Petrographic and Sr–Nd–Pb–Li isotope characteristics of a complex lamproite intrusion from the Saxo-Thuringian Zone. A unique example of peralkaline mantle-derived melt differentiation

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985831%3A_____%2F20%3A00534163" target="_blank" >RIV/67985831:_____/20:00534163 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/00216224:14310/20:00117219 RIV/00216305:26110/20:PU137692 RIV/41601670:_____/20:N0000027

Výsledek na webu

<a href="https://www.sciencedirect.com/science/article/pii/S0024493720303728" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0024493720303728</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.lithos.2020.105735" target="_blank" >10.1016/j.lithos.2020.105735</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Petrographic and Sr–Nd–Pb–Li isotope characteristics of a complex lamproite intrusion from the Saxo-Thuringian Zone. A unique example of peralkaline mantle-derived melt differentiation

Popis výsledku v původním jazyce

Variscan orogenic lamproites in the Bohemian Massif predominantly occur as 1 to 2 m wide and petrographicallyuniform dykes along the eastern borders of the Moldanubian and Saxo-Thuringian zones. Variscan orogeniclamproites were derived by preferential melting of subduction-related olivine-free metasomatic vein assem-blages stabilised in the lithospheric mantle. These lamproitic melts may subsequently undergo extensive differ-entiation. In this study, we present thefirst combined petrographic and Sr–Nd–Pb–Li isotope characteristics of acomplex lamproite exposed at ca 100 m long profile near Horní Rokytnice (Czech Republic) in the Saxo-Thuringian Zone. This lamproite is characterised by the primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz that petrographically varies from relatively primitive (fine-grained, mafic) tomore differentiated (medium- to coarse-grained, felsic) pegmatitic lamproite domains. These domains may rep-resent the product of crystallisation of immiscible liquids that had separated from the maficmelt.Theprimitivelamproite zone is characterised by the typomorphic minerals–baotite, benitoite, and henrymeyerite. The moredifferentiated pegmatitic domains are free of aegirine and show replacement of primary red-luminescent (Fe3+-rich) K-feldspar by blue-luminescent (Fe-poor) K-feldspar. Residualfluids rich in Ca, Ti, and HFSE in combinationwith the decreasing peralkalinity of the lamproite system resulted in the local formation of secondary zircon,titanite and quartz at the expense of the primary Ti–Ba–Zr–K lamproitic mineral assemblages. Lamproites fromthe Moldanubian and Saxo-Thuringian zones fall on separate mixing trends in the 87Sr/86Sr(t) - εNd(t) diagram,which indicates that the mantle beneath these two zones had been metasomatised by different crustal material.The scatter in the peralkalinity index vs. δ7Li diagram indicates that the Li isotope composition is not controlledbymixing of two end members metasome and ambient depleted mantle alone, but may also be affected by late-stage magmatic and hydrothermal processes. The compositionally zoned Horní Rokytnice dyke is special as thepetrographically different types show a variation of about 4 δ-units in δ7Li due to dyke-internal processes, suchas fractionation, which increases δ7Li in late-stage lamproitic melts, and post-emplacement interaction withfluids that reduced δ7Li in samples that have lost Li. Post-emplacement alteration also led to the disturbance inthe Pb isotope systematics of the differentiated orogenic lamproite as indicated by variable over-correction of in situ radiogenic Pb ingrowth.

Název v anglickém jazyce

Petrographic and Sr–Nd–Pb–Li isotope characteristics of a complex lamproite intrusion from the Saxo-Thuringian Zone. A unique example of peralkaline mantle-derived melt differentiation

Popis výsledku anglicky

Variscan orogenic lamproites in the Bohemian Massif predominantly occur as 1 to 2 m wide and petrographicallyuniform dykes along the eastern borders of the Moldanubian and Saxo-Thuringian zones. Variscan orogeniclamproites were derived by preferential melting of subduction-related olivine-free metasomatic vein assem-blages stabilised in the lithospheric mantle. These lamproitic melts may subsequently undergo extensive differ-entiation. In this study, we present thefirst combined petrographic and Sr–Nd–Pb–Li isotope characteristics of acomplex lamproite exposed at ca 100 m long profile near Horní Rokytnice (Czech Republic) in the Saxo-Thuringian Zone. This lamproite is characterised by the primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz that petrographically varies from relatively primitive (fine-grained, mafic) tomore differentiated (medium- to coarse-grained, felsic) pegmatitic lamproite domains. These domains may rep-resent the product of crystallisation of immiscible liquids that had separated from the maficmelt.Theprimitivelamproite zone is characterised by the typomorphic minerals–baotite, benitoite, and henrymeyerite. The moredifferentiated pegmatitic domains are free of aegirine and show replacement of primary red-luminescent (Fe3+-rich) K-feldspar by blue-luminescent (Fe-poor) K-feldspar. Residualfluids rich in Ca, Ti, and HFSE in combinationwith the decreasing peralkalinity of the lamproite system resulted in the local formation of secondary zircon,titanite and quartz at the expense of the primary Ti–Ba–Zr–K lamproitic mineral assemblages. Lamproites fromthe Moldanubian and Saxo-Thuringian zones fall on separate mixing trends in the 87Sr/86Sr(t) - εNd(t) diagram,which indicates that the mantle beneath these two zones had been metasomatised by different crustal material.The scatter in the peralkalinity index vs. δ7Li diagram indicates that the Li isotope composition is not controlledbymixing of two end members metasome and ambient depleted mantle alone, but may also be affected by late-stage magmatic and hydrothermal processes. The compositionally zoned Horní Rokytnice dyke is special as thepetrographically different types show a variation of about 4 δ-units in δ7Li due to dyke-internal processes, suchas fractionation, which increases δ7Li in late-stage lamproitic melts, and post-emplacement interaction withfluids that reduced δ7Li in samples that have lost Li. Post-emplacement alteration also led to the disturbance inthe Pb isotope systematics of the differentiated orogenic lamproite as indicated by variable over-correction of in situ radiogenic Pb ingrowth.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GX19-29124X" target="_blank" >GX19-29124X: VÝVOJ STAVEB A GEOCHEMICKÉ SIGNATURY KARBONATITŮ V ČASE: VÝZNAM MOBILITY A KONCENTRACE KRITICKÝCH KOVŮ</a><br>

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2020

Kód důvěrnosti údajů

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

Název periodika

Lithos

ISSN

0024-4937

e-ISSN

—

Svazek periodika

374

Číslo periodika v rámci svazku

15 November 2020

Stát vydavatele periodika

NL - Nizozemsko

Počet stran výsledku

15

Strana od-do

105735

Kód UT WoS článku

000576647400005

EID výsledku v databázi Scopus

2-s2.0-85089511607