Drying colloidal systems: laboratory models for a wide range of applications

The drying of complex fluids provides a powerful insight into phenomena that take place on time and length scales not normally accessible. An important feature of complex fluids, colloidal dispersions and polymer solutions is their high sensitivity to weak external actions. Thus, the drying of complex fluids involves a large number of physical and chemical processes. The scope of this review is the capacity to tune such systems to reproduce and explore specific properties in a physics laboratory. A wide variety of systems are presented, ranging from functional coatings, food science, cosmetology, medical diagnostics and forensics to geophysics and art

Reply to the comment by Quartau et al. on “Construction and destruction of a volcanic island developed inside an oceanic rift: Graciosa Island, Terceira Rift, Azores”, J. Volcanol. Geotherm. Res. 284, 32–45, by Sibrant et al. (2014)

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Rheological control on the segmentation of the mid-ocean ridges: Laboratory experiments with extension initially perpendicular to the axis

International audienceMid-ocean ridges (MOR) axes are not straight, but segmented over scales of 10s to 100s of kilometers by several types of offsets including transform faults (TF), overlapping spreading centers (OSC) and non-transform, non-overlapping offsets (NTNOO). Variations in axial morphology and segmentation have been attributed to changes in magma supply, axial thermal structure (which depends on mantle temperature and spreading rate), and axial mechanical properties. To isolate the effect of each of these processes is difficult with field data alone. We therefore present a series of analogue experiments using colloidal silica dispersions as an Earth analogue. Diffusion of salt from saline solutions placed in contact with these fluids, causes formation of a skin, whose rheology evolves from viscous to elastic and brittle with increasing salinity. Applying a fixed spreading rate to this pre-formed, brittle plate results in cracks, faults, and ridge segments. Lithospheric thickness is varied independently by changing the surface water layer salinity. Experimental results depend on the axial failure parameter ΠF, the ratio of a mechanical length scale (Zm) and the axial elastic thickness (Zaxis), which depends on mantle temperature and spreading velocity. Slow-spreading fault-dominated, and fast-spreading fluid intrusion-dominated, ridges on Earth and in the laboratory are separated by the same critical value ΠFc±0.024, suggesting that the axial failure mode governs ridge geometry. Here, we examine ridge axis segmentation. Measurements of >4000 experimental ridge segments and offsets yield an average segment length Lm that is quasi-constant at all spreading velocities. Scaled to the Earth, Lm∼55 km, in agreement with the natural data. Experiments with low ΠF show offset size varying as dl=csteLmZaxis regardless of offset type, a correlation well explained by fracture mechanics. Finally, as on Earth, experimental ridge segments are separated by transform and non-transform discontinuities, and their nature and occurrence vary with ΠF. NTNOOs develop when ΠFΠFc. In contrast, TF may form at any ΠF, but the proportion of TFs relative to OSCs or NTNOOs decreases when ΠF/ΠFc>> 1 or << 1, in agreement with natural MO

Variable Crustal Production Originating From Mantle Source Heterogeneity Beneath the South East Indian Ridge and Amsterdam‐St. Paul Plateau

International audienceThe Amsterdam-St. Paul (ASP) Plateau formed by interaction between the South East Indian Ridge (SEIR) and the ASP mantle plume during the last 10 Myr. The combined bathymetry and gravity-derived crustal thickness anomalies along the present and paleoaxes of the SEIR atop the plateau indicate: (1) a thicker crust and shallower water depth along the southern part of segment I2 during much of the last 10 Myr; (2) an earlier decrease (~1.4 Ma) in crustal thickness along the southern part of I2 compared to the northern part (~0.9 Ma) during the most recent period of reduced magmatism; (3) a topographic transition at ~0.7 Ma and during the last 0.1 Myr; and (4) an approximately uniform crustal thickness (8 km) along the entire I2 segment today. These observations require spatial and temporal variations in magma production during construction of the ASP Plateau over the last 3 Myr. We propose that during periods of weaker plume magma flux, spatial variations in upper mantle temperature and composition are small, and lead to small variations in crustal thickness along-axis. In contrast, during periods of stronger plume magma flux, spatial contrasts in upper mantle temperature and composition (fertility) are large, leading to significant variations in crustal thickness. Along-axis variations of 3 He/ 4 He, Δ8/4Pb, K/Ti, and Na 8 in "zero-age" basalts indicate that there is a gradient in the underlying mantle material, from a "common" mantle plume component (Δ8/4Pb~60) stronger in the north to a DUPAL component (Δ8/4Pb~110) dominating in the south. keywords: oceanic plateaus, plume-ridge interaction, Amsterdam St. Paul Plateau, South East Indian Ridge, geophysical and geochemical evidence key points:-Crustal architecture of the Amsterdam St. Paul Plateau records high and low plume flux stages during mantle plume-spreading ridge interaction-Plume magma flux decreased earlier in the south than in the north along a single spreading segment.-Along-axis differences in crustal thickness and Pb and He isotopes suggest both shallow mantle and plume heterogeneities

