A rapid X-ray method of assessing the structural state of monoclinic K-feldspars

Jiránek, Jiří

doi:10.1016/0024-4937(82)90001-9

Cited by 1 publication

(1 citation statement)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the presence of broad-shaped profiles for the (131)K reflection (cf. Jiranek, 1982) in some samples (11 A, 17-2,24,31,38) may indicate small but variable amounts of incipient development of triclinic domains. This is perhaps most evident in sample 38-1 which may contain a significant amount of intergrown triclinic K-feldspar.…”

Section: Mineral Chemistrymentioning

confidence: 98%

The role of fluids in the late-stage evolution of the South Mountain Batholith, Nova Scotia: further geochemical and oxygen isotopic studies

Kontak

Kerrich

Strong

1991

atgeol

View full text Add to dashboard Cite

In order to evaluate the late-stage physical and chemical evolution of the Upper Devonian, peraluminous South Mountain Batholith, mineral chemistry (muscovite, feldspars), oxygen isotopes (whole rock, mineral separates) and Al/Si ordering of Kfeldspar have been investigated. Muscovite, K-feldspar and albite define coherent chemical trends with respect to compatible (B a, Sr, Eu) and incompatible (Li, Cs, Rb) elements such that crystal fractionation processes are reflected. However, the influence of a fluid phase is seen in terms of Eu/Eu* of greisen muscovite and the light REE profiles (chondritic) of chemically evolved K-feldspar. The dominance of monoclinic K-feldspar, even in pegmatitic environments, indicates that either single or multiple processes impeded Al/Si ordering (e.g., cooling rate, fluid and/or rock composition). However, locally the development of triclinic K-feldspar dominates where intense fluid-rock interaction occurred (e.g., greisens), thus reflecting alteration at temperatures <450"C. 5lsO values of minerals from pegmatites reflect disequilibrium conditions related to variable degrees of fluid-rock interaction after crystallization. Calculated 81 * 0^ (mostly 5-10 %>) indicates a dominantly magmatic fluid reservoir; bo th 1 ®Q-enriched (to +18 %») and -depleted (to <+4 %<>) fluids infiltrated the system, indicating that local fluid mixing occurred.Dans le but d'6valuer Involution physique et chimique dans ses demiers stades du batholite peralumineux devonien superieur de South Mountain, on a 6tudie la chimie des min£raux (muscovite, feldspaths), les isotopes de l'oxygene (sur roche totale et sur fractions monominerales) et l'ordonnance Al/Si au sein des feldspaths potassiques. La muscovite, le feldspath potassique et l'albite d&erminent des tendances chimiques coh&entes vis-a-vis des elements compatibles (Ba, Sr, Eu) et incompatibles (Li, Cs, Rb), de fa5on telle qu'elles refletent des processus de cristallisation fractionnee. Cependant, l 'influenee d 'une phase fluide s 'exprime en termes du rapport Eu/Eu* des muscovites dans les greisens et des profils (chondritiques) des T.R. legeres de feldspaths potassiques ayant subi une Evolution chimique. La dominance du feldspath potassique monoclinique, meme dans les environnements pegmatitiques, indique qu'un ou plusieurs processus firent entrave a l'ordonnance Al/Si (e.g., taux de refroidissement, composition du fluide et/ou de la roche). Cependant, d 'une faijon locale, le developpement de feldspath potassique triclinique domine la oil l 'int^raction entre le fluide et la roche fut intense (e.g., dans les greisens), refletant ainsi une alteration a des temperatures atteignant 450°C. Le dosage 81 ®0 des mineraux preleves dans les pegmatites reflete des conditions de desequilibre reliees a divers degres d 'interaction entre le fluide et la roche apres leur cristallisation. La valeur calcuiee 81 * 0^^ (pour la plupart 5-10 %<>) indique un reservoir de fluide a dominance magmatique; le systeme fut infiltre par des fluides aussi bien enrichis (jusqu...

show abstract

Section: Mineral Chemistrymentioning

confidence: 98%