Genesis of ultra-high pressure garnet pyroxenites in orogenic peridotites and its bearing on the compositional heterogeneity of the Earth’s mantle

Varas-Reus, Maŕia Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly

doi:10.1016/j.gca.2018.04.033

Cited by 23 publications

(18 citation statements)

References 128 publications

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“…However, since MgO is lower than in N-and E-MORB, KLA and RUB samples display a typical Fe-rich basaltic composition. Such MgO values are in the range of low-MgO mantle garnet pyroxenite when compared with the database of Isabel Varas-Reus, Garrido, Marchesi, Bosch, and Hidas (2018), and their Mg# is the lowest with respect to the other pyroxenites and kyanite eclogite of the Moldanubian Zone. By contrast, Al 2 O 3 content is rather high, in the range of high-Al 2 O 3 mantle garnet pyroxenite (Isabel Varas-Reus et al, 2018).…”

Section: The Host Rock: a Mantle Eclogite With Crustal Subduction-mentioning

confidence: 78%

“…Such MgO values are in the range of low-MgO mantle garnet pyroxenite when compared with the database of Isabel Varas-Reus, Garrido, Marchesi, Bosch, and Hidas (2018), and their Mg# is the lowest with respect to the other pyroxenites and kyanite eclogite of the Moldanubian Zone. By contrast, Al 2 O 3 content is rather high, in the range of high-Al 2 O 3 mantle garnet pyroxenite (Isabel Varas-Reus et al, 2018). Consistent with the Fe-rich nature of the rocks, clinopyroxene and garnet are generally more Fe-rich than in the equivalent phases in the other pyroxenites.…”

Section: The Host Rock: a Mantle Eclogite With Crustal Subduction-mentioning

confidence: 78%

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Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite, Granulitgebirge, Germany

Borghini

Ferrero

O’Brien

et al. 2020

Journal Metamorphic Geology

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Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re‐homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe‐rich basalt and the enrichment in LILE and U suggest a subduction‐related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene‐bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so‐called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high‐grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T‐7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal‐derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.

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Section: The Host Rock: a Mantle Eclogite With Crustal Subduction-mentioning

confidence: 78%

Section: The Host Rock: a Mantle Eclogite With Crustal Subduction-mentioning

confidence: 78%

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite, Granulitgebirge, Germany

Borghini

Ferrero

O’Brien

et al. 2020

Journal Metamorphic Geology

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“…During their study, Gimeno‐Vives et al found one zircon grain dated at 450–460 Ma in the Kef el Ghar gabbro. They argue that this “confirms the emplacement of the magmas in a continental setting.” Even adding the case of the Paleoproterozoic zircon (~2 Ga) reported by Michard et al (), this argument is not robust, as inherited zircons can be stirred in the upper mantle through varied processes (Pilot et al, ; Varas‐Reus et al, ).…”

Section: Are the Mesorif Gabbros Camp Intrusions Into The Continentalmentioning

confidence: 98%

Comment on “The Mesozoic Margin of the Maghrebian Tethys in the Rif Belt (Morocco): Evidence for Polyphase Rifting and Related Magmatic Activity” by Gimeno‐Vives et al.

et al. 2020

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“…The origin of mantle pyroxenites can be related to a variety of magmatic and metamorphic processes, including recycling of subducted material (e.g. Allègre & Turcotte, 1986;Kornprobst et al, 1990;Morishita & Arai, 2001;Morishita et al, 2003;Yu et al, 2010;Varas-Reus et al, 2018), or high-pressure melt infiltration and/ or meltrock reaction (e.g. Bodinier et al, 1987a,b;Rivalenti et al, 1995;Takazawa et al, 1999;Garrido & Bodinier, 1999;Mukasa & Shervais, 1999;Keshav et al, 2007;Bodinier et al, 2008;van Acken et al, 2010;Borghini et al, 2016;Tilhac et al, 2016Tilhac et al, , 2017.…”

Section: Introductionmentioning

confidence: 99%

Ligurian pyroxenite-peridotite sequences (Italy) and the role of melt-rock reaction in creating enriched-MORB mantle sources

et al. 2020

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Deep melt intrusion and melt-peridotite interaction may introduce small-scale heterogeneity in the MORB mantle. These processes generate pyroxenite-bearing veined mantle that represent potential mantle sources of oceanic basalts. Natural proxies of such veined mantle are very rare and our understanding of mechanisms governing the chemical modification of mantle peridotite by MORBtype pyroxenite emplacement is very limited. We report the results of detailed spatially-controlled chemical profiles in pyroxenite-peridotite associations from the Northern Apennine ophiolitic mantle sequences (External Liguride Units, Italy), and investigate the extent and mechanism driving the local modification of peridotite by the interaction with pyroxenite-derived melt. Pyroxenites occur as cm-thick layers parallel to mantle tectonite foliation and show diffuse orthopyroxene-rich reaction rims along the pyroxenite-peridotite contact. Relative to distal unmodified peridotites, wall-rock peridotites show i) modal orthopyroxene enrichment at the expense of olivine, ii) higher Al, Ca, Si contents and slightly lower X Mg , iii) Al-richer spinel and lower-X Mg pyroxenes. Clinopyroxenes from wall-rock peridotites exhibit variable LREE-MREE fractionation, always resulting in Sm N /Nd N ratios lower than distal peridotites. From the contact with pyroxenite layers, peridotite clinopyroxenes record a REE compositional gradient up to about 15 cm marked by a overall REE increase away from the pyroxenite. Beyond 15 cm, and up to 23 cm, the MREE and HREE content decreases while the LREEs remain at nearly constant abundances. This REE gradient is well reproduced by a two-step numerical simulation of reactive melt percolation assuming variable amounts of olivine assimilation and pyroxene crystallization. Percolative reactive flow at decreasing melt mass and rather high instantaneous melt/peridotite ratio (initial porosity of 30%), combined with high extents of fractional crystallization (i.e. relatively low M a /M c ratio), accounts for the overall REE enrichment in the first 15 centimeters. Change of melt-rock reaction regime, mostly determined by the drastic decrease of porosity (Φ i = 0.01) due to increasing crystallization rates, results in more efficient chemical buffering of the host peridotite on the HREE composition of the differentiated liquids through ion-exchange chromatographic-type processes, determining the observed increase of the LREE/HREE ratio. Emplacement of thin (cm-sized) pyroxenite veins by deep melt infiltration is able to metasomatize a much larger volume of the host peridotite. Hybrid mantle domains made by pyroxenite, metasomatized peridotite and unmodified peridotite potentially represent mantle sources of E-MORB. Results of this work stress the key role of melt-peridotite reactions in modifying the upwelling mantle prior to oceanic basalts production.

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Genesis of ultra-high pressure garnet pyroxenites in orogenic peridotites and its bearing on the compositional heterogeneity of the Earth’s mantle

Cited by 23 publications

References 128 publications

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite, Granulitgebirge, Germany

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite, Granulitgebirge, Germany

Comment on “The Mesozoic Margin of the Maghrebian Tethys in the Rif Belt (Morocco): Evidence for Polyphase Rifting and Related Magmatic Activity” by Gimeno‐Vives et al.

Ligurian pyroxenite-peridotite sequences (Italy) and the role of melt-rock reaction in creating enriched-MORB mantle sources

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