Petrogenesis of migmatites and leucogranites from Sierra de Molinos, Salta, Northwest Argentina: A petrologic and geochemical study

Sola, Alfonso; Becchio, Raúl; Pimentel, Márcio Martins

doi:10.1016/j.lithos.2013.07.025

Cited by 29 publications

(35 citation statements)

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“…Consequently, experiments might not always be appropriate or sensitive enough to assess the effects of subtle changes of free water during partial melting, such as those presented in Figure a. Our results yielded granitic melts with very low contents of FeO+MgO, whether or not aqueous fluids were added, and thus variations of natural leucosomes and associated granitoids are interpreted to reflect a combination of residue entrainment and crystal fractionation (see Sola et al., ), or different source compositions.…”

Section: Discussionmentioning

confidence: 81%

“…In the study area, LA‐ICPMS U–Pb zircon dating from granitoids and migmatites provided identical ages within the analytical errors, indicating that the metamorphic peak and granite generation occurred at c . 470 Ma (Sola et al., ).…”

Section: Regional Settingmentioning

confidence: 99%

“…The temperature during partial melting was estimated by Sola et al. () from the saturation temperature of zircon and monazite in residuum‐poor leucosome and leucogranite samples, to be in the ranges 624–698°C and 620–687°C, respectively.…”

Section: Regional Settingmentioning

confidence: 99%

“…All compositions used in the calculations, except for sample MO1108, were obtained from XRF analyses presented in Sola et al. (). The major element composition of sample MO1108 was obtained from thin section area analysis through integration of several X‐ray compositional maps (e.g.…”

Section: Phase Equilibria Modellingmentioning

confidence: 99%

“…Figure shows a P–T pseudosection calculated for the reference metapelite (MO40_10408) that extends from high‐grade subsolidus conditions to suprasolidus conditions (1–6 kbar/625–800°C). In Sierra de Molinos primary muscovite is abundant up to and at the migmatite front (Sola et al., ). This implies that the regional metamorphic field gradient in Sierra de Molinos passed above the low‐variance point “P1” in Figure , below which no muscovite should be present.…”

Section: Phase Equilibria Modellingmentioning

confidence: 99%

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Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling

Sola

Hasalová

Weinberg

et al. 2017

Journal Metamorphic Geology

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Water‐fluxed melting has long been thought to have a minor influence on the thermal and chemical structure of the crust. We report here on amphibolite facies metasedimentary rocks from the 490–450 Ma Famatinian Orogen, in northwest Argentina, that have undergone water‐fluxed incongruent biotite melting at relatively low temperature, which have produced and lost a significant volume of melt. The protoliths consist of the turbiditic Puncoviscana Formation (Neoproterozoic to Early Cambrian). The field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low pressure almost isobaric path, reaching peak conditions estimated at 700°C at 4 kbar. Thermodynamic modelling in the MnNCKFMASHTO system is applied to investigate melting at such low pressure as a function of water content. Calculations using a typical turbidite composition show how small amounts of added free H2O may increase significantly the melt fraction with little or no change in either the melt or residual phase compositions. They indicate negligible difference in normative An–Ab–Or proportions and ferromagnesian contents between melts derived by dehydration and water‐fluxed melts. The same is true for the content of H2O dissolved in melts, which remains constant and the melt produced is granitic whether or not aqueous fluids are present. Thus, neither the residue nor the melt composition are indicators of the presence of aqueous fluids during anatexis. Recognizing the impact of small additions of H2O to an anatectic terrane may therefore be difficult. The most significant change related to water‐fluxing is the relative proportions of minerals and melt fraction, rather than the actual mineral assemblage. The modal proportion of feldspar decreased while those of cordierite and biotite increased in the residual assemblages, as <5 mol.% of free H2O was added. The impact of this addition is to more than double the proportion of water‐undersaturated melt to 25–30 mol.%. We have also developed a simple way to estimate how much melt a residual rock has lost, if the compositional trends of the protoliths are known. In summary, we find that even though the addition of small amounts of free H2O impacts significantly on rock fertility, there is little obvious record in the field. The combined application of careful petrological investigation and thermodynamic modelling is the key to identify the influence of aqueous fluids, and exploit systems that became open not only to fluid influx but also to the extraction of melt.

