Ca/Al of plagioclase-hosted melt inclusions as an indicator for post-entrapment processes at mid-ocean ridges?
DOI:
https://doi.org/10.1344/GeologicaActa2016.14.1.1Keywords:
Melt inclusion, Plagioclase, Ca/Al, Post-entrapment crystallization, South Mid-Atlantic Ridge 19°SAbstract
The composition of melt inclusions in basalts erupted at mid-ocean ridges may be modified by post-entrapment processes, so the present composition of melt inclusions may not represent their original composition at the time of entrapment. By combining the melt inclusion composition in samples from the South Mid-Atlantic Ridge at 19ºS analyzed in this study, and from the Petrological Database, we found that post-entrapment crystallization processes resulted in higher Ca/Al, Mg#[100°—atomic Mg2+/(Mg2++Fe2+)], MgO and FeO contents, and lower CaO and Al2O3 contents of plagioclase-hosted melt inclusions relative to those hosted in olivine. In addition, melt inclusions hosted in plagioclase with anorthite content larger than 80mol.% had been modified more readily than others. By discussing the relationships between Ca/Al and fractional crystallization, post-entrapment crystallization, and the original melt composition, we propose that Ca/Al can be regarded as an indicator of the effect of post-entrapment processes on melt inclusion composition. Specifically, i) when Ca/Al<0.78, melt inclusion compositions corrected for fractional crystallization to Mg#=72 can represent the primary magma at mid-ocean ridges; ii) when 0.78<Ca/Al<1.0, melt inclusions are mainly modified by post-entrapment crystallization effects, and can reveal the original melt composition after correcting for these effects; iii) when Ca/Al>1.0, the compositions of melt inclusions do not reflect the original melt composition nor preserve information about the mantle source. According to these criteria, plagioclase-hosted melt inclusions with Ca/Al>1.0 in basalts from the South Mid-Atlantic Ridge at 19ºS cannot represent the composition of the melt at the moment of their entrapment.
References
Asimow, P.D., Hirschmann, M.M., Ghiorso, M.S., 1995. The effect of pressure-induced solid-solid phase transitions on decompression melting of the mantle. Geochimica et Cosmochimica Acta, 59, 4489-4506.
Baker, D.R., 2008. The fidelity of melt inclusions as records of melt composition. Contributions to Mineralogy and Petrology, 156(3), 377-395.
Cottrell, E., Spiegelman, M., Langmuir, C.H., 2002. Consequences of diffusive re-equilibration for the interpretation of melt inclusions. Geochemistry, Geophysics, Geosystems, 3(5), 1-26. DOI: 10.1029/2001GC000205.
Danyushevsky, L.V., Della-Pasqua, F.N., Sokolov, S., 2000. Re-equilibration of melt inclusions trapped by magnesian olivine phenocrysts from subduction-related magmas: petrological implications. Contributions to Mineralogy and Petrology, 138, 68-83.
Danyushevsky, L.V., McNeill, A.W., Sobolev, A.V., 2002. Experimental and petrological studies of melt inclusions in phenocrysts from mantle-derived magmas: an overview of techniques, advantages and complications. Chemical Geology, 183, 5-24.
Danyushevsky, L.V., Perfit, M.R., Eggins, S.M., Falloon, T.J., 2003. Crustal origin for coupled ‘ultra-depleted’ and ‘plagioclase’ signatures in MORB olivine-hosted melt inclusions: evidence from the Siqueiros Transform Fault, East Pacific Rise. Contributions to Mineralogy and Petrology, 144, 619-637.
Danyushevsky, L.V., Leslie, R.A.J., Crawford, A.J., Durance, P., 2004. Melt inclusions in primitive olivine phenocrysts: The role of localized reaction processes in the origin of anomalous compositions. Journal of Petrology, 45, 2531-2553.
Demets, C., Gordon, R. G.D., Argus, F., Stein, S., 1994. Effect of recent revisions to the geomagnetic reversal time scale on estimates of current plate motions, Geophysical Research Letters, 21(20), 2191–2194.
Dungan, M.A., Rhodes, J.M., 1978. Residual glasses and melt inclusions in basalts from DSDP Legs 45 and 46 evidence for magma mixing. Contributions to Mineralogy and Petrology, 67, 417-431.
Faure, F., Schiano, P., 2005. Experimental investigation of equilibration conditions during forsterite growth and melt inclusion formation. Earth and Planetary Science Letters, 236, 882-898.
