Leucosome-forming small-scale geochemical processes in the metapelitic migmatites of the Turku area, Finland

Mengel, K.; Richter, Max; Johannes, Wilhelm

doi:10.1016/s0024-4937(00)00059-1

Cited by 30 publications

(18 citation statements)

References 18 publications

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“…Calculated zircon saturation temperatures (T Zr ) of the leucosome veins are 599e685 C (Table 3), which represents magmatic crystallization temperatures, and the pressure of magma formation was 1.2e3.2 GPa. These estimates of magmatic PeT conditions are consistent with the metamorphic PeT conditions of the melanosome bands (605e658 C; 1.22e1.43 GPa), suggesting that the leucosome veins and melanosome bands in the migmatites formed in the same setting (Mengel et al, 2001).…”

Section: Relationship Between Leucosome Veins and Melanosome Bandssupporting

confidence: 74%

“…Raith et al (2010) reported that corundum-bearing leucosomes in aluminous gneisses from the Ayyarmalai southern granulite terrain of India is a classic example of vapor-absent muscovite melting in silica-undersaturated aluminous rocks. Mengel et al (2001) concluded that different leucosome types result from various degrees of melt segregation and transportation. Nevertheless, there are many factors regarding leucosome formation in migmatites that remain unclear.…”

Section: Introductionmentioning

confidence: 99%

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U–Pb zircon geochronology and geochemical constraints on the age and origin of late Neoarchean leucosomes in migmatites from the Maevatanana area, Madagascar

Yang

Liu

Hou

2016

Journal of African Earth Sciences

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Section: Relationship Between Leucosome Veins and Melanosome Bandssupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

U–Pb zircon geochronology and geochemical constraints on the age and origin of late Neoarchean leucosomes in migmatites from the Maevatanana area, Madagascar

Yang

Liu

Hou

2016

Journal of African Earth Sciences

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“…A decrease in the La/Yb ratio, accompanied by the overall decrease in the bulk REE concentration in leucosome relative to parental rocks (paleosome), has been documented in amphiboliteand granulite-grade migmatite complexes (e.g., Watt and Harley, 1993;Nabelek, 1999;Mengel et al, 2001;Milord et al, 2001; Nehring et al, 2009;Acosta-Vigil et al, 2012 Milord et al, 2001). Only the most segregated leucocratic diatexite and leucosome compositions from the latter work (Milord et al, 2001) are plotted in Fig.…”

Section: Rare-earth Element Partitioningmentioning

confidence: 99%

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Manning

Aranovich

2014

Precambrian Research

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a b s t r a c tA number of observations point to the participation of brines in high-grade metamorphic processes. These include findings of alkali and alkaline-earth halides as daughter crystals in fluid inclusions, appreciable concentrations of Cl measured in amphiboles, biotite, scapolite and apatite, and direct observations on high-temperature halides present in the intergranular space in high-grade rocks. This paper reviews some thermodynamic, petrologic and geochemical effects of these brines. Thermodynamic mixing properties of concentrated water-salt fluids at high pressure (P) and temperature (T) differ greatly from those of water-non-polar gas mixtures: the former are characterized by a large negative deviation from ideal solutions, while the latter exhibit positive deviation from ideality. The contrasting behavior has three major petrologic implications. First, compared to mixtures of water and non-polar gases, brines more strongly increase the melting temperature of quartzofeldspathic rocks and more strongly decrease dehydration temperature of water-bearing minerals. This allows a wide P-T window in which subsolidus deep-crustal metasomatism may take place at relatively low H 2 O activity (a H 2 O ) via migrating fluids. In addition, above 2-3 kbar, brine-saturated solidi for simple granite melting show positive dP/dT at constant H 2 O mole fraction (X H 2 O ), favoring ascent of fluid-saturated liquids. Finally, a large miscibility gap exists in H 2 O-CO 2 -salt ternaries at lower crustal conditions, which may concentrate salts in a separate phase and help explain the common observation of CO 2 -rich inclusions in high-grade minerals. We discuss three geochemical consequences of high-grade brines. We report new experimental data on melting of a model granitoid liquid (69 wt% NaAlSi 3 O 8 , 31 wt% SiO 2 ) at 2 kbar in the presence of aqueous NaCl solutions ranging in concentration from a salt mole fraction (X NaCl ) of 0.1-0.3. The results show that Na preferentially partitions into the silicate liquid, enriching the coexisting fluid in HCl. This hydrolysis effect, known previously for granite melts equilibrated with dilute solutions, therefore also extends to more saline brines. Mineral solubilities depend strongly on salt concentration in the coexisting fluid. Below 5 kbar at 700• C, quartz initially salts in with addition of NaCl to H 2 O, reaches a maximum, and then declines; however, it salts out at all X NaCl at higher P. At granulite-facies P-T conditions, the solubilities of other oxide and silicate minerals (corundum, wollastonite, grossular) salt in and then either reach a plateau or salt out slightly at high X NaCl . In contrast, the solubility of Ca-salt minerals increases exponentially with rising X NaCl . The solubility patterns reflect variations in complexing and H 2 O activity in the brine. Partitioning of REE between rock forming minerals and brines, and between felsic melts and brines, differs strongly from that between minerals, melts and water (±non-polar gas). Brines extract REE f...

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“…We have examined leucosome width statistics in six drill cores of the Estonian Proterozoic basement (Soesoo et al 2004a(Soesoo et al , 2004b, at an outcrop near Masku in southwestern Finland (Mengel et al 2001), and at an outcrop near Montemor-o-Novo in central Portugal (Pereira & Silva 2002). Migmatites at these localities represent rocks with a variety of chemical compositions and metamorphic histories.…”

Section: Leucosome Width Statistics In Migmatitesmentioning

confidence: 99%

“…They have undergone Proterozoic granulite facies metamorphism (Mengel et al 2001;Johannes et al 2003).…”

Section: Leucosome Width Statistics In Migmatitesmentioning

confidence: 99%

Stepwise magma migration and accumulation processes and their effect on extracted melt chemistry

Urtson¹,

Соэсоо²

2009

Estonian J. Earth Sci.

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Numerical and analogue models suggest that melt production, its segregation from the solid matrix and subsequent transport and accumulation are highly dynamic and stepwise processes exhibiting scale invariant patterns in both time and length scales, which is characteristic of self-organized critical systems. This phenomenon is also observed in migmatites at several localities, where the leucosome thickness statistics obey power laws. Stepwise melt transport and deformation-enhanced melt mobility affect melt production dynamics by determining the distribution of extracted melt batch sizes and residence times of melt pockets within the host rock, which in turn would influence the geochemistry of extracted melts. We introduce a numerical approach, which enables qualitative and quantitative assessment of the effects of stress-induced melt migration and accumulation on the chemistry of partial melts. The model suggests that apart from different sources and melting percentages, deformation can be an important factor in producing geochemical variations within and between intrusive/extrusive complexes.

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Leucosome-forming small-scale geochemical processes in the metapelitic migmatites of the Turku area, Finland

Cited by 30 publications

References 18 publications

U–Pb zircon geochronology and geochemical constraints on the age and origin of late Neoarchean leucosomes in migmatites from the Maevatanana area, Madagascar

U–Pb zircon geochronology and geochemical constraints on the age and origin of late Neoarchean leucosomes in migmatites from the Maevatanana area, Madagascar

Brines at high pressure and temperature: Thermodynamic, petrologic and geochemical effects

Stepwise magma migration and accumulation processes and their effect on extracted melt chemistry

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