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- Title
High-Ti amphibole as a petrogenetic indicator of magma chemistry: evidence for mildly alkalic-hybrid melts during evolution of Variscan basic–ultrabasic magmatism of Central Iberia.
- Authors
Molina, José F.; Scarrow, Jane H.; Montero, Pilar G.; Bea, Fernando
- Abstract
Central Iberian Variscan granite batholiths and anatectic complexes are punctuated by coeval stocks of hydrous, high-K calc-alkaline, ultrabasic to intermediate rock series. Despite their overall calc-alkaline affinity, the mafic–ultramafic members contain high-Ti amphibole oikocrysts rimmed by lower-Ti amphibole ± cummingtonite and high-Ti amphibole replacing early phlogopite. To understand the factors controlling the saturation of high-Ti amphibole in the parental magmas, clinopyroxene-melt, phlogopite-melt and amphibole-melt relationships are reviewed. This analysis reveals that for melts with intermediate compositions, the affinity of TiO2 for amphibole rises in alkalic magmas. Accordingly, mildly alkalic trachytoid to subalkaline medium- to high-K andesite and dacite compositions are estimated for interstitial high-Ti amphibole-saturated melts. Amphibole Ce/Pb ratios reveal a mantle–crust hybrid nature for interstitial melts with subalkaline trachytoid compositions. The hydrous character of the Variscan basic magmas favoured an overall magmatic evolutionary trend with a low rate of variation of Na2O with respect to silica during amphibole crystallization.
- Subjects
BATHOLITHS; IGNEOUS intrusions; SILICON compounds; MAGMATISM; HYDROCHARA; HYDROPHILIDAE; WATER beetles; BEETLES; PHLOGOPITE
- Publication
Contributions to Mineralogy & Petrology, 2009, Vol 158, Issue 1, p69
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-008-0371-4