Search results for "Rust"

Further evidence of length- and sex-dependent variation of some morphological characters in Bathyporeia guilliamsoniana (Bate, 1857) (Crustacea: Amph…

2011

Pliocene tourmaline rhyolite dykes from Ikaria Island in the Aegean back-arc region: geodynamic implications

2009

Very rare rhyolite dykes cross-cutting a Miocene I-type biotite-granite were discovered on Ikaria Island in the Aegean back-arc region. Their intrusion postdates exhumation of the granite to brittle crust at about 6.0-3.6 Ma; hence a Pliocene age is inferred. Petrological, geochemical and isotopic arguments indicate an origin through melting of crustal lithologies (tourmaline greywackes/semipelites) with no detectable contribution from asthenospheric sources. Strontium isotope ratios are relatively low unlike values for sediments entering the Hellenic trench but similar to those for certain Miocene Cycladic I-type granites and low-Rb Permo-Carboniferous Cycladic basement acid orthogneisses.…

Mechanism and time of deformation and metamorphism of mylonitic orthogneisses from the Shagou Shear Zone, Qinling Belt, China

1990

Abstract The Shagou Shear Zone south of Xian (Shaanxi Province) is a branch of the Shangdan Fault Zone in the Qinling Belt and documents ductile deformation that affected granitoid rocks. Mylonitization took place under conditions of the lower amphibolite facies at temperatures of ca. 530°C, followed by a phase of stagnation, still under the same metamorphic conditions. The last deformation was a weak event during retrogressive greenschist metamorphism. The emplacement of the granitoid precursors of the mylonite is dated at 211 ± 8 Ma by the U/Pb zircon method, much younger than Nd model ages of 1.2–1.3 Ga, which indicates the involvement of older continental crust, probably in an active co…

Crust–mantle transition and Moho model for Iceland and surroundings from seismic, topography, and gravity data

2005

An increasing data set exists on the nature and thickness of the Iceland crust. This paper relates topography, i.e., elevation and bathymetry (TOP), Bouguer gravity anomalies (BA) and Moho depths to each other to assess the consequences of the “thick crust model” for Iceland in the context of the North Atlantic. Results of regression of TOP and BA vs. Moho depth are converted into “Airy densities” Δρ* (mantle crust density contrasts in the case of ideal Airy isostasy). For Iceland, Δρ* is very low (105±10 kg/m3); for the adjacent continental margins and relicts, it is high and intermediate for the Jan Mayen Ridge. The values are affected by lithosphere cooling and systematic variations of i…

Constraints on mantle source and interactions from He-Sr isotope variation in Italian Plio-Quaternary volcanism

2008

[1] Helium isotope ratios of olivine and pyroxene phenocrysts from Plio-Quaternary volcanic rocks from southern Italy (seven Aeolian Islands, Mt. Vulture, Etna, Ustica, and Pantelleria) range from 2.3 to 7.1 Ra. Importantly, the phenocryst 3He/4He correlate well with whole rock Sr isotopic composition (0.70309–0.70711), reflecting the mixing of two sources. A significant contribution of He from crustal contamination is recorded only occasionally (e.g., pyroxenes from Vulcano). When merged with data from the Roman Comagmatic Province, a remarkably strong near-linear He-Sr isotope correlation is apparent. The general northward decrease in 3He/4He corresponds to an increase in 87Sr/86Sr (and a…

The formation of large quartz veins by rapid ascent of fluids in mobile hydrofractures

2001

Abstract This paper aims to resolve two main problems related to the formation of quartz veins: (1) the predominance of quartz veins at shallow crustal levels and not deeper in the crust, close to the source of metamorphic fluids where the temperature sensitivity of quartz solubility is much higher than at lower, upper-crustal temperatures and (2) the formation of very large 100–1000 m scale quartz veins that would require huge amounts of fluid flow in current models of vein formation. It is proposed here that these problems are resolved by the recognition of very fast (m/s) mobile hydrofracture ascent of batches of fluid. Mobile hydrofractures are fluid-filled fractures that propagate at t…

Eastern Pontides and Black Sea: gravity inversion, crustal structure, isostasy and geodynamics

2002

Abstract Lacking detailed seismic data on the crustal structure of Anatolia and the transition to the Black Sea, it is attempted to invert gravity for crust-mantle structure with constraints from the limited a priori information available, as average continental and oceanic crust, local topography, an isostatic model, published marine seismic data and a tentative “fix point” from recent seismological receiver functions near the Black Sea coast. An initial 2D-model for a north–south profile along about 40°E longitude is constructed and adjusted to fit the Bouguer anomaly taken from a published Turkish map and results from satellite radar altimetry. Isostasy, seismic data and gravity inversio…

An active oblique-contractional belt at the transition between the Southern Apennines and Calabrian Arc: The Amendolara Ridge, Ionian Sea, Italy

2014

High-resolution, single-channel seismic and multibeam bathymetry data collected at the Amendolara Ridge, a key submarine area marking the junction between the Apennine collision belt and the Calabrian subduction forearc, reveal active deformation in a supposedly stable crustal sector. New data, integrated with existing multichannel seismic profiles calibrated with oil-exploratory wells, show that middle to late Pleistocene sediments are deformed in growth folds above blind oblique-reverse faults that bound a regional pop-up. Data analysis indicates that ~10 to 20 km long banks that top the ~80 km long, NW-SE trending ridge are structural culminations above en echelon fault segments. Numeric…

Partial Melting and Counterclockwise P T Path of Subducted Oceanic Crust (Sierra del Convento Melange, Cuba)

2007

Continental collision and the dynamic and thermal evolution of the Variscan orogenic crustal root — numerical models

2001

Abstract Orogeny is modelled numerically by treating continental collision within full convection solutions, in order to better understand some aspects of the Variscan structures and processes. Three different approaches are taken: (1) collision where one ‘continental plate’ is ‘pushed’ against another across a zone of weakness; (2) gravitational instability of a lithospheric mantle root leading to delamination, slab break-off and crustal root reduction; (3) melting in the lower part of a crustal orogenic root. The first approach demonstrates that thick (but in the models: cool) roots can accumulate, in which upper crustal rocks are carried to great depth and mantle material may be carried …