Please use this identifier to cite or link to this item: http://hdl.handle.net/10316/14304
Title: Geochemistry of Volcanic Rocks from Faial Island (Azores)
Authors: Machado, Adriane 
Azevedo, José M. M. 
Almeida, Delia P. M. 
Chemale Jr., Farid 
Keywords: Volcanism; Alkaline rocks; Sodic series; Faial; Azores
Issue Date: 2008
Publisher: GEOTIC - Sociedade Geológica de Portugal
Citation: MACHADO, Adriane [et al.] - Geochemistry of Volcanic Rocks from Faial Island (Azores). "e-Terra". ISSN 1645-0388. 5:1 (2008)
Serial title, monograph or event: e-Terra
Issue: 1
Abstract: Whole rock geochemistry of nine rocks from Faial Island (Azores) was used to characterize Faial Island volcanism. Studied rocks are lavas and were classified based on chemical data as basalts, hawaiites and trachyte. These rocks represent five stratigraphic units of island, from the base to the top: Ribeirinha Volcanic Complex, Cedros Volcanic Complex, Almoxarife and Capelo formations. The rocks belong to the sodic alkaline series, with the exception of the trachytic rock, that exhibits potassic affinity. Faial Island volcanism is characterized by low SiO2 contents (45 to 49 %), high TiO2 (2 to 3 %) and P2O5 (0.29 to 0.74 %). MgO shows values varying from medium to high (2 to 15 %). The trachyte has 62 % of SiO2, low MgO (0.42 %), TiO2 (0.53 %) and P2O5 (0.13 %) contents. Al2O3 varies from low to high (11 to 18 %) and reflects the plagioclase abundance variation. Na2O+K2O values increase with fractionation and K2O/Na2O ratio is less than 0.54, with the exception of the trachyte (0.73). Ni content decreases with magmatic evolution, from 356 to 5 ppm. The presence of the cumulate phases in basalts of Almoxarife and Capelo formations explains the MgO and Ni high values. Almost all the samples show Rb, Ba, Ta, Nb, Zr enrichment and Th, Sm impoverishment. The trachyte shows Ba enrichment and K depletion. Zr positive anomaly and U, Sr, P, Ti negative anomalies are observed in the trachyte. The REE patterns are typical of oceanic island lavas, showing LREE enrichment relative to MREE and HREE. The REE patterns suggest a continuous fractionation from a common melt generated by low partial melting rates. The rocks of Faial Island are the result of fractional crystallization and derived from a magma, which has mixed characteristics, mainly reflecting PREMA and EM II reservoirs, with minor contribution of HIMU.
URI: http://hdl.handle.net/10316/14304
ISSN: 1645-0388
Rights: openAccess
Appears in Collections:FCTUC Ciências da Terra - Artigos em Revistas Nacionais

Files in This Item:
File Description SizeFormat
Geochemistry of Volcanic Rocks from Faial Island.pdf4.3 MBAdobe PDFView/Open
Show full item record

Page view(s) 50

254
checked on Oct 16, 2019

Download(s)

27
checked on Oct 16, 2019

Google ScholarTM

Check


Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.