CO2-rich fluid inclusions in mantle xenoliths from Barombi-Mbo and Nyos maars (Cameroon volcanic line, central Africa): Upper mantle equilibria and history of magma ascension

Studying the isotopic composition of fluids trapped in mantle xenoliths opens avenues to understanding the origin and cycling of volatiles in the Earth&#8217;s upper mantle. Here, we present the first isotopic results for noble gases and CO2 in fluid inclusions (FI) trapped in mantle xenoliths from El Hierro the youngest island of the Canarian archipelago. Our results are based on 6 mantle xenolith samples (3 Spinel-lherzolites and 3 Spinel-harzburgites) collected from the El Julan cliff valley (Oglialoro et al., 2017), from which we hand-picked crystals of Ol, Opx, and Cpx. Isotopic determinations were performed at the INGV (Sezione di Palermo) noble gas and stable isotopes laboratories, following the preparation methods and analytical procedures described in Rizzo et al. (2018 and references therein).The Ne-Ar isotopic compositions reveal the presence of an atmospheric component in the FI. Most of the samples exhibit 4He/20Ne ratios > 60, 20Ne/22Ne ratios between 9.84 and 10.49, 21Ne/22Ne ratios from 0.0295 to 0.0330, and 40Ar/36Ar > 800, suggesting mixing between MORB-like mantle fluids and an air-derived component. We argue this latter may (at least in part) derive from upper mantle recycling of atmospheric fluids via paleo-subduction event(s). Excluding samples possibly affected by diffusive fractionation processes, the average Rc/Ra ratio (3He/4He ratio corrected for atmospheric contamination) measured in El Hierro xenoliths is ~7.45 + 0.26 Ra, within the MORB range (8 + 1 Ra; Graham, 2002). The He homogeneous signature of these xenoliths agrees well with the 3He/4He compositions previously reported in lava phenocrysts and cumulates (Day and Hilton, 2011) and is slightly below the maximum ratios measured in groundwater samples during the 2012 volcanic unrest (~8.2 Ra; Padron et al., 2013). All these pieces of evidence argue against a primordial source involved in the local lithospheric mantle. Putting these data in the context of previous literature results for FI and surface gases in the Canary Islands (La Palma, La Gomera, Tenerife, Gran Canaria, and Lanzarote), we identify an eastward 3He/4He decreasing trend that parallels a corresponding increase of the oceanic crust thickness. In addition to the mantle heterogeneity, we propose that part of the 3He/4He east-to-west variation along the archipelago is caused by the variable thickness of the oceanic crust (and hence, different interactions with 4He-rich crustal fluids during emplacement).The FI &#948;13C(CO2) isotopic composition ranges from -2.38 to -1.23&#8240; in pyroxenes and -0.2 to +2.0&#8240; in olivine. These unusually positive &#948;13C compositions support the existence of a recycled crustal carbon component in the local source mantle, likely pointing to mantle metasomatism (Oglialoro et al., 2017) from fluids carrying carbon from subducted sediments and/or altered oceanic crust (AOC).

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Amphibole lamellae formation in the upper mantle due to interaction of fluid inclusions and host minerals: a case study from Persani Mountains Volcanic Field, Transylvania

10.5194/egusphere-egu2020-1192 ◽

2020 ◽

Author(s):

Thomas Pieter Lange ◽

Zsófia Pálos ◽

Levente Patkó ◽

Márta Berkesi ◽

Nóra Liptai ◽

...

Keyword(s):

Fluid Inclusion ◽

Fluid Inclusions ◽

Upper Mantle ◽

Volcanic Field ◽

Planetary Science ◽

Mantle Xenoliths ◽

Fluid Inclusion Study ◽

Chemical Components ◽

Major Element Composition ◽

Host Mineral

Amphibole is one of the most abundant &#8217;water&#8217;-bearing minerals in the Earth&#8217;s upper mantle. Amphiboles occur as interstitial grains, lamellae within pyroxenes or as daughter minerals within fluid inclusions. &#160;Most commonly amphibole formation is related to mantle metasomatism, where the agent has a subducted slab (e.g. Manning 2004) or an asthenospheric origin (e.g. Berkesi et al. 2019). &#160;After the formation of fluid inclusions, a subsolidus interaction can take place where the H2O content of fluid inclusions may crystallize pargasite (e.g. Plank et al. 2016).Here we present amphibole lamellae formation in mantle xenoliths from the Persani Mountains Volcanic Field that is interrelated to a reaction between fluid inclusions and host clinopyroxene. &#160;Newly formed amphibole lamellae occur only in the surroundings of the fluid inclusions and grow within the host clinopyroxene in a preferred crystallographic direction. &#160;Studied lamellae do not reach the rim of the host mineral implying that components needed for formation of amphibole lamellae in clinopyroxene could have only originated from the fluid inclusion itself. &#160;We measured the major element composition of amphibole lamellae and host clinopyroxene (1) and used Raman spectroscopy and FIB-SEM on fluid inclusion study situated next to the lamellae (2). &#160;Results support the hypothesis that chemical components (dominantly H+) migrated sub-solidus from the fluid inclusion into the host mineral after fluid entrapment via subsolidus interaction. &#160;Beyond the clinopyroxene-hosted fluid inclusions, fluid inclusions in orthopyroxenes were also studied as a reference. &#160;Our study shows that post-entrapment diffusion from a fluid inclusion into the host mineral changes the solid/fluid ratio of the mantle &#160;which could modify the rheology of the lithospheric mantle.Berkesi, M. et al. 2019. Chemical Geology, 508, 182-196.Kov&#225;cs et al. (2017) Acta Geodaetica et Geophysica, 52(2), 183-204.Manning C. E. 2004. Earth and Planetary Science Letters, 223, 1-16.Plank, T. A. et al. 2016. In AGU Fall Meeting Abstracts.

