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The lithosphere–asthenosphere boundary (LAB) represents the base of the Earth's lithosphere, the rigid and relatively cool outer shell characterised by a conductive thermal regime, isolated from the convecting asthenosphere. Chemically, the LAB should divide a lithospheric mantle that is variably depleted in basaltic components from a more fertile asthenosphere. In xenolith suites from cratonic areas,...
The Lithosphere–Asthenosphere Boundary (LAB) is a fundamental boundary in the plate tectonic paradigm — it is the most pervasive on the planet, yet comparatively it is one we know little about. Defined initially on the basis of the mechanical response of the Earth to loading, its usage has become ubiquitous across the geosciences but the natural differences in its definition, due to differences in...
We characterise the nature and thickness of the seismological lithosphere beneath Hudson Bay, using dispersion analysis of fundamental-mode Rayleigh waves along two-station paths crossing the region. Hudson Bay is largely underlain by the Paleoproterozoic Trans-Hudson Orogen, and is surrounded by Archean cratons. This study region thus provides an opportunity to investigate whether fundamental differences...
A joint inversion method of simultaneously inverting regional multimode surface waveforms and fundamental-mode surface wave dispersion curves is used to better constrain a 3-D S-wave velocity model for the upper mantle beneath China. Thousands of broadband vertical-component seismograms were processed, and ∼16,500 Rayleigh-wave group-velocity measurements were retrieved at a period of 20s, with fewer...
Several recent studies have imaged discontinuities interpreted as the lithosphere–asthenosphere boundary using receiver function methods. These are exciting results since this boundary is fundamental and yet relatively elusive. Its location is not well imaged nor are its properties well understood. The receiver function method provides high depth resolution, and the multitude of studies using this...
The lithosphere–asthenosphere boundary (LAB) remains a controversial subject in Earth sciences, and beneath cratonic regions appears to be a particularly difficult boundary to consistently image. Seismic methods give different indicators on the velocity structure of the upper mantle: tomographic models provide estimates of the velocity variations at a variety of lateral scales, but have limited vertical...
We describe a simplified thermal and dynamical model of the Archean continental lithosphere that is described by the evolution in time of two state variables: the thickening factor f, which describes the thickness of the crustal layer relative to a reference section, and the depth-averaged lithospheric temperature T―′. These quantities are explicitly linked by the advection of heat when extensional...
The Cape Verde Islands lie in the Atlantic Ocean off West Africa, in a clearly oceanic setting. The lavas of some islands carry mantle-derived xenoliths of depleted peridotites petrologically similar to those derived from cratonic lithospheric mantle. Oceanic lithospheric mantle, in contrast, consists mainly of less-depleted lherzolites and harzburgites formed by the extraction of mid-ocean ridge...
Water plays an important role in the ductile deformation and evolution of the upper mantle. Water contents of natural olivine from 240 samples reveal a wide variation of 0–170ppm H 2 O, suggesting heterogeneous water distribution in the continental upper mantle. The average water contents (17±13ppm H 2 O) in kimberlite nodules provide the best estimation of water concentrations in...
We present a uniform updated model of the European lithosphere–asthenosphere boundary (LAB) recalculated from data collected during our regional studies of seismic anisotropy and other tomographic experiments, and show results of mapping of large-scale domains of mantle lithosphere characterized by uniform fossil fabrics. Exploiting the long memory of the fabric of the deep continental lithosphere,...
The physical interaction of the convecting asthenosphere and the highly viscous lower lithosphere determines the transmission of plate driving stresses from the mantle to the plates, and controls the stress state of deep cratonic roots, which is important for cratonic diamond formation models. A growing number of studies have highlighted a high degree of heterogeneity in root zones, however, little...
The N–S Languedoc volcanic province between the French Massif Central and the Mediterranean Sea is characterized by sporadic, scattered, low volume (∼2km 3 ) and geochemically homogeneous alkali basaltic activity, spanning from 161 to 0.5Ma. The existence of magmatic activity of such a long duration within such a small area (∼140km long and ∼60km wide), in spite of the extensive shift to the...
The garnet websterites from Bardane (Western Gneiss Region, Norway) derive from cold Archean subcontinental lithosphere involved in Scandian continental subduction to ultrahigh-pressures. Subduction zone metamorphism was promoted by slab fluid infiltration into the cold overlying mantle wedge. The earliest subduction transformation (M3-1) consists of garnet/clinopyroxene exsolution from old pre-subduction...
This study presents an integrated study of the North China Craton (NCC) based on recent high-resolution seismic images combined with observations on surface geology, regional tectonics and mantle dynamics. Seismic images reveal markedly concordant and rapid variations in crustal and lithospheric structure and thickness, upper mantle anisotropy, and discontinuity structures and thickness of the mantle...
The present-day thermal and compositional 3D structure of the lithosphere beneath the Atlantic–Mediterranean Transition Region and the lithosphere–asthenosphere interaction from Jurassic times to present has been studied. The Atlantic–Mediterranean Transition Region comprises the western segment of the Africa–Eurasia plate boundary, encompassing two main large-scale tectonic domains: the Gibraltar...
Combined interpretation of seismic velocity and attenuation models can provide a powerful tool to investigate the physical state of the upper mantle. We jointly analyze the global shear-velocity model of Kustowski et al. (2008) and the global shear-attenuation model of Dalton et al. (2008). In plots of attenuation versus velocity at fixed depths, the seismological model values form distinct regional...
The Xiaodingxi and Manghuihe volcanic sequences represent key components of the Lancangjiang igneous zone in southwest China. Their petrogenesis provides important constraints on the tectonic evolution of the eastern Paleotethys ocean. The basaltic rocks from the Xiaodingxi and Manghuihe sequences yield SHRIMP zircon U–Pb weighted mean ages of 214±7Ma and 210±22Ma, respectively, which is 15–20Ma younger...
The timing and extent of polymetamorphism in the Mangalwar and Sandmata Complexes from the Aravalli–Delhi Orogenic Belt of Rajasthan (NW India) remains contentious, with Archaean, Paleoproterozoic and Neoproterozoic events having previously been postulated. Monazite SHRIMP U–Pb and electron microprobe (EPMA) chemical ages obtained from metasediments in the amphibolite-facies Mangalwar Complex show...
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