Search results for "LITHOSPHERE"
showing 10 items of 96 documents
On thrusting, regional unconformities and exhumation of high-grade greenstones in Neoarchean orogens. The case of the Waroonga Shear Zone, Yilgarn Cr…
2017
Abstract During the Neoarchean, the dominant tectonic style progressively changed from an episodic-overturn/stagnant-lid regime to modern-style plate tectonics. The Neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts. The case study presented here provides insights into how such transition in tectonic style occurred, a matter that is generally controversial. We present structural and metamorphic data from the c. 2660 Ma Waroonga Shear Zone (WSZ) in the Neoarchean Yilgarn orogen (Western Australia). The WSZ contains a syntectonic pluton and older, high-grade greenstones. The tectonic fabric in the pluton developed during melt-present thrusti…
Numerical modeling of eastern Tibetan-type margin: Influences of surface processes, lithospheric structure and crustal rheology
2013
The eastern Tibetan margin is characterized by a steep topographic gradient and remarkably lateral variations in crustal/lithospheric structure and thermal state. GPS measurements show that the surface convergence rate in this area is strikingly low. How can such a mountain range grow without significant upper crustal shortening? In order to investigate the formation mechanism of the eastern Tibetan-type margins, we conducted 2D numerical simulations based on finite difference and marker-in-cell techniques. The numerical models were constrained with geological and geophysical observations in the eastern Tibetan margin. Several major parameters responsible for topography building, such as th…
Rift nucleation, rift propagation and the creation of basement micro-plates within active rifts
2008
Abstract In this contribution we study the dynamics of rift nucleation and the interaction of propagating rift segments. We use the East African Rift System (EARS) as a case study with special emphasis on the Albertine rift system situated within the western branch of the EARS with the 5000 m high Rwenzori horst, a basement block that was captured by two rift segments. Fieldwork in the Rwenzori mountains shows that the range is not only affected by range parallel faults but that major fault sets cut across the Rwenzoris. In order to understand these complex fault patterns and the dynamics of the process that leads to the capturing of basement blocks within the extending rift system we devel…
Melt infiltration of the lower lithosphere beneath the Tanzania craton and the Albertine rift inferred from S receiver functions
2012
[1] The transition between the lithosphere and the asthenosphere is subject to numerous contemporary studies as its nature is still poorly understood. The thickest lithosphere is associated with old cratons and platforms and it has been shown that seismic investigations may fail to image the lithosphere-asthenosphere boundary in these areas. Instead, several recent studies have proposed a mid-lithospheric discontinuity of unknown origin existing under several cratons. In this study we investigate the Tanzania craton in East Africa which is enclosed by the eastern and western branches of the East African Rift System. We present evidence from S receiver functions for two consecutive discontin…
The Palermo (Sicily) seismic cluster of September 2002, in the seismotectonic framework of the Tyrrhenian Sea-Sicily border area
2009
The northern coast of Sicily and its offshore area represent a hinge zone between a sector of the Tyrrhenian Basin, characterized by the strongest crustal thinning, and the sector of the Sicilian belt which has emerged. This hinge zone is part of a wider W-E trending right-lateral shear zone, which has been affecting the Maghrebian Chain units since the Pliocene. Seismological and structural data have been used to evaluate the seismotectonic behavior of the area investigated here. Seismological analysis was performed on a data set of about 2100 seismic events which occurred between January 1988 and October 2002 in the Southern Tyrrhenian Sea. This paper focuses…
Numerical modelling of PT-paths related to rapid exhumation of high-pressure rocks from the crustal root in the Variscan Erzgebirge Dome (Saxony/Germ…
2002
Abstract The Bohemian Massif in the Central European Variscides contains many crustal slices with (ultra-)high-pressure rocks related to continent-continent collision. After closure of pre-existing oceans during the Devonian, excess crustal thickness was maintained for about 50 Ma until at around 340 Ma large volumes of high-pressure rocks from the crustal root were exhumed within a few million years. We relate this event to delamination and complete detachment of the lithospheric mantle, causing a crustal-scale isostatic instability. In the Erzgebirge dome, a model region in the northern part of the massif, an array of interrelated PTtd-paths with “decompression/cooling” and “decompression…
Andean Cenozoic volcanic centers reflect basement isotopic domains
1992
Isotopic data for Quaternary volcanic centers from lat 17.5° to 22°S in northern Chile provide evidence for crustal contributions to arc magma genesis in the central Andes and delineate basement domains. Crustal thickness, distance from trench, height of volcanic edifices above the seismically active subduction zone, and sediment supply to the trench are all constant along this segment of the arc. The only significant variable is crustal age (Paleozoic in the south, Proterozoic in the north). Pb isotopic compositions of Quaternary lavas in the northern sector are lower ( 206 Pb/ 204 Pb = 17.89-18.28) and Sr and O isotope ratios are less variable ( 87 Sr/ 86 Sr = 0.7058-0.7077, δ 18 O = +6.5…
Constraining effective rheology through parallel joint geodynamic inversion
2014
Abstract The dynamics of crust and lithosphere is to a large extent controlled by its effective viscosity. Unfortunately, extrapolation of laboratory experiments indicates that viscosity is likely to vary over many orders of magnitude. Additional methods are thus required to constrain the effective viscosity of the present-day lithosphere using more direct geophysical observations. Here we discuss a method, which couples 3D geodynamic models with observations (surface velocities and gravity anomalies) and with a Bayesian inversion scheme on massively parallel high performance computers. We illustrate that the basic principle of a joint geodynamic and gravity inversion works well with a simp…
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…
Formation of arcuate orogenic belts in the western Mediterranean region
2004
The Alpine orogen in the western Mediterranean region, consisting of the Rif-Betic belt and the Apennine-Calabrian-Maghrebide belt, is a classic example of an arcuate orogen. It contains fragments of Cretaceous to Oligocene high-pressure/low-temperature (HP/LT) rocks, which were exhumed and dispersed during post-Oligocene extensional deformation and are presently exposed in the soles of metamorphic core complexes. In this paper, we illustrate that the arcuate shape of the orogenic belt was attained during extensional destruction of the earlier HP/LT belt, driven by subduction rollback in a direction oblique or orthogonal to the direction of convergence. Since the Oligocene, sub-duction of M…