircon that yield either Neoproterozoic results or much younger ZHe dates, points to more abrupt differences in t-T paths at the tens of kilometers scale. Moreover, Chuar sample EGC1 is stratigraphically higher and younger (729 Ma) than the other samples in the UGG (1.7 Ga; Fig. 1D) but yields post-729 Ma ZHe dates, which also suggests differing thermal histories across short spatial wavelengths.Broad uniformity in Phanerozoic sedimentary thickness and resultant burial heating across the region implies that the spatial differences in thermal history recorded by ZHe must date to the Proterozoic. Paleozoic sedimentary rocks across the region thicken slightly westward (Beus and Morales, 2003; Timmons and Karlstrom, 2012), and Mesozoic burial thickened eastward (Robinson Roberts and Kirschbaum, 1995; DeCelles, 2004; Wernicke, 2011) but both over spatial wavelengths too large to explain the variability in ZHe data patterns. Instead, we suggest that variable Neoproterozoic burial and exhumation histories across small spatial scales induced by Neoproterozoic faulting during deposition of the Grand Canyon Supergroup is the most likely explanation for the data set.In the Neoproterozoic, grabens and half-grabens offsetting the basement and Supergroup (Timmons et al., 2005) created conditions for disparate mid-late Proterozoic burial and exhumation histories across major faults. Fault systems in the UGG (Fig. 1B) were activated multiple times during the Proterozoic and culminated in normal faults during the Neoproterozoic based on observations such as offsets in basement and Supergroup-equivalent units to the north of the Grand Canyon, reverse offsets within the Unkar Group units, and reconstruction of pre-Laramide extensional offsets (Shoemaker et al., 1978; Timmons et al., 2001, 2005; Beus and Morales, 2003). The Chuar Syncline and bounding Butte Fault in the eastern UGG (Fig. 1B) were active during the Tonian as documented by stratigraphic thinning and were reactivated in the late Neoproterozoic to Early Cambrian as indicated by incision below the Cambrian Sixtymile Formation (Elston and McKee, 1982; Timmons et al., 2001; Karlstrom et al., 2020).In the LGG, the absence of Grand Canyon Supergroup suggests that Proterozoic deposition may have been restricted to the UGG east of the Sinyala Fault System. To test this hypothesis, we carried out inverse thermal history simulations of the LGG data using the HeFTy software package (Ketcham, 2005) and the ZRDAAM model (Guenthner et al., 2013) for two endmember t-T histories (Fig. 3): (1) the Supergroup hypothesis (SG), applying the Supergroup burial and exhumation history as preserved in the eastern UGG (Elston and McKee, 1982; Timmons et al., 2005; Dehler et al., 2017; Rooney et al., 2017; Karlstrom et