scholarly journals Equilibrium crystallization of massif-type anorthosite residual melts: a case study from the 1.64 Ga Ahvenisto complex, Southeastern Finland

2020 ◽  
Vol 175 (9) ◽  
Author(s):  
Riikka Fred ◽  
Aku Heinonen ◽  
Jussi S. Heinonen
Keyword(s):  
Magma Chambers ◽  
Equilibrium Crystallization ◽  
Liquid Line ◽  
Rock Types ◽  
Residual Magma ◽  
Icp Ms ◽  
Mineral Assemblages ◽  
Residual Melt ◽  
Liquid Line Of Descent

Abstract Fe–Ti–P-rich mafic to intermediate rocks (monzodiorites and oxide–apatite–gabbronorites, OAGNs) are found as small intrusions in most AMCG (anorthosite–magnerite–charnokite–granite) suites. The origin of the monzodioritic rocks is still debated, but in many studies, they are presumed to represent residual liquid compositions after fractionation of anorthositic cumulates. In the 1.64 Ga Ahvenisto complex, SE Finland, monzodioritic rocks occur as minor dike-like lenses closely associated with anorthositic rocks. We report new field, petrographic, and geochemical (XRF, ICP-MS, EMPA) data complemented with crystallization modeling (rhyolite-MELTS, MAGFRAC) for the monzodioritic rocks, apatite–oxide–gabbronorite, and olivine-bearing anorthositic rocks of the Ahvenisto complex. The presented evidence suggest that the monzodioritic rocks closely represent melt compositions while the apatite–oxide–gabbronorite and olivine-bearing anorthositic rocks are cumulates. The monzodioritic rocks seem to form a liquid line of descent (LLD) from primitive olivine monzodiorites to more evolved monzodiorites. Petrological modeling suggests that the interpreted LLD closely corresponds to a residual melt trend left after fractional crystallization (FC) and formation of the cumulate anorthositic rocks and minor apatite–oxide–gabbronorite in shallow magma chambers. Consequent equilibrium crystallization (EC) of separate monzodioritic residual magma batches can produce the observed mineral assemblages and the low Mg numbers measured from olivine (Fo25–45) and pyroxenes (En48–63, Mg#cpx 60–69). The monzodioritic rocks and apatite–oxide–gabbronorites show similar petrological and geochemical characteristics to corresponding rock types in other AMCG suites, and the model described in this study could be applicable to them as well.

scholarly journals The importance of in situ crystallisation and loss of interstitial melt during formation of the Kærven Syenite Complex, Kangerlussuaq, East Greenland

2020 ◽  
Vol 67 ◽  
pp. 107-146
Author(s):  
Paul Martin Holm ◽  
Niels-Ole Prægel
Keyword(s):  
Alkali Feldspar ◽  
Fractional Crystallisation ◽  
Geochemical Data ◽  
Magma Chambers ◽  
Quartz Syenite ◽  
East Greenland ◽  
The North ◽  
Rock Types ◽  
Host Rocks ◽  
Residual Melt

The Kærven Syenite Complex (KSC) is one of the oldest felsic intrusions in the Tertiary East Greenland province. Here we update our previous description of the KSC and supply a greatly expanded and comprehensive geochemical dataset. New data allow us to present a more detailed petrogenetic model for the evolution of the KSC and to investigate the geochemical characteristics of igneous cumulates subjected to loss and, occasionally, replacement of residual liquid. The KSC comprises eleven mappable units that generally young westwards. Rock types range from quartz syenite to quartz alkali feldspar syenite and alkali feldspar granite. Individual intrusive units are relatively narrow and steep-sided and are collectively suggested to represent a ring dyke complex. Basement gneiss and gabbro host rocks have locally contaminated the oldest quartz syenite KSC unit, but most of the main part of the complex escaped significant influence from host rocks. A late suite of E–W to NE–SW striking peralkaline dykes of trachytic to phonolitic compositions intrude the KSC. Compositions of the KSC rocks span a considerable range in SiO2, 59–73 wt%. Concentrations of several elements vary widely for a given SiO2 (especially at SiO2 < 66 wt%), and variation diagrams do not suggest a single model for the evolution of the units of the complex. A cumulative origin is envisaged for several KSC units. Geochemical modelling suggests that KSC magmas were derived from more than one primary magma, and that the complex evolved through a four-stage process: fractional crystallisation in precursory magma chambers was followed by final emplacement of each unit, establishment of a crystal/melt mush, expulsion of part of the residual melt and, finally, crystallisation of the remaining melt. Trace element disequilibria between alkali feldspar and host rocks in two closely associated quartz alkali feldspar syenite units indicate that highly evolved residual melt was replaced by a less evolved melt phase. Modelling of potential parent melt compositions to the Kærven magmas suggests an origin not in the Iceland plume asthenosphere, but rather in a moderately enriched source, possibly in the continental lithosphere. The course of melt evolution by fractional crystallisation is indicated to have taken place in magma chambers at depth, and repeated rise of magma into the upper crustal magma chambers and crystallisation there formed the KSC. Based on our survey of published geochemical data, the inferred parental magmas seem to have few equivalents in the North Atlantic Igneous Province and may have been generated mainly from melting of enriched dry lithospheric mantle of possibly Archaean age.

