Metasomatizing effects of serpentinization-related hydrothermal fluids in abyssal peridotites: new contributions from Hyblean peridotite xenoliths (southeastern Sicily)

Manuella, Fabio Carmelo; Ottolini, Luisa; Carbone, Serafina; Scavo, Lidia

doi:10.1016/j.lithos.2016.09.010

Cited by 9 publications

(11 citation statements)

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“…According to Reference [83], olivine produced by serpentine dehydroxilation may host inclusions of magnetite, serpentine, and hydrous fluids, as it occurs in most of the aforementioned olivine micrograins. Magnetite as a reaction product may indicate that the serpentine reactant was bearing some iron, as highlighted by Reference [50]. Alternatively, iron that formed magnetite was mostly derived from the reactant silicate melt.…”

Section: Discussionmentioning

confidence: 99%

“…The same authors also presented a geochemical model suggesting that different degrees of partial melting of a Hyblean-like mantle, in the pressure range 1-2 GPa, with the addition of about 0.03-0.1 wt% H 2 O, can give rise to different mafic melts that includes the entire geochemical spectrum of the Etnean magmas. [50]. A full discussion is given in the text.…”

Section: Discussionmentioning

confidence: 99%

“…Serpentine formed a complex network of veins that that pass through both the porphyroclast and subgrain olivine grains. Serpentine veins in some peridotite xenoliths from Valle Guffari, close to and similar to the sample, were studied by [50]. The veins generally consisted of two polytypes, chrysotile 2M c1 and lizardite 1T.…”

Section: Optical and Sem Petrographymentioning

confidence: 98%

“…Serpentine veins in the sample were coaxially intruded by a late vein of microcrystalline, Sr-bearing, low-Mg, Ca carbonate (likeky aragonite [51]). Ni-rich sulfide (e.g., millerite-NiS: Reference [50]) and magnetite micrograins, as by-products of the serpentinization reactions [35,49], were evenly distributed along the serpentine veins. A further set of late-stage carbonate veins, either parallel or discordant with respect to the serpentinite veins, also occurred in the sample (Figure 3d; Reference [51]).…”

Section: Optical and Sem Petrographymentioning

confidence: 99%

“…Compatibility diagram (sample vs. normal-MORB) of the vein glass ICPMS-LA spot-analyses, the juvenile lava of the diatremic eruption, a typical alkaline-basalt from the Hyblean area[27], the peridotite xenolith hosting the vein glass and the average values of spot analyses in serpentine veins in Hyblean peridotite xenoliths (after[50]) as indicated in the Legend. The shadowed area represents published analyses of worldwide meimechites and alkaline-picrites (References[67][68][69][70][71][72][73]).…”

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confidence: 99%

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A Volcanological Paradox in a Thin-Section: Large Explosive Eruptions of High-Mg Magmas Explained Through a Vein of Silicate Glass in a Serpentinized Peridotite Xenolith (Hyblean Area, Sicily)

2019

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Ultramafic magmas (MgO ≥ 18 wt%) are generally thought to be primary mantle melts formed at temperatures in excess of 1600 °C. Volatile contents are expected to be low, and accordingly, high-Mg magmas generally do not yield large explosive eruptions. However, there are important exceptions to low explosivity that require an explanation. Here we show that hydrous (hence, potentially explosive) ultramafic magmas can also form at crustal depths at temperatures even lower than 1000 °C. Such a conclusion arose from the study of a silicate glass vein, ~1 mm in thickness, cross-cutting a mantle-derived harzburgite xenolith from the Valle Guffari nephelinite diatreme (Hyblean area, Sicily). The glass vein postdates a number of serpentine veins already existing in the host harzburgite, thus reasonably excluding that the melt infiltrated in the rock at mantle depths. The glass is highly porous at the sub-micron scale, it also bears vesicles filled by secondary minerals. The distribution of some major elements corresponds to a meimechite composition (MgO = 20.35 wt%; Na2O + K2O < 1 wt%; and TiO2 > 1 wt%). On the other hand, trace element distribution in the vein glass nearly matches the nephelinite juvenile clasts in the xenolith-bearing tuff-breccia. These data strongly support the hypothesis that an upwelling nephelinite melt (MgO = 7–9 wt%; 1100 ≤ T ≤ 1250 °C) intersected fractured serpentinites (T ≤ 500 °C) buried in the aged oceanic crust. The consequent dehydroxilization of the serpentine minerals gave rise to a supercritical aqueous fluid, bearing finely dispersed, hydrated cationic complexes such as [Mg2+(H2O)n]. The high-Mg, hydrothermal solution "flushed" into the nephelinite magma producing an ultramafic, hydrous (hence, potentially explosive), hybrid magma. This hypothesis explains the volcanological paradox of large explosive eruptions produced by ultramafic magmas.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Optical and Sem Petrographymentioning

confidence: 98%