al., 2018), and (2) the Neoproterozoic exhumation hypothesis (NeoExh), in which the LGG was exhumed synchronously with Supergroup deposition in the UGG. Exhumation begins at 823 ± 26 Ma and represents the likely onset of normal faulting that accommodated the Chuar Group, as dated by K-Ar in the UGG (Elston and McKee, 1982), and is consistent with ca. 782 Ma detrital zircon in the base of the Chuar Group (Dehler et al., 2017). Phanerozoic constraints are the same in both models. LGG samples were modeled together (Table S3), and representative eU zonation profiles for each sample were used (Fig. 3D; Table S4). The HeFTy implementation of the widely used ZRDAAM model with fission-track annealing kinetics enables inclusion of zonation profile inputs, so modeling was done using this approach to honor this complexity. Model details are provided in the Supplemental Material and Tables S3–S7. The NeoExh model yielded t-T paths with better fits to the data than the SG model (Fig. 3A). This remains true when endmember combinations of grain size and observed zonation profile are used (Fig. 3C). These outcomes imply that of the two hypotheses tested, the NeoExh model is most consistent with the LGG ZHe data, compatible with the preserved Supergroup extent.In the UGG, the spatial heterogeneity in data patterns suggests variability in the timing and/or magnitude of Proterozoic burial and exhumation across normal faults. To test this, we performed t-T forward and inverse models of several UGG samples (see the Supplemental Material text and Tables S8–S12). The outcomes illustrate that differences in the Proterozoic thermal history are required to explain the UGG data if the same Phanerozoic thermal history is assumed (Figs. S4 and S5). This is consistent with Neoproterozoic fault-induced variability in Supergroup burial, as also implied by the ZHe data patterns and preserved geologic constraints.We interpret the different thermal histories of the LGG and UGG and within the UGG as caused by late Meso-Neoproterozoic faulting that produced paleotopography and syntectonic deposition and erosion. The “Upper” and “Lower” basins were likely separated by a paleo high bounded on either side by fault systems as is suggested by west-dipping normal faults between the LGG and UGG (Fig. 1A) and supported by inverse t-T modeling. Variation in thermal history among UGG samples can be explained by relationships to paleotopographical features inferred from preserved geology (Fig. 1): UG96–1 was in a paleo low in the hanging wall of the Crystal Fault (Timmons et al., 2001), where it underwent greater Neoproterozoic burial and associated He loss and now yields younger ZHe dates than sample CP06–52, which was located on a Neoproterozoic paleo high on the footwall of a normal