Font, L., Murton, B.J., Roberts, S., Tindle, A.G., 2007, Variations in melt productivity and melting conditions along SWIR (70 degrees E-49 degrees E): evidence from olivine-hosted and plagioclase-hosted melt inclusions. Journal of Petrology, 48, 1471-1494.
Gaetani, G.A., Grove, T.L., Bryan, W.B., 1993. The influence of water on the petrogenesis of subduction-related igneous rocks. Nature, 365, 332-334.
Gaetani, G.A., Watson, E.B.,2000. Open-system behavior of olivine-hosted melt inclusions. Earth and Planetary Science Letters, 183, 27-41.
Hansen, H., Gronvold, K.,2000. Plagioclase ultraphyric basalts in Iceland: the mush of the rift. Journal of Volcanology and Geothermal Research, 98, 1-32.
Hartley, M.E., Thordarson, T., 2013. The 1874–1876 volcanotectonic episode at Askja, North Iceland: Lateral flow revisited. Geochemistry, Geophysics, Geosystems, 14(7), 2286-2309.
Hartley, M.E., Thordarson, T., Fitton, J.G., 2013. Oxygen isotopes in melt inclusions and glasses from the Askja volcanic system, North Iceland. Geochimica et Cosmochimica Acta, 123, 55-73.
Kamenetsky, V.S., Eggins, S.M., Crawford, A.J., Green, D.H., Gasparon, M., Falloon, T.J., 1998. Calcic melt inclusions in primitive olivine at 43ºN MAR: evidence for melt-rock reaction/melting involving clinopyroxene-rich lithologies during MORB generation. Earth and Planetary Science
Letters, 160, 115-132.
Kent, A.J.R., 2008. Melt inclusions in basaltic and related rocks. Reviews in Mineralogy & Geochemistry, 69, 273-331.
Laubier, M., Schiano, P., Doucelance, R., Ottolini, L., Laporte, D., 2007. Olivine-hosted melt inclusions and melting processes beneath the FAMOUS zone (Mid-Atlantic Ridge). Chemical Geology, 240, 129-150.
Lehnert, K., Su Y., Langmuir C.H., Sarbas, B., Nohl, U., 2000. A global geochemical database structure for rocks, Geochemistry, Geophysics, Geosystems, 1, 1012.
Namur, O., Charlier, B., Toplis, M., Vander-Auwera, J., 2011. Prediction of plagioclase-melt equilibria in anhydrous silicate melts at 1-atm. Contributions to Mineralogy and Petrology, 163,133-150. DOI:10.1007/s00410-011-0662-z
Neave, D.A., Passmore, E., Maclennan, J., Fitton, G., Thordarson, T., 2013. Crystal-melt relationships and the record of deep mixing and crystallization in the AD 1783–84 Laki eruption, Iceland. Journal of Petrology, 54, 1661-1690. DOI:10.1093/petrology/egt027
Neave, D.A., Maclennan, J., Hartley, M.E., Edmonds, M., Thordarson, T., 2014. Crystal storage and transfer in basaltic systems: the Skuggafjöll eruption, Iceland. Journal of Petrology, 55, 2311-2356. DOI:10.1093/petrology/egu058
Neave, D.A., Maclennan, J., Thordarson, T., Hartley, M.E., 2015. The evolution and storage of primitive melts in the Eastern Volcanic Zone of Iceland: the 10 ka Grímsvötn tephra series (i.e. the Saksunarvatn ash). Contributions to Mineralogy and Petrology, 170(2), 1-23.
Nielsen, R.L., 2011. The effects of the re-homogenization on plagioclase hosted melt inclusions. Geochemistry, Geophysics, Geosystems, 12(10), 1241-1249. DOI:10.1029/2011GC003822
Nielsen, R.L., Crum, J., Bourgeois, R., Hascall, K., Forsythe, L.M., Fisk, M.R., Christie, D.M., 1995.
Melt inclusions in high-An plagioclase from the Gorda Ridge: an example of the local diversity of MORB parent magmas. Contributions to Mineralogy and Petrology, 122, 34-50.
Niu, Y.L., Batiza, R., 1991. An empirical method for calculating melt compositions produced beneath mid-ocean ridges: application for axis and off-axis (seamounts) melting. Journal of Geophysical Research, 96, 21753-21777.
Niu, Y.L., Batiza, R., 1997. Trace element evidence from seamounts for recycled oceanic crust in the eastern Pacific mantle. Earth and Planetary Science Letters, 148, 471-483.