scholarly journals Kyanite petrogenesis in migmatites: Resolving melting and metamorphic signatures

2021 ◽  
Author(s):  
Stacy Phillips ◽  
Tom Argles ◽  
Clare Warren ◽  
Nigel Harris ◽  
Barbara Kunz
Keyword(s):  
Partial Melting ◽  
Geochemical Zoning ◽  
Additional Information ◽  
Rock Types ◽  
Icp Ms ◽  
Dehydration Reactions ◽  
Mineral Assemblages ◽  
Geochemical Investigation ◽  
Sample Set ◽  
Combining Information

Aluminosilicates (kyanite, sillimanite and andalusite) are useful pressure-temperature (P-T)indicators that can form in a range of rock types through different mineral reactions, including thosethat involve partial melting. Their involvement in melting reactions means that the presence ofaluminosilicates in migmatite mineral assemblages can help to (broadly) constrain the P-T conditionsof melt formation, which then has implications for evaluating models of orogenic tectonics.Xenocrystic grains could lead to spurious tectonic interpretations, so being able to distinguishbetween different petrogenetic sources is important. Petrological and geochemical investigation ofmigmatite-hosted kyanite from Eastern Bhutan shows that kyanite petrogenesis may be constrainedby combining information from morphology, cathodoluminescence response, microtextural positionand geochemical zoning patterns. Mg, Ti, Ca, Fe, Cr and Ge concentrations provide diagnostic cluesthat distinguish sub-solidus kyanite from kyanite that crystallised directly from melt, or grewperitectically during muscovite dehydration reactions. The abundance of these elements in kyanite isalso strongly controlled by protolith composition, with considerable inter-sample variation observedin this sample set. LA-ICP-MS maps, especially of Cr/V, provide additional information aboutchanging geochemical environments during kyanite growth. These data and observations show thatmost kyanite is of xenocrystic origin in the analysed samples, and therefore that its presence does notnecessarily constrain the P-T conditions of the melt reaction(s). This finding has significantimplications for the interpretation of kyanite-bearing migmatites as representing early stages ofmelting during Himalayan evolution.

Application of LA-ICP-MS trace-element analysis for precious metal deportment: a case study of the Kevitsa mine, Finland

2017 ◽  
Vol 29 (4) ◽  
pp. 635-644 ◽  
Author(s):  
Louis J Cabri ◽  
Michelle Kelvin ◽  
Zhaoping Yang ◽  
Simon E Jackson ◽  
Okan Altun
Keyword(s):  
Trace Element ◽  
Precious Metal ◽  
Trace Element Analysis ◽  
Element Analysis ◽  
Icp Ms

scholarly journals Supplemental Material: Himalayan Miocene adakitic rocks, a case study of the Mayum pluton: Insights into geodynamic processes within the subducted Indian continental lithosphere and Himalayan mid-Miocene tectonic regime transition

2020 ◽  
Author(s):  
Chao Lin ◽  
Jinjiang Zhang ◽  
et al.
Keyword(s):  
Isotopic Composition ◽  
Continental Lithosphere ◽  
Isotopic Data ◽  
Element Geochemistry ◽  
Adakitic Rocks ◽  
Icp Ms ◽  
Geodynamic Processes ◽  
Data Statistics

Table S1: Bulk element geochemistry and isotopic composition of the Mayum pluton; Table S2: Zircon LA-ICP-MS U-Pb data for the Mayum pluton; Table S3: Zircon in situ Lu-Hf isotopic data for the Mayum pluton; Table S4: Data statistics for Himalayan Eocene and Miocene adakitic rocks.

