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Boletín de Geología 2005, 27 2

Autor: C.A. Ríos

Fuente: http://www.redalyc.org/articulo.oa?id=349631990001


Introducción



Boletín de Geología ISSN: 0120-0283 bolgeo@uis.edu.co Universidad Industrial de Santander Colombia Ríos, C.A. CATION SUBSTITUTIONS GOVERNING THE CHEMISTRY OF AMPHIBOLE IN THE SILGARÁ FORMATION METABASITES AT THE SOUTHWESTERN SANTANDER MASSIF Boletín de Geología, vol.
27, núm.
2, julio-diciembre, 2005, pp.
13-30 Universidad Industrial de Santander Bucaramanga, Colombia Available in: http:--www.redalyc.org-articulo.oa?id=349631990001 How to cite Complete issue More information about this article Journals homepage in redalyc.org Scientific Information System Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Non-profit academic project, developed under the open access initiative Boletín de Geología Vol.
27, No.
2, julio-diciembre de 2005 CATION SUBSTITUTIONS GOVERNING THE CHEMISTRY OF AMPHIBOLE IN THE SILGARÁ FORMATION METABASITES AT THE SOUTHWESTERN SANTANDER MASSIF Ríos, C.A.
1 ABSTRACT Amphibole-bearing parageneses from the Silgará Formation metabasites at the southwestern Santander Massif record evidence of prograding metamorphism.
Optical and microprobe analyses, together with thermobarometric estimates on IV these rocks, show that the main variation in Ca-amphibole is the simultaneous substitution of Al into the T1 site (Al ) IV and Na K into the A-site of the amphibole’s crystal structure.
Al is strongly temperature dependant, and this dependancy masks any pressure effect.
Changes in the chemical composition of Ca-amphibole grains are interpreted through coupled substitutions, and reactions with co-existing minerals during an increase in metamorphic conditions from greenschist to lower amphibolite facies, being favourable circumstances record not only the metamorphic facies reached by rocks but also the P-T conditions by which these were attained. Keywords: amphibole, Silgará, metabasites, substitution, metamorphic conditions SUSTITUCIONES CATIÓNICAS QUE GOBIERNAN LA QUÍMICA DEL ANFÍBOL EN METABASITAS...





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