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Petrography and geological history of upper mantle xenoliths from the matsoku kimberlite pipe

Physics and Chemistry of the Earth ◽

10.1016/0079-1946(75)90035-x ◽

1975 ◽

Vol 9 ◽

pp. 477-506 ◽

Cited By ~ 48

Author(s):

B. Harte ◽

K.G. Cox ◽

J.J. Gurney

Keyword(s):

Upper Mantle ◽

Kimberlite Pipe ◽

Mantle Xenoliths ◽

Geological History ◽

History Of

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Petrography and geological history of upper mantle xenoliths from the Matsoku Kimberlite

International Kimberlite Conference Extended Abstracts: 1973 ◽

10.29173/ikc872 ◽

2019 ◽

Keyword(s):

Upper Mantle ◽

Mantle Xenoliths ◽

Geological History ◽

History Of

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Carbonatite melt–CO2 fluid inclusions in mantle xenoliths from Tenerife, Canary Islands: a story of trapping, immiscibility and fluid–rock interaction in the upper mantle

Lithos ◽

10.1016/s0024-4937(02)00178-0 ◽

2002 ◽

Vol 64 (3-4) ◽

pp. 77-96 ◽

Cited By ~ 47

Author(s):

Maria Luce Frezzotti ◽

Tom Andersen ◽

Else-Ragnhild Neumann ◽

Siri Lene Simonsen

Keyword(s):

Canary Islands ◽

Fluid Inclusions ◽

Upper Mantle ◽

Mantle Xenoliths ◽

Rock Interaction

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A history of botanical collections in the Luangwa Valley, Zambia

Archives of Natural History ◽

10.3366/anh.1998.25.2.283 ◽

1998 ◽

Vol 25 (2) ◽

pp. 283-291

Author(s):

P.S.M. PHIRI ◽

D.M. MOORE

Keyword(s):

Eighteenth Century ◽

Environmental Impact ◽

Impact Assessment ◽

Vascular Plants ◽

Central Africa ◽

Peak Activity ◽

Historical Account ◽

History Of ◽

The 1960S ◽

Made In

Central Africa remained botanically unknown to the outside world up to the end of the eighteenth century. This paper provides a historical account of plant explorations in the Luangwa Valley. The first plant specimens were collected in 1897 and the last serious botanical explorations were made in 1993. During this period there have been 58 plant collectors in the Luangwa Valley with peak activity recorded in the 1960s. In 1989 1,348 species of vascular plants were described in the Luangwa Valley. More botanical collecting is needed with a view to finding new plant taxa, and also to provide a satisfactory basis for applied disciplines such as ecology, phytogeography, conservation and environmental impact assessment.

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From Stonehenge to Samarkand

10.1093/oso/9780195160918.001.0001 ◽

2006 ◽

Author(s):

Brian Fagan

Keyword(s):

Gustave Flaubert ◽

Central Africa ◽

British Museum ◽

Holy Land ◽

Cruise Ship ◽

Modern Times ◽

Ancient Civilization ◽

Machu Picchu ◽

History Of ◽

The Silk Road

Ever since Roman tourists scratched graffiti on the pyramids and temples of Egypt over two thousand years ago, people have traveled far and wide seeking the great wonders of antiquity. In From Stonehenge to Samarkand, noted archaeologist and popular writer Brian Fagan offers an engaging historical account of our enduring love of ancient architecture--the irresistible impulse to visit strange lands in search of lost cities and forgotten monuments. Here is a marvelous history of archaeological tourism, with generous excerpts from the writings of the tourists themselves. Readers will find Herodotus describing the construction of Babylon; Edward Gibbon receiving inspiration for his seminal work while wandering through the ruins of the Forum in Rome; Gustave Flaubert watching the sunrise from atop the Pyramid of Cheops. We visit Easter Island with Pierre Loti, Machu Picchu with Hiram Bingham, Central Africa with David Livingstone. Fagan describes the early antiquarians, consumed with a passionate and omnivorous curiosity, pondering the mysteries of Stonehenge, but he also considers some of the less reputable figures, such as the Earl of Elgin, who sold large parts of the Parthenon to the British Museum. Finally, he discusses the changing nature of archaeological tourism, from the early romantic wanderings of the solitary figure, communing with the departed spirits of Druids or Mayans, to the cruise-ship excursions of modern times, where masses of tourists are hustled through ruins, barely aware of their surroundings. From the Holy Land to the Silk Road, the Yucatán to Angkor Wat, Fagan follows in the footsteps of the great archaeological travelers to retrieve their first written impressions in a book that will delight anyone fascinated with the landmarks of ancient civilization.

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Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient

Scientific Reports ◽

10.1038/s41598-021-90844-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Costanza Bonadiman ◽

Valentina Brombin ◽

Giovanni B. Andreozzi ◽

Piera Benna ◽

Massimo Coltorti ◽

...

Keyword(s):

Oxygen Fugacity ◽

Upper Mantle ◽

Mantle Xenoliths ◽

Spinel Peridotite ◽

Simultaneous Formation ◽

Empirical Potentials ◽

Elastic Data ◽

Mineralogical Study ◽

Semi Empirical ◽

T Locus

AbstractThe occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity.

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