The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
G.r. Watt - One of the best experts on this subject based on the ideXlab platform.
-
Relationships between Zircon U–Pb SHRIMP Ages and Leucosome Type in Migmatites of the Halls Creek Orogen, Western Australia
Journal of Petrology, 1999Co-Authors: Nicholas H.s. Oliver, S. Bodorkos, Alexander A. Nemchin, Peter D. Kinny, G.r. WattAbstract:Field relations, and zircon zoning and SHRIMP U–Pb patterns INTRODUCTION from an outcrop of deformed pelitic migmatites reveal relationships Both the amount and isotopic variability of accessory between Leucosome type and the amount of zircon growth during minerals incorporated into granitic magmas and their migmatization. Zircons from the oldest, stromatic migmatites show constituent trace elements are a complex function of several Pb/Pb intragrain analyses with 1850–1840 Ma source and crystallization processes (Bea et al., 1994; anatectic ages and distinctive cathodoluminescence (CL) patterns, Brown, 1994; Ayres et al., 1995; Barbey et al., 1995; Bea, although the sample is dominated by inferred pre-1855 Ma detrital 1996). It is recognized that initial bulk compositions (X ) zircons. Subsequent thick ‘contact–sheath’ Leucosomes and ‘backand pressure (P )–temperature (T ) conditions of anatexis veins’ developed at 1845–1830 Ma in response to intrusion of are major controls on the chemistry and subsequent mafic dykes into the stromatic migmatites. Zircons show CL evidence behaviour of granitic magmas (e.g. Clemens, 1990; for substantial anatectic growth and overgrowths with post-1850 Brown, 1994). Also, there is increasing awareness that Ma ages, and a single population age 20 my younger than the deformation in the source region can also control the early other migmatites. Zircons from the structurally youngest, shearand physical pathways and chemical evolution of magmas (e.g. vein-hosted Leucosomes show few overgrowths and retain a large Sawyer, 1991; Hand & Dirks, 1992; Brown et al., 1995; detrital population. Correlation between shear zones and minimal Rushmer, 1995; Watt et al., 1996; Oliver & Barr, 1997), anatectic zircon growth is inferred to reflect rapid deformationwhich in turn may have a profound impact on subsequent induced melt extraction from the protolith, and/or rapid quenching. granitic magma evolution. For a given bulk source comThe earlier contact–sheath and stromatic Leucosomes probably had position, magma extracted at low melt fractions from a combination of slow melt segregation, larger interacting melt an actively deforming partially molten zone may differ volume and longer residence times at high temperatures. Results substantially in composition from one extracted at high suggest that rapid melt extraction by deformation will increase the melt volumes from rocks undergoing little deformation tendency for preservation of source rock isotopic patterns in some (Rushmer, 1995). The link between ‘frozen’ migmatites granites. and complete granite bodies may not be direct (Clemens
-
relationships between zircon u pb shrimp ages and Leucosome type in migmatites of the halls creek orogen western australia
Journal of Petrology, 1999Co-Authors: Nicholas H.s. Oliver, S. Bodorkos, Alexander A. Nemchin, Peter D. Kinny, G.r. WattAbstract:Field relations, and zircon zoning and SHRIMP U–Pb patterns INTRODUCTION from an outcrop of deformed pelitic migmatites reveal relationships Both the amount and isotopic variability of accessory between Leucosome type and the amount of zircon growth during minerals incorporated into granitic magmas and their migmatization. Zircons from the oldest, stromatic migmatites show constituent trace elements are a complex function of several Pb/Pb intragrain analyses with 1850–1840 Ma source and crystallization processes (Bea et al., 1994; anatectic ages and distinctive cathodoluminescence (CL) patterns, Brown, 1994; Ayres et al., 1995; Barbey et al., 1995; Bea, although the sample is dominated by inferred pre-1855 Ma detrital 1996). It is recognized that initial bulk compositions (X ) zircons. Subsequent thick ‘contact–sheath’ Leucosomes and ‘backand pressure (P )–temperature (T ) conditions of anatexis veins’ developed at 1845–1830 Ma in response to intrusion of are major controls on the chemistry and subsequent mafic dykes into the stromatic migmatites. Zircons show CL evidence behaviour