Metasomatism versus host magma infiltration: A case study of Sal mantle xenoliths, Cape Verde Archipelago

2011 ◽  
pp. 283-305 ◽  
Author(s):  
Costanza Bonadiman ◽  
Massimo Coltorti ◽  
Luigi Beccaluva ◽  
William L. Griffin ◽  
Suzanne Y. O'Reilly ◽  
...  
Keyword(s):  
Cape Verde ◽  
Mantle Xenoliths ◽  
Host Magma

Petrology of ultramafic xenoliths from Rayfield River, south-central British Columbia

1987 ◽  
Vol 24 (8) ◽  
pp. 1679-1687 ◽  
Author(s):  
Dante Canil ◽  
Mark Brearley ◽  
Christopher M. Scarfe
Keyword(s):  
British Columbia ◽  
Phase Equilibrium ◽  
Partial Melting ◽  
Upper Mantle ◽  
Mantle Xenoliths ◽  
Spinel Lherzolite ◽  
Equilibrium Constraints ◽  
Host Magma ◽  
South Central ◽  
Ultramafic Xenoliths

One hundred mantle xenoliths were collected from a hawaiite flow of Miocene–Pliocene age near Rayfield River, south-central British Columbia. The massive host hawaiite contains subrounded xenoliths that range in size from 1 to 10 cm and show protogranular textures. Both Cr-diopside-bearing and Al-augite-bearing xenoliths are represented. The Cr-diopside-bearing xenolith suite consists of spinel lherzolite (64%), dunite (12%), websterite (12%), harzburgite (9%), and olivine websterite (3%). Banding and veining on a centimetre scale are present in four xenoliths. Partial melting at the grain boundaries of clinopyroxene is common and may be due to natural partial melting in the upper mantle, heating by the host magma during transport, or decompression during ascent.Microprobe analyses of the constituent minerals show that most of the xenoliths are well equilibrated. Olivine is Fo89 to Fo92, orthopyroxene is En90, and Cr diopside is Wo47En48Fs5. More Fe-rich pyroxene compositions are present in some of the websterite xenoliths. The Mg/(Mg + Fe2+) and Cr/(Cr + Al + Fe3+) ratios in spinel are uniform in individual xenoliths, but they vary from xenolith to xenolith. Equilibration temperatures for the xenoliths are 860–980 °C using the Wells geothermometer. The depth of equilibration estimated for the xenoliths using geophysical and phase equilibrium constraints is 30–40 km.

Applicability of satellite rainfall estimates for erosion studies in small offshore areas: A case study in Cape Verde Islands

CATENA ◽  
2014 ◽  
Vol 121 ◽  
pp. 365-374 ◽  
Author(s):  
Juan Francisco Sanchez-Moreno ◽  
Chris M. Mannaerts ◽  
Victor Jetten
Keyword(s):  
Cape Verde ◽  
Cape Verde Islands ◽  
Satellite Rainfall ◽  
Rainfall Estimates

Petrography and mineral chemistry of mantle xenoliths in a carbonate-rich melilititic tuff from Mt. Vulture volcano, southern Italy

2000 ◽  
Vol 64 (4) ◽  
pp. 593-613 ◽  
Author(s):  
A. P. Jones ◽  
T. Kostoula ◽  
F. Stoppa ◽  
A. R. Woolley
Keyword(s):  
High Pressure ◽  
Heat Flow ◽  
Southern Italy ◽  
Mineral Chemistry ◽  
Continental Rift ◽  
Mantle Xenoliths ◽  
Chrome Spinel ◽  
Partial Melt ◽  
Host Magma ◽  
Mineral Assemblages

AbstractWe present petrographic and mineralogical data for 21 mantle xenoliths (12 lherzolites, 8 wehrlites and 1 composite) selected from a suite of more than 70 samples collected from the Monticchio Formation, Mt. Vulture volcano, southern Italy. The xenoliths are rounded, coarse- to porphyroclastic-textured, and very fresh, with the following equilibrated mineral assemblages; olivine (Fo90–92), orthopyroxene (∼En89, Wo2.0), clinopyroxene (Mg90–92, 3–6% Al2O3, 1–1.5% Cr2O3), and chrome-spinel (14–20% MgO, ∼30–40% Cr2O3). Many xenoliths contain partial melt glasses and accessory sulphide (pentlandite) Some contain primary mica (phlogopite with ∼4% FeO, 1.8% Cr2O3, 1.4–2.8% TiO2) with slightly zoned rims (Fe-, Ti-, Al-enriched). One contains relics of garnet (pyrope; Mg84). Secondary veins in several xenoliths contain carbonate with significant Sr levels (∼0.5–1.0% SrO), occasional apatite and scarce melanite, all typical of carbonatites and presumably related to the host magma (melilitite/carbonatite). Although amphibole is a common megacryst in the same volcanic units, no primary amphibole was found in the xenoliths themselves. Calculated pressures and temperatures using a range of geothermometers/barometers give values of 14–22 kbar and 1050–1150°C. In particular, the En-Sp and Di-Sp thermo/barometers (Mercier, 1980) show a good positive correlation between P and T. The Monticchio xenoliths lie on the high-T side of an ‘oceanic’ geotherm. The xenolith geotherm is hotter than general heat flow values in this region at the current day (50 mWm−2) but it compares well with the high-pressure end of a typical alkaline continental rift.