fault (Timmons et al., 2001).Our study outcomes are consistent with multiphase faulting and erosion in the Grand Canyon region contributing to Great Unconformity development over a protracted Proterozoic interval. Figure 4 shows our schematic reconstruction of the deposition, erosion, faulting, and paleotopographic history, with each time slice corresponding to a known faulting period. The Unkar Group was deposited in a fault-bounded basin at ca. 1255 Ma (Fig. 4A), and syn-depositional tectonic activity continued through ca. 1100 Ma (Fig. 4B). After Unkar deposition, normal faulting and erosion occurred at ca. 830–800 Ma with the onset of Chuar Group deposition at ca. 780 Ma (Elston and McKee, 1982; Dehler et al., 2017), while normal-fault exhumation of the present-day LGG began simultaneously (Fig. 4C). This geometry may have isolated deposition of the Grand Canyon Supergroup from areas farther west and thus from the proposed Tonian intracontinental seaway (Dehler et al., 2017). Tonian sedimentary rocks were deposited syn-tectonically in the deepening Chuar Syncline with shallower burial elsewhere in the UGG. The final pre-Tonto Group tectonic and erosion event occurred at ca. 520–510 Ma (Fig. 4D). This model proposes that the Great Unconformity in the Grand Canyon developed via multiple erosional events driven by tectonism differing on the scale of tens of kilometers, which indicates that small scale topography played an important role in erosion and deposition during the protracted breakup of the Rodinian supercontinent.This work was supported by U.S. National Science Foundation grants EAR-1822119 and EAR-1916698 to R. Flowers and F. Macdonald and a University of Colorado–Boulder Chancellor's Fellowship to B. Peak. We thank Karl Karlstrom for organizing Grand Canyon trips resulting in sample archives. We thank Jim Metcalf for help with ZHe data acquisition, Emmy Smith for locating archived separates, and Mark Pecha at Arizona LaserChron (Tucson, Arizona, USA) for providing reconnaissance data. We thank David Foster and two anonymous reviewers for feedback that improved this manuscript.

中文翻译：

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锆石 (U-Th)/He 热年代学揭示美国大峡谷地区大不整合前古地形

大不整合是一个标志性的地质特征，与地球历史的一个神秘时期相吻合，这个时期跨越了罗迪尼亚超级大陆和雪球地球冰川的组装和分裂。我们使用锆石 (U-Th)/He 热年代学 (ZHe) 来探索美国亚利桑那州经典大峡谷地区大不整合面下方的侵蚀历史。ZHe 日期的年代为 809 ± 25 Ma，其数据模式在长（~100 公里）和短（数十公里）空间波长上有所不同。这些数据所暗示的空间变化的热历史最好用元古代同沉积正断层解释，该断层导致整个地区的挖掘和埋藏差异。数据、地质关系、和热历史模型表明新元古代岩石折返和在今天的下花岗岩峡谷与大峡谷超群沉积在今天的上花岗岩峡谷同步的基底古高的存在。古高形成了一个地形障碍，可能限制了海洋或非海洋条件的沉积。这种古地形演变反映了罗迪尼亚岛组装和分裂过程中长期的多相构造活动，这些活动引发了数亿年来形成不整合面的多次事件，所有这些事件都被称为“大不整合面”。美国亚利桑那州西北部的大峡谷（图 1）。1) 并将寒武纪通托群与下伏的古元古代基底或中元古代-新元古代大峡谷超群分开。它代表了多达 1.2 倍的缺失时间（Timmons 和 Karlstrom，2012 年）。最近的研究已经确定了可能与大不整合面侵蚀表面相关的各种事件，其中包括 >800 Ma Rodinia 合并，约。