A Possible Primary Melt Composition For the Ultramafic Lavas of the Margi area, Troodos Ophiolite, Cyprus

Sobolev, A.; Dmitriev, L. V.; Tsameryan, O P; Kononkova, N N; Robinson, Philip

doi:10.4095/133540

Cited by 5 publications

(7 citation statements)

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“…Melt inclusions in olivine from subduction-related suites with anomalous low FeO t contents were also described by Sobolev et al (1993), Kamenetsky et al (1995a, b), Portnyagin et al (1997) and Kamenetsky et al (1997). Information presented in these papers is not sucient to construct the Fe-loss triangles with con®dence.…”

Section: Discussioǹ`fmentioning

confidence: 80%

“…Such inclusions may represent snapshots' of magmatic conditions, and they are increasingly used to establish the chemical characteristics and early evolution of primitive subduction-related melts (e.g. Anderson 1974;Roedder 1984;Danyushevsky et al 1992;Sobolev et al 1993;Sisson and Layne 1993;Sobolev and Danyushevsky 1994;Sisson and Bronto 1998;Lee and Stern 1998).…”

Section: Introductionmentioning

confidence: 99%

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Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications

Danyushevsky¹,

Della-Pasqua²,

Sokolov

2000

Contrib Mineral Petrol

405

299

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We describe and model a potential re-equilibration process that can aect compositions of melt inclusions in magnesian olivine phenocrysts. This process, referred to as``Fe-loss'', can operate during natural pre-eruptive cooling of host magma and results in lower FeO t and higher MgO contents within the initially trapped volume of inclusion. The extent of Fe-loss is enhanced by large temperature intervals of magma cooling before eruption. The compositions of homogenised melt inclusions in olivine phenocrysts from several subduction-related suites demonstrate that (1) Fe-loss is a common process, (2) the maximum observed degree of re-equilibration varies between suites, and (3) within a single sample, variable degrees of re-equilibration can be recorded by melt inclusions trapped in olivine phenocrysts of identical composition. Our modelling also demonstrates that the re-equilibration process is fast going to completion, in the largest inclusions in the most magnesian phenocrysts it is completed within 2 years. The results we obtained indicate that the possibility of Fe-loss must be considered when estimating compositions of parental subduction-related magmas from naturally quenched glassy melt inclusions in magnesian olivine phenocrysts. Compositions calculated from glassy inclusions aected by Fe-loss will inherit not only erroneously low FeO t contents, but also low MgO due to the inherited higher Mg# of the residual melt in reequilibrated inclusions. We also demonstrate that due to the higher MgO contents of homogenised melt inclusions aected by Fe-loss, homogenisation temperatures achieved in heating experiments will be higher than original trapping temperatures. The extent of overheating will increase depending on the degree of re-equilibration, and can reach up to 50°C in cases where complete re-equilibration occurs over a cooling interval of 200°C.

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Section: Discussioǹ`fmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications

Danyushevsky¹,

Della-Pasqua²,

Sokolov

2000

Contrib Mineral Petrol

405

299

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“…Very high MgO contents and Mg# (up to 24 wt% on an anhydrous basis, with molar Mg/ (Mg+Fe) s 0.85) suggest the presence of accumulated olivine phenocrysts in some rocks. On the other hand Sobolev and co-workers [25] have argued that high MgO, high-temperature liquids were indeed an important lava type in Cyprus. We adopt a maximum cuto¡ at an Mg# of 0.73 which eliminates all outliers on a plot of MgO vs Mg#.…”

