Search results for "HOS"

Ductile strain rate measurements document long-term strain localization in the continental crust

2013

cited By 24; Quantification of strain localization in the continental lithosphere is hindered by the lack of reliable deformation rate measurements in the deep crust. Quartz-strain-rate-metry (QSR) is a convenient tool for performing such measurements once calibrated. We achieve this calibration by identifying the best piezometer-rheological law pairs that yield a strain rate in agreement with that measured on the same outcrop by a more direct method taken as a reference. When applied to two major continental strike-slip shear zones, the Ailao Shan-Red River (ASRR; southwest China) and the Karakorum (northwest India), the calibrated QSR highlights across-strike strain rate variations, from …

2018

Abstract. The orientation and tectonic regime of the observed crustal/lithospheric stress field contribute to our knowledge of different deformation processes occurring within the Earth's crust and lithosphere. In this study, we analyze the influence of the thermal and density structure of the upper mantle on the lithospheric stress field and topography. We use a 3-D lithosphere–asthenosphere numerical model with power-law rheology, coupled to a spectral mantle flow code at 300 km depth. Our results are validated against the World Stress Map 2016 (WSM2016) and the observation-based residual topography. We derive the upper mantle thermal structure from either a heat flow model combined with …

The Impact of a Very Weak and Thin Upper Asthenosphere on Subduction Motions

2019

Recent geophysical observations report the presence of a very weak and thin upper asthenosphere underneath subducting oceanic plates at convergent margins. Along these margins, trench migrations are significantly slower than plate convergence rates. We use numerical models to assess the role of a weak upper asthenospheric layer on plate and trench motions. We show that the presence of this layer alone can enhance an advancing trend for the motion of the plate and hamper trench retreat. This mechanism provides a novel and alternative explanation for the slow rates of trench migration and fast-moving plates observed globally at natural subduction zones.

An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism

2019

Abstract Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed “orogenic lamproites” and are compositionally distinct from K-rich “anorogenic lamproites” that show lower 87Sr/86Sr and a trace element pattern that r…

Submarine morphology of the Comoros volcanic archipelago

2021

co-auteur étranger; International audience; A detailed morpho-bathymetric study of the Comoros archipelago, based on mostly unpublished bathymetric data, provides a first glimpse into the submarine section of these islands. It offers a complete view of the distribution of volcanic structures around the archipelago, allowing to discuss the origin and evolution of this volcanism. Numerous volcanic cones and erosional-depositional features have been recognized throughout the archipelago. The magmatic supply is focused below one or several volcanoes for each island, but is also controlled by lithospheric fractures evidenced by volcanic ridges, oriented along the supposed Lwandle-Somali plate bo…

Seafloor expression of oceanic detachment faulting reflects gradients in mid-ocean ridge magma supply

2019

International audience; Oceanic detachment faulting is a major mode of seafloor accretion at slow and ultraslow spreading mid-ocean ridges, and is associated with dramatic changes in seafloor morphology. Detachments form expansive dome structures with corrugated surfaces known as oceanic core complexes (OCCs), and often transition to multiple regularly-spaced normal faults that form abyssal hills parallel to the spreading axis. Previous studies have attributed these changes to along-axis gradients in lithospheric strength or magma supply. However, despite the recognition that magma supply can influence fault style and seafloor morphology, the mechanics controlling the transition from oceani…

Numerical modelling of magma dynamics coupled to tectonic deformation of lithosphere and crust

2013

Many unresolved questions in geodynamics revolve around the physical behaviour of the two-phase system of a silicate melt percolating through and interacting with a tectonically deforming host rock. Well-accepted equations exist to describe the physics of such systems and several previous studies have successfully implemented various forms of these equations in numerical models. To date, most such models of magma dynamics have focused on mantle flow problems and therefore employed viscous creep rheologies suitable to describe the deformation properties of mantle rock under high temperatures and pressures. However, the use of such rheologies is not appropriate to model melt extraction above …

The chronic effects of fullereneC 60 -associated sediments in the midge Chironomus riparius – Responses in the first and the second generation

2017

Abstract The life cycle parameters of the benthic invertebrate Chironomus riparius make it a relevant organism for use in multi-generation chronic ecotoxicology tests. Since studies on chronic exposures with fullerene carbon nanoparticles have revealed adverse effects at lower concentration ranges, it is crucial to gain understanding of the consequences in following generations. The aims of this study were to investigate whether sediment-associated fullereneC 60 impacts on C. riparius emergence and breeding, thus affecting the growth of the second generation. Larvae were exposed to fullerene-spiked sediment at concentrations of 0.5, 10 and 40 mg/kg sediment dw. Total emergence and breeding …

Responses of aquatic plants to eutrophication in rivers:a revised conceptual model

2018

Compared to research on eutrophication in lakes, there has been significantly less work carried out on rivers despite the importance of the topic. However, over the last decade, there has been a surge of interest in the response of aquatic plants to eutrophication in rivers. This is an area of applied research and the work has been driven by the widespread nature of the impacts and the significant opportunities for system remediation. A conceptual model has been put forward to describe how aquatic plants respond to eutrophication. Since the model was created, there have been substantial increases in our understanding of a number of the underlying processes. For example, we now know the thre…

Oxygen isotope compositions of phosphate from arvicoline teeth and Quaternary climatic changes, Gigny, French Jura

2004

Oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high- and mid-latitudes. An oxygen isotope fractionation equation was determined by using present-day European arvicoline (rodents) tooth phosphate: δ18Op = 20.98(±0.59) + 0.572(±0.065) δ18Ow. This fractionation equation was applied to the Late Pleistocene karstic sequence of Gigny, French Jura. Comparison between the oxygen isotope compositions of arvicoline tooth phosphate and Greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence. …