Crystallographic control on lithium isotope fractionation in
Archean to Cenozoic lithium-cesium-tantalum pegmatites

J 2016

Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites

MAGNA, T., Milan NOVÁK, Jan CEMPÍREK, V. JANOUŠEK, C.V. ULLMANN et. al.

Základní údaje

Originální název

Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites

Autoři

MAGNA, T. (203 Česká republika), Milan NOVÁK (203 Česká republika, domácí), Jan CEMPÍREK (203 Česká republika, domácí), V. JANOUŠEK (203 Česká republika), C.V. ULLMANN (276 Německo) a U. WIECHERT (276 Německo)

Vydání

Geology, 2016, 0091-7613

Další údaje

Jazyk

angličtina

Typ výsledku

Článek v odborném periodiku

Obor

Geochemie

Stát vydavatele

Spojené státy

Utajení

není předmětem státního či obchodního tajemství

Odkazy

URL

Impakt faktor

Impact factor: 4.635

Kód RIV

RIV/00216224:14310/16:00088761

Organizační jednotka

Přírodovědecká fakulta

DOI

http://dx.doi.org/10.1130/G37712.1

UT WoS

000380121500016

Klíčová slova anglicky

lithium isotopes; pegmatites; crystallography; continental crust

Štítky

AKR, rivok

Příznaky

Mezinárodní význam, Recenzováno

Změněno: 31. 3. 2017 10:37, Ing. Andrea Mikešková

Anotace

V originále

The age distribution of LCT pegmatites largely overlaps with major phases of collisional orogenic events and assembly of super-continents. Some of the largest known LCT pegmatite deposits formed in very short intervals, 2.7-2.5 and 1.9-1.8 billion years ago (Ga), corresponding to two major pulses of continental crust growth. However, the exact process of generation and segregation of large volumes of Li-bearing pegmatite liquids, perhaps involving disequilibrium fractional crystallization and leaving residual melts enriched in fluxing elements such as B, F, H2O, Li, and P, remains largely obscure. The new data on Li contents and isotope compositions in major mineral phases from temporally and geographically separated pegmatite bodies document extreme variations in d7Li values among individual large LCT pegmatites, in particular Archean occurrences. The observed >10‰ variations in d7Li values for the same mineral phases from different localities (i.e., beryl, petalite, spodumene, lepidolite, amblygonite, muscovite) contrast with globally homogeneous Li isotope systematics of major mineral phases from unmodified mantle rocks. Consistent Li isotope offsets between coexisting mineral phases are best explained by Li isotope fractionation as a function of the bond length between Li and neighboring ions (O, OH, F). We suggest that spatially distinct Li isotope patterns act as fingerprints for different pegmatites and can be explained by the pre-existing Li isotope differences of their crustal sources at the time of pegmatite formation owing to differences in crustal age and evolution. This would imply secular evolution of the continental crust over Earth history toward present-day globally broadly uniform crustal 7Li/6Li ratios (d7Li ~0‰). The differences among Archean occurrences could reflect possible Archean paleogeography and perhaps be linked with different thermal regimes of individual cratons as a consequence of variations in crustal thickness.

Návaznosti

GA14-13347S, projekt VaV

Název: Variabilita lehkých prvků (Li, Be, B) ve vybraných horninotvorných a akcesorických minerálech z felsických magmatických a metamorfovaných hornin

Investor: Grantová agentura ČR, Variabilita lehkých prvků (Li, Be, B) ve vybraných horninotvorných a akcesorických minerálech z felsických magmatických a metamorfovaných hornin

Citovat

MAGNA, T., Milan NOVÁK, Jan CEMPÍREK, V. JANOUŠEK, C.V. ULLMANN a U. WIECHERT. Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites. Geology. 2016, roč. 44, č. 8, s. 655-658. ISSN 0091-7613. Dostupné z: https://dx.doi.org/10.1130/G37712.1.

@article{1375105,
   author = {Magna, T. and Novák, Milan and Cempírek, Jan and Janoušek, V. and Ullmann, C.V. and Wiechert, U.},
   article_number = {8},
   doi = {http://dx.doi.org/10.1130/G37712.1},
   keywords = {lithium isotopes; pegmatites; crystallography; continental crust},
   language = {eng},
   issn = {0091-7613},
   journal = {Geology},
   title = {Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites},
   url = {http://geology.gsapubs.org/},
   volume = {44},
   year = {2016}
}

TY  - JOUR
ID  - 1375105
AU  - Magna, T. - Novák, Milan - Cempírek, Jan - Janoušek, V. - Ullmann, C.V. - Wiechert, U.
PY  - 2016
TI  - Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites
JF  - Geology
VL  - 44
IS  - 8
SP  - 655-658
EP  - 655-658
SN  - 00917613
KW  - lithium isotopes
KW  - pegmatites
KW  - crystallography
KW  - continental crust
UR  - http://geology.gsapubs.org/
N2  - The age distribution of LCT pegmatites largely overlaps with major phases of collisional orogenic events and assembly of super-continents. Some of the largest known LCT pegmatite deposits formed in very short intervals, 2.7-2.5 and 1.9-1.8 billion years ago (Ga), corresponding to two major pulses of continental crust growth. However, the exact process of generation and segregation of large volumes of Li-bearing pegmatite liquids, perhaps involving disequilibrium fractional crystallization and leaving residual melts enriched in fluxing elements such as B, F, H2O, Li, and P, remains largely obscure. The new data on Li contents and isotope compositions in major mineral phases from temporally and geographically separated pegmatite bodies document extreme variations in d7Li values among individual large LCT pegmatites, in particular Archean occurrences. The observed >10‰ variations in d7Li values for the same mineral phases from different localities (i.e., beryl, petalite, spodumene, lepidolite, amblygonite, muscovite) contrast with globally homogeneous Li isotope systematics of major mineral phases from unmodified mantle rocks. Consistent Li isotope offsets between coexisting mineral phases are best explained by Li isotope fractionation as a function of the bond length between Li and neighboring ions (O, OH, F). We suggest that spatially distinct Li isotope patterns act as fingerprints for different pegmatites and can be explained by the pre-existing Li isotope differences of their crustal sources at the time of pegmatite formation owing to differences in crustal age and evolution. This would imply secular evolution of the continental crust over Earth history toward present-day globally broadly uniform crustal 7Li/6Li ratios (d7Li ~0‰). The differences among Archean occurrences could reflect possible Archean paleogeography and perhaps be linked with different thermal regimes of individual cratons as a consequence of variations in crustal thickness.
ER  -

MAGNA, T., Milan NOVÁK, Jan CEMPÍREK, V. JANOUŠEK, C.V. ULLMANN a U. WIECHERT. Crystallographic control on lithium isotope fractionation in Archean to Cenozoic lithium-cesium-tantalum pegmatites. \textit{Geology}. 2016, roč.~44, č.~8, s.~655-658. ISSN~0091-7613. Dostupné z: https://dx.doi.org/10.1130/G37712.1.

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