The effect of melt infiltration on metagranitic rocks (the Snieznik dome, Bohemian Massif)

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F19%3A00000296" target="_blank" >RIV/00025798:_____/19:00000296 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/67985530:_____/19:00505819

Výsledek na webu

<a href="https://doi.org/10.1093/petrology/egz007" target="_blank" >https://doi.org/10.1093/petrology/egz007</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1093/petrology/egz007" target="_blank" >10.1093/petrology/egz007</a>

Jazyk výsledku

angličtina

Název v původním jazyce

The effect of melt infiltration on metagranitic rocks (the Snieznik dome, Bohemian Massif)

Popis výsledku v původním jazyce

Highly-deformed banded phengite-biotite metagranite from the Snieznik dome in the Bohemian Massif have been modified locally to have stromatic, schlieren or nebulitic textures typical of migmatites. This occurred mostly along subvertical deformation zones at eclogite-facies conditions at a scale of several centimetres to several metres, mostly parallel to the foliation. The transition from banded to migmatite types of orthogneiss is marked by an increase in the amount of phases interstitial along grain boundaries in the dynamically recrystallized monomineralic feldspar and quartz aggregates, and by increasing consumption of recrystallized K-feldspar grains by fine-grained plagioclase and quartz as well as myrmekite (intergrowth of Pl−Qz). The new minerals are in textural equilibrium with phengite. The myrmekite, quartz and feldspars may be coarse-grained (grain size ≤ 0.5 cm). The features are considered to be the result of grain-scale melt infiltration that caused dissolution-reprecipitation along grain boundaries in the presence of phengite. The infiltration was pervasive at the grain-scale, but localized at hand-specimen to outcrop scales. All the rock types have the same mineral assemblage of Grt−Ph−Bt−Ttn−Kfs−Pl−Qz±Rt±Ilm; they have similar garnet, phengite and biotite composition, and based on mineral equilibria modelling, we infer equilibration at a pressure of 1.5−1.7 GPa and a temperature of 690–740 °C. Because the rocks are inferred to be H2O-undersaturated and above the temperature conditions of the wet solidus, infiltration must have involved a hydrous melt, as opposed to an H2O fluid. Stability of melt-bearing mineral assemblages and mineral compositions are almost independent of the melt proportion in the system, thus explaining the identical assemblage and mineral compositions observed in all the migmatite types. This precludes the estimation of the amount of melt infiltrated. Migmatite textures however suggest that variable degrees of melt-rock interaction occurred, being low in the banded migmatite types and higher in the nebulitic and schlieren types. Retrograde equilibration was largely restricted to retrograde zoning in phengite, garnet and plagioclase, and crystallization of biotite around phengite and garnet, presumably in a continuous reaction consuming melt. This may have occurred down to ~0.7−1.0 GPa. According to Sr-Nd isotopes, the infiltrating melt is likely derived from similar rocks, structurally-beneath the observed ones. The infiltration may have facilitated exhumation of a 2 km wide structural domain from ~1.7 to ~0.7 GPa, within which are the subvertical deformation zones along which the infiltration occurred.

Název v anglickém jazyce

The effect of melt infiltration on metagranitic rocks (the Snieznik dome, Bohemian Massif)

Popis výsledku anglicky

Highly-deformed banded phengite-biotite metagranite from the Snieznik dome in the Bohemian Massif have been modified locally to have stromatic, schlieren or nebulitic textures typical of migmatites. This occurred mostly along subvertical deformation zones at eclogite-facies conditions at a scale of several centimetres to several metres, mostly parallel to the foliation. The transition from banded to migmatite types of orthogneiss is marked by an increase in the amount of phases interstitial along grain boundaries in the dynamically recrystallized monomineralic feldspar and quartz aggregates, and by increasing consumption of recrystallized K-feldspar grains by fine-grained plagioclase and quartz as well as myrmekite (intergrowth of Pl−Qz). The new minerals are in textural equilibrium with phengite. The myrmekite, quartz and feldspars may be coarse-grained (grain size ≤ 0.5 cm). The features are considered to be the result of grain-scale melt infiltration that caused dissolution-reprecipitation along grain boundaries in the presence of phengite. The infiltration was pervasive at the grain-scale, but localized at hand-specimen to outcrop scales. All the rock types have the same mineral assemblage of Grt−Ph−Bt−Ttn−Kfs−Pl−Qz±Rt±Ilm; they have similar garnet, phengite and biotite composition, and based on mineral equilibria modelling, we infer equilibration at a pressure of 1.5−1.7 GPa and a temperature of 690–740 °C. Because the rocks are inferred to be H2O-undersaturated and above the temperature conditions of the wet solidus, infiltration must have involved a hydrous melt, as opposed to an H2O fluid. Stability of melt-bearing mineral assemblages and mineral compositions are almost independent of the melt proportion in the system, thus explaining the identical assemblage and mineral compositions observed in all the migmatite types. This precludes the estimation of the amount of melt infiltrated. Migmatite textures however suggest that variable degrees of melt-rock interaction occurred, being low in the banded migmatite types and higher in the nebulitic and schlieren types. Retrograde equilibration was largely restricted to retrograde zoning in phengite, garnet and plagioclase, and crystallization of biotite around phengite and garnet, presumably in a continuous reaction consuming melt. This may have occurred down to ~0.7−1.0 GPa. According to Sr-Nd isotopes, the infiltrating melt is likely derived from similar rocks, structurally-beneath the observed ones. The infiltration may have facilitated exhumation of a 2 km wide structural domain from ~1.7 to ~0.7 GPa, within which are the subvertical deformation zones along which the infiltration occurred.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GA16-17457S" target="_blank" >GA16-17457S: Tavení metagranitoidů: důležitý avšak málo pochopený aspekt vývoje kontinentální kůry</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2019

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Journal of Petrology

ISSN

0022-3530

e-ISSN

—

Svazek periodika

60

Číslo periodika v rámci svazku

3

Stát vydavatele periodika

GB - Spojené království Velké Británie a Severního Irska

Počet stran výsledku

28

Strana od-do

591-618

Kód UT WoS článku

000465225500005

EID výsledku v databázi Scopus

2-s2.0-85064263619