Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

Author(s)

Vilalva, F. C. J. ^[1] ; Vlach, S. R. F. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Geociencias, Dept Mineral & Geotecton, BR-05508080 Sao Paulo - Brazil

• Document type: Journal article
• Source: MINERALOGICAL MAGAZINE; v. 74, n. 4, p. 645-658, AUG 2010.
• Web of Science Citations: 10

Abstract

Turkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite-steacyite group was found in evolved peralkaline granites from the Morro Redondo Complex, south Brazil. It occurs with quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO(2), Na(2)O and K(2)O contents of 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE(2)O(3) abundances (5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite-steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluids carrying Ca, the circulation of which was enhanced by deformational events. (AU)

• FAPESP's process: 08/00562-0 - Mantle-crust interaction and the genesis and evolution of the A-type: post-collisional magmatism: geochemical and isotopic records from the Graciosa Province, S-SE Brazil
• Grantee: Silvio Roberto Farias Vlach
• Support Opportunities: Regular Research Grants