Niu, Y.L., O’Hara, M.J., 2008. Global correlations of ocean ridge basalt chemistry with axial depth: A new perspective. Journal of Petrology, 49, 633-664.
Niu, Y.L., Collerson, K.D., Batiza, R., Wendt, J.I., Regelous, M., 1999. The origin of E-Type MORB at ridges far from mantle plumes: The East Pacific Rise at 11º20′N. Journal of Geophysical Research, 104, 7067-7087.
Niu, Y.L., Regelous, M., Wendt, J.I., Batiza, R., O’Hara, M.J., 2002. Geochemistry of near-EPR seamounts: Importance of source vs. process and the origin of enriched mantle component. Earth and Planetary Science Letters, 199, 329-348.
Portnyagin, M., Almeev.R., Matveev, S., Holtz, F., 2008. Experimental evidence for rapid water exchange between melt inclusions in olivine and host magmas. Earth and Planetary Science Letters, 272, 541-552.
Qin, Z., Lu, F., Anderson, A.T.J., 1992. Diffusive reequilibration of melt and fluid inclusions. American Mineralogist, 77, 565-576.
Shen, Y., Forsyth, D.W., 1995. Geochemical constraints on initial and final depth of melting beneath mid-ocean ridges. Journal of Geophysical Research, 100, 2211-2237.
Shimizu, N., 1998. The geochemistry of olivine-hosted melt inclusions in a FAMOUS basalt ALV519-4-1. Physics of the Earth and Planetary Interiors, 107, 183-201.
Sinton, C.W., Christie, D.M., Coombs, V.L., Nielsen, R.L., Fisk, M.R., 1993. Near-primary melt inclusions in anorthite phenocrysts from the Galapagos Platform. Earth and Planetary Science Letters, 119, 527-537.
Sobolev, A.V., Shimizu, N., 1993. Ultra-depleted primary melt included in an olivine from the Mid-Atlantic ridge. Nature, 363, 151-154.
Sobolev, A.V., Danyushevsky, L.V., Dmitriev, L.V., Sushchevskaya, N.M., 1988. High-Alumina Magnesium Tholeiite as One of Primary Melts of Basalts of the MidOceanic Ridges. Geokhimiya, (10): 1522-1528.
Sobolev, A.V., Hofmann, A.W., Nikogosian, I.K., 2000. Recycled oceanic crust observed in ‘ghost plagioclase’ within the source of Mauna Loa lavas. Nature, 404, 986-990.
Sours-Page, R., Johnson, K.T.M., Nielsen, R.L., Karsten, J.L., 1999. Local and regional variation of MORB parent magmas: Evidence from melt inclusions from the Endeavour Segment of the Juan de Fuca Ridge. Contributions to Mineralogy and Petrology, 134, 342-363.
Sours-Page, R., Nielsen, R.L., Batiza, R., 2002. Melt inclusions as indicators of parental magma diversity on the northern East Pacific Rise. Chemical Geology, 183, 237-261.
Spandler, C., O’Neill, H.S.C., Kamenetsky, V.S., 2007. Survival times of anomalous melt inclusions from element diffusion in olivine and chromite. Nature, 447, 303-306.
Tait, S., 1992. Selective preservation of melt inclusions in igneous phenocrysts. American Mineralogist, 77, 146-155.
Yoder, H.S., 1965. Diopside-anorthite-water at five and ten kilobars and its bearing on explosive volcanism. Carnegie Institution of Washington Yearbook, 64, 82-89.
Downloads
Published
Issue
Section
License
![Creative Commons License](http://i.creativecommons.org/l/by-sa/4.0/88x31.png)
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Copyright
Geologica Acta is the property of the UB, GEO3BCN, IDAEA and UAB. Geologica Acta must be cited for any partial or full reproduction. Papers are distributed under the Attribution-Share Alike Creative Commons License. This license allows anyone to reproduce and disseminate the content of the journal and even make derivative works crediting authorship and provenance and distributing possible derivative works under the same or an equivalent license.
Author Rights
Authors retain the copyright on their papers and are authorized to post them on their own web pages or institutional repositories. The copyright was retained by the journal from the year 2003 until 2009. In all cases, the complete citation and a link to the Digital Object Identifier (DOI) of the article must be included.
The authors can use excerpts or reproduce illustrations of their papers in other works without prior permission from Geologica Acta provided the source of the paper including the complete citation is fully acknowledged.