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Section: Discussionmentioning

confidence: 81%

Section: Regional Settingmentioning

confidence: 99%

Section: Regional Settingmentioning

confidence: 99%

Section: Phase Equilibria Modellingmentioning

confidence: 99%

Section: Phase Equilibria Modellingmentioning

confidence: 99%

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Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling

Sola

Hasalová

Weinberg

et al. 2017

Journal Metamorphic Geology

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Provenance, nature, and U–Pb zircon geochronology of Ngaye rocks (Adamawa‐Yadé Shield, Central Cameroon): New insights into the evolution of Archean crust within the Pan‐African belt

et al. 2021

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and geochronological data obtained from Ngaye highgrade metasedimentary rocks have contributed to determine the provenance, nature, and evolutionary history of the Adamawa-Yadé Domain from the Archean to Pan-African events. The rocks are migmatites formed after TTG and granitic crusts were reworked by partial melting at T = 683-994 C. Geochemical features, for example, low Rb/Sr ratio (0.03-0.53), high Cr/V, and Cr/Th ratios (9.91-100.75; 28.41-686.15), respectively, indicate that these samples were derived predominantly from a mafic crust source. The primordial mantle-normalized spidergrams are characterized by negative Nb-Ta anomalies, suggesting melting of crustal rocks. REE fractionation shown (La/ Yb) N = 8.48-197.89) indicate melting of crustal source rocks (meta-TTGs). Low Hf and Zr contents (0.95-5.65 ppm and 23-262.85 ppm, respectively), low Sr/Y ratios (9.17-200.65), and a positive correlation between Th/Sc and Zr/Sc, point to crustal reworking. U-Pb ages on detrital zircon in tonalitic and granodioritic gneisses indicate contribution of Mesoarchean and Paleoproterozoic sources and suggest a maximum deposition age during the Early Paleoproterozoic for their magmatic protoliths. Magmatic zircon grains of granodiorite, with a round shape, Th/U ratio values ranging from 0.02 to 1.23, and an oscillatory zonation yield post emplacement metamorphic ages at 2,077 Ma. The lower intercept ages obtained in this study, match the tectonic reworking of the crust during the Pan-African event associated with partial melting due probably to regionalscale shear zone activities and magmatic accretion of juvenile magmas.

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The Pre-Andean Phases of Construction of the Southern Andes Basement in Neoproterozoic–Paleozoic Times

Heredia

Garcı́a-Sansegundo

Gallastegui

et al. 2018

The Evolution of the Chilean-Argentinean Andes

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During the late Neoproterozoic and Paleozoic times, the Southern Andes of Argentina and Chile (21º-55º S) formed part of the southwestern margin of Gondwana. During this period of time, a set of continental fragments of variable extent and allochtony was successively accreted to that margin, resulting in six Paleozoic orogenies of different temporal and spatial extension: Pampean (Ediacaran-early Cambrian), Famatinian (Middle Ordovician-Silurian), Ocloyic (Middle Ordovician-Devonian), Chanic (Middle Devonian-early Carboniferous), Gondwanan (Middle Devonian-middle Permian) and Tabarin (late Permian-Triassic). All these orogenies culminate with collisional events, with the exception of the Tabarin and a part of the Gondwanan orogenies that are subduction-related.

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Petrogenesis of migmatites and leucogranites from Sierra de Molinos, Salta, Northwest Argentina: A petrologic and geochemical study

Cited by 29 publications

References 50 publications

Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling

Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling

Provenance, nature, and U–Pb zircon geochronology of Ngaye rocks (Adamawa‐Yadé Shield, Central Cameroon): New insights into the evolution of Archean crust within the Pan‐African belt

The Pre-Andean Phases of Construction of the Southern Andes Basement in Neoproterozoic–Paleozoic Times

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Petrogenesis of migmatites and leucogranites from Sierra de Molinos, Salta, Northwest Argentina: A petrologic and geochemical study

Cited by 29 publications

References 50 publications

Low‐P melting of metapelitic rocks and the role of H2O: Insights from phase equilibria modelling

Low‐P melting of metapelitic rocks and the role of H2O: Insights from phase equilibria modelling

Provenance, nature, and U–Pb zircon geochronology of Ngaye rocks (Adamawa‐Yadé Shield, Central Cameroon): New insights into the evolution of Archean crust within the Pan‐African belt

The Pre-Andean Phases of Construction of the Southern Andes Basement in Neoproterozoic–Paleozoic Times

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Product

Resources

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Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling

Low‐P melting of metapelitic rocks and the role of H₂O: Insights from phase equilibria modelling