scholarly journals A Liquid Line of Descent of the Jotunite (Hypersthene Monzodiorite) Suite

1998 ◽  
Vol 39 (3) ◽  
pp. 439-468 ◽  
Author(s):  
J. Vander Auwera ◽  
J. Longhi ◽  
J.-C. Duchesne
Keyword(s):  
Liquid Line ◽  
Liquid Line Of Descent

Sur quelques aspects de la zoneographie alpine dans les Alpes cottiennes meridionales

1962 ◽  
Vol S7-IV (4) ◽  
pp. 477-491
Author(s):  
Andre Michard
Keyword(s):  
Tectonic Activity ◽  
Structural Units ◽  
Zonal Distribution ◽  
Rock Types ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Alpine Metamorphism

Abstract A Permo-Carboniferous series and a polymetamorphic series are distinguished in the rocks of the southern Cottian Alps, Italy. The metamorphic mineral assemblages and facies of the principal rock types represented in each series and their zonal distribution are discussed. Alpine metamorphism is considered to have occurred after the tectonic activity responsible for superposition of the three structural units recognized in the region between Varaita and Stura.

Bulk Liquid for the Skaergaard Intrusion and Its PGE-Au Mineralization: Composition, Correlation, Liquid Line of Descent, and Timing of Sulphide Saturation and Silicate–Silicate Immiscibility

2019 ◽  
Vol 60 (10) ◽  
pp. 1853-1880 ◽  
Author(s):  
Troels F D Nielsen ◽  
C Kent Brooks ◽  
Jakob K Keiding
Keyword(s):  
Precious Metal ◽  
Bulk Composition ◽  
Precious Metals ◽  
Bulk Liquid ◽  
Skaergaard Intrusion ◽  
Liquid Line ◽  
Multi Stage ◽  
Silicate Liquids ◽  
Crystallization Zone ◽  
Liquid Line Of Descent

Abstract Preferred and modelled bulk composition of the Skaergaard intrusion are compared to coeval basaltic compositions in East Greenland and found to relate to the second evolved cycle of Geikie Plateau Formation lavas and coeval Skaergaard-like dikes in major and trace element (Mg# ∼45, Ce/Nb ∼2·5, (Dy/Yb)N ∼1·35), and precious metal composition (Pd/Pt ∼3, Au/Pt ∼2) as well as in age (∼56 Ma). Successful comparisons of precious metal compositions only occur with Skaergaard models based on mass balance. The bulk liquid of the intrusion evolved along the liquid line of descent to immiscibility between Si- and Fe-rich silicate liquids after ∼90% of crystallization (F = ∼0·10) in agreement with experimental constraints. Immiscibility led to accumulation and fractionation of the Fe-rich silicate melt in the mushy floor of the intrusion and continued accumulation of granophyre component in the remaining bulk liquid. The composition of plagioclase in the precious metal mineralized gabbro and modelling of Pd/Pt and Au/Pt in first formed droplets of sulphide melt suggest that sulphide saturation was reached in interstitial melts in crystal mushes in the floor and roof and in bulk liquid with a composition equivalent to that of the bulk liquid at lower UZa times and after crystallization of 82–85% of the bulk liquid (F = 0·19–0·16). Prior to sulphide saturation in UZa type melt, the precious metals ratios of the bulk liquid were controlled by the loss of Pt relative to Pd and Au in agreement with the low empirical and experimental solubility of Pt of ∼9ppb compared to a much higher value for Pd and Au. The relative timing between sulphide saturation (F = ∼0·18) and immiscibility between silicate melts (F = ∼0·10) and modelled precious metal ratios underpin the proposed multi-stage model for the mineralization, advocating initial accumulation in the mushy floor of the magma chamber controlled by sulphide saturation in mush melts rather than bulk melt, followed by redistribution of precious metals in a macro-rhythmic succession of gabbroic layers of the upward migrating crystallization zone.

Using Depositional and Petrographical Rock-Types to Define Hydraulic Rock-Types - A Case Study from the Permian-Carboniferous Unayzah Formation, Offshore Abu Dhabi

2019 ◽  
Author(s):  
Patricio Silva Gonzalez ◽  
Melissa Fernandes ◽  
Saad Siddiqi ◽  
Loay Hannon ◽  
Stefan Steiner ◽  
...  
Keyword(s):  
Abu Dhabi ◽  
Rock Types
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