Water prospection in volcanic islands by Time Domain Electromagnetic (TDEM) surveying: The case study of the islands of Fogo and Santo Antão in Cape Verde

2016 ◽  
Vol 134 ◽  
pp. 226-234 ◽  
Author(s):  
F.J. Martínez-Moreno ◽  
F.A. Monteiro-Santos ◽  
J. Madeira ◽  
I. Bernardo ◽  
A. Soares ◽  
...  
Keyword(s):  
Time Domain ◽  
Cape Verde ◽  
Time Domain Electromagnetic ◽  
Volcanic Islands

Is orthopyroxene really a reliable recorder of mantle water signatures? Insights from an experimental study

2020 ◽  
Author(s):  
Alexandra Demers-Roberge ◽  
Michael Jollands ◽  
Peter Tollan ◽  
Othmar Müntener
Keyword(s):  
Diffusion Coefficients ◽  
Mantle Xenoliths ◽  
Spinel Peridotite ◽  
Alkaline Magma ◽  
Silica Activity ◽  
Exponential Factors ◽  
Natural Olivine ◽  
Natural Settings ◽  
Water Contents

<p>Experiments have been conducted to assess the effects of temperature, oxygen fugacity, crystallographic orientation, silica activity and chemical composition on the diffusivity and substitution mechanisms of hydrogen in orthopyroxene (opx). Axially oriented ~cuboids of natural Tanzanian opx were dehydrated at 1 bar in a gas mixing furnace (H<sub>2</sub>-CO<sub>2</sub> mix) at three different oxygen fugacities (~QFM-1,~QFM+1, ~QFM-7), and two different silica activity buffers (olivine+pyroxene or pyroxene+quartz) between 700°C and 1000°C. Profiles of hydrogen content versus distance were extracted from experimental samples using Fourier-Transform Infrared (FTIR) spectroscopy, with diffusion coefficients extracted using relevant analytical solutions and numerical approximations of Fick’s second law. Diffusion is the fastest along [001] ( D<sub>[001]</sub>>D<sub>[010]</sub>>D<sub>[100]</sub>). Fitting the diffusion coefficients to the isobaric Arrhenius relationship (logD=logD<sub>0</sub>+(-Q/(2.303RT)) gives activation energies (Q) and pre-exponential factors (logD<sub>0</sub>) between 127 to 162 kJmol<sup>-1</sup> and –4.29 to -5.42  m<sup>2</sup>s<sup>-1</sup> , respectively, for ~QFM-1.</p><p>The extracted hydrogen diffusivities are faster than previously measured by 0.5 to 5 orders of magnitude at ~1000 °C and ~700°C, respectively (Carpenter (2003), Stalder and Skogby (2003), Stalder and Behrens (2006), Stalder and al. (2007)) and are slightly slower, but strikingly close, to those of the fastest experimentally-determined diffusivity of H in olivine (Kohlstedt and Mackwell, 1998), suggesting a mechanism akin to proton-polaron exchange. This presents a paradoxical decoupling between natural and experimental observations. In most cases for mantle xenoliths, natural olivine has low water contents (<35 ppm), or are dry, and show H diffusive loss of water, where natural opx contains between 10 and 460 ppm and rarely show H diffusive loss (Demouchy and Bolfan-Casanova (2016), suggesting opx is more capable of recording the mantle water signature. With hydrogen diffusivities of olivine and opx being quite similar, however, both minerals should suffer from the same rate of dehydration during ascent, thus show low or zero water content in natural settings, which is not the case. Therefore, the inference that pyroxenes are better recorder of water in the mantle (e.g. Warren et Hauri (2014), Peslier (2010)) cannot be a simple function of diffusivities. A case study on an opx crystal showing a dehydration profile from a spinel-peridotite xenolith, hosted in an alkaline magma, from Patagonia supports this. Using the H diffusion coefficients from this study, the calculated rates of ascent of the mantle xenolith in alkaline magma are comparable to those associated with kimberlite magmas. The two suggestions we present are the following: i) Changing the boundary conditions may modify the hydrogen diffusive flux through the xenolith history and ii) The measured diffusivities would be apparent diffusivities as there might be different pathways or mechanisms of diffusion.</p>

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