of granitic magmas (e.g. Clemens, 1990; for substantial anatectic growth and overgrowths with post-1850 Brown, 1994). Also, there is increasing awareness that Ma ages, and a single population age 20 my younger than the deformation in the source region can also control the early other migmatites. Zircons from the structurally youngest, shearand physical pathways and chemical evolution of magmas (e.g. vein-hosted Leucosomes show few overgrowths and retain a large Sawyer, 1991; Hand & Dirks, 1992; Brown et al., 1995; detrital population. Correlation between shear zones and minimal Rushmer, 1995; Watt et al., 1996; Oliver & Barr, 1997), anatectic zircon growth is inferred to reflect rapid deformationwhich in turn may have a profound impact on subsequent induced melt extraction from the protolith, and/or rapid quenching. granitic magma evolution. For a given bulk source comThe earlier contact–sheath and stromatic Leucosomes probably had position, magma extracted at low melt fractions from a combination of slow melt segregation, larger interacting melt an actively deforming partially molten zone may differ volume and longer residence times at high temperatures. Results substantially in composition from one extracted at high suggest that rapid melt extraction by deformation will increase the melt volumes from rocks undergoing little deformation tendency for preservation of source rock isotopic patterns in some (Rushmer, 1995). The link between ‘frozen’ migmatites granites. and complete granite bodies may not be direct (Clemens
Jean-françois Moyen - One of the best experts on this subject based on the ideXlab platform.
-
The processes that control Leucosome compositions in metasedimentary granulites: perspectives from the Southern Marginal Zone migmatites, Limpopo Belt, South Africa
Journal of Metamorphic Geology, 2014Co-Authors: J. Taylor, Gautier Nicoli, Gary Stevens, Dirk Frei, Jean-françois MoyenAbstract:International audienceAnatexis of metapelitic rocks at the Bandelierkop Quarry (BQ) locality in the Southern Marginal Zone of the Limpopo Belt occurred via muscovite and biotite breakdown reactions which, in order of increasing temperature, can be modelled as: (1) Muscovite + quartz + plagioclase = sillimanite + melt; (2) Biotite + sillimanite + quartz + plagioclase = garnet + melt; (3) Biotite + quartz + plagioclase = orthopyroxene ± cordierite ± garnet + melt. Reactions 1 and 2 produced stromatic Leucosomes, which underwent solid-state deformation before the formation of undeformed nebulitic Leucosomes by reaction 3. The zircon U–Pb ages for both Leucosomes are within error identical. Thus, the melt or magma formed by the first two reactions segregated and formed mechanically solid stromatic veins whilst temperature was increasing. As might be predicted from the deformational history and sequence of melting reactions, the compositions of the stromatic Leucosomes depart markedly from those of melts from metapelitic sources. Despite having similar Si contents to melts, the Leucosomes are strongly K-depleted, have Ca:Na ratios similar to the residua from which their magmas segregated and are characterized by a strong positive Eu anomaly, whilst the associated residua has no pronounced Eu anomaly. In addition, within the Leucosomes and their wall rocks, peritectic garnet and orthopyroxene are very well preserved. This collective evidence suggests that melt loss from the stromatic Leucosome structures whilst the rocks were still undergoing heating is the dominant process that shaped the chemistry of these Leucosomes and produced solid Leucosomes. Two alternative scenarios are evaluated as generalized petrogenetic models for producing Si-rich, yet markedly K-depleted and Ca-enriched Leucosomes from metapelitic sources. The first process involves the mechanical concentration of entrained peritectic plagioclase and garnet in the Leucosomes. In this scenario, the volume of quartz in the Leucosome must reflect the remaining melt fraction with resultant positive correlation between Si and K in the Leucosomes. No such correlation exists in the BQ Leucosomes and in similar Leucosomes from elsewhere. Consequently, we suggest disequilibrium congruent melting of plagioclase in the source and consequential crystallization of peritectic plagioclase in the melt transfer and accumulation structures rather than at the sites of biotite