Abstract
Trondhjemitic leucosomes, hosted in late Variscan metasedimentary migmatites from the upper amphibolite-facies basement of the north-eastern Peloritani Mountains (southern Italy), have petrographic and geochemical features consistent with their origin as near-pure melts derived from in situ water-fluxed melting of their paragneiss host-rocks. Comparison with results of experimental melting and thermodynamic modelling of metasedimentary rocks suggests a dominant derivation of the leucosomes by melting, at c. 1.0 GPa and 700 °C, metagreywackes with a high pelitic content. Migmatization likely began at the thickening-related baric peak, or during the early post-collisional exhumation stages. A subsequent heating stage following the decompression and solidification of the leucosomes triggered a second melting stage, involving muscovite and biotite incongruent breakdown, with an associated production of peritectic sillimanite and garnet, and small leucogranitic patches within the trondhjemitic leucosomes. These melting events can be framed in the typical clockwise P-T-(t) evolution of the Variscan Belt in western and southern Europe, depicting collision-related thickening followed by widespread migmatization, starting close to the baric peak at c. 345 Ma and continuing during exhumation, with a duration of c. 25 Ma, up to c. 320 Ma.
Highlights
Trondhjemitic leucosomes and small plutons produced by water-fluxed melting of metasedimentary rocks are rather uncommon occurrences in the geological record of the continental crust
This study aimed to investigate in more detail the origin of the above trondhjemitic leucosomes, taking into account a more complete geochemical dataset including the major, trace and rare earth elements of both leucosomes, mesosomes and melanosomes, in a significantly updated geo-petrological background
Evidence from the experimental melting and thermodynamic modelling of metapelites, in conjunction with petrographic and geochemical studies of leucosomes and nanogranitoids from several migmatitic complexes worldwide, all converge to indicate that, where free-water is present, the first melts produced by partial melting of the continental crust during an orogenic cycle are of trondhjemitic composition
Summary
Trondhjemitic leucosomes and small plutons produced by water-fluxed melting of metasedimentary rocks are rather uncommon occurrences in the geological record of the continental crust. They are, important markers of crustal evolution, since their occurrence is typically associated with the inception of crustal melting in collisional-related settings This is both because metasedimentary rocks such as metapelites and metagreywackes are the most fertile crustal rock types, and because the addition of water has the effect of further lowering their solidus, allowing significant amounts of melt to be produced at relatively low temperatures (e.g., >20 % vol at T
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
