Salt-magma interactions influence intrusion distribution and salt tectonics in the Santos Basin, offshore Brazil

Many sedimentary basins host thick evaporite (salt) deposits. Some of these basins also host extensive igneous intrusion networks. It thus seems inevitable that, in some locations, magma will interact with salt. Yet how interaction between these materials may influence salt tectonics or magma emplacement, particularly at the basin‐scale, remains poorly understood. We use 3D seismic reflection data from the Santos Basin, offshore Brazil to image 38 igneous intrusions spatially related to thick Aptian salt. Based on identified seismic–stratigraphic relationships, we suggest sill emplacement likely occurred during the late Albian‐to‐Santonian. We show intra‐salt sills are geometrically similar to but laterally offset from supra‐salt sills. We suggest ascending magma was arrested by the salt in some areas, but not others, perhaps due to differences in evaporite lithology. Our mapping also reveals most sills occur within and above the presalt Merluza Graben, an area characterized by Albian‐to‐Neogene, salt‐detached extension. In adjacent areas, where there are few intrusions, salt deformation was driven by post‐Santonian diapir rise. We suggest emplacement of hot magma within evaporites above the Merluza Graben enhanced Albian‐to‐Santonian salt movement, but that crystallization of the intrusion network restricted post‐Santonian diapirism. Our work indicates salt–magma interaction can influence salt tectonics, as well as the distribution of magma plumbing systems, and thus could impact basin evolution

First bedrock samples dredged from submarine outcrops in the Chukchi Borderland, Arctic Ocean

The Chukchi Borderland, a prominent bathymetric feature within the Arctic Ocean, has been interpreted as a fragment of an undeformed continental platform sequence rifted from the passive margin of Arctic Canada. Dredges collected for the U.S. Extended Continental Shelf project aboard the icebreaker U.S. Coast Guard Cutter Healy (cruise number HLY0905) recovered hundreds of kilograms of broken crystalline basement lithologies consisting of mylonitically deformed biotite-bearing amphibolite, garnet-bearing feldspathic gneiss, and augen-bearing orthogneiss from the Chukchi Borderland. Metamorphic zircon within the amphibolite and associated leucogranitic seams within these rocks yielded U-Pb zircon ages between ca. 480 and 530 Ma. Garnet-bearing feldspathic gneisses contain variably discordant Mesoproterozoic zircon, ca. 600 Ma igneous zircon, and ca. 485–505 Ma metamorphic overgrowths. While we interpret these gneisses as deformed and metamorphosed granitoids, they could, instead, have a very immature sedimentary protolith. The youngest rocks sampled were K-feldspar augen orthogneisses that yield ca. 430 Ma zircon crystallization ages. Whole-rock geochemistry and Sr-Nd isotopic data indicate that the orthogneisses are I-type calc-alkaline granitoids. All of the basement rocks including the orthogneisses are variably metamorphosed and mylonitized. Collectively, the U-Pb age, geochemistry, and fabric of the dredged Chukchi Borderland basement samples indicate that they represent Neoproterozoic–Ordovician orogenic crust and Silurian arc batholithic rocks. This geologic origin is inconsistent with the Neoproterozoic to early Paleozoic passive margin history of western Arctic Canada to which the Chukchi Borderland has been previously correlated. We alternatively propose that the basement of the Chukchi Borderland is related to the peri-Laurentian composite terranes of Pearya and western Svalbard that have similar geologic histories

Deformational history and thermochronology of Wrangel Island, East Siberian Shelf and coastal Chukotka, Arctic Russia

Sample localities, details of the analytical methods, data tables and the full discussion of the results of electron back-scatter diffraction studies of quartz lattice preferred orientations

Multi-scenario interpretations from sparse fault evidence using graph theory and geological rules

Preprint submitted to Journal of Geophysical Research - Solid EarthInternational audienceThe characterization of geological faults from geological and geophysical data is often subject to uncertainties, owing to data ambiguity and incomplete spatial coverage. We propose a stochastic sampling algorithm which generates fault network scenarios compatible with sparse fault evidence while honoring some geological concepts. This process proves useful for reducing interpretation bias, formalizing interpretation concepts, and assessing first-order structural uncertainties. Each scenario is represented by an undirected association graph, where a fault corresponds to an isolated clique, which associates pieces of fault evidence represented as graph nodes. The simulation algorithm samples this association graph from a possibility graph, whose edges represent the independent association of any two pieces of fault evidence. Each edge carries a likelihood that the endpoints belong to the same fault surface is computed, expressing general and regional geological interpretation concepts. The algorithm is illustrated on several incomplete data sets made of three to six two-dimensional seismic lines extracted from a three-dimensional seismic image located in the Santos Basin, offshore Brazil. In all cases, the simulation method generates a large number of plausible fault networks, even when using restrictive interpretation rules. The case study experimentally confirms that retrieving the reference association is tedious due to the problem combinatorics. Restrictive and consistent rules increase the likelihood to recover the reference interpretation and reduce the diversity of the obtained realizations. We discuss how the proposed method fits in the quest to rigorously (1)~address epistemic uncertainty during structural uncertainty studies and (2)~ quantify subsurface uncertainty while preserving structural consistency