Miocene climate cooling and aridification of Antarctica may have enhanced syn-extensional magmatism in the western Ross Sea

Continental rift systems are commonly characterized by volcanism with parental basaltic magmas sourced from the mantle. Erosion of the rift shoulders and sedimentation in the adjacent basins can affect the stress and thermal fields at depth, thereby affecting partial mantle melting. However, the sensitivity of magmatic activity to such surface forcing is elusive. Geological observations from the western Ross Sea, Antarctica, suggest rift onset in the Cretaceous with a transition from wide-rifting to narrow-rifting at the boundary between the Antarctic craton and the Transantarctic Mountains. Miocene climate cooling during rifting in the western Ross Sea, in addition, leads to an abrupt decrease in sedimentation rate, synchronous to the emplacement of the McMurdo Volcanic Group. This represents the largest alkali province worldwide, extending both inland and offshore of Transantarctic Mountains and western Ross Sea, respectively. Here, we use coupled thermo-mechanical and landscape evolution numerical modeling to quantify melt production in slowly stretching rift basins due to changes in erosion/deposition rates. The model combines visco-elasto-plastic deformation of the lithosphere and underlying mantle during extension, partial rock melting, and linear hillslope diffusion of the surface topography. The parametric study covers a range of slow extension rates, crustal thicknesses, mantle potential temperatures and diffusion coefficients. Numerical simulations successfully reproduce the ~150–200-km-wide extension of western Ross Sea and Miocene-to-present asthenospheric melt production (McMurdo Volcanic Group). Results further show that slow rifts magmatism is highly sensitive to sediment deposition within the basin, which inhibits mantle decompression melting and delays the crustal breakup. Regional climate-driven sedimentation rate changes are thus likely to have affected the syn-rift magmatic history of the western Ross Sea, Antarctica, supporting the relevance of interactions between surface and deep-seated processes across extensional settings

Working Memory Maintenance of Visual and Auditory Spatial Information Relies on Supramodal Neural Codes in the Dorsal Frontoparietal Cortex

The frontoparietal attention network plays a pivotal role during working memory (WM) maintenance, especially under high-load conditions. Nevertheless, there is ongoing debate regarding whether this network relies on supramodal or modality-specific neural signatures. In this study, we used multi-voxel pattern analysis (MVPA) to evaluate the neural representation of visual versus auditory information during WM maintenance. During fMRI scanning, participants maintained small or large spatial configurations (low- or high-load trials) of either colour shades or sound pitches in WM for later retrieval. Participants were less accurate in retrieving high- vs. low-load trials, demonstrating an effective manipulation of WM load, irrespective of the sensory modality. The frontoparietal regions involved in maintaining high- vs. low-load spatial maps in either sensory modality were highlighted using a conjunction analysis. Widespread activity was found across the dorsal frontoparietal network, peaking on the frontal eye fields and the superior parietal lobule, bilaterally. Within these regions, MVPAs were performed to quantify the pattern of distinctness of visual vs. auditory neural codes during WM maintenance. These analyses failed to reveal distinguishable patterns in the dorsal frontoparietal regions, thus providing support for a common, supramodal neural code associated with the retention of either visual or auditory spatial configurations.</p

Spatio-temporal evolution of intraplate strike-slip faulting: the Neogene-Quaternary Kuh-e-Faghan Fault, Central Iran

Central Iran provides an ideal region to study the long-term morphotectonic response to the nucleation and propagation of intraplate faulting. In this study, a multidisciplinary approach that integrates structural and stratigraphic field investigations with apatite (U+Th)/He (AHe) thermochronometry is used to reconstruct the spatio-temporal evolution of the Kuh-e-Faghan Fault (KFF) in northeastern Central Iran. The KFF is a narrow, ca. 80 km long, deformation zone that consists of three main broadly left stepping, E-W trending, dextral fault strands that cut through the Mesozoic-Paleozoic substratum and the Neogene-Quaternary sedimentary cover. The AHe thermochronometry results indicate that the intra-fault blocks along the KFF experienced two major episodes of fault-related exhumation at ~18 Ma and ~4 Ma. The ~18 Ma faulting/exhumation episode is chiefly recorded by the structure and depositional architecture of the Neogene deposits along the KFF. A source-to-sink scenario can be reconstructed for this time frame, where topographic growth caused the synchronous erosion/exhumation of the pre-Neogene units and deposition of the eroded material in the surrounding fault-bounded continental depocenters. Successively, the KFF gradually entered a period of relative tectonic quiescence and, probably, of regional subsidence during which a thick pile of fine-grained onlapping sediments were deposited. This may have caused resetting of the He ages of apatite in the pre-Neogene and the basal Neogene successions. The ~4 Ma faulting episode caused the final exhumation of the fault system, resulting in the current fault zone and topography. The two fault-related exhumation episodes fit with the regional early Miocene collision-enhanced uplift/exhumation, and the late Miocene–early Pliocene widespread tectonic reorganization of the Iranian plateau. The reconstructed long term, spatially and temporally punctuated fault system evolution in intraplate Central Iran during Neogene-Quaternary times may reflect states of far-field stress changes at the collisional boundaries

Soulèvement et déformation Cénozoïques dès la région des Admiralty Mountains (Victoria Land septentrionale, Antarctique).