melting. This induces co-precipitation of quartz in the structures by increasing SiO2 content of the melt. This process is characterized by an absence of plagioclase-induced fractionation of Eu on melting, and the formation of Eu-enriched, quartz + plagioclase + garnet Leucosomes. From these findings, we argue that melt leaves the source rapidly and that the Leucosomes form incrementally as melt or magma leaving the source dumps its disequilibrium Ca load, as well as quartz and entrained ferromagnesian peritectic minerals, in sites of magma accumulation and escape. This is consistent with evidence from S-type granites suggesting rapid magma transfer from source to high level plutons. These findings also suggest that Leucosomes of this type should be regarded as constituting part of the residuum from partial melting
-
The processes that control Leucosome compositions in metasedimentary granulites: perspectives from the Southern Marginal Zone migmatites, Limpopo Belt, South Africa
Journal of Metamorphic Geology, 2014Co-Authors: J. Taylor, Gautier Nicoli, Gary Stevens, Dirk Frei, Jean-françois MoyenAbstract:Anatexis of metapelitic rocks at the Bandelierkop Quarry (BQ) locality in the Southern Marginal Zone of the Limpopo Belt occurred via muscovite and biotite breakdown reactions which, in order of increasing temperature, can be modelled as: (1) Muscovite + quartz + plagioclase = sillimanite + melt; (2) Biotite + sillimanite + quartz + plagioclase = garnet + melt; (3) Biotite + quartz + plagioclase = orthopyroxene ± cordierite ± garnet + melt. Reactions 1 and 2 produced stromatic Leucosomes, which underwent solid-state deformation before the formation of undeformed nebulitic Leucosomes by reaction 3. The zircon U–Pb ages for both Leucosomes are within error identical. Thus, the melt or magma formed by the first two reactions segregated and formed mechanically solid stromatic veins whilst temperature was increasing. As might be predicted from the deformational history and sequence of melting reactions, the compositions of the stromatic Leucosomes depart markedly from those of melts from metapelitic sources. Despite having similar Si contents to melts, the Leucosomes are strongly K-depleted, have Ca:Na ratios similar to the residua from which their magmas segregated and are characterized by a strong positive Eu anomaly, whilst the associated residua has no pronounced Eu anomaly. In addition, within the Leucosomes and their wall rocks, peritectic garnet and orthopyroxene are very well preserved. This collective evidence suggests that melt loss from the stromatic Leucosome structures whilst the rocks were still undergoing heating is the dominant process that shaped the chemistry of these Leucosomes and produced solid Leucosomes. Two alternative scenarios are evaluated as generalized petrogenetic models for producing Si-rich, yet markedly K-depleted and Ca-enriched Leucosomes from metapelitic sources. The first process involves the mechanical concentration of entrained peritectic plagioclase and garnet in the Leucosomes. In this scenario, the volume of quartz in the Leucosome must reflect the remaining melt fraction with resultant positive correlation between Si and K in the Leucosomes. No such correlation exists in the BQ Leucosomes and in similar Leucosomes from elsewhere. Consequently, we suggest disequilibrium congruent melting of plagioclase in the source and consequential crystallization of peritectic plagioclase in the melt transfer and accumulation structures rather than at the sites of biotite melting. This induces co-precipitation of quartz in the structures by increasing SiO2 content of the melt. This process is characterized by an absence of plagioclase-induced fractionation of Eu on melting, and the formation of Eu-enriched, quartz + plagioclase + garnet Leucosomes. From these findings, we argue that melt leaves the source rapidly and that the Leucosomes form incrementally as melt or magma leaving the source dumps its disequilibrium Ca load, as well as quartz and entrained ferromagnesian peritectic minerals, in sites of magma accumulation and escape. This is consistent with evidence from S-type granites suggesting rapid magma transfer from source to high level plutons. These findings also suggest that Leucosomes of this type should be regarded as constituting part of the residuum from partial melting.
