Infracrustal reworking and cryptic crustal growth during the Variscan Orogeny: Stable isotopic evidence from (ultra-) potassic magmatic rocks of the Moldanubian Zone, Bohemian Massif

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F25%3A10169536" target="_blank" >RIV/00025798:_____/25:10169536 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/00216208:11310/25:10507622

Výsledek na webu

<a href="https://doi.org/10.1016/j.lithos.2025.108115" target="_blank" >https://doi.org/10.1016/j.lithos.2025.108115</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.lithos.2025.108115" target="_blank" >10.1016/j.lithos.2025.108115</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Infracrustal reworking and cryptic crustal growth during the Variscan Orogeny: Stable isotopic evidence from (ultra-) potassic magmatic rocks of the Moldanubian Zone, Bohemian Massif

Popis výsledku v původním jazyce

Isotopic ratios of some elements in rocks derived from a mixture of mantle and crust-derived components can mask the true extent of mantle involvement in melt generation. The mantle trace-element budget (including, for example, Sr and Nd) can be swamped by metasomatism via fluids/melts from deeply subducted mature continental crust, whereas the major-element budget can remain largely intact. Such a scenario may occur in hot collisional orogens and result in underestimation of &apos;juvenile&apos; (mantle-derived) material added to the crust in these settings (&apos;cryptic crustal growth&apos;). Variscan (ultra-)potassic magmatic rocks from the Moldanubian Zone of the Bohemian Massif have crust-like delta 7Li (-2.0 %o to +2.3 %o) and delta 18O (+7.8 %o to +9.9 %o), consistent with the above-described situation. Together with previously published Sr-Nd-Mg isotopic data, geological, geophysical, and petrographic information, those metasomatic components were identified as Ordovician-Silurian felsic metaigneous rocks and metabasites of the Saxothuringian bimodal magmatic association. During deep subduction, these lithologies sampled adjacent mantle lithosphere and were transformed into typical Moldanubian (U)HP-(U)HT granulites, releasing fluids/ melts that reacted with surrounding depleted mantle, forming glimmerite veins. Moldanubian (ultra-)potassic magmatic rocks derived from the glimmerite-veined mantle domains therefore have a dual geochemical character: incompatible elements (and Sr, Nd, Pb, Li isotopic systems) have the isotopic fingerprint of subducted continental crust, whereas high MgO, mg#, transition metal contents and Mg isotopic ratios reflect their origin from mantle peridotite. In detail, the fate of each elements/isotopic systems depends on the crustal slab and mantle wedge compositions, partitioning into slab-derived fluid/melt, mode of metasomatism and melting of the resulting incompatible-element-enriched metasomes. The picture is further blurred by crystal fractionation and interactions with the overriding orogenic crust at a stage of advanced anatexis. Based on our study, we propose two new terms: (1) &apos;infracrustal reworking&apos; for contamination of lithospheric mantle by deeply subducted material (partial melts/fluids derived therefrom) followed by its swift re-emergence in the (ultra-)K magmas, and (2) &apos;intracrustal reworking&apos; for remobilization of pre-existing crust by partial melting and/or erosion and sedimentation, i.e. solely within continental crustal reservoir. Use of the term &apos;juvenile&apos;, canonical depleted mantle end-member composition and Nd isotopes mapping in hot collisional orogens (e.g. Variscan and Himalayan-Tibetan belts) is discouraged.

Název v anglickém jazyce

Infracrustal reworking and cryptic crustal growth during the Variscan Orogeny: Stable isotopic evidence from (ultra-) potassic magmatic rocks of the Moldanubian Zone, Bohemian Massif

Popis výsledku anglicky

Isotopic ratios of some elements in rocks derived from a mixture of mantle and crust-derived components can mask the true extent of mantle involvement in melt generation. The mantle trace-element budget (including, for example, Sr and Nd) can be swamped by metasomatism via fluids/melts from deeply subducted mature continental crust, whereas the major-element budget can remain largely intact. Such a scenario may occur in hot collisional orogens and result in underestimation of &apos;juvenile&apos; (mantle-derived) material added to the crust in these settings (&apos;cryptic crustal growth&apos;). Variscan (ultra-)potassic magmatic rocks from the Moldanubian Zone of the Bohemian Massif have crust-like delta 7Li (-2.0 %o to +2.3 %o) and delta 18O (+7.8 %o to +9.9 %o), consistent with the above-described situation. Together with previously published Sr-Nd-Mg isotopic data, geological, geophysical, and petrographic information, those metasomatic components were identified as Ordovician-Silurian felsic metaigneous rocks and metabasites of the Saxothuringian bimodal magmatic association. During deep subduction, these lithologies sampled adjacent mantle lithosphere and were transformed into typical Moldanubian (U)HP-(U)HT granulites, releasing fluids/ melts that reacted with surrounding depleted mantle, forming glimmerite veins. Moldanubian (ultra-)potassic magmatic rocks derived from the glimmerite-veined mantle domains therefore have a dual geochemical character: incompatible elements (and Sr, Nd, Pb, Li isotopic systems) have the isotopic fingerprint of subducted continental crust, whereas high MgO, mg#, transition metal contents and Mg isotopic ratios reflect their origin from mantle peridotite. In detail, the fate of each elements/isotopic systems depends on the crustal slab and mantle wedge compositions, partitioning into slab-derived fluid/melt, mode of metasomatism and melting of the resulting incompatible-element-enriched metasomes. The picture is further blurred by crystal fractionation and interactions with the overriding orogenic crust at a stage of advanced anatexis. Based on our study, we propose two new terms: (1) &apos;infracrustal reworking&apos; for contamination of lithospheric mantle by deeply subducted material (partial melts/fluids derived therefrom) followed by its swift re-emergence in the (ultra-)K magmas, and (2) &apos;intracrustal reworking&apos; for remobilization of pre-existing crust by partial melting and/or erosion and sedimentation, i.e. solely within continental crustal reservoir. Use of the term &apos;juvenile&apos;, canonical depleted mantle end-member composition and Nd isotopes mapping in hot collisional orogens (e.g. Variscan and Himalayan-Tibetan belts) is discouraged.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GA22-34175S" target="_blank" >GA22-34175S: Interpretace geochemických dat magmatických hornin: použití jazyka R k vývoji nových a integraci existujících freewareových nástrojů</a><br>

Návaznosti

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

Rok uplatnění

2025

Kód důvěrnosti údajů

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

Název periodika

Lithos

ISSN

0024-4937

e-ISSN

1872-6143

Svazek periodika

510

Číslo periodika v rámci svazku

108115

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

19

Strana od-do

1-19

Kód UT WoS článku

001500619400002

EID výsledku v databázi Scopus

2-s2.0-105005940638