International audienc

Soulèvement et déformation Cénozoïques dès la région des Admiralty Mountains (Victoria Land septentrionale, Antarctique).

International audienc

Erosione e sollevamento nell'arco calabro-peloritano

The Calabrian-Peloritani arc represents key site to unravel evolution of surface processes on top of subducting lithosphere. During the Pleistocene, in fact the arc uplifted at rate of the order of about 1mm/yr, forming high-standing low-relief upland (figure 2). Our study is focused on the relationship between tectonic and land evolution in the Sila Massif, Messina strait and Peloritani Mts. Landforms reflect a competition between tectonic, climatic, and surficial processes. Many landscape evolution models that explore feedbacks between these competing processes, given steady forcing, predict a state of erosional equilibrium, where the rates of river incision and hillslope erosion balance rock uplift. It has been suggested that this may be the final constructive stage of orogenic systems. Assumptions of steady erosion and incision are used in the interpretation of exhumation and uplift rates from different geologic data, and in the formulation of fluvial incision and hillslope evolution models. In the Sila massif we carried out cosmogenic isotopes analysis on 24 samples of modern fluvial sediments to constrain long-term (~103 yr) erosion rate averaged on the catchment area. 35 longitudinal rivers profiles have been analyzed to study the tectonic signal on the landscape evolution. The rivers analyzed exhibit a wide variety of profile forms, diverging from equilibrium state form. Generally the river profiles show at least 2 and often 3 distinct concave-up knickpoint-bounded segments, characterized by different value of concavity and steepness indices. River profiles suggest three main stages of incision. The values of ks and θ in the lower segments evidence a decrease in river incision, due probably to increasing uplift rate. The cosmogenic erosion rates pointed out that old landscape upland is eroding slowly at ~0.1 mm/yr. In the contrary, the flanks of the massif is eroding faster with value from 0.4 to 0.5 mm/yr due to river incision and hillslope processes. Cosmogenic erosion rates mach linearly with steepness indices and with average hillslope gradient. In the Messina area the long term erosion rate from low-T thermochronometry are of the same order than millennium scale cosmogenic erosion rate (1-2 mm/yr). In this part of the chain the fast erosion is active since several million years, probably controlled by extensional tectonic regime. In the Peloritani Mts apatite fission-track and (U-Th)/He thermochronometry are applied to constraint the thermal history of the basement rock. Apatite fission-track ages range between 29.0±5.5 and 5.5±0.9 Ma while apatite (U-Th)/He ages vary from 19.4 to 1.0 Ma. Most of the AFT ages are younger than the overlying terrigenous sequence that in turn postdates the main orogenic phase. Through the coupling of the thermal modelling with the stratigraphic record, a Middle Miocene thermal event due to tectonic burial is unravel. This event affected a inner-intermediate portion of the Peloritani belt confined by young AFT data (<15 Ma) distribution. We interpret this thermal event as due to an out-of–sequence thrusting occurring in the inner portion of the belt. Young (U-Th)/He ages (c. 5 Ma) record a final exhumation stage with increasing rates of denudation since the Pliocene times due to postorogenic extensional tectonics and regional uplift. In the final chapter we change the spatial scale to insert digital topography analysis and field data within a geodynamic model that can explain surface evidence produced by subduction process

Increased erosion of high-elevation land during late Cenozoic: evidence from detrital thermochronology off-shore Greenland

Mountain regions at high altitudes show deeply incised glacial valleys that coexist with a high-standing low-relief landscape, whose origin is largely debated. Whether the plateaus contributed to sediment production during the late Cenozoic is a currently debated issue in glacial geomorphology and paleoclimatology. In this study, we used detrital apatite fission-track dating of marine sediments to trace provenance and spatial variation in focused erosion over the last 7 million years. The decomposition of age distributions into populations reveals that, moving upwards through the sections, two young populations get younger, while two older populations get progressively older. We interpreted these trends as the effect of glacial erosion on the valley floors and an increased sediment contribution from the high elevations. To test this hypothesis, we compared the measured ages with synthetic age distributions, which represented a change in the elevation of focused erosion. We conclude that the central-eastern Greenland region is the main source of sediments, and in addition to enhanced valley incision, sediments have also been sourced from progressively higher elevations since 7 Ma. The ageing trend provides an unusual case in detrital thermochronology and a strong evidence that intensified Quaternary glaciations amplify the erosional process both in valley bottoms and at high elevations