Volcano-tectonic evolution of the Santa Maria Island (Azores) : implications for paleo-stress evolution at the western Eurasia-Nubia plate boudnary

International audienceThe growth and decay of oceanic volcanoes developed close to plate boundaries are intrinsically related to a competition between construction and destruction processes, partly controlled by tectonic strain and stresses. From morphologic, stratigraphic, tectonic and new high-precision K-Ar data, we present a comprehensive picture of the volcano-tectonic evolution of Santa Maria, and discuss its significance regarding the stress evolution and regional deformation in the Azores. Our new data show that: (1) the western flat portion of the island is mostly composed of west-dipping volcanic rocks here dated between 5.70 ± 0.08 and 5.33 ± 0.08 Ma, which we consider the remnants of an Older Shield Volcano; (2) more than half of this early volcanic complex has been removed by an east-directed large-scale sector collapse; (3) a second volcano, here coined the Younger Shield Volcano, grew rapidly on the collapse scar between at least 4.32 ± 0.06 and 3.94 ± 0.06 Ma; (4) more than half of this new volcano was removed by a second large-scale sector collapse most probably around 3.6 Ma, based on the ages of parasitic scoria cones sitting unconformably on the Younger Shield Volcano; (5) the latest parasitic volcanic activity is here dated at 2.84 ± 0.04 Ma, extending significantly the known eruptive history of Santa Maria. Morpho-structural data (shape of the island, faults, dikes, and distribution of volcanic cones) show a significant control of construction and destruction along the N045° and N150° directions. The age of the lavas intruded by dikes suggests that the N045° and the N150° trends are ca. 5.3 Ma old and younger than ca. 4.3 Ma, respectively. Based on the new data, we conclude that a change in the regional stress field occurred between 5.3 and 4.3 Ma, most likely associated with a major reconfiguration of the Eurasia/Nubia plate boundary in the Azores

Catastrophic flank collapses and slumping in Pico Island during the last 130 kyr (Pico-Faial ridge, Azores Triple Junction)

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Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data : the Faial Island example (Azores)

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Morpho-structural evolution of a volcanic island developed inside an active oceanic rift: S. Miguel Island (Terceira Rift, Azores)

International audienceThe evolution of volcanic islands is generally marked by fast construction phases alternating with destruction by a variety of mass-wasting processes. More specifically, volcanic islands located in areas of intense regional deformation can be particularly prone to gravitational destabilisation. The island of S. Miguel (Azores) has developed during the last 1 Myr inside the active Terceira Rift, a major tectonic structure materializing the present boundary between the Eurasian and Nubian lithospheric plates. In this work, we depict the evolution of the island, based on high-resolution DEM data, stratigraphic and structural analyses, high-precision K–Ar dating on separated mineral phases, and offshore data (bathymetry and seismic profiles). The new results indicate that: (1) the oldest volcanic complex (Nordeste), composing the easternmost part of the island, was dominantly active between ca. 850 and 750 ka, and was subsequently affected by a major south-directed flank collapse. (2) Between at least 500 ka and 250 ka, the landslide depression was massively filled by a thick lava succession erupted from volcanic cones and domes distributed along the main E-W collapse scar. (3) Since 250 kyr, the western part of this succession (Furnas area) was affected by multiple vertical collapses; associated plinian eruptions produced large pyroclastic deposits, here dated at ca. 60 ka and less than 25 ka. (4) During the same period, the eastern part of the landslide scar was enlarged by retrogressive erosion, producing the large Povoação valley, which was gradually filled by sediments and young volcanic products. (5) The Fogo volcano, in the middle of S. Miguel, is here dated between ca. 270 and 17 ka, and was affected by, at least, one southwards flank collapse. (6) The Sete Cidades volcano, in the western end of the island, is here dated between ca. 91 and 13 ka, and experienced mutliple caldera collapses; a landslide to the North is also suspected from the presence of a subtle morphologic scar covered by recent lava flows erupted from alignments of basaltic strombolian cones. The predominance of the N150° and N75° trends in the island suggest that the tectonics of the Terceira Rift controlled the location and the distribution of the volcanism, and to some extent the various destruction events