800 Ma 早期 Rodinia 分裂，717-635 Ma 低温雪球冰川，以及约。580–500 Ma 晚期 Rodinia 破裂和泛非造山运动（例如，DeLucia 等人，2018 年；Keller 等人，2019 年；Flowers 等人，2020 年）。所有这些时期的侵蚀证据都保存在上花岗岩峡谷的大峡谷超群中（UGG；图 1C）；Unkar 群内的不整合面 (>800 Ma)，Cardenas 玄武岩之间的不整合面，Nankoweap 组和 Chuar 组（约 800 Ma），以及分离 Chuar 组和 Sixtymile 组/Tapeats 砂岩的不整合面（跨越约 730-520 Ma；Karlstrom 等，2020）。下花岗岩峡谷 (LGG) 并未保留大峡谷超群，因此尚不清楚 LGG 和 UGG 是否具有共同的新元古代历史。总之，这些地质关系表明大不整合面发展的多阶段和可能在空间上变化的历史。在这里，我们提供了 ZHe 数据来破译该特征在其标志性的大峡谷暴露中的起源。大峡谷的 UGG 和 LGG 暴露了 1.8-1.4 Ga 基底，其深度保持在与温度 >400 °C（~12-15公里）直到大约。1.4 Ga（威廉姆斯和卡尔斯特罗姆，1996 年；杜蒙德等人，2007 年）。在 UGG 中，元古界大峡谷超群出现在基底之上，完整的超群和60英里组（总厚约3km）仅保存在峡谷最东端（图1）。该地区被与基底和超群偏移的断层切割（Timmons 等，2005），但在显生宙单元中只有很小的偏移是明显的，这表明前寒武纪构造作用是造成大部分观测位移的原因。在 LGG 中，大不整合面由 Tonto Group Tapeats 砂岩覆盖的基底定义，而在 UGG 中，大约为 1255 Ma，Unkar Group 位于地下室。目前尚不清楚超群是否最初延伸到 LGG 并在很大程度上被子 Tapeats 不整合面移除，或者 LGG 中的不整合面是否是 Tapeats 覆盖旧地形的复合表面。先前的研究表明 Chuar 盆地在中部 Chuar 时间受到拟议的 Tonian 陆内海道的限制（例如，Dehler 等人，2017 年；Rooney 等人，2017 年）。这种限制可能是由古地形引起的。在整个大峡谷中，塔佩茨被古生代地层所取代，地层具有奥陶纪-泥盆纪间断。这些单元被中生代前陆沉积物掩埋，后来被移除（DeCelles，2004）。以前的磷灰石裂变径迹和磷灰石 (U-Th)/He 数据记录了河流水平样品的显生宙埋藏温度 >80 °C，并有助于限制随后的侵蚀历史（例如，Dumitru 等人，1994 年；Flowers 等人，2008 年） ；Flowers 和 Farley，2012 年；Lee 等人，2013 年；Winn 等人，2017 年）。岩石在被挖掘时变凉，而这种变冷的历史——以及通过代理，挖掘历史——可以用 ZHe 热年代学记录（例如，Reiners 等，2002）。该方法利用 U 和 Th 向 He 的放射性衰变。在 >220 °C 的温度下，He 将完全从锆石晶体中扩散出来；在较低温度下，He 将被保留。确切的温度​​-扩散关系因辐射损伤而变化，辐射损伤随 tim 作为温度的函数而累积和退火（Guenthner 等人，2013 年；Ginster 等人，2019 年）。损坏由经历相同热历史的锆石套件的有效铀浓度 (eU) 或 α 剂量估计来代替。随着 eU 或 α 剂量增加到 ∼1 × 1018，锆石的 He 滞留性变得更强，但在更高的损伤下，He 的滞留性降低。这可能会分别导致低和高损害的日期-欧盟正相关和负相关。可以使用 He 扩散的辐射损伤累积和退火模型来探索解释给定 ZHe 数据集的热历史，其中可以包括各种损伤退火动力学 (Guenthner, 2021)。其他因素会影响 (U-Th)/He 日期，包括 α 喷射、He 注入、夹杂物、eU 带状分布和晶粒尺寸。使用适当的信息，可以纠正或避免其中的一些影响（有关更多详细信息，请参阅补充材料 1）。对这项研究特别重要的是欧盟区划。分区谷物的 (U-Th)/He 日期可能与具有相同批量 eU 的未分区对应物不同。颗粒间分带模式的变化会导致日期-eU 关系的分散，这些影响会因小颗粒尺寸而被放大（例如，Hourigan 等人，2005 年；Farley 等人，2011 年；Ault 和 Flowers，2012 年）。我们从 LGG 和 UGG 中获取了四个样品的 ZHe 数据（补充材料中的表 S1 和 S2）。其中七个样品是在河流水平附近收集的前寒武纪花岗岩基底，一个是靠近 Chuar 群顶部的 729 ± 0.9 Ma Walcott 成员凝灰岩（图 1D）。为了更好地了解 eU 分带对 ZHe 日期及其解释的影响，我们使用激光烧蚀-电感耦合等离子体质谱法进行深度分析，获得了每个基底样品 7-8 个锆石颗粒的单个 U、Th 和 Sm 浓度分布图（ LA-ICP-MS）（图 S2）。没有获得凝灰岩样品的分区数据，因为所有足够大小的锆石在分区分析之前都已确定年代。有关详细信息，请参阅补充材料。 LGG ZHe 数据落在跨越 740 ± 27 Ma 至 69 ± 4 Ma 的单个负日期-欧盟趋势（图 2A）。日期和颗粒半径之间没有相关性（图 S1A）。这些样品的大多数锆石分带剖面具有相对于岩心富含母核素的边缘，并且 eU 分带模式的样本内变异性有限（图 S2 和 S3）。UGG 样本之间的 ZHe 数据模式不同（图 2B）。样品 CP06-52 和 UG90-2 产生低 eU 锆石，最大日期 >700 Ma 并且缺乏明显的日期-eU 相关性。相比之下，尽管锆石的 eU 相对较低，但其他 UGG 样品（UG96-1 和 EGC1）产生的 ZHe 日期均小于 400 Ma，其中一个呈现负的日期-eU 趋势，另一个呈现正趋势。与 LGG 样品一样，ZHe 日期和晶粒半径之间没有明显的关系（图 S1B），并且大多数锆石的边缘 eU 高于核（图 S2 和 S3）。样品 UG90-2 显示其 eU 分区模式的样品内高度变化（图 S2E），这可能有助于解释其大量的 ZHe 日期-eU 散射。 LGG 和 UGG 文档在地下室热历史中的差异的 ZHe 数据。在 LGG 中，新元古代日期记录了元古代时间-温度 (tT) 路径的一部分，样本间日期-eU 模式的一致性表明存在共享的热历史（图 2A）。在 UGG 中，数据模式与 LGG 中的数据模式不同（图 2B），这意味着跨越 100 公里分隔这些样本套件的 tT 路径存在差异。