The Labrador Sector of the Laurentide Ice Sheet is characterized by a complex network of ice divides and an extensive landform record outlining two broad and opposing ice flows that are separated by a narrow Horseshoe Intersection Zone (HIZ). This geomorphic system gave rise to contrasting reconstructions, which reflect uncertainties on the temporal evolution of ice divides, the nature and age of the main landform systems and the overall pattern of ice retreat during the last deglaciation. Here, we address these issues through systematic mapping of glacial landforms and ice-flow indicators in a large area of northeastern Quebec and Labrador. The application of cosmogenic (¹⁰Be and ²⁶Al) dating to esker-fed glaciomarine deltas and different rock surfaces brings new constraints on the chronological framework and insights on the subglacial thermal regime. Our results outline four main landform assemblages, two of which relating to a major system of opposite ice flows that delineate the position of the eastern Ancestral Labrador ice divide. Our reconstruction shows that the HIZ occurs several tens of km to the west of this divide and that these two features are genetically distinct. The HIZ relates to the late-glacial development of ice streams showing a massive convergent ice flow into Ungava Bay. The upstream extent of this ice flow system shows a strong coupling with the outline of Ungava Bay drainage divide, suggesting that the configuration of the HIZ could be the expression of a topographic control on the late-glacial ice sheet dynamics. Landforms also indicate a significant shift in the deglaciation mode, which evolved from an overall warm-based to an areally-confined cold-based ice retreat near the center of the former ice mass – a change in dynamics that also played a role in the configuration of the HIZ. Overall, areas indicative of cold-based ice conditions are limited to highly elevated terrains, thus ruling out models arguing for an extensive cold-based ice cover over Ungava Bay throughout the last deglaciation.

Laurentide冰原的拉布拉多地区的特征是复杂的冰层网络和广泛的地貌记录，概述了由狭窄的马蹄形交汇区（HIZ）隔开的两条相对的，相对的冰流。这个地貌系统引起了对比的重建，这反映了冰块的时间演变，主要地貌系统的性质和年龄以及最后一次冰消期间冰层撤退的总体格局方面的不确定性。在这里，我们通过系统地绘制魁北克东北部和拉布拉多东北地区的冰川地貌和冰流指标来解决这些问题。宇宙成因的应用（¹⁰ Be和²⁶Al）追溯到esker喂养的冰川海洋三角洲和不同的岩石表面，这给时间框架带来了新的限制，并为冰川下的热状况提供了新的见识。我们的研究结果概述了四种主要的地貌组合，其中两种与主要的反向冰流系统有关，这些系统描述了东拉布拉多祖先冰区的位置。我们的重建结果表明，HIZ发生在该鸿沟以西数十公里处，并且这两个特征在遗传上是截然不同的。HIZ与冰河后期冰川发育有关，表明大量的汇聚冰流涌入Ungava湾。该冰流系统的上游范围与Ungava湾排水沟的轮廓紧密相关，这表明HIZ的构造可能是冰川后期冰盖动力学的地形控制的表达。地貌还表明，冰消模式发生了重大转变，从原来的冰块中心附近的整体暖基向有限的冷基冰层退缩–动力变化也对构造产生了影响HIZ。总体而言，指示基于寒冷的冰况的区域仅限于高度升高的地形，因此排除了模型争论的观点，即在最后一次冰消期期间，在Ungava湾上广泛的基于寒冷的冰盖。它从以前的冰块中心附近的整体变暖为基础，逐渐发展成为受区域限制的变冷为基础的冰层撤退–动力学变化也对HIZ的构造起了作用。总体而言，指示基于寒冷的冰况的区域仅限于高度升高的地形，因此排除了模型争论的观点，即在最后一次冰消期期间，在Ungava湾上广泛的基于寒冷的冰盖。它从以前的冰块中心附近的整体变暖为基础，逐渐发展成为受区域限制的变冷为基础的冰层撤退–动力学变化也对HIZ的构造起了作用。总体而言，指示基于寒冷的冰况的区域仅限于高度升高的地形，因此排除了模型争论的观点，即在最后一次冰消期期间，在Ungava湾上广泛的基于寒冷的冰盖。