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

Result code in 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>

Alternative codes found

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

Result on the web

<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>

Result language

angličtina

Original language name

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

Original language description

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.

Czech name

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Czech description

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Type

J_imp - Article in a specialist periodical, which is included in the Web of Science database

CEP classification

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OECD FORD branch

10504 - Mineralogy

Project

Result was created during the realization of more than one project. More information in the Projects tab.

Continuities

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

Publication year

2023

Confidentiality

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

Name of the periodical

Journal of Geosciences

ISSN

1802-6222

e-ISSN

1803-1943

Volume of the periodical

68 (2023)

Issue of the periodical within the volume

3

Country of publishing house

CZ - CZECH REPUBLIC

Number of pages

18

Pages from-to

185-202

UT code for WoS article

001125566400004

EID of the result in the Scopus database

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