C. Srikantappa - One of the best experts on this subject based on the ideXlab platform.
-
Corundum–Leucosome-bearing aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-absent muscovite-melting in silica-undersaturated aluminous rocks
American Mineralogist, 2010Co-Authors: Michael M. Raith, Pulak Sengupta, Ellen Kooijman, Dewashish Upadhyay, C. SrikantappaAbstract:An aluminous gneissic rock associated with high-pressure mafic and felsic granulites in the Palghat-Cauvery Shear Zone of southern India provides a classic example of quartz-absent muscovite melting. The anatectic gneiss shows a conspicuous migmatitic structure defined by closely spaced centimeter to decimeter sized, corundum-bearing Leucosomes developed in a weakly foliated mesosome of plagioclase (An 21 Ab 77 Or 2 ) and biotite (4.9 wt% TiO 2 , X Mg = 0.51–0.47). The boundaries between Leucosome and mesosome domains are sharp, and no melanosome selvages are developed at the interface. Corundum occurs as euhedral crystals up to 2 cm in diameter, typically centered in the Leucosome matrix of coarse-grained perthitic alkali feldspar (integrated composition: An 2 Ab 35 Or 63 ), minor relict biotite (4.2–5.1 wt% TiO 2 , X Mg = 0.48–0.46) and plagioclase (An 21 Ab 78 Or 1 ). In some domains, the mesosomes also contain elongate clusters of similarly oriented smaller corundum plates that are intergrown with perthitic alkali feldspar, presumably replacing former kyanite blades. The textural and mineralogical characteristics and petrogenetic grid considerations indicate breakdown of muscovite through two successive dehydration-melting reactions: (1) formation of corundum+K-feldspar-clusters via the reaction muscovite+aluminosilicate → corundum+liquid at the sites of kyanite/sillimanite, and (2) development of corundum-bearing Leucosomes through the reaction muscovite → corundum+K-feldspar+liquid, focused around the sites of nucleation and growth of peritectic corundum. P - T pseudosection modeling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 system locates the onset and completion of the muscovite-melting reaction 2 in the steep narrow quadrivariant field Ms+Bt+Pl+Kfs+Crn+Liq, which extends from ~6 kbar, 720 °C to higher pressures. Biotite remained stable and was not involved in the melting reactions. Two-feldspar thermometry gives peak-temperatures of 800 ± 50 °C. Combined with P - T estimates for metapelitic granulites in the area, these P - T constraints appear to be consistent with a clockwise P - T evolution of the eastern Palghat Cauvery shear zone with peak P - T conditions not exceeding ca. 800 °C and 10–12 kbar. The timing of partial melting and HT-metamorphism is constrained at ~529 Ma by U-Pb spot dating of oscillatory zoned individual grains and overgrowths on detrital zircon cores included in peritectic corundum of Leucosome domains. The zircon cores indicate a Paleoproterozoic (2.5–2.0 Ga) provenance of the sedimentary protolith.
Daniela Utzeri - One of the best experts on this subject based on the ideXlab platform.
-
Amphibole-bearing migmatites from the Variscan Belt of NE Sardinia, Italy: Partial melting of mid-Ordovician igneous sources
Lithos, 2008Co-Authors: Gabriele Cruciani, Marcello Franceschelli, Stefan Jung, Mariano Puxeddu, Daniela UtzeriAbstract:Abstract Amphibole-bearing migmatites from north-eastern Sardinia, Italy, are characterized by tonalitic to granodioritic Leucosomes made up of quartz, plagioclase, K-feldspar, biotite, ± amphibole, and garnet. The Leucosomes show higher SiO2, Na2O, Sr and lower TiO2, Fe2O3tot, MgO, MnO, P2O5, K2O and Rb content as compared to the mesosomes. The granodioritic Leucosomes differ from the tonalitic Leucosomes for significantly higher Ba and K2O content. The mesosomes and the Leucosomes show slightly fractionated REE patterns with moderate negative and positive Eu anomalies, respectively. The Leucosomes show lower 87Rb/86Sr ratios (0.279–0.581) than the mesosomes (0.634–1.121), whereas the 147Sm/144Nd ratios are similar in Leucosomes (0.12–0.14) and mesosomes (0.11–0.14). Mineralogical, geochemical and isotopic data suggest that the migmatites formed by in situ partial melting of a biotite + plagioclase + quartz-bearing protolith with 2–4 wt.% added water. Variable degrees of melt loss were responsible for the observed compositional variability in the Leucosomes, whereas solid-state re-equilibration of the migmatites leads to a general re-equilibration of mineral compositions after partial melting. The amphibole-bearing migmatites record maximum P–T conditions of 700–750 °C and 1.0–1.2 GPa, probably lower than, but near to, the P–T conditions of peak metamorphism. Zircon morphology suggests an igneous origin for the migmatite protolith. Pb–Pb zircon dating yielded a mean value of 452 ± 3 Ma and an isochron age of 461 ± 12 Ma which is interpreted as the emplacement age of the migmatite protolith.
