Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F41601670%3A_____%2F23%3AN0000003" target="_blank" >RIV/41601670:_____/23:N0000003 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/00216224:14310/23:00134385 RIV/00216305:26310/23:PU150437

Výsledek na webu

<a href="http://doi.org/10.3190/jgeosci.374" target="_blank" >http://doi.org/10.3190/jgeosci.374</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.3190/jgeosci.374" target="_blank" >10.3190/jgeosci.374</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar

Popis výsledku v původním jazyce

Chemical compositions and mineral assemblages of tourmalines from the elbaite-subtype Manjaka pegmatite in the Sahatany Valley, central Madagascar, and its exocontact were examined using EPMA and LA-ICP-MS. Several textural, compositional and paragenetic types of tourmalines were recognized in the individual pegmatite units and in the zones located towards the host rock in the order: wall pegmatite unit → border pegmatite unit → contact zone → recrystallization zone; the latter zone evidently originated after the host Mg-rich calc-silicate rock (Di+Tr+Qz>Pl+Kfs˃Phl+ Dol˃Cal). Zoned prismatic crystals from the border unit evolved from the core Tur Ia (dravite < Fe-rich elbaite), Tur Ib (Mn,Fe-rich to Mn-rich fluor-elbaite > elbaite), to the crystal rims Tur II (elbaite > darrellhenryite) via the substitutions: (1) 2Y R2+ = Y LiAl, (2) Y MnWF = Y Fe2+WOH, (3) Y Li0.5 WOH = Y Al0.5 WO, and (4) Y LiT AlWOH3 = Y AlT SiWO3 . The contact zone, ~2 mm thick, contains abundant Tur IV (Li,Fe,Al-enriched dravite > oxy-dravite), and the recrystallization zone, ~1.5 cm thick, common Tur V (fluor-uvite > dravite > fluor-dravite, magnesio-lucchesiite, uvite) via the substitutions: (1) 2Y R2+ = Y LiAl and (5) Y R2+WOH = Y AlWO,(6) XNaWOH = XCaWO and (7) XNaY Al = XCaY R2+. The chemical compositions of the individual types of tourmalines suggest that the mobility of elements between calc-silicate rock and pegmatite was low. Only weak influx of Mg, V and Cr into pegmatite and Li and Al from the pegmatite to the host rock – recrystallization zone, respectively, were observed. The existence of thin B-rich contact zone with dominant Tur IV suggests low influx of B into the host rock in early magmatic stage. High contents of F in Tur V from the recrystallization zone were very likely triggered by influx of B,F-enriched residual pegmatite fluids. Very high a(B2 O3 ), but low a(H2O) and a(F) in the pegmatite melt constrained very low degree of external contamination of the pegmatite. Compositional evolution in tourmalines from Manjaka was compared with the pegmatites and their exocontact at Stoffhütte, Koralpe, Austria, and Bližná I, Moldanubian Zone, Czech Republic.

Název v anglickém jazyce

Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar

Popis výsledku anglicky

Chemical compositions and mineral assemblages of tourmalines from the elbaite-subtype Manjaka pegmatite in the Sahatany Valley, central Madagascar, and its exocontact were examined using EPMA and LA-ICP-MS. Several textural, compositional and paragenetic types of tourmalines were recognized in the individual pegmatite units and in the zones located towards the host rock in the order: wall pegmatite unit → border pegmatite unit → contact zone → recrystallization zone; the latter zone evidently originated after the host Mg-rich calc-silicate rock (Di+Tr+Qz>Pl+Kfs˃Phl+ Dol˃Cal). Zoned prismatic crystals from the border unit evolved from the core Tur Ia (dravite < Fe-rich elbaite), Tur Ib (Mn,Fe-rich to Mn-rich fluor-elbaite > elbaite), to the crystal rims Tur II (elbaite > darrellhenryite) via the substitutions: (1) 2Y R2+ = Y LiAl, (2) Y MnWF = Y Fe2+WOH, (3) Y Li0.5 WOH = Y Al0.5 WO, and (4) Y LiT AlWOH3 = Y AlT SiWO3 . The contact zone, ~2 mm thick, contains abundant Tur IV (Li,Fe,Al-enriched dravite > oxy-dravite), and the recrystallization zone, ~1.5 cm thick, common Tur V (fluor-uvite > dravite > fluor-dravite, magnesio-lucchesiite, uvite) via the substitutions: (1) 2Y R2+ = Y LiAl and (5) Y R2+WOH = Y AlWO,(6) XNaWOH = XCaWO and (7) XNaY Al = XCaY R2+. The chemical compositions of the individual types of tourmalines suggest that the mobility of elements between calc-silicate rock and pegmatite was low. Only weak influx of Mg, V and Cr into pegmatite and Li and Al from the pegmatite to the host rock – recrystallization zone, respectively, were observed. The existence of thin B-rich contact zone with dominant Tur IV suggests low influx of B into the host rock in early magmatic stage. High contents of F in Tur V from the recrystallization zone were very likely triggered by influx of B,F-enriched residual pegmatite fluids. Very high a(B2 O3 ), but low a(H2O) and a(F) in the pegmatite melt constrained very low degree of external contamination of the pegmatite. Compositional evolution in tourmalines from Manjaka was compared with the pegmatites and their exocontact at Stoffhütte, Koralpe, Austria, and Bližná I, Moldanubian Zone, Czech Republic.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10504 - Mineralogy

Projekt

Výsledek vznikl pri realizaci vícero projektů. Více informací v záložce Projekty.

Návaznosti

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

Rok uplatnění

2023

Kód důvěrnosti údajů

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

Název periodika

Journal of Geosciences

ISSN

1802-6222

e-ISSN

1803-1943

Svazek periodika

68 (2023)

Číslo periodika v rámci svazku

3

Stát vydavatele periodika

CZ - Česká republika

Počet stran výsledku

18

Strana od-do

185-202

Kód UT WoS článku

001125566400004

EID výsledku v databázi Scopus

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