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[1] Based on a dense grid of multichannel reflection seismic lines we study the evolution of a volcanic rifted margin segment off Argentina. The segment under study is located between 44°S and 41°S. We describe in detail the facies of the extrusive basaltic complexes across the margin. These include single and multiple Inner Seaward Dipping Reflectors (SDRs) with varying architecture along the margin, Outer Highs, and Outer SDR wedges. A detailed interpretation of a transitional zone between the Inner and Outer SDR wedges is presented. Multiple Inner SDRs are concentrated at the southern part of the margin segment, while in the north only one steeply dipping wedge is present. The dip of the Inner SDR wedges changes along the margin, and we propose subsidence by loading as main cause. The transitional zone between the Inner and Outer SDR wedges becomes narrower toward the north. By correlating with magnetic data we conclude that the emplacement of the 30-100 km wide multiple Inner SDRs occurred episodically. We propose an injection center which migrated in a seaward direction with proceeding extension as the origin for the multiple Inner SDRs. A scissor-like opening of the margin segment resulted in different amounts of stretching along-strike of the margin segment and is likely the cause for the varying distribution of the extrusive basaltic complexes. The varying extension rates within the margin segment contribute to decreasing volumes of melts generated in a northward direction within this rift segment.Components: 9834 words, 12 figures, 1 table.

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Lago Argentino hosts various calving glaciers, among them the famous Perito Moreno. Whereas the onland late Pleistocene–Holocene glacial history is rather well constrained, the submerged glacier-related features were until now undisclosed. Here we present a series of high-resolution seismic profiles revealing moraine bodies associated with the late-glacial glacier dynamics and the first bathymetric map of the Brazo Rico and Brazo Sur, the two southern arms of Lago Argentino. At the eastern termination of Brazo Rico, we identified at the lake floor the submerged expression of the Puerto Bandera 3 moraine mapped onshore, which represents the oldest event (12,660 ± 70 cal yr BP oldest minimum age) recognized in this lake arm, and seven other younger events expressed by a series of terminal and recessional moraines. Along the Brazo Sur, few moraine bodies have been imaged by seismic data. Here, the youngest temporal constraint comes from the Frías moraine (ca. 6000 cal yr BP), which closes off the southern end of the Brazo Sur. At the confluence of the two arms, the Perito Moreno and the former Frías glacier merged and flowed toward east during their late-glacial maximum advance (i.e., Puerto Bandera 1 moraine). The subaqueous evidence of moraine bodies testifies to the occurrence of previously undocumented pulses of the Perito Moreno and former Frías glaciers within the general phase of late Pleistocene–Holocene regression.