-
Petrogenesis of Al–silicate-bearing trondhjemitic migmatites from NE Sardinia, Italy
Lithos, 2007Co-Authors: Gabriele Cruciani, Marcello Franceschelli, Mariano Puxeddu, Franco Marco Elter, Daniela UtzeriAbstract:Abstract The migmatites from Punta Sirenella (NE Sardinia) are layered rocks containing 3–5 vol.% of centimeter-sized stromatic Leucosomes which are mainly trondhjemitic and only rarely granitic in composition. They underwent three deformation phases, from D 1 to D 3 . The D 1 deformation shows a top to the NW shear component followed by a top to the NE/SE component along the XZ plane of the S 2 schistosity. Migmatization started early, during the compressional and crustal thickening stage of Variscan orogeny and was still in progress during the following extensional stage of unroofing and exhumation. The trondhjemitic Leucosomes, mainly consisting of quartz, plagioclase, biotite ± garnet ± kyanite ± fibrolite, retrograde muscovite and rare K-feldspar, are locally bordered by millimeter-sized biotite-rich melanosomes. The rare granitic Leucosomes differ from trondhjemitic ones only in the increase in modal content of K-feldspar, up to 25%. Partial melting started in the kyanite field at about 700–720 °C and 0.8–0.9 GPa, and was followed by re-equilibration at 650–670 °C and 0.4–0.6 GPa, producing fibrolite–biotite intergrowth and coarse-grained muscovite. The Leucosomes have higher SiO 2 , CaO, Na 2 O, Sr and lower Al 2 O 3 , Fe 2 O 3 , MgO, TiO 2 , K 2 O, P 2 O 5 , Rb, Ba, Cr, V, Zr, Nb, Zn and REE content with respect to proximal hosts and pelitic metagreywackes. Sporadic anomalous high content of calcium and ferromagnesian elements in some Leucosomes is due to entrainment of significant amounts of restitic plagioclase, biotite and accessory phases. The rare granitic Leucosomes reveal peritectic K-feldspar produced by muscovite-dehydration melting. Most Leucosomes show low REE content, moderately fractionated REE patterns and marked positive Eu anomaly. Proximal hosts and pelitic metagraywackes are characterized by higher REE content, more fractionated REE patterns and slightly negative Eu anomaly. The trondhjemitic Leucosomes were generated by H 2 O-fluxed melting at 700 °C of a greywacke to pelitic–greywacke metasedimentary source-rock. The disequilibrium melting process is the most reliable melting model for Punta Sirenella Leucosomes.
Gabriele Cruciani - One of the best experts on this subject based on the ideXlab platform.
-
Geothermobarometry of Al-silicate-bearing migmatites from the Variscan chain of NE Sardinia, Italy: a P-T pseudosection approach
Periodico Di Mineralogia, 2014Co-Authors: Gabriele Cruciani, Dario Fancello, Marcello Franceschelli, Massimo Scodina, Maria Elena SpanoAbstract:This paper investigates Al-silicate-bearing migmatite from NE Sardinia by using the P-T pseudosection approach with the aim to determine the P-T conditions of partial melting and those of melt crystallization. P-T pseudosections were calculated in the NCKFMASH system within the P-T range 500-800 °C, 0.1-1.5 GPa by using the average compositions of metapelitic greywacke, average mesosome and average trondhjemitic Leucosome, respectively. The P-T pseudosections calculated for the average metapelitic greywacke and for the average mesosome, contoured for melt volume %, Si/Al and Na/K molar ratios in melt point to P-T conditions ~ 700-740 °C, 1.1-1.3 GPa which are indicative of partial melting. The P-T pseudosection calculated for the average composition of trondhjemitic Leucosomes, contoured for kyanite and biotite modal content and for X Mg ratio in biotite indicates P-T conditions of 660-730 °C, 0.75-0.90 GPa for the crystallization of the melt. The comparison between the Na/K and Si/Al ratios in Leucosomes, and the same ratios modeled for the anatectic melt by an haplogranitic melt model is thus a powerful tool for the reconstruction of P-T conditions of partial melting also in pelitic rocks, provided that Leucosomes represent pure melts and are not contaminated by restitic phases or feldspar cumulates.