此外，UGG 数据中的样本间变异性，具有低 eU 锆石的空间交替基底样本产生新元古代结果或更年轻的 ZHe 日期，表明在数十公里尺度上 tT 路径的差异更大。此外，Chuar 样品 EGC1 在地层学上比 UGG 中的其他样品（1.7 Ga；图 1D）更高和更年轻（729 Ma），但产生 729 Ma ZHe 后的日期，这也表明短空间波长的热历史不同。广泛显生宙沉积厚度的均匀性和该地区由此产生的埋藏加热意味着 ZHe 记录的热历史的空间差异必须追溯到元古代。该地区的古生代沉积岩略微向西增厚（Beus 和 Morales，2003 年；Timmons 和 Karlstrom，2012 年），中生代埋藏向东增厚（Robinson Roberts 和 Kirschbaum，1995 年；DeCelles，2004 年；Wernicke，2011 年），但都超过了空间波长大来解释 ZHe 数据模式的可变性。反而，我们认为大峡谷超群沉积期间由新元古代断层引起的小空间尺度上的可变新元古代埋藏和折返历史是对数据集最可能的解释。 et al., 2005) 为跨越主要断层的不同的中晚元古代埋藏和挖掘历史创造了条件。UGG 中的断层系统（图 1B）在元古代期间被多次激活，并根据大峡谷以北的基底和超群等效单元的偏移等观察结果在新元古代期间以正断层达到顶峰，在大峡谷以北的反向偏移Unkar Group 单元，以及重建前 Laramide 延伸偏移量（Shoemaker 等人，1978 年；Timmons 等人，2001 年，2005; Beus 和 Morales，2003 年）。如地层减薄所记录的那样，UGG 东部的 Chuar 向斜和边界 Butte 断层（图 1B）在 Tonian 期间活跃，并在新元古代晚期至早寒武世重新激活，如寒武纪 60 英里组（Elston 和 McKee， 1982；Timmons 等，2001；Karlstrom 等，2020。在 LGG 中，大峡谷超群的缺失表明元古代沉积可能仅限于 Sinyala 断层系统以东的 UGG。为了验证这一假设，我们使用 HeFTy 软件包（Ketcham，2005 年）和 ZRDAAM 模型（Guenthner 等人，2013 年）对 LGG 数据进行了逆向热历史模拟，用于两个端元 tT 历史（图 3）：（ 1）超群假设（SG），应用保存在 UGG 东部的超群埋葬和挖掘历史（Elston 和 McKee，1982 年；Timmons 等人，2005 年；Dehler 等人，2017 年；Rooney 等人，2017 年；Karlstrom 等人，2018 年），以及(2) 新元古代出土假说(NeoExh)，其中LGG与UGG中的超群沉积同步出土。剥脱开始于 823 ± 26 Ma，代表了容纳 Chuar 群的正常断层的可能开始，如 UGG 中的 K-Ar（Elston 和 McKee，1982），并且与约 Chuar 群底部的 782 Ma 碎屑锆石（Dehler 等，2017）。两种模型中的显生宙约束条件相同。LGG 样品一起建模（表 S3），并使用每个样品的代表性 eU 分区剖面（图 3D；表 S4）。具有裂变径迹退火动力学的广泛使用的 ZRDAAM 模型的 HeFTy 实现能够包含分带剖面输入，因此使用这种方法进行建模以尊重这种复杂性。模型详细信息在补充材料和表 S3-S7 中提供。NeoExh 模型产生的 tT 路径比 SG 模型更适合数据（图 3A）。当使用晶粒尺寸和观察到的分带剖面的端元组合时，这仍然是正确的（图 3C）。这些结果意味着在测试的两个假设中，NeoExh 模型与 LGG ZHe 数据最一致，与保留的超群范围兼容。穿过正常断层的埋藏和挖掘。为了测试这个，我们对几个 UGG 样本进行了 tT 正向和反向模型（参见补充材料文本和表 S8-S12）。结果表明，如果假设显生宙热历史相同，则需要元古代热历史的差异来解释 UGG 数据（图 S4 和 S5）。这与新元古代断层引起的超群埋藏变异一致，这也由 ZHe 数据模式和保留的地质约束所暗示。产生了古地形和同构造沉积和侵蚀。正如LGG和UGG之间的西倾正断层所暗示的那样，“上”和“下”盆地很可能被一个古高地分隔开来，两侧有断层系统（图1）。1A) 并由逆 tT 建模支持。UGG 样品之间的热历史变化可以通过与保存地质推断的古地形特征的关系来解释（图 1）：UG96-1 位于晶体断层上盘的古低处（Timmons 等，2001），它经历了更大的新元古代埋藏和相关的 He 损失，现在产生的 ZHe 日期比样品 CP06-52 更年轻，CP06-52 位于正断层下盘高处的新元古代古地层上（Timmons 等，2001）。我们的研究结果是与大峡谷地区的多相断层和侵蚀相一致，导致大不整合面在漫长的元古代间隔期间发展。图 4 显示了我们对沉积、侵蚀、断层和古地形历史的重建示意图，每个时间片对应一个已知的故障周期。Unkar 群沉积在一个断层边界的盆地中。1255 Ma（图 4A），同沉积构造活动持续到大约 10 年。1100 毫安（图 4B）。在 Unkar 沉积之后，大约发生了正常的断层和侵蚀。830-800 Ma，Chuar Group 沉积开始于约。780 Ma（Elston 和 McKee，1982 年；Dehler 等人，2017 年），而现代 LGG 的正常断层剥落同时开始（图 4C）。这种几何形状可能将大峡谷超群的沉积与更远的西部地区隔离开来，从而与拟议的托尼亚大陆内海道隔离开来（Dehler 等人，2017 年）。Tonian 沉积岩同构造沉积在加深的 Chuar 向斜中，在 UGG 的其他地方埋藏较浅。最后的前通托群构造和侵蚀事件发生在大约 10 年。520–510 Ma（图 4D）。该模型认为大峡谷的大不整合面是由数十公里尺度的构造运动驱动的多次侵蚀事件形成的，表明小尺度地形在罗迪尼亚超大陆长期分裂过程中对侵蚀和沉积起到了重要作用。 .这项工作得到了美国国家科学基金会授予 R. Flowers 和 F. Macdonald EAR-1822119 和 EAR-1916698 以及科罗拉多大学博尔德校长奖学金给 B. Peak 的支持。我们感谢 Karlstrom 组织了 Grand Canyon 之旅并提供了样本档案。我们感谢 Jim Metcalf 在 ZHe 数据采集方面的帮助、Emmy Smith 对存档分离的定位以及亚利桑那 LaserChron 的 Mark Pecha（图森，美国亚利桑那州）提供侦察数据。我们感谢大卫福斯特和两位匿名审稿人的反馈意见，他们改进了这份手稿。