Search results for "petrology"

METAMORPHIC EVOLUTION OF SPESSARTINE QUARTZITES (COTICULES) IN THE HIGH-PRESSURE, LOW-TEMPERATURE COMPLEX AT BAHIA MANSA, COASTAL CORDILLERA OF SOUTH…

2001

Lenses of spessartine quartzites (coticules) are associated with greenschist intercalations in coastal exposures at Bahia Mansa within the mainly metapsammopelitic Western Series, which forms most of the basement in the Coastal Cordillera of central to southern Chile. The chemical compositions of the coticules can be explained by protoliths formed from ferriferous and manganiferous hydrothermal precipitates mixed with aluminous alteration-derived material on top of oceanic crust. The peak conditions of metamorphism were calculated with multivariant reactions: 270–370 °C, 6–8 kbar. A retrograde P–T evolution was marked by decompression to 2 kbar during cooling below 300°C, influx of an exter…

Vertical ductile thinning and its contribution to the exhumation of high-pressure rocks: the Cycladic blueschist unit in the Aegean

2008

The contribution of vertical ductile thinning to the exhumation of high-pressure rocks is evaluated by estimating finite strain in 75 exhumed high-pressure rocks of the Cycladic blueschist unit in the Aegean Sea, Greece, and western Turkey. Strain data indicate heterogeneous deformation; principal stretches are 1.24–5.03 for S X , 0.63–2.53 for S Y and 0.10–0.81 for S Z , with a tensor average of S X : S Y : S Z =1.52:1.28:0.51. A 1D numerical model, which integrates velocity gradients along a vertical flow path with a steady-state orogen, is used to estimate the contribution of ductile thinning of the overburden of the high-pressure rocks to exhumation. Using a strain-rate law that is prop…

Horizontal contraction or horizontal extension? Heterogeneous Late Eocene and early Oligocene general shearing during blueschist and greenschist faci…

1995

Mylonitic structures related to two orogenic events are described from the upper and lower contacts of the Combin zone and the immediately overlying upper Austroalpine Dent Blanche nappe/Mont Mary klippe and the directly underlying lower Austroalpine Etirol-Levaz slice. The first event, Late Eocene in age, commenced during blueschist facies P-T conditions, but pre-dated the peak of subsequent greenschist facies overprint. The second event, Early Oligocene in age, took place during retrograde greenschist facies conditions. Most sense of shear indicators associated with the retrograde mylonites indicate top SE shearing, but subordinate top NW displacing shear sense indicators have also been m…

3-D attenuation image of fluid storage and tectonic interactions across the Pollino fault network

2021

SUMMARYThe Pollino range is a region of slow deformation where earthquakes generally nucleate on low-angle normal faults. Recent studies have mapped fault structures and identified fluid-related dynamics responsible for historical and recent seismicity in the area. Here, we apply the coda-normalization method at multiple frequencies and scales to image the 3-D P-wave attenuation (QP) properties of its slowly deforming fault network. The wide-scale average attenuation properties of the Pollino range are typical for a stable continental block, with a dependence of QP on frequency of $Q_\mathrm{ P}^{-1}=(0.0011\pm 0.0008) f^{(0.36\pm 0.32)}$. Using only waveforms comprised in the area of seism…

Halogen diffusion in a basaltic melt

2007

Abstract The diffusion of the halogens fluorine, chlorine and bromine was measured in a hawaiitic melt from Mt. Etna at 500 MPa and 1.0 GPa, 1250 to 1450 °C at anhydrous conditions; the diffusion of F and Cl in the melt was also studied with about 3 wt% of dissolved water. Experiments were performed using the diffusion-couple technique in a piston cylinder. Most experiments were performed with only one halogen diffusing between the halogen-enriched and halogen-poor halves of the diffusion couple, but a few experiments with a mixture of halogens (F, Cl and Br) were also performed in order to investigate the possibility of interactions between the halogens during diffusion. Fluorine and chlor…

A Multiphysics Approach to Constrain the Dynamics of the Altiplano‐Puna Magmatic System

2021

Continuous Interferometric Synthetic Aperture Radar (InSAR) monitoring (> 25 years) has revealed a concentric surface deformation pattern above the Altiplano-Puna magma body (APMB) in the central Andes. Here, we use a joint interpretation of seismic imaging, gravity anomalies and InSAR data to constrain location, 3D geometry and density of the magma body. By combining gravity modelling, thermomechanical modelling, scaling law analysis and Bayesian inference, we are able to create a relationship between the geometry of a mid-crustal magma body and surface observations. Furthermore, we can estimate the uncertainties associated with the geometry of the APMB and identify the most important para…

2021

Abstract. The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental m…

Shrinkage Bubbles: The C–O–H–S Magmatic Fluid System at San Cristóbal Volcano

2018

New analytical results for the composition of shrinkage bubbles (09-70 vol. %) in olivine-hosted (Fo <80%) primary melt inclusions (MIs) have been incorporated into a novel geochemical model for San Cristó bal volcano, Nicaragua. The vapour, liquid, and mineral components found inside shrinkage bubbles may represent relics of early C-O-H-S fluids exsolved from a magmatichydrothermal system. This conclusion is supported by high-resolution Raman microspectroscopy revealing: (1) gaseous CO2 (d=0·17-0·31 g/cm3 in 31 samples) coexisting with liquid H2O (in seven samples) at ambient temperature (<22°C) inside the shrinkage bubbles of naturally quenched inclusions; (2) several mineral phases (i.e.…

Refractory metal nuggets in different types of cosmic spherules

2014

Abstract Out of the three basic cosmic spherule types collected from the seafloor, RMNs (refractory metal nuggets) have been reported from I-type spherules commonly, rarely from S-type spherules and never from the G-type spherules. Nuggets in the I-type cosmic spherules have formed by melting and complete oxidation during atmospheric entry, whereas no clear understanding emerged so far regarding the formation of the rare nuggets in S-type spherules. We collected cosmic spherules by raking the deep seafloor with magnets, and carried out systematic and sequential grinding, polishing and electron microscopic investigations on 992 cosmic spherules to identify RMNs. Fifty-four nuggets (RMNs) are…

Origin, age, and significance of deep-seated granulite-facies migmatites in the Barrow zones of Scotland, Cairn Leuchan, Glen Muick area

2018

Funding for this work was provided by the Johannes-Gutenberg University of Mainz. Petrological modelling of granulite‐facies mafic and semipelitic migmatites from Cairn Leuchan, northeast Scotland, has provided new constraints on the pressure (P) and temperature (T) conditions of high‐grade metamorphism in the type‐locality Barrow zones.Phase diagrams constructed in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O2 system have constrained the P–T conditions of peak metamorphism in the Glen Muick region of the upper‐sillimanite zone (Sill+Kfs) to have been at least ~840 ◦C at ~9 kbar (high‐pressure granulite facies). These conditions are approximately ~120 ◦C and ~3 kbar higher than those reco…