-
Amphibole-bearing migmatites from the Variscan Belt of NE Sardinia, Italy: Partial melting of mid-Ordovician igneous sources
Lithos, 2008Co-Authors: Gabriele Cruciani, Marcello Franceschelli, Stefan Jung, Mariano Puxeddu, Daniela UtzeriAbstract:Abstract Amphibole-bearing migmatites from north-eastern Sardinia, Italy, are characterized by tonalitic to granodioritic Leucosomes made up of quartz, plagioclase, K-feldspar, biotite, ± amphibole, and garnet. The Leucosomes show higher SiO2, Na2O, Sr and lower TiO2, Fe2O3tot, MgO, MnO, P2O5, K2O and Rb content as compared to the mesosomes. The granodioritic Leucosomes differ from the tonalitic Leucosomes for significantly higher Ba and K2O content. The mesosomes and the Leucosomes show slightly fractionated REE patterns with moderate negative and positive Eu anomalies, respectively. The Leucosomes show lower 87Rb/86Sr ratios (0.279–0.581) than the mesosomes (0.634–1.121), whereas the 147Sm/144Nd ratios are similar in Leucosomes (0.12–0.14) and mesosomes (0.11–0.14). Mineralogical, geochemical and isotopic data suggest that the migmatites formed by in situ partial melting of a biotite + plagioclase + quartz-bearing protolith with 2–4 wt.% added water. Variable degrees of melt loss were responsible for the observed compositional variability in the Leucosomes, whereas solid-state re-equilibration of the migmatites leads to a general re-equilibration of mineral compositions after partial melting. The amphibole-bearing migmatites record maximum P–T conditions of 700–750 °C and 1.0–1.2 GPa, probably lower than, but near to, the P–T conditions of peak metamorphism. Zircon morphology suggests an igneous origin for the migmatite protolith. Pb–Pb zircon dating yielded a mean value of 452 ± 3 Ma and an isochron age of 461 ± 12 Ma which is interpreted as the emplacement age of the migmatite protolith.
-
Petrogenesis of Al–silicate-bearing trondhjemitic migmatites from NE Sardinia, Italy
Lithos, 2007Co-Authors: Gabriele Cruciani, Marcello Franceschelli, Mariano Puxeddu, Franco Marco Elter, Daniela UtzeriAbstract:Abstract The migmatites from Punta Sirenella (NE Sardinia) are layered rocks containing 3–5 vol.% of centimeter-sized stromatic Leucosomes which are mainly trondhjemitic and only rarely granitic in composition. They underwent three deformation phases, from D 1 to D 3 . The D 1 deformation shows a top to the NW shear component followed by a top to the NE/SE component along the XZ plane of the S 2 schistosity. Migmatization started early, during the compressional and crustal thickening stage of Variscan orogeny and was still in progress during the following extensional stage of unroofing and exhumation. The trondhjemitic Leucosomes, mainly consisting of quartz, plagioclase, biotite ± garnet ± kyanite ± fibrolite, retrograde muscovite and rare K-feldspar, are locally bordered by millimeter-sized biotite-rich melanosomes. The rare granitic Leucosomes differ from trondhjemitic ones only in the increase in modal content of K-feldspar, up to 25%. Partial melting started in the kyanite field at about 700–720 °C and 0.8–0.9 GPa, and was followed by re-equilibration at 650–670 °C and 0.4–0.6 GPa, producing fibrolite–biotite intergrowth and coarse-grained muscovite. The Leucosomes have higher SiO 2 , CaO, Na 2 O, Sr and lower Al 2 O 3 , Fe 2 O 3 , MgO, TiO 2 , K 2 O, P 2 O 5 , Rb, Ba, Cr, V, Zr, Nb, Zn and REE content with respect to proximal hosts and pelitic metagreywackes. Sporadic anomalous high content of calcium and ferromagnesian elements in some Leucosomes is due to entrainment of significant amounts of restitic plagioclase, biotite and accessory phases. The rare granitic Leucosomes reveal peritectic K-feldspar produced by muscovite-dehydration melting. Most Leucosomes show low REE content, moderately fractionated REE patterns and marked positive Eu anomaly. Proximal hosts and pelitic metagraywackes are characterized by higher REE content, more fractionated REE patterns and slightly negative Eu anomaly. The trondhjemitic Leucosomes were generated by H 2 O-fluxed melting at 700 °C of a greywacke to pelitic–greywacke metasedimentary source-rock. The disequilibrium melting process is the most reliable melting model for Punta Sirenella Leucosomes.