@article{BerkesiCzupponSzaboetal.2018,
  author    = {Berkesi, Marta and Czuppon, Gyorgy and Szabo, Csaba and Kovacs, Istvan and Ferrero, Silvio and Boiron, Marie-Christine and Peiffert, Chantal},
  title     = {Pargasite in fluid inclusions of mantle xenoliths from northeast Australia (Mt. Quincan)},
  series = {Chemical geology : official journal of the European Association for Geochemistry},
  volume    = {508},
  journal   = {Chemical geology : official journal of the European Association for Geochemistry},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0009-2541},
  doi       = {10.1016/j.chemgeo.2018.06.022},
  pages     = {182 -- 196},
  year      = {2018},
  abstract  = {Three spinel lherzolite xenoliths from Mt. Quincan (Queensland, northeastern Australia) were studied with special attention to their enclosed fluid inclusions. The xenoliths are deformed, have porphyroclastic textures and overall show very similar petrographic features. The only significant difference is manifested in the abundance of fluid inclusions in the samples, mostly in orthopyroxene porphyroclasts. Xenolith JMTQ11 is fluid inclusion-free, whereas xenolith JMTQ20 shows a high abundance of fluid inclusions (fluid inclusion-rich). Xenolith JMTQ45 represents a transitional state between the previous two, as it contains only a small amount of fluid inclusions (fluid inclusion-bearing). Previous studies revealed that these xenoliths and the entrapped fluid inclusions represent a former addition of a MORB-type fluid to the pre-existing lithosphere, resulting from asthenosphere upwelling. There is a progressive enrichment in LREE, Nb, Sr and Ti from the fluid inclusion-free xenolith through the fluid inclusion-bearing one to the fluid inclusion-rich lherzolite. This suggests an increase in the extent of the interaction between the fluid-rich melt and the lherzolite wallrock. In addition, the same interaction is considered to be responsible for the formation of pargasitic amphibole as well. The presence of fluid inclusions indicates fluid migration at mantle depth, and their association with exsolution lamellae in orthopyroxene suggests fluid entrapment following the continental rifting (thermal relaxation) during cooling. A series of analyses, including microthermometry coupled with Raman spectroscopy, FTIR hyperspectral imaging, and Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) was carried out on the fluid inclusions. Based on the results, the entrapped high-density fluid is composed of 7589 mol\% CO2, 918 mol\% H2O, 0.11.7 mol\% N-2 and <= 0.5 mol\% H2S with dissolved trace elements (melt component). Our findings suggest that the metasomatic fluid phase could have been either a fluid/fluid-rich silicate melt released from the deeper asthenosphere, or a coexisting incipient fluid-rich silicate melt. Further cooling, possibly due to thermal relaxation and the upward migration of the fluid phase, caused the investigated lherzolites to reach pargasite stability conditions. We conclude that pargasite, even if only present in very limited modal proportions, can be a common phase at spinel lherzolite stability in the lithospheric upper mantle in continental rift back-arc settings. Studies of fluid inclusions indicate that significant CO2 release from the asthenosphere in a continental rifting environment is resulting from asthenosphere upwelling and its addition to the lithospheric mantle together with fluid-rich melt lherzolite interaction that leaves a CO2-rich fluid behind.},
  language  = {en}
}
@article{HalamaKonradSchmolke2015,
  author    = {Halama, Ralf and Konrad-Schmolke, Matthias},
  title     = {Retrograde metasomatic effects on phase assemblages in an interlayered blueschist-greenschist sequence (Coastal Cordillera, Chile)},
  series = {Lithos : an international journal of mineralogy, petrology, and geochemistry},
  volume    = {216},
  journal   = {Lithos : an international journal of mineralogy, petrology, and geochemistry},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0024-4937},
  doi       = {10.1016/j.lithos.2014.12.004},
  pages     = {31 -- 47},
  year      = {2015},
  abstract  = {Interlayered blueschists and greenschists of the Coastal Cordillera (Chile) are part of a Late Palaeozoic accretionary complex. They represent metavolcanic rocks with oceanic affinities based on predominantly 01B-type REE patterns and immobile trace element ratios. Both rock types have similar mineralogies, albeit with different mineral modal abundances. Amphibole is the major mafic mineral and varies compositionally from glaucophane to actinolite. The presence of glaucophane relicts as cores in zoned amphiboles in both blueschists and greenschists is evidence for a pervasive high-pressure metamorphic stage, indicating that tectonic juxtaposition is an unlikely explanation for the cm-dm scale interlayering. During exhumation, a retrograde greenschist-facies overprint stabilized chlorite + albite + winchitic/actinolitic amphibole + phengitic white mica +/- epidote +/- K-feldspar at 0.4 +/- 0.1 GPa. Geochemical variability can be partly ascribed to primary magmatic and partly to secondary metasomatic processes that occurred under greenschist-facies conditions. Isocon diagrams of several adjacent blueschist-greenschist pairs with similar protolith geochemistry were used to evaluate metasomatic changes due to retrograde fluid-rock interaction. The most important geochemical changes are depletion of Si and Na and addition of water in the greenschists compared to the blueschists. Transition metals and LILE are mobilized to varying degrees. The unsystematic deviations from magmatic fractionation trends suggest open system conditions and influx of an external fluid. Pseudosection and water isopleth calculations show that the rocks were dehydrating during most of their exhumation history and remained at water-saturated conditions. The mineralogical changes, in particular breakdown of blue amphibole and replacement by chlorite, albite and calcic/sodic-calcic amphibole, are the prime cause for the distinct coloring. Pseudo-binary phase diagrams were used as a means to link bulk rock geochemical variability to modal and chemical changes in the mineralogy. The geochemical changes induced by fluid-rock interaction are important in two ways: First, the bulk rock chemistry is altered, leading to the stabilization of higher modal proportions of chlorite in the greenschists. Second, the retrograde overprint is a selective, layer-parallel fluid infiltration process, causing more intense greenschist-facies recrystallization in greenschist layers and therefore preferential preservation of blue amphibole in blueschist layers. Hence, the distinct colors were acquired by a combination of compositional variability, both primary magmatic and secondary metasomatic, and the different intensity of retrograde fluid infiltration. (C) 2014 Elsevier B.V. All rights reserved.},
  language  = {en}
}