Section: Viscosity Of the Cy-1/1a Lavasmentioning

confidence: 99%

Melt viscosity, temperature and transport processes, Troodos ophiolite, Cyprus

Schouten

Kelemen

2002

Earth and Planetary Science Letters

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The lava section in the Troodos ophiolite, Cyprus, is chemically stratified and divided into a shallow lava sequence with low TiO 2 content and a deeper lava sequence with high TiO 2 content. We calculate the viscosity at magmatic temperature based on major element chemistry of lavas in Cyprus Crustal Study Project (CCSP) Holes CY-1 and 1A. We find that typical shallow low-Ti lavas have a magmatic viscosity that is two to three orders of magnitude lower than that of the deeper high-Ti lavas. This implies that, after eruption on-axis, Troodos low-Ti lavas would have been able to flow down the same slope faster and farther than high-Ti lavas. The calculated lava viscosity increases systematically from the lava^sediment interface to the bottom of the composite Hole CY-1/1A. This suggests that an efficient process of lava segregation by viscosity on the upper flanks of the paleo Troodos rise may have been responsible for the chemical stratification in the Troodos lava pile. Calculated magmatic temperature and molar Mg/ (Mg+Fe), or Mg#, decrease systematically down-section, while SiO 2 content increases. Correlation of Mg# in the lavas with Mg# in the underlying, lower crustal plutonic rocks sampled by CCSP Hole CY-4 shows that the shallow lavas came from a high-temperature, lower crustal magma reservoir which is now represented by high-Mg# pyroxenite cumulates, while the deeper lavas were erupted from a lower-temperature, mid-crustal reservoir which is now represented by gabbroic cumulates with lower Mg#. ß 2002 Published by Elsevier Science B.V.

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“…The boninitic lavas of the Troodos ophiolite contain large olivine phenocrysts. Previous studies of melt inclusions in these phenocrysts suggest that they crystallized from a primary boninitic magma (Hu et al, 2021;Sobolev et al, 1991). The olivine phenocrysts and chromite inclusions record low fO 2 (∆QFM −0.52 ± 0.20) under their crystallization conditions (0.1 GPa, 1334°C).…”

Section: Discussionmentioning

confidence: 85%

“…The Margi area on Mt Olympos' northern flank is a classic locality for boninites in the ophiolite (Bailey et al., 1991; Gass, 1958; Malpas & Langdon, 1984; Sobolev et al., 1991) (Figure 2d). The LPL in Margi comprise aphyric to plagioclase and clinopyroxene micro‐phyric volcanic rocks, and are separated from the UPL by a discontinuous thin sedimentary layer (Bailey et al., 1991).…”

Section: The Troodos Ophiolitementioning

confidence: 99%

The Redox State of Incipient Oceanic Subduction Zones: An Example From the Troodos Ophiolite (Cyprus)

Zhou

Ribeiro

et al. 2023

JGR Solid Earth

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To understand the oxygen fugacity (fO2) during subduction initiation, we examined proto‐arc boninites and associated mantle peridotites from the Troodos ophiolite, Cyprus. The Troodos ophiolite represents an exhumed piece of oceanic lithosphere that formed during subduction initiation in Neo‐Tethys in Late Cretaceous. Dunites and surrounding harzburgites in the Kokkinorotsos podiform chromite deposit of the ophiolite were formed by reactions between peridotites and ascending boninitic magmas. The olivine‐chromite oxybarometers show that the fO2 values (∆QFM −0.41 ± 0.37) of the dunites are slightly higher than those (∆QFM −0.85 ± 0.52) of the harzburgites under mantle conditions, indicating that the mantle fO2 was raised limitedly by percolation of the boninitic magmas. Meanwhile, the boninitic upper pillow lavas in the Margi area also recorded relatively reduced fO2 values (∆QFM −0.52 ± 0.20) during olivine‐chromite crystallization, comparable to the fO2 of mid‐ocean ridge basalts. Shallow‐level processes (i.e., magma ascent, crystallization, crustal assimilation, and degassing) appear to have limited influence on the estimated fO2 values in Troodos. The similarly low fO2 values of the mantle peridotites and boninitic magmas suggest that the Troodos primary boninitic magmas were perhaps not as oxidized as the Izu‐Bonin‐Mariana (IBM) proto‐arc boninitic magmas, though both mantle sources have captured the slab fluids released during subduction inception. This difference might be attributed to the different nature of the slab components (i.e., a more reduced subduction input for Troodos). Our study thus suggests that subducted slabs might not always release oxidized fluids, and the oxidation processes might be different for each nascent subduction zones.

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A Possible Primary Melt Composition For the Ultramafic Lavas of the Margi area, Troodos Ophiolite, Cyprus

Cited by 5 publications

References 0 publications

Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications

Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications

Melt viscosity, temperature and transport processes, Troodos ophiolite, Cyprus

The Redox State of Incipient Oceanic Subduction Zones: An Example From the Troodos